| Traditional Cr13 martensitic stainless steel has high strength,hardness and good corrosion resistance,but with low plasticity and toughness.Although its mechanical properties can be adjusted by quenching and tempering,the strength and plastic toughness of this change,can not obtain good comprehensive mechanical properties,which greatly limits the application of industrial production.Quenching and partitioning(Q&P)process is a new heat treatment for martensitic stainless steel,It is intended to stabilize the austenite by the secondary equilibrium diffusion of carbon atoms during the partitionging process,and obtain martensite and carbon-rich austenite multiphase microstructure to improve the plasticity and toughness of steel.At the same time,based on the Q&P process,combined with the alloying method can ensure high strength conditions,to further improve the plastic toughness.Based on 20Cr13NiN,30CrNi,30Cr13NiMn as tested steel,study the influence of different Q&P heat treatment process and alloying elements on microstructure and mechanical properties were investigated by laser scanning confocal microscope(LSCM),electron microscope(TEM),X-ray diffraction(XRD),backscattered electron diffractometer(EBSD)and tensile testing machine.The conclusion was obtained as followed:1.In the Q&P treatment,as the austenitizing temperature increase,the amount of carbonitride dissolution increased and the carbonitride-forming elements are dissolved in the austenite matrix as much as possible,lowered the Ms temperature,resulting in residual microstructure austenite content increased;at too high austenitizing temperature,carbonitride completely dissolved,austenite grain too big.The optimum austenitizing temperature of 20Cr13NiN steel is 1030?.2.When the steel of 20Cr13NiN steel was austenitized at 1030? subjected to partitioning at 450?500? for 30?60min after quenching to 30-60?.The volume fractions of residual austenite increased monotonically with the quenching temperature increasing in the Q&P process,the yield strength decreased,the tensile strength fluctuated less,the elongation rate first increased and then decreased,and the volume fractions of residual austenite at 50? was more and less secondary martensite is produced,and the maximum elongation rate is 24.1%and the comprehensive mechanical performance is the best.The volume fractions of residual austenite and elongation rate first increased and then decreased with the partitioning temperature increasing in the Q&P process.At 480 tempemrature,the carbides precipitated well and the comprehensive mechanical properties was the best.With the extension of the partitioning time,the diffusion of C in austenite is more uniform,the retained austenite content increases,and the mechanical properties of the steel are improved.3.The volume fractions of residual austenite increased monotonically with the quenching cooling rate increasing in the Q&P process when the steel of 20Cr13NiN steel was austenitized at 1030C0 for 30min subjected to partitioning at 450C° for 30min after by air cooling,fog cooling,oil cooling and salt bath cooling respectively.With the quenching cooling rate increase,less and less precipitation of carbide,elongation rate increased,yield strength decreased,tensile strength fluctuations are small.The mechanical properties of steel was the best under the salt bath cooling.4.When the sheet of 2Cr13NiN steel was austenitized at 1030C0 for 30min subjected to partitioning at 480C° for 60min after quenching to 50C°,the experimental steel could obtain the best combination of strength and plasticity:Rp0.2=964MPa,Rm=1583MPa,A=24.1%,Rm × A=38150 MPa·%;5.When the sheet of 30Cr13Ni Steel was austenitized at 1100C°for 30min subjected to partitioning at 480C° for 60min after quenching to 20C°,the experimental steel could obtain the best combination of strength and plasticity:Rp0.2=1089MPa,Rm=1695MPa,A=21.4%,Rm×A=36273MPa·%;6.When the sheet of 30Cr13NiMn Steel was austenitized at 1060C° for 30min subjected to partitioning at 480C° for 30min after quenching to 30C°,the experimental steel could obtain the best combination of strength and plasticity:Rp0.2=980MPa,Rm=1719MPa,A=20.8%,RmxA=35755MPa·%;7.By N atom instead of part C atom,using the effect of solid solution strength of N,while ensuring high strength,increased the elongation rate of the steel.At the same time,the optimum austenitized temperature reduced 70?,saved energy consumption.The optimum austenitized temperature of 30Cr13NiMn steel reduced 40? by adding a certain amount of Mn atom. |
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