- 學位論文
碳勢控制對碳工具鋼熱處理性質的影響
Effect of Carbon Potential Control on the Heat Treatment Properties of Carbon Tool Steel
摘要
木精分解氣是一般工業上常使用的爐氣，為了能有效控制此種爐氣的碳勢，本研究事先將各種比例的蒸餾水和木精相互混合，並調整木精分解溫度或鋼料加熱溫度以產生不同碳勢的爐氣，再把爐氣的生成條件與碳勢的關係以統計學的觀點進行迴歸分析，而得到碳勢的預測方程式。藉此可以方便地配製成各種碳勢的爐氣，以滿足各種熱處理的需求。此外，將高碳工具鋼薄工件置於不同碳勢的爐氣中加熱淬火，以探討爐氣碳勢對工件熱處理後之硬度及韌性的影響，期能針對特定的工件找出最適宜的爐氣碳勢，使其熱處理後具有最佳的機械性質。所得的結果如下： 1.當鋼料加熱溫度一定時，若木精分解溫度愈高，則爐氣的碳勢也愈高；當木精分解溫度一定時，若鋼料加熱溫度愈高，則爐氣的碳勢愈低；當木精分解溫度及鋼料加熱溫度均一定時，若木精中添加愈多的蒸餾水，則爐氣碳勢愈低。 2.經由迴歸分析後所得的方程式能了解木精分解溫度、蒸餾水添加量及鋼料加熱溫度這三個自變數與爐氣碳勢的關係，也能夠準確的估算出爐氣的碳勢，其誤差為0.09%以下。 3.高碳工具鋼薄工件於較高碳勢的爐氣中加熱淬火後，其抵抗回火軟化的能力較佳，但韌性較差；而於較低碳勢的爐氣中加熱淬火時，其抵抗回火軟化的能力較差，但韌性較佳。 4.高碳工具鋼薄工件經淬火後，若回火到相同的硬度值，則採用330℃回火比採用400℃回火可得到較佳的韌性。 5.高碳工具鋼薄工件熱處理時最佳的爐氣碳勢為0.70%~0.80%，在此碳勢的爐氣中加熱淬火，並回火到相同的硬度時，可得到最佳的韌性。 6.增加爐氣碳勢、提高滲碳溫度及延長滲碳時間，均可增加硬化深度，但會使過剩滲碳組織愈來愈明顯，而導致表層硬度偏低。
並列摘要
The atmosphere produced from the decomposition of methanol is generally used in the industry. In order to control the carbon potential of atmosphere effectively, different ratio of distilled water was mixed with methanol in advance. Additionally, the decomposed temperature of methanol or heating temperature of workpiece was adjusted to produce atmosphere with different carbon potential and then these experimental data were analyzed with linear regression method of statistics. The carbon potential could be expressed by a linear equation in terms of decomposed temperature of methanol, heating temperature of workpiece and addition amount of distilled water. Referred to this equation, it is capable of generating the atmosphere with a specific carbon potential to satisfy the requirement of different heat treatment. Besides, the workpiece of high carbon tool steel was heated in the atmosphere with various carbon potential before quenching. The effect of carbon potential of the atmosphere on the hardness and toughness are investigated. The results obtained are as follows: 1.For a given temperature of workpiece, the carbon potential of the atmosphere will be raised, when the decomposed temperature of methanol increases. For a given temperature of methanol, the carbon potential of the atmosphere will be decreased, when the heating temperature of workpiece increases. If the decomposed temperature of methanol and heating temperature of workpiece are fixed, the carbon potential of the atmosphere will be decreased, when the ratio of distilled water to methanol increases. 2.The influence of the decomposed temperature of methanol, heating temperature of workpiece and addition amount of distilled water on the carbon potential of the atmosphere can be understood quantitatively by linear regression analysis. The carbon potential can be estimated accurately by the regression equation. The error is less than 0.1%. 3.The thin workpiece of high carbon tool steel which has been heated in the atmosphere with a higher carbon potential before quenching will possess a higher hardness and a lower toughness after tempering. Whereas for the workpiece heated in the atmosphere with a lower carbon potential, its hardness will decrease fast during tempering, but its toughness is better. 4.For the thin workpiece of high carbon tool steel quenched and tempered to the same hardness level, those tempered at 330℃ are tougher than those tempered at 400℃. 5.The thin workpiece of high carbon tool steel will possess the best toughness for the same hardness level after quenching and tempering, when the carbon potential of the atmosphere is 0.70%~0.80%. 6.Although either raising the carbon potential of the atmosphere, the carburizing temperature, or the carburizing time can enhance the hardened depth, a hyper-eutectoid structure will be formed near the surface. It will result in lowering the hardness on the surface.