Type 347 is an austenitic stainless steel stabilized by additions of columbium (plus tantalum) to reduce or prevent carbide precipitation during welding and in service at 800/1650ºF (430/900ºC.) The columbium addition also improves high temperature properties. The grade has good resistance to corrosion and oxidation and good creep strength. Type 347 is good for applications at temperatures where carbide precipitation occurs in non – stabilized grades.
| CHEMICAL ANALYSIS | |
|---|---|
| C | Carbon .08 max |
| Mn | Manganese 2.00 max |
| P | Phosphorus .045 max |
| S | Sulfur .030 max |
| Si | Silicon 1.00max |
| Cr | Chromium 17.00 – 19.00 |
| Ni | Nickel 9.00 – 13.00 |
| (Cb + Ta)% | Niobium 10 x C min |
APPLICATIONS
Type 347 is used for aircraft collector rings and exhaust manifolds, expansion joints and high temperature chemical process equipment.
FORGING
Type 347 has good inherent forgeability, but its differences from carbon and alloy steels must be taken into account. Type 347 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 347 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) | 2300 (1260) |
| Moderate reductions (finish forging and upsetting) | 2200 (1200) |
| Slight reductions (coining, restriking and end upsetting) | 2050 (1120) |
For maximum corrosion resistance, parts should be water quenched after forging or subsequently annealed and water quenched.
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