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Conghui Hu,Jianlei Zhang,Yunhu Zhang,Ke Han,Changjiang Song,Qijie Zhai 대한금속·재료학회 2022 METALS AND MATERIALS International Vol.28 No.2
High-entropy alloys (HEAs) are novel multi-element alloys based on five or more constituent elements in a range of 5–35 at%. Here we present a method to improve strength of a body-centered cubic (bcc) matrix HEA without loss of ductility. Theimprovement was achieved by phase modulation combined other strengthening effect of interstitial carbon addition. Carbonaddition can enhance strength and retain good ductility in some steels because carbon increases the volume fraction offace-centered cubic (fcc) phase. We used the same principle to design and fabricate a set of Al8(FeCuCrMn)92Cx (x = 0, 1,2, 3, 4 at%) HEAs under near-rapid solidification. Our results showed that carbon addition modulated constituent phases byincreasing the volume fraction of fcc phase and carbides. As a result, addition of carbon increased yield strength of this bccmatrix HEA. But the ductility decreased, especially when carbon content was higher than 3 at%, which was ascribed to unevendistribution of Cu-rich fcc phase and carbides precipitated in bcc phase region. After annealing at 1173 K for 2 h, additionof 1 at% carbon improved yield strength without compressive fracture. It demonstrated that a proper carbon content additionwith annealing can enhance the yield strength without loss of ductility for this bcc matrix HEA. Thus, interstitial carbon additionis a meaningful method to improve the mechanical properties by phase modulation combined other strengthening effect.
Jianlei Zhang,Yueshan Jiang,Conghui Hu,Gang Ji,Changjiang Song,Qijie Zhai 대한금속·재료학회 2022 METALS AND MATERIALS International Vol.28 No.11
The influence of Cr on the microstructural evolution of austenite in Fe-20Mn-9Al-1.2C-xCr (wt%, x = 0, 3 and 6) low-densitysteels during isothermal aging at 650 °C for various durations was systematically investigated. With the isothermal agingprocessed, the 0Cr and 3Cr samples underwent the divorced eutectoid transformation followed by the eutectoid transformation,while only the eutectoid transformation was observed in the 6Cr sample. Meanwhile, increasing Cr content changedthe eutectoid transformation products from ferrite + κ-carbide in the 0Cr sample to ferrite + κ-carbide + M23C6carbide in the3Cr sample, and to ferrite + M7C3carbide in the 6Cr sample. The Cr addition significantly increased the A1 temperature (655°C) of the 0Cr sample to 712 °C of the 3Cr sample, and to 841 °C of the 6Cr sample. As a result, the temperature differencebetween the A1 temperature and experimental phase transformation temperature (650 °C) was enlarged, which provided agreater driving force for the eutectoid transformation and accelerated the transformation rate of eutectoid transformation. Inaddition, the Cr addition had a significant effect on the diffusion of constituent elements, decreased the interlayer spacingof pearlite structure from 625 ± 30 nm in the 0Cr sample to 385 ± 25 nm in the 3Cr sample, and to 150 ± 20 nm in the 6Crsample, refining the eutectoid structure. These findings revealed the mechanism regarding the effect of Cr addition on theeutectoid transformation of austenite, offering valuable insights into the microstructure design of high-performance lowdensitysteels.
Improving the Carbon Macrosegregation in High-Carbon Steel by an Electric Current Pulse
Jianhong Ma,Jie Li,Yulai Gao,Lixing Jia,Zheng Li,Qijie Zhai 대한금속·재료학회 2009 METALS AND MATERIALS International Vol.15 No.4
Thus far, the relationship between the macrosegregation and refinement of solidification structures in metals is not clearly understood. In this paper, the effect of an electric current pulse (ECP) on the refinement of the solidification structure as well as carbon macrosegregation in high-carbon steel was investigated. The experimental results revealed that if central porosity exists in the solidification structure, the carbon macrosegregation in high-carbon steel cannot be improved by applying an ECP, although increased equiaxed dendrites and a reduced primary dendritic arm in a solidification structure were obtained after an ingot was exposed to an ECP. In contrast, after central porosity was eliminated, carbon macrosegregation was improved through the refinement of the solidification structure in high-carbon steel through the use of an ECP. Thus far, the relationship between the macrosegregation and refinement of solidification structures in metals is not clearly understood. In this paper, the effect of an electric current pulse (ECP) on the refinement of the solidification structure as well as carbon macrosegregation in high-carbon steel was investigated. The experimental results revealed that if central porosity exists in the solidification structure, the carbon macrosegregation in high-carbon steel cannot be improved by applying an ECP, although increased equiaxed dendrites and a reduced primary dendritic arm in a solidification structure were obtained after an ingot was exposed to an ECP. In contrast, after central porosity was eliminated, carbon macrosegregation was improved through the refinement of the solidification structure in high-carbon steel through the use of an ECP.