## 3 Results  
### Structure Formation under Isothermal Hardening  
To increase the wear resistance of 38 CrNi3 MoV 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].  
The hardness of the investigated samples depending on the temperature of isothermal holding is shown in Figure 2, and their microstructures are presented in Figure 3.  
Figure 1: Schemes of heat treatment of 38 CrNi3 MoV steel: (**a**) basic mode, (**b**) basic mode + DCT.  
The microstructure of steel at isothermal holding temperatures of 750-600 \({}^{\circ}\)C consisted mainly of martensite with high hardness (Figure 3a). At the isothermal holding temperature of 500 \({}^{\circ}\)C, a small amount of troostite was formed in the steel structure (see Figure 3b). The amount of troostite increased with the decrease in isothermal holding temperature (Figure 3c,d). When holding 38 CrNi3 MoV steel at the temperature of 750 \({}^{\circ}\)C for 20 min, no primary ferrite was precipitated. Upon subsequent cooling, structural components of the eutectoid and quasi-eutectoid types were formed.  
Steel hardness had the required values (less than 40 HRC) at the holding temperature of 450-400 \({}^{\circ}\)C. The basic mode of heat treatment guaranteed the initial hardness of 38 CrNi3 MoV steel of less than 40 HRC, and the stabilization of RA (see Figures 3d and 4).  
Figure 3: Microstructures of 38 CrNi3 MoV steel samples after isothermal treatment at 600 \({}^{\circ}\)C (a), 500 \({}^{\circ}\)C (b), 450 \({}^{\circ}\)C (c), and 400 \({}^{\circ}\)C (d).  
Figure 2: Dependence of steel hardness on isothermal holding temperature.  
The microstructure of the sample processed by this mode consisted mainly of troostite (homogeneous areas), with a microhardness of 3620 MPa, and light inhomogeneous areas of bainite + RA, with a microhardness of 6350 MPa (Figure 4a,b).  
The bainite of steel, which was formed in 38 CrNi3 MoV steel during the isothermal treatment, contained particles of carbides, predominantly of cementite type, light small particles of 0.2-1.0 \(\upmu\)m in size (Figure 4c). The steel structure also had areas with high austenite contents and semi-coherent precipitation of carbide particles (Figure 4d).  
The subsequent X-ray microanalysis showed (see Figure 5 and Table 1) that the quasi-eutectoid and bainitic components were formed mainly in the inter-dendritic areas of the structure, with high contents of nickel, silicon, chromium, and molybdenum, while vanadium was uniformly distributed in the solid solution.  
Holding the steel at an intermediate temperature of 750 \({}^{\circ}\)C contributed to the release of these carbides and the stabilization of RA, which was part of the bainite-austenite formations. The amount of RA reached values of about 10.8%.  
Figure 4: Microstructures of 38 CrNi3 MoV steel samples after isothermal treatment at 750 \({}^{\circ}\)C for 20 min, cooling to 400 \({}^{\circ}\)C, holding for 20 min, cooling in the air (see description in the text): (**a**,**b**) troostite (homogeneous areas) and bainite + RA (inhomogeneous areas); (**c**,**d**) the bainite structure of steel with carbides.