Comparative analysis of the microstructure of the heat-affected zone metal in welding of high-strength steels

Abstract

To cite this article: M. Pirinen, Yu. Martikainen, S.Yu. Ivanov & V.A. Karkhin (2015) Comparative analysis of the microstructure of the heat-affected zone metal in welding of high-strength steels, Welding International, 29:4, 301-305,The welding of joints 8 mm thick in high-strength steels, produced by the quenching and tempering method and thermomechanical rolling with accelerated cooling, was investigated. It is shown that at the same strength of the steels (821 -835 MPa), the microstructure of the heat-affected zone (HAZ) greatly differs for the same welding conditions. The distribution of hardness in all zones of the welded joints was determined. The results show that in the steel produced by thermomechanical rolling with accelerated cooling, the softened zone of the HAZ is wider than in the steel produced by QT and equals 5 mm for two-pass arc welding.At the present time, high-strength steels are steels with a yield limit higher than 550 MPa [1]. There are three main methods of production of these steels: quenching and tempering (QT), thermomechanical rolling with accelerated cooling (or thermomechanically controlled processed [TMCP] steels) and direct quenching.The technological cycle of QT of steel includes initial hot rolling with cooling in air, heating to temperature Ac 3 followed by rapid cooling with water. The high cooling rates suppress the diffusion processes of formation of ferrite and pearlite, and this results in the formation of a mainly martensitic structure with low impact toughness. Subsequent annealing reduces the internal stresses and results in the required mechanical properties [2].In TMCP of steels, the optimum level of the mechanical properties is obtained by producing a microstructure with very fine grains. The controlled rolling parameters are carefully selected in relation to the thickness of the sheet and chemical composition. The conditions include the high degree of deformation in the temperature range of inhibited recrystallization, which results in marked refining of the final microstructure [3].Steels of the same strength grade may greatly differ in chemical composition and, consequently, the microstructure and mechanical properties of the HAZ. The mechanical behaviour of the HAZ determines the efficiency of the entire welded joint. Therefore, investigation of the microstructure and local mechanical properties of the HAZ metal in welding of high-strength steels is of interest for practice [4 -8].The aim of the present work is the analysis of the microstructure and hardness of the HAZ metal in arc welding of sheets of high-strength steels with a tensile strength of 821-835 MPa, produced by quenching and thermomechanical rolling with accelerated cooling.Two QT and TMCP steels greatly differ in the chemical composition (Table 1) but have similar mechanical properties (Table 2); 8 mm sheets with V-shaped edge preparation (angle 608, root face 1 mm, gap 1.5 mm) were welded with OK Autrod 12.51 wire with a diameter of 1.2 mm in a shielding gas (15% CO 2 and 85% Ar)

Evaluation of High Strength Cast Steel Welded Joints Suitable to Mooring Components

“…According to Kah et al [54], the welding of quenched and tempered steels is usually limited by the risk of cold cracking and the HAZ softening phenomena. The lower carbon and carbon equivalent contents permit the adoption of lower preheat temperatures to avoid cold cracking, while the HAZ softening is usually associated with microstructural changes such as the coalescence of the carbides at the subcritical region and/or the formation of upper, granular, or coalesced bainite and polygonal ferrite at the intercritical region of the HAZ are more sensitive in steels containing higher carbon contents [55]. In addition, nickel also exerts an important effect on hardenability [51,52].…”

Effect of weld on the mechanical properties of high strength and ultra-high strength steel tubes in fabricated hybrid sections

“…Indeed it has been shown that a quenched and tempered high strength steel compared to a thermomechanically processed high strength steel with same strengths and under similar arc welding conditions, possess different HAZ widths and microstructures [17]. Depending on the steel chemical composition, heat input in welding should be limited to a specific amount so the presence of carbides in the heat affected zone (HAZ) can be removed which increases the impact toughness of microstructure in this region [18].…”

“…Welding results in the formation of material softening at the Heat Affected Zone (HAZ) which is of decisive influence on the response of the structure. Various analytical and experimental analyses have been conducted on high strength steel plates to find the governing phenomenon in the behavior of high strength material affected by welding from a metallurgical point of view [14][15][16][17][18][19]. The HAZ microstructure depends on the steel material, type of weld, heat input during welding, and the post welding conditions.…”

Effect of heat input on the mechanical properties of welded joints in high-strength steels

“…The latter depends mostly on the heat input, weld geometry and the thermophysical properties of the metal. The results of comparative analysis of the microstructure of the HAZ metal in welding of high-strength steels were published in [1]. The dependence of the mechanical properties on the welding conditions was studied in [2 -5], but the effect of heat input has been studied insufficiently.…”