Whichof the following is the best answer? A. Beijing is China’s political center. B. Beijing is China’s culture center. C. Beijing is China’s educational center. D. all of above
【单选题】下列关于热处理的叙述错误的是( ) A .渗碳是使碳原子渗入低碳钢或低碳合金钢工件表层的热处理工艺 B .渗氮是使氮原子向工件表层扩散的热处理工艺 C .渗碳、渗氮、渗硼、碳氮共渗等是比较常用的物理热处理工艺 D .表面淬火是将工件的表面层淬硬到一定深度,而心部仍保持未淬火状态的一种局部淬火热处理工艺