高強度厚壁球墨鑄鐵冒口設計方法之探討

Study of Riser Design for High Strength and Heavy Section Ductile Iron

林振昆(Cheng-Kung Lin)

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(2014年)

https://doi.org/10.6342/NTU.2014.11168

摘要

球墨鑄鐵兼具強度及延性之特性，在工業上已有相當廣泛之應用，鑑於對鑄件品質之高度要求，不僅機械性質必須符合規格要求，且收縮缺陷必須極力避免。本研究係針對高強度厚壁球墨鑄鐵件(120mm之立方體)，探討最佳冒口設計，所採用之冒口型式為頂冒口。在合金設計上，C、Si含量分別設定在3.6%及2.4%，又，為得到全波來鐵基地而添加了Fe-Mn及純Cu。
研究結果顯示，在澆注溫度為1400oC時，無保溫套之最佳冒口設計為：冒口直徑=70mm，冒口高度=70mm，冒口頸直徑=40mm，冒口頸高度=20mm。若採用保溫型保溫套或發熱型保溫套，其最佳冒口設計均為：冒口直徑=54mm，冒口高度=54mm，冒口頸直徑=40mm，冒口頸高度=20mm。由此可知，採用保溫型保溫套或發熱型保溫套之冒口體積，可較無保溫套之冒口體積縮小達到55%。
研究結果亦顯示，為符合FCD-800-2之合金規格，最佳合金設計為：Mn：0.2%、Cu：1.0%。在成份及顯微組織(球化率、石墨數目、波來鐵比例)皆達到標準之前提下，鑄態下之機械性質已幾乎達到規格要求：抗拉強度、降伏強度、伸長率及硬度分別為797MPa、500MPa、6.3%及290HB。若再施以最佳熱處理程序：890oC/1hr/OQ/600oC/1hr/furnace cooling to RT，則抗拉強度、降伏強度及伸長率分別為864MPa、720MPa及4.5%，均符合規格要求。

關鍵字

高強度球墨鑄鐵 ； 冒口設計 ； 冒口保溫套 ； 充填及凝固模擬 ； 淬火及回火 ； 機械性質

並列摘要

Ductile cast irons have been widely applied in the industry due to their high strength and ductility. In view of the stringent quality requirements for the castings, not only the mechanical properties must meet the specification, but also the shrinkage defects should be prevented. In this study a high strength grade (FCD-800-2) ductile cast iron was chosen as the target alloy, and a heavy section ductile iron casting (120mm cube) was selected for the study of the optimal riser design.
Regarding the riser design, top risers were employed in this study. The experimental results indicate that under the condition of 1400oC pouring temperature, the optimal riser design obtained is：Dr=70mm, Hr=70mm, Dn=40mm, Hn=20mm. On the other hand, as the insulated riser sleeve or exothermic riser sleeve was used, the optimal riser designs for both types are：Dr=54mm, Hr=54mm, Dn=40mm, Hn=20mm. Accordingly, a reduction of riser size (volume) as high as 55% can be obtained when insulated or exothermic riser sleeves were employed.
Regarding the alloy design and heat treatment that are required to meet the FCD-800-2 specification, the C and Si contents are set at 3.6% and 2.4%, respectively. Moreover, in order to attain a merely fully pearlitic matrix, Fe-Mn alloy and copper (Cu) were added. 25mm-Y blocks were cast for tensile specimens. The experimental results show that the optimal alloy design is 0.2%Mn, 1.0%Cu, with the as-cast mechanical properties of 797MPa, 500MPa, 6.3% and 290HB for tensile strength, yield strength, elongation and hardness, respectively. Furthermore, as the optimal heat treatment condition of 890oC-1hr/oil quench at 600oC-1hr/furnace cooling to RT was conducted on the specimens, the following mechanical properties: 864MPa in tensile strength, 720MPa in yield strength and 4.5% in elongation can be obtained, all meeting the FCD-800-2 specification.

並列關鍵字

High strength ductile iron ； Riser design ； Computer simulation ； Quenching and tempering ； Mechanical properties

參考文獻

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