Solidification Structure of Low Carbon Steel Strips with Different Phosphorus Contents Produced by Strip Casting

In the present paper, low carbon steel strips with different phosphorus contents were produced using a twin roll strip casting process. The solidification structure was studied and its features were analyzed in detail. It was found that the strips possessed a fine microstructure compared with the mould cast steels. With increasing phosphorus content more ferrite has been formed with finer grains.

Thermodynamic Research on Precipitates in Low Carbon Nb-Microalloyed Steels Produced by Compact Strip Production

Microalloying element Nb in low carbon steels produced by compact strip production （CSP） process plays an important role in inhibiting recrystallization, decreasing the transformation temperature and grain refinement.With decreasing the rolling temperature, dislocations can be pinned by carbonitrides and the strength is increased. Based on the two sublattice model, with metal atom sublattice and interstitial atom sublattice,a thermodynamic model for carbonitride was established to calculate the equilibrium between matrix and carbonitride. In the steel produced by CSP, the calculation results showed that the starting temperature of precipitation of Ti and Nb are 1340℃ and 1040℃, respectively. In the range of 890-950℃, Nb rapidly precipitated. And the maximum of the atomic fraction of Nb in carbonitride was about 0.68. The morphologies and energy spectrum of the precipitates showed that （NbTi） （CN） precipitated near the dislocations. The experiment results show that Nb rapidly precipitated when the temperature was lower than 970℃, and the atomic fraction of Nb in carbonitride was about 60%-80%. The calculation results are in agreement with the experiment data. Therefore the thermodynamic model can be a useful assistant tool in the research on the precipitates in the low carbon steels produced by CSP.

Analysis of surface microcracks in low-carbon steel produced via twin-roll strip casting

In this study,morphological and microstructural analyses were conducted on net-shaped microcracks appearing on the surface of low-carbon steel manufactured via twin-roll strip casting. The fractograph and microscale distribution of elements in the cracked region were also analyzed. Results revealed that the cracked surfaces were characterized by slight pits,along with inclusions composed of manganese and silicon oxide distributed along both the sides of the cracks. Fractograph analysis revealed that the crack and smooth dendrite surfaces were oxidized. These phenomena indicate that microcracks on the cast strip surface form at the hightemperature stage of the solidification process during twin-roll casting and rolling. Microcracks were present in each region with pits in the cast strip and extended along the dendrite interface because of the combined effects of phasechange stress,thermal stress,mechanical stress,and fractional crystallization during the solidification process.

Aspects of microstructure in low carbon steels produced by the CSP process

The solidification structure, microstructure evolution during rolling andprecipitates with nanometers in dimension of the low carbon steels produced by CSP process with thinslabs have been studied in recent years. Important differences in microstructure and mechanicalproperties between the CSP products and the conventional one were observed. These differences mayarise from the much rapider solidification rate and cooling rate after casting of the thin slabs.Some aspects of the microstructure for the low carbon steels of the CSP thin slabs are summarizedand compared with the conventional one.

Grain refinement of low carbon steel produced by CSP process

In comparison with conventional production for hot strips, compact strip production (CSP) brings about some new micro-structural phenomena. Investigations were carried out to clarify the grain refinement mechanism of low carbon steel strips produced by the EAF-CSP process. Samples, obtained from the same rolling stock during continuous rolling, were examined through SEM, TEM and XEDS. Thin slabs have a dominant columnar structure and the spacing of the secondary dendrite arms ranges from 90 to -125 μm. The average grain sizes for the central area of the samples from the 1st to 6th pass are 41.6, 25.2, 21.4, 20.2, 13.1, 6.7 μm, respectively. Large number of nanometer oxide and sulfide have been found in the low carbon steel produced by the CSP process. The grain refinement mechanism can be summarized as follows: finer solidification structure of the thin slab; austenite recrystalliza-tion at higher temperature and stain accumulation at lower temperature caused by the great reduction of single rolling pass during continuous rolling; nano-scaled precipitates of sulfide and oxide which drag grain boundaries of austenite or ferrite to prevent the grain coarsening.

Static Recrystallization Behavior of Twin Roll Cast Low-Carbon Steel Strip

The static recrystallization kinetics of low carbon steel cast strip was investigated by means of interrupted hot tensile tests. As-cast strip was reheated and soaked and its austenite grain size was similar to the width level of the as-cast columnar structure. The tests were carried out on Gleeble-3500 thermomechanical simulator. The deformation temperature is in the range of 800 to 1 200 ℃ with strain rate of 0.01 to 1 s ^-1. The prestrain is fixed at 0. 04 to 0.12, and the inter-hit delay time varies from 1 to 3 000 s. Effect of deformation conditions and initial microstructure on static recrystallization behavior was investigated. The activation energy （Qsrx） and Avrami exponent （n） of static recrystallization were determined to have 241 kJ/mol and 0.54 respectively by linear regression of the experimental results. A kinetics model was proposed to describe the static recrystallization kinetics in low-carbon steel cast strip. The predicted softening fractions are in good agreement with the experimental results, indicating that the proposed equations can give an accurate estimate of the softening behaviors for the low-carbon steel cast strip.

新型铁路信号继电器重锤片的研制

重锤片是铁路信号继电器磁路系统衔铁组件中的一个零件,在继电器的机械负载和磁路平衡中起着配重的作用,用于保证继电器衔铁可靠落下。通过对比原重锤片的结构尺寸及材料,结合新工艺技术对重锤片的结构尺寸及材料重新研制,主要从重锤片研制的设计输入、理论计算、实物验证等内容,并对重锤片研制前后的实物进行对比分析。新型重锤片的成功研制将提高重锤片零件的防腐性能及应用环境,彻底取消电镀工序对环境质量的影响,同时提高零件的生产效率,缩短产品的生产周期。

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.

FTSR线铁素体轧制低碳钢板的组织性能分析

对FTSR线采用铁素体轧制工艺生产的3.0 mm低碳钢板进行了微观组织分析和力学性能测定.结果表明,FTSR薄板坯连铸连轧生产线可以实现用铁素体轧制工艺生产低碳钢板,运用此工艺生产的3.0 mm低碳钢板组织为不均匀的铁素体,平均晶粒尺寸约29μm,铁素体晶粒的边界存在少量片层间距约几十纳米的珠光体组织;钢板的屈服强度为215～240 MPa,抗拉强度为305～335 MPa,伸长率为33%～41%,比采用奥氏体轧制工艺生产的钢板强度低且延伸性好;室温下钢板的冷弯性能、成形性能及冲击韧性等都较为优良.

低碳钢碳氮析出物的热力学计算

钢中的碳氮析出物通过细晶强化和析出强化方式对钢的力学性能有非常重要的作用.基于规则溶液的双亚点阵模型(其中一个为金属亚点阵,另一个为间隙原子亚点阵)建立了碳氮化钛、氮化铝以及硫化锰的热力学计算模型用以研究析出物的析出开始温度、给定温度的奥氏体成分,并将这一结果应用于CSP过程.经计算得Ti(CxN1-x),MnS和AlN的析出温度分别是1200℃,1440℃和1010℃,最大的体积分数分别为2·315×10-5,4·18×10-4和3·1×10-4.对比发现热力学的计算结果与Thermo-Calc的计算结果和有关文献的实验数据有较好的一致性.

薄板坯连铸连轧CSP生产低碳钢板的组织特征

4对珠钢 CSP线生产的低碳钢 (ZJ40 0 )连铸坯及轧后的组织特征观察和硬度测定表明 :CSP线生产的连铸坯铸态组织为较细的树枝晶 ,枝晶宽度为几微米到 30μm,靠近表面层的枝晶宽度与中心区域差别很小。经第一道次 5 0 %变形后 ,板坯组织明显细化 ,具有局部“树枝晶”特征 ,“枝晶”宽度约 5μm,中心区域硬度降低。成品薄板的晶粒尺寸平均为 5μm,大多呈尖角型。变形区应力。

薄板坯连铸连轧生产冷轧用低碳热轧带钢的力学性能

综述了板坯连铸连轧生产冷轧用低碳热轧带钢力学性能偏高的现状以及性能强化机理。讨论了性能软化的途径。指出通过提高钢的纯净度、降低夹杂物含量、采用铁素体温度范围轧制、高温卷取(≥700℃)工艺以及硼微合金化等措施,可以得到屈服强度不超过255 MPa的冷轧用低碳热轧带钢,并生产出合格的冷轧深冲板。

深冲用超低碳冷轧带钢铁素体区热轧的现场试验

研究和对比了经1 880 mm热轧机组在奥氏体区(945～848℃)和铁素体区(803～755℃)热精轧,卷取温度700℃以及73%压下率冷轧的3.0 mm超低碳带钢(%:0.008C、0.029Als、0.000 8B、0.001 4N)退火后的组织和性能。结果表明,与奥氏体区轧制比较,热轧采用铁素体区轧制的710℃退火后冷轧带钢具有较高的伸长率、塑性应变比(r值)和应变硬化指数(n),因而具有较好的深冲性能。

低碳钢的高温力学性能

利用Gleeble 1500热模拟实验机,采用加热法和凝固法两种加热变形制度,研究了实验用低碳钢的热塑性及强度,测定了该钢种的零塑性温度(ZDT)θd及零强度温度(ZST)θs,分析了其裂纹敏感性及断口组织·结果表明,凝固法所测结果更符合实际;实验钢的高温脆性温度范围为1300℃至熔点,在1100～1300℃范围内,此钢的断面收缩率均大于60%,具有良好的塑性·实验用低碳钢的高温脆性区较小,具有较强的抗高温裂纹特性·其θd和θs分别为1350℃和1400℃·

含磷0.08%铸轧薄带的研究

通过组织观察、拉伸实验、冲击实验、加速腐蚀实验等研究了含磷0.08%的双辊铸轧低碳钢薄带。实验结果表明,厚1.7mm的铸带在表面附近富磷而在基体中贫磷,且被冷轧至0.8mm后,仍有大约70μm宽的表面富磷层被保留;表面富磷层的存在使源自铸带的退火态薄带(TRCA)耐候性能明显优于源自铸锭的退火态薄带(IHCA),但却没有给TRCA薄带的力学性能带来不利的影响。与IHCA薄带相比,TRCA薄带的脆韧性转变温度低12℃左右,塑性基本相同。

薄带连铸Kiss点前界面热流模型与凝固过程

设计了一套可测定双辊薄带连铸Kiss点之前钢液-铜辊界面热流的模拟装置,重点分析了模拟装置的数据处理方法,并通过对一种低碳钢的实例分析演示了计算方法的具体应用.建立了双辊薄带连铸Kiss点之前的界面热流分布模型,给出了液态接触、凝固过程以及坯壳生长等3个阶段的热流密度,并由此计算了凝固前沿的生长速率与凝固速率.结果表明,集总参数法适用于计算界面热流密度,低碳钢界面传热分为3个阶段:①热流密度随着时间逐渐增大,12 ms时到达最大值18 MW/m2;②热流密度随着时间快速下降,30 ms时达到相对稳定值,约7 MW/m2;③随着时间延长,热流密度呈轻微下降趋势.

Nb-V-Ti低碳微合金钢的热变形加工图及其应用

为了优化Nb-V-Ti低碳微合金钢的变形工艺参数,利用Gleeble-1500热/力模拟实验机对其进行了热压缩实验,得到热加工图用于研究热变形行为.研究发现,加工图中存在两个动态再结晶峰区及失稳区:峰区Ⅰ:峰值对应的变形温度和变形速率分别为1000℃,2 s-1,峰值效率21%;峰区Ⅱ:变形温度1050℃,变形速率0.01～0.001 s-1,峰值效率45%.将加工图与CSP生产工艺参数进行对比,合理解释了CSP生产过程中出现混晶的现象.因此,动态材料模型加工图可作为研究新材料变形参数的有力工具.

双辊铸轧新型耐候带钢的研究

采用场发射电子探针显微分析仪、扫描电镜、光学显微镜以及恒温恒湿实验箱等研究手段,对双辊铸轧含磷铜低碳钢薄带进行了系统的分析.实验结果表明,铸轧薄带表面附近有富磷层形成,而基体中磷的浓度远低于薄带的名义磷含量.铸轧磷铜钢薄带经冷轧和退火处理后,具有较好的塑性,甚至当磷质量分数高达0.26%时,延伸率仍然在30%以上.同时,它的耐蚀性远优于通过传统工艺方法而获得的磷铜钢薄带,特别是当磷质量分数超过0.15%后,经过一定的腐蚀时间后,它的表面将会产生一层致密的磷化层保护膜,从而使其具有极强的耐蚀性.

经济型低碳贝氏体复相钢的开发及应用

在实验室研究的基础上，以硅、锰为主元素，并通过热轧工艺的控制和优化，开发了一种低碳贝氏体复相热轧薄板，并在宝钢集团上海梅山钢铁公司热连轧机上进行了屈服强度450MPa级别的贝氏体热轧板的生产试制。结果表明，试验钢的平均屈服强度为500MPa，抗拉强度为590MPa，伸长率为24％，且具有良好的冲击韧性。实验钢已成功用于工程结构，能有效地降低材料消耗，减轻构件重量。