Investigating How Welding Heat Input Affects the Microstructure and Tensile Properties of BH 220 GMAW Joints

Bake-hardened (BH) steel is widely used in automotive body structures for its unique balance of strength and toughness. The aim of this particular study is to determine how the welded joints of BH220 steel plates change with increasing welding heat in gas metal arc welding (GMAW). In order to achieve the intention of this study, different welding heat inputs were used for welding, their specific values being 191.7, 223.7, 242.3 and 242.6 J/mm. The resulting welds were then subjected to metallographic examination and tensile testing. The results showed that acicular ferrite (AF) surrounded by polygonal boundary ferrite (GBF), Weidmanstette ferrite and bulk ferrite (BF) was observed in the fusion zone (FZ) of the weld, which was very different from the base material (BM). The heat affected zone (HAZ) consists mainly of ferrite and some cementite. As the welding heat increases, the pre-austenite grain size also increases. Although the different welding heat causes the growth of grains in the weld area and the different proportions of phases in the microstructure, according to the tensile properties of the welded joints observed by digital image correlation (DIC), it is on display that the maximum tensile force that all the welded samples can withstand is 389 MPa and is broken at BM. This shows that the tensile strength of FZ and HAZ is better than that of BM and does not change with the variation in welding heat studied in this article.