Influence of Post-Weld Heat Treatment on Mechanical Properties and Fracture Character of Welded Joints of Steel Grade P91

Steel P91 is a heat-resistant steel with a high chromium content used in the manufacture of boiler and steam pipeline components operating at steam pressures up to 31 MPa and temperatures up to 600 °C. However, increased diffusion creep, which causes the formation of type III or IV cracks in the heat-affected zone (HAZ) of a welded joint, significantly reduces the service life of welded structures made from this steel. The purpose of the work is to develop a technology combining preand post-weld heat treatment (PWHT) of steel to ensure equality of the microhardness values of the weld and HAZ, while maintaining its high impact toughness. The work investigates the effect of PWHT regimes of P91 steel on the mechanical properties and nature of destruction during impact bending testing of a weakened sector in the HAZ. Experimental dependences of the fracture force on time during a pendulum impact and the deflection of samples on the fracture force were obtained, using which the following were determined: crack initiation energy, total fracture energy, maximum deflection of the sample before fracture, maximum force and fracture force, time before fracture. It is shown that a combination of fivefold pre-weld thermal cycling treatment (TCT) in the temperature range of 700–1050 °C with subsequent TIG welding with heat input of no more than 4.4 kJ/cm in each pass and fivefold post-weld TCT in the range of 700–1050 °C with subsequent fivefold TCT in the range of 300–700 °C allows to increase the impact toughness values to – 96.8 J/cm2 in the weakened HAZ zone, which significantly exceeds the impact toughness value (29 J/cm2) in the weakened HAZ zone during standard heat treatment. At the same time, due to preand post-weld TCT, it was possible to achieve maximum stability of microhardness values – in the HAZ

1. Hurtado-Noreña C., Danón C. A., Luppo M. I., Bruzzoni P. (2015) Evolution of Minor Phases in a P91 Steel Normalized and Tempered at Different Temperatures. Procedia Materials Science, 8, 1089–1098. https://doi.org/10.1016/j.mspro.2015.04.172.

2. Panteleenko F. I., Zelenin V. A., Minkov A. L. (2024) Research of Fracture Mechanism of Steel Grade P91 on Impact Bending After Preheat Treatment Before Welding. Litiyo i Metallurgiya = Foundry Production and Metallurgy, (4), 85–94. https://doi.org/10.21122/1683-6065-2024-4-85-94 (in Russian).

3. Panteleenko F. I., Zelenin V. A., Minkov A. L. (2024) The Influence of Preliminary Heat Treatment Regimes on the Structure and Mechanical Properties of Welded Joints Made of P91 Steel. Sovremennye Metody i Tekhnologii Sozdaniya i Obrabotki Materialov: sb. nauch. tr. Kn. 2 [Modern Methods and Technologies for the Creation and Processing of Materials Collection of Scientific Papers. Book 2]. Minsk, Physical-technical Institute of the National Academy of Sciences of Belarus, 48–63 (in Russian).

4. Herzberg R. V. (1989) Deformation and Fracture Mechanics of Engineering Materials. Moscow, Metallurgiya Publ. 1989. 576 (in Russian).

5. Efimenko L. A., Prygaev A. K., Elagina O. Yu. (2007) Metal Science and Heat Treatment of Welded Joints. Moscow, Logos Publ. 456 (in Russian).

6. Khromchenko F. A. (2002) Resource of Welded Joints of Steam Pipelines. Moscow, Mashinostroenie Publ. 352 (in Russian).

7. Panteleenko F. I., Snarsky A. S. (2010) Methodology for Assessing the Condition of Materials of Critical Metal Structures. Minsk, Belarusian National Technical University. 196 (in Russian).

8. Gu Z., Zhong M., Minkov A., Panteleyenko F., Wang C. (2024) Enhanced creep lifetime in P91 steel weldments via stabilizing tempered martensite structure. International Journal of Pressure Vessels and Piping, 212, 105361. https://doi.org/10.1016/j.ijpvp.2024.105361.

9. Fedyukin V. K. (1991) Thermal Cycling: Technology, Structure and Properties of Metallic Materials. Leningrad, Institute of Mechanical Engineering of the USSR Academy of Sciences. 310 (in Russian).

10. Smagorinsky M. E., Bulyanda A. A., Kudryashov S. V. (1992) Handbook of Thermomechanical and Thermal Cycling Processing of Metals. Saint Petersburg, Politekhnika Publ. 414 (in Russian).