Quench Temperature-Dependent Mechanical Properties During Nonisothermal Partitioning

Abstract

The present study demonstrates the role of hot rolling and quench temperature in determining the mechanical properties of low alloy steel processed through quenching and nonisothermal partitioning (Q&P) route. The results indicate that the abrasive wear resistance does not show any significant variation with quench temperature. However, a reduction in tensile strength and an increase in charpy impact toughness and elongation is observed with increasing quench temperature. Interestingly, the retained austenite shows high thermal stability at sub-zero temperature. Furthermore, during deformation through the wear process, the retained austenite experiences the TRIP effect that leads to improvement in wear resistance. The incorporation of hot rolling prior to Q&P led to a significant improvement in strength, energy absorption capability and wear resistance due to a considerable refinement of the microstructural constituents.

Effect of Finish Rolling Temperature on Microstructure and Mechanical Properties of Low-Si Steel After Quenching and Nonisothermal Partitioning

“…Both the samples show three distinct stages in the work-hardening behaviour with increasing strain, which has also been observed by other Fig. 7 a Engineering stress-strain curves and b work-hardening plots of the samples finish rolled at 940°C (H-FRT) and 900°C (L-FRT) researchers [23,29,43]. Each stage in the work-hardening curve represents a uniform work-hardening behaviour which is denoted by a constant value of the work-hardening exponent (n).…”

“…The other reason for higher strength in hot-rolled condition is a significant refinement of grains and microstructural constituents when compared with their undeformed counterpart. For example, the average grain size for undeformed sample has been reported to be 102.2 ± 25.7 lm [29], which reduces to 43.0 ± 11.6 and 48.0 ± 14.4 lm for L-FRT and H-FRT samples, respectively (Fig. 4).…”

“…stage-1, the work-hardening is from the plastic deformation of low-carbon primary martensite and retained austenite, which are relatively soft phases. Within these two, retained austenite will deform first, followed by low-carbon primary martensite [29]. However, the contribution from retained austenite to overall work-hardening will be relatively lower due to its lesser content as shown in the XRD profiles (Fig.…”

“…The initial work on this quenching and nonisothermal partitioning process was reported by Thomas et al in 2009 [14]. Thereafter, some other researchers, including the present authors, have also investigated the various aspects of this energy-efficient quenching and nonisothermal partitioning process [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30]. These studies have shown to achieve the desired microstructural combination [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] and, therefore, improved mechanical properties, in comparison to the steel treated by direct quenching [19,23], quenching and tempering [21], and quenching and isothermal partitioning process [14,15,17,18], within similar alloy compositions.…”

Strong and ductile medium-Mn steel achieved via controlled martensite tempering

“…The benefit of non-isothermal tempering is to utilise the waste heat of the steel plates after coiling and is available to improve the ductility compared with the directly quenched ones [60,63]. However, such procedure appears to be difficult to obtain ultra-high strength in low alloy steels because of the pre-transformed ferrite and bainite [61,64,65]. Nevertheless, by utilising the RT Q&P steel with sufficient hardenability, the decomposition of austenite into ferrite during slow cooling can be avoided.…”