Model for the industrial prediction of carbonitride precipitation in HSLA steels cast by a thin slab casting plant

In HSLA steels (high strength low alloys) the strengthening mechanisms, in addition to the control of the combination and quantity of the structural constituents (ferrite, pearlite or bainite), are: the solid solution hardening, the grain refinement hardening, the precipitation hardening. Surely the most important are grain refinement, that can be obtained with a fine dispersion of precipitates in austenitic temperature ranges, and the precipitation hardening by the second phases (carbonitrides of microalloying elements such Ti, V, Nb). Precipitation hardening can be divided into three principal mechanisms: the deformation of coherency hardening, chemical hardening, dispersion hardening. The last one is the prevailing of these mechanisms because of the size, on the order of a few nanometers, and of the hardness of the precipitates. What has been just described shows the great importance of the control of precipitation and chemical composition of the second phases. In fact, for example, the precipitation in liquid steels has to be avoided because these precipitates are very large, a few micrometers in size, and they don't have any effect on the grain refinement of the primary austenitic grain. This is fundamental especially in the processes with high casting speed where high speed can prohibit the precipitation of complex carbonitrides at certain temperatures. This paper introduces a kinetic model that accounts for the effect of thin slab casting on the precipitation of carbonitrides.