Dear respected fellows,
Need your valuable suggestions for annealing process temperature .
H13 tool steel with Aluminium chromium base coating used
for die casting dies.
for protection against decarburization you have to use vacuum or controlled atmosphere. heat to 845 to 900 depending on your specimen. higher temp for bigger sections. you have to heat your sample slowly and uniformly specially if it is a hardened tool and hold it from 1 to 4 hours by considering its section size then cool it slowly to 540 dont use higher cooling rates than 30 C degree per hour after 540 cooling rate will not effect your final hardness which will about 190 to 230 HB.
There are two annealing regimes for H13 and are used as per our requirements.
1. Soft annealing by heating to 850 deg.C holding for 1hour /inch followedby cooling @10 deg.C per hour to 500 deg.C and then air cool.
2. Stress relieve anneal by heating to 650 deg.C holding for 1 hour/inch thickness and then slow cooling to 500 deg.C and subsequently cooling in air.
In my opinion you shold use option 2 and use vacuum annealing furnace if available
When heat treating, vacuum furnace is suggested. If not used, except decarburization at surface (after quenching, first 0.5-1 mm low on carbon). Holding time when annealing should be at least 2 hours (depending on the dimensions).
When used for die casting, this kind of steel is first soft annealed (so it can be machined) at 850 C. Cooled 10 C per hour.
Then it is annealed for stress relief (stresses from machining). Cooled slowly to 500 C. Then it can be cooled by air.
Next it is quenched (step-heating, calculate carbon equivalent). It is usually cooled by air.
Immediately after quenching (when cooled to about 50 C) it should be annealed. Avoid temperatures from 400 to 550 C (reduction in toughness and retained austenite). About 600 degrees should be ok.
It is suggested to repeat the annealing process at least 2 times. Reasons are stress relief, achieving work hardness and dimensional stability when in exploitation.
To select the right temperature for achieving work hardness, consult hardness/tempering temperature diagrams (ask from material manufacturer).
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