Dr. Robert Buck of Carpenter Technology Corp., Philadelphia, Pa., prepared a presentation announcing development of a strong, tough, carburizable stainless steel for high-performance gear and bearing applications exposed to harsh environments. This paper was scheduled for the ASM International AeroMat 2020 conference, and now will be part of an AeroMat Virtual Session to be presented June 2.
A-21 (UNS S41429) is a new stainless carburizing steel designed to create a deep, hard, and stainless case and a strong, tough, and ductile core. Its unique chemistry results in a fine grain size and permits streamlined carburization and heat treatment. A-21 achieves a surface hardness of 64 Rc while maintaining its stainless properties. It is also nitridable, and achieves a nitrided surface hardness of 70 Rc.
Salt fog testing per ASTM B117 was done to compare the corrosion resistance of carburized A-21 with that of carburized Pyrowear 675, as well as 440C and BG42. All alloys were tested in the hardened condition, having surface hardness values of 59 Rc to 63 Rc.
Results indicate that carburized A-21 exhibited superior corrosion resistance in salt fog testing versus the other stainless steels. It also maintained good core mechanical properties of 138 ksi yield strength, 178 ksi UTS, 14% elongation, 47% RA, 48 ft-lb. CVN impact energy, and 87 ksi √in. fracture toughness.
A-21 could replace carburizing alloy steels, such as AISI 9310, that are currently coated for corrosion resistance. It would eliminate the need to coat (and inspect), and replace carburizing and through-hardening “stainless” steels with a true stainless steel, thereby improving corrosion resistance in atmospheric, humid, and harsh (i.e., salt water) environments.
AeroMat 2020 presentation
Development of an Advanced Stainless Carburizing and Nitriding Steel
Dr. Robert Buck, Carpenter Technology Corp.
