Heat Affected Zone Toughness Research Articles

Mechanical Properties Evaluation of Metal Components Repaired by Direct Metal Lamination

Direct metal lamination using arc discharge was applied to the repair of metal components such as metallic parts, dies and molds by adding equivalent metal to them. In this method, a heat-affected zone which has different mechanical properties from the base metal is formed near the laminated metal. This is because the rapid temperature change by welding heat input can cause phase transformation or metallic structure change. Therefore, the mechanical properties of the laminated metal, heat-affected zone and base metal after repair by direct metal lamination need to be explored. In addition, the region which needs to be repaired must be removed in advance because worn and defective parts aren’t adequate as the base for lamination of further layers. Thus, the most suitable removal shape for repair by direct metal lamination was investigated. Finally, the hardness distribution and toughness of the metal components after repair was explored. It was found that the hardness distribution of metal components after repair was uneven. However, the toughness of the heat-affected zone was found to be comparable to those of the laminated metal and the base metal.

A new method to study the effect of M–A constituent on impact toughness of IC HAZ in Q690 steel

Abstract

Relationship between crystallographic structure of the Ti2O3/MnS complex inclusion and microstructure in the heat-affected zone (HAZ) in steel processed by oxide metallurgy route and impact toughness

A new method based on electron back scattered diffraction (EBSD) is proposed to determine the structure of titanium oxide/MnS complex inclusion which induced the formation of intragranular acicular ferrite (IAF) in heat-affected zone (HAZ) in steel processed by oxide metallurgy route. It was found that the complex inclusion was Ti2O3/MnS, the orientation relationship between Ti2O3 and MnS was also examined, and the crystallographic orientation relationship among IAF, Ti2O3/MnS complex inclusion, austenite, bainite formed at lower temperature is researched systematically. It was observed that MnS precipitated on Ti2O3 at specific habit plane and direction and MnS had a specific orientation relationship ({0001} Ti2O3//{111} MnS), <10–10> Ti2O3//<110> MnS) with respect to Ti2O3. Intragranular acicular ferrite (IAF) nucleated on MnS part of the Ti2O3/MnS complex inclusion had no specific orientation relationship with MnS. IAF and the surrounding bainite had different Bain groups, so that there was an increase in high angle boundaries, which was beneficial for the toughness of HAZ.

Micromechanism of Decrease of Impact Toughness in Coarse-Grain Heat-Affected Zone of HSLA Steel with Increasing Welding Heat Input

This paper analyzes the micromechanism of decrease of impact toughness with increasing the welding heat input in coarse-grain heat-affected zone (CGHAZ) of a low-alloy high-strength ship-building steel plate. By comparing the microstructures, measuring the extending length of the fibrous crack, identifying the critical event of cleavage fracture, measuring the critical length, and calculating the local cleavage fracture stress σ f, and then using the basic principles of the micromechanism of cleavage fracture, this work reveals the essential causes of deteriorated toughness in the CGHAZ of high-strength steel welded joints.

Some Studies on Heat-Affected Zone (HAZ) Toughness Behavior of API 5L X52 Steel

Heat Affected Zone (HAZ) simulation by Gleeble is a useful method for evaluating welding process parameters to improve the toughness of weld HAZ by optimizing process parameters. The HAZ Toughness in low alloy steels is strongly influenced by the welding parameters (as HAZ microstructure is influenced by the heat input and cooling rate). In the present work different regions of weld HAZ of API 5L X52 steel have been simulated by using Gleeble @ 3800 Thermal- Mechanical Simulator. Two cooling rates (t 8/5 ) 10 s to simulate low heat input (LHI) welding conditions without preheating, (t 8/5 ) 40s to simulate high heat input (HHI) welding were used. Charpy V-notch impact tests were conducted on the simulated as well as on the base material at room temperature (25° C) and at -40° C. Results showed that HHI simulated coarse grain HAZ (CGHAZ) region attributed highest Impact energy of 300 J in comparison to 199 J of base material at 25° C. In HAZ regions, lowest room temperature toughness was observed in sub critical HAZ (SCHAZ) for both HHI and LHI conditions. Lowest impact energy at -40° C was observed in fine grained HAZ (FGHAZ) for both HHI and LHI conditions. Hardness test showed that LHI samples exhibited slightly higher hardness than HHI condition and the hardness profile for HAZ regions was similar for both HHI and LHI conditions.

Some Studies on Heat-Affected Zone (HAZ) Toughness Behavior of API 5L X52 Steel

Heat Affected Zone (HAZ) simulation by Gleeble is a useful method for evaluating welding process parameters to improve the toughness of weld HAZ by optimizing process parameters. The HAZ Toughness in low alloy steels is strongly influenced by the welding parameters (as HAZ microstructure is influenced by the heat input and cooling rate). In the present work different regions of weld HAZ of API 5L X52 steel have been simulated by using Gleeble @ 3800 Thermal- Mechanical Simulator. Two cooling rates (t 8/5 ) 10 s to simulate low heat input (LHI) welding conditions without preheating, (t 8/5 ) 40s to simulate high heat input (HHI) welding were used. Charpy V-notch impact tests were conducted on the simulated as well as on the base material at room temperature (25° C) and at -40° C. Results showed that HHI simulated coarse grain HAZ (CGHAZ) region attributed highest Impact energy of 300 J in comparison to 199 J of base material at 25° C. In HAZ regions, lowest room temperature toughness was observed in sub critical HAZ (SCHAZ) for both HHI and LHI conditions. Lowest impact energy at -40° C was observed in fine grained HAZ (FGHAZ) for both HHI and LHI conditions. Hardness test showed that LHI samples exhibited slightly higher hardness than HHI condition and the hardness profile for HAZ regions was similar for both HHI and LHI conditions.

Improvement of HAZ Toughness of Steel Plate for High Heat Input Welding by Inclusion Control with Mg Deoxidation

The effect of Mg content on the evolution behavior of inclusions in the steel plates with Mg deoxidation was investigated based on the experimental studies and thermodynamic calculations. Simulating welding process and Charpy impact test were also carried out to evaluate the Heat Affected Zone (HAZ) toughness of steel plates. The typical inclusions found in the steels were the complex inclusions comprising central oxide and peripheral MnS. With the increase of Mg content in the steel samples from 0 to 27, 38 and 99 ppm, the phase of central oxide inclusions changed sequentially from Al2O3 to (Mg‐Ti‐O), and MgO, which is consistent with the thermodynamic calculation results. Furthermore, the size of inclusions decreases and the number density of inclusions increases with the increase of Mg content. The HAZ toughness of steel plates after welding with heat input of 400 kJ cm−1 has been greatly improved by inclusion control with Mg deoxidation.

AStudy on the Effects of Heat Input on Size of Heat-Affected Zone (HAZ) and Mechanical Properties of AISI 1518 Grade Steel in Submerged Arc-Welding Process

Submerged arc welding is a fusion-joining process which is known for its high deposition capabilities and high heat input (HI) rate. Proper management of HI in welding is important, because power sources can be used more efficiently if one knows how the same HI can be applied to get the better results. In this paper, the influence of welding HI on width of heat-affected zone (HAZ), cooling rate (CR) and mechanical property such as hardness, toughness of weld zone (WZ) in AISI 1518 grade steel with different welding condition has been systematically investigated. The results show that increasing the welding HI could due to be the HAZ, and CR are increased and decreased, respectively. However, hardness of WZ and toughness of weldments is decreased with the increase in HI. To create a good relationship between HIs with HAZ size, CR, hardness and toughness of weld is also discussed.

Effect of Nb Content on the Impact Toughness of Coarse-Grained Heat-Affected Zone of Pipeline Steels under Large Heat Input

The effect of large heat inputs (200 kJ/cm) on the microstructures and toughness of heat-affected zone of Nb microalloyed X70 pipeline steels were simulated utilizing Gleeble-3800. The microstructures were observed by optical microscope, scanning electron microscope and electron backscattered diffraction technique. Results showed that when the large heat input welding was applied, big austenite grains and coarse microstructures were formed in the coarse-grained heat-affected zone, and thus the toughness of the coarse-grained heat-affected zone was seriously reduced. With the increase of Nb content, the toughness of the CGHAZ did not change remarkably under the large heat input welding.

Characteristic of martensite–austenite constituents in coarse grained heat affected zone of HSLA steel with varying Al contents

The fine microstructure of martensite–austenite (M–A) constituents in simulated coarse grained heat affected zone (HAZ) of high strength low alloy steel with varying aluminium content (0·038 and 0·070 wt-%) at 100 kJ cm−1 heat input welding was investigated. The result shows that M–A constituents with 0·038%Al consisted of lath martensite and retained austenite. The retained austenite was distributed along the martensite lath. Whereas, the M–A constituents with 0·070%Al consisted of lath martensite and retained austenite, as well as a small amount of twinned martensite. The amount of retained austenite in M–A constituents with 0·070%Al was becoming higher slightly than that with 0·038%Al. Accordingly, the volume fraction of M–A constituents was reduced with 0·070%Al. Appropriate aluminium addition could decrease not only the area fraction but also the size of M–A constituents, which are beneficial for improving the toughness of HAZ.

Microstructure transformation of X70 pipeline steel welding heat-affected zone

The continuous cooling transformation curve of heat-affected zone (HAZ) of X70 pipeline steel was measured by Gleeble-3500 thermal mechanical simulator, optical microscope (OM) and hardness analysis. The microstructure transformation rule at different cooling rates and solution behaviors of microalloy carbonitride during heating process of simulated specimens were investigated. When the cooling rate changes from 10 to 20 °C·s−1, microstructures at HAZ are identified as granular bainite, lathy bainite, and quasi-polygonal ferrite. This microstructure is featured with fine ferrite grains, martensite/austenite islands dispersed, high-density dislocations, and fine carbonitride particles, resulting in improving the strength and toughness of HAZ. With the cooling rate increasing to above 40 °C·s−1, the microstructure is predominantly coarse lathy bainite with clear primary austenite grain boundary. While the cooling rate decreases to below 1 °C·s−1, a fairly small amount of pearlite can be observed at the boundaries. The strength and toughness of HAZ are deteriorated because of coarse grains among these microstructures. Most of microalloy carbonitrides in HAZ could be dissolved in the matrix during heating process. A few of TiN particles existing as residues in the matrix can prevent austenite grain from growing, and then improve the strength and toughness of HAZ.

Microstructure and Toughness of Simulated Heat-Affected Zone of Laser Welded Joint for 960 MPa Grade High Strength Steel

The microstructure and toughness of coarse grain zone (CGZ) and mixed grain zone (MGZ) for laser welded 960 MPa grade high strength steel joints were investigated by thermal simulation with a Gleeble-3500 thermal simulator. The results show that microstructure of the stimulated CGZ mainly consists of uniform interweaved lath martensite, and grain growth is not severe upon increasing the cooling time (t 8/5). Microstructure of the stimulated MGZ presents strip-like in low peak temperature, and small block martensite is formed on the grain boundary. However, in high peak temperature, the strip-like microstructure disappears and small block martensite presents net-like structure. The lath character for MGZ and CGZ is very obvious under TEM observation, and the average lath thickness of BM, MGZ, and CGZ is 100, 150 and 200 nm, respectively. The impact energy and microhardness of CGZ are higher than MGZ and reduce with increasing the cooling time. The fracture toughness deteriorating drastically for MGZ may be related with the formation of the mixture microstructure, in which the small block martensite is distributed in the shape of a network.

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.

Effect of Nb on Mechanical Properties of HAZ for High-Nb X80 Pipeline Steels

The mechanical properties of heat affected zone (HAZ) of two commercial high-Nb X80 grade pipeline steels with different alloy elements were investigated using thermal simulation performed on a Gleeble-3500 thermal simulator. The results showed that the high-Nb steels have excellent weldability. Embrittlement regions appear in coarse grain heat affected zone (CGHAZ) and intercritically heat affected zone (ICHAZ); Softening region appears in fine-grain heat affected zone (FGHAZ), and the strength here was even lower than 555 MPa as required in the standard. Meanwhile, with the increase of heat input, the strength and the toughness of HAZ of steel with high Nb, C and lower alloy decrease notably. Therefore, take into account the welding procedure during manufacture of weld pipe, suitable amount of alloy elements, such as Cr, Ni, Cu, Mo and so on, is necessary for high Nb X80 heavy-thick steel plate.

Transformation behavior of a Ti–Zr deoxidized steel: Microstructure and toughness of simulated coarse grain heat affected zone

Continuous cooling and isothermal transformation behavior of a Ti–Zr deoxidized microalloyed steel was studied and compared with that of C–Mn steel, in conjunction with the evolution of microstructure and measurement of toughness of simulated high heat input welding coarse grain heat-affected zone (CGHAZ). The study indicates that the inclusions in Ti–Zr steel were primarily composite inclusions (ZrO2·MnS) with high density of inclusions of size less than 1μm. Polygonal ferrite, acicular ferrite, multi-directional bainite, and segmented martensite were the typical microstructures obtained with increase in cooling rate. Each of these phases was analyzed with decreasing isothermal temperature. Intragranular ferrite nucleation was significantly promoted by ZrO2·MnS inclusions. Inclusions of smaller size were more effective with decreasing temperature such that greater fraction of ferrite plates nucleated on one inclusion. Mn-depletion is the operating mechanism and precipitation of TiN was complementary. The simulated CGHAZ was characterized by interlock acicular ferrite microstructure and high impact toughness such that the dimple fracture and fine cleavage facets contributed to high impact energy.

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.

High toughness in the intercritically reheated coarse-grained (ICRCG) heat-affected zone (HAZ) of low carbon microalloyed steel

Motivated by the small lattice mismatch between ferrite and vanadium nitride (VN), we describe here the welding thermal cycle simulation that provides high toughness in the ICRCG HAZ of low carbon V–N steel. This unique behavior is attributed to the formation of ultra-fine grained ferrite along prior austenite grain boundaries generated by the first pass welding thermal cycle with high misorientation boundaries, where V(C, N) precipitates provide potential nucleation sites for ferrite, leading to extraordinary refinement of martensite/austenite (M/A) constituent. Nitrogen stimulates the precipitation behavior of V(C, N). The nucleation of high density of V(C, N) precipitates consumes carbon-content in the austenite, leading to decrease in the carbon-content in the M/A constituent, with consequent decrease in hardness. The increase in toughness is explained in terms of Griffith's crack propagation theory.

Simulated Welding Heat Affected Zone Toughness and Microstructure Transformation of a Ti-Zr Microalloyed Low Carbon Steel

Acicular ferrite (AF) can significantly improve the performance of steels and can be promoted through special inclusions. The present experimental steel was a low carbon Ti-Zr deoxidized and microalloyed steel. The welding heat affected zone (HAZ) simulation indicated that under high heat input (100 kJ/cm) and peak temperature (1400°C) conditions, the HAZ exhibited high impact toughness (150 J, -20°C) and desired microstructure. Isothermal heat treatment data suggested that grain boundary ferrite formed at ~600°C and AF formed at ~500°C. Intragranular plates sheaves formed at ~450°C. MnS coherent precipitation on ZrO2TiOx inclusions promoted AF nucleation.

Effects of Mo, Cr and Nb on microstructure and mechanical properties of heat affected zone for Nb-bearing X80 pipeline steels

The microstructure and mechanical properties of welding heat affected zone (HAZ) of three typical X80 pipeline steels, i.e. Mn–Cr–Nb, Mn–Mo–Nb and/or Mn–Cr–Mo–Nb steels, have been studied using the welding thermal simulation method on a Gleeble-3500 thermal simulator. The results show that the chemical compositions and welding process parameters have significant effects on the microstructure and properties of HAZ. With increase of the cooling rate, the amount of microstructure transformed at lower temperature increases, and the microstructure becomes finer, furthermore, the strength and toughness of HAZ show a rising trend. Within the range of the peak temperature from 600 to 1350°C, there are two brittle zones and one major strength weakening zone in HAZ, especially for high-Nb added Cr steel, weaken of HAZ is very serious. Effects of the key chemical elements such as Mo, Cr and Nb on microstructure transformation of HAZ have been discussed. Although these three alloy system steels in this work display good weldability, the Mn–Mo–Nb and/or Mn–Cr–Mo–Nb steels show better combination of strength and toughness of HAZ compared with the Mn–Cr–Nb steels. Therefore, for high-Nb steels, it is necessary to add suitably Mo to improve the toughness and strength of HAZ, especially, increase the strength.

Physical Simulation of Weldability of Weldox 1300 Steel

In the present study, the investigation of weldability of new ultra-high strength - Weldox 1300 steel has been presented. The thermal simulated samples were used to investigate the effect of welding cooling time t8/5on the microstructure and mechanical properties of the heat affected zone (HAZ). In the frame of these investigation the microstructure was studied by the light (LM) and transmission electron microscopies (TEM). It has been shown that the microstructure of the Weldox 1300 steel is composed of tempered martensite, and inside the laths the minor precipitations mainly V(CN) and molybdenum carbide Mo2C were observed. Mechanical properties of parent material were analysed by the tensile, impact and hardness tests. In details the influence of cooling time in the range of 2,5 - 300 s. on hardness, impact toughness and microstructure of simulated HAZ was studied by using welding thermal simulation test. The results show that the impact toughness and hardness decrease with the increase of t8/5under the condition of a single thermal cycle in simulated HAZ. The continuous cooling transformation diagrams (CCT-W for welding conditions) of Weldox 1300 steel for welding purposes was also elaborated. The steel Weldox 1300 for cooling time in the range of 2,5 - 4 s showed martensite microstructure, for time from 4 s to 60 s mixture of martensite and bainite, and for longer cooling time mixture of ferrite, bainite and martensite. The results indicated that the weldability of Weldox 1300 steel is limited and to avoid the cold cracking the preheating procedure or medium net linear heat input should be used.