Improvement of the Properties of Mild Steel for Hot Strip.

The mechanical properties and ageing resistance of StW 24 hot strip steel depend to a large extent on the degree of fixation of the dissolved nitrogen. At coiling temperatures below 650 degree C, only a small fraction of nitrogen is precipitated as aluminiumnitride and the hot strip features a relatively low ageing resistance. Coiling temperatures higher than 720 degree C result actually in an improved properties after ageing, however, the dispersion of the mechanical properties over the strip length increases also. A stable fixation of nitrogen independently of the coiling temperature is ensured by stoichiometric addition of titanium relation to the nitrogen content. This results in improved cold deformability, ageing stability and consistency of the properties.