EP4093888A1

EP4093888A1 - Volume heat treatment method and related system

Info

Publication number: EP4093888A1
Application number: EP21702881.0A
Authority: EP
Inventors: Axel Stefan M Kupisiewicz; Jose Antonio Ramos De Campos; David BRUNEEL; Anne HENROTTIN; Liliana CANGUEIRO; Marc DECULTOT; Paul-Etienne MARTIN
Original assignee: Laser Engineering Applications SA
Current assignee: Laser Engineering Applications SA
Priority date: 2020-01-22
Filing date: 2021-01-22
Publication date: 2022-11-30
Also published as: US20230078751A1; WO2021148600A1; AU2021209391A1; MX2022008882A; JP2023511329A; CA3165012A1; BE1027475B1

Abstract

Disclosed is a method for volume heat treatment of a part (2) having an outer surface (22) delimiting its volume, the method comprising the following steps: a. providing a laser source (3); b. providing the part (2); c. providing support means (4) for supporting the part (2); d. positioning the part (2) such that it is held in position by the support means (4); e. irradiating at least one portion (23) of the outer surface (22) of the part (2) with the laser source (3) at a laser power and for a laser exposure time in order to obtain an increase in temperature in substantially the whole of the volume of the part (2).

Description

VOLUME HEAT TREATMENT PROCESS AND ASSOCIATED SYSTEM

Technical area

[0001] According to a first aspect, the invention relates to a heat treatment process by volume. According to a second aspect, the invention relates to a system for the volume heat treatment of parts.

State of the art

[0002] The heat treatment by volume (quenching, tempering, annealing) is a metallurgical operation which is known to a person skilled in the art. A heat treatment by volume consists in heating a part to a heating temperature and then cooling it at a predefined speed in order to maintain, for example at room temperature, the metallurgical structure of the part obtained at the heating temperature. During a volume heat treatment, essentially the entire volume of the part and preferably the entire volume of the part undergoes such a heat treatment. The mechanical properties of a part which has undergone such a heat treatment by volume are generally much greater for a specific application than those of a part which has not undergone any heat treatment (for example when the heat treatment is quenching, it is necessary to generally speaks of part hardened by volume quenching). For example, it is often possible to achieve significantly greater resistance to deformation by volume heat treatment. For aluminum alloys, volume quenching heat treatment reduces hardness but improves mechanical properties.

[0003] The heat treatment by volume is generally carried out by heating a part in an oven and by keeping it long enough in the oven in order to reach a predetermined temperature in essentially the entire room (or in essentially its entire volume) and which allows to obtain a structural modification of the material constituting the part or a relaxation of the stresses present in the part. Then, the latter is generally cooled, for example rapidly by exposing it to a liquid or gaseous fluid, often by immersing it therein. The fluids are, for example, water, oil or a gas. Rapid cooling is often necessary in order to keep the material in the induced structure at room temperature. by temperature rise. Furthermore, techniques are known for the local heat treatment by laser or by induction of metal parts having a thickness equal to or less than 1, 2 mm, these parts having the general shape of a plate (resulting for example from rolling steps ). The laser or thickness induction treatment of these parts is not a volume treatment because these techniques require a relative movement of the heat source with respect to the parts to be heated, treat if you want to heat all of these parts . Indeed, for each relative position between the heat source and the part to be treated, only a small section transverse to the length of the parts is subjected to heating. As the treatment is only local, it is necessary to repeat the treatment operation over the entire length of the parts. Such a treatment is therefore not a volume treatment. Moreover, such a heat treatment has various drawbacks such as, for example: need to provide a system allowing relative movement between the part to be heated and the heat source, risk of inhomogeneous heating. Furthermore, induction heat treatments are industrially effective for certain materials only, such as for example ferromagnetic materials.

Summary of the invention

[0004] According to a first aspect, one of the aims of the present invention is to provide a volume heat treatment process that is simpler to implement and faster to perform. To this end, the inventors propose a method of heat treatment by volume of a part having an external surface delimiting its volume, the method comprising the following steps: a. providing a laser source; b. provide the part; vs. providing support means for supporting the part; d. placing the part so that it is held in position by the support means; e. irradiating with the laser source at least a portion of the external surface of the workpiece with laser power and duration of exposure to achieve a temperature rise in substantially the entire volume of the workpiece. Preferably, the support means have a degree of thermal insulation between them and the part. As will be explained below, the inventors suggest having such a fairly large degree of thermal insulation, so that the heat (or thermal energy) generated by the laser source at the level of the outer surface portion of the part which is irradiated has a greater tendency to diffuse into the material constituting the part than into the support means. The inventors have observed, against all expectations, that it was possible to apply a heat treatment in volume to a part, to harden it for example, with the sole use of a laser source. The method of the invention makes it possible to carry out heat treatments without apparent deformation of the part. Preferably, said temperature rise is greater than 200 ° C, more preferably greater than 400 ° C, even more preferably greater than 700 ° C, and even more preferably greater than 850 ° C.

The method of the invention is particularly effective, because it allows, thanks to the laser source, to heat a room in volume without however heating its external environment. Thus, when the cooling of the room is initiated, it is necessary to dissipate only the heat stored in the room. In particular, it is not necessary to remove a quantity of heat stored by the support means of the part, or by the walls of an oven. Thanks to the use of the laser source for heating the room, it is possible to heat only the room and not to heat its direct external environment. This is in particular possible thanks to the high surface radiative power of the laser source compared to conventional heating techniques by direct flame, by radiant tube, or by electric resistances for example. An advantage of the invention over an induction heating technique is that it allows the heat treatment of non-ferromagnetic materials. Such an advantage is not achieved to the detriment of the ease of controlling the heat treatment parameters or to the detriment of the geometry of the parts that the method of the invention makes it possible to heat treat. Preferably, the combination of the laser source for heating and the support means with a degree of thermal insulation between them and the part makes it possible to confine in the part the heat supplied by the laser source and to reach temperatures of modification. of structure. This same combination of a laser source and support means with a degree of thermal insulation between them and the part, allows, as soon as the laser beam coming from the source is extinguished, to initiate a sufficiently rapid cooling to freeze the material constituting the part in the structure obtained during the heating step (step e.). As soon as the room no longer receives energy from the laser source, the heat in the room is very quickly evacuated to the environment outside the room, for example by radiation, convection, or any other heat exchange means. . For all these reasons, the process according to the invention can be qualified as more efficient compared to the known volume heat treatment methods.

[0007] When the method of the invention is implemented, the heat supplied to the room generates very little heating of its direct external environment. This stems in particular, where appropriate, from the support means which have a degree of thermal insulation between them and the part, and from the fact that it is possible to confine a laser beam only on the part to be heated or on a part of it. this one. The absence of significant heating of the environment outside the room allows it to quickly absorb heat from the room since the thermal energy supplied by the laser source only has to heat the room and not its environment. Thus the process of the invention, requiring only the part to be heat treated to be heated, allows considerable energy savings both for the temperature rise phase and for the cooling phase. The method of the invention is therefore particularly advantageous in comparison with the methods of the state of the art when it is desired to reduce the energy consumption associated with the heat treatment of parts.

[0008] During step e. the laser exposure power is preferably chosen to be substantially equal to the thermal losses of the part at a given temperature. Thus, when a heat treatment temperature is reached, it is possible to maintain the part at a stable temperature for several seconds, or even several minutes, and this easily because it suffices to choose an appropriate power of the laser source. The laser exposure power to maintain the workpiece at a predetermined temperature will directly depend on the predetermined temperature chosen. A preferred embodiment of the invention provides for reducing the laser power supplied during step e. in order to obtain temperature stabilization in essentially the entire volume of the room and to maintain this temperature for a predetermined time at a temperature below the temperature reached during step e. ; such a temperature is typically that of an isothermal bearing. Such an isothermal bearing is known to those skilled in the art and is intended to adapt the heat treatment as a function of the metallurgical phases desired at the end of the heat treatment and of the materials treated. The method and the system of the invention are particularly advantageous for implementing such an isothermal bearing during a heat treatment; in particular, the invention makes it possible to have a rapid transition between the initial heat treatment temperature and the isothermal bearing temperature. Preferably, the isothermal bearing has an isothermal bearing duration of between 10 minutes and 5 hours, preferably between 30 minutes and 2 hours. For parts of small volumes as defined by a preferred embodiment of the invention, it could be envisaged to have an isothermal bearing with a duration of less than 10 minutes.

In essentially the entire volume of the room means in at least 80% of the volume of the room, preferably in at least 90% of the volume of the room, more preferably in at least 95% of the volume of the room and even more preferably in at least 99% of the volume of the room. The part or sample has a certain volume which can be expressed in mm ³ and an external surface which can be expressed in mm ² . However, it is possible to use other units for volume and external surface.

[0010] In a nonlimiting manner, the heat treatment process of the invention can be used for the following applications:

- medical parts, in particular medical implants, for example, dental implants, joint prostheses, ...;

- precision mechanical parts, or precision mechanisms;

- safe rooms;

- parts comprising a shape memory material.

Another advantage of the method according to the invention is that it is very easy to implement, requiring only control means relatively simple. In fact, the programming of the heat treatment according to the invention requires, in most cases, a control of the electric power supplied to the laser source as a function of time by the control means. The control means thus make it possible to adapt the power of the laser source as a function of the physical and geometric characteristics of the part to be heat treated and as a function of the desired heat treatment (slope, level, etc.). Thus the control means define a laser power to be delivered as a function of time in order to heat treat the part according to the slopes and levels corresponding to the heat treatment programmed by the operator. It is thus possible, by virtue of the method of the invention, with the same heat treatment system, to carry out heat treatments for a large number of different materials, for parts of different geometry and over extended temperature ranges. The control means are therefore extremely simple and the power to be delivered to the laser is low compared to the powers to be delivered for other types of electric heating means. Preferably, the method further comprising, after step e., The following step: f. stop the irradiation of step e. to cool the room.

In this preferred embodiment, a step is added to allow the part to cool after it has been heated by the laser source. Compared to the known heat treatments where there is also a cooling phase, this preferred embodiment is simpler. Indeed, this method does not require movement or manipulation of the sample (or part) between the step of raising the temperature and the cooling step. In particular, step f. cooling system does not require immersing the part in a liquid. For this reason also the method according to the invention is simpler. The absence of these manipulations also makes it possible to obtain a volume heat treatment process with a faster cooling phase. The cooling rates known from the state of the art vary between 10 and 100 ° C / s. The method and the system of the invention make it possible to achieve during step f. cooling rates greater than 100 ° C / s, preferably greater than 150 ° C / s. A heat treatment process is volume quenching which consists in heating a part to a heating temperature and then cooling it at a sufficiently high speed to maintain, for example at room temperature, the metallurgical structure of the part obtained at the heating temperature. During volume quenching, essentially the entire volume of the part and preferably the entire volume of the part undergoes such a heat treatment. The mechanical properties of a part having undergone such a volume quenching process are generally much higher than those of an unhardened part (we generally speak of a part hardened by volume quenching, but if for certain materials such as for example aluminum alloys the quenching operation can have the effect of reducing the hardness but nevertheless improving its mechanical properties). By way of example, it is often possible to obtain a resistance to deformation and / or a resistance to wear which is appreciably greater by virtue of the volume quenching.

[0015] Volume quenching is generally carried out by heating the part in an oven and maintaining it long enough to reach a predetermined temperature in essentially the entire room (or in essentially its entire volume), which makes it possible to obtain a structural modification of the material constituting the part. Then, the latter is cooled rapidly by exposing it to a liquid or gaseous fluid, often by immersing it. The fluids are, for example, water, oil or a gas. The rapid cooling allows the material to freeze in the structure induced by the temperature rise.

Preferably, one of the aims of the present invention is to provide a volume quenching process that is simpler to implement and faster to perform. Quenching is a term known to those skilled in the art. Preferably, the process of the invention is a process for quenching the part by volume, step e. makes it possible to induce a modification of the structure of the material constituting the part, and, step f. is capable of freezing the material constituting the part in a structure different from that which it exhibited before the irradiation of step e. For example, the modification of the structure of the material constituting the part is a phase change, or else a change in metallurgical structure. This is known to a person skilled in the art. A phase change is an allotropic transformation. For example, a phase change can occur when, for a phase diagram of the material constituting the part, a phase change line is crossed during the rise in temperature of the part induced by the irradiation by the laser source. Preferably, during quenching, the material is frozen in the structure obtained in step e. For this, the cooling in step f. should generally be fairly fast, although this will depend on the type of material.

The volume quenching process proposed by the inventors is quite surprising. They observed, against all odds, that it was possible to apply volume quenching to a part to harden it with the sole use of a laser source. The method of the invention makes it possible to perform the quenching without apparent deformation of the part. The inventors have found that the absence of apparent deformation of the part is due to the fact that the quenching process allows the entire volume of the part to be treated in a very short time. The method of the invention allows the volume quenching of a part in a simple way because the method does not require movement or manipulation of the sample between the step of raising the temperature and the step of cooling. Step f. cooling freezing the material constituting the part in a new structure, for example that obtained during heating (step e.) does not require immersing the part in a liquid. For this reason also the method according to the invention is simpler. The absence of these manipulations also allows for a faster volume quenching process.

The method of the invention is particularly effective, because it allows thanks to the laser source to heat the room effectively without heating the environment outside the room. Thus, when step f. is initiated so as to have a rapid cooling of the whole room, it is then necessary to dissipate only the heat stored in the room. In particular, it is not necessary to evacuate a quantity of heat stored by the support means of the part, or by the walls of an oven, or even by the gaseous environment surrounding the part. Thanks to the use of the laser source for heating the room, it is possible to heat only the room and not to heat its direct external environment. This is in particular possible thanks to the high surface radiative power of the laser source compared to conventional heating techniques by direct flame, by radiant tube, by electric resistances or else by induction. Preferably, the combination of the laser source for heating and the support means with a degree of thermal insulation between them and the part makes it possible to confine in the part the heat supplied by the laser source and to reach temperatures of modification. of structure. This same combination of a laser source and support means with a degree of thermal insulation between them and the part, allows, as soon as the laser beam coming from the source is extinguished, to initiate a sufficiently rapid cooling to freeze the material. constituting the part in a new structure, for example that obtained during the heating step (step e.). As soon as the room no longer receives energy from the laser source, the heat in the room is very quickly evacuated to the environment outside the room, for example by radiation, convection, or any other heat exchange means. . For all these reasons, the process according to the invention can be qualified as more efficient compared to known volume quenching methods.

When the volume quenching process of the invention is implemented, the heat supplied to the part generates very little heating of its direct external environment. This stems in particular, where appropriate, from the support means which have a degree of thermal insulation between them and the part, and from the fact that it is possible to confine a laser beam only on the part to be heated or on a part of it. this one. The absence of significant heating of the environment outside the part then allows it to rapidly dissipate heat from the part during the cooling step, step f, which is important for having a quenching process. efficient where the material constituting the part is fixed in a given structure.

For example the part is made of steel, the quenching temperature of a steel part is very often between 700 ° C and 950 ° C. For example, for an aluminum part, the quenching temperature is very often between 440 ° C and 535 ° C. For example, for a titanium part, the quenching temperature is between 300 ° C and 600 ° C.

In essentially the entire volume of the room means in at least 80% of the volume of the room, preferably in at least 90% of the volume of the room, more preferably in at least 95% of the volume of the room and even more preferably in at least 99% of the volume of the room. For example, the part comprises a material having a thermal conductivity greater than 15 W.nv ^1. ° C ^{· 1.} , So that the part can preferably be affected by the heat treatment of the invention in 100% of its volume. .

Preferably, the irradiation of step e. is able to impose an essentially homogeneous temperature in essentially the entire volume of the room. The inventors have indeed observed, with surprise, that it is possible to choose such laser power and duration of exposure in step e. to achieve a substantially uniform temperature throughout the volume of a room, using laser irradiation. This ultimately allows for an efficient and good quality volume quenching process because the different regions of the part volume undergo essentially the same temperature increase in step e.

An essentially homogeneous temperature means that the maximum relative temperature difference between two points of the volume of the room is at most equal to 20%, preferably at most equal to 10%, and even more preferably at most equal to 1% .

Thus, for this embodiment, along a section (transverse or longitudinal) of the part, the latter is irradiated during step e. until an essentially flat or homogeneous temperature profile is obtained between the external surface and the core of the part. A longitudinal or transverse section here means a section made parallel to the direction of the laser beam coming from the laser source. Preferably, the laser source is configured to emit a collimated light beam, and to irradiate during step e. said at least a portion of the external surface of the part with the collimated light beam. The use of a collimated laser beam for the irradiation of the part makes it possible not to have to make any adjustment in relation to a distance relative to the focusing or beam divergence. Furthermore, the collimated laser beam allows the irradiation of a part during step e. whatever the profile of the external surface of the part (profile with several heights). Thus, the collimated laser beam makes it possible to irradiate a portion of the external surface of the part having a non-plane profile in a more homogeneous manner because the collimated laser beam makes it possible to irradiate simultaneously with the most homogeneous possible power density, portions of pieces having different heights. The use of a collimated laser beam therefore makes it possible to have a heat treatment suitable for parts having more complex surface geometries in comparison with a heat treatment with a focused laser beam. According to another embodiment of the invention, the laser beam is homogenized and then focused in the direction of the part.

Preferably, step f. further includes an action of directing a fluid toward the workpiece to cool it by convection. Such an action is optional but makes it possible to speed up the cooling of the room by heat transfer by convection in particular. The fluid can be a gas or a liquid. [0026] Preferably, the method further comprises the action of exposing the part to a treatment gas to modify its external surface. For example, the gas is nitrogen, so that during heat treatment nitriding of the outer surface of the part occurs.

Preferably, the support means have a flat support surface for supporting the part. This increases the mechanical stability of the part, by minimizing high temperature stress on the part to prevent material from creeping, when the part has at least a portion of a flat outer surface.

Preferably, the support means comprise a refractory material. The inventors have observed that the process of the invention, and in particular the preferred embodiment corresponding to a volume quenching process, is all the more effective when the support means have a large degree of thermal insulation between them and the room. This makes it possible to minimize any heat transfer from the part to the support means, during step e. and ultimately to have a temperature rise with great homogeneity in the volume of the room because the heat tends to diffuse more inside the room rather than outside. In this context, the inventors propose to preferably use support means made of thermally insulating material and more preferably of refractory material, a term known to a person skilled in the art. The term refractory is known to a person skilled in the art. Preferably, the support means comprise a material having a thermal conductivity of less than 20 W.nr ^1. ° C ¹ , more preferably less than 10 W.nr ^1. ° C ¹ , even more preferably less than 5 W.nr ^1. ° C ¹ . A unit equivalent to Wm ¹ .K ¹ is W.nr ^1. ° C ¹ . Thermal conductivity is a term known to those skilled in the art. Preferred thermal conductivity values are given for a temperature of 25 ° C. Thanks to this preferred variant, it is possible to have a relatively high thermal conductivity of the part to be quenched in comparison with the thermal conductivity of the support means, for a wide range of possible materials of the part, in particular for a wide range. of metals. This makes it possible to have a great homogeneity of the temperature rise throughout the volume of the room while heating the support means as little as possible. Note that it is possible to envisage support means having a thermal conductivity of less than 20 Wm-1 ° C-1, preferably less than 10 Wm-1. ° C-1, even more preferably less than 5 Wm-1 ° C-1, without necessarily using a refractory material for them. This constitutes another preferred embodiment of the method of the invention.

Preferably, there is a contact surface between the workpiece and the support means, the contact surface having an area less than 10% of the area of the outer surface, more preferably the latter is less than 2%, even more preferably this is less than 1%. For the same thermal conductivity of the support means, a heat exchange between the part and the support means will be lower when the contact surface between the part and the support means is smaller.

Preferably, the heat treatment method of the invention is particularly well suited to support means having low thermal conductivity and a contact surface between part and reduced support means. Thus, it is particularly desirable to have a product (thermal conductivity of the support means) x (contact surface between part and support means) as small as possible.

Preferably, the part is made of a material having a thermal conductivity greater than 10 W.nr ^1. ° C ¹ , more preferably this is greater than 35 W.nr ^1. ° C ^{· 1} and even more preferably this is greater than 50 W.nv ^1. ° C ^{· 1} . As has already been suggested above, the inventors have observed that the process of the invention and in particular the preferred embodiment corresponding to a volume quenching process is all the more efficient when the heat transfer generated by the heat transfer. level of the external surface of the part takes place above all within the volume of the part itself, rather than towards the outside, as for example towards the support means. This ultimately makes it possible to have a temperature rise exhibiting great homogeneity in the volume of the room because the heat has a greater tendency to diffuse within the room itself rather than outside. In this context, the inventors propose to preferably use a part made of a material having a sufficiently high thermal conductivity.

Preferably, the volume of the part is between 0.01 mm ³ and 5 cm ³ , more preferably the latter is between 0.1 mm ³ and 500 mm ³ , and even more preferably between 1 mm ³ and 100 mm ³ . The inventors have surprisingly noticed that parts of small volume, that is to say less than one cm ³ (and therefore also having a fairly small mass), make it possible to have a method according to the invention that is particularly effective. This is also true for the preferred embodiment corresponding to a volume quenching process. This is quite surprising. A plausible explanation would be the following. When the part to be thermally treated (to be soaked) has a small volume, that is to say less than cm ³ for example, there is little material allowing the heat generated at the external surface to be removed and therefore the the entire volume of the room tends to heat up very quickly. Thus, the mass of a part having a small volume is not sufficient to produce a high thermal gradient in the part due to the rise in temperature at its external surface. The process is therefore different from a surface hardening where the volume of the part makes it possible to absorb a heating on the surface without heating up in a homogeneous manner and reaching a temperature close to that of the irradiated surface. For example, the volume of the part is less than 5 cm ³ for an aluminum or brass part. For example, the volume of the part is less than 2 cm ³ for a part made of steel or titanium. Examples of the mass of small parts for the process of the invention are between 1 and 100 grams, preferably between 10 and 50 grams and more preferably between 15 and 30 grams. It is also possible to provide parts having a mass less than 1 gram, for example parts having a mass between 0.005 and 0.1 gram. Preferably, the part has a specific surface area of between 0.01 mm ^-1 and 150 mm ^-1 , more preferably between 0.1 mm ^-1 and 100 mm ^-1 , even more preferably between between 1 mm ^-1 and 10 mnr ¹ . The specific surface area of a part is equal to the area of its external surface divided by the volume of the part. To obtain a virtual absence (absence) of a metallurgical structure gradient in the heat-treated part and therefore volume homogeneity of the metallurgical structure of the part, for example during step f. for the preferred embodiments comprising such a step, it is preferred to have parts that are not very compact, having a specific surface area at least 10 times greater than that of a sphere having the same volume. This makes it possible to cool the part, for example in step f. for the preferred embodiments comprising such a step, more easily and more quickly. Such constraints and therefore such a preferred embodiment is particularly advantageous when the volume treatment method of the invention corresponds to a volume quenching method.

Preferably,

- said external surface consists of a first and a second external surface portions, and

- step e. consists in irradiating only the first outer surface portion with a laser power and duration of exposure to have a substantially equal temperature between the first and second outer surface portions.

A substantially equal temperature between the first and second external surface portions of the part means that they have a temperature difference of less than 50 ° C, preferably less than 25 ° C, preferably less than 10 ° C, preferably less than 5 ° C, and even more preferably less than 2 ° C.

This preferred embodiment makes it possible to have a method which is particularly easy to implement because it requires irradiating only a portion of the external surface of the part. In particular, one can imagine irradiating the room from only one side.

Preferably,

- the external surface comprises a first and a second external surface portions, and

- step e. consists in irradiating the first and second external surface portions.

According to this other possible embodiment, the inventors propose to irradiate at least two different portions of the external surface of the part. It is for example possible to irradiate the part from two of its faces which are for example opposite: for example irradiate a right side and a left side of the part. This helps to induce a rise in temperature from two different ends of the part, which can be particularly useful for thicker parts.

Preferably, step e. consists in irradiating at least a portion of the external surface of the part for an exposure time less than or equal to 10 s, more preferably less than or equal to 8 s, even more preferably less than or equal to 5 s. The inventors have found that particularly good results are obtained using such laser exposure times. In particular, such exposure times make it possible to have a temperature rise in essentially the entire volume of the irradiated part and in many cases to have a uniform temperature rise throughout the volume of the room.

Preferably, the laser source is a continuous laser source or with pulses of durations greater than 1 ms or with pulses of durations between 20 and 30 ms. The inventors have found that it is possible to have very good results using inexpensive continuous laser sources. Good results are also obtained with laser sources with relatively long pulses, that is to say greater than 1 ms. Laser sources continuous or with such pulse durations are inexpensive, but also very common and easy to implement in the context of the method of the invention. Such laser sources are available with a wide choice of wavelengths. This can be useful in order to have a wavelength adapted to the material constituting the part and thus maximize the absorption of radiation by the part and its conversion into heat for the rise in temperature thereof. According to a preferred embodiment, it is possible to adapt the polarization of the radiation in order to maximize the absorption of the radiation by the part. For example the polarization of the laser beam on the part can be linear s or p, elliptical or circular. When heat treating parts with curved outer surfaces or having different slopes, the reflection coefficients may change depending on the angle of incidence of the laser beam (angle between the direction of propagation of the laser beam and the normal to the surface at the point of irradiation). In order to maximize the absorption of the laser beam by the part to be heat treated, preferably when the laser beam has an angle of incidence with a portion of the part greater than 10 °, it may be advantageous to modify the polarization of the laser beam in a linear polarization, preferably a p polarization so as to obtain a better absorption by the part over its entire irradiated surface. In the case of curved parts or having different slopes, the use of a specific linear polarization (preferably p) can lead to a better homogeneity of absorption of the laser beam by the irradiated portion of the external surface.

Preferably, step e. consists in irradiating at least a portion of the external surface of the part with a laser beam of a power less than 100 W, more preferably less than 50 W, even more preferably less than 10 W. The inventors have found that it was possible to have very good results, and in particular very good quenching results when the method of the invention is a volume quenching method, even with low power laser sources. Thus, for certain parts, it is possible to have temperature rises of 1400 K with continuous laser sources having a power less than 10W or 6W for example. In such a case, the inventors have observed that a natural cooling of the part to ambient temperature (about 20 ° C), that is to say without forced cooling such as for example by convection, took less than 35 s.

Preferably, the laser source is able to provide an intensity modulated laser beam and step e. consists in irradiating at least a portion of the external surface of the part with an irradiation power which decreases over time during step e. Thanks to this preferred embodiment, it is possible to reduce the risk, or even avoid too much overheating of a part of the part, in particular too much overheating of the portion of the external surface irradiated by the laser source. Too much overheating is generally unacceptable and induces local or total melting of the part. By virtue of this preferred embodiment of the invention, this risk is reduced because the intensity of the laser beam is reduced during the heating step e.

Preferably, the laser source comprises:

a laser beam generator, beam control means configured to modulate the intensity profile of the laser beam emitted by the laser beam generator.

In this preferred embodiment, the laser beam generator is optically coupled with the laser beam control means. Preferably, the laser beam control means are laser beam shaping means. The laser beam control means make it possible to model the intensity profile of the laser beam which is determined according to a plane perpendicular to its direction of propagation. The beam control means make it possible to obtain a beam having a more uniform intensity distribution and therefore make it possible to irradiate a part with more uniformity in terms of power density.

Preferably, the beam control means comprise:

- an optical fiber comprising an input and an output, capable of conveying a laser beam emitted by the laser beam generator between the input and the output, more preferably, the optical fiber is multimode;

a laser beam projection device configured to project on the part, an image of the laser beam at its exit from the optical fiber.

In this preferred embodiment, the laser beam generator is optically coupled with the input of the multimode optical fiber so that essentially the entire laser beam is conveyed by the multimode optical fiber to its exit. When the laser beam generator is a multimode laser beam generator, the multimode laser beam conveyed by the multimode optical fiber is mixed as it travels through the multimode optical fiber, so as to illuminate the exit face (the exit) of the fiber with homogeneous laser beam intensity. Preferably, a better mixing of the modes and therefore a better homogeneity of beam intensity on the exit face is obtained when the multimode optical fiber is bent. For example the multimode optical fiber is bent forming an "8". Preferably, the multimode optical fiber has a length greater than 2 m, and more preferably a length between 6 m and 10 m, for example 8 m in order to allow good mixing of the modes and therefore good uniformity of the intensity profile in multimode optical fiber output.

The laser beam projection device makes it possible to project the image of the exit (of the exit face) of the multimode optical fiber on the part to be heat treated. This laser source embodiment makes it possible to modify the intensity profile of the laser beam, so that at the input of the multimode optical fiber, the laser beam (multimode) has an essentially Gaussian intensity profile as emitted by the laser beam generator, and, at the output, the laser beam has a uniform intensity profile over essentially the entire output face that it illuminates. The laser beam projection device then makes it possible to form an image of the exit face of the multimode optical fiber illuminated with uniform intensity, on the part to be heat treated.

Preferably, the laser beam projection device is configured to project the image of the laser beam onto the workpiece with a collimated laser beam.

Another advantage of this embodiment of the laser source is that it allows the part to be irradiated with a collimated laser beam. This is all the more advantageous (as already described above) as it allows a simplification of the method by not requiring an additional step of adjusting the distance of the part relative to the laser source. Moreover, such a collimated laser beam of uniform intensity makes it possible to irradiate with more homogeneity in terms of power density of parts having complex geometries characterized by high form factors, or having curved surfaces.

Preferably, the laser beam projection device is able to adjust a magnification between the predetermined section of multimode optical fiber taken at the output and the image of the laser beam when the latter is projected onto the workpiece.

In this preferred embodiment, the laser beam projection device preferably comprises a first and a second converging lenses, so as to project the laser beam at the output of the multimode optical fiber (which is then divergent) in one laser beam image on the workpiece to be heat treated with a laser beam which is collimated. Preferably, the first and second lenses can be moved relatively relative to each other in a translation parallel to an optical axis defined by a main direction of propagation of the laser beam at the output of the multimode optical fiber. Preferably, the first lens is movable with respect to the exit of the multimode optical fiber in order to adjust the distance of the first lens - the exit of the multimode optical fiber. Preferably, an increase in the distance between the first and second lenses allows an increase in the magnification. Thus the laser beam projection device makes it possible to adapt the size of the laser beam on the part to be heat treated as a function of the size of the latter. For example, the multimode optical fiber has a section of 400 μm and the image of the laser beam at the output thereof projected onto the part has a diameter of 6 mm. Thanks to this preferred embodiment of the laser source of the invention, it is possible to obtain an irradiation of the part with a uniform laser intensity and adjustable in size. The uniform beam intensity on the part makes it possible to carry out a heat treatment with a high quality because the increase in temperature of the part is then generated with a thermal gradient at the level of the surface of the part which is almost zero or even zero . Whereas heating by a laser source of the state of the art inevitably introduces a thermal gradient at the surface of the part given the Gaussian intensity profile of such laser sources. Another advantage of the laser beam projection device is that it allows modulation of the diameter of the image of the laser beam exiting it on the part without altering its uniformity in intensity.

Preferably, the beam control means comprise: a meniscus lens configured to modify the diameter of the laser beam emitted by the laser beam generator into a modified collimated laser beam. Preferably, the beam control means comprise a plurality of meniscus lenses aligned along their respective optical axes. For example, at least one side of each of the meniscus lenses is aspherical so as to limit aberrations due to the use of meniscus lenses. Preferably, the beam control means comprise: an optical element having an aspherical optical surface or an optical surface capable of inducing a phase shift.

Preferably, the beam control means comprise:

- an optical diffraction element.

Preferably, the laser source further comprises beam focusing means positioned between the beam control means and the part.

Preferably, the process of the invention is a quenching process followed by tempering and it further comprises the following additional steps, after step f. : i. irradiating with the laser source at least a portion of the outer surface of the workpiece with a tempering laser exposure power that is less than the laser exposure power used in step e. for quenching.

The part is tempered by maintaining the part at a tempering temperature (below the quenching temperature) for a predetermined time. The part is then subjected to appropriate cooling to room temperature. Tempering makes it possible to attenuate the effects of quenching by generally making the part more ductile and more tenacious. Such tempering can advantageously be carried out after quenching without modifying the position of the part, which greatly simplifies the implementation of the method and of the system making it possible to implement such a tempering step. Preferably, a tempering temperature for a steel part is included between 200 ° C and 450 ° C. Preferably, the tempering temperature of an aluminum part is between 150 ° C and 200 ° C, for example 170 ° C.

Preferably, the method of the invention is a quenching process preceded by annealing and it further comprises the following additional steps before step a. : g. irradiating with the laser source at least a portion of the outer surface of the workpiece with an annealing laser exposure power that is less than the laser exposure power used in step e. ; h. cool the part after heating it to an annealing temperature in the previous step to a temperature below 100 ° C, preferably at room temperature.

Annealing consists in heating the part to a predetermined temperature (called the annealing temperature), in maintaining the part at this annealing temperature for a predetermined time, then in cooling the part with a predetermined cooling rate in order to obtain, after returning to ambient temperature a structural state of the material constituting the part close to the state of stable equilibrium. The purpose of this operation is to eliminate or reduce the residual stresses linked, for example, to a previous heat treatment, or to obtain the formation of a structure favorable to a subsequent action without fracturing (deformation, machining, heat treatment, etc. ). Such annealing can advantageously be carried out before quenching without modifying the position of the part on the support means, which greatly simplifies the implementation of the method and of the system making it possible to implement such an annealing step. With the method of the invention, it is possible to provide the following three heat treatment phases with the same device, without having to modify the position of the part (and possibly in a very short time): annealing, then quenching, then income. In such a case, there is a first heating phase at a Trecuit temperature, holding at Trecuit for a predetermined time, followed by controlled cooling, then a second heating phase at a temperature Thardening, holding at Thardening for a time. predetermined, followed by controlled cooling, T hardening being greater than T annealing, then a third heating phase to a temperature Trevenu, holding at Trevenu for a predetermined time, followed by controlled cooling, Thardening being greater than Trevenu.

Preferably, the method of the invention further comprises the following additional steps: j. provide a vacuum chamber and insert the part inside the vacuum chamber; k. achieve a partial vacuum in the vacuum chamber enclosing the part of less than 50,000 Pa, preferably less than 10,000 Pa and even more preferably less than 5,000 Pa.

It is then possible to carry out steps e. and / or f. and / or g. and / or h. in a high or partial vacuum. The advantage is to be able to better control or even avoid any contamination of the material constituting the part.

Preferably, the method of the invention further comprises the following additional steps:

L. provide a heat exchanger; mr. contacting the part with the heat exchanger during step f .. Such a preferred embodiment allows the part to be cooled faster and more efficiently.

Preferably, the method of the invention further comprises the following additional steps: n. provide a liquid bath; o. partially immerse the part in the liquid bath during step f., more preferably, fully immerse the part.

Such a preferred embodiment allows the room to be cooled faster and more efficiently.

Preferably, the material constituting at least partially the part is a metallic material. The method of the invention is indeed particularly suitable for this type of material (metals).

For example, the metallic material constituting at least partially the part is a carbon steel, preferably a steel comprising 1% carbon by weight. A carbon steel is a term known to those skilled in the art. It generally designates a steel whose main component of alloy is carbon, in portions of, for example, between 0.02% and 2% by mass.

The inventors also propose a system for the heat treatment by volume of a part having an external surface delimiting its volume, the system comprising:

- a laser source configured to irradiate at least a portion of the external surface of the part with a laser power and duration of exposure to obtain a temperature rise in essentially the entire volume of the part to induce a structural modification the material constituting the part;

- support means for supporting the part.

Preferably, the system of the invention is used for volume quenching of a part. Preferably, the support means have a degree of thermal insulation between them and the part.

[0062] The particular embodiments and associated advantages presented for the method of the invention apply to the system of the invention, mutatis mutandis.

Preferably, the laser source is a continuous laser source, or with pulses of durations greater than 1 ms, or with pulses of durations between 20 and 30 ms.

Preferably, the temperature rise is a temperature rise greater than 200 ° C, preferably greater than 400 ° C, more preferably greater than 700 ° C, even more preferably greater than 850 ° vs.

Preferably, the temperature rise in substantially the entire volume of the room is a temperature rise in at least 80%, more preferably at least 90%, more preferably 95%, still more. most preferred 99% of room volume.

[0066] According to one possible embodiment, the support means have a support surface for coming into contact with the part, the support surface having an area less than 10% of the external surface of the part, preferably less than 5%, even more preferably less than 1% of the external surface of the part. With this preferred embodiment, the contact between the part to be quenched and the support means is reduced, reducing the possibility of heat transfer by conduction from the part to the support means. This makes it possible to further increase the temperature within the part during heating by laser irradiation because the heat generated on the external surface portion of the part to be quenched has little other solution than to diffuse within the volume. of the room. The heat transfer from the part to the support means is all the more reduced when they include a refractory material. Preferably, the support means have a thermal conductivity of less than 20 W.nr ^1. ° C ¹ at 25 ° C.

According to another possible embodiment, the support means have a flat support surface for supporting the part. In such a case, it is possible to have a system where the part to be quenched remains in position easily. There is then no need, in general, to have means such as clamps which hold the part in position.

Preferably, the support means have a thermal conductivity of less than 20 W.nr ^1. ° C ¹ , more preferably less than 10 W.nr ^1. ° C ¹ , even more preferably at 5 W .nr ^1. ° C ¹ .

Preferably, the part is made of a material having a thermal conductivity greater than 15 W.nr ¹ . ⁰ C ^{· 1} , more preferably greater than 35 W.nr ^1. ° C ^{· 1} and even more preferably greater than 50 W.nr ^1. ° C ¹ .

Preferably, the volume of the part is between 0.01 mm ³ and 1 cm ³ , more preferably between 0.1 mm ³ and 500 mm ³ , and even more preferably between 1 mm ³ and 100 mm ³ .

Preferably, the laser source is configured to irradiate the outer surface portion of a workpiece with a laser beam of a power less than 100 W, more preferably less than 50 W, even more preferably less. at 10 W.

According to another possible embodiment, the system further comprises an optical fiber and it is designed so that a laser beam from the laser source is able to reach through the optical fiber at least one external surface portion of a part supported by the support means. The use of optical fiber makes it possible to guide a laser beam coming from the laser source. This provides greater flexibility to the system. In particular, it is possible to move the laser source away from the part to be quenched. For certain applications, such a configuration may be preferred.

According to another preferred embodiment, the laser source comprises:

- a laser beam generator,

- Beam control means configured to modulate the intensity profile of the laser beam emitted by the laser beam generator.

Preferably, the beam control means comprise:

an optical fiber of predetermined section comprising an input and an output, capable of transporting a laser beam emitted by the laser beam generator between its input and its output, more preferably, the optical fiber is multimode;

a laser beam projection device capable of projecting onto the part an image of the laser beam at its exit from the optical fiber, more preferably from the multimode optical fiber.

Preferably, the laser beam projection device is able to adjust a magnification between the predetermined section of multimode optical fiber taken at the output and the image of the laser beam when the latter is projected onto said part.

Preferably, the beam control means comprise:

a meniscus lens configured to modify the diameter of the laser beam emitted by the laser beam generator into a modified collimated laser beam.

Preferably, the beam control means comprise:

an optical element having an aspherical optical surface or an optical surface capable of inducing a phase shift.

Preferably, the beam control means comprise:

- an optical diffraction element. Preferably, the laser source further comprises beam focusing means positioned between the beam control means and the part.

According to another possible embodiment, the multimode optical fiber has a length of between 1 m and 12 m, more preferably a length of between 2 m and 8 m.

Preferably, the system further comprises a scanner to be able to direct a laser beam from the laser source on different parts to be quenched in volume. This makes it possible to have an even more efficient heat treatment system and process because several parts can be treated easily and quickly. For example, a work in tray is possible, where different parts to be treated are supported by a tray and where the laser beam is directed on the different parts thanks to the scanner.

Preferably, the system further comprises a temperature sensor, preferably a pyrometer, for measuring a room temperature. Thanks to this embodiment, it is possible to provide a regulation loop to adjust the power of the laser source as a function of the temperature measured by the temperature sensor. For example, a pyrometer which is an example of a temperature sensor measures the temperature of the portion of the external surface of the part which is irradiated by the laser source. The inventors also propose an assembly comprising the system as described above with all its preferred embodiments and the part to be quenched.

[0085] The inventors provide the following theoretical explanation of the method and system of the invention.

TEMPERATURE RISE / Heat input by laser Energy is supplied to the part via a laser beam (L) having a determined fluence (flux = laser power (W) / irradiation surface (cm ² ) ). Preferably, and as described above for certain embodiments, multiple beams could strike the entire casing (or external surface) of the part to further reduce the temperature gradient between the core of the part and the portion. of irradiated external surface. The laser of predetermined power P illuminates the portion of the external surface of the part with a diameter D, for example for a laser spot having a circular section. Study of the heat balance in the irradiated part The heat transfer between the part and its external environment is governed by three phenomena: conduction, convection, radiation. The physical properties to take into account are the following:

- the coefficient of thermal conductivity k (or thermal conductivity) measures the propensity of a body to develop a heat flow when it experiences a difference in T °; - specific heat c (or specific heat capacity) measures the rate of change of internal energy with T °; this quantity reflects the ability of a material to accumulate energy in thermal form as its temperature increases;

- the calorific capacity C (or thermal capacity) measures the capacity of a medium to accumulate (or release) heat. Conversely, this quantity measures the energy that must be transferred to it to increase its temperature by one Kelvin.

From these coefficients, it is possible to calculate for different materials of the part, the thermal diffusivity a = k / (pc) which measures the ease of heat propagation in the material of the part. The distances traveled by thermal information after t seconds are proportional to the square root of at In the equation a = k / (pc), p is the density (eg in g. Cm ^-3 ) and c is the heat specific (usually expressed in J kg— 1 K-1).

Examples of thermal diffusivity a for materials commonly used: a (steel) = 4.30E-06 m ² / s; a (aluminum) = 9.79E-05 m ² / s; a (brass) = 3.79E-05 m ² / s; a (titanium) = 7.66E-06 m ² / s.

Table 1 shows an estimate of the thermal gradient by estimating a penetration depth for some known metals.

Table 1 - Estimation of thermal gradients

These estimates show, for the same illumination power on the external surface, the distance from the illuminated external surface which reaches a temperature close to that of the external surface. The higher the thermal diffusion coefficient, the faster the heat diffuses into the heart of the room. These estimates are intended to give orders of magnitude because the different coefficients used are taken under normal conditions (20 ° C), but such coefficients vary with temperature (for example, k decreases with temperature for steel while k increases with temperature for certain alloys and brass).

It is possible to determine an order of magnitude of the time so that the opposite surface of the part is at the same temperature as the surface of the part illuminated by the laser beam (which makes it possible to give an idea of the amplitude of the gradient of room temperature / room thickness). Such orders of magnitude are shown in Table 2.

Table 2 - Heat propagation times from the irradiated surface to the opposite surface

It is noted that for parts of thickness less than 2 mm for steel and titanium, 5 mm for brass and 10 mm for aluminum, the time for the heat to propagate from the irradiated surface to the opposite surface is less than 1 s. Such an approach makes it possible to determine an order of magnitude of a maximum gradient between the irradiated surface and the opposite surface as shown in Table 3. Table 3 - Amplitude of the temperature gradient

Calculations of the temperature rise times of the part The inventors have found that if the rise time is 200 ° C / s, part thicknesses of up to 1 mm give acceptable temperature gradients in the part. for most of the applications targeted by the process of the invention and for most materials. In contrast, acceptable temperature gradients for a part thickness of 5 mm require the use of materials with high thermal conductivity coefficients such as aluminum. Thus, the rate of temperature rise of the part will be proportional to the amount of energy supplied by the laser on the irradiated surface of the part per unit of time, that is, the fluence of the laser beam multiplied by the irradiated surface.

For the temperature rise phases, the calculation of the amount of energy to be supplied by the laser beam will depend on the heat balance in the room. As a first approximation, the quantity of heat absorbed, generated by the part following a phase change, or even internal work, Q _ge n, is neglected. [0091] 1. Energy input by the laser: CW

We assume an upper surface of the part irradiated with a laser beam (no multi-beam) with a laser energy P:

Qin = P x (irradiated surface / beam surface) x (1-R) where R is the reflectivity of the material constituting the part, preferably constituting the external surface of the part.

2. Energy loss:

2. a. by conduction:

The part is in contact with the support means. In order to minimize conduction losses, it is assumed that the support means comprise very small contact surfaces and / or ceramic to minimize the extent of the transfer zone and the interstitial conduction coefficient. 2. b. by convection:

Convection during the rise phase can be minimized by:

- limitation to natural convection (no external air flow)

- partial vacuum in a vacuum chamber (the partial vacuum being generated by a vacuum pump); such a partial vacuum, in addition to limiting the losses by convection, also has the advantage of slowing down oxidation very strongly (see decarbonization of the surface of the part at a higher temperature).

2.c. by radiation: The loss by radiation is maximized during the implementation of the method of the invention compared to the use of an oven since the external environment remains at a moderate temperature, generally at room temperature (between 15 and 25 ° C, preferably at 20 ° C). As the radiation loss varies with T ⁴ , it must be taken into account at the end of the room temperature rise phase, when the difference between the temperature of the environment is large (significant) compared to that of the room. room.

An estimate of the losses by conduction, convection and radiation show that they are very low compared to the energy input of the laser if the temperature rises in the room are of the order of 100 to 200 ° C / s . An approximation which would neglect such losses makes it possible to determine an order of magnitude for the laser power to be supplied as a function of the target temperature, of the material and of the time desired to obtain this temperature.

Example 1:

According to the invention, it is desired to bring a steel part, held by support means, to 820 ° C in 4 s (starting from an ambient temperature of

20 ° C), i.e. a temperature difference DT of 800 ° C requiring a temperature rise time of 200 ° C / s. We assume that the part is a cylinder 0.6 mm in section by 4 mm long:

- for the first 400 ° C, the losses by convection will be of the order of 2 to 10% of the heat input Qin, the losses by radiation will be of the order of 1 to 2% of the heat input Qin; - for the last 400 ° C, the losses by convection will be of the order of 4 to 20% of the heat input Qin, the losses by radiation will be of the order of 5 to 15% of the heat input Qin.

If we neglect these losses (including losses with the support means by providing for example thermal insulation between the support means and the part, or assuming that the support means are completely thermally insulating), the amount of energy to bring Q _a to the part will then be:

Q _a = P x (1 -R) = pc x DT x V, or 3.1 J in 4 s, or approximately 0.75 W. p is the density and c the specific heat.

The power of the laser P will have to take into account the reflectivity R of the material which will depend on its surface condition, the wavelength of the laser, and the polarization of the laser beam. For example if R = 70%, a laser power of less than 3 W is necessary to carry out the heat treatment of the part of Example 1 according to step e. and in the system according to the invention.

[0093] Example 2:

According to the invention, it is desired to bring an aluminum part, held by support means, to 420 ° C in 4s, (starting from an ambient temperature of 20 ° C), ie a temperature difference DT of 400 ° C requiring a rise time of 100 ° C / s. The part is a rod of 2 x 2 mm section by 6 mm long:

- for the first 200 ° C, the losses by convection will be of the order of 5 to 15% of the heat input Qin, the losses by radiation will be of the order of 1 to 2% of the heat input Qin _;

- for the last 200 ° C, the losses by convection will be of the order of 15 to 30% of the heat input Qin, the losses by radiation will be of the order of 5 to 10% of the heat input Qin heat.

If we neglect these losses (including losses with the support means by providing for example thermal insulation between the support means and the part, or assuming that the support means are completely thermally insulating), the amount of energy to bring Q _a will then be:

Q _a = px (1 -R) = pc ^* DT ^* V, or 24 J in 4 s, or 6 W.

The laser power must take into account the reflectivity R of the material which will depend on its surface condition, the wavelength of the laser, and the polarization of the laser beam. For example, for R = 70%, a laser power of less than 20W is necessary to carry out the heat treatment of the part of example 2 according to step e. and in the system according to the invention. Considering that the losses by convection and radiation in particular would not be negligible and would require multiplying by 2 the necessary laser power Q _a , a laser power of 40W would then be necessary, which is a relatively low (laser) power.

Power of current diode and fiber lasers:

Current lasers make it possible to have powers of the order of:

- compact, air-cooled and inexpensive laser: 10W to 400W with a wall plug efficiency> 40%;

- More powerful water-cooled lasers are available up to 120kW with wall plug efficiency> 40%.

A wall plug efficiency of 40% means that 100W of electrical power is converted into 40W of laser power.

The powers available to carry out the heat treatment (quenching, for example) at the heart of small-volume parts correspond perfectly to the order of magnitude of power required for the heat treatment (quenching) of at least one part. The use of much more powerful laser sources would make it possible to carry out heat treatment (quenching for example) according to the method and system of the invention in parallel on many parts. So,

- a compact 400 W laser would make it possible to simultaneously harden a series of 50 to 100 parts of Example 1;

- a more powerful laser of 4 kW would make it possible to simultaneously perform the quenching of a series of 500 to 1000 pieces of example 1, or of 50 to 100 pieces of example 2.

STABILIZATION AND DECREASE IN THE TEMPERATURE Once the temperature of the room for the desired heat treatment has been reached, if the laser is cut according to step f. of the process, the energy input is then zero. The room will then reject a quantity of energy (quantity of heat Q _or t) by conduction, convection and radiation. As explained previously, the system and the method of the invention make it possible to optimize the losses by radiation since the external environment is only slightly affected by the localized heat input. The temperature difference between the room and the outside environment will then be optimal since the outside environment remains at room temperature (for example 20 ° C). This radiation loss will be significant for high temperatures given the T ⁴ dependence.

For convection losses, they can be:

- either minimized by working under partial vacuum or

- either increased by increasing the convection coefficient by: o adding a gas (air, neutral gas, or nitrogen) at room temperature; o the supply of a gas (air, neutral gas, or nitrogen) cooled via adiabatic expansion or by vortex; o immersion of the part in a liquid (descent into a bath (water, oil, glycol ".

For conduction losses, they can be:

- or minimized by working on insulating support means (ceramic) and with a small contact surface (example cylinder deposited on a plate, plate on spikes)

- or increased by increasing: o the contact surface (installation allowing surface contact); o conduction through a conductive interface.

If we want a gentle slope of temperature drop (cooling rate), we will favor an insulating installation (support means), natural convection or under partial vacuum (in a vacuum chamber).

If you want a steeper slope, you will prefer in order:

- the use of a gas stream at room temperature;

- the use of a gas stream at low temperature;

- placing the part in contact with a thermally conductive surface (heat exchanger).

If you want to reach a very steep slope (for example for hyperquenching), you will allow the immersion (partial immersion) of the part in a liquid. All these phenomena can be combined and used successively depending on the stages and changes from one phase to another (depending on the materials and the initial structure of the part).

[0096] Example 3:

A. After the room temperature has been raised by laser (with power P1) according to step e., Losses by radiation and convection will lower the temperature of the room. If we want to keep an isothermal bearing, it is proposed to counterbalance these losses by a limited input of laser power P2 (P2 <P1) to balance the thermal balance of the part.

B. After raising the temperature of the room by laser (Power P), according to step e., Under partial vacuum (to avoid oxidation or decarbonization), a cooled neutral gas is injected to increase the losses by convection .

C. After raising the temperature of the part by laser (Power P), according to step e., Under partial vacuum (to avoid oxidation or decarbonization), the part is lowered to bring it into contact with a thermally conductive surface (heat exchanger) which will facilitate conduction losses.

D. After the temperature of the part has been raised by laser (Power P), the part is immersed (immersed) by means of a jack in a liquid bath (molten salt, oil, etc.) to make a hyperquenching.

The cooling means used depend, for example, on the desired cooling rate but also on the geometry of the part. For example, a part having a large external surface in the same plane could be effectively cooled by bringing it into contact with a thermally conductive surface (heat exchanger).

Control of the energy balance of the room.

The laser power P is very easily controlled via its interface converting the electric current into light power P.

The gas supply and the control of its pressure are carried out via the control of a pneumatic island, for example.

The descent of a jack for the movement of the part on a thermally conductive surface (heat exchanger) or in a bath (as will be described below in connection with the figures) is carried out for example by transmitting an electric signal to the control means of a pneumatic or electric cylinder.

A control of the temperature of the room can be carried out:

- via a temperature probe placed on the support means. This then generates a conductive link with the part which will increase the conduction loss and increase the temperature drop slope;

- via non-contact measuring means which will not disturb the thermal treatment cycles (quenching): thermal camera, pyrometer.

Brief description of the figures

These and other aspects of the invention will be clarified in the detailed description of particular embodiments of the invention, with reference being made to the drawings of the figures, in which:

- Fig.1a shows an embodiment of the system according to the invention;

- Figs. 1 b and 1 c show other embodiments of the system according to the invention;

- Fig.2 shows another possible embodiment of the system according to the invention;

- Figs. 3a, 3b and 3c show different examples of part that can be quenched in volume with the process of the invention;

- Figs. 4a, 4b show another possible embodiment of the method and the system according to the invention;

- Figs. 5a, 5b show another possible embodiment of the method and the system according to the invention;

- Figs. 6a, 6b, and 6c illustrate a temperature simulation when carrying out a process according to the invention;

- Fig. 7 shows an example of a thermal cycle that can be carried out in part or in its entirety by the method or the system according to the invention;

- Figs. 8a, 8b and 8c show preferred embodiments of a laser source according to the invention;

- Fig. 9 shows an intensity profile of the laser beam projected onto a part according to a preferred embodiment of the invention; - Figs. 10a and 10b represent preferred embodiments of the system according to the invention.

The drawings of the figures are not to scale. Generally, like elements are denoted by like references in the figures. The presence of reference numbers in the drawings cannot be considered as limiting, including when these numbers are indicated in the claims.

Detailed description of certain embodiments of the invention

[0100] FIG. 1 a shows an exemplary embodiment of the system for the heat treatment by volume of a part 2 according to the invention. Preferably, the heat treatment corresponds to volume quenching. The system according to the invention comprises a laser source 3 which can be continuous or pulsed. Support means 4 make it possible to support the part 2, to be soaked for example. In the example shown in Figure 1a, these support means have an essentially flat upper surface to support and hold in position the part 2 to be quenched, the lower face 28 of which is in contact with the support means 4.

Once the part 2 has been placed and held in position by the support means 4, the method of the invention consists in irradiating with the laser source 3 at least a portion 23 of the external surface 22 of the part 2. In the example of FIG. 1 a, the laser source 3 emits a collimated light beam so as to limit the settings concerning the position of a focusing distance of the collimated light beam with respect to the external surface 22 of the part 2. In the example of FIG. 1 b, the laser source 3 emits a diverging light beam in order to be able to irradiate a large portion 23 of the external surface 22 of the part 2. In the example of FIG. 1 c, the laser source 3 emits a converging light beam in order to be able to direct the light beam onto a selected portion 23 of the external surface 22 of the part 2. This example of FIG. 1 .c illustrates for example the use of a light beam that is homogenized and then focused. This external surface 22 delimits the volume of the part 2 to be quenched. This irradiation by the laser source 3 can be direct or indirect. Thus, it is possible to insert one or more optical elements between the laser source 3 and the part 2, for example to deflect a laser beam produced by the laser source 3. and direct it towards the part 2. In the examples shown in Figures 1 a, 1 b, and 1 c, the part 2 is irradiated from its upper surface only. Following this laser irradiation, the temperature of the room 2 will increase from the portion 23 of the surface illuminated by the laser source 3.

[0102] The support means 4 have a certain degree of thermal insulation between them and the part 2 or, in an equivalent manner, a certain thermal insulation capacity between them and the part 2. A degree of thermal insulation can be defined by an ability to limit heat exchange between the part 2 and the support means 4. It is possible to have such a technical effect in different ways. Thus, it is possible to use support means 4 having a low thermal conductivity limiting heat exchange by conduction following contact between the part 2 and the support means 4. It is also conceivable to limit the contact areas between. the part 2 and the support means 4. Limited contact areas between the part 2 and the support means 4 also make it possible to limit any heat exchange by conduction between the part 2 and the support means 4. For the same conductivity thermal of the support means 4, a heat exchange between the part 2 and the support means 4 will be lower when the contact surface (the contact areas) between the part 2 and the support means 4 is smaller. For the invention, it is preferred to have support means 4 such that the thermal energy (or heat) present at a location of the part 2 (for example on a point of its external surface 22) has a greater tendency to be diffused in the room 2 rather than diffused towards the support means 4.

When the part 2 is irradiated with the laser source 3, the heat generated at the level of the surface portion 23 illuminated by the laser source 3 tends to diffuse throughout the entire volume of the part 2. The inventors have noticed that 'it is possible to have a rise in temperature throughout the volume of the part 2 (and therefore not only at the level of the illuminated portion 23) inducing a modification of the structure of the material constituting the part 2.

In the examples shown in Figures 1a, 1b, 1c, and assuming that the support means 4 limit any heat exchange between them and the part 2, the inventors have the following physical interpretation to explain this phenomenon astonishing. The heat generated at the level of the irradiated portion 23 reaches the opposite lower surface 28 after some time. It is preferred to have a part 2 of relatively small thickness (5 mm or less, for example between 2 and 1 mm) so that the heat quickly arrives at the lower surface 28: between 1 and 4 s. Once the heat reaches the lower surface 28, it will 'bounce back' in view of the low heat transmissions to the support means 4. The only significant heat diffusion possible is therefore towards the core of the material, leading to an increase appreciably, even completely homogeneous in temperature.

After this heating step, the invention preferably consists in stopping the laser irradiation used for heating. In the case of a volume quenching process, this allows the material to be fixed in a structure other than that present before the heating. For certain parts 2, for example of small size (that is to say, the volume of which is less than 1 cm ³ ), it is not necessary to provide forced cooling to freeze the part 2 in this new structure. material. This provides a huge advantage over known volume quenching processes where the use of a fluid is often required to cool part 2 and freeze it in a new crystallographic structure. [0106] The inventors have surprisingly noticed that it was not necessary to have very powerful laser sources 3 in order to carry out volume quenching of parts 2 using the method of the invention. Thus, it is possible to have volume quenching with continuous laser sources 3 having powers of the order of or less than 50 W, for example 20W or 6W. This is all the more true as part 2 has a small volume, that is to say less than cm ³ . It is then possible to obtain temperature rises of the order of 3000 K on the irradiated portion 23.

[0107] FIG. 2 shows another embodiment of the invention for which part 2 is irradiated by two laser sources so as to have an irradiated portion 23 of part 2 that is larger than with a laser source. This is advantageous in order to obtain a rise in temperature throughout the volume of the room as quickly as possible. This embodiment is particularly advantageous for parts 2 that are thick and / or having complex geometries in order to have heat inputs distributed around the part 2. This embodiment can be implemented either from of embodiments comprising different examples of support means 4. With the embodiment of FIG. 2, for the same part 2, the heat generated at the level of the irradiated portion 23 reaches the opposite lower surface 28 after a shorter time. than for the embodiment of Figure 1. This embodiment of FIG. 2 can be implemented without distinction from the embodiments of FIGS. 1a, 1b and 1c.

[0108] Figures 3a-c show various examples of part 2 which can be quenched by volume with the method of the invention. Figures 3a-c illustrate the heart 27 of parts 2 of different geometries. The heart is often located in the volume of the part 2 at an equidistant position relative to the external surface 22. The method of the invention makes it possible to quench the entire volume of the part 2 including the quenching of the part. heart 27 of part 2.

[0109] FIGS. 4a and 4b illustrate a particular embodiment of the invention. The support means 4 here have the shape of points so as to minimize the contact surface between them and the part 2. As can be seen in FIG. 5a, the inventors also propose for this particular embodiment a heat exchanger 18. positioned at a certain distance from the external surface 22 (preferably from the opposite lower surface 28) of the part 2. At the end of step e. of the method of the invention, cooling of the part 2 is initiated (for example during step f. for embodiments comprising such a step). In FIG. 4b, according to this particular embodiment of the invention, the laser radiation is stopped. Almost simultaneously, the part 2 is placed in physical contact with the heat exchanger 18 via its opposite lower surface 28. This results in accelerated cooling of the part 2 thanks to the significant increase in temperature. heat exchange by conduction between the part 2 and the heat exchanger 18. The contacting can be slightly delayed compared to the start of the cooling phase, for example compared to the start of step f., in order to to wait until a certain quantity of heat can be emitted by radiation from the room 2 towards the external environment. In such a configuration, placing the part 2 in contact with the heat exchanger 18 then allows optimization of the heat exchanges from the part to the outside environment when the radiation losses are lower. Preferably the heat exchanger 18 has a thermal conductivity (much) greater than that of the support means 4. As can be seen in Figures 4a and 4b, the heat exchanger 18 is preferably able to undergo a relative movement with respect to the part 2. For this, it can for example be mounted on an electric or pneumatic cylinder which allows it to describe a relative movement with respect to part 2.

[0110] Figures 5a and 5b illustrate another particular embodiment of the invention. The support means 4 also have the shape of points so as to minimize the contact surface between the part 2 and the support means 4 and thus reduce heat transfer by conduction between them and the part 2. In this embodiment In particular, the inventors propose to use a liquid bath 19, the upper surface of which is positioned at a certain distance from the external surface 22 (preferably from the opposite lower surface 28) of the part 2. At the end of step e. of the method of the invention, cooling is initiated (and for example step f. for embodiments comprising such a step). This corresponds to FIG. 5b where it can be seen that the laser source 3 has been switched off. Almost simultaneously, the part 2 is immersed (partially or completely) in the liquid bath 19. Its external surface 22 is then in contact with the liquid bath 19. This results in accelerated cooling of the part 2. thanks to the significant increase in the heat exchange by conduction and / or convection between the part 2 and the liquid bath 19. The immersion can be slightly delayed compared to the end of step e. and with respect to the start of step f. for the embodiments comprising such a step, in order to wait for a maximum of heat to be emitted by radiation from the part 2 to the external environment. When the radiation losses are lower, then the immersion of the part 2 in the liquid bath 19 allows the part 2 to be further cooled by losses by convection between the part 2 and the liquid bath 19. To allow the immersion of the part 2 in the liquid bath 19, the inventors propose for example to mount the support means 4 supporting the part 2 on an electric or pneumatic cylinder. This makes it possible to impose a vertical movement of the part 2 and therefore its immersion in the liquid bath 19. [0111] Figures 6a, 6b, and 6c illustrate the results of a finite element simulation. Fig. 6a shows a half longitudinal sectional portion of a 1mm ³ steel cylinder 90 having an axial length of 4mm and a cross section of 0.6mm in diameter. Points 91, 92, 93 represent the center of cylinder 90. Points 91 and 93 are located on the outer face of the part, point 92 is located at the heart of the part, equidistant between points 91 and 93. The points points 94, 95, 96 represent a side face of cylinder 90. Points 94 and 96 are located on the outer face of the part, point 95 is located in the center of the side face of the part, equidistant between points 94 and 96. The following assumptions are used for the simulation, the results of which are presented in figure 6b and 6c:

- laser power received on the upper part between points 1 and 4 = 0.7W (electrical power: 1.8W);

- reflectivity R: 70%;

- irradiation for 5 s;

- k and c are a function of the room temperature;

- cooling: o by radiation with constant e (emissivity) = 0.25, o by natural convection with h (heat transfer coefficient generally expressed in Wm ² .K ¹ ) constant = 10.

- power absorbed (Pa) by the part: 0.2W.

FIG. 6b illustrates the evolution of the temperature as a function of time for each of the points 91 to 96 of the simulated part. With the scale of FIG. 6b, the various curves are superimposed: thus, one deduces an absence of significant temperature gradient between the various points: the evolution of the temperature at each of the points 91 to 96 is approximately the same. Figure 6c shows a zoom as the laser irradiation is terminated. At a given moment, thermal gradients are observed between the different points not exceeding 10 ° C. The irradiation by the laser beam is centered on the point 91, in the direction 91 - 93. This illustrates that the method of the invention is very well suited to the heat treatment (for example quenching) of (metal) parts having volumes. of the order of cm ³ . [0112] FIG. 7 shows a thermal cycle which can be implemented in part or in its entirety by the method according to the invention. Such a thermal cycle shows:

- temperature rises with a slope defined by controlling the laser power, illustrated by the segments: AB, GH and KL;

- temperature stabilization via loss control (by radiation and / or convection and / or conduction) and the provision of residual laser power to counterbalance these, illustrated by the segments BC, DE, FG, Hl and LM;

- temperature drops by optimizing heat loss from the room to the outside environment, illustrated by the segments CD, EF, IJ, MN. Preferably, the laser source 3 is switched off during these drops in temperature or cooling.

The temperature rises and falls can be:

- very soft: conductive insulation, natural convection or maintenance in partial vacuum and if necessary very light supply of laser power,

- gentle: natural to forced convection (gas at room temperature),

- rapid: forced convection (with cooled gas), conductive link,

- very fast: displacement in a liquid solution (molten salts, oil, glycol) at a given temperature; strong laser power for rapid warm-up.

The KLMN thermal cycle portion is often associated with annealing. The ABCDEF thermal cycle portion is often associated with quenching. For a quenching without isothermal bearing DE, point D is at a temperature close to the temperature of point A and points E and F are omitted. The GHIJ heat cycle portion is often associated with income.

[0113] Experimental example

In this experimental example, a hardening process according to the invention was implemented with a continuous laser source 3 with an output laser beam power of 0.7 W directed towards a portion of the external surface 22 of a part 2 made of steel. . The part is held by support means. At t = 0 s, the part is at room temperature (20 ° C); according to step e., after 2 s of irradiation with a laser power of 0.7 W, the part reaches a temperature of 750 ° C, after 3 s, the temperature is 950 ° C, between 4 s and 5 s the room temperature reaches 1300 ° C, which corresponds to a target temperature for the desired heat treatment. The laser source 3 is then turned off. After 6 s, the temperature in the room drops to 800 ° C, after 7 s the temperature is 575 ° C. A metallurgical study of the part reveals a transformation of the part at the metallurgical level and an increase in hardness to about 800 HV (unit of Vickers hardness).

The conclusion of this experimental test reveals that only 0.2 W of laser power absorbed by a volume of 1 mm ³ for 5 s leads to exceeding the melting temperature (1300 ° C), no temperature gradient in different places of the piece was found. The temperature drop shows a speed greater than 400 ° C / s until it reaches a room temperature 2 of approximately 800 ° C, then a slowing down to approximately 200 ° C / s.

A comparison of the experimental results and the model shows that the temperature rise conforms to the model / simulation shown in Figures 6a, 6b, 6c and explained above. However, the heat losses from room 2 to the outside environment are underestimated because the temperature drops are much faster than that of the model / simulation. The differences between simulations and this experimental result can be explained at least in part by the following limitations:

- the coefficient h = 10 is only valid for natural convection (DT <100 ° c). The DT »100 ° c increase considerably h,

- losses by interstitial conduction (ceramic / steel) are not taken into account in the simulation,

- the coefficient e is considered to be constant with temperature in the case of the present simulation, which is not the case in reality but represents a reasonable approximation.

[0114] Figures 8a, 8b and 8c show preferred embodiments of a laser source 3 of the invention.

The example of the embodiment of Figure 8a shows a laser source 3 comprising a laser beam generator 31 and control means. beam 35 configured to modulate the intensity profile of the laser beam emitted by the laser beam generator 31.

The example of the embodiment of Figure 8b shows a laser source 3 comprising a laser beam generator 31 and beam control means 35 configured to modulate the intensity profile of the laser beam emitted by the laser beam generator 31. The beam control means 35 comprise a multimode optical fiber 32, and a laser beam projection device 33. The multimode optical fiber 32 comprises an input and an output. Multimode optical fiber 32 is configured to carry a laser beam emitted by laser beam generator 31 from the input of multimode optical fiber 32 to its exit. Multimode optical fiber 32 has a predetermined section which is constant between its input and its output. The laser beam projection device 33 is configured to project onto the part 2, an image of the output of said multimode optical fiber 32, and consequently, an image of the laser beam transported by the multimode optical fiber 32 whose contour is defined. by the output section of the multimode optical fiber 32. The example of the embodiment of FIG. 8c shows a laser source 3 comprising a laser beam generator 31, beam control means 35 configured to modulate the intensity profile the laser beam emitted by the laser beam generator 31 and the focusing means 36.

[0115] FIG. 9 shows a graph representing a distribution of the intensity of a laser beam transported by the multimode optical fiber 32 and projected by the laser beam projection device 33 on an external surface 22 of the flat part 2 and perpendicular to the main direction of propagation of the collimated light beam. This graph shows an intensity distribution at diameter 39 of the laser beam image on workpiece 2. Here, the diameter 39 of the laser beam image on workpiece 2 is approximately 5mm. The laser beam image exhibits uniform irradiation over almost the entire irradiated surface 23 of part 2.

[0116] FIG. 10a shows a preferred embodiment of the system for the heat treatment by volume of a part 2 comprising the laser source 3 shown in FIG. 8. The laser source 3 shown in FIG. 8 comprises a laser beam generator 31 , a multimode optical fiber 32, and a device laser beam projection device 33, wherein the laser beam projection device 33 comprises a first converging optical element 37 and a second converging optical element 38. The first 37 and the second 38 converging optical elements are preferably converging lenses, of more preferably lenses of the plane convex type. Even more preferably, the convex face of the first converging plane convex lens 37 faces the convex side of the second converging plane convex lens 38. The laser beam projection device 33 makes it possible to form an image having a diameter 39 on it. the part 2 supported by the support means 4. The diameter 39 is defined by the configuration of the laser beam projection device 33 (power of the lenses 37, 38 and their relative positions with each other and with respect to the output of the optical fiber multimode 32) and by the section of multimode optical fiber 32 (at its exit). When the output of the multimode optical fiber 32 is imaged by the laser beam projection device 33, and the laser beam generator 31 emits a laser beam which is carried by the multimode optical fiber 32, then the image of the output of the multimode optical fiber corresponds to a light spot of diameter 39.

FIG. 10b shows the embodiment of FIG. 10a for a part 2 of larger size for which it is necessary to increase the diameter 39 of the image of the multimode optical fiber output 32 on part 2 in order to be able to carry out a heat treatment with thermal gradients on the surface 22 of the part 2 as small as possible. The laser beam projection device 33 makes it possible to modulate such a diameter 39 of the image of the output of multimode optical fiber 32 on the part 2 by modifying the relative position of the first converging lens 37 with respect to the output of the fiber. multimode optics 32 and / or the position of the second converging lens 38 relative to the first converging lens 37. Such a modulation makes it possible to obtain magnifications allowing adaptation to parts having sizes that can vary greatly. Preferably, the first converging lens 37 is driven into position between the output of the multimode optical fiber 32 and the second converging lens 38 so as to adjust the size of the laser beam on the part 2. The temperature rise in a room in step e. is carried out by a single step of irradiating the part, which has the advantage of offering a homogeneous heat treatment of the part. In particular, with the invention, it is not necessary to provide a significant displacement between the laser source (heating source) and the part to be treated. One can imagine a small relative movement between the part to be treated and the laser source (of the oscillation type around a reference position), but it is not necessary to provide a translational movement of several tens of mm or more between the laser source the part to be treated. The present invention applies in particular to parts which have a longest dimension less than 10 mm, preferably equal to or less than 8 mm.

The present invention has been described in relation to specific embodiments, which have a purely illustrative value and should not be considered as limiting. In general, the present invention is not limited to the examples illustrated and / or described above. The use of the verbs "to understand", "to include", "to include", or any other variant, as well as their conjugations, can in no way exclude the presence of elements other than those mentioned. The use of the indefinite article "a", "a", or of the definite article "the", "the" or "", to introduce an element does not exclude the presence of a plurality of these elements . Reference numbers in the claims do not limit their scope.

[0120] In summary, the invention can also be described as follows. A method of heat treatment by volume of a part 2 having an external surface 22 delimiting its volume, the method comprising the following steps: a. providing a laser source 3; b. provide Exhibit 2; vs. providing support means 4 for supporting the part 2; d. placing said part 2 so that it is held in position by said support means 4; e. irradiating with said laser source 3 at least a portion 23 of the external surface 22 of said part 2 with a laser power and duration of exposure to obtain a temperature rise in essentially the entire volume of the room 2.

Preferably, the support means 4 for supporting the part 2 has a degree of thermal insulation between them and said part 2. The invention can also be described as follows.

A system for the heat treatment by volume of a part having an external surface delimiting its volume, the system comprising:

- support means for supporting the part.

Preferably, the support means have a degree of thermal insulation between them and the part.

Claims

1. A method of heat treatment by volume of a part (2) having an outer surface (22) delimiting its volume, the method comprising the following steps: a. providing a laser source (3); b. provide part (2); vs. providing support means (4) for supporting the workpiece (2); d. placing said part (2) so that it is held in position by said support means (4); e. irradiating with said laser source (3) at least a portion (23) of the outer surface (22) of said workpiece (2) with laser power and duration of laser exposure to achieve a temperature rise in substantially the whole of the room volume (2).

2. Method according to the preceding claim further comprising, after step e., The following step: f. stop irradiation of step e. to cool the room (2).

3. Method according to the preceding claim, characterized in that it is a volume quenching process of said part (2), in that step e. makes it possible to induce a structural modification of the material constituting the part (2), and in that step f. is capable of freezing the material constituting the part (2) in a structure different from that which it had before the irradiation of step e.

4. Method according to any one of the preceding claims, characterized in that the irradiation of step e. is able to impose an essentially homogeneous temperature in essentially the entire volume of the room (22).

5. Method according to any one of the preceding claims, characterized in that said laser source (3) is configured to emit a collimated light beam, and to irradiate during step e. said at least one portion (23) of the outer surface (22) of said part (2) with said collimated light beam.

6. Method according to any one of the preceding claims, characterized in that step f. further comprises an action of directing a fluid towards the workpiece (2) to cool it by convection.

7. Method according to any one of the preceding claims, characterized in that it further comprises the action of exposing the part (2) to a treatment gas to modify its external surface (22).

8. Method according to any one of the preceding claims, characterized in that said support means (4) have a flat support surface for supporting the workpiece (2).

9. Method according to any one of the preceding claims, characterized in that said support means (4) comprise a refractory material.

10. Method according to any one of the preceding claims, characterized in that said support means (4) comprise a material having a thermal conductivity of less than 20 W.nr ^1. ° C ¹ , preferably less than 10 Wm ^1. ° C ¹ , even more preferably less than 5 W.nr ^1. ° C ¹ .

11. Method according to any one of the preceding claims characterized in that there is a contact surface between said part (2) and said support means (4), said contact surface having an area of less than 10% of l. 'area of said outer surface (22), preferably less than 2%, even more preferably less than 1%.

12. Method according to any one of the preceding claims, characterized in that said part (2) consists of a material having a thermal conductivity greater than 10 W.nr ^1. ° C ¹ , preferably greater than 35 W.nr. 1. ° C ¹ and even more preferably greater than 50 W.nv ^1. ° C ¹ .

13. Method according to any one of the preceding claims, characterized in that the volume of the part (2) is between 0.01 mm ³ and 5 cm ³ , preferably between 0.1 mm ³ and 500 mm ³ , and even more preferably between 1 mm ³ and 100 mm ³ .

14. Method according to any one of the preceding claims, characterized in that the part (2) has a specific surface area of between 0.01 mm ^-1 and 150 mm ^-1 , preferably between 0.1 mm ^-1 and 100 mm ^-1 , even more preferably between 1 mm ^-1 and 10 mm ^-1 .

15. Method according to any one of the preceding claims, characterized in that:

- said outer surface (22) consists of a first (23) and a second (28) outer surface portions (22), and in that

- step e. consists in irradiating only said first portion (23) of external surface (22) with a laser power and duration of exposure to have a temperature substantially equal between the first (23) and second (28) portions of external surface (22) .

16. A method according to any one of claims 1 to 14 characterized in that:

- said outer surface (22) comprises a first (23) and a second (28) outer surface portions (22), and in that

- step e. consists in irradiating said first (23) and second (28) outer surface portions (22).

17. Method according to any one of the preceding claims, characterized in that step e. consists in irradiating at least a portion of the external surface (22) of said part (2) for an exposure time less than or equal to 10 s, preferably less than or equal to 8 s, even more preferably less than or equal at 5 s.

18. Method according to any one of the preceding claims, characterized in that the laser source (3) is a continuous or pulsed laser source. durations greater than 1 ms or pulsed durations between 20 and 30 ms.

19. Method according to any one of the preceding claims, characterized in that step e. consists in irradiating at least a portion of the external surface (22) of said part (2) with a laser beam of a power less than 100 W, preferably less than 50 W, even more preferably less than 10 W.

20. Method according to any one of the preceding claims, characterized in that said laser source (3) is adapted to provide an intensity modulated laser beam and in that step e. consists in irradiating at least a portion of the external surface (22) of said part (2) with an irradiation power which decreases over time during step e.

21. Method according to any one of the preceding claims, characterized in that said laser source (3) comprises:

- a laser beam generator (31),

- beam control means (35) configured to modulate the intensity profile of said laser beam emitted by said laser beam generator (31).

22. Method according to the preceding claim characterized in that said beam control means (35) comprise:

- an optical fiber (32) comprising an input and an output, capable of conveying a laser beam emitted by said laser beam generator (31) between said input and said output, preferably, the optical fiber is multimode;

- a laser beam projection device (33) configured to project onto said part (2), an image of the laser beam at its output from said optical fiber (32).

23. Method according to the preceding claim characterized in that the laser beam projection device (33) is configured to project said image of said laser beam onto said part (2) with a collimated laser beam.

24. Method according to the preceding claim characterized in that the laser beam projection device (33) is able to adjust a magnification between the predetermined section of multimode optical fiber taken at said output and said image of the laser beam when the latter is. projected onto said part (2).

25. The method of claim 21 characterized in that said beam control means (35) comprise:

- a meniscus lens configured to modify the diameter of said laser beam emitted by said laser beam generator (31) into a modified collimated laser beam.

26. The method of claim 21 characterized in that said beam control means (35) comprise:

27. The method of claim 21 characterized in that said beam control means (35) comprise:

- an optical diffraction element.

28. A method according to any one of claims 21 to 27 characterized in that said laser source (3) further comprises beam focusing means (36) positioned between said beam control means (35) and said part ( 2).

29. Method according to any one of the preceding claims, characterized in that it is a quenching process preceded by annealing and in that it further comprises the following additional steps before step a. : g. irradiating with said laser source (3) at least a portion (23) of the outer surface (22) of said workpiece (2) with an annealing laser exposure power which is less than the laser exposure power used during of step e. ; h. cooling the part after having heated it to an annealing temperature during the previous step to a temperature below 100 ° C., preferably at room temperature.

30. Method according to any one of the preceding claims, characterized in that it is a quenching process followed by tempering and in that it further comprises the following additional steps, after step f . : i. irradiating with said laser source (3) at least a portion (23) of the outer surface (22) of said workpiece (2) with a tempering laser exposure power which is less than the laser exposure power used in step e. for quenching.

31. Method according to any one of the preceding claims, characterized in that it further comprises the following additional steps: j. providing a vacuum chamber and inserting said part (2) inside said vacuum chamber; k. producing a partial vacuum in said vacuum chamber enclosing said part (2) of less than 50,000 Pa, preferably less than 10,000 Pa and even more preferably less than 5,000 Pa.

32. A method according to any one of claims 2 to 31 characterized in that it further comprises the following additional steps:

L. provide a heat exchanger (18); mr. contacting said part (2) with said heat exchanger (18) during step f ..

33. Method according to any one of claims 2 to 32, characterized in that it further comprises the following additional steps: n. providing a liquid bath (19); o. partially immersing said part (2) in said liquid bath (19) during step f., preferably fully immersing said part (2).

34. Method according to any one of the preceding claims, characterized in that the material constituting at least partially said part (2) is a metallic material.

35. Method according to the preceding claim characterized in that the metallic material constituting at least partially said part (2) is a carbon steel, preferably a steel comprising 1% carbon by weight.

36. Method according to one of the preceding claims, characterized in that the support means (4) have a degree of thermal insulation between them and the part (2).

37. System for the heat treatment by volume of a part (2) having an external surface (22) delimiting its volume, said system comprising:

- a laser source (3) configured to irradiate at least a portion (23) of the external surface (22) of said part (2) with a power and a duration of laser exposure to obtain a temperature rise in essentially the the entire volume of the part (2) to induce a structural modification of the material constituting the part (2);

- support means (4) for supporting said part (2).

38. System according to the preceding claim, characterized in that the laser source (3) is a continuous laser source, or with pulses of durations greater than 1 ms, or with pulses of durations between 20 and 30 ms.

39. System according to any one of the two preceding claims characterized in that said temperature rise is a temperature rise greater than 200 ° C, preferably greater than 400 ° C, preferably greater than 700 ° C, so even more preferred above 850 ° C.

40. System according to any one of the three preceding claims characterized in that said temperature rise in substantially the entire volume of the room (2) is a temperature rise in at least 80%, preferably at least 90%. , preferably 95%, even more preferably 99% of the volume of the part (2).

41. System according to any one of the four preceding claims characterized in that the support means (4) have a support surface for coming into contact with the part (2), said support surface having an area of less than 10%. of said outer surface (22) of said part (2), preferably less than 5%, even more preferably less than 1% of said outer surface (22) of said part (2).

42. System according to any one of the five preceding claims characterized in that said support means (4) comprises a refractory material.

43. System according to any one of the six preceding claims characterized in that said support means (4) have a planar support surface for supporting the part (2).

44. System according to any one of the seven preceding claims characterized in that said support means (4) have a thermal conductivity of less than 20 W.nr ^1. ° C ¹ , preferably less than 10 W.nr ^1. ° C 1, even more preferably at 5 W.nr ^1. ° C- ¹ .

45. System according to any one of the eight preceding claims characterized in that said part (2) consists of a material having a thermal conductivity greater than 15 W.nr ¹ ° C ¹ , preferably greater than 35 W.nr ¹ . ⁰ C ¹ and even more preferably greater than 50 W.nr ¹ ° C

1

46. System according to any one of the nine preceding claims, characterized in that the volume of the part (2) is between 0.01 mm ³ and 1 cm ³ , preferably between 0.1 mm ³ and 500 mm ^3. , and even more preferably between 1 mm ³ and 100 mm ³ .

47. System according to any one of the ten preceding claims characterized in that said laser source (3) is configured to irradiate said portion (23) of the external surface (22) of a part (2) with a laser beam of a power less than 100 W, preferably less than 50 W, even more preferably less than 10 W.

48. System according to any one of the eleven preceding claims, characterized in that it further comprises an optical fiber and in that it is designed so that a laser beam from said laser source (3) is capable of reach via said optical fiber at least a portion (23) of the outer surface (22) of a part (2) supported by the support means (4).

49. System according to any one of the twelve preceding claims characterized in that said laser source (3) comprises:

- a laser beam generator (31),

50. System according to the preceding claim characterized in that said beam control means (35) comprise:

- an optical fiber (32) of predetermined section comprising an input and an output, capable of transporting a laser beam emitted by said laser beam generator (31) between its input and its output, preferably, the optical fiber is multimode;

- a laser beam projection device (33) capable of projecting onto said part (2) an image of the laser beam at its output from said multimode optical fiber (32).

51. System according to the preceding claim characterized in that the laser beam projection device (33) is configured to project said image of said laser beam onto said part (2) with a collimated laser beam.

52. System according to the preceding claim characterized in that the laser beam projection device (33) is able to adjust a magnification between the predetermined section of multimode optical fiber taken at said output and said image of the laser beam when the latter is projected onto said part (2).

53. System according to claim 49 characterized in that said beam control means (35) comprise:

54. System according to claim 49 characterized in that said beam control means (35) comprise: - an optical element having an aspherical optical surface or an optical surface capable of inducing a phase shift.

55. System according to claim 49 characterized in that said beam control means (35) comprise: - an optical diffraction element.

56. System according to any one of claims 49 to 55 characterized in that said laser source (3) further comprises beam focusing means (36) positioned between said beam control means (35) and said part ( 2).

57. System according to any one of claims 50 to 52 characterized in that the multimode optical fiber (32) has a length of between 1 m and 12 m, preferably a length of between 2 m and 8 m.

58. System according to any one of the twenty-one preceding claims, characterized in that it further comprises a scanner to be able to direct a laser beam from the laser source (3) on various parts (2) to be soaked in. volume.

59. System according to any one of the twenty-two preceding claims characterized in that it further comprises a temperature sensor, preferably a pyrometer, for measuring a temperature of the room (2).

60. System according to one of claims 37 to 59 characterized in that the support means (4) have a degree of thermal insulation between them and the part (2).