Low-cycle fatigue of steel 15NiCuMoNb5 (WB36) and its welded joint

The results of studying the low-cycle fatigue characteristics of steel 15NiCuMoNb5 (WB36) and its welded joints are presented. Brief information is given on the specific features of WB36 steel proceeding from the nalysis of literature data. An emphasis is made on the absence of available information on the studies of WB36 steel and its welded joints produced in Russia. The study was carried out on an experimental welded metal billet produced by standard technology and simulating a full-scale fragment of a high-pressure drum. The methodological aspects of the conducted research are described. Tests for low-cycle fatigue of WB36 steel and its welded joints were performed in the mode of hard loading in a symmetrical cycle at room (20 – 25°C) and operating (350°C) temperatures. Corset-type tensile and compression samples were used; the onset of a macro-fracture on the surface of the corset part was taken as the criterion for the destruction of the sample. It is shown that with an increase in the test temperature, the resistance to low-cycle fatigue of steel and weld metal decreases. At the same time, the base metal and the weld metal demonstrate identical characteristics of low-cycle fatigue at each of the test temperatures. A certain part of the study touched the effect of temperature ageing on the low-cycle fatigue of steel. It is shown that the values of the low-cycle strength of the material under study slightly exceeds the results of similar tests of WB36 steel presented in foreign technical literature. A comparative analysis of experimental low-cycle fatigue curves and corresponding standard calculation curves obtained using analytical expressions for the actual mechanical properties of steel has shown that experimental data on the low-cycle fatigue of steel demonstrate a higher fatigue resistance at room temperature and approximately a similar level at operating temperature compared with calculated fatigue curves obtained using the mechanical properties of the metal. An example of the low-cycle fatigue calculation for a high-pressure drum of a steam-gas recovery boiler is given. It is confirmed that for the given initial parameters and resource indicators, conditions of the drum strength met the criteria of low-cycle fatigue.

1. Yannan D., Bin R., Longxian L., et al. Analysis of Mechanical Properties of 15NiCuMoNb at Different Temperatures / IOP Conf. Series: Earth and Environmental Science. 2019. Vol. 330(2019). 042046. P. 1 – 5. DOI: 10.1088/1755-1315/330/4/042046

2. Fohl J., Willer D., Katerbau K.-H. Effect of Copper Precipitates on the Toughness of Low Alloy Steels for Pressure Boundary Components / 30th MPA-Seminar in conjunction with the 9th German-Japanese Seminar. Stuttgart. 2004. October 6 and 7. P. 11.1 – 11.15.

3. Ney H., Cawelius R., Hanus F., Richter K. DIWA — the favourized steel for boilers and pressure vessels. Dillinger Hutte GTS, describe the production, materials and working properties of boiler making steel 15NiCuMoNb5 otherwise known as DIWA 373/H / Hydrocarbon engineering. 2002. December. P. 7.

4. Grin E. A., Pchelintsev A. V., Zelenskii A. V., Sarkisyan V. A. Set of drum steel 15NiCuMoNb5 (WB36) metal and welded joint service properties / Power Technol. Eng. 2023. Vol. 57. N 3. P. 431 – 437. DOI: 10.1007/s10749-023-01681-y

5. Mail K., Blind D., Vasoukis G., et al. Determination of cycle dependent material properties for a design concept on the basis of limited plastic strains with regard to environmental effects / International conference on low cycle fatigue and elasto-plastic behavior of materials, 1987, Munich, Germany. P. 512 – 517. DOI: 10.1007/978-94-009-3459-7

6. Altpeter I., Dobmann G., Katerbau K., et al. Copper precipitates in the steel 15 NiCuMoNb 5 (WB 36): Material properties and microstructure, atomistic simulation, NDE by micromagnetic techniques / Proceedings of the 25 MPA Seminar. Stuttgart. 1999. 7 – 8 October.

7. Izotov V. I., Iliuhin D. S., Getmanova M. E., Filippov G. A. The influence of copper on the structure and mechanical properties of pearlitic steel / Fiz. Met. Metalloved. 2016. Vol. 117. N 6. P. 609 – 614 [in Russian]. DOI: 10.7868/S0015323016040070

8. Kumar S., Ramesh T., Asokkumar K. Welding Studies on WB36 for Feed Water Piping / International Journal of Computational Engineering Research (IJCER). 2016. Vol. 6. Issue 5. P. 36 – 52.

9. Dobmann G., Boller C., Herrman H.-G., Altpeter I. R&D to lifetime management — ND-characterization of ageing phenomena / E-Journal of Advanced Maintenance. 2013. Vol. 5-1. P. 15 – 24.

10. Schmauder S., Uhlmann D., Zies G. Experimental and numerical investigations of two material states of the material 15 NiCuMoNb5 (WB 36) / Computational Materials Science. 2002. Vol. 25(1). P. 174 – 192.

11. Grin E. A., Pchelintsev A. V., Zelenskii A. V., et al. Investigation of the effect of temperature aging on the complex of service characteristics of steel 15NiCuMoNb5 (WB36). Part I. The effect of temperature exposure on the structural parameters and microdistribution of the elemental composition of WB36 steel / Élektr. Stantsii. 2023. N 12. P. 10 – 21 [in Russian]. DOI: 10.34831/EP.2023.1109.12.002

12. Grin E. A., Pchelintsev A. V., Zelenskii A. V., Sarkisyan V. A. Basic properties of steel 15NiCuMoNb5 (WB36) workpiece / Power Technol. Eng. 2023. Sept. Vol. 57. N 3. P. 424 – 430. DOI: 10.1007/s10749-023-01680-z

13. Grin E. A., Sarkisyan V. A., Zelenskii A. V., Pchelintsev A. V. Investigation of the effect of temperature aging on the complex of service characteristics of steel 15NiCuMoNb5 (WB36). Part III. The effect of thermal aging on mechanical properties and critical temperature of brittleness / Élektr. Stantsii. 2024. N 2. P. 2 – 10 [in Russian]. DOI: 10.34831/EP.2024.1111.2.001

14. Makhutov N. A., Gadenin M. M., Cherniavsky O. F., Cherniavsky A. O. Mechanical properties of materials in calculations of low cycle deformation of structures / Industr. Lab. Mater. Diagn. 2022. Vol. 88. N 6. P. 52 – 59 [in Russian]. DOI: 10.26896/1028-6861-2022-88-6-52-59

15. Gadenin M. M. Study of the regularities of resistance to deformation and damage accumulation under irregular low cycle loading / Industr. Lab. Mater. Diagn. 2021. Vol. 87. N 11. P. 55 – 63 [in Russian]. DOI: 10.26896/1028-6861-2021-87-11-55-63

16. Serensen S. V. Resistance of materials to fatigue and brittle fracture. — Moscow: Atomizdat, 1975. — 192 p. [in Russian].

17. Makhutov N. A. The generalized regularities of damageability and integrity in estimations of the endurance in conditions of variability of loading regimes / Industr. Lab. Mater. Diagn. 2019. Vol. 85. N 9. P. 61 – 65 [in Russian]. DOI: 10.26896/1028-6861-2019-85-9-61-65

18. Komisarchik I. N. Temperature fields and stresses in the walls of boiler drums during kindling and stoppages / JSC «NPO TsKTI» collection. Issue 118. — Leningrad, 1972. P. 38 – 54 [in Russian].