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:

Standards:

Processing:

Weldability

Heat Treatment

Chemical Properties:

Grade C Cr Mn Ni P S Si Cb/Ta
347 0.08 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 max min: 9.0
max: 13.0
0.03 max 0.30
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) min Elongation (% in 50mm) min Hardness (Brinell) MAX Hardness (Rockwell B) MAX
347/347H

75
(515)

30
(205)

40 201 95

Physical Properties:

Density
lbm/in3
Coefficient of
Thermal Expansion (min/in)-°F
Thermal Conductivity BTU/hr-ft-°F Specific Heat BTU/lbm -°F Modules of Elasticity (annealed)2-psi
at 68 °F at 68 – 212°F at 68 – 1832°F 68-932°F at 32 – 212°F in tension (E)
0.288 9.2 11.4 14.7 0.12 28 x 106

 



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