Correlation of Microstructure and Cracking Phenomenon Occurring during Hot Rolling of Lightweight Steel Plates

An investigation was conducted into the correlation of microstructure and the cracking phenomenon that often occurred in hot-rolled lightweight steel plates. Two kinds of steels were fabricated with varying Mn and Al contents, and their microstructures, tensile properties, and high-temperature transformation behavior were investigated. In the two steels, banded structures containing ferrite grains and κ-carbides were well developed along the rolling direction. Detailed microstructural analyses showed that cracks initiated at film-type κ-carbides continuously formed interfaces between bands, while the band populated with κ-carbides did not play an important role in initiating cracks. Thus, the formation of band structures and film-type interfacial κ-carbides must be minimized to prevent the cracking. The decreased content of hardenability elements, including aluminum, higher finish-rolling temperature, reduced central segregation during the slabmaking process, and decreased material variation during hot rolling, were suggested as practical methods for preventing the cracking.     

Effect of Carbon Content on Cracking Phenomenon Occurring during Cold Rolling of Three Light-Weight Steel Plates

Effects of carbon content on cracking phenomenon, which often occurred in cold-rolled light-weight steel plates, were investigated in this study. Three steels were fabricated by varying carbon content, and their microstructures and tensile properties were investigated. The steel containing low carbon content of 0.1 wt pct consisted of thin κ-carbide bands, coarse band boundary κ-carbides, and ferrites. As the carbon content increased, volume fractions of κ-carbide bands and total κ-carbides increased, and band boundary κ-carbides were finely distributed in relatively wide band boundary areas. Microstructural observation of the deformed region of tensile specimens revealed that coarse κ-carbides continuously formed along band boundaries worked to initiate the cracking or to facilitate the abrupt crack propagation into ferrites or band boundaries in a cleavage fracture mode, while bands densely populated with fine, lamellar κ-carbides did not play a critical role in the cracking. Thus, the increase in carbon content effectively minimized the formation of band boundary carbides and reduced their size, thereby resulting in the prevention of cracking during cold rolling and in the simultaneous improvement of ductility and strength.     

热轧钢带边裂原因分析

针对济钢J55热轧钢带边裂问题,通过低倍组织检验、金相和光谱分析、化学成分试验等方法,分析了生产过程控制参数,研究了热轧钢带边裂的成因,提出了改进措施,并取得了显著效果。     

Texture Evolution in Ferritic Rolled Ti-IF Steel during Cold Rolling

 Texture evolution of ferritic hot rolled Ti-IF steel was investigated during cold rolling in the reduction from 15% to 85%. It was found that, α fibre intensified monotonously with the increase of the cold reduction, but γ fibre changed in a different way. As the cold reduction was in the range of 15%-35% or 45%-75%, γ fibre intensified. While the reduction was between 35%-45% or 75%-85%, the intensity of γ fibre reduced. γ fibre displayed the maximum intensity at 75% and the highest average plastic strain ratio due to the favorable recrystallization texture was obtained at this point.     

Effects of Annealing Temperature on Microstructure and Tensile Properties in Ferritic Lightweight Steels

An investigation was conducted into the effects of annealing temperature on microstructure and tensile properties of ferritic lightweight steels. Two steels were fabricated by varying the C content, and were annealed at 573 K to 1173 K (300 °C to 900 °C) for 1 hour. According to the microstructural analysis results, κ-carbides were formed at about 973 K (700 °C), which was confirmed by equilibrium phase diagrams calculated from a THERMO-CALC program. In the steel containing low carbon content, needle-shaped κ-carbides were homogeneously dispersed in the ferrite matrix, whereas bulky band-shaped martensites were distributed in the steel containing high carbon content. In the 973 K (700 °C)-annealed specimen of the steel containing high carbon content, deformation bands were formed throughout the specimen, while fine carbides were sufficiently deformed inside the deformation bands, thereby resulting in the greatest level of strength and ductility. These results indicated that the appropriate annealing treatment of steel containing high carbon content was useful for the improvement of both strength and ductility over steel containing low carbon content.     

冷轧不锈钢连续退火在线检测

为快速反馈不锈钢带退火质量,减少退火工艺调整时间,降低取样费用,根据奥氏体不锈钢和铁素体不锈钢的特点,用超声波和剩磁法在线检测退火后晶粒尺寸,有效控制连续退火酸洗线带钢退火性能,目前已在国内外多条冷轧不锈钢连续退火酸洗线上得到了成功应用。     

冷轧过程中IF钢的织构演变

以铁素体区热轧低温卷取的Ti-IF钢为研究对象,选择13%~75%的冷轧压下率,观察在冷轧过程中织构的演变。研究表明,压下率为46%是一个转折点,冷轧压下率较小(13%~35%)时,表面上取向变化为{110}001→{554}225→{111}112→{111}110→{223}110,{114}110转向{001}110;压下率达到46%时,{111}织构消失;继续增加压下率,{111}织构再次出现,并随压下率增加而增强。随着冷轧压下率的增加,中心面上的{111}织构强度先增加,压下率达到46%后又降低,最强组分先由{001}110向{223}110转动;压下率达46%时,又向反方向转动。     

预先冷轧变形对马氏体时效钢强化的影响

系统研究了预先冷轧变形对马氏体时效钢强化的影响,研究结果表明:510℃×3 h时效引起的强度净增加值恒定,与冷轧变形量无关,最终的强度为:σ=σ0 △σCR △σAge,即初始强度、冷加工强化和时效强化的叠加,其中只有冷加工强化△σCR随变形量变化.电子衍射花样及衍射斑强度分布证实:510℃×3 h时效后马氏体基体内析出六方结构的Ni3(Ti,Mo)和正交结构的Ni3 Mo,冷轧变形量对时效析出行为没有明显的影响.     

Influence of the Cold Rolling and Annealing Sequence on the Ridging Behaviour of Ti‐Stabilized 18% Cr Ferritic Stainless Steel

The influence of the cold rolling and annealing sequence on the ridging resistance and the crystallographic texture distribution of AISI 439 type ferritic stainless steel was studied in order to determine optimal processing conditions for surface quality improvement. In the present study, the effect of two sequences of cold rolling and annealing were analysed: a single cold rolling and annealing, and an interrupted cold rolling with an intermediate and a final anneal. In the conventional single step cold rolling, the ridging resistance was found to deteriorate with increasing cold reduction ratio. For a fixed total cold reduction ratio in the two stage cold rolling, ridging was less pronounced when a higher reduction was applied in the second step. Band‐like clusters of grains with similar crystallographic orientations were observed in the mid‐thickness of sheets with severe ridging. The results show that severe ridging is related to the presence of band‐like clusters of 〈111〉//ND oriented grains. The two stage cold rolling was found to result in less band‐like clusters and an improved surface quality.     

Effects of Prior Cold Rolling and Post Temper Rolling on the Properties of Continuously Annealed Low Carbon Dual Phase Steel

The effects of two processing variables, prior cold reduction and temper rolling, on the mechanical properties of a continuously annealed 0.05 pct C low alloy dual phase steel were studied. It was found that cold rolling affected the strength of the dual phase steel through its influence on the recrystallized ferrite grain size. The correlation between yield strength and mean free path in ferrite was shown to follow a Hall-Petch type relationship. Similarly, temper rolling also had a pronounced effect on the yield strength of the steel. The effect was strongly dependent upon the previous overaging treatment; the lower the overaging temperature, the stronger the effect. Basically, the effect of temper rolling on dual phase steel was not much different from that on mild steel and HSLA in terms of the change in yield strength and yield point elongation. Another interesting observation was the influence of quenching rate on the strength of the dual phase steel. A slower quenching rate in the heavier gauge dual phase steel caused pearlite rims to form around martensite colonies and thus decreased the strength of the steel.     

冷轧薄钢板退火再结晶的计算机模拟

采用Monte Carlo方法和简化的物理模型所编制的程序较好地模拟了冷轧钢板退火组织的演变过程及变化规律，模拟程序所演示的退火过程晶粒尺寸和再结晶百分比变化与实验所得到的结果一致。     

酒钢炉卷轧机生产铁素体不锈钢黑卷边损缺陷控制

边损是不锈钢热轧黑卷生产过程中常见的质量缺陷,通过统计、分析边损产生原因,制订了相应的技术措施,优化铁索体不锈钢加热温度、在炉时间和出炉温度等热轧工艺制度,以降低边损质量缺陷数量和比例。结果表明：边损缺陷数量由2006年的1909．630t减少至113．431t,减少1796．199t,边损缺陷比例由1．469下降至0．050％,下降幅度为96．58％。     

无取向电工钢冷轧及退火织构的演变

运用不同冷轧、退火工艺的实验及ODF分析方法,分析了电工钢50W600的热轧织构、冷轧织构及再结晶织构的演变.研究表明:热轧带几乎是随机织构,α线非常弱;随着冷轧变形量的提高,晶粒在α线取向附近聚集程度不断提高,变形81%时,{001}《110》和{112}《110》取向密度分别为12和14.随退火温度升高和保温时间延长,α线的取向密度下降,{001}《110》和{112}《110》取向密度急剧降低,γ线{111}《112》密度显著增加,晶粒取向绝大多数聚集在γ线{111}《112》取向附近.通过控制冷轧及退火工艺,可有利于发展高{100}织构组分的冷轧无取向电工钢.     

冷轧压下量和退火温度对Ti-IF钢性能的影响

采用正交试验法研究了冷轧压下量(65%～80%)和退火温度(660～780℃)对Ti-IF钢(/%:0.02C、0.012Si、0.10Mn、0.013P、0.011S、0.064Ti、0.0020N)组织、力学和成形性能的影响。试验结果表明,≥700℃退火Ti-IF钢再结晶基本完成,当压下量75%700℃退火时,该钢具有较好的综合性能:屈服强度120 MPa,屈强比0.38,应变硬化指数n值0.25,塑性应变比r值1.65。     

窄带钢冷轧边鼓产生原因及预防

根据半连续窄带钢生产车间生产工艺特点,结合已有窄钢带断面厚度控制研究成果,针对唐山国丰钢铁有限公司轧钢厂具体工艺控制及设备装备情况,调整加热制度、修改精轧机立轧孔型、提高精轧机轧辊耐磨度、改善轧辊冷却条件,消除了热轧窄钢带边部局部高点。     

酒钢不锈钢冷轧连续退火炉技术

从不锈钢冷轧退火工艺开始,介绍了酒钢不锈钢冷轧连续退火炉设备特点和生产工艺。     

冷轧压下率和再结晶退火温度对Ti-IF钢织构和成型性能的影响

采用背散射衍射技术(EBSD)研究了3.13 mm热轧板的冷轧压下量(65%~80%)和再结晶退火温度(660~780℃)对0.64~1.10 mm Ti-IF钢冷轧板(/%:0.02C、0.01Si、0.10Mn、0.013P、0.011S、0.064 Ti、0.028Al、0.002 0N)的织构和成型性能应变硬化指数(n)、塑性应变比(r)的影响。结果表明,Ti-IF钢冷轧板在冷轧压下率为75%时{111}织构含量最大,成型性能最佳;在740℃以下再结晶退火时材料{111}<110>织构含量高,高于740℃时材料{111}<112>织构含量高;在660~780℃再结晶退火随温度增高,材料{111}织构含量增加,成型性能提高。     

Analysis of Microstructure Effects on Edge Crack of Thin Strip During Cold Rolling

Edge cracks in cold rolling of the thin strip affect the strip quality and productivity significantly. In this study, an experimental and mechanical investigation on microstructures has been carried out to study the edge crack formation during cold rolling of the thin strip. The effects of the feed material microstructures on the edge crack evolution were studied employing optical microscopy and scanning electron microscopy (SEM). Experimental observation indicates that fine grain occurs in hot-rolled microstructure and coarse grain is produced in ferritic rolled microstructure. Different grain sizes affect significantly the formation mechanics of the microcrack, crack initiation, and orientation of crack extension. The grain size and grain boundaries effects on crack retardation are discussed also during edge crack initiation. During the crack growth in coarse grain, most edge crack tips will blunt, which improves the crack toughness by causing less stress concentration. Overall, the fine microstructure shows a good crack initiation resistance, whereas the coarse microstructure has a better resistance to crack propagation. This research provides additional understanding of the mechanism of microstructure influence on edge crack evolution of cold strip rolling, which could be helpful for developing defect-free thin strip.