以超高頻感應加熱於鋼料表面被覆鈷基及鎳基合金的研究

Abstract

本研究是將Stellite 6鈷基合金粉末(Co-28Cr-4W-1.1C)和NiCrBSi型的鎳基合金粉末(Ni-14.4Cr-3.2B-4.4Si)事先預敷於中碳鋼及高碳鋼的表面，再用高週波感應加熱進行被覆處理。配合不同的製程參數，利用光學顯微鏡(OM)、電子微探儀(EPMA)與X光繞射分析儀(XRD)分析合金層顯微組織、化學組成以及相的鑑定，並以微硬度試驗機量測合金層的硬度分佈，之後再將試片浸泡於腐蝕液中，觀察其耐腐蝕能力。 研究結果顯示鈷基合金被覆層的組織可以區分為樹狀晶、樹枝間共晶組織及針狀組織三種。被覆層為樹狀晶與樹枝間共晶組織時，樹狀晶內為富鈷相固溶Cr、Fe等元素，共晶組織則為鈷的固溶體與碳化物M7C3，被覆層的硬度會隨著加熱時間增長而降低。但當被覆層中的Fe含量超過40％之後，被覆層組織會轉變為針狀組織，硬度則會隨著加熱時間增長而有升高的趨勢。 鎳基合金被覆層是由γ-Ni、Ni3B、Ni31Si12、CrB、Cr7C3及Ni-Cr-Fe化合物所組成。隨著加熱時間的增長，交界處的Ni-Cr-Fe化合物數量有變多，而CrB與Cr7C3數量則有減少的的趨勢，使得交界處的硬度略微降低。而被覆層中的CrB與Cr7C3隨著加熱時間的增長有粗大化的現象，使得強化相佔的比例增加，造成被覆層的硬度有上升的趨勢。而以高功率短時間進行被覆處理，被覆層中的CrB與Cr7C3數量較多，且單位面積中γ-Ni＋Ni3B佔的比例也比較多，使得被覆層的硬度較以低功率長時間進行被覆處理的為高。 經被覆鈷基或鎳基合金的試片對鹽酸、硝酸與硫酸的耐蝕能力都有顯著提升。不論是被覆鈷基或鎳基合金，隨著加熱時間的增長，被覆層的耐腐蝕能力會因為Fe的稀釋率上升而下降。

In this research, Co-based alloy Stellite6（Co-28Cr-4W-1.1C）and Ni-based alloy Deloro60（Ni-14.4Cr-3.2B-4.4Si）were clad on carbon steel using high frequency induction heating. With different processing parameters, the properties of the clad layer were studied through observing the microstructure, measuring the chemical composition and hardness distribution, indentifying the phases in the layer, and conducting the corrosion test. The results show that the microstructure of Co-based alloy layer can be divided into dendrite, interdendritic eutectics and needle structure. If the microstructure of the clad layer is dendrite and interdendritic eutectics, the matrix is Co-rich solid solution containing chromium, iron and other elements with network M7C3 carbide distributed along the grain boundary. The hardness of the clad layer will decrease with increasing the heating time. However, when the content of iron is more than 40％, the microstructure will transform into needle structure, and the hardness of the clad layer will increase with increasing the heating time. Ni-based alloy layer consists of γ-Ni matrix, Ni3B, Ni31Si12, CrB, Cr7C3 and Ni-Cr-Fe compounds. The interface compound of Ni-Cr-Fe will increase and both CrB and Cr7C3 will decrease with increasing the heating time, leading to a slightly decrease in the hardness near the interface. In the clad layer, the coarsening of CrB and Cr7C3 becomes more obvious as the heating time increases. In other words, the volume fraction of hardening phases（CrB and Cr7C3）increases and lead to the increasing of hardness. High heating power and short heating time will increase the compounds of CrB and Cr7C3 as well as the volume fraction ofγ-Ni and Ni3B ,and lead to increase in hardness of the clad layer. The specimen clad with Co-based alloy or Ni-based alloy has excellent resistance to the corrosion of hydrochloric acid, nitric acid and sulfuric acid. No matter which alloy is clad, the ability of anti-corrosion will decrease with increasing the heating time, owing to the dilution of iron in the clad layer.