Effect of Boron on Liquid Zinc Induced Embrittlement in Heat Affected Zone of STKT590 Steel Tube for Power Transmission Tower

Abstract

This paper represents the effect of boron on liquid zinc induced embrittlement in the heat affected zone of STKT590. To determine the susceptibility toward liquid metal zinc induced embrittlement at a fracture time of 400s (S_LM-40), 64 kinds of carbon steel whose boron content was varied in 4 levels, have been tested by the notched-bar-tensile test method.
S_LM-400 is reduced linearly if a small amount of boron, less than 4 mass ppm, is added. In the case of more than 4 mass ppm of boron, S_LM-400 is minimized to 10 to 20%. Therefore, boron is considered to intensify liquid zinc induced embrittlement, because the ferrite ratio at the grain boundary is reduced.
Additionally, we reconsidered the JIS regression formula of carbon equivalent for susceptibility liquid zinc induced cracking (CEZ). As a result, a modified formula of CEZ was suggested to revise the JIS formula. This formula has been considered to be effective in predicting resistance to zinc induced cracking in large steel structures.