347 (UNS S34700 / W.Nr. 1.4550)

347 (UNS S34700 / W.Nr. 1.4550) stainless steel is a columbium/tantalum stabilized austenitic chromium-nickel stainless steel. Type 347 has excellent intergranular corrosion resistance and oxidation resistance. at high temperatures. This material is stabilized against chromium carbide formation by the addition of columbium and tantalum. Since these elements have a stronger affinity for carbon than chromium, columbium-tantalum carbides precipitate within the grains instead of forming at the grain boundaries. 347 should be considered for applications requiring intermittent heating between 800ºF (427ºC) and 1650ºF (899ºC) or for welding under conditions which prevent a post-weld anneal. 347 is non-magnetic.

Equivalent Grades

Trademark	GB	GOST	ASTM	UNS	DIN	W.Nr.	NF	BS	JIS	SS
–	–	–	AISI 347	S34700	X6CrNiNb 18-10	1.4550	–	–	–	–

Chemical Composition, %

Alloy	C	Si	Mn	P	S	Cr	Ni	Mo	Nb+Ta	Fe
347	≤0.08	≤0.75	≤2.00	≤0.045	≤0.030	17.0-19.0	9.0-13.0	–	10(C+N)	Bal

Typical Physical and Mechanical Properties (RT, Annealed)

Density, g/cm3	Melting Point, ℃	Tensile Strength, MPa	Yield Strength, MPa	ELongation, %	Hardness, HB
7.9	1030-1180	510-740	≥205	≥40	/

Available Products and Specifications

Rod, Bar, Wire and Forgings	ASTM A276, ASTM A479
Plate, Sheet and Strip	ASTM A167, 240
Pipe and Tube	ASTM A312
Welding Product	–
Others	ASTM A193, ASTM A193

Features

Good creep strength up to 1500°F
Maintains good corrosion resistance in applications where the temperature is between 800°F and 1500°F.
Good resistance to intergranular corrosion in the as welded condition.

Applications

Oil Refineries
Fluid catalytic cracking units (FCC)
Firearms production
Hanger rods
Recuperator tube sheets, shell, supports
Especially where temperatures exceed 550°F and resistance to sulfidation is needed
Fired heater tubes
Distributor trays and thermowells
Equipment in and around reactors (good resistance to polythionic acid)