Grade 303 represents the optimum in machinability among the austenitic stainless steels. It is primarily used when production involves extensive machining in automatic screw machines. Machinability Rating (compared to B1212) is approximately 78%.

303 is also available as a "Ugima" Improved Machinability grade, with machinability even higher than that of the standard 303.

The sulphur addition which is responsible for the improved machining and galling characteristics of Grade 303 lowers its corrosion resistance to below that of Grade 304. As for other austenitic grades the structure gives 303 excellent toughness, although the sulphur in 303 reduces its toughness slightly.

Grade 303Se (UNS S30323) has a selenium rather than sulphur addition, improving the hot and cold forming characteristics over those of 303 and providing a smoother machined surface finish. The machinability rate is also slightly reduced. Grade 303Se is not readily available in Australia.
Key Properties

These properties are specified for long product (bar) in ASTM A582. Similar but not necessarily identical properties are specified for other products such as wire and forgings in their respective specifications. Grade 303 is not produced in flat rolled products.
Composition

Typical compositional ranges for grade 303 stainless steels are given in table 1.

Table 1. Composition ranges for 303 grade stainless steel

Grade


C


Mn


Si


P


S


Cr


Mo


Ni


Se

303


min.

max.


-

0.15


-

2.00


-

1.00


-

0.20


0.15

-


17.0

19.0


-


8.0

10.0


-

303Se


min.

max.


-

0.15


-

2.00


-

1.00


-

0.20


0.06

-


17.0

19.0


-


8.0

10.0


0.15

min
Mechanical Properties

Typical mechanical properties for grade 303 stainless steels are given in table 2.

Table 2. Mechanical properties of 303 grade stainless steel

Grade


Tensile Strength (MPa)


Yield Strength 0.2% Proof (MPa)


Elongation (% in 50mm)


Hardness

Rockwell B (HR B)


Brinell (HB)

303


-


-


-


-


262 max
Physical Properties

Typical physical properties for annealed grade 303 stainless steels are given in table 3.

Table 3. Physical properties of 303 grade stainless steel in the annealed condition

Grade


Density (kg/m3)


Elastic Modulus (GPa)


Mean Coefficient of Thermal Expansion (mm/m/°C)


Thermal Conductivity (W/m.K)


Specific Heat 0-100°C (J/kg.K)


Electrical Resistivity (nW.m)

0-100°C


0-315°C


0-538°C


at 100°C


at 500°C

303


8027


193


17.3


17.8


18.4


16.3


21.5


500


720
Grade Specification Comparison

Approximate grade comparisons for 303 stainless steels are given in table 4.

Table 4. Grade specifications for 303 grade stainless steel

Grade


UNS No


Old British


Euronorm


Swedish SS


Japanese JIS

BS


En


No


Name

303


S30300


303S31


58M


1.4305


X8CrNiS18-9


2346


SUS 303

303Se


S30323


303S42


-


-


-


-


SUS 303Se

These comparisons are approximate only. The list is intended as a comparison of functionally similar materials not as a schedule of contractual equivalents. If exact equivalents are needed original specifications must be consulted.
Possible Alternative Grades

Possible alternative grades to grade 303 stainless steels are given in table 5.

Table 5. Possible alternative grades to 303 grade stainless steel

Grade


Why it might be chosen instead of 303

304


Better corrosion resistance, formability or weldability are needed, at the expense of lower machinability.

316


Higher resistance to pitting and crevice corrosion is required, in chloride environments. A lower machinability can be accepted.

416


Even higher machinability than 303 is needed, and a lower corrosion resistance can be tolerated.

Or hardening by thermal treatment is required, while maintaining a high machinability.
Corrosion Resistance

Good resistance to mildly corrosive atmospheres, but significantly less than Grade 304 due to the sulphur addition; the sulphide inclusions act as pit initiation sites. Grade 303 should not be exposed to marine or other similar environments, as these will result in rapid pitting corrosion. Because the sulphide inclusions in 303 are primarily aligned along the rolling direction the corrosion resistance is particularly reduced in cross-sections.

Grade 303, like other common austenitic stainless steels, is subject to stress corrosion cracking in chloride containing environments above about 60°C.