Effect of Magnetic Field on Weld Zone by Spot-welding in Stainless Steel

Abstract

Spot welding is performed through a resistance welding process in which the components to be welded are clamped between two electrodes supplying heat current. It is known that a weld fusion zone and a heat-affected zone (HAZ), which experience high temperature followed by rapid cooling to room temperature, exhibit very different microstructures, compared with those of base materials. The microstructure of the weld fusion zone and HAZ (weld zone) is influenced by many factors such as chemical composition, welding condition and peak temperature. In this study, the effect of magnetic field on HAZ in spot welded stainless steel was studied. For this purpose, deformed and undeformed 301 type stainless steel (Fe17mass%Cr-7mass%Ni-0.1mass%C-0.5mass%Si-0.99mass%Mn) samples with aЈ martensite phase and g austenite phase, respectively, were spot-welded under a magnetic field up to 2 T. The welded surfaces and the cross-section planes were examined using an optical microscope. It was found that the area of HAZ was increased with increasing magnetic field, as well as the heat input power. Moreover, the area of weld zone in deformed stainless steel is larger than that in undeformed stainless steel. Based on the experimental results, the effect of magnetic field on HAZ in spot-welded stainless steel was discussed.KEY WORDS: stainless steel; phase transformation; welding; magnetic field; process control; Lorentz force.ISIJ International, Vol. 46 (2006), No. 9, pp. 1292-1296 experimental results, the effect of magnetic field on weld zone in spot-welded stainless steel was discussed. ExperimentalThe specimen for the present investigation was a SUS 301 type stainless steel with the dimensions of 10 mmϫ 10 mmϫ1 mm. The chemical composition (mass%) of the stainless steel studied was: Cr 17.0, Ni 7.0, C 0.1, Mn 0.99, Si 0.5 and Fe bal. After austenitization at 1 323 K (1 050°C) for 2 h, some specimens were compression deformed at 77 K to introduce the aЈ martensite phase. Magnetic measurement of deformed specimen was conducted in a vibrating sample magnetometer (VSM; BHV-55, Riken Denshi Co. Ltd.) at room temperature with a maximum magnetic field of 1 T to calculate the amount of the aЈ martensite phase. Since the saturation magnetization of the deformed specimen was 37 emu/g, the amount of aЈ martensite phase in the deformed specimen was estimated to be about 20-25 % by using the saturation magnetization of SUS 304 type stainless steel.Heating by a spot welding machine under a magnetic field was carried out for both deformed and undeformed samples with aЈ martensite and austenite g phases, respectively. Hereafter, this operation will be called as "welding", although no material was jointed with the stainless steel sample. Heat input power and maximum magnetic field is 10 W s and 2 T, respectively. Magnetic field was applied perpendicular to the spot welding direction, as shown in Fig. 1.The welded surfaces were examined using an OM. To observe the weld zone in the deformed stainless steel with aЈ martensite phase, a magnetic etchin...

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