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303 Stainless Steel

Penn Stainless inventory includes 303 grade stainless steel (UNS S30300) in plate, round bar, square bar, hex bar, and rolled flat bar.


General Properties

Alloy 303 is a non-magnetic, austenitic stainless steel that is not hardenable by heat treatment. It is the free machining modification of the basic 18% chromium / 8% nickel stainless steel. Alloy 303 was specially designed to exhibit improved machinability while maintaining good mechanical and corrosion resistant properties Due to the presence of sulfur in the steel composition, Alloy 303 is the most readily machineable austenitic stainless steel; however, the sulfur addition does lower Alloy 303’s corrosion resistance to below that of Alloy 304. Like other austenitic grades, Alloy 303 demonstrates excellent toughness, although the sulfur does reduce this a little as well.


Alloy 303 is frequently used in applications that require parts to be heavily machined. Some examples include:

  • Nuts and bolts
  • Aircraft fittings
  • Gears
  • Screws
  • Shafts
  • Electrical switchgear components
  • Bushings

Standards – Alloy 303

ASTM/ASME ……………. UNS S30300

EURONORM ……………. FeMi35Cr20Cu4Mo2

DIN …………………………  2.4660


Corrosion Resistance

  • Good resistance to mildly corrosive atmospheres, but significantly less than Alloy 304
  • When additional sulfur is added to improve machinability, it can often slightly reduce corrosion resistance
  • In most dry and mild corrosive environments, Alloy 303 is comparable to other unmodified alloys
  • Should not be exposed to moist, marine environments as it is subject to rapid-pitting corrosion and a rust film will tend to form
  • Like other common austenitic stainless steels, it is subject to corrosion cracking in chloride environments above 60oC

Heat Resistance

  • Good oxidation resistance at temperatures up to 1700oF (927 oC)
  • Continuous use at temperatures above 1400oF (760oC) is not usually recommended due to carbide precipitation which can lead to irregular scaling
  • Does not have a low carbon content so it is also vulnerable to sensitisation

Welding Characteristics

  • Not generally recommended, but may be welded with some difficulty
  • May be welded with Alloy 310 electrodes
  • Should be annealed after welding to re-dissolve precipitated carbides


  • High machining rates can be obtained in the annealed condition with hardness in the range of 200 to 240 Brinell
  • Will work harden, therefore, it should be machined at reduced surface feet per minute and heavier feeds to prevent glazing at the tool interface.

Chemical Properties:

% Cr Ni C Si Mn P S Mo Fe
303 min: 17.0
min: 8.0
max: 10.0
0.15 min 0.75 balance

Mechanical Properties:

Grade Tensile Strength
ksi (min.)
Yield Strength 0.2%
Offset ksi (min.)
Elongation -
% in
50 mm (min.)
(Brinell) MAX
(Rockwell B) MAX
303 75 30 35 228

Physical Properties:

Coefficient of
Thermal Expansion (min/in)-°F
Electrical Resistivity mW-in Thermal Conductivity BTU/hr-ft-°F Melting
at 68 °F at 68 – 212°F at 68 – 932°F at 68 – 1450°F at 68°F at 212°F at 392°F at 752°F at 1112°F at 1472°F at 68 – 212°F
0.29 9.2 10.4 10.9 28.3 30.7 33.8 39.4 43.7 47.6 113.2 2552°F

Alloy 303 PDF