Crack Resistance of Drum Steel 15NiCuMoNb5 (Wb36) and Its Welded Joint

A brief description of drum steel 15NiCuMoNb5 (WB36) is presented. The relevance of the analysis of static crack resistance of this steel and its welded joints is substantiated. The metal (WB36 steel) of welded blanks simulating natural drum elements in three modifications (batches) was studied: base, welded, and fusion zones. The tests were carried out at room temperature. The testing methodology complied with the requirements of GOST 25.506-85. For all samples, clearly expressed type IV failure diagrams were obtained (according to GOST 25.506-85). Taking into account their (destruction) viscous nature, the J-integral criterion was used as a characteristic of the static crack resistance of the material. By means of special processing of diagrams with the allocation of the plastic component of the destruction energy, the J-integral values were determined for each sample. The final analysis of the test results is performed in graphical format in accordance with the requirements of the standard. Based on the obtained data, J-integral dependencies on the length of the grown static crack were found for each batch of metal studied. Taking into account the significant spread of experimental points for each modification of the metal, it is proposed to generalize the obtained dependencies and consider their generalized version as an estimated characteristic of the critical J-integral of the metal (steel WB36) of welded products, which corresponds in quantitative terms to a range of values of approximately 0.4–0.6 MJ/m². The characteristics of the critical stress intensity factors (SIF) calculated from these values were approximately 300 to 370 MPa m^0.5. A calculation of the load-bearing capacity of a drum with a surface crack in the longitudinal weld zone carried out using the research results showed that the maximum permissible depth for extended cracks should not exceed approximately one third of the shell wall thickness.