????20#????????20???????20??????20#???????????????????? ???? 20#????????20?? ????20#????????GB/T8162-2008 GB/T8163-2008 GB/T6479-2000 GB/T9948-2006????20#????????????÷?Χ?? ????????15???????????????????????????????????????????????????????????綃???????????????????????????С???????????????????????????????????????????????λ???????????????á??????????????????????????????? ??????20#?????????? ????? C ??0.17??0.24"?? Si??0.17??0.37?? Mn??0.35??0.65?? S ????0.035?? P ????0.035?? Cr????0.25?? Ni????0.25? Cu????0.25