TITLE:
Sigma Phase Formation and Embrittlement of Cast Iron-Chromium-Nickel (Fe-Cr-Ni) Alloys
AUTHORS:
A. M. Babakr, A. Al-Ahmari, K. Al-Jumayiah, F. Habiby
KEYWORDS:
Sigma-phase, Corrosion; Microstructure; Heat resistant steels; Hardness
JOURNAL NAME:
Journal of Minerals and Materials Characterization and Engineering,
Vol.7 No.2,
June
20,
2008
ABSTRACT: HK alloy is a member of the heat resistant cast alloy family (H-Series) steels. They
are widely used in the petrochemical industry for components requiring enhanced
high temperature properties. Microstructural changes occurring at high temperature
clearly affects its mechanical properties. These properties have been shown in HK-40
steel subjected to high-temperature degradation and prone to the formation of sigma
phase. The investigation carried out included metallurgical analysis, materials
characterization and mechanical analysis. Metallurgical analysis included advanced
metallography techniques to characterize its microstructure morphology and
properties. Significant depletion of vital precipitates observed that definitely degraded
its high temperature properties. Mechanical analysis included hardness profile, tensile
testing of samples taken from the tree supports and tested in room temperature and in
800°C environments. Experimental results revealed that the structure of HK-40
affected by the formation of the high temperature brittle sigma-s-phase. Nonetheless,
mechanical properties did not suffer much at higher temperature.