When heat treating self-tapping screws used for steel plates, the industry usually uses carburizing, instead of thermal refinement which is commonly used on bolts. The reason is that thermal refinement cannot withhold thread hardness whereas carburizing can improve surface hardness. However, if you were to use carburized self-tapping screws on a steel plate that requires strong axial force, you would find the ductility weaker than thermal refined screws as well as higher risk of metal fatigue. Even now some people still use thermal refined bolts to tap threads. – See more at: http://www.fastener-world.com.tw/new/news_detail.php?id=4417#sthash.plDxs6jh.dpuf
When heat treating self-tapping screws used for steel plates, the industry usually uses carburizing, instead of thermal refinement which is commonly used on bolts. The reason is that thermal refinement cannot withhold thread hardness whereas carburizing can improve surface hardness. However, if you were to use carburized self-tapping screws on a steel plate that requires strong axial force, you would find the ductility weaker than thermal refined screws as well as higher risk of metal fatigue. Even now some people still use thermal refined bolts to tap threads. – See more at: http://www.fastener-world.com.tw/new/news_detail.php?id=4417#sthash.plDxs6jh.dpuf
When heat treating self-tapping screws used for steel plates, the industry usually uses carburizing, instead of thermal refinement which is commonly used on bolts. The reason is that thermal refinement cannot withhold thread hardness whereas carburizing can improve surface hardness. However, if you were to use carburized self-tapping screws on a steel plate that requires strong axial force, you would find the ductility weaker than thermal refined screws as well as higher risk of metal fatigue. Even now some people still use thermal refined bolts to tap threads. – See more at: http://www.fastener-world.com.tw/new/news_detail.php?id=4417#sthash.plDxs6jh.dpuf