Computer simulation of core filling process of cast high speed steel roll

Core filling process of cast high speed steel roll was simulated.Ductile iron was used as core material.The influences of filling parameters,such as core filling time and core filling temperature,on the filling process were investigated.Based on the simulated results,optimal core filling parameters were determined.The predicted temperature fields show that the temperature at the roll shoulder is the lowest during the core filling process and usually causes binding defects there.Method for solving this problem was presented.

A study on centrifugal casting of high speed steel roll

High speed steel (HSS) rolls can replace traditional rolls such as alloyed cast iron rolls and powder metallurgical (PM) hard alloy rolls. The main reasons for the replacement are that the wear resistance of low-cost alloyed cast iron rolls is poor and the cost of high-quality PM hard alloy rolls is very high. By means of centrifugal casting, HSS rolls having excellent wear resistance have been manufactured. The hardness of the HSS roll is 6.5~67 HRC, the range of variation is smaller than 2 HRC and its impact toughness is 15 J/cm2. The wear rate of HSS rolls used in the pre-finishing stands of high-speed hot wire-rod rolling mill reaches 2.5×10-4mm per ton steel. Furthermore, the manufacturing cost of HSS rolls is significantly lower than that of PM hard alloy rolls; it is only 30 percent of that of PM hard alloy rolls.

Effect of quenching temperature on structure and properties of centrifugal casting high speed steel roll

The critical points and time-temperature-transformation(TTT)curves of the isothermal transformation diagrams for a high-speed steel casting on a horizontal centrifugal casting machine had been determined experimentally in the study.The effects of quenching temperature on the microstructures and properties of centrifugal casting high speed steel(HSS)roll has been investigated using scanning electron microscopy(SEM), light optical microscopy(LOM)and X-ray diffraction(XRD)as well as using tensile,impact,and hardness tests. The results show that the HSS roll has excellent hardenability and its matrix structure can be transformed into the martensite after being quenched in the sodium silicate solution.The retained austenite in the quenching structure increases and the hardness decreases when the quenching temperature exceeds 1,040℃.The tensile strength and impact toughness of HSS roll increase once the quenching temperature is raised from 980℃to 1,040℃. However,the tensile strength and impact toughness have no significant change when the quenching temperature exceeds 1,040℃.The HSS roll quenched at 1,040℃exhibits excellent comprehensive mechanical properties.

Development and Application of Die-Casting High Speed Steel Rolls

Due to its high hardness,good red hardness and excellent wear resistance at high temperature,high speed steel(HSS)is fit for the roll manufacture.In order to overcome the segregation of centrifugal casting of HSS roll,die-cast processes were developed and its effects on the properties of the HSS roll were investigated.It was found that pressure,pressing time and speed are three important factors affecting shrinkage cavity.For pouring temperature of 1 400-1 450 ℃,pressure of 150-160 MPa,pressing time of 120-150 sand pressing speed of 14-16mm/s,a compact HSS roll was obtained,which has no segregation and small working allowance.In the high speed wire rod rolling mill,service life of the HSS roll is 5to 8times longer than that of high nickel chromium infinite chilled cast iron roll.

Effects of heat treatment on structures and properties of high speed steel rolls

The effects of quenching temperature, cooling pattern, temper temperature andtemper times on the structure and properti-es of high speed steel (HSS) rolls have beeninvestigated. The results show that, when the quenching temperature is lower than 1050℃ thehardness of HSS increases with the quenching temperature increasing in oil cooling, but when thequenching temperature exceeds 1100℃ the hardness decreases. In the conditions of salt bath coolingand air cooling, the effect of quenching temperature on the hardness is similar to the above law,but the quenching temperature obtaining the highest hardness is higher than that in oil cooling.When the temper temperature below 350℃ the hardness of HSS has a little change, when above 475℃the hardness will increase with the temper temperature increasing, and the highest hardness isobtained at 525℃. When the temper temperature continues to increase, the hardness decreases. Twicetemper has little effect on the hardness, but three times temper decreases the hardness. HSS in aircooling has lower hardenability, oil cooling can easily produce crackle, and HSS quenching in saltbath has high harde-nability and excellent wear resistance.

Development of centrifugal casting high speed steel rolls

The present study aims at developing the high speed steel (HSS) as rollmaterials to replace the traditional roll materials such as the alloy cast iron and powdermetallurgical (PM) hard alloy. The HSS roll billet was formed by centrifugal casting, and the billetwas rough machined alter soften annealing heat treatment, then it was quenched and tempered to getsuitable hardness and toughness. After that the HSS roll was finish machined to the final dimensionof phi 285 mm in the outer diameter, phi 160 mm in the inner diameter and 120 mm in width and itssurface hardness was tested. Finally the HSS roll was used in high speed wire rod mill. The testresults show that a high and homogeneous hardness can obtain on the work surface of HSS rolls, thesurface hardness is 63-65HRC and its variation is smaller than 2HRC. The impact toughness of thiskind of HSS is about 16 J/cm^2. The results of on-line service investigation in high speed wire rodmill indicate that the HSS rolls have excellent wear resistance, the steel rolling quantity per mmof HSS rolls is 3120 t, the service life-span of HSS rolls is 4 times longer than that of highchromium cast iron rolls and it is close to that of the PM hard alloy rolls. The manufacturingburden of HSS rolls is obviously lower than that of the PM hard alloy rolls, it is only 25 percentof that of the PM hard alloy rolls.

Development of Centrifugal Cast High Speed Steel Roll with High Wear Resistance for Pre-Finishing Stands of a Hot Rod-Wire Mill

The present study aims at developing high speed steel (HSS) as roll materialsto replace traditional roll materials such as the alloy cast iron and powder metallurgical (PM)hard alloy, because low-cost alloy cast iron rolls have poor wear resistance and the cost ofhigh-quality PM hard alloy rolls is too high to be accepted by some users. By means of a centrifugalcasting method, HSS rolls with excellent wear resistance have been developed. Its hardness is 65-67 HRC, and its variation is smaller than 2HRC; its impact toughness excels 15J/cm^2. Usingpre-finishing stands of a high-speed hot wire-rod rolling mill, the wear rate of HSS rolls per onethousand ton of steel is 0. 25mm. However, the manufacturing burden of HSS rolls is obviously lowerthan that of PM hard alloy rolls; it is only 30% of that of PM hard alloy rolls.

Effect of rare earth elements on the thermal cracking resistance of high speed steel rolls

The effect of rare earth elements on the thermal cracking resistance of high speed steel （HSS） rolls was investigated. Laser rapid heating was used for thermal fatigue experiments. Thermal cracks and microstructure were observed using metalloscopy and scanning electron microscopy. The results showed that thermal cracks initiated from the interface between the matrix and eutectic carbides （including M6C and M7C3 type carbides）,and propagated along the interface between the two phases. MC type carbides enriched with vanadium could prevent the propagation of thermal cracks. The presence of rare earth elements decreased the quantity of big eutectic carbides,and proportionally increased spherical and rod-shaped MC type carbide content. HSS0 （0.00% RE） had approximately three times the thermal cracking density of HSS3 （0.12 wt.% RE）. Rare earth elements were shown to significantly improve the microstructure and thermal cracking resistance of HSS rolls.

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.

Experimental research on electromagnetic continuous casting high-speed steel composite roll

A high speed steel composite roll billet was fabricated, which is regular in shape, smooth in surface, slight in trace, compact in internal structure, free of slag inclusion, shrinkage cavity, cracks and other flaws, and good in macro quality of junction surface using a vertical continuous casting machine. The interface zone microstructure of bimetallic in billet of high speed steel composite roll was analyzed by metallurgical microscope(OM), X-ray diffractmeter(XRD), scanning electron microscopy(SEM) and energy-dispersive X-ray analysis(EDS). The results indicate that the microstructure of roll billet is composed of chilled solidified layer, dendrite zone, interfacial zone of bimetal and core material zone. The microstructure of outer shell material is composed of martensite + bainite + residual austenite + some small labyrinth-shape, small-short lath-shape, or dollop-shape eutectic carbides. The microstructure of core material is slice-shape pearlite and a little ferrite along boundary of cells. The interface region microstructure of bimetallic composite roll consists of diffusion region, chilled solidified layer and columnar grain region.

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.

Microstructure and Eutectic Carbide Morphology of the High Speed Steel Strips Produced by Twin Roll Strip Casting Process

The M2 high-speed steel strip was produced by using the laboratory scale twin roll strip caster. The microstructure and eutectic carbide morphology of thus produced products were observed and analyzed, and the comparison of those with conventional products was carried out. The effects of the processing parameters such as the melting temperature, the pouring temperature, rolling speed and separating force on the microstructure and eutectic carbide morphology and their distribution were analyzed. The spheroidizing process of the strips in the annealing process was investigated. The relations between the growth and spheroidizing of the eutectic carbide and the annealing technology were obtained, and the mechanism of the twin roll strip casting process improving the eutectic carbide spheroidizing was discussed. The theoretical instruction for determining the subsequent treatment process was provided.

Effect of rare earth addition on continuous heating transformation of a high speed steel for rolls

The effect of rare earth（RE） on continuous heating transformation of a high speed steel for rolls was investigated by using differ-ential scanning calorimetry（DSC） with combination of microstructure analysis.Determination of the Ac1 and Ac3,the starting temperature of carbide dissolution and melting upon heating,the enthalpy change for the α→γ transformation and overall carbide dissolution were also es-tablished.It was found that RE could reduce the volume fraction of large eutectic carbides and the chrysanthemum-like eutectic colonies but could not change the phase composition.RE made a little change to Ac1,but the variation in Ac3 and enthalpy for the α→γ followed an in-creasing pattern as the RE addition increased.The start temperatures of carbides dissolution increased with increase of RE addition,which may be associated with the influences of RE on the morphology of carbides,but the overall enthalpy change of carbides dissolution decreases as the RE addition increased.Moreover,the start temperature of melting also increased with increasing RE addition.

Influence of rare earth elements on solidification behavior of a high speed steel for roll using differential scanning calorimetry

The influence of rare earths（RE） on solidification behavior of a high speed steel for roll was investigated by using differential scanning calorimetry（DSC） in combination of microstructure analysis.It was found that the sequence of solidification was L→γ,L→γ＋MC,L→γ＋M2C,L→γ＋M6C,respectively.The start temperature and the latent heat liberated by unit mass of L→γ and L→γ＋MC increased with increase of RE addition,indicating that RE could trigger the crystallization of the primary γ and the MC carbide more effectively.The promoting effect of RE on the heterogeneous nucleation was believed to be an important cause of this effect.Grain refinement,discontinuous network of eutectic carbides and disperse and finer MC were observed in the samples with RE addition,moreover,RES could act as the heterogeneous nucleus of the MC.RE addition was favorable for stable M6C at the expense of the metastable M2C.

高速钢复合轧辊表面大面积剥落的原因

通过化学成分分析、力学性能检测、显微组织和断口形貌观察等方法,对高速钢复合轧辊表面大面积剥落的原因进行了分析。结果表明:三次浇注工艺控制不当及心部球墨铸铁液纯净度不够导致复合轧辊中间层与高速钢表层及心部铸铁层的界面处存在大量粗大碳化物、片状分布的疏松孔洞以及聚集分布的夹杂物带等严重缺陷,使得界面处的结合不良;在轧制力的作用下,裂纹在上述缺陷处萌生,并沿缺陷处快速扩展,最后导致轧辊表面发生大面积剥落失效。

抛丸工艺对60Si2Mn热轧弹簧钢表面残余应力的影响

采用不同抛丸时间、抛丸电流的抛丸工艺对高速铁路扣件用弹条原材料(60Si2Mn热轧弹簧钢)进行抛丸,弹丸为粒径0.6~0.7 mm的S230铸钢丸,并通过X射线应力测定仪测量60Si2Mn热轧弹簧钢表面残余应力。结果表明:经不同抛丸工艺处理后,热轧弹簧钢表面残余应力均为压应力;在抛丸电流相同抛丸时间减小、抛丸时间相同抛丸电流减小两种情况下,残余应力场特征参数(最大残余应力、最大残余应力对应的深度和残余应力影响深度)和半高宽(层深相同时)均减小,抛丸效果变差;抛丸覆盖率100%、抛丸时间16 s、抛丸电流50 A时,残余应力场特征参数和半高宽最大,抛丸效果最好。

Conversion Excess Coal Gas to Dimethyl Ether in Steel Works

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.

国产高速上钢系统的应用与改进

高速上钢系统主要应用在高速棒材精轧机后,将倍尺材以18~40 m/s的成品速度输送到冷床矫直装置,小型单线棒材12~16 mm机时产量由60 t提高至110 t。国产高速上钢系统在制造水平、控制系统工艺和操作维护水平等方面较进口设备(达涅利、西马克等)存在一定的优势与劣势。通过在应用中不断进行改进与提高,必将全面达到或超过进口设备的水平。

激光熔覆HSS涂层滚滑动摩擦磨损及热疲劳损伤研究

针对再制造轧辊使用过程中受高压高温作用,轧件易发生复杂的失效行为,文章采用激光熔覆技术在球墨铸铁芯材上制备M4高速钢(high-speed steel,HSS)涂层,利用高温滚滑动摩擦磨损与热疲劳试验机研究HSS涂层的摩擦磨损及热疲劳性能。结果表明:HSS涂层显微组织主要为马氏体、少量残留奥氏体和合金碳化物,涂层维氏硬度为823 HV 0.5,具有良好的耐磨性、耐热性。在滚滑动摩擦磨损形式下,随着表面接触温度的升高,涂层磨损机制发生改变,磨损量逐渐降低。440℃时表现为疲劳磨损和轻微氧化磨损,525℃时表现为氧化磨损和疲劳磨损,580℃时以氧化磨损为主。

高端离心铸造热轧板带工作辊开发和制造技术

以热轧板带离心铸造工作辊产品为代表的高合金材料是铸造工具钢和高合金材质领域应用最广泛、最成熟的大型工业产品之一。我国热轧板带工作辊的研发和制造伴随着钢铁行业的发展突飞猛进,轧辊材质和规格的多样性以及产品可靠性、使用性能和制造能力不断提高。随着新兴技术特别是集成计算材料工程的快速发展和制造业信息化、智能化的变革,离心铸造热轧板带轧辊的开发和生产制造能力得到进一步的提升。本文主要介绍了热轧板带工作辊的发展历史以及市场对新型轧辊的需求,简述了轧辊材质开发和轧辊产品未来发展方向,并且讨论了轧辊制造业发展的趋势。