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。     

高层建筑用Q345GJC钢板表面裂纹成因分析

采用宏观分析、化学成分分析、金相检验、扫描电镜观察和能谱分析等方法对某批轧制后表面存在纵向裂纹的高层建筑用Q345GJC钢板的裂纹形成原因进行了分析。结果表明:钢板表面裂纹在连铸板坯上就已经存在,裂纹产生的主要原因是在连铸过程中结晶器涂层严重磨损致使铜板外露,从而使铜元素渗入到连铸板坯中,降低了钢的热塑性,导致了裂纹的产生;在随后的轧制过程中,裂纹沿轧制方向进一步扩展形成纵向裂纹。     

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。     

连铸二冷区红外测温

冶金行业目前已广泛采用的连铸工艺的关键技术是在不断裂、不漏钢的前提下保持最高的拉速。中间包的钢水通过结晶器成型，并在外表面形成薄壳，再经雾冷室逐步从薄壳向内部冷却，依据结晶器模的形状，最后形成所需要的圆坯、方坯或板坯。全部过程的温度控制是极其重要的，冷却不足，温度过高，容易发生断裂和漏钢事故；     

马钢热轧薄板连铸生产中的称重装置

马鞍山钢铁股份公司在新建热轧薄板连铸生产线时,为了满足大型板坯连铸工艺的要求,从德国引进了处于当今国际先进水平的连铸大包回转台钢水称重装置、中间包台车钢水称重装置。其中大包称重装置用来控制大包内不断降低的钢水液位,并在渣层接近     

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。     

SPHD热轧带钢边部翘皮缺陷分析

在SPHD热轧带钢边部发现有翘皮缺陷。通过宏观检验、化学成分分析、金相检验、扫描电镜及能谱分析等方法对带钢边部翘皮的原因进行了分析。结果表明:连铸时结晶器内的保护渣卷入铸坯表层,轧制变形后被拉长存在于带钢皮下表层是引起SPHD带钢翘皮缺陷的主要原因。SPHD带钢经过粗轧道次的变形,中间坯角部低温区在一定的立辊侧压作用下产生了超出板坯材料热塑性容限的变形,形成角部裂纹,这种裂纹在随后的轧制过程中不能被焊合,形成沿轧制方向断续迭层分布的翘皮缺陷,并随中间坯侧边"翻边"过程的进行向板坯上下表面翻转,最终分布在热轧板边部区域。     

310S不锈钢中厚板表面裂纹缺陷形成原因

针对310S不锈钢中厚板表面出现裂纹缺陷的问题,对其连铸坯进行了低倍组织检测及表面渗透检测,再对产生裂纹缺陷的热轧钢板进行了扫描电镜分析及金相检验。结果表明：热轧钢板明显分成再结晶和未再结晶区域,裂纹均位于再结晶区域;由于再结晶和未再结晶区域组织的变形抗力不同,在钢板轧制过程中,变形抗力弱的区域开始出现裂纹,并扩展到钢板表面,这是产生表面裂纹缺陷的主要原因。     

冷轧镀锌板表面缺陷分析

采用宏、微观检验、扫描电镜观察和能谱分析等方法对冷轧和镀锌钢板表面缺陷进行分析。结果表明：夹层状和短细线状表面缺陷属于夹杂类缺陷,长细线状表面缺陷则源于板坯纵向裂纹。产生表面夹杂和裂纹缺陷的主要原因与钢液质量和连铸坯质量有关。     

连铸钢板坯凝固壳横截面变形与内部裂纹的关系

对实际观察到的连铸钢板坯拉出结晶器时的横截面形状与最终形成的内部裂纹进行了理论分析，找到了凝固壳横截面形状变化与内部裂纹的形成及种类之间的因果关系及规律性，为预防连铸钢板坯内部裂纹提供了理论依据。同时对YB／T4003-1991标准中的有关问题进行了讨论，并从生产工艺角度概述了影响连铸钢板坯内部裂纹的各种因素。     

On the Occurrences of “Frizzle-Type” Surface Defects in a Hot-Rolled Steel Plate

Metallurgical investigations were directed to probe into the genesis of “frizzle” and fissure-type surface defects on 10-mm hot-rolled steel plates meant for application in flat-bed wagons for carrying heavy machinery. The thin hairline fissures on the steel plates were identified as skin laminations associated with long, shallow, and branched cracks, intruding from the plate surfaces to the interior with curved contours, replete with fragmented oxide scale entrapments and debris. The incidence of these superficial defects on the plates was linked to surface damage to the solidifying skin of continuously cast steel slabs, induced by the extensive pitting and cavitation of caster pinch rolls. It is presumed that during hot rolling of the steel slabs, surface blemishes like indentations and folds got rolled over by metal flow, entrapping copious amounts of primary as well as secondary scales underneath the laminated skin. Under the influence of shear forces during rolling, the defects are believed to have ingressed further into the plate interior leading to the formation of long, shallow, and branched cracks with curved contours and entrapped fragmented oxide scales.     

Effect of carbon on the mechanical properties of powder-processed Fe-0.45wt% P alloys

The present paper records the results of mechanical tests on iron-phosphorus powder alloys which were made using a hot powder forging technique. In this process mild steel encapsulated powders were hot forged into slabs. Then the slabs were hot rolled and annealed to relieve the residual stresses. These alloys were characterized in terms of microstructure, porosity content/densification, hardness and tensile properties. Densification as high as 98.9% of theoretical density; has been realized. Microstructures of these alloys consist of single-phase ferrite only. Alloys containing 0.45 wt% P; such as Fe-0.45P-2Cu-2Ni-1Si-0.5Mo and Fe-0.45P-2Cu-2Ni-1Si-0.5Mo-0.15C show very high strength. Alloys developed in the present investigation were capable of being hot enough to be worked to very thin sheets and fine wires.     

Investigation into the Cracking of SAILMA 350 HI During Forming

Vanadium microalloyed hot rolled steel of 13.8 mm thickness, when hot formed at 900 °C into axle housings were rejected because of a prominent crack running along the length of the component. A detailed metallurgical investigation revealed that the cracking during forming was the result of the opening up of pre-existing fine crack along the length of the hot rolled coils. These cracks were barely visible on the hot rolled coils that were formed into the axle housings. Metallographic and hardness tests indicated that these cracks might have been generated as a result of decarburization of the slab during soaking that led to a softer surface layer of the slab. During subsequent hot rolling mechanical defect might have been caused on the decarburized surface that is much softer than a material with a usual carbon content. It was concluded that soaking in the reheating furnace with low carbon potential might have led to extensive decarburization of the slabs. Soaking in a furnace atmosphere with adequate carbon potential was recommended as a remedial measure to prevent decarburization of the surface layers of the slabs.     

10MnNiCr钢板应变时效敏感性研究

对10MnNiCr钢板进行了应变时效敏感性试验。结果表明,10MnNiCr钢热轧薄板、调质厚板具有较低的应变时效敏感性,而正火+高温回火热处理的10MnNiCr钢中板具有较高的应变时效敏感性。改善钢的微观组织,提高钢的韧性,可降低钢的应变时效敏感性。     

热轧高Ni高强钢的表面晶界特征和电化学行为

采用EBSD技术和原子力显微镜(AFM)测试了10CrNi5Mo高强钢热轧态和热处理态试样的表面晶界分布特征和微观形貌, 用模拟海水全浸实验方法及电化学阻抗谱技术测试了10CrNi5Mo高强钢在模拟海水中的腐蚀行为。结果表明: 热轧态试样表面具有更高比例的小角度晶界, 经硝酸酒精腐蚀后热处理态试样表面腐蚀更为均匀, 粗糙度更小。进行模拟海水全浸实验时热轧态试样呈现出更好的耐腐蚀性能, 浸泡中期阻抗值增大, 表面腐蚀产物与基体结合更为紧密, 能保护基体防止其与溶液发生电化学反应。     

Elimination of Surface Defects in High Tensile Steel for Wheel Rim Application

One of the important applications of high tensile steel grades is in wheel rims by the automotive industry. High tensile steel facilitates vehicle weight reduction under the ‘Go Green’ initiative. Along with weight reduction, in recent times, the surface quality requirement of steels for wheel rim applications has also gained a significant focus, and in many cases, it is becoming the cause of rejection at the customers’ processing line. It is known that owing to chemistry requirements such high strength steel grades generally show peritectic behavior during solidification and are prone to surface defects. Tata Steel India produces several wheel rim grades of varying strength levels. In one such high manganese and micro-alloyed peritectic steel grade, the rejection by the customer on account of surface defects was a major concern. The defects consisted of typical longitudinal cracks of varying dimensions along with the unique defects in transverse direction named tear marks on the surface of 100-mm-thick plates rolled from 215-mm-thick slab. In subsequent stages, these plates were processed into rim profiles through hot working by the wheel customer. The paper highlights how systematic study led to arrive at root causes and helped redesign steel chemistry to ensure zero rejection for surface quality without affecting mechanical property requirements.     

Effect of carbon on mechanical properties of powder-processed Fe-0.35%P alloys

The present paper records the results of mechanical tests on iron-phosphorus powder alloys which were made using a hot powder forging technique. In this process mild steel encapsulated powders were hot forged into slabs, hot rolled and annealed to relieve the residual stresses. These alloys were characterized in terms of microstructure, porosity content/densification, hardness and tensile properties. Densification as high as 98.9% of theoretical density, has been realized. Microstructures of these alloys consist of single-phase ferrite only. Alloys containing 0.35 wt% P, such as Fe-0.35P-2Cu-2Ni-1Si-0.5Mo and Fe-0.35P-2Cu-2Ni-1Si-0.5Mo-0.15C show very high strength. It was observed in this present investigation that, the alloying additions, such as Si, Mo, Ni, and C to Fe-P based alloys caused increase in strength along with reduction in ductility. Cu reduces porosity of Fe-P alloys. Alloys developed in the present investigation were capable of hot working to very thin gauge of sheets and wires.     

连铸坯热送轧制对钢的组织与性能影响初探

对连铸坯热送轧制工艺进行了探索,同时对冷、热送坯所轧制钢材的组织和性能进行了对比试验。提出了较为合适的轧制工艺,在此工艺条件下,热送坯所轧制的钢材比冷送坯所轧制的钢材力学性能略好。     

Two-staged guillotine cut,two-dimensional bin packing optimisation with flexible bin size for steel mother plate design

This paper looks into the steel mother plate design problem. A slab, which is an intermediate work in process, is subsequently rolled into a mother plate with the specific dimensions of thickness, length, and width. The mother plate is then cut into customer order plates. As a slab is rolled into a mother plate through a series of horizontal and vertical rolling processes, different-sized mother plates can be generated from a single-slab type. This flexibility allows for the size of a mother plate to be determined according to the order plates assigned to it. Furthermore, when the order plates are cut from a mother plate, a guillotine cut is required to reduce the production cost. The steel mother plate design problem involves the placing of order plates on the mother plates in a guillotine cut pattern and determining the sizes of the mother plates with the objective of minimising the number of slabs; thus it may be considered as a two-staged guillotine cut, two-dimensional bin packing problem with flexible bin size. This paper introduces the problem, presents several mathematical models, and proposes an iterative two-phase heuristic method consisting of several algorithms to solve the problem. Computational results for the benchmark problems show the effectiveness of the proposed method.     

Design of Complex Sheet Metal Forming Processes: A New Computer Aided Progressive Approach

Ridge-buckle defects in cold rolled thin strip originate from the formation of ridges in hot rolled coil and corresponding ridges left in the strip following annealing, cold rolling and tempering. A numerical solution was developed to calculate three-dimensional stress distribution in a wound coil built up wrap-by-wrap and subsequent flatness change in the uncoiled product. The model takes into account both nonlinear compressible characteristic of interwrap layer and uneven strip profile, especially ridges, on the stress evolution during the coiling process. The sensitivity of ridge-buckle defects in cold rolled thin strip to ridges in hot rolled coil profile has been investigated in details. The results show that the ridge-buckle defects in tin plate are much dependent on the height, width and location of ridges in hot coil profile. The permissible tolerance of ridges in hot rolled coil, below which does not produce the ridge-buckle defects in subsequent cold rolling of thin strip, are recommended for different steel grades.