Ordinary high-carbon steel lacks the durability and heat tolerance to perform well in high-speed drilling tasks. Special alloys blend specific elements with high-carbon steel, producing tool steel with enhanced properties. High-speed steel (HSS) bits--harder and more resistant to abrasion than high-carbon steel--retain temper at higher working temperatures. Varying the alloy of the steel makes the HHS bit suitable for many different industrial applications.
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Adding carbon to iron creates steel, with hardness and strength superior to pure iron. Carbon content between 0.8 percent and 2.11 percent creates steel that can be tempered to a variety of hardness levels. As hardness increases, the alloy becomes more fragile. Heating the metal above a critical temperature anneals or softens the steel, destroying the temper. Adding rare elements to high-carbon steel creates alloys with new strengths and critically important characteristics--including heat resistance.
The HSS classification refers to several different alloy steels used in HSS drill bits. Chrome-vanadium steel, for example, tempers harder than plain high-carbon steel and lasts longer at high drilling speeds. Adding other elements customizes HSS steel to specific industrial needs. Some elements increase impact strength and flexibility while others raise the maximum working temperature and durability of the cutting edge.
Choose M-50 HSS drills for general woodworking applications. Blended with molybdenum, chromium and vanadium, M-50 steel bits resist flexing stresses and abrasion. While this alloy does not hold an edge as well as more expensive carbide bits, M-50 HSS drill bits do more work with less breakage and re-sharpening than plain carbon steel bits.
Adding molybdenum to steel increases the flexibility of the HSS bit. M-2 HSS, with a high molybdenum content, combines toughness and wear resistance with red hardness--the ability to hold a cutting edge even when red hot. M-2 is commonly used for tool dies, punches and high-production machining bits.
Tungsten & Cobalt
Tungsten and cobalt create carbides that raise the working temperature of HSS bits to higher levels of red hardness. Either element also makes steel less flexible. With the highest heat and abrasion resistance, cobalt steel tips the working edges of long-lived, but expensive blades and drill bits. Joined to tougher and more flexible HSS bit shanks, cobalt steel cutting edges survive working temperatures above 1,000 degrees F without losing hardness or showing excessive wear.