Influence of vacuum carburizing treatment on fatigue crack growth characteristic in DSG2

Abstract

ABSTRACT.The aim of this research is to clarify the influence of vacuum carburizing on the fatigue-crack progress characteristics of DSG2 steel. The test specimen tempering material (QT material) and vacuum carburizing material (VC material) has been used. The fatigue-crack progress was examined by subjecting the samples to four-point bending. The loading-capacity fixed experiment was done using a maximum load of P max = 4000-7000 N. The ΔK fixed experiment was done using a load of ΔK = 18-36 MPa√m. The crack progress speed of VC material fell, after the high crack progress speed was shown, and after it showed the minimum, it showed the tendency to go up again. This is considered to be what is depended on the compressive residual stress given to the carburizing layer. From this, it is thinkable that there is a crack progress depression effect in a carburizing layer. In VC material, a carburizing layer has a crack progress depression effect from a plunger-helix bottom to about 2.6 mm, and it turned out that it is larger than an effective carburizing layer. Moreover, in each ΔK, it was shown that depression effect revelation differs and the crack progress process accompanying it was able to be shown typically.

Multi-parameter fracture mechanics

“…In connection with the experimental research intended by the authors, following recommendations can be concluded: The experimental campaign should be performed (as much as possible) on SCB specimens with larger cracks and larger initial deflection angles  in order to be able to investigate the effect of the higher-order terms considered in the generalized fracture criteria on estimation of further crack propagation angles. If the suggested approach is not able to describe the crack path in the fine-grained composite based on the alkali-activated slag as a quasi-brittle material, other fracture criteria (that are more suitable for non-brittle fracture and mixed-mode conditions) should be applied, such as maximum average tangential stress (MATS) criterion [29] or others. Another possibility is to use so-called Equivalent Material Concept (EMC) suggested recently by Torabi [30] and consider a virtual brittle material exhibiting linear elastic behaviour instead of the real quasi-brittle one; details on this concept can be found in the referred literature.…”