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.

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.

Investigation of Impact Toughness of Electromagnetic Centrifugal Cast High Speed Steel

The effect of external magnetic field on the solidification structure and impact toughness of high-speed steel(HSS)produced by electromagnetic centrifugal casting(EMCC)have been investigated.It was found that the solidification structure could be improved effectively by electromagnetic stirring,which was characterized by elimination of the inclined columnar dendrites and refinement of the grain size.The results may be related to the changes of the fluid layers of liquid-solid phase interface.Moreover,the impact toughness of the test steel increased with the exciting current increasing from 12 to 18 A,but decreased when the current was above 18 A.SEM analysis showed that impact fracture surface was dimple fracture due to effect of the refined equiaxed grains when the current was 18 A,which was considered an important reason for the improvement of impact toughness.

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.

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.

基于误差最小化的铸造不锈钢零件高速切削工艺方法研究

铸造不锈钢零件在切削过程中容易产生变形和振动,导致表面粗糙、切削尺寸偏差大。为了解决这一问题,提出基于误差最小化的铸造不锈钢零件高速切削工艺方法研究。在数控机床的支持下,采用在线测量的方式测量铸造不锈钢零件数据,将数控机床测量的坐标值转换为零件表面实测点,获取合适的测量点完成对加工路径的规划,在此基础上通过粗加工和精加工结合的形式对铸造不锈钢零件进行高速切削处理,并以误差最小为目的对加工误差进行补偿处理。实验结果表明:提出的基于误差最小化的高速切削工艺方法加工误差小、精度高,零件表面质量高,该工艺方法的实用性得到了增强。

连铸过程中的提拉速工业试验研究

高效连铸的核心是高拉速技术,目前高拉速技术在钢铁工业生产中占据着十分重要的地位。为探究拉速对于钢水洁净度的影响,以镀锡板钢种为研究对象,在连铸过程中开展了提拉速工业试验研究,对中间包、铸坯和冷轧卷夹杂物的密度、平均尺寸、夹杂物形态比及夹杂物种类进行了分析检验。结果表明:拉速对于夹杂物类别影响不大,夹杂物均为Al_(2)O_(3)夹杂、Al_(2)O_(3)-CaS/(CaS-MnS)复合夹杂、Al_(2)O_(3)-CaO-MgO复合氧化物夹杂、MnS/(CaS-MnS)硫化物夹杂;但与低拉速相比,高拉速下产量有明显增加,且有利于减少Al_(2)O_(3)-CaS/(CaS-MnS)复合夹杂的产生。这些结果为提拉速后的夹杂物研究提供了重要的理论指导。

小方坯连铸机提高拉速攻关实践

针对福建泉州闽光钢铁有限责任公司炼钢厂现有160 mm×160 mm方坯连铸机生产设备条件,通过提高结晶器冷却强度、优化二次冷却制度、增加切割前冷却装置等措施进行高拉速技术改造,成功将铸机生产平均拉速由2.6 m/min提高至3.2 m/min,最高拉速达到3.45 m/min。

Effect of N and Zr on as-cast microstructure and properties after annealing of a high-speed steel

Effects of N and Zr on the as-cast microstructure and properties after annealing of high-speed steel （HSS） were investigated by using electronic probe micro-analysis, Rockwell hardness test, X-ray diffractometry and differential scanning calorimetry with combination of microstructure analysis. The results indicate that the addition of N and Zr will refine the eutectic structures and enhance the stability of carbides which are mainly MC, M2C and M7C3. The coarse dendritic structures decrease significantly and most of the carbides are distributed in the microstructure uniformly. Moreover, a kind of Zr-Si compound which only exists in VC is discovered, and this new phase is speculated to be related with the spheroidization of VC. The annealing process is set up to 6 different time periods which are 1, 3, 6, 10, 15 and 20 h, respectively. In different annealing processes at 750 ℃ which is lower than austenitizing temperature, the addition of N and Zr makes the decrease of hardness more obvious and restrains the precipitation of secondary carbides with the extension of time. Moreover, when the annealing time reaches 20 h, some clusters appear in the matrix of the two samples, and the density of clusters in HSS1 is lower, but the matrix of HSS1 contains more C and alloying elements which indicate more carbides precipitate.

Evolving Mechanism of Eutectic Carbide in As-cast AISI M2 High-speed Steel at Elevated Temperature

The evolution in type, size and shape of carbides in as-cast American Iron and Steel Institute （AISI） M2 high-speed steel before and after annealing were investigated. The micromechanism which was responsible for those changes was also analyzed and discussed. At the initial stage of reheating, metastable M2C-type carbide decomposed continuously. M6C-type carbide nucleated at the interface of M2C/γ firstly and grow from surface to center. Then MC-type carbide nucleated at both surface of M6C/M6C and inner of M6C. With the increasing decomposition of the metastable M2C-type carbide, the rod-shaped construction of eutectic carbide began neck- ing, fracturing and spheroidizing gradually. Held enough time or reheated at higher temperature, particle-shaped product aggregated and grew up apparently, while secondary carbide precipitated in cell and grew up less sig- nificantly than the former. Based on the above microstructural observation, the thermodynamic mechanism for decomposition of M2C carbide, for spheroidization of products, and for the growth of particles were analyzed. The rate equations of carbides evolution were derived, too. It shows that the evolving rate is controlled by diffusion coefficients of alloy atoms, morphology of eutectic carbides and heating temperature.

Effect of Mischmetal on As-cast Microstructure and Mechanical Properties of M2 High Speed Steel

High speed steel has been widely used in various fields due to their excellent red hardness and good wear resistance. However, the influence of mischmetal （Ce-La） on the as-cast microstructures and mechanical properties of high speed steel has rarely been reported. Thus, the microstructure and mechanical properties of M2 high speed steel with addition of mischmetal （Ce-La） were investigated. The morphology and distribution of the eutectic carbides of the steel were observed by using optical microscopy and scanning electron microscopy, and the impact toughness and bending strength were tested. The results show that adding mischmetal has an obvious effect on the microstructure and mechanical properties of M2 high speed steel. The coarse eutectic structure is refined, the weak connection of the carbide networks is broken and the flake carbides become short and fine. More networks of eutectic carbides dissolve into the matrix. When a suitable adding content of mischmetal is selected, for example, 0.3 mass%, the impact strength and bending strength can increase by 27% and 10.76% compared with that without misehmetal, respectively.

Effects of mischmetal addition on phase transformation and as-cast microstructure characteristics of M2 high-speed steel

The influence of mischmetal （Ce-La） addition on phase transformation and as-cast microstructure characteristics of M2 high-speed steel （HSS） was investigated using Thermo-Calc software, differential scanning calorimetry, X-ray diffractometry and scanning electron microscopy with energy dispersive spectrometry. The results showed that the measured phase transition points of M2 HSS were broadly consistent with the theoretical results. After mischmetal addition, the liquidus peak temperature, the peak temperature of the eutectic precipitation of M6C and MC were all increased, especially for the M6C which was affected significantly and increased about 31 °C. The contents of Mo and V in the eutectic carbide decreased and that of Fe increased, while in the matrix, the Mo, V and Cr contents all increased slightly. Furthermore, the microstructure of as-cast dendrite and ledeburite were refined, the total eutectic carbide content decreased and distributed into a discontinuous network, the lamellar spacing of M2C was reduced and the lamellae became thinner.

Study on Level Fluctuation of Twin Roll Strip Caster by Water Modeling

An industrial trial was conducted on a billet casting machine at Atlas Steel, Canada, during which a mould was instrumented with 52 thermocouples. The measured data of ten heats were collected to determine mould wall temperature profiles for different steel grades at different casting speeds. Based on these data, heat fluxes were calculated with inverse heat conduction model. Heat fluxes for different operating parameters were compared and analyzed.

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.

IF钢板坯结晶器电磁搅拌数值模拟与工艺实践

针对高拉速IF钢铸坯夹杂与气泡缺陷封闭率偏高的问题,通过数值模拟研究了水口浸入深度和拉速对结晶器流场的影响,结果表明,在结晶器电磁搅拌电流为600 A、频率3.5 Hz工况下,随着拉速增高,自由液面活跃指数呈现先增大后减小再增大的趋势,在拉速1.05 m/min附近,最高达0.67,在1.6 m/min附近,最低达0.35,流场均匀性指数略有降低,最佳的自由液面活跃指数为0.5±0.05;当拉速低于1.0 m/min时,随着水口浸入深度的增加,自由液面活跃指数逐步增大至0.40,当拉速大于1.0 m/min时,随着水口浸入深度增加,自由液面活跃指数逐步降低,当拉速大于1.4 m/min时,随着水口浸入深度的增加,自由液面活跃指数大幅下降至0.37;IF钢结晶器电磁搅拌工艺优化后,铸坯夹杂与气泡缺陷封闭率均值下降4%,取得了显著的效果。

保护气氛电渣重熔对DZ2高速车轴钢成分及夹杂物的影响

对DZ2高速车轴钢铸坯进行氩气保护气氛电渣重熔并轧制成车轴坯成分分析和检测轴坯、氢氧含量及夹杂物的数量、尺寸和形貌,并与铸坯直接轧制成的车轴坯进行比较。结果表明:电渣重熔后,轴坯纵横向上的成分较均匀(0.25%~0.27%C),但平均Si和Al含量分别从锭头的0.25%和0.018%降至锭尾的0.23%和0.015%;钢中氢和氧含量分别由铸坯的0.85×10^(-6)和9×10^(-6)增至电渣锭的1.52×10^(-6)和10×10^(-6)。电渣重熔轴坯中的夹杂物主要是小球状的钙铝酸盐,其尺寸在10μm以上的很少,5~10μm的数密度为0.068个/mm^(2),1~5μm的为0.04个/mm^(2)。保护气氛电渣重熔不仅可以去除钢中的大型夹杂物,还可以使小尺寸夹杂物的数量显著降低。

高速列车制动盘用钢现状与发展趋势

制动盘作为高速列车制动系统的核心零部件,其性能直接影响制动系统的使用寿命及高速列车的运行安全。常见的制动盘有铸铁制动盘、钢系制动盘和新型复合材料制动盘。而铸钢制动盘在经过适当的合金化和热处理之后具有较高的耐磨性、耐热性和良好的强韧性。

保护渣添加剂组成对M2高速钢模铸锭表面质量的影响

介绍了模铸对保护渣的要求及常用添加剂的作用,并根据M2高速钢的成分、熔点等特性,通过向通用型模铸保护渣中添加萤石粉、碱粉和可膨胀石墨,对保护渣的熔点、黏度、铺展性进行调整,在生产中进行了大量试验。当单独添加萤石粉7%以上或同时添加萤石粉、碱粉各4%以上时,M2高速钢模铸锭表面粘渣面积比例降低至2%,但锭身恶化严重,出现超5%的凹坑;当萤石粉、碱粉及可膨胀石墨均添加4%时,铸锭表面粘渣面积比例降低至0%,锭身表面良好,满足了M2模铸高速钢的使用要求。适合M2系列高速钢模铸保护渣的化学成分为(18~21)%TC,(29~34)%SiO_(2),(14~17)%Al2O3,(12~15)%CaO,(4~7)%Na_(2)O,(2~4)%Fe_(2)O_(3),(1~3)%MgO,(2~4)%F,(0.5~2)%K2O。

硅钢高拉速生产工艺的探索与实践

介绍了马钢四钢轧3号连铸机硅钢高效化生产的工艺实践,通过优化硅钢二冷水,优化保护渣性能,改善电磁搅拌参数等措施,实现了硅钢的拉速提升,显著提高硅钢生产效率,取得了良好的效果。