Lattice Defect Formation Behavior of Cold-drawn Pearlitic Steel Fractured under Elastic and Plastic Region in the Presence of Hydrogen

Factors causing hydrogen embrittlement of cold-drawn pearlitic steel fractured in plastic/elastic region have been investigated from the viewpoint of lattice defects. Tensile tests were conducted for hydrogen-charged specimens containing 1.5 and 4.0 ppm hydrogen under various crosshead speeds. The amount of tracer hydrogen which corresponds to the amount of lattice defects in the specimens subjected to plastic strain or elastic stress was measured using a thermal desorption analysis. As a result, specimens containing 1.5 ppm hydrogen fractured in the plastic region under all experimental conditions in the present study. In contrast, specimens containing 4.0 ppm hydrogen fractured in the elastic region at crosshead speed of 0.01 mm.min(-1) or less and fractured in the plastic region at 0.1 mm.min(-1) or more. Subjecting plastic strain in the presence of hydrogen increased the amount of lattice defects corresponding to vacancies. In contrast, the presence of hydrogen had no effects on the formation of lattice defects under subjecting elastic stress. The amount of lattice defects in the specimens fractured in plastic region with hydrogen was equivalent to that of lattice defects in the specimens fractured under same conditions without hydrogen. The amount of lattice defects in the specimens fractured in elastic region with hydrogen was less than that of lattice defects in the specimens fractured under same conditions without hydrogen. These results indicated that lattice defects enhanced by hydrogen affected the fracture in plastic region with hydrogen. However, the effects of lattice defects on the fracture in elastic region with hydrogen were small.