Hardness, Microstructure, and Residual Stresses in Low Carbon Steel Welding with Post-weld Heat Treatment and Temper Bea
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POST-WELD heat treatment (PWHT) is commonly employed to recover deteriorated mechanical properties, relieve the locked-in residual stresses, diffuse trapped hydrogen, and temper the microstructure of the heat affected zone (HAZ).[1–4] PWHT is usually performed depending on the thickness or the alloy content of the component being repaired. Even though PWHT is essential after any weld repair, there are a number of associated limitations. For example, PWHT on large and heavy steel components in electrical utilities and petrochemical refineries is extremely expensive and time consuming. Sometimes PWHT is almost impossible to carry out if there are any mechanical loads attached to the structure, since significant deformation may occur at the elevated temperatures of the PWHT cycle. Multi schemes of PWHT may also cause degradation of the material properties, especially creep and tensile strength. PWHT is also very difficult to employ if it desired to treat complex geometries because it requires heating of larger areas.
ABDULKAREEM S. ALORAIER, is with the Department of Manufacturing and Welding Technology, The Public Authority for Applied Education and Training, Shuwaikh, Kuwait City 70654, Kuwait. SURAJ JOSHI, is with the Department of Mechanical and Industrial Engineering, Concordia University, 1515 St. Catherine Street West, Montre´al, QC H3G 2W1, Canada. Contact e-mail: [email protected] JOHN W.H. PRICE, is with the Department of Mechanical and Aerospace Engineering, Monash University, Clayton, VIC 3168, Australia. KHALED ALAWADHI, is with the Department of Automotive and Marine Technology, The Public Authority for Applied Education and Training. Manuscript submitted August 23, 2013. METALLURGICAL AND MATERIALS TRANSACTIONS A
An alternative to PWHT is temper bead welding (TBW), which attempts to control deposition of the weld layers during weld repairs.[5–9] The first layer (buttering layer) should be deposited with low heat input to ensure minimum penetration but must be sufficient to secure fusion into the parent material, whereas the subsequent layer (tempering layer) is deposited with higher heat input to allow penetration through the first layer. The heat of the second layer will refine and temper the coarse grained heat affected zone (CGHAZ) of the first layer and thus provide substantially improved HAZ notch toughness and eliminate the possibility of reheat cracking. Tempering of the HAZ is very important because it makes the HAZ less susceptible to cracking during exposure to service conditions. TBW requires the production of many test welds and metallographic examination before sufficient confidence can be gained to perform the actual repair weld. In industry, most weld repairs that use the TBW technique are carried out by the manual metal arc welding (MMAW) process. However, using flux cored arc welding (FCAW) in weld repairs can provide better control over the current, voltage, heat input, stick-out distance, gas flow rate, wire feeding rate, and the velocity of the weld torch, which are very important fac
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