ABSTRACT. This work was part of a na-tionwide program for the development ofnew high-performance steels with 70 ksi(485 MPa) minimum yield strength, im-proved toughness, and lower manufac-turing costs through the elimination ofpreheat for welding. The purpose of thepresent work was to evaluate the fusionzone hydrogen-induced cracking suscep-tibility of single-pass weld deposits madeusing four different welding processes atequivalent diffusible hydrogen levels.The gapped bead-on-plate test was usedto compare shielded metal arc (SMAW),submerged arc (SAW), gas metal arc( G M AW), and flux cored arc (FCAW )welding processes. Equivalent net heatinputs were produced and the weld cross-sectional areas were normalized at differ-ent arc energies, including the heat trans-fer efficiency for each process. The minimum predicted preheatswere different, lower for SAW than forG M AW, FCAW, and SMAW at similardiffusible hydrogen levels and heat in-puts. This difference was attributed to thedifferent solidification microstructuresand weld bead geometries. Pr e h e a t i n gguidelines based on the SMAW processremained the most conservative, con-firming the validity of the past practice ofusing SMAW to find minimum preheats.It was concluded that preheat recom-mendations should not be extrapolatedfrom one welding process to another. Theinformation generated was used for man-ufacturing recommendations for weldinghigh-performance steels.BackgroundFuture construction and retrofitting ofbridges involves the search for economi-cal and safe methods of manufacturing.Weathering steels such as USS Cor-Te n( ASTMA 485W) have traditionally of-fered significant cost savings to the bridgeindustry due to their ability to resist cor-rosion without paint. Corrosion damageand prevention can be a significant factorin bridge maintenance costs, reaching upto 30% of initial costs. Improvements insteel manufacturing processes such asvacuum degassing, lowering carbon andsulfur content, and the addition of cal-cium for sulfide shape control resulted inhigh-performance steels (HPS). Thesesteels have good corrosion resistance, upto 100 ksi (690 MPa) yield strength, lowyield-to-tensile strength ratio, and hightoughness (Refs. 1, 2). Modern high-performance weather-ing steels offer many advantages to thebridge industry, such as high strength, ex-cellent toughness, and less variability inproperties between heats of steels. Inorder for these high-performance steelsto be considered by the bridge construc-tion industry, realistic welding proce-dures must be developed that will capi-talize on the cost saving aspects of thesteels. One such target was reduction orelimination of preheat to lower fabrica-tion costs. Indeed, with the lower hard-enability in the heat-affected zone(HAZ), preheat might not be needed toavoid hydrogen-induced cracking. How-ever, the weld deposit is usually an as-cast microstructure where only chemistryand solidification morphology can beused to control cold cracking susceptibil-ity. Therefore, cracking susceptibility inthese high-strength steels can be ex-pected to be higher in the weld fusionzone (FZ) rather than in the HAZ (Re f s .1, 2).IntroductionHydrogen-induced cracking of welddeposits for joining HPS (A 485W orHPS 70W) quenched-and-temperedsteel, 2-in.- (50.8-mm-) thick plate hasbeen extensively evaluated using thegapped bead-on-plate (G-BOP) test(Refs. 3, 4) — Figs. 1, 2. This test was cho-sen from many simulative weldabilitytests for two reasons: simplicity and reli-ability in quantifying weld fusion zonecracking susceptibility as opposed toHAZ cracking (Refs. 5, 6). Initially, mosttests used the submerged arc welding( SAW) process because bridge fabrica-tors were the first users of this weathering70 ksi HPS, or HPS 70W. The HAZ of HPS 70W has particu-larly low hardenability (Pcm = 0.256) be-cause of low carbon content, small HAZgrain size, and bainitic microstructurethat reaches only 300–350 HV maximum.Previous Tekken (Y -groove) testingshowed these steels do not need preheatto avoid hydrogen-induced cracking inthe HAZ for thicknesses up to 2 in. andlow (up to 4 mL/100g) diffusible hydro-gen (Ref. 3). Therefore, minimum preheat levelsfor the weld fusion zone had been estab-lished for different electrode wire/fluxcombinations, heat inputs, and electrodepolarity using the G-BOP test. However,when trying to compare results with thoseobtained by previous investigators whoused the shielded metal arc welding(SMAW) process, it became obvious thatfor all conditions being equal, use of theS M AW process predicted higher mini-mum preheat temperatures than theSAW process (Refs. 7–9).It was hypothesized there were severalreasons for this difference. First, the weldWelding Process Effects in Weldability Testing of SteelsBY G. ATKINS, D. THIESSEN, N. NISSLEY, AND Y. ADONYIMinimum preheats for avoiding weld deposit hydrogen-induced cracking candepend on the welding process usedKEY WORDSWeldability TestingSAW, GMAW, FCAW, SMAWGapped Bead-on-Plate (G-BOP)G-BOP Testing High-Performance SteelsWeathering SteelsHydrogen-Induced CrackG. ATKINS is Research Associate, D.T H I E SS E N, former Research Associate, is cur-rently with CB&I, and N. NISS L E Y, former Re-search Associate, is currently a graduate studentat The Ohio State University, Columbus, Ohio. Y.ADONYI is Professor and Omer Blodgett Chairof Welding and Materials Joining Engineering atL e Tourneau University, Longview, Te x .61-SWELDING J OURNALWELDING RESEARCH
