JPS58100620A - Manufacture of welded structure - Google Patents

Abstract

PURPOSE:To manufacture a welded structure having much less heat treated strain and high strength easily in a short time by irradiating welded toe zones with a beam having high energy density and surface hardening. CONSTITUTION:While a shaft 1 where a rib 2 is welded is rotated by a driving mechanism 14, laser light 12a generated by a laser oscillator 11 is converged through a convergent mirror 13 to irradiate a weld toe zone 3 with laser light 12b converged to high energy density. This irradiation heats the toe zone 13 speedily up to temperature higher than a transition point A1 and lower than a fusion point, and the beam irradiation is stopped. The heated part is coolded rapidly by heat diffusion, so it is hardened locally. When residual stress in welding is held specially high because of the shape of the structure, this welded structure is annealed to remove the stress, and then beam irradiation in said method is carried out to obtain the same effect.

Description

DETAILED DESCRIPTION OF THE INVENTION (51) Technical Field of the Invention The present invention relates to a method for manufacturing a high-strength welded structure in which a welded toe is subjected to rapid (double-surface hardening) treatment and has extremely low heat treatment distortion.

(b) Prior Art 1 Figure 6: Shows a cross section when shafts 1 and 2 of a rotating body are welded - When such a shaft 1 is used as a rotating body, the stress generated in the welded toe 3 Due to concentration and welding residual stress, fatigue strength decreases, and accidents such as breakage during use often occur.

Conventionally, methods for improving fatigue strength in such cases include ■
This method of finishing the weld toe with a grinder or machining is used, such as remelting the weld toe with a TIG arc. Although it is extremely effective as a means to improve
Finishing the 9th 6; requires mastery of Kanatae. Moreover, it has drawbacks such as a large number of man-hours and poor economic efficiency. Furthermore, due to the nature of the work, automation is extremely unlikely. Finishing according to the machining manual also requires a large number of man-hours and the shape of the part is complex, so setting the working conditions (: also has the disadvantage of requiring a lot of time and skill.

Although the method of remelting with a TIG arc is an excellent method for improving fatigue strength, the arc phenomenon is subject to many conditions 6; requires skill. How to remelt it again =
In some cases, if the base material has a large amount of carbon (= cracks may occur).

(C) Purpose of the Invention The present invention does not require any skill, and moreover, after treatment (:
It is an object of the present invention to provide a method for manufacturing a welded structure that does not cause distortion.

(d) Summary of the Invention The present invention is characterized in that a welding toe (: heat-treated by irradiating with a beam having a high energy density).

(・) Embodiment of the Invention An embodiment of the present invention will be described below with reference to the drawings.
11 is a laser fMm device, 121 is a laser beam generated by the laser oscillator 11, 13 is a condenser, 12b is a laser beam condensed by this condenser 13, and 14 is a laser beam 12b. Welded toe part 3 of shaft 1
15 is a control device that controls the laser oscillator 11 and the drive mechanism 14.

Here, the laser oscillator 11 is a welded toe portion 3 of the shirt) 1.
C: A device that supplies the necessary energy for surface hardening), and in this example, a carbon dioxide laser oscillator is used. The laser beam 12a generated by the laser oscillator 11 is focused by a focusing mirror 13 to an energy density that can harden the surface of the weld toe portion 3 of the shaft 1. Drive mechanism 14
(=The shaft 1 is rotated to perform continuous C: surface hardening heat treatment of the weld toe portion 3. The control device 15 determines that the surface hardening heat treatment is desired. Controls the rotation speed of the shaft.

The laser beam used in this example has an energy density of 10 to
It can focus extremely high light at 10 W/7, and as a result, the area irradiated with the laser light is rapidly heated (-heated.
After the irradiation is stopped, the heat diffuses into the heating section (which occupies a much larger volume than the two), so
The heating section is rapidly cooled down.

As a result, the weld tow portion irradiated with the laser is rapidly cooled and locally hardened. In addition, the laser irradiation part is equipped with C before irradiation.
; Apply a laser light absorber (for example, graphite) to improve absorption of laser light.

In this example (2), in order to harden the weld toe, the temperature of the heating part is set to be above the transformation point and below the melting point of the material of that part = laser irradiation conditions and shaft rotation speed. Since the laser beam is a heat source with high energy density, the shaft can be rotated at high speed.By adjusting in this way, the metal structure of the laser irradiated area can be
If the shaft has a relatively small amount of carbon (about 0,296), it will be a mixture of martensite and troostite, if it has a large amount of carbon (α3- or more), it will be mainly martensite 1',
Become. For this reason, the laser-hardened part becomes a local expansion effect hole due to martensitic transformation), and finally becomes a compressive residual stress state C2. Due to the accompanying laminar flow on the surface of the material and microscopic melting due to overheating of the convex parts, it becomes partially smooth.

If the residual stress during welding is particularly high due to the shape of the structure (for example, if the welded part is large), only local irradiation with a laser will generate compressive residual stress in Table I01. may not be possible.

In this case, the same effect can be obtained by performing stress relief heat treatment on post-weld structure 1 and then curing the welded toe by laser irradiation.

Furthermore, if the weld toe has large irregularities (2), it is possible to irradiate this part with a high laser energy density (2) to partially melt it (2) to reduce the irregularities by irradiating this part with a high laser energy density;
After that, the energy density of the laser is reduced and this portion is reheated and cured at a temperature above the transformation point and below the melting point.

In the above description, a laser beam is used as a heating source (although there are two cases, it is also possible to use an electron beam similar to this or an electron beam having a high energy density).

(f) Effects of the Invention According to the present invention, by laser irradiating the parts where fatigue cracks are likely to occur during use, the metal structure of the parts is hardened and the strength is increased. Since it is possible to improve the S* residual stress and reduce the unevenness of the #*) portion, it is possible to obtain a method for manufacturing a welded structure with high strength.

In addition, the process does not require any skill on the part of the operator, can be easily automated, and does not generate fine powder or the like that deteriorates the quality of work 11, making it possible to improve work efficiency.

[Brief explanation of the drawing]

FIG. 1 is a partially cutaway front view of a welded structure related to the present invention, and FIG. 2A is an explanatory diagram showing an apparatus according to an embodiment of the present invention. 1... Shaft 3... Welding toe part 11...
・Laser oscillator 12M, 12b... Laser light (7
317) Agent: Patent Attorney Noriyuki Chika (and 1 other person) // -9'l

Claims (1)

[Claims] (1) The weld toe of the welded structural material is irradiated with a beam having an energy density and heated to a low temperature above the transformation point and below the melting point to harden it.
Method for manufacturing a welded structure that produces mold (A) After welding, the welded structural material is annealed to remove stress, and then the am welded material is irradiated with a beam having a very high energy density to A method for manufacturing ms structure characterized by curing by heating to a temperature lower than the melting point◎