Effects Of Nb And Mo On Micro-structure And Properties Of Low Alloy Wear-resistant Steel

Against the actual operating condition of the low alloy wear-resistant steel lining board the influence of Nb and Mo and heat-treatment on the microstructure and properties of the low alloy wear-resistant steel were studied based on the reasonable chemical composition design, got excellent combination of hardness and impact toughness to reach the requirements of lining board.The effects of Nb and Mo and heat-treatment on the microstructure and properties were investigated using test facilities such as DTA thermography and metalloscope, X-ray Diffractometer(XRD), Scanning Electron Microscopy(SEM), rockwell hardness tester, impact-toughness tester, ML-100 abrasive wear testing machine and analysis methods such as microstructure, impact fracture morphology, Rockwell hardness, impact toughness, hardenability characteristic, wear-resisting property.Experimental results showed that (Nb Ti)C was gained directly in the as-cast steel with Nb addition. Reasonable Nb addition in the steel refined efficiently the microstructure. Nb dissolved partly in austenite after heat-treatment. With the increase of Nb, the hardness and impact toughness are improved gradually. When the steel added 0.06% Nb after quenching at 900℃and tempering at 250℃, the hardness and impact toughness reached to 54.5HRC and 28.5J/cm2, respectively. The steel with 120mm thickness were full hardening after quenching at 900℃. The wear-resistance of the steel with 0.06% Nb addition was 32.67% higher than that of steel without Nb after heat-treatment.The microstructure of steel is refined effectively with Mo addition. Mo formed (Cr Mo Fe) ₇C₃ and dissolved in austenite. With the increase of Mo, the hardness of the as-cast steel increased from 38.5HRC to 42.6HRC. After quenching at 900℃and tempering at 250℃, the hardness of steel with 0.08% Mo addition was 3.3HRC higher than that of steel with 0.04% Mo addition. The temper brittle resistance increased with Mo addition tempering at 250～300℃.The results of heat treatment showed as follows: After quenching at 900℃and tempering at 250℃, the microstructure of steel consisted of tempered martensite and residual austenite and trace amount of carbide, and got excellent combination of hardness and impact toughness. The impact fracture belongs to gliding fracture with lots of dimple.The dimension of the low alloy wear-resistant steel lining board with Nb and Mo addition was 320×200×120mm. The reasonable chemical composition was C0.40～0.45%, Si1.0～1.5%, Mn0.8～1.2%, Crl.8～2.2%, Mo0,45～0.65%, Nb0.50～0.70%. The heat-treatment was quenching at 900℃and tempering at 250℃, quenchant was No 10 coarse oil. The microstructure of lining board consisted of tempered martensite and residual austenite, and hardness was between 52HRC and 56HRC, impact toughness was between35J/cm² and 45J/cm².