Effect of Plastic Deformation Percentage Variations in SMAW Welding of AISI 1020 Steel on Microstructure and Mechanical Properties

This chapter investigates the profound effects of plastic deformation on the microstructure and mechanical properties of AISI 1020 steel subjected to Shielded Metal Arc Welding (SMAW). The study meticulously examines four levels of cold rolling deformation (0%, 25%, 50%, and 75%) and their impact on the steel's hardness, tensile strength, and microstructure. The research reveals that increasing plastic deformation leads to significant changes in the grain structure, with ferrite and pearlite grains becoming more elongated and smaller in the base metal region. In the Fine Grain Heat Affected Zone (FGHAZ), the microstructure shows a tendency towards recrystallization, forming new, equiaxed grains free from internal stress. Conversely, the Coarse Grain Heat Affected Zone (CGHAZ) exhibits grain growth, with ferrite grain boundaries widening and pearlite becoming more regular. Hardness tests confirm that the base metal's hardness increases with higher deformation percentages, while the Heat Affected Zone (HAZ) and Weld Metal (WM) regions show decreased hardness. Tensile tests further illustrate that yield strength (YS) and ultimate tensile strength (UTS) increase with plastic deformation in unwelded specimens but decrease in welded specimens, particularly after 25% deformation, with most failures occurring in the HAZ. This chapter provides a detailed analysis of the macroscopic and microscopic observations, offering a deep understanding of the complex interactions between plastic deformation and welding processes in AISI 1020 steel.