Easier welding and fabrication without Intergranular Corrosion

Intergranular Corrosion due to welding

The microstructure of metals and alloys consists of grains, separated by boundaries. Intergranular corrosion (IGC) is a selective attack near these grain boundaries. Usually associated with chemical segregation, it’s caused by chromium depletion, mainly due to the precipitation of chromium carbides in the grain boundaries.

Chromium carbides can be precipitated if the stainless steel is sensitized in the temperature range 550–850°C (1020–1560°F), for example during welding.

If the material is exposed to this critical temperature range for too long, chromium carbides start to form in the grain boundaries. These become susceptible to intergranular corrosion, creating a potentially serious impact on the material’s mechanical properties.

How to reduce the risk of IGC

Materials with less than 0.05% carbon normally have sufficient resistance against IGC after welding. Extra-low carbon content steels with maximum 0.030% carbon have very good resistance to IGC.

This is also true for steels stabilized with titanium (Ti) or niobium (Nb). These types of steel form niobium or titanium carbides instead of chromium carbides. This avoids the critical decrease in the chromium content.

The Sandvik solution

To eliminate the risk of ICG in welding, Sandvik Materials Technology recently launched Sanicro® 825 – a titanium-stabilized nickel-iron-chromium alloy with extra low carbon content. Containing more than 40% nickel, Sanicro® 825 is a tough all-around performer with excellent corrosion resistance. It’s a cost-efficient alternative to superalloys like 625 and 718 with far better corrosion resistance than 316L or 904L.

Sanicro® 825 was designed with high mechanical strength and structural stability in mind to avoid the risk of intermetallic phases during welding at higher temperatures. Even in the heaviest sizes, it can be welded without the risk of carbide precipitation and ICG.

ICG testing using the Huey method is performed as a standardized pre-delivery test. It’s carried out as a rule on samples from finished bars in the as-delivered condition or on material that has been sensitized by heating in the critical temperature range in a furnace.

Available in bar and hollow bar, both Sanicro® 825 options have the same chemical composition, making uniform fabrication welding straightforward.

Sanicro® 825 meets the ASTM B425 and ASME SB 425 standards and is approved by the American Society of Mechanical Engineers (ASME) for use under ASME Boiler and Pressure Vessel Code, Section I and Section VIII, div. 1. It also has NACE approvals MR0175/ISO15156 and MR0103/ISO17945. Manufacturing approvals include AMS2750 and API 6A. Pre-approval for PMA for PED 2014/68/EU is pending.

The material is available in a selected stock assortment or made to order, ranging from 20 to 260 millimeters (0.787 – 10.24 inches) in three to seven-meter lengths (118.11– 257.6 inches), depending on the diameter.

Find out how you can extend your possibilities with Sanicro® 825 at our upcoming webinar here.

Name: Magnus Brink
Title: Technical Marketing Specialist
Business Unit: Tube EMEA
Location: Sweden