Investigation on boronizing of N80 tube steel

Abstract

In present paper, boronizing was applied to N80 steel tube by pack boronizing, and its effect on mechanical properties, wear and corrosion of N80 tube steel was investigated. A dual-phase boride layer composed of FeB and F2B phases was formed on the surface of the steel substrate in a hardness range of 1 220-1 340 HV. A set-up was designed to reduce usage of the boriding agent and accelerate the pipe's cooling process after boronizing treatment. In order to meet the tensile properties of N80 steel required by API SPEC 5L, different cooling methods were employed including annealing, normalizing, fan-cooling and graphite-bar assisted rapid cooling. Among these methods, graphite-bar assisted rapid cooling resulted in the highest amount of pearlite in the steel substrate and the highest mechanical properties, satisfying the mechanical properties of API SPEC 5L. The boronized N80 steel exhibited an abrasive wear mechanism and showed a higher wear resistance under a given sliding condition due to the great hardness and integrity of the boride layer, and it also displayed an excellent corrosion resistance in both H 2S04 and HCI acid environments. © 2009 ISIJ.