Abstract Scope |
Introduction: This study investigates the effect of multipass/temper bead welding on Stress Relief Cracking (SRC) in Grade 11 and Grade 22 steels. Experimentation and modeling are utilized to correlate SRC susceptibility to thermal history and microstructure. The CGHAZ, which is commonly associated with SRC, can be reheated from subsequent weld passes affecting both carbide precipitation behavior SRC susceptibility and. The objective of this study is to determine how CGHAZ reheating from subsequent weld passes affects cracking susceptibility and to simulate the related HAZ carbide precipitation kinetics during multipass weld and PWHT. Procedure: The OSU SRC Test was used to quantify SRC susceptibility. Dog bone samples were preloaded with tensile stress at room temperature, brought to the PWHT temperature, and held at constant displacement until crack nucleation and failure. Test samples with simulated CGHAZ microstructure were reheated to various peak temperatures, ranging from 700C to 1150C before SRC testing. TC-PRISMATM was utilized to create carbide precipitation models and determine the kinetics of M23C6, M7C3, M2C, and Cementite during reheating cycles and PWHT. TEM diffraction analysis was utilized to identify carbides and validate TC-PRIMSA model findings. Results/Discussion: SRC testing found that reheats greater than 750C and less than 1050C reduced SRC susceptibility. 1050C is theorized to be the temperature complete carbide dissolution occurs leading to a strong carbide reprecipitation reaction during PWHT and SRC susceptibility. With adequately high or multiple reheats below the AC1 temperature, SRC susceptibility was eliminated. The two controlling factors for cracking were the level of tempering in samples reheated below AC1 and the onset of complete carbide dissolution for samples reheats above AC3. TC-PRIMSA results found tempering that occurs during the rapid heating and cooling of subsequent weld passes is primarily carried out through Cementite precipitation. However, the slow heating rate to PWHT temperature promoted M2C precipitation. Mo2C is commonly associated with increased SRC susceptibility. If adequate Cementite precipitation occurred before SRC testing, Mo2C precipitation was suppressed. TC-PRIMSA models of reheat conditions that showed Mo2C suppression corresponded to SRC resistant test results. TEM diffraction analysis was able to identify various carbides in the Grade 22 microstructure. Cementite carbides were found in the CGHAZ sample that was reheated to 785C, which corresponds to modeling predictions. M23C6 carbides were identified in the base metal which corresponds to the stable equilibrium carbide state. Further TEM analysis aims to validate the TC-PRIMSA carbide predictions during PWHT in the various samples simulating multipass welding. Conclusions: CGHAZ reheats from simulated subsequent weld passes greatly impacted SRC susceptibility. SRC resistance was observed when reheats below the AC1 temperature adequately tempered the microstructure through cementite precipitation, or reheats above AC3 temperature led to significant grain refinement or incomplete carbide dissolution. TC-PRISMA found a correlation between Mo2C precipitation and SRC susceptibility based on pretest cementite formation. Further work is being conducted to identify carbides and validate models through TEM analysis. |