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Stainless Steel 303

Stainless Steel 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 below. 

Chemical Composition of Type 303 Stainless Steel

UNS No Grade C Si Mn P S Cr Mo Ni N
     0.0-0.07  0.0-1.0  0-2.0  0-0.05  0-0.02 16.5-18.5   2-2.5 10.0-13.0   0

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 crosssections.

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

Heat Resistance

Good oxidation resistance in intermittent service to 760°C and in continuous service to 870°C. Continuous use in 425­860°C range not usually recommended due to carbide precipitation ­ 303 usually does not have a low carbon content so is susceptible to sensitisation.

Fabrication

As well as reducing the corrosion resistance, the sulphur additions in 303 also result in poor weldability and reduced formability compared to Grade 304. Sharp bends should not be attempted in 303. A practical compromise alternative may be a 304 Ugima Improved Machinability grade ­ this does not machine as readily as 303, but does offer better formability (as well as better weldability and corrosion resistance).

Heat Treatment

Solution Treatment (Annealing); Heat to 1120°C and cool rapidly. This grade cannot be hardened by thermal treatment.

Welding

Not generally recommended but, if unavoidable and a lower strength can be tolerated, use Grade 308L or 309 electrodes. AS 1554.6 does not pre-qualify welding of 303. Welds must be annealed for maximum corrosion resistance.

Machining

A "Ugima" improved machinability version of grade 303 is available in round bar products. This machines significantly better even than standard 303, giving very high machining rates and lower tool wear in many operations.

Applications

Typical applications include:

  • Nuts and Bolts
  • Bushings
  • Shafts 
  • Aircraft Fittings
  • Electrical Switchgear Components
  • Gears
  • In general any component that is heavily machined and where the corrosion resistance and fabrication properties of 303 are viable.

Forms Available

Stainless Steel 303 is available from stock as:

Round bar

Type 316L Stainless Steel 

Overview

Grade 316L, the low carbon version of 316 and is immune from sensitisation (grain boundary carbide precipitation). Thus it is extensively used in heavy gauge welded components (over about 6mm)

Chemical Composition of Type 316l Stainless Steel

UNS No Grade C Si Mn P S Cr Mo Ni N
     0.0-0.03  0.0-1.0  0-2.0  0-0.05  0-0.02 16.5-18.5   2-2.5 10.0-13.0   0

Mechanical Properties ...

UNS No Grade

Proof Stress

Tensile Strength

Elongation

Hardness
    0.2% (MPa) (MPa) A5(%) HB HRB
             

Forms available

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Type 316H Stainless Steel for Elevated Temperature Conditions (UNS31609)

Overview

Type 316H is a higher carbon variant of 316 making the steel more suitable for use in applications where elevated temperatures are present. Stabilised Grade 316Ti offers similar qualities. 

The increased carbon content delivers a greater tensile and yield strength. The austenitic structure of the material also gives this grade excellent toughness, even down to cryogenic temperatures.

Benefits of Grade 316H stainless steel

Benefits of using Grade 316H stainless steel include:

  • Increased carbon content heat resistant qualities
  • Greater tensile yield strength
  • Greater short and long term creep strength

Chemical Composition of Type 316H Stainless Steel

UNS No Grade C Si Mn P S Cr Mo Ni N
                     

Mechanical Properties ...

UNS No Grade

Proof Stress

Tensile Strength

Elongation

Hardness
    0.2% (MPa) (MPa) A5(%) HB HRB
             

Forms available

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