Conditions for Complex Precipitate Formation and Their Effect on Low-Carbon Steel Cold-Rolled Product Properties

Resumo

The effect of chemical composition and recrystallization annealing regimes in continuously operating units on the mechanical properties of cold-rolled product of type 08Yu steels is studied. It is established that with a sulfur content of 0.012–0.018% during hot rolling an optimum amount and size distribution of manganese sulfide particles is achieved providing the formation on them of cementite and aluminum nitride precipitates. Complex MnS-cementite particles formed in an equalization chamber of a continuously operating hot galvanizing unit facilitate an increase in formability as a result of a reduction in the degree of the difference in grain size of the microstructure and an increase in cementite distribution uniformity. Precipitation of AlN on MnS particles in the course of metal hot rolling and cooling provides more complete removal of nitrogen from solid solution, and consequently a reduction in steel tendency towards strain ageing. A significant reduction in the proportion of fine AlN particles increases the rate of cold worked metal recrystallization, and this leads to a reduction in fineness of the microstructure and a corresponding reduction in yield strength and an increase in relative elongation.