Duplex stainless steel Alloy 2205 is nominally 22% Cr, 5% Ni, and 3% Mo with nitrogen added. The ER2209 filler metal matches the base metal in all respects except nickel content, which is nominally 9% to improve austenite formation in the as-welded condition. There are two embodiments of 2205 (two UNS Numbers) shown in Table 1, as given in ASTM A240, along with the composition of ER2209 as given in AWS A5.9/A5.9M. The S32205 version is usually preferred for welding because the greater lower limit for nitrogen improves austenite formation in the HAZ, but the fabricator did not advise which embodiment was used in the PQR testing. Many steel suppliers provide dual classified material meeting both S31803 and S32205 requirements. It is fairly common to experience unusual corrosion results in ferric chloride exposure tests. Results seem to be much affected by surface preparation. I can’t be sure that surface preparation has affected the fabricator’s results. But it seems safe to say that the fabricator has put the cart in front of the horse. The purpose of ASTM A923-14, as stated in the Scope, Clause 1.1, is “to allow detection of the presence of intermetallic phases in duplex stainless steel to the extent that toughness or corrosion resistance is affected significantly.” To this end, A923 provides for three test methods. Test Method A is a sodium hydroxide etch test of a metallographic specimen. This test produces a dark etching appearance where intermetallic compounds exist. Test Method B is a Charpy V-notch impact test conducted at –40°C (–40°F), looking for evidence of low toughness as a result of intermetallic precipitation. Impact energy below 40 ft-lb (54 J) is taken as evidence of unacceptable intermetallic precipitation. Test Method C is the ferric chloride exposure test the fabricator used. Weight loss greater than 10 mdd is taken as evidence of unacceptable intermetallic precipitation. It should be noted that both Test Method B and Test Method C are indirect means of determining unacceptable intermetallic precipitation. This is where putting the horse in front of the cart comes into play. In introducing Test Method B, Clause 9.1 of A923 states, “Before testing by the Charpy impact test, specimens of the steel may be given a rapid screening test in accordance with Test Method A … Specimens showing Unaffected Structure in Test Method A are acceptable with respect to the absence of intermetallic phases, without the necessity of performing the Charpy test as described in Test Method B.” Likewise, in introducing Test Method C, Clause 15.1 of A923 states, “Before testing by the ferric chloride corrosion test, specimens of the steel may be given a rapid screening test in accordance with the procedures of Test Method A … Specimens showing Unaffected Structure in Test Method A are acceptable with respect to absence of intermetallic phases and need not be tested by the ferric chloride corrosion test as described in Test Method C.” Further, there is no risk to the fabricator in performing Test Method A because Clause 3.1 of A923 begins, “The sodium hydroxide etch test may be used for the acceptance of material but not for rejection.” ASTM A923 provides sets of photomicrographs of S31803 observed after conducting Test Method A. Figure 1 is reproduced from ASTM A923, with microstructure component indicators added. Figure 1A is an Unaffected Structure, which would be accepted without resorting to Test Method B or Test Method C. Figure 1B is a Possibly Affected Structure, which would not be accepted without successfully passing Test Method B or Test Method C — a successful test of either Test Method B or Test Method C is still possible. Figure 1C is an Af- STAINLESS Q&A 18 WELDING JOURNAL / MARCH 2016 BY DAMIAN J. KOTECKI Q: A fabricator prepared a welding procedure qualification for duplex stainless steel Alloy 2205, ½ in. thick. The welding was done by GTAW using ER2209 filler metal, and the maximum heat input was measured as less than 45 kJ/in. (1.8 kJ/mm). The interpass temperature was restricted to 230°F (110°C) maximum. In order to make the PQR as broadly applicable as possible, the fabricator decided to test samples of the weldment for possible intermetallic phase precipitation according to ASTM A923 Standard Test Methods for Detecting Detrimental Intermetallic Phase in Duplex Austenitic/Ferritic Stainless Steels. Test Method C of that standard was used for the evaluation. ASTM A923 Method C involves immersion of the weld in 6% ferric chloride solution at 22°C (71.6°F) for 24 h. The required result for acceptance according to ASTM A923 is no more than 10 milligrams per square decimeter (mdd) weight loss. But the fabricator observed 22 mdd weight loss and asked how to interpret this result. Table 1 — Composition of 2205 Base Metal and ER2209 Filler Metal Composition, wt% (single value is a maximum) Alloy Grade C Mn P S Si Cr Ni Mo N S31803 0.003 2.00 0.030 0.020 1.00 21.0 to 4.5 to 2.5 to 0.08 to 23.0 6.5 3.5 0.20 S32205 0.030 2.00 0.030 0.020 1.00 22.0 to 4.5 to 3.0 to 0.14 to 23.0 6.5 3.5 0.20 ER2209 0.03 0.50 to 0.03 0.03 0.90 21.5 to 7.5 to 2.5 to 0.08 to 2.00 23.5 9.5 3.5 0.20
Welding Journal | March 2016
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