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

Abstract

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.