A Study Of Holding Time On Temper Embrittlement In 12Cr1MoV Steel

In this thesis, the tensile test and hardness analysis in 12CrlMoV steel in isothermal 540 and different holding time have been carried out. The results show that with the holding time prolonged the value of tensile strength increases gradually; yield strength , elongation and cross-section begin to decrease after gradual increasing for some time, and arrive at minimum at holding 500h. Meanwhile the hardness of 12ClMoV steel tends to decline with the holding time prolonged.By instrumented Charpy impact test, the changing law of the ductile to brittle transition temperature (DBTT) versus holding time is investigated at 540 The results indicate that when holding time is less than 500h, the DBTT enhances gradually and the brittleness increases; when the holding time is 500h, the DBTT reaches highest and brittleness largest; when the holding time is more than 500h, DBTT decreases gradually and the brittleness declines.Microstructure analysis indicates that the structure of 12CrlMoV steel is typical streaky martensite before isothermal holding treatment and the base of 12CrlMoV steel is low carbon bar bainite after holding 500h. The scan picture analysis shows that the fracture of 12CrlMoV steel take on a shape of fiber before isothermal holding treatment and the material behaves some ductile-fracture characters. The specimen after holding 500h appears a shape of rock candies and blocks, presenting a typical brittle fracture. However the fracture takes on a shape of fiber after holding 800h.At last, the grain boundary segregation phenomena of phosphorus was studied and analyzed in 12CrlMoV steel in isothermal 540 and different holding time in this paper. By AES, the non-equilibrium grain boundary segregation level of phosphorous in specimen is measured and the curve of phosphorous concentration in grain boundary has been achieved. The result of AES test illustrates that the contentof phosphorous in grain boundary is the largest when isothermal holding time is 500h. With the theory of non-equilibrium segregation in grain boundary of phosphorous that Xu Tingdong has put forward, the critical time is estimated at 478.2h. The testing results are effective and consistent with theoretic analysis.