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5062468 
Journal Article 
Stress-State, Temperature, and Strain Rate Dependence of Vintage ASTM A7 Steel 
Brauer, SA; Whittington, WR; Rhee, H; Allison, PG; Dickel, DE; Crane, CK; Horstemeyer, MF 
2019 
Yes 
Journal of Engineering Materials and Technology
ISSN: 0094-4289 
141 
2 
WOS:000459211000002 
The structure-property relationships of a vintage ASTM A7 steel is quantified in terms of stress state, temperature, and strain rate dependence. The microstructural stereology revealed primary phases to be 15.8% +/- 2.6% pearlitic and 84.2% +/- 2.6 ferritic with grain sizes of 13.3 mu m +/- 3.1 mu m and 36.5 mu m +/- 7.0 mu m, respectively. Manganese particle volume fractions represented 0.38-1.53% of the bulk material. Mechanical testing revealed a stress state dependence that showed a maximum strength increase of 85% from torsion to tension and a strain rate dependence that showed a maximum strength increase of 38% from 10(-1) to 10(3) s(-1) at 20% strain. In tension, a negative strain rate sensitivity (nSRS) was observed in the quasi-static rate regime yet was positive when traversing from the quasi-static rates to high strain rates. Also, the A7 steel exhibited a significant ductility reduction as the temperature increased from ambient to 573 K (300 degrees C), which is uncommon for metals. The literature argues that dynamic strain aging (DSA) can induce the negative strain rate sensitivity and ductility reduction upon a temperature increase. Finally, a tension/compression stress asymmetry arises in this A7 steel, which can play a significant role since bending is prevalent in this ubiquitous structural material. Torsional softening was also observed for this A7 steel. 
A7 Steel; high strain rate; stress state; compression; tension; torsion; dynamic strain aging; negative strain rate sensitivity; embrittlement