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 wear resistance of highchromium cast iron containing niobium

In the paper, the effect of niobium addition on the microstructure, mechanical properties and wear resistance of high chromium cast iron has been studied. The results show that the microstructure of the heattreated alloys is composed of M7C3 and M23C6 types primary carbide, eutectic carbide, secondary carbide and a matrix of martensite and retained austenite. NbC particles appear both inside and on the edge of the primary carbides. The hardness of the studied alloys maintains around 66 HRC, not significantly affected by the Nb content within the selected range of 0.48%-0.74%. The impact toughness of the alloys increases with increasing niobium content. The wear resistance of the specimens presents little variation in spite of the increase of Nb content under a light load of 40 N. However, when heavier loads of 70 and 100 N are applied, the wear resistance increases with increasing Nb content.

Microstructure and Property of Hypereutectic High Chromium Cast Iron Prepared by Slope Cooling Body-Centrifugal Casting Method

In this paper, the ring-type ingot of hypereutectic high Cr cast iron was obtained by slope cooling bodycentrifugal casting method （SC-CCM）, and its microstructure and impact toughness were investigated, respectively. The results indicated that, first, the primary carbides in the microstructure are prominently finer than those in the hypereutectic high Cr cast iron prepared by conventional casting method. Second, in the ring-type ingot, the primary carbides near radial outer field are finer than those near radial inner field; furthermore, there is dividing field in the microstructure. Finally, the impact toughness values of the specimens impacted on the radial outer face and on the radial inner face are improved respectively about 36% and 138% more than that of the hypereutectic high Cr one prepared by conventional casting method.

Impact Properties of Austempered Spheroidal Graphite Cast Irons

This study aims to clarify the influence of external notch on impact characteristics of high toughness ductile cast irons prepared by austempering heat treatment. We produced ductile cast irons samples with various matrix microstructure tested by Charpy impact within five kinds of external notches whose stress concentration factors (α), with values taken from 1.0 (Un-notched) to 4.8. In addition, to clarify the initiation process of impact characteristics, we observed the evolution of microstructure surface during bending tests with a slow loading speed for the un-notched and the notched impact samples. The results showed that the impact fracture energy decreases strongly in the range of α from 1 to 2.3 but decreases slightly for α larger than 3. Moreover, the impact value of samples with austempered microstructure is sensitive to the external notch shape. The impact transition temperature increases with increasing the stress concentration factor. The fracture energy is decreasing with the external notch from the impact test since the crack initiation energy is directly affected by this later. This work contributes to get a better understanding in the basic theories of external notch effect on impact characteristics of austempered spheroidal graphite cast irons (ADI).

铁包覆氧化锆增韧氧化铝颗粒增强高铬铸铁复合材料的冲击性能

采用铸渗工艺制备了铁包覆和无铁包覆氧化锆增韧氧化铝颗粒(ZTAp)增强高铬铸铁复合材料,对比研究了不同复合材料的微观形貌、微区成分和冲击性能。结果表明:无铁包覆ZTAp增强高铬铸铁复合材料中ZTAp与高铬铸铁间存在界面间隙,在制样中ZTAp发生脱落;铁包覆ZTAp增强高铬铸铁复合材料中的ZTAp嵌在高铬铸铁中,界面处无空洞、脱黏和分层等明显缺陷,且形成连续的厚度在15~30μm的界面层,可以提升界面结合性能;铁包覆ZTAp增强高铬铸铁复合材料的冲击韧度(2.1 J·cm^(-2))提升至无铁包覆时(0.5 J·cm^(-2))的4.2倍,失效方式由拔出失效转变为颗粒断裂失效,基体区断裂机制为准解理性断裂,界面层局部存在韧窝、撕裂棱等断裂特征。

Thermal Fatigue Behavior and Cracking Characteristics of High Si-Mo Nodular Cast Iron for Exhaust Manifolds

The thermal fatigue cracking behavior of high Si-Mo nodular cast iron （NCI） is investigated by means of optical microscope （OM）, scanning electron microscope （SEM） and energy dispersive spectroscope （EDS）, in order to find a new material used in exhaust manifolds in First Automotive Works （FAW） .Nodular cast irons with silicon content about 4.7% , in combination with up to 1.1% molybdenum , were produced by Jilin University and FAW. The repeated heating / cooling test was performed under cyclic heating at various maximum heating temperatures （Tmax） ranging from 800to 900℃.Experimental results indicate that the thermal fatigue cracking resistance of high Si-Mo NCI decreases with increasing the maximum heating temperature.The periods for crack initiation are 24-36 , 40-50and 70-90times associated with heating temperature of 900 , 850and 800℃ , respectively , when the holding time is about 10min at Tmax.When thermal fatigue cracking occurs , the cracking always initiates at the bigger surface of specimen.The major positions of cracks propagation are generally at the eutectic oxide boundary region and the region of the graphite disappearance.At the same time , the oxidation may accelerate crack initiation and propagation.On the other hand , micro-crack number varied from large to little because of shielding effect.As exhaust manifolds , the reasonable working temperature of high Si-Mo NCI is no more than 840℃ by test and analysis.

淬火温度对Cr23高铬铸铁组织性能的影响

通过光学显微镜、显微硬度、洛氏硬度及冲击试验,研究了不同淬火温度对Cr23高铬铸铁组织性能的影响,并采用MMW-1立式万能磨损试验机对Cr23的磨损性能进行了测试分析。结果表明:900℃淬火后Cr23高铬铸铁中铸态组织未完全消失;950℃淬火回火后Cr23高铬铸铁的组织为白色的块状、条状碳化物和回火马氏体,二次碳化物弥散分布在基体上;1000℃淬火回火后Cr23高铬铸铁中的组织由回火马氏体、残余奥氏体及长条状碳化物组成,残余奥氏体及回火马氏体都呈现灰黑色。随着淬火温度的增加,高铬铸铁的硬度先升后降,冲击韧性呈下降趋势。高铬铸铁中弥散分布的碳化物可有效提高其耐磨性,回火马氏体基体为碳化物提供支撑,防止其剥落。试样经过950℃淬火+250℃回火后抗磨性最好,较l000℃淬火+250℃回火处理的试样提高了41.4%。

高强韧珠光体球墨铸铁的研究

在球墨铸铁成分优化基础上,用万能材料试验机、布氏硬度计和金相分析显微镜研究了球墨铸铁经多元合金化、型内孕育处理和等温正火后的组织和和性能。结果表明:经Cu、Mo、Sb多元合金化和型内孕育处理的球墨铸铁,其铸态和等温正火处理后的组织明显改善,共晶团数目增加,基体组织细化,石墨球形态圆整、细小,珠光体数量增多,比例均大于90%,力学性能显著提高。与未合金化的球墨铸铁比,Cu,Mo,Sb多元合金化的球墨铸铁,其铸态和等温正火处理后的屈服强度R_(0.2)、抗拉强度R_(m)和硬度HB分别提高了25%、20%,47%、17%,41%、11%,达到502、620 MPa,811、975 MPa,256HB、298HB,伸长率A均大于6%。

液态模锻高铬铸铁亚温淬火工艺研究

对比压128 MPa液态模锻工艺制备的KmTBCr20Mo合金进行亚温淬火热处理工艺研究。结果表明,亚温热处理工艺能改变液态模锻高铬铸铁组织的形貌尺寸与数量,改变其洛氏硬度与冲击韧性。500℃亚温淬火相比于无热处理的对照组马氏体基体增多,基体析出小颗粒二次碳化物,同时生成了较多形状规则、断续块状分布的M_(7)C_(3)型碳化物,硬度和韧性均有明显提高,此温度为最佳亚温淬火温度。当淬火温度为530℃和550℃时,共晶团与晶界的碳化物存在微裂纹,形状粗大且不规则,洛氏硬度较高但韧性显著降低。当淬火温度为580℃和630℃时,马氏体基体形状粗大,碳化物呈针状与小块状分布,容易割裂基体,洛氏硬度下降,韧性显著降低。

基于振动条件下高铬铸铁组织和性能的变化

高铬铸铁在凝固过程中,易形成粗大的初生碳化物,降低了材料的冲击韧性。通过在高铬铸铁凝固过程中外加机械振动处理,探究了振动工艺参数对碳化物形态、冲击韧性及耐磨性能的影响。采用光学显微镜和扫描电镜观察高铬铸铁显微组织的变化;利用X射线衍射和电子探针分析了物相组成。结果表明:与未经过振动处理的高铬铸铁相比,振动处理的高铬铸铁中M_(7)C_(3)型碳化物得到了细化,其冲击韧性较未处理高铬铸铁提高了16.36%;耐磨性提高了2.9倍。

QT400-18铸态高韧性球墨铸铁拉伸断口特征与断裂机理

通过对QT400 18铸态高韧性拉伸断口特征及断裂机理的分析,发现伸长率超过20%时,试样断口具有韧性断裂的微观特征,在断口上留下较大、较深的韧窝,甚至有撕裂带。而伸长率为15%～16%时,试样断口具有混合型断裂的微观特征,在尖角处易形成微裂纹源,受外力作用时,裂纹源迅速扩展,造成局部穿晶断裂;同时由于铁素体含量减少,珠光体含量增多,基体塑性变形相对较差,在试样断口上留下大量较浅的韧窝。

高强度高韧性球墨铸铁曲轴铸造技术

为了提高球墨铸铁曲轴的强韧性和铸造质量、降低铸造废品率,研究了曲轴的微合金化技术、铁液共晶点控制技术、球化处理技术、曲面分型方法和组织均匀化正火工艺,成功生产出高强韧性球墨铸铁曲轴。球铁曲轴抗拉强度由原来的872 MPa提高到927 MPa,冲击韧度由26 J/cm2提高到40 J/cm2,缩松缺陷由原来的1.44%降低到0.19%。

Cr20高铬白口铸铁磨片的热处理工艺

研制了Cr20高铬白口铸铁磨片,设计正交试验方案研究了不同热处理参数对应试样的硬度和冲击韧性。结果表明,以硬度为试验指标的热处理工艺参数中,回火温度最重要,其次为淬火保温时间,再次为淬火温度及回火保温时间;在本热处理试验范围内,Cr20铸铁试样的硬度均达到了57·5HRC以上,以960℃×2·5h空冷淬火+450℃×3·5h回火的优方案热处理可获得最高硬度61·6HRC、冲击韧度2·31J/cm2。Cr20铸铁的铸后热处理能在保持冲击韧性基本不变的同时有效提高Cr20铸铁的硬度,其金相组织主要由坚硬的条状共晶碳化物(Fe,Cr)7C3和马氏体基体组成。

改性纳米SiC粉体强化球墨铸铁的耐磨损性能

采用改性纳米SiC粉体对球墨铸铁进行了强韧化处理,研究了不同的纳米SiC粉体加入量对球墨铸铁的微观组织、力学性能以及耐磨损性能的影响。结果表明,经改性纳米SiC粉体强韧化处理后,球墨铸铁中的石墨球尺寸减小,圆整度提高,铁素体含量增多,球墨铸铁的韧性和耐磨损性能提高。当粉体加入量为0.1%(质量分数)时,其延伸率和冲击功分别增加了19%和194%。耐磨损性能提高的原因是石墨球形态的改善和基体组织韧性的提高。

高韧性高铬铸铁衬板的研制和应用

介绍新型高韧性高铬铸铁衬板的化学成分、熔炼、复合变质处理、造型、热处理工艺以及装机运行试验。新型高韧性高铬铸铁衬板不含价格昂贵的钼、铜,采用了适合我国资源特点的高效稀土复合变质剂,价格低廉;热处理采用空气冷却,硬度达到60HRC以上,冲击韧度达到8J·cm-2以上,耐磨性为ZGMn13高锰钢衬板的2.6倍。

过共晶超高铬铸铁合金的组织与性能

研究了过共晶超高铬铸铁的组织和热处理工艺对其性能的影响,过共晶超高铬铸铁的铸态组织由初生碳化物M7C3+共晶(M7C3+M23C6)+马氏体+残余奥氏体组成,其中初生碳化物(M7C3)为六方形长秆状。在1050℃淬火的条件下,低温回火时,材料的硬度、冲击韧性的变化不大,回火温度提高到450℃后,材料的硬度显著升高,相应的冲击韧性下降;回火温度继续上升,材料的硬度下降,冲击韧性升高。

电脉冲对铸态高韧性球墨铸铁凝固组织及性能的影响

对铸态高韧性球墨铸铁QT400-18的凝固过程进行电脉冲处理,电脉冲参数为电压2 600 V,频率0.88 Hz,电容200μF,处理时间15min。通过对比试验可知:电脉冲处理可使铸铁的过冷度相比未处理的升高12K,改善了石墨形核和生长的动力学条件,从而使球状石墨的粒径减小,石墨球数量增加。铸铁经过电脉冲处理,球化率由未处理的平均80%提高到平均91%,石墨球数由平均172/mm^2提高到209/mm^2,石墨不易变态生长,圆整度得到改善。同时,球墨铸铁的凝固组织得到了改善,铁素体数量增加,达到83%,相比未电脉冲处理的试样提高了26.6%,铁素体晶粒小于未处理试样,基体中分布的珠光体数量和片层间距减少,在抗拉强度符合要求的条件下,伸长率提高了4.89%,-233K的冲击功Akv提高了3.56J。

硅对铸态厚断面高韧性球墨铸铁组织及性能的影响

研究了硅对铸态厚断面高韧性球墨铸铁组织及性能的影响。试验结果表明,硅主要分布于基体中,富集于奥氏体壳局部区域时,降低奥氏体壳的熔点,延长石墨自由生长的时间,造成石墨畸变。在铸件壁厚为100mm,树脂砂工艺条件下,硅含量为2.0%～2.5%时,石墨球化等级2～3级,球径等级6～7级,基体为铁素体。抗拉强度大于400 MPa,伸长率大于20%,-20℃时的冲击韧度在16J/cm2以上。硅含量达到2.9%时,易产生开花状石墨和碎块状石墨,铸件的性能严重下降。

镍和硅对低温高韧性球墨铸铁耐蚀性能的影响

通过模拟海水静态全浸腐蚀试验,研究了镍和硅对低温高韧性球墨铸铁的耐蚀性能的影响。结果表明:在硅量一定时,腐蚀速率随镍量的增加而降低;在镍量一定时,腐蚀速率随硅量的增加而降低。在所设计的成分范围内,低温高韧性球墨铸铁的腐蚀速率都小于0.1 g.m-2.h-1,属于1级耐蚀等级。当Si量为2.46%,Ni量为1.74%时,在3.5%NaCl腐蚀液中的腐蚀速率最低为0.042 86 g.m-2.h-1。

回火温度对KmTBCr26高铬铸铁组织和力学性能的影响

利用X射线衍射及光学显微镜,研究了回火温度对KmTBCr26高铬铸铁显微组织的影响并测定了相应的硬度和冲击韧性。结果表明,所研究的KmTBCr26高铬铸铁属于过共晶成分,低温回火组织由回火马氏体、残余奥氏体及碳化物组成;高温回火组织由碳化物及共析组织组成。对于1000℃空淬试样,在460℃回火处理时可获得较好的综合力学性能。