锶硅铁孕育剂在双联熔炼灰铸铁中的应用

论述了孕育剂的孕育原理及特性,通过锶硅铁孕育剂和普通75硅铁孕育剂在双联熔炼中孕育效果的对比试验分析,锶硅铁孕育剂可显著提高铸件质量。     

感应炉熔炼与双联熔炼的灰铸铁力学性能的比较

运用数理统计的方法,统计分析了大量使用感应炉熔炼与双联熔炼灰铸铁的单铸试棒的力学性能数据,通过比较发现:尽管铸件和材料牌号相同,化学成分、孕育剂及其加入量基本相同,原材料的规格、质量标准和产地基本相同,但双联熔炼灰铸铁与感应炉熔炼灰铸铁相比,其单铸试棒的抗拉强度高约26.5 MPa,硬度高HBW6,冶金质量也好.     

双联熔炼生产冰箱压缩机灰铁件的实践

论述了用双联熔炼生产冰箱压缩机灰铁件的一些主要工艺问题,提出了生产中控制好铁水温度和成分的方法。     

双联熔炼中如何选用无芯感应炉

现在有许多厂家为了产品延伸,需要将高炉或冲天炉铁水作升温处理,常采用无芯感应电炉作为升温设备。由于我国无芯炉系列以熔化炉为主,其特点是:功率大,炉身细高,线圈高度也高。这些特点对熔化金属用是合适的,电效率高,启熔时有效加热层总面积大,有利于熔化。但若作为铁水升温用这三点都是不合适的。一、功率和容量的矛盾     

感应电炉熔炼与双联熔炼成本比较

采用感应电炉熔炼取代"冲天炉+电炉"双联熔炼工艺。2种工艺成本核算结果显示:采用电炉熔炼后材料成本节约475元/t,铸件单吨标煤消耗下降279.6 kgce/t,车间燃动成本降低521元/t,基本消除了CO2、SO2排放,减少了炉渣的排放,降低了工人的劳动强度,改善了工作环境。此外还介绍了该项改造及试产过程中出现的主要问题,包括冷却塔水蒸气、炉渣结壳、回炉料清理、球铁白口倾向增大等,以及相应的改进措施。     

铸铁熔炼材料的选用及其对铸件质量的影响

对铸铁生产流程中的预处理及其它各前置工序中所用的熔炼材料作了归类。分述了生铁、废钢、增碳剂、脱硫剂、增硫剂、脱磷剂、净化剂、清渣剂、预处理剂和燃料焦炭等的品质、品种和选用等问题,并介绍了它们对铸铁件质量的影响情况,提出了选用原则建议。     

双联熔炼过程中HT250成分的稳定控制

本文通过对双联熔炼过程的数据分析，探讨稳定控制化学成分的方法，以确保获得优良内在质量的发动机缸体铸件。     

现代灰铸铁熔炼技术

严格控制冶金因素提高灰铸铁性能，从炉料选材到熔炼操作，结合生产经验和认识做了论述。对铸铁质量提出应在结晶过程做深入研究，从而进一步提高性能。     

双联熔炼在我厂的实际应用

结合本单位的生产实际,提出了主要用于过热的炉容量之比在0.5以下,亦可实行双联熔炼匹配的观念,并在生产中采取各种办法使之实现,分析了采用双联熔炼时要注意的问题和取得的效果.     

冲天炉—工频炉双联熔炼效果的探讨

在相同配比条件下，对比了一汽铸造厂冲天炉－工频炉双联熔炼与冲天炉熔炼灰铸铁的效果，评价了双联熔炼灰铸铁的铁水质量。     

铸铁表面激光熔凝行为及温度场数值模拟

为明确铸铁表面激光熔凝过程的热响应规律,考虑随温度变化的材料热物性参数和相变潜热影响,建立铸铁表面激光动态熔凝的三维数值模型并进行了验证,预测值与试验值吻合良好,采用该模型分析了热响应温度场规律及不同工艺参数的映射关系.结果表明,铸铁表面激光熔凝较钢材可获得更大的熔透深度,熔池内、外形成较大温度梯度且分别以深、宽方向分...     

Different thermal fatigue behaviors between gray cast iron and vermicular graphite cast iron

The initiation and propagation of thermal fatigue cracks in gray cast iron and vemicular graphite cast iron were investigated by Uddeholm method to reveal the complex thermal fatigue behaviors of cast iron. Differences of thermal fatigue behaviors of gray cast iron and vemicular graphite cast iron were observed and analyzed. It is found that the observed differences are related to the combination of graphite morphology and the oxidization of matrix. More oxidized matrix is observed in gray cast iron due to its large specific surface area. The brittle oxidized matrix facilitates the propagation of microcracks along the oxidization layer. By contrast, the radial microcracks are formed in vermicular graphite at the edge of graphite due to fewer oxidization layers. It indicates that the thermal fatigue resistance of gray cast iron is dominated by graphite content and morphology while that of vermicular graphite cast iron strongly relates to the strength of the matrix.

     

工艺参数对蠕墨铸铁激光熔凝淬火带裂纹率和形貌的影响

采用3 kW固体光纤激光器在蠕墨铸铁基体上进行了激光熔凝淬火试验,分析了淬火带的裂纹率、熔凝区形貌、显微硬度和组织.结果表明,当保护气体流量一定时,提高激光功率或降低扫描速率有利于降低激光熔凝淬火带的裂纹率;而激光功率一定时,不同的扫描速率对应的最佳保护气体流量大小不同.随着激光功率的增加,淬火带形貌会向基体扩展,扩展规律是先主要沿熔凝区宽度和深度方向扩展,然后沿其它方向扩展,到一定程度后,又沿着宽度和深度方向扩展,如此循环,熔凝区总面积不断增加,淬火带形貌也由扁平状逐步变化为帽子状.     

镍硬铸铁Ⅳ的热处理工艺

以镍硬铸铁Ⅳ为研究对象,进行了热处理工艺试验,并探讨了热处理工艺对其组织及硬度的影响,拟定了镍硬铸铁Ⅳ的最佳热处理工艺。试验表明,硬化处理时合适的奥氏体化温度范围为800～820℃,为消除应力可考虑硬化处理后进行450℃回火;550℃+450℃的双重退火工艺,但对于零件硬度要求在60 HRC以上者不可取,对硬度要求在58 HRC左右的,则可采用。镍硬铸铁Ⅳ具有良好的热处理工艺性能,生产中易于掌握。     

Construction and analysis of dynamic solidification curves for non-equilibrium solidification process in lost-foam casting hypoeutectic gray cast iron

Most lost-foam casting processes involve non-equilibrium solidification dominated by kinetic factors, while construction of a common dynamic solidification curve is based on pure thermodynamics, not applicable for analyses and research of non-equilibrium macro-solidification processes, and the construction mode can not be applied to nonequilibrium solidification process. In this study, the construction of the dynamic solidification curve (DSC) for the nonequilibrium macro-solidification process included: a modified method to determine the start temperature of primary austenite precipitation (TAL) and the start temperature of eutectic solidification (TES); double curves method to determine the temperature of the dendrite coherency point of primary austenite (TAC) and the temperature of eutectic cells collision point (TEC); the "technical solidus" method to determine the end temperature of eutectic reaction (TEN). For this purpose,a comparative testing of the non-equilibrium solidification temperature fields in lost-foam casting and green sand mold casting hypoeutectic gray iron was carried out. The thermal analysis results were used to construct the DSCs of both these casting methods under non-equilibrium solidification conditions. The results show that the transformation rate of non-equilibrium solidification in hypoeutectic gray cast iron is greater than that of equilibrium solidification. The eutectic solidification region presents a typical mushy solidification mode. The results also indicate that the primary austenite precipitation zone of lost-foam casting is slightly larger than that of green sand casting. At the same time, the solid fraction (fs) of the dendrite coherency points in lost-foam casting is greater than that in the green sand casting.Therefore, from these two points, lost-foam casting is more preferable for reduction of shrinkage and mechanical burntin sand tendency of the hypoeutectic gray cast iron. Due to the fact that the solidification process (from the surface to center) at primary austenite growth area in the lost-foam cylinder sample lags behind that in the green sand casting,the mushy solidification tendency of lost-foam casting is greater and the solidification time is longer.     

微合金化铸铁同质焊条焊接工艺

应用微合金化铸铁同质焊条,采用小电流打底、大电流连续焊工艺,研究了预热温度与焊缝组织及性能之间的相关性.结果表明,微合金化铸铁焊条石墨化能力强,焊缝白口倾向小;小电流打底、大电流连续焊工艺可有效地减小熔深,在很大程度上抑制了熔合区白口的产生.微合金化铸铁焊条可实现常温焊接.预热温度小于200℃即可获得组织和性能与母材一致的同质焊缝.随着焊件预热温度的升高,焊缝中的石墨形态由细小的点状逐渐向菊花状、片状过渡,铁素体含量增多,焊缝硬度减小.焊件预热至200℃所获得的焊缝组织由珠光体、铁素体和细片状石墨及菊花状石墨组成,熔合区则由珠光体、少量碎块状铁素体及过冷石墨片组成,接头力学性能良好.     

灰铸铁件激光熔覆NiCuFeBSi合金的气孔行为

通过对比分析45钢与HT250两种基体成形熔覆层内气孔形态,研究了熔覆层内气孔气体类型、分布规律以及影响因素.结果表明,熔覆层内气孔气体为CO,由石墨和氧或氧化物反应生成,气孔形状不规则、具有棱角状特征.气孔上浮形式并非垂直上浮,而是弥散式上浮.熔池内部强对流是影响气孔分布的内在因素.气孔运动幅度取决于熔池对流加速度,熔池温度越高,熔池表面张力梯度也越大,熔池对流的加速度越大.激光熔覆工艺是影响气孔分布的外在因素,适当降低激光功率和扫描速度、提高灰铸铁预热温度可有效消除熔覆层气孔缺陷,降低孔隙率.     

定向石墨灰口铸铁的拉伸行为

提出了一种新的灰口铸铁(GCI)热加工工艺,即包覆压缩(CCC)。采用该工艺,经大于45%热变形压缩,制备了定向石墨灰口铸铁。经80%热变形的GCI拉伸性能显著提高,抗拉强度从117MPa提高到249MPa,伸长率从0提高到5.2%;热变形量超过45%的GCI,拉伸断口有分层现象,出现了一些韧性断裂的特征。     

气体渗氮工艺对NbVTi合金化灰铸铁组织与性能的影响

针对发动机高速重载的发展趋势,对新型NbVTi合金化灰铸铁气缸套材料进行了不同温度的气体渗氮处理。通过光学显微镜、维氏硬度计、摩擦磨损试验机、扫描电镜等手段,研究了NbVTi合金化灰铸铁气缸套表面的气体渗氮工艺对组织性能的影响。结果表明:随着渗氮温度的增加,NbVTi合金化灰铸铁气缸套的渗氮层深度都有所增加,距离表面100 μm和130 μm处的显微硬度先增后降。在最佳的渗氮温度570 ℃渗氮后,气缸套尺寸膨胀量在0.010~0.055 mm标准范围内,渗氮层平均厚度约140 μm,距离表面100 μm扩散区平均硬度达到500 HV0.1以上,可满足高速重载气缸套的使用要求。气体渗氮后,气缸套的摩擦磨损性能得到了大幅提高,随着载荷的增大和速度的增加,磨损率随之增大,其磨损机理由磨粒磨损向粘着磨损转变。     

Laser surface hardening of gray cast iron used for piston ring

The process parameters for laser surface-hardening has been experimentally established for improving the wear life of piston rings used for marine diesel engines by the formation of a proper hardened layer on it. The parameters of interest were the laser power and travel speed. Various hardened layers of gray cast iron were analyzed with respect to microstructure, hardness value, hardening depth, surface roughness, and wear resistance. The hardness of the laser-hardened layer was in a range between 840 and 950 Hv0.1, regardless of the laser power and travel speed range studied. Both the surface roughness and hardening depth increased in an almost linear manner with the increase in the heat input applied. Thus, the hardened layers formed with heat input ranges between 30 and 45 J/mm satisfied the piston ring application requirements for surface roughness (<6.3 μm in Ra) and the minimum effective hardening depth of 0.3 mm (>450 in Vickers number). Wear-test results obtained using a pin-on-disk-type wear-test machine showed that the wear life of the laser-hardened layer was almost twice that of the untreated one. This was directly attributed to the formation of the martensitic microstructure.