ISSN: 1945-7553
CODEN: JTEVAB
Page Count: 9

Threshold Corrosion Fatigue Crack Growth in Steels

Tu, LKL
Advanced engineer and managerMembers of ASTM, Materials Engineering, Westinghouse Electric Corp.Exxon Production Research Co., PhiladelphiaHouston, Pa.Tex

Seth, BB
Advanced engineer and managerMembers of ASTM, Materials Engineering, Westinghouse Electric Corp.Exxon Production Research Co., PhiladelphiaHouston, Pa.Tex

Abstract

The threshold stress intensity factor range ΔK_th of three steels was studied in air and steam. Constant load and constant crack opening displacement (COD) tests were conducted by using tension-tension sinusoidal wave function loading. The COD tests were controlled by a high frequency clip-on strain gage. Crack growth rate was measured by both optical and COD compliance techniques and verified by metallographic examination of the broken specimens. The ΔK_th value was determined as the asymptote to the best-fit data below a crack growth rate of 2.5 × 10⁻⁸ cm/cycle. The ΔK_th values were higher in steam than in air. Crack growth rates in air and steam generally crossover or merge in the range of 2.5 × 10⁻⁶ to 2.5 × 10⁻⁷ cm/cycle; below this range the growth rate is lower in steam than in air. The higher values in steam tests were explained by environmentally assisted crack branching and corrosion products formed at the crack tip after long-time testing at growth rates of less than one lattice spacing per cycle of loading.

Keywords:
corrosion fatigue, steels, crack propagation, steam, crack branching

Paper ID: JTE10921J
DOI: 10.1520/JTE10921J
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