| Martensitic stainless steels(MSSs)is the preferred steel in high load and corrosive environments,but it is difficult to achieve a balance of strength and ductility in the traditioanal Quenching-Tempering(Q&T)heat treatment.Recently,Quenching-Partitioning(Q&P)process is proposed to achleve a good strength-ductility fit by obtaining a mixed structure of low carbon martensite and carbon enrichment austenite.In this paper,the commercial 20Cr13 steel was taken as the research object.The effects of Q&P heat treatment parameters on the microstructure and mechanical properties of the experimental steel were studied from the aspects of quenching temperature,partition temperature and distribution time,and determined the correspondence relationships of composition-process-tissue-performance;the corrosion resistance of Cr13-type MSSs after Q-T process and Q-P process was evaluated by salt spray simmulative corrosion test and electrochemical corrosion test.The effect of heat treatment and alloying elements on corrosion resistance was determined.The conclusion was obtained as following findings:(1)The microstructure and properties of the 20Cr13 steel was seriously affected by the quenching temperature after Q&P treatment.When the quenching temperature is lowered from 180? to 80?,the retained austenite content in the Q&P microstructure is reduced from 19%to 6%,resulting in a monotonous increase of yield strength in the range of 450 MPa,and tensile strength of 100 MPa.Within the fluctuation range,the first increase and then increase,the elongation rate rises first and then falls within the fluctuation range of 6%,and the impact energy of 40 J.The Q&P treatment at quenching temperature at 140? gives the best mechanical properties.(2)Carbide precipitation and retained austenite decomposition in martensite in the incompletely quenched microstructure of 20Cr13 steel at different temperature treatments will affect the carbon diffuse from martensite to austenite,which will change the properties of steel.When 20Cr13 steel is quenched to 140? and then partitioned at 350?,the low austenite content leads to insufficient ductility toughness;the austenite content is high and stable at 450?,the ductility toughness reaches a high state;At 500?,the retained austenite content decreased with the extension of the partitioning time,and the impact toughness decreased.(3)For obtaining the best mechanical properties of 20Cr13 steel,the Q&P process must conducted under these conditions:austenitizing temperature is 1000?,then quenched to 140?,distribution temperature is 450?,holding for 20 min.After the heat treatment,the retained austenite content of steel is 15.0%,Rp0.2=1103 MPa,Rm=1492 MPa,A=26.9%,Akv=68 J,and Rm×A=40.1 GPa%.(4)The results of salt spray test,electrochemical corrosion test show that the corrosion resistance of Q&P treatment of martensitic stainless steel is higher than that of Q&T treatment.It is indicated that the corrosion resistance of the C and N elements in the carbonitride precipitation state is lower than that in the solid solution state,which is related to the chromium-depleted zone caused by carbonitride precipitation.(5)0Cr15Ni5MoN and 00Cr13Ni5Mo,the martensite chrome-nickel stainless steel,show a good corrosion resistance in acetic acid spray(AASS)test,the weight loss ratio in copper-accelerated acetic acid-spray(CASS)test was increased by more than 20 times in AASS test.Martensitic chromium stainless steel 20Cr13 steel,10Cr13N steel,10Cr13Si2N and 10Cr13NiSiN steel show relatively low corrosion resistance in AASS test,and corrosion resistance is further deteriorated in CASS test.The weight loss ratio in the CASS test was increased by more than 4 times.(6)The corrosion resistance of 0Cr15Ni5MoN steel is better than that of 00Cr13Ni5Mo steel.Martensitic chromium stainless steel is improved in corrosion resistance according to the order of 20Cr13 steel?10Cr13Si2N steel?10Cr13N steel?10Cr13NiSiN steel.It shows that in martensitic chromium stainless steel,N and Ni element obviously improve corrosion resistance,Si element slightly deteriorates corrosion resistance. |
PDF Full Text Request