Study On Effects Of Q&P Treatment Processes On Microstructures And Properties Of Cr-Ni-C Series Of Ultra-High Strength Martensitic Stainless Steel

Crl3martensitic stainless steel is a kind of martensitic stainless steel has a broad application prospect for its good corrosion resistance in the atmosphere, water vapor and organic acid. The traditional heat treatment process for this kind of martensitic stainless steel is quenching-tempering, which brings the steel very high strength and hardness but low plasticity and toughness. Quenching-partitioning (Q&P) process is a new heat treatment process for martensitic steel that can obtain martensite and carbon-rich austenite multiphase microstructure to improve the plasticity and toughness of the steel. With the improving heat treatment process, combining with the method of alloying will make the plasticity and toughness of martensitic stainless steel much better.Based on36Crl3Ni2and42Crl3Ni2as tested steels, the influence of different Q&P heat treatment systems on microstructure and mechanical properties were investigated by using laser scanning confocal microscope (LSCM), X-ray diffraction (XRD), transmission electron microscope (TEM) and tensile testing machine. The Conclusion was obtained as follows:1. The addition of ausenite stabilizing element-Ni into the steel of36Crl3Ni2and42Crl3Ni2expands (γ+M23C6)/(α+γ+M23C6) and (α+γ+M23C6)/(α+M23C6) temperature range, which brought the carbide and martensite microstructure with more than HRC40.0hardness after annealing treatment and makes the steels cold working impossible.2. The volume fractions of residual austenite increased monotonically with the quenching temperatures increasing in the Q&P process when the steel of36Crl3Ni2was austenizationed at1000℃for1.5h subjected to partitioning at400℃for20min after quenching to30～90℃.The yield strength and hardness decreased with the quenching temperatures increasing in the Q&P process, but the elongation and Charpy impact energy increased monotonically with the quenching temperatures increasing. The tensile strength presented the extremum varitation tendency as the quenching temperatures increased. The mechanical properties values of Steel36Cr13Ni2obtained the best coorperation of strength and plasticity as the quenching temperature was75℃:Rp0.2=1143MPa, Rm=1543MPa, A=16.1%, Akv=14J, Hardness=HRC45.5.But the mechanical properties values can reach the most strength and hardness when the quenching temperature was30℃:Rp0.2=1255MPa, Rm=1634MPa, A=11.8%, Akv=12J, Hardness=HRC46.6.3. The volume fractions of residual austenite presented the extremum varitation tendency with the quenching temperatures increasing in the Q&P process when the steel of42Cr13Ni2was austenizationed at1000℃for1.5h subjected to partitioning at400℃for20min after quenching to30～90℃.The yield strength and tensile strength decreased with the quenching temperatures increasing in the Q&P process, but the elongation, Hardness and Charpy impact energy presented the extremum varitation tendency with the quenching temperatures increasing. The mechanical properties values of Steel42Cr13Ni2obtained the best coorperation of strength and plasticity as the quenching temperature was75℃: Rp0.2=1125MPa, Rm=1617MPa, A=16%, Akv=15J, Hardness=HRC46.8. But the strength and hardness reached the most when the quenching temperature was30℃:Rp0.2=1291MPa, Rm=1683MPa, A=10.1%, Akv=14J, Hardness=HRC49.3.4. The values of tensile strength and hardness increased slightly with the increasing of carbon content when the two steels were treated in the same Q&P process. But the elongation showed the opposite varitation.