Abstract
Fiber laser welding of cold rolled TRIP steel (transformation Induced Plasticity steel) sheet with tensile strength of 820MPa and thickness of 1.4mm was carried out using shielding gases Ar and He, respectively. For the same laser power and welding speed, the effects of different shielding gases on penetration and bead section morphologies were investigated. The microstructures and properties of the TRIP steel joints were also studied. The investigation showed that higher penetration and lower porosity could be obtained under shielding gas He using the same laser power and welding speed. The microstructures of the TRIP joint mainly included martensite and retained austenite. But the joint microhardness and tensile strength were higher under the shielding gas He. The tensile strength of the welded joint perpendicular to the weld line was equal to that of the base metal. But the tensile strength of the joint parallel with the weld line was higher than that of the base metal. The plasticity and formability of the welded joint were impaired due to the formation of martensite in the weld metal.
Highlights
Weight reduction of automobiles is one of the effective measures for decreasing gas consumption and minimizing environmental pollution on the premise that safety provisions are guaranteed
Ultra-high strength steels (UHSS) such as transformation induced plasticity (TRIP) steels and dual phase (DP) steels were increasingly applied in automobile industry due to their good combination of high strength and formability
The excellent mechanical properties of TRIP steel mainly contribute to the ferrite matrix, for ductility, bainite, for strength, and retained austenite, for uniform elongation produced by martensite transformation from austenite when subjected to external tensile stress
Summary
Weight reduction of automobiles is one of the effective measures for decreasing gas consumption and minimizing environmental pollution on the premise that safety provisions are guaranteed. It was estimated that 10% of weight reduction generally may bring about 5% less of gas consumption [1]. These years light metal materials such as Al alloys and Mg alloys have been increasingly used in automobile industry. Ultra-high strength steels (UHSS) such as transformation induced plasticity (TRIP) steels and dual phase (DP) steels were increasingly applied in automobile industry due to their good combination of high strength and formability. Microstructural characteristics and mechanical properties of fiber laser welded TRIP steel sheet with tensile strength of 820MPa were investigated to provide some fundamental knowledge about laser welding TRIP steels for the engineers in automobile industry
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