SPECIFIC FEATURES OF THE GROWTH OF FATIGUE CRACKS IN 36G2S STEEL OF DRILL PIPES AFTER THE RECOVERY HEAT TREATMENT

摘要

We study the influence of repeated normalization of operating 36G2S steel of drill pipes on their structure, fatigue-cracks growth, and fractographic features of fracture. It is shown that the crack-growth rate decreases and brittle elements in the fracture surfaces disappear after the removal of the texture of ferritic precipitates and carbides from grain boundaries as a result of the repeated heat treatment of steel. At the same time, 5% of all investigated specimens do not exhibit any positive influence of the recovery heat treatment on the fatigue crack growth rate in the operating metal, which means that it is reasonable to perform the preliminary (prior heat treatment) control of the engineering state of the metal according to the parameters sensitive to scattered damage.