Method and apparatus for treating a steel article

Abstract

A method for forming and treating a steel article of a high strength and ductile alloy. The method includes the steps of providing a starting steel composition for the steel article, preheating the composition, heating the starting material to a peak temperature range in less than forty seconds, holding the heated steel composition at the peak temperature range for between two and sixty seconds, quenching the heated steel composition from the peak temperature range to below 177° C. (350° F.) at a temperature rate reduction of 200 to 3000° C./sec (360 and 5400° F./sec), removing residual quench media from the surface of the quenched steel composition, tempering the quenched steel composition at a temperature of 100 to 704° C. (212 to 1300° F.); and air cooling the tempered steel composition to less than 100° C. (212° F.) to form a steel having desired mechanical properties.

What is claimed is: 
     
         1 . 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 no greater than 0.5 inches (12.7 mm), having an initial microstructure of at least 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 0.40 and 1.10%,   nickel less than 4.5%,   molybdenum between 0.15 and 0.35%,   sulfur less than 0.040%,   phosphorus less than 0.035%,   balance iron and other elements and compounds in making steel;   (b) preheating the provided steel composition to not more than 594° C. (1100° F.);   (c) heating the preheated steel composition to a peak temperature of between 800° C. (1472° F.) and 1150° C. (2102° F.) in less than forty seconds;   (d) holding the heated steel composition at the peak temperature range for between two and twenty seconds;   (e) quenching the heated steel composition from the peak temperature range to below 177° C. (350° F.) at a temperature rate reduction of between 200 and 3000° C./sec (360-5400° F./sec);   (f) tempering the quenched steel composition at a temperature from 100° C. to 704° C. (212-1300° F.) for less than ninety minutes; and   (g) 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 weight, a yield strength of at least 160 Ksi (1100 MPa), and a total elongation between 5% and 22%.   
     
     
         2 . The method for treating a steel article as claimed in  claim 1  where the air cooled steel composition has a V 50  protection ballistic limit at 30° obliquity angle at least 2300 feet per second (701 m/s) with a 0.30 caliber armor piercing round for a thickness of 0.25 inches (6.35 mm). 
     
     
         3 . The method for treating a steel article as claimed in  claim 1 , where the air cooled steel composition has a microstructure having no more than 1% bainite by weight. 
     
     
         4 . 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 no greater than 0.5 inches (12.7 mm), having an initial microstructure of at least 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 0.40 and 1.10%,   nickel less than 4.5%,   molybdenum between 0.15 and 0.35%,   sulfur less than 0.040%,   phosphorus less than 0.035%,   balance iron and other elements and compounds in making steel;   (b) preheating the provided steel composition to not more than 594° C. (1100° F.);   (c) heating the preheated steel composition to a peak temperature of between 800° C. (1472° F.) and 1150° C. (2102° F.) in less than forty seconds;   (d) holding the heated steel composition at the peak temperature range for between two and twenty seconds;   (e) quenching the heated steel composition from the peak temperature range to below 177° C. (350° F.) at a temperature rate reduction of between 200 and 3000° C./sec (360-5400° F./sec); and   (f) air cooling the 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 weight, a yield strength of at least 160 Ksi (1100 MPa), and a total elongation between 5% and 22%.   
     
     
         5 . The method for treating a steel article as claimed in  claim 4  where the air cooled steel composition has a V 50  protection ballistic limit at 30° obliquity angle at least 2300 feet per second (701 m/s) with a 0.30 caliber armor piercing round for a thickness of 0.25 inches (6.35 mm).