Significance of Partial Substitution of Carbon by Nitrogen on Strengthening and Toughening Mechanisms of High Nitrogen F
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UCTION
THE bearings in service have to tolerate high speed, heavy load, and corrosive environment, thus requiring high hardness, good fatigue resistance, wear resistance, and corrosion resistance for bearing steels.[1] In aerospace engines, bearings must meet more and more demanding requirements, such as elevated temperature and increased reliability.[2] The conventional high carbon (C) martensitic stainless steels (MSSs), such as 440C and BG42, exhibit poor impact toughness due to the existence of coarse eutectic carbides,[2,3] making bearings easily fracture upon sustained impact load. Therefore, improving the impact toughness of bearing steels
HAO FENG, HUA-BING LI, WEI-CHAO JIAO, ZHOU-HUA JIANG, and HONG-CHUN ZHU are with the School of Metallurgy, Northeastern University, Shenyang, 110819, P.R. China. Contact email: [email protected] MING-HUI CAI is with the School of Materials Science and Engineering, Northeastern University, Shenyang, 110819, P.R. China. ZHI-GANG CHEN is with the Centre for Future Materials, University of Southern Queensland, Springfield, QLD, Australia and also with the Materials Engineering, The University of Queensland, Brisbane, QLD, 4072, Australia. Manuscript submitted February 17, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS A
without significantly deteriorating their strength and hardness is essential. Nitrogen (N) is one microalloying element that may be an answer to the increasingly demanding requirements of MSSs. In practice, partial substitution of C by N in conventional MSSs has been proposed mainly because of good strength and hardness as well as toughness compromise.[4–9] However, the low N solubility in MSSs restricts further applications of N-bearing MSSs.[10,11] The recent development of pressurized metallurgy, such as pressurized electroslag remelting and pressurized induction melting (PIM), makes it possible to commercially produce the MSSs with N contents of > 0.4 wt pct without gas pores.[12] Accordingly, some studies related to partial substitution of C by N in MSSs (e.g., Cronidur 30 and XD15NW) have been reported, in order to obtain a good trade-off between overall mechanical and service properties.[5,13–16] Gavriljuk et al.[13,14] revealed that N-induced shortrange ordering could prevent the clustering of the Cr element, and thereby delay the precipitation of Cr-rich particles and thus reduce the size of precipitates. Wang et al.[5] demonstrated that the overall tensile properties of 0.19C-12.8Cr-0.5Mo-1.3Ni MSSs were improved by partially replacing C by N (0.07 wt pct), together with vanadium and niobium microalloying. Horovitz et al.[7] and Ono et al.[17] found that the partial substitution of C
by N (0.16 to 0.19 wt pct) in 0.3C-13Cr (AISI 420) steels reduced the fraction and size of precipitates and enhanced the hardness and corrosion resistance. Berns and Ehrhardt[18] revealed that the partial substitution of C by N (~ 0.2 wt pct) in nickel MSSs retarded the formation of pre-eutectoid carbides, refining the size of carbides and meanwhile improving their distr
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