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Steel U8. Plasma hardening of U8 steel with local cooling. Hardening temperature 900 °С. M s =+260 °C; M f =-60 °С. The structure has a small amount of residual austenite (1). The main structure is martensite (2) HRC 64. Magnification ×400
Source publication
The martensitic transformation interval of some hypoeutectoid, all eutectoid and all hypereutectoid steels covers to a large extent the region of negative temperatures. Due to the fact that the plasma hardening operation is carried out in workshops where the minimum temperature is +20 °С, the surface temperature of the part after plasma heating can...
Contexts in source publication
Context 1
... hardening U8 steel with local cooling, residual austenite is detected in an insignificant amount (5-10 %) (Fig. 8). During hardening of U10 steel, the amount of residual austenite is approximately 15-20 %. There is some secondary cementite. Residual austenite (1) and secondary cementite (2) are present in the structure. The main structure is martensite (3) HRc 62-64. Magnification ...
Context 2
... temperature during hardening of eutectoid and hypereutectoid steels either completely passes the martensitic temperature range, or most of it. This circumstance makes it possible to obtain a minimum amount of residual austenite during plasma hardening of these steels and makes low tempering unnecessary for the decomposition of residual austenite (Fig. 8, ...
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Citations
Results are given for electrolytic-plasma treatment of grade 1 wheel steel. Regime, input, and output parameters of the plasma treatment production system are determined. A modified layer with increased hardness and wear resistance is obtained as a result of electrolytic-plasma treatment. Results of microhardness measurements are obtained, and the microstructure is studied before and after electrolyticplasma treatment.
Structural-phase transformations in 0.34C–1Cr–1Ni–1Mo–Fe steel during plasma electrolytic hardening were investigated. Electrolytic-plasma hardening of steel samples was carried out by surface quenching with rapid concentrated heating of the surface by plasma action and subsequent rapid cooling by heat removal from the depth of the sample by electrolyte jet. Plasma electrolytic hardening was carried out in the cathode mode in an electrolyte made from an aqueous solution containing 20 % sodium carbonate and 10 % carbamide. To study the structural-phase states of the modified layer, we used the method of transmission diffraction electron microscopy on thin foils. The study of steel samples was carried out before and after the plasma electrolytic hardening. Initially, the steel was a mixture of pearlite and ferrite grains. Surface hardening of 0.34C–1Cr–1Ni–1Mo–Fe ferrite-pearlite steel led to a change in the structural-phase state and the formation of a packet-lamellar martensite structure. It was found that PEH leads to distortion of the crystal lattice and the formation of long-range internal stresses, as well as to the release of small particles of cementite and carbide of M23C6 type, uniformly distributed throughout the volume of the material. Surface hardening led to the increase in all quantitative parameters of the fine structure (ρ, ρ ±, χ, σL, σd).
