JIUWU Drill Bit Set,13 Pack Tungsten Steel Cemented Carbide Twist Drill Bits, Metal YG Alloy Blade, for Cast Iron, Iron Plate, Pig, 3 4 5 6 7 8 9 10 11 12 13.5 14 15 mm Drill Bit Set

Material: YG Cemented Carbide + Chrome Vanadium Steel. Ideal for drilling in tough metal, including heavy-duty abrasive alloy metal drilling on hardened steel. The mistake that a lot of people make is using high speed steel twist drills at high speeds. If you search for "machining speeds and feeds" you will find a lot of information about the correct speeds to run cutting tools against different types of metal. Twist drills are the category of cutting tool you are looking for. As soon as the heat starts to build up on the tip, the drill bit can lose the hardness that make it a cutting tool. Using HSS drills at low rpm with cooling fluid or lubricant can provide a large quantity of successful holes in metal. TThere have chunks of carbide on the end, and carbide will make easy work of even the hardest steel, and allow you to use high rpms. (In the process of opening holes to continue to add water for cooling.) High toughness, abrasion resistance, high-speed cutting for the high hardness. Size: 3mm 4mm 5mm 6mm 7mm 8mm 9mm 10mm 11mm 12mm 13.5mm 14mm 15mm.