Influence of Heat Input and Shielding-Gas Composition on Microstructures and Properties of Weld Metal of HSLA-100 Class Steel

摘要

The present study provides a detailed assessment of the effects of heat input and shielding gas composition on the properties and microstructures of single pass welds which was produced on 950MPa class high strength steel (HSAL-100) by gas metal arc groove welding. Several mixtures of argon (Ar) and carbon dioxide (CO_2) (0-25 percent) and different heat inputs ranging from 2.5 to 4.5 kJ/mm were employed. The microstructures of the welds obtained, consisting principally of martensite and bainite, were altered from martenistic to bainitic, as the CO_2 content in the shielding gas was increased. The effect of the increase in the heat input on the weld-metal microstructure exhibited similar tendency, but the observed difference in the microstructures was less significant than those caused by the CO_2 addition to the shielding gas. The weld metals produced by pure Ar shielding gas at heat inputs not more than 4 kJ/mm have superior mechanical properties and fine microstructures compared with the other weld metals. It was also found that the M-A constituent, embitterment microstructure, was formed in the granular bainitic area, the volume fraction of which was increased with the CO_2 content of the shielding gas and weld heat input.