Showing papers by "C.J. Van Tyne published in 2005"

Effect of strain and strain rate on the bauschinger effect response of three different steels

Abstract: The Bauschinger behavior after a strain reversal was evaluated for samples with microstructures representative of production sheets for a low-carbon (LC) steel, a high-strength low-alloy (HSLA) steel, and a dual-phase (DP) steel. The microstructures were produced in the samples by laboratory hot rolling and heat treatment. Bauschinger tests were run at strain rates of 0.0001, 0.001, and 0.01 s−1, with tensile prestrains between 1 and 7 pct. After the reversal, the samples were strained 2 pct in compression. The Bauschinger effect is described by a Bauschinger effect parameter (BE), which is the difference between the steel strength at reversal and the 0.05 pct offset yield strength on the reversal, normalized by the steel strength at reversal. It is found that the Bauschinger effect is a continuous increasing function of the strength of the steel, provided the steel is prestrained at least 2.5 pct or beyond the yield point elongation. A single trend line describes the Bauschinger effect variation with steel strength, for all three steels in the present study and for an aluminum-killed drawing quality (AKDQ) steel from a previous investigation. No strain rate influence on the BE was found, due to the limited strain rate range and data uncertainty.

Bauschinger Effect Response of Automotive Sheet Steels

Abstract: In a study of the Bauschinger effect, data were collected from three sources in the published literature. Quantitative stress-strain data were taken from these papers, and the results re-analyzed. The resulting database has 44 lots of sheet steels, including drawing quality, interstitial free, bake hardening, HSLA (and related grades), dual phase, TRIP, recovery annealed, and martensitic grades. In analyzing the data, it is found that use of the 0.05% yield strength on reversal instead of the conventional 0.2% yield strength provides more generality in explaining the results. In this analysis, the Bauschinger effect is characterized by a term (BE), which is the difference between the steel strength just prior to reversal and the 0.05% yield strength on reversal normalized by the strength just prior to reversal. An initial prestrain of 2% is needed to establish a dislocation morphology that can be generalized across many of the steel grades. For steels with a predominantly ferrite microstructure and no added interstitial elements, BE exhibits a single monotonic trend line with respect to the strength just prior to reversal. For the bake hardenable grades, the 0.05% yield strength on reversal is slightly greater than the trend line. For the DP980, TRIP, and martensite grades, the 0.05% yield strength on reversal is considerably greater than the trend line. These steel grades either initially or after deformation have a greater volume fraction of martensite. The recovery annealed steels, which possess a much greater dislocation density, also exhibit 0.05% yield strengths that are significantly greater than the trend line. For steels with a predominantly ferrite microstructure over a wide range of strength, the single characteristic curve indicates that the initial reverse yield strength can be determined from the strength at the point just prior to the reversal. For modelers of sheet forming processes, the relationship between strength and yield on reversal can be used in material constitutive equations.

Feasibility of electro-slag cast steel for hot-working tools

Abstract: A study on electro-slag cast steel has been performed to assess the feasibility of its use in hot-working tools in place of traditional forged steels. In this study, some important material properties that are essential for the proper performance of hot-working tool steels have been measured. The properties of the electro-slag cast steel are compared with those of hot-working tool steels currently used in industrial practices. The use of electro-slag cast steel in specific applications has been evaluated and compared with the operational performance of currently used steels in industrial environments. The wear resistance, impact toughness, thermal fatigue resistance, and repair weldability of electro-slag cast steel have been determined. The material properties were found to be comparable to existing hot-working tool steels. The number of effective blows obtained from an industrial application test also confirms that electro-slag cast steel is a feasible material for hot-working tools.