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Features and Uses of D2 Cold Work Tool Steel
D2 is an air hardening high carbon, high chromium type tool steel which
offers very high wear resistance, yet it is tough and machinable.
It hardens in air up to large sections with a low order of movement and offers a
measure of corrosion resistance when polished.
D2 has low distortion characteristics which are superior to the more commonly
used oil hardening (O1) and medium alloy (A2) grades. It also exhibits
considerably better wear resistance than these grades, but its comparative
toughness is lower than either.
Typical Applications
D2 is used for tools operating under conditions of severe wear and abrasion
or as an alternative to oil hardening tool steels when longer runs are required.
Applications include blanking dies and punches for steel sheet and plate, high
silicon transformer materials, stainless steel and iron, brass, copper, zinc and
hard abrasive materials generally.
Deep drawing dies, cupping dies, forming dies.
Sheet metal forming rolls, shear blades for strip and sheet including flying
shears.
Circular cutters for cold rolled strip. Trimmer dies, thread rolling dies, cold
extrusion dies. Broaches, plug gauges, ring gauges, special taps, staybolt
taps.
Brick and tile mould liners. Master hobs for cold hobbing plastic moulds. Cut
moulds for plastics.
Available Forms
Working and Heat Treatment
Forging
Pre-heat at 900°/950°C then raise the temperature to
1050°/1100°C. soak until uniformly heated. This steel is relatively hard at
elevated temperatures; therefore, initial hammer blows must be light and the
temperature must not be allowed to fall below 1020°C. until the metal begins to
flow. Final forging should not be done below 900°C.
Stress Relieving
When tools are heavily machined, ground or otherwise subjected
to cold work, the relief of internal strains is advisable before hardening to
minimise the possibility of distortion. Stress relieving should be done after
rough machining. To stress relieve, heat carefully at 600/650°C. Soak well and
cool in the furnace or in air. The tools may then be finish-machined before
hardening.
Hardening
It is preferable to heat the tools in a controlled atmosphere.
If this is not possible, pack hardening is recommended. A reducing atmosphere is
desirable. Pre-heat slowly to 750°/800°C. and allow to soak at this
temperature. The tools may then be brought up to 1000°/1020°C. for air
cooling, or 980°C. for oil quenching. Soak thoroughly at the temperature for
twenty to thirty minutes per inch of ruling section, then cool or quench
accordingly. It is important not to exceed 1020°C. when heating for hardening.
Exceeding this temperature will cause indifferent hardening. A deterioration in
magnetic properties indicates that the steel has been overheated in hardening.
For pack hardening the tools must be wrapped in brown paper, and packed into a
lidded container with spent charcoal or clean cast iron chips or turnings, then
heated to the necessary temperature for air cooling or oil quenching. Sufficient
time must be allowed for the heat to penetrate the box and packing so that the
tools attain full temperature. Soak for thirty minutes per inch of section of
the container. Withdraw the container from the furnace and quench the tools in
oil or allow to cool in air as desired. Tempering will then be necessary.
Annealing
KE A. 180 is supplied in the annealed and machinable condition.
Re-annealing will only be necessary if the steel has been forged by the tool
maker or if it is desired to machine a hardened tool. To anneal, heat slowly and
uniformly to 900°C. in a closed container. Soak for three to four hours and
allow to cool in the furnace to shop temperature. Then, without removing the
steel from the tube or container, re-heat to 800°C. and again soak for three to
four hours. Allow to cool in the furnace to shop temperature.
Martempering
An alternative hardening procedure which may be used when
suitable salt bath equipment is available. By this method internal strain,
distortion and risk of quench cracking are reduced to the minimum. Pre-heat dry
at 300°/400°C. Pre-heat in salt at 800°/850°C. holding in the salt for ten
minutes per inch of ruling section. Raise to the hardening temperature of
1000°/1020°C. holding in the salt for ten minutes per inch of ruling section.
Marquench in salt at 230°/250°C., holding in the bath for twenty minutes per
inch of ruling section. Cool in still air. Tempering will be necessary.
Tempering
Double tempering is recommended. Tempering should be done with
the least possible delay after hardening, preferably when the tools are still
hand warm. Refer to the tempering curve and select a suitable temperature
bearing in mind the service requirements. Heat slowly and uniformly. When the
tool has reached the desired temperature, soak for at least sixty minutes,
withdraw from the furnace and allow to cool in air. The second tempering should
be a repetition of the first.
Guide to Tempering Temperatures
TOOLS FOR LIGHT SHOCK APPLICATIONS
Hardness Rockwell C 60-63
Maximum wear resistance.
e.g. moulding dies, thin sheet punching dies.
Temper 190°-250°C.
MEDIUM DUTY APPLICATIONS
Hardness Rockwell C58-60.
e.g. slitting cutters, plate punching dies,
master hobbing tools, trimming dies,
cold extrusion dies.
Temper 500°/520°C.
MEDIUM TO HEAVY DUTY APPLICATIONS
Hardness Rockwell C55-58.
e.g. slitting cutters, shear blades, punching tools, forming tools, trimming
dies, cold extrusion dies,
bolt cutters.
Temper 520°/540°C.
HEAVY DUTY APPLICATIONS
Hardness Rockwell C52/56.
e.g. heavy shear blades, flying shears,
heavy plate punching tools and forming tools.
Temper 540°/560°C.
Final Grinding
Select the correct grade of wheel in consultation with the
grinding wheel manufacturer. Keep the wheel in good condition by means of a
suitable dressing tool. Wet grinding is preferable using a copious supply of
coolant. If dry grinding is resorted to, use a very soft wheel.
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