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利用SEM,OM和XRD等手段分析了HK40合金铸件铸造疏松形成原因,并研究了添加微量B对HK40合金的凝固组织及疏松形成的影响.结果表明:HK40合金铸件主要存在A和B 2种铸造疏松缺陷.A类疏松主要由于枝晶的快速生长并架桥联接导致架桥枝晶之间区域的补缩不足引起;B类疏松产生原因是相邻枝晶间区域生长的枝晶状M7C3型碳化物堵塞枝晶间补缩通道.B微合金化能降低HK40合金铸件较强的柱状晶生长趋势,细化枝晶,能抑制HK40合金A类铸造疏松缺陷的产生.同时,B微合金化增加了HK40合金枝晶间共晶相的体积分数,使枝晶间呈枝晶状M7C3型碳化物转变为层片状的M23C6型碳化物析出,避免碳化物堵塞相邻枝晶间的补缩通道,因而也减小了B类铸造疏松缺陷的形成倾向.
The causes of loose casting in HK40 alloy casting were analyzed by means of SEM, OM and XRD, and the effects of adding trace amount of B on the solidification microstructure and loose formation of HK40 alloy were studied.The results show that there are mainly two kinds of A and B casting Loosen defects.The reason for the looseness of Category A is mainly due to the rapid growth of dendrites and the lack of make-up of bridging dendrites due to the rapid growth of dendrites. Type B looseness is caused by the dendritic M7C3 type Carbide plugging dendrite interspersed channels.B Microalloying can reduce the stronger columnar crystal growth tendency of HK40 alloy castings and refine the dendrite, which can inhibit the generation of loose casting defects of Class A castings of HK40 alloy.At the same time, B microalloying Increase the volume fraction of the eutectic phase between HK40 alloy dendrites, dendrite M7C3 type dendrite transition into lamellar M23C6 type carbide precipitation, to avoid the blockage between adjacent dendrite filling carbide Channel, thus also reducing the propensity for formation of B-type casting loose defects.