Submicron and Nanoscale Structure of an Ultra-High Strength Precipitation Hardenable Stainless Steel

摘要

Carpenter Custom 475 is an ultra-high strength precipitation-hardenable stainless steel capable of tensile strengths in excess of 280-ksi. The material possesses an iron-nickel lath martensite matrix and it has been previously assumed that a number of submicron scale precipitates were involved in the age-hardening mechanism. A series of investigations were carried out to fully characterize both the structure of the grade and its response to variations in thermo-mechanical processing. The material was determined to reach full solution at approximately 1650℉, with no degradation of strength with solution temperatures up to 1800℉. Peak strength, as determined by hardness testing, was observed to occur at 1000℉ for a four hour one-step aging treatment, although hardening was found to occur at temperatures as low as 650℉. Preliminary TEM and STEM characterization of multiple precipitates was performed along with a determination of the amount and distribution of retained and reverted austenite contents.