HYDROGEN OCCLUSION BEHAVIOR OF SI OR SI, CA ADDED HIGH-STRENGTH STEELS WITH HIGH-RESISTANCE TO DELAYED FRACTURE

Medium carbon steels added 2.0% Si or 1.5% Si-30ppm Ca with 1400N/mm2 tensile strength show high resistance to delayed fracture. It is impor tant to clarify the hydrogen occlusion behavior to delayed fracture of steels with high resistance to delayed fracture. The hydrogen diffusi on coefficient and hydrogen content were measured by electrochemical p ermeation technique, and hydrogen evolution content after accelerated delayed fracture test was directly measured by hydrogen thermal analys is. It is found that high resistance to delayed fracture of 2.0% Si st eel is due to the high hydrogen content needed for fracture, in spite of its high hydrogen occlusion rate. Also the high resistance to delay ed fracture of 1.5% Si-30ppm Ca steel is found to be due to the low hy drogen occlusion rate and the low hydrogen content needed for fracture .