Medium Carbon Low Alloy Steel Research Articles

Evaluation of Mechanical Properties of Medium Carbon Low Alloy Steels

Medium carbon low alloy steel is being used in the forged condition in the automobile, aerospace and transport industry. Reliability of critical components made of EN Series is directly based on the fatigue strength of this steel, which in turn is dependent on forging process. A review of literature shows that substantial information is available relating to structure and mechanical properties of medium carbon low alloys forged steels. Some information is available regarding the evaluation of mechanical properties of steels. In the light of the above, the present investigation was taken up to study the effect of variables on the chemical composition of EN Steels. Mechanical properties such as UTS, percentage of elongation, Percentage of reduction (%RA) and hardness,of the alloy was assessed. The aim of the study is to evaluate the possibility of replacement of this steel with lower Ni content. Keywords: EN series; elongation; Hardness; Medium carbon steel; reduction; Ultimate Tensile strength (UTS);

Effect of matrix carbon content and lath martensite microstructures on the tempered precipitates and impact toughness of a medium-carbon low-alloy steel

Different austenitizing temperatures were used to obtain medium-carbon low-alloy (MCLA) steels with different initial states of tempering, including lath martensite microstructures and matrix carbon contents. The effects of these factors on the tempered carbides and impact toughness of the MCLA steels were investigated via optical microscopy (OM), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results showed that the matrix carbon content and lath martensite substructure sizes could be effectively controlled by the austenitizing temperature. The morphologies of the tempered carbides precipitated at the boundaries were controlled by both the matrix carbon content and the lath martensite substructure sizes. Higher matrix carbon content and boundary densities increased the nucleation rate and promoted the formation of spherical carbides. The spheroidization of carbides was conducive to improving the impact toughness. However, the decrease in the density of high-angle grain boundaries and the appearance of long strip-shaped carbides drastically reduced the impact toughness.

Optimization the working parameters of as-forged 42CrMo steel by constitutive equation-dynamic recrystallization equation and processing maps

42CrMo steel belongs to low-alloy medium carbon steel and also belongs to ultra-high-strength steel. In this study, thermal compression tests (800°C - 1200°C, 0.01s-1 - 10s-1) and subsequent calculations proved that many material constants of 42CrMo alloy steel have a similar functional relationship with Z parameter: Material constants=a*Zb. The thermal processing maps under strains of 0.2, 0.4, 0.6 and 0.8 were established, and the practical application of the processing maps was verified in combination with metallographic diagram analysis. The optimum thermal processing parameters range of the material was obtained: the temperature range of 1000°C - 1125°C and the strain rate range of 3.16 s-1 - 10s-1.The dynamic recrystallization volume fraction model and grain size model of the material were established, and the typical sigmodal curve was obtained. The hot workability and recrystallization behavior of 42CrMo were further analyzed.

Mechanical Property Association of Dual Phase and Austempered AISI 4140 Normalized Steel

The present investigation intended to analyse the mechanical properties of medium carbon low alloy steel (AISI 4140) under dual phase heat treatment condition. Formation of dual phase, ferrite and martensite (F+M) from normalized condition followed by heating in the intercritical temperature range to form different volume fractions of ferrite and martensite alters tensile, hardness and impact strength of medium carbon steel. Effect of alloying elements in dual phase treatment will change the mechanical properties. Tensile strength and hardness of austempered steel shows higher value followed by dual phase condition. Ductility of normalized shows better as compared to as bought and dual phase, but austempered shows almost similar to normalized result. Impact strength of the austempered is excellent followed by dual phase condition. Heat treated specimen microstructures reveal the different phase’s present.

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.

The Effect of Lath Martensite Microstructures on the Strength of Medium-Carbon Low-Alloy Steel

Different austenitizing temperatures were used to obtain medium-carbon low-alloy (MCLA) martensitic steels with different lath martensite microstructures. The hierarchical microstructures of lath martensite were investigated by optical microscopy (OM), electron backscattering diffraction (EBSD), and transmission electron microscopy (TEM). The results show that with increasing the austenitizing temperature, the prior austenite grain size and block size increased, while the lath width decreased. Further, the yield strength and tensile strength increased due to the enhancement of the grain boundary strengthening. The fitting results reveal that only the relationship between lath width and strength followed the Hall–Petch formula of. Hence, we propose that lath width acts as the effective grain size (EGS) of strength in MCLA steel. In addition, the carbon content had a significant effect on the EGS of martensitic strength. In steels with lower carbon content, block size acted as the EGS, while, in steels with higher carbon content, the EGS changed to lath width. The effect of the Cottrell atmosphere around boundaries may be responsible for this change.

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.

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.

Influence of Deep Cryogenic Treatment and Secondary Tempering on Microstructure and Mechanical Properties of Medium-Carbon Low-Alloy Steels

Deep cryogenic treatment (DCT) and secondary tempering for 40CrNiMoA steel were carried out to obtain the desirable microstructures corresponding to excellent mechanical properties suiting for the preparation of flex spline of harmonic drive reducer. The effects of DCT and secondary tempering on microstructural characteristics and mechanical properties were investigated by x-ray diffraction, scanning electron microscopy, electron backscattered diffraction and transmission electron microscopy, in association with property measurements. The results show that the DCT promotes the transformation of retained austenite to martensite, the precipitation and homogeneous distribution of carbides as well as the refinement of martensitic substructures. The structural and morphological changes significantly improve the hardness, yield and tensile strength of steels, but slightly lower the elongation of them. Further secondary tempering at special temperatures can successively increase the elongation and fracture toughness of the DCT-treated 40CrNiMoA steels at the cost of slight decrease in hardness and strength due to the reduction in dislocation density. Therefore, the DCT in combination with secondary tempering can improve the comprehensive mechanical properties of 40CrNiMoA steels to produce the flex spline with a higher lifetime.

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.

Real time observation of martensite transformation for a 0.4C low alloyed steel by neutron diffraction

A high-intensity and high-resolution neutron diffractometer with a thermomechanically controlled processing simulator was employed in-situ to investigate martensite transformation behavior with and without ausforming for a medium-carbon low-alloy steel. Serial neutron diffraction profiles have revealed that the transformation behavior could be successfully monitored during quenching with and without the ausforming process. The fresh martensite exhibits a body-centered tetragonal structure when it forms immediately below the martensite start (Ms) temperature, and its c/a ratio decreases rapidly as time elapses. The lattice parameter and the full width at half maximum of austenite peaks significantly decreases and increases upon martensite transformation, respectively. After ausforming, the data reveal that lattice parameters are larger in austenite whereas smaller in martensite compared with those in the non-ausformed case, which is ascribed to the introduced dislocations. Thus, the lattice defects affect the lattice parameter during martensite transformation. Ausforming also slightly raises the Ms temperature and increases the amount of retained austenite at room temperature as a result of different dislocation densities. The cutting-edge operant quantitative measurements with neutron diffraction for steel production is demonstrated.

Real Time Observation of Martensite Transformation for a 0.4C Low Alloyed Steel by Neutron Diffraction

A high-intensity and high-resolution neutron diffractometer with a thermomechanically controlled processing simulator was employed in-situ to investigate martensite transformation behavior with and without ausforming for a medium carbon low-alloy steel. Serial neutron diffraction profiles have revealed that the transformation behavior could be successfully monitored during fast cooling and during the ausforming process. The hkl diffraction intensity of austenite increased at the beginning of transformation due to the primary extinction effect. The fresh martensite exhibits a body-centered tetragonal structure when it forms immediately below the martensite start (Ms) temperature, and its c/a ratio decreases rapidly as time elapses. The lattice parameter and the full width at half maximum of austenite peaks significantly decreases and increases upon martensite transformation, respectively. Ausforming slightly increases the Ms temperature, the amount of retained austenite at RT and the austenite lattice parameter. The dislocation densities in martensite and the retained austenite estimated using the convolutional multiple whole profile fitting method increase by ausforming.

Design and property study of a new type centrifugal crusher wear block

A new type wear block made of medium carbon low alloy steel was designed to improve the service of a centrifugal crusher. A reasonable casting technology was chosen and ViewCast software was used to simulate the solidification process, then the location of the defeats was predicted, the scheme was optimized and the production verification was carried out. Annealing, quenching and tempering of wear resistant block was carried for performance testing. The observed metallographic microstructure indicates that it was organized as a strip martensite and a small amount of needle martensite after heat treatment. The analysis of mechanical properties indicates the hardness was 54.8HRC, the tensile strength was 1325MPa, the impact energy of V-notch and no notch was 15.7J and 142.7J respectively. Analysis of tensile and impact fracture scanning electron microscopy indicates that the fracture mechanism is subject to eutectic fracture. The performance test results show that the new type centrifugal crusher wear block can meet the requirements of the actual condition.

Development of Dual Phase Microstructure in Medium Carbon Low Alloy Steel by Continuous Cooling Heat Treatment

Development of Dual Phase Microstructure in Medium Carbon Low Alloy Steel by Continuous Cooling Heat Treatment

On the Role of Chromium in Dynamic Transformation of Austenite

The effect of Chromium (Cr) on the dynamic transformation (DT) of austenite to ferrite at temperatures up to 430 °C above Ae3 was studied in a medium-carbon low-alloy steel. Hot compression tests were performed using Gleeble 3800® thermomechanical simulator followed by microstructural examinations using electron microscopy (FESEM-EBSD). Driving force calculation using austenite flow stress and ferrite yield stress on an inverse absolute temperature graph indicated that Cr increases the driving force for the transformation of austenite to ferrite; however, when the influence of stress and thermodynamic analysis are taken into account, it was observed that Cr increases the barrier energy and therefore, emerges as a barrier to the transformation. An analysis, based on lattice and pipe diffusion theories is presented that quantifies the role of stress on the diffusivity of Cr and is compared with other the main alloying elements such as C, Si and Mn and its impact, positive or negative, on the DT barrier energy. Finally, a comparison is made on the differential effects of temperature and stress on the initiation of DT in medium-carbon low-alloy steels.

A Study on the Nanoscale Austenite Stabilized by Q&P Heat Treatment in a Low-alloy Medium-carbon Steel

A Study on the Nanoscale Austenite Stabilized by Q&P Heat Treatment in a Low-alloy Medium-carbon Steel

Retained Austenite Decomposition and Carbide Precipitation during Isothermal Tempering of a Medium-Carbon Low-Alloy Bainitic Steel.

The effect of isothermal tempering on retained austenite decomposition and carbide precipitation were investigated in a medium-carbon low-alloy bainitic steel. High-resolution dilatometry was used to perform isothermal tempering at 350 °C, 550 °C and 600 °C for different holding times up to 16 h. The decomposition of retained austenite, morphology and composition of carbides were investigated by analyzing the dilatometric curves and were confirmed through scanning and transmission electron microscopy observations. The decomposition behavior of retained austenite varied significantly as a function of the tempering temperature with a full decomposition observed at 600 °C. It was also found that by increasing the tempering temperature from 550 °C to 600 °C, carbides precipitate approximately twice as fast, and evolve from M3C type to Cr7C3 and Cr23C6 after 16 h of tempering at 600 °C.

Microstructure and Wear Properties of Laser Treated Ni3Al Coatings on Low Alloy Medium Carbon Steel

Laser modification of nickel-aluminide (Ni3Al) coatings on low alloy medium carbon steel substrate was carried out with the help of industrial CO2 laser. The depth of the laser melted zone (modified surface) was controlled as a function of input energy by varying the laser beam travel speed. The laser treated specimens were characterized for microstructure, chemical composition, and micro-hardness profile with respect to the laser penetration depth. Microstructural examination revealed that the laser treated surface was composed of ultrafine grain structure which evolved as a result of laser re-melting and solidification (cooling) rate used in this experiment. Microhardness results showed that as the depth of the laser melted zone increases the hardness of the modified surface decreases and vice versa. Further, the wear behavior of the laser treated surface was also studied with the help of ball-on-disc tribometer and by selecting 2000 m sliding distance. Wear test showed that as the depth of laser melted zone increases the wear of the surface increases as well and vice versa. The possible reason behind this phenomenon was the migration of iron (Fe) atoms from substrate into the surface layer which resulted the dissolution of Ni3Al coating particles in the surface layer and this was confirmed by the EDX analysis.

Numerical Simulation of Water Quenching of Large Size Steel Forgings: Effects of Macrosegregation and Grain Size on Phase Distribution

In this paper, water quenching of large ingots was simulated using FORGE NxT 1.1® Finite Element code. Simulations were carried out for as-forged medium-carbon low-alloy steel. A novel method is proposed to simulate the different parts of a large size forged block with different chemical compositions and grain sizes using the multiple materials method. The effects of macrosegregation, grain size variation and cooling rate on phase distribution through the volume of the forged block were investigated. The delay in transformation kinetics, which is due to the effect of grain size variation and carbon content, was analyzed. Results show that macrosegregation and grain size variations significantly influence transformation start points and the volume fraction of phases that are present in each location of the forged ingot. The proposed prediction method was validated using high-resolution dilatometry experiments and X-ray diffraction measurements to evaluate accurately the volume fraction of martensite, bainite and the percentage of retained austenite for each condition.

Influence of strain rate on dynamic transformation of austenite in an as-cast medium-carbon low-alloy steel

In this work, the effect of strain rate on the dynamic transformation (DT) of austenite to ferrite during high temperature forging of an as-cast medium-carbon low-alloy steel was investigated. Hot deformation experiments were carried out in the 1150 °C to 1200 °C temperature range (400–450 °C above Ae3) and 0.25 s−1 to 2 s−1 strain rate range using a Gleeble 3800® thermomechanical simulator. The critical strains for DT and dynamic recrystallization (DRX) were determined to be in the 0.08 to 0.18 strain range. A microstructural analysis was conducted using optical and electron microscopy. The kernel average misorientation (KAM) technique was applied to electron back-scattered diffraction (EBSD) images to quantify the internal misorientation of grains for the characterization of DT ferrite. Furthermore, it was found that an increase in strain rate decreased the amount of dynamically formed ferrite under the same applied strain and testing temperature. The obtained results were correlated with the influence of deformation parameters on carbon diffusivity and its impact on the growth of dynamically formed ferrite. It was found that an increase in the strain rate decreased the diffusion distance of carbon, which was the responsible mechanism for decreased ferrite formation at higher strain rates.