Precipitation hardening steel with improved toughness and method

Abstract

In some aspects, a heat treatment process is described for precipitation hardening steel. The heat treatment process can include a solution treatment for a precipitation hardening steel part. The solution treatment includes heating the precipitation hardening steel part to an austenitizing temperature. The heat treatment process can also include a quenching or cooling treatment, in which the precipitation hardening steel part is cooled to a martensitizing temperature. The heat treatment process can also include an aging treatment, in which the precipitation hardening steel part is heated to a temperature of 1000° F. and held at that temperature for five or more hours until a fracture toughness of the precipitation hardening steel part is greater than 120 ksi√in.

1 . A heat treatment process for precipitation hardening steel comprising:
 a solution treatment for a precipitation hardening steel part, wherein the precipitation hardening steel part is heated in a furnace to an austenitizing temperature;   a cooling treatment for a precipitation hardening steel part, wherein the precipitation hardening steel part is cooled to a martensitizing temperature of at least −100° F.; and   an aging treatment for a precipitation hardening steel part, including heating the precipitation hardening steel part in a furnace at a temperature of at least 950° F. for at least 6 hours until a fracture toughness of the precipitation hardening steel part is greater than 120 ksi√in and until a yield strength is greater than 175 ksi.   
     
     
         2 . The heat treatment process of  claim 1 , wherein the quenching treatment includes cooling the stainless steel part in a protective atmosphere. 
     
     
         3 . The heat treatment process of  claim 1 , wherein the austenitizing temperature is a temperature of 1700° F. 
     
     
         4 . (canceled) 
     
     
         5 . The heat treatment process of  claim 1 , wherein the temperature for the aging treatment is 1000° F. or greater. 
     
     
         6 . (canceled) 
     
     
         7 . The heat treatment process of  claim 1 , wherein the aging treatment is for at least 7 hours. 
     
     
         8 . The heat treatment process of  claim 1 , wherein the aging treatment is for at least 8 hours. 
     
     
         9 . The heat treatment process of  claim 1 , wherein the precipitation hardening steel part is composed of precipitation-hardened 13Cr-8Ni stainless steel (PH 13-8, UNS S13800, XM-13). 
     
     
         10 - 19 . (canceled)