Martensite Formation from Reverted Austenite at Sub-zero Celsius Temperature

Abstract

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Review on the Effect of Deep Cryogenic Treatment of Metallic Materials in Automotive Applications

“…Shallow cryogenic treatment (SCT) occurs from −80 to −160 • C (193 to 113 K) [34,[43][44][45]. In Celsius scale, the deep cryogenic treatment (DCT) is in some literature below −160 • C (113 K) [46] and other literature −153 • C (120 K) [47,48], depending on the corresponding author. DCT can be also found in literature named as sub-zero treatment (SZT) [42] or ultra-low temperature process (ULTP) [18].…”

“…Holding time is the second factor, which influences on the effect of DCT on metallic material. However, the variety of time periods applied on the steel show that the mechanism and dynamics of DCT is still not well understood, as some studies get the same resulting effect with shorter holding time [3,47,73] and others with longer soaking period. Cooling and warming rate in conducted studies differs from 0.25 [47] to 3 • C/min [53].…”

“…However, the variety of time periods applied on the steel show that the mechanism and dynamics of DCT is still not well understood, as some studies get the same resulting effect with shorter holding time [3,47,73] and others with longer soaking period. Cooling and warming rate in conducted studies differs from 0.25 [47] to 3 • C/min [53]. Even though the generally accepted recommended cooling and warming rate is 0.5 • C/min [28,39].…”

“…But in other cases properties improvement of metallic materials were insignificant [48,82] or even deteriorated [74,75]. The DCT improves dimensional stability [72,73], resistance to electro-chemical corrosion [72], hardness [3,73,74], wear resistance [3,74,81,85], machining time and machinability [3], impact toughness [47], free energy absorption [74], ductility [83,84] and smooth surface of alloys is improved [82]. Furthermore, it provides more homogeneous and finer distribution of precipitated secondary carbides [53,75].…”

“…Koneshlou et al (2011) [96] and Prudhvi et al (2016) [3] concluded that the main mechanism behind the DCT is also the transformation of austenite to martensite, where smaller martensite laths are uniformly formed in the matrix. Niessen et al (2018) [47] provided useful input on the thermal formation of the martensite from austenite, from which strong influence of holding time on properties of steel has been indicated, especially in terms of impact toughness. Zhirafar et al (2007) [74] explained changed properties after DCT by the higher amount of the "freshly-formed" martensite.…”