Ultrahigh strength steels

Abstract

An ultrahigh strength material made from ordinary 18-8 stainless steel has a tensile strength in excess of 400,000 p.s.i. The method of producing the ultrahigh strength is accomplished by thermo-mechanical operations. The material can have any desired geometric cross section configuration and is adaptable for use as a spring material.

We claim: 
     
       1. A high strength stainless steel material having a composition by weight consisting essentially of .15% maximum carbon, 1.5% maximum silicon, 2% maximum manganese, about 17% to about 19% chromium, about 7to about 10% nickel, minor amounts of other metals, and the balance constituent iron, and characterized in that said material has a tensile strength in excess of 400,000 p.s.i. 
     
     
       2. The material of claim 1 wherein said material exhibits approximately not more than a 20% decrease in strength up to approximately 500° F. 
     
     
       3. The material of claim 1 wherein the material has a preselectedly sized configuration. 
     
     
       4. The material of claim 1 which is formed into a spring. 
     
     
       5. The material of claim 1 further including a tightly adhering sheath material. 
     
     
       6. The material of claim 5 which is formed into a spring. 
     
     
       7. A method of obtaining a tensile strength of at least 400,000 p.s.i. from an 18-8 stainless steel material closely controlling the steps comprising: (1) rapidly quenching a solution annealed 18-8 stainless steel material to prevent carbide precipitation,   (2) cold deforming and material to at least a 75% cold worked state; and   (3) heat treating said cold deformed material at a sub-transformation temperature to inhibit dynamic recovery and provide an increase in strength.   
     
     
       8. The method of claim 7 further including the step of cold deforming said material subsequent to said heat treating. 
     
     
       9. The method of claim 7 wherein the sub-transformation heat treatment temperature ranges from 775° F. to 800° F. 
     
     
       10. The method of claim 7 wherein the material is further worked to an 84% cold worked state during cold deforming. 
     
     
       11. The method of claim 7 wherein the material is further worked to a 95% cold work state during cold deforming. 
     
     
       12. The method of claim 7 wherein the material is further cold worked to at least a 97.6% cold work state during cold deforming. 
     
     
       13. The method of claim 12 wherein after the sub-transformation temperature heat treatment the material is further cold worked to at least a 98.7% cold worked state with the material exhibiting a tensile strength in excess of 575,000 p.s.i. 
     
     
       14. A method of obtaining a tensile strength of at least 400,000 p.s.i. from an 18-8 stainless steel material comprising the steps of: (1) rapidly quenching a solution annealed 18-8 stainless steel material to prevent carbide precipitation; and   (2) cold deforming said material to at least a 97% cold worked state. .Iadd. 15. A process for thermo-mechanically treating 18-8 stainless steel, comprising the steps of:   (a) cold deforming the 18-8 steel,   (b) heating the steel to a temperature in the sub-transformation temperature range of 700°F to 825°F to prevent carbide precipitation, and   (c) cooling the steel to a temperature below about 700°F and then again cold deforming the steel, the 18-8 steel totally being deformed a minimum of 75%. .Iaddend. .Iadd. 16. A process for thermo-mechanically treating 18-8 stainless steel, comprising the steps of:   (a) heating the steel to a temperature in the recrystallization temperature range to anneal said steel,   (b) cooling the steel to a temperature range of 700°F to 825°F and then cold deforming said steel,   (c) heating the steel to a temperature in the sub-transformation temperature range, and   (d) cooling the steel to a temperature below about 700°F and then again cold deforming the steel, the 18-8 steel totally being cold deformed a minimum of 75%. .Iaddend.  .Iadd.17. The process of claim 15 wherein the total amount of deformation is in excess of 75%..Iaddend.