Scheduling the operations of a double-load crane in slab yards

This paper studies a double-load crane scheduling problem (DLCSP) in steel slab yards. A slab yard stores slabs in stacks. To prepare for use in production, some slabs need to be moved from one place to another. These movement tasks are performed by a double-load crane which can hold up to two slabs simultaneously. Given a set of tasks and possibly precedence relationships among them, the scheduling problem is to allocate the tasks to double-load operations and determine the schedule for the crane to perform the tasks so as to minimise the makespan. The problem is first formulated as a mixed integer linear programming (MILP) model with variables representing the order of tasks. Based on properties of the problem, it is then reformulated from a crane operation perspective. Computational experiments are carried out on practical data collected from a steel company. The results show that both models can solve practical sized problems optimally, with the second model being more efficient.     

Behaviour of surface oxide scale before roll bite in hot rolling of steel

Abstract

Hot stalling rolling tests using mild steel slabs with thin and thick scale layers, and cold stalling rolling simulation tests using lead slabs coated with brittle lacquer layers, have been conducted to investigate the behaviour of the surface oxide scales before hot rolling. The effects of rolling reduction, temperature, scale thickness and structure, and slab geometry were examined. The experimental results indicate that the oxide scale can either adhere and deform with the parent steel, or delaminate from the parent steel, or suffer from cracking before hot rolling, depending on the hot strength of the scale and the stress status in the scale, which depend on rolling reduction and temperature, and scale thickness and structure. Therefore, the cracks observed in the oxide scales on the steel slab after hot rolling are generally the combined results of cracking before rolling and further cracking in the roll gap. On the basis of comparative analysis, the prerolling behaviour of the oxide scales in a laboratory scale rolling mill and in an industrial hot strip mill is discussed.     

A nested column generation algorithm to the meta slab allocation problem in the steel making industry

This paper addresses one of the key operational decision problems in the steel industry which is related to the allocation of orders to stock materials in the surplus inventory. The meta slab allocation problem can be stated as the ‘multi-stage multiple knapsack problem’ where the problem is to design slabs using orders with similar properties (the first stage) and allocating these designed slabs into the existing meta slabs in the inventory yard (the second stage). The objective of the problem is to maximise the allocated order weights in slabs and meta slabs. For the given problem, we propose a column generation algorithm, where a column in the master problem represents meta slabs and the sub problem is to design ‘bins’, here slabs with the given orders. The sub problem itself also becomes a multiple knapsack problem and we proposed a practical set-partitioning heuristic. The proposed algorithm was tested with daily operation data given from an integrated steel company in the Asia Pacific. The computational results showed that the proposed heuristic solved the real instances pretty well. The proposed algorithm was successfully deployed to the integrated steel mill.     

Thin-slab casting: New possibilities

Changes in the IT industry are known to proceed at a scorching pace. In sharp contrast, the rate of development in the steel industry is generally slow. Nonetheless, the unpact of recenr technical development on the steel industry has been quite significant. The production chain from iron ore to final rolled steel is a long one and the shortening of this length has long been the endeanvour of scientists and engineers. The initial development came in the form of speeding up the process of steelmaking by reducing the slow open-hearth process (8 h tap-to-tap time with the 45 min tap-to-tap time of the Basic Oxygen Furnace (BOF) process. Significant development thereafter have been in the process of continuous production of billets and blooms from liquid steel thereby doing away with the large blooming mills needed for rolling ingots. For a fairly long time after the stabilition of continuous casting, hot rolling involved reheating thick (200–250mm) slabs and reducing them in a hot strip mill. The advent of thin-slab casters has made even these large hot strip mills redundant. The new installations produce thin slabs (50–70mm) that are directly nil led hin strip without the need of an intermediate furnace for raising the stock temperature; the so-called cunnel furnace prior to the rolling stands serving only to equalise stock temperatures. Additionally, what started as a step for reducing investment in hot rolling has in fact, given new opportunity for direct hot rolling of thickneses that were, for long, considered to be feasible only through the cold-rolling route. This article discusses the slow but steady encroachment of hot-rolled sheets into the domain of strip thicknesses hitherto produced by cold rolling and tries to show how the development of thin-slab casters has allowed this process to be accelerated. A techno-economic analysis of thin-slab casting: been presented along with the benefits that arise when a thin-slab caster is linked to the blast furnace and basic oxygen route of steel making.     

薄板坯连铸连轧生产石油套管用J55钢板的实践

结合本钢FTSR薄板坯连铸连轧生产线设备和工艺,开发了薄板坯连铸连轧石油套管专用J55钢。分析了薄板坯连铸连轧工艺与材料组织性能的特点,设计了舍金成分、炼钢工艺和轧钢工艺,进行了现场试生产,检验了产品微观组织和性能。在C—Mn基础上加Nb、Ti微合金化,采用LF＋RH的炉外精炼工艺,结合合理的控轧控冷工艺,达到净化钢质、改善夹杂物形态及分布,提高钢材综合力学性能的目的。     

CSP生产低碳钢的组织演变和析出物研究

为了阐明EAF-LF-CSP工艺生产的低碳钢组织细化机理,在薄板坯和不同道次变形后的同一轧件上取样,利用金相、SEM、TEM、XEDS等技术研究了连轧过程中显微组织演变和钢中第二相析出物.结果表明:与普通连铸板坯相比薄板坯的凝固组织更加细小;随轧制道次增加,薄板坯表面和心部的组织差异逐渐减小,轧后室温组织细化;CSP生产的低碳钢中存在大量纳米尺寸的氧化物和硫化物,起到细化晶粒的作用.CSP生产中采用快速冷却和凝固工艺、单道次大压下连轧工艺和层流冷却工艺,是成品组织细化的主要原因.     

A robust optimization approach for integrated steel production and batch delivery scheduling with uncertain rolling times and deterioration effect

Efficient collaboration between various sub-processes of steel production is of considerable significance, which directly affects a product’s production cycle and energy consumption. However, current collaborative optimisation models and methods in steel production are still limited: (1) Most of the current collaborative manufacturing problems in steel production focus on obtaining joint schedule between steel-making and continuous casting (SCC), and the works considering continuous casting and hot rolling (CCHR) are very few. (2) The processing time is assumed as a constant in most of the existing SCC scheduling models. However, the rolling time of a product in hot rolling operation is actually uncertain and deteriorating. (3) Exact algorithms cannot be applied to solve the complicated collaborative optimisation problems because of their high complexities. To address these problems, we propose an integrated CCHR and batch delivery scheduling model where interval rolling time and linear deterioration effect are considered. With the concept of min–max regret value, we formulate the collaborative optimisation problem as a robust optimisation problem. Instead of using the exact algorithm, we develop an Improved Variable Neighborhood Search (IVNS) algorithm incorporated a novel population update mechanism and neighbourhood structures to solve the robust optimisation problem. Moreover, we develop an exact algorithm that combines CPLEX solver and two dynamic programming algorithms to obtain the maximum regret value of a given rolling sequence. The results of computational experiments show the excellent performance of the proposed algorithms.

Abbreviations: IVNS: improved variable neighbourhood search; TOPSIS: technique for order of preference by similarity to ideal solution; PUM-TOPSIS: population update mechanism based on TOPSIS; DP: dynamic programming; NSs-PUC: neighbourhood structures based on the parameterised uniform crossover; SNRT: shortest normal rolling time; SNRT-DP: DP algorithm based on SNRT rule; BRKGA: biased random-key genetic algorithm; SCC: steelmaking and continuous casting; MINP: mixed integer nonlinear programme; CCHR: continuous casting and hot rolling; PSO: particle swarm optimisation; GA: genetic algorithm; VNS-HS: variable neighbourhood search and harmony search; HPSO?+?GA: hybrid PSO and GA; SA: simulated annealing; B&B: branch-and-bound; TPSO: two-phase soft optimisation; TSAUN: tabued simulated annealing with united-scenario neighbourhood; VNS: variable neighbourhood search; ABC: artificial bee colony; PRVNS: population-based reduced variable neighbourhood search; NS1: neighbourhood structure 1; NS2: neighbourhood structure 2; DE: differential evolution; WSR: Wilcoxon signed-rank test; ENS: exchange neighbourhood structure; IVNS-ENS: IVNS with ENS; RPI: relative percentage increase; ARPI: average RPI; SD: standard deviation.     

Inter-process synchronization in steel production

The development of strategies for sequencing slabs through the reheat furnace and rolling mill of a modern steel production facility is complicated by multiple, and often conflicting production objectives. Optimal energy efficiency through the reheat furnace may lead to inefficient rolling sequences or less than desirable product delivery schedules. Not only is model formulation complicated, but the combinatorial nature of the problem precludes optimal solution. A heuristic procedure for solving this multi-objective product sequencing problem has been developed and tested under production conditions in a Danish steel mill. The methodology, which is based on a modified ‘greedy’ algorithm is presented and results using actual production data are discussed     

钢板表面纵向裂纹的金相检验和分析

在连铸轧制的钢板表面有沿轧制方向的裂纹。采用化学成分分析,宏、微观检验等方法对裂纹进行了分析。结果表明,裂纹中存在氧化物及其脱碳等缺陷,这说明连铸坯表面在轧制前已存在裂纹并在轧前加热中裂纹内发生氧化和脱碳,导致轧制后的钢板表面出现裂纹。     

Effect of roll pass schedule on through thickness texture development in Al–Mn alloy

Abstract

During hot rolling a texture gradient is developed through the thickness of the slab. This is directly related to the different strain paths experienced by the material between the surface and the centre plane. The difference in strain path not only affects the texture, but can also give differences in stored energy though the thickness, which in turn affects the recrystallisation kinetics and ultimately the recrystallisation texture. The strain path is further complicated when a number of roll passes are involved, since the material is subjected to more complex strain paths. In the current investigation the effects of roll pass schedule (rolling direction, i.e. reverse rolling or continuous rolling) on the texture development during deformation and subsequent annealing have been characterised for an Al-1%Mn alloy. The study has shown that the texture of the surface region of the slabs is dependent on the roll pass schedule. This effect is at a maximum in the near surface region, although the effect of roll pass schedule on the recrystallisation kinetics is at a maximum 20% of the half thickness below the surface of the slabs.     

Q235B钢热轧板带孔洞及边裂缺陷成因分析

采用宏观分析、化学成分分析、金相检验以及能谱分析等方法,对某钢铁公司生产的Q235B钢热轧板带中部孔洞和边裂缺陷的成因进行了分析。结果表明：该类热轧钢板的中部孔洞和边裂缺陷是由于连铸工艺出现异常,造成连铸板坯边部产生表层气孔以及中部产生较严重的硫偏析,从而使钢板中部生成了大量的条带状硫化物,特别是低熔点FeS的生成导致了中部孔洞缺陷的产生;而连铸板坯边部的表层气孔在轧制过程中导致了边裂缺陷的产生。     

A 0-1 integer programming model and solving strategies for the slab storage problem

We consider the slab storage problem (SSP) in slab yard operations. A set of slabs enter a slab yard in a specific order. A proper stack needs to be selected for each inbound slab, so that the number of relocations in the subsequent retrieval stage is minimised. We present a 0-1 integer programming model of the SSP that minimises the lower bound of the number of relocations. Four solving strategies are derived from several interesting properties of the mathematical model to speed up the solving process of the model. Making use of randomly generated instances and practical instances, we testify the effectiveness of the solving strategies and study the influence of problem parameters on the computational time of the model. Computational results show that the solving strategies can effectively reduce the computational time of the model and is applicable in medium-sized practical instances.     

利用电磁力的新型连续铸造技术

结合电磁流体力学的基本理论,介绍了几种利用电磁力的新型连续铸造技术,包括利用交换磁场的电磁铸造,冷坩埚熔炼和钢的连续铸造初期凝固控制技术及利用稳恒磁场的电磁闸,连续铸造双层钢和水平电磁铸造技术等。     

A 2.5D finite element model for bending and straightening in continuous casting of steel slabs

This paper presents a bi‐dimensional slice model of the continuous casting process developed to focus on the risk of transverse cracking during bending and straightening of steel slabs. The model is based on the finite element method and it integrates both thermal and mechanical aspects: temperature evolution, solidification, stress and strain developments. Generalized plain strain conditions are applied in the casting direction, allowing taking account of the extraction force applied to the slab as well as strains in this direction. The model also includes an original solution to counteract the generally wrong modelling of slab bulging with such slice models. The model has been applied to an industrial case of slab casting. Some numerical results illustrate the accuracy of the model compared to results of other models, measurements and observations on the caster. Transverse cracks are predicted to be the most likely to occur at the edge on the upper face, at the end of straightening of the slab. This is due to the combination of low ductility of the material with tensile stress and elongation in the casting direction in the straightening zone. This conclusion has been confirmed by the examination of slabs that present transverse cracks. Copyright © 2006 John Wiley & Sons, Ltd.     

热轧带钢高速钢复合轧辊周期性热冲击下的温度波

建立了高速钢复合轧辊在带钢热轧过程中的2维传热模型,以Flunet6.3为计算平台,利用移动坐标系技术和自定义函数功能,研究周期性热冲击下辊内温度波的传播特点和咬入温度及轧制速度对温度波的影响,探讨高速钢复合轧辊工作层的适宜厚度。结果表明:辊内的温度场表现为以轧辊转动一周为周期的高频波和以轧制一块带坯为周期的低频波。高频波具有强烈的薄层效应,而低频温度波随深度衰减缓慢,影响范围较深。同一深度处温度波动的幅度随咬入温度的增加而增大,随轧制速度的增加而减小,且轧制参数对高频温度波的影响远大于对低频温度波的影响。工作层有足够厚度时,才能消除低频温度波对高速钢复合轧辊双金属复合界面结合质量的影响。     

棒材连轧二级过程控制系统的应用

结合企业信息化建设,阐述了建立二级过程控制系统在轧钢生产中的意义和作用,详细介绍了二级过程控制系统的硬件和软件构成、人机界面及软件功能描述等,并分析了石钢棒材连轧二级过程控制系统在生产管理中的应用特点.     

Achievements of New Generation Steel Project in China

Major achievements of the national project, Fundamental Research on New Generation of Iron and Steel Materials in China (NG Steel), are reviewed in the paper. Ultrafine grained steel technology, based on deformation induced ferrite transformation (DIFT)and successive microstructure changes, is illustrated for grain refinement in both plain low carbon steel and microalloyed steel. Delayed fracture resistance of alloy structure steel can be improved through prior austenite grain refinement. It is shown by results that nano scale precipitates play an important role to grain refinement in thin slab casting and rolling (TSCR)process. Progresses on super cleanliness, high homogeneity, welding and metallurgical process simulation are also briefly introduced.     

钢板表面发裂缺陷成因的初步探讨

热轧钢板和镀锌板多次出现表面发裂缺陷,利用光学金相和扫描电镜分析方法,对发裂缺陷的宏、微观形貌特征、缺陷部位钢的冶金质量变化等进行了检验和分析。认为,发裂缺陷是板坯连铸时产生的较深沟形振痕残余造成的。     

Achievements of New Generation Steel Project in China

Major achievements of the national project, Fundamental Research on New Generation of Iron and Steel Materials in China (NG Steel). are reviewed in the paper. Uhrafine grained steel technology, based on deformarion induced ferrite trartsformation (DIFT)and successivechanges, is illustrated tor grain refinement in both plain low carbon steel and mieroalloyed steel. Delayed fracture resistance of alloy structure steel can be improved through prior austenite grain refinement. It is shown by results that nano scale precipitates play an important role to grain refinement in thin slab casting and rolling (TSCR)process. Progresses on super cleanliness, high homogeneity, welding and metallurgical process simulation are also briefly introduced.     

取向硅钢制备工艺及其发展趋势

取向硅钢作为一种重要的铁芯材料,在电力行业中有着广泛的应用.基于生产工艺及技术特点,取向硅钢的制备工艺可以分为传统厚板坯工艺、薄板坯连铸连轧工艺及双辊薄带连铸工艺.传统的厚板坯工艺是工业生产取向硅钢的主要方法,其按加热温度又可分为板坯高温加热、板坯中温加热以及板坯低温加热工艺,其中板坯低温加热工艺具有加热温度低、能耗少...