Study on Wear Resistance Property of High-Cr Cast Iron

高鉻鑄鐵正被廣泛應用在耐磨耗及耐沖蝕之環境中，如：滾軋輥輪、礦業及水泥業磨球、管路輸送設備等。本研究針對高鉻鑄鐵探討化學組成與熱處理參數對於沖蝕磨耗及刮磨磨耗性質之影響。研究結果顯示，經淬火後之顯微組織主要包含共晶碳化物M7C3、麻田散鐵(內含M7C3及M23C6二次碳化物) 及大量之殘留沃斯田鐵；經回火熱處理後之顯微組織主要包含共晶碳化物M7C3、回火麻田散鐵(內含M7C3及M23C6二次碳化物) 及少量之殘留沃斯田鐵(取決於回火溫度)。結果顯示，不同化學組成（C, Cr and Mo）對於顯微組織雖有所影響，但對於耐沖蝕磨耗性質則無明顯的影響。另，進一步探討不同角度進行沖蝕磨耗之試驗結果顯示，淬火態在沖蝕角度45°及回火態在沖蝕角度60°出現最大沖蝕率及沖蝕深度。又，在相同沖蝕角度條件下，回火態之耐沖蝕磨耗性優於淬火態。此外，本研究選取一些特定高鉻鑄鐵進行一系列的回火熱處理(不同回火溫度)，並以60°角之沖蝕試驗結果比較，得知沖蝕率及沖蝕深度均與合金之硬度成正相關，及硬度較高者，耐沖蝕磨耗性反而較差。然而，在刮磨磨耗測試中卻獲得相反之結果，此現象是由於在沖蝕過程中，材料移除的主因是裂縫成長，硬脆的較易產生裂縫，進而使材料移除，而在刮磨磨耗中材料移除的主因是切削，因此較硬的相能夠抵抗材料移除。High-Cr white cast irons have been used extensively in industries with both abrasive and erosive environments, such as mining and mineral processing (hammers, crushers, ball mills, pulverized rolls, etc.) and steel rolling process (rolling rolls) which require high wear resistance property. In this study, both erosion and pin-on-disc tests were performed to evaluate the effects of chemical composition and heat treatment condition on wear resistance property of high-Cr white cast irons. Microstructure observations show that alloys in quenched state consist of eutectic M7C3 carbides, martensite, M23C6 secondary carbides and a substantial amount of retained austenite. On the other hand, alloys in quenched and tempered state consist of eutectic M7C3 carbides, tempered martensite, M23C6 secondary carbides dispersed in tempered martensite and a small amount of retained austenite (depending upon tempering temperature). Erosion test results indicate that varying chemical composition (C, Cr and Mo contents), but maintaining at similar heat treatment conditions, exerts little influence on erosion property in terms of erosion rate and depth, although the microstructures were changed somewhat. Furthermore, erosion testing on selected alloys with different tempering temperatures concludes that the erosion property correlated positively with alloy hardness, that is, the resistance to erosion decreases with increasing alloy hardness. However, reverse results were obtained in the pin-on-disc testing. This can be explained by that facts the material removal is the main cause of crack growth when erosion, but when pin-on-disk test the main cause of material removal is cutting