Oxide formation and alloying elements enrichment on TRIP steel surface during inter-critical annealing

The gas atmosphere in continuous annealing and galvanizing lines alters both composition and microstructure of the surface and sub‐surface of sheet steels. The alloying element enrichments and the oxide morphology on transformation‐induced plasticity steel surfaces are strongly influenced by the dew point of the furnace atmosphere and annealing temperature. The formation of a thin oxide film and enrichment of the alloying elements during annealing may result in surface defects on galvanized sheet products. The present contribution reports on the use of microanalysis techniques such as electron backscatter diffraction, glow discharge optical emission spectroscopy and electron probe micro‐analysis for the detailed surface analysis of inter‐critically annealed transformation‐induced plasticity steel such as oxide phase determination, microstructure and microtexture evolutions.     

A study on the annealing characteristics of BAF for cold rolled steel strip

The cold spot temperature control system for BAF (Batch Annealing Furnace) has been established in order to reduce energy consumption to improve productivity and to stabilize the properties of products. We improved material quality, increased output, and decreased the annealing cost and homogeneous distribution of cold spot temperature in BAF. The introduction of H₂ instead of N₂ as atmospheric gas, combined with high convection in BAF, has resulted in a considerable increase in furnace efficiency and material quality. By the low density, high diffusibility, and reducing character of H₂, a better heat transfer resulting in uniform material temperature and improved coil surface can be achieved. The results in this study are as follows: Heating time is reduced to one half by increasing the inflow rate of atmospheric gas and changing of atmospheric gas component from HN_x(H₂: 5 %, N₂: 95%) to Ax(₂: 75%, N₂: 25%) gas. The annealing cycle time is also reduced to 2.7 times. In the case of HNx BAF the cold spot moved to the center after 32 hours of heating, while in the case of H₂ BAF it moved from the one-third position of the B coli inside to the center juster after 12 hours of heating, resulting from a heat transfer increase to the radius direction. The temperature in this part is higher than any other parts when cooling. Soaking time at batch annealing cycle is decided by input coil width, and the time for quality homogenization of 1219 mm width coil must be longer by 2.0 hours than that of 914 mm width coil with the same coil weight at H₂ BAF, however, it is necessary to make 2.5 hours longer at HNx BAF.     

连铸连轧生产电工钢板的工艺技术优势

论述我国钢板生产技术的现状,分析电工钢现有生产工艺技术关键及其所存在的问题.阐述连铸连轧工艺技术的发展情况,研究和分析采用中薄板坯连铸连轧生产电工钢的技术优势及可行性,提出连铸连轧生产电工钢的课题开发研究方向.     

Recrystallization phenomena in an IF steel observed by in situ EBSD experiments

In situ electron backscatter diffraction microstructural analysis of recrystallizing interstitial free steels deformed to strains of 0.75 and 1.6 has been carried out in a FEG‐SEM. The experimental procedures are discussed, and it is shown that there is no degradation of the electron backscatter diffraction patterns at temperatures up to 800°C. Analysis of the surface and interior microstructures of annealed samples shows only minor difference, which suggests that in situ annealing experiments are of value. In addition, it is shown that in situ measurements allow a detailed comparison between the same areas before and after annealing, thereby providing information about the recrystallization mechanisms. Sequential recrystallization phenomena, such as initiation and growth of new grains, are observed at temperatures over 740°C, and depending on the deformation histories, different recrystallization behaviour is observed. It is found that {111}〈123〉 recrystallized grains are preferentially formed in the highly deformed material, whereas no strong recrystallization texture is formed in the lower strained material.     

Scanning electron microscopy observation of the substructural evolution of aluminium alloys during cold rolling and partial annealing

Classical etching techniques for revealing cold deformation and partial recrystallisation in metals have been optimised for optical microscopy, which is limited by its resolution. Detailed studies of the mechanisms involved in recovery and recrystallisation during heat treatment are generally made by transmission electron microscopy. The limitation of this technique, with a few exceptions, is its small field of view and the small fraction of the sample available for inspection. The present article departs from the statement that etching, which is a surface alteration technique, must have effects that are detectable by scanning electron microscope (SEM). It was found that carefully adapted polishing and etching procedures allow for substructural investigations by SEM, resulting in various advantages compared with both optical microscopy and TEM.     

碳钢冷轧罩式退火炉粘接缺陷种类及原因分析

罩式炉退火的冷轧卷的粘接缺陷是普遍存在的问题,严重影响冷轧钢卷的成材率,粘接缺陷的产生涉及从炼钢到平整的各道工序,主要是从粘接缺陷的表现形貌来分类,分析产生粘接的主要因素,从而提出控制方法。     

Oxide scale characterization of ferritic stainless steel and its deformation and friction in hot rolling

The oxidation kinetics of ferritic stainless steel 430 was studied in dry and humid air at 1090 °C by Thermo Gravimetric Analysis (TGA). Different atmospheres and heating times were adopted for reheating to obtain different compositions and thickness of the oxide scale. Hot rolling was performed on a 2-high Hille 100 experimental rolling mill at various reductions. Oxide scale thickness and composition were analysed with optical microscopy (OM), scanning electron microscope (SEM) and X-ray diffraction (XRD). The surface profiles were examined by a digital microscope, and the topographic features of the thin oxide scale surface were examined with an atomic force microscope (AFM) before and after rolling. The oxide scale surface and steel/oxide interface roughness were measured after rolling. Inverse calculation of the coefficient of friction was employed to analyse and the effect of oxide scale on friction in hot rolling. The coefficient of friction depends not only on the thickness of the oxide scale, but also on its composition and surface topography before hot rolling.     

冷轧生产线硅钢激光辅助切割有限元模拟

研究了激光加热辅助圆盘剪高速切割技术,以解决现有冷轧生产线硅钢切边技术存在的微裂纹、应力、毛刺和边浪等问题。建立了激光加热温度场有限元分析模型,根据生产线上圆盘剪加工的实际过程,探讨了数值模拟中热源的加载形式,研究了激光对板材进行辅助加热时各个工艺参数如激光功率、光斑尺寸以及激光入射角度对切割工艺的影响,并通过实验对工艺参数进行了优化。最后,进了验证实验。实验结果显示:当激光加热点运动至圆盘剪刃口位置时,温度为100℃左右,此时材料硬度降低到原有硬度的70%~80%,降低了切削力,减少了圆盘剪的磨损,可有效提高圆盘剪的寿命。     

Development of a meta-stable semi-synthetic lubricant for cold rolling of steel

A semi-synthetic meta-stable oil system for cold rolling of steel was developed as a substitute for a mineral oil based ‘stable emulsion’-type soluble oil. The developed oil system, comprising a ‘coating oil’ for post-pickling application and a ‘rolling oil’ for the rolling operation, was tested in the laboratory and subsequently subjected to extensive field trials in an integrated steel plant. Use of the developed oil system resulted in 25–50 per cent lower roll loads and 30–50 per cent reduction of inter-stand tensions compared with the mineral oil-based ‘stable emulsion’. It was also possible to increase the ‘strip reduction ratio’ and input coil width with the use of the newly-developed oil. Overall performance of the new semi-synthetic oil was found to be far superior to that of the mineral oil based ‘stable emulsion’.     

Evaluation of intragranular misorientation parameters measured by EBSD in a hot worked austenitic stainless steel

An extensive characterization of hot deformed austenitic stainless steel was carried out using the electron backscatter diffraction technique. Special emphasis was given to the misorientation parameters related to different length scales. These parameters show a behaviour that is sensitive to the amount of applied strain and also lead to increasing values for both the strain and the scale length.
At the same time, the use of different thresholds and scan steps in the evaluation of the parameters were analyzed in order to assess the validity of the results.     

铅浴淬火珠光体钢丝冷拔过程中显微组织及织构的演变

采用透射电镜、扫描电镜和电子背散射衍射系统等对铅浴淬火处理的珠光体钢丝以及经不同道次冷拔后钢丝的显微组织与织构进行了分析。结果表明:铅浴淬火处理后钢丝重新形成了无畸变的等轴晶粒,且获得了均匀的索氏体组织;钢丝在冷拔过程中,珠光体片层间距和渗碳体片层厚度随着钢丝直径减小而近似呈线性减小,渗碳体片层具有一定的塑性变形能力;在整个冷拔变形过程中,钢丝心部、中部和边部各区域的铁素体基体协调变形,平行于拉拔方向的铁素体〈110〉丝织构组分的面积分数逐渐增加,但其增加速度在某一区域内并不是不变的,而是具有交替性;随着真应变增大,〈110〉丝织构的强度不断增加,非关联最小取向差-频率曲线偏离Mackenzie分布,并在10°~20°和45°~60°取向差范围内出现峰值。     

Energy conservation in stainless steel cold rolling applications

In order to predict the performance of rolling oils in actual production mills, from tests in laboratory mills, the influence of various factors, such as shape factors work roll diameter (D), strip thickness (h₁), operating conditions (reduction rate (r), peripheral velocity of roll (U₀), strip velocity (U₁)) and kinematic viscosity of the rolling oil (υ₀) was investigated. A parameter RLI (Rolling Lubrication Index = u₀(U₀+U₁)(1−r)(D/2h₁.r)^½) was found to be useful in predicting lubricating conditions in actual production mill applications. The coefficients of friction of mineral oils, some synthetic hydrocarbons including polybutene, and several kinds of additives were obtained from laboratory mills under the same condition of RLI value as that for finish rolling in actual production mills. With hydrocarbons, paraffins showed the lowest coefficient offriction, while aromatics exhibited a higher coefficient of friction, with naphthenes showing the highest. A high-quality rolling oil was formulated using a combination of ester and paraffinic mineral oil. It is observed that this new oil can save 14% of energy consumed by a laboratory mill compared with conventional rolling oils. In production mills, nearly the same energy conservation level can be achieved.     

Role of synthetic esters in the overall performance of cold rolling oil for steel

Cold rolling mill productivity and product quality depend on the lubricant chemistry and composition, as well as on such physical factors as operation and maintenance. This paper discusses new requirements for rolling mill oils. Ester-based rolling oil formulations have been developed and their performance is evaluated, notably in respect of lubricity, strip cleanliness, and emulsion stability. Changes in these properties during operation and storage are also considered. It is found that the properties are greatly influenced by chemical constitution and the fat-to-ester ratio.     

冷拔高碳钢丝在退火过程的性能及织构演变

采用电子背散射衍射技术分析了冷拔高碳钢丝在600℃退火过程(0～4 h)中的织构变化,并采用扫描电镜和显微硬度计研究了此过程中钢丝的显微组织和显微硬度的变化.结果表明:该钢丝在600℃退火过程中,随着退火时间的延长,显微组织由纤维状转变为等轴晶,硬度显著下降;不同时间退火后的织构与拉拔态的织构类型相同,以<110>丝织...     

Texture control and grain refinement of AA1050 Al alloy sheets by asymmetric rolling

Asymmetric rolling, in which the circumferential velocities of the upper and lower rolls are different, can give rise to intense plastic shear strains and in turn shear deformation textures through the sheet thickness. The ideal shear deformation texture of fcc metals can be approximated by the {0 0 1}1 1 0 plus 1 1 1ND orientations, among which the latter improves the Lankford values or the deep drawability. The intense shear strains can result in the grain refinement and hence improve mechanical properties. In this paper, a study has been made of effects of asymmetric rolling variables such as reductions per pass, changes in shear direction each pass, reductions in the last pass, roll rotation rate ratios, changes in shear direction in the last pass, and different frictions on the upper and lower surfaces of AA1050 Al alloy sheets on the evolution of their deformation and annealing textures and grain refinement.     

Prediction of precipitation kinetics during homogenisation and microstructure evolution during and after hot rolling of AA5083

Because previous history of the material such as heat treatment influences the microstructure evolution during hot working, modelling of the microstructure evolution along the process chain is necessary in order to predict the resulting microstructure and hence the mechanical properties. The precipitation kinetics during homogenisation was investigated using the thermodynamic calculation software MatCalc. A physically based internal state variable model was implemented into the commercial Finite Element (FE) analysis package FORGE 2008 for hot rolling simulations of AA5083. The model allowed to predict both the stored deformation energies, i.e. dislocation density, the subgrain structure during hot rolling ,as well as the statically recrystallised volume fraction (SRX) after hot rolling. Two nucleation sites for recrystallised grains were considered to achieve a better understanding of recrystallisation kinetics.To validate the simulation results hot rolling experiments were performed by means of a laboratory mill. The grain structure evolution was analysed by the electron backscatter diffraction (EBSD). The thermo-physical data of the investigated aluminium alloy were determined experimentally.The study shows the applicability of the model to describe the microstructure evolution from casting to the hot rolled product.     

EBSD investigation of the microstructure and texture characteristics of hot deformed duplex stainless steel

The microstructure and crystallographic texture characteristics were studied in a 22Cr‐6Ni‐3Mo duplex stainless steel subjected to plastic deformation in torsion at a temperature of 1000 °C using a strain rate of 1 s^?1. High‐resolution EBSD was successfully used for precise phase and substructural characterization of this steel. The austenite/ferrite ratio and phase morphology as well as the crystallographic texture, subgrain size, misorientation angles and misorientation gradients corresponding to each phase were determined over large sample areas. The deformation mechanisms in each phase and the interrelationship between the two are discussed.     

Mathematical model for cold rolling and temper rolling process of thin steel strip

A mathematical model for cold rolling and temper rolling process of thin steel strip has been developed using the influence function method. By solving the equations describing roll gap phenomena in a unique procedure and considering more influence factors, the model offers significant improvements in accuracy, robustness and generality of the solution for the thin strip cold and temper rolling conditions. The relationship between the shape of the roll profile and the roll force is also discussed. Calculation results show that any change increasing the roll force may result in or enlarge the central flat region in the deformation zone. Applied to the temper rolling process, the model can well predict not only the rolling load but also the large forward slip. Therefore, the measured forward slip, together with the measured roll force, was used to calibrate the model. The model was installed in the setup computer of a temper rolling mill to make parallel setup calculations. The calculation results show good agreement with the measured data and the validity and precision of the model are proven.     

冷、热连轧机液压系统污染度的控制

从液压油污染的形态，液压油污染的来源，液压系统污染的原因及危害性，液压油污染度的检测和过滤器滤芯的更换，液压元件和系统的污染度等级等方面对液压系统的污染度进行分析，提出了冷、热连轧机液压系统污染度控制的具体措施，对从事冷、热连轧机液压系统设计、制造和实际使用维护的工程技术人员有其实际的启发作用。     

A study of recrystallization in single-phase aluminium using in-situ annealing in the scanning electron microscope

In‐situ annealing experiments were performed in the scanning electron microscope on a single‐phase Al?0.13Mg alloy cold rolled to different strain levels. Once the validity of the technique had been verified by comparison of the recrystallization kinetics and final grain size with bulk annealed samples, the method was used in combination with electron back‐scattered diffraction (EBSD) to study the potential mechanisms for recrystallization in this alloy. During annealing of material rolled to moderate strains (?_t < 0.7), the primary mechanism was strain‐induced boundary migration (SIBM). In material rolled to higher true strains (?_t > 1.4), recrystallization occurred extensively along pre‐existing cube bands and EBSD measurements showed that the mean size of cells within the cube bands was larger than for all other orientations measured, suggesting a size advantage was responsible for the strengthening of cube texture during recrystallization. SIBM was shown to occur concurrently with the nucleation along cube bands but this contributed a lower proportion of nucleation sites during recrystallization.