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中低碳齒輪鋼中合金元素的偏析行為及其對帶狀組織的影響

Microsegregation behaviors of alloy elements and their effects on the formation of banded structure in pinion steels

  • 摘要: 帶狀組織是影響中低碳齒輪鋼內在質量的主要缺陷之一.本研究利用光學顯微鏡觀察到了20CrMnTiH和SAE8620H齒輪鋼工業樣品的帶狀組織,電子探針分析表明兩鋼種樣品中均存在著Cr、Mn、Si等合金元素的帶狀偏聚.分析結果表明,元素偏聚只是產生帶狀組織的必要和前提條件,而非充分條件.除了微觀偏析之外,合金元素對γ→α轉變溫度Ar3的影響趨勢、在鋼液中的溶解度或含量、對C活度的影響趨勢、以及對CCT曲線的影響趨勢等均對帶狀組織的形成或消除具有重要影響.減弱或消除帶狀組織的形成,一方面需要獲得細小的鑄坯二次枝晶間距,促進元素均勻分布,另一方面即便是在存在元素偏聚的條件下,若控制適當的軋制冷卻工藝及合適的奧氏體晶粒尺寸,也有可能從根本上消除帶狀組織.

     

    Abstract: Banded structure is one of the main defects which influence inner quality of medium-and low-carbon pinion steels. In this paper, the banded structures of industrial pinion steel samples of 20CrMnTiH and SAE8620H were observed by optical microscope, and the results of EPMA analysis showed obvious banded segregation of alloying elements, such as chromium, manganese and silicon in these two types of samples. However, the results revealed that element segregation is, not a sufficient, but a necessary condition of forming banded structures, since in some examples even the banded segregation of elements was observed while the banded structures did not exist. In addition to micro segregation, other properties of alloying elements, such as their effect trend on the transition temperature from austenite to ferrite (Ar3), their solubility or content in steel, their effect on the carbon activity and CCT curves, also give significant influence on the formation of banded structures. In order to weaken or eliminate banded structures, several possible ways were suggested for the industrial practice.

     

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