Stainless steel grade 303 is the most readily machineable of all the austenitic grades of stainless steel.

Type 303 has mechanical properties that are comparable to both 304 and 316 stainless. The primary reason to use 303 is when you need a stainless steel with machining capabilites better than that of 304 and 316. It has roughly the same corrosion resistance as 304, but not as good as 316. The main drawback with the alloy is that it is not generally considered to be weldable. This material is hardenable by cold work.

The machineable nature of Grade 303 stainless steel is due to the presence of Sulphur in the steels composition. While the Sulphur improves machining, it also causes a decrease in the corrosion resistance and a slight lowering of the toughness. The corrosion resistance of grade 303 stainless steel is lower than that for 304. The toughness is still excellent as with other austenitic grades.

Property data given in this document is typical for bar products covered by ASTM A582. It is reasonable to expect specifications in these standards to be similar but not necessarily identical to those given in this article.

Sulphur is an addition to the composition act as initiation sites for pitting corrosion. This decreases the corrosion resistance of grade 303 stainless steel to less than that for 304. However corrosion resistance remains good in mild environments.

In chloride containing environments over 60°C, grade 303 stainless steel is subject to pitting and crevice corrosion. Grade 303 stainless is not suitable for use in marine environments.

Grade 303 stainless steel has good resistance to oxidation when intermittently exposed to temperature up to 760°C temperatures. It also has good oxidation resistance in continuous service to 870°C. This, however, is not recommended as 303 is sensitive to carbide precipitation with continuous use at 425-860°C.

Fabrication of all stainless steels should be done only with tools dedicated to stainless steel materials. Tooling and work surfaces must be thoroughly cleaned before each use, as this is necessary to avoid cross contamination of stainless steel.

Type 303 is not readily cold workable but it has excellent machinability.

Specifications:

UNS S30300, DIN 1.4305, ASTM A582, AMS 5640, ASME SA-194, ASME SA-320, ASTM A-194, ASTM A-314, ASTM A-320, ASTM A-473, ASTM A-581, ASTM A-582, MIL Spec. MIL-S-862. MIL-S-52263, QQ-S-764

Applications:

Nuts, bolts, bushings, shafts, aircraft fittings, electrical switchgear components, shafts, valve bodies, valves, valve trim, gears.