WEN Juan, ZHANG Qiaoying, YAN Chunlian, JU Xinhua, MENG Yang
The morphology and size of sulfide inclusions in free-cutting steel have a significant impact on the cutting performance of the steel.Currently,there is a lack of effective methods for the evaluation of sulfide inclusions in free-cutting steel in China,which affects the determination of cutting performance and quality of free-cutting steel.In this study,based on the evaluation standards,including the national standard GB/T 10561-2023,the German standard SEP 1572-2019,the French standard NF A04-108-1986,and the newly formulated industry standard in China YB/T 6458-2026,for sulfides in free-cutting steel at home and abroad,4 methods for evaluating sulfides in free-cutting steel were introduced.The evaluation process,content,and results of each method were introduced.The methods adopted in these 4 standards were different.In national standard GB/T 10561-2003,the grade of various types of inclusions is evaluated based on their length and width,and the inclusions include sulfides,aluminum oxide,silicates and oxides.This method is not applicable for the evaluation of sulfide inclusions in free-cutting steel.German standard SEP 1572-2019 is a set of 26 spectra arranged in rows and columns based on the length,width,and area of sulfides.Comparison and image analysis methods are used for evaluation,and the results are represented by K.Z indicating the rows and columns.In French standard NF A04-108-1986,the sulfides are divided into two morphologies,i.e.,spindle-shaped and stringer-shaped.The sulfide inclusions are classified into 9 levels from A to I for comparative evaluation based on the ratio of spindle-shaped to stringer-shaped inclusions.The newly formulated sulfide industry standard in China YB/T 6458-2026 includes the grade assessment of vertical sulfide inclusions and the distribution uniformity assessment of horizontal sulfide inclusions.Wherein the grade assessment of vertical sulfide inclusions is developed based on the adoption of German standard SEP 1572-2019,while the distribution uniformity assessment of horizontal sulfides adopts Delaunay triangulation method.In this paper,some examples were provided to illustrate the image analysis method in German standard and the evaluation method for the transverse distribution uniformity of sulfides in the domestic industrial standard which were relatively difficult to understand,so as to facilitate their better application.Through the description and introduction of various methods,it is hoped that appropriate sulfide evaluation methods can be adopted in practice.This article provided useful reference and support for the research and development of free-cutting steel products.