Strain partition, uniform elongation and fracture strain in dual-phase steels

Abstract Heat treatment of a commercial dual-phase steel by either intercritical annealing or step quenching produced dual-phase steels of the same compositions but different amounts and morphologies of martensite and ferrite. The average local surface strains in martensite and alloy were evaluated microscopically during tensile deformation of several step-quenched steels by means of a fine grid applied by photolithography. The strain ratio ϵ α / ϵ m (where α means ferrite and m martensite) increases with increasing martensite content and alloy strain. The derived stress ration σ m / σ α , a measure of load transfer, decreases with increasing martensite content but is fairly constant with increasing strain. It is shown analytically and experimentally that the uniform strain of the alloy may be regarded as a force-weighted average of the in situ necking strains of the constituents (after Garmong and Thompson), if alloy strain is linearly dependent on the constituents' strain. Also, a descriptive expression was derived which relates the fracture strain to the strain-hardening parameter of the alloy, the void fraction and the rate of increase in void fraction with increasing strain. The expressions derived for uniform strain and for fracture strain also describe the behavior of spheroidized steels.

[1]  A. C. Mackenzie,et al.  On the influence of state of stress on ductile failure initiation in high strength steels , 1977 .

[2]  J. Gurland,et al.  A Study of the Deformation and Fracture of a Dual-Phase Steel , 1982 .

[3]  N. C. Goel,et al.  A theoretical model for the flow behavior of commercial dual-phase steels containing metastable retained austenite: Part II. calculation of flow curves , 1985 .

[4]  R. G. Davies.  Influence of martensite composition and content on the properties of dual phase steels , 1978 .

[5]  W. Tyson,et al.  Grain size dependence of yield and flow stresses for an FeMnSi alloy , 1984 .

[6]  F. A. McClintock,et al.  A Criterion for Ductile Fracture by the Growth of Holes , 1968 .

[7]  D. M. Tracey,et al.  On the ductile enlargement of voids in triaxial stress fields , 1969 .

[8]  J. Hancock,et al.  On the mechanisms of ductile failure in high-strength steels subjected to multi-axial stress-states , 1976 .

[9]  J. D. Embury,et al.  A model of ductile fracture based on the nucleation and growth of voids , 1981 .

[10]  George Krauss,et al.  A consideration of models describing the strength and ductility of dual-phase steels , 1980 .

[11]  B. Karlsson,et al.  Inhomogeneity in plastic deformation of two-phase steels , 1974 .

[12]  W. S. Owen,et al.  The dependence of some tensile and fatigue properties of a dual-phase steel on its microstructure , 1985 .

[13]  S. Mileiko.  The tensile strength and ductility of continuous fibre composites , 1969 .

[14]  J. R. Fisher,et al.  Void nucleation in spheroidized carbon steels Part 1: Experimental , 1981 .

[15]  G. Krauss,et al.  The effect of structure on the deformation of as-quenched and tempered martensite in an Fe-0.2 pct C alloy , 1976 .

[16]  R. B. Thompson,et al.  A Theory for the mechanical properties of metal-matrix composites at ultimate loading , 1973 .

[17]  H. Margolin,et al.  Alpha-Beta Interface Sliding in Ti-Mn Alloys , 1983 .

[18]  J. R. Fisher,et al.  Void nucleation in spheroidized carbon steels Part 2: Model , 1981 .

[19]  L. Durand,et al.  Tensile deformation of a two-phase copper-silver alloy , 1981 .

[20]  T. C. Lei,et al.  Microscopic deformation behaviour of martensitic–ferritic dual-phase steels , 1986 .

[21]  W. C. Leslie,et al.  The physical metallurgy of steels , 1981 .

[22]  G. Thomas,et al.  Effects of morphology on the mechanical behavior of a dual phase Fe/2Si/0.1C steel , 1981 .

[23]  R. G. Davies.  The deformation behavior of a vanadium-strengthened dual phase steel , 1978 .

[24]  H. Margolin,et al.  A rationalization of stress-strain behavior of two-ductile phase alloys , 1986 .

[25]  T. Gladman,et al.  Work hardening of dual-phase steels , 1981 .

[26]  K. Tsumuraya.  Reply to comments on “coarsening models incorporating both diffusion geometry and volume fraction of particles” , 1984 .

[27]  H. Stüwe,et al.  Evidence for lattice-diffusion controlled superplasticity in a SnPb-eutectic , 1981 .