CTS-20CP is a steel made by Carpenter Steel and consists of:
Some information from the Spyderco website:
Carpenter specifically developed CTS-20CP as a blade tool steel. Its high vanadium content results in elevated corrosion-resistance and is manufactured with their proprietary Micro-Melt powdered steel technique. The Micro-Melt process enables the finished blade to be machined to an ultra-fine edge with superior surface finish.