| Spherodization and cold forgeability of 4140 steel have been studied by two stage heat-treatments. The temperatures of the first stage heat-treatment (T-1) were 740℃ and 760℃, which are a little above A_I point and A_(CI) point, respectively. The second stage (T-2) heating temperature was 700 ℃. Heating times were varied at these temperatures. The cooling rate from T-1 to T-2 temperature was 300 ℃/h, which is relatively high speed. Lamellar carbides were not formed during the fooling stage from T-1 to T-2 temperature, when the T-1 temperature was 740℃. This result is contrary to other authors` results. They found the lamellar carbides when the cooling rate from T-1 to T-2 is not low. However, the lamellar carbides were produced at this stage when T-1 temperature was 760℃. Among the two stage heat-treatments studied, the T-1 treatment at 740℃ for 3 hours was the most effective process for the spherodization and cold forgeability, not much depending on the T-2 treating times. |
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