Investigation on Temper Embrittlement of TS1100 MPa Grade Ultra-High Strength Steel
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TRODUCTION
ULTRA-HIGH strength steels (UHSS) are widely applied as structural components for bridges, offshore platforms, pressure vessels, etc. They are usually delivered in the heat-treated state, especially through quenching and tempering (Q-T). Therefore, how to avoid temper embrittlement (TE) is one of the major challenges faced by manufacturers. There are typically two types of TE, i.e., reversible and irreversible. The well-accepted explanation for reversible TE is the segregation of impurity elements, e.g., phosphorus (P) to highly disordered interfaces such as prior austenite grain boundaries and high-angle random sub-structural boundaries.[1,2] Recently, the segregation phenomenon has been confirmed by Auger spectroscopy and the atom probe technique, respectively.[3,4] Using quantum mechanical calculations at absolute zero, it was demonstrated that the segregated impurity elements would draw charges from manganese
MEIYING LI, TAO JIA, LI MA, XIANMING ZHAO, and ZHAODONG WANG are with the State Key Lab of Rolling and Automation, Northeastern University, 3-11 Wenhua Rd., Shenyang, 110819, People’s Republic of China. Contact e-mail: [email protected]; [email protected] Manuscript submitted on February 27, 2020.
METALLURGICAL AND MATERIALS TRANSACTIONS A
(Mn) and chromium (Cr) onto themselves and weaken the metal-metal bonds.[5] To suppress reversible TE, alloying with molybdenum (Mo) and tungsten (W) has been long recognized as the most effective way. As described by Song et al.,[5] there are mainly two mechanisms, i.e., the delaying effect on the process of P segregation, and the increased boundary cohesive strength upon addition of Mo which reduces the ionic property of the interatomic bonds of Fe-P. Irreversible TE is in general attributed to the precipitation of thin film-like carbides at the microstructural interfaces, which is inherent to almost all structural steels. Petrov and Tsukanov[6] investigated the irreversible TE of 20Kh3MVF and 25KhMF steels and found its correlation with carbides precipitated at prior austenite grain boundaries. They also suggested that alloying with Mo and other carbide-forming elements such as Cr shifted the range of irreversible TE from 250 to 400 C to higher temperatures. Yang et al.[7] applied a slow quenching rate to M152 martensitic heat-resistant steel. They found that the continuous distribution of M23C6 along prior austenite grain boundaries and M2C along prior residual austenite film was responsible for the sharp decrease of impact toughness. Li et al.[8] presented a similar morphology of precipitates in 10Cr12Ni martensitic heat-resistant steel which played a nucleating role in the development of cracks and led to the TE.
Early in 1950s, intercritical quenching which was introduced originally between preliminary quenching from the austenite region and subsequent tempering was employed to decrease the susceptibility to TE. It was then widely applied to the heat treatment of structural components. Wada and Doane[9] put forward possible mechanism to explain it
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