Process for making exhaust valves

A method for making work-hardened poppet exhaust valves for internal combustion engines comprising the steps of:

• (a) providing an annealed work-hardenable stainless steel coil or bar stock comprising 14-18% by weight chromium, 9-14% by weight nickel, 1-3% by weight manganese, 2-4% by weight copper, 0.09-0.4% by weight interstitial elements, wherein carbon comprises 0.05-0.2% by weight of the composition and nitrogen 0.04-0.2% by weight of the composition, and 3-5% by weight molybdenum;
• (b) solution treating said stainless steel coil or bar stock and water quenching the same;
• (c) extruding said coil or bar stock to a poppet valve preform configuration at a temperature in the range of room temperature to 1,000.degree. F. under conditions effective to work harden said coil or bar stock;
• (d) heading said preform to a final pre-machined configuration while maintaining the head of said preform at a temperature in the range of room temperature to 2,200.degree. F.;
• (e) said work-hardened poppet valve having a stem hardness more than R.sub.c =31.

A method for making work-hardened poppet exhaust valves for internal combustion engines comprising the steps of:

• (a) providing an annealed work-hardenable stainless steel coil or bar stock comprising 13%-25% by weight chromium, 4%-16% by weight nickel, 0.25%-8% by weight manganese, 0.5%-7% by weight copper, at least 0.04 weight % each of carbon and nitrogen with the carbon content being less than 0.2 weight % and the total interstitial content being less than 0.45 weight %, and 1%-5% by weight of a refractory metal selected from the group consisting of molybdenum, niobium, vanadium, tungsten and tantalum;
• (b) extruding said coil or bar stock to a poppet valve preform configuration at a temperature in the range of room temperature of 1,000.degree. F., at a true stress less than 150 ksi, and at a true strain of more than 0.8 to work harden said coil or bar stock;
• (c) heading said preform to a final pre-machined configuration while maintaining the head of such preform at a temperature in the range of room temperature to 2,200.degree. F., said heading being carried out at a true strain of 1.4-2;
• and
• (d) said work hardened poppet valve having a stem hardness more than R.sub.c =25.

A method for making work-hardened poppet exhaust valve for internal combustion engines comprising the steps of:

• (a) providing an annealed work-hardenable strainless steel coil or bar stock comprising 14-18% by weight chromium, 9- 14% by weight nickel, 1-3% by weight manganese, 2-4% by weight copper, 0.09-0.4% by weight interstitial elements, wherein carbon comprises 0.05-0.2% by weight of the composition and nitrogen 0.04-0.2% by weight of the composition, and 3-5% by weight molybdenum;
• (b) solution treating said stainless steel coil or bar stock and water quenching the same;
• (c) extruding said coil or bar stock to a poppet valve preform configuration at a temperature in the range of room temperature to 1,000.degree., at a true stain of more than 0.8 to work harden said coil or bar stock, and at a true stress less than 150 ksi;
• (d) heading said preform to a final pre-machined configuration while maintaining the head of said preform at a temperature in the range of room temperature to 2,200.degree. F.;
• (e) said work-hardener poppet valve having a stem hardness more than R.sub.c =31.