Development of weld filler material to match the advanced martensitic heat resistance steel G115 and tailoring the performance by tempering temperature

Abstract

The lack of filler materials is the crucial issue that restricts the wide application of the advanced heat-resistance steel G115 in ultra-super critical (USC) power plants. In the present work, a new welding filler material with alloying system of 8.8Cr-2.7W-2.8Co was successfully developed to fabricate the G115 steel welded joint by the gas tungsten arc welding (GTAW), and post weld heat treatments (PWHT) involving different temperatures were proposed to tailor the mechanical properties. The filler material exhibited perfect compatibility with the base material (BM), and the manufactured welded joint displayed satisfactory appearance and defect-free weld section. After PWHT, full martensitic lath structure decorated with high density of dislocations and dispersed strengthening precipitates M23C6 and MX formed in the weld metal (WM), which was similar with that of the BM. Meanwhile, the welded joint was sensitive to the PWHT temperature, and an optimal combination of hardness (∼240 HV), tensile strength (∼679.9 MPa at 25 °C, and ∼344.6 MPa at 650 °C), elongation (∼13.1% at 25 °C, and ∼15.6% at 650 °C) and impact toughness (∼73.8 J/cm2) could be achieved after PWHT at 760 °C for 240 min. Comprehensively considering the obtained results, the designed filler material was feasible and reliable for matching the novel G115 steel, and satisfied the service demands of the G115 steel pipes in USC power plants.

Keywords

• G115 steel
• Developed filler material
• Post weld heat treatments
• Microstructure
• Mechanical properties