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| Polak K. |
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| Keywords: |
| No 2 (2006), p. 111-118 |
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| Ševčík A., Ševčíková J. |
| ANALYSIS OF THE REDUCTION OF AREA VALUES DROP AT HIGH TEMPERATURE TESTING OF LOW CARBON STEELS IN THE AS-CAST STATE |
Abstract
High temperature properties of 24 various low carbon steels in the as-cast state were investigated by high temperature tensile tests in a temperature region from 850 - 900 oC up to the melting temperature at a deformation rate of 4,7 . 102 . s-1. The plasticity was evaluated as reduction of area values. High reductions of area values, as high as 99.99 %, were measured in the austenite region of steels at the middle testing temperatures of the above mentioned region. A reduction of area values drop was established at lower testing temperatures, from 850 up to 1190 oC, and at the very high ones, from 1290 up to 1410 oC.
The fractures formed in the regions with reduction of area drop were studied by SEM and optical microscopy on the crossections through the fractures. At lower testing temperatures, decohesion and ductile intercrystalline fractures were formed. The plasticity drop at very high temperatures was accompanied by formation of intercrystalline decohesion fractures, interdendrite fractures, and fractures with mixed morphology. The interdendrite fracture formation was promoted by increasing the C and N content in the steel.
Characteristic points were determined on the curve of reduction of area values vs. temperature. These parameters were then statistically analyzed. It can be followed from these analyses that at lower testing temperatures the temperature of plasticity loss predominantly increases with the increasing of As content and the austenite grain size. The probable reason is that As preferentially diffuses on the austenite grain boundaries and thus causes a drop of the cohession strength values. The reduction of area values at 900 oC are negatively affected by increasing the austenite grain size values, predominantly. At very high temperatures the temperature of the reduction of area values drop is primarily influenced by the P content via weakening strength of the grain boundaries and by liquid phase formation. It influences location of characteristic points and steepness of the plasticity drop, as well as the fracture characteristics.
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| Keywords: low carbon steels|slabs|high temperature properties|hot ductility|intercrystalline fracture|interdendritic fracture|statistic analysis| |
| No 2 (2006), p. 128-138 |
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