Influence of tempering temperature on damping capacity in a high carbon steel

Abstract

Tempering is the process of heating a martensitic steel at elevated temperatures below Ae1 to improve the toughness of as-quenched martensitic microstructure. It is well known that various solid-state reactions (carbon segregation, carbide precipitation, decomposition of retained austenite, recovery, and recrystallization) have substantial influences on the mechanical properties of tempered martensites. Despite a number of investigations about tempered martensites [1–10], however, there is little information available on their damping properties. Accordingly, in the present study, we examine the damping capacity of an Fe-0.7%C martensitic steel with tempering temperature up to 600 ◦C, and discuss the results on the basis of a dislocation damping mechanism. The experimental steel with the chemical composition (wt.%) of Fe-0.670C-0.024Si-0.520Mn was prepared by a high frequency vacuum induction melting. The ingot of 5 kg was homogenized at 1200 ◦C for 24 h in a protective atmosphere and hot-rolled into rods of 13 mm diameter. From these rods, specimens for damping measurements, X-ray diffractometry (XRD) tests, and microstructural observations were prepared by machining. The specimens were solution-treated at 1000 ◦C for 1 h, water-quenched followed by cooling to liquid nitrogen (−196 ◦C), and tempered for 1 h up to 600 ◦C. The XRD test was performed at room temperature using a Cu-Kα radiation. Thin foils for transmission electron microscopy (TEM) were electro-polished in a solution of 5 vol.-% HClO4 + 95 vol.-% CH3COOH and observed in a Jeol JEM-200CX operating at 200 kV. Damping capacity was measured at room temperature in a range of 7 × 10−5 to 5 × 10−4 maximum surface strain amplitude (γmax) using a Fopple-Pertz type inverted pendulum apparatus vibrating in a torsional mode [11]. Dimensions of the specimen were 186 mm in total length, 7 mm in gauge diameter, and 79 mm in gauge length. To examine an effect of