| A thorough examination has been carried out on the change of microstructure and hardness of cold-worked modified Hadfield steel by isothermal heating, from which the following conclusions could be drawn. 1) Precipitation of the carbide and pearlitic constituents was promoted considerably by cold-working. 2) Carbide precipitation occurred, when cold-worked modified Hadfield steel was reheated, in the temperature range between 270 and 940℃. This precipitation took place most rapidly between 500 and 850℃. Formation of pearlitic constituents was restricted to the temperature range 380-760℃, and was the most rapid in the vicinity of 650℃. 3) Formation of the carbide was preferentially preceded on the slip line in the lower temperature range, but with the increase in temperature and heating time, it was found both on the grain boundary, and slip line. On further increase in temperature, the carbide was spheroidized. 4) Increased amounts of transformation products led to higher hardness with a maximum of about Hv 470 obtained on heating at 550℃ for 100 hours. A more effective hardner contributing to the maximum hardness appeared to be acicular carbide rather than pearlitic constituents. |
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