Original Article

Low-temperature impact toughness and embrittlement mechanism of a 460 MPa-grade steel used in a supporting equipment of a nuclear reactor pressure vessel

¹ State Key Laboratory of Metallic Materials for Marine Equipment and Applications, Anshan 114009, PR China
² Iron and Steel Research Institute of Ansteel Group Corporation, Anshan 114009, PR China
³ Angang Steel Company Limited, Anshan 114009, PR China

^* e-mail: gaotianyu01@hotmail.com

Received: 27 March 2024
Accepted: 13 April 2025

Abstract

The service safety of nuclear reactor pressure vessel (RPV) and its supporting equipment subject to external rapidly varying loads is very important for nuclear power plants. In this paper, the effect of temperature on the impact energy and fracture mode of a 460 MPa-Grade RPV-supporting steel was investigated based on Charpy V-notch impact tests. By quenching and subsequent tempering, a mixed microstructure with lath bainite and grain bainite is obtained. Depending on temperature, the curves of impact energy and shear fracture appearance (SFA) exhibit a three-stage variation: upper shelf region, transition region and lower shelf region. It is found that the Boltzmann function fits the curves of impact energy and SFA well and that the ductile-brittle transition temperature (DBTT) for the present steel is estimated as −65 °C, which shows excellent anti-notch sensitivity. Compared with temperatures below DBTT, crack-tip shielding plays a vital role in impeding cleavage crack propagation above DBTT owing to inhibited mobility of screw dislocation, leading to the transition of fracture mode from ductile-fracture to brittle-fracture.