Study On Effects Of Q&P Processes On Microstructures And Properties Of 4Cr13 Martensitic Stainless Steel

4Cr13 martensitic stainless steel with higher strength and hardness, widely used in all kinds of cutting tool material, but low plasticity and toughness are its weaknesses which is difficult to overcome. Martensitic stainless steel as cutting tool material, the organization acquired from traditional heat treatment process (quenching and tempering at low temperature) is tempered martensite, which has high hardness but the elongation is very low. This study can bring a certain volume fraction of retained austenite into martensitic microstructure through quenching and partitioning process to improve its plasticity and toughness.Based on 40Cr13SiNiN and 40Cr13N as tested steels, a variety of Q&P heat treatment system was designed in view of quenching temperature, austenitizing temperature and austenitizing time. And the influence of Q&P heat treatment process on the microstructure transformation and mechanical properties of 40Cr13 martensitic stainless steel were investigated by observing the microstructure and comparing its mechanical properties. The evaluation of the possibility of the Q&P heat treatment process using in the traditional martensitic stainless steel was done as well. The conclusion was obtained as follows:1. The addition of element-Ni into 40Cr13SiNiN enlarged the range of (γ+M23C6)/(α+γ+M23C6) and (α+γ+M23C6)/(α+M23C6), the microstructure after annealing is crypto-crystal martensite with granular carbides which has a Rockwell hardness of 36, the distribution of carbides is uneven, mainly concentrate on the original austenite grain boundary; the microstructure of 40Cr13N steel after annealing is ferrite with granular carbides which has a Rockwell hardness of 8.0 and both dimension and distribution of carbides are uniform.2. The specimen quenched to various temperatures after austenitizing at 1000℃ for 1h and partioned at 400℃ for 20min, with the increase of quenching temperature, the content of retained austenite in 40Cr13SiNiN increased at first and then decreased, reached the maximum value at 80℃ (about 35%); the content of retained austenite in 40Crl3N increased, reached the maximum value at 120℃ (about 29%).3. When the specimen quenched to various temperatures after austenitizing at 1000℃ for 1h and partitioned at 400℃ for 20min, the mechanical properties of 40Cr13SiNiN achieved the best combination of strength and plasticity (product of strength and ductility is 26500 MPa%) at 75℃:Hardness=48.5HRC, Rp0.2=1260Mpa, Rm=1660Mpa, A=16.0%, Akv=12.3J; the mechanical properties of 40Cr13N achieved the best combination of strength and plasticity (product of strength and ductility is 26500 MPa%) at 90℃:Hardness=47.0HRC, RpO.2=1250MPa, Rm=1700MPa, A=18.0%, Akv=15.0J.4. The specimen quenched to various temperatures after austenitizing at 1000℃ for 1h and partitioned at 400℃ for 20min, the mechanical properties of 40Cr13SiNiN achieved good combination of hardness and ductility when quenching to 30℃ Hardness=51.1HRC, Rp0.2=1310MPa, Rm=1760MPa, A=11.0%, Akv-8.0J; the mechanical properties of 40Cr13N achieved good combination of hardness and ductility when quenching to 45℃:Hardness=51.0HRC, Rp0.2=1420MPa, Rm=1780MPa, A=10.0%,Akv=8.0J.5.40Cr13N steel quenched to 30℃after austenitizing at 1000℃ for 5-40min and partitioned at 400℃for 20 min, with the increase of austenitizing time, the content of retained austenite increased, reached the maximum value at 40min (about 30%); the mechanical properties achieved the best combination of strength and plasticity at 10min: Hardness=50.5HRC, Rp0.2=1420MPa, Rm=1850MPa, A=12.9%, Akv=14.51...