Method of making a low cost, high strength, high toughness, martensitic steel

A method of making a low cost, high strength, high toughness martensitic steel comprising the steps of applying a mathematical model to define an optimum low cost chemical composition of said steel having specified levels of strength and toughness;

• predicting the content of retained austenite and critical temperatures with said mathematical model;
• melting said optimum chemical composition;
• processing ingots of said optimum chemical composition;
• producing articles from said ingots;
• heat treating said articles using said critical temperatures and said content of retained austenite;
• and verifying the properties of said articles by mechanical testing, said steel comprising by weight of about:
• C:
• 0.3 to 0.45%;
• Cr:
• at most 2.5%;
• Mo:
• at most 1.0;
• Ni:
• at most 3.5%;
• Mn:
• 0.3 to 1.5%;
• Si:
• 0.1 to 1.3%;
• Cu:
• about 0.1 to 1.0%, where Cu is less than Si;
• (V+Ti+Nb):
• about 0.1 to 1.0%;
• Al:
• at most 0.25%;
• a sum of alloying elements being less than about 11.5%;
• the balance being essentially Fe and incidental impurities, said heat treating comprising subjecting said articles to austenization at about 1885 to 1925° F., oil quenching, refrigerating, and low tempering at about 350 to 400° F.

A method of making a low cost, high strength, high toughness martensitic steel comprising the steps of applying a mathematical model to define an optimum low cost chemical composition of said steel having specified levels of strength and toughness;

• predicting the content of retained austenite and critical temperatures with said mathematical model;
• melting said optimum chemical composition;
• processing ingots of said optimum chemical composition;
• producing articles from said ingots;
• heat treating said articles using said critical temperatures and said content of retained austenite;
• and verifying the properties of said articles by mechanical testing, said steel comprising by weight of about:
• C:
• 0.3 to 0.45%;
• Cr:
• at most 2.5%;
• Mo:
• at most 1.0;
• Ni:
• at most 3.5%;
• Mn:
• 0.3 to 1.5%;
• Si:
• 0.1 to 1.3%;
• Cu:
• about 0.1 to 1.0%, where Cu is less than Si;
• (V+Ti+Nb):
• about 0.1 to 1.0%;
• Al:
• at most 0.25%;
• a sum of alloying elements being less than about 11.5%;
• the balance being essentially Fe and incidental impurities, said heat treating comprising subjecting said articles to austenization at about 1885 to 1925° F., oil quenching, refrigerating at about −40 to −60° F., and middle tempering at about 750 to 950° F. for about 5 to 6 hours.