Kinetics and fractography of 15Kh2MFA steel fatigue fracture at low temperatures

The effect of temperature test on micro- and macro-rate of fracture is determined, and relation of transition coefficients of stress intensity with peculiarities of fracture is revealed. Studies have been conducted on samples of 15Kh2MFA steel for excentric tensile and fatigue tests at -5 and -40 deg C. Rate of crack propagation has been determined by change in electroresistance of the sample. Fractures of samples obtained at both temperatures of tests had two vividly expressed zones: fatigue propagation of crack and fracture finishing. Two critical lengths (l0 sub(s)and l) and corresponding to them critical values of the coefficient of stress intensity ΔK0 and ΔKsub(s) can be pointed out for both temperatures of tests on the curve of dependence of medium distance between fatigue grooves on crack length, ΔK0 practically coinciding with beginning of straight section on kinetic diagrams of fatigue fracture described by the paris equation. The chosen temperatures of test (-5 and -40 deg C) are not stated to affect the above given regularities for they are above the cold brittleness threshold of the investigated steel