JPS60218421A - Heat treatment of steel by laser - Google Patents

Abstract

PURPOSE:To heat-treat safely and efficiently the irradiated part of a steel material having an intricate shape without using a paint for absorption by using a cavity to converge the laser beam reflected on the surface of the steel material to the heat treating part with multiple reflection. CONSTITUTION:A laser beam 20 is condensed by a condenser lens 11 to the incident face 41 of an optical fiber 40 and is introduced into the optical fiber. Said beam is irradiated from the output part 42 of the fiber set in the hole 55 of a cavity 50 for introducing the beam 20 to the heat treating surface 31 of a steel material 30. The diameter of the hole 55 is determined by the diameter of the fiber 40. As the fiber is finer, the hole is made smaller correspondingly and therefore the effective reflecting area of the inside surface 54 of the cavity increases. The beam width Bw on the surface 31 is determined by the diverging angle of the beam as well as the spacing between the cavity 50 and the material 30. If the beam 20 is set adequately in the power thereof and is irradiated, the beam 20 having the width Bw is irradiated to the surface 31 and the beam 20 reflected by the surface 30 is further reflected by the surface 54 and arrives at the surface 31. The beam is thereafter converged by multiple reflection to the surface 31.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a heat treatment method for rust, and in particular to heat treatment using a laser.

[Prior Art] As is well known, the energy density of a laser beam is extremely high, and can easily be increased to more than 10,000 times that of arc welding. For example, the energy density W/cd of an oxyacetylene flame is about 10, and the energy density of an argon arc (20OA) is about 1.5 x 10', whereas in the case of a continuous laser beam it is about 109; The energy density of is about 1013.

Therefore, the use of such a high-energy-density laser beam facilitates processing such as surface hardening, welding, and cutting of steel materials, and has been used in various fields in the past. Although laser beams are very useful in this way,
This does not necessarily mean that there are no problems.

In other words, the efficiency of melting steel by the laser beam is ■Proportional to the square of the laser power, ■Proportional to the fourth power of the beam diameter, ■Proportional to the square of the energy absorption rate.

Among these, (2) and (2) are determined by the laser oscillator, but (2) is largely influenced by the irradiation technique. Therefore, it is necessary to increase the energy absorption rate on the steel surface, and in order to do this, 1) use the multiple reflection effect due to surface roughness, 2) improve wavelength absorption with an oxide film, 3) use laser plasma, etc. Measures such as indirectly increasing energy efficiency using secondary effects are required, and generally, for example, JOM.

As shown on pages 5 to 11 of the April 1976 issue, in order to reduce the reflection of the laser beam on the surface of the steel material, a method is to pre-coat the heat-treated area with paint, etc. that has a high laser beam absorption rate. It is being

This conventional method involves a step of applying paint or the like, which complicates the process. In addition, scattered substances are generated when paint or the like is heated and melted by a laser beam. This scattered material not only absorbs the laser beam and reduces the intensity of the laser beam, but also causes uneven irradiation during continuous irradiation processing, and has a negative impact on the human body, so it is essential to dispose of this scattered material. be.

In addition, mirrors are usually used to transmit the laser beam to the irradiation section, but the mirror system is determined by the shape of the object to be irradiated, so if the shape of the object becomes complex, the mirror system also becomes complicated. There is a problem.

[Objective of the Invention] The present invention is capable of reducing the amount of laser beam reflection on the steel surface without the troublesome work of applying an absorbing substance to the steel surface or the accompanying harm. The purpose of the present invention is to provide a method for stably and efficiently heat-treating steel materials, even on complex-shaped irradiation parts, by increasing the effective absorption rate.

[Configuration 2 of the invention] In the present invention, the heat treatment section is shielded by a cavity having a laser beam introduction hole, the laser beam is transmitted to the cavity through an optical fiber, and the heat treatment section is irradiated with the laser beam from the introduction hole. The reflected and radiant energy from the cavity is focused on the heat treatment section by multiple reflections on the inner surface of the cavity.

According to this, the effective absorption rate of the laser beam on the surface of the heat-treated portion is increased, and efficient heat treatment is performed.

The present invention will be described in detail below with reference to the drawings.

FIG. 1 shows an apparatus configuration for carrying out one embodiment of the present invention. In the figure, 10 is a laser oscillator, and 11 is a laser beam condensing lens. 20 is a laser beam, 30 is a steel material to be heat treated, and 31 is a surface thereof to be treated. 40 is an optical fiber for transmitting light. Reference numeral 50 denotes a cavity that covers the heat-treated portion, and its inner surface 54 is, for example, mirror-finished and plated with gold to have an extremely high reflectance. 55 is a laser beam introduction hole provided in the upper part of the cavity 50, and serves as an introduction hole for the fiber 40. 51 is an atmospheric gas inlet, 52 is a cavity cooling water inlet, and 53 is a cooling water outlet.

In order to heat-treat steel materials according to the present invention, the laser beam 20 is focused on the laser introduction surface 41 of the fiber 40 using the condenser lens 11 and introduced into the fiber.
The laser beam 20 is transmitted from the output part 42 of the fiber set in the laser beam introduction hole 55 to the heat-treated surface 3 of the steel material 30.
Irradiate to 1.

The diameter of the introduction hole 55 is determined by the diameter of the fiber 40.

The thinner the fiber, the smaller the introduction hole, which increases the effective reflective area of the cavity inner surface 54. Further, the beam Bw at the heat-treated surface 31 is determined by the divergence angle of the beam, the diameter of the cavity 50, and the distance between the cavity 50 and the steel material 30.

Also, the power of the laser beam is determined by the width W of the heat treatment section.

The heating/melting energy PM of the heat treatment section, which is determined from the depth d and the processing speed ■, is set with some efficiency η taken into consideration.

Therefore, when the laser beam 20 is irradiated, the surface 31 of the steel material 30 is irradiated with a laser beam having a beam width Bw. The light is reflected and reaches the surface 31 of the steel material 30, and is then subjected to multiple reflections and converged on the surface 31 of the steel material 30. As a result, the effective absorption rate de of the irradiated part is c(e=c<+(1-c()cf+(1-d)2ri+
...ζl - Old... As shown in (1), the value is almost 1. Here, d is the absorption rate of the laser beam on the steel surface.

FIGS. 2a to 2c and 3a to 3c are explanatory diagrams showing the differences between the conventional method and the method of the present invention. That is, Fig. 2a shows the case where the surface of the steel material is directly irradiated with a laser beam, and the amount of energy incident on the steel material is expressed as El,
If the amount of reflected energy is E2 and the amount of absorbed energy is E3, then E, = E2 + E3, and the absorption coefficient cf, a is σa = E3/Ei, which is 0.1-0 for a CO2 laser on a normal steel surface.
．． 15. VAG rate i: 0.31-0.4 is low and impractical from the point of view of energy efficiency.

FIG. 2b shows a conventionally used method in which paint I2 is applied to the surface of a steel material in order to increase the absorption rate of the laser beam. In this case, the absorption coefficient will be 0.8 or more.

Figure 2c shows the method of the present invention, and the absorption coefficient of the steel surface is the same as (7 (a) in Figure 2a, but the effective absorption coefficient ■C is close to 1.0 due to the multiple reflection effect of the cavity. Become.

Further, FIGS. 3a, 3b, and 3c show cross-sectional shapes of the heat treatment section corresponding to FIGS. 2a, 2b, and 2c, respectively, and the laser output and processing speed are constant. In addition, 33 is a heat treatment part, da, db, and d.
a is its depth, W a , W d and We are its width.

Comparing the efficiency of the heat treatment zone, since the treatment speed is constant as mentioned above, the ratio of the cross-sectional area is sufficient, and the result is da
-Wa(b-Wb(dc-Wc).

It can thus be seen that the method of the present invention has a high effective absorption rate and is therefore energy efficient.

Note that in the method of the present invention, atmospheric gas can be introduced into the cavity as shown in FIG.
This gas is used to prevent oxidation in the heat-treated portion and to prevent oil and the like adhering to the surface of the steel material from evaporating and adhering to the inner surface of the cavity.

Figures 4a to 4d show the structure of the fiber,
If the laser power that can be transmitted by one fiber is Po, and the required laser power is two (=ηPs) taking into account the heating/welding energy PM and some efficiency η, then the required number of fibers N is calculated by the following formula. become that way.

N = (77'PM/PO) = PT /PO However, III
N is a decimal number, and if a decimal point occurs, round it up to 1.

Figure 4a shows the case of one fiber, Figure 4b shows the case of two fibers, Figure 4c shows the case of three fibers, and Figure 4d shows the case of 7 fibers.
The case of a book is shown.

FIG. 5 shows an example in which a plurality of fibers are used in the present invention. That is, a plurality of fibers 40 are bundled and fixed in a laser beam introduction hole 55 provided at the upper part of the cavity 50 with a fiber holder 56, and the laser output part 42 of the fiber is on the same plane as the reflection surface 54 inside the cavity so that the laser beam is not transmitted. uniform emission and avoid preventing laser reflection effects within the cavity.

In addition, in the fiber arrangement, it is desirable to make the fiber surface as small as possible in order to increase the reflection efficiency from the reflection distribution of the laser beam from the processing section.

Figures 6a to 6e show the shape of the cavity,
The shape is not limited to the hemispherical one shown in Fig. 6b, but the distance MΩ between the center point Pc of the sphere and the heat-treated surface 33 can be changed as shown in Figs. 6a to 6C, taking into account the distribution of reflected light. It is possible.

Also, instead of being spherical, it may be cone-shaped as shown in Figure 6d, or parabolic as shown in Figure 6e; in these cases, the angle θ and the center point, respectively. The reflected beam distribution is set by Pc and gap g.

This makes it possible to control the required heating and melting range.

FIG. 7 shows a schematic diagram of an apparatus configuration when the present invention is applied to butt welding of ultra-thin steel plates.

When butt welding the thin plates 30 and 30', the thinner the plate thickness t is, the more the molten metal drips off if the amount of energy input is excessive, so it is necessary to use low-energy welding, and the heat treatment is carried out taking the butt interval into consideration. Part (melting area) width W of 33.34
Set m.

Wm>2t. In this case, there is a lot of reflection on the steel plate surface 31, and if there is no reflection on the cavity 50, the welded part cannot be melted.

[Example] Three YAG lasers with output of 6001, core diameter of 1.2m
When carbon tool steel was quenched using three fibers of 20 mm diameter and a copper water-cooled cavity with a gold-plated inner surface and a radius of 20 mm, the depth of the hardened layer was 0.5 mm without a light-absorbing coating. , width 8nn, processing speed 40I
111 heat treatments could be performed.

The absorption energy efficiency (dXWXV, /η-P) at this time was 110 mW+3/kJ.

In 22, η is the laser beam transmission efficiency using a fiber, which is 80%.

On the other hand, when the steel surface coated with manganese phosphate was heat-treated using a Co2 laser with an output of IKw and a beam diameter of 4.7 mφ, the hardened layer depth was 0.5 mm and width was 3 mm.
．． 5 m, and the processing speed was 21 mn/sec.

Incidentally, the amount of absorbed energy at this time was 36.8 on'/kJ. Therefore, the efficiency of the method of the present invention is about three times or more than that of the conventional method.

[Effects of the Invention] As explained above, the method of the present invention uses a cavity to multiple-reflect the laser beam reflected on the surface of the steel material and absorbs it into the heat treatment area. It is possible to increase the effective absorption rate on the surface of the steel material and perform efficient heat treatment without having to do so.

Furthermore, since the laser beam is transmitted into the cavity through a fiber and irradiated by internal reflection of the cavity, no condensing lens is used, and therefore the irradiation width of the laser beam can be widened.

Furthermore, since the present invention does not require high energy density as in the case of laser welding, it is possible to achieve a relatively quiet heating and melting phenomenon similar to that of a heat conduction type without generating plasma.

Furthermore, the method of the present invention has great effects, such as being able to easily heat-treat steel materials while rotating or moving.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing the configuration of an apparatus for implementing the present invention in one embodiment, FIGS. 2a, 2b, and 2C are explanatory diagrams showing the difference in absorption rate between the method of the present invention and the conventional method, and FIG. 3a ,
3b and 3C are explanatory diagrams showing the cross sections of the heat-treated portion in the method of the present invention and the conventional method; FIGS. 4a, 4b, 4c, and 4d are sectional views showing the structure of the fiber; The figure is a longitudinal cross-sectional view of the cavity, Figure 6a, Figure 1. Chapter 6b
6C are cross-sectional views showing various shapes of the cavity, and FIG. 7 is a cross-sectional view showing an embodiment in which the method of the present invention is applied to butt welding of ultra-thin steel plates. 10: Laser oscillator 11: Lens 1゛2: Paint 20
: Laser beam 30: Steel material 31; Steel material surface 33: Heating/melting area 40: Optical fiber 41: Incident surface 42:
Radiation surface 50: Cavity 51: Atmospheric gas inlet 52.53
: Cavity cold water drawer 54: Cavity inner surface 55: Laser beam introduction hole 56
: Fiber holder Bw: Laser beam width of irradiation part Patent applicant: Nippon Steel Corporation 68 AjU 6d 6e 6b - 6C 7 Mr. Manabu Shiga, Commissioner of the Patent Office Display 1982 Patent Application No. 074422 2
, Title of the invention Laser heat treatment method for steel 3, Relationship to the amended case Patent applicant address 2-6-3 Otemachi, Chiyoda-ku, Tokyo Name (6
65) Nippon Steel Corporation Representative Takeshi 1) Yutaka 4, Agent 103 Phone: 03-864-6052
Address: 2-27-6-5 Higashi Nihonbashi, Chuo-ku, Tokyo; date of amendment order: July 11, 1980 (shipment date: July 31 of the same year) 6;
Target of amendment: column of title of invention, scope of claims, column 7 of brief explanation of drawings, contents of amendment (1) “Steel treatment by laser” column of title of invention on page 1 of the specification. "heat treatment method for steel" should be corrected to "heat treatment method for steel by laser". (2) The entire text of the scope of claims column on page 1 of the specification shall be corrected as follows. 2. Scope of Claims In a steel heat treatment method in which the surface of steel is irradiated with a laser beam to heat or melt the surface and modify the surface properties, the heat treatment part is blocked by a cavity, and an optical fiber is introduced into the cavity. A hole is prepared, a laser beam is transmitted into the cavity through an optical fiber, the laser beam is irradiated onto the heat treatment area without focusing, and the reflected and radiant energy from the heat treatment area is multi-reflected on the inner surface of the cavity to generate heat. A method for heat treatment of steel using a laser, which is characterized by converging the laser beam onto a treatment section.'' (3) ``and 6
6c, 6d and 6e are corrected.

Claims (1)

[Claims] In a steel heat treatment method in which the surface of the steel is irradiated with a laser beam to heat or melt the surface and modify the surface properties, the heat treatment part is shielded by a cavity, and the cavity is provided with an optical fiber introduction hole. The laser beam is transmitted into the cavity through an optical fiber, and the laser beam is irradiated onto the heat treatment area without condensing, and the reflected and radiant energy from the heat treatment area is transmitted to the heat treatment area through multiple reflections on the inner surface of the cavity. A method of heat treating steel using a laser characterized by convergence.