Typical compositional ranges for grade 304 stainless steel are given in table 1.

Table 1. Composition ranges for 304 grade stainless steel

Mechanical Properties

Typical mechanical properties for grade 304 stainless steels are given in table 2.

Table 2. Mechanical properties of 304 grade stainless steel

Physical Properties

Typical physical properties for annealed grade 304 stainless steels are given in table 3.

Table 3. Physical properties of 304 grade stainless steel in the annealed condition

Grade Specification Comparison

Approximate grade comparisons for 304 stainless steels are given in table 4.

Table 4. Grade specifications for 304 grade stainless steel

Possible Alternative Grades

Possible alternative grades to grade 304 stainless steels are given in table 5.

Table 5. Possible alternative grades to 304 grade stainless steel tube

Corrosion Resistance

Excellent in a wide range of atmospheric environments and many corrosive media. Subject to pitting and crevice corrosion in warm chloride environments, and to stress corrosion cracking above about 60°C. Considered resistant to potable water with up to about 200mg/L chlorides at ambient temperatures, reducing to about 150mg/L at 60°C.

Aqueous
As a rough guide the following examples are given for certain pure acid-water mixtures-

 Key:         0 = resistant    -    corrosion rate less than 100 mm/year
                 1 = partly resistant    -    corrosion rate 100m to 1000 mm/year
                 2 = non resistant    - corrosion rate more than 1000 mm/year
 
Atmospheric

The performance of 304 compared with other metals in various environments is shown in the following table. The corrosion rates are based on a 10 year exposure.

Thermal Processing

1.    Annealing.  Heat from 1010oC to 1120oC and cool rapidly in air or water.  The best corrosion resistance is obtained when the final annealing is above 1070oC and cooling is rapid.

2.    Stress relieving.  SX 304L can be stress relieved at 450-600oC for one hour with little danger of sensitisation.  A lower stress relieving temperature of 400oC maximum must be used.

3.     Hot working
        Initial forging and pressing:                              1150  to 1260oC
        Finishing temperature:                                         900 to 925oC

All hot working operations should be followed by annealing.

Cold Working

304 / 304L being extremely tough and ductile, are readily fabricated by old working.  Typical operations include bending, forming, deep drawing and upsetting

Heat Resistance

Good oxidation resistance in intermittent service to 870°C and in continuous service to 925°C. Continuous use of 304 in the 425-860°C range is not recommended if subsequent aqueous corrosion resistance is important. Grade 304L is more resistant to carbide precipitation and can be heated into the above temperature range.

Grade 304H has higher strength at elevated temperatures so is often used for structural and pressure-containing applications at temperatures above about 500°C and up to about 800°C. 304H will become sensitised in the temperature range of 425-860°C; this is not a problem for high temperature applications, but will result in reduced aqueous corrosion resistance.

Heat Treatment

Solution Treatment (Annealing) – Heat to 1010-1120°C and cool rapidly. These grades cannot be hardened by thermal treatment.

Welding

Excellent weldability by all standard fusion methods, both with and without filler metals. AS 1554.6 pre-qualifies welding of 304 with Grade 308 and 304L with 308L rods or electrodes (and with their high silicon equivalents). Heavy welded sections in Grade 304 may require post-weld annealing for maximum corrosion resistance. This is not required for Grade 304L. Grade 321 may also be used as an alternative to 304 if heavy section welding is required and post-weld heat treatment is not possible.

Machining

A “Ugima” improved machinability version of grade 304 is available in bar products. “Ugima” machines significantly better than standard 304 or 304L, giving higher machining rates and lower tool wear in many operations.

Dual Certification

It is common for 304 and 304L to be stocked in “Dual Certified” form, particularly in plate and pipe. These items have chemical and mechanical properties complying with both 304 and 304L specifications. Such dual certified product does not meet 304H specifications and may be unacceptable for high temperature applications.

Applications

Typical applications include: