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Thermomechanically controlled rolling of steel plate can involve substantial straining in the intercritical temperature region, which may result in the final ferrite grains not fully recrystallizing, and, hence, the presence of low-angle grain boundaries. It is shown in this article that a Nb-microalloyed thermomechanically controlled rolled (TMCR) steel can contain a high proportion of low-angle grain boundaries (the extent depending on the thermomechanically controlled rolling schedule) and that during toughness testing, the crack front ignores boundaries with less than a 12 deg misorientation. Thus, the average microstructural unit experienced by the crack front (i.e., the cleavage facet) is significantly larger than the average metallographic, two-dimensional grain size. Consequently, use of the metallographic grain size gives a poor prediction of the impact transition temperature (ITT) and fracture stress for these steels. It is also shown that the micromechanism of crack initiation and propagation involves grain-boundary carbides and groups of closely aligned grains that act as single "effective" grains.

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Blast furnace operation is a complex phenomenon; maximising productivity requires a balance of burden characteristics. Meeting the targets of optimum sinter strength and minimum slag volume is a matter of concern for high alumina (2 . 0-2 . 1%) iron ore fines. To achieve reduced slag volume MgO in the sinter may be reduced and sinter strength maintained by addition of coke breeze. However, the associated increase in fuel rate during sintering raises the FeO content. The effects of increasing FeO and lowering MgO on the softening melting behaviour of burden materials have been assessed in laboratory experiments and the results compared with data from blast furnace operations at Tata Steel. It was found that with sinter containing .12%FeO, erratic furnace behaviour was encountered and energy adjustment was required with the reduction in MgO (1 . 77-1 . 48%) to ensure smooth operation.

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