Stainless Steel 304 & Stainless Steel 304L Forgings
| Chemical Analysis | |
|---|---|
| C | Carbon .08 max |
| Mn | Manganese 2.00 max |
| P | Phosphorus .045 max |
| S | Sulfur .030 max |
| Si | Silicon 0.75 max |
| Cr | Chromium 18.00 – 20.00 |
| Ni | Molybdenum 8.00 – 12.00 |
| N | Nitrogen 0.10 max |
General characteristics of 304 Stainless Steel
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.
Applications of 304 Stainless Steel
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.
Forging 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 2300/1700ºF (1260/930ºC,) and air cooled, but to be more specific, a forging temperature coincident with forging conditions might be used, as follows:
Severe reductions (ingot breakdown, roll forging, drawing, blocking, and backward extrusion) 2300ºF (1260ºC)
Moderate reductions (finish forging and upsetting) 2200ºF (1200ºC)
Slight reductions (coining, restriking and end upsetting) 2050ºF (1120º)
Heat treatment
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/ 900ºF (815/480ºC.) then grain-boundary chromium carbide precipitation will occur with a resulting very significant loss of corrosion resistance. As such annealing at around 1950ºF (1065ºC) followed by a water quench is a necessary part of the production process for type 304 forgings.
Machinability
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.
Weldability
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 much loss of corrosion resistance due to carbide precipitation and for certain applications the steel can be used in the as-welded condition. For use in the most corrosive environments however, the welded structure should be re-annealed.
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