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1、河南科技大学 硕士学位论文 过共晶高硼铸钢组织细化研究 姓名：葛会军 申请学位级别：硕士 专业：材料物理与化学 指导教师：祝要民 20091201 摘 要 I 论文题目：过共晶高硼铸钢组织细化研究论文题目：过共晶高硼铸钢组织细化研究 专专 业：材料物理与化学业：材料物理与化学 研研 究究 生：葛会军生：葛会军 指导教师：祝要民指导教师：祝要民 摘 要 摘 要 在过共晶高硼铸钢中由于存在粗大的初生硼化物，严重降低了合金的韧性和 在较高冲击力工况下的耐磨性，从而限制了该合金在实际生产中的应用。为了改 善韧性和提高耐磨性，本文采用变质处理、随流孕育和合金化等方法改善组织中 初生 Fe2B 和包晶 F
2、e3（C,B）的尺寸、形态和分布，并利用 SEM、XRD 等手段， 系统地研究了变质处理、合金化和随流孕育对过共晶高硼铸钢中初生硼化物和包 晶硼化物尺寸、形态的影响。主要得到了以下结果： 1.经稀土硅铁与 K/Na 金属盐变质处理后，过共晶高硼铸钢中的初生硼化物 和包晶硼化物的尺寸和形态得到不同程度的细化和改变。在 0.6%RE 变质与 0.3 %K /Na 金属盐变质时初生相尺寸各达到最小值，分别从未变质时的 81.4m 细化 到 30.4 m 和 23.4m。研究发现 RE 除了可以脱硫、脱氧净化钢液以外，RE 化合 物 CeB6和 CeO2S 与初生硼化物和包晶硼化物之间的错配度很小，可
3、以作为它们 的异质形核核心，起到细化硼化物的作用。K/Na 易引起成分过冷，通过增加初生 相结晶晶核来达到细化目的的。此外，K/Na 是表面活性元素，通过吸附到硼化物 生长最快的晶面上，改变晶体的生长惯习面来实现对初生硼化物团球化和颗粒化 的。 2.通过 Nb、Ti 合金化可以显著细化初生硼化物颗粒，在 Ti 含量为 0.5%与 Nb 含量为 0.9%时可以取得最优细化效果， 使初生硼化物从未变质时的 81.4m 分 别细化到 50.4m 和 23.9m。Nb、Ti 合金化对包晶硼化物和共晶硼化物的形态、 数量也有很大的细化和改变作用。铌和钛都是强碳化物形成元素，加入合金后可 与钢中的碳原子形
4、成高熔点的 TiC 和 NbC，它们与初生硼化物之间的二维错配度 很小，作为初生相的异质形核核心而使之细化。分布在初生相边缘的碳化物颗粒 还对其自由生长还起到阻碍作用。 3.初生硼化物颗粒大小与钢液冷速关系密切，随冷速增大，合金初生相逐渐 细化。在随流孕育过程中，随着悬浮剂的增加，初生硼化物颗粒持续细化，并在 其含量为2.8%时达到最小值， 使初生硼化物从未变质时的81.4m细化到20.2 m。 4.提出了一个计算细化率的公式。该公式是普通细化率和其自然底数 e 次幂 的算术平均值。用该公式得出的细化率更能体现变质剂对组织的细化能力。 摘 要 II 5.多组元复合变质对初生硼化物具有更好的细化
5、作用。0.9%Nb +0.4%RE 复 合变质不仅可以细化初硼化物，还可以使其横截面的形状由四边形的尖角变成圆 角，可以有效减小由凝固和外力引起的应力集中。这主要是由于曲率小的晶体部 分在高温凝固过程中溶解所致。0.9%Nb +0.4%RE 复合变质还可以使组成初生相 颗粒的晶簇之间发生粘合而生成单一的柱状晶体，使系统的表面能下降。 6.随着热处理温度的提高， 包晶硼化物、 初生硼化物依次溶解， 在 1050时， 包晶硼化物完全溶解，初生硼化物部分溶解由四方柱状变为骨状。稀土元素可以 有效地提高硼化物的高温稳定性，使其溶解温度提高，且含量越高效果越显著。 由于初生硼化物具有非常好的高温稳定性，
6、利用热处理工艺很难改变其形态和分 布。 关关 键键 词词：过共晶高硼铸钢；细化；变质；合金化；热处理 论文类型论文类型：应用基础研究 ABSTRACT III Subject: Study in the Technology of Microstructure Refinement in Hypereutectic High Boron Cast Steels Specialty: Materials Physics and Chemistry Name: Ge Hui-jun Supervisor: Zhu Yao-min ABSTRACT Due to existence of hard
7、and coarse primary borides, the toughness of hypereutectic high boron cast steels as well as their abrasion resistance at high impact conditions is decreased definitely, which limits its application in industrial conditions. In this paper, inoculating treatment, suspension casting and alloying treat
8、ment were used to refine the primary Fe2B borides and the peritectic Fe3(C,B) borides in the hypereutectic high-B cast steel. The results were drawn as follows: The dimension of the primary borides was refined as well as the morphology of the peritectic was altered in the hypereutectic high-boron ca
9、st steel(the HFBC alloy) after modified by the rare earth ferrosilicon and potassium/sodium salts.The contents of modifier at 0.6%RE or 0.3%K/Na have a maximum refinement making the primary seperately from 81.4m undisposed to 30.4 m and 23.4m. It was found that RE can purify molten steel by eliminat
10、ing sulfur and oxygen. CeB6 andCeO2S can rifine the particals of both primary and peritectic borides by becoming their heterogeneous nucleation,because the mismatch between them is small enough. K/Na can easily cause constitutional supercooling leading the primary phase smaller by increasing its cry
11、stal nucleus.As surface-active elements, K/Na make primary borides becoming balllike by absurbing onto the surface of the primary and liquid. Adding Nb,Ti into the alloy has a refinement to the primary,peritectic and eutectic borides,also changes the amount of the peritectic and eutectic ones. The c
12、ontents of modifier at 0.9%Nb or 0.5%Ti have a maximum refinement making the primary seperately from 81.4m undisposed to 50.4 m and 23.9m. TiC and NbC serve as the heterogeneous nucleation of the primary making it smaller as the ABSTRACT IV mismatch between them is small enough.Carbides on the edge
13、of primary phase also impede its growth. The development of primary boride slows down along with the high cooling rate.Primary boride has a sustained refinement with the increasing of suspending agent,and has a minimum at 2.8% content making the primary from 81.4m undispo -sed to 20.2m. Propose a fo
14、rmula to calculate the rate of refinement.It is the arithmetic mean of the commen refinement rate and its to the eth power,in which e is the natural background. Rate of refinement derived from this formula can better show the refinement ability of modifiers. Several multimodifiers have great refinem
15、ent to the primary boride in the HFBC alloy. 0.9%Nb +0.4%RE multimodifier makes the primary refiner as well as change the shape of lateral section from quadrangle with sharp point into a nearly round shape, avoiding to lead to stress concentration caused by freezing and external force.The vary of sh
16、ape is due to the shape point dissolves into liquid while freezing. The multimodi fier make the druse of primary phase glue into the whole crystal causing the energy of system decreasing. The peritectic and primary borides dissolve in turn with increasing of the heat temperature. The peritectic resolves com
