Abstract
<abstract><p>Numerical studies were conducted to investigate the applicability of cooling strategies for controlledly producing a microstructure in the steel strip or plate, which changes as function of the plate length. In the numerical simulations, the water spray cooling was varied as function of the plate length and as a result, the different parts of the plate were cooled at different rates. We applied the previously developed numerical code where the transformation latent heat is coupled with the heat conduction and transfer model, which has also been calibrated to correspond to experimental laboratory cooling line. The applicability of the method was investigated for controlledly creating alternating bainite and polygonal ferrite regions in plates of two different thicknesses (0.8 cm and 1.2 cm thick plates) by cooling different parts of the plate to different temperatures before switching off the water cooling so that polygonal ferrite forms in the part which has been cooled to higher temperature and bainite forms in the low temperature part. The simulation results indicate that the controlled production of such alternating regions is possible, but the resulting regions in the studied scenario cannot be very thin. The transition regions between the ferrite and bainite regions in the simulated cases are in the range of 5–15 cm. Controlled production of zones consiting of softer phase in the otherwise bainitic steel could offer a possibility for creating designed tracks in a steel bainitic strip or plate, where the mechanical working or cutting of the material is easier.</p></abstract>
Highlights
Controlled differential treatment of materials offer possibility for tailoring the mechanical properties of the finished or semi-finished part to be suited for a specific application purpose
The applicability of the method was investigated for controlledly creating alternating bainite and polygonal ferrite regions in plates of two different thicknesses (0.8 cm and 1.2 cm thick plates) by cooling different parts of the plate to different temperatures before switching off the water cooling so that polygonal ferrite forms in the part which has been cooled to higher temperature and bainite forms in the low temperature part
Numerical simulations were used for studying controlled production of alternating polygonal ferrite and bainite regions in a steel plate or strip by means of applying differential water spray cooling at different positions of the plate/strip
Summary
Controlled differential treatment of materials offer possibility for tailoring the mechanical properties of the finished or semi-finished part to be suited for a specific application purpose. Differential heating and cooling has been used in context of hot stamping for producing B-pillars for automobiles, which require high strength at the upper part and lower strength and high plasticity under crash conditions at the lower part. This is achieved by controlling the local temperature of the applied mold [3]. Differential heat treatment has been used to adjust the mechanical properties of rails by controlling local cooling rate by using controlled mixing of water and air [5]. Distortions can occur since the thermal dilatation and volume changing transformations can occur at different places at different times [6]
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