Influence of modes of thermal hardening and the subsequent cryogenic processing on structure and properties of steel 38Ni3CrMoV

Abstract

For the production of various machine-building products - rolling rolls, parts of power equipment, piercing mandrels - complex alloy steels containing chromium and a significant number of other deficient alloying elements (nickel, vanadium, molybdenum) type 38Ni3CrMoV are used. The paper presents the results of research on the influence of modes of hardening and subsequent cryogenic treatment on the parameters of the structure, hardness and wear resistance of this steel. Visible changes in the microstructure of thermally improved steel samples during cryogenic treatment were not found, which can be explained by the high thermodynamic stability of the sorbitol structure and the practical absence of residual austenite due to its decomposition during high tempering. It is shown that cryogenic treatment of thermally improved 38Ni3CrMoV steel contributes to an increase in the hardness, toughness and wear resistance this steel (~3.8 %). In this case, there is a slight increase in the parameter and magnitude of microstresses of the crystal lattice, an increase in the density of dislocations due to the removal of thermal stresses. To obtain a multiphase structure of 38Ni3CrMoV steel with retained austenite, isothermal quenching from the γ - α region has been proposed. The use of cryogenic treatment for the experimental mode of hardening of 38Ni3CrMoV steel samples promotes the transformation of retained austenite in the final structure of the samples into martensite with a significant increase in the microhardness of its structural components at the 22.3 %. The experimental hardening mode + cryogenic treatment provides a significant increase in the hardness and wear resistance of 38Ni3CrMoV steel at the 21.6 % while ensuring a certain level of its impact toughness (more than 4 J/cm2) and can be recommended for the implementation of the technology of differentiated hardening of large-sized products made of 38Ni3CrMoV steel. Keywords: steel, structure, hardness, wear resistance, isothermal hardening, cryogenic treatment.

Increasing the Wear Resistance of Structural Alloy Steel 38CrNi3MoV Subjected to Isothermal Hardening and Deep Cryogenic Treatment

“…To increase the wear resistance of 38CrNi3MoV steel products while ensuring the required hardness (less than 40 HRC before machining), the option of obtaining a multiphase troostite-bainite-martensite structure was considered [3,4]. As a technology that allows one to obtain such a structure, isothermal hardening was used [5].…”

“…Today, to produce various parts of industrial machines-mill rolls, shafts of powergenerating equipment-structural steels are used alloyed with different elements (Cr, Ni, Mo, V), such as 38CrNi3MoV steel, which is investigated in this work. This steel has a high stability of austenite in the range of 400-500 • C [1][2][3][4][5]. Studies on the mechanical properties and microstructure of 38CrNi3MoV steel have been carried out in a significant number of works [1][2][3][4][5].…”

“…This steel has a high stability of austenite in the range of 400-500 • C [1][2][3][4][5]. Studies on the mechanical properties and microstructure of 38CrNi3MoV steel have been carried out in a significant number of works [1][2][3][4][5]. For steels with high austenite stability, a step-like mode or isothermal cooling is often used [3].…”

“…For steels with high austenite stability, a step-like mode or isothermal cooling is often used [3]. It was proposed that isothermal treatment of 38CrNi3MoV steel from the intermediate (γ+α)-area should be used to increase its wear resistance [5]. The nearest steel analogues, 35NiCrMoV12-5 (DIN) and 4340 (AISI), are used for special-purpose products, and were studied in previous works [6,7].…”