Influence of impurities and microalloying on the delayed failure resistance of steels

The mechanical properties and delayed failure resistance of high-strength bolts made of steels of different degrees of purity and microalloyed with additions of titanium, boron, and niobium were studied. Bolts made of 40Kh steel, 40Kh-PV steel, and 20Kh2NMTRB steel were used for the investigation. Three-point bend tests were conducted and fracture toughness and the work for crack origin and propagation were determined from the test results. Delayed failure tests were made under conditions of cathodic polarization and hydrogen impregnation. Results of the investigations were comparatively analyzed and relations between the failure resistance, structure, composition, and impurity content of the microalloyed steels were established.