Precipitation Hardened Stainless Steels -- New Alloys and ApplicationsFred McMann
Carpenter Specialty Alloys
Carpenter Specialty Alloys is a global supplier of an extemely diverse set of metals and alloys. It is seeking recognition as the one-stop-shop for all metallic needs. Despite the global nature of its marketing and distribution system, virtually all of it alloys are produced in the U.S.A. and to the highest possible industry standards.
Precipitation Hardening Stainless Steels have been around a long time. They are know for thier martinsitic structure. These alloys are based on Chromium and Nickel, with the addition of additives to promote a precipitating phase such as Titanium. The treatment of these alloys involves 1)Solution Annealing (also referred to a Quenching or Condition A), 2) Precipitaion Hardening (also referred to as Aging or Tempering or "H" Condition).
Recently, Carpenter came out with a new PH Stainless "Custom 465" which was originally developed for an aircraft application. It is the strongest of all Stainless Steels in the "PH" family (>255,000 psi in the H900 condition). This exceeds it predecessor (Custom 455) by about 10,000 psi. In most aged conditions it is also superior to other PH Stainless Steels in fracture toughness (about 110,000 psi).
Funding was lost for the original application of this alloy, but it has found a new and very successful market in the golf club head industry. The much publicized Orlimar Trimetal clubs use Custom 465 for the face. The alloy was not selected so much based on mechanical properties, but rather for its unique sound as it strikes a golf ball. Other applications are expected to follow.
Another recent Carpenter Development is AerMet, which is quite simply the highest combination of strength and toughness of any metal alloy known to man. It achieves maximum hardness of about 55 HRC and tensile of 310,000 psi with an age treatment at about 875 F with ductility around 17%, and fracture toughness of about 90,000 psi/in-2. With higher aging temperatures, fracture toughness can exceed 150,000 psi/in-2 with some loss of strength. Its introduction won distinction for Carpenter as one of the ten most significant inventions of its year.
Besides its optimized composition, AerMet achieves its remarkable properties by being Vacuum melted three times, during its production. It is extremely clean and free of sulfur and other contaminates. In fact, while it has a crystaline microstructure, it is virtually impossible to bring out any grain boundries by conventional metallography, since it is so very clean. This enables remarkable toughness and impact properties for a very strong material. The biggest drawback to AerMet is its high cost of production, which is about 5 times that of typical tool steels.
AerMet has found usefulness is very demanding tool steel applications such as: punches, blanking dies, crimping dies, collets, chuck jaws, shear blades, coining dies and swaging tools, where longevity of service is of primary importance and the high cost can be justified.