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  • 學位論文

高碳高矽鋼之麻田散鐵微結構分析

Substructure of Martensite in High Carbon and High Silicon Steel

指導教授 : 楊哲人

摘要


鐵碳系統麻田散鐵根據外型通常可區分成三種型態,分別為板條狀、透鏡狀和板片狀麻田散鐵。不同合金成分的材料會產生不同的麻田散鐵相變起始溫度(Ms),而不同麻田散鐵起始溫度則會進一步決定將形成其中一種型態的麻田散鐵。此三種不同外觀之麻田散鐵在鐵碳系統中取決於碳含量的多寡進而影響Ms溫度。在相對較高溫度下,麻田散鐵透過差排的滑移完成晶格不變應變(LIS), 形成板條狀麻田散鐵;在相對較低溫下,麻田散鐵透過產生相變雙晶完成LIS,形成板片狀麻田散鐵;在中間溫度區間,麻田散鐵同時透過差別滑移及相變雙晶完成LIS,形成透鏡狀麻田散鐵。 此研究中,所用鋼材為參雜三種不同碳成分及鈷的高碳高矽合金鋼,藉由水淬至低於其Ms溫度的室溫產生麻田散鐵。經由觀察得知,此三種成分麻田散鐵形成的外型幾乎為透鏡狀和板片狀。藉由穿透式電子顯微鏡觀察透鏡狀麻田散鐵的外貌和微結構,並討論加入不同碳含量及鈷的影響,含碳量越高,麻田散鐵平板越窄而相變雙晶的寬度越細,而加入鈷會使麻田散鐵介面較平滑。除此之外,藉由控制不同沃斯田鐵化溫度產生不同先前沃斯田鐵晶粒大小也會影響麻田散鐵外貌,較大先前沃斯田鐵晶粒下之麻田散鐵寬長比較小。藉由光學顯微鏡觀察其形貌、長寬比。X光繞射分析儀則用來做麻田散鐵體積百分比之定量分析。綜合以上觀察結果加上透過穿透式電子顯微鏡進行更微觀的研究得到對於透鏡狀麻田散鐵奈米結構更多的資訊。此外,經由本研究對於不同先前沃斯沃斯田鐵晶粒大小和合金成分對麻田散鐵相變態的影響也將在之後詳細討論之。

並列摘要


Martensite in steels can usually be classified into three different morphologies including lath martensite, lenticular martensite and thin plate martensite. The morphological evolution relies on the martensite start (Ms) temperature related to the chemical composition of alloy. The transition among three types of martensite in Fe-C alloys can be determined by carbon compositions which affects the Ms temperature. Lath martensite, formed at the highest temperature, is associated with lattice invariant strain (LIS) occurring by dislocation slips. Thin plate martensite, formed at the lowest temperature, consists of transformation twins due to LIS. For lenticular martensite, usually formed at intermediate temperature, its fine structure brings about tons of attentions because it contains both transformation twin and dislocations. In this study, the chemical compositions of high carbon and high silicon steels are containing three different contents of carbon and cobalt. Martensite from steels are obtained by quenching to room temperature which below its Ms temperature. By Observation, The major types of martensite in the three different alloys are lenticular and plate martensite. The fine nano/microstructure of lenticular martensite was investigated by transmission electron microscopy (TEM) to make clear the effects of carbon and cobalt on morphology of lenticular martensite. The twin width and aspect ratio decreases with the increasing of carbon content, and the interface becomes smooth by adding cobalt. Moreover, the effect of prior austenite grain size, which was controlled by austenization temperature in this study, on the formation of lenticular martensite will also be further elucidated. Optical microscope (OM) was used to observe the morphology and the aspect ratio of lenticular martensite; X-Ray diffraction spectra (XRD) was applied to measure the volume fraction of martensite. The above synergetic results coupled with TEM investigations will provide an extended knowledge in the nanostructure of lenticular martensite. Besides, the effects of austenite grain size and chemical compositions on the martensitic transformation and the corresponding nanostructure will be also further understood in this study.

參考文獻


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