Table 2 — Example of a Carbon-Steel Filler Metal Intended for Stress-Relieved Applications APRIL 2015 / WELDING JOURNAL 55 rusting, which would be a source of hydrogen. The AWS classification number for low-hydrogen shielded metal arc, fluxcored and submerged arc wire/flux combination filler metals often carries an optional designator, such as H16, H8, or H4. This indicates its maximum diffusible hydrogen level. For example, an H16 electrode will have a maximum of 16 milliliters (mL) of hydrogen for every 100 grams (g) of weld metal. Many low-hydrogen filler metals have at least an H8 rating, with some having a very low hydrogen rating of H4. Low-hydrogen covered electrodes may also carry an optional “R” designator in their AWS number, indicating they have a moisture-resistant coating. This indicates the time that the electrode can be exposed outside a rod oven to increase from 4 h to as much as 9 h (i.e., an entire standard work shift). Notch Toughness Sometimes welding codes or customer specifications require using filler metals with a certain notch toughness and, therefore, must meet a minimum Charpy V-notch (CVN) test value. A weld metal specimen made with a particular filler metal must meet a minimum force rating at a designated test temperature (e.g., 20 ft-lb @ –200F (27J @ –290C)). Most often tests are conducted with weld specimens chilled to colder temperatures in order to get an indication of the metal’s ductile brittle transition temperature (DBTT) or the point where the weld metal’s and HAZ’s microstructure transforms from ductile to brittle. Thus, it becomes more susceptible to failure. As the test temperature decreases, it becomes more difficult to meet the specified minimum force value. Many filler metal classifications (but not all) have a minimum impact toughness requirement and will meet CVN values of 20 ft-lb @ 00F (27 J @ –180C) or even 20 ft-lb @ –200F (27 J @ –290C) (Table 1). Some filler metal classifications will have an optional “J” designator, indicating the consumable meets an even more robust toughness of 20 ft-lb @ –400F (27 J @ –400C). Occasionally, there will be toughness requirements at temperatures as low as –500 to –600F (–450 to–510C). You may need to use a low-alloy filler metal with nickel in order to meet such stringent CVN requirements. Stress Relieved Sometimes welding codes or customer specifications require the weldment to be stress relieved after welding (i.e., PWHT). This is often the case with pressure vessel/power and process piping applications, which are subject to the ASME code, in which “BX” series (e.g., B2, B3, B9) chromium molybdenum (Cr Mo) low-alloy filler metals are used. Regarding filler metal, you should note two things. First, many filler metals typically are not used for stressrelieved applications. Therefore, the filler metal’s mechanical properties may only have been tested in the aswelded condition and not in the stress-relieved condition. Second, while stress relieving does reduce internal stresses caused by welding and increases ductility, it also reduces the weld’s tensile and yield strengths. It might even result in a 10 ksi (69 MPa) drop or more in tensile Mechanical Properties of AWS E71T-12MJ — As required per AWS A5.36/5.36M Yield Tensile Elongation % Charpy V-Notch Strength Strength J (ft lbf) MPa (ksi) MPa (ksi) @ –40°C (–40°F) @ –46°C (–50°F) Requirements AWS A5.36-E71T-12M-JH8 As-welded with 75–80% Ar/Balance CO2 480–620 (70–90) 27 (20) min. — AWS A5.36-E71T1-M21A5-CS2-H8 As-welded with 75–80% Ar/Balance CO2 400 (58) min. 480–655 (70–95) 22 min. — 27 (20) min. AWS A5.36-E71T1-M21P5-CS2-H8 Stress Relieved 1 h @ 620°C (1150°F) with 480–655 (70–95) — 27 (20) min. 75–80% Ar/Balance CO2 Test Results As-welded with 75–80% Ar/Balance CO2 500 (73) 590 (86) 25 134 (99) 125 (92) Stress Relieved 1 h @ 620°C (1150°F) with 440 (64) 545 (79) 33 — 117 (86) 75–80% Ar/Balance CO2 Table 3 — Mechanical Characteristics of AISI 1040 Carbon Steel AISI 1040 Carbon Steel Treatment Tensile Strength Yield Strength Elongation (%) Hardness (Bhn) MPa (ksi) MPa (ksi) Hot Rolled 620 (90) 414 (60) 25 201 Normalized (1650°F (900°C)) 586 (85) 372 (54) 28 170 Annealed (1450°F (790°C)) 517 (75) 352 (51) 30 149
Welding Journal | April 2015
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