Dynamic Microstructure Transition Of Super 13Cr Martensitic Stainless Steel

In this paper,the microstructure of Super 13Cr martensitic stainless steel was observed dynamically by high-temperature laser scanning confocal microscope(LSCM).Combined with the X-ray diffractometry,scanning electron microscope and transmission electron microscopy for studying the phase composition of microstructures and content and morphology of inverted austenite.The experimental process parameter window of LSCM was obtained by measuring and analyzing the performance variation law under different processes by Vickers hardness tester.Super 13Cr martensitic stainless steel was carried out general heat treatment in combination with the process parameter window,and the microstructures and properties of the Super 13Cr martensitic stainless steel after general heat treatment were analyzed to study the process parameter window that satisfies the industrial production of Super 13Cr martensitic stainless steel finally.The research results are as follows:1.When Super 13Cr is austenitized in LSCM,with the austenitizing temperature being in the range of 950 ℃~1050 ℃,austenite grain size slowly increases which is from 15.2 μm to 24.8 μm;with the austenitizing temperature being in the range of 1050 ℃~1150 ℃,austenite grain size increases rapidly,which is from 24.8 μm to 49.5 μm.With austenitizing temperature of 1050 ℃,holding for 1 h,as the holding time increases,the austenite grain grows fast at the range of 0 min~5 min;the austenite grain growth rate is slow at the range of5 min~30 min;abnormal large grains appear in partial area,and austenite grain coarsening is obvious at the range of 30 min~60 min.2.When Super 13Cr martensite transformation occurs in LSCM,Cooling at a cooling rate of 5 ℃/s at austenitizing temperature 950 ℃,1050 ℃ and 1150 ℃,the martensitic transformation initiation temperature increases as the austenitizing temperature increases.The martensitic transformation rate of Super 13Cr increases with the increase of austenitizing temperature,and the microhardness of Super 13Cr decreases with the increase of austenitizing temperature.Full lath martensite can be obtained by austenitizing at 1050 ℃for 5 min and cooled to room temperature at different cooling rates;the cooling rate has little effect on the martensite transformation initiation temperature;the martensite transformationinitiation temperature is maintained at about 180 ℃.The cooling rate is in the range of 5 ℃/s~ 20 ℃/s,Super 13Cr microhardness is almost unchanged,the microhardness value is 347 Hv.The excellent process window for quenching Super 13Cr in LSCM is 1050 ℃austenitizing temperature,holding for 5 min,cooling rate 5 ℃/s.3.When Super 13Cr tempering process in LSCM,tempered martensite always exists in the form of slats.The tempering temperature has a significant effect on the content of the inverted austenite : When the tempering temperature is lower than 590 ℃,the inversion austenite content is extremely small;Inverted austenite content reaches maximum peak at tempering temperature of 620 ℃.When the tempering temperature is 700 ℃,holding time 1h,the inverted austenite is cut into lath martensite during the cooling process.In the tempering temperature at 620℃,the cooling rate is 0.5 ℃/s~ 10 ℃/s,the initial austenite content increases and then decreases.The Super 13Cr inversion austenite content with a cooling rate of 1 ℃/s is up to 15.26%.It is observed by EBSD that the inverted austenite is located in the lath martensite bundle or the prior austenite grain boundary.Through TEM observation,it is known that the inverted austenite is distributed in a long rod shape on the tempered martensite lath base.The excellent process parameter window for tempering Super13Cr in LSCM is 620 ℃ tempering temperature with 1 h holding and cooling rate 1 ℃/s.4.In the ordinary heat treatment experiment simulating industrial production,combined with the LSCM process parameter window,the quenching temperature was calculated to be1050 ℃ with 0.5 h holding time and oil cooling,and the tempering temperature was calculated to 620 ℃ with 2 h holding time and air cooling,then the inverted austenite content reached 13.42%.When tempered at 580 ℃ ~ 700 ℃,the microhardness reached a minimum at a tempering temperature of 620 ℃.