Ultratough high-strength weldable plate steel and its method of manufacturing thereof

A method for manufacture of a hardened steel alloy comprising the steps of:

• (a) forming a melt into a steel alloy casting comprised in weight percent of about 0.030 to 0.055 carbon (C), 3.5 to 5.0 copper (Cu), 6.0 to 7.5 nickel (Ni), 1.6 to 2.0 chromium (Cr), 0.2 to 0.6 molybdenum (Mo), 0.05 to 0.20 vanadium (V) and the balance iron;
• (b) homogenizing the steel alloy casting at a temperature in the range of about 1200° C.±50°for about 6 to 8 hours;
• (c) hot working said steel alloy;
• (d) ambient cooling said steel alloy;
• (e) annealing said steel alloy at a temperature in the range of about 480° C.±40° C. for about 8 to 12 hours;
• (f) solution heating said steel alloy at a temperature of about 900° C.±50° C. for about 30 to 90 minutes;
• (g) cooling said steel alloy to form an essentially martensitic microstructure;
• (h) tempering said steel alloy at a temperature of about 500° C. to 575° C. for about 5 to 90 minutes to achieve Ni-stabilized austenite precipitation;
• and
• (i) further tempering said steel alloy at a temperature of about 400° C. to 500° C. for about 1 to 10 hours to achieve M2C carbide particle formation where M is one or more elements selected from the group consisting of Cr, Mo, and V, and BCC copper hardening precipitates.

A method for manufacture of a hardened steel alloy comprising the steps of:

• (a) forming a melt into a steel alloy casting comprised in weight percent of about 0.030 to 0.055 carbon (C), 3.5 to 5.0 copper (Cu), 6.0 to 7.5 nickel (Ni), 1.6 to 2.0 chromium (Cr), 0.2 to 0.6 molybdenum (Mo), 0.05 to 0.20 vanadium (V) and the balance iron;
• (b) heat treating and working said steel alloy to form an essentially martentsitic microstructure;
• (c) tempering said steel alloy at a temperature of about 500° C. to 575° C. for about 5 to 90 minutes to achieve dispersed austenite precipitation;
• and
• (d) further tempering said steel alloy at a temperature of about 400° C. to 500° C. for about 1 to 10 hours to achieve M2C carbide particle formation where M is one or more elements selected from the group consisting of Cr, Mo, and V, and BCC copper hardening precipitates.