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Microstructure and Properties of Metallic Heat-Affected Zones

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A special issue of Metals (ISSN 2075-4701).

Deadline for manuscript submissions: closed (31 January 2021) | Viewed by 38301

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Special Issue Editor

Dr. Igor Velkavrh

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Guest Editor

V-Research GmbH, Industrial Research and Development, Stadtstrasse 33, 6850 Dornbirn, Austria
Interests: friction and wear; experimental methods; surface engineering; coatings; tribology of snow and ice; gas tribology; polymer tribology
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Welding is one of the most important joining techniques for metal constructions and various mechanical applications. Since the microstructure and properties of the heat-affected zone (HAZ) determine the quality of the joint, they have been a matter of interest to material scientists, metallurgists, and mechanical engineers for many decades already, resulting in a comprehensive knowledge base on this topic. As with the development of new materials and welding techniques, novel possibilities have arisen, and at the same time advanced analytical tools have enabled deeper insights into these structures; the study of their properties is today as relevant as ever.

This Special Issue on “Microstructure and Properties of Metallic Heat-Affected Zones” intends to collect the last developments in the field, written by researchers who have contributed significantly to development and characterization of the microstructure and the properties of metallic heat-affected zones.

Topics addressed in this Special Issue may include but are not limited to the following:

Material properties;

Microstructure properties;

Metallurgical characterization;

Mechanical testing;

Numerical simulations;

Industrial applications.

Dr. Igor Velkavrh
Guest Editor

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Keywords

Heat-affected zone (HAZ)
Microstructure properties
Mechanical properties
Impact toughness
Fracture behavior
Fatigue behavior
Creep behavior
Tribological properties
Numerical prediction
Corrosion resistance

Published Papers (12 papers)

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Research

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20 pages, 12652 KiB

Open AccessFeature PaperArticle

Creep Rate, Friction, and Wear of Two Heat-Affected Zone Regions of 9–12 wt.% Cr Steels

by Igor Velkavrh, Joël Voyer, Fevzi Kafexhiu and Bojan Podgornik

Metals 2021, 11(4), 558; https://doi.org/10.3390/met11040558 - 29 Mar 2021

Viewed by 1634

Abstract

Coarsening of precipitates can have a profound effect on the mechanical properties of martensitic 9–12 wt.% Cr steels, which are typically used in critical parts of fossil-fuel power plants such as turbines, headers, and main steam pipes. In the present study, changes in precipitates’ size and distribution in the simulated heat-affected zone of two different 9–12 wt.% Cr steels (X20 and P91) after different aging conditions were analyzed and correlated with their creep, friction, and wear behaviors. It was shown that prior to aging, the morphology of the steel matrix (prior austenite grain size and microstructure homogeneity) governed the creep rate and the tribological performance of both steels, while after aging their response was additionally determined by the combination of the number and the size of precipitates. For the selected samples (prepared under identical conditions), number of precipitates was found to be within a narrower range for the X20 steel as compared to the P91 steel. For both steels, aging for a shorter time at the higher temperature yielded significantly higher stationary creep rate values as compared to aging for longer time at the lower temperature. The increase was more pronounced in the P91 than in the X20 steel. Both prior to and after aging, the P91 steel typically provided slightly higher creep resistance than the X20 steel, while the latter provided slightly better tribological performance. Furthermore, as a function of the increasing number of precipitates, static coefficient of friction in air atmosphere was approximately linearly decreasing, while the wear rate initially decreased. Full article

(This article belongs to the Special Issue Microstructure and Properties of Metallic Heat-Affected Zones)

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21 pages, 17059 KiB

Open AccessArticle

Evaluation of Stationary Creep Rate in Heat-Affected Zone of Martensitic 9–12% Cr Steels

by Fevzi Kafexhiu and Jaka Burja

Metals 2020, 10(12), 1612; https://doi.org/10.3390/met10121612 - 30 Nov 2020

Cited by 1 | Viewed by 1577

Abstract

The purpose of the present study was to evaluate the contribution of distinct regions of the simulated heat-affected zone (HAZ) to the overall creep behavior of welded joints in the X20 and P91 steels. The HAZ was simulated by means of dilatometry at four peak temperatures (900, 1000, 1200, and 1350 °C) with a consequent tempering at 650 °C. Microstructure features of the four simulated HAZ regions including precipitates, prior austenite grains, and subgrains were quantified by means of electron microscopy. The quantified parameters and the measured hardness were used in three physical models for evaluation of the stationary creep rate (

\dot{ε}

at 170 MPa and 580 °C. The resulting

\dot{ε}

values fall within the range 10⁻⁸–10⁻⁷ s⁻¹, being in good agreement with the experimental data with a similar thermal history, but an order of magnitude lower than the measured values for the parent metal of the studied steels (10⁻⁷–10⁻⁶ s⁻¹). Depending on the model utilized, their output can be linearly related to hardness, subgrain size, or interparticle spacing. The model relating

\dot{ε}

to hardness was the most consistent one in prediction, being always lower for higher peak temperatures. Full article

(This article belongs to the Special Issue Microstructure and Properties of Metallic Heat-Affected Zones)

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17 pages, 20998 KiB

Open AccessArticle

Effects of Thermal Simulation on the Creep Fracture of the Mod. 9Cr-1Mo Weld Metal

by Chien-Chun Liao, Chu-Chun Wang, Tai-Cheng Chen, Ren-Kae Shiue and Leu-Wen Tsay

Metals 2020, 10(9), 1181; https://doi.org/10.3390/met10091181 - 2 Sep 2020

Cited by 4 | Viewed by 1870

Abstract

The effects of thermal simulation on the short-term creep fracture of modified 91 (mod. 91) weld metal (WM) were evaluated at elevated temperature. The reheated zones in the WM during multiple passes were simulated by an infrared heater. The simulated WM specimens after post-weld tempering at 1023 K/2 h were loaded with dead weight either at 903 K/120 MPa or 933 K/80 MPa. In this work, the simulated WM specimens after tempering were loaded either at 903 and 933 K during the tests. The loss in creep lives of various specimens at elevated temperature was determined accordingly and further compared with the Gr. 91 steel base metals, which were normalized either at 1213 K or 1333 K and then tempered at 1033 K for 2 h. The coarse, solidified structure of the WM had much better creep resistance than the base metal even that of the base metal normalized at 1333 K. However, the imposed welding thermal cycles would cause a significant decrease in creep resistance of the WM. Creep lives were shortened obviously in the simulated WM samples, especially in the simulated sample that underwent partial transformation. The combination of a fine-grained structure and soft ferrite present in the simulated WM was responsible for their huge decline in creep resistance, as compared with the WM in the as-tempered condition. Full article

(This article belongs to the Special Issue Microstructure and Properties of Metallic Heat-Affected Zones)

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18 pages, 20328 KiB

Open AccessFeature PaperArticle

On the Intergranular Corrosion Properties of Thin Ferritic Stainless Steel Sheets Welded by Fiber-Laser

by Niklas Sommer, Igor Kryukov, Christian Wolf, Michael Wiegand, Martin Kahlmeyer and Stefan Böhm

Metals 2020, 10(8), 1088; https://doi.org/10.3390/met10081088 - 12 Aug 2020

Cited by 9 | Viewed by 3101

Abstract

In the present investigation, thin sheets of stabilized and unstabilized ferritic stainless steel were welded in butt joint configuration using irradiation of a 1070

n m

fiber-laser. Using optical microscopy, the microstructural evolution upon alternating heat input was characterized. In addition to that, [...] Read more.

In the present investigation, thin sheets of stabilized and unstabilized ferritic stainless steel were welded in butt joint configuration using irradiation of a 1070

n m

fiber-laser. Using optical microscopy, the microstructural evolution upon alternating heat input was characterized. In addition to that, hardness and tensile tests were carried out on the specimens. Detailed focus was given to the intergranular corrosion properties, which were investigated on basis of the Strauss test with different times of exposure to the corrosive environment. Following these tests, the mechanical properties of the joints were characterized using tensile tests. A combination of the latter with an inspection by

μ

-CT analysis allows for the proposition of an intergranular corrosion rate with regard to the degradation of the joint strength. Full article

(This article belongs to the Special Issue Microstructure and Properties of Metallic Heat-Affected Zones)

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14 pages, 4284 KiB

Open AccessArticle

Microstructural Evolutions and its Impact on the Corrosion Behaviour of Explosively Welded Al/Cu Bimetal

by Mohammad Reza Jandaghi, Abdollah Saboori, Gholamreza Khalaj and Mohammadreza Khanzadeh Ghareh Shiran

Metals 2020, 10(5), 634; https://doi.org/10.3390/met10050634 - 13 May 2020

Cited by 43 | Viewed by 2796

Abstract

In this study, the microstructural evolutions and corrosion resistance of aluminium/copper joint fabricated through explosive welding process have been thoroughly investigated, while stand-off distance was variable. Microstructural analyses demonstrate that, regardless of grain refinement in the welding boundary, increasing the stand-off space is followed by a higher thickness of the localized melting pool. X-Ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDS) analyses recognized the binary intermetallic layers as a combination of Al₂Cu and AlCu. Polarization and electrochemical impedance spectroscopy (EIS) corrosion tests revealed that a higher stand-off distance resulted in the increment of corrosion potential, current rate, and concentration gradient at the interface owing to the remarkable kinetic energy of the collision, which impaired corrosion resistance. Full article

(This article belongs to the Special Issue Microstructure and Properties of Metallic Heat-Affected Zones)

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14 pages, 14503 KiB

Open AccessFeature PaperArticle

Remote Fibre Laser Welding of Advanced High Strength Martensitic Steel

by Urban Prijanovič, Marica Prijanovič Tonkovič, Uroš Trdan, Matej Pleterski, Matija Jezeršek and Damjan Klobčar

Metals 2020, 10(4), 533; https://doi.org/10.3390/met10040533 - 20 Apr 2020

Cited by 11 | Viewed by 3292

Abstract

The study presents the results of remote robotic laser welding of advanced high strength Docol^® 1200 M martensitic steel. One mm thick samples were welded in a lap joint configuration using a special clamping system. Welding was done using a continuous-wave (CW) fibre laser with a constant welding power of 300 W and constant focus diameter Ø 1.8 mm. Welding was done using 12 different welding speeds in the range from 0.15 to 1 m/min, whereas the inclination angle was kept constant at 0°. The influence of various welding speeds and linear heat inputs during welding on microstructural changes were examined by the occurrence of acicular and allotriomorphic ferrite or martensite. Results revealed big influence of the clamping system on the accumulation of the laser beam energy, heat sink and consequently weld size and geometry, as well as its microstructure and joint strength. Tensile-shear strength, microstructure and hardness results confirmed laser power of 300 W and 0.6 m/min welding speed as the optimal parameters, at which a martensitic structure was obtained in the weld. The width of the heat affected zone (HAZ) in this case is 1100 μm. Full article

(This article belongs to the Special Issue Microstructure and Properties of Metallic Heat-Affected Zones)

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19 pages, 4351 KiB

Open AccessArticle

Energy Density Effect of Laser Alloyed TiB₂/TiC/Al Composite Coatings on LMZ/HAZ, Mechanical and Corrosion Properties

by Dunja Ravnikar, Uroš Trdan, Aleš Nagode and Roman Šturm

Metals 2020, 10(3), 411; https://doi.org/10.3390/met10030411 - 23 Mar 2020

Cited by 3 | Viewed by 3021

Abstract

In the present work, TiC/TiB₂/Al composite coatings were synthesized onto a precipitation hardened AlSi1MgMn alloy by laser surface alloying (LSA), using 13.3 J/mm² and 20 J/mm² laser energy densities. Microstructure evaluation, microhardness, wear and corrosion performance were investigated and compared with the untreated/substrate Al alloy sample. The results confirmed sound, compact, crackles composite coating of low porosity, with a proper surface/substrate interface. Microstructural analyses revealed the formation of extremely fine nano-precipitates, ranging from of 50–250 nm in the laser melted (LMZ) and large precipitates, accompanied with grain coarsening in the heat-affected zone (HAZ), due to the substrate overheating during the LSA process. Nonetheless, both coatings achieved higher microhardness, with almost 7-times higher wear resistance than the untreated sample as a consequence of high fraction volume of hard, wear resistant TiB₂ and TiC phases inside the composite coatings. Further, cyclic polarization results in 0.5 M NaCl aqueous solution confirmed general improvement of corrosion resistance after LSA processed samples, with reduced corrosion current by more than a factor of 9, enhanced passivation/repassivation ability and complete prohibition of crystallographic pitting, which was detected with the untreated Al alloy. Full article

(This article belongs to the Special Issue Microstructure and Properties of Metallic Heat-Affected Zones)

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15 pages, 9139 KiB

Open AccessArticle

Mechanism of Improving Heat-Affected Zone Toughness of Steel Plate with Mg Deoxidation after High-Heat-Input Welding

by Longyun Xu, Jian Yang, Joohyun Park and Hideki Ono

Metals 2020, 10(2), 162; https://doi.org/10.3390/met10020162 - 21 Jan 2020

Cited by 10 | Viewed by 2335

Abstract

In the present study, the mechanism of improving HAZ toughness of steel plate with Mg deoxidation after the simulated welding with the heat input of 400 kJ/cm was investigated through in situ observation, characterization with SEM-EDS and TEM-EDS, and thermodynamic calculation. It was found that intragranular acicular ferrite (IAF) and polygonal ferrite (PF) contributed to the improvements of HAZ toughness in steels with Mg deoxidation. With the increase of Mg content in steel, the oxide in micron size inclusion was firstly changed to MgO-Ti₂O₃, then to MgO with the further increase of Mg content in steel. The formation of nanoscale TiN particles was promoted more obviously with the higher Mg content in the steel. The growth rates of austenite grains at the high-temperature stage (1400~1250 °C) during the HAZ thermal cycle of steels with conventional Al deoxidation and Mg deoxidation containing 0.0027 and 0.0099 wt% Mg were 10.55, 0.89, 0.01 μm/s, respectively. It was indicated that nanoscale TiN particles formed in steel with Mg deoxidation were effective to inhibit the growth of austenite grain. The excellent HAZ toughness of steel plates after welding with a heat input of 400 kJ/cm could be obtained by control of the Mg content in steel to selectively promote the formation of IAF or retard the growth of austenite grain. Full article

(This article belongs to the Special Issue Microstructure and Properties of Metallic Heat-Affected Zones)

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13 pages, 8656 KiB

Open AccessArticle

The Mechanism for HAZ Liquation of Nickel-Based Alloy 617B During Gas Tungsten Arc Welding

by Shanlin Li, Kejian Li, Mengjia Hu, Yao Wu, Zhipeng Cai and Jiluan Pan

Metals 2020, 10(1), 94; https://doi.org/10.3390/met10010094 - 6 Jan 2020

Cited by 10 | Viewed by 3307

Abstract

The mechanism for HAZ (heat-affected zone) liquation of alloy 617B during gas tungsten arc welding (GTAW) was investigated. Welding thermal simulation work was conducted to investigate the effects of thermal parameters (peak temperature, holding time, and thermal cycle numbers) on M₂₃C₆ carbides’ evolutionary behavior in nickel-based alloy 617B. OM (optical microscopy), SEM (scanning electron microscopy), TEM (transmission electron microscopy), and SIMS (secondary ion mass spectrometry) were employed to characterize HAZ carbides. It was found that the constitutional liquation of M₂₃C₆ carbides is responsible for HAZ liquation in alloy 617B. Rapid heating meant that solute atoms released from partially dissolved M₂₃C₆ carbides did not have enough time to sufficiently diffuse into the matrix, resulting in eutectic reaction M₂₃C₆ + γ → liquid in the temperature range from 1250 °C to 1300 °C. In the following cooling process, the liquid phase transformed into γ and M₂₃C₆ (or M₆C) carbides simultaneously, creating a eutectic microstructure. Subsequent thermal cycles with peak temperature 1100 °C and proper holding time brought about a tempering effect to precipitate fine M₂₃C₆ carbides from the Cr supersaturated zone around the eutectic microstructure. Boron was found to be enriched in carbides and was expected to promote HAZ liquation by two mechanisms. No cracking caused by HAZ liquation has been found, indicating that GTAW is a suitable method for joining alloy 617B. Full article

(This article belongs to the Special Issue Microstructure and Properties of Metallic Heat-Affected Zones)

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15 pages, 12761 KiB

Open AccessArticle

Microstructural Evolution and Short-Term Creep Rupture of the Simulated HAZ in T92 Steel Normalized at Different Temperatures

by Tai-Jung Wu, Chien-Chun Liao, Tai-Cheng Chen, Ren-Kae Shiue and Leu-Wen Tsay

Metals 2019, 9(12), 1310; https://doi.org/10.3390/met9121310 - 5 Dec 2019

Cited by 7 | Viewed by 2405

Abstract

T92 steel tubes have been widely applied in advanced supercritical boilers to replace Gr.91 tubes. Simulated samples with microstructures similar to those present in the heat-affected zone (HAZ) of a T92 steel weld were subjected to short-term creep tests in the study. T92 steel tubes were normalized at either 1213 K (L) or 1333 K (H) for 1 h, followed by tempering (T) at 1033 K for 2 h. After the normalizing and tempering treatments, the HT samples comprised finer precipitates but in greater numbers along the prior austenite grain boundaries (PAGBs) and martensite lath boundaries, as compared with those of the LT samples. The HAZ microstructures in the T92 steel welds were simulated by using an infrared heating system, which included over-tempering (OT, below A_C1) and partial transformation (PT, slightly below A_C3) zones. Martensite laths in the OT sample were more likely to be replaced by numerous cellular structures or subgrains together with spherodized carbides mainly located at the lath and austenite grain boundaries. Furthermore, coarser but fewer carbides were found along the refined lath and grain boundaries in the PT samples, in comparison with other samples in each group. Short-term creep tests showed that the PT samples were more likely to fracture than other samples in each group. Moreover, under the same testing conditions, the microstructures of T92 steel were more stable and resistant to degradation than those of T91 steel after welding or loading at elevated temperatures. Such events were responsible for higher creep resistance of the simulated T92 samples than that of the simulated T91 samples under the same creep-rupture conditions. Full article

(This article belongs to the Special Issue Microstructure and Properties of Metallic Heat-Affected Zones)

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16 pages, 8704 KiB

Open AccessArticle

Effect of Cooling Rate on Microstructure and Mechanical Properties in the CGHAZ of Electroslag Welded Pearlitic Rail Steel

by Adnan Raza Khan, Shengfu Yu, Hao Wang and Yuan Jiang

Metals 2019, 9(7), 742; https://doi.org/10.3390/met9070742 - 30 Jun 2019

Cited by 11 | Viewed by 7725

Abstract

The effect of cooling rate, ranging from 6 to 1 °C/s, on microstructure and mechanical properties in the coarse-grained heat affected zone (CGHAZ) of electroslag welded pearlitic rail steel has been investigated by using confocal scanning laser microcopy (CSLM) and Gleeble 3500 thermo-mechanical simulator. During heating, the formed austenite was inhomogeneous with fractions of untransformed ferrite, which has influenced the pearlite transformation during cooling by providing additional nucleation sites to pearlite. During cooling, at 6 °C/s, the microstructure was composed of martensite and bainite with little pearlite. From 4 to 1 °C/s, microstructures were completely pearlite. Lowering the cooling rate of the CGHAZ from 4 to 1 °C/s increased the pearlite start temperature and reduced the pearlite growth rate. Meanwhile, this increase in pearlite start temperature enlarged the pearlite interlamellar spacing. Alternatively, increasing pearlite interlamellar spacing in the CGHAZ by lowering the cooling rate from 6 to 1 °C/s reduced the hardness and tensile strength, whereas toughness was found unaffected by the pearlite interlamellar spacing. It has been found that a cooling rate of 4 °C/s leads to the formation of pearlite with fine interlamellar spacing of 117 nm in the CGHAZ of electroslag welded pearlitic rail steel where hardness is 425 HV, tensile strength is 1077 MPa, and toughness is 9.1 J. Full article

(This article belongs to the Special Issue Microstructure and Properties of Metallic Heat-Affected Zones)

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Review

Jump to: Research

21 pages, 10493 KiB

Open AccessReview

A Review of Austenite Memory Effect in HAZ of B Containing 9% Cr Martensitic Heat Resistant Steel

by Xiaogang Li, Kejian Li, Zhipeng Cai and Jiluan Pan

Metals 2019, 9(11), 1233; https://doi.org/10.3390/met9111233 - 18 Nov 2019

Cited by 10 | Viewed by 4026

Abstract

During the welding process of B containing 9% Cr martensitic heat resistant steel (9Cr-B steel), austenite memory effect (referred to that the prior austenite grains in the heat affected zone (HAZ) after welding inherit the shape and size of prior austenite grains before welding) occurs in its normalized sub-zone of HAZ and the grain refinement is suppressed, which can effectively prevent type IV crack, and improve the service life of the welded joint at high temperatures. In the present article, α/γ reverse transformation behavior in the normalized sub-zone of 9Cr-B steel HAZ is reviewed. Austenite memory effect of 9Cr-B steel is derived from B addition. The main mechanisms of austenite memory effect during α/γ reverse transformation are discussed. Various models of boron causing austenite memory effect are discussed in detail. Matrix microstructure also plays an important role in austenite memory effect. Effects of heating rate, peak temperature, and holding time at peak temperature on austenite memory effect are also discussed. Full article

(This article belongs to the Special Issue Microstructure and Properties of Metallic Heat-Affected Zones)

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