Effect of thermal ageing on impact ductility of the nuclear reactor pressure vessel steel SA533B and its weld metal

Investigation of embrittlement of step cooling heat treatment on pressure vessel steel

“…The Holloman-Jaffe parameter, as a function of time and temperature, is commonly used to express the degree of tempering. 4,17,20 However, this parameter is unable of fully describing the material's composition and heat treatment before tempering, consequently limiting its extensively application. In order to explore the correlation between step cooling embrittlement and the temper parameters, a repeated accumulating tempering parameter equation proposed by Inoue 21 is adopted in the present work.…”

“…Therefore, any treatment in tendency to carbide growth will make the toughness deteriorate because the relatively larger carbides facilitate microcrack nucleation. The Holloman–Jaffe parameter, as a function of time and temperature, is commonly used to express the degree of tempering 4,17,20. However, this parameter is unable of fully describing the material's composition and heat treatment before tempering, consequently limiting its extensively application.…”

“…The fractographs exhibit a typical characteristic of the transgranular fracture. In the past few decades, it was well recognized that step cooling heat treatment can make steel embrittlement because the impurity segregation at grain boundaries weakens the binding energy between grain boundary, resulting in steel intergranular cracking in Charpy impact testing 3,4. However, intergranular fracture was not observed in QSC steel from Fig.…”

“…1 Conventionally, the treatment of long time thermal aging in some temperature was often used to obtain the embrittlement tendency of the vessel steel by comparing the changes in impact toughness. [2][3][4][5] However, an obvious problem of this method is that it is very time consuming, requiring thousands of hours, or even several years. Step cooling heat treatment, as an accelerating temper embrittlement method, can make steel embrittled within 200 h and therefore is widely applied in engineering to evaluate the embrittlement tendency.…”