单项选择题
A.高碳钢 B.中碳钢 C.低碳钢 D.高级优质高碳钢
A.0.60%~0.90% B.0.45%~0.70% C.0.45%~0.90% D.0.60%~1.20%
A.40Cr B.55Si2Mn C.9SiCr D.35CrMo
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