Study On Microstructure And Properties Of Dissimilar Metal Welding Between Ferrite And Austenite Stainless Steels

Based on the efficiency of ferritic stainless steel and the advantages of good comprehensive performance austenitic stainless steel. The dissimilar metal welding between443ferritic and304austenitic stainless steels can make full use of both their respective advantages, to meet the requirement of welding structure and reduce the production cost. This paper mainly studied that the effect of ER309L and ER385two kinds of austenitic stainless steel welding wire as filler material on the microstructure, mechanical properties and corrosion resistance of443ferritic/304austenitic stainless steel dissimilar steel welded joint.The microstructure and XRD results showed that the weld metal with filler material ER309L composed by y-austenite and δ-ferrite phase and the microstructure distribution were nonuniform; but the weld metal with filler material ER385included only y-austenite and the microstructure distribution were uniform and columnar crystal distribution was obvious.The microhardness results showed that microhardness distribution of weld metal A fluctuated obviously, the morphology and content of δ-ferrite are different at different region, and the microhardness changed with morphology and content of δ-ferrite, the more acicular δ-ferrite, the higher hardness; weld metal B presented stable value (approximately200Hv0.3); compare with two base metals, the microhardness both side of heat effect zone decreased slightly the microhardness of both welding joints changed obviously near the fusion line. Compare with welding jointA, Yield strength, tensile strength and elongation of the welding joint B improved3%,7%and15%, respectively; both of welding joints fracture occurred at443base metal and were ductile fracture. The different gap position of welding joints possessed higher impact abstract energy at room temperature, but impact abstract energy of443the heat effected zone and base metal dropped dramatically with the temperature decreased to minus20degree Celsius, reduced to5J and3.4J, respectively, and fracture surface scan completely presented to brittle fracture; the weld metal B increased10%and20%at room, minus20degree Celsius, respectively, compare with weld metal A.Studying the corrosion resistance of both base metals and welded joints in different corrosion environmental through intergranular corrosion test, salt spray corrosion test and electrochemical corrosion test. The measurement of intergranular corrosion resistance in copper sulfatesulfuric acid test, if there were not microcrack bending the intergranular corrosion samples under180angle, which proved the welded joint has excellent intergranular corrosion performance. The salt spray corrosion test in3.5%NaCl solution for simulating the coastal environment demonstrated that two base metals possessed good corrosion resistance just slight loss of metallic luster and no corrosion products. However, there were distribution corrosion products along both sides of the welded joints toe, the corrosion rate of304,443, welded joint A and welded joint B were7.71×10-8g·mm-2·h-1、7.89×10-8g·mm-2·h-1、12.98×10-8g·mm-2·h-1and11.75×10-8g·mm-2·h-1, respectively. In3.5%NaCl solution of electrochemical corrosion test by polarization curves and electrochemical impedance spectroscopy test showed that corrosion resistant ability from strong to weak, in order:welding B,304base metal,443base metal and weld joint A; and by observing using Scanning Electron Microscope showed that two base metals and welded joints without pitting point.