| OOCr11Ni11MoTi stainless steel is a new development of ultra-high strength maraging stainless steel, which have excellent overall performance and good corrosion resistance and the key to be used in high load and poor special environment construction materials.(Tensile Strength Rm≥1600MPa, Yield strength Rp0.2≥1450MPa, Elongation A≥8%, Reduction in area Z≥45%, Charpy impact energy AKU2≥50J).Because of ultra-high strength steel for brittle more sensitive, the alloy element content of Ti and C of research steel was fine controled on the paper, targented smelting three furnaces for steel. which was key researched on effect of the mechanical properties in high temperature slow cooling process.Through different heat treatment process optimization of solution treatment temperature of grain refinement,thereby enhancing the OOCr11Ni11MoTi maraging stainless steel on the comprehensive properties.About OOCr11Ni11MoTi maraging stainless steel was conducted in-depth research in this paper.The result was first discovered two new features, which is occur the high temperature brittleness in slow cooling and coarse austenite grain size of heredity in treatment processing.the findings of the study on the high temperature slow cooling under thermal brittleness as follows:(1) OOCr11Ni11MoTi maraging stainless steel have significant phenomena of thermal embrittlemnet after slow cooling from high temperature the study was verified that susceptibility to warm embrittlement of maraging stalinless steel and degree of embrittlement was related to the alloy content of Ti and C in the steel.On the comparison of three furnaces steels, the more content of Ti,and the stronger the .susceptibility to thermal embrittlement.The fuinace steel that the alloy content of Ti is 1.38% is the strongest on susceptibility to thermal embrittlement,whose the embrittle phases was precipitated on about 1100℃; The more content of C in 00Cr11Ni11MoTi maraging stainless steel,the more degree of embrittlement. The fuinace steel that the alloy content of C is 0.0039% is the most degree of embrittlement, and the Charpy impact energe declined more than 83.7% after solution treatment. (2) The reasons of embrittlement is that embrittling phases of Ti(N, C)are precipitated in the grain boundaries of OOCr11Ni11MoTi maraging stainless steel during slow cooling form high temperature. With high temperature slow cooling to low temperature and embrittlement, the embrittling phases are precipitated by discrete in grain boundaries, and continue to grow up linear distribution of precipitation, result in brittle fracture of materials, and decline the mechanical properties of the acute largest lever of reduction in area Z up to 87% and the lowest of elongation A at 35.5%.The study was found coarse original austenite grain heredity on OOCr11Ni11MoTi maraging stainless steel,as follow:(1) In the course of solution treatment,it is exist coarse austenite grain size of hereditary due to austenite grain boundary strain-hardening possibly.With solution temperature increase the hereditable coarse austenite grain boundaries began to move being zigzag,and set recrystallization temperature AC (875℃-900℃) that far higher than the Af.Between Af and AC, pretreatment and multiple circulating solution treatment process cannot refine coarse grain, but multiple circulating solution treatment have certain effected on growing up sawtooth of grain boundaries.Starting recrystallization above temperature of AC, which is confirmed the recrystallization temperature range between 875-900℃; unclosed complete grain boundary was finished about 950℃.the nucleation temperature AC declined after the second or third cycle of solution treatment lead to the austenite grain nucleation in advance, and nucleation interval at 850-875℃.With the circulation of solution treatment on many occasions, completed recrystallization temperature has been reduced, and the interval at 900-925℃.
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