FATIGUE LIFE OF SPECIMENS AFTER WEAR-RESISTANT, MANUFACTURING AND REPAIR SURFACING

摘要

Cyclic fatigue life of specimens surfaced by flux-cored wire PP-Np-25Kh5FMS that provides a deposited metal of the type of tool semi-heat-resistant steel was studied. Design of the deposited specimens and procedure of their testing simulated the operating conditions of mill rolls, for surfacing of which flux-cored wire PP-Np-25Kh5FMS is widely used. Cyclic fatigue life of the specimens directly after surfacing, as well as the effectiveness of application of repair surfacing were evaluated to increase the residual cyclic fatigue life of the specimens, in which preliminary testing revealed fatigue cracks in the deposited wear-resistant layer. The numerical method was used to determine the stress-strain state and calculate the stress intensity factor on the front of a nonthrough corner fatigue crack that propagated in a specimen of 40Kh steel with a wear-resistant deposited layer at a three-point zero-to-load cyclic loading. It is shown that the maximum values of the stress intensity factor along the crack front are located at approximately 1 mm distance from the vertical side face in the deepest point of the crack front and during fracture they reach the value of 52-64 MPa√m. During investigations it was shown that application of repair surfacing to the products with fatigue cracks after their long-term service does not result in a significant extension of their cyclic fatigue life after repair. This is related to the fact that after long-term service the defect-free layer of the deposited metal has a considerable level of accumulated fatigue damages. That is why performance of repair of the product region damaged by a fatigue crack, is not effective without a complete removal of the deposited metal layer. The results obtained in this work will be further used as base ones during performance of comparative assessment of the impact of surfacing technique and technology, as well as surfacing materials, on the fatigue life of specimens.