Method to Predict Tempering of Steels Under Non-isothermal Conditions
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JMEPEG (2017) 26:1986–1992 DOI: 10.1007/s11665-017-2641-7
Method to Predict Tempering of Steels Under Non-isothermal Conditions D.R. Poirier and A. Kohli (Submitted November 7, 2016; in revised form February 17, 2017; published online April 4, 2017) A common way of representing the tempering responses of steels is with a ‘‘tempering parameter’’ that includes the effect of temperature and time on hardness after hardening. Such functions, usually in graphical form, are available for many steels and have been applied for isothermal tempering. In this article, we demonstrate that the method can be extended to non-isothermal conditions. Controlled heating experiments were done on three grades in order to verify the method. Keywords
heat treatment, steel, thermal analysis
1. Introduction In 2008, Canale et al. (Ref 1) published an extensive review of tempering of steel that refers to early works Hollomon and Jaffee (Ref 2) and Grange and Baughmann (Ref 3) and how the use of their so-called tempering parameter was extended by subsequent researchers to not only account for the extent of tempering during isothermal schedules but also during nonisothermal heating schedules. The usual property to monitor tempering is hardness, but Canale et al. (Ref 1) included in their review works that quantified tempering kinetics with other mechanical properties, such as tensile properties, toughness metrics, creep rupture times, and hydrogen embrittlement. They also pointed out how others have incorporated the effects of tempering on improving the properties of welded steel and on foundry heat-treating issues when processing castings that inherently do not heat and/or cool with uniform temperatures. In this article, we show that the classical tempering parameters devised for isothermal tempering can be used to predict the extent of tempering in non-isothermal schedules without the need for defining effective times or reference times in calculation methods that have been previously devised, as reviewed by Canale et al. (Ref 1). Tempering data of plain carbon steels and some low-alloy steels, based on the classical works published in 1945 (Ref 2) and 1956 (Ref 3), are presented as graphs in Brooks (Ref 4). From the original works, the plain carbon steels selected for this study include 0.31% C steel, 0.56% C steel, and 0.74% C steel (Ref 2), and the lowalloy steels selected include 4340, 4140, and 3140 (Ref 3). The compositions are given in Table 1, which are reproduced from the original works (Ref 2, 3).
D.R. Poirier and A. Kohli, Department of Materials Science and Engineering, The University of Arizona, Tucson, AZ. Contact e-mail: [email protected].
1986—Volume 26(5) May 2017
2. Tempering Response Curves for the Steels in Table 1 In this article, we use the isothermal tempering data of the six steels in Table 1 to derive the tempering parameters (P) as a function of the time-temperature coordinates. The parameter is directly related to hardness, so once P is calculated, the hardness can be very closely estimated. Then the u
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