Abstract: Networked cementite and martensite abnormal microstructure appeared in the core of 82B high carbon steel hot rolled wire rods of a steel plant. The formation causes of the abnormal core microstructure were analyzed by chemical composition analysis, metallographic examination, scanning electron microscopy analysis and other methods. The results show that the martensite in the core of 82B high carbon steel hot rolled wire rods is due to the intragranular micro-positive segregation of manganese and chromium alloy elements in the core of the billet, and the fast cooling rate of martensite formation period after rolling. The occurrence of core networked cementite is due to the presence of severe macro-positive segregation of element carbon in the core of the billet, and the slow cooling rate of sorbate formation period after rolling. After several process trials and improvements of rolling process and cooling process after rolling, the core martensite was eliminated and the probability of existence of networked cementite was also reduced.