Abstract
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.
Highlights
Quenched and tempered constructional steel has a higher ratio of yield strength to tensile strength, a higher elongation, a less reduction of area, and a greater impact strength than steel without any heat treatment [1]
In Reference [19], the results of fatigue tests of high-strength spring steel showed that the highest endurance limit, ductility, and toughness were achieved when the tempering temperature was 450 ◦ C
The effects of tempering temperature on 4300 sintered steel have been investigated by Williams et al [21], who found that an increase in tempering temperature of 54% resulted in a 2%
Summary
Quenched and tempered constructional steel has a higher ratio of yield strength to tensile strength, a higher elongation, a less reduction of area, and a greater impact strength than steel without any heat treatment [1]. The effects of tempering temperature on fatigue properties have been reported by some researchers It was observed by London et al [13] that in cantilevered bending fatigue samples, the growth rate of small surface cracks slowed slightly at the same cyclic stress intensity with an increase of the tempering temperature from 200 ◦ C to 700 ◦ C. Similar conclusions were obtained by Tsay et al [15], with fatigue crack growth rates decreasing as the tempering temperature increased from 400 ◦ C to 600 ◦ C for both D6AC steel plates and laser welds They showed that the endurance limit was affected by the tempering temperature.
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