冷激型低合金球墨鑄鐵之顯微組織探討

Study on the Microstructure of Low-Alloy Chilled Ductile Cast Iron

江尚儒(Shang-Ju Chiang)

指導教授 ： 潘永寧

國立臺灣大學/工學院/機械工程學研究所/碩士(2009年)

https://doi.org/10.6342/NTU.2009.02076

摘要

本研究的主要目的在於探討不同C與Si含量、接種處理及表面冷激對於低合金球墨鑄鐵之顯微組織(石墨形態、碳化物含量、基地組織)及硬度之影響。在合金設計方面，固定2.5%Ni-1.0%Cr-0.5Mo-0.4Mn，探討C與Si含量(A：3.76%C- 1.15%Si，B：3.55%C-1.68%Si，C：3.44%C-1.48%Si，D：3.81%C-1.44%Si，其中A與B爐次之碳當量相同)，與接種情形對於鑄件顯微組織及硬度的影響。
在碳當量相同之條件下，增加Si含量會明顯增加石墨數目並減少碳化物的生成，而BX鑄件及BY鑄件在顯微組織(石墨形態、碳化物含量、基地組織)上的差異比AX與AY兩鑄件之間差異要大，可看出二次接種的效果在Si含量高時較為明顯。另，在Si含量相同之情形下，DY鑄件因碳含量較高又施以二次接種，故有較多的球墨數目及較低的碳化物量，但碳化物在四個鑄件之間差異不大。又，二次接種使鑄件表面與鑄件內部之變韌鐵/波來鐵比例差異極大，無二次接種的鑄件之變韌鐵/波來鐵比例在各位置之間差異較小。四個鑄件之硬度值以AX為最高，其值介於HRC50~HRC54之間。另，成份對基地組織各相所佔比例之影響極大。在冷卻條件不同的情形下，冷激鐵放置處之表面具有最高的球墨數目，碳化物含量高且分佈較細密，其硬度值亦最高；在冷卻較慢的部份(鑄件內部)，其球墨數目較少且其尺寸較大，碳化物之分佈也較分散。
本研究亦針對一些特定位置進行熱分析，並將所獲得之冷卻曲線對照相近成份之連續冷卻變態圖，來預測鑄件之基地組織。分析結果與實驗觀察結果頗為吻合。

關鍵字

冷激 ； 低合金球墨鑄鐵 ； 顯微組織 ； 硬度 ； 連續冷卻變態圖

並列摘要

The primary purpose of this research is to study the effects of C and Si contents, method of post inoculation and the employment of chills on the (surface) microstructure and hardness of low-alloy ductile cast irons.
The results show that, at a fixed CE, increasing Si content (from 1.15%Si to 1.68%Si) increases nodule count, but reduces carbide content. In addition, late inoculation exerts more effect on irons with higher Si than with lower Si. On the other hand, at a fixed Si content, irons with a higher C content and/or were late inoculated, have higher nodule count and less carbide content. In addition, late inoculation promotes bainite formation rather than pearlite, while no significant difference in matrix structure was obtained for irons without late inoculation. Regarding the hardness, casting AX has the highest hardness value HRC 50-54, among the four castings studied. Surface chilling significantly increases the nodule count, promotes uniform distribution of carbides and also refines carbide phase, and increases hardness.
Finally, thermal analyses were performed to attain the cooling curves at different locations in the castings and correlated the cooling curves with the continuous cooling transformation diagram of similar compositions to predict the matrix structure formed.

並列關鍵字

Chill ； Low-alloy ductile cast iron ； Microstructure ； Hardness ； Continuous cooling transformation diagram

參考文獻

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