Annealing steel coils

Abstract

Cold rolled steel in the form of coiled sheets requires heat treatment (annealing) in order to release stresses and reform the crystalline structure. During this process the whole coil must be heated to the required temperature and then maintained at this temperature for a period of time.

At New Zealand Steel the process takes place inside a batch annealing furnace. The MISG group considered the problem of where the cold point lies within the steel coils, i.e. what is the last part of the coil to reach the required temperature, and how long does it take to reach this temperature? Challenges include deciding what the boundary conditions are on a coil, and dealing with the nonlinearity and anisotropy caused by height-dependent gaps within coils.