Low carbon steel

Hello, I have no knowledge about metals and maybe this question is too obvious. My problem is that I have to decide between C1018, C1022 and
C15 steel for screws. I have no idea about type of steels but I think that these ones are low carbon steels and that 1018 means that the carbon content is 0.1018%. Am I right?
Anyway, Is C1018 better (in terms of hardeness and robustness) than C15 or viceversa?
Any help is welcome. Thanks.
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http://www.metalinfo.com/MetPChem_check.cfm?cKEY=ais0103&cFN=F&cCountry=USA&cSociety=AISI%20&cStandard 22&cGrade22
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