Influence of Rare Earth Elements on Microstructure and Mechanical Properties of Cast High-Speed Steel Rolls

The influence of rare earth （RE） elements on the solidification process and eutectic transformation and mechanical properties of the high-V type cast, high-speed steel roll was studied. Test materials with different RE additions were prepared on a horizontal centrifugal casting machine. The solidification process, eutectic structure transformation, carbide morphology, and the elements present, were all investigated by means of differential scanning calorimetry （DSC） and scanning electron microscopy energy dispersive spectrometry （SEM-EDS）. The energy produced by crack initiation and crack extension was analyzed using a digital impact test machine. It was found that rare earth elements increased the tensile strength of the steel by inducing crystallization of earlier eutectic γ-Fe during the solidification process, which in turn increased the solidification temperature and thinned the dendritic grains. Rare earth elements with large atomic radius changed the lattice parameters of the MC carbide by forming rare earth carbides. This had the effect of dispersing longpole M C carbides to provide carbide grains, thereby, reducing the formation of the gross carbide and making more V available, to increase the secondary hardening process and improve the hardness level. The presence of rare earth elements in the steel raised the impact toughness by changing the mechanism of MC carbide formation, thereby increasing the crack initiation energy.

Effect of car-body lower-center rolling on aerodynamic performance of a high-speed train

The interaction between the car-body vibration and aerodynamic performance of the train becomes more prominent motivated by the vehicle’s light-weighting design.To address this topic,this study firstly analyzes the posture characteristics of the car-body based on the previous full-scale test results.And then the aerodynamic performance under different vibration cases(different car-body roll angles)is studied with an improved delayed detached eddy simulation(IDDES).The results revealed that car-body rolling had a significant impact on the aerodynamic behavior of bogies,which significantly increased the lateral force and yaw moment of a bogie and further may have aggravated the operational instability of the train.The unbalanced distribution of the longitudinal pressure on both sides of the bogie caused by the car-body rolling motion was the primary cause for the bogie yaw moment increase.The tail vortex of the train was also affected by the car-body rolling,resulting in vertical jitter.

Thermal Model of High-Speed Spindle Units

For the purpose to facilitate development of high-speed Spindle Units (SUs) running on rolling bearings, we have developed a beam element model, algorithms, and software for computer analysis of thermal characteristics of SUs. The thermal model incorporates a model of heat generation in rolling bearings, a model of heat transfer from bearings, and models for estimation of temperature and temperature deformations of SU elements. We have carried out experimental test and made quantitative evaluation of the effect of operation conditions on friction and thermal characteristics of the SUs of grinding and turning machines of typical structures. It is found that the operation conditions make stronger effect on SU temperatures when rpm increases. A comparison between the results of analysis and experiment proves their good mutual correspondence and allows us to recommend application of the models and software developed for design and research of high-speed SUs running on rolling bearings.

Design of a high-precision twin-roll strip caster

During strip casting,the thickness deviation of casting strip directly affects the quality of the hot-rolled sheet because the casting strip needs to be rolled only once.To accurately control the gap between casting rolls and reduce the thickness deviation of the casting strip,a conceptual design of a prestressed twin-roll caster is proposed herein;this caster involves the setting of a constant pressure balancing cylinder between the chocks of two casting rolls.The balancing cylinder hydraulic system adopts a three-way servo valve that controls the hydraulic cylinder.The parameters of the hydraulic power components are determined using the principle of optimal power matching,and the hydraulic system model of the balancing cylinder is thus established.The dynamic analysis and simulation of the hydraulic system are performed using finite element model to obtain relevant evaluation indexes.Finally,the hydraulic system is corrected using proportional-integral-derivative (PID) correction to achieve a well-controlled effect.Thus,the engineering requirements of the strip casting process can be met.

Centrifugal Casting of High Speed Steel/Nodular Cast Iron Compound Roll Collar

The centrifugal casting of compound HSS/nodular cast iron roll collar was studied,and the factors affecting transition zone quality were analyzed.The pouring temperature and interval in pouring are the main factors affecting transition zone quality.By controlling process parameter and flux adding during casting,high quality roll collar was obtained.The cause,why in the casting of HSS part,segregation appears easily,was analyzed and the countermeasure eliminating segregation was put forward,the measure eliminating heat treatment crackling was also put forward.

High Speed Twin Roll Casting of Aluminum Alloy Strips

The twin roll caster for aluminum alloys has many a dv antages. For example, rapid solidification, low equipment cost, and low running cost, etc. However, the twin roll caster has some disadvantages. They are slow c asting speed and limitation of alloys. In the conventional twin roll caster, the casting speed is slower than 10 m/min. Aluminum alloys, which freezing range is wide, can not be cast. In the present study, break through of these problems wa s tried, and a new type twin roll caster was devised. A vertical type twin roll caster equipped with a nozzle was devised in order to cast aluminum strips at the speeds higher than 60 m/min. Characteristic features of this caster were vertical type, use of copper rolls, low separating force (n o operation of rolling), no use of lubricant, and equipment of the nozzle. In th e high speed roll casting, feed of molten metal of the vertical type twin roll c aster was easier than that of the conventional horizontal type caster. The use o f the copper rolls made cooling rate higher. The low separating force and the us e of the copper rolls prevented sticking of the strip to the roll. The lubricant was not needed, as the sticking of the strip to the roll did not occur. No use of the lubricant was useful to increase the cooling rate and casting speed of th e strip. The nozzle was used in order to improve contact condition (heat transfe r) between the melt and the rolls by hydrostatic pressure. In the twin roll cast er of the present study, many devices were done to improve the cooling condition of the strip in order to increase the casting speed. It was said that the roll casting of A5182 was very difficult, as freezing zone of A5182 was very wide. However, A5182 strip could be cast at high speeds up to 120 m/min using the twin roll caster of the present study. The microstructure of the strip cast using the conventional type twin roll caster is columnar structu re. The microstructure of the strip cast using the twin roll caster of the prese nt study was not columnar but equiaxed structure. It is said that mechanical pro perties of the strip cast using the twin roll caster is cheaper than that of the strip made from DC casting. However, the mechanical properties of the strip cas t using the twin roll caster in the present study were almost same as the proper ties of the strip made from DC casting. The thickness of the strip cast using th e twin roll caster of the present study was from 1.5 mm to 2.5 mm, and this thic kness was thinner than that of the strip cast using the conventional twin roll c aster. Semisolid roll casting was tried in order to increase the roll speed more and mo re. The twin roll caster of the present study was equipped with a cooling slope in order to make semisolid slurry. The cooling slope was the simplest process to make the semisolid slurry. Solid rate of the semisolid slurry was about 10%. Th e casting speed increased up to 180 m/min by the effect of semisolid casting. Me chanical properties were improved by the semisolid casting, too.

Dynamic recrystallization behavior and microstructural evolution of Mg alloy AZ31 through high-speed rolling

High-speed rolling （HSR） is known to improve the workability of Mg alloys significantly, which makes it possible to impose a large reduction in a single pass without fracture. In the present study, dynamic recrystallization （DRX） behavior and microstructural and textural variations of Mg alloy AZ31 dur-ing a HSR process were investigated by conducting rolling with different imposed reductions in the range of 20%-80% at a high rolling speed of 470 m/min and 400℃. High-strain-rate deformation during HSR suppresses dislocation slips but promotes twinning, which results in the formation of numer-ous twins of several types, i.e., {10-12} extension twins, {10-11} and {10-13} contraction twins, and {10-11}-{10-12} double twins. After twinning, high strain energy is accumulated in twin bands because their crystallographic orientations are favorable for basal slips, leading to subsequent DRX at the twin bands. Accordingly, twinning activation and twinning-induced DRX behavior play crucial roles in accommodating plastic deformation during HSR and in varying microstructure and texture of the high- speed-rolled （HSRed） sheets. Area fraction of fine DRXed grains formed at the twin bands increases with increasing rolling reduction, which is attributed to the combined effects of increased strain, strain rate, and deformation temperature and a decreased critical strain for DRX. Size, internal strain, and texture intensity of the DRXed grains are smaller than those of unDRXed grains. Therefore, as rolling reduction increases, average grain size, stored internal energy, microstructural inhomogeneity, and basal texture intensity of the HSRed sheets gradually decrease owing to an increase in the area fraction of the DRXed grains.

Dynamic deformation behavior and microstructural evolution during high-speed rolling of Mg alloy having non-basal texture

The dynamic deformation behaviors and resultant microstructural variations during high-speed rolling(HSR) of a Mg alloy with a non-basal texture are investigated. To this end, AZ31 alloy samples in which the basal poles of most grains are predominantly aligned parallel to the transverse direction(TD) are subjected to hot rolling with different reductions at a rolling speed of 470 m/min. The initial grains with a TD texture are favorable for {10–12} twinning under compression along the normal direction(ND); as a result, {10–12} twins are extensively formed in the material during HSR, and this consequently results in a drastic evolution of texture from the TD texture to the ND texture and a reduction in the grain size. After the initial grains are completely twinned by the {10–12} twinning mechanism, {10–11} contraction twins and {10–11}-{10–12} double twins are formed in the {10–12} twinned grains by further deformation.Since the contraction twins and double twins have crystallographic orientations that are favorable for basal slip during HSR, dislocations easily accumulate in these twins and fine recrystallized grains nucleate in the twins to reduce the increased internal strain energy. Until a rolling reduction of 20%, {10–12}twinning is the main mechanism governing the microstructural change during HSR, and subsequently,the microstructural evolution is dominated by the formation of contraction twins and double twins and the dynamic recrystallization in these twins. With an increase in the rolling reduction, the average grain size and internal strain energy of the high-speed-rolled(HSRed) samples decrease and the basal texture evolves from the TD texture to the ND texture more effectively. As a result, the 80% HSRed sample, which is subjected to a large strain at a high strain rate in a single rolling pass, exhibits a fully recrystallized microstructure consisting of equiaxed fine grains and has an ND basal texture without a TD texture component.

非对称式辊式搅拌在宽板坯连铸机的设计与应用

辊式搅拌是板坯连铸机的核心设备,主要用于提高铸坯等轴晶率,改善铸坯中心疏松和中心偏析,提升铸坯内部质量。对于铸坯宽度大于1 800 mm宽板坯连铸机,采用通辊式辊式搅拌经常出现辊端轴断裂和螺栓松动等故障,导致辊式搅拌使用寿命无法与连铸机正常自由辊相匹配,设备无法连续稳定运转。宽板坯连铸机上采用了非对称式辊式搅拌技术,通过对非对称式辊式搅拌辊进行建模仿真与实际磁学性能测试,验证该类型结构能达到改善铸坯中心质量所需磁场性能要求。通过改造扇形段适配非对称式辊式搅拌的安装,开展了430、0Cr13、439、409、2Cr13等不锈钢钢种的冶金试验,试验结果满足预期铸坯中心质量要求,铸坯中心等轴晶、中心疏松和中心偏析改善效果明显,改造后设备未出现辊端轴断裂和螺栓断裂问题,设备使用稳定性大幅提高,搅拌辊与自由辊寿命基本持平,满足连铸机稳定无故障运行要求。

Rolling Along China steps into the high-speed rail age as two new projects get final government approval

The Beijing-Shanghai railway, linking the two biggest cities in China, is the busiest railway in the world, having an annual cargo capacity of 120 million tons and transporting 30 million passengers. Connecting two economically developed regions-the Yangtze Delta and Circum-Bohai (sea) area-the railway

双辊薄带连铸熔池液面波动及流体混合特征模拟研究

按照相似理论的原理 ,制作了模拟熔池内液面波动和流体混合的物理模型 ,分别采用超声波浪高仪和电导仪测定了不同结构尺寸的水口和工艺条件下熔池内液面波动和流体混合状况 ,得到了水口结构尺寸和工艺参数对熔池液面波动和流体混合状况影响的定量关系 。

车身侧倾时前轮主销后倾角对转向稳定性的影响

为了提高4×4越野车弯道高速行驶的稳定性,计及前轮定位参数的影响,建立了转向行驶时整车4自由度动力学模型;计算了车辆在不同车速下,不同前轮主销后倾角时的横摆角速度瞬态响应。结果表明,车速提高时,横摆角速度超调量增大,稳定时间延长;而在适当范围内增大主销后倾角,可减小横摆角速度超调量和稳定时间,改善高速行驶车辆的转向稳定性。同时说明主销后倾角对横摆角速度超调量有阻尼作用。

板坯连铸机辊式电磁搅拌的应用实践

武钢第二炼钢厂在应用辊式电磁搅拌装置的过程中,对辊式电磁搅拌器的安装位置和搅拌参数进行多次试验与研究,确定电磁搅拌器的合适安装位置,并对搅拌工艺参数进行优化,使之达到较好的冶金效果。

双辊薄带高速铸轧机新技术

本文介绍了近年来出现的MDTRC、METRC和HPTRC等新型双辊铸轧机,对设备和工艺特点以及所得铸带的组织性能等参数进行了对比分析,指出立式TRC、铜质铸辊、无润滑、低过热度和半固态铸轧是提高铸轧速度的有效方法。

中国铝板带箔加工设备现状及发展方向

该文对中国铝、板、带、箔轧制的主导设备作了全面的介绍,并对其发展趋势作了展望。截止到2004年底,中国铝板带箔产能(预计)如下:扁锭生产能力850kt/a;双辊式铸轧机170台(其中引进13台);双辊式带坯生产能力1400kt/a,带坯热轧机16台,生产能力1050kt/a;双辊块片热轧机125台,生产能力650kt/a;现代化四辊与六辊冷轧机108台(含可轧单零箔的),生产能力2100kt/a;可轧单零箔的冷轧机46台,生产能力230kt/a;四辊铝箔轧机62台,生产能力240kt/a。在建的热轧生产线11条,生产能力2100kt/a;铝箔轧机22台,生产能力120kt a。

板坯连铸机ASTC动态辊缝精度控制实践

为解决中心偏析、疏松及裂纹对连铸坯表面及内部质量造成的影响及避免连铸机拉坯阻力过大导致的夹坯事故,对连铸机辊缝精度低下的原因进行了分析,提出了解决方法,通过采取控制连铸辊零部件及其装配精度、辊子堆焊表面硬度、提高扇形段维修安装对弧精度、计算并分析在线辊缝校正规律等措施,提高了连铸机产品的质量。

辊缝测量仪测量误差分析及改进

分析辊缝仪的工作原理,找到辊缝测量传感器触头容易磨损、弹簧强度不够等制约辊缝仪测量数据准确性提高的主要原因,并通过制定辊缝测量传感器校验规范、优化辊缝测量时间和角度仪的安装规范,使辊缝仪测量数据的准确性大幅度提高。

SPHD薄板坯连铸漏钢原因分析及控制措施

分析了唐钢FTSC薄板坯连铸机生产低碳冷轧用钢过程中漏钢的成因;提出了优化锥度控制、改进结晶器窄面铜板形状和优化水口形状等技术措施。这些措施实施后,低碳钢生产过程中的漏钢得到有效控制。

连铸机精度提高方法的研究

针对连铸机精度不高的问题,从扇形段的设计参数、安装质量、连铸机的传动稳定性和辊缝仪的使用情况四个方面进行了分析,找到了扇形段参数设计不合理、安装质量不高以及连铸机传动稳定性差这三个主要原因,最后通过改进扇形段材质、修订扇形段修复和在线维护规范、优化设计扇形段万向轴结构尺寸等措施,有效提高连铸机的精度,降低备件成本.

哈兹列特连铸连轧技术

本文介绍哈兹列特铝带坯连铸连轧的工艺特点、产品范围、技术进展及工业应用。