Nondestructive Testing of Mechanical Properties of Rolled Steel (Review): 2. Testing of Ductile Properties

Abstract

The results of the first studies that established a correlation between impact ductility and coercivity are considered in this review. The data of studies on the search for the factors that encourage or inhibit this correlation are analyzed. The methods based on estimation of the coercivity, which ensure increased reliability of nondestructive testing of rolled steel with a tendency toward brittle fracture, are discussed. The experimental data on nondestructive tests of impact ductility carried out using a sharp notch are analyzed.In the first part of this review [1], the nondestructive testing techniques used to examine strength and plastic properties of low-carbon and low-alloy hot-rolled steels are considered. Emphasis should be placed on nondestructive testing of impact ductility. Firstly, the absence of nondestructive tests for this characteristic lessens the value of applying a testing technique for the strength and plasticity of rolled steel, because the test is intrinsically incomplete. Secondly, development of this technique has encountered objections from specialists who, however competent in their field of knowledge, are unfamiliar with the modern advances in technologies that provide high purity of a metal. The essence of these objections is that nonmetallic inclusions, impurities, etc., when distributed mainly at grain and phase boundaries and, consequently, loosening intergrain (interphase) bonds, are indistinguishable from the boundaries themselves for any characteristics used in nondestructive testing.Thus, first of all, the experiments that attempt to determine the relations between impact ductility and coercivity will be considered. The factors that promote or inhibit this correlation and the techniques developed to increase reliability of ductile tests will be discussed.A curve of impact ductility at -40 ° C KCU -40 plotted versus the coercivity ( I r 0 readings of a äàîå -1 ‡ coercimeter [2, 3]) for 09 É 2-steel sheets 16-20 mm thick is shown in Fig. 1 [4 , 5]. This plot is based on the data from coercimetric tests of sheets' strength and plastic properties that were obtained over the course of a year during measurements of I r 0 of impact-test samples. The statistical database was based on 2500 results of magnetic and impact tests. The mean value of impact ductility is = 0.84 MJ/m 2 , the rms deviation of impact ductility from the regression line is σ n = 0.24 MJ/m 2 , and the correlation ratio is η y / x = 0.6. The plot also shows the calculated lower confidence boundary (LCB) of the experimental points spread around the regression line at a confidence level of 0.95. The mean square deviations of KCU -40 were determined over intervals I r 0 . According to the State Standards GOST 5521-76, GOST 19281-73, KCU 40 -MAGNETIC METHODS 20 40 60 80 100 0 0.2 0.4 0.6 0.8 1.0 AL CI LCB I r 0 , div KCU -40 , MJ/m 2 Fig. 1. Correlation curve of impact ductility versus-äàîå -1a coercimeter readings measured at − 40 ° C for 09 É 2-steel sheets 16-20 mm thick.

Modern Technologies of Metal Processing in the Socio-Cultural Context

“…They allow to obtain characteristics of mechanical properties without taking the necessary material for manufacturing samples and testing them in the laboratory. The greatest application in the practice into non-destructive testing of mechanical properties for steel products is obtained by residual magnetization and coercive field force [4][5][6].…”