On the Rolling Contact Fatigue Test of Back-Up Roll Materials
1971 Volume 57 Issue 1 Pages 47-58
Details
1971 Volume 57 Issue 1 Pages 47-58
In order to know the spalling phenomena and to develop the material for back-up rolls, the rolling contact fatigue strength of the back-up roll materials is examined by using 3 high roll type rolling contact testing machine. The problems tested here are the effect of microstructure, of forging ratio, of direction of flow caused by hot working and of the surface defects on the resistance to spalling. The results obtained are as follows:
(1) The specimen with martensitic structure shows better rolling contact fatigue resistance than those with bainitic and pearlitic structures.
(2) The materials with high yield strength is good for back-up roll materials from the point of resistance to spalling.
(3) The effect of forging ratio on the resistance to spalling is very small; i. e. the resistance to spalling slightly deteriorates with increase of forging ratio, but this tendency is indistinct.
(4) On the surface where metal flows cross to this surface, resistance to spalling is brought lower than else where.
(5) Ghost spots behave as ductile part as same to matrix on the rolling contact surface.
(6) Surface layer of rolling contact is work hardened. Within this layer, matrix flows plastically in the direction of rotating direction.
(7) Initial crack of spalling generates on the surface and grows obliquely along the plastic flows and finally spalls by radial brittle fracture.
(8) Defects caused by casting workmanship, if they are located within the surface layer flown plastically, will become the source of crack initiation during rolling contact.
(9) The defects near the surface layer of the specimens make the resistance to spalling low, but it depends on the size and location of the defects.
(10) It is very difficult to apply the results of rotating bending fatigue test to those of rolling contact fatigue test.
From these results, it is suggested that the back-up rolls with high spalling resistance have martensitic microstructure, Vhigh yield strength and sound surface.
