Effect of high temperature tempering on microstructure and mechanical properties of wear-resistant plate
With the development of all kinds of exploration projects in the world to the deep and the increase of reaming diameter, the force of drilling tools is large and complex, and the high-hardenability alloy tempered structural steel is generally selected. Wear-resistant plate is a kind of alloy wear-resistant steel, which has high strength after modulation, and has good plasticity and toughness, and is widely used in the production of large-diameter drilling tools. Based on the mechanical properties requirements of wear-resistant plate alloy steel as drilling tool material in exploration field: tensile strength above 1033MPa, hardness higher than 321HBW, longitudinal impact absorption energy KV2≥90J, this work studies the effects of different high temperature tempering temperatures on the microstructure and mechanical properties of wear-resistant plate.
The experimental material is the residual material of a large petroleum mechanical annealed wear-resisting plate, the size is 60mm×60mm×125mm, the grain size is ASTM4.0, and the main composition (wt%) is: 0.333C, 0.977Cr, 2.45Ni, 0.469Mo, 0.0902V, 0.212Si, 0.559Mn, 0.0054P, 0.0015S. The austenitic heating temperature of the wear-resistant plate sample was 880℃, the heat preservation was 2h oil cooling, and the samples were tempered at 560, 590, 620 and 650℃ respectively after quenching, and the heat preservation was 2h water cooling. According to GB/T2975, cut the tensile sample and impact sample at the corresponding position of the bar steel. Tensile test according to GB/T228 standard; Impact test according to GB/T229 standard. Hardness measurement is carried out on DHB-3000 Brinell hardness tester according to GB/T231-2012 standard. The steel ball diameter is 10mm, the pressure is 29.4kN, and the holding load is 15s. The microstructure of metallographic samples was observed by AE2000MET inverted metallographic microscope after pre-grinding, polishing and etching with 3% nitrate alcohol solution for 10 ~ 15s.
The results show that the microstructure of wear-resistant plates after quenching at 880℃ and tempering at 560 ~ 650℃ are tempered sorbite + flake or massive ferrite + carbide. Wear-resistant plate has excellent strength and toughness matching after tempering at 620℃; After tempering at 560℃, the room temperature strength and Brinell hardness reach the maximum, and the impact absorption energy measurement is the lowest, while the reverse is true after tempering at 650℃. With the increase of tempering temperature, the tensile strength, yield strength and hardness of the wear plate gradually decreased, and the impact absorption energy gradually increased. Considering the strength and plasticity of the material, after tempering the wear-resistant plate at 560 ~ 650 ° C, 620 ° C is the optimal tempering temperature for the wear-resistant plate as a large diameter special drilling tool material for mining.
