Residual stress formation in DED-Arc manufactured high strength low alloy steel thin-walled structures with solid-state phase transformations

Welding of dissimilar metal between austenitic stainless steel (γ-SS) and, high strength low-alloy (HSLA) steel are widely used in high-temperature applications in power station and petrochemical plants. Fusion welding is one of the most widely used methods for joining of dissimilar metal. Therefore, continuous efforts are made to apply this method for joining of dissimilar metal of various combinations and despite many difficulties encountered. These difficulties include problems associated with microstructure of the weld metal and heat-affected zone (HAZ). Considering the lack of such knowledge some understanding in this regard has been presented in reference to dissimilar Austenitic stainless steel (γ-SS) and high strength low alloy (HSLA) steel under controlled pulsed current GMAW. This paper focus on effect of grain size, microstructure and the width of the heat affected zone by pulsed current gas metal arc welding (PGMAW) of dissimilar γ-SS and HSLA steel. The observations show that in PGMA welds, the decrease in grain size at heat affected zone and lower HAZ Width in both HSLA steel and γ-SS especially with the lowering of summarized influence of pulse parameters factor () at similar heat input per unit length of weld (Ω) has been observed.

<div class="htmlview paragraph">Continuing pressure to reduce mass and cost of vehicles is driving the development of new high strength steel products with improved combinations of strength and formability. Galvanized, cold rolled dual phase steel products are new alternatives to conventional high strength low alloy (HSLA) steel for strength limited applications in vehicles. These steels have higher tensile strengths than HSLA products with nearly equivalent formability.</div> <div class="htmlview paragraph">This paper compares the performance of HSLA and dual phase sheet steel products in a series of drop tower tests. Samples were prepared by stamping the steel sheets into typical rail-type parts using a production-intent die process. The parts were sectioned, and subsequently fabricated into hat-shaped assemblies that were then dynamically crushed by a drop weight. The experiments were designed such that the entire energy input by the drop weight was absorbed by the samples.</div> <div class="htmlview paragraph">Results discussed in the paper include comparisons of the forces and total displacements measured during the tests. The results are presented as direct comparisons of energy absorption among the materials, as well as through correlation with mechanical properties. The results lead to the conclusion that dual phase steel absorbs approximately 10% more energy per unit mass than HSLA steel with similar yield strength and formability, and that energy absorption scales with the tensile strength of the sheet product.</div>

This article considers four types of high-strength structural steels: heat-treated low-alloy steels, as-rolled carbon-manganese steels, heat-treated (normalized or quenched and tempered) carbon steels, and as-rolled high-strength low-alloy (HSLA) steels (which are also known as microalloyed steels). The article places emphasis on HSLA steels, which are an attractive alternative in structural applications because of their competitive price per-yield strength ratios. HSLA steels are primarily hot-rolled into the usual wrought product forms and are furnished in the as-hot-rolled condition. In addition to hot-rolled products, HSLA steels are also furnished as cold-rolled sheet and forgings. This article describes the different categories of HSLA steels and provides a summary of characteristics and intended uses of HSLA steels described in the American Society for Testing and Materials (ASTM) specifications. The article also presents some applications of HSLA steels.

In automotive applications, high-strength low alloy (HSLA) steels are providing enhanced material properties, due to the high yield strength, less fragility, and lower weight, which also promotes lower fuel consumption. HSLA steels contain a small amount of carbon (under 0.2%) and also contain small amounts of alloying elements such as copper, nickel, niobium, vanadium, chromium, molybdenum and zirconium. This eliminates the toughness reducing effect of a pearlitic volume fraction, yet maintains and increases the material's strength by refining the grain size. Therefore, HSLA steels are used for structures intended to handle large amounts of stress or that need a good strength-to-weight ratio. Traditional manufacturing methods for steel (e.g., blast furnace or electric arc furnace methods) fail to provide the necessary optimization for best output in terms of performance and application. The quality of molten steel is greatly affected by scrap steel. The smelting period is longer, and the power consumption is large. In addition, these processes allow more impurities into the molten steel, which compromises the quality of the final product. However, additive manufacturing (AM) can can be used to fabricate HSLA steel components without these drawbacks. In addition, AM can provide a relatively faster process with low manufacturing costs, in comparison with traditional processing methods. Although AM has several benefits, studies shows that AM processes can result in HSLA steels with microstructural defects, such as non-homogeneity, internal cavities, inclusions, and impurities. Consequently, these microstructural features have a significant affect on the corrosion properties of AM parts as corrosion tends to initiate in defective regions. The AM processing parameters directly impact the microstructure of the fabricated part. Hence, it is important to understand the relationship between the AM processing parameters on resulting microstructural features. The present work evaluated the electrochemical corrosion properties of HSLA steels fabricated by AM via selective laser melting (SLM) under different processing conditions. The goal of the work was to investigate the role of microstructure on electrochemical corrosion in high-strength low alloy steels due to SLM processing conditions.Two types of HSLA steels, Fe 367 and Fe 398, were fabricated by AM via (SLM). Fe 398 differs from Fe 367 as it contains molybdenum and nickel. Each type was fabricated at a laser power of 100W, and scan speed of 600, 800, 100 and 1200 mm/s. The samples were exposed to 3.5% NaCl for 15 days, individually. To acquire the electrochemical corrosion data and to perform analysis, a Gamry reference 600 potentiostat/galvanostat was used. The electrochemical data were obtained by collecting the impedance spectra, and measuring the polarization resistance every 5 days. On day 15, cyclic polarization data was collected for each sample. These measurements helped to identify the localized corrosion as well as provide detailed information about the corrosion properties, such as passive layer growth, initiation and secession of pitting, and corrosion rate. The topography of the materials was observed by SEM before and after the corrosion tests. Energy Dispersive Spectroscopy (EDS) was performed on the samples to identify the chemical elements. The surface roughness was observed through confocal microscope.The Confocal and SEM images showed the change in surface microstructure and topographical properties of the samples before and after the corrosion testing. The difference in laser power and scan speed affected the microstructure and corrosion properties of the materials. As the samples were manufactured at same laser power, the scan speed was responsible for different topographical and corrosion behavior. Samples manufactured at lower scan speed showed less flaws on the surface of the materials than the samples manufactured at higher scan speed. Therefore, both Fe 398 and Fe 367 showed better surface topography at 600 mm/s and 800 mm/s. They also demonstrated significantly lower corrosion rate than the other samples. EDS identified chemical oxides and chlorides which were formed during the corrosion test. Overall, this work demonstrated that Fe 398 shows better microstructural and corrosion properties than Fe 367 at lower scan speed.

This paper is a continuation of work that shows results to help better understand the behavior of a quenched and tempered (Q & T) high strength low alloy (HSLA) steel. The first set of results was presented in NACE-2014. Experiments showed multiple through-thickness-cracks emanating from the circumferential weld on the shell-side after a short time of service in the heat exchangers.. The failure has been preliminary diagnosed as Environmentally Assisted Cracking (EAC), which is general term for brittle mechanical failures that result from a combination between residual tensile stress, susceptible microstructure and corrosive environment. Slow Strain Rate Testing (SSRT), which is conducted in a high temperature-high pressure autoclave, has been carried out using a Constant Extension Rate Test (CERT) machine. Stress corrosion testing of this Q&T HSLA steel has been carried out from 25 to 175 °C at a constant strain value (10-4 s-1) in two alkaline environments. After the fracture of the specimen, Scanning Electron Microscope (SEM) was used to study the crack morphology as a function of the applied strain. To calculate the stress corrosion cracking (SCC) susceptibility, the plastic strain-to-failure ratio (EPR) was calculated from the stress-strain curve and the reduction-in-area ratio (RAR) calculated from the fracture surface of the broken specimens. Results indicate that SCC susceptibility increased with increasing temperature and the percentage of salt in the solution. Understanding the SCC behavior of Q&T HSLA steel at higher temperatures and in alkaline environments and taking proper preventive measures can help to avoid failures in the future.

The heat exchangers (coolers) made of a quenched and tempered (Q&T) High Strength Low Alloy (HSLA) Steel developed multiple cracks emanating from the circumferential weld in the shell after a short time of service. Some of the cracks had grown through the thickness and started to leak. The failure has been diagnosed as Environmentally Assisted Cracking (EAC), which is a general term for brittle mechanical failures that result from a combination between residual tensile stress, susceptible microstructure and corrosive environment. Environmentally assisted cracking includes stress corrosion cracking (SCC) and hydrogen-induced cracking (HIC). Slow Strain Rate Testing (SSRT), which is in connection with a high temperature-high pressure autoclave, has been carried out using a Constant Extension Rate Test (CERT) machine. Stress corrosion testing of this Q&T HSLA steel has been carried out from 25 to 175 °C at a constant strain value (10-4 s-1) in two alkaline environments. After the fracture of the specimen, Scanning Electron Microscope (SEM) was used to study the crack morphology as a function of the applied strain. To calculate the SCC susceptibility, the plastic strain-to-failure ratio (EPR) was calculated from the stress-strain curve and the reduction-in-area ratio (RAR) from the fracture surface of the broken specimens. Results indicate that SCC susceptibility increased with increasing temperature and the percentage of salt in the solution. Understanding the SCC behavior of Q&T HSLA steel at higher temperatures and in alkaline environments and taking proper preventive measures can help to avoid failures in the future.

This study attempts to incorporate the effect of elastic deformation in a previously proposedmodel for the nucleation and growth of precipitates. We adapt the KWN-model by Robson to incor-porate the effect of strain energy arising from elastic deformation on the homogeneous nucleation andgrowth of NbC particles in a High Strength Low Alloy (HSLA) steel at constant temperature. Simula-tions of the nucleation and growth of NbC particles in an HSLA steel on the cylindrical region showthat the incorporation of elastic strain energies has a noticeable impact on the process. The derivedquantities of homogeneous nucleation and growth, such as the particle number density and the meanparticle radius, show a clear spatial correlation with the calculated strain energy.

High Strength Low Alloy (HSLA) steels are the materials of choice in pipeline construction with the API X70 grade as the steel for the majority of pipeline networks constructed during the late 20th and early this century. This paper reports on the influence of Post-Weld Heat Treatment (PWHT) on the reduction of residual stresses, resulting changes in the microstructure, and mechanical properties of a multi-pass, X70 HSLA steel, weld joints made by a combined Modified Short Arc Welding (MSAW) and Flux Cored Arc Welding (FCAW) processes. Neutron diffraction results highlighted high magnitude of tensile residual stresses, in excess of yield strength of both parent and weld metal, in the as-welded specimen (650 MPa), which were decreased substantially as a result of applying PWHT (144 MPa). Detailed microstructural studies are reported to confirm the phase transformation during PWHT and its interrelationship with mechanical properties. Transmission Electron Microscopy (TEM) analysis showed polygonization and formation of sub-grains in the PWHT specimen which justifies the reduction of residual stress in the heat-treated weld joints. Furthermore, microstructural changes due to PWHT justify the improvement in ductility (increase in the elongations) with a slight reduction in yield and tensile strength for the PWHT weld joint.

Mild steel reinforcing bars embedded in concrete exposed to marine environment are prone to severe corrosion leading to serious damage to the structures. The various technologies developed and adopted to reduce the corrosion of steel reinforcement, have been discussed in this paper along with a new high strength low alloy (HSLA) steel reinforcing bar. The bare HSLA rebars have been tested extensively along with mild steel rebars for comparative study in saline and sulphurous electrolytes in the laboratory by Potentiodynamic tests as well as in natural marine and industrial environments. The HSLA and mild steel rebars embedded in concrete were also tested in saline water by alternate immersion test and by impressed anodic current methods. The bare HSLA rebars showed 2-3 and 1.5- 1.9 times better corrosion resistance to mild steel rebars in laboratory and field exposure tests respectively. The HSLA rebars embedded in concrete and exposed to saline water with impressed anodic current of 200 µA/ sq. cm showed 2.5 times better corrosion resistance to mild steel rebars. The XRD analysis of the rust formed on the samples of field exposure tests conducted in marine and industrial environments, clearly showed the formation of compounds which reduce the corrosion rate of steel.

An electrical resistivity technique has been employed to provide an insight into the phase transformations occurring in a plain low carbon and in a copper bearing high strength low alloy (HSLA) steel. It has been established that the phase transformation temperatures can be accurately estimated when there is a simultaneous magnetic transition. Thus, the Curie temperature of the HSLA steel was observed to be 690° C as against 730° C for the plain carbon steel. Furthermore, Bs (550° C) and Bf (~390° C) (start and finish temperatures for bainite) were determined using continuous resistivity data. In the HSLA steel, the amount of copper precipitation could be estimated during heating from the quenched condition, the value of which matched well with those derived from isothermal resistivity experiments reported elsewhere.

Formation mechanism and control methods of acicular ferrite in HSLA steels: A review

Effect of alloy element on corrosion behavior of the huge crude oil storage tank steel in seawater

Dissimilar metal weld between austenitic stainless steel (γ-SS) and, high strength low-alloy (HSLA) steel are widely used in high-temperature applications in power station and petrochemical plants. Fusion welding is one of the most widely used methods for the joining of dissimilar metal. Therefore, continuous efforts are made to apply this method to the joining of dissimilar metal of various combinations, despite many difficulties encountered. These difficulties include problems associated with basic thermal aspects dictating the metallurgical mechanical characteristics of the weld joint are not well understood so far. Considering the lack of such knowledge some understanding in this regard has been presented in reference to dissimilar Austenitic stainless steel (γ-SS) and high strength low alloy (HSLA) steel under controlled pulsed current GMAW. The work demonstrates the weld isotherm as a function of controlled pulse current GMA welding. The observations show some superiority of using pulse current GMA welding over the conventional one with respect to the weld quality which can be explored in preparation of weld joint of HSLA and γ-SS of improved characteristics.

<div class="section abstract"><div class="htmlview paragraph">Advanced high strength steels (AHSS) such as dual phase (DP) steels are now being extensively used to achieve light weighting goals of vehicles because of their attractive combination of formability and high strength. High strength low alloy (HSLA) steels are also used in lightweight bodies-in-white; DP and HSLA steels are therefore often laser butt-welded together into tailor welded blanks and to create other joints. Among the laser welding processes, fiber laser welding (FLW) has been shown to provide excellent quality welds, including superior weld mechanical properties, at higher speeds than those possible with other laser welding processes. Using dissimilarly welded DP980-HSLA blanks made with different welding parameters, the tensile properties were found to not change in spite of the HSLA being weaker than the soft zone on the DP980 side of the weld. The high heat input weld was found to have more softening in comparison to its base metal (BM) (55 HV versus 46 HV) and less bainite (8% versus 15%) in its FZ in comparison to the low heat input weld. The fatigue properties of the high heat input weld were also found to be better than those of the low heat input weld.</div></div>

Acicular ferrite is a desirable microstructure in high strength low alloy steel weld metal. This is due to its improved toughness and the enhanced mechanical properties of the weld metal. Although the nucleation of acicular ferrite has been studied by many researchers, the exact mechanisms of its nucleation and growth are still under discussion and remained unclear. In this research work, the mechanism of acicular ferrite formation in the weld metal as cast structure has been clarified as diffusion controlled solid state phase transformation. This is based on the classic theory of nucleation and growth which can contribute to possible increase of nucleation sites and growth of intergranular ferrite in HSLA steel weld metal. Therefore, it could be considered that inclusions are not acting as a nucleation site for the intergranular acicular ferrite. Consequently, our results revealed that, in austenite transformation to pro-eutectoid and acicular ferrite, manganese as an austenite stabilizer alloying element is playing an important role in the nucleation and growth of the ferrite grains. It should be added that cooling rate accompanied with the presence of other alloying elements has influenced the type and morphology of the final ferrite microstructure and constituent products.