Stainless Steel 347/347H

Products Description

Alloy 347 (S34700) is a stabilized stainless steel plate that offers excellent resistance to intergranular corrosion. This resistance is particularly advantageous following exposure to temperatures in the chromium carbide precipitation range, which is typically between 800 to 1500°F (427 to 816°C).The main advantage of Alloy 347 is its ability to resist intergranular corrosion, which can occur when chromium carbides precipitate at grain boundaries in certain temperature ranges. The addition of columbium (niobium) and tantalum to the alloy helps stabilize it, preventing the formation of harmful chromium carbides and preserving its corrosion resistance.In addition to its corrosion resistance, Alloy 347 stainless steel plate is also well-suited for high-temperature service due to its good mechanical properties. It offers higher creep and stress rupture properties compared to Alloy 304 and Alloy 304L. These properties make Alloy 347 a suitable choice in situations 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.

Corrosion Resistance

Alloy 347 stainless steel plate exhibits good general corrosion resistance, which is comparable to that of Alloy 304 stainless steel. It was specifically developed for use in the chromium carbide precipitation range of 800 to 1500°F (427 to 816°C), where unstabilized alloys like 304 are susceptible to intergranular attack.Within this temperature range, the overall corrosion resistance of Alloy 347 stainless steel plate is superior to that of Alloy 321 stainless steel plate. Additionally, Alloy 347 performs somewhat better than Alloy 321 in strongly oxidizing environments up to 1500°F (816°C).Alloy 347 stainless steel plate can be used in various environments. It is suitable for nitric solutions, most diluted organic acids at moderate temperatures, and pure phosphoric acid at lower temperatures, as well as up to 10% diluted solutions at elevated temperatures. It also resists polythionic acid stress corrosion cracking in hydrocarbon service.However, Alloy 347 does not perform well in chloride solutions, even in small concentrations, or in sulfuric acid. It is important to avoid exposing Alloy 347 stainless steel plate to such corrosive environments to prevent potential corrosion issues.In chloride-containing environments or when encountering sulfuric acid, alternative stainless steel grades with better resistance to these corrosive agents should be considered.Overall, Alloy 347 stainless steel plate offers excellent corrosion resistance in specific temperature ranges and environments but may have limitations in certain highly corrosive conditions. It is crucial to assess the compatibility of the material with the specific corrosive environment and select an appropriate stainless steel grade accordingly.

Chemical Analysis

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

Mechanical Properties

Typical Values at 68°F (20°C)