process for manufacture of hot-rolled steels with high strength and extraordinary zaehigkeit, particularly for use at negative temperatures

摘要

A ferritic hot-rolled high-strength low-alloy steel having a yield strength in excess of 65 ksi and excellent subzero impact properties which contains 0.03 to 0.15% carbon, 0.5 to 2.0% magnanese, 0.1 to 0.40% molybdenum and 0.01 to 0.10% columbium. The steel is strengthened by the combined effects of grain refinement, precipitation hardening and a high dislocation density which are effected by partially hot rolling the steel above the Ar3 transition temperature and then hot rolling to effect a 10 to 40% thickness reduction at intercritical temperatures between the Ar3 and Ar1 transition temperatures. Some embodiments of this steel may be further strengthened by a subcritical temper, or a small amount of cold working.