Experimental and numerical investigations of two material states of the material 15 NiCuMoNb5 (WB 36)

Abstract

In this contribution, results are presented of mechanical, technological and fracture-mechanical characterization of low alloyed warm strength steel 15 NiCuMoNb5 (WB 36, material No. 1.6368) in two states of the melt E60 at a temperature of 90 °C including the determination of damage mechanical parameters for the Rousselier model. The two states of the material are the initial state (denominated as E60A) and the aged state (denominated as E60B). The aged condition characterizes the material after 57,000 h at a service temperature of 350 °C. In service this material produces significant copper precipitates above 300 °C. These copper precipitates are the reason for strength increase as well as a shift of the transition temperature regime of the “notch” impact energy to higher temperatures. Size, shape, orientation and frequency distribution of non-metallic inclusions are found to be similar for both material states. In comparing the frequency distributions of the copper particles for both material states a significant increase of copper particles with a size between 2 and 7 nm results. The damage mechanical results show that the Rousselier parameters for the initial state can be transferred to the aged state. The strength increase due to aging can be considered through the respective yield curves in the computer simulations. A comparison of multiaxiality relations for different specimen geometries shows that the curves of the multiaxiality coefficient q in the ligament remains principally unchanged by the strength increase at identical specimen geometries. The crack resistance behaviour determined in the experiment at CT specimens correlates with the numerically determined q-values in the ligament for both material states E60A and E60B.