Stainless Steel Type 347 Information By yaang.com

by yane Yang Sales Manager

Stainless Steel Type 347 is a columbium/tantalum stabilized austenitic stainless steel. Like Type 321, it has superior intergranular-corrosion resistance compared to typical 18-8 type alloys. Since columbium and tantalum have stronger affinity for carbon than chromium, carbides of those elements tend to precipitate randomly within the grains instead of forming continuous patterns at the grain boundaries. Type 347 should be considered for applications requiring intermittent heating between 800ºF (427ºC) and 1650ºF (899ºC).

347 Stainless Steel should be considered for use in aircraft collector rings and exhaust manifolds, expansion joints and high temperature chemical process equipment.

Scaling
The safe scaling temperature for continuous service is 1600ºF (871ºC).

Identification

UNS Number

S34700

Type Analysis

Single figures are nominal except where noted.

Carbon (Maximum)	0.08	%	Manganese (Maximum)	2.00	%
Phosphorus (Maximum)	0.045	%	Sulfur (Maximum)	0.030	%
Silicon (Maximum)	1.00	%	Chromium	17.00 to 19.00	%
Nickel	9.00 to 13.00	%	Columbium + Tantalum	10 X C Minimum
Iron	Balance

Corrosion Resistance

Annealed Stainless Steel Type 347 is resistant to atmospheric corrosion, foodstuffs, sterilizing solutions, many organic chemicals and dyestuffs, and a wide variety of inorganic chemicals. It has excellent intergranular-corrosion resistance.
For optimum corrosion resistance, surfaces must be free of scale, lubricants, foreign particles, and coatings applied for drawing and heading. After fabrication of parts, cleaning and/or passivation should be considered.

Important Note:The following 4-level rating scale is intended for comparative purposes only. Corrosion testing is recommended; factors which affect corrosion resistance include temperature, concentration, pH, impurities, aeration, velocity, crevices, deposits, metallurgical condition, stress, surface finish and dissimilar metal contact.

Nitric Acid	Good	Sulfuric Acid	Moderate
Phosphoric Acid	Moderate	Acetic Acid	Moderate
Sodium Hydroxide	Moderate	Salt Spray (NaCl)	Good
Sea Water	Restricted	Sour Oil/Gas	Moderate
Humidity	Excellent

Properties
Physical Properties
Specific Gravity
--	7.89
Density
--	0.2850	lb/in³
Mean Specific Heat
32 to 212°F	0.1200	Btu/lb/°F
Mean CTE
32 to 1200°F	10.4	x 10^-6 in/in/°F
Modulus of Elasticity (E)
--	28.0	x 10³ ksi
Electrical Resistivity
73°F	433.0	ohm-cir-mil/ft
Typical Mechanical Properties
Typical Elevated Temperature Mechanical Properties
Typical Room Temperature Mechanical Properties
Typical Stress Rupture Strength

Heat Treatment
Annealing
Heat to 1850/2000ºF (1010/1093ºC) and quench in water. Brinell hardness approximately 150.
Hardening
Can only be hardened by cold working.
Stabilizing
When temperatures up to about 1600ºF (871ºC) are expected in service, a stabilizing treatment at 1550/1650ºF (843/899ºC) may be used to provide optimum intergranular corrosion resistance.

Workability
Hot Working
Stainless Steel Type 347 is readily forged, hot headed, riveted and upset. Because of its high red-hardness, more power for a given reduction is required than with mild steel.
Forging
Heat uniformly to 2100/2250ºF (1149/1232ºC). Do not forge below 1700ºF (927ºC). Forgings can be air-cooled. For full corrosion resistance, forgings must be water quenched or annealed.
Cold Working
Stainless Steel Type 347 is readily fabricated by cold working. Being extremely tough and ductile, it responds to deep drawing, bending, forming and upsetting. After cold working, it is slightly magnetic. The tensile strength and hardness ofStainless Steel Type 347 can be significantly increased by cold working.
Machinability
Like all austenitic steels, Stainless Steel Type 347 machines with tough and stringy chips. Rigidly supported tools, with as heavy a cut as possible, should be used to prevent glazing. Moderate cold working can improve machined surface finish. Following are typical feeds and speeds for Stainless Steel Type 347.
Additional Machinability Notes
When using carbide tools, surface speed feet/minute (sfpm) can be increased between 2 and 3 times over the high speed suggestions. Feeds can be increased between 50 and 100%. Figures used for all metal removal operations covered are average. On certain work, the nature of the part may require adjustment of speeds and feeds. Each job has to be developed for best production results with optimum tool life. Speeds or feeds should be increased or decreased in small steps.
Weldability
Stainless Steel Type 347 can be satisfactorily welded by the shielded fusion and resistance welding processes. Oxyacetylene welding is not recommended, since carbon pickup in the weld may occur. Since austenitic welds do not harden on air cooling, the welds should have good toughness. When a filler metal is required, AWS E/ER347 welding consumables should be considered. To decrease the susceptibility to hot cracking, keep heat inputs, base metal dilution, and joint restraint to a minimum. The alloy can be used in the as-welded condition; however, for elevated temperature service, a postweld stabilizing treatment should be considered.