Bauschinger effect and residual phase stresses in two ductile-phase steels: Part II. The effect of microstructure and me
- PDF / 747,517 Bytes
- 8 Pages / 594 x 774 pts Page_size
- 39 Downloads / 208 Views
I.
INTRODUCTION
IN the first part of this investigation, the forward and reverse stress-strain curves of dual-phase steels were calculated from those of the ferrite and martensite single phase constituents. The results support the idea that the phase stress, a long-range internal stress produced by the misfit of strain between two phases, is the dominant factor controlling the Bauschinger effect in multiphase materials. In this part of our paper, we attempt to correlate the BE parameters with the microstructural features and mechanical properties of these materials. The finite-element method (FEM) has been used to calculate the effect of matrix, particle size and shape, phase volume fraction, etc., on the forward stress-strain curves of two ductile-phase materials and has also been studied to evaluate the average internal stress and inhomogeneity of plastic deformation in each constituent phase, tl-51 We will apply the finite-element method to calculate the reverse flow curves of dual-phase steels with different martensite contents. In addition, the effects of degree of prestrain, particle size, and yield strength ratio, C* (C* = martensite yield strength divided by ferrite yield strength) on the BE parameters and the phase stresses are also calculated. We also discuss the factors related to inelastic unloading and associated unloading plasticity, the elimination of the BE, and the variation of phase stresses by reverse deformation. Based on the decay of the residual phase stress (which is often called "back stress") during reverse straining, the relationship between back stress and permanent softening has been elucidated. Some of the calculated results can be compared with corresponding experimental results, and good agreement between the results is found. LI ZHONGHUA, Associate Professor, and GU HAICHENG, Professor, are with the Department of Engineering Mechanics and Research Institute for Strength of Metals, respectively, Xi'an Jiaotong University, Xi'an, People's Republic of China. Manuscript submitted November 16, 1988. METALLURGICAL TRANSACTIONS A
It is believed that a fundamental understanding of the BE in commercial materials is significant not only for improvement in deformation processing techniques (e.g., plate fabrication, pipe forming, and pressure vessel making) but also for development of new materials with optimum microstructures.
II.
CALCULATION PROCEDURES
The experimental forward and reverse stress-strain curves for alloy 1 (100 pet ferrite), alloy 2 (ferrite plus 16 pct martensite), alloy 3 (ferrite plus 40 pct martensite), and alloy 4 (nearly 100 pet martensite) are shown in Figure 1 of Part I.[Z31 In order to determine precisely the role of phase volume fraction on the BE parameters and phase stresses, three other martensite contents were used in FEM calculations by exchanging the meshes occupied by two phases in Figures 3(b) and 4(b) of Part I.t231We evaluated the behavior of 84 pct martensite (previously 16 pct martensite) and 60 pct martensite (previously 40 pet martensite). By choosi
Data Loading...
