JPS6332557B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for welding materials whose hardness increases significantly upon welding, such as martensitic stainless steel.

In recent years, martensitic stainless steels such as 13Cr-3.8Ni steel have been used in hydraulic machinery and the like as relatively inexpensive materials with excellent strength and corrosion resistance. However, when these materials are welded, the hardness increases significantly at the boundary between the weld metal and the base metal (BOND) and the heat affected zone (HAZ). Since crack propagation speed is high in such a high hardness part, if a defect such as a crack exists in a high hardness part, there is a risk that it will rapidly grow due to repeated stress and cause the member to break. In order to avoid this risk, conventional methods have generally been adopted in which the entire article is placed in a furnace after welding and heat treated to reduce hardness and residual stress.

However, if the entire large part is placed in a furnace and heated for a long time, deformation or deterioration of the base material may occur.
Furthermore, when the base material and the welding material are different in quality, it is difficult to avoid the generation of residual stress due to the difference in thermal expansion coefficient between the two during cooling. Furthermore, in the case of repair welding of large parts installed on-site, it is extremely difficult to perform the above heat treatment (SR) due to problems such as disassembly/assembly work, on-site furnace equipment, or transportation to a factory that has a furnace. I was in a situation.

An object of the present invention is to provide a welding method that improves the properties of welded parts by heating in a simple manner in materials where the interface between the weld metal and the base plate and the heat-affected zone harden significantly during welding. It's about doing.

An embodiment of the present invention will be described below with reference to FIGS. 1 and 2. Figures 1 and 2 show cross sections of welded parts, where 1 is the base metal, 2 is the weld metal, 3 is the boundary between the weld metal 2 and the base metal 1 (BOND), and 4 (3 and 2). The area between the dotted and dashed lines) is the heat affected zone (HAZ). First, as shown in FIG.
Place it over the entire groove. Next, the first layer of weld bead 2a is smoothed to a thickness of 1 to 2 mm, and the second and subsequent layers of weld bead 2b are placed on top of it as shown in FIG. Further, at the final weld toe of the welding bead 2b after the second layer, a temper bead 6 is placed by Teig welding or a welding rod 5 made of the same material as the welding rod after the second layer and having a small diameter,
The toe of this temper bead 6 is placed so as not to overlap the weld bead 2a of the first layer.

Next, the effect will be explained. The heat-affected zone 4, which has undergone a structural change due to the placement of the first layer weld bead 2a, is heated by the welding arc heat of the second layer weld bead 2b via the first layer weld bead 2a and the boundary portion 3. Ru. In this case, the heat-affected range of the second layer is within the fine grain part of the initial heat-affected zone 4 of the base material 1 due to the thickness of the weld bead 2a of the first layer, and due to this heating. The tempering action improves the structure by making coarse crystal grains near the boundary 3 finer. On the other hand, in the vicinity of the surface of the base material 1 formed by the final toe of the weld bead 2b of the second layer and subsequent layers and the weld bead 2a of the first layer, the temperature drop rate is high, so the temper bead generates a small amount of heat. 6 to avoid rapid cooling and perform a tempering action on the heat affected zone 4.

Therefore, according to this embodiment, the weld bead 2a of the first layer is made of 1-2 which does not impede heat conduction.
Since the weld bead 2b from the second layer onwards is placed after smooth finishing to a thickness of mm, the heat affected zone 4 can be heated uniformly by the own welding arc heat without using other heating means. be able to. Therefore, the structure of the heat affected zone 4 can be easily improved, the hardness can be reduced, and the susceptibility to cracking can be reduced. Furthermore, since the structure can be improved over the entire welded area, not only does post-weld heat treatment become unnecessary, but even if heat treatment is performed due to other factors, deformation of the welded area or generation of residual stress can be suppressed.

As explained above, according to the present invention, the structure of the entire heat-affected zone can be easily improved using the own welding arc heat without using other heating methods, thereby reducing hardness and cracking susceptibility. Welds can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a welding process diagram according to an embodiment of the present invention, and FIG. 2 is a sectional view of a welded part according to an embodiment of the present invention. 1...Base metal, 2, 2a, 2b...Weld metal, 3
... Boundary zone, 4... Heat affected zone.

Claims (1)

[Claims] 1. In a welding method for materials in which the boundary between the weld metal and the base metal and the heat-affected zone harden significantly during welding, a first layer bead is placed over the entire groove surface, and this first layer bead is After finishing it smoothly to a predetermined thickness considering heat conduction, the beads of the second and subsequent layers are placed on top of the beads of the first layer, and the welding arc heat of the second and subsequent layers causes the welding of the first layer. A welding method characterized in that heating is applied via a bead to produce a tempering effect on the boundary with the base metal and the heat affected zone.