Abstract After Severe Plastic Deformation (SPD), the strength of the Armco iron sharply increases with the number of Equal-Channel Angular Pressing (ECAP) passes. So, the ultimate tensile stress (UTS) reached up to 800 MPa after eight passes, reflecting an increment of around four times than the as-received material strength. The original grain size of the annealed iron of about 70 μm also experimented with drastic changes after ECAP, reaching grain sizes approaching to 300 nm. Samples were then welded by the Gas Tungsten Arc Welding (GTAW) process varying the voltage and current conditions. Metallographic analysis by Light Optical Microscopy (LOM) and Electron Backscatter Diffraction (EBSD), was carried out to analyze the weld penetration, Fusion Zone (FZ), and the size and microstructure morphology across the Heat Affected Zone (HAZ). Special attention was given to microstructure changes of the nanostructured base metal. A microstructural gradient was observed throughout the welded joint with hardness reduction concerning the nanostructured material but still superior to the material without ECAP. The temperature heterogeneity gave rise to different grain sizes and morphologies like Widmanstatten ferrite around the FZ, especially at high heat inputs.

中文翻译：

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Armco 铁纳米结构的钨极氩弧焊 (GTAW) 接头的表征通过等通道角挤压 (ECAP)

摘要 在严重塑性变形（SPD）后，Armco 铁的强度随着等通道角挤压（ECAP）通过次数的增加而急剧增加。因此，在八次通过后，极限拉伸应力 (UTS) 达到 800 MPa，反映了大约四倍于原样材料强度的增量。退火后的铁的原始晶粒尺寸约为 70 μm，在 ECAP 后也发生了剧烈变化，达到了接近 300 nm 的晶粒尺寸。然后通过改变电压和电流条件的气体钨极电弧焊 (GTAW) 工艺焊接样品。通过光学显微镜 (LOM) 和电子背散射衍射 (EBSD) 进行金相分析，以分析焊缝熔深、熔合区 (FZ) 以及整个热影响区 (HAZ) 的尺寸和微观结构形态。特别注意纳米结构贱金属的微观结构变化。在整个焊接接头处观察到微观结构梯度，纳米结构材料的硬度降低，但仍优于没有 ECAP 的材料。温度不均匀性导致了不同的晶粒尺寸和形态，如 FZ 周围的 Widmanstatten 铁素体，尤其是在高热输入时。