不同石墨型態低熱膨脹鑄鐵之尺寸熱穩定性分析

Thermal Dimensional Stability of Different Low Thermal Expansion Graphitic Cast Irons

陳翰霖(H. L. Chen) ； 潘永寧(Y. N. Pan)

《鑄造工程學刊》 42卷3期 (2016/09) Pp. 31-42

摘要

本研究主要包含三部份，第一部份係針對具不同石墨型態之低熱膨脹鑄鐵，探討均質化熱處理對於合金元素Ni之偏析程度及基地固溶C量之影響，並進一步探討其對於熱膨脹係數(α值)的影響。以固溶C量和Ni偏析程度對α值進行複迴歸分析得到相關式如下: α =0.68%C + 1.05Ni(seg) + 2.41；R2 = 0.96。顯示，欲降低α值，則必須同時降低合金之Ni偏析程度及固溶C量，但Ni偏析程度之影響較固溶C量高；第二部份係以拘束型熱循環試驗來比較具不同石墨型態之低熱膨脹鑄鐵的尺寸穩定性；第三部份係針對不同石墨形態之低熱膨脹鑄鐵試片經拘束型熱循環試驗後，以三維實體模型模擬分析溫度分佈、熱應力值以及尺寸變化量，並進一步探討α值與熱應力及尺寸穩定性之關聯性。實驗結果得知，三種石墨鑄鐵在經過T1均質化熱處理後，尺寸穩定性均獲得改善，其ΔPV(試片平坦度變化量)值大小依序為: 片墨 ＞ 縮墨 ＞ 球墨。同時，利用有限元素法模擬熱循環試片之溫度分佈及熱應力大小顯示，熱應力與ΔPV值大致呈正相關。此外，三種不同石墨鑄鐵(經T1均質化熱處理)之形狀變化量之模擬分析結果顯示與實際試驗結果相同，亦即三種石墨鑄鐵之尺寸穩定性依序為：球墨 ＞ 縮墨 ＞ 片墨。

關鍵字

低熱膨脹鑄鐵 ； 熱膨脹係數 ； 均質化熱處理 ； 鎳偏析 ； 固溶碳量 ； 尺寸穩定性 ； 有限元素法

並列摘要

The primary purposes of this research are threefold: (1) to investigate the effect of a specific heat treatment (T1: 1150°C/4hr/FC/750°C/4hr/WQ) on the Ni segregation, C content dissolved in the matrix, and α value in three different graphitic cast irons, (2) to conduct the constrained thermal cyclic tests to evaluate the dimensional stability of the alloys studied, and (3) to employ the finite element method (ANSYS) to simulate the temperature field, thermal stress and shape change of specimens after the thermal cyclic tests, and further to assess the correlation among α value, thermal stress and dimensional stability. Regression analyses were performed to correlate the carbon content dissolved in the matrix and/or degree of Ni segregation with α value, with the results being: α = 0.68%C + 1.05Ni_(seg) + 2.41; R^2 = 0.96. Based upon the regression analysis results, α value can be decreased by reducing both the carbon content dissolved in the matrix and degree of Ni segregation, with the latter being the dominant factor. Shape changes (△PV) of the specimens after constrained thermal cyclic tests (500 cycles) were measured for low thermal expansion cast irons (T1) with different graphite shapes. Among the low thermal expansion cast irons studied, the shape change (△PV) or the dimensional stability is closely related with α value, that is, the lower the α value, the less the shape change or the better the dimensional stability is. Therefore, the order of dimensional stability is SG＞CG＞FG.

並列關鍵字

Low thermal expansion cast iron ； Thermal expansion coefficient ； Homogenization heat treatment ； Ni segregation ； Carbon content in the matrix ； Dimensional stability ； Finite element method ； ANSYS