Stainless Steel 347

Stainless Steel 347

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

General characteristics of Stainless Steel 347

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.

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.

Heat treatment

Type 347 stainless steel cannot be hardened by heat treatment, in fact the only heat treat operation that is performed on it is that of annealing, at around 1950ºF (1065ºC,) followed by a water quench. This treatment gives maximum corrosion resistance for type 347 forgings.

Machinability

Type 347, like all austenitic stainless steels, 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 347 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 at elevated temperatures however, a post-weld stabilizing heat treatment at 1550/1650ºF (840/900ºC) is recommended.

 

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