Factors influencing the occurrence of Zinc Induced Cracking in square steel pipe

Abstract

A roll forming type square steel pipe (BCR) has high sensitivity than a press forming type square steel pipe (BCP) to Zinc Induced Cracking (ZIC) . ZIC is observed at the corner showing the initiation site at inner side. Some factors are estimated to control the occurrence of ZIC, plastic strain, residual stress at inner side, and free C and⁄or free N of steel. At heating process to galvanizing temperature, the corner of pipe becomes brittle due to the strain aging. Micro crack is easily initiated under the condition if yield stress exists. BCR has high residual stress equal to yield stress that can initiate micro crack. BCP has low residual stress that is not sufficient to initiate micro crack.