Low Alloy Wear Resistant Steel For Excavator Bucket Performance Optimization

Compared with manganese steel and wear-resistant cast iron,low alloy high-strength wearresistant steel has good wear resistance and weldability,simple production process and relatively low cost.It is widely used in construction machinery,such as excavator bucket.Based on the relevant theories and research results of the relationship between alloy composition,microstructure,mechanical properties and wear resistance,and according to the requirements of excavator bucket for the performance of wear-resistant steel plate,this paper sets the goal of improving the wear resistance of bucket steel plate by 15% on the premise of maintaining the cost and weldability of existing NM400 steel,and adopts the idea of controlling carbon equivalent and welding crack coefficient and optimizing low alloy content.The chemical composition and heat treatment process of NM400 steel were optimized by using JMat Pro software simulation calculation and combined with laboratory and engineering tests.The optimized chemical composition is 0.17-0.20% C,0.2-0.4% Si,1.0-1.3% Mn,P≤0.01,S≤0.004,0.85-0.95% Cr,0.15-0.25% Mo,0.01-0.03% Nb,0.001-0.003% B,0.01-0.03% Ti.Heat treatment process parameters: 920 ± 30 ℃ quenching + 150 ～ 250 ℃ tempering.The hardness of the alloy is 411 ～ 435 HB,the yield strength is 1091 ～ 1172 MPa,and the tensile strength is 1348 ～1425 MPa.When 0.18% C,0.3% Si,1.2% Mn,0.002% B,0.02% Ti and 0.02% Nb,the three components of 0.85% Cr + 0.25% Mo,0.90% Cr + 0.20% Mo and 0.95% Cr + 0.15% Mo are simulated.The results show that the complete austenitizing temperature of the three components is no more than920 ℃,and the maximum critical cooling rate is no more than 10 ℃/s.After quenching at a rate higher than the critical cooling rate,the three NM400 wear-resistant steels can achieve the optimization goal.The yield strength of the third steel is 1121 MPa,the tensile strength is 1376 MPa and the hardness value is 419 HB.NM400 wear-resistant steel samples were prepared according to the design composition,and the microstructure and mechanical properties were tested in the laboratory.When the Cr and Mo composition of the optimized NM400 steel is 0.90% Cr + 0.20% Mo,the mechanical properties meet the national standard,with yield strength of 1118 MPa,tensile strength of 1430 MPa,elongation after fracture of 12.6%,impact absorption energy of 44 J at-20 ℃ and surface hardness of 430 HB,which are in good agreement with the simulation results.The optimized NM400 steel plate was welded to the bucket with the original bucket steel plate of Sany company,and the field excavation test was carried out.After 500 h field excavation,it is proved that the wear amount of the optimized NM400 steel plate is about 1/2 of that of the original bucket steel,the wear resistance is improved by 50.4%,and the target of > 15% is achieved.