Electric-resistance-welded steel pipe for boiler having excellent stress corrosion cracking resistance, and method for manufacturing same

Abstract

Provided is an electric-resistance-welded steel pipe for a boiler, having excellent stress corrosion cracking resistance, and in which ferrite grain boundary strength of a weld part is increased, andcracking in the weld part is suppressed. The component composition of the present invention includes, in terms of mass%, 0.05-0.35% C, 0.10-0.35% Si, 0.25-1.50% Mn, 0.035% or less of S, 0.035% or lessof P, 0.005-0.050% Al, 0.010% or less of N, and 0.010% or less of O, and furthermore includes, optionally and selectively, at least one of 1.00% or less of Cr, 1.00% or less of Mo, 2.00% or less of Ni, 2.00% or less of Cu, 0.0030% or less of B, 0.20% or less of Nb, 0.20% or less of V, 0.20% or less of Ti, 0.0050% or less of Ca, and 0.0050% or less of Mg, the remainder being Fe and unavoidable impurities, the difference between the hardness at an outermost layer of a base material part and the hardness at a position at a depth of 1 / 2 the thickness of the base material part being 20 Hv or less,and the difference between the hardness of a welding abutment part to an extent 1 mm from an outer surface and the hardness of the base material part to an extent 1 mm from the outer surface being 20Hv or less.

Description

technical field [0001] The present invention relates to an electric-resistance-welded steel pipe for boilers having excellent stress corrosion cracking resistance on the outer surface of the steel pipe. Moreover, this invention relates to the manufacturing method of such an electric resistance welded steel pipe. Background technique [0002] Boiler piping made of carbon steel heat transfer tubes is sometimes used in nitrate environments, etc. Therefore, such boiler piping may be damaged by stress corrosion cracking caused by ammonium nitrate. Therefore, stress corrosion cracking resistance (hereinafter sometimes referred to as "SCC resistance") is required for the boiler piping. [0003] Damage to boiler piping due to NO in the exhaust when starting up the plant 2 , NH 3 Ammonium nitrate caused by condensed water dissolved on the piping, and tensile residual stress caused by bending and fin welding are the causes, and these factors are complementary to each other. [00...

AI Technical Summary

Problems solved by technology

In such a case, there is a high possibility that SCC will occur in the boiler piping during plant operation, and the piping may burst depending on the situation.

Images