Influence of laser surface hardening on low cycle fatigue performance of homogeneous-structure super austenitic stainless sheets by laser beam welding

Abstract

In this investigation, low cycle fatigue (LCF) studies were carried out on the super austenite stainless steel (SASS) sheets by laser surface hardened (LSH) method using laser beam welding process. Microstructure and LCF studies were conducted at the fusion zone. Parameters such as laser beam of 1200 W, welding speed of 200 mm/min and focus distance of 10 mm were used in laser beam welding process to achieve the narrow weld profile and increased mechanical properties of the materials. Two different types of heat inputs were applied in the LSH method and high-power diode laser of 600–700 W and focal plane position of 18 mm were applied. The heat inputs of laser beam welding reached full depth of penetration of the materials. Moreover α’ prior austenite structure was converted into β shapes and widmanstatten structure. The heat inputs were the deciding factor of grain boundaries growth. Further, more amount of α ferrite structures were transformed into basket twin boundaries in fusion zone and LSH process. Hardness profile indicated that the hardness values of LSH showed 6% improvement compared to fusion zone. Heat inputs were the main problem making of dropping the hardness value of fusion zone. Tensile sample displayed the failure in the fusion zone and a higher tensile strength of 850 MPa was observed due to the plastic strain amplitude which depended on the grain boundaries growth and α’martensite structures. Microstructure studies indicated no major holes in the fusion zone; however, LCF life was significantly improved after LSH process. Potential dynamic polarization studies were conducted in the fusion zone and SASS material processed with LSH & observed that high corrosion resistance was achieved without the formation of CrN and Cr2N.