What are precipitation hardening stainless steels based on?

Precipitation hardening stainless steels are specifically characterized by their composition, which includes a significant amount of chromium and nickel, along with other alloying elements. The option mentioning the 17 Cr-4 Ni composition accurately represents a well-known type of precipitation hardening steel, often identified as 17-4 PH. This stainless steel variant derives its properties from both its chemical composition and the heat treatment processes it undergoes, leading to enhanced strength and hardness through controlled precipitation of certain phases during aging.

This composition serves as a foundation for the precipitation hardening process, wherein the resulting microstructure allows for meaningful improvements in tensile strength and corrosion resistance. Therefore, the focus on the specific 17 Cr-4 Ni combination directly ties to the essential characteristics that define this type of stainless steel, making it the most accurate choice in relation to the question.