Studies on Ultra Fine Grain Steel Sheet with High Speed High Strain Hot Rolling and Rapid Cooling Method.

研究钢在热轧过程中的回复或再结晶是非常困难的。在本研究中，一个独特的高速实验室轧机和水冷设备的组合，使淬火后立即轧制显微组织。等效应变的不均匀性和再结晶现象在轧制试样的整个厚度范围内都有观察到。为了获得精确的轧制组织，建立了一种新的轧制温度控制系统（多喷嘴喷水法）。结果表明，在18 Cr-8 Ni不锈钢高速高应变热轧过程中，冷却速度可达1300 K/s，轧后金属无变形，纵向温度分布均匀。高速高应变热轧的主要结果是：1）尽管润滑条件良好，但采用大压下量轧制，轧后材料的剪切变形增大; 2）轧后材料的细晶显微组织（5- 10 μ m）明显细化，但在轧制过程中，轧后材料的剪切变形明显增大。3）大压下量轧制后的板材性能与冷轧退火后的板材相当; 4）再结晶后的板材，X射线衍射测定的晶体取向变得随机; 5）大压下量轧制后的板材，其表面层中的晶粒尺寸明显大于冷轧退火后的板材<micro>。研究了陶瓷轧辊在高速高应变热轧中应用的可能性。

It is very difficult to investigate how recovery or recrystallization proceeds during hot rolling of steel. In the present study, a unigue combination of high speed laboratory rolling mill and water cooling facility enables quenching the microstructure immediately after rolling. Inhomogeneity of equivalent strain and recrystallization are observed through the thickness of rolled specimens. A layer of finely recrystallized grains is formed at the position of maximum equivalent strain below the surface.A new rolling temperature control system (multi nozzle water spray method) was established to get the precise microstructure of rolled materials. It is found that cooling velocity becomes 1300K/s and no distortion of rolled metal occur and uniform longitudinal temperature distribution is shown.The result obtained in high speed high strain hot rolling of 18Cr-8Ni stainless steel is summarized as follows.1) The shear deformation in rolled materials increases with heavy reduction rolling method in spite of good lubrication condition.2) The fine grain micro structure(5-10 <micro> m) occurs in the surface layer of rolled material with heavy reduction rolling method.3) Property of the rolled material in heavy reduction rolling equals to the steel plate produced with cold rolling and annealing.4) Crystallographic orientation measured with X-ray becomes random in the the fully recrystallized rolled materials.5) Possibility of using ceramic roll in high speed high strain hot rolling was investigated in this study.