Strong Bolts with Increased Resistance to Delayed Brittle Failure

Heat-treated steel for bolts of strength 1400–1600 N/mm2 is created on the basis of concepts regarding delayed hydrogen-initiated brittle failure. The hydrogen content of the steel is reduced to 0.2%; boron is introduced, as well as microalloying with titanium; the sulfur and phosphorus content is strictly limited; and the steel is alloyed with chromium, nickel, molybdenum, and niobium. Experimental and experimental industrial batches of blanks and bolts are produced from the new steel. Their resistance to delayed brittle failure is 1.5–2 times better than for select 40Kh steel. Experimental use of the bolts in aggressive atmospheres confirms their reliability.