Microstructure and strain rate sensitivity behavior of SM490 structural steel weld zone investigated using indentation

Abstract

In this study, a series of optical microscope examinations, constant loading rate indentation (CLR), and creep indentation (CI) tests were performed on room temperature to investigate the strain rate sensitivity behavior of the SM490 structural steel weld zone. Microstructures of weld metal (WM), fine-grain heat-affected zone (HAZ), and base metal (BM) in the weld zone were observed using optical microscopy. Numerous CLR tests were performed at a wide range of strain rate indentation from 0.02 s−1 to 0.2 s−1 in the middle regions of WM, fine-grain HAZ, and BM across the weld zone, and as a result strain rate indentation effects on both indentation hardness and yield strength were investigated. The results showed that both yield strength and indentation hardness of WM, fine-grain HAZ, and BM exhibit the strain rate-dependent behavior, in which yield strength and indentation hardness tend to increase with increasing strain rate indentation. Strain rate sensitivity (SRS) values of WM, fine-grain HAZ, and BM were determined by using three different models: indentation hardness, yield strength, and creep indentation models. The SRS behavior of SM490 structural steel weld zone was investigated. The results indicated that, while both yield strength and indentation hardness of BM are lower than those when compared with HAZ and WM, BM has the highest SRS value than does fine-grain HAZ and WM. Furthermore, WM has the lowest SRS value compared with the SRS values of other components in the weld zone. The results of this study were used to assess and understand the strain rate sensitivity behavior of SM490 structural steel weld zone.