Effects of Weld Metals and Heat Input on the Softening of Gas Metal Arc Welded Joint for Abrasion Resistant Steel

The softening of welded joints for abrasion resistant steel NM450 was systematically investigated by combining numerical simulation and welding experiments including surfacing and butt welding. The dependence of welded joint softening on heat input and filler material is discussed. The surfacing results show that the points of minimum value of hardness are located within intercritical heat-affected zone (ICHAZ). The simulated peak temperature of the heat-affected zone (HAZ) increases with an increase in the heat input, whereas the cooling rate decreases with increase in the heat input, leading to the more serious softening of HAZ. It is demonstrated that the lower dislocation density and the high volume fraction of ferrite result in the softening of ICHAZ. The softening of the welds is improved by changing filler SLD-70 to SLD-90. This is predominantly attributed to solid-solution strengthening and fine-grain strengthening due to high alloying element content such as Ni and Cr in SLD-90. The hardness and ultimate tensile strength of weld, irrespective of specimens with filler SLD-70 and SLD-90, are significantly smaller than that of base metal. In addition, the plasticity and toughness of butt weld deteriorate resulting from the M–A constituents at grain boundaries for weld with SLD-90 as filler. A new matching filler is needed urgently to improve the strength and remain the high toughness of joints for abrasion resistant steel.