臺灣博碩士論文加值系統

在維持低熱膨脹特性及兼顧良好鑄造、加工性的材料需求下，低熱膨脹鑄鐵的開發已逐漸受到業界重視，本研究即是以進一步改善低熱膨脹鑄鐵的性質為目標，探討化學組成及熱處理方式對於其熱膨脹性質之影響，另外包括：凝固溫度特性（初、共晶溫度）、合金回收率以及凝固收縮等的資料收集，亦屬本研究之探討範圍。
實驗中所設計之合金成份係在NiE（Nickel equivalent）＝36%之前提下，包含三種不同等級之C、Si含量（1.0%、1.5%、2.0%）及Ni-Co組合（36%Ni、33%Ni-3%Co、30%Ni-6%Co），其石墨形態包括片墨及球墨兩種，從中探討各成份從常溫到400oC以上之熱膨脹係數變化情形，另外並設計三種不同條件之熱處理，探討其對於熱膨脹係數及金相組織等各方面的影響。
實驗結果顯示，C、Si含量（或CE值）愈低，其α值愈低，本實驗以1.0%C+1.0%Si及36%Ni成份所鑄得之片墨鑄鐵及球墨鑄鐵，其50oC處之α值（α50）分別為3.3×10-6 /oC及3.5×10-6 /oC；若以Co取代部份Ni時，則可進一步降低α值，在同樣之C、Si成份下，以30%Ni+6%Co組合取代36%Ni，其150oC以下溫度之α值大致低於2.3×10-6 /oC。
實施均質化熱處理，亦可進一步降低合金之α值，本實驗中，在同樣升溫至900oC並保持2小時的條件下，以水淬冷者可得最低之α值，以1.0%C+1.0%Si及36%Ni的成份而言，α50∼α150可達（1∼2）×10-6 /oC左右；試片在爐中冷卻者，其α值大致與鑄態下相同，甚至反而有上升之情形；此外，在不同Ni-Co組合之情形下，經由同樣熱處理後所得之α值大致相同，換言之，以熱處理之方式來降低α值應可取代較不經濟之添加Co的作法。
材料之抗拉性質與石墨形態最具關係，除此之外，添加Co成份亦可提升材料之抗拉強度，對於球墨鑄鐵方面，其降伏強度及伸長率也有同等比例的提升，以1.0%的C、Si含量為例，在片墨鑄鐵方面，添加6%Co，其抗拉強度從250MPa提升至300MPa左右；在球墨鑄鐵方面，其抗拉強度從485MPa提升至585MPa、0.2%降伏強度從300MPa提升至380MPa、而伸長率則從20%提升至35%左右。在硬度方面，C含量愈高，硬度愈低，且此一趨勢以片墨鑄鐵最為明顯，以36%Ni成份為例，當C含量從1.0%提高至2.0%時，其硬度值從HB 150降至HB 90左右，而球墨鑄鐵則從HB 160降至HB 140左右；此外，添加Co以及熱處理對於硬度的影響則並不明顯。
在凝固收縮特性方面，以1.0%C+1.0%Si+36%Ni的片墨鑄鐵而言，總收縮率約為5.2%（已扣除固態收縮之體積），若以6%Co取代6%Ni時，總收縮率約可降至2.92%；此外，球墨鑄鐵之總收縮率則又比同成份之片墨鑄鐵高約1.5%左右。

The objective of this research is to study the influence of chemical composition and heat treatment on thermal expansion coefficient of both flake and spheroidal graphite cast irons. In addition, recoveries of alloying elements on melting, solidification temperatures (liquidus and eutectic), and solidification shrinkages were evaluated in this study. The alloy design includes three different levels of C and Si (1.0%C+1.0%Si, 1.5%C+1.5%Si, and 2.0%C+2.0%Si), and three Ni-Co combinations (36%Ni, 33%Ni+3%Co, and 30%Ni+6%Co), with a constant NiE (Nickel Equivalent) of 36%. Further, three different heat treatment cycles were performed to examine their effects on the microstructure and α value of the alloys studied herein.
The experimental results indicate that the α value decreases with decreasing C and/or Si contents (or CE value). For cast irons containing 1.0%C, 1.0%Si and 36%Ni, the α values at 50oC (α50) of 3.3×10-6 /oC and 3.5×10-6 /oC were obtained for flake and spheroidal graphite cast irons, respectively. Coefficient values can be further lowered by replacing a fraction of the Ni with Co at a constant NiE of 36%. As an example, α values less than 2.3×10-6 /oC for temperatures below 150oC were obtained for the alloys which contain 1.0%C, 1.0%Si, 30%Ni and 6%Co.
Regarding the effect of homogenizing heat treatment, the results show that the α value was reduced further when the alloy was homogenized at 900oC for 2 hours and then quenched in water. Very low α values of (1~2)×10-6 /oC in the temperature range of 50 oC ~ 150oC were obtained for alloys containing 1.0%C, 1.0%Si and 36%Ni. However, an adverse effect for α value was resulted for alloys that were furnace cooled after homogenizing treatment. Furthermore, not much benefit in reducing α value was gained by homogenizing heat treatment in alloys that contain Co. This may imply that homogenizing heat treatment can substitute for Co addition.
The tensile properties of low thermal expansion austenitic cast irons are largely affected by the graphite morphology. For the case of 1.0%C, 1.0%Si and 36%Ni, the tensile strength of 250 MPa and 485 MPa were obtained for flake and spheroidal graphite cast irons, respectively. The tensile properties were significantly upgraded when part of Ni was replaced with Co. For instance, the tensile properties of spheroidal graphite cast iron with different Ni and Co contents can be summarized as follows:
For 1.0%C, 1.0%Si and 36%Ni: TS= 485 MPa, YS= 300 Mpa, El= 20%.
For 1.0%C, 1.0%Si, 30%Ni and 6%Co: TS=585 MPa, YS= 380 MPa, El= 35%.
The measurements of alloy solidification shrinkage concluded that the amount of solidification shrinkage (including liquid contraction) of FG cast iron that contains 1.0%C, 1.0%Si and 36%Ni was around 5.2%. The replacement of 6%Ni by an equal amount of Co reduces the solidification shrinkage to 2.92%. For SG cast irons, the solidification shrinkage was found to be higher (by about 1.5%) than that for FG cast irons.

中文摘要 .................................................I
英文摘要 ...............................................III
目錄 .....................................................V
表目錄 ................................................VIII
圖目錄 ...................................................X
第一章 緒論 .............................................1
第二章 文獻探討 .........................................4
2.1 淺談熱膨脹之微觀原子現象 ............................4
2.2 低熱膨脹現象之成因探討 ..............................5
2.3 低熱膨脹鑄鐵的開發、性質及應用 ......................7
2.3.1 低熱膨脹鑄鐵的開發 ................................7
2.3.2 低熱膨脹鑄鐵／鑄鋼的規格及其性質 ..................8
2.3.3 低熱膨脹鑄鐵在工業上的應用 ........................9
2.4 影響低熱膨脹鑄鐵性質的各項因素 ......................9
2.4.1 主要合金元素的影響 ...............................10
2.4.1.1 Ni的影響 .......................................10
2.4.1.2 C的影響 ........................................10
2.4.1.3 Si的影響 .......................................11
2.4.1.4 Co的影響 .......................................11
2.4.1.5 Nb的影響 .......................................12
2.4.1.6 Cr的影響 .......................................13
2.4.1.7 Ce等稀土元素的影響 .............................13
2.4.1.8 補充說明 .......................................14
2.4.2 碳當量及石墨形態的影響 ...........................14
2.4.3 熱處理及冷加工對熱膨脹係數的影響 .................15
2.4.4 其他參數的影響 ...................................17
第三章 研究目的與實驗方法 ..............................18
3.1 研究目的 ...........................................18
3.2 實驗方法 ...........................................18
3.2.1 合金設計 .........................................18
3.2.2 模型設計及熔鑄作業 ...............................19
3.2.2.1 模型設計 .......................................19
3.2.2.2 熔鑄作業 .......................................20
3.2.3 凝固溫度曲線量測 .................................20
3.2.4 熱膨脹係數量測 ...................................21
3.2.5 凝固收縮特性量測 .................................21
3.2.6 機械性質試驗 .....................................22
3.2.7 熱處理 ...........................................22
3.2.8 金相組織及偏析現象觀察 ...........................23
第四章 結果與討論 ......................................24
4.1 合金回收率調查 .....................................24
4.1.1 Ni、Co回收率統計..................................24
4.1.2 C之熔解損失量分析.................................25
4.1.3 Si之熔解損失量分析................................26
4.1.4 Mg回收率分析......................................26
4.2 凝固溫度分析及金相組織觀察 .........................26
4.2.1 凝固溫度分析 .....................................27
4.2.2 基地組織 .........................................29
4.2.3 石墨形態 .........................................30
4.2.4 熱處理對金相組織的影響 ...........................31
4.3 機械性質 ...........................................32
4.3.1 密度 .............................................33
4.3.2 抗拉性質 .........................................33
4.3.3 硬度 .............................................34
4.4 熱膨脹性質 .........................................35
4.4.1 化學組成的影響 ...................................35
4.4.1.1 C含量的影響 ....................................35
4.4.1.2 Ni-Co含量組合的影響 ............................36
4.4.2 石墨形態的影響 ...................................38
4.4.3 熱處理的影響 .....................................39
4.5 Ni的偏析現象觀察 ...................................41
4.5.1 石墨形態的影響 ...................................41
4.5.2 熱處理的影響 .....................................42
4.6 凝固收縮特性 .......................................43
4.6.1 凝固收縮現象觀察 .................................44
4.6.2 化學組成及石墨形態的影響 .........................44
第五章 結論 ............................................47
參考文獻 ................................................51

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