耐候钢层冷边浪缺陷原因分析与控制

针对某产线SPA-H耐候带钢层冷边浪缺陷问题,分析了其产生机理,即是由于带钢宽度方向冷却不均,中部与边部相变不同步,热应力和相变应力的耦合作用而产生的。结合SPA-H钢的CCT曲线,开展了轧制速度、终轧温度、卷取温度对层冷后带钢板形影响的试验研究。结果表明,轧制速度、终轧温度和卷取温度对带钢层冷后板形均有影响。为此,对工艺参数进行了优化,将轧制速度控制在8 m/s以内,终轧温度由850 ℃降低到840 ℃,卷取温度由540 ℃提高到580 ℃,带钢板形明显改善;提高卷取温度后带钢强度降低,通过增加合金元素Mn、Cr的含量,可以确保带钢性能;同时,结合设备排查措施,使耐候带钢层冷边浪缺陷得到了有效控制。     

热轧带钢氧化层卷取与冷却过程中相变研究

利用Gleeble3500试验机模拟热轧带钢氧化层在不同卷取温度和冷却速度条件下的相变过程,采用激光拉曼光谱区分氧化层中细小析出相和分层组织结构。结果表明：氧化层中FeO在不同卷取温度和冷却速度条件下可形成几种典型的相变组织形态;降低带钢卷取温度和增加卷取后的冷却速度,有利于抑制Fe3O4在FeO层中的析出,提高热轧带钢表面氧化层酸洗去除效果。     

厚规格宽带钢卷取温度优化研究

针对安钢热轧厚规格宽带钢卷取温度命中率偏低的问题进行了分析,通过投用保温罩,改善精轧过程控制,优化带钢卷取温度控制模型,提高了厚规格宽带钢的卷取温度命中率,改善了产品的同卷性能均匀性.     

提高薄规格带钢卷取温度控制精度的措施

卷取温度是影响带钢组织性能的重要工艺参数之一,受头尾板形、速度变化等因素影响,薄规格带钢卷取温度控制较为困难。首钢京唐钢铁联合有限责任公司1 580 mm热轧生产线采用优化钢种族、差异化的目标卷取温度策略和干头温度补偿等手段,较好地提高了薄规格带钢卷取温度控制的稳定性和头尾温度控制的精度。     

卷取机芯轴张力对热轧带钢卷取温度控制的影响分析

热轧带钢卷取温度控制过程中,带钢速度是最重要的影响因素之一。当带钢尾部离开精轧末机架后,带钢速度由轧辊线速度转化为卷取机芯轴速度,复杂的卷取过程影响了带钢速度的稳定,导致带钢尾部卷取温度控制出现严重偏差。为了解决该问题,将温度模型、张力扭矩模型以及热轧生产大数据进行有机结合并进行了系统性分析。结果表明：卷取机芯轴张力控制异常是造成带钢卷取温度偏差的主要原因。因此,开发了卷取机芯轴张力报警功能,细化了芯轴张力与夹送辊压力控制的带钢厚度层别,优化了控制参数以保证带钢速度稳定,同时开发了带钢尾部卷取温度补偿模型。结合多目标优化,取得了较好的应用效果,带钢尾部温度超差占比下降3.26%,卷取温度命中率提升2.29%,为全面解决带钢通长方向卷取温度命中率提供了新的技术方案。     

卷取温度对CSP铁素体轧制低碳钢组织性能的影响

采用不同卷取温度的CSP铁素体轧制工艺生产低碳钢,通过显微组织、微观析出物、位错密度及性能测试研究了卷取温度对CSP铁素体轧制低碳钢组织和性能的影响。研究结果表明：试样组织均由较粗的铁素体+少量珠光体组成,析出物为Al、Ti、Si的氧化物或氮化物,部分还与MnS复合;卷取温度由700℃下降至620℃时,屈服强度和抗拉强度分别增加了31.6和25.9 MPa,硬度波动范围由12 HRB上升至25 HRB。提高卷取温度可以促进铁素体晶粒均匀化长大、降低位错密度,能够有效降低强度并提高性能的均匀性。     

SS400B热轧带钢四次氧化铁皮成因分析及控制

针对厚规格（h≥8 mm）SS400B热轧带钢用户开平后出现黑色起粉问题,从板坯规格、轧制温度、轧制速率以及轧后冷却过程等方面详细分析了其氧化铁皮形成原因,通过提高轧制速率、降低卷取温度、将钢卷放置通风处等措施,减少了氧化铁皮残留和四次氧化铁皮的形成,解决了卷取后带钢表面氧化铁皮起粉问题。     

热轧带钢椭圆卷缺陷成因分析与控制

针对某厂2 250 mm热轧产线带钢在卷取过程中产生椭圆卷缺陷的问题,结合设备状态和生产实际,分析了产生椭圆卷缺陷的原因,并提出了有效的控制措施。结果表明：热轧带钢椭圆卷缺陷产生的主要原因为带钢板形或横断面形状不良、卷形工艺控制和卷取温度控制不合理。通过优化带钢板形和横断面控制,优化带钢头部跟踪,提高卷取张力,采用助卷辊压力控制,优化助卷辊压力设定和芯轴扩张时机,调整卷取温度,改变相变过程等控制措施,使椭圆卷缺陷得到了有效控制,卷形质量得到了大幅提升,提高了产品竞争力。     

冷却工艺对Ti微合金热轧带钢组织和性能的影响

对两种厚度(1.5、8.0 mm)的Ti微合金热轧带钢进行了不同冷却工艺的现场试验,研究了稀疏冷却、优化稀疏冷却,前段冷却以及前段密集冷却工艺下热轧带钢组织和力学性能。结果表明,1.5 mm带钢卷取温度520和500℃时,优化稀疏冷却工艺比稀疏冷却工艺屈服强度稍有提高;在卷取温度480℃时,屈服强度和抗拉强度分别提高24和30 MPa。与前段冷却工艺的8.0 mm热轧带钢相比,采用前段密集冷却工艺的屈服强度和抗拉强度分别提高51和46MPa,断后伸长率和低温冲击前段功稍有降低,但在-60℃时冲击功仍能达到160 J,保持较高的冲击性能。     

深冲用SPHC钢开裂原因分析及改进措施

针对某厂生产的SPHC热轧酸洗卷在制作压缩机壳体过程中出现了制耳甚至开裂的现象,对其产生原因进行了研究。结果表明,SPHC低碳钢的Ar3温度较高,而终轧温度偏低,导致其在两相区轧制且带钢长度和宽度方向温度不均,使SPHC带钢产生混晶或粗晶组织,这是产生深冲开裂和制耳的主要原因。为此,提出了工艺改进措施,如提高加热温度、减少除鳞水;增加中间坯厚度、提高穿带和轧制速度、加盖保温罩、采用热卷取箱等,以保证薄规格SPHC带钢的终轧温度不小于910 ℃且改善带钢温度均匀性。生产实践表明,采用改进措施后,显著提高了薄规格SPHC带钢深冲性能,开裂率由30%降低至3‰。     

低屈服强度微碳钢冷轧带钢的生产实践

针对汽车冲压零部件对冷轧带钢提出的低屈服强度、高伸长率、低成本的要求,采用降低钢中碳质量分数至0.010%～0030%、适当添加B元素（质量分数0.001 5%～0.002 5%）的微碳钢,并采取U形卷取温度控制、高温卷取和连续退火等措施,微碳钢成品钢卷屈服强度下降到180 MPa以下的占比达95%以上,产品性能满足汽车零部件冲压要求。     

罩退冷轧薄规格IF钢横向性能波动原因及控制

针对罩退冷轧薄规格IF钢产品横向性能波动大的问题,系统分析了带钢宽度不同位置的性能、组织、化学成分差异特点,以及从冶炼、热轧、酸轧到退火等不同工序下的碳含量变化情况。结果表明:性能异常带钢边部强度和碳含量明显高于中部,屈服强度差值可达89 MPa,带钢宽度方向碳含量不一致是导致横向组织变化及性能波动的主要原因;而横向性能波动主要产生于退火工序,因为酸轧工序残留在带钢表面的乳化液在罩退过程中发生裂解,随着退火温度的升高,裂解后的碳与氢气反应生成CH₄,当退火温度超过700 ℃时,CH₄再分解出活性碳吸附于带钢表面从而产生渗碳现象,最终由于带钢横向增碳不均而导致性能波动。通过增加400 ℃保温平台、降低退火温度、降低退火升温速度、增加吹氢流量、降低酸轧卷取张力等改进措施,显著提高了带钢横向性能的均匀性。     

Nb对0.2C-1.5Si-1.8Mn淬火配分钢组织和力学性能的影响

在C-Si-Mn系传统Q&P钢的基础上,通过适当添加微合金元素Nb,探讨了微合金元素Nb对淬火配分钢组织性能的影响。结果表明,无Nb钢与加Nb钢的显微组织基本相同,均由铁素体、板条马氏体与M/A岛组成,但加Nb钢马氏体板条明显细化,板条间距明显减小。Nb促进铁素体析出并抑制珠光体生成,Nb的加入有效细化了组织,缩短了C配分距离,有利于碳向奥氏体中扩散,增加奥氏体的稳定性。经相同Q&P工艺处理后含Nb试验钢的屈服强度、抗拉强度均有所提高,其抗拉强度达989.07 MPa,伸长率为18.36%,强塑积为18.16 GPa·%。     

薄规格铝镇静钢板形缺陷的控制研究

对薄规格铝镇静钢高次浪形缺陷问题进行了研究,从目标板形曲线补偿、轧辊磨损以及性能均匀性方面开展了试验工作。存在高次浪形缺陷的带钢,宽度方向的性能存在较大的性能差异。提高退火温度、降低快冷温度以及提高卷取温度,理论上都会改善连退带钢的性能。试验结果表明：提高卷取温度,明显改善了带钢宽度方向上的性能均匀性,同时有效地抑制了薄规格铝镇静钢高次浪形缺陷的产生。     

热轧卷取温度对HC340LAD+Z带钢力学性能的影响

为了研究热轧卷取温度对热镀锌HC340LAD+Z带钢力学性能的影响规律,对同一炉次、相同规格的3批次钢坯,分别采用580、620、660 ℃3个卷取温度,以及相同的冷轧、热镀锌、退火工艺进行了试验研究。结果表明,随着卷取温度的升高,成品带钢的屈服强度、抗拉强度降低,伸长率稍有增加,均满足EN10346标准对HC340LAD+Z带钢力学性能的要求。热轧卷取温度为620 ℃时,HC340LAD+Z带钢的屈服强度为389.2 MPa,抗拉强度为474.3 MPa,伸长率A80为26.5%,其综合力学性能对比标准指标,富裕量最佳。     

硼对高强度低碳贝氏体钢组织和性能的影响

采用多功能材料试验机和光学显微镜分析了硼对高强度低碳贝氏体钢组织和性能的影响.结果表明,在其它条件基本一致的前提下,加入0.005%硼元素对提高低碳贝氏体钢的综合力学性能非常有效.其中轧制后直接油淬至室温的钢板,含硼钢的屈服强度、抗拉强度及伸长率分别为687 MPa、891 MPa及21.3%,比不含硼钢分别高71 MPa、137 MPa和1.3%.硼元素对试验钢的回火工艺及回火处理后的力学性能也有显著影响,不同温度回火的含硼钢的综合力学性能均优于不含硼钢,且对于含超微量合金元素硼的钢,在600 ℃回火较为适宜;而对于不含硼的钢,在650℃回火更合适.微观组织观察表明,轧制及不同温度回火处理后,试验钢均由准多边形铁素体、粒状贝氏体、板条状贝氏体及极少量的针状铁素体组成,含硼钢与不含硼钢中各种组织所占的比例有很大不同;钢中加入0.005%硼对获得细小的微观组织极为有效.     

FTSR产线低屈强比高强钢的开发实践

针对市场对500 MPa以上、屈强比低于0.9的冷加工成形用热轧带钢的需求,唐钢在FTSR产线上对其进行了开发。对其化学成分、加热制度、轧制制度、卷取工艺进行了优化设计,形成了一整套具有FTSR产线特色的低屈强比薄规格高强钢的生产工艺。生产实践表明,采用碳锰钢+Nb微合金化化学成分设计和合理的TMCP工艺,带钢组织为典型的铁素体组织,抗拉强度不小于500 MPa、屈强比不大于0.9,提升了Nb微合金化高强薄规格带钢性能和轧制的稳定性,并解决了卷取后易扁卷的问题。     

Influence of cooling rate and boron content on the microstructure and mechanical properties of hot-rolled high strength interstitial-free steels

A pilot hot strip rolling and cooling test that simulates an actual hot strip rolling and continuous cooling process was performed. We then examined the effect of cooling rates ranging from 0.1 °Cs^?1 to 100 °Cs^?1 on the microstructure and mechanical properties of high strength interstitial-free (IF) steels containing 0.003 wt% of boron, 0.0005 wt% of boron and no boron. The mechanical properties and microstructures of the boron-added high strength IF steels were analyzed using uni-axial tensile test and electron back-scattered diffraction (EBSD) following the pilot hot strip rolling and cooling test. Results show that the microstructure of high strength IF steel with no boron is influenced significantly by cooling rates. There is a critical cooling rate for building up polygonal ferrite (PF) grains. PF grains do not occur when high strength IF steels with a boron content of 0.0005 wt% and 0.003 wt% undergo a cooling rate of 5.0 °Cs^?1, however widmanst?tten ferrite (WF), granular ferrite (GF) and quasi-polygonal ferrite (QF) grains are present. Under the same hot rolling and slow cooling conditions, high strength IF steel with no boron has recrystallized PF grains. On the contrary, high strength IF steel with boron cooled at above 3 °Cs^?1 doesn??t have GF or QF grains, and subsequently generates the unrecrystallized ferritic grains and WF grains, which increase the yield and tensile strengths. It is deduced that we need to control both the cooling rate and coiling temperature when boron-added high strength IF steel sheet is manufactured in an actual hot strip rolling mill.     

Effect of Hot Rolling Process on Microstructure and Properties of Low-Carbon Al-Killed Steels Produced Through TSCR Technology

Low-carbon Al-killed hot rolled strips for direct forming, cold rolling, and galvanizing applications are produced from the similar chemistry at Ezz Flat Steel (EFS) through thin slab casting and rolling (TSCR) technology. The desired mechanical and microstructural properties in hot bands for different applications are achieved through control of hot rolling parameters, which in turn control the precipitation and growth of AlN. Nitrogen in solid solution strongly influences the yield strength (YS), ductility, strain aging index (SAI), and other formability properties of steel. The equilibrium solubility of AlN in austenite at different temperatures and its isothermal precipitation have been studied. To achieve the formability properties for direct forming, soluble nitrogen is fixed as AlN by coiling the strip at higher temperatures. For stringent cold forming, boron was added below the stoichiometric ratio with nitrogen, which improved the formability properties dramatically. The requirements of hot band for processing into cold rolled and annealed deep drawing sheets are high SAI and fine-grain microstructure. Higher finish rolling and low coiling temperatures are used to achieve these. Fully processed cold rolled sheets from these hot strips at customer’s end have shown good formability properties. Coil break marks observed in some coils during uncoiling were found to be associated with yielding phenomenon. The spike height (difference between upper and lower yield stresses) and yield point elongation (YPE) were found to be the key material parameters for the break marks. Factors affecting these parameters have been studied and the coiling temperature optimized to overcome the problem.     

Effect of alloying elements and coiling temperature on the recrystallization behavior and the bainitic transformation in TRIP steels

The effects of alloying elements and coiling temperature on recrystallization behavior and bainitic transformation were investigated based on 0.07C-Mn-Cr-Nb steel with a low carbon equivalent. Based on the ferrite recrystallization behavior, the proper intercritical annealing temperature of all studied steels was suggested to produce TRIP steel with good strength and elongation balance. All steels coiled at 550 °C showed much faster ferrite recrystallization behavior than steels coiled at 700 °C. In addition to the coiling temperature, the effect of increasing carbon content on the ferrite recrystallization was minor at a coiling temperature of 550 °C, but much more prominent at a coiling temperature of 700 °C. The highest Mo added steel showed the best strength and elongation balance, and the highest carbon and Mo added steel showed the highest tensile strength at a coiling temperature of 550 °C. The steel containing a higher amount of elemental Al (0.7 wt.% Al) exhibited much better elongation than the lower Al added steel (0.04 wt.% Al) in TS 780 MPa grade, about 24 % and 19 %, respectively.