Determination of strength characteristics of high-strength sheet steels by hardness and instrumented indentation

Abstract

The paper considers the method of instrumented indentation to evaluate the strength of high-strength steel sheets as one of the fastest and more accurate methods of nondestructive testing. Many different types of tests are used to determine the strength characteristics of metals. Tensile and hardness tests are the most common. Tensile tests are labor and energy-intensive, whereas hardness tests are less accurate compared to the instrumented indentation. The advantage of the instrumented indentation method as compared to the standard hardness measurement method lies in the following: the possibility to directly register the entire process of continuous local deformation of the material using the indenter, high speed and simplicity due to the process automation, as well as no visual measurement of the indentation imprint diameter. In addition, the correlation relationships for determining the strength characteristics of the indentation diagram parameters are valid for a wide class of materials. The authors use different methods, namely, uniaxial tension tests, Brinell hardness tests and instrumented indentation method, comparative analysis of the strength characteristics of 28GKhNMR and 20GR sheet steels with the thickness of 10 mm, and 30Kh2CN2MFA and 28GR steels with the thickness of 6 mm for special structures production to confirm the efficiency of the instrumented indentation test method. To assess the accuracy of the determination of strength characteristics by the method of instrumented indentation, the authors employed the procedure to determine the strength of high-strength steels via the Brinell hardness. As a result, deviations of certain strength characteristics Rp0.2 and Rm of the studied steels, as compared with the corresponding strength characteristics in uniaxial tension, do not exceed 10.4%. At the same time, deviations of strength characteristics obtained by the instrumented indentation method from the tensile strength characteristics do not exceed 5.2%.