Carbides precipitation and kinetics of H13 steel subjected to deep cryogenic treatment

Abstract

The influence of deep cryogenic treatment (DCT) on carbides precipitation and isothermal softening behaviour as a function of both temperature and time during tempering of H13 steel was investigated. The results show that the retained austenite transformed into martensite leading to an increase in hardness. The carbon content of martensite decreased after DCT and tempering according to the calculation of the X-ray diffraction spectrum. This indicates that more fine carbides precipitated from the martensitic matrix after DCT. The morphology of microstructure and distribution of carbides have verified the properties improvement mainly depending on the retained austenite transformation and more fine carbides precipitated after tempering. In addition, the carbides precipitating and coarsening are the main causes of thermal softening.

A Novel Heat Treatment Strategy Based on Quenching and Carbides Preprecipitation and Subsequent Critical Quenching to Improve the Thermal Fatigue Performance of AISI H13 Tool Steel

“…Khajuria et al [ 21 ] have pointed out that the prior austenite grain boundaries (PAGB) and lath grain boundaries are decorated with fine M 23 C 6 in different morphologies and sizes during tempering of P91 steel. According to the obtained results of Li et al, [ 22 ] the type of the precipitated carbides has been determined as M 23 C 6 during tempering, and the type of precipitated carbide are not changed after deep cryogenic treatment. The white precipitates that decorate PAGB region were analyzed by EDS.…”

Cryogenic Treatment of Martensitic Steels: Microstructural Fundamentals and Implications for Mechanical Properties and Wear and Corrosion Performance

“…For instance, Villa et al [152,176,177] reported almost no change in tetragonality for cryogenically treated 1% C-1.5% Cr steel. Other investigators [21,125,184,194] have proven experimentally the very low tetragonality of the martensitic lattice for cryogenically treated Vanadis 6, X220CrVMo13-4, DC 53, and AISI H13 steels, while Das et al [12,53] assumed and Pellizzari et al [195] experimentally proved increased lattice tetragonality in AISI D2 steel (note that these steels will be discussed in Section 3.4).…”

“…However, the outcomes manifested clear differences. For instance, Li et al [125] and Lopez-Leyva et al [257] reported a significant reduction (but not complete elimination) of retained austenite, while Amini et al [258] claimed complete elimination of this phase by cryogenic treatment at −196 • C. Figure 13 shows the differences between conventionally quenched, conventionally quenched and tempered, and cryogenically treated and tempered AISI H13 steel. It is seen that conventionally quenched and untempered steel contains well-visible primary austenite grains, whereas the microstructure is martensitic, shown in Figure 13a.…”

“…In these cases, the RA is visible as white blocks in the room-temperature quenched microstructures. In high-carbon, high-alloy tool steels, the retained austenite usually appears as more or less thick films (several tens to > 100 nm) between the martensitic laths, as an example in Figure 5 shows for conventionally heattreated H13 steel [125]. In these steels, the amounts of retained austenite can be up to 20 vol.% [30].…”

“…One exception is the work by Koneshlou et al [155], tioned that martensite laths are smaller and distributed more uniformly in the m ture after holding the samples of AISI H13 steel for a long time at deep cryogen atures. On the other hand, there is clear evidence of a higher number and a more uniform distribution of nano-sized precipitates in cryogenically treated and high-temperature tempered AISI H11 [122,259], H13 [51,118,125,199,256], and H21 [200] steels. The maximum populations of carbides were found for treatment durations between 16 and 24 h. However, it should be noted that this feature appeared in steel microstructures independent of the heat treatment strategy used.…”