High Speed Steel generally contains large amounts
of Alloys such as molybdenum, chromium, tungsten, vanadium, and
cobalt with sufficient carbon to provide excess alloy carbides in
the final heat treated structure. These grades can easily be hardened
to a range of 64 – 70 Rockwell “C”. Maximum hardness
is attained through secondary hardening after tempering. Aside from
its hardness, one of the most important characteristics of high
speed steel is its ability to retain this high degree of hardness
at elevated temperature.
High Speed Grades
M-1: One of the earliest and most simple of the
high molybdenum HSS. It has an exceptional balance of toughness,
wear resistance, and red hardness. It is especially suitable for
a large variety of cutting tools. It is readily machinable, hardens
uniformly to a high hardness, and possesses excellent cutting qualities.
While it is possible to obtain high levels of hardness, its relative
toughness is nearly equal to that of M-2. “HSS” is used
for making drills that will be used in a wide variety of applications.
M-1 has some of the increased red-hardness properties of M-2, is
less susceptible to shock, and has “flex” capabilities
generally favored for general purpose work.
M-2: Is a high molybdenum HSS that has also been
a standard for a number of years. It has extremely high toughness
coupled with good hardness, wear resistance and red hardness. Its
balance of properties lends itself to a wide and diverse range of
applications from taps and general cutting tools to dies, rolls,
punches, and other general purpose tools. “HSS” is the
standard material for HSS cutting tools. M-2 has good red-hardness
and retains its cutting edge longer than other general purpose high
speed steels, not as shock resistant or as flexible as other HSS
grades with less tungsten. Generally favored for high production
M-7: Is a modified molybdenum high speed steel
containing more carbon and vanadium than grades M-1 and M-2, and
includes a small addition of nitrogen. This makes it possible for
M-7 to attain a greater hardness and faster heat treat response.
It is ideally suited for special cutting tools where wear resistance
and red hardness are required for maximum cutting efficiency. “HSS”
is used for making heavier construction drills that can be used
for portable drilling of hard sheet metal alloys. Generally favored
for work in Aircraft plants where flexibility and extended drill
life are equally important.
M-35: “5%” COBALT is only used for
making tool bits. It has some of the increased red-hardness properties
of M-42, and is not quite so susceptible to shock.
M-42: Is a high cobalt steel that finishes to
a very high red hardness and has excellent cutting hardness. Due
to its lower vanadium content, the grindability is relatively good
in spite of the high hardness levels which can generally be obtained.
Because of its unique combination of properties, this grade has
gained broad acceptance in the aerospace industry for machining
superalloys and other difficult high strength alloy compositions.
“SUPER COBALT” is the standard material used for all
cobalt cutting tools. It has excellent resistance to abrasion and
very good red-hardness for working difficult materials.
M-50: Is an intermediate type high speed steel
of the molybdenum-chromium, vanadium variety. M-50 is recommended
for applications involving moderate cutting conditions, such as
wood working tools where toughness properties are most important
and there is less of a need for red-hardness than is typical of
standard high speed steel. “HSS” is used for making
drills that will be used for portable drilling and where breakage
is a problem due to flexing the drill. Does not have the red-hardness
of other grades of HSS with tungsten. Generally favored for Hardware
and Contractor use, although they are also sold for industrial uses.
TOOL DATA: Reference and Documentation
Tungsten – Note
Generally speaking, a cutting tool made of high speed steel containing
the element tungsten will possess the very desirable property of
“red-hardness”. This enables tools to cut at a dull
red heat (up to 1000 degrees F) without loss of hardness or rapid
dulling of cutting edge. Cobalt high speed steel will exhibit even
greater red-hardness and wear resistance.
Super HSS – Note
The term “SUPER HSS” is not definitive and can mean
almost anything that one wants it to mean from ordinary M-50 to
High Cobalt material.