The effect of as-cast structure and macrosegregation on the mechanical properties of a direct-quenched low-alloy martensitic ultrahigh-strength aluminum killed and calcium treated steel cast at different superheats was studied. Samples from the castings were laboratory hot rolled with two different finishing rolling temperatures to distinguish the effect of hot rolling. Using optical emission spectrometry, the steel composition was analyzed as a function of slab thickness in order to detect the variations in steel chemistry due to macrosegregation. Further, hardness profiles, prior austenite grain sizes and tensile and impact toughness were determined for the hot-rolled specimens. It was found that interdendritic segregation was more intense at the higher superheat, which led to more pronounced positive segregation in the columnar-to-equiaxed transition (CET) zone, and negative segregation between CET and the centerline. These macrosegregation patterns were inherited by the hot-rolled samples causing local variations in hardness, which followed the variations in carbon content. However, altering the superheat had a minor effect on the nominal transformed microstructures and nominal prior austenite grain sizes. This occurred because of the interdendritic segregation induced composition variations both enlarged and decreased by turns the grain sizes. The CET also reduced measured impact toughness values.

中文翻译：

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铸态组织和宏观偏析对直接淬火低合金超高强度钢力学性能的影响

研究了铸态组织和宏观偏析对直接淬火低合金马氏体超高强度铝镇静钙处理铸钢在不同过热度下力学性能的影响。来自铸件的样品用两种不同的精轧温度进行实验室热轧，以区分热轧的效果。使用光学发射光谱法，分析钢成分作为板坯厚度的函数，以检测由于宏观偏析引起的钢化学变化。此外，还测定了热轧试样的硬度分布、原始奥氏体晶粒尺寸以及拉伸和冲击韧性。发现在较高的过热度下枝晶间偏析更强烈，这导致柱状到等轴过渡 (CET) 区域中更明显的正偏析，以及 CET 和中心线之间的负偏析。这些宏观偏析模式由热轧样品继承，导致局部硬度变化，随着碳含量的变化而变化。然而，改变过热度对标称转变微观结构和标称原始奥氏体晶粒尺寸的影响很小。这是因为枝晶间偏析引起的成分变化依次增大和减小晶粒尺寸。CET 还降低了测量的冲击韧性值。随着碳含量的变化。然而，改变过热度对标称转变微观结构和标称原始奥氏体晶粒尺寸的影响很小。这是因为枝晶间偏析引起的成分变化依次增大和减小晶粒尺寸。CET 还降低了测量的冲击韧性值。随着碳含量的变化。然而，改变过热度对标称转变微观结构和标称原始奥氏体晶粒尺寸的影响很小。这是因为枝晶间偏析引起的成分变化依次增大和减小晶粒尺寸。CET 还降低了测量的冲击韧性值。