钢液凝固与冷却过程及固体钢加热过程钢中非金属夹杂物成分动力学转变的几个概念和特征曲线

利用钢中非金属夹杂物成分变化的集成模型,介绍了夹杂物成分随时间和冷却速率的变化,提出了夹杂物成分转变分数的概念,然后介绍了夹杂物成分转变的等温转变曲线（TTT）、连续冷却转变曲线（CCT）和等径转变曲线（TDT）的概念及应用.该集成模型考虑了钢液流动、传热、凝固和元素偏析,也考虑了钢与夹杂物反应的热力学和动力学.然后以管线钢、重轨钢和轴承钢为例,进一步分析讨论了钢液凝固与冷却过程中的冷却速率、固体钢加热过程中的加热温度和加热时间、钢成分以及夹杂物尺寸等参数对夹杂物成分转变的影响.这些概念和特征曲线能够直观展示在钢液凝固冷却过程及固体钢加热过程钢中非金属夹杂物的成分转变,将钢中夹杂物的控制方略从钢液拓展到固体钢中.     

冷却速率对薄带连铸低碳钢微观组织的影响

摘要：为了探究冷却速率对薄带连铸低碳钢微观组织的影响,采用相变仪设备对铸带重新加热并进行不同冷却速率冷却,采用光学显微镜、场发射电子探针和电子背散射衍射等手段对微观组织和针状铁素体形核所利用的夹杂物进行了分析。结果表明,铸带经1200℃保温3min后,原奥氏体晶粒尺寸约为150～650μm,可以满足晶内针状铁素体形核对原奥氏体晶粒尺寸的需要。在2～5℃/s的冷却速率范围内,试样中得到了大量的针状铁素体组织,冷却速率为2℃/s的试样中大角度晶界所占比例约为60%;当冷却速率大于20℃/s,针状铁素体的形成受到抑制。铸带中针状铁素体形核所利用的夹杂物是Ti-Al-Si-Mn-O+MnS复合夹杂物。     

冷却速率对薄带连铸低碳钢微观组织的影响

为了探究冷却速率对薄带连铸低碳钢微观组织的影响,采用相变仪设备对铸带重新加热并进行不同冷却速率冷却,采用光学显微镜、场发射电子探针和电子背散射衍射等手段对微观组织和针状铁素体形核所利用的夹杂物进行了分析。结果表明,铸带经1 200℃保温3 min后,原奥氏体晶粒尺寸约为150～650μm,可以满足晶内针状铁素体形核对原奥氏体晶粒尺寸的需要。在2～5℃/s的冷却速率范围内,试样中得到了大量的针状铁素体组织,冷却速率为2℃/s的试样中大角度晶界所占比例约为60%;当冷却速率大于20℃/s,针状铁素体的形成受到抑制。铸带中针状铁素体形核所利用的夹杂物是Ti-Al-Si-Mn-O+MnS复合夹杂物。     

Al脱氧钢中氧化物对MnS析出的影响

使用10 kg真空感应炉Al脱氧冶炼较高S含量超低氧高强度钢,钢中T[O]降到0.0010%,S的质量分数为0.0190%.采用ASPEX explorer全自动扫描电镜对钢中非金属夹杂物进行检测,发现98%非金属夹杂物都是弥散分布的MnS和MnS+Al₂O₃复合夹杂物.MnS夹杂物棱角分明,从形貌特征来看应属于第Ⅲ类硫化物.MnS+Al₂O₃复合夹杂物以Al₂O₃为核心,外层包裹MnS,其数量约占9%~32%;作为核心的Al₂O₃平均直径为1.5μm.其生成过程可描述为:凝固过程中,小尺寸Al₂O₃被推至固液两相区,而选分结晶作用使得钢中的Mn和S在凝固前沿富集,并以Al₂O₃作为异质形核质点析出MnS夹杂物.对凝固过程中Al₂O₃的推动和捕获行为进行了相关计算.计算结果表明:直径小于4μm的Al₂O₃可被推动,并作为MnS的异质形核质点.      

低合金高强钢中针状铁素体控制的综述

在低合金高强钢中，形成大量的针状铁素体是满足高强度和高韧性的主要方法。影响针状铁素体体积分数的几个关键因素在不同的文献均有体现，也有综述文献总结了针状铁素体形核机制和有利于形核的夹杂物特征，但是并没有系统地总结各因素变化带来的影响。本文总结了奥氏体晶粒尺寸、冷却速率、夹杂物成分、夹杂物尺寸的变化对针状铁素体体积分数的影响。得出结论如下：奥氏体晶粒尺寸为100～200μm、冷却速率为5～10℃/s、夹杂物尺寸为1～2μm和（Ti、Mg、Zr）O_x夹杂物均有利于促进针状铁素体形核。     

板坯凝固过程夹杂物运动行为

 本文使用离散相模型,利用数值模拟的方法对结晶器中的钢液流动、传热、凝固以及夹杂物的运动进行了耦合计算。通过追踪夹杂物的运动轨迹,并在钢渣界面处对夹杂物进行采样分析,最终计算出夹杂物在结晶器中的上浮率。研究表明,夹杂物在结晶器中的上浮率与其尺寸及拉速的大小均有关系,但受夹杂物密度的影响很小。夹杂物越大、拉速越小,越有利于夹杂物上浮至自由液面。小颗粒夹杂在结晶器中并不能被有效去除。对于粒径为50μm的夹杂物,当拉速为1m/min时其上浮率仅为46%,有37%的夹杂物被凝固坯壳捕捉,主要分布在铸坯表皮下10~25mm处。夹杂物被宽面坯壳捕捉的位置多集中在宽面靠近窄面处,在水口下方被捕捉的夹杂物较少。以往的研究认为只要夹杂物上浮至钢渣界面就能够被保护渣吸收,J.Strandh等的研究表明,夹杂物能否被吸收还取决于保护渣的粘度和润湿性等因素。因此,对于粒径较小的夹杂物,必须在精炼后的软吹氩过程中适当增大钢液的静置时间,尽量减少钢液中小颗粒夹杂的数量。另外,结晶器保护渣的选用对钢液中夹杂物的去除也很重要,不仅要满足其对钢液的保温润滑作用,还要考虑其对夹杂物吸附的影响。     

通过钛脱氧细化低碳高锰钢显微组织-夹杂物沉淀和凝固结构

在C（0．07％）-Mn（0．9％）钢中,研究用钛作为脱氧剂代替铝有2个目的,第一个目的是确认凝固过程中（二次脱氧）能否促进夹杂物沉淀,第二个目的是调查初始氧含量和钛含量以及凝固过程中冷却速率发生变化时,二次夹杂物对钢凝固结构的后序演变影响。在钛镇静钢试样中,当试样初始氧含量较高时（全氧（T．O）=50—80ppm）,氧化物夹杂组成为MnO—TiO2（0．5—5μm）和MnS（1—3μm）,而在低氧含量试样中（T．O=7—10ppm）,夹杂物组成为Ti—Al-（Mg）-O（0．3—1μm）。与热力学计算结果相比,认为后者说的夹杂物为在中间枝晶区域的单独二次脱氧沉淀产物。对于较高氧含量试样来说,发现其夹杂物组成为初生和二次脱氧产物的共同体。通过控制冷却速率介于3-10K／之间,在真空感应炉中采用不同模型,研究了凝固过程中冷却速率的影响。除此之外,将在金像炉中重熔的试样,在冷却过程中,冷却速率分别控制为1．1,14和84K／s,此炉放于共焦扫描激光显微镜中（CSLM）。随着冷却速率的增加,钛镇静钢试样中的夹杂物密度也随之增加,而在铝镇静钢中观察不到这种现象。在凝固过程中,通过溶质偏析模型预测钛镇静钢试样中二次粒子的尺寸与观察到的平均粒子尺寸相吻合。在钛镇静钢试样中,随着夹杂物密度的增加,凝固组织较细,夹杂物尺寸小于1μm,然而,在铝镇静钢试样中观察不到此现象。     

304奥氏体不锈钢亚快速凝固组织演化和形成机理

通过感应炉熔化的304钢(/%:0.053C、0.55Si、1.50Mn、0.030P、0.002S、17.02Cr、8.01 Ni、0.50Cu、0.08Mo)直接浇铸在水冷铜模上得到厚7 mm直径25 mm的圆形试样,研究了Cr、当量/Ni当量和1.5～1 000℃/s的冷却速率对奥氏体不锈钢铸态凝固组织形态和分布的影响。结果表明,随冷却速率增加至75～90℃/s,该钢的凝固模式由FA(铁素体-奥氏体)模式向AF(奥氏体-铁素体)模式转变,初生相由枝晶铁素体转变成枝晶奥氏体,但冷却为～1 000℃/s时,观察到块状铁素体组织,并且枝晶状奥氏体转变成胞状奥氏体。     

通过钛脱氧细化低碳高锰钢显微组织：奥氏体晶粒长大和分解

本文研究了脱氧夹杂物对低碳钢显微组织演变的影响。将低碳（0．07％wt％）、高锰（0．9wt％）钢在A2O3或MgO坩埚中通过添加铝（0．05wt％）或钛（0．05、0．03或0．015wt％）进行脱氧。试验在容量400g真空炉中完成，然后在铜模中浇铸，冷却速率介于2．0～6．0K／s之间。为了研究冷却速率的影响，将这些浇铸试样重新熔化并且以各种不同冷却速率进行冷却，冷却速率从1—100k／s，采用高温共焦激光扫描显微镜（CSLM）予以分析。 在所有钛镇静钢试样中，氧化物夹杂尺寸均较小并且夹杂物密度高于那些铝镇静钢试样。在钛镇静钢试样中，夹杂物尺寸和密度随氧含量的增加而增加，夹杂物尺寸随着冷却速率的增加而减少，夹杂物密度随冷却速率的增加而增加。 采用共焦激光扫描显微镜（CSLM）研究钛镇静钢和铝镇静钢试样两者之间固态显微组织变化的差别。研究了等温条件下奥氏体晶粒的长大，并且从中发现：钛镇静钢试样中的晶界迁移率和最终晶粒尺寸均低于其它镇静钢。至于奥氏体分解，在从相似的奥氏体晶粒结构连续冷却过程中，由于沉淀反应导致较高的韦氏板条密度，最终导致钛镇静钢试样中的奥氏体分解，使其结构更为细小。夹杂物尺寸对奥氏体晶粒尺寸和奥氏体分解结构均有显著影响，在钛镇静钢试样中可观察到来自夹杂物的铁素体沉淀物不同取向。在最小平均夹杂物尺寸试样中获得最高板条浓度，而不是在最高密度的亚微米夹杂物中获得最高板条浓度。     

稀土处理C-Mn钢显微组织和夹杂物演化

对稀土处理C-Mn钢的夹杂物和显微组织进行分析,统计稀土处理C-Mn钢中针状铁素体形核核心尺寸,并将稀土处理钢在不同温度下淬火,研究稀土夹杂物生成和长大过程.实验结果表明:C-Mn钢加入少量稀土后钢中夹杂物从MnS＋硅铝酸盐夹杂转变为La₂O₂S＋LaAlO₃＋MnS＋硅铝酸盐夹杂,尺寸得到细化,显微组织也从马氏体＋贝氏体组织变成侧板条铁素体、针状铁素体和块状铁素体组织;稀土处理C-Mn钢中针状铁素体有效形核核心的尺寸集中在1~4μm,主要是在钢液中形成,冷却和凝固过程形成的数量较少;稀土夹杂物在钢液温度和冷却及凝固过程容易碰撞黏合长大,上浮从钢液中去除,MnS能在稀土夹杂物颗粒间析出.      

转炉炉壳热应力分析

根据实际转炉建立实体模型。以有限元为手段,考虑了炉衬和炉壳材料的物性参数随温度变化的特点和炉衬与炉壳之间膨胀间隙,计算了转炉炉壳在温度载荷和炉衬膨胀压力同时作用下的热应力。所得结果可为转炉炉壳设计提供依据。     

焦炭热性能指标意义浅析

通过对焦炭在高炉内的历程及其变化规律的剖析,阐述焦炭热性能指标的意义,形象地把焦炭在高炉内的损耗分为三部分(M1,M2,M3)。指出M2对焦比及焦炭价格有一定的指导作用。     

Results of treatment of cancer of the cardia

Cancer of the cardia is traditionally discussed with cardiac cancer of the lower portion of the esophagus and upper gastric cancer invading the esophagus, and the specific characteristics of cancer of the cardia have never been clearly defined. We reviewed the outcome of 172 patients with adenocarcinoma of the cardia who had undergone radical surgery between 1949 and 1994 in the Division of Gastrointestinal Surgery of the Cancer Institute Hospital. The centers of the tumors were located within 2 cm above and below the boundary between the esophagus and the stomach, and their longitudinal diameter was less than 8 cm. We divided the patients into an early period (1949-1979; n = 79) and a late period (1980-1994; n = 93), and focused on the historical transition. There were no differences in patient gender or histology between the two periods. However, the late period was associated with fewer cases of esophageal invasion and shorter longitudinal diameter, as the age of the population advanced. The number of advanced cancers such as the localized and infiltrative type had decreased, and early cancer and early clinical stage had become more common, but despite the fact that the number of early cancers had increased, extended dissection, such as thoracic and paraaortic lymph node dissection, was performed more frequently. By clinical stage, the long-term outcome markedly improved in Stage I patient in the late period, and tended to improve in Stage II and III patients. This appears to have been attributable to the prevention of micrometastasis by extended dissection, although the number of early cancers is another major potential cause. There were no differences in the outcome of Stage IV patients between the two periods, and further advances in multimodality therapy must be awaited. The range of resection is basically proximal gastrectomy, and if there are adequate indications, the prognosis is favorable. In view of the status of lymphatic flow and lymph node metastasis, and long-term results, lateroaortic lymph node dissection is important. Since the number of early cancer patients has been increasing, if intraabdominal recurrence is prevented, intrathoracic lymph node dissection will contribute greatly to the outcome of such patients.     

The effect of amount of possession of the trait of hostility on accuracy of perception of hostility in others.

Some theories of personality hold that an individual's perception of others is influenced by his own personality characteristics; more specifically, that a trait of low social value will be projected more into others, and that insight into the possession of these characteristics reduces this distortion. These 2 hypotheses were tested by having a group of college students rate each other (including themselves) on degree of friendliness or hostility. Agreement with group rating about self yielded the insight score. In general, the hypotheses were supported; the "friendly" Ss were most accurate in their perception of others, and insight was positively associated with accurate perception. From Psyc Abstracts 36:04:4HL16M. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Comparison of rates of infection of two methods of emergency ventricular drainage

The rates of infection of two methods of external ventricular drainage in use at Atkinson Morley's Hospital--namely, (a) percutaneous drainage with Rickham reservoirs and (b) tunnelled ventriculostomies--were compared in this retrospective review. Percutaneous drainage of CSF with Rickham reservoirs was associated with a 27% rate of infection as identified by positive microbiological cultures; tunnelled ventriculostomy catheters had a 10% infection rate. The difference in the infection rate between the two methods was statistically significant (P < 0.015). Other variables examined, including the age and sex of the patients and the reasons for ventricular drainage, were not associated with an increased rate of infection. Most infections from either method were caused by a coagulase negative staphylococcus. The average duration of ventricular drainage before identification of positive cultures was 5.7 days for Rickham reservoirs and 6.0 days for ventriculostomies.     

浅析《野草》的版画特征

鲁迅先生一生热爱美术作品,对版画中木刻兴趣尤甚.<野草>作为其"写心之作",亦呈现出一些与木刻版画一致的审美特征:一是具有木刻版画的色彩特征,多对比、多冷色,有阴郁的美感;二是具有木刻版画的力度特征,环境描写、人物刻画处处刀锋毕现,遒劲有力,有一种"力之美".     

四辊破碎机车刀架的改造

针对四辊破碎机车刀架车削中存在的几个问题,详细介绍了电动车刀架的结构和工作原理,建立主要设计参数的数学表达式,并进行适当的分析。改造后,这种电动车刀架运行平稳、可靠、方便、省力,取得了预期的效果。     

Effect of antibiotics of chemotaxis of human leukocytes

The effect of 20 different antibiotics on chemotaxis by human neutrophils was studied. Human leukocytes incubated with chloramphenicol, rifampin, sodium fusidate, and tetracyclines in vitro showed markedly depressed migration. The mechanisms by which these antibiotics affect leukotaxis are discussed.