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.

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.

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 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 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.

高速钢轧辊及其热处理

综述了冷、热轧辊材料的发展过程;轧辊高速钢的种类、成分;高速钢轧辊的生产工艺以及高速钢轧辊的热处理工艺。指出高速钢在轧辊领域具有一个非常大的市场,应于重视。另外,为了提高高速钢轧辊的质量,需要解决高速钢偏析问题及热处理问题。

离心铸造高速钢轧辊偏析控制技术研究

在高速钢轧辊离心铸造凝固过程中加入电磁搅拌,可明显减轻高速钢轧辊偏析,研究了磁场强度对高速钢轧辊偏析的影响,随着磁场强度的增加,元素偏析减轻,但磁场强度超过0 053T后,钒元素偏析反而增大。分析了外加电磁场减轻离心铸造高速钢轧辊偏析的原因。

碳化物对冷轧条件下轧辊中裂纹行为的影响

利用扫描电镜、透射电镜研究碳化物对冷轧过程中高铬铸铁及高钒高速钢轧辊中裂纹行为的影响。结果表明,裂纹萌生及扩展与碳化物的精细结构、碳化物与基体界面结构及碳化物形态有关。高铬铸铁中的M_7C_3具有层错结构,轧制过程中M_7C_3内部易于造成位错塞积而萌生裂纹,经短距离扩展后形成贯穿的主裂纹,导致轧辊迅速失效。高钒高速钢中的VC内部弥散分布着大量富钼的纳米级MC型碳化物,起到钉扎VC内部位错的作用,促使形成位错环而吸收轧制能量,裂纹不易在VC内部萌生,而主要萌生于VC与基体界面,并沿球形VC的表面扩展,扩展到VC侧面时出现裂纹钝化现象。VC与基体界面的部分共格关系能够延缓界面裂纹萌生,VC良好的形态有助于裂纹钝化,提高轧辊的抗疲劳性能及寿命。

轧辊用高钒高速钢的滚-滑动磨损性能及失效行为研究

在高应力滚-滑动(滑动率约10%)条件下,利用自制的磨损试验机研究了高钒高速钢的磨损性能,并利用电子显微镜分析了失效行为.结果表明:高钒高速钢的相对耐磨性是高铬铸铁(Cr20)的2倍以上.磨损失效形式为显微切削与疲劳剥落的复合,兼有碳化物碎裂.碳化物对磨损失效有重要作用,高铬铸铁中的杆状M7C3型碳化物易于弯曲、碎裂而在其内部形成大量裂纹,促进磨损表面产生大块的疲劳剥落;高钒高速钢中团块状VC硬度高、形态好、具有精细亚结构、不易碎裂,可有效地抵御显微切削和疲劳剥落,是高钒高速钢耐磨性优良的原因.

高速钢复合轧辊的研制及生产

论述了一种高速钢复合轧辊的生产方法，是以硬度高、耐磨性好的高速钢作为轧辊的工作层材料，以强度高、韧性好的合金球墨铸铁或铸钢作为轧辊的芯部材料，将两种不同的材料通过离心铸造复合而成。该种轧辊用于热轧窄带钢轧机成品机架，其综合使用寿命比原来提高１０倍以上。

高钒高速钢与高铬铸铁的滚动磨损性能对比研究

以高铬铸铁为参照,在自制的模拟轧辊磨损试验机上研究了高钒高速钢的滚动磨损性能.结果表明:随磨损循环次数的增加,两种材料的磨损量均直线地增加,高钒高速钢的相对耐磨性是高铬铸铁的4倍以上;高铬铸铁中的裂纹主要由于M7C3的严重碎裂而萌生于M7C3的内部,高钒高速钢中的裂纹则主要萌生于VC与基体的界面,并沿VC的表面扩展.高钒高速钢中VC形状好、不易碎裂及基体硬度高是其耐磨性优良的主要原因.

离心铸造高硼高速钢辊环组织及性能研究

针对高速钢轧辊生产成本高的问题,设计一种用廉价硼元素部分取代昂贵合金元素的新型耐磨材料,离心铸造出辊环。借助扫描电镜(SEM)和X射线衍射(XRD)等手段对高硼高速钢辊环组织进行了研究,为高硼高速钢复合轧辊生产奠定基础。结果表明:铸态高硼高速钢辊环组织由马氏体、少量残余奥氏体及硼碳化物组成,硼碳化物由M2(B,C),(W,Mo)(2B,C),M(3B,C)以及M2(3B,C)6组成,呈鱼骨状、筛网状和块状沿晶界分布;快速冷却下,辊环径向上合金元素无偏析。经1 050℃水淬后,共晶硼碳化物形貌和分布没有变化,部分二次硼碳化物溶解,局部有断网现象,基体中出现细小、弥散的二次析出物,经525℃回火后数量明显增加。热处理后,硬度达到HRC60.8,冲击韧性可达到8.4 J/cm2。

双辊铸轧高速钢薄带退火时碳化物的球化机理

在实验室新建的水平式双辊铸轧机上进行了W9高速钢薄带的铸轧实验研究,得到了主要工艺参数对铸带显微组织分布的影响规律,给出了实验室条件下W9高速工具钢薄带铸轧工艺参数的最佳变化范围·研究了铸轧对高速钢薄带的组织及碳化物形态的影响,铸轧高速钢显微组织主要由马氏体、残余奥氏体及共晶碳化物组成,不存在鱼骨状莱氏体组织,薄带内的残余奥氏体的质量分数仅为10%左右·碳化物以片层状M2C型为主,呈断续网状分布在晶界上,而M6C型的鱼骨状碳化物很少·铸轧高速钢薄带的退火组织主要为索氏体组织和碳化物·碳化物球化的机理在于铸轧改善了共晶碳化物球化的动力学条件,使碳化物层片明显细化,有利于碳化物的球化,同时铸轧有利于亚稳定的M2C型碳化物的形成,使铸轧状态高速钢薄带的球化退火变得容易·

离心铸造高速钢复合轧辊外层材料性能的研究

研究了稀土变质和稀土加钒变质对离心铸造高速钢轧辊的显微组织及力学性能的影响,测定了其最终热处理后的碳化物类型,结果表明,采用0.3%稀土变质处理对碳化物的形状、分布改善效果不明显,但可以促进加热过程中网状碳化物的球团化;采用稀土加钒变质对碳化物的形状、大小和分布改善情况较好。经过最终热处理后,高速钢中的碳化物类型为MC和M6C型。

离心铸造高速钢轧辊裂纹形成机理研究

通过分析离心铸造高速钢轧辊凝固过程和裂纹形成条件,发现离心铸造高速钢轧辊裂纹形成的主要原因是高速钢轧辊凝固层强度低,且与铸型产生间隙,不足以承受离心压力所致。裂纹源萌生后,在离心铸造系统长时间工作环境下,轧辊不能自由凝固收缩,促进裂纹的扩展。中间层凝固和轴向凝固的出现,不利于获得致密的轧辊组织,促进轧辊产生裂纹。

快速铸轧条件下轧制压力的建模与仿真

通过建立轧制压力模型，对常规铸轧进行了仿真计算，计算结果与实测数据相符合，从而验证了模型的合理性．在此基础上，对快速铸轧进行了虚拟仿真研究，研究结果表明：不增强铸轧辊内、外冷却能力，单纯减薄铸轧板坯厚度即可提高铸轧速度；随着铸轧速度降低与铸轧区增大以及铸轧坯厚度减薄，轧制压力峰值增大；随着铸轧辊径增大，轧制压力提高，因此铸轧机力能设计参数也要相应增大．

离心铸造高速钢轧辊裂纹控制技术研究

在分析了轧辊材质、铸型参数、浇注参数和冷却参数等对离心铸造高速钢轧辊裂纹影响的基础上,采用钾 稀土复合变质处理改善高速钢的组织和性能,降低热裂温度,使热裂力提高32 77%,达到158N,线收缩也略有减小。采用变速离心铸造技术、变流量浇注工艺,结合铸型的变速冷却技术,改善了轧辊温度场和应力场分布,有利于钢液的充填和凝固,有利于消除离心铸造高速钢轧辊裂纹。

高速列车用铜合金接触线用材料及其加工工艺

在研究和分析国内外高速列车用铜合金接触线的基础上,结合目前铜合金接触线的生产现状,对我国铜合金接触线材料和加工工艺进行了分析。随着电气化铁路运行向高速化发展,开发新型的Cu-Cr-Zr系、Cu-Mg系铜合金接触线是必要且可行的。目前我国铜合金接触导线制造技术比较落后,在铜熔体洁净化处理和连铸成形两个关键工序上,缺乏有效手段,大大影响了产品的最终性能。综合考虑产品的最终性能和大规模连续化生产的要求,在加工工艺方面,连铸连轧法和连续挤压法是未来开发的重点。