Effect of Microstructure Evolution on Mechanical Properties of 87Mnsi Steel Wire Rod for Bridge Cable

Abstract

 According to the abnormal fracture phenomenon of 87MnSi steel wire rod for bridge cable， the evolution of microstructure and mechanical properties during production processing were systematically analyzed. The results show that the microstructure of the rod is composed of pearlite and a small amount of proeutectoid ferrite， and the cementite lamellae are randomly distributed. After cold drawing， the cementite lamellae are rotated or fibrotic， and some cementite are broken and dissolved， the dissolution amount is 1.40wt.%（9.69%）. After ho-dip galvanizing， the dissolved cementite is spheroidized. In the process of cold drawing， hot-dip galvanizing and stabilization treatment， the microhardness of wire rod （329.8HV） increases （450.2HV） firstly， then decreases （447.9HV） and increases （474.8HV） finally. The cementite dissolved in the cold drawing process increases the hardness of the steel wire to 468.3HV， while the spheroidized cementite in the hot galvanizing process decreases the hardness to 439.8HV， and deteriorates tensile property. When the degree of spheroidization of cementite on the edge is obvious， the microstructure and mechanical properties of the steel wire inside and outside are greatly different， and the fracture is eventually caused by uneven force during stabilizing treatment.

Keywords

•  bridge cable； 87mnsi steel； hot-dip galvanizing； stabilizing treatment； fracture； cementite spheroidization