JPS61221330A - Laser post heat treatment - Google Patents

Abstract

PURPOSE:To make the hardness of a weld metal lower and the toughness thereof higher and to decrease thermal strain in the stage of welding a member to be welded by a laser beam by branching part of the laser beam and irradiating the weld metal with the out-of-focus laser beam. CONSTITUTION:The laser beam 1 is converged by a condenser lens 4 and is focused to the weld zone of the base metal 9 to be welded so that the base metal is welded by the weld metal 8. Part of the laser beam 1 is taken out by a beam splitter 2 and is reflected toward the metal 9 by a bent mirror 3 facing the splitter. Such beam is passed through a condenser lens 5 to deviate the focus so that a suitable irradiation area and power density are obtd. Such beam is irradiated to the weld metal 8 to heat the weld metal to the temp. just below the A1 transformation point thereof then to temper the same. The weld metal is continuously tempered in succession to welding, by which the hardness of the weld metal 8 is decreased and the toughness thereof is improved with the simple operation. The productivity is thus improved.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a post-laser heat treatment method.

[Conventional technology and its problems]

In general, laser welding has significantly lower heat input and faster speed than other welding methods, so it is a highly accurate and highly efficient welding method.

However, for this reason, the hardness of the weld metal is higher than that of other welding methods, and the toughness of the weld metal portion is reduced. Therefore, depending on the product, post-heat treatment is performed to reduce the hardness of the weld metal and heat affected zone. However, this method of performing post-heat treatment has the following drawbacks.

(1) A considerably large amount of energy is required to heat the product to 500-600°C.

(2) Heat distortion is likely to occur, reducing processing accuracy.

(3) It is necessary to maintain the product temperature at 500 to 600° C. for about 1 hour, which impairs the high efficiency that is a characteristic of laser welding.

[Means for solving problems]

The present invention is a post-laser heat treatment method characterized by irradiating a welded member with a laser beam to form a weld metal, and then irradiating the weld metal with a defocused laser beam to the weld metal immediately after welding.

[Action/effect of the invention]

According to the post-laser heat treatment method of the present invention, the weld metal formed on the workpiece by laser beam irradiation is irradiated with a branched part of the welding laser beam or a predetermined output and Since the laser beam with the irradiation area is irradiated with a blurred focus, it reduces the hardness of the weld metal and increases the toughness of the weld, and heats only the weld, reducing thermal strain and increasing efficiency. Since post-heat treatment can be performed at the same time as welding, productivity can be improved.

[Example] - Hereinafter, an example of the present invention will be described with reference to FIG. 9 in the figure is a base material which is a member to be welded. A condenser lens 4 is provided above the welding start point of the base material 9 so that a welding beam 6 of the laser beam 1, which will be described later, is focused on the welding start point. A laser beam splitter 2 is provided above and opposite the condensing lens 4 to take out a portion of the laser beam I. A part of the extracted laser beam 1 is supplied to a pent mirror 3 provided opposite to the laser beam sinter 2. A condenser lens 5 is provided below the pent mirror 3 so as to face the weld metal 8 formed on the base material 9 by the welding beam 6. The focal length of the third condenser lens 5 is set to be shorter than that of the condenser lens 4 below the laser beam splitter 2 described above. A part of the laser beam I guided from the pent mirror 3 to the condensing lens 5 is defocused and then supplied onto the weld metal 8 as a heat treatment laser beam 7.

A part of the laser beam L taken out by the beam splitter 2 is sent to the mirror 3, where it is
The light is bent downward by 0' and sent to the condenser lens 5. on the other hand,
The laser beam that has passed through the beam sinter 2 is focused and irradiated onto the base material 9 by a condensing lens 4 to perform welding. A part of the laser beam l that has passed through the condensing lens 5 is once focused and then expanded again to become a heat treatment laser beam 7, which irradiates the weld metal 8 at a position where an appropriate irradiation area and power density can be obtained. be done. The lower density of the post-heat treatment laser beam 7 raises the temperature of the weld metal 8 to A, just below the transformation point temperature. After irradiation, the temperature of the weld metal 8 is the same as that of the base metal 9.
However, since the temperature of the base metal near the weld metal 8 is somewhat high immediately after welding, the irradiation with the laser beam 7 for post-heat treatment does not cause the temperature to rise rapidly like during welding. The temperature does not increase, and the hardness of the weld metal 8 decreases due to the effect of tempering.

As described above, according to the post-laser heat treatment method of the present invention, the hardness of the weld metal can be reduced and the toughness of the welded part can be increased. Furthermore, since post-heat treatment can be performed simultaneously while welding, productivity can be increased. Furthermore, since only the welded area is heated, thermal distortion can be reduced and efficiency can be increased.

Note that the hardness of the weld metal 8 can be similarly reduced by lowering the output of the welding laser beam and defocusing the welding laser beam to irradiate the weld metal 8 after welding is completed without using a beam splitter.

Incidentally, in order to confirm the effect of the present invention, the state of post-heat treatment of the butt welded part of the base material 9 made of low alloy steel by the laser is shown. After researching each, I found that the second
We obtained the results shown in the figure. As is clear from the figure, the hardness of the weld metal 8 is sufficiently reduced by the method of the present invention.

Note that in the SR method, a welded test piece is annealed by holding it at 625°C for 1 hour, and in the laser method, the output is 1. Ok
W, irradiation speed Q, 3 m/rm, irradiation beam diameter 5
■Welded under closed conditions.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing an example of the present invention, and FIG. 2 is a characteristic diagram showing the relationship between the hardness of weld metal and the measurement range. 1... Laser beam, 2... Laser beam fritter, 3... Pent mirror, 4, 5... Condenser lens,
6... Welding beam, 7... Beam for post-heat treatment, 8.
...Weld metal, 9...Base metal.

Claims (1)

[Claims] A post-laser heat treatment method characterized by irradiating a welded member with a laser beam to form a weld metal, and then irradiating the weld metal with a defocused laser beam to the weld metal immediately after welding.