Influence of different deep cryogenic treatment routes on the properties of high speed steel

Abstract

An intensive research work was carried out in the frame of a RFCS (Research Found for Coal and Steel) project, to investigate the influence of different deep cryogenic treatments (DCT) on hardness, strength, toughness and wear resistance of AISI M2. Short and a long classical DCT, providing the soaking at temperature close to the boiling point of liquid nitrogen (−196 °C) for 6 h and 20 h, respectively, were carried out prior to and after tempering. Furthermore, a third short DC route, providing temperature cycling between RT and low temperature was also considered. Care was taken to avoid stabilization of retained austenite or self tempering due to wait at room temperature prior to DCT and/or tempering. All treatments were calibrated to get 840 HV 10, in order to compare the properties of steel with the same reference hardness. DCT does not allow the complete transformation of retained austenite in the investigated high speed steel, due to the stabilizing effect of alloying elements. Tempering is necessary to completely transform this phase and to allow proper secondary hardening. If carried out after quenching, DCT shifts the secondary hardness peak to lower temperature, evidencing the need to adjust the tempering parameters to avoid overtempering. The microstructure didn't show any significant influence of DCT in terms of carbides distribution, due to the conditioning of martensite at low temperature. The same can be also concluded for the other properties (toughness, tensile strength and wear resistance), which are practically the same for samples having the same hardness.

Effect of Deep Cryogenic Treatment on Wear and Galling Properties of High-Speed Steels

“…In turn, the initial removal of material mostly results from the accommodation of this effect, which is then considerably reduced with the intensified agglomeration of carbides over time. However, at low sliding speeds, the absence of the matrix softening promotes carbides pull-out (mostly MC carbides, as also observed by Pellizzari et al 2012 [9]) and microcracking (M23C6 and M6C), which may act as third-body particles and cause microploughing, thus resulting in an increased wear rate at an increased level of carbides precipitation via DCT. This effect strongly depends on the size and shape of carbides.…”

“…Leskovšek et al, 2006 [6], Pellizzari et al, 2008 and2012 [7-9], Fantineli et al, 2020 [10] and Zhou et al, 2020 [11] clearly stated that DCT has a positive effect on the abrasive wear resistance of AISI M2 steel, whereas studies on other HSS are rather limited and show contradictory results in terms of wear resistance change after DCT. This is proposed to be a consequence of different microstructural changes (carbide precipitation, carbide distribution and characteristics of the matrix), which then influences the material's mechanical and tribological properties [6][7][8][9]. Nevertheless, most cases indicate DCT to have a positive effect [4,12,13]; some negative effects on wear resistance were also reported [8].…”

Multiphase Microstructure Optimization to Enhance the Mechanical Properties of AISI M35 High‐Speed Steel

“…about DCT focused on PM HSS, [30,46] and few mentioned cast HSS. [22,45] Nevertheless, there are notable differences between cast HSS and PM HSS in terms of their grain size and carbide distribution. It has been observed that DCT has a stronger effect on the precipitation of nano carbides in cast high-alloyed ferrous alloys compared to PM high-alloyed ferrous alloys.…”

“…[ 40–43 ] This has resulted in poor utilization of DCT in the industry as well as considerable controversy over the increase in the performance of metal materials caused by DCT. [ 7,44,45 ] Therefore, only by an understanding of the mechanisms during DCT and the evolution of multiphase microstructures during CHT and DCT, can the enhancements of targeted properties be understood. Furthermore, most research about DCT focused on PM HSS, [ 30,46 ] and few mentioned cast HSS.…”

In Situ X‐Ray Diffraction Analysis of Microstructure Evolution during Deep Cryogenic Treatment and Tempering of Tool Steels

“…As a consequence of this lack of understanding, the large scatter in data on the improvement of tool life of steel products reported in the literature remains largely unexplained and DCT is still not accepted widely in industrial practice. [19,20] The present study was performed to shed light on the microstructure changes induced by DCT and the subsequent tempering. Specifically, laboratory X-ray diffractometers have been used to examine the phase transformation of three tool steels X38CrMoV5-3, X153CrMoV12, and ~X190CrVMo20-4 during cryogenic treatment and during subsequent tempering.…”