JP2019042748A - Manufacturing method of weldment - Google Patents

Abstract

To provide a manufacturing method of a weldment capable of suppressing generation of a white pig iron organization exerting a striking influence on tenacity decline of a weld zone.SOLUTION: A manufacturing method of a weldment has a preheating process for applying preheating before welding until a weld zone reaches a prescribed temperature, in lazer welding between cast iron and a metal weldable with the cast iron, in which the prescribed temperature in the preheating process is over 20°C and 150°C or lower.SELECTED DRAWING: None

Description

  The present invention relates to a method of manufacturing a weld, which can prevent whitening, particularly in dissimilar welding using cast iron.

  In the manufacture of an automobile or the like using a large number of metal members, for example, it is necessary to combine different materials such as cast iron and steel. When different materials are combined, 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 the combination of cast iron and steel (see, for example, Patent Document 1), when welding cast iron having a high carbon content, the welding heat affected zone on the cast iron side reduces welding strength. There has been a problem that it is easy to generate an influential birch tissue.

Japanese Examined Patent Publication 8-32362

  An object of the present invention is to provide a method of manufacturing a weld which is capable of suppressing the formation of a white-collar structure significantly affecting the decrease in toughness of a weld.

  In order to achieve the above object, the method of manufacturing a weldment according to the present invention provides preheating before welding until the weld reaches a predetermined temperature in laser welding between cast iron and cast iron and a weldable metal material. A preheating step is included, and the predetermined temperature in the preheating step is characterized by being greater than 20 ° C. and 150 ° C. or less.

  According to the method of manufacturing a weldment of the present invention, it is possible to provide a weldment in which the formation of a white rattan structure which significantly affects the decrease in toughness of a weld zone is suppressed.

FIG. 1 is a graph comparing the white area of the example and the comparative example. FIG. 2 is a cross-sectional structure photograph of welds of the example and the comparative example.

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

  In the method of manufacturing a weldment according to 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 weld portion is increased to over 20 ° C. and 150 ° C. or less It has been found that the whitening is suppressed by a simple means of preheating.

  For example, conventionally as a member for vehicles, a differential case made of cast iron and a ring gear made of steel are fastened by bolts. If laser welding is performed using a fiber laser with the differential case and the ring gear in the usual way, weight reduction becomes possible by eliminating the need for bolts, but whitening occurs on the welding heat affected zone on the cast iron side. There has been a problem of bleaching that can be generated by hemorrhoid tissue. The term "whitening" refers to a phenomenon in which brittle eutectic carbides crystallize and the cast iron becomes hard and brittle. The whitened cast irons appear white when shattered. When cast iron has a high carbon content, it tends to form a birch structure, and when a birch structure is formed, a marked decrease in the strength (fatigue strength, impact strength) of the weld occurs.

  The inventors have found that the whitening can be suppressed by performing the preheating step under predetermined conditions when performing laser welding. This makes it possible to prevent quenching (slow cooling) of the molten part by the preheating step, and accelerate discharge of carbon in the matrix (graphitization) to promote cementite (the compound of iron and carbon, which is the main component of the birch. It is thought that it is because precipitation of can be suppressed. The preheating is to bring the welded portion to a temperature above 20 ° C. and below 150 ° C., preferably within the range of 80 to 150 ° C.

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

  Although a fiber laser can be used suitably for laser welding, it is not limited to this, For example, lasers, such as YAG laser, a semiconductor laser, DISK laser, an electron beam, can also be used.

  In the present invention, it is preferable to have a post-heating step under predetermined conditions after the laser welding. By having a post-heating step, bleaching can be further suppressed. It is considered that this is because the post-heating step makes it possible to prevent further quenching (slow cooling) of the melted portion. The post-heating is preferably performed under the same conditions as the above-described preheating conditions for setting the weld temperature to more than 20 ° C. and 150 ° C. or less, more preferably within the range of 80 to 150 ° C. under the preheating conditions And the same conditions.

  For preheating and postheating, it is preferable to use the same laser as that used for laser welding, changing its output or irradiation time. It is preferable to use the same laser as that 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.

  EXAMPLES The present invention will be described more specifically by the following Examples and Comparative Examples, but the present invention is not limited by the following Examples and Comparative Examples.

Example 1
The cast iron (FCD500 material) and the steel (S50 material) were used to join together by laser welding. A fiber laser was used as a 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 welding site is 1.5 to 2.1 mm in width and 4 to 8 mm in welding depth.

  Before the laser welding, laser irradiation was performed until the welded portion 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. In addition. The temperature of the welded portion is a value obtained by measuring 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 laser irradiation was performed until the weld temperature reached 62 ° C.

[Example 3]
In the preheating step, laser welding was performed in the same manner as in Example 1 except that laser irradiation was performed until the weld temperature reached 104 ° C.

Example 4
In the preheating step, laser welding was performed in the same manner as in Example 1 except that laser irradiation was performed until the weld temperature reached 140 ° C.

Comparative Example 1
The weld was at 20 ° C. without the preheating step. Before the laser welding, laser welding was performed in the same manner as in Example 1 except that the laser irradiation to the welded portion was not performed.

(Whitening evaluation)
After laser welding, the extent of the whitening was evaluated by calculating the area of the white area at the 1 mm depth of welding (white area) from the cross-sectional structure photograph. FIG. 1 shows a graph comparing the white area of the example and the comparative example. The cross-section structure | tissue photograph of the welding part of Example 1 is shown to Fig.2 (a). This photograph is obtained by polishing the cut surface of the sample and observing the structure of a cross section with a welding depth of 1 mm. 2 (b) is a cross-sectional structure photograph of the weld portion of Example 2, FIG. 2 (c) is a cross-sectional structure photograph of the weld portion of Example 3, and FIG. 2 (d) is a cross-sectional structure photograph of the weld portion of Example 4. 2 (e) is a cross-sectional structure photograph of the weld of Comparative Example 1. FIG. In each drawing of FIG. 2, the white ridge portion is a portion surrounded by a solid line. The evaluation of the whitening was performed by calculating the area of the white area from stereomicrographs taken at an imaging magnification of 200 times. It can be understood from FIGS. 1 and 2 that the area of the white area is smaller in each of Examples 1 to 4 than in Comparative Example 1.

(Vickers hardness evaluation)
The Vickers hardness at a welding depth of 1 mm of the weld was measured. There are welds performed without preheating (corresponding to Comparative Example 1), welds with preheating (output 2 kW, speed 10 m / min) and post-heating in addition to preheating (power 1 kW, speed 2 m / min) It measured about three levels of what did welding in. In the case of no preheating, the maximum hardness was about 730 HV, but the preheating reduced it to about 650 HV. Further postheating reduced to about 620 HV. It can be seen that the hardness is reduced and the whitening is suppressed by preheating and postheating.

  From the whitening evaluation results and the Vickers hardness evaluation results, it is understood that by performing preheating under predetermined conditions, the area of the white area can be reduced, and the fatigue strength and impact strength of the weld can be improved. Furthermore, it is understood that it is more preferable to apply post-heat in addition to preheating.

  As described above, according to the present invention, it is possible to provide a method of manufacturing a weld that can suppress the formation of a white-collar structure that significantly affects the reduction in toughness of a weld. The present invention can expand the range that can be performed by welding for joining between members, which has conventionally been joined using bolts or the like, so cost reduction can be achieved by reducing the members. is there.

Claims (1)

In laser welding of cast iron, cast iron and weldable metals,
It has a preheating process that gives preheating before welding until the weld reaches a predetermined temperature,
The predetermined temperature in the preheating step is more than 20 ° C. and 150 ° C. or less.