Statistical analysis and fatigue life estimations for quenched and tempered steel at different tempering temperatures

In this paper, the statistical properties and fatigue life estimations of 0.44% carbon steel at different tempering temperatures are presented. The specimens were austenized at 900°C for 10 min, quenched in water, tempered at different temperatures, and then machined to the design geometry and average surface roughness of Ra = 0.4 µm. The effect of tempering temperature on the fatigue life of 0.44% carbon steel was investigated using 75 fatigue tests, divided into three groups at temperatures 500°C, 600°C, and 700°C. S–N and P–S–N curves were established. Two methods of estimating the mean fatigue life are presented. One is based on dislocation dipole accumulation and Paris’ law; another is based on the kriging model. Six more fatigue tests were carried out to validate the presented methods. Test results showed that the first method is superior to the second in terms of estimating accuracy from the validation datum. However, the second method could estimate the mean fatigue life of quenched and tempered 0.44% carbon steel with an average surface roughness of Ra = 0.4 µm when the tempering temperature was set to a value other than 500°C, 600°C, or 700°C, with no additional fatigue test needed.