检查喷层厚度时要求每()m打一组至少3个均匀布置的观测孔。

单项选择题According to the NIST (The National Institute of Standards and Technology), _____ of the defects are introduced in the specification phase. A、25% B、50% C、35% D、70%

单项选择题正火处理用来强化内部结构，正火处理要把钢材加热到( )。