High speed steels: High speed steel (18:4:1), Molybdenum based high speed steel, Cobalt based high speed steel, Vanadium High Speed Steel

High speed steels (HSS)

High Speed Steels (HSS) have
been given this name due to the fact that these steels may be operated as
cutting tools at much higher speeds that are possible with plain carbon tool
steel. High speed steels cutting tools operate at cutting speed 2 to 3 times
higher than for High carbon steels. At higher cutting speeds, sufficient heat
may be developed during the cutting process. This heat causes the cutting edge
of the tool to reach a high heat (red heat). This heat softens the carbon tool
steel and thus the tool will not work efficiently for a longer period. These
steels have the property of retaining their hardness even when heated to red
heat. High hardness at elevated temperatures is developed by addition of
elements such as tungsten, chromium vanadium to high carbon steels. These steel
are generally used for making lathe cutting tools, planner cutting tools,
shaper cutting tools, slotting cutting tools, drills, reamers, broaches,
milling cutter and punches. There are four general types of high speed steels
used in machine shop.

1. High speed steel (18:4:1)

High speed steels (HSS) are most
commonly operated as cutting tools at much
higher
speed i.e. twice or thrice where as tool steel. It is the most common
kind of cutting tool. It contains 18% tungsten, 4% chromium and 1 % vanadium,
0.8 carbon and remaining iron. It
  is
considered to be one of the best of all purpose tool steels. This brand of high
speed steel
     is used for machining
operations on steel and non-ferrous materials. This is generally used for
lathe,
planer and shaper
tools, drills, millings
cutters, punches etc.

2. Molybdenum based high speed steel

It contains 6% Mo, 6% W, 4% Cr,
2% V, 0.8% C and remaining Fe. It has excellent toughness and cutting ability.
Molybdenum high speed steels are cheaper than other types of steels and are
particularly used for drilling and tapping tools. These steels are also used
for making rough cutting tools, lathe tools and various kinds of milling
cutters.

3. Cobalt based high speed steel

It contains 1 to 12% Co, 20%  W, 4% Cr,
2% 
V,  0.8 carbon and remaining iron. This
is
  also
known as super high speed steel, because cutting tool made of this steel can be operated at much higher speeds in comparison to high
speed steel of 18:4:1 kind. In this steel,
cobalt   is added from 2 to 15 per cent in
order to increase the cutting efficiency especially at high
temperature. Cobalt high speed steel
generally contains 20%
W, 4% Cr, 2%
V and 12% Co and remaining Fe.
Since the cost of this steel is more, therefore, it is principally used for
making cutting tools for heavy operations
which impose high pressure and temperature on the tool.
  It is extensively used for making high
production tools of heavy work for high production
lathe, planer,
shaper, milling
and boring machine.

4. Vanadium High Speed Steel

Generally, this steel contains more
than
1% V and 0.70% C. This steel possesses better abrasive resistance in comparison to
normal HSS type steel. It is preferred for machining materials which are highly
difficult to machine by conventional means. These steels cutting tools are
close competitors of carbides cutting tools such as drills, reamers, milling
cutters etc. In addition to having heat resistance properties of high speed
steels possesses desirable properties of high hardness, high compressive strength
and outstanding wear resistance. 

Leave a Comment