Alloy 347/347H

Sandmeyer Steel Company stocks Alloy 347 stainless steel plate in thicknesses from 3/16" through 4". A high carbon version, Alloy 347H (UNS S34709) stainless steel plate, can also be ordered in the same thickness range.

Available thicknesses for Alloy 347/347H:

Alloy 347 (S34700) is stabilized stainless steel plate which offers as its main advantage an excellent resistance to intergranular corrosion following exposure to temperatures in the chromium carbide precipitation range from 800 to 1500°F (427 to 816°C). Alloy 347 stainless steel plate is stabilized by the addition of columbium and tantalum.

Alloy 347 stainless steel plate is also advantageous for high temperature service because of its good mechanical properties. Alloy 347 stainless steel plate offers higher creep and stress rupture properties than Alloy 304 and, particularly, Alloy 304L, which might also be considered for exposures where sensitization and intergranular corrosion are concerns.

General Properties

Alloy 347 (UNS S34700) is columbium stabilized austenitic stainless steel plate with good general corrosion resistance and somewhat better resistance in strong oxidizing conditions than 321 (UNS S32100). It has excellent resistance to intergranular corrosion after exposure to temperatures in the chromium carbide precipitation range of 800 – 1500°F (427 – 816°C). The alloy has good oxidation resistance and creep strength to 1500°F (816°C). It also possesses good low temperature toughness.

Alloy 347H (UNS S3409) stainless steel plate is the higher carbon (0.04 – 0.10) version of the alloy. It was developed for enhanced creep resistance and for higher strength at temperatures above 1000°F (537°C). In most instances, the carbon content of the plate enables dual certification.

Alloy 347 stainless steel plate cannot be hardened by heat treatment, only by cold working. It can be easily welded and processed by standard shop fabrication practices.

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Corrosion Resistance

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.

Chemical Analysis

Weight % (all values are maximum unless a range is otherwise indicated)

Mean Coefficient of Thermal Expansion

Temperature Range
°F	°C	in/in °F	cm/cm °C
68-212	20-100	9.2 x 10-6	16.0 x 10-6
68-1112	20-600	10.5 x 10-6	18.9 x 10-6
68-1832	20-1000	11.4 x 10-6	20.5 x 10-6

Mechanical Properties

Typical Values at 68°F (20°C)

NOTE: The information and data in this product data sheet are accurate to the best of our knowledge and belief, but are intended for informational purposes only, and may be revised at any time without notice. Applications suggested for the materials are described only to help readers make their own evaluations and decisions, and are neither guarantees nor to be construed as express or implied warranties of suitability for these or other applications. Stainless Steel, Nickel Alloy and Titanium products are classified as sheet if the thickness of the metals is less than 3/16” (4.7mm). If the thickness of the metal is 3/16” (4.7mm) or more, then it is considered a plate.