Nondestructive Testing of Mechanical Properties of Rolled Steel (Review): 1. Tests of Strength and Plastic Properties

Abstract

This review considers the creation and development of a nondestructive technique based on coercive-force measurements used to determine strength and plastic properties of industrial rolling products made from Russian-produced low-carbon and low-alloy steels. The operating principle for a coercimeter equipped with a field electromagnet is described briefly. Regression lines of mechanical properties versus coercimeter readings are presented for 20 Í -and 09 É 2-steel sheets produced by Nizhni Tagil Iron and Steel Works. Different methods for considering sheet thickness and tube dimensions are discussed.Determined by a steel's strength and plasticity on the basis of only magnetic characteristics H c , four mechanical characteristics of low-carbon and low-alloy hot-rolled steel (ultimate tensile strength σ t , yield stress σ y , relative elongation δ 5 , and reduction in area ψ ) are tested by a nondestructive method that is possible primarily because of a correlation between strength and plasticity. Structural defects in steel impede the motion of dislocations during plastic deformation and thus cause the mechanical strength to increase and the plasticity to decrease. They also contribute to an increase in coercivity that results from the action of various factors.Such rolled products as thick and thin sheets, heavy sections and small shapes, conventional tubes and other articles made of carbon are used in the hot-rolled or normalized state. No substantial structural changes occur during production of these steels. All variations in physical properties are caused by changes in ferrite and ferrite-pearlite structures. These properties are determined by the following main factors [1 − 3]: ferrite-grain size, pearlite content, presence and content of needlelike structures (bainite and Widmanstatten pattern), solid-solution hardening, dispersion hardening, etc. [4][5][6][7].Physical principles of nondestructive magnetic tests of rolled steel's mechanical properties are considered in detail in [8,9]. Therefore, we will not discuss this problem here. We shall only consider the practical use of coercive-force measurements in nondestructive tests of these properties. FIRST STEPSIn 1945, a correlation between mechanical properties and coercivity of rolled steel was already substantiated for 10 ÍÔ steel [10] and the sensitivity of a coercimeter to the free-cementite content, ferrite-grain size, and carbon percentage was established. The linear dependence of ultimate tensile strength σ t on coercimeter readings I p c was established in tensile tear tests and used to substantiate the choice of the correlation model developed to describe the correlation between other mechanical characteristics, including yield stress σ y , relative elongation δ 5 , and reduction in area ψ , on the one hand, and I p c , on the other hand.The techniques developed to determine mechanical properties of rolled steel at Russian manufacturing plants are regulated by both State Standards (GOSTs) and other standards. Consequently, in order to replace suc...

Predicting mechanical properties of cold rolled low carbon steel based on magnetic parameter measurement using artificial neural network

“…In 1945, a correlation between mechanical properties and coercivity of rolled steel was already substantiated for 10KII steel and the sensitivity of a coercimeter to free-cementite content, ferrite-grain size and carbon percentage was established. In the mid-1960s, a correlation between Ultimate Tensile Strength (UTS), Yield Strength (YS), hardness and relative elongation of convectional tubes, on one hand and coercivity H c were studied at Pervouralsky Novotrubny Works [2].in addition in 1960, Mikheev has studied the correlations between magnetic hysteresis loop parameters, like coercivity, Hc, and hysteresis loses, W h , with microstructure and hardness. Swartzendruber and his co-workers have shown that in low carbon steel, H c increases as the square root of plastic strain in 1970 [3].…”

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

“…Equations for the correlation between the impact ductility of I-beam ‹ 60 and I p c readings of a äàîå -1 coercimeter [6] are expressed in a quadratic approximation as (1) (2)…”

“…Normalized equations correlating the impact ductility at various temperatures 1 and the coercivity ( I p c readings of a coercimeter) with ferrite and Widmanstatten grain sizes and structural parameters, on the one hand, and with the volume fractions of pearlite and bainite in 09 É 2 rolled steel (State Standard GOST 19282-73), on the other hand, were obtained in [7][8][9]: 1 Hereinafter, variables with a superscript "n" are presented in equations as X n = ( X -)/ σ x . …”

“…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.…”