单项选择题
A.4Cr13B.ZGMn13C.GCr15D.1Cr18Ni9
A.模具B.刃具C.渗碳件D.轴承
A.3Cr18Mn12 B.1Cr11Mo C.15MnVR D.7Cr17
A.20Mn B.20Cr C.20g D.20R
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