电磁搅拌在大方坯合金钢连铸机上的研究与应用

通过对结晶器电磁搅拌的各工艺参数进行了重新优化、设定,调整后的工艺参数大大提高了铸坯内部质量,中心缩孔、疏松、中间裂纹等常见缺陷的等级都控制在0.5级以内,中心偏析指数由原来的1.18降到1.03,铸坯中心等轴晶率比原来提高38%。     

高强度船板断口合格率影响机理探讨

通过低倍酸浸、断口形貌、金相组织等分析方法,对高强度船板拉伸断口不合的机理进行了讨论分析,指出断口分层是断口不合的主要表现形式,分层与钢板内部的马氏体、贝氏体异常组织和长条状MnS夹杂有关,而异常组织和长条状MnS夹杂的出现是由于铸坯的中心偏析和中间裂纹造成的。     

宽厚板连铸坯中间裂纹成因分析及控制

针对某钢厂100t转炉→LF钢包精炼炉→板坯连铸机工艺流程和生产试验数据,探讨了板坯连铸一种内外弧型中间裂纹的发生机制。结果表明,连铸坯鼓肚收缩应变是中间裂纹产生的外因,钢的化学成分决定其高温力学性能,是中间裂纹产生的内因。某钢厂连铸板坯中间裂纹的产生是连铸坯鼓肚收缩应变和钢种的高温力学性能共同作用的结果,而弯曲矫直应变是中间裂纹扩展的重要影响因素,可能导致中间裂纹的扩展。结合钢种和铸坯规格的合理辊缝设计对控制中间裂纹至关重要。     

厚板铸坯内部质量控制实践

通过酸浸低倍等手段,获取中间裂纹产生的位置和规律。采取提高铸机辊缝精度、优化二冷水强度、调整动态轻压下区间等手段,中间裂纹的发生率由66.7%下降至11.7%,同时改善了中心偏析和中心疏松,提高了铸坯的质量。     

1650板坯压下过程热/力学行为及压下工艺优化

为了控制梅钢1 650板坯连铸包晶钢过程铸坯内裂纹发生,基于梅钢1 650板坯连铸机生产实际,建立了1 560mm×230mm断面包晶钢铸坯凝固过程三维热/力耦合有限元模型,揭示了铸坯凝固过程各冷却区内的温度场分布规律和铸坯压下过程应力与变形行为演变规律。结果表明,铸坯在结晶器及零段内冷却强度大,沿拉坯及其垂直方向的温度分布梯度大;在实施铸坯凝固末端压下过程中,铸坯宽面中心与宽向1/4处的表面变形及应力变化较为同步,且靠近铸坯内弧侧凝固前沿的塑性应变最大,铸坯应力最大值集中在角部区域;目前梅钢包晶钢连铸压下区间设置不当,易引发铸坯产生内部裂纹。     

连铸板坯表层网状裂纹的成因研究

统计分析了攀钢所产管线钢、梁板钢等200 mm×1300 mm连铸坯表层网状裂纹的影响因素;发现钢中碳、锰硫比、合金元素（Al,Ti,V）、连铸机设备和浇注状况对其形成和扩展都有重要影响。通过金相显微镜、SEM、TEM和EDS等手段,研究了铸坯表层网状裂纹的形貌特点,认为此裂纹是连铸坯表面冷却不均匀而产生γ→α→γ反复相变,并伴有各种碳氮化物在晶界析出,连铸坯在外力(热应力、弯曲矫直应力等)作用下沿晶界开裂所致。     

铸坯及板卷典型质量缺陷成因与控制技术

热轧板卷的表面质量缺陷主要是夹杂类缺陷(夹杂、气泡和翘皮)及裂纹类缺陷(纵裂纹、横裂纹和星状裂纹)等,内部质量缺陷主要是带状组织和分层现象等,其中大多数缺陷与连铸坯的质量有关。为解决连铸板坯轧制板卷过程中产生的表面及内部质量问题,在综合分析现场生产环境和样品检测结果的基础上,系统研究了铸坯及板卷典型质量缺陷的产生原因或机理,并针对性地提出了相关缺陷的控制技术。     

280 mm×380 mm连铸坯结晶器电磁搅拌技术的应用

试验研究了电磁搅拌的电流(150～500 A)对重轨钢U75V等钢种(mm)280×380、280×325连铸坯冶金质量的影响。结果表明,当电流由250A提高至500A时,重轨钢U75V铸坯中心区等轴晶率由18.8%增至36.2%,夹杂总量由8.53mg/10kg降至4.68mg/10kg,中心疏松、偏析、缩孔、中心裂纹和中间裂纹等缺陷≤1.0级别的比例达98%。中碳钢连铸电磁搅拌电流为350～400A,低碳钢连铸电磁搅拌电流为250A时,铸坯内部缺陷≤1.0级的比例分别为93%和90%。     

提高Q345B钢板探伤合格率的工艺措施

针对南阳汉冶特钢有限公司250mm×1 650mm断面连铸坯生产的低合金Q345B钢板探伤不合格现象,通过对不合格钢板取样进行电镜检测分析,得出中心锰偏析、硫化锰夹杂、氧化铝夹杂是导致探伤不合格的主要原因。通过优化成分来降低钢中锰元素质量分数、提高钢水洁净度、降低钢水硫质量分数、优化连铸二冷制度、严控铸机开口度等措施,铸坯中心偏析得到了改善,轧后钢板探伤质量合格率得到了提高。     

360mm×450mm大方坯连铸二冷技术研究

针对攀钢360 mm×450 mm连铸大方坯存在的表面纵裂、中间裂纹、中心裂纹等质量问题,通过采用适当增大连铸比水量、调整二冷区各回路的冷却能力及水量分配比例的方法,优化了大方坯连铸二冷制度.生产应用表明,大方坯表面质量和内部质量明显提高,因铸坯中间裂纹严重而产生的表面纵裂缺陷率由53.85%降至0.30%,铸坯中心疏松评级≤1.0级的比例由74.87%增至99.53%,无中心裂纹的比例由68.83%增至82.77%,无中间裂纹的比例由82.95%增至90.98%.     

Influence of hot working on internal cracks in continuously-cast steel billets

Continuously cast billet sections containing halfway cracks and in-plant, hot rolled rod from the same heat have been examined for open defects. It was found that significant open defects were present in the steel after a reduction of 4:1. A direct correlation between initial crack dimensions and open defects after a given reduction could not be made as the initial crack configuration varied appreciably along the billet length. Laborav scale, hot rolling of small continuously cast billet sections containing a known halfway crack configuration showed hot reductions greater than 6:1 are necessary to effectively close halfway cracks. This is applicable for cracks oriented both parallel and prependicular to the rolling plane. Small pores and lines of inclusions present in material reduced 10:1 did not affect the low temperature fracture stress of the steel.     

Cost-effectiveness of providing insurance benefits for posthospital psychiatric halfway house stays.

A model insurance benefit package for posthospitalization psychiatric halfway house care was developed and administered to 32 hospitalized mentally ill persons. The therapeutic and cost effectiveness of providing a 120-day benefit package was examined over a 14-mo posthospitalization period. This was compared with the effectiveness of hospitalization benefits alone for the same patients over the 42 mo prior to halfway house admission. In terms of therapeutic efficacy, there was no significant deterioration after hospitalization release in either the symptom or behavioral coping scales, except for an increase in somatization. Yearly hospital recidivism rates fell from 79% to 29%, and the average yearly length of hospital stay per patient fell from 83 days to 18 days. In terms of cost-effectiveness, halfway house benefits saved the insurers 59% of their hospitalization costs. The implications of these findings are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Coordinating optimisation of F-EMS and soft reduction during bloom continuous casting process for special steel

To control the halfway cracks and shrinkage cavities during bloom continuous casting (CC) process, final electromagnetic stirring (F-EMS) and soft reduction techniques have been coordinately optimised. The halfway crack and shrinkage cavity can be successfully controlled by adopting the CC technique parameters described as follows: (1) casting speed is 0.62 m min-1, (2) secondary cooling water ratio is 0.2?L?kg^?1, (3) reduction amount is 18?mm; (4) reduction region ranges from 19.9?m (location of M3 roller) to 25.4?m (location of M9 roller) distance from meniscus; and (5) corresponding distributions of reduction amount for each roller are 1, 1, 2, 3, 4, 4, and 3?mm along the casting direction. As compared to origin scheme for bearing steel, the difference between the maximum and minimum segregation degrees at the strand centre can be reduced from 0.35 to 0.09 under the optimal case.     

连铸板坯中心裂纹成因分析及预防措施

本文针对酒泉钢铁公司连铸机的实际生产情况,分析了影响连铸板坯中心裂纹的因素,提出了相应的预防措施。在设备管理上,确定铸机使用标准及精度值,保证连铸机良好的运行状况是防止产生中心裂纹的基础;在工艺操作上,通过控制钢水过热度、控制钢水硫、磷含量及适当降低二冷水强度有效地降低了板坯中心裂纹。     

超声波探伤不合格T91钢棒材的分析和工艺改进

试验T91钢(/%:0.10C,0.30Si,0.45Mn,0.012P,0.005S,8.90Cr,0.95Mo,0.08Nb,0.22V)的生产流程为60t UHP EAF-AOD-LF-VD-240 mm×240 mm坯连铸-加热-连轧。对超声波探伤不合格的T91钢Φ90 mm材低倍检验结果表明,钢材存在中心裂纹和孔洞;通过金相分析得出,缺陷出现三种特征:(1)过烧型孔洞和裂纹;(2)连铸坯带来的轴心晶间裂纹;(3)铸坯的缩孔。通过连铸Ⅰ、Ⅱ和Ⅲ区二冷水量分别由原28、31和17 L/min优化成15、18和10 L/min,并通过控制连铸坯加热温度,使连铸坯中心的等轴晶比率由原14%提高至25%以上,铸坯的中心裂纹级别由2.0降至0.5以下,T91钢材的超声波探伤不合格率由5%降至0.2%以下     

Halfway houses for alcoholics: a review, analysis and comparisons with other halfway house facilities

Eight halfway houses for alcoholics were surveyed and compared to other halfway houses for alcoholics, and halfway houses for the non-alcoholic mentally ill, as described in previous studies. The halfway houses for alcoholics surveyed in the present report may be separated into two principal groups: (a) a self-supporting profit-oriented type with an autonomous owner-operator, and (b) a board-controlled and supported type usually receiving group or institutional support. Regardless of group membership, however, none of the halfway houses for alcoholics in the present study matched the high standards set by halfway houses for the non-alcoholic mentally ill as described in other reports. Recent events indicate that halfway houses will be responsible for an increasing portion of persons requiring a structured, supportive or sheltered environment. This paper examines the ability of halfway houses for alcoholics to provide adequate residential care services. Additionally, disparities between alcoholism and non-alcoholism halfway houses regarding staffing, professionalised orientation, and adjunct services are scrutinised. The effectiveness of halfway houses is analysed, and suggestions for future utilisation of alcoholic halfway houses are advanced.     

25mm7A09厚板心部裂纹成因分析

25mm7A09厚板边部区域沿厚度方向中心部位产生小裂口，小裂口的产生非铸锭冶金缺陷引起的。这是由于轧制初期板材心部存在低塑性铸态组织，在此情况下板材进行滚边处理，滚边量过大导致板材边部出现内部开裂。为了消除此类小裂口，热轧时应控制铸锭加热温度，合理分配道次压下量及控制滚边时机和滚边量。     

小方坯内部裂纹成因研究

研究了小方坯的表面裂纹和中心裂纹的成因，指出完善二冷配水制度，严格规范操作和保持连铸机的状态良好很重要。     

异型连铸坯结晶器内表面纵裂萌生区域

 针对异型坯连铸过程中出现较多表面纵裂的问题,使用有限元软件ABAQUS建立铸坯二维微段模型,使用Fortran语言编写表面热流子程序DFLUX模拟铸坯在结晶器内的凝固传热过程,使用接触算法与重启动技术分析铸坯在热应力、表面摩擦力及钢水静压力下坯壳的受力状态。结合材料力学属性分析得出,[R]角、腹板中心、翼缘中心与窄面中心位置为异型坯表面纵裂纹最易萌生区域,[其中R]角处距离弯月面约200 mm处更容易萌生表面纵裂纹,腹板、翼缘中心与窄面中心距离弯月面180 mm处更容易萌生表面纵裂纹。     

板坯中间裂纹产生的原因及预防措施

根据本钢炼钢厂工艺流程的生产数据,通过对板坯中间裂纹出现规律及形态的研究,探讨了中间裂纹的成因。认为钢中硫、磷等杂质元素的晶间偏析是中间裂纹产生的内因,而辊缝、二冷系统、拉速、钢水过热度是裂纹产生和扩展的外因.提出了相应的控制措施.