| Budget Amount *help |
¥1,800,000 (Direct Cost: ¥1,800,000)
Fiscal Year 1992: ¥400,000 (Direct Cost: ¥400,000)
Fiscal Year 1991: ¥1,400,000 (Direct Cost: ¥1,400,000)
|
|---|
| Research Abstract |
Rolling technologies of steels today have been developed to save energy and to provide high quality products. Rolling conditions have become much severer and this has resulted in strong demands for improving qualities of rolls, especially their durability. Many types of rolls have been developed in response to this request.
High chromium cast irons have been widely used as hot working rolls. The most significant reason for the good wear resistance of these cast irons is the presence of hard chromium carbides embedded in a matrix of martensite or austenite. Carbides in the microstructure, depending on their type, morphology and volume fraction, provide the hardness required for application without degradation. Addition of molybdenum in high chromium cast irons causes the formation of Mo_2C which crystallize in finely dispersed form as an eutectic at a final stage of solidification. These finely dispersed Mo_2C carbides bring about very good resistivity for high temperature rolling wear.
In the present paper, by adding molybdenum up to 10 mass% in 20 mass% Cr cast irons, microstructure, solidification and transformation behaviors, mechanical properties and wear characteristics were discussed. Mo_2C was formed as an eutectic at a final stage of solidification of high Cr cast iron containing Mo. These finely dispersed carbides which are harder than Cr_7C_3 are expected to give good wear resistivity of hot rolls. The effect of addition of Mo up to 10 mass% in 3 mass% C-20 mass% Cr irons are investigated. With increasing Mo content, tensile strength and fracture toughness decrease monotonically, and hot wear resistivity increases. These effects can be explained by the amount of Mo_2C. Fine carbides of Mo_2C provide crack initiation and growth sites to cause fracture. However they can prevent the propagation of wear cracks. Eutectic carbides should be controlled within about 35 vol% considering a balance between mechanical properties and wear resistivity.
|
