Carbon Low Alloy Research Articles

Microstructure and Properties Formed at Different Cooling Rates of Low Carbon Alloy Steel for Welding Wire Production

Physical simulation of steel Mn3Ni1CrMo continuous cooling with different speeds from austenitic state was performed using GLEEBLE 3500 complex. The phase transformations are analyzed and the effect of the cooling rate on the structure and hardness is investigated. A continuous cooling transformation diagram of the undercooled austenite decomposition is constructed. It was concluded that it is possible to reduce the hardness of the hot-rolled billet by reducing the cooling rate compared to the existing in the processing at the STELMOR line of PJSC “MMK”, and this will eliminate the heat treatment of welding wire on the hardware processing.

The Formation Mechanisms and Improvement Measures for Penetrating Cracks in QAl9-4/Q345B Welded Joint

The dissimilar joining of QAl9-4 aluminum-bronze alloy to Q345B low carbon low alloy steel was performed by fusion welding using different techniques. The results indicated a certain amount of transverse cracks and voids in the QAl9-4/Q345B joints welded by the SMAW process, while defect-free joints were obtained using the GTAW process. The microstructure of samples produced by the SMAW process exhibited transverse cracks with typical partially oxidized intergranular cracking characteristics. Banded films rich in Cu at the grain boundaries were observed, which were demonstrated to be related to premature failure of the samples under tensile and impact load, indicating that the transverse cracks are hot cracks caused by the penetration of Cu element. Good strength and good toughness of QAl9-4/Q345B welded joints were obtained by the GTAW process.

Abnormal mechanical response in a silicon bearing medium carbon low alloy steel following quenching and bainitic holding versus quenching and partitioning treatment

Multiphase advanced high strength low alloy steels having a refined microstructure of hard bainite and/or martensite laths, interspersed with finely divided retained austenite films, are the potential candidate materials for futuristic industrial applications, such as automotive industry, structural parts, crankshafts and shafts, and powertrain components. In this study, a silicon-bearing, medium-carbon low alloy steel grade of DIN 1.5025 was subjected to both quenching and bainitic holding (Q&B), as well as quenching and partitioning (Q&P) isothermal heat treatments at temperatures closely above and below the martensite start temperature (Ms), respectively. The mechanical response of heat treated samples was evaluated by conducting hardness and tensile tests, corroborated by XRD analysis and metallography using both scanning electron microscopy combined with electron backscatter diffraction as well as transmission electron microscopy. The experimental results showed that a number of Q&B heat treated samples displayed a superior combination of high strength levels with good ductility and work hardening capacity in comparison to that of Q&P ones, akin to the requirements for third generation high strength multiphase steels. It was also found that the superior mechanical response of Q&B heat treated samples was rationalized in respect of the formation of tough strong multiphase microstructures involving a fine mixture of hard bainite and/or martensite laths along with thin films of mostly interlath retained austenite that imparted superior combination of ductility and tensile strength through TRIP phenomenon. Moreover, limited tensile test results conducted in this study, supported by XRD and electron microscopy analyses, suggested that the TRIP response was quite effective in the Q&B multiphase samples containing more than 18 vol.% of retained austenite.

Atomic-scale study on the mechanism of formation of reverted austenite and the behavior of Mo in a low carbon low alloy system

The mechanism of formation of reverted austenite in a low carbon low alloy system was comprehensively studied by 3D atom probe tomography and Thermo-Calc simulation. It was observed that low C-content provided the condition for nucleation of reverted austenite at lath boundaries, while the alloying elements, Mn, Ni and Cu led to the growth of reverted austenite. Mo provided diverse impact on mechanical properties of steel at high temperature. (1) The diffusional direction of Mo atoms was controlled by the partitioning of Mo; (2) MoC co-segregation layers, nano MoC clusters, nano Mo clusters and MoC precipitates were formed at two-phase interfaces; (3) Mo formed nano MoC clusters and MoC precipitates at lath boundaries or in the matrix; (4) Mo promoted the formation of Nb carbides and was dissolved in carbides to produce (NbxMo1-x)C precipitates. High resolution transmission electron microscopy images of (NbxMo1-x)C precipitates showed that they had face-centered cubic structure and the lattice constant was in the range of 0.440–0.445 nm. Nano Cu precipitates were observed in reverted austenite. MoC co-segregation layers, nano MoC clusters, nano Mo clusters and MoC precipitates formed at γ/α interfaces effectively enhanced the grain boundary strength. Nano MoC clusters, MoC precipitates and (NbxMo1-x)C precipitates in the matrix effectively pinned dislocations and prevented movement of dislocations. The combined effect led to good fire resistance and heat resistance properties of studied steel.

Influence Mechanism of Silicon on Carbide Phase Precipitation of a Corrosion Resistance Nickel Based Superalloy.

The effect of silicon on diffusion behavior of the carbide forming elements in Ni-Mo-Cr-Fe based corrosion-resistant alloy is studied by diffusion couple experiment. One group of diffusion couples are made of the alloy with a different silicon content, another group of diffusion couples are made of pure nickel and the alloy with different silicon content (0Si, 2Si). Two groups of alloys with same silicon content and different carbon content are also prepared, the microstructure of solution and aging state of these two groups alloys are analyzed, and their stress rupture properties are tested. The effect of silicon on the diffusion of alloy elements and the interaction effect of carbon and silicon on the microstructure and stress rupture properties of the alloy are analyzed. The mechanism of Si on the precipitation behavior of carbide phase in Ni-Mo-Cr-Fe corrosion resistant alloy is discussed. The results show that silicon can promote the diffusion of carbide forming elements and the formation of carbide. The precipitation behavior of the secondary phase is the result of the interaction effect of silicon and carbon, and is related to the thermal history of the alloy. Combined with the characteristic of primary carbides, it is confirmed that the precipitation of M12C type secondary carbide is caused by the relative lack of carbon element and the relative enrichment of carbide forming elements such as molybdenum. The stress rupture properties of two silicon-containing alloys with different carbon contents in solution and aging state are tested. The stress rupture life of low carbon alloy is lower compared with high carbon alloy at solution state, but after aging treatment, the stress rupture life of low carbon alloy is significantly improved, and higher than that of high carbon alloy. The main aim of this research is to reveal the influence mechanism of silicon on carbide phase precipitation of a Ni-Mo-Cr-Fe based corrosion-resistant superalloy, which provides theoretical basis and reference for later alloy design and engineering application.

Investigating the fracture behaviour of carburized and carbonitrided 16MnCr5

Low carbon alloys are low in cost and easily shapeable. Chemical composition of a material determines the mechanical properties. In this paper 16MnCr5, low alloy steel is surface treated via carburizing and carbonitriding in sealed quench furnace and quenched with oil. The effects of tensile deformation, strain rate behaviour and fracture characteristics were investigated by scanning electron microscope (SEM). A detailed investigation was done on case hardness how the surface treatment alters the hardness of the material from surface to core. The fracture of the specimen after surface treatment shows results with an intergranular fracture with projected burs on the fractured specimen. This paper investigates the fracture mechanism of surface treated material.

Electrochemical Inhibitory Effects of Non-edible Vegetable Oils on Low-Alloyed Low Carbon Steel in H2SO4

Corrosion inhibition mechanisms of Rubber, Neem and Jatropha seeds oils on low-alloyed low-carbon steel in 0.5 M·H2SO4 environment have been investigated herein. Potentiodynamic polarization, electrochemical impedance spectroscopy and scanning electron spectroscopy techniques were employed for the experimental process. The results obtained showed that inhibition efficiencies for Rubber, Neem and Jatropha seeds oils reached values of 99.957, 99.275 and 99.998%, respectively. The most shifts in corrosion potentials were > 85 and < 85 in positive directions for Rubber and Neem seeds oils, respectively, while Gibbs free energy of adsorption had values − 29.29 and − 15.06 and − 11.90 kJ/mol for Rubber, Neem and Jatropha seeds oils, respectively. Addition of oil inhibitors initiated formation of protective oxide films on substrate which contributed to increased inhibition efficiencies. The porosity of formed oxide film directly had impact on corrosion inhibition process as it led to localized reactions on substrate. Morphological examination of corroded substrates revealed that RSO was less prone to local corrosive attack. Inhibition efficiencies under the two electrochemical techniques employed corroborated, and corrosion inhibition occurred by retarding charge transfer reactions.

Revealing the mechanism of extraordinary hardness without compensating the toughness in a low alloyed high carbon steel

There is a continuous quest for discovery of a steel grade which has better properties and lower production cost. To design steel with superior properties for industrial application, it is essential to understand the effect of microstructure and engineer it to fit the purpose. In this study, a counter intuitive strategy has used to reveal the mechanism of high carbon steel with ultrahard structure. High compact force has been used to produce a structure which has ceramic-like hardness without compensating the toughness significantly. The behaviour of high carbon low-alloy steel as the starting material under different stages of deformation has been studied to differentiate various deformation paths and microstructural transformation processes. Microscopy investigation by secondary electron microscopy, high-resolution electron backscattered diffraction (HR-EBSD) analysis and Transmission electron microscopy (TEM) showed that the key point to achieve ~75% increased hardness in this steel is through generation of nano-structured martensite of less than 50 nm grains size which can be formed due to high impact force. In this paper, we reveal a nano grained steel structure with excellent mechanical properties resulting from phase transformation, uniform dislocation distribution, grain refinement and recrystallization.

Machinability Studies on Abrasive Water Jet Machining of Low Alloy Steel for Different Thickness

This paper reports some results of experimental investigation conducted on abrasive water jet machining (AWJM) of medium carbon low alloy (EN24) steel. EN24 steel samples of different thickness have been machined at various combinations of AWJM parameters. Three important AWJM parameters namely water jet pressure, nozzle traverse speed, and stand-off distance have been varied at three levels each. Three important responses i.e. material removal rate, kerf wall inclination, and surface roughness (average roughness) have been considered as the machinability indicators. The variation of these machinability indicators with a range of thicknesses of EN24 steel samples has been investigated. It is found that AWJM is capable to machine EN24 steel at very high MRR even at the increased thickness. But, surface finish deterioration is prominent with sample having higher thickness. Moreover, nozzle traverse speed is identified as the most significant parameter. It is concluded that the jet pressure of 240MPa with traverse speed of 20mm/min can produce good machinability for AWJM of EN24 Steel.

Mechanical and corrosion properties of medium carbon low alloy steel after cyclic quenching and tempering heat–treatments

Cyclic quenching and tempering (QT) heat–treatment processes have the potential to improve the mechanical properties of steel due to the formation of fine grain size microstructure. This work aims to investigate the mechanical and corrosion properties of experimental medium carbon low alloy steel under cyclic heat–treatment processes. Cyclic single quenching and tempering (SQT), double quenching and tempering (DQT), and triple quenching and tempering (TQT) heat–treatment processes were carried out on the medium carbon low alloy steel. X–ray diffraction analysis validated the formation of fine ε–carbide (Fe2.4C) after intermediate low–temperature tempering in DQT and TQT heat–treatments. These fine carbides provided preferential nucleation sites for the formation of new austenitic grain, resulting in a refined microstructure composed of supersaturated (carbon) lath martensite (α′) and retained austenite (γ). The DQT and TQT heat–treatments improved 19% tensile strength, 100% elongation, and 95% impact absorption energy in comparison to SQT heat–treatment. DQT and TQT heat–treatments also transformed the brittle behavior of SQT steel into a ductile behavior. It was also revealed by the small number and size of dimples along with a large number of short tear ridges in fractographs. Morphology of corrosion products of heat–treated experimental steel was also studied in a 5% NaCl solution. The SQT heat–treated sample showed porous morphology of corrosion products, while the TQT sample showed morphology with less porosity on the surface. The DQT sample showed solid corrosion morphology with little porosity. As the grain size went on decreasing in the cyclic heat–treatments the corrosion rate was also dropped.

Influence of shot peening on corrosion behavior of low alloy steel

Surface modification is an important technique for maintaining relatively favorable mechanical properties to surface properties and corrosion resistance. In this study, Surface shot peening technology is applied to low alloy steel production nanocrystallines. The microstructure near the surface layer was characterized by x-ray diffraction, transmission electron microscopy and electron backscatter diffraction. The corrosion behavior of the shot-treated surface layer was analyzed by polarization and pitting test, and the surface morphology of the corroded sample was observed by a scanning electron microscope. The results showed that the surface layer of the alloy after shot peening can be divided into three parts: equiaxed nanoparticle layer (NG), ultrafine grain layer (FG) and elongated fine grain layer (EG). Surface nanocrystallization improved the potential polarization behavior of low alloy steel in 3.5% NaCl solution. The microhardness of the near surface region showed a significant increase compared to the as-received steel sample, showing a more stable electrochemical performance. Shot peening also significantly reduced the pitting rate and maximum pitting depth in 10% FeCl3 solution. The surface nano-layer structure produced by the shot peening process could provide more nucleation sites, thereby improving the uniformity and compactness of the passivation film, resulting in better corrosion resistance. The above experimental results clearly showed that the overall and local corrosion resistance of the low alloy carbon steel in the chloride ion-containing solution can be improved by shot peening.

Hard Turning on JIS S45C Structural Steel: An Experimental, Modelling and Optimisation Approach

The present research is performed while turning of JIS S45C hardened structural steel with the multilayered (TiN-TiCN-Al2O3-TiN) CVD coated carbide insert by experimental, modelling and optimisation approach. Herein, cutting speed, feed rate, and depth of cut are regarded as input process factors whereas flank wear, surface roughness, chip morphology are considered to be measured responses. Abrasion and built up-edge are the more dominant mode of tool-wear at low and moderate cutting speed while the catastrophic failure of tool-tip is identified at higher cutting speed condition. Moreover, three different Modelling approaches namely regression, BNN, and RNN are implemented to predict the response variables. A Back-propagation neural network with a 3-8-1 network architecture model is more appropriate to predict the measured output responses compared to Elman recurrent neural network and regression model. The minimum mean absolute error for VBc, Ra and CRC is observed to be as 1.36% (BNN with 3- 8-1 structure), 1.11% (BNN with 3-8-1 structure) and 0.251 % (RNN with 3-8-1 structure). A multi-performance Optimisation approach is performed by employing the weighted principal component analysis. The optimal parametric combination is found as the depth of cut at level 2 (0.3 mm)-feed at level 1 (0.05 mm/rev) – cutting speed at level 2 (120 m/min) considered as favourable outcomes. The predicted results were validated through a confirmatory trial providing the process efficiency. The significant improvement for S/N ratio of CQL is observed to be 9.3586 indicating that the process is well suited to predict the machining performances. In conclusion, this analysis opens an avenue in the machining of medium carbon low alloy steel to enhance the machining performance of multi-layered coated carbide tool more effectively and efficiently.

Shock and Spall in the Low-alloy Steel AF9628

The shock and spall behavior of tempered AF9628, an ultra-high strength (UHSS) martensitic low-alloy carbon steel, is investigated using gun-driven, symmetric, planar impacts. The study utilized laser velocimetry to obtain transmitted wave velocity histories that were analyzed to obtain the Hugoniot Elastic Limit (HEL), the shock Hugoniot, and the spall strength. The work was limited to the stress range below 13 GPa (below the e phase transition), and an HEL of 2.35 GPa and a spall strength of 6.8 GPa are reported. The HEL and spall strength of AF9628 are both above the typical values for inexpensive low-alloy steels, and only slightly below those for a much more expensive Aermet steel. The dynamic compressive yield strength (as calculated from the HEL) is only slightly higher than the quasi-static compressive yield strength when compared using a similar yield assignment convention, indicating a small, but positive, value of strain-rate sensitivity. The Hugoniot for AF9628, US = 0.67uP + 5.01 km/s, is in good agreement with other low-alloy martensitic steels for which data is available, and distinctly different than the Hugoniot for ferritic steels. The Hugoniot extrapolates to a bulk sound speed significantly higher than what is measured at ambient conditions, an incongruity that is unusual among metals and that the authors attribute to the unsteady nature of the shock waves generated in this work. Finally, it is suggested that there may be a relationship between dynamic compressive yield strength (calculated from the HEL) and dynamic tensile failure strength (the spall strength).

Strain-rate sensitive ductility in a low-alloy carbon steel after quenching and partitioning treatment

We investigate an extraordinarily high ductility in a low alloy carbon steel at an elevated temperature after a quenching and partitioning (Q&P) treatment. The conventional (quenched and tempered) reference material does not show similar behavior. Interestingly, the Q&P treated material’s ductility is considerably reduced at increasing strain rates while strength remains almost constant. These results indicate the presence of a diffusion-controlled deformation mechanism at elevated temperatures. Our research shows that interlath retained austenite is more stable during deformation at higher temperatures, resulting in a delayed transformation to martensite and therefore to a more pronounced contribution to plastic deformation at (and in the vicinity of) the many interfaces inherently present in this multi-phase steel.

High cycle fatigue behavior of a low carbon alloy steel: The influence of vacuum carburizing treatment

The present investigation attempts to explore the influence of vacuum carburizing treatment on the high cycle fatigue behavior of a low carbon alloy steel 20Cr2Ni4 by using rotating bending fatigue test. The same heat steel subjected to conventional quenched & tempered (QT) treatment was used for comparison. It was found that the vacuum carburizing treatment significantly promoted the formation of a particular area of granular bright facet in the vicinity of non-metallic inclusion in the fatigue crack initiation region with fatigue life beyond ~106 cycles and thus caused mainly an interior inclusion-induced failure mode compared with the QT treatment. Both the high cycle fatigue strength and the threshold value of stress intensity factor range controlling macroscopic crack growth were significantly enhanced on condition that the crack initiation site was still within the carburized case layer. These beneficial enhancements are mainly ascribed to the introduction of a case layer with much higher hardness and compressive residual stress.

Plastic Behavior of Ferrite–Pearlite, Ferrite–Bainite and Ferrite–Martensite Steels: Experiments and Micromechanical Modelling

In this work, low carbon low alloy steel specimens were subjected to suitable heat treatment schedules to develop ferrite–pearlite (FP), ferrite–bainite (FB) and ferrite–martensite (FM) microstructures with nearly equal volume fraction of hard second phase or phase mixture. The role of pearlite, bainite and martensite on mechanical properties and flow behaviour were investigated through experiments and finite element simulations considering representative volume elements (RVE) based on real microstructures. For micromechanical simulation, dislocation based model was implemented to formulate the flow behaviour of individual phases. The optimum RVE size was identified for accurate estimation of stress–strain characteristics of all three duplex microstructures. Both experimental and simulation results established that FM structure exhibited superior strength and FP structure demonstrated better elongation while FB structure yielded moderate strength and ductility. The von Mises stress and plastic strain distribution of the individual phase was predicted at different stages of deformation and subsequent statistical analyses indicated that hard phases experienced maximum stress whereas, maximum straining occurred in soft ferrite phase for all three structures. Micromechanical simulation further revealed that strain accumulation occurred at the F–P and F–B interfaces while the same was observed within the martensite particles apart from the F–M interfaces for FM. These observations were further substantiated through the identification of void and crack initiation sites via subsurface examinations of failed tensile specimens.

Prediction and comparison of the dilution and heat affected zone in submerged arc welding (SAW) of low carbon alloy steel joints

The present investigation has been made to realize the effect of submerged arc welding (SAW) process parameters in ‘Purging’ condition and has been compared to the traditional 'as weld' condition. It uses open-circuit-voltage (OCV), wire-feed-rate (WFR), welding-speed (WS) and nozzle-to-plate distance (NPD) as process parameters. The design of experiments is utilized to carryout efficient experimentation and multiple regression analysis is to build mathematical models to foresee responses like dilution and heat affected zone. The performance evaluation of control levels, which has been shown through the S/N ratio, its significance, along contributions is computed via ANOVA. The models are developed to build correlation among the parameters. The Grey Relational Analysis (GRA) is to normalize and optimize the results. These developed models are adequate; GRA responses are agreeable and are found to be within limits through confirmation tests. Results indicate that the best combination for Heat Affected Zone (HAZ) minimization is lower level of OCV and higher levels of WFR, WS and NPD; High dilution, in percentage, in both welding conditions. The Purging condition values are shown better than the as-weld condition values.

Microstructure analysis of martensitic low alloy carbon steel samples subjected to deformation dilatometry

Low alloy martensitic steels are commonly used in structural and wear resistant applications due to their excellent mechanical properties and abrasion resistance. Martensite phase is generally achieved by rapid cooling, and prior deformation in the austenite region also affects the martensite transformation. It is important to understand the martensite transformation when there is deformation above Ae3. Deformation and quenching simulations have been performed using dilatometry on a low alloy carbon steel. The aim was to determine the influence of deformation above Ae3 (prior deformation) on, firstly, the austenite grain size and shape, and secondly, the martensitic microstructure and variant selection. In addition, the hardness of the martensitic structure due to prior deformation has been investigated. The experimental results obtained from electron backscatter diffraction and microhardness tests on the deformation dilatometry test samples were analysed. The orientation relationship Kurdjumov-Sachs has been used to analyse the martensitic variants. The results revealed a deeper understanding of prior austenite grain structure's effect on the martensitic transformation kinetics and its morphology. The martensite laths' misorientation interval 15–48° were used to visualise the prior austenite grain size. The martensitic lath structure is more refined due to increased prior deformation. Shorter martensite formation time promotes a single dominating packet within the prior austenite grain.

Analysis of Acoustic Emission Parameters Changes with the Growth of Fatigue Racks in Steel Samples

This work presents the analysis of damage assessment for dangerous industrial objects of acoustic emission method. Samples of low carbon and low alloy steels were researched. The aim of this work is to experimentally determine damage assessment for the state of developed and unacceptable sources of acoustic emission. Cracks of various lengths have been obtained by low-cycle loading. According to research, it is necessary to use several criteria simultaneously to increase the reliability of inspection of each growing crack.

Every midwife matters

Low alloy martensitic steels are commonly used in structural and wear resistant applications due to their excellent mechanical properties and abrasion resistance. Martensite phase is generally achieved by rapid cooling, and prior deformation in the austenite region also affects the martensite transformation. It is important to understand the martensite transformation when there is deformation above Ae3. Deformation and quenching simulations have been performed using dilatometry on a low alloy carbon steel. The aim was to determine the influence of deformation above Ae3 (prior deformation) on, firstly, the austenite grain size and shape, and secondly, the martensitic microstructure and variant selection. In addition, the hardness of the martensitic structure due to prior deformation has been investigated. The experimental results obtained from electron backscatter diffraction and microhardness tests on the deformation dilatometry test samples were analysed. The orientation relationship Kurdjumov-Sachs has been used to analyse the martensitic variants. The results revealed a deeper understanding of prior austenite grain structure's effect on the martensitic transformation kinetics and its morphology. The martensite laths' misorientation interval 15–48° were used to visualise the prior austenite grain size. The martensitic lath structure is more refined due to increased prior deformation. Shorter martensite formation time promotes a single dominating packet within the prior austenite grain.