| 20Cr13-type martensitic stainless steel(MSSs)was widely used due to its good corrosion resistance in atmosphere,steam and organic acid.The traditional quenching and tempering was carried out for a long time to improve the strength and hardness of MSSs,but be poor in the ductility and toughness through this heat treatment.Recently,quenching and Partitioning(Q&P)process has been suggested as an alternative heat treatment proposed for martensitic steel.The purpose of using MSSs for Q&P heat treatment is to acquire the combination of high strength and toughness.Targeting at two kinds of Cr13 MSSs,10Cr13NiSiN and 10Cr13NiN,we researched the influence of Q&P in microstructure and mechanical properties of Cr13 MSSs from austenitizing,quenching temperature,partitioning temperature and partitioning time.Finally,we determined the relationships of component-process-microstructure-properties.The conclusion was obtained as follows:1.After treated by Q&P,the microstructure of 10Cr13NiSiN and 10Cr13NiN are mixed by martensite and retained austensite.Martensite is composed of lath and twined martensite,retained austensite is composed of film and bulk austensite.Through observing by TEM,we haven't find carbide in two steels.2.The Q&P process of MSSs must be conducted in the appropriate austenitizing temperature,quenching temperature,partitioning temperature and partitioning time.Austenitizing temperature affect the dissolution degree of alloy carbonitride,then can change the Ms temperature,quenching temperature directly determines the content of lath martensite,and indirectly determines the volume fraction of retained austensite and martensite after the Q&P heat treatment,partitioning temperature and partitioning time affects the degree of diffusion of carbon and nitrogen atoms,directly influence the morphology and volume fraction of retained austenite and the stability of austenite.3.The contents of retained austensite of 10Cr13NiSiN and 10Cr13NiN reaches at 18.4%and 13.8%respectively while they are in Q&P heat treatment process at the optimum quenching temperature.And it is less than the content of retained austenite generated in the CCE model.Under the same condition of partitioning,the content of retained austenite generated from 10Cr13NiSiN is higher than that in 10Cr13NiN.It shows that Si element plays an important role in inhibiting carbonitride precipitation and improving the utilization ratio of stabling residual austenite by carbon and nitrogen.4.The experiments showed that the quenching temperature that needed to get the best mechanical properties is lower 20? to 30? than the optimium temperature.To get best mechanical properties,the quenching and partitioning heat treatment process of 10Cr13NiSiN must be conducted under these conditions:austenitizing at 1000?,quenching temperature at 135?,partitioning temperature at 500? for 5 min,after the above Q&P heat treatment,it obtained the mechanical properties as follows:Rp0.2=1051 MPa,Rm=1462 MP a,A=238%,Akv=64 J,Rm×A=34.8 GPa·%.Similarly,the Q&P heat treatment process of 10Cr13NiSiN must be conducted under these conditions:austenitizing at 1000?,quenching temperature at 160?,partitioning temperature at 450? for 40 min,after the above Q&P heat treatment,it obtained the mechanical properties as follows:Rp0.2=941 MPa,Rm=1331 MPa,A=25.8%,Akv=92 J,Rm × A=34.3 GPa·%.5.There didn't appear apparent volume expansion in the curve of the thermal expansion when the 10Cr13NiSiN steel is partitioning at 350??450 ?,while there appeared apparent volume expansion when it is partitioning at 500?for a long time.Differently,as for the 10Crl3NiN steel,there appeared apparent volume expansion when it is partitioning both at 450? and 500? for a long time.The reason of volume expansion may be that a part of the retained austenite decomposed to generate some ferrites while partitioning under high temperature for a long time.But it's hard to figure out what the real products are. |
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