Thermomechanical simulations have been carried out on two Ti-microalloyed steels and one reference steel without Ti. The pinning forces exerted by TiN particles in the Ti-steels have been determined and compared with the driving forces for austenite grain growth and static recrystallisation between hot rolling passes. The driving forces for recrystallisation were found to be approximately two orders of magnitude higher than the pinning forces, which explains why the austenite in these steels barely experiences hardening during rolling and why the accumulated stress prior to the austenite→ferrite transformation is insufficient to refine the ferritic grain. On the other hand, austenite grain size hardly varies during hot rolling, as the TiN precipitates exert a strong control from the reheating temperature to the last pass. A Ti/N ratio close to 2 is able to control austenite grain growth at high austenitisation temperatures. So, both aspects-high driving forces for static recrystallisation and control on austenite grain size-allow reducing the number of passes applied. In this case, ferrite grain refinement should be reached by austenite strengthening and accelerated cooling during the transformation to ferrite.
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机译：对两种钛微合金钢和一种不含钛的参考钢进行了热力学模拟。已经确定了TiN颗粒在Ti钢中施加的钉扎力，并将其与奥氏体晶粒长大和热轧道次之间的静态再结晶的驱动力进行了比较。发现再结晶的驱动力比钉扎力高大约两个数量级，这解释了为什么这些钢中的奥氏体在轧制过程中几乎没有硬化，以及为什么奥氏体→铁素体相变之前的累积应力不足以精炼钢。铁素体晶粒。另一方面，奥氏体晶粒尺寸在热轧过程中几乎不变，因为TiN析出物对从再加热温度到最后道次施加了强有力的控制。 Ti / N比接近2能够在高奥氏体化温度下控制奥氏体晶粒的生长。因此，这两个方面-静态再结晶的高驱动力和奥氏体晶粒尺寸的控制-都可以减少通过次数。在这种情况下，应在转变为铁素体的过程中通过奥氏体强化和加速冷却来实现铁素体晶粒细化。
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