Patent ID: 8894781

Claim:
A method for treating a steel article to form a high yield strength and ductile alloy comprising the steps of: (a) providing a steel composition having a material thickness less than 0.5 inches (12.7 mm), having an initial microstructure of ferrite and pearlite, and having a composition of, by weight, carbon between 0.25 and 0.55% silicon between 0.15 and 0.35%, manganese between 0.40 and 1.0%, chromium between 0.80 and 1.10%, molybdenum between 0.15 and 0.25%, sulfur less than 0.040%, phosphorus less than 0.035%; balance with iron and other elements and compounds in making steel; (b) preheating the provided steel composition at least 0.7° C. (33.3° F.) per second to not more than 538° C. (1000° F.); (c) heating the preheated steel composition to a peak temperature of between 850° C. (1562° F.) and 1150° C. (2102° F.) in less than ten seconds; (d) holding the heated steel composition at the peak temperature range for between two and ten seconds; (e) quenching the heated steel composition from the peak temperature range to below 100° C. (212° F.) at a temperature rate reduction of between 400 and 3000° C./sec (752-5432° F./sec); (f) removing residual quench media from the surface of the quenched steel composition; (g) tempering the quenched steel composition at a temperature from 100° C. to 260° C. (212-500° F.) for less than ninety minutes; (h) air cooling the tempered steel composition to less than 100° C. (212° F.) to form a steel article having at least 80% martensite and up to 5% bainite by volume, a yield strength of at least 1800 MPa, a total elongation between 5% and 12%, and having a V 50 protection ballistic limit at 30° obliquity angle between 2300 and 2510 feet per second (701-765 m/s) with a .30 caliber armor piercing round for a thickness of 0.25 inches (6.35 mm).