Weld Metal Toughness Research Articles

Effect of the FCAW Welding Process and Post Weld Heat Treatment on the Properties and Microstructure of the Weld Joints of Heat Treated 4330V Steel

4330V is a high strength, high toughness, heat treatable low alloy steel for application in the oil, gas and aerospace industries. It is typically used for large diameter drilling parts where high toughness and strength are required. The research describes the effect of preheat temperature, interpass temperature, heat input, and post weld heat treatment on strength, hardness, toughness, and changes to microstructure in the weld joint. Welding with the lower heat input and no post weld heat treatment resulted in optimal mechanical properties in the weld metal. Austempering at 400 °C resulted in optimal mechanical properties in the HAZ. Increasing preheat and interpass temperature from 340 °C to 420 °C did not improve Charpy V-notch values or ultimate tensile strength in the weld metal or heat affected zones. The higher temperature increased the width of the heat affected zone. Austempering at 400 °C reduced HAZ hardness to a level comparable to the base metal. Both tempering and austempering at 400 °C for 10 hours reduced toughness in the weld metal.

Influence of microstructural aspects on impact toughness of multi-pass submerged arc welded HSLA steel joints

Multi-pass submerged arc welding was performed on the HSLA steels using multi-microalloyed electrodes in the present work, and three different heat input processes were employed to investigate the microstructure evolution and corresponding mechanical properties of weldments. The emphasis was placed on studying the influence of microstructure aspects on impact toughness of weld metal and HAZ with different heat inputs to reveal fracture micromechanism and to optimize the welding system. According to the experimental results, the acceptable welding parameters were ascertained for the studied steel to obtain a good balance of high strength and toughness welded joint. The optimal range of size distribution of non-metallic inclusion formed in the weld metal was determined and the essential causes of deteriorated HAZ toughness were revealed.

Effect of cooling rate on microstructure, inclusions and mechanical properties of weld metal in simulated local dry underwater welding

Quenched and tempered E550 steel was joined using flux-cored arc welding. The effect of cooling rate on microstructure, inclusions and mechanical properties of the weld metal was investigated by optical microscope, scanning electron microscope, transmission electron microscope and mechanical testing. Results show that weld metal microstructures consist of proeutectoid ferrite, ferrite side plate and acicular ferrite. As the cooling rate increased, the volume fraction of proeutectoid ferrite and ferrite side plate decreased, acicular ferrite increased accompanied with refined grain. Furthermore, inclusions of Ti, Mn oxide with diameter below 2.0μm were found in the weld metal and rapid cooling rate causes distinct Mn-depleted zone between inclusions and matrix. Excellent balance of high strength and toughness is obtained as more acicular ferrite in weld metal with rapid cooling rate. This can attribute to the increased of acicular ferrite with its refined grain and high density dislocation. These findings suggest that the rapid cooling rate can improve the impact toughness and tensile strength of weld metal in local dry underwater welding.

Characterization of the multi-pass weld metal and the impact of retained austenite obtained through intercritical heat treatment on low temperature toughness

In this study, we explore the relationship between the microstructure and low temperature toughness of weld metal obtained from a real multi-pass weld joint (up to 55mm) by submerged arc welding, which was developed for high strength (yield strength over 550MPa) and heavy wall pipe fitting applications with composition of 0.1wt% C, 2.0wt% Mn and other micro-alloys. The study indicated that the necklace-type coarse martensite–austenite (M–A) constituent formed in the interlayer heat affected zone (IHAZ) of weld metal was responsible for low impact energy of 39J at −40°C. To enhance the toughness, conventional tempering and new intercritical heat treatment were designed. The results suggested that there was insignificant effect on toughness through conventional tempering, but obvious improvement through combination of quenching plus intercritical annealing and tempering. The impact energy was increased to ~98J. The microstructure that benefit toughness primarily comprised of intercritical lath-like ferrite or acicular-type ferrite, bainite/martensite, and fine acicular retained austenite, with average size of ~0.3μm. Retained austenite with volume fraction of ~6% was formed by the enrichment of Mn and Ni in reversed austenite during intercritical tempering process.

Effect of heat input on cryogenic toughness of 316LN austenitic stainless steel NG-MAG welding joints with large thickness

Abstract In this paper, Narrow Gap Metal Active Gas (NG-MAG) arc welding system was introduced, aiming at efficiently jointing AISI 316LN thick plate used in International Thermonuclear Experimental Reactor (ITER) device. Effect of heat input on cryogenic impact toughness of the WM was investigated and suitable welding parameters were explored to optimize the cryogenic toughness of weld metal (WM) and avoid weld defects simultaneously. Impressively, the maximum low temperature toughness of the NG-MAG arc welded WM could reach more than 100 J, which could be comparable with that of the Tungsten Inert Gas (TIG) arc welded WM. More importantly, the NG-MAG arc welding showed much higher efficiency than the counterpart TIG. The less compositional segregation, and smaller dendrite size due to the lower level of heat input in NG-MAG arc welding were believed to play the critical role in enhancing the cryogenic toughness.

Effect of Long-Term Post-Weld Heat Treatment on the Microstmeture and Mechanical Properties of P91 Weld Metal

Modified 9Cr-lMo (P91) steel is used in fossil-fuel fired power plants due to its good thermo-physical, weldability, fabricability and high temperature mechanical properties. Toughness of the P91 weld metal, deposited by the shielded metal arc welding (SMAW) process, is reported to be lower than that deposited by the gas tungsten arc welding (GTAW) process. In spite of this, considering the higher deposition rate and economics, the SMAW process is very popular in industry. Thus, achieving adequate toughness in the P91 weld metal deposited using the SMAW process is an important requirement to qualify the weld joints. Weld joints were prepared using the SMAW process and subjected to post-weld heat treatment (PWHT) at 760°C for durations of 3, 10 and 100 hours. Microstructural observations revealed coarsening of the lath martensite and the precipitates accompanied by an increase in toughness with increase in PWHT duration from 3 to 10 hours. The effect of PWHT duration on subzero toughness was found to be significant, with the subzero toughness increasing with increase in PWHT duration upto 10 hours and then decreasing on PWHT for 100 hours. Increase in sub-zero toughness could be attributed to adequate tempering, while the decrease in toughness on PWHT for 100 hours was attributable to the formation of fresh martensite during cooling from the PWHTtemperature. This variation of toughness of the SMA weld metal with duration of PWHT needs better understanding from the view point of the composition of the weld metal. Detailed microstructural analysis was carried out to understand the reasons for the variations in the mechanical properties. This paper presents and discusses the results of this experimental investigation.

English

Reinforcement strength, ductility and bendability properties are important components in design of reinforced concrete members, as the strength of any member comes mainly from reinforcement. Strain compatibility and plastic behaviors are mainly depending on reinforcement ductility. In construction practice, often welding of the bars is required. Welding of reinforcement is an instant solution in many cases, whereas welding is not a routine connection process. Welding will cause deficiencies in reinforcement bars, metallurgical changes and re-crystallization of microstructure of particles. Weld metal toughness is extremely sensitive to the welding heat input that decreases both of its strength and ductility. For determining the effects of welding in reinforcement properties, 48 specimens were tested with 5 different bar diameters, divided into six groups. Investigated parameters were: properties of un-welded bars; strength, ductility and density of weld metal; strength and ductility reduction due to heat input for bundled bars and transverse bars; welding effect on bars’ bending properties; behavior of different joint types; properties of three weld groove shapes also the locations and types of failures sections. Results show that, strength and elongation of the welded bars decreased by (10-40%) and (30-60%) respectively. Cold bending of welded bars and groove welds shall be prevented.

Influence of PWHT on Toughness of High Chromium and Nickel Containing Martensitic Stainless Steel Weld Metals

Commonly used 12.5Cr-5Ni consumable specified for welding of martensitic stainless steels is compared with newly designed 14.5Cr-5Ni consumable in terms of their suitability for repair welding of 410 and 414 stainless steels by gas tungsten arc welding process. Changes in microstructure and austenite evolution were investigated using optical, scanning electron microscopy, X-ray diffraction techniques and Thermo-Calc studies. Microstructure of as-welded 12.5Cr-5Ni weld metal revealed only lath martensite, whereas as-welded 14.5Cr-5Ni weld metal revealed delta-ferrite, retained austenite, and lath martensite. Toughness value of as-welded 12.5Cr-5Ni weld metal is found to be significantly higher (216 J) than that of the 14.5Cr-5Ni weld metal (15 J). The welds were subjected to different PWHTs: one at 923 K (650 °C) for 1, 2, 4 hours (single-stage PWHT) and another one at 923 K (650 °C)/4 h followed by 873 K (600 °C)/2 h or 873 K (600 °C)/4 h (two-stage heat treatment). Hardness and impact toughness of the weld metals were measured for these weld metals and correlated with the microstructure. The study demonstrates the importance of avoiding formation of delta-ferrite in the weld metal.

The impact of heat input on the strength, toughness, microhardness, microstructure and corrosion aspects of friction welded duplex stainless steel joints

The impact of heat input on mechanical aspects like joint strength, toughness, microhardness and metallurgical and corrosion characterization of UNS S31803 duplex stainless steel (DSS) in solid state continuous drive friction welding was studied. The experiments were carried out according to Design of Experiments (DOE) with L9 orthogonal array by varying the four different parameters namely friction pressure, friction time, upsetting pressure and upsetting time, keeping spindle speed as constant. Detailed analysis of fracture morphology, presence of elements and its distribution on joint zone were performed through scanning electron microscopy (SEM) attached with energy dispersive spectroscopy (EDS). No intermetallic phases were observed by X-ray diffraction (XRD) technique. Tensile strength results showed that higher the heat input the better was the preservation of joint strength. At room temperature, toughness decreased as heat input increased. At −100°C and −196°C, toughness of weld metal was comparatively higher than other fusion processes. Microhardness increased with an increase in heat input due to grain refinement. In addition, the corrosion behavior of the weld metal was also evaluated through potentio-dynamic polarization curve. Corrosion resistance of weld was better than that of base material and it is increased with an increase in the heat input.

Effect of the Temperature of Post Weld Heat Treatment on Microstructure and Performance of Weld Metal for 1 000 MPa Grade High Strength Steel

1 000 MPa high-strength steel plates for construction machinery are welded by metal active gas(MAG) welding method with GHS90 welding wire as filler material and the weld joints are treated at 250 ℃, 480 ℃, 600 ℃ for 2 h, respectively. Microstructure and mechanical properties of welded joints with different post weld heat treatment(PWHT) is analyzed by tensile test, microhardness measurement, optical microscope(OM), scanning electron microscope(SEM), transmission electron microscopy(TEM) and electron back-scattered diffraction(EBSD). The results show that with the increase of PWHT temperature from 250 ℃ to 600 ℃, the average strength of welded joint reduces from 1 014.5 MPa to 934.5 MPa and the average –20 ℃ impact absorbing energy of weld metals decreases from 66 J to 24 J. With higher PWHT temperature, larger bainitic lath and coarser carbide precipitates result in lower toughness of weld metal. Meanwhile, the size of effective grains becomes larger and the density of high-angle grain boundary is decreased, which led to the degradation of impact property of weld metal.

An Investigation on Effect of Process Parameters on Weld Bead Profile of Modified 9Cr-1Mo Steel by Pulsed GMAW

Environmental regulations requiring reduced C02 emissions coupled with demand for greater efficiency are demanding greater use of advanced creep resisting steels such as modified 9Cr-lMo (P91) for high temperature components in the power generation industry. Traditionally, modified 9Cr-lMo steels are welded using gas tungsten arc welding, shielded metal arc welding and submerged arc welding processes. In order to reduce costs and downtime, particularly for site repairs, recently there is much interest in the use of high productivity welding processes; particularly gas shielded welding processes such as Gas Metal Arc Welding (GMAW). However, the situation with GMAW, particularly with active gas mixtures, is more complex because of the variable recovery of key elements such as Mn, Si, and Nb/Cb. It has been reported that the solid wire Gas Metal Arc Welding (GMAW) process has not found widespread use in the industry mainly due to concerns over lack-of-fusion, sensitivity to welder error and demands for more sophisticated power sources. However, in recent past, as a process of potentially high productivity, interest in GMAW for welding P91 materials is increasing for Industrial applications. In the present investigation, bead-in-groove trials are performed on a 12mm thick modified 9Cr-lMo material by pulsed current gas metal arc welding (GMAW-P) process. Two primary parameters like current and weld travel speed are considered in the present experiment and their effect on weld bead geometry, weld metal toughness and weld metal microstructure are discussed. The samples are also subjected to chemical analysis, oxygen content measurement, and inclusion level&hardness survey after PWHT. Response surface methodology (RSM) design approach is used to develop a mathematical relation between the input variables (current and speed) and responses. The developed model is then compared with the experimental results; it is found that the deviation falls within the limit of a 95% confidence level. The direct and interactive effects of the process parameters are also discussed in the present paper.

An investigation on microstructure and properties of dissimilar welded Inconel 625 and SUS 304 using high-power CO2 laser

Microstructure and properties of laser deep penetration welded Inconel 625 nickel-based alloys and SUS304 stainless steel were investigated. Weld microstructures, room temperature tensile properties and stress rupture properties, impact toughness, and hardness of dissimilar welded joints were evaluated. The experimental results showed that the microstructure of fusion zone near the fusion line in the SUS304 side was mainly cellular, whereas that near the fusion line in the Inconel 625 was predominantly columnar dendrites. Laves phases were precipitated at the grain boundary of cellular and in the interdendritic regions of fusion zone in the different form. The white transition layer was generated, and the signification change of concentrations was occurred at the fusion boundary between weld metal and SUS304. The microstructure at the fusion boundary between weld metal and Inconel 625 was characterized by dendritic boundary melting and thickening and accompanied with a lot of Laves phases precipitated in the interdendritic regions. The tensile strength tests indicated that the dissimilar butt joints ruptured in the fusion zone. The toughness of dissimilar weld metal was declined sharply compared to the two base metals. Fractographic analysis revealed that segregation of Nb and Mo in the interdendritic regions deteriorated the tensile strength and toughness of laser dissimilar weld metal. The corrosion resistance of weld metal was higher than that of SUS304 as a considerable amount of Mo elements in the weld metal inhibiting the generation and development of pitting corrosion.

LPG선 탱크용 FH 강재 FCAW 용접금속의 인장성질과 충격인성에 미치는 후열처리의 영향

This paper has an aim to study the effect of PWHT and its conditions(peak temperature and holding time) on the tensile properties and impact toughness of FCAW weld metal in relation to microstructure. Impact toughness was evaluated to apply the cargo tank of liquified gas carriers under the various PWHT condition of each class societies. On the basis of these study, it was found that PWHT conditions within all class societies affect charpy absorbed energy of weld metal little or no, all PWHT weld metals kept similar level of charpy absorbed energy as as-weld weld metal down-to <TEX>$-60^{\circ}C$</TEX> and finally indicated lower energy value than that of as-weld weld metal at <TEX>$-75^{\circ}C$</TEX>. It is because the precipitation of 2nd phase was controlled from welding consumable and the grain size was grown by PWHT.

Effect of chemical composition on microstructure and mechanical properties of laser weld metal of high-tensile-strength steel

Laser beam welding (LBW) and laser-arc hybrid welding are expected to be applied to welding of high-strength steel plates over 780 MPa, because they have advantages such as low distortion and a narrow heat-affected zone. This research examined the relationship between the chemical composition of high-strength steel plates and the microstructure and mechanical properties of the weld metal with the aim of improving the toughness of welded joints of high-strength steels by the LBW process. The results revealed that weld metal toughness is strongly dependent on the carbon (C) content of the steel plates, and excellent toughness can be obtained in weld metals with low C contents having an almost fully lower bainite structure without formation of slender martensite austenite constituent (MA). Based on these results, a guideline for appropriate alloying element design for high-strength steels for LBW was proposed, targeting mechanical properties of tensile strength ≥980 MPa and toughness vE−40 °C ≥ 47 J.

Effect of microstructural heterogeneities on scatter of toughness in multi-pass weld metal of C–Mn steels

Often, scatter in mechanical properties of multi-pass steel weldments is qualitatively attributed to the underlying heterogeneous microstructure brought about by spatial variations of multiple thermal cycles. In this research, a method for quantitative heterogeneity calculation based on measured variations of microstructure and hardness throughout the multi-pass weld metals including various reheated regions was explored. Published data from multi-pass welds with controlled titanium additions (7–32 wt ppm) were correlated to comprehensive microstructure characterization. The scatter in 7 wt ppm Ti steel welds was larger than that of 32 wt ppm Ti steel welds. This change in scatter is correlated to spatial distributions of microstructural heterogeneity parameter, rather than the average value of heterogeneity parameter for the whole weldment.

Mechanical properties of similar and dissimilar weldments of RAFMS and AISI 316L (N) SS prepared by electron beam welding process

Effect of weld metal composition on microstructure and toughness of weld metal is studied in this paper. Weld joints of reduced activation ferritic/martensitic (RAFM) steel containing 1.0 and 1.4wt.%W were prepared using electron beam welding (EBW) process. Dissimilar weld joints between 1.0wt.%W RAFM steel and AISI 316L (N) SS were also prepared using EBW process. The effect of post weld heat treatment (PWHT) temperatures on microstructure and mechanical properties was also studied. Microstructural observation reveals delta–ferrite in 1.4wt.%W containing weld metal, which is absent in 1.0wt.%W weld metal. In the case of the dissimilar weld metal, microstructure shows presence of lath martensite and retained austenite. Austenite was stable even after PWHT and its presence is attributed to high nickel (5–6wt.%) content in the dissimilar weld metal. Hardness of RAFM steel weld metal was found to be 270–290 VHN after PWHT at 750°C for 2h. Impact toughness of both 1.0 and 1.4wt.%W RAFM steel is high (>250J) at ambient temperature. However, after PWHT, variation of toughness with temperature is more drastic for 1.4wt.%W RAFM steel weld metal than the other. As a result, ductile brittle transition temperature (DBTT) for the 1.4wt.% steel weld metal is close to 0°C while that of the 1.0wt.% W steel is close to that of the base metal (∼−80°C).

How Specimen Geometry and Microstructure Influence Fracture Toughness Properties of Ferritic Materials

Abstract This article identifies several factors that are not fully addressed in most fracture toughness test standards and explains how they may influence calculated values obtained from ferritic steels. Of particular consequence are test temperatures within the ductile-to-brittle transition regime and test specimen geometries when measuring the toughness of weld metal and heat-affected zones.

Investigation of Microstructural Features Determining the Toughness of 980 MPa Bainitic Weld Metal

The microstructural features that control the impact toughness of weld metals of a 980 MPa 8 pct Ni high-strength steel are investigated using instrumented Charpy V tester, optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM), electron back-scattered diffraction (EBSD), and finite-element method (FEM) calculation. The results show that the critical event for cleavage fracture in this high-strength steel and weld metals is the propagation of a bainite packet-sized crack across the packet boundary into contiguous packets, and the bainitic packet sizes control the impact toughness. The high-angle misorientation boundaries detected in a bainite packet by EBSD form fine tear ridges on fracture surfaces. However, they are not the decisive factors controlling the cleavage fracture. The effects of Ni content are essential factors for improving the toughness. The extra large cleavage facets seriously deteriorate the toughness, which are formed on the interfaces of large columnar crystals growing in welding pools with high heat input.

Effect of Ti on the Microstructures and Toughness of TMCP-600 Steel Weld Metals

The Ti addition effect on the characteristics of weld metal, such as impact energy, microstructure and nonmetallic inclusions, was investigated to develop a suitable gas metal arc welding wire for the high strength of TMCP (Thermo Mechanical Control Process)-600 steel. The fraction of acicular ferrite which was known to be a favorable weld metal microstructure for toughness was increased with Ti content from 0.002% to 0.025%, The impact energy of weld metal was increased whereas the ductile to brittle transition temperature was decreased with increasing Ti content. The size of nonmetallic inclusion was decreased while the density of inclusions was decreased with increasing Ti content. It was found that Ti content on the weld metal toughness had a plus effect by increasing the fraction of acicular ferrite in the weld metal microstructure.

Study for TIG–MIG hybrid welding process

Tungsten inert gas (TIG) and metal inert gas (MIG) welding are the most popular gas-shielded arc-welding processes used in many industrial fields. MIG welding is a high-efficiency process compared to TIG welding. However, improvements are needed to reduce spatter and improve weld metal toughness. Although pure argon shielding gas is desirable for weld metal toughness, MIG arcs are unstable in pure Ar to the extent that executing welding is difficult. We have found that MIG arcs become stable even using pure argon by simply using a hybrid TIG and MIG system. This process has the possibility of becoming a new welding process giving high quality and efficiency. In this study, we investigate the influence of the balance of current between the TIG and MIG arcs, which is most important in determining arc stability and arc penetration. We have confirmed the suitable range of conditions both experimentally and through numerical simulation and have applied this process for butt and fillet joints. We show that the welding time can be reduced to 17 ~ 44 % of the time required using a conventional TIG process.