FATIGUE LIFE OF STEEL SPECIMENS 40KH AFTER WEAR-RESISTANT SURFACING WITH A SUBLAYER OF LOW-CARBON STEEL

摘要

The resistance to fatigue fracture of steel 40Kh after wear-resistant surfacing using PP-NP-25Kh5FMS flux-cored wire with a sublayer of a low-carbon plastic material formed by Sv-08A wire was investigated. The design of the deposited specimens and the procedure of their testing simulated the operating conditions of the mill rolls, for the surfacing of which PP-NP-25Kh5FMS flux-cored wire is widely used. A comprehensive procedure for evaluating the resistance of multilayer material to fatigue fracture included three stages: establishment of cyclic life of specimens after manufacturing surfacing; study of cyclic crack resistance of different metal layers; determination of fatigue life of specimens, which in the course of preliminary tests had fatigue cracks in the deposited layer after repair surfacing. It was established that the cyclic life of the specimens of carbon steel 40Kh, deposited using PP-NP-25Kh5FMS flux-cored wire with a sublayer of low-carbon steel 08kp (rimmed) exceeds the cyclic life of the specimens deposited without a sublayer, approximately by 2 times. The maximum values of SIF (140... 180 MPa√m) obtained on the specimens with a multilayer surfacing with a sublayer, are 2... 3 times higher than the maximum values of SIF obtained on the specimens without a sublayer, which indicates the feasibility of using a low-carbon sublayer to increase the crack resistance of a multilayer material with wear-resistant surfacing. It was shown that performance of repair surfacing according to the scheme of removal and a subsequent surfacing of only areas of the metal with fatigue cracks of long-term operating parts does not lead to a significant increase in the cyclic life after repair. This is related to the fact that after long operation, the defect-free layer of deposited metal has a significant level of accumulated fatigue damages. Therefore, to increase the efficiency of repair surfacing, it is recommended to remove not only the metal around the detected fatigue cracks, but the entire deposited layer to the depth of detected fatigue cracks with the subsequent restoration surfacing.