JP7042576B2 - Welding method - Google Patents

Description

The present invention relates to a method for producing a welded product, which can prevent whitening, particularly in welding different materials using cast iron.

In the manufacture of automobiles and the like that use a large number of metal members, it is necessary to combine different materials such as cast iron and steel. When combining different materials, methods such as bolt fastening are used, but weight reduction is expected by changing from bolt fastening to welding. Although it has been considered to use welding for bonding cast iron and steel (see, for example, Patent Document 1), when welding cast iron having a high carbon content, the welding strength is reduced at the heat-affected zone on the cast iron side. There was a problem that the white cast iron tissue that affected was easily generated.

Special Fair 8-32362 Gazette

An object of the present invention is to provide a method for producing a welded product, which can suppress the formation of a white pig iron structure which significantly affects the decrease in toughness of a welded portion.

In order to achieve the above object, in the method for manufacturing a welded product of the present invention, in laser welding of cast iron and a metal material that can be welded to the cast iron, preheating is applied before welding until the welded portion reaches a predetermined temperature. It has a preheating step, the predetermined temperature in the preheating step is 62 ° C. or higher and 150 ° C. or lower, and further, it has a postheating step after laser welding, and the preheating step and the postheating step are It is characterized by using a laser .

According to the method for producing a welded product of the present invention, it is possible to provide a welded product in which the formation of a white pig iron structure, which significantly affects the toughness of the welded portion, is suppressed.

FIG. 1 is a graph comparing the white pig iron areas of Examples and Comparative Examples. FIG. 2 is a cross-sectional structure photograph of a welded portion of an example and a comparative example.

Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to and is not limited to the following description.

In the method for producing a welded product of the present invention, in laser welding of cast iron and a metal material that can be welded to cast iron, a preheating step is performed before laser welding, and the welded portion is preheated to 62 ° C. or higher and 150 ° C. or lower. It was found that the whitening is suppressed by a simple means of performing the above.

For example, as a member for an automobile, a differential case made of cast iron and a ring gear made of steel are conventionally fastened by bolts. If laser welding is performed between the differential case and the ring gear by a normal method using a fiber laser, the weight can be reduced by eliminating the need for bolts, but the weld heat-affected zone on the cast iron side is white. There was a problem of whitening that was generated by the iron tissue. White pig iron formation is a phenomenon in which brittle eutectic carbides crystallize and cast iron becomes hard and brittle. When a cast iron product turned into white pig iron is destroyed, its fracture surface appears to glow white. When cast iron has a high carbon content, a white pig iron structure is likely to occur, and when a white pig iron structure is formed, the strength (fatigue strength, impact strength) of the welded portion is significantly reduced.

The inventors have found that white pig iron formation can be suppressed by performing a preheating step under predetermined conditions when performing laser welding. This is because the preheating process makes it possible to prevent rapid cooling (slow cooling) of the molten part, promote the discharge (graphitization) of carbon in the base metal, and cementite (a compound of iron and carbon), which is the main component of white pig iron. ) Can be suppressed. The preheating is to bring the welded portion to 62 ° C. or higher and 150 ° C. or lower, preferably in the range of 80 to 150 ° C.

Examples of the cast iron used in the present invention include those containing 3.4 to 3.9% of C (carbon) in mass%.

A fiber laser can be preferably used for laser welding, but the present invention is not limited to this, and for example, a laser such as a YAG laser, a semiconductor laser, a DISK laser, and an electron beam can also be used.

In the present invention, after laser welding, a post-heating step is further provided under predetermined conditions . By having a post-heating process, white pig iron formation can be further suppressed. It is considered that this is because the post-heating process enables further prevention of rapid cooling (slow cooling) of the molten portion. The post-heating is preferably performed under the same conditions as the preheating conditions for keeping the welded portion at 62 ° C. or higher and 150 ° C. or lower, and more preferably within the range of 80 to 150 ° C. under the preheating conditions. The same conditions.

For preheating and postheating, it is preferable to use the same laser used for laser welding with its output or irradiation time changed. It is preferable to use the same laser used for laser welding for preheating and postheating because it is possible to perform all of the preheating step, the laser welding step, and the postheating step with the same equipment.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples and Comparative Examples.

[Example 1]
Cast iron (FCD500 material) and steel (S50 material) were used and bonded to each other by laser welding. A fiber laser was used as the laser, and welding was performed under the conditions of an output of 5 kW and a speed of 1.2 m / min. The size of the welded portion is 1.5 to 2.1 mm in width and 4 to 8 mm in welding depth.

Prior to laser welding, the welded portion was irradiated with a laser until it reached 144 ° C. (preheating step). The laser irradiation in the preheating step was performed under the conditions of an output of 2 kW and a speed of 10 m / min. note that. The temperature of the welded portion is a value measured at the groove portion using a non-contact thermometer (infrared ray).

[Example 2]
In the preheating step, laser welding was performed in the same manner as in Example 1 except that the welded portion was irradiated with a laser until the temperature reached 62 ° C.

[Example 3]
In the preheating step, laser welding was performed in the same manner as in Example 1 except that the welded portion was irradiated with a laser until the temperature reached 104 ° C.

[Example 4]
In the preheating step, laser welding was performed in the same manner as in Example 1 except that the welded portion was irradiated with a laser until the temperature reached 140 ° C.

[Comparative Example 1]
The temperature of the weld was 20 ° C. without the preheating step. Laser welding was performed in the same manner as in Example 1 except that the welded portion was not irradiated with the laser before the laser welding.

(Evaluation of white pig iron)
After laser welding, the degree of white iron formation was evaluated by calculating the area of the white metal portion (white metal area) at a depth of 1 mm from the cross-sectional structure photograph. FIG. 1 shows a graph comparing the white pig iron areas of Examples and Comparative Examples. FIG. 2A shows a photograph of the cross-sectional structure of the welded portion of Example 1. In this photograph, the cut surface of the sample was polished and the structure of the cross section having a welding depth of 1 mm was observed. FIG. 2B is a photograph of the cross-sectional structure of the welded portion of Example 2, FIG. 2C is a photograph of the cross-sectional structure of the welded portion of Example 3, and FIG. 2D is a photograph of the cross-sectional structure of the welded portion of Example 4. 2 (e) is a cross-sectional structure photograph of the welded portion of Comparative Example 1. In each figure of FIG. 2, the white pig iron portion is a portion surrounded by a solid line. The white iron formation was evaluated by calculating the white iron area from a stereomicrograph taken at a magnification of 200 times. From FIGS. 1 and 2, it can be seen that in each of Examples 1 to 4, the area of the white pig iron portion is smaller than that in Comparative Example 1.

(Vickers hardness evaluation)
The Vickers hardness of the welded portion at a welding depth of 1 mm was measured. Welding without preheating (corresponding to Comparative Example 1), welding with preheating (output 2 kW, speed 10 m / min), and post heat (output 1 kW, speed 2 m / min) in addition to preheat are also available. Welded in, but measured for 3 levels. Without preheating, the maximum hardness was about 730 HV, but with preheating, it decreased to about 650 HV. Further post-heating reduced the temperature to about 620 HV. It can be seen that the hardness is reduced and the white pig iron is suppressed by the application of preheating and postheating.

From the white metal formation evaluation result and the Vickers hardness evaluation result, it can be seen that the area of the white metal portion can be reduced and the fatigue strength and impact strength of the welded portion can be improved by performing preheating under predetermined conditions. Further, it can be seen that it is more preferable to apply postheat in addition to preheat.

As described above, according to the present invention, it is possible to provide a method for producing a welded product capable of suppressing the formation of a white pig iron structure which significantly affects the decrease in toughness of the welded portion. INDUSTRIAL APPLICABILITY The present invention makes it possible to reduce the cost by reducing the number of members because the range that can be performed by welding can be expanded for the joining between members, which has been conventionally performed by bolts and the like. be.

Claims (1)

In laser welding of cast iron and cast iron and weldable metal materials,
It has a preheating process that preheats before welding until the weld reaches a predetermined temperature.
The predetermined temperature in the preheating step is 62 ° C. or higher and 150 ° C. or lower.
In addition, it has a post-heat process after laser welding.
A method for manufacturing a welded product, wherein the preheating step and the postheating step are performed by using a laser .

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