Method for quantitatively evaluating retained austenite in steel by EBSD (electron back scattering diffraction)

Abstract

The invention discloses a method for quantitatively evaluating retained austenite in steel by EBSD (electron back scattering diffraction), belonging to the technical field of measurement of tissue in the steel. The method comprises the steps: carrying out surface scanning on the surface of a sample, of which the stress is removed, to obtain a back scattering diffraction signal, distinguishing each phase by the diffraction signal, finding out the retained austenite and outlining all retained austenite crystalline grains, and then providing the content of the retained austenite in various shapes by data processing and statistics. The optical signal display tissue is replaced by the electron back scattering diffraction signal; a grain boundary is defined according to an orientation difference; each phase can be accurately identified, and a plurality of adjacent crystalline grains can be distinguished. The method has the advantages that the problem of quantitative evaluation of the shapes of the retained austenite in TRIP (transformation-induced plasticity) steel is solved; the defect of tissue confusion in an optical method is overcome, and the shapes of the retained austenite can be accurately quantified.

Description

technical field [0001] The invention belongs to the technical field of microstructure measurement in steel, in particular to a method for quantitatively evaluating retained austenite in steel by using EBSD (Electron Backscattered Diffraction). Background technique [0002] TRIP (Transformation Induced Plasticity) steel is transformation-induced plasticity steel, which uses the residual austenite in the steel to undergo martensitic transformation under stress, thereby inducing high plasticity. The TRIP effect is related to the content of retained austenite, the high content of retained austenite, high strain hardening rate, high strength; but high content of retained austenite does not necessarily correspond to high elongation, because TRIP effect It is also related to the stability of retained austenite, the carbon content in retained austenite determines the chemical stability of retained austenite, and the morphology of retained austenite is associated with mechanical stab...

AI Technical Summary

Problems solved by technology

However, the EBSD signal is very sensitive to the sample surface, and stress and geometric fluctuations will destroy the quality of the backscattered diffraction pattern.

Generally, electrolytic polishing is used to eliminate stress, but the residual austenite grain size in multiphase structure materials, especially TRIP steel, is only a few microns, but it is harder and corrosion-resistant than ferrite matrix, so after conventional electrolytic polishing, The retained austenite grains are raised, the backscattered signal of the residual austenite grains and the surrounding ferrite will be blocked, and the quality of the area scan is not high

Images