Stainless Steel 303

Principal Design Features

303 is one of the most popular of all the free machining stainless steels. It offers good strength, corrosion resistance and great machinability. It will resist scaling at temperatures up to 1600 F(871 C).

General Characteristics

Type 303 stainless is a free-machining grade that owes its machining properties to the addition of sulfur. The 18/8 type austenitic stainless steels are normally tough to machine, but type 303 has been accepted for use on automatic screw machines where it can be machined at about 70% of the speed of B1112 screw stock.

Chemical Analysis

C% Mn% P% S% Si% Cr% Ni%
0.12 max 2.00 max 0.200 max 0.150 min 1.00 max 17.00/19.00 8.00/10.00


Type 303 stainless is suitable for use in forged shafts, valve bodies, valves, valve trim and fittings.


The piece to be forged should be heated to 2100/2300ºF (1150/1260ºC) and not forged below 1700ºF (925ºC.) Parts may be air cooled with no danger of cracking and for maximum corrosion resistance small parts may be water quenched directly off the hammer. Large parts should be annealed after forging.

Heat Treatment


This operation should be carried out at 1850/1950 ºF (1010/1065ºC) followed by water quenching. Type 303, as type 302, should not be subjected to temperatures between 800/1650 ºF (425/900ºC) nor slowly cooled through that temperature range, to prevent intergranular corrosion.


Type 303 machines easily and forms a brittle chip.


The grade is not recommended for welding as the high sulfur content may cause hot cracking. If the material must be welded then a type 312 filler metal and minimum heat input are applicable.


This alloy does not respond to hardening by heat treatment. Cold work will raise both the hardness and strength characteristics.

Density: 0.282

Specific Gravity: 7.84

Specific Heat: 0.12

Electrical Resistivity: 432

Melting Point: 2650

MoETensile: 28


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