SS347 - 347H

A Stabilized Austenitic Stainless Steel with Excellent Resistance to Intergranular Corrosion After Exposure to Temperatures in the Chromium Carbide Precipitation Range of 800–1500°F (427–816°C)

Difference between SS347 and SS347H

• Stainless Steel 347 is a niobium-stabilized chromium-nickel austenitic stainless steel with corrosion resistance similar to 304/304L. 347 stainless steel is a columbium/tantalum stabilized austenitic chromium-nickel stainless steel. This grade is typically used in the 800-1500˚F temperature range where it is stabilized against chromium carbide precipitation by the addition of niobium, which results in the precipitation of niobium carbides. Type 347 has excellent intergranular corrosion resistance after exposure to this temperature range, and this grade resists oxidation up to 1500˚F and has higher creep and stress rupture properties than 304/304L. It also possesses good low-temperature toughness and is non-magnetic in the annealed condition. 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 is non-magnetic.

• Stainless Steel 347H is another stainless steel in a class of metals labeled of precipitation-hardened steels. It possesses many of the same properties and characteristics of stainless steel 347. In addition to its higher carbon content, the alloy is stabilized with an addition of columbium, or sometimes tantalum. Both these properties allow 347H to be exposed to higher temperatures than both 347 and the 304 stainless steel grades can withstand. Because of its elevated resistance to corrosion, 347H is often applied in high-stress, high-corrosion environments where exposure tends to be severe. High-temperature manufacturing, steam pipes, boiler tubes, chemical processes and steam servicing all benefit from 347H’s resilience. This resilience in turn is due to the potentially elevated levels of chromium in 347H’s composition. The metal can contain anywhere from 4-30%. The metal displays high workability under the most common welding techniques. It can be treated with heat, however, it will not respond. Only cold working is sufficient to increase 347H’s toughness and strength.

 Specification

• ASTM A/ASME SA213/A249/A269/A312/A358 CL. I to V ASTM A789/A790
• UNS: S34700 / 34709
  
• AMS: 5512 / 5546
  

Chemical Composition SS 347/347H (%)

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Applications of Stainless Steel 347 - 347H

For construction parts which should be resistant to scaling up to about 1050°C and extensively inured to the effect of sulfurous gases, especially above 900°C, is very low.

They are used for:

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

Physical Properties 

• Density: 7.96 g /cm³ (0.288 lbs / in³)
• Melting Range:  1398 – 1446°C (2550 – 2635°F)
• Modulus of Elasticity: 28.0 x 10⁶ psi 193 GPa
• Electrical Resistivity:  72 Microhm-cm at 20°C
• Thermal Conductivity: 212°F (100°C) 133 BTU/hr/ ft²/ft -°F 16.3 W/m-°K
• Thermal Expansion:: 16.0 µm/m °C
• Annealed: 1040 – 1100 (°C) / 1900 – 2000 (°F)
• Quenched:  Rapid Air/Water

For more details click the PDF here with all regulations here

Linear Coefficient of Thermal Expansion

Thermal Conductivity

Electrical Resistivity (Annealed Condition)

Specific Heat

Heat Resistance of Stainless Steel 347 - 347H

347 stainless steel has better heat resistance than 304 stainless steel. This is due to the addition of columbium to the alloy, which helps to stabilize it at high temperatures. 304 stainless steel is still able to withstand high temperatures, but it may suffer from some degree of scaling at temperatures above 1600 degrees Fahrenheit.

 Hot Working of Stainless Steel 347 - 347H

Working temperatures of 2100 – 2250°F (1149 – 1232°C) are recommended for forging, upsetting and other hot working processes. Do not work this alloy at temperatures below 1700°F (927°C). The material must be water quenched or fully annealed after working to re-attain maximum corrosion resistance.

 Cold Working of Stainless Steel 347 - 347H

The alloy is quite ductile and forms easily.

Heat Treatment of Stainless Steel 347 - 347H

The annealing temperature range for Types 321 and 347 is 1800 to 2000°F (928 to 1093°C). While the primary purpose of annealing is to obtain softness and high ductility, these steels may also be stress relief annealed within the carbide precipitation range 800 to 1500°F (427 to 816°C), without any danger of subsequent intergranular corrosion. Relieving strains by annealing for only a few hours in the 800 to 1500°F (427 to 816°C) range will not cause any noticeable lowering in the general corrosion resistance, although prolonged heating within this range does tend to lower the general corrosion resistance to some extent. As emphasized, however, annealing in the 800 to 1500°F (427 to 816°C) temperature range does not result in a susceptibility to intergranular attack.

For maximum ductility, the higher annealing range of 1800 to 2000°F (928 to 1093°C) is recommended

Fabrication of Stainless Steel 347 - 347H

Alloy 347 can be easily welded and processed by standard shop fabrication practices.

Mechanical Properties of Stainless Steel 347 - 347H

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Corrosion Resistance of Stainless Steel 347 - 347H

• Alloy 347 stainless steel plate exhibits good general corrosion resistance that is comparable to 304.
• It was developed for use in the chromium carbide precipitation range of 800 – 1500°F (427 – 816°C) where un-stabilized alloys such as 304 are subject to intergranular attack.
• In this temperature range, the overall corrosion resistance of Alloy 347 stainless steel plate is superior to Alloy 321 stainless steel plate.
• Alloy 347 also performs somewhat better than Alloy 321 in strongly oxidizing environments up to 1500°F (816°C).
• The alloy can be used in nitric solutions, most diluted organic acids at moderate temperatures and in pure phosphoric acid at lower temperatures and up to 10% diluted solutions at elevated temperatures.
• Alloy 347 stainless steel plate resists polythionic acid stress corrosion cracking in hydrocarbon service.
• It can also be utilized in chloride or fluoride-free caustic solutions at moderate temperatures.
• Alloy 347 stainless steel plate does not perform well in chloride solutions, even in small concentrations, or in sulfuric acid.

Machinability

• Machining grade 347H stainless steel is slightly tougher than that of grade 304 steel. However, the hardenability of this steel can be minimized by the use of constant positive feeds and slow speeds.
• The cold work hardening rate of 347 stainless steel plate makes it less machinable than 410 stainless steel, but similar to 304. The table below provides relevant machining data.

 Welding of Stainless Steel 347 - 347H

Alloy 347 stainless steel plate can be readily welded by most standard processes. A post-weld heat treatment is not necessary.

Two important considerations in producing weld joints in the austenitic stainless steels are:

• preservation of corrosion resistance
• avoidance of cracking

It is important to maintain the level of stabilizing element present in Types 321, 347 and 348 during welding. Type 321 is more prone to loss of titanium. Types 347 and 348 are more resistent to loss of columbium. Care needs to be exercised to avoid pickup of carbon from oils and other sources and nitrogen from the air. Weld practices which include attention to cleanliness and good inert gas shielding are recommended for these stabilized grades as well as other non-stabilized austenitic alloys.

Weld metal with a fully austenitic structure is more susceptible to cracking during the welding operation. For this reason, Types 321, 347 and 348 alloys are designed to resolidify with a small amount of ferrite to minimize cracking susceptibility. Columbium-stabilized stainless steels are more prone to hot cracking than titanium-stabilized stainless steels

Matching filler metals are available for welding Types 321 and 347 stabilized stainless steels. The Type 347 filler metal is sometimes used to weld the Type 321 alloy as well as the Type 348 alloy.

These stabilized alloys may be joined to other stainless steels or carbon steel. Type 309 (23% Cr-13.5% Ni) or Nickel-base filler metals have been used for this purpose.