Stainless Steel 347 is similar to the 321 stainless steels in that it is often used as a stabilized alternative to Type 304. In the case of 347, however, the stabilizing agent is columbium. This metal intensifies 347’s already present ability to withstand intergranular corrosion for maximum capabilities. Additionally, the columbium allows for 347 to undergo repeated heating in temperatures up to 1650° F. As a result, the metal is commonly applied to high temperature equipment, such as gaskets and expansion joints, along with rocket engine and chemical manufacturing.
In addition to its heat resistance properties, 347 also enjoys better resistance against creep and stress rupture corrosions. This is another advantage of type 304, as 347’s characteristics may be better suited for environments where stabilization is a primary concern.
Type 347 is known for being workable under all common welding techniques, along with hot and cold working. However, when being heat treated the metal must be heated up in the range of 2100 to 2250°F. This is due to 347’s inability to work harden under heat treatment. Cold reduction is the only method that will utilize the alloy’s elevated properties.
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 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.