| 20Cr13-type martensitic stainless steels(MSSs)have good corrosion resistance in the surroundings of atmosphere,water vapor and organic acids,which is a kind of promising material with the heating processing of quenching-tempering to the traditional MSSs.Although it possesses very high strength and hardness,the less plastic toughness is going on.To obtain the better martensitic steel,Quenching-Partitioning(Q&P)process is proposed,and in this way,the multiphase of martensite and carbon-rich austenite can be obtained.In the multiphase,martensite can improve the strength,while the retained austenite can improve the plasticity.In the same time,the plasticity and corrosion resistance of the martensitic stainless steel could be improved by the way of combining alloying.In this study,10Cr13N and 10Crl3Si2N martensitic stainless steel are used as the samples to research the structural transformation and mechanism of strengthening and toughening of the experimental steel during Q&P treatment,and to analyze the austenite stabilization law in one-step Q&P process.What's more,the influences of quenching temperature,partitioning temperature and time to the micro structure and properties of two step Q&P are discussed to identify the best technological parameters and corresponding structures.Finally,the effect and mechanism of additional Si elements are determined by comparing with different samples.The results of the study are as follows:(1)The thermal expansion behavior of 10Cr13N austenitizing steel,which has experienced the processes of quenching to Ms temperature,holding at.a constant temperature for a certain time,and cooling to room temperature(equivalent to one-step Q&P),has been studied by fully automatic metal phase transformation.The results show that the volume contraction of the experimental steel'at the quenching stop temperature decreases with the 'decrease o f temperature;austenite stabilization occurs when the experimental steel stays at the quenching and stopping temperature,and the austenite stabilization temperature interval increases with the decrease of quenching temperature from several to tens of degrees,but it is not enough for retained austenite to remain at room temperature.(2)The thermal expansion behavior of 10Cr13N austenitizing steel and 10Cr13Si2N austenitizing steel are studied by automatic metal phase transformation,when the two kinds of samples are quenched to 120'C and 140`C respectively before increasing to different temperatures for a period of time and then cooling to room temperature(two steps Q&P).The results show that the volume expansion of 10Cr13N steel could occur at the time of distribution after incomplete quenching,and the expansion is changed with the change of quenching temperature and distribution temperature;the volume change of 10Cr13Si2N steel partitioning at 350? and 450? is very small,while expanding appears at the partitioning temperature of 500?.(3)After quenching the 10Cr13N and 10Cr13Si2N austenitizing steel at 120? and 140 ? respectively,distribution processing at different temperature to the two steels is also conducted.The results show:when partition is conducted at 350?,the least amount of austenite can be retained,and the longer time,the more volume fraction;when partition is conducted at 450?,the most austenite can be obtained,but the volume fraction of 10Cr13N steel could decrease after reaching the extreme value in about 40 minutes and the volume fraction of 10Cr13Si2N steel could decrease after reaching the extreme value in 20 minutes;when partition is conducted at 550?,the less austenite could be obtained,and there is nearly no change for the volume fraction of 10Cr13N steel along alternating time,while the volume fraction of 10Cr13Si2N steel may decrease with the extension of time.(4)After quenching the 10Cr13N and 10Cr13Si2N austenitizing steel at 120? and 140? respectively,distribution processing at different temperature to the two steels is also conducted.The results show:after partitioning at 350?,the steel has the lowest yield strength,and the best impact toughness,and it can obtain the better plasticity in the longer partitioning time;after partitioning at 450?,the yield strength could increase,and the impact toughness could decrease comparing to the former,and the plasticity can reach the extreme value at about 40min;after partitioning at 500?,the yield strength could increase,and the impact toughness can deteriorate,and the plasticity can decrease.(5)After partitioning at 450? for 40 min,,10Cr13N steel,which is austenitizing and quenched at 120?,can obtain the best comprehensive performance.To this steel,the content of austenite is 10.3%,,the yield strength is 101 8MPa,the tensile strength is 1336MPa,the elongation is 24.8%,the impact absorption work is 100J,and the strong plastic product can reach 33133MPa%.Comparing to it,10Cr13Si2N steel,which is austenitizing and quenched at 140?,can obtain the best comprehensive performance after partitioning at 450? for 40min.To this steel,the content of austenite is 10.4%,the yield strength is 1019MPa,the tensile strength is 1457MPa,the elongation is 25.4%,the impact absorption work is 55J,and the strong plastic product can reach 37591MPa%.(6)The precipitation of carbonitride in martensite could be inhibited by increasing the amount of Si element in 10Cr13N steel.In this way,the stability of retained austenite in steel could increase,and the tensile strength and elongation of steel can be advanced,while the impact toughness may reduce. |
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