New research highlights the benefits of an innovative welding technique, Activated Tungsten Inert Gas (A-TIG), over its conventional counterpart—Tungsten Inert Gas (TIG) welding—revealing significant advantages in terms of thermal and mechanical properties when applied to P91 steel. An in-depth thermo-mechanical analysis indicates that A-TIG exhibits reduced detrimental effects, not only enhancing penetration depth but also minimizing distortion and residual stress.
Conducted by a team of researchers, the study utilized 4 mm thick P91 steel plates, employing a custom-developed oxide flux during the welding process. The experimental setup recorded thermal cycles via thermocouples and assessed residual stresses with X-ray diffraction (XRD) methods. This combination allowed for precise measurement of welding impacts, ensuring rigorous analysis of results.
During the comparison, it was found that A-TIG produced a narrow and deep penetration with less heat transferred to the base metal relative to traditional TIG welding. Specifically, the fusion zone (FZ) and heat-affected zone (HAZ) were 10% and 34% wider with the TIG process, respectively. Furthermore, the maximum stress observed in A-TIG reached 471 MPa near the weld bead, whereas TIG resulted in a slightly higher peak of 509 MPa, demonstrating an 8% reduction in stress with A-TIG.
Another significant finding of the study was the reduction in distortion associated with A-TIG welding, with values 36% lower than those observed with traditional TIG methods. The researchers achieved this through a finite element method (FEM) simulation using SYSWELD, which aided in accurately predicting the thermal and mechanical results, closely aligning with experimental measurements.
The experimental process involved fabricating square butt joints from P91 steel plates, with specific measurements of 300 x 250 mm dimensions. Initial welding was conducted using conventional TIG before applying the A-TIG technique to the same plates. Measurements showed that the size of the FZ in the TIG-welded joints measured 7.44 mm, which was reduced to 6.72 mm in the A-TIG counterparts. HAZ sizes also demonstrated a decrease, from 17 mm in the TIG process to 11.2 mm using A-TIG.
Thermal analysis indicated peak temperatures during welding, reaching a maximum of 1713 °C for TIG and 1645 °C for A-TIG. Additional measurements at a 10 mm distance from the weld centerline confirmed that A-TIG welding had lower peak temperatures (653 °C) compared to TIG (721 °C). These findings emphasized that A-TIG provides better thermal control during the welding process, ultimately improving the quality of the weld.
Mechanical analysis further reinforced the benefits of A-TIG. Stress distribution patterns revealed high-stress concentrations following the HAZ due to material shrinkage during cooling. A comparative analysis showed that A-TIG not only achieved a maximum stress of 471 MPa—lower than TIG’s 509 MPa—but also presented a compressive stress profile, advantageous for weld integrity. In contrast, TIG welding exhibited tensile stresses predominantly.
Distortion measurements post-welding highlighted significant differences, with traditional TIG demonstrating a maximum distortion of 3.64 mm, while A-TIG showed reduced distortion at 2.35 mm. This represents a quantifiable 27% reduction, thereby showcasing A-TIG’s effectiveness in minimizing shape alterations during cool-down periods.
The study's conclusions stress the reliability and efficacy of the FEM-based simulations, affirming their relevance in predicting welding outcomes. The findings advocate for broader adoption of A-TIG in various industries, particularly those requiring high precision in welding applications like power plants and nuclear facilities.
In summary, this comparative analysis reveals that A-TIG welding is a superior method for working with P91 steel, offering enhanced penetration, reduced residual stresses, and lower distortion—making it a compelling choice for future welding applications.
