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The objective of the study is to understand the effect of martensite-austenite (MA) constituents along with the neighbouring bainitic matrix and its effect on low-temperature impact toughness in the thermo-mechanically simulated inter-critically reheated coarse-grained heat-affected zone (ICCGHAZ) of offshore High Strength Low Alloy (HSLA) steels. ICCGHAZ was simulated using a Gleeble 3500 thermomechanical simulator between the inter-critical temperature near Ac1 (lower ICT) and at a temperature 50 °C higher (upper ICT) for two different steels (steel A and steel B) with predominant microstructures composed of granular bainite (GB) and bainitic ferrite (BF), respectively. MA constituents were observed in the form of necklaces along prior austenitic grain boundaries (PAGB) of simulated ICCGHAZ for both steel A and steel B. Steel A combrised of discrete island MA constituents inside the GB grains and steel B consists of lath shaped MA constituents inside BF grains. Fractographical analysis showed that secondary cracks were initiated at the MA constituents along PAGB and propagated linearly into the GB/BF grains in the ICCGHAZ. The cracks initiated at the bulky MA at grain boundaries of steel A moved towards the pre-cracked or de-bonded discrete MA inside the grains and propagated through the interlinking of microcracks. In contrast, for steel B a notable percentage of cracks were initiated through the necklace-like MA at the grain boundaries and propagated through the BF lath. Pre-cracking of the slender MA present at the lath boundaries facilitated crack propagation in steel B. Furthermore, increasing the inter-critical temperature improved the impact toughness of steel A with a predominantly GB microstructure, whereas impact toughness improvement was limited in steel B with a BF microstructure.

In this study, using flux cored wire, S235JR and S460MC structural steels with a thickness of 16 mm were joined by MAG welding method. Welding processes were carried out to join the same (S235JR-S235JR, S460MC-S460MC) and different types of materials (S235JR-S460MC). In the microstructure examinations, grain coarsening occurred in all conditions, from the base material to the weld metal. From the tensile test results, in all combinations, fracture occurred on the S235JR side. Since fractures are not from the weld zone (weld nugget and HAZ), the weld zone strengths are clearly understood to be higher than the main material tensile strengths. On microhardness tests, the highest microhardness was obtained from the welded metal in all combinations, followed by HAZ and base material. Also, the highest microhardness measured on dissimilar joints of S235JR-S460MC on weld metal was 269 HV (Vickers). The welded specimens were also subjected to fatigue tests; the failure occurred on the base material in all three joints. S460MC-S460MC joint had the highest fatigue strength at the most elevated stress, 625 MPa; however, S235JR-S235JR joint had the lowest fatigue strength at the lowest priority, 300 MPa. Although the fatigue strength results of the same and different combinations and the tensile test results have parallelism, the highest microhardness is seen in S460MC-S235JR dissimilar joints, and its fatigue strength is lower than S460MC-S460MC joints. [ABSTRACT FROM AUTHOR]

Precipitation in a high-strength low-alloy steel containing V and Nb additions during coiling at 500 °C, was investigated by advanced characterization techniques including electron backscattered diffraction, focused ion beam, transmission electron microscopy and atom probe tomography. During coiling, nano precipitates were preferentially formed around dislocations and grain/sub-grain boundaries in the high Kernel Average Misorientation (KAM) areas associated with bainite. Precipitates were frequently observed around cementite in the low KAM areas with cementite which were identified as granular bainite. Interphase clusters were found in the low KAM areas associated with ferrite. The site-specific methods reveal the co-existence of different kinds of precipitates. Analysis of the results indicates that the precipitation of microalloy particles close to cementite could lower the precipitation hardening contribution that could be achieved through microalloying.

A model has been developed for describing the competition between the formation of microalloyed carbonitrides by strain-induced precipitation (SIP) and by epitaxial growth on pre-existing TiN particles in γ-Fe. It is assumed that Nb and C/N atoms in the matrix will either feed the growth of pre-existing TiN precipitates or precipitate as new strain-induced particles. The model is successfully applied to the data set obtained by transmission electron microscopy (TEM) in a model alloy. Using this model, it is possible to estimate the effects of process parameters (T, applied strain), the number density of pre-existing TiN, and the Nb, C, N and Mn content on precipitate evolution and precipitation hardening. Notably, it is shown that the presence of a high number density of pre-existing TiN precipitates can suppress SIP. The conditions where epitaxial growth dominates and those in which strain-induced precipitation dominates are predicted and summarized in the form of processing maps.

The current research examines gas metal arc welding (GMAW) joints generated in naval grade high-strength low-alloy (HSLA) steel using both continuous wave GMAW (CW-GMAW) and double pulse GMAW (DP-GMAW). The joint was created in four passes with DP-GMAW, whereas CW-GMAW required eight passes. Weld joints were characterized using various techniques, including optical microscopy (OM), scanning electron microscopy (SEM), residual stress analysis, and mechanical evaluation. The mechanical evaluation consisted of microhardness, impact, and tensile tests. The Charpy V-notch (CVN) impact test was performed at room temperature and −60°C. For both CW-GMAW and DP-GMAW, the heat-affected zone and the fusion zone were harder than the base metal. The fracture occurred in the base metal region in all the tensile test specimens containing the weld joints. The DP-GMAW joints showed higher impact toughness at both room temperature and −60°C. In comparison to the fusion zone of the CW-GMAW joint, the fusion zone of the DP-GMAW joint had a greater volume fraction of acicular ferrite, a finer grain size, and a higher percentage of high-angle grain boundaries. These factors have contributed, it is believed, to the higher impact toughness of the DP-GMAW joint. [ABSTRACT FROM AUTHOR]

In order to optimize the heat treatment process following hot induction forming, our study focused on investigating the impact of quenching and tempering temperature on the mechanical properties and microstructure of ASTM A860 Gr WPHY 65 hot formed 30-inch elbow steel, which is utilized in high strength low alloy (HSLA) pipelines for oil and gas applications. The desired properties for these steels include high mechanical strength, toughness, ductility, and weldability. Our experimental approach involved varying the soaking temperatures at 960 °C, 1000 °C, and 1050 °C, and subsequently cooling the samples in water at 20 °C, followed by tempering at 670 °C and 700 °C. Through the use of experimental design techniques, we determined the optimal heat treatment parameters. The results indicate that soaking at 1050 °C and tempering at 700 °C were the most effective treatment conditions in terms of mechanical strength. Furthermore, microstructural analysis revealed that heat treatment not only restored the microscopic structure of the base material, but also resulted in finer grain sizes.

Additive manufacturing with steel offers new opportunities for the construction sector. In particular, direct energy deposition (DED) processes such as Wire Arc Additive Manufacturing (WAAM or DED-Arc), are able to create large structures with a high degree of geometric freedom, like force-flow-optimized steel nodes and frameworks, as well as truss structures. By using high-strength steel, manufacturing times can be shortened because less material has to be applied. In order to enable the usage of WAAM components in the construction industry, profound knowledge of the material behavior is necessary. Based on reliable process parameters, extensive experimental and numerical investigations are carried out to characterize the influence of layer orientation and overhang angle on the mechanical parameters of WAAM high-strength low-alloy steel (HSLA) walls. The results have been compared to HSLA steel sheet material. It is shown that comparable characteristics exist for Young's modulus E, yield strength R p , 0.2 and tensile strength R m with regard to civil engineering applications. The influence of the loading direction on the material level is similar. Only the yield strength shows a slight dependence on the layer orientation for WAAM walls (difference 4.5%). The overhang angle has no influence on the material parameters. [ABSTRACT FROM AUTHOR]

The balance between softening and hardening is still a great challenge for the laser welding of the high strength low alloy steel. For example, welding with low heat input was commonly used to avoid softening, but it would inversely harden the joint and introduce the undesired welding defects such as hydrogen-induced cracks. This work proposed a simple and robust processing technique, denominated High Frequency electric cooperated Laser Welding. Laser heat source was combined with high-frequency electric heat source to balance heat input distribution and reconcile the contradiction between softening and hardening in the welding of high strength low alloy steel. As a structural material sensitive to welding softening and hardening, S690QL steel was adopted to show the fundamental advancement of the new process. Benefitted from the skin effect and proximity effect of high-frequency current that improve the heat input distribution and the regulation of the high-frequency heat input proportion, the martensite content in the heat affected zone was greatly reduced, whilst the grain size was limited to a low value. Under the high-frequency heat input proportion of 47.1 %, lower bainite distributed throughout the heat affected zone. The softening and hardening issues of the joint therefore have been improved simultaneously: the tensile strength of the joint was almost equal to that of the base material, the impact energy of weld seam and the heat affected zone reached 77.6 J and 66.2 J respectively. [Display omitted] • Skin and proximity effect of high-frequency current improved heat distribution. • High frequency heating reduced cooling rate under low power laser welding. • Balanced heat distribution relieve the problem of martensitic hardening. • Suitable cooling rate under high-frequency heating benefited generation of bainite. • Excessive high frequency heating resulted in precipitation of carbides. [ABSTRACT FROM AUTHOR]

High-strength low-alloy (HSLA) steels are an important class of steels that meet combinations of varied properties demanded by critical engineering applications. Microstructures of this class of steels are engineered to meet the targeted mechanical properties. Thorough understanding of phases that evolve during decomposition of austenite in these steels after hot working or after austenitizing treatments is essential to optimize their key processing parameters. This is achieved through establishment of continuous cooling transformation diagrams. These diagrams shed light on details of cooling transformations like the phases formed during transformation, sequence of transformation when multiple phase transformations are involved and the temperatures at which the transformations start and end, all as a function of cooling rate. These diagrams are constructed from dilatometry experiments together with corroborating microstructural investigations and mechanical property assessments. However, analyses of dilatograms, identification and quantification of microstructural constituents and correlating the same with mechanical properties (usually hardness) are not trivial, especially, in low-carbon HSLA steels where the microstructure is often composed of martensite and bainite that have rather similar morphological features and practically difficult to distinguish from each other. Advanced data processing of electron backscattered diffraction (EBSD) data has been used in recent times with considerable success to differentiate bainite and martensite. This work highlights the salient aspects involved in decomposition of austenite in an indigenously developed Cu-bearing HSLA steel. Details of methodology employing grain average misorientation obtained through EBSD experiments to identify and quantify martensite and bainite are discussed in detail. [ABSTRACT FROM AUTHOR]

Boron shows potential to improve the mechanical properties of a niobium (Nb) and titanium (Ti) high-strength low-alloy (HSLA) steel, although there are controversies about the effects on the toughness, avoiding the boron addition to shipbuilding and line pipe steel grades. One heat of Nb-Ti HSLA steel was melted, and the slabs were rolled into coils. Variations in the thermomechanical controlled process parameters were performed, and the effects on the microstructure, tensile, toughness, and hardness properties were analyzed. The predominant acicular microstructure of the sample with high toughness result is related to a greater amount of boron segregated to the grain boundaries in nonequilibrium conditions, inducing a suppression on polygonal ferrite nucleation. Differences on the rolling reduction and cooling are related to inter-particle distance between niobium carbide (NbC) and titanium nitride (TiN), which allows diffusional growth of TiN-NbC compound on austenite grain boundaries, thus building up the acicular ferrite nucleation. The high angle boundaries, typical for acicular ferrite, are efficient in blocking microcracks before they grow to larger sizes, thus justifying the high toughness found in one sample at very low temperatures. Boron can be used to achieve high toughness values while keeping higher tensile properties and lower cost. [ABSTRACT FROM AUTHOR]

Cu-containing steels can suffer from hot shortness unless Ni is added to protect them but whether this problem also influences the straightening operation is not clear. Previous work on hot ductility has found that only when the tensile samples from Cu-containing steels are oxidised can any deleterious influence of copper be found. However, this paper shows that oxidation is not essential. It is more complex than that and, as Cu has been suggested for TRIP steels at levels up to 2.5% Cu to increase their strength and ductility, a greater understanding is required, both of hot shortness and cracking during straightening. The present paper explores the hot ductility behaviour of steels alloyed with Cu and Ni in the straightening temperature range, 700–1000 °C, when tested in air and in an argon atmosphere. Segregation of Cu to the sulphides and grain boundaries occurred allowing the formation of fine Cu2S particles at the austenite grain boundaries favouring intergranular failure and this was more pronounced under oxidising conditions and required strain. It was concluded that a Cu addition, as well as causing hot shortness at higher temperatures will also cause cracking problems in the straightening temperature range in the more sensitive to cracking grades of steel and although the problems are different they are nevertheless interrelated and provided there is sufficient Ni, both may be avoided. [ABSTRACT FROM AUTHOR]

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Hydrogen-Induced Cracking (HIC) is a primary failure mechanism of pipeline-welded joints in the absence of external loading in the oil and gas exploration industries. Three different cooling rates after austenitization were used to simulate in the laboratory different regions of the heat-affected zone (HAZ) formed when welding an API X80 pipeline steel specially designed to enhance the HIC resistance. The samples were characterized with regard to microstructure and crystallography as well as HIC resistance. The HIC resistance test used NACE TM0284-2011 methodology. The microstructure and its homogeneity varied as a function of cooling rates. Samples containing inclusions and segregation zone from the segregation bands of specimens showed reduced HIC resistance, while specimens containing only acicular ferrite and granular bainite coupled with the absence of segregation zone showed significant improvement in HIC resistance. The best HIC resistance results came from samples presenting fine acicular ferrite consisting of fine interlocking plates, with divergent crystallographic orientations, preventing the formation of localized strain distribution inside the grain and at grain boundaries. It was also found that a large proportion of medium-angle boundaries prevent microcrack initiation and the transgranular mode of crack propagation.

New alloys are needed to adapt the material properties and to improve the weldability of arc-based additive manufacturing processes. The classic development of welding filler materials is time-consuming and cost-intensive. For this reason, an alternative alloy concept is investigated and qualified here. This is based on the thin-film coating of welding filler materials by means of PVD coating. An HSLA steel DIN EN ISO 14341-A G 50 7 M21 is used as the base material. This is alloyed with the elements Al, Cr, Nb, Ni and Ti by means of PVD thin-film coating. This procedure represents an alternative alloy concept. In the scope of the qualification, the influence of the process and material properties is investigated, and the alternative alloying concept is compared with the classical alloying concept of secondary metallurgy. The investigations have shown that the thin film coating on the surface of the welding filler metal affects the process properties in the form of a changed arc length. Furthermore, the mechanical properties and the effect on the microstructure morphology were investigated. These were compared in the same chemical composition with a Mn4Ni2CrMo produced by secondary metallurgy. The results are in agreement with regard to the mechanical properties and the effect on the microstructure morphology. [ABSTRACT FROM AUTHOR]

The paper is based on laboratory experiments of heat treatments applied to samples of A537/A537M steel. The work continues other previous works aimed at modifying structures and properties of this steel, including through surface treatments. The experiments were performed using Taguchi methods from Quality Engineering. A number of four factors were selected as influencing the structure after heat treatment: heating temperature for hardening, cooling rate on hardening, time and tempering temperature. A number of nine experiments were performed using an L9 orthogonal matrix. Objective function was changed to maximum hardness after the heat treatment regime. The results show that the tempering temperature has the greatest influence on the final hardness of the A537 steel samples.

Additive manufacturing with steel offers new opportunities for the construction sector. In particular, direct energy deposition (DED) processes such as Wire Arc Additive Manufacturing (WAAM or DED-Arc), are able to create large structures with a high degree of geometric freedom, like force-flow-optimized steel nodes and frameworks, as well as truss structures. By using high-strength steel, manufacturing times can be shortened because less material has to be applied. In order to enable the usage of WAAM components in the construction industry, profound knowledge of the material behavior is necessary. Based on reliable process parameters, extensive experimental and numerical investigations are carried out to characterize the influence of layer orientation and overhang angle on the mechanical parameters of WAAM high-strength low-alloy steel (HSLA) walls. The results have been compared to HSLA steel sheet material. It is shown that comparable characteristics exist for Young’s modulus E, yield strength Rp,0.2 and tensile strength Rm with regard to civil engineering applications. The influence of the loading direction on the material level is similar. Only the yield strength shows a slight dependence on the layer orientation for WAAM walls (difference 4.5%). The overhang angle has no influence on the material parameters.

In this paper, the effect of hydrogen embrittlement in High-strength low-alloy steel (HSLA) material was studied. HSLA steels are known for their susceptibility to hydrogen induced failure especially when subjected to hydrogen rich environment. In this research, samples from HSLAS were surface-treated using chemical vapor deposition (CVD) techniques, followed by direct Zinc coating using physical vapor deposition (PVD). Other samples were additionally post-heat treated at a temperature of 260∘C for 4 h to optimize the coating process. The hydrogen embrittlement test was performed by immersing the tensile samples in a solution containing H2SO4 diluted with water for 24 h. Hardness, and mechanical properties were evaluated using tensile testing. XRD and SEM were used for microstructural and topographical features' examination of the treated samples. The results indicate that the samples of combined PVD + CVD coating that was backed at 260∘C show superior resistance to hydrogen embrittlement compared to other conditions. This could be attributed to the buildup of a strong outer layer that prevents hydrogen from diffusing towards the base HSLAS material. The greater mechanical properties are possibly due to the reduction of hydrogen amount generated by the surface reaction associated by the formation of Zn(N 3 ) 2 phase and the reduction of hydrogen amount passed through Zn and C3N4 layers. [ABSTRACT FROM AUTHOR]

The formation causes and oxidation behaviour of two types of small-sized and irregular morphological surface cracks on S355 hot-rolled thick plate were investigated. The study employed surface pickling, microstructure analysis and inclusion observation to characterise the cracks. It was observed that the surface morphology of two types of cracks exhibited similarities, while their subsurface morphology differed. The Type-A cracks displayed a bulge shape with a rounded tail, while the Type-B cracks had a V-shaped morphology with a slender tail. The Type-A cracks predominantly consisted of FeO. The surface part of the Type-B cracks contained unusual large-sized carbon particles and Al2O3 inclusions, and the iron oxides within the subsurface part followed the sequence of FeO–Fe2O3–Fe from the centre of the cracks to the steel matrix. It was observed that the Type-A cracks originated from subsurface bubbles in the continuous casting slab, which deformed and developed into surface cracks during the rolling process. The iron oxide inside these cracks was formed through a single oxidation process, and the bulge shape in the subsurface part was a distinguishing characteristic. The Type-B cracks were attributed to surface microcracks on the continuous casting slab, which were linked to the presence of unusual large-sized inclusions. The iron oxides within these cracks underwent two oxidation processes. The subsurface morphology and oxide characteristics are the significant features to identify these small-sized and irregular morphological cracks. [ABSTRACT FROM AUTHOR]

Bu çalışmada, rijit duvar testi sanal ortamda simule edilerek yüksek mukavemetli düşük alaşımlı çelik ön çarpışma kolu et kalınlığının aracın çarpışma performansına etkisi incelenmiş ve en uygun et kalınlığı tespit edilmiştir. Ön çarpışma kollarında HSLA (High-Strength Low-Alloy) çelik grubundaki FEE340 malzemesi kullanılmış ve altı farklı et kalınlığının aracın çarpışma performansına etkileri karşılaştırılmıştır. Simülasyonlarda çarpışma kolu, çarpışma kutusu ve ön tampon (destek) traversinden oluşan yarım araç modeli kullanılmıştır. Farklı kalınlığa sahip ön çarpışma kollarının çarpışma analizleri Abaqus sonlu elemanlar yazılımı ile gerçekleştirilmiştir. Simülasyonlardan, toplam deplasman, çarpışma kuvveti verimliliği (CFE), yolcu kabinine iletilen kuvvet miktarı ve her bir çarpışma elemanı tarafından sönümlenen enerji miktarı sonuçları elde edilmiştir. Simülasyonda kullanılan taşıt modeli için, yolcu kabinine iletilen kuvvet, ivme ve deplasman miktarları değerlendirildiğinde HSLA çelik ön çarpışma kolu için en uygun et kalınlığının 2 mm olduğu görülmüştür.

Cu-containing steels can suffer from hot shortness unless Ni is added to protect them but whether this problem also influences the straightening operation is not clear. Previous work on hot ductility has found that only when the tensile samples from Cu-containing steels are oxidised can any deleterious influence of copper be found. However, this paper shows that oxidation is not essential. It is more complex than that and, as Cu has been suggested for TRIP steels at levels up to 2.5% Cu to increase their strength and ductility, a greater understanding is required, both of hot shortness and cracking during straightening. The present paper explores the hot ductility behaviour of steels alloyed with Cu and Ni in the straightening temperature range, 700–1000 °C, when tested in air and in an argon atmosphere. Segregation of Cu to the sulphides and grain boundaries occurred allowing the formation of fine Cu2S particles at the austenite grain boundaries favouring intergranular failure and this was more pronounced under oxidising conditions and required strain. It was concluded that a Cu addition, as well as causing hot shortness at higher temperatures will also cause cracking problems in the straightening temperature range in the more sensitive to cracking grades of steel and although the problems are different they are nevertheless interrelated and provided there is sufficient Ni, both may be avoided.

This paper is concerned with the effect of welding on the fatigue behaviour of X100 material for steel catenary risers. The methodology includes both modelling and experimental characterisation. The modelling combines (i) a physically-based yield strength model to capture the thermally-induced microstructural heterogeneity and associated spatial variations in relative contributions of the key strengthening mechanisms due to welding, and (ii) a five-material cyclic plasticity model with a Coffin-Manson strain-life fatigue model for prediction of cross-weld heterogeneity in cyclic plasticity and fatigue response. The combined non-linear isotropic-kinematic cyclic plasticity behaviour of the five weld joint constituent materials (PM, weld metal (WM) and heat-affected zone (HAZ) subregions) is implemented via a user material (UMAT) subroutine, including Kocks-Mecking monotonic-cyclic evolution of yield stress. The experimental methodology consists of tensile tests with digital image correlation (DIC) for X100 PM and cross-weld samples. The results indicate that the primary phenomenon driving the detrimental effect of welding on fatigue is the evolution of cyclic strain localisation in the inter-critical heat-affected zone (ICHAZ), leading to predicted ICHAZ failure.

New alloys are needed to adapt the material properties and to improve the weldability of arc-based additive manufacturing processes. The classic development of welding filler materials is time-consuming and cost-intensive. For this reason, an alternative alloy concept is investigated and qualified here. This is based on the thin-film coating of welding filler materials by means of PVD coating. An HSLA steel DIN EN ISO 14341-A G 50 7 M21 is used as the base material. This is alloyed with the elements Al, Cr, Nb, Ni and Ti by means of PVD thin-film coating. This procedure represents an alternative alloy concept. In the scope of the qualification, the influence of the process and material properties is investigated, and the alternative alloying concept is compared with the classical alloying concept of secondary metallurgy. The investigations have shown that the thin film coating on the surface of the welding filler metal affects the process properties in the form of a changed arc length. Furthermore, the mechanical properties and the effect on the microstructure morphology were investigated. These were compared in the same chemical composition with a Mn4Ni2CrMo produced by secondary metallurgy. The results are in agreement with regard to the mechanical properties and the effect on the microstructure morphology.

The paper is based on laboratory experiments of heat treatments applied to samples of A537/A537M steel. The work continues other previous works aimed at modifying structures and properties of this steel, including through surface treatments. The experiments were performed using Taguchi methods from Quality Engineering. A number of four factors were selected as influencing the structure after heat treatment: heating temperature for hardening, cooling rate on hardening, time and tempering temperature. A number of nine experiments were performed using an L9 orthogonal matrix. Objective function was changed to maximum hardness after the heat treatment regime. The results show that the tempering temperature has the greatest influence on the final hardness of the A537 steel samples. [ABSTRACT FROM AUTHOR]

This paper describes the results of the investigations done to adapt the thermal cycles applied to High Strength Low Alloy (HSLA) steels to the new furnace configuration of a galvanizing line. During the revamping of a hot dip galvanizing line, new radiant tubes were installed in the soaking furnace with the purpose of increasing the line capacity. This modification eliminated the soaking stage and forced to redesign the thermal cycles of the furnace. As the classical cycles proposed for the HSLAs worrisomely increased the percentage of rejections, it was defined a new control parameter based on the strip thickness, time in the furnace and strip temperature to guarantee the mechanical characteristics of these steels. [ABSTRACT FROM AUTHOR]

Flash butt welding is a high-efficiency welding technology that is widely used in industrial development. However, the inclusions and defects generated during the process are unacceptable. The presence of inclusions is one of the main factors affecting the quality of flash butt welding. Suitable flash butt welding parameters such as the preheating temperature and upset distance are essential to eliminate inclusions. In this study, because the number of inclusions on the end face is greatly affected by the flash welding time and upset distance, the impact of different upset distances on the number of inclusions was studied by fixing the flash welding time. Further observations were conducted using a scanning electron microscope. Image analysis software was used on the obtained photos to quantitatively analyze the inclusions on the welding surface. A statistical analysis of the experimental data showed that the upset distance was related to the number of inclusions, and the total number of inclusions on the welding surface had a negative impact on the strength of the product.

Surface morphology of a high strength low alloy steel is analyzed on wire electric discharge machining (WEDM) process with a cold-treated (CT) brass wire. Cold treatment process is carried out at − 70 °C for 24 h to refine the microstructure of brass wire for smooth discharge energy during machining process. Fractional factorial design is used to measure the response of recast layer thickness (RLT), wire material infusion (WMI), and micro-hardness (MH) of hardened HSLA steel. CT brass wire, servo voltage (SV), pulse on time (Ton), pulse off time (Toff), wire tension (Tw), and flushing pressure (Fp) of deionized water are selected as input process parameters. Analysis of variance (ANOVA) is performed to test the adequacy and significance of the developed mathematical models. Ton is observed as the most effective input process parameter followed by Toff and CT brass wire. Low-energy parameters with CT brass wire exhibits results with reduced RLT and WMI on machined surface as compared to NCT brass wire. CT brass wire is less wear off with respect to NCT brass wire while machining workpiece at same input process parameters. [ABSTRACT FROM AUTHOR]

Isothermal hot compressive deformation tests were performed on a new high-strength low-alloy (HSLA) steel designated as "Steel A" over a range of temperatures (950–1100 °C) and constant strain rates (0.0003—1 s−1). Using the hot deformation flow behaviour data, material constants to establish constitutive relations using revised Zerilli–Armstrong and phenomenological strain-included Arrhenius model were identified. The potential of the established constitutive equations to describe the high-temperature flow behaviour of the material was then compared with standard statistical parameters such as correlation coefficient (R) and average absolute relative error (AARE). The Arrhenius constitutive model proposed by Sellars and Tegart was found to describe the high-temperature flow behaviour of "Steel A" quite accurately, and hence, this model can be used in simulations of complicated metal-forming processes. The results obtained are presented and discussed here. [ABSTRACT FROM AUTHOR]

The present study elucidates the effect of the reheating rate and tempering temperature on the type, size, and distribution of carbides/cementite formed within martensite (M)/lower bainite (LB) during the tempering of a high-strength low-alloy (HSLA) steel. A comparison is made between conventional reheating and induction reheating. All the experimental samples were quenched from the austenitization temperature of 920 °C for 30 min. An ultra-high yield strength of 1180 MPa and a good toughness of 94 J at 0 °C were obtained after tempering at 400 °C for 15 min by induction reheating (~ 100 °C/s), while in the case of conventional reheating (~ 2 °C/s) and tempering at 400 °C for 15 min, the steel had a high strength of 1159 MPa, but a poor toughness of 47 J at 0 °C. After induction reheating to 500 °C and tempering for 15 min, a higher toughness was obtained (91 J at 0 °C), but the strength was decreased to 967 MPa. Microstructural characterization revealed that fine needle-like carbides (ε-Fe2.4C) were obtained by induction reheating to 400 °C and tempering for 15 min. However, samples tempered at 400 °C by conventional reheating and 500 °C by induction reheating both precipitated coarse θ-Fe3C. In the former, θ-Fe3C precipitated at locations that were previously austenite grain boundaries and led to tempered martensite embrittlement (TME). In the latter, Ostwald ripening occurred, and the precipitates could not maintain high strength. The excellent mechanical properties of induction reheated steel (400 °C, 15 min) are attributed to the following aspects: (a) The selection of appropriate tempering temperature did not lead to decarburization and ensured high strength, and (b) a high reheating rate promoted carbide dispersion and avoided TME in steel. [ABSTRACT FROM AUTHOR]

Load-carrying capacity of weld joints could be identified by its shape and size where weld bead geometry and shape relationship parameters are of utmost importance. Heat input and preheating temperature together can control the cooling time of weld, which in turn determines the weld microstructure and its mechanical properties. To control the shape and geometry of weld bead, it is necessary to understand its relationship with cooling time. In present work, preheating temperature is used as process variable along with heat input varying parameters for understanding their effects on weld bead geometry and shape relationship parameters using submerged arc welding process on high-strength low alloy pipeline steel. The experimental investigation was then analyzed by using the mathematical modeling in context with response surface methodology. The mathematical model predicts the influential dependency of cooling time on the preheating temperature than the other weld process parameters. The associated effects in relation to the process parameters have been discussed and analyzed in the present study. [ABSTRACT FROM AUTHOR]

Wire electric discharge machining (WEDM) is a thermo-electric spark erosion non-traditional type manufacturing process. The applications of WEDM have been found in aerospace and die manufacturing industries, where precise dimensions were the prime objective. This process is applied in case of processing difficult to machine material. Brass wire is used as an electrode and High strength low alloy (HSLA) steel as a work-piece during experimentation. The present research deals with the effect of process parameters on the overcut while machining the HSLA steel on WEDM. The mathematical model has been developed with the help of Response Surface Methodology (RSM). Further this model is processed with help of Genetic Algorithm (GA) to find out the optimum machining parameters. The percentage error between the predicted and experimental values lies in the range of ±10%, which indicates that the developed model can be utilized to predict the overcut values. The experimental plan was executed according to central composite design. The optimal setting of process parameters is pulse on-time-117 μs; pulse off-time-50 μs; spark gap voltage-49 V; peak current-180 A and wire tension-6 g; for minimum overcut, whereas at the optimal setting overcut is 9.9922 μm.

A high-strength low-alloy steel, AISI 9254 (54SiCr6), is widely used for suspension spring production in the automotive industry. In this work, industrially manufactured zinc phosphate coated helical springs are subjected to detailed microstructural and surface analysis for better understanding of corrosion evolution. The material’s free corrosion potential and anodic/cathodic behaviour were investigated in NaCl solutions and corrosion propagation mechanisms were studied using potentiostatic polarisation on cross-sectional and external surfaces. The bulk material is fully martensite with uniformly distributed MnS inclusions, while the spring surface has a 2-3 μm mechanically deformed region introduced by shot-peening and a thin zinc phosphate coating. The corrosion open circuit potential of bulk material and shot-peened spring surface was about -0.7VSCE without significant difference, while phosphated surface is more noble (more positive potential). MnS inclusions, stimulating the anodic attack in the steel, influence corrosion propagation and pit morphology to a large extent that can have an impact on the spring performance. [ABSTRACT FROM AUTHOR]

To increase the limiting drawing ratio (LDR) in deep drawing, experiments are conducted on DP600, IF, and HSLA steels. The flange region of blank is heated up to temperatures in the warm range by inductance heating. During heating, the central portion of blank is cooled by water to prevent the reduction of the strength of the material in the central region. The temperature increase of flange region is observed by two infrared sensors focusing on two different points, one on the blank rim and the other near the die radius. An intensive cooling by cold water is applied to the bottom side of a blank during deep drawing. Increases up to 25.58% on LDR are obtained. There is no significant change in the microstructure of the material due to warm forming. Material characterization is obtained by a Gleeble 3800 thermo-mechanical testing machine for the temperature range 150-300 °C. [ABSTRACT FROM AUTHOR]

In this paper, the numerical distribution of residual stresses in the girth weld were determined in two (hoop an axial) direction. Two API X70 steel pipes of 56 inch outside diameter were girth welded first. Hole drilling strain gage test were conducted for strain measurement on the external surface of the pipes. The values of residual stresses were determined then from strain data using ASTM 837 standard. The values of residual stresses were determined. Next, distribution of residual stresses were assessed using spline and approximating polynomials. The well-behaved spline and polynomials, confirm the accuracy of residual stress results from experiment. The result showed lower-order polynomials have more suitable behavior in residual stress distribution. Noting to impossibility of using semi-destructive hole drilling strain gage test in project’s real situations, we can make use of these curves in assessing and estimating residual stresses distribution of similar welding. The most stable polynomial estimation curves for evaluating hoop and axial residual stress distribution are respectively third and second order. The closeness and uniformity of axial residual stress distribution curve compared to the hoop residual stress distribution curve is representative of more balanced behavior of these stresses distribution. [ABSTRACT FROM AUTHOR]

High temperature confocal microscopy (using cooling rates of 1 and 20 °C s−1) has been used in conjunction with segregation modeling (for cooling rates of 0.1–100 °C s−1) to understand the implications that high cooling rates, representative of that seen for belt casting, has on compositional inhomogeneity and precipitation in high strength low alloy steels. Due to the increased level of segregation (and reduced back diffusion) precipitates are predicted, and shown, to form in the interdendritic solute rich regions at temperatures higher than would be expected under equilibrium conditions at the higher cooling rate. This results in a larger volume fraction of precipitates in samples held at 1000 °C after being cooled at 20 °C s−1 compared to those cooled at 1 °C s−1. [ABSTRACT FROM AUTHOR]

By using the gleeble-3500 simulator, three different two-pass weld thermal cycles were applied to base metal of a high strength low alloy (HSLA) steel with the purpose of obtaining martensite-austenite (MA) constituents of different morphologies in intercritically reheated coarse-grained heat-affected zones (ICGHAZ). Morphology of each MA constituent was characterized by maximum length, maximum width and aspect ratio (maximum length/ maximum width). Toughness of thermal simulated specimens was examined by using an instrumented Charpy impact tester. Behaviour of cracks was present by Charpy impact curve and typical data. Correlation between behaviour of cracks and morphologies of MA constituents was further analysed by observing crack propagation and microstructure of MA constituent. Fracture modes of MA constituents with slender and massive shape were proposed. Results show that slender MA constituents are more harmful to toughness compared with massive ones. [ABSTRACT FROM AUTHOR]

In the present work, low-medium heat inputs of 15, 30, and 50 kJ cm−1 are adopted to simulate Coarse-Grain Heat-Affected Zones (CGHAZ) of a designed HSLA steel by Gleeble-3500 thermal simulator. Microstructures are characterized by optical microscope (OM), scanning electron microscope (SEM), and transmission electron microscope (TEM). Charpy impact tests are performed to evaluate toughness of CGHAZs. Results show that impact toughness (−50 °C) of CGHAZs with heat inputs of 15, 30, and 50 kJ cm−1 is 156.18, 172.86, and 181.49 J, respectively. Toughness stays in high level though heat input varies within low-medium range. Evolution of microstructures is investigated and micro-mechanisms of high toughness in all of the three heat inputs are discussed in detail. An original alloy design for HSLA steels with high toughness CGHAZ is proposed as well. [ABSTRACT FROM AUTHOR]