Hybrid Laser-arc Welding of 17-4 PH Martensitic Stainless Steel

Abstract

17-4 PH stainless steel has wide applications in severe working conditions due to its combination of good corrosion resistance and high strength. The weldability of 17-4 PH stainless steel is challenging. In this work, hybrid laser-arc welding was developed to weld 17-4 PH stainless steel. This method was chosen based on its advantages, such as deep weld penetration, less filler materials, and high welding speed. The 17-4 PH stainless steel plates with a thickness of 19 mm were successfully welded in a single pass. During the hybrid welding, the 17-4 PH stainless steel was immensely susceptible to porosity and solidification cracking. The porosity was avoided by using nitrogen as the shielding gas. The nitrogen stabilized the keyhole and inhibited the formation of bubbles during welding. Solidification cracking easily occurred along the weld centerline at the root of the hybrid laser-arc welds. The microstructural evolution and the cracking susceptibility of 17-4 PH stainless steel were investigated to remove these centerline cracks. The results showed that the solidification mode of the material changed due to high cooling rate at the root of the weld. The rapid cooling rate caused the transformation from ferrite to austenite during the solidification stage. The solidification cracking was likely formed as a result of this cracking-susceptible microstructure and a high depth/width ratio that led to a high tensile stress concentration. Furthermore, the solidification cracking was prevented by preheating the base metal. It was found that the preheating slowed the cooling rate at the root of the weld, and the ferrite-to-austenite transformation during the solidification stage was suppressed. Delta ferrite formation was observed in the weld bead as well no solidification cracking occurred by optimizing the preheating temperature.

Laser-based welding of 17-4 PH martensitic stainless steel in a tubular butt joint configuration with a built-in backing bar

“…The base metal used in this study was 17-4 PH martensitic SS H1150 which has the density of 7820 kg/m 3 Table 1 [9].…”

“…The weldability of 17-4 PH martensitic SS is good for the traditional arc welding processes, such as gas tungsten arc welding (GTAW) [7], and shielded metal arc welding (SMAW) [8]. It is reported that welding of thick 17-4 PH martensitic SS plates is typically done in an overaged condition in order to reduce the crack susceptibility [9]. Das et al [10] studied the GTA welding of 12 mm thick 17-4 PH SS plates in a single bevel groove configuration where the overaging was done at 621 °C.…”

Welding of stainless steel using defocused laser beam

“…As it was previously noted, the authors [16] found that the speed and depth of the melted through material non-linearly depend on each other, for example at the speed of 30 mm/s the depth of melted through material is 13.6 mm, at the speed of 20 mm/s the depth is 14.8 mm, at the speed of 10 mm/s the depth is 16.1 mm. For studying of this phenomenon in the case of the defocused beam a test was performed on melting of the continuous sheet by the defocused beam (+20 mm) at different welding speeds (Fig.…”

“…The authors [16] study weldability of 17-4 PH martensitic stainless steel, and the following facts were found out: the welding speed does not have significant effect on the depth of the melted through material, but significantly affects formation of pores (10 mm/s, 20 mm/s, 30 mm/s), i.e. the higher the speed the less pores.…”

The effect of laser beam wobbling mode in welding process for structural steels

“…Currently, however, there are technological solutions that reduce hardness of the weld joints during the welding process, such as defocused laser beam welding, bifocal beam, or laser-arc welding. The authors [18] use two-pass method or heat treatment of the whole weld for reducing hardness of the welded joint obtained by laser-arc welding of martensitic steel. Two-pass method can reduce the temperature of preheating by 100°C; the authors note that, in laser welding of large thickness, there is high hardness of the weld root side in Electronic supplementary material The online version of this article (doi:10.1007/s00170-015-7312-y) contains supplementary material, which is available to authorized users.…”