Increase Of Welding Heat Input Research Articles

Influence of heat input on temperature and stress field of X80 steel pipeline cirumferential weld using type-B sleeve repairing

Abstract The multi-pass fillet welds of casing pipe were welded onto the in-service pipeline, which is widely used in pipeline repairs. However, the influence of welding heat input of B-type sleeve circumferential fillet weld on the temperature and stress field at the pipe circumferential weld is still unclear. In this paper, a double ellipsoid heat source model is developed to investigate the weld temperature field, residual stress field, and deformation field of the repair welding in service. The results show that the increase of weld heat input can effectively increase the size of the weld pool and the size of the high-temperature zone of the B-type sleeve circumferential fillet weld. And the peak temperature of the inner wall of the pipe girth weld increases with the increase of welding heat input of the sleeve circumferential fillet weld. The axial stress peak of the inner wall of the pipe girth weld reduces with the increase of welding heat input of sleeve circumferential fillet weld, and the axial deformation peak of the inner wall of the pipe girth weld increases first and then decreases with the increase of welding heat input of sleeve circumferential fillet weld.

Effect of Weld Design of Transition Layer on Microstructure and Properties of Welded Joints of S32304/Q390C Composites

Due to the large difference in physical and chemical properties between the substrate and the cladding material, the welding of composite materials is much more difficult than that of single materials. In our work, S32304/Q390C composite material was considered as the research object. By adjusting the welding parameters, two kinds of joint geometry were obtained, namely, the transition layer weld lower (joint A) and higher the composite material interface (joint B). We studied the influence of the transition layer weld on the microstructure and properties of welded joints. The microstructure of the transition layer weld, the distribution of elements, the Schmidt factor of the interface between the transition layer and base layer weld, and the tensile strength of the joint were evaluated. The results show that with the increase of welding heat input, the microstructure of the transition layer weld changes from austenite and skeleton ferrite to austenite and lathy ferrite and austenite and acicular ferrite, while ferrite grows towards the weld center, showing a dendritic shape and a local network structure. At the side of the base layer weld of the interface between the transition and the base layer weld, the thickness of the low-carbon-content layer increased from 100 μm to 150 μm. Iron, chromium, and nickel elements on both sides of the interface were diffused, and the thickness of the diffusion layer increased from 3 μm to 10 μm. The tensile strength values of joints A and B were 648 MPa and 668 MPa, respectively, and the Schmidt factor values were 0.446 and 0.454, respectively. Combination with the analysis of the fracture morphology showed that when the transition layer weld was higher than the interface of the composite plate, the joint had better plastic deformation ability and higher tensile strength.

Study on the Hot Cracking Law of Inconel 690/52M Welding Material on F304LN Base Metal by Multi-Layer Cladding

During the welding of 690 nickel-based alloy, solidification cracking (SFC) and ductility-dip cracking (DDC) easily forms, which has a negative effect on the quality of welded joints and service life. The present study examined the effects of welding heat input and cladding layers on the SFC and DDC, as well as their formation mechanism. The microstructure observation, elemental distribution, and Varestraint test were carried out. The results show that SFC and DDC were formed for the Inconel filler metal 52M, and SFC is more prone to form than DDC. The alloy elements such as Fe, Si, C, and P from base metal can expand the solidification temperature range, such that the SFC sensitivity increases. With the increase of welding heat input, the grain size of cladding metal is increased with a great SFC sensitivity. The increasing welding heat input also makes DDC possible due to the formation of a large angle grain boundary.

Microstructure and mechanical properties of flash butt welding joint of high nitrogen austenitic stainless steel

The microstructure and properties of high nitrogen stainless steel welded joints under different flash currents were studied by flash butt welding. The results show that, the flash welding parameters have obvious influence on the joint structure and mechanical properties. The joint is organized into symmetrical distribution, and the grains obtained in the interface area are small, mostly pearlite and ferrite. With the increase of flash current, grain coarsening in overheated zone (OZ) and welding zone (WZ) of joint, which was mainly attributed to the increase of welding heat input. Martensite exists on both sides of the weld, in which the hardness reaches the peak. The tensile strength of welded parts can reach up to 97% of the base material, and the fracture is in the form of ductile fracture.

Study on Microstructure and Mechanical Properties of TP321 Thick-Walled Stainless Steel Tube by CMT Welding

The CMT welding process of TP321 thick-walled stainless steel pipe was analyzed. The tensile properties, microstructures and phase composition of the welded joint were tested, and the effect of welding current on the microstructures and properties was studied. The results show that for the CMT welding of TP321 thick-walled stainless steel pipe, when the optimum welding current is 110A, the maximum tensile strength of welded joints reaches 643 MPa, 92.7% of base metal, and the elongation reaches 58.7%. The fracture location of welded joints is heat-affected zone, basically ductile fracture. With the increase of welding heat input, the precipitation of ferrite and carbide gradually increases in the weld structure of TP321 stainless steel. When the current is too high, the brittle σ phase of ferrite transformation will decrease, resulting in the decrease of strength and plasticity of welded joints.

Microstructure and mechanical properties of cold metal transfer welded galvanized steel/magnesium alloy dissimilar joints

The joining of magnesium alloy to galvanized steel was realized by cold metal transfer method with AZ31 magnesium alloy welding wire. Weld appearance, microstructure and tensile properties of Mg–steel joints under various welding parameters were investigated with different welding heat inputs. The results showed that magnesium alloy-steel brazed joints had good weld appearance. When the welding heat input was 141 J/mm, Zn elements were enriched in the Zn-rich zone (ZRZ), and the interface layer was composed of a large portion of Mg–Zn phases and minor Mg–Al phases. With the increase of welding heat input, Zn elements in the ZRZ gradually decreased, Fe/Al phase appeared in the interface layer, and the strength of welding joint increased. When the welding heat input was 159 J/mm, the tensile strength of welding joint reached the maximum value of 198 MPa. However, when the welding input was increased to 181 J/mm, Zn element in the ZRZ was burnt and volatilized seriously, resulting in poor wetting and spreading properties of liquid phase at the interface zone of the steel.

Effect of Heat Input on Weld Structure and Mechanical Properties of Marine Engineering Steel

Zhu, H.-L., 2019. Effect of heat input on weld structure and mechanical properties of marine engineering steel. In: Gong, D.; Zhu, H., and Liu, R. (eds.), Selected Topics in Coastal Research: Engineering, Industry, Economy, and Sustainable Development. Journal of Coastal Research, Special Issue No. 94, pp. 352–356. Coconut Creek (Florida), ISSN 0749-0208.This study studied the influence of submerged arc welding heat input on the microstructure and mechanical properties of E36 welds for marine engineering, and determined the influence of different welding heat input conditions on the microstructure and properties of welds. The results show that with the increase of welding heat input, the martensite content in the weld microstructure is reduced; the nucleation rate of the carbide-free bainite is also reduced, resulting in the carbide-free bainite roughening. And when the bainite phase change, the increase of heat input makes the diffusion distance of carbon atoms farther, which promotes the transformation of retained austenite shape from film to block. In addition, as the heat input increases, the weld metal strength decreases, and the impact toughness is not sensitive to heat input.

An Investigation of TIG welding parameters on microhardness and microstructure of heat affected zone of HSLA steel

Nowadays a wide variety of metal joining methods are used in fabrication industries. In this study, the effect of various welding parameters of the TIG welding process on microhardness, depth, and microstructure of the heat-affected zone (HAZ) of L450 HSLA steel and optimizing these process parameters following Taguchi experimental design was investigated. The microhardness tended to increase significantly with the increase of welding speed from 1.0 to 2.5 mm/s whereas the width of HAZ decreased. The current and arc voltage was found to be less significant in relative comparison. Microstructures of the welded samples were also studied to analyze the changes in the microstructure of the material in terms of ferrite, pearlite, bainite, and martensite formations. Welding speed was found to be the most significant factors leading to changes in microhardness and metallurgical properties. The increase of welding heat input caused an increase in width (depth) of HAZ and the growth of prior austenite grains and then enlarged the grain size of coarse grain heat affected zone (CGHAZ). However, the amount of martensite in the HAZ decreased accompanied by an opposite change of paint. It was observed that the hardness properties and the microstructural feature of HAZ area was strongly affected by the welding parameters.

Cryogenic fracture toughness of 9%Ni steel flux cored arc welds

The fracture toughness was investigated by using Crack Tip Opening Displacement (CTOD) test at room temperature (23°C) and low temperature (−193°C). With the increase of welding heat input, the austenitic fraction of the weld increased but the number of precipitated phases decreased. At room temperature, the fatigue cracks propagated transgranularly when precipitation was scarce. When precipitation was extensive on grain boundaries, crack propagation was intergranular. At −193°C, most cracks propagated in intergranular mode. A small amount of precipitated phases also caused fatigue cracks to grow along grain boundaries. Some large precipitates on the propagation path of fatigue cracks were broken. Precipitates reduced the resistance of crack propagation at austenite grain boundaries. The influence of precipitates on grain boundaries increased at low temperature. The number and size of precipitates should be controlled strictly in the FCAW process of 9%Ni steel.

Study on the thermo-effect of P-GMAW characterized by structure-borne acoustic emission signals detected in welding on aluminum alloy

According to the structure-borne acoustic emission (AE) signals detected in pulsed gas metal arc welding (P-GMAW), the effects of welding heat input and pulses to the microstructures and the characteristics of AE signals were analyzed. The experiment results showed that the welding arc was the source of most vibration energy in GMAW. The increase of welding heat input caused the growth of grain in weld and the increase of average AE count. The mean grain size was increased with the average AE count increasing, which was attributable to the welding heat input. Both the welding arc and the pulses used in welding were the source of vibration energy in P-GMAW. The mean grain size decreased with the average AE count increasing, which was attributable to the pulses provide additional vibration energy to refine the grain structure. The welding heat input effect played a more important role than the pulses effect to the grain structure in P-GMAW.

Microstructures and mechanical properties of H62 brass-316L stainless steel in overlap welded joints by continuous-wave laser

A continuous-wave Nd/YAG laser was used to weld overlap joints between H62 brass and 316 L stainless steel. Effects of laser power and welding speed on microstructure, element distribution, microhardness, and tensile shear strength were investigated. Optical microscopy (OM), scanning electron microscope (SEM), and energy dispersive spectrometer (EDS) were used to analyze the microstructure and the content of zinc in the welded joints. Microhardness test and tensile test were performed to identify the mechanical property of the obtained overlap joints. The results showed that penetration-to-width ratio, evaporation of zinc, and microhardness increase with the increase of welding heat input. The elements in stainless steel and brass had homogeneous distribution and mixing. The coarse microstructure in the fusion zone was the main factor to reduce the tensile shear force of the welded joint, which resulted in the poor mechanical properties. The suitable range of the welding heat input was 37.5 ~ 40 J/mm.

Influence of Heat Input on Grain Size in the Structure of 316LN Stainless Steel Welded Joints

316LN stainless steel is a material with excellent mechanical properties, good resistance to intergranular corrosion and good weldability, and it has been used in many fields of industry. Welding quality has great influence on the strength and corrosion resistance of weldment. In this study, one group of submerged arc welding and three groups of shielded metal arc welding were taken to study the influence of heat input on grain size in the structure of 316LN welded joints. The results show that the microstructures of the weld zones in experiment were all consist of austenite and a small amount of banding or dendritic δ-ferrite and the amount of ferrite decrease with the increase of heat input. It also can be concluded from the experiment that with the increase of welding heat input the grain size of overheated zone decrease.

Effect of Welding Heat Input on Microstructure and Mechanical Properties of HSLA Steel Joint

Gas tungsten arc welding of HSLA steel was conducted with different welding heat inputs, and the influences of welding heat input on the microstructure, Vickers hardness, and impact toughness of heat-affected zone (HAZ) in prepared joints were systematically investigated. The microstructure in HAZ with low welding heat input mainly consisted of martensite, and the microhardness of coarse grain HAZ was measured higher than that of fine grain zone. The results show that increasing the welding heat input could suppress the formation of martensite and reduce the microhardness of HAZ. However, the impact toughness of HAZ was not monotonously improved with the increase of welding heat input. It is deemed that the coarsened grain, the formation of upper bainite, and the non-uniform distribution of carbides and inclusions in HAZ could degrade the impact toughness. Tests demonstrate that the optimum comprehensive properties of HAZ were obtained when the welding heat input was 0.67 kJ/mm.

Microstructure, hardness and petroleum corrosion evaluation of 316L/AWS E309MoL-16 weld metal

The current work presents some observations about the effect of welding heat input on the microstructure, hardness and corrosion resistance of AWS E309MoL-16 weld metal, diluted with AISI 316L austenitic stainless steel plates. Such welds are widely used during overlay of equipment in the petroleum and gas industries. Results show that the welds contained δ-ferrite varying between vermicular to lathy morphology, typically encountered in welds which solidify in ferrite–austenite mode (FA). Conversely, contents and morphology of δ-ferrite in the weld metals were altered, showing an increase of welding heat input. The corrosion rate of the weld metal indicated that when higher levels of welding heat input are used the corrosion rate is reduced. This may be attributed to metallurgical changes, especially variations in the proportion of δ-ferrite, caused by changes in cooling rate.

An investigation into welding parameters affecting the tensile properties of titanium welds

Grain size and amount of martensite formation affect the tensile strength of the alloy and these two factors are in turns related to the cooling rate of the welding process. There was found a trend of decreased tensile strength with the increase of welding heat input and a trend of increased tensile strength with the increase of welding cooling rate. Considering the effect of cooling rate on ductility, it was found that the higher the cooling rate, the larger is the relative elongation and hence the higher the weld's ductility.

構造用鋼のエレクトロスラグ溶接金属の靭性向上に関する研究 （第１報） 構造用鋼のエレクトロスラグ溶接金属内における衝撃特性の不均一性に関する研討

The purpose of this paper is to clarify the weld joint performance, especially the impact characteristics of the weld metal produced by electroslag welding (ESW) and submerged arc welding (SAW) by directing our attention to the high heat input welding processes which are usually applied for the manufacture of four side thick plate box column. Two types of SM490A 40 mm thickness have been used in this test. The test results are summarized in the following.(1) As for the impact characteristics of high heat input weld metal, the absorption energy values (vE value) of weld metal made by ESW are generally lower than those by SAW.(2) As for the vE values of various locations in high heat input weld metal by ESW, the vE value in the center of weld metal (Core) is considerably lower than those in peripheral locations of weld metal (Rim).(3) Macrostructure of ESW weld metal suggested that fine crystal grains were generated in the core with coarse crystal grains in the rim.(4) In the weld metal by ESW the impact value of fine grain core area is low and those in the peripheral coarse grain rim area are high on the contrary. This result disagrees with the conventional theory about the general relation between impact value and grain size.(5) It is found that the vE value of weld metal by ESW shows a tendency to decrease according to the increase of welding heat input (Q) and becomes low at the Q of 30.0 kJ/mm (up to 80.0 kJ/mm). Furthermore, the decrease of vE value related to the increase of welding heat input has not be caused by the change of chemistry such as C, Si, Mn, P and S in the weld metal.

Effects of distribution of solute elements on mechanical properties of aluminum alloy welds

Experiments were conducted to study the effects of distribution of solute elements on the mechanical properties of solidified weld metal in Al-4.5%Mg and Al-4%Zn-2%Mg alloys.The mechanical properties of welds were more deteriorated with the increase of welding heat input. After homogenizing, tensile strength and hardness of the deposited metal were increased on the whole; but Charpy impact value only showed a reverse result. However, both of the tensile strength and impact value still depended on the initial welding heat input or dendrite cell size even after homogenizing, but the hardness did not.After the above treatment, principal solute elements such as Mg and Zn were almost homogenized, which led to the vanishing of their segregations on the dendrite cell boundaries; but their concentrations in the cell matrix were increased. However, the distribution of impurities of Fe and Si (particularly, Fe) remained in as welded state even after homogenzing.It was clear from the above facts that the hardness of welds was markedly affected by the dispersion of the 2nd phases containing Mg or Zn on grain and dendrite cell boundaries and their concentrations in the cell matrix. Whereas, the tensile property and Charpy impact value, which will lead to rupture, would be affected by the distribution of Fe and Si as well as the above two factors.The above facts were proved by the experimental results that the mechanical properties of welds and permanent mould castings were deteriorated with the increase of Fe and Si. The network of the 2nd phases containing Fe and Si on grain and dendrite cell boundaries seemed to promote the crack propagation in rupture.However, the effects of Fe and Si were observed in only Al-4.5% Mg and Al-4%Zn-2%Mg alloys containing considerable amounts of Mg and (or) Zn as strengthening elements. Whereas, these effects were not observed in commercially pure aluminum, in which Fe and Si rather act as strengthening elements for mechanical properties.