介在物對冷軋鋼片斷面銹蝕之影響研究

Effects of Inclusions on the Rusting Behavior of Shear Surface of Cold-Rolled Steel Sheets

本文主要研究介在物數量、種類和形態對冷軋鋼片斷面銹蝕程度的影響。研究方法包括：FGA（分氣體分析）法、恆溫恆濕試驗、電化學試驗及微腐蝕試驗。研究結果顯示：⑴冷軋鋼片之氧化介在物和脫氧方式有關，隨著鋁添加，介在物逐漸從以SiO2為主，轉為以Al2O3為主之複合氧化物，且Mns會同時析出，或析出於氧化介在物之外側。⑵隨著氧含量增加，鋼片剪切面發生銹蝕之機會下降，隨著介在物中硫及錳含量之增加，鋼片發生銹蝕之機會增加。⑶冷軋鋼片之Eo（起始電位）及Eeq（平衡電位）隨著鋼材中硫含量增加而下降，τ（電位降至平衡電位前轉折之時間）和硫含量之相關性則較差。⑷隨著冷軋鋼片硫含量增加，其表面及橫截面試片之腐蝕電流均較大，耐均勻腐蝕性變差；而相同硫含量下，橫截面之耐蝕性又較表面為差。⑸介在物是點銹最重要之起始源，特別是Mns或含有Mns之複合硫氧化合物。

The effects of amount, type and morphology of inclusions on the rusting behavior of shear surface of cold-rolled steel sheets have been investigated in this study. The fractional gas analysis (FGA), humidity cabinet test, electrochemical method and micro-corrosion test were employed. The main results are shown as follows. (1) The variation of type of oxide inclusion was related to the del-oxygen process. The main inclusion was transformed from SiO2 base oxide to Al2O3 base oxide and MnS inclusion precipitated in the matrix or the outside of oxide inclusion while the addition of Al increased. (2) The rusting possibility of the shear surface decreased with increasing oxygen content and increased with increasing S and Mn contents in the inclusion. (3) The Eo and Eeq of the cold-rolled steel decreased with the increase of S content, while the relationship between τ and S content was not clear. (4) The corrosion current densities of surface and cross section raised with increasing the S content, especially in the cross section. (5) The inclusion was the main pitting initiation site, particularly the MnS and the complex oxi-sulfide inclusion.