Case hardened: a case hardened fastener is a fastener of ferrous material having a surface which has been made harder than the core.
表面硬化：表面硬化的紧固件是黑色金属，其表面经过处理后比内心硬度要高。
The principle materials used for tools can be divided into three major categories: ferrous material, nonferrous material, and nonmetallic material.
用来做工具的主要材料可以被分为三大类：黑色金属材料，有色金属材料，非金属材料。
The Current research status, potential advantages and outlook of ferrous, nonferrous rare metals and precious metals material of Yunnan in 2005 are summarized and reviewed.
评述了云南省2005年黑色金属、有色金属、稀贵金属和陶瓷材料等的研究状况，分析了潜在优势并展望了未来前景。
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