S. S. 347 / 347H

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UNS - S34700 / S34709

Alloy 347 is a balanced, austenitic, chromium steel containing columbium which takes into consideration the end of carbide precipitation, and thus intergranular corrosion.

Alloy 347 is balanced out by the increases of chromium and tantalum and offers higher creep and stress rupture properties than alloy 304 and 304L, which may also be utilized for exposures where sensitization and intergranular corrosion are of concern.The expansion of columbium likewise permits Alloy 347 to have outstanding corrosion resistance, better than that of alloy 321. Alloy 347H is the higher carbon composition form of Alloy 347and display enhanced high temperature and creep properties.

  • Higher creep stress and rupture properties when compared with 304
  • Ideal for high temperature service
  • Overcomes sensitization and intergranular corrosion concerns
  • Can be used in elevated temperature applications
  • Due to stabilisation the material offers better overall corrosion resistance when compared to 304/304L

  • Chemical Processing
  • Food Processing equipment and storage
  • Petroleum Refining fluid catalytic cracking units, polythionic acid service
  • Pharmaceutical Production
  • Waste Heat Recovery recuperators

Corrosion Resistance

Alloy 347 stainless steel plate displays good general corrosion resistance that is similar to 304. It was produced for use in the chromium carbide precipitation scope by 800 – 1500°F (427 – 816°C) where unbalanced alloys such as 304 are subject to intergranular attack. In this temperature scope, the overall corrosion resistance of Alloy 347 stainless steel plate is better than Alloy 321 stainless steel plate. Alloy 347 additionally performs somewhat superior to Alloy 321 in strongly oxidizing situations up to 1500°F (816°C). The alloy can be utilized as a part of nitric solutions; most diluted organic acids at moderate temperatures and in pure phosphoric acid at lower temperatures and up to 10% diluted solutions at high temperatures. Alloy 347 stainless steel plate resists polythionic acid stress corrosion cracking in hydrocarbon service. It can also be used in chloride or fluoride free caustic solutions at moderate temperatures. Alloy 347 stainless steel plate doesn't perform well in chloride solutions, even in small concentrations, or in sulfuric acid.


Stainless steel 304 are not tougher than stainless steel 347; this material will produce the same tough stringy chips. For work harden, slow speeds and heavy feeds will minimize this alloy’s tendency.


With the help of fusion and resistance technique 347 may be welded. Oxyacetylene welding is not recommended. When compulsory, use AWS E/ER347 filler metal.

Hot Working

Working temperatures of 2100-2250 F (1149-1232 C) are suggested for forging, upsetting and other hot work process. Don’t work this alloy at temperatures beneath 1700 F (927 C). Material must be water quenched or completely annealed after working to reattain maximum corrosion resistance.

Cold Working

In spite of the fact that this material requires higher initial forces than 304 stainless steels, it is slightly tough and ductile and can be easily stamped, blanked, spun and drawn.


1850-2000 F (1010-1093 C), water quenches. This process will result in maximum ductility. For maximum corrosion resistance, see the note on settled anneal under corrosion.


This alloy doesn’t harden by heat treating. High properties may only be obtained through cold reduction.

Chemical Composition %

GradeCSiPSCrMnNiFeCb (Nb+Ta)
347 0.08 max0.75 max 0.045 max0.03 max 17.0 - 19.02.0 max9.0-13.0Remainder 10x (C + N)- 1.0
347H 0.04-0.100.75 max 0.045 max 0.03 max 17.0 - 19.02.0 max9.0-13.0Remainder 8x (C + N)- 1.0

Mechanical Properties

Tensile Strength (ksi)0.2% Yield Strength (ksi)Elongation% in 2 inches

Physical Properties

UnitsTemperature in °C
Density7.97 g/cm³Room
Specific Heat0.12 Kcal/kg.C22°
Melting Range1398 - 1446 °C-
Modulus of Elasticity 193 KN/mm²20°
Electrical Resistivity72 µΩ.cmRoom
Coefficient of Expansion16.0 µm/m °C20 - 100°
Thermal Conductivity16.3 W/m -°K20°

ASTM Specifications

Pipe / Tube (SMLS)Sheet / PlateBar ForgingFittings
A 213A 240, A 666A 276A 182A 403


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