Effects of microstructure on the dynamic strain aging of ferriticpearlitic steels at high strain rates

Ahmad Mardoukhi,Amandine Roth,Mikko Hokka,Taina Vuoristo,Jari Rämö,Veli-Tapani Kuokkala,E Buzaud,A Cosculluela,E Cadoni,H Couque

doi:10.1051/epjconf/201818303009

Ahmad Mardoukhi, Amandine Roth + Show 8 more

Open Access

https://doi.org/10.1051/epjconf/201818303009

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Abstract

This paper presents an experimental study of the effects of dynamic strain aging on the mechanical behavior of selected high carbon and chromium-manganese steels in dynamic loading condition. In ferritic-pearlitic steels, the dynamic strain aging is typically caused by carbon, nitrogen, and possibly some other small solute atoms. Therefore, the thermomechanical treatments affect strongly how strong the dynamic strain aging effect is and at what temperature and strain rate regions the maximum effect is observed. In this work, we present results of the high temperature dynamic compression tests carried out for two different ferritic-pearlitic steels, 16MnCr5 and C60, that were heat treated to produce different microstructure variants of these standard alloys. The microstructures were analyzed using electron microscopy, and the materials were tested with the Split Hopkinson Pressure Bar device at three different strain rates at temperatures ranging from room temperature up to 680 °C to study the effect of the heat treatments and the resulting microstructures on the dynamic behavior of the steels and the dynamic strain aging effect. The results indicate that for both steels, a coarse grain structure has the strongest dynamic strain aging sensitivity at small plastic strains. However, at higher strains, all microstructures show similar strain aging sensitivities.

Highlights

The strength of steels is very sensitive to both deformation rate and ambient temperature
This paper presents an experimental study of the effects of dynamic strain aging on the mechanical behavior of selected high carbon and chromium-manganese steels in dynamic loading condition
The microstructures were analyzed using electron microscopy, and the materials were tested with the Split Hopkinson Pressure Bar device at three different strain rates at temperatures ranging from room temperature up to 680 °C to study the effect of the heat treatments and the resulting microstructures on the dynamic behavior of the steels and the dynamic strain aging effect

Summary

Introduction

The strength of steels is very sensitive to both deformation rate and ambient temperature. The deformation mechanism changes from thermally activated dislocation motion to drag controlled dislocation motion at strain rates close 103 s-1 This leads to the commonly observed strong transient hardening, i.e., increase of the momentary flow stress of the steels. Dynamic strain aging can cause an increase in the strength of the material at higher temperatures This behavior has been observed for many metals and alloys, such as titanium [2], niobium [3], vanadium [4], molybdenum [5], and stainless steels [6]. Shahriary et al [9] analyzed the stress-strain curves of the 4340 steel at different temperatures They reported that both the work hardening exponent as well as the ductility of the steel were affected by the dynamic strain aging, the former increasing and the latter decreasing in the temperature range of 250-300 ̊C. The correlation between the microstructure and the strength of the dynamic strain aging offers new insight for a better understanding of the phenomena affecting the strength and hardening of steels at high temperatures

Experimental procedure

Results and discussion

Concluding remarks