Tetsu-to-Hagane
Online ISSN : 1883-2954
Print ISSN : 0021-1575
ISSN-L : 0021-1575
The Effect of Interrupted Accelerated Cooling after Controlled Rolling on the Mechanical Properties of Steels
Chiaki OOUCHITomoyoshi OOKITASadahiro YAMAMOTO
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1981 Volume 67 Issue 7 Pages 969-978

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Abstract

The effects of accelerated cooling after controlled rolling(CR) on the mechanical properties were investigated for the various microalloyed steels. The controlled rolling conditions were the reheating temperature of 1100°C or 1200°C, the cumulative rolling reduction of 70% below 900°C, and the finishing rolling temperature of 800°C with the plate thickness of 20 mm. The interrupted accelerated cooling (IAC) was carried out in the temperature range from 780°C to 600°C, followed by air cooling, and the maximum cooling rate was 12 °C/s. The increase of cooling rate in IAC caused the microstructural changes such as the refinement of ferrite grain size, disappearance of pearlite banding, and formation of refined bainite in place of pearlite. The increment of strength due to IAC with cooling rate around 10 °C/s that gave rise to the very refined duplex structure of ferrite and bainite was 5 to 10 kg/mm2, depending on the content of the microalloying elements such as Nb, V, or Ti. The Charpy transition temperature was improved by IAC under the reheating temperature of 1100°C, and the superior low temperature toughness such as the transition temperature below -100°C was attained with occurrence of very few separation on the fracture surface in Charpy impact test specimens. The optimum cooling conditions and the transformation behaviors in IAC were discussed. The increment of strength due to IAC was analyzed on the basis of the quantitative investigation of the transformed microstructure.

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© The Iron and Steel Institute of Japan
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