STEELS WITH 1-PERCENT CHROME-BORON FOR HIGH-STRENGTH BOLTS

Application of boron steels for high-strength, heat-treated bolts. Improvement of cold formability prior to bolt manufacture and of full hardening during the subsequent heat treatment. Development of boron-alloyed steels 32 CrB 4 and 36 CrB 4 for high-strength bolts of strength classes 10.9 and 12.9 according to DIN ISO 898-1. Effect of boron on the time-temperature-transformation curve and full hardenability. Application of boron in metallurgical processes. Hardenability scatter ranges, core hardness and cold formability of the boron-alloyed steels. Strength and toughness of the boron-alloyed steels after heat treatment. Strength and toughness of the heat-treated bolts at ambient temperature and higher temperatures. Fatigue strength of the bolts. Conclusions and accuracy realized in the adjustment of the boron contents required.