Automatic Detection of Pearlite Spheroidization Grade of Steel Using Optical Metallography

Abstract

To eliminate the effect of subjective factors during manually determining the pearlite spheroidization grade of steel by analysis of optical metallography images, a novel method combining image mining and artificial neural networks (ANN) is proposed. The four co-occurrence matrices of angular second moment, contrast, correlation, and entropy are adopted to objectively characterize the images. ANN is employed to establish a mathematical model between the four co-occurrence matrices and the corresponding spheroidization grade. Three materials used in coal-fired power plants (ASTM A315-B steel, ASTM A335-P12 steel, and ASTM A355-P11 steel) were selected as the samples to test the validity of our proposed method. The results indicate that the accuracies of the calculated spheroidization grades reach 99.05, 95.46, and 93.63%, respectively. Hence, our newly proposed method is adequate for automatically detecting the pearlite spheroidization grade of steel using optical metallography.

Label Noise Learning Method for Metallographic Image Recognition of Heat-Resistant Steel for Use in Pressure Equipment

“…However, these estimation processes are always affected by the subjective judgments of these inspectors. Therefore, automatic recognition techniques have become an important approach to elimination of the influence of these subjective factors during manual determination of the spheroidization grades [ 3 ]. Deep learning models require manually labeled data for training to allow them to obtain optimal parameters.…”

“…However, pearlite spheroidization will occur in chrome-molybdenum steel after long-term exposure to a high-temperature environment, and this results in material degradation or even structural failure. Therefore, spherular pearlite gradation is an important evaluation indicator used to judge the performance of chrome-molybdenum steel [ 2 , 3 ]. In practice, the gradation of spherular pearlite is determined by metallographic examination, which is a microscopic examination method used to establish the microstructures and damage modes of metal materials, as illustrated in Figure 1 .…”