This cooling water provides an ideal electrolyte in which corrosive processes can become established, and ensures that the rolls will experience rapid thermal cycling and be vulnerable to cracking. Perhaps most significantly, the rolling rates and levels of gauge reduction demanded by modern hot mills mean the working loads are tremendous. Wear is high and welding materials must have both high hardness and improved resistance to high temperature softening.
Uniquely, the product being rolled will also have a strong bearing on the type of alloy recommended for cladding. High Cr alloys tend to be vulnerable to pick up when rolling stainless steel products. This can then lead to marking or printing on the surface of the product
Welding Products Designed for Purpose
Applying Corewire's principle of designing the solution to fit the problem, a range of Weldclad consumables have been developed specifically to resist these environmental conditions.
As an example of our approach, consider the material recommended of edger rolls. These rolls need to maintain their integrity over a wide range of strip temperatures as well as resist impacts from the strip's leading edge, and abrasion for the sides of the strip. Weldclad 4 is an alloy with excellent thermal fatigue properties, and elevated abrasion resistance. As remarkable as the performance of Weldclad 4 is, it is a difficult material to apply correctly. Therefore, we only recommend its use when controls in the welding shop are without question.
An often suitable alternative to Weldclad 4 is Weldclad 17, also a low Cr alloy, and therefore also suitable for mills that roll stainless steel products. The slightly finer alloying levels of Weldclad 17 mean it strikes a careful balance between ease of application and optimisation of properties and performance. Weldclad 17 is often used in back-up roll and pinch roll applications.
Where higher a Cr content is required or permitted, for example when rolling carbon steel grades, or where thermal fatigue failures are a particular problem, Weldclad 8 can be used. A lower C content, 12%Cr and additions of Mo, Nb and V have produced an alloy with hardness's around 55HRc, and excellent resistance to thermal cycling failures.
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