Showing papers on "High-strength low-alloy steel published in 2015"

Evaluation of microstructure and texture across the welded interface of super duplex stainless steel and high strength low alloy steel

Abstract: The evolution of microstructure and texture across the fusion boundary of a dual-layer super duplex stainless steel clad metal produced on a high strength low alloy steel substrate by gas tungsten arc welding process was examined by optical microscopy, X-ray diffraction, electron backscatter diffraction, and energy-dispersive X-ray spectroscopy. It was found that a martensitic band with occasional Type I and Type II boundaries separated the substrate's heat affected zone from the high austenite containing region of the clad metal. Due to the competitive growth, both the ferrite and austenite grains showed almost the same ║ ND orientation near the fusion boundary. While the texture of the austenite was not as strong as that of the ferrite across the cladding layers, the results confirmed that the austenite daughter phase was formed with a close Kurdjumov–Sachs orientation relationship with respect to the parent ferrite phase. It was also found that although both the residual stress and reheating caused some microstructural transformation and texture modification to some parts of the cladding, the major factors affecting the texture were unidirectional solidification, competitive growth, and δ/γ orientation relationship. The only exception was related to the occasional highly deformed mostly austenite area adjacent to the fusion boundary, where partial recrystallization led to formation of some annealing twins. The findings suggested that the reheating which occurred during the deposition of the second layer generated higher ferrite content and produced some secondary austenite with dominant Widmanstatten morphology across the first cladding layer. Moreover, it imposed higher residual strain and also promoted limited recrystallization adjacent to the fusion boundary.

Evaluation of the cold formability of high-strength low-alloy steel plates with the modified Bai–Wierzbicki damage model

Abstract: While strength and toughness properties of construction steels are major mechanical properties with respect to the safety assessment of components, increasingly often requirements are defined on th...

Effect of microstructure variation on the corrosion behavior of high-strength low-alloy steel in 3.5wt% NaCl solution

Abstract: The effect of microstructure variation on the corrosion behavior of high-strength low-alloy (HSLA) steel was investigated. The protective property of the corrosion product layer was also explored. Experimental results reveal that the type of microstructure has significant effect on the corrosion resistance of HSLA steel. The measurement results of weight loss, potentiodynamic polarization curves, and electrochemical impedance spectroscopy indicate that the steel with acicular ferrite microstructure exhibits the lowest corrosion rate. Martensite exhibits a reduced corrosion resistance compared with polygonal ferrite. It is found that the surface of the acicular ferrite specimen uniformly covered by corrosion products is seemingly denser and more compact than those of the other two microstructures, and can provide some amount of protection to the steel; thus, the charge transfer resistance and modulus values of the acicular ferrite specimen are the largest. However, corrosion products on martensite and polygonal ferrite are generally loose, porous, and defective, and can provide minor protectiveness; thus, the charge transfer resistance values for polygonal ferrite and martensite are lower.

In situ observation of acicular ferrite formation and grain refinement in simulated heat affected zone of high strength low alloy steel

Abstract: The phase transformation from austenite to acicular ferrite in the simulated coarse grained heat affected zone of a high strength low alloy steel was investigated by means of analytical characterisation techniques such as in situ microscopy, transmission electron microscopy and electron backscattered diffraction analysis. The acicular ferrite grains nucleated on inclusions (Zr–Ti oxides) in coarse austenite grain grew in different directions and effectively partitioned coarse austenite grain into several finer and separate regions. The crystallographic grain size became small for coarse austenite grains due to the effective partitioning by acicular ferrite laths or plates.

Dualism of precipitation morphology in high strength low alloy steel

Abstract: While the role of microalloying elements on precipitation strengthening in ferrite matrix during austenite/ferrite transformation is quite clear, some uncertainty still exists concerning the variability of the microhardness distribution of ferrite grains in the isothermal holding condition. The objective of the present study was to clarify the intrinsic characteristics of carbide precipitation morphology in the ferrite matrix under different processing temperatures and times and to correlate it with austenite decomposition kinetics to elucidate why a large microhardness distribution occurs at low isothermal holding temperature. Better understanding of carbide precipitation behavior can help researchers to determine the root cause of variation in microhardness distribution, which would allow metallurgists to produce high quality steels. Measurement with a Vickers hardness indenter revealed that, in specimens isothermally held at 625 °C, the range of Vickers hardness distribution was 240–420 after 5 min of isothermal holding, and 270–340 after 60 min. For specimens isothermally held at 725 °C, the range of Vickers hardness distribution was 200–330 for 5 min of isothermal holding, and 200–250 for 60 min. Therefore, the average microhardness decreased with the isothermal holding temperature and time, and a larger range of distribution occurred with short isothermal holding times. Transmission electron microscopy (TEM) images showed that interface precipitation and random precipitation can occur within the same ferrite grain. The reason is that the austenite decomposition rate varies with transformation temperature and time. An excessively fast austenite/ferrite interface movement velocity, which usually happens in small ferrite grains, would cause these ferrite grains with microalloying elements to exceed their solubility. Furthermore, these microalloying elements will be precipitated randomly after isothermal holding at longer times. Consequently, a large microhardness distribution can usually be detected in specimens with tiny ferrites because some ferrite grains are in a fresh state, without carbides, due to high austenite/ferrite interface movement velocities. Furthermore, one important technological limit that should be kept in mind is the difficulty of developing only one type of precipitation morphology (i.e., interface precipitation or random precipitation) within every ferrite grain.

Interfacial Characterization of Dissimilar Joints Between Al/Mg/Al-Trilayered Clad Sheet to High-Strength Low-Alloy Steel

Abstract: Magnesium (Mg) alloys are increasingly used in the automotive and aerospace sectors to reduce vehicle weight. Al/Mg/Al tri-layered clad sheets are deemed as a promising alternative to improve the corrosion resistance and formability of Mg alloys. The structural application of Al/Mg/Al tri-layered clad sheets inevitably involves welding and joining in the multi-material vehicle body manufacturing. This study aimed to characterize the bonding interface microstructure of the Al/Mg/Al-clad sheet to high-strength low-alloy steel with and without Zn coating using ultrasonic spot welding at different levels of welding energy. It was observed that the presence of Zn coating improved the bonding at the interface due to the formation of Al-Zn eutectic structure via enhanced diffusion. At a higher level of welding energy, characteristic flow patterns of Zn into Al-clad layer were observed with an extensive penetration mainly along some high angle grain boundaries. The dissimilar joints without Zn coating made at a high welding energy of 800 J failed partially from the Al/Fe weld interface and partially from the Al/Mg clad interface, while the joints with Zn coating failed from the Al/Mg clad interface due to the presence of brittle Al12Mg17 phase.

Variation in the Chemical Driving Force for Intragranular Nucleation in the Multi-pass Weld Metal of Ti-Containing High-Strength Low-Alloy Steel

Abstract: The variation of the Mn-depleted zone (MDZ) around the inclusion during multi-pass welding of Ti-containing high-strength low-alloy (HSLA) steel was investigated by taking the changes in the impact toughness and microstructure into account. As-deposited weld metal specimens were prepared by single-pass, bead-in-groove welding, and reheated weld metal specimens were obtained by a thermal simulation technique. Two types of chemical compositions were prepared, mainly by controlling the Ti content in order to form two types of phases at inclusion/matrix interface: spinel and ilmenite. When the reheating thermal cycle is applied to the as-deposited weld metal, the MDZ depth varied depending on the inclusion surface phase; this could be explained by the competition of the homogenization effect and the dissolution effect, which occurred near the inclusion/matrix interface. In order to enhance the chemical driving force for intragranular nucleation in both as-deposited weld metal and reheated weld metal, the formation of ilmenite phase is recommended.

Surface Modification of Micro-Alloyed High-Strength Low-Alloy Steel by Controlled TIG Arcing Process

Abstract: Surface modification of micro-alloyed HSLA steel plate has been carried out by autogenous conventional and pulse current tungsten inert gas arcing (TIGA) processes at different welding parameters while the energy input was kept constant. At a given energy input the influence of pulse parameters on the characteristics of surface modification has been studied in case of employing single and multi-run procedure. The role of pulse parameters has been studied by considering their summarized influence defined by a factor Φ. The variation in Φ and pulse frequency has been found to significantly affect the thermal behavior of fusion and accordingly the width and penetration of the modified region along with its microstructure, hardness and wear characteristics. It is found that pulsed TIGA is relatively more advantageous over the conventional TIGA process, as it leads to higher hardness, improved wear resistance, and a better control over surface characteristics.

Prediction of element transfer due to flux and optimization of chemical composition and mechanical properties in high-strength low-alloy steel weld

Abstract: The transfer of elements C, Si, Mn, P and S from slag into the weld metal or from weld metal into the slag and microhardness has been studied using formulated fluxes. The fluxes have been formulate...

The role of Ti carbonitride precipitates on fusion zone strength-toughness in submerged arc welded linepipe joints

Abstract: The role of micro-alloying in the submerged arc welding (SAW) of high strength low alloy steel linepipe is paramount in facilitating the high strength properties of the linepipe. In this study, transmission electron microscopy analysis revealed the presence of large (0.85 µm) Ti (C,N) precipitates within the predominantly acicular ferrite SAW joint. Cross-weld Vickers hardness and Charpy impact tests revealed that the fusion zone has high hardness and low toughness properties in relation to the base metal and heat affected zone. Fractography observations made on the ductile fracture surface of the fusion zone revealed a high number of the large Ti (C,N) precipitates to be located within the microvoids – suggesting their role in nucleating microvoids. Finally, fracture micro-mechanics are used to evaluate the relationship between the coarse precipitates and reduced strength-toughness properties in the SAW weld of the API-5L grade X65 linepipe steel.

Influence of Ti on weld microstructure and mechanical properties in large heat input welding of high strength low alloy steels

Abstract: The influence of Ti on weld microstructure and mechanical properties in large heat input welding of high strength low alloy steels is investigated. The results indicate that a moderate amount of Ti is still effective for grain refinement even under larger heat input and a large amount of acicular ferrite (AF) is formed in the weld metal when Ti content is within 0.028%–0.038%. With increasing Ti content, proeutectoid ferrite in the weld metal decreases, whereas bainite and M-A constituent increase. The type of inclusion in the welds varies from Mn-Si-Al-O to Ti-Mn-Al-O and finally to Ti-Al-O as Ti content increases from 0 up to 0.064 %. As for adding 0.028%–0.038% Ti, high weld toughness could be attained since most inclusions less than 2 µm which contain Ti2O3 provide the effective nuclei for acicular ferrite formation. However, the toughness of the weld metals severely reduces when Ti content is over the optimum range of 0.028%–0.038%.

Research on the Origin of Nonmetallic Inclusions in High-Strength Low-Alloy Steel Using Automated Feature Analysis

Abstract: The aim of this paper is an investigation of thermo-temporal nature of nonmetallic inclusions, which were found in samples taken from high-strength low-alloy (HSLA) steel forgings and plates, treated with silico-calcium. For an objective assessment of the chemistry of non-metallic inclusions, a SEM-EDS microanalysis method called automated feature analysis (AFA) was used. This technique makes it possible to examine large quantities of inclusions only comparable to optical microscopy methods, but AFA provides also a compositional data along with conventional metrics [1]. By chemical composition, the inclusions in the acquired database mostly belong to the Al-Mg-Ca-S-O system. Note that the composition of these inclusions also contains small concentrations of manganese and silicon.

Study on Dissimilar Butt Joining of Aluminum Alloy, AA5052 and High Strength Low Alloy Steel through a Modified FSW Process

Abstract: In the preset investigation, aluminum alloy, AA5052 and HSLA steel are successfully butt welded using a modified FSW process wherein the work pieces submerged in a liquid medium are stirred by the FSW tool. The trials are conducted by varying the tool rotational speed from 400 rpm to 900 rpm while keeping the other parameters constant. The welded joints are tested for ultimate tensile strength (UTS) and the joint interface microstructure is analyzed using SEM and EDS. The results show that when compared to the normal FSW process, the peak value of UTS is marginally low but the range of tool rotational speed that could produce defect free joints with good joint strength is almost doubled in the modified FSW process.

Optimization of calcium addition to high-strength low-alloy steels

Abstract: Nozzle blockage is a common problem during continuous casting of Al-killed steel, and calcium treatment is widely used to resolve it. In consideration of the production costs, the technology of nonmetallic inclusion control was studied to optimize the Ca consumption. The proposed process of slag washing was employed, and the refining slag composition, deoxidation conditions and alloying systems were optimized. Using these measures, the steel cleanliness before Ca addition was improved significantly, and the corresponding Ca consumption was reduced. Moreover, the continuous casting could be conducted smoothly.

Super-high Strength Low Alloy Steel OCTG with Improved Sour Resistance

Abstract: Material design concepts and the applicability of 125ksi (862MPa) grade super-high strength low alloy steel OCTG (oil country tubular goods) for sour service are described in this paper. Following metallurgical techniques were necessary for enhancing sour (SSC) resistance - prevention of pitting by minimizing inclusion size, decrease in dislocation density by high temperature tempering using nano-sized carbides, and improvements of carbides morphologies at grain boundaries - spheroidizing M 3 C and preventing M 23 C 6 formation. The developed steel showed superior SSC resistance to conventional steels on the H 2 S-pH domain map. The 125ksi sour grade OCTG was commercialized in 2003, the first material of that kind in the world. This new OCTG has been used in deep gas wells in the UK and Norwegian North Sea, and the Caspian Sea.

Influence of Specimen Thickness on Thermal Desorption Spectrum of Hydrogen in High Strength SCM435 Steel

Abstract: Thermal desorption analysis (TDA) is widely used to identify the trap site and the state of presence of hydrogen in steel.1) In a previous study we developed a finite difference computer program which simulates the spectrum of thermal desorption analysis (TDA) of hydrogen in steel.2) The simulation model was based upon the McNabb-Foster model3) with the hydrogen trap sites of discrete binding energies. The key parameters, e.g. trap energy and detrapping coefficient, were determined by fitting with the spectra of cylindrical specimens of 2.5 mm in radius by trial and error. From the value of the detrapping coefficient p0=25–30 s −1,2) it was thought that hydrogen desorption seemed to occur almost in the detrapping-controlled condition because the interval of detrapping events, i.e. inverse of p0, was calculated to be greater than the diffusion time to the surface of the specimen. The TDA spectrum is highly dependent on the specimen thickness. In a thin specimen lattice diffusion of hydrogen does not play a significant role in desorption because detrapped hydrogen almost instantly diffuses to the surface of the specimen. On the other hand, in a thick specimen lattice diffusion has a major influence on the spectrum shape because hydrogen atoms can escape from the trap site to such an extent that the hydrogen concentration in the lattice maintains equilibrium with that in the trap site. This is called diffusion-controlled desporption. If peak temperatures are measured at several ramp rates, the detrap energy of hydroInfluence of Specimen Thickness on Thermal Desorption Spectrum of Hydrogen in High Strength SCM435 Steel

Phase transformation mechanism of low-carbon high strength low alloy steel upon continuous cooling

Abstract: The transformation characteristics of low-carbon high strength low alloy steel for various cooling rates were systematically investigated by means of dilatometric measurements and microstructure observations. According to the results, it is recognised that the increase of the cooling rate could lead to microstructure evolution from a mixture of polygonal ferrite, acicular ferrite and bainite ferrite to the dual phase of acicular ferrite and bainite ferrite. The kinetics mechanism of the phase transformation was further studied by a modified analytical phase transformation model, which involves site saturation, diffusion/interface-controlled growth, impingement correction for randomly distributed growing particles. It is demonstrated that diffusion-controlled polygonal ferrite and acicular ferrite phase transformation precedes the interface-controlled bainite ferrite phase transformation. For the diffusion-controlled growth, the transformation is slowed down with the increase of the cooling rate, w...

Effect of Fiber YAG Laser Parameters on the Microstructural and Mechanical Properties of High Strength Low Alloy Steel

Abstract: This article reports on an experimental investigation to weld high strength low alloy steel using YAG fiber laser at different processing conditions. Three level of the laser power were investigated: 2500 W, 2000 W and 1500 W, at fixed welding speed of 40 mm/s. Welding speeds of 50 mm/s, 40 mm/s and 25 mm/s were used at a fixed power of 2500 W. Moreover, the defocusing distance was changed from -2 mm to +1.5 mm at a fixed power of 2500 W and speed of 40 mm/s. Full penetration joints without any macro defects were produced by laser power more than 2000 W. While at 1500 W, partial penetration defect was occurred. The microstructure of the weld zone show acicular ferrite and bainite at higher power and martensite and some ferrite at lower power. When the laser speed was decreased to 25 mm/s, the width of the weld and heat affected zone became wide. Lack of penetration and other defects (porosity) with wide weld zone were appeared at defocusing distance more than -1 mm. The welded joints that welded with higher laser powers and negative defocusing distance gave fracture strength values very close to that of the base metal.

Laser treatment of high strength low alloy steel and electrochemical response of the surface

Abstract: Purpose – The purpose of the present study is to report the results of the laser treatment of high-strength low-alloy (HSLA) steel surface and corrosion response of the treated surface that was carried out. Metallurgical and morphological changes in the laser-treated layer are also examined. Laser treatment of the alloy surface improves the surface properties; however, development of high thermal stress field in the treated layer can exceed the yielding limit of the alloy lowers, particularly, the corrosion resistance of the resulting surface. Design/methodology/approach – Pre-prepared workpiece surfaces are laser-treated and electrochemically tested in an electrolytic solution. Corrosion rate of the resulting surface is analyzed and pit sites are examined. Findings – It is found that the presence of nitride compounds and fine grains acts like as a self-protective layer at the laser-treated surface while lowering the corrosion resistance. Consequently, laser gas-assisted treatment provides a positive effe...

Effect of microstructure variation on the corrosion behavior of high-strength low-alloy steel in 3.5wt% NaCl solution

Abstract: 高张力的腐蚀行为上的微观结构变化的效果低合金(HSLA ) 钢被调查。腐蚀产品层的保护的性质也被探索。试验性的结果表明微观结构的类型在 HSLA 钢的腐蚀抵抗上有重要效果。重量损失， potentiodynamic 极化曲线，和电气化学的阻抗光谱学的测量结果显示有针状的铁酸盐微观结构的钢展出最低腐蚀率。马氏体与多角形的铁酸盐相比展出一个减少的腐蚀电阻。腐蚀产品一致地盖住的针状的铁酸盐标本的表面比另外的二微观结构的那些看起来更稠密、更紧缩，这被发现，并且能提供保护的某数量给钢；因此，针状的铁酸盐标本的费用转移抵抗和模量价值最大。然而，马氏体上的腐蚀产品和多角形的铁酸盐通常松开、多孔、有缺点，并且能提供次要的保护；因此，为多角形的铁酸盐和马氏体的费用转移抵抗价值更低。

Effects of cooling techniques after heat treatment of reinforced hsla steels on their structure, tensile and impact properties

Abstract: Article History: Received 14, April, 2015 Received in revised form 23, April, 2015 Accepted 13, May, 2015 Published online 28, May, 2015 The effect of cooling methods after heat treatment on the microstructure and mechanical properties of reinforced high strength low alloy steel were studied. The microstructure characteristics were observed under OM (optical microscope), SEM (Scanning Electron Microscope). Charpy V Notch impact tests at different temperatures (-30°C, -10°C, 25°C) along with Tensile tests were performed and the mechanical properties were evaluated. The evaluated results indicated that cooling with water led to a mix of ferritic matrix and tempered martensite, whereas after air cooling the microstructure was a mix of ferritic matrix and tempered bainite. This is basically due to the intensity of cooling rate in both the cooling techniques. Ultimate tensile strength, yield strength, % elongation were compared for the different cooling techniques. In air cooling the combination of strength and toughness was better than in comparison with water cooling.

Cold rolled high strength low alloy steel

Abstract: The invention relates to a high strength low alloy steel. According to the invention the high strength low alloy steel strip, sheet or blank, coated with zinc or a zinc alloy, has the following composition in weight%: C: 0.03 - 0.07, Mn: 0.70 - 1.60, Si: ≤ 0.01 - 0.2, Al: 0.005 - 0.1, Cr: ≤ 0.1, Cu: ≤ 0.2, N: ≤ 0.008, P: ≤ 0.03, S: ≤ 0.025, O: ≤ 0.01, Ti: 0.02 - 0.07, V: 0.04 - 0.15, Mo: ≤ 0.03, Nb: ≤ 0.03, Ca: ≤ 0.05, the remainder being iron and unavoidable impurities, wherein the steel strip, sheet or blank has a yield strength Rp0,2 of at least 420 MPa.

Literature review on the effect of processing on the mechanical and metallurgical properties of low carbon

Abstract: In this paper the effect of the mechanical/thermo mechanical processing on the mechanical and metallurgical properties of low carbon steels, viz, Cold Reduced low carbon Steel (CRS) and Themo Mechanically Treated (TMT) steel are discussed. These steels are widely used in automobile, railways, naval architecture, petroleum industry, etc, applications with exposure to extreme temperature conditions and subjected to stress and exposed to corrosive environment [1]. The most commonly used type of steel are low carbon steel, High Strength Low Alloy Steel (HSLA), Cold Rolled Steel and Hot Rolled steel (HRS). The mechanical properties like ductility, strength and metallurgical properties like microstructure, grain size, etc, influence the properties of the rolled steels. In this paper an effort is made to study the research reported in literature, on the innovations in processing of low carbon steel through grain refinement and heat treatment to produce steel possessing good mechanical and metallurgical properties.