Abstract
Cold-drawn pearlitic steel wires are nanostructured and the flow stress at room temperature can reach values above 6 GPa. A typical characteristic of the nanostructured metals, is the low ductility and thermal stability. In order to optimize both the processing and application of the wires, the thermal behaviour is of interest. This has been studied by annealing the wires for 1h at temperatures from ambient temperature to 300 °C (573 K). It is expected that a raising temperature may lead to structural changes and a reduction in strength. The change in strength is however not expected to be large. For this reason we have applied a very precise technique to measure the tensile properties of the wires from a strain of 10-4 to the maximum strain of about 1-2%. The structural changes have also been followed to estimate and relate strength changes to changes in structural parameters and morphology.
Highlights
High carbon cold drawn pearlitic steel wires have the highest strength of mass-produced steel products
Nominal stress-strain curves for annealing at temperatures in the range from 20 °C to 300 °C (293 K 573 K) are shown in figure 4. These curves can be divided into three groups based on the annealing temperature: (i) RT - 100 °C where the temperature effect is small; (ii) 100 – 200 °C showing a significant increase in flow stresses but only a small change in UTS and total elongation; (iii) 200 – 300 °C showing a decrease in strength with increasing temperature and no change in elongation to 260 °C and a significant increase to a total elongation of 5.5% reached at 300 °C
The microstructural evolution with increasing annealing temperature has been followed by transmission electron microscopy focusing on the interlamellar spacing (ILS) between the cementite lamellae and the density and arrangement of dislocations
Summary
High carbon cold drawn pearlitic steel wires have the highest strength of mass-produced steel products. The influence of temperature on the mechanical property is of interest for both scientific and technological communities and many investigations have covered the effect of annealing on the mechanical properties of drawn wires [2, 4,5,6] These investigations focus mainly on temperatures above 200 °C and limited work has been done on the quantitative stress and strain relationship due to the difficulty of precise strain measurement as the wire diameters are small of the order of 0.1 mm (wire diameter range: 0.175 - 0.5 mm), the high sensitivity of total elongation measurements to the extensometer knife/tensile axis alignment.
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