连铸对M2高速钢偏析与碳化物的影响

为了加快实现M2高速钢连铸工业生产，改善M2连铸坯组织均匀性、降低宏观偏析、细化碳化物、提高铸坯内部质量，采用金属原位分析仪、直读光谱仪、扫描电子显微镜、X射线衍射仪等手段研究弧形连铸工艺生产M2高速钢弧形的铸态组织以及热加工后组织情况，特别是宏观偏析和碳化物演变，并与模铸工艺生产M2高速钢进行对比。结果表明，M2高速钢弧形连铸坯的碳化物最大尺寸相比于模铸情况降低了约44%,二次枝晶间距降低约20%;另外，连铸坯碳化物呈纤维状，经过高温热处理后更易分解，碳化物得到了进一步细化；锻轧后，连铸坯碳化物尺寸均匀，无明显大块碳化物，最大碳化物尺寸小于10μm。     

连铸56SiMnVB弹簧钢的碳化物研究

对５５ＳｉＭｎＶＢ钢连铸坯的低倍缺陷及铸坯、轧材中的碳化物特征、类型及分布等分析研究。研究结果表明：５５ＳｉＭｎＶＢ钢连铸坯的低倍缺陷主要为中心偏析；铸坯中的碳化物与偏析有一定对应关系，偏折区出现大量碳化物，其特征主要以沿晶界析出的合金渗碳体和分散的细小ＶＣ及Ｖ（Ｃ，Ｎ）形式存在。提出了降低和改善偏析以减少碳化物的措施。     

60高碳硬线钢的生产实践

对国内某钢厂60高碳硬线钢生产情况进行了介绍,对60高碳钢铸坯低倍组织、盘条力学性能、显微组织及夹杂物进行了检验分析.结果表明:60高碳钢铸坯低倍缺陷级别≤1.0级,低倍组织缺陷少且尺寸小,有利于轧材性能的稳定控制和塑韧性的改善;60高碳钢盘条力学性能优异,强度波动范围小,断面收缩率大于41.5％; 60高碳钢盘条显微组织细小均匀,索氏体含量80％～90％,夹杂物数量少、尺寸小,B、D、Ds类氧化物夹杂≤1.0级,有利于盘条拉拔性能的改善.     

喷射成形M3型高速钢碳化物组织特征与加热过程演化

采用常规铸造和喷射成形工艺分别制备了M3型高速钢铸坯和沉积坯.利用扫描电子显微镜、X射线能谱和X射线衍射等分析方法对冷却速度对合金的显微组织的影响,加热温度对M3高速钢中M₂C共晶碳化物分解行为的影响,以及热加工变形后铸态和沉积态组织的变化进行了研究.结果表明:铸态合金含有粗大的一次枝晶和M₂C共晶碳化物,而喷射成形沉积坯主要为等轴晶且碳化物细小均匀;冷却速度的提高极大地抑制了碳化物的析出和晶粒长大;加热温度的提高有利于M₂C共晶碳化物分解,过高的温度使得分解后的M₆C长大,不利于合金性能的提高;沉积坯经恰当的预热处理和热变形可以获得理想的变形组织.      

30Cr13不锈钢冷轧边裂原因分析与工艺改进

针对30Cr13边裂缺陷样品进行分析,发现开裂的根本原因是组织中存在碳化物偏析.对热轧板碳化物偏析、铸坯低倍检测和金相检测结果、电磁搅拌电流等进行分析,发现造成碳化物偏析的主要原因是电磁搅拌工艺参数不当,电磁搅拌电流降低至250 A后碳化物偏析现象得到了明显改善.     

高碳钢150 mm×150 mm连铸坯堆垛缓冷对碳偏析的影响

高碳钢SWRH82B(0.81%C)盘条用于生产预应力钢丝钢绞线,其中网状碳化物是造成冷拔断裂的重要原因。试验了该钢150 mmn×150 mm铸坯堆垛缓冷时间(0~48 h)对铸坯碳偏析和φ12.5 mm盘条碳化物的影响。结果表明,直接空冷时的铸坯中碳含量的差值为0.116%,堆垛缓冷12,24,36,48 h后碳含量差值分别降至0.088%,0.080%,0.075%和0.076%,盘条中网状碳化物也相应降低;SWRH82B钢150 mm×150 mm连铸坯堆垛缓冷24 h,可以满足盘条冷拉工艺要求。     

GCr15轴承钢盘条孔洞缺陷分析及改善

对GCr15高碳铬轴承钢热轧盘条的低倍组织孔洞缺陷进行SEM电镜分析,说明孔洞缺陷的产生与钢中碳、铬元素的分布存在直接关系.GCr15轴承钢在凝固组织的二次枝晶间形成碳、铬偏析生成粗大的M3C、M7C3等共晶碳化物.由于扩散时间及温度的限制,该碳化物未能充分均化固熔在轧制后的拉伸带状组织中,所以酸蚀后的轴承钢热轧盘条断面出现低倍组织孔洞缺陷.为了改善该缺陷,共进行了8组高温扩散试验,结果表明：热轧盘条的低倍组织孔洞缺陷在1 100℃高温扩散后得到明显改善.     

M2高速钢铸带组织特征及其后续处理

研究了M2高速钢在不同制备条件下的凝固组织特征以及工业铸带中碳化物在高温热处理、热变形作用下的变化,测量了在不同制备条件下高速钢的凝固速度和共晶碳化物网的厚度,采用透射电镜研究了后续高温热处理、热变形对工业铸带中碳化物相的影响,采用定量金相法分析了制备条件和后续处理工艺对铸带组织的影响.研究结果表明,双辊薄带连铸工艺可以细化高速钢凝固组织的枝晶和共晶碳化物网的厚度,改善碳化物的分布,后续高温热处理和热变形可以进一步优化工业铸带中的碳化物组织.建议在工业铸带的后续处理中同时采用高温热处理和热变形工艺以改善铸带组织.     

GCr15轴承钢盘条高线工艺开发

为满足使用要求,通过研究加热、控轧控冷工艺、重新设定工艺参数、控制表面质量等措施,使用150mm×150 mm的连铸坯开发出轴承钢GCr15盘条。该盘条的金相组织、表面脱碳层、碳化物不均匀性及表面质量等各项指标良好,可满足国家标准要求,且能够保证产品的加热质量,实现安全生产。     

50 t EAF-AOD-LF-VD-CC-轧制高碳不锈钢9Cr18盘条的工艺实践

采用50 t EAF-AOD-LF-VD-150 mm×150 mm坯连铸-高速线材连轧工艺生产9Cr18钢(/%:0.95C,0.35Si,0.37Mn,0.032P,0.002S,17.42Cr,0.01Mo)Φ5.5 mm盘条。通过控制[S]≤0.008%,添加0.05%稀土元素,连铸坯经1160℃高温扩散处理,Φ5.5 mm成品盘条采用860℃球化退火等工艺措施,检验结果表明,盘条中心和一般疏松,以及偏析均≤1.0级,共晶碳化物不均匀度1.0~2.0级,球化退火组织为球状珠光体+块状碳化物,抗拉强度750~780 MPa,伸长率20%~26%,具有良好的冷拔性能。     

A decade of quality steel production: Developing a production technology for steel used in metal-cord manufacture

The introduction of high-carbon wire-rod production at OAO Moldavskii Metallurgicheskii Zavod is considered, with particular attention to wire rod for the production of metal cord. The influence of various factors—the chemical composition of the steel, its content of nonmetallic inclusions, its macrostructure and microstructure, decarburization, surface defects, and the scale—on wire rod performance is considered, individually and in aggregate. An effective production technology is developed, including steel production, ladle treatment, casting, rolling, and thermomechanical treatment of the wire rod for metal-cord production.     

Microstructure Evolution in 9Cr Martensitic Steel During Long-Term Creep at 650℃

 Standardarized creep and rupture strength tests were conducted for commercial T91 martensitic heat-resistant steel at 650 ℃ and corresponding microstructure was characterized by BSED, TEM and EDS. The martensitic microstructure degenerated seriously during creep exposure, including martensitic substructure recovering, carbides coarsening, dissolving and precipitating. EDS analysis shows that the M23C6 carbides in different morphologies have dissimilar compositions. The rod/sheet like M23C6 particles within the matrix contain more additions, which might precipitate in situ while fine MX particles were re-solving. The high content of silicon in these rod/sheet like M23C6 carbides is probably related to self diffusion coefficient increasing for the exposed condition at 650 ℃ close to Curie temperature Tc. For those reasons, martensite substructure becomes unstable, and microstructure evolution is accelerated and leads to creep strength deteriorating severely.     

高碳钢盘条中心偏析的控制

研究了不同铸坯中心偏析成分在控冷过程中的相变行为,结果表明,铸坯中心成分偏析是导致高碳钢盘条中心出现马氏体的主要原因,而马氏体又是导致盘条拉伸出现尖状断口的主要原因;铸坯中心碳偏析指数不能超过1.12及综合偏析指数小于1.20,才能在控冷过程中不出现中心马氏体;通过降低过热度、实施末端电磁搅拌、轻压下并适当调整盘条控冷工艺等措施,连铸坯中心碳偏析指数由1.18减小到1.10,盘条的中心马氏体、尖断明显减少.     

Study on exogenous inclusions in rotary bending fatigue fracture of Si- killed spring steel 55SiCr

The size, distance from surface and composition of macro inclusions in rotary bending fatigue fracture of 1950MPa- class Si- killed 55SiCr suspension spring wire were analyzed by SEM- EDS. The composition distribution of endogenous oxide inclusions in the Si- killed 55SiCr wire rod were analyzed by means of FEI Explorer 4 automated scanning electron microscope, and the results show that macro inclusions in rotary bending fatigue fracture are exogenous inclusions. The distribution characteristics of these exogenous inclusions in the continuous casting bloom were studied by wire rod solidification dendritic display method. The results show that exogenous inclusions in fatigue fracture mainly are caused by the entrapment of mold powder, erosion of tundish line and submerged entry nozzle, and these exogenous inclusions mainly concentrate at the bloom loose side corner.     

82B高碳钢连铸坯中心偏析及线材质量的改善

为了解决用连铸坯直接轧制的82B高碳钢线材易脆断的问题,进行了试验研究,通过金相组织检验分析等方式,找出了导致82B线材易脆断的主要原因是铸坯中心偏析,并在生产中采取了降低中包钢水过热度、用拉矫辊实施轻压下等措施,使82B高碳钢铸坯中心偏析及轧制的线材质量得到明显改善。     

Experimental investigation on solidification of GCr15 bearing steel by the simulated continuous casting

ABSTRACT

An experimental apparatus for simulation of continuous casting process of GCr15 bearing steel billet is established. With the apparatus, the billets of diameter 140?mm are casted in various superheats and cooling conditions. The solidification macrostructure, dendrite morphology, segregation and carbide are investigated. It is shown that melting superheats and cooling conditions remarkably influence the microstructure and solute segregation. It is found that the secondary dendrite arm spacing of the steel increases with the increase of the superheat temperature, and with decrease of the cooling rate. Lower superheat with higher cooling rate promotes the refining of the microstructure. Refining equiaxed grains structure in the centre of the billet leads to lower segregation of carbon. Furthermore, with increasing cooling rates, the spacing of the pearlite laminar is refined and the precipitation of proeutectic carbides is suppressed.     

高碳钢盘条SWRH82BCr试制

为了满足出口用户的要求,进行了高碳钢盘条SWRH82BCr的生产试制。介绍了该盘条的试制过程,对采用200mm×200mm连铸坯直接轧制的盘条实物质量进行了检验,给出了试制结果。针对首次试制的盘条中心网状碳化物级别、中心马氏体级别偏高的问题,进行了斯太尔摩风机风量的调整,稳定了盘条的出厂性能。试制结果表明:该钢种试制工艺路线合理,优化后的高线斯太尔摩控冷工艺得到固化,盘条的中心网状碳化物、中心马氏体级别均不大于0.77级,索氏体体积分数不小于90%,断面收缩率不小于42.5%。     

82B线材笔尖状断裂形貌成因分析

82B线材在拉拔、绞股过程中断裂成笔尖状,其断裂起源是在心部,表现形式是心部的纵向串状“人”字形微裂纹和网状孔隙。“人”字形微裂纹和网状孔隙则跟心部的少量马氏体和网状碳化物有关。成分分析结果表明,心部薄弱环节主要起因于线材中心的成分偏析。     

Diffusion aluminide coatings for internal surface of rhenium- and rhenium-ruthenium-containing single-crystal superalloys turbine blades: Part I

Process of formation rhenium or refractory carbides based diffusion barrier layer (coating) on internal surface of rhenium- and rhenium-ruthenium-containing single-crystal high-temperature alloys (superalloy) turbine blades, prior to diffusion aluminide coating deposition, is studied. It is shown that diffusion barrier layer is preventing deleterious secondary reaction zone formation under aluminide coating during long-term high-temperature operation. The kinetics of powder carburizing process of rhenium- and rhenium-ruthenium-containing high-temperature alloys is investigated, and conditions for carburizing these alloys are determined. The phase composition of the surface layer after carburizing is studied, and the effect of the fractional composition of a carbon-based powder mixture on the carburizing rate is determined.