低碳鋼在連續鑄造中形成橫向裂紋仍然是一大難題，先前研究提出提升模具振動頻率或控制鑄胚表面之顯微結構降低橫向裂紋形成，但橫向裂紋於次表面處仍被發現，因肥粒鐵在高溫時相對脆弱，特別是片狀肥粒鐵，連續鑄造之矯直過程中應變常集中於此，易形成橫向裂紋，由過去文獻指出，添加其他元素會影響初析肥粒鐵生成溫度及速率，進而改變表面形貌，因此探討高溫時不同元素添加對肥粒鐵形成之影響。
本研究針對以不同錳含量及碳含量對初析肥粒鐵形成之影響，首先設計三組不同錳含量(0.2、1.1、2.0 wt%)及碳含量(0.046、0.15、0.25 wt%)之低碳鋼試片，待熔煉鑄造取樣完成後，藉由熱膨脹儀在固定的冷卻速率下量測相變態溫度，後續再使用高溫紫光雷射共聚焦顯微鏡觀測初析肥粒鐵顯微組織演化之過程，分析錳含量及碳含量對肥粒鐵生成速率之影響，最後藉由熱處理製備表面相比例為10%初析肥粒鐵之試片，觀察初析肥粒鐵形貌，以及統計尺寸分析。
實驗結果顯示，隨著錳含量由0.2增加至2.0 wt%，以及碳含量由0.046增加至0.25 wt%，均會造成初析肥粒鐵之相變態溫度下降，同時錳含量與碳含量會影響初析肥粒鐵之厚度。當錳含量上升時，初析肥粒鐵生成速率亦隨之下降，使生長趨緩 ; 當碳含量上升時，初析肥粒鐵生成速率隨之下降，也亦使生長趨緩。隨著錳含量上升時，初析肥粒鐵之平均長寬比由2.42降至1.94 ; 碳含量上升時，初析肥粒鐵之平均長寬比由2.42降至2.15，結果指出當錳以及碳含量減少時，具有較多含量之初析肥粒鐵朝片狀形貌發展，造成矯直過程中產生橫向裂紋。

Transverse cracks in low carbon steel, which are perpendicular to the casting direction in straightening, are still a major problem in continuous casting. The previous works showed that the formation of transverse cracks can be suppressed by increasing oscillation frequency in casting mold. However, transverse cracks are still found at the depth of about 2 to 15 mm below the surface, which especially are influenced by proeutectoid ferrites. Therefore, this work studied the effect of manganese and carbon content on the formation of proeutectoid ferrite at high temperature. The experimental materials are manganese content of 0.23, 1.1 and 2.0 wt% together with carbon content of 0.046, 0.15 and 0.25 wt%. Firstly, Ar3 and Ar1 temperatures were measured by using DIL802. Secondly, In-situ morphology of proeutectoid ferrite was observed during phase transformation from austenite to ferrite with HT-CSLM. Thirdly, OM and ImageJ software was used to analyze the morphology and size statistics of proeutectoid ferrite on sample surface.
In the first part, as the manganese content increased from 0.23 to 2.04 wt%, the Ar_3 temperature decreased from 889℃ to 763℃.When carbon content increased from 0.046 to 0.25 wt%, the Ar3 temperature decreased from 889℃ to 809℃. In the second part, initial growth rate increased from 8.99∙10^(-6) μm/s to 1.13∙10^(-5) μm/s when manganese content increased from 0.23 to 2.04 wt%, moreover, when the carbon content increased from 0.046 to 0.25 wt%, the initial growth rate decreased from 8.99∙10^(-6) to 1.41∙10^(-6) μm/s during phase transformation of austenite. In the third part, as the manganese content increased from 0.23 wt% to 2.04 wt%, the average aspect ratio of proeutectoid ferrite decreased from 2.42 to 1.94. As the carbon content was increased from 0.046 to 0.25 wt%, the average aspect ratio of proeutectoid ferrite decreased from 2.42 to 1.94. The results show the film-like proeutectoid ferrite can be reduced by increasing the content of manganese and carbon.

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