Quantitative Correlation between Thermal Cycling and the Microstructures of X100 Pipeline Steel Laser-Welded Joints

Abstract

Due to the limitations of the energy density and penetration ability of arc welding technology for long-distance pipelines, the deterioration of the microstructures in the coarse-grained heat-affected zone (HAZ) in welded joints in large-diameter, thick-walled pipeline steel leads to insufficient strength and toughness in these joints, which strongly affect the service reliability and durability of oil and gas pipelines. Therefore, high-energy-beam welding is introduced for pipeline steel welding to reduce pipeline construction costs and improve the efficiency and safety of oil and gas transportation. In the present work, two pieces of X100 pipeline steel plates with thicknesses of 12.8 mm were welded by a high-power robot laser-welding platform. The quantitative correlation between thermal cycling and the microstructure of the welded joint was studied using numerical simulation of the welding temperature field, optical microscopy (OM), and scanning electron microscopy (SEM) with energy-dispersive spectroscopy (EDS). The results show that the heat-source model of a Gaussian-distributed rotating body and the austenitization degree parameters are highly accurate in simulating the welding temperature field and characterizing the austenitization degree. The effects of austenitization are more significant than those of the cooling rate on the final microstructures of the laser-welded joint. The microstructure of the X100 pipeline steel in the HAZ is mainly composed of acicular ferrite (AF), granular bainite (GB), and bainitic ferrite (BF). However, small amounts of lath martensite (LM), upper bainite (UB), and the bulk microstructure are found in the columnar zone of the weld. The aim of this paper is to provide scientific guidance and a reference for the simulation of the temperature field during high-energy-beam laser welding and to study and formulate the laser-welding process for X100 pipeline steel.

Development of Laser Welding and Surface Treatment of Metals

“…This Special Issue, entitled “Development of Laser Welding and Surface Treatment of Metals”, is a complementary and valuable resource of knowledge in the following fields: Study of technological conditions of laser welding, investigation of test joints properties [ 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 ]; Analytical and numerical models of heat sources of laser beam and arc welding processes [ 19 , 20 , 22 , 23 ]; Study of laser cladding and investigations of the coating’s properties and tribological characteristics [ 27 , 28 , 29 , 30 , 31 , 32 , 33 ]; Study and development of fusion welding processes, investigation of properties of the deposit produced under forced cooling or underwater conditions [ 34 , 35 , 36 ]; Study of cladding, surfacing, and thermal spraying processes of wear-resistant coatings, characterization of the coatings [ 37 , 38 , 39 ]; Study of application of local strengthening of the thin-walled structure by laser treatment [ 40 ]. …”

“…Study of technological conditions of laser welding, investigation of test joints properties [ 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 ];…”

Investigation of Weld Root Defects in High-Power Full-Penetration Laser Welding of High-Strength Steel

“…Laser welding has become a mature process of fabricating thin components in some manufacturing sectors, such as the automotive sector. Currently, high-power lasers (10–100 kW) are available for welding, which is of considerable interest for the joining of thick components, such as shipbuilding, power plants, pressure vessels, high-speed trains, lifting equipment, wind power towers, and oil/gas pipelines [ 3 , 4 ]. However, defects frequently occur in the welding of thick components using a high-power laser.…”

Effect of Welding Heat Input on Microstructure and Impact Toughness in the Simulated CGHAZ of Low Carbon Mo-V-Ti-N-B Steel

“…Coarse grains formed in the CGHAZ at a peak temperature of 1320 • C or higher [7][8][9][10][11]. In CGHAZ, austenite grains coarsened and brittle structures, such as a M/A constituents, coarse-grain boundary ferrite, and granular bainite, formed in the grains and significantly deteriorated the toughness [11][12][13][14]. This reduction is particularly serious in high heat inputs.…”