用15钢制造的齿轮，要求齿轮表面硬度高而心部具有良好的韧性，采用（ ）热处理。

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SQL Error: select id,body,options from ***_enewstiku where sourceid='24890' and id < 2124360 and id<>'2124360' order by id desc limit 5 SQL Error: select id,body,options from ***_enewstiku where sourceid='24890' and id > 2124360 and id<>'2124360' order by id asc limit 5