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在用含镍达6％的Cr—Ni—Mo马氏体不锈钢铸造重达42吨的水轮机叶片时发现:当这种铸钢中有形貌如图1所示的黑穗状组织时,其塑性韧性极差。在扫描电镜下通过人工衬度调制后其放大形貌如图2,从照片可以看出:在这种组织中有贯穿性的一次铸造晶界存在,而其组织有如一棵棵麦穗堆于低碳马氏体基体之上,经放大后观察,这些黑穗均由片层组成,只不过片层的厚薄和长度不等罢了。而一次晶中的析出物则或如条状或如竹叶状排列。经电子探针分析,这种黑穗的片层为(CrFe)_(23)C_6,而一次晶中的析出物则是Cr_(23)C_6,而且在一次晶附近还有一个铬偏析带(如图3)。用金相一断口匹配试样观察表明:试样沿一次晶界断裂。据化学分析发现:试件的碳含量普遍偏高,在靠近铸件心部区域竟远远超过了正常的含碳量。一般认为,碳是以间隙固溶体和
When casting 42 tons of turbine blades with Cr-Ni-Mo martensitic stainless steel containing up to 6% Ni, it was found that when such a cast steel has black spikes having a topography as shown in FIG. 1, Very tough plasticity. Scanning electron microscopy through the artificial contrast after the modulation of its enlargement morphology shown in Figure 2, can be seen from the photo: In this organization there is a penetration of the first casting grain boundaries exist, and its organization like a barley pile in On the low carbon martensite matrix, after magnification and observation, these black spikes are composed of lamellae, but the lamellae have different thickness and length. The precipitates in primary crystals are either arranged like stripes or bamboo leaves. By electron probe analysis, the layer of this black ear is (CrFe) _ (23) C_6, while the primary precipitates are Cr_ (23) C_6, and there is also a chromium segregation zone Figure 3). Metallographic fracture surface with a sample observation shows that: along the first grain boundary fracture. According to chemical analysis, it was found that the carbon content of the test piece was generally high, far exceeding the normal carbon content near the center of the casting heart area. It is generally believed that carbon is interstitial solid solution and