EFFECT OF SILICON ON PRODUCING DUCTILE IRON WITH COMPLEX STRUCTURE OF BAINITE AND MARTENSITE

This paper deals with an important role of silicon in producing ductile iron with quenched complex structure of bainite and martensite. The samples are cast in permanent mold and quenched in solution of sodium silicate. The result of thc experiments shows that the austenizing temperature should rise with increasing silicon content, otherwise much undissolved ferrite is present in the matrix after quenching. However the undissolvec ferrite can be decreased greatly or even eliminated by adding appropriate amount of ooron. On this condition, the amount of bainite gets increasing and the amount of residual austenite decreasing with the silicon cortent increasing. An approach has also been made to the mechanism of the effect of silicon on the transformation of bainite in ductile iron. The T.T.T. curves measured show that the increase of sllicon content causes the curve to shift to the left. This is quite different from the fact in steel.

Influence of Mold Preheating and Silicon Content on Microstructure and Casting Properties of Ductile Iron in Permanent Mold

The effects of the mold preheating and the silicon content of ductile iron on the percentage of carbides,graphite nodule counts and shrinkage volume were investigated.The results showed that the percentage of carbides and the shrinkage volume decreased when the mold preheating increased.The ductile iron with the carbon equivalent of 4.45 % and the silicon content of 2.5% without any porosity defects was achieved when the mold preheating was 450 ℃.Increasing the silicon content in the range of 2.1%-3.3% led to the increase in graphite nodule count and graphite size and the decrease in percentage of carbides.It is due to the increase in induced expansion pressure during the graphite formation with the increasing of silicon content.The suitable condition for casting a sound product of ductile iron without the riser at the mold preheating temperature of 300 ℃ is the silicon content of 3.3% and carbon equivalent of 4.7%.

球墨铸铁的塑性变形及奥贝组织研究

利用Gleeble-1500热力学模拟机、光学和透射电子显微镜对球墨铸铁变形前后以及等温淬火处理后的组织进行了分析。结果表明，球铁热塑性变形最佳温度在750—800℃区间，此时流变应力接近950℃时的流变应力；变形后球铁为三层组织结构“球状石墨＋蠕虫状石墨＋流线型石墨”；在透射电镜下清楚地观察到不同形状的下贝氏体和上贝氏体形貌以及典型的隐“M”型马氏体形貌。

具有性能梯度特性的贝-马-奥球墨铸铁磨球的制备工艺

采用10 kg真空中频感应炉熔炼铁液,经炉前一次球化及两次孕育处理,真空浇注得到球墨铸铁球。使用电热炉加热磨球到不同的奥氏体化温度,并在不同温度的硝酸盐和亚硝酸盐混合介质中进行连续冷却淬火,后经低温回火得到球墨铸铁磨球。其中,性能最佳的为贝-马-奥球墨铸铁磨球,其显微组织为:球状石墨(体积分数12%左右)+下贝氏体+高碳针状马氏体+残留奥氏体(质量分数16.6%~18.1%)。石墨球化率达到92%、球化级别为2级,球墨尺寸级别为9.2级;磨球表面硬度为55~58 HRC,表面与心部硬度差【5 HRC;磨球表层的常温冲击韧性为20.5 J/cm2,心部冲击韧性为25.3 J/cm2,表现出表层高硬度,耐磨损;心部高韧性,抗破碎的性能梯度特性。进一步研究表明:下贝氏体和残留奥氏体组织对提高磨球的性能有着显著的作用,而上贝氏体组织则不利于磨球的综合性能。

贝氏体—马氏体抗磨球铁磨球的研制

试验研制 1种新型抗磨球铁磨球 ,确定磨球化学成分和生产工艺 ,获得了优良的性能。磨球本体硬度HRC48～ 5 5 ,冲击韧性aK=9～ 12J/cm2 , 80mm磨球落球试验次数达 2万次以上。电厂装机应用磨耗 <12 0 g/t煤 ,磨球破碎率 <0 .5 %。

二次孕育及终硅量对铸态铁素体球墨铸铁组织性能的影响

将铸态球墨铸铁经退火处理生产铁素体球墨铸铁的工艺复杂、周期长。本研究进行了调整终硅量及采用二次瞬时孕育处理工艺直接得到铸态铁素体球墨铸铁的试验。结果表明，采用稀土镁球化剂和硅铁孕育剂，对铁液进行立即孕育、立即浇注的瞬时孕育处理，并控制终硅量为2.95％～2.99％，可直接获得铁素体球墨铸铁，石墨球径仅为0．019～0．017mm，球化级别提高至3～2级，铁素体量多达88．4％～94．7％，力学性能完全达到国家标准。

马氏体-贝氏体合金球铁焊管机轧辊

试验研究了用马氏体贝氏体合金球铁代替 Ｇ Ｃｒ１５ 钢制作高频焊管机轧辊，介绍了该材质的工艺技术要点。结果表明：合金球铁轧辊较 Ｇ Ｃｒ１５ 钢轧辊寿命提高５０％ 以上，生产成本下降２０％ ～３０％ ，具有一定的经济效益。

分级淬火中硅诱发贝氏体相变的研究

采用新型分级淬火工艺生产高硅贝氏体球铁,将试样奥氏体化后,入常温介质中分级淬火,使球铁在230℃箱式电炉中等温转变成贝氏体组织,与传统的盐浴等温淬火贝氏体球铁进行比较.利用SEM、硬度计、冲击试验机等分析测试技术,对材料的微观组织和力学性能进行了研究.结果表明:采用分级淬火工艺生产高硅贝氏体球铁时,在Si含量大于3.3wt%时,对贝氏体相变具有显著的诱发作用,从而使贝氏体球铁组织细化,力学性能提高(52～56HRC、αk达12～15J/cm2),并对此进行了理论分析.

奥氏体-贝氏体球墨铸铁中奥氏体对接触疲劳性能的影响

奥氏体-贝氏体球墨铸铁中有20—40％的奥氏体,在滚动接触疲劳过程中,表面层奥氏体仅有5—10％发生应力诱发马氏体相变,产生于未转变的奥氏体区中,这种相变对于表面硬度的提高贡献不大,对接触疲劳性能没有明显的影响。

硅在分级淬火生产贝氏体球铁工艺中的作用

研究了采用分级淬火工艺生产贝氏体球铁时硅对相变组织及机械性能的影响，发现硅对贝氏体有诱发相变作用，从而可细化组织，提高机械性能，并对此作了理论分析。

As-Cast Acicular Ductile Aluminum Cast Iron

The effects of nickel （2.2 %） and molybdenum （0.6 % ） additions on the kinetics, microstrueture, and mechanical properties of ductile aluminum cast iron were studied under the as-cast and tempered conditions. Test bars machined from cast to size samples were used for mechanical and metallurgical studies. The results showed that adding nickel and molybdenum to the base iron produced an upper bainitic structure, resulting in an increase in strength and hardness. The same trend was shown when the test bars were tempered at 300 ℃in the range of 300 ℃ to 400 ℃. The elongation increased with increasing the temperature from 300 ℃ to 400 ℃. The carbon content of the retained austenite also increased with increasing the temperature. The results also showed that the kinetics, microstructure, and mechanical properties of this iron were similar to those of Ni-Mo alloyed silicon ductile iron.

硅对大断面球铁石墨形态的影响

研究了Ｓｉ对大断面球铁石墨形态的影响，测试了厚大球铁试块心部的冷却曲线．观察了相应部位的石墨形态，结果表明，当Ｓｉ大于２．１％时，强烈促进碎块状石墨的形成，防止碎块状石墨的关键是减少Ｓｉ，使球铁碳当量不超过共晶碳当量．

马氏体球墨铸铁磨球的研制和生产应用

采用 1.5t工频感应电炉熔炼铁液 ,经炉前球化孕育处理 ,金属型浇注得到球墨铸铁磨球、配之RT 32 0 9推杆步进式电阻炉加热、水玻璃液模拟等温淬火及低温回火得到的马氏体加贝氏体球墨铸铁磨球 ;其金相组织为 :高碳隐针马氏体 ( 70 %～75 % ) +球状石墨 +上贝氏体 ( 2 5 %～ 30 % ) +少量合金碳化物 ( <5 % ) +少量残余奥氏体 ;其表面硬度为HRC 5 5～ 5 7,表面与心部硬度差HRC≤ 2 ;通过工业性试验平均单耗为 0 .6 6kg/t原矿、破碎率 <1%。

地铁轨道用铁素体球墨铸铁垫板的开发

采用二次孕育处理和控制终硅量方法对铁路轨道用可锻铸铁垫板的生产工艺进行改进,开发地铁轨道用铁素体球墨铸铁垫板。结果表明,经过二次孕育处理后,石墨球化率增加,分布均匀。该垫板的抗拉强度为460～520 MPa,伸长率为12%～15%,达到国家标准,可以替代可锻铸铁垫板。

硅对连续冷却贝氏体球铁的影响

探讨含铬、钼、铜多元微量元素的合金球铁经连续冷却获得贝氏体组织的新工艺中,硅对热处理工艺参数、球铁显微组织和强韧性能的影响。结果表明,硅对奥氏体化工艺参数影响显著,硅量在2.6%~3.3%(质量分数)时,可以稳定地获得以下贝氏体为主的组织和良好的力学性能(HRc>50,冲击韧度>10J/cm2)。

ADI适宜碳硅量优化设计与控制

适宜碳硅含量是获得优质等温淬火球墨铸铁(ADI)的前提条件。分析研究了碳硅含量对ADI铸件凝固过程、奥氏体化过程、等温淬火过程及其组织的影响。结果表明,ADI铸件适宜碳硅含量范围较球墨铸铁更窄,一般为:3.4%~3.8%C、2.3%~2.7%Si;适宜碳硅含量、合理的孕育球化及等温淬火工艺是获得ADI理想微观组织及优异力学性能的关键。

硅量对消失模铸造高硅球墨铸铁组织和性能的影响

研究了硅含量对消失模铸造高硅球墨铸铁组织和性能的影响。用光学显微镜和扫描电镜对石墨形貌及基体组织进行观察,用万能拉伸试验机和数显布氏硬度仪测量其力学性能。结果表明,采用消失模铸造工艺,浇注温度为1487℃、负压0.05 MPa、球化剂加入量1.3%制得的含硅量为2.9%~4.6%的高硅球墨铸铁基体组织为全铁素体;硅含量增加使球状石墨尺寸减小,铁素体晶粒平均尺寸减小形成细晶强化;同时由于硅固溶于铁素体中形成置换固溶体,随着硅含量的增加在铁素体晶界上产生偏析且程度越来越大,使铁素体基体产生晶格畸变,对铁素体产生显著的强化作用,因此高硅球墨铸铁的强度和硬度随着硅含量的升高而升高。当硅含量为2.92%时,球状石墨平均尺寸为35.6μm,抗拉强度为441 MPa,布氏硬度为128 HBW,伸长率为17%;当硅含量为4.59%时,球状石墨平均尺寸为26μm,抗拉强度为683 MPa,布氏硬度为186.1 HBW,伸长率为17.5%,综合力学性能较高。