Korean Institute of Surface Engineering

pISSN : 1225-8024 | eISSN : 3399-8403


공학

한국표면공학회지 (37권4호 226-233)

Behavior of the Residual Stress on the Surfaces of 12Cr Steels Generated by Flame Hardening Process

화염경화 표면처리 공정에 의한 12Cr 강의 잔류응력 거동

이민구;김광호;김경호;김흥회;

한국원자력연구소 원자력재료기술개발부;

Abstract

The residual stresses on the surfaces of low carbon 12Cr steels used as a nuclear steam turbine blade material have been studied by controlling the flame hardening surface treatments. The temperature cycles on the surfaces of 12Cr steel were controlled precisely as a function of both the surface temperature and cooling rate. The final residual stress state generated by flame hardening was dominated by two opposite competitive contributions; one is tensile stress due to phase transformation and the other is compressive stress due to thermal contraction on cooling. The optimum processing temperatures required for the desirable residual stress and hardness were in the range of $850^{circ}C$ to $960^{circ}C$ on the basis of the specification of GE power engineering. It was also observed that the high residual tensile stress generated by flame hardening induced the cracks on the surfaces, especially across the prior austenite grain boundaries, and the material failure virtually, which might limit practical use of the surface engineered parts by flame hardening.

Keywords

Surface treatment;Flame hardening;12Cr steel;Hardness;Residual stress;Martensitic transformation;