A Novel Classification Method for Carbide Grade by Using a New Shape Factor with Stress Distribution Analysis

The carbide gradation related to geometry size and local stress concentration sensitivity significantly impacts the performance of the carburized 16Cr3NiWMoVNbE steel. The conventional metallurgical graphic comparison method by manual comparison is not capable of grading the carbide gradation automatically. A novel method is thus introduced to automatically evaluate the carbide grade by using a new shape factor φsc with stress distribution analysis instead of using the circularity or roundness shape factor which only considers the geometry shape of carbide particles. The logarithm of the stress concentration factor ln(K) is linearly related to the logarithm of the shape factor ln(φsc). The gradient b of the fitted straight line shows sensitivity to the carbide grade. The gradients are b1 = 0.039, b3 = 0.049, and b5 = 0.055 for the three carbide classes from low to high. Furthermore, there is also a linear relationship between hardness in different grades of carbide microstructure and the gradient b. This study aims to explore a new carbide shape factor φsc$\left(\varphi\right)_{\text{sc}}$ and a novel classification method to quantify the influence of geometry shape on the stress concentration of microstructure. The stress concentration coefficient linearly increases with increasing the shape factor in the double logarithmic coordinate. The linear relationship between the shape factor and the hardness is established.