304 Stainless Steel: Forging Facts & Characteristics
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Type 304 is an austenitic stainless steel. It has good corrosion resistance in many environments and may be formed and welded with ease. It has excellent ambient and low temperature toughness properties.
Type 304 stainless steel is an austenitic stainless steel that finds applications in a wide range of corrosive environments.
Care must be taken to avoid – or to remove – intergranular carbide precipitation. Parts forged from type 304 stainless steel will in most cases require an annealing treatment following forging to take precipitated carbides back into solution.
Forging Type 304 Stainless Steel
Type 304 has good inherent forgeability, but its differences from carbon and alloy steels must be taken into account. Type 304 has higher hot strength than carbon, alloy, even martensitic stainless steels, hence much higher forging pressures or more hammer blows are required to forge it – and other austenitic stainless steels. In fact two to three times as much energy is required to forge 300 series stainless steels as is required for carbon and alloy steels.
Type 304 is forged between 2300 º F and 1700 º F (1260 º C and 930 º C,) and air cooled, but
to be more specific, a forging temperature coincident with forging conditions might be specified, as follows:
|Severe reductions (ingot breakdown, roll forging, drawing, blocking, and backward extrusion)||2300 (1260)|
|Moderate reductions (finish forging and upsetting)||2200 (1200)|
|Slight reductions (coining, restriking and end upsetting)||2050 (1120)|
This grade of stainless steel is the general purpose austenitic stainless steel used in chemical processing, pulp and paper mills, and many other industries such as food and dairy, where its corrosion resistance is suitable and adequate.
Type 300 series austenitic stainless steels cannot be hardened by heat treatment, in fact the only heat treat operation that is performed on them is that of annealing. If these grades are slow cooled from forging, particularly through the temperature range 1500 – 900 º F (815 – 480 º C.) then grain-boundary chromium carbide precipitation will occur with a resulting very significant loss of corrosion resistance. As such annealing at around 1950 º F (1065 ºC) followed by a water quench is a necessary part of the production process for type 304 forgings.
Type 304 machines to give tough, stringy chips. Chip breakers are recommended and since the alloy has a rapid work hardening rate, positive feeds are recommended.
Type 304 may be welded by shielded fusion and resistance welding operations. Austenitic stainless steel welds do not harden on cooling, hence the welds will show good toughness.
Oxyacetylene welding is not recommended due to the possibility of carbon pick up in the weld area.
The alloy can be welded without loss of corrosion resistance due to carbide precipitation and the steel can be used in the as-welded condition. For use in the most corrosive environments however, the welded structure should be reannealed.
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