Microstructure and Mechanical Properties of Friction Stir Welded Austenitic-Ferritic Stainless Steels Using Staggered Jo

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JMEPEG (2020) 29:5263–5272 https://doi.org/10.1007/s11665-020-05037-9

Microstructure and Mechanical Properties of Friction Stir Welded Austenitic-Ferritic Stainless Steels Using Staggered Joint Configuration Guolin Guo and Yifu Shen (Submitted October 19, 2018; in revised form December 30, 2019; published online August 17, 2020) Dissimilar friction stir welding of 304 austenitic stainless steel and 430 ferritic stainless steel was performed by using staggered butt joint configuration. Under proper heat input, welding experiments were carried out to study the effect of tooth dimension on material flow, microstructure evolution and mechanical properties of the joint. The results indicate that the material flow tends to improve with reduced the tooth width. However, when the tooth width is reduced to 1 mm, the mixing degree of base metals in stir zone becomes worse due to the lack of softened metal. It is noted that joint 2 with a tooth width of 2 mm is characterized by river pattern and shows various flow directions in different regions of the stir zone. This pattern is formed by the mixed structure of austenite and ferrite with various grain sizes. Joint 2 presents the maximum tensile strength in all specimens and failed in the ferritic base metal. Keywords

austenitic/ferritic stainless steels, friction stir welding, mechanical properties, microstructure, staggered joint configuration

1. Introduction The welded structures made from austenitic-ferritic stainless steels are widely used in petrochemical industry, medical equipment, automobile manufacturing and daily industry with acid, alkali and high temperature (Ref 1). For example, in the manufacturing of superheater and reheater of power plant boiler, austenitic stainless steel has been applied in hightemperature section due to its excellent oxidation resistance and thermal stability, while ferritic stainless steel has been used in low-temperature section to reduce the cost. However, using the traditional fusion welding process to join dissimilar stainless steel, there may be some problems, such as high-temperature crack produced by impurity segregation, grain coarsening in HAZ and joint embrittlement caused by martensite and sigma phase, reducing the joint strength and toughness. For example, the literatures (Ref 2, 3) reported the fusion welding of austenitic and ferritic stainless steels and found that the joint failed in the weld at the ferritic side, which was due to thermal stresses and metallurgical deterioration caused by elevated temperatures. Ghasemi et al. (Ref 4) applied three filler metals to produce the dissimilar welds of AISI 304/AISI 430 stainless steels by using gas tungsten arc welding (GTAW) process. The

Guolin Guo, College of Materials Science and Technology, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China; and School of Automotive Engineering, Changshu Institute of Technology, Changshu 215500, China; and Yifu Shen, College of Materials Science and Technology, Nanjing University of Aeronautics and Astronautics, Nan

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