Whilst Sulphur and Phosphorous are usually removed from steels due to their impact on mechanical properties during the Desulphurisation and Oxygen Blowing stages of the process, they can be finely controlled to provide desirable properties for Engineering steels to produce a free cutting characteristic and to increase the strength and weathering performance of some strip steels.
Another important element, investigated by Irvine, Pickering and Gladman, is Niobium.
Very Fine precipitation, increasing strength
This is used to increase strength and toughness in combination with specific rolling techniques, Vanadium is used for similar purpose in the United States. These elements restrain grain boundaries giving improved toughness and the internal strength of the grains is strengthened by very fine precipitation.
Movement restricted, increasing strength and toughness