Transformation behavior of TRIP steels |
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Authors: | G B Olson M Azrin |
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Affiliation: | (1) Department of Materials Science and Engineering, 02139 MIT, Cambridge, MA;(2) Army Materials and Mechanics Research Center, 02172 Watertown, MA |
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Abstract: | True-stress (σ), true-strain (ε) and volume fraction martensite(f) were measured during both uniform and localized flow as a function of temperature on TRIP steels in both the solution-treated
and warm-rolled conditions. The transformation curves(f vs ε) of materials in both conditions have a sigmoidal shape at temperatures above Ms
σ (maximum temperature at which transformation is induced by elastic stress) but approach initially linear behavior at temperatures
below Ms
σ where the flow is controlled by transformation plasticity. The martensite which forms spontaneously on cooling or by stress-assisted
transformation below Ms
σ exhibits a plate morphology. Additional martensite units produced by strain-induced nucleation at shear-band intersections
become important above Ms
σ. Comparison of σ-ε andf-ε curves indicate that a “rule of mixtures” relation based on the “static” strengthening effect of the transformation product
describes the plastic flow behavior reasonably well above Ms
σ, but there is also a dynamic “transformation softening” contribution which becomes dominant below Ms
σ due to the operation of transformation plasticity as a deformation mechanism. Temperature sensitivity of the transformation
kinetics and associated flow behavior is greatest above Ms
σ. Less temperature-sensitive TRIP steels could be obtained by designing alloys to operate with optimum mechanical properties
below Ms
σ. |
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Keywords: | |
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