Effect of Reforming and Annealing Temperature Variations on the Microstructure and Mechanical Properties of GMAW Welded SM490 Steel for Train Bogies

Abstract

This study analyzes the effect of varying reforming and annealing temperatures on the microstructure and mechanical properties of SM490 steel joined via Gas Metal Arc Welding (GMAW). The reforming process was conducted at temperatures of 500°C, 600°C, and 700°C, followed by annealing at 635°C with a holding time of 1 hour and 15 minutes. Testing included microstructural observation using an optical microscope (ASTM E3), tensile testing (ASTM E8/E8M), and Vickers hardness testing (ASTM E92). Microstructural analysis revealed that increasing the reforming temperature led to ferrite and pearlite grain growth due to recrystallization; however, the resulting microstructure was more homogeneous than that of the raw material. Tensile test results showed the highest ultimate tensile strength (537.6 MPa) in the specimen subjected to reforming at 500°C followed by annealing, while the highest elongation (20.5%) was observed in the specimen reformed at 600°C followed by annealing. Hardness test results indicated that the reforming and annealing treatments reduced hardness values ​​in the weld metal (WM), heat-affected zone (HAZ), and base metal (BM) due to the reduction of residual stresses following heat treatment. Variations in reforming and annealing temperatures influenced the microstructure and mechanical properties of the GMAW-welded SM490 steel.