High-strength low-alloy steels

Abstract

Fully killed high-strength low-alloy steels consisting essentially of .12% to .20% carbon, 1.10% to 1.65% manganese, .05% to .20% vanadium, .005% to .025% nitrogen, .04% maximum phosphorus, .025% maximum sulfur, .60% maximum silicon and balance iron are characterized in a hot-rolled finished condition by yield strengths in excess of 80,000 p.s.i., ultimate tensile strengths in excess of 95,000 p.s.i., ductilities as measured by percent elongation (2 inches) in excess of 18% and good toughness. The steels are hot-rolled finished in the temperature range 1550° F. to 1650° F., cooled at a rate within the range 20° F. to 135° F. per second and collected by coiling or piling within a temperature range of 1025° F. to 1175° F. The steels modified by the incorporation of .01% to .10% of a rare earth are further characterized by improved formability.

We claim: 
     
       1. A killed, low-alloy high-strength steel hot-rolled finished in the temperature range 1550° F. to 1650° F., cooled at a rate within the range 20° F. to 135° F. per second, and collected within a temperature range of 1025° F. to 1175° F., the steel being characterized in a hot-rolled condition by a yield strength in excess of 80,000 p.s.i., an ultimate tensile strength in excess of 95,000 p.s.i., ductility as measured by percent elongation (2 inches) in excess of 18%, and good toughness, said steel consisting essentially of at least about .12% carbon, a maximum of about 1.65% manganese, at least about .05% vanadium, .005% to .025% nitrogen, .04% maximum phosphorus, .025% maximum sulfur, .60% maximum silicon, .01% to .10% of a rare earth or mixture of rare earths, balance iron. 
     
     
       2. The steel of claim 1 containing .12% to .20% carbon, 1.10% to 1.65% manganese and .05% to .20% vanadium. 
     
     
       3. A process for manufacturing a low-alloy high-strength steel characterized in the hot-rolled condition by a yield strength in excess of 80,000 p.s.i., an ultimate tensile strength in excess in about 95,000 p.s.i., ductility as measured by percent elongation (2 inches) in excess of about 18% and good toughness, comprising, hot-rolling a steel consisting essentially of at least .12% carbon, a maximum of about 1.65% manganese, at least about .05% vanadium, .005 to .025% nitrogen, .04% maximum phosphorus, .025% maximum sulfur, .60% maximum silicon, .01% to .10% of a rare earth or mixture of rare earths, balance iron at a finishing temperature within the range of 1550° F. to 1650° F., cooling the hot-rolled product at a rate within the range 20° F. to 135° F. per second and collecting the cooled material at a temperature within the range 1025° F. to 1175° F. 
     
     
       4. The process of claim 3 wherein the steel contains .12% to .20% carbon, 1.10% to 1.65% manganese and .05% to .20% vanadium. 
     
     
       5. A .Iadd.killed .Iaddend.low-alloy high-strength steel .Iadd.hot-rolled finished in the temperature range 1550° F. to 1650° F., cooled at a rate within the range 20° F. to 135° F. per second, and collecting within the temperature range of 1025° F. to 1175° F. the steel being characterized in a hot-rolled condition by a yield strength in excess of 80,000 p.s.i., an ultimate tensile strength in excess of 95,000 p.s.i., ductility as measured by percent elongation (2 inches) in excess of 18%, and good toughness, .Iaddend.having improved bending properties and consisting essentially of .[.at least.]. about .12% .Iadd.to .20% .Iaddend.carbon, .[.a maximum of.]. about .Iadd.1.10% to .Iaddend.1.65% manganese, at least about .05% vanadium, .005% to .025% nitrogen, .04% maximum phosphorus, .025% maximum sulfur, .60% maximum silicon, .01% to .10% of a rare earth or mixture of rare earths, balance iron. 
     
     
       6. The steel of claim 5 containing .[..12% to .20% carbon, 1.10% to 1.65% manganese and.]. .05% to .20% vanadium.