The effects of gas composition and the extent of reduction on the compressive strength of direct reduced iron (DRI) were investigated. Gas mixtures containing different proportions of hydrogen, carbon monoxide, water vapor, carbon dioxide and methane were tested. The structure of laboratory and industrial DRI was examined and correlated with gas composition and mechanical properties. After reduction, structural changes accompanying reduction and carburization were investigated with scanning electron microscopy, swelling was measured, and phases were quantified by X-ray diffraction. The major strength loss occurred in the first reduction step, when hematite grains transformed to porous magnetite. Carburization after reduction had a minor effect on strength, except when extensive precipitation of elemental carbon caused lower strength, similar to the metal dusting corrosion mechanism. Higher strengths were obtained when water vapor was added to the reducing gas.

中文翻译：

---

气基还原渗碳直接还原铁的强度

研究了气体成分和还原程度对直接还原铁 (DRI) 抗压强度的影响。测试了含有不同比例的氢气、一氧化碳、水蒸气、二氧化碳和甲烷的气体混合物。检查了实验室和工业 DRI 的结构，并将其与气体成分和机械性能相关联。还原后，用扫描电子显微镜研究伴随还原和渗碳的结构变化，测量溶胀，并通过 X 射线衍射对相进行量化。当赤铁矿晶粒转变为多孔磁铁矿时，主要的强度损失发生在第一个还原步骤中。还原后的渗碳对强度的影响很小，除非元素碳的大量沉淀导致强度降低，类似于金属粉尘腐蚀机理。当水蒸气加入还原气体时，强度会更高。