27th IFHTSE CONGRESS & EUROPEAN CONFERENCE ON HEAT TREATMENT 2022

The optimal strip flatness of stainless martensitic steels is a mandatory requirement for many components in microelectronics or medical technology in order to fulfil the function or manufacture of the products. In the context of energy efficiency, there are increasing demands for thinner materials, e.g. for valves in compressors.
In modern plants, stainless steel strips are quenched using various cooling methods. The temperature is not measured and controlled across the width of the strip but gradients have a significant influence on the flatness. A lack of temperature measurement and control forces manufacturers to produce in larger widths and then cut the strips into narrower ones. Depending on the flatness of the manufactured strips, the belt is sold or scrapped. Above a strip thickness of 0.25 mm the required flatness is achieved and the scrap is quite low. However, the output of strips with the desired flatness decreases the thinner and the wider they are. The rejection rate is up to 99 %.
Familiar plants for the quenching and tempering of the thinnest stainless martensitic strips cool the material in the final quenching and tempering phase via a mechani-cal quench. An exact adjustment of the temperature over the strip width is impossi-ble. Therefore, for the first time in this project, a system is to be developed whose nozzle cooling makes the cooling capacity individually adjustable over the strip width. This forms the basis for controlling the flatness of the strip over its width, since the cooling capacity is defined locally for each width.
With the aim of finding the best possible cooling concept using nozzles to optimize strip flatness, a basic study of the state of the art was executed. The various cooling concepts with different nozzle arrays are presented and evaluated regarding their application to the project objective.