Abstract
Forged steel rolls for 4-high cold reversing mill (work roll dia. 16 1/2") were practically investigated on the standpoint of roll users. The authors checked the hardening depth curves of work rolls (about 200 rolls) for several years by Shore hardness tester.
These curves were estimated by their individual rolling condition, that is, production tonnage, difficulties of rolling operation, quantities of surface cracks during operation, etc.
As a conclusion, the hardness depth curves of bad rolls have a different type from that of good rolls. These bad rolls extremely softenat the point of 5-`6mm from the original roll surface.On the other hand, the hardness of good rolls decrease linearly from their surfaces. Then, the authors investigated the surface structures of rolls by means of electron microscopic method, and could classify them in the following three groups.
A group: martensite matrix+0.5-2μ cementite particles.
B group: martensite matrix. with net structure+cementite. particles.
C group: No cementite particle structure (martensite and austenite.)
The authors compared these structures with their practical rolling results. B and C groups, especially C group, were not suitable for good rolling operation. Furthermore, both structures before rolling and after rolling on the same position of the roll were checked. Each group of roll structures has not been changed to another group during rolling operation
