Perspectives on Quenching and Tempering 4340 Steel

• DOI: 10.1007/s11661-020-05972-1
• Publication Date: 2020-08-27T21:05:14Z
• Authors: A. J. Clarke; J. Klemm-Toole; K. D. Clarke; D. R. Coughlin; D. T. Pierce; V. K. Euser; J. D. Poplawsky; B. Clausen; D. Brown; J. Almer; P. J. Gibbs; D. J. Alexander; R. D. Field; D. L. Williamson; J. G. Speer; G. Krauss
• Keywords: Tempering; Isothermal process; Ledeburite

Steels are ubiquitous due to their affordability and the landscape of useful properties that can be generated for engineering applications. But further expand performance envelope, one must able understand control microstructure development by alloying processing. Here we use multiscale, advanced characterization better structural chemical evolution AISI 4340 steel after quenching tempering (Q&T), including role quench rate short-time, isothermal below 573 K (300 °C), with an emphasis on carbide formation. We compare and/or property changes produced conventional those higher temperature, short-time “rapid” tempering. underscore no single technique fully capture subtle like carbon redistribution, transition cementite formation, retained austenite decomposition occur during Q&T. Only multiple techniques begins unravel these complexities. After controlled fast or slow quenching, η carbides clearly exist in microstructure, likely associated autotempering this high martensite start temperature (Ms) steel. Isothermal 598 (325 °C) results relief supersaturation martensite, primarily formation exhibit a range levels, seemingly without substitutional element partitioning between matrix phases. Hägg is present 300 °C 325 °C. at above 2 h, predominant, but small amounts also other conditions, even quenching. Previous work has indicated silicon (Si) elements partition cementite, which initially forms under paraequilibrium matrix. Phosphorous (P) may preferentially located cementite/matrix interfaces Slower rates result greater compared attribute increased stability resulting from “autopartitioning”. Rapid, found diminish tempered embrittlement (TME) believed extent decomposition, mechanical not attainable tempering, have important implications respect industrial heat treatment processes induction Controlling amount only relevant Q&T steels, next-generation strength steels (AHSS) austenite/martensite mixtures.