1.4021 and X20Cr13 are not different materials, but two different designations for the same martensitic stainless steel. This material is commonly known as AISI 420 or ASTM 420 in the international market.

The main difference between 1.4521 and 1.4404 is that 1.4521 is a ferritic (magnetic) stainless steel, while 1.4404 (316L) is an austenitic (non-magnetic) stainless steel. 1.4521 is titanium-stabilized, offering superior resistance to stress corrosion cracking, while 1.4404 provides excellent overall corrosion resistance and high ductility.

ASTM A182 F53 (UNS S32750) and F55 (UNS S32760) are both super duplex stainless steels used in the manufacture of high-strength, corrosion-resistant components. Their main difference is that F55 contains added tungsten (0.5%–1.0%) and molybdenum, giving it superior resistance to pitting and crevice corrosion compared to F53 in harsh, acidic, or high-chloride environments.

17-7 PH is a semi-austenitic precipitation-hardening stainless steel (chromium-nickel-aluminum alloy) designed for high strength, excellent fatigue performance, and good corrosion resistance (comparable to 304 stainless steel), with a maximum operating temperature of 600°F (316°C). Due to its minimal distortion during heat treatment and high strength, it is commonly used in aerospace, springs, washers, and bellows applications.

17-7 PH stainless steel spring wire is a high-strength precipitation-hardening (PH) alloy (UNS S17700) known for its excellent fatigue resistance, corrosion resistance similar to 302/304 stainless steel, and minimal distortion during heat treatment. It is widely used in aerospace applications for springs, rings, and fasteners, and can operate at temperatures up to 600°F (316°C).