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347/347H Stainless Steel

 

347/347H stainless steel is similar to 321 albeit stabilised by the addition of Columbium and Tantalum. This offers as its main advantage an excellent resistance to intergranular corrosion following exposure to temperatures in the chromium carbide precipitation range 427-816 Degrees C.

Alloy 347 is a stabilized, austenitic, chromium steel containing columbium which allows for the elimination of carbide precipitation, and, consequently, intergranualr corrosion.

Alloy 347 is stabilized by the additions of chromium and tantalum and offers higher creep and stress rupture properties than alloy 304 and 304L which may also be used for exposures where sensitization and intergranualr corrosion are of concern. The addition of columbium also allows Alloy 347 to have excellent corrosion resistance, even superior to that of alloy 321.


347H is the higher carbon composition form of Alloy 347 and demonstrates improved high temperature and creep properties.

Specifications: UNS S34700 / S34709

Applications:

Alloy 347 is frequently used for the fabrication of equipment, which must be placed in service under severe corrosive conditions, and is also common to the petroleum refining industries. Applications that consistently used Alloy 347 include:

  • High temperature chemical processes
  • Heat exchanger tubes
  • High temperature steam service
  • High pressure steam pipes
  • Radiant superheaters
  • Boiler tubes
  • Heavy duty exhaust systems
  • General refinery piping

Standards:

  • ASTM/ASME: UNS S34700 / S34709
  • EURONORM: FeMi35Cr20Cu4Mo2
  • DIN: 2.4660

Processing:

Weldability

  • Austenitic stainless steels are considered to be the most weldable out of all high alloy steels
  • Can be welded by all fusion and resistance welding processes

Heat Treatment

  • Annealing temperature range is 1800 to 2000°F
  • May be stress relief annealed within the carbide precipitation range of 800 to 1500°F without any danger of subsequent intergranualr corrosion
  • Cannot be hardened by heat treatment

Chemical Properties:

GradeCCrMnNiPSSiCb/Ta
3470.08 max

min: 17.0
max: 20.0

2.0 max

min: 9.0
max: 13.0

0.04 max

0.30
max

0.75
max

min:10x C
max: 1.0

347H

min: 0.04
max: 0.10

min: 17.0
max: 20.0

2.0 maxmin: 9.0
max: 13.0		0.03 max0.30
max		0.75
max		min:10x C
max: 1.0

Mechanical Properties:

Grade

Tensile Strength ksi (MPa) min

Yield Strength 0.2% ksi offset ksi (MPa) minElongation (% in 50mm) minHardness (Brinell) MAXHardness (Rockwell B) MAX
347/347H

75
(515)

30
(205)

4020195

Physical Properties:

Density
lbm/in3		Coefficient of
Thermal Expansion (min/in)-°F		Thermal Conductivity BTU/hr-ft-°FSpecific Heat BTU/lbm -°FModules of Elasticity (annealed)2-psi
at 68 °Fat 68 – 212°Fat 68 – 1832°F68-932°Fat 32 – 212°Fin tension (E)
0.2889.211.414.70.1228 x 106

 

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