Effect of Welding Methods on Microstructure and Mechanical Properties of Welded Joints of Low‐Temperature Carbon–Manganese Steel VL4‐4

Carbon–manganese steel is widely used in the transportation and storage of liquefied petroleum gas (LPG) as a low‐cost and high‐performance low‐temperature steel. This article investigates the microstructure and mechanical properties of the VL4‐4 (a novel low‐temperature carbon‐manganese steel used in LPG fuel tanks) welded joint, with a focus on the effects of three welding methods: shielded metal arc welding (SMAW), submerged arc welding (SAW), and flux‐cored wire gas‐shielded welding (FCAW). Microstructural analysis reveals similar microstructures across all methods: the weld metal primarily consists of acicular ferrite and primary eutectic ferrite, while the heat‐affected zone (HAZ) features slate martensite and bainite. In addition, nonmetallic inclusions are found in the HAZ, which contributed to the generation of needle‐like ferrite, refined grain size, and improved strength and toughness. Fractographic analysis shows that the HAZ fracture surfaces of SMAW and SAW joints exhibit tough‐brittle mixed fractures. In contrast, FCAW joints display a typical tough fracture. In terms of mechanical performance, the welded joints produced by all three welding methods exhibit superior mechanical properties compared to the VL4‐4 low‐temperature carbon–manganese steel base material. Among them, FCAW joints demonstrate superior overall performance.