Change of 0.34Cr-1Ni-Mo-Fe Steel Dislocation Structure in Plasma Electrolyte Hardening.

Bauyrzhan Rakhadilov,Nurdaulet Shektibayev,Gulzhaz Uazyrkhanova,Sherzod Ramankulov,Natalya Popova,Zhuldyz Sagdoldina,Laila Zhurerova,Zarina Satbayeva

doi:10.3390/ma14081928

Abstract

This work deals with the study of changes in the dislocation structure and quantitative characteristics, as well as morphological components, of 0.34Cr-1Ni-Mo-Fe steel before and after plasma electrolytic hardening. According to the electron microscopic studies of the fine structure of 0.34Cr-1Ni-Mo-Fe steel before and after plasma electrolytic hardening, 0.34Cr-1Ni-Mo-Fe steel is a multiphase material containing an α-phase, a γ-phase (retained austenite), and a cementite and carbide phase. It was revealed that, morphologically, the α-phase in the initial state, generally, is present in the form of: lamellar pearlite with a volume fraction of 35%, a ferritocarbide mixture with a volume fraction of 45%, and fragmented ferrite with a volume fraction of 20% of the material. After surface hardening, the morphological components of the structure changed: packet–lamellar martensite with volume fractions of 60% and 40%, 5% and 7% of γ-phase as residual austenite in the crystals of packet–lamellar martensite, 0.6% and 1.5% of cementite in crystals of packet–lamellar martensite, and 0.15% and 0.35% of complex carbide M23C6 in crystals of packet–lamellar martensite, respectively, were observed. The quantitative characteristics of the dislocation structure were estimated by the following calculated indices of packet and lamellar martensite: scalar (ρ) and excess (ρ±) density of dislocations, the value of the curvature-torsion of the crystal lattice (χ), the amplitude of long-range internal stresses (σd), and the amplitude of shear stresses (σL), according to which the plastic nature of the bending-torsion of the crystal lattice was confirmed (σL > σd).

Highlights

The heating of metals in electrolytic plasma during the anodic or cathodic process, due to the favorable combination of the high temperature of the active electrode and the flow of electrical discharges in the vapor–gas envelope between the electrodes, allows us to carry out a number of processes of high-speed local thermal and chemical heat treatments on steel parts [1,2,3]
The known plasma electrolytic hardening (PEH) methods have certain disadvantages associated with a low heating rate
The aim of this work is to study the morphology of phase transformations and quantitative characteristics of the dislocation structure of the modified surface layers of alloyed 0.34Cr-1Ni-Mo-Fe steel during PEH

Summary

Introduction

The heating of metals in electrolytic plasma during the anodic or cathodic process, due to the favorable combination of the high temperature of the active electrode and the flow of electrical discharges in the vapor–gas envelope between the electrodes, allows us to carry out a number of processes of high-speed local thermal and chemical heat treatments on steel parts [1,2,3] These processes include: plasma electrolytic oxidation (PEO) [4], plasma electrolytic hardening (PEH) [5], and plasma electrolytic saturation (PES) processes such as plasma electrolytic nitriding (PEN) [6], plasma electrolytic carburizing (PEC) [7], etc. The use of rapid heating, which helps yield a finer structure of the hardened steel, makes it possible to obtain a more favorable combination of strength and toughness properties This is especially important for increasing the service life of gears. At present, surface thermal hardening is one of the most effective ways to increase the service life of loaded elements of machines and mechanisms made of alloyed medium-carbon steels

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