Super duplex grades provide an unrivalled mixture of high power, corrosion resistance and worth. However, they are sensitive to the formation of harmful microstructural phases if cooled too slowly during production or heated too extremely during fabrication.
In easy terms, a bar of metal is a crystalline materials. The inner construction is made up of particular person crystal grains of differing sizes and orientations, the nature of which influences its bodily and mechanical properties. The microstructure is a factor of composition and thermal historical past. For this purpose, steelmaking is usually compared with baking – controlling the recipe and the time and temperature within the ‘oven’.
Super duplex stainless steels are a combination of ferritic and austenitic grains that give them their beneficial properties. Solution annealing ensures a consistent composition throughout the item, frozen in place by fast quenching.
If cooling is merely ไดอะแฟรม , other crystal grains often known as ‘phases’, may type. Sigma and chi ‘intermetallic phases’ are wealthy in chromium, that means the encompassing area has a decrease chromium content. As chromium encourages corrosion resistance, the areas across the sigma phase are of much decrease corrosion resistance. Also, these hard, brittle phases significantly decrease impression strength.
So, how does this phenomenon limit the utmost diameter of tremendous duplex chrome steel bars? Even when quenched, it’s not attainable to take away the warmth from massive bars shortly sufficient to keep away from the formation of those negative phases. Norsok-qualified manufacturers control the switch time from furnace to quench, and the utmost water temperature. However, above 16” /, the cooling rate remains to be too sluggish to ensure no sigma or chi formation.
For this cause, Langley Alloys chooses not to stock tremendous duplex stainless steel bars in bigger diameters. If you should produce bigger parts what are your options?

We inventory super duplex plate up to 3” / seventy six.2mm thickness. This permits bigger diameter objects to be provided, albeit limited to the maximum thickness of the plate.
If the part cannot be machined from 3”/76.2mm thick plate or 16”/406.4mm diameter bar then bespoke forgings could probably be a work round, if the ruling part doesn’t exceed this most allowable dimension.
Hot isostatic pressing (HIP) is less extensively used, on account of its relative cost, lead time and availability. Parts are produced from powder in high-pressure furnaces. As the mould (‘pattern’) for the powder to create the element can embody central bores, the ruling part could be decrease than a solid item. Subsequent heat treatment can obtain the required cooling rates.
Heat treatment after machining is viable for some elements. Machining may take away as much as half the starting weight of a solid bar. diaphragm seal may dramatically reduce the ruling section. The only danger after warmth therapy is potential distortion during cooling. Therefore, heat therapy ought to be undertaken after proof machining to allow a final end machine stage.
Let the Langley Alloys group assist your sourcing of corrosion resistant alloys, with our extensive shares, added services and technical support.