Roymech engineering encyclopedia

303 Stainless Steel Material Properties



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303 Stainless Steel


Overview

Stainless steel type 1.4305 is popularly known as grade 303 stainless steel. Grade 303 is the most readily machineable of all the austenitic grades of stainless steel. The machineable nature of grade 303 is due to the presence of Sulphur in the steel composition. Whilst the Sulphur improves machining, it also causes a decrease in the corrosion resistance and a slight lowering of the toughness. The corrosion resistance of type 303 is lower than that for 304. The toughness is still excellent as with other austenitic grades.

Applications

Grade 303 is used in applications that require parts to be heavily machined. These applications include: Nuts and bolts, Screws, Gears, Aircraft fittings, Bushings and Shafts.

Cold Working

Type 303 is not readily cold workable. Some cold working is possible but sharp bending should not be attempted.

Corrosion Resistance

Sulphur additions to the composition act as initiation sites for pitting corrosion. This decreases the corrosion resistance of 303 stainless steel to less than that for 304. However. corrosion resistance remains good in mild environments. In chloride containing environments over 60°C, 303 stainless steel is subject to pitting and crevice corrosion. Grade 303 stainless is not suitable for use in marine environments.

Fabrication

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 use. These precautions are necessary to avoid cross contamination of stainless steel by easily corroded metals that may discolour the surface of the fabricated product.

Heat Resistance

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.

Heat Treatment

Grade 303 stainless steel cannot be hardened by heat treatment. Solution treatment or annealing can be done by rapid cooling after heating to 1010-1120°C.

Hot Working

Fabrication methods, like forging, that involve hot working like should occur after uniform heating to 1149-1260°C. The fabricated components should then be rapidly cooled to ensure maximum corrosion resistance.

Machinability

Grade 303 stainless steel has excellent machinability. Machining can be enhanced by adhering to the following rules: Cutting edges must be kept sharp. Dull edges cause excess work hardening. Cuts should be light but deep enough to prevent work hardening by riding on the surface of the material. Chip breakers should be employed to assist in ensuring swarf remains clear of the work Low thermal conductivity of austenitic alloys results in heat concentrating at the cutting edges. This means coolants and lubricants are necessary and must be used in large quantities.

Weldability

The sulphur addition present in 303 stainless steel results in poor weldability. If 303 must be welded the recommended filler rods or electrodes are grades 308L and 309 stainless steels. For maximum corrosion resistance, the welds must be annealed.

Related Specifications and Trade Names

Stainless Steel Grade 1.4305/303 also corresponds to the following designations but may not be a direct equivalent: UNS S30300, BS 303S31, EN 58M

Composition

Carbon (C) 0.0 - 0.10
Chromium (Cr) 17.00 - 19.00
Manganese (Mn) 0.0 - 2.00
Silicon (Si) 0.0 - 1.00
Phosphorous (P) 0.0 - 0.05
Sulphur (S) 0.15 - 0.35
Nickel (Ni) 8.00 - 10.00
Copper (Cu) 0.0 - 1.00
Nitrogen (N) 0.0 - 0.11
Iron (Fe) Balance



Electrical Properties

Metric Imperial
Dielectric Strength∞V/m∞V/ft
Magnetic Permeability1.0081.008

Mechanical Properties

Metric Imperial
Ductility50 %50 %
Friction Coefficient (static)0.60-0.150.60-0.15
Hardness, Rockwell B9696
Poissons Ratio0.250.25
Mass Density8030 Kg/m3501.30 lb/ft3
Shear Modulus77.2  Mpa11196.91 PSI
Tensile Strength620  MPa89923.37 PSI
Yield Strength240  MPa34809.05 PSI
Youngs Modulus193-200  GPa27992.28-29007.54 KSI

Thermal Properties

Metric Imperial
Coefficient of Thermal Expansion (Linear @ 0-100°C)17.2 x 10-6 °C-19.56 x 10-6 °F-1
Melting Point1455 °C2651.00-32.00 °F
Service Temperature in Air Intermittent760 °C1400.00 °F
Service Temperature in Air Continous870 °C1598.00 °F
Specific Heat Capacity0.5 J/g-°C207.80 BTU/lb-°F
Thermal Conductivity16.2 W/mK9.36 BTU/hr ft°F