Effect Of Multi-pass Bead Welding On Microstructureand Mechanical Properties Of Medium Quenched And Tempered Carbon Steel

Roll crusher has crucial function in the crushing operation. crushing roller is the main component of roll crusher, which is the working part that roll crusher contacts with materials straightly to pull pressure by. Wearing of roll surface is serious, and the roll wear will be worse as the increase of run duration. That is the main disadvantage of roll crusher, which has serious effect and restriction on the wide applications of roll crusher. However, the working life of roll crusher can be extended to a large extent after being repaired through bead welding.In this paper,45steel quenched and tempered was used as base metal. The single-pass welding and single-layer multi-pass bead welding were performed under ice cooling condition. In order to optimize the welding parameters, the Microstructure of heat affected zone (HAZ) were observed. The corresponding microhardness and impact toughness of HAZ were tested. Multi-pass welding was performed using the optimized welding parameters. The influence of multi-pass welding on the Microstructure, microhardness and impact toughness of HAZ of45steel during multi-pass welding were investigated by microstructure analysis, mechanical properties test, and impact fracture morphology observation.Under ice cooling condition, the optimized welding parameters are as follows: the welding current is300A, voltage is29V, walking velocity is60mm/min, and width of weld is60mm. The Microstructure in HAZ of samples welded by the optimized parameters are finer, microhardness is higher and the distribution is more uniform, and impact toughness is better than those of HAZ obtained by other welding samples.The Microstructure in HAZ of45steel as quenched and tempered state consist of complete-quenched, partial-quenched and tempered zones. The complete-quenched and partial-quenched zones are mostly composed of M-A, ferrite and a little sorbite/troostite. The tempered zone is mainly composed of fine bulk ferrite.The grain in HAZ of45steel as quenched and tempered state is much finer, and the morphology changed after multi-pass bead welding. Grain size of equiaxed crystal of welding seam decreases, and columnar crystal transforms into fine equiaxed crystal in multi-pass bead welding sample. The microstructure morphology of HAZ of multi-pass welding remains the same as that of single-layer multi-pass welding. However, the M-A volume fraction of quenched zone becomes lower after multi-pass bead welding, and gradually stabilizes, and average length of M-A decreases obviously.Multi-pass bead welding has significant influence on microhardness and its distribution in HAZ of45steel as quenched and tempered state. Microhardness of quenched zone becomes lower, and there has a tendency to be a stable one, and the fluctuation of microhardness decreases obviously after multi-pass bead welding.Multi-pass bead welding has remarkable improvement effect on impact toughness of HAZ, especially of quenched zone. Impact energy of quenched zone increases obviously after multi-pass bead welding, but the increase rate reduces gradually with the layer and pass of bead welding increase. It is illustrated that impact toughness of quenched zone won’t change eventually when the layer and pass of bead welding are up to a given value.