Effects of Technological Parameters on Microstructures and Properties of Low Cost Hot Rolled Dual-Phase Steel on CSP Line

The effects of technological parameters on microstructures and properties of low cost hot rolled dual-phase steel was researched by design different finish rolling temperature,mid cooling temperature between laminar cooling and UFC (ultra fast cooling) and stable UFC rate on the same gauge strips with the same chemistry composition during the manufacture process.It is the key for controlling coil temperature to control finish rolling temperature and mid cooling temperature between laminar cooling and UFC that based on stable UFC rate precondition.The lower finish rolling temperature,with mid cooling temperature between laminar cooling and UFC,the better to form martensite is.The foundation of developing the similar productions on the similar product line was supplied.It is good to technological advancement of developing high affixation value production as hot rolled DP steel,TRIP steel etc.in CSP line.     

热轧轧后层流冷却工艺设备及控制

讨论轧后层流冷却系统的系统工作原理和结构特点,并对带钢层流冷却控制模型进行了分析,同时归纳了国内部分热轧厂的层流冷却装置的布置参数．     

大型热连轧线基于超快速冷却的新一代控轧控冷技术开发与应用

超快速冷却作为近年来热轧钢材控轧控冷技术领域最重要的技术突破，为热连轧产线产品的生产工艺进步提供了重要支撑。基于热连轧板带钢超快速冷却系统的开发与应用实践，在阐明高温运动钢板高强度均匀化冷却机理机制的基础上，重点介绍了超快冷系统在热连轧产线的工艺配置，以及采用超快冷工艺，在系列细晶钢、高钢级管线钢、热轧双相钢、低残余应力热轧板带钢等特色化产品领域的工艺开发及应用情况。基于超快冷系统冷却速度无级调控优势，开发了基于超快冷装备的层流冷却、加强型冷却、超快速冷却3种冷却模式及模型系统，进一步结合粗轧中间坯超快冷控温系统，构建了基于超快速冷却的热连轧线新一代控轧控冷多工序温度协同控制系统，相关技术应用取得良好效果。     

热轧带钢氧化铁皮厚度演变的数值模拟

为了降低热轧结构钢510L氧化铁皮缺陷的发生率,对其热轧过程氧化铁皮厚度的演变进行了数值模拟,研究了精轧入口温度、精轧终轧速度、机架间冷却、层流冷却模式和成品厚度规格对氧化铁皮厚度演变的影响。模拟结果表明:在保证力学性能的热轧工艺条件下,采取较低精轧入口温度、提高终轧速度、投入机架间冷却水、使用前段冷却可有效地降低氧化铁皮的厚度。     

不锈钢热轧层流冷却过程的温度模拟

通过对不锈钢热轧层流冷却过程的传热特性分析,建立了不锈钢热过程数学模型,并对层流冷却过程的典型工况进行了数值模拟,得出了不锈钢层流冷却过程中温度的变化规律,为不锈钢层流冷却过程的优化控制提供了依据。     

Microstructural Changes after Control Rolling and Interrupted Accelerated Cooling Simulations in Pipeline Steel

The γ‐α transformation and final microstructure in pipeline steel was studied by carrying out a number of physical simulations of industrial hot rolling schedules. Particularly, the effect of the reheating temperature, deformation and cooling parameters on the transformation temperatures and final grain size were considered with a goal to obtain an appropriate thermo‐mechanical processing route which will generate appropriate microstructures for pipeline applications. The CCT diagram of the steel was derived experimentally by means of dilatometric tests. Hot torsion experiments were applied in a multi‐deformation cycle at various temperatures in the austenite region to simulate industrial rolling schedules. By variation of the reheating temperature, equivalent strain, and accelerated cooling, different types of microstructures were obtained. It was found that the deformation increases the transformation temperatures whereas the higher cooling rates after deformation decrease them. Post‐deformation microstructure consists of fine bainitic‐ferrite grains with dispersed carbides and small amount of dispersed martensite/austenite islands which can be controlled by varying the reheating temperature, deformation and post‐deformation cooling. The detailed microstructure characteristics obtained from the present work could be used to optimize the mechanical properties, strength and toughness of pipeline steel grades by an appropriate control of the thermo‐mechanical processing.     

Model Algorithm Research on Cooling Path Control of Hot-rolled Dual-phase Steel

With the development of advanced high strength steel,especially for dual-phase steel,the model algorithm for cooling control after hot rolling has to achieve the targeted coiling temperature control at the location of downcoiler whilst maintaining the cooling path control based on strip microstructure along the whole cooling section.A cooling path control algorithm was proposed for the laminar cooling process as a solution to practical difficulties associated with the realization of the thermal cycle during cooling process.The heat conduction equation coupled with the carbon diffusion equation with moving boundary was employed in order to simulate temperature change and phase transformation kinetics,making it possible to observe the temperature field and the phase fraction of the strip in real time.On this basis,an optimization method was utilized for valve settings to ensure the minimum deviations between the predicted and actual cooling path of the strip,taking into account the constraints of the cooling equipment′s specific capacity,cooling line length,etc.Results showed that the model algorithm was able to achieve the online cooling path control for dual-phase steel.     

TRIP钢在分段冷却过程中的相变行为

 建立了热轧低碳Si Mn系TRIP钢相变动力学模型。将该模型用于模拟热轧TRIP钢分段冷却过程中显微组织的演变,并定量分析了热变形和冷却速率对热变形奥氏体相变行为的影响。结果表明,预测值与实测值符合较好;降低终轧温度、提高终轧变形量,延长两相区缓冷时间都能促进铁素体相变,从而有利于提高残余奥氏体中的碳含量。     

Prediction of Microstructure and Mechanical Properties of Hot Rolled Steel Strip: Part I ‐ Description of Models

A metallurgical through‐process model is presented which describes the microstructural evolution and predicts the final mechanical properties of low carbon steel during hot strip rolling. Process models concern the thermal and deformation phenomena, which take into account the strain, strain rate and temperature distribution along the length of the strip. And the metallurgical models cover five modules, which are (i) austenitization of cast slab in reheating furnace, (ii) recrystallization of austenite in hot rolling, (iii) phase transformation of austenite‐ferrite in laminar cooling on the run‐out‐table, (iv) grain growth after coiling, and (v) final structure‐mechanical properties of products. Temperature is the main parameter and has dominant influence on the microstrutural evolution and the mechanical properties. The related temperature variation in hot strip rolling concerns air cooling, scaling, water cooling, heat transmission by roll contact, heat generation by deformation and friction. These complex factors are incorporated into the thermal models to simulate the temperature distribution along the length of the strip from the reheating furnace exit to the down‐coiler. A self‐learning algorithm is employed to improve the calculation accuracy and the computational temperatures are compared with the measured ones at typical locations. In the structure‐property relationships, two key process parameters (e.g., finishing exit temperature (FT7) and coiling temperature (CT)) are introduced in the model to consider the influence of morphology of microstructure on mechanical properties.     

成分对经济型热轧双相钢性能的影响研究

在试验室研究了不添加贵重合金元素的经济型热轧铁素体-马氏体双相(DP)钢的成分对组织力学性能的影响.结果表明:添加微量的Nb和Ti元素可提高钢的抗拉强度,同时也可提高钢的屈服强度和屈强比;锰过高或过低都会阻碍组织中马氏体的形成;适当增加硅可以提高钢的抗拉强度并降低延伸率.通过成分控制和配合适当的控轧、控冷工艺可满足DP600和DP800热轧双相钢的性能要求.     

含钼双相钢DP600相变研究和工艺实践

采用热模拟试验研究了含钼双相钢DP600在不同冷却模式、转变温度和冷却速率时的显微组织转变,分析了相变后的马氏体比例和晶粒度级别,根据热模拟结果设计了DP600钢的生产工艺,并探讨了钼元素对双相钢的影响。结果表明,DP600钢在热轧组织转变时,两段式冷却工艺比一段式工艺形成的马氏体细小,且晶粒度提升1级。奥氏体向铁素体转变过程中,存在最佳相变温度平衡点;590 ℃以上减缓DP600钢铁素体＋珠光体的过冷转变速率,可以细化晶粒、增加马氏体比例。生产的DP600钢金相显微组织为铁素体＋马氏体,马氏体比例为17%,晶粒度为11级;纵向、横向抗拉强度分别为592和620 MPa,伸长率分别为28.5%和26.5%。钼元素可以强烈抑制C- Si- Mn- Cr- Mo系DP600钢的铁素体转变,缩小铁素体转变区。     

热轧双相钢DP600关键工艺技术

在热轧双相钢中,终轧温度、卷曲温度、控冷时间和控冷温度对铁素体晶粒的大小和马氏体的形态、分布和含量都有重要影响,直接影响双相钢力学性能。通过对双相钢动态CCT曲线的模拟,制定出了合理的工艺制度,系统分析了热轧双相钢DP600热轧生产过程中终轧温度、卷取温度、控冷时间和控冷温度对双相钢的影响,对热轧双相钢的关键技术参数进行了研究,最终确定了合适的双相钢热轧生产工艺。     

加工条件对管线钢组织影响的实验研究

管线钢的最终组织和性能与控轧工艺以及加速冷却直接相关。采用一种新型的模拟轧制过程设备来研究X70级别管线钢在热变形冷却后的组织；设计了一系列的平面应变压缩实验来模拟板带轧制过程参数特别是精轧温度和冷却速率对最终组织的影响。采用恒定的变形速度70 s-1以及恒定的道次间隙时间，在850、900、950 ℃温度下的单道次和多道次压缩变形，随后研究2种不同冷却速率（3 ℃/s，6 ℃/s）获得的最终微观组织。观察发现，对于950、900、850 ℃的变温变形，出现了严重的混晶现象，而850 ℃下进行的3次压缩试样在6 ℃/s冷却到660 ℃后铁素体晶粒尺寸达到4.3 μm。     

薄板坯连铸连轧钢的组织性能综合控制理论及应用

在对国内外薄板坯连铸连轧工艺及产品开发现状及发展趋势分析的基础上,通过大量的试验研究提出了连铸连轧组织性能综合控制的概念,对钢中夹杂物超细化,锰和硫的控制,热连轧过程中的再结晶、组织细化及沉淀析出,层流冷却过程特征及对组织性能的影响以及柔性轧制工艺控制进行了研究分析,给出了通过组织性能综合控制得到的高性能低碳高强钢板（HSLC）在汽车上应用的实例。     

控轧控冷TRIP钢的微观相组成及其与力学性能的关系

采用电子背散射衍射技术等实验方法,研究了控轧控冷工艺制备的铌钒微合金化C-Mn-Si系热轧TRIP钢的显微组织及相组成,并分析了与其对应的力学性能.奥氏体轧制过程中的热变形及随后的冷却工艺对最终各相组织的形貌、大小和分布都有直接影响,并决定TRIP钢最终的力学性能.对TRIP钢卷取温度的模拟结果显示,与450和350℃模拟卷取温度相比,400℃模拟卷取温度能使该钢获得更好的综合力学性能.      

2250 mm宽带热连轧层流冷却模型的参数优化

武钢2250 mm热连轧机组在生产X60管线钢等新钢种时,原有的层流冷却系统不能适应冷却要求,影响了卷取温度的控制,导致产品组织和性能不稳定。通过层流冷却系统控制模型的优化和冷却系统相关参数的调整,使卷取温度控制命中率由原来的60%提高到89.3%,保证了产品目标组织和性能。     

304与301B奥氏体不锈钢在线固溶热处理工艺研究

通过双道次热压缩和热轧试验研究了在线固溶热处理工艺对304和301B奥氏体不锈钢组织和性能的影响,提高终了压缩温度、冷却速度,降低卷取温度,可以改善奥氏体不锈钢微观组织,减少碳化物析出,提高抗晶间腐蚀能力和力学性能.将该工艺应用于工业生产的304奥氏体不锈钢热轧卷板,测试结果表明304各项性能得到改善,冷轧前退火工序可被在线固溶取代.     

Experimental study of boiling heat transfer during subcooled water jet impingement on flat steel surface

Abstract

The growth in demand for high quality metal alloys has placed considerable emphasis on the type of cooling methods used in manufacturing processes, in particular, the production of highly tailored steel through controlled cooling on the runout table. The present study focuses on the heat transfer (cooling of hot rolled steel strips) on a runout table. The purpose of the study was to develop an efficient experimental method and collect temperature data under conditions similar to those that occur during industrial runout table conditions in a steelmill. Surface and internal temperatures were measured during transient cooling of a flat, upward facing fixed steel plate cooled by a highly subcooled single, circular, free surface jet of water. Measurements were made at stagnation and several streamwise distances from the stagnation point. A numerical, finite difference model was applied to calculate the surface heat flux using measured temperatures. The effect of water flowrate and subcooling on the overall heat transfer with emphasis on the maximum heat flux is discussed.     

济钢1700mm热轧层流冷却系统改造

针对济钢1700mm热连轧生产线原层流冷却卷取温度控制系统中存在的不足和弊端,通过采用数学模型,开发多种冷却策略,修正带钢速度变化,抛钢后处理,采用反馈控制,开发模型维护工具等措施对层流冷去系统进行改造。系统改造后稳定可靠,卷取温度命中率有了较大幅度的提高。     

Development of Fine‐Grained High‐Carbon Steel in High Reduction Low Temperature Rolling

After blanking and bending to form parts with the desired shape, high‐carbon steels are quenched and tempered to produce various machine parts. Thus, the spheroidization, formability and hardenability are very important properties for high‐carbon steels. Thermo‐Mechanical control Process of rolling has been widely used in the steel industry. However, it is difficult to apply this process to high‐carbon steels because of the heavy rolling load. Thus, fine‐grained high‐carbon hot strips were developed through high‐reduction and low‐temperature rolling by using single roll rolling mills with different diameters and laminar flow cooling devices in the finishing train, the grain size of these steels was about 3 microns. Also developed annealed strips with fine homogeneously dispersed spheroidal cementite had many excellent characteristics. For example, burring formability investigated by the hole‐expanding and surface hardness evaluated by laser hardening of the developed high‐carbon annealed steels, were excellent.