The dynamic tensile behavior of tough, ultrahigh-strength steels at strain-rates from 0.0002 s-1 to 200 s-1

The present Study examines the strain-rate sensitivity Of four high-strength, high-toughness steels at strain-rates ranging from 0.0002 s(-1) to 200 s(-1): AerMet 100, modified 4340, modified HP9-4-20, and a recently developed Eglin AFB steel alloy, ES-1c. A newly developed dynamic servohydraulic method was employed to perform tensile tests over this entire range from quasi-static to near split-Hopkinson or Kolsky bar strain-rates. Each of these alloys exhibits only modest strain-rate sensitivity. Specifically, the semi-logarithmic strain-rate sensitivity factor beta Was found to be in the range of 14-20 MPa depending on the alloy. This corresponds to a similar to 10% increase in the yield strength over the 6-orders of magnitude change in strain-rate. Interestingly, while three of the alloys showed a concomitant similar to 3-10% drop in their ductility with increasing strain-rate, the ES-1c alloy actually exhibited a 25% increase in ductility with increasing strain-rate. Fractography suggests the possibility that at higher strain-rates ES-1c evolves towards a more ductile dimple fracture mode associated with microvoid coalescence. Published by Elsevier Ltd.