WO2020115531A1 - Acier inoxydable, produits réalisés en cet acier et leurs procédés de fabrication - Google Patents
Acier inoxydable, produits réalisés en cet acier et leurs procédés de fabrication Download PDFInfo
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- WO2020115531A1 WO2020115531A1 PCT/IB2018/059714 IB2018059714W WO2020115531A1 WO 2020115531 A1 WO2020115531 A1 WO 2020115531A1 IB 2018059714 W IB2018059714 W IB 2018059714W WO 2020115531 A1 WO2020115531 A1 WO 2020115531A1
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21B—MANUFACTURE OF IRON OR STEEL
- C21B5/00—Making pig-iron in the blast furnace
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/18—Hardening; Quenching with or without subsequent tempering
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/004—Very low carbon steels, i.e. having a carbon content of less than 0,01%
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/001—Austenite
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/008—Martensite
Definitions
- the invention relates to a stainless steel whose particularity is its ability to be shaped at room temperature from a sheet with an austenitic microstructure to easily give it a shape which can be complex, then to be heat treated at low temperature for it to give a partially martensitic structure with particularly interesting mechanical properties and finely adaptable to its intended use, this steel being intended, for example, for the automobile industries, for road transport in general, or for rail transport.
- martensitic steels that is to say whose microstructure is martensite for more than 50%
- Another way to obtain a martensitic structure consists in starting from an austenitic structure which will be shaped at room temperature from a sheet to make complex parts thanks to the great capacity of deformation of the austenitic structure. The part is then treated at low temperature during a cryogenic treatment, in order to transform part of the austenite into martensite and to give the part high mechanical characteristics.
- the object of the invention is to provide an austenitic stainless steel which is particularly well suited to cryogenic treatment after shaping of the part, in that it leads to the production of a partially martensitic structure providing high mechanical properties and which , above all, would be easily adjustable by playing on the precise conditions of the cryogenic treatment, and having good corrosion resistance. These characteristics should make it suitable, in particular, for use in the automotive industry, road or rail transport.
- the subject of the invention is a stainless steel, characterized in that its composition, in weight percentages, consists of: - traces ⁇ C ⁇ 0.15%; preferably 0.01% ⁇ C ⁇ 0.10%;
- composition satisfies the following conditions:
- the subject of the invention is also a steel product in stainless steel, characterized in that:
- the invention also relates to a steel product in stainless steel, characterized in that:
- the invention also relates to a process for manufacturing a steel product of stainless steel of the above type, characterized in that:
- - Shaping is carried out hot and, optionally, cold and at least one heat treatment of said steel between 900 ° C and 1200 ° C, to give it an austenitic structure at least 97%, the rest being ferrite residual, or even carbides and nitrides, the heat treatment ending in hyper quenching at a cooling rate of at least 2 ° C / s between 900 ° C and 500 ° C.
- the invention also relates to a process for manufacturing a steel product of stainless steel of the above type, characterized in that:
- a part is optionally produced with said steel by cold forming
- a cryogenic treatment of the steel or of the part is carried out, at a temperature between -50 and -130 ° C, preferably between -70 and -1 10 ° C, for 1 to 60 min, preferably between 1 min and 30 min.
- a surface treatment can be carried out on the surface of the product, increasing the roughness of said surface.
- the cryogenic treatment is carried out, in a conventional manner, by making the part stay in a medium at very low temperature, obtained with dry ice or with liquid or gaseous nitrogen. After the cryogenic treatment, the part is typically allowed to warm up to room temperature. It is also possible to carry out a stress relieving after the cryogenic treatment, either after the part has returned to ambient temperature, or as soon as the cryogenic treatment has ended, the return to ambient temperature then being effected by natural cooling at the air in the room returned.
- the invention also has the advantageous consequence that this stainless steel, before its cryogenic treatment, remains for the most part in the austenitic state, even during prolonged storage or prior transportation, taking place in winter conditions, before the possible shaping of the part which typically precedes the cryogenic treatment.
- FIGS. 1 and 2 An example of microstructures obtained with a steel of the invention before (FIG. 1) and after (FIG. 2) cryogenic treatment makes it possible to understand the principle of the invention.
- the horizontal direction corresponds to the rolling direction
- the vertical direction corresponds to the direction along the thickness of the sheet, perpendicular to the rolling direction.
- the steel whose microstructure is illustrated in FIGS. 1 and 2 has the composition of the steel of the invention I6 given in table 1.
- hypo-soaking is meant that the sheet has been cooled at high speed, 2 ° C / s or more, at least in the temperature range between 900 and 500 ° C.
- This compromise is a function of the respective proportions of the two phases, which can be adjusted by combining the composition of the steel and the parameters of the cryogenic treatment.
- the martensite and austenite bands, oriented in the rolling direction, have thicknesses whose order of magnitude can vary according to the proportion of martensite, these thicknesses being in the tens of pm, typically fifty pm.
- parts with more complex shapes than with known steels can be produced by known shaping processes on steel in the predominantly austenitic state, therefore before the cryogenic treatment.
- This is possible thanks to the good deformability of the sheet in the austenitic state of the steels of the invention, which is characterized by an elongation at break in uni-axial tension of at least 35%.
- the fine optimization of the mechanical properties of said steel in the partially martensitic state makes it possible to reduce the thickness of the sheet in order to lighten the part, with equal performance.
- the invention makes it possible to reduce this safety margin.
- the cryogenic treatment which gives the steels of the invention a very essentially two-phase structure of austenite and martensite makes it possible to find the optimal strength-ductility compromise for the future use of the part considered. Indeed, by modifying the temperature and time conditions of the cryogenic treatment, as will be explained below, it is possible to finely adjust the proportion of martensite. The higher this proportion, the more the mechanical resistance increases and the more the elongation at break decreases.
- the steelmaker will be able to carry out mass production of a steel according to the given invention, in a quantity which will enable it to take advantage, under good economic conditions, of the high production capacity of its installations.
- the customer such as an automotive subcontractor or an automobile manufacturer, who has purchased these steels in their predominantly austenitic state, can then cold-form them, to produce a wide range of parts using its conventional equipment.
- shaping The final mechanical properties of said steel are only adjusted at the final stage of the process, during the cryogenic treatment specific to each part, in order, for example, to respond correctly to stresses mechanical that will undergo the vehicle structure in which the part is inserted. Like shaping in the austenitic state, this cryogenic treatment can be carried out by the client, according to their precise needs.
- the chemical composition of the stainless steel used in the process according to the invention is as follows. All percentages are weight percentages.
- traces is meant values which are at the level of impurities resulting simply from the fusion of the raw materials and the processing, and correspond to:
- Its C content is between traces and 0.15% and preferably between 0.01% and 0.10%.
- C is also used in combination with N, Nb, and V in formula (1) to guarantee sufficient mechanical strength and impact resistance.
- N content is between 0.05% and 0.25%, and preferably draws between 0.10% and 0.25%.
- N has the same hardening effect as C, but is less embrittling due to the absence of primary nitrides.
- a content of at least 0.05%, and preferably at least 0.10%, is necessary to ensure sufficient hardening of the martensite that C, even at its maximum permissible content, cannot alone provide. Its maximum content is limited to 0.25%, because beyond that it also ends up weakening the metal after the cryogenic treatment.
- N is no longer soluble in liquid steel, which leads to the formation of nitrogen bubbles at the solidification, which degrade the internal health of the steel by leaving porosities in the solidified steel.
- N is also used in combination with C, Nb and V to guarantee sufficient mechanical resistance and resistance to impact.
- N is also used in combination with Cr, W and Mo to guarantee good resistance to corrosion.
- N is also involved in all formulas that balance the grade of steel, and its low cost makes it a particularly economical way to adjust the different values required for formulas (1) to (5) which will be seen below.
- Its Cr content is between 11.0% and 18.0%.
- the minimum content of 11.0% is justified to ensure the stainless steel's oxidability.
- a content higher than 18.0% no longer guarantees that a sufficient amount of martensite is obtained after cryogenic treatment, which degrades the mechanical properties.
- Mn content is between 2.0% and 8.0%, and preferably between 4.0% and 8.0%.
- Mn is used to promote the presence of the austenitic structure, but its gamma-like character only appears markedly from 2.0%. Its presence in large quantities makes it possible to reduce the content of Ni, an element which is also gammagenic but is of higher cost; therefore a minimum of 4.0% Mn is preferred. However above 8.0% of Mn in combination with the contents of the other elements, the amount of martensite after cryogenic treatment is too low, and no longer allows the desired mechanical characteristics to be obtained. Mn also intervenes in formulas (2) to (4) which will be seen later.
- Cu content is between traces and 3.0%, preferably between 1.5% and 3.0%.
- Cu promotes the austenitic structure and reduces the Ni content to reduce the cost of steel. Its effect is significant especially from 1.5%. However, above 3.0%, Cu poses problems during the pickling of steel, because it pollutes the pickling baths and then redeposits on the surface of the sheet. It also degrades the weldability. Cu is also involved in formulas (2), (3) and (4).
- Ni content is between traces and 2.0%, and preferably between traces and 1.0%.
- Ni is the most classic gamma element that stabilizes the austenitic structure of stainless steels. Its content is here limited to 2.0% and preferably to 1.0% to limit the cost of steel, the stabilization of the austenite also being ensured by Mn and, optionally, Cu.
- Mn which is compulsory and Cu which is preferably present in significant quantity
- Cu which is preferably present in significant quantity
- Ni also intervenes in formulas (2), (3) and (4).
- An excessive Ni content would be likely to lead to too low IMd and IMs values and the upper limit of 2.0% and preferably 1.0% is a summary of the metallurgical and economic imperatives linked to Ni.
- Mo improves resistance to corrosion. But, like Ni, it is a particularly expensive item. Its content is limited to 2.0% so as not to increase the cost of the steel too much and, because of its alphagenic nature, to limit the presence of delta ferrite which degrades the forgeability of the steel. Mo is also involved in formulas (2), (3), (4) and (5).
- W content is defined as a function of that of Mo by respecting the trace relationship £ Mo + 2W £ 2.0%.
- the advantages and disadvantages of W are qualitatively comparable to those of Mo. In practice, it is not usually added voluntarily, but it is mainly brought by the materials used for the addition of Mo, which contain it. W is also involved in formula (5).
- Si content is between traces and 1.0%.
- Si is an element commonly used in the steel making process. It is very reducing, and it therefore makes it possible to reduce the Cr and Mn oxides in the reduction phase of the steel which follows the decarburization phase in the AOD or VOD converter where the liquid steel is produced, as well as maintain a low level of dissolved oxygen in the liquid steel.
- the Si content in the final steel must be less than or equal to 1.0%, since this element has a hot hardening effect which limits the possibilities of hot deformation during hot rolling or shaping. generally hot.
- Al is a reducing element which can be conventionally used as a deoxidizer during the production of liquid steel. But it has the disadvantage of forming nitrides. These precipitates can alter the mechanical properties of steel, in particular by constituting crack initiation points. Finally, significant formation of inclusions of alumina during deoxidation, if these inclusions are not sufficiently well removed during the subsequent production of the liquid steel, can lead to clogging of the nozzles of the containers containing the liquid steel when it is poured into the mold. The upper limit of 0.1% takes account of all these drawbacks.
- Nb + Ta and V contents are each between traces and 0.20%, and preferably its Nb + Ta + V content is between 0.05% and 0.3%.
- Ta has no particular utility in the steels of the invention, but it is an element which is present in low content in the materials containing Nb used by the steelmaker to regulate the content of this element, and of which We must take in account.
- Nb and V improve the resilience of the martensite formed during the cryogenic treatment. This is why, preferably, a minimum of 0.05% for the sum of the contents of Nb, Ta and V is recommended. However, beyond 0.20% of each of the elements Nb + Ta and V, or preferably beyond 0.3% of (Nb + Ta + V), the excessive formation of carbides, nitrides and carbonitrides of V and Nb softens the martensite too much by reducing the contents of C and N in solid solution. To take this effect into account, Nb and V also intervene in formulas (1) and (3). Nb is also involved in formulas (2) and (4).
- these non-essential elements are capable of forming nitrides and coarse carbides in the liquid and during solidification which are particularly detrimental to the mechanical properties of the steel. Its S content is between traces and 100 ppm (0.0100%).
- a very low O content is an indication of very good inclusiveness, which is favorable to the mechanical properties of steel and its ability to be shaped. 200 ppm appears as the limit not to be exceeded for this purpose.
- This non-essential element is likely to help austenitization. But do not put more than 0.30% in order not to deteriorate the weldability if the steel is intended to be transformed into a part to be welded.
- austenitization it can be promoted, in addition by Ni, using other elements which are less costly than Co, such as Mn and Cu, so that the metallurgical interest of a high addition of Co would not justify the additional raw material costs it would entail.
- Y, Ce and La improve the oxidation resistance properties, which can be an advantage during hot forming.
- the possible total addition of Y + Ce + La is limited to 100 ppm.
- this element is not justified for reasons which are linked to the final properties of the steel. However, it may be present in a relatively residual manner, following the preparation of the liquid steel, if it has been used, as is conventional, for the deoxidation of the liquid steel and the control of the composition and morphology of oxidized inclusions.
- the rest of the steel consists of iron and impurities resulting from the production which were not added voluntarily.
- composition of the steel must also obey several conditions linking several of these elements.
- the contents of the various elements are in% by weight.
- This formula (1) translates the hardening of the martensite by the C and the N available in solution (which one calls (C + N) Mbre ), ie not precipitated in the form of nitrides, carbides and carbonitrides of Nb or V. This hardening of the martensite will affect the mechanical properties of the steel after cryogenic treatment.
- IMd is an indicator of the stability of austenite to deformation.
- the higher IMd the more austenite will transform into martensite during deformation. Its value will influence the mechanical properties of the steel before the cryogenic treatment, when the sheet is formed in an austenitic state to produce the part. It will also influence the properties after the cryogenic treatment of the part, because all of the austenite is not completely transformed into thermal martensite (i.e. the martensite obtained by cryogenic treatment, as opposed to martensite of deformation, which is formed during operations of forming a steel with an initially austenitic microstructure).
- An IMD of at least 40 is necessary to improve the mechanical properties after cryogenic treatment. Indeed, the portion of austenite which is not transformed into martensite during the cryogenic treatment must be able to partially transform into martensite during the deformation during the tensile test and lead by TRIP effect to the joint increase in resistance and elongation at break.
- An IMD greater than 140 is not suitable, since the shaping capacity of the initially austenitic sheet would be degraded by an excessive transformation of the austenite into martensite during the deformation.
- IMs is an indicator of the temperature at which transformation from austenite to martensite begins. It reflects the stability of austenite when the temperature drops.
- IMs must be at least -25 ° C for a sufficient amount of martensite to be formed during cryogenic treatment.
- the martensitic transformation is too limited whatever the time and temperature conditions of the cryogenic treatment.
- too limited martensitic transformation is meant a rate of martensite of less than 20% which no longer makes it possible to achieve the mechanical characteristics sought for structural applications.
- IMs must not exceed +15 so that the steel in the austenitic state before shaping of the part does not risk forming more than 10% of martensite during its storage or transport, during the winter. Above 10% martensite, the product is weakened and risks breaking during the shaping of the part. Too high an IMs makes also more difficult to control the rate of martensite obtained after cryogenic treatment.
- IMS is a particularly important and major parameter in the invention. A precise study was carried out by making steels of various chemical compositions to define the range of IMS allowing to ensure a compromise which allows:
- Creq / Nieq translates the more or less ferritic nature of the chemical composition.
- Creq / Nieq should not exceed 1.6 to avoid the excessive presence of delta ferrite (£ 3%) during hot rolling, which would degrade the forgeability of the steel and lead to cracks on the edges of the sheet.
- the PREN Platinum Resistance Equivalent Number
- the PREN is an indicator of the corrosion resistance of stainless steels. It accounts for the cumulative effects of the four elements Cr, Mo, W and N, which improve corrosion resistance.
- the PREN must be greater than or equal to 14.5 in the case of the invention, so that the steel can sufficiently resist pitting corrosion in a weakly chlorinated medium.
- a PREN of at least 15.5 provides resistance to pitting corrosion in a more concentrated chlorinated medium, and is therefore considered to be preferred since it widens the possibilities of using the steel of the invention.
- a steel according to the invention may comply with one or more several of said preferential ranges, while respecting only the most general ranges for the other contents / formulas
- the steel according to the invention lends itself very well to obtaining products of two different classes:
- One of the advantages of the invention lies precisely in the capacity of steels with an austenitic microstructure according to the invention to be shaped easily in the form of a part, before said part undergoes the cryogenic treatment at precisely adjusted parameters, which will give it the precise mechanical properties desired by the end customer but which would be likely to deteriorate this ability to be shaped.
- Performing this additional shaping of the steel in the form of a part before performing the cryogenic treatment makes it possible to take advantage of the great shaping capacities of the steel with an austenitic microstructure which has been obtained at this stage.
- One of the other advantages of the invention essential in an industrial manufacturing context, resides in the assurance that the product will undoubtedly remain very austenitic before it is shaped, even if it is stored or transported at low outside temperature. , this can go down to -15 ° C.
- the composition of the steel according to the invention also makes it possible to guarantee it.
- these properties can be further improved by stress relieving which is after the cryogenic treatment.
- This annealing can be carried out for itself, or can only be a consequence of a treatment which would have another aim, for example the hot deposition of a layer of paint on the product, for aesthetic reasons and / or corrosion protection. It can be carried out just after the end of the cryogenic treatment, or after the product has returned to room temperature.
- compositions of the various steel samples tested are shown in Table 1, expressed in% by weight.
- the values underlined are those which are not in accordance with the invention.
- the rest is iron and impurities resulting from processing.
- the elements not mentioned are therefore present at most only in the form of traces or impurities without metallurgical effects.
- the values of C + N - Nb / 7 - V / 4, IMd, IMs, Creq / Nleq and PREN have also been reported for each sample in Table 2.
- the steel sheets were then cold rolled to a thickness of 1.5 mm, annealed at a temperature of 1100 ° C, hyper-quenched at a cooling rate of 10 ° C / s between 900 and 500 ° C, then pickled.
- cryogenic treatment 30 min at -90 ° C was carried out on a sample of each steel sheet.
- steel I6 several samples were cut from the sheet in order to test different conditions of cryogenic treatment at temperatures ranging from -50 ° C to -130 ° C for periods ranging from 1 min to 60 min.
- Table 2 Values of formulas (1) to (5) from the chemical compositions of the samples tested
- Table 3 presents the results of tests and observations carried out on these steels, at various stages of their manufacture. The underlined values correspond to performances considered insufficient.
- the internal health is evaluated on a raw solidification state after casting, mainly on the presence or not of porosities due to an excessively high N content, knowing that the subsequent transformation operations will not degrade it. "1" means "good internal health”, "0” means "insufficient internal health”.
- the rate of martensite is determined by the magnetic measurement of the saturation magnetization. This measurement includes all the magnetic phases, and therefore a small amount of possible residual ferrite (generally ⁇ 3%). The rate of martensite is measured on the annealed state after treatment for one week at -15 ° C, and also after the cryogenic treatment for 30 min at -90 ° C noted "Cryo.” in table 3.
- a rate of martensite of less than 20% after the cryogenic treatment is not satisfactory in the case of the treatment described for the steel obtained, because it does not make it possible to reach a sufficiently high mechanical resistance for the structural parts.
- a rate of martensite greater than 90% after cryogenic treatment is also not satisfactory, at least for the preferred applications of the invention, since the ductility of the steel is then too low to allow sufficient deformation of the part before its rupture in the event of a violent shock, which greatly reduces its energy absorption capacity.
- Uniaxial tensile tests are carried out according to ISO 6892-1, part 1 of November 2016 at a deformation speed of 2.10 3 s 1 , in the direction perpendicular to the direction of rolling on the annealed condition treated one week at -15 ° C and on the condition after cryogenic treatment.
- An A% elongation at break on the annealed condition treated for one week at -15 ° C by at least 35% is considered necessary in all cases, to allow the production of complex parts by cold stamping.
- a mechanical strength of at least 1300 MPa and an elongation of at least 6% after cryogenic treatment for 30 min at -90 ° C are deemed necessary in the example described to resist the mechanical stresses to which the most structural parts are subjected. solicited.
- the impact resistance or resilience KCV is measured at -40 ° C on the state after cryogenic treatment by a Charpy mutton test on test pieces of length 55mm (depending on the direction of rolling), width 10 mm (depending on the direction perpendicular to the rolling direction), 1.5 mm thick (sheet thickness) notched in a “V” across the width with a radius at the bottom of the notch of 0.5 mm, a notch angle of 45 ° and a remaining width at the bottom of the cut of 0.8 mm.
- the energy is calculated from the level of rise of the arm of the Charpy sheep after the breakage of the test tube.
- the toughness is considered acceptable if KCV at -40 ° C is at least 60 J / cm 2 .
- the corrosion resistance is evaluated by an electrochemical pitting corrosion test in a medium composed of 0.02M NaCl, at 23 ° C. and at pH 6.6.
- the electrochemical test carried out on 24 samples makes it possible to determine the potential E 0.i for which the elementary probability of pitting is equal to 0.1 cm 2 .
- the corrosion resistance is considered unsatisfactory if the potential E 0.i is less than 350 mV, measured with respect to the calomel electrode saturated with KCI (350 mV / DHW). It is considered satisfactory, in particular for coated steels, if the potential E 0.i is between 350 mV / DHW and 500 mV / DHW. It is considered very satisfactory if the potential E 0.i is greater than 500 mV / DHW and less than 600 mV / DHW. It is considered excellent if the potential E 0.i is greater than 600 mV / DHW.
- Steels I9 and 112 represent the extremes among the steels of the invention in terms of elongation at break in the annealed condition after treatment for one week at -15 ° C.
- Steel I9 has the highest elongation due to the total absence of martensite and a low level of (C + N)
- the transformation of austenite into martensite began at -15 ° C because steel 112 has, by virtue of its chemical composition, the highest IMs of the steels of the invention.
- Steels I4, I6 and I7 are remarkable for their particularly high mechanical strength after cryogenic treatment. This is due to the beneficial effects of a relatively high (C + N)
- steels I2, I8, I9 and 113 are distinguished by higher resilience after cryogenic treatment, due to the presence of Nb or V, associated either with a weak IMs (less martensite) or with a (C + N)
- the best resilience is moreover obtained for the I2 steel which has both a high Nb content, a low IMS and a relatively low (C + N)
- a lower rate of martensite, martensite which can moreover be less hard because overall containing less C and N, leads for these steels to satisfactory mechanical strengths but lower than those of the other steels of the invention.
- the steels according to the invention 11 to 18 and 112 and 113 are characterized by satisfactory corrosion resistance. This resistance to corrosion was obtained, for several of the examples, without very significant addition of Mo, or even without addition of Mo at all (I2, I6, I7 and I8), and therefore at lower cost, because it is an element expensive. For steels I6, I7 and I8, this satisfactory corrosion resistance was obtained by virtue of sufficient Cr and N contents for this purpose, and for steel I2 thanks to a high content of N.
- Steels I9, 110 and 11 1 have superior corrosion resistance and are considered to be very satisfactory thanks to their Cr, Mo and N contents, leading to a PREN greater than 20.
- Steels 114 and 115 have an even higher corrosion resistance thanks to the high contents of Cr, Mo and N allowing a PREN higher than 23.
- Steel R1 has too high a N content to allow its complete dissolution in the liquid metal, which leads to the appearance of nitrogen bubbles during solidification. steel and therefore degrades its internal health. This too high N content also leads to too low elongation after cryogenic treatment.
- Too low elongations after treatment at -15 ° C are also obtained for steels R3 and R9. This comes for R3 from a too high IMd leading to too much formation of martensite during the deformation. For R9 this is due to a too high level of (C + N)
- Steels R1, R4, and R9 have too low resilience after cryogenic treatment.
- the steel R1 is weakened by an excessive content of N while the steels R4 and R9 are weakened by excessive contents of C.
- R2 and R4 steels have unsatisfactory corrosion resistances, as indicated by the too low values of pitting potential in correspondence with PREN levels (formula 5) too low.
- the highest tensile strengths that can be achieved by cryogenic treatment of the steels of the invention can be of the order of 1600-1700 MPa. Depending on the function and the mechanical stresses of the part within the whole structure, it is not always a maximum mechanical resistance that is sought for the material.
- this may be the energy absorption capacity in the event of an impact on the vehicle which is the factor to be considered in a privileged manner, or a compromise between the mechanical strength and the energy absorption capacity. It can be estimated in a simple manner by considering the product A x Rm.
- the advantage of the invention is that it is possible, by appropriate conditions of duration and temperature of the cryogenic treatment, to adjust the final mechanical properties steels of the invention according to the desire of the user, by acting on the proportion of martensite obtained during the cryogenic treatment, from a steel having a given unique composition.
- the temperature that transforms the most austenite into martensite in the shortest time is -90 ° C.
- the transformation is less complete, for an equal treatment time.
- the optimum temperature for transforming the most austenite into martensite, and in the shortest time is between -70 ° C and -1 10 ° C .
- the optimum speed and magnitude of the isothermal martensitic transformation for the steels according to the invention therefore lies at a value belonging to the above-mentioned range.
- the temperature range for transforming the most austenite into martensite is between -50 ° C and -130 ° C . It is unnecessary and more expensive to carry out the cryogenic treatment at a temperature below -130 ° C, the transformation rate remaining equal, or even lower, than that obtained at a higher temperature.
- a person skilled in the art will conventionally know how to determine by testing the temperature and the duration of the cryogenic treatment necessary to obtain the desired martensite level in the whole product, and this for a product of given dimensions, in particular its thickness. .
- the cryogenic treatment takes place for 1 to 60 min, preferably between 1 min and 30 min.
- Table 4 also shows that the mechanical properties of I6 steel vary with the rate of martensite. The higher the rate of martensite, the higher the tensile strength Rm and the elongation at break A% low, because martensite is harder and less ductile than austenite.
- the rate of martensite to target is between 20% and 28% for l steel I6.
- This rate of martensite can be obtained by carrying out a treatment for 5 to 10 min at -70 ° C or from 30 to 60 min at -50 ° C.
- the impact resistance characterized by the KCV impact test at -40 ° C is also given in Table 4. It is always greater than 60J / cm 2 for I6 steel and increases when the rate of martensite decreases.
- the part can, for example, be painted by staying in a paint bath for one hour at a temperature of the order of 200 ° C.
- This treatment which plays a role of stress relieving income, provides a further improvement in properties. mechanical. It allows an increase of around 150 MPa in the elastic limit, as well as an increase in elongation at break of around 5%. Thus the elongations after cryogenic treatment presented in Tables 3 and 4 will be improved if the part is painted hot.
- a stress relieving income following the cryogenic treatment can be practiced by other means than dipping in a hot paint bath, with the sole aim of improving the mechanical properties of the steel.
- the conditions for this income are, in general, a temperature between 90 and 500 ° C and a duration between 10 s and 1 hour. The room is then naturally air-cooled.
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- Organic Chemistry (AREA)
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- Physics & Mathematics (AREA)
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- Heat Treatment Of Steel (AREA)
Abstract
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Priority Applications (3)
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BR112021010278A BR112021010278B8 (pt) | 2018-12-06 | 2018-12-06 | Aço inoxidável, produtos siderúrgicos em aço inoxidável e métodos de fabricação do produto siderúrgico em aço inoxidável |
PCT/IB2018/059714 WO2020115531A1 (fr) | 2018-12-06 | 2018-12-06 | Acier inoxydable, produits réalisés en cet acier et leurs procédés de fabrication |
EP18840036.0A EP3891316A1 (fr) | 2018-12-06 | 2018-12-06 | Acier inoxydable, produits réalisés en cet acier et leurs procédés de fabrication |
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PCT/IB2018/059714 WO2020115531A1 (fr) | 2018-12-06 | 2018-12-06 | Acier inoxydable, produits réalisés en cet acier et leurs procédés de fabrication |
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WO2020115531A1 true WO2020115531A1 (fr) | 2020-06-11 |
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PCT/IB2018/059714 WO2020115531A1 (fr) | 2018-12-06 | 2018-12-06 | Acier inoxydable, produits réalisés en cet acier et leurs procédés de fabrication |
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EP (1) | EP3891316A1 (fr) |
BR (1) | BR112021010278B8 (fr) |
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Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
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CN114875324A (zh) * | 2022-05-19 | 2022-08-09 | 山西太钢不锈钢股份有限公司 | 一种预硬态耐蚀模板用钢及其制造方法 |
Citations (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO2006068610A1 (fr) * | 2004-12-23 | 2006-06-29 | Sandvik Intellectual Property Ab | Acier inoxydable martensitique durcissable par précipitation |
WO2008087249A1 (fr) * | 2007-01-17 | 2008-07-24 | Outokumpu Oyj | Procédé de fabrication d'un objet en acier austénitique |
WO2015141674A1 (fr) * | 2014-03-17 | 2015-09-24 | 新日鐵住金ステンレス株式会社 | Tôle d'acier inoxydable ferritique à utiliser dans une pièce découpée sur mesure, matériau de pièce découpée sur mesure présentant une excellente usinabilité, et son procédé de production |
EP2952602A1 (fr) * | 2013-02-04 | 2015-12-09 | Nippon Steel & Sumikin Stainless Steel Corporation | Feuille d'acier inoxydable ferritique ayant une excellente aptitude au façonnage |
EP3214198A1 (fr) * | 2014-10-31 | 2017-09-06 | Nippon Steel & Sumikin Stainless Steel Corporation | Acier inoxydable à base de ferrite présentant une haute résistance à la corrosivité provoquée par du gaz d'échappement et la condensation et des propriétés au brasage élevées et procédé pour la fabrication de ce dernier |
EP2480693B1 (fr) * | 2009-09-21 | 2018-09-12 | Aperam | Acier inoxydable à variations locales de résistance mécanique |
-
2018
- 2018-12-06 WO PCT/IB2018/059714 patent/WO2020115531A1/fr unknown
- 2018-12-06 BR BR112021010278A patent/BR112021010278B8/pt active IP Right Grant
- 2018-12-06 EP EP18840036.0A patent/EP3891316A1/fr active Pending
Patent Citations (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO2006068610A1 (fr) * | 2004-12-23 | 2006-06-29 | Sandvik Intellectual Property Ab | Acier inoxydable martensitique durcissable par précipitation |
WO2008087249A1 (fr) * | 2007-01-17 | 2008-07-24 | Outokumpu Oyj | Procédé de fabrication d'un objet en acier austénitique |
EP2480693B1 (fr) * | 2009-09-21 | 2018-09-12 | Aperam | Acier inoxydable à variations locales de résistance mécanique |
EP2952602A1 (fr) * | 2013-02-04 | 2015-12-09 | Nippon Steel & Sumikin Stainless Steel Corporation | Feuille d'acier inoxydable ferritique ayant une excellente aptitude au façonnage |
WO2015141674A1 (fr) * | 2014-03-17 | 2015-09-24 | 新日鐵住金ステンレス株式会社 | Tôle d'acier inoxydable ferritique à utiliser dans une pièce découpée sur mesure, matériau de pièce découpée sur mesure présentant une excellente usinabilité, et son procédé de production |
EP3214198A1 (fr) * | 2014-10-31 | 2017-09-06 | Nippon Steel & Sumikin Stainless Steel Corporation | Acier inoxydable à base de ferrite présentant une haute résistance à la corrosivité provoquée par du gaz d'échappement et la condensation et des propriétés au brasage élevées et procédé pour la fabrication de ce dernier |
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
CN114875324A (zh) * | 2022-05-19 | 2022-08-09 | 山西太钢不锈钢股份有限公司 | 一种预硬态耐蚀模板用钢及其制造方法 |
Also Published As
Publication number | Publication date |
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BR112021010278B1 (pt) | 2023-10-24 |
EP3891316A1 (fr) | 2021-10-13 |
BR112021010278A2 (pt) | 2021-08-17 |
BR112021010278B8 (pt) | 2023-11-21 |
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