Investigation On Mechanical Properties And Microstructure Characteristics Of Modified Medium Manganese Steel Weld Joint

Because of its excellent work hardening ability, high manganese steel has been an ideal wear-resistant material for a long time, which is widely used in the heavy impacts conditions. In the conditions of less impact, however, the work hardening ability cannot be fully realized. The modified medium manganese steel was developed to meet the market demand, such as mining machinery; alloying treatment was employed to reduce the stability of austenitic and to produce strain-induced martensite under low-impact conditions with its strengthening capacity higher than Mn13 steel. But its poor welding efficiency and lower toughness of weld joint have been serious impediment to the industrial popularization and the application of the medium manganese steel, because it is the new developed steel with thick plate and high alloy contents.Concerning the issues that emerged during the welding process of medium manganese steel, gas metal arc welding technique and G18-8Mn wire were used to study fusion zone of the joint which is the weakness of the joint. It was found that the fusion zone consists of partial melted zone(PMZ) and heterogeneous mixture zone(HMZ). The fusion line was in saw-tooth shape with small island and peninsula around it. The hardness of PMZ was higher than weld metal and HAZ. Results of XRD test and EDS analysis showed the formation of brittle phase and microsegregation of elements. Besides, the weld metal obtained by Pulse-GMAW was also analyzed. The use of pulse signals causes effective vibration in the molten pool, improves the segregation conditions, and thus produces smaller dendrites and refined substructure, resulting in a noteworthy enhancement of the plastic deformation capacity of the weld joint while maintaining comparable tensile properties.In this paper, the position and reasons of crack initiation and the modification techniques were analyzed. The process of Pulse-GMAW was proposed to improve the toughness of the joint, which provides an important theoretical basis for guiding the actual application of welding of this kind of steel.