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It is usually and additional component added to HSS to make it more durable: Vanadium high-speed steel jobber-length drill bits are made from high-speed steel, carbon, vanadium carbide, and other alloys. They provide more abrasion resistance and wear resistance than standard high-speed steel drill bits. Jobber-length drill bits are the most commonly used drill-bit length. They provide a good balance of strength and accuracy when drilling into a range of materials. In the hierarchy would probably be Carbon Steel - HSS - HSS/Molybdenum - HSS/Vandium - HSS/Cobalt - Carbide, there are many different alloys and also the drill structure/coating that makes it more suitable for different materials.
I have been using the Norseman/Viking and Cleveland M42 cobalt drills 135 degree twist drills, they have proven to be very durable and give clean accurate holes in different materials. I prefer the coated Norseman/Viking because they have a small web. I keep different sets for the mill vs. hand drills, the latter tends to chew up the shank. On the mill I primarily use a mechanics/stubby drill length which provide greater rigidity and less walking of the drill tip when starting a hole. Flats on the shank may help with hand drills to prevent the drill from twisting, but I do not like to use them on the mill.
The Norseman site has a good explanation of the differences.
Why Choose Magnum™?
Substantially longer cutting life - The nitro-carburized flute has an increased Rockwell hardness.
Cuts harder materials - The flatter point takes a smaller chip. More torque is directed to a smaller area. This allows drilling into materials with hardness of over 30 on the Rockwell "C" scale.
Stops drill walking - The split point design gives accurate starting without the use of a center punch.
Holds tighter hole size - The split point design is self centering. This limits the normal oversize drilling characteristics.
Outstanding quality appearance - The rich amber gold color sets it apart from commodity cutting tools.
Runs cooler, uses less torque - 135° point takes a smaller chip resulting in less heat. Friction is reduced by amber gold surface treatment.
Stops chuck slippage - Flats on drill shanks allow easy positive chuck grip.
(Flats are machined only on Mechanics Length drill bits & Silver & Deming drill bits, not on jobber length drill bits.)
Magnum™ Vs. Cobalt
The Magnum™ drills will substantially outperform cobalt drills in work hardening stainless steel applications. This performance advantage is the result of construction differences between the two types of drills. Cobalt drills, manufactured to Type J NAS 907 specs, have a very thick web. This web is necessary to limit breakage of the brittle cobalt steel. Magnum drills are made of special hi-moly tool steel, which is much tougher than cobalt steel. The web on a Magnum drill can be thinned considerably due to the toughness of the steel.
A Magnum drill with its thin web will penetrate the work hardening stainless fast enough to continually cut beneath the chip which is hardening from deformation. This means the drill is cutting softer steel.
The cobalt drill, with its thick web, cannot be fed at a fast enough rate to cut beneath the area which is hardening. As a result the cobalt drill is continually drilling into hardened steel.
Stainless Steel: Work Hardening Vs. Free Machining
Work hardening grades of stainless are the 300 series with the exception of 303, which is free machining. Free machining grades include the 400 series in addition to type 303. A quick way to identify work hardening vs. free machining stainless is to observe the chip formation. Work hardening chips break up during the drilling process, while free machining chips are long and stringy.
Cobalt Applications
Cobalt drills are recommended for free machining stainless ( 400 series & 303), titanium alloys and other high tensile strength materials. These applications require the high red hardness of cobalt steel to counter the substantial heat generated in the drilling process.
I have been using the Norseman/Viking and Cleveland M42 cobalt drills 135 degree twist drills, they have proven to be very durable and give clean accurate holes in different materials. I prefer the coated Norseman/Viking because they have a small web. I keep different sets for the mill vs. hand drills, the latter tends to chew up the shank. On the mill I primarily use a mechanics/stubby drill length which provide greater rigidity and less walking of the drill tip when starting a hole. Flats on the shank may help with hand drills to prevent the drill from twisting, but I do not like to use them on the mill.
The Norseman site has a good explanation of the differences.
Why Choose Magnum™?
Substantially longer cutting life - The nitro-carburized flute has an increased Rockwell hardness.
Cuts harder materials - The flatter point takes a smaller chip. More torque is directed to a smaller area. This allows drilling into materials with hardness of over 30 on the Rockwell "C" scale.
Stops drill walking - The split point design gives accurate starting without the use of a center punch.
Holds tighter hole size - The split point design is self centering. This limits the normal oversize drilling characteristics.
Outstanding quality appearance - The rich amber gold color sets it apart from commodity cutting tools.
Runs cooler, uses less torque - 135° point takes a smaller chip resulting in less heat. Friction is reduced by amber gold surface treatment.
Stops chuck slippage - Flats on drill shanks allow easy positive chuck grip.
(Flats are machined only on Mechanics Length drill bits & Silver & Deming drill bits, not on jobber length drill bits.)
Magnum™ Vs. Cobalt
The Magnum™ drills will substantially outperform cobalt drills in work hardening stainless steel applications. This performance advantage is the result of construction differences between the two types of drills. Cobalt drills, manufactured to Type J NAS 907 specs, have a very thick web. This web is necessary to limit breakage of the brittle cobalt steel. Magnum drills are made of special hi-moly tool steel, which is much tougher than cobalt steel. The web on a Magnum drill can be thinned considerably due to the toughness of the steel.
A Magnum drill with its thin web will penetrate the work hardening stainless fast enough to continually cut beneath the chip which is hardening from deformation. This means the drill is cutting softer steel.
The cobalt drill, with its thick web, cannot be fed at a fast enough rate to cut beneath the area which is hardening. As a result the cobalt drill is continually drilling into hardened steel.
Stainless Steel: Work Hardening Vs. Free Machining
Work hardening grades of stainless are the 300 series with the exception of 303, which is free machining. Free machining grades include the 400 series in addition to type 303. A quick way to identify work hardening vs. free machining stainless is to observe the chip formation. Work hardening chips break up during the drilling process, while free machining chips are long and stringy.
Cobalt Applications
Cobalt drills are recommended for free machining stainless ( 400 series & 303), titanium alloys and other high tensile strength materials. These applications require the high red hardness of cobalt steel to counter the substantial heat generated in the drilling process.
