Simulation of the hot rolling and accelerated cooling of a C-Mn ferrite-bainite strip steel

By means of torsion testing, the microstructures and mechanical properties produced in a 0.14 Pct C-1.18 Pct Mn steel were investigated over a wide range of hot-rolling conditions, cooling rates, and simulated coiling temperatures. The austenite grain size present before accelerated cooling was varied from 10 to 150 μm by applying strains of 0 to 0.8 at temperatures of 850 °C to 1050 °C. Two cooling rates, 55 °C/s and 90 °C/s, were used. Cooling was interrupted at temperatures ranging from 550 °C to 300 °C. Optical microscopy and transmission electron microscopy (TEM) were employed to investigate the microstructures. The mechanical properties were studied by means of tensile testing. When a fine austenite grain size was present before cooling and a high cooling rate (90 °C/s) was used, the microstructure was composed of ferrite plus bainite and a mixture of ferrite and cementite, which may have formed by an interphase mechanism. The use of a lower cooling rate (55 °C/s) led to the presence of ferrite and fine pearlite. In both cases, the cooling interruption temperature and the amount of prior strain had little influence on the mechanical properties. Reheating at 1050 °C, which led to the presence of very coarse austenite, resulted in a stronger influence of the interruption temperature. A method developed at Institut de Recherche Sidérurgique (IRSID, St. Germain-en-Laye, France) for deducing the Continuous-Cooling-Transformation (CCT) diagrams from the cooling data was adapted to the present apparatus and used successfully to interpret the observed influence of the process parameters.     

Improving the accelerated cooling of rolled steel

The basic stages in improving the accelerated cooling of rolled steel are considered for the 350 small- and medium-bar mill in bar-rolling shop 2 at OAO Oskol’skii Elektrometallurgicheskii Kombinat.     

Review of accelerated cooling of steel plate

Abstract

The cooling of steel plates after the completion of rolling, while a universal requirement, was historically accomplished using "home-made" systems contrived by individual mills. In recent times, commercial solutions suitable for general application have evolved. This article reviews the development of such systems and explains the metallurgical and operational factors that dictate their design. It has a particular focus on MULPIC® technology and its uses.     

Modelling water cooling of steel strip during hot rolling

Several tests of water cooling of steel samples are presented in the paper. The water spray and quenching conditions are considered. The temperature variations during the tests are monitored using the thermocouples embedded in the side of the samples. The experimental time – temperature profiles are compared with the results of calculations based on the finite element model. Comparison of the theoretical and experimental results allowed to suggest heat transfer coefficients of 10000 W/m²K for water in quenching, 6000 W/m²K for the top surface during water spray cooling and 4000 W/m²K for the bottom surface during water spray cooling.     

Modelling of microstructural evolution during accelerated cooling of hot strip on the runout table

Microstructural evolution in the hot strip after finishing and subsequent accelerated cooling on the runout table has been modelled in order to assess their suitability for further processing. Transient heat transfer and kinetics of phase change comprising austenite to ferrite plus pearlite have been coupled to ascertain temperature profile, taking into accout the heat generated during phase change. Johnson-Mehl-Avrami relation together with Scheil's rule of additivity have been invoked. Several process parameters such as, coefficient of heat transfer, temperature at the exit of finishing stand, thickness and the speed of strip have been varied to determine their influence on the extent of phases engendered on the runout table. It has been demonstrated that greater spreadout in cooling arrangement with relatively lower heat transfer coefficient ensures homogeneity in microstructure. Cooling from comparatively higher finishing temperatures may result in greater microstructural uniformity. Two grades of steel – namely 0.05C-0.23Mn-0.015Si and 0.08C-0.37Mn-0.06Si – were chosen to carry out plant trials to validate the model. Special features of the microstructure have been brought out and the mechanical properties have been correlated.     

Accelerated strip cooling to form ferritic-bainitic microstructure in low-alloy X70 steel strip

The influence of two-stage accelerated cooling of hot-rolled strip on the microstructure of X70 steel with different alloying (C_equ = 0.36 and 0.43%) is investigated, in laboratory conditions. The types of bainitic-transformation products present are found to depend on the final accelerated-cooling temperature in the first cooling section (T _wi1) and the initial temperature of bainitic transformation (B _s ), which are determined experimentally. The final accelerated-cooling temperature in the second cooling section (T _wi2) determines the type and morphology of the secondary (carbon-bearing) phase. Reducing T _wi2 increases the content of acicular ferrite when T _wi1 ?? $T_{wil} \leqslant B_{S_e } $ . Such accelerated-cooling conditions are used to produce industrial batches of steel strip with guaranteed mechanical properties and DWTT data. The formation of disperse ferritic-bainitic microstructure results in an extension diagram with a degenerate yield area and consequently ensures the required strength of straight-seam K60 pipe (diameter 1020 mm).     

40Cr钢线材控冷技术的研究

以控制轧制理论为基础，对40Cr钢过冷奥氏体转变进行了试验与研究。通过THERMECMAS TOR试验建立了40Cr钢的冷却转变曲线，以此来确定高线吐丝温度、斯太尔摩速度、风机及保温盖开启等重要工艺参数。     

Prediction of shape defects during cooling of hot rolled low carbon steel strip

Abstract

Shape defects are found in hot rolled steel strip when unwrapping tightly wound coils. This problem is particularly acute in thin strips that were considered to be defect free while processing. A model developed to predict the occurrence and magnitude of such defects in hot rolled low carbon steel strip is described in the present paper. The model assumes that the strip is free of shape defects as it exits the last stand of a continuous mill, but, as a result of processing conditions, thermal and microstructural gradients are present across the width of the strip. It is considered that the variation of ferrite and austenite mixture is caused by the chemical composition of the steel and the actual temperature of the strip. On cooling to room temperature, the distribution of both temperature and microstructure will cause variation in the local contraction that the steel is subjected to, and will promote shape defects.     

冷却速率对薄带连铸低碳钢微观组织的影响

摘要：为了探究冷却速率对薄带连铸低碳钢微观组织的影响,采用相变仪设备对铸带重新加热并进行不同冷却速率冷却,采用光学显微镜、场发射电子探针和电子背散射衍射等手段对微观组织和针状铁素体形核所利用的夹杂物进行了分析。结果表明,铸带经1200℃保温3min后,原奥氏体晶粒尺寸约为150～650μm,可以满足晶内针状铁素体形核对原奥氏体晶粒尺寸的需要。在2～5℃/s的冷却速率范围内,试样中得到了大量的针状铁素体组织,冷却速率为2℃/s的试样中大角度晶界所占比例约为60%;当冷却速率大于20℃/s,针状铁素体的形成受到抑制。铸带中针状铁素体形核所利用的夹杂物是Ti-Al-Si-Mn-O+MnS复合夹杂物。     

Improving properties of a low-carbon microalloyed steel by means of accelerated cooling of dynamically recrystallized austenite

Ferrite formation from the ultra-fine dynamically recrystallized austenite (d_γ < 5 μm) was investigated on a microalloyed steel with 0.11%C. Hot rolling conditions were simulated by the hot deformation simulator Wumsi. Due to accelerated cooling a corresponding fine homogeneous ferrite grain of d_α < 2 μm was achieved with a pearlite free acicular microstructure after a cooling rate of more than 20 K/s. Excellent mechanical properties (2.0% proof stress of over 700 MPa and impact transition temperature of -180°C) were obtained, superior to those after thermomechanical processing of the same steel without dynamic recrystallization of the low-temperature austenite.     

基于密集冷却工艺的700MPa级高强带钢减小残余应力研究

目前密集冷却工艺已广泛用于生产高强度带钢,但是该技术冷却速率较快的特点易造成带钢冷却不均匀等问题,导致带钢残余应力过大,进而产生边浪等板形缺陷.本文利用有限元方法,使用ABAQUS有限元软件建立某700 MPa级高强度带钢在密集冷却工艺下的模型,实现温度-相变-应力耦合计算,并进行多个实验验证了模型的准确性.通过修改有限元模型边界条件和初始条件,研究边部遮挡和初始温差对带钢层流冷却阶段产生的残余应力分布的影响规律.对于减小带钢层流冷却过程中产生的残余应力,减小带钢进入层流冷却前的初始温差更加有效.本研究成果经过现场试验验证,可靠性较高,可用于指导该种类型高强带钢生产,以减少带钢的残余应力,提高带钢板形质量.     

热轧钢板在加速冷却时的温度模型

介绍了一个采用有限差分法开发的温度模型.该模型可预测热轧钢板在冷床加速冷却时横断面的温度变化,算法的精确性得到商业有限元软件包的验证.模型中考虑了实际生产中钢板在空气中、水平流区、水紊流区的温度演变,同时还可耦合实测的热物理参数进行计算,这有助于提高模型的精确度.     

Structure formation in the accelerated cooling of rolled reinforcement

The structure and metallic properties of hot-rolled rolled reinforcement (strength class 400) made from moderate-carbon Si-Mn and manganese steel are analyzed. Thermomechanical treatment is proposed for improvement in these characteristics.     

Fabrication of stainless steel foil utilizing chromized steel strip

Stainless steel foil has properties which are, in many respects, unmatched by alternative thin films. The high strength to weight ratio and resistance to corrosion and oxidation at elevated temperatures are generally advantageous. The aerospace and automotive industries have used Type 430 and 304 foil in turbine engine applications. Foil around 2 mils (5.1 × 10^-3 cm) thick has been appropriate for the recuperator or heat exchanger and this product has also been used in honeycomb and truss-core structures. Further, such foil has been employed as a wrap to protect tool steel parts from contamination during heat treating. A large part of the high cost of producing stainless steel foil by rolling is due to the complicated and expensive rolling mill and annealing equipment involved. A method will be described which produces (solid) stainless steel foil from chromized (coated) steel which can be cheaper than the conventional processing stainless steel, such as Type 430, from ingot to foil. Also, the material is more ductile and less work hardenable during processing to foil and consequently intermediate annealing treatments are eliminated and scrap losses minimized. Formerly with National Steel Corporation, Research and Development Department, Weirton, WV An erratum to this article is available at .