The alloy retains oxidation to 1500 degrees F (816 degrees C) and has better ruptured creep and stress properties than the 304 and 304L alloys. This also maintains significant tolerance to low temperatures. The higher carbon (0.04–0.10) variant of the alloy is SS 321H Fasteners. It was manufactured to boost creep resistance and for greater strength at temperatures above 1000 degrees F (537 degrees C). The carbon content of the fasteners makes for dual certification in most occurrences.
SS 321 fasteners cannot be hardened by heat treatment, only by cold operation. It can be welded and processed easily using normal welding techniques in the factory. SS 321 Fasteners can be utilized at moderate temperatures in most diluted organic acids and at lower temperatures in pure phosphoric acid and up to 10 percent diluted solutions at high temperatures. Alloy 321 opposes polythionic acid stress corrosion cracking in hydrocarbon service. They can also be used in caustic solutions free of chloride or fluoride at moderate temperatures. 321 SS Fasteners do not operate well in chloride solutions, even in small concentrations, or in the sulphuric acid service.