| After solidification Ni-hard, the effects of cooling rate on abrasive wear resistance are investigated. When most of retained austenite is transformed to bainite by tempering, the change of abrasive wear resistance is also investigated. The heardess of Ni-hard increases with increasing the temperature from which slow cooling begins. But the hardness remains at the maximum value even though the temperature gets over about 650℃. This may mean that when the temperature is about 650℃ or above, the carbon concentration of austenite comes to be near equilibrium. By tempering, retained austenite is transformed to bainite and hardness is increased. But the wear resistance of this transformed Ni-hard is lower than that of original one. It may be because of the fact that the transformed Ni-hard has much less retained austenite to be transformed to martensite by wear at abrading surface than original one. Using scratch test, the effect of grain size to wear resistance was investigated. As a result, the existing abrasive formula may be modified as follow: V= (K"W·L/H)·1/N^¼ N : numoer of carbide or aggregate grains in a unit area of wear surface. |
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