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AWS D10.18M/D10.18:2018 pdf free download
AWS D10.18M/D10.18:2018 pdf free download.Guide for Welding Ferritic / Austenitic Duplex Stainless Steel Piping and Tubing.
5.2 Precipitating Phases. As noted above, after the molten metal solidifies as ferrite, some ferrite transforms to austenite down to a temperature of about I (XX)°C [1832°F]. As the DSS cools below this temperature, other phases such as carhides, nitrides, sigma, and other intermetallic phases can form. Chi phase and other intermetallic phases are often lumped together with sigma phase, and the term bsigrna phase” will be taken hereafter to include these other intermetallic phases. Sigma, in significant amounts, can be particularly detrimental in that toughness and corrosion resistance may be reduced. Sigma forms in the temperature range of 700°C to 980°C [1300°F to I 800°F1 with the most rapid formation at 870°C [1600°F]. It is formed whenever the alloy is in the 700°C to 980°C [1 300°F to 1 800°F] temperature range, being there is an accumulative effect. The total exposure time for sigma formation includes time at the steel mill during in-process heating and exposure time during welding including repair welding unless there is an intervening anneal above 1040°C [1 9(X)°FJ. The proper level of nitrogen delays sigma formation, hut does not prevent it. It has been shown that in the case of alloy 2205 with nitrogen in the upper range of 0.14% to (L20%, there is about a five-minute exposure time at 870°C [1600°F] available before the amount of sigma formed causes a significant loss of toughness and corrosion resistance.
As time at temperature in processing the wrought products is equally as important as time incurred during welding, ASTM A923, Standard Test Methods frr Detecting Detrimental Intermetallic Phase in Duplex Austenitic/Ferritic Stainless Steels, is a very useful document to utilize as it describes three test methods for detecting detrimental intermetallic phases. The methods include illustrations of acceptable microstructures, Charpy impact test acceptance criteria, and a ferric chloride corrosion test. ASTM A923 can be specified as a procurement requirement and is particularly useful for the thicker product forms. It is an aid in assuring that a significant portion of the allowable ‘6five minutes at sigma formation temperature” has not been used at the steel mill, allowing less time at temperature during welding. ASTM A 1084 is a standard for the lean DSS for detecting detrimental intermetallic phases and should he used in place of ASTM A923 for the lean DSS.
With nitrogen present in the duplex stainless steels, there is a potential to form chromium nitrides in the interior of large ferrite grains in the heat-affected zone (HAZ) that can result from too rapid cooling andlor inappropriate alloy balance. Large amounts of chromium nitrides could create chromium depleted areas that if not corrected by annealing could reduce corrosion resistance.AWS D10.18M/D10.18:2018 pdf free download.
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