This review compiles and compares recent research on the influence of various heat treatments on the hardness, impact toughness, and microstructural evolution of AISI 1040, 4140, and 4340 medium carbon structural steels. These steels vary in alloy composition - AISI 1040 is a plain carbon steel, AISI 4140 is Cr-Mo steel, and AISI 4340 is Ni-Cr-Mo alloy steel. For consistent comparison, hardness and impact toughness values reported in the literature were standardized to Rockwell C (HRC) and Charpy impact energy (J). It was observed that due to formation of a ferrite – pearlite structure, annealing produced the softest steels ( 20 HRC, > 120 J). Normalizing refined pearlite grains and balanced the properties (26–37 HRC, 140 J). Quenching, because of martensite formation, yielded highest hardness (59–70 HRC) but lowest toughness ( 35 J), while tempering improved toughness (80–150 J) while maintaining a moderate hardness. Heat treatments such as austempering, up-quench austempering (UQA), ultra-fast heat treatment (UFH), laser heat treatment (LHT), deep cryogenic treatment (DCT) and shallow cryogenic treatment (SCT), improved performance by altering mechanical properties through bainitic transformation, carbide precipitation, and surface hardening. Overall, the findings highlight that the hardness-to-toughness relationship varies significantly with the selected heat treatment, underscoring the critical role of tailored heat treatment processes in optimizing the mechanical performance of these steels.

The tribological performance and surface degradation behavior of medium carbon steels are strongly governed by microstructural evolution induced through heat treatment. In this study, the influence of annealing, normalizing, and oil quenching on the dry sliding wear behavior of AISI 1040 steel was systematically investigated under controlled tribological conditions. Pin on disc experiments were conducted in accordance with ASTM G99 using a hardened EN31 steel counter face, while varying applied load (20–60 N), sliding speed (0.5–1.5 m/s), and track diameter (0.04–0.08 m). Microstructural characterization revealed coarse ferrite–pearlite structures in annealed specimens, refined pearlite in normalized specimens, and martensitic transformation in oil quenched specimens, leading to progressive enhancement in load bearing capacity and hardness. 197, 203 and 227 HV were the measured hardness values for the annealed, normalized and oil quenched specimens respectively. The tribological response demonstrated a significant reduction in mass loss with increasing microstructural refinement, with oil quenched samples exhibiting superior wear resistance. The maximum measured mass loss decreased from 87 mg for annealed specimen, to 50 mg for normalized specimen, and to 45 mg for oil quenched specimen, showing a 48

Abstract The investigation was conducted to study the corrosion inhibition performance of cerium as an inhibitor for Sn–3Ag–0.5Cu (SAC305) lead-free solder alloy in 3.5% NaCl solution. The investigation is useful to suggest an inhibitor for SAC305 solder for microelectronic applications in marine environments. Weight loss measurement results for 30 °C showed the maximum inhibition efficiency as 33.33% when 700 ppm of cerium were added to 3.5% NaCl solution. However, polarization experiments displayed a better corrosion resistance for the alloy in 3.5% NaCl solution at 700 ppm of inhibitor concentration almost at all higher temperatures (40 and 50 °C). At room temperature, the corrosion rate decreases at 700 ppm, indicating that a high inhibitor concentration increases protective efficacy. Hence, cerium appeared to be a capable inhibitor for the alloy under the NaCl acidic environment.

Laser surface hardening is a technique that improves various mechanical characteristics of different materials. The methods are being extensively used in the automobile, aerospace, tool manufacturing, and construction industries for various components. The present review highlights the hardness and hardened surface depth improvement of different steels and non-ferrous alloys in as-bought and pre-heat treatment conditions. Diode and fibre lasers have rendered higher surface hardness and hardened depth, while consuming higher power. Nd:YAG lasers have resulted in a precise increase in hardness and a very minimal 0.8 in ferrous and 2 mm in surface-hardened depth of non-ferrous alloys, proving a better efficiency. The pre-heat treatments are selected to enhance mechanical properties and reduce the deformations and defects. An increase of 300.43 and 282.38% of surface hardness due to laser hardening as compared to the core material of AISI 420 was observed using a high-power diode laser. A huge 281.41% of increase in surface hardness was observed for ICD-5 tool steel using Nd:YAG lasers. The annealing pre-heat treatment has also affected the hardenability, resulting in high hardness. Non-ferrous alloys such as titanium and A356 alloys have recorded 200 and 125% increase in surface hardness compared to their core using Nd:YAG lasers.

42CrMo4 steel is one of the hardest and most brittle steels in the structural grade steel family. This research investigates the mechanical characterisation and microstructural behaviour of 42CrMo4 steel subjected to isothermal annealing heat treatment. Two key variables are analysed using the Taguchi method and their influence on the tensile strength and hardness of the material. The variables are isothermal temperature and soaking time, their effect on the tensile strength, hardness and microstructural behaviour using experimentation for the L27 orthogonal array. There is a significant reduction in tensile strength and hardness as the temperature and soaking time increase, which is attributed to the formation of pearlitic structure and grain coarsening. A huge reduction of 46.74

This study investigates the dry turning machinability of heat treated AISI 4340 steel by correlating heat treatment condition, hardness, microstructure, tool life, surface roughness and tool wear behavior. Specimens were annealed, normalized and SAE 40 oil quenched after austenitizing at 900, 925 and 950 degrees C for 1, 1.5 and 2 h. Turning experiments were carried out using a Taguchi L27 orthogonal array by varying heat treatment temperature, soaking time, cutting speed, feed rate and depth of cut. The responses were analyzed using ANOVA, regression modeling, response surface multi response optimization and confirmation assessment. Results showed that annealed specimens resulted in the highest tool life due to their softer ferrite-pearlite matrix, whereas oilquenched specimens showed the lowest tool life because of hard martensitic phase. Heat treatment temperature was the dominant factor for tool life, while feed rate was the dominant factor for surface roughness (Ra). Linear models predicted tool life reliably, whereas surface roughness required interaction or quadratic consideration because of chip formation, built up edge tendency and tool wear evolution. SEM observations of the heat treated microstructures and the worn tool analysis support the heat treatment, microstructure, machinability relationship. The study provides a practical framework for selecting heat treatment and turning parameters for improved machinability of high hardenability AISI 4340 steel.

Commercially available pure aluminium is an alloy with Si, Cu and Mg impurities lacking in strength and surface hardness compared to its conventional alloys due to small quantity of alloying elements. This study investigates the property alteration with a process of high temperature thermochemical diffusion of silicon by packing commercially available silicon powder of 80–100 micron size, and application of age hardening treatment. Mechanical properties (ultimate tensile strength,

Aluminium–silicon (Al–Si) eutectic alloys are the most common materials for automotive and light structural applications due to their good castability and high strength-to-weight ratio. Nevertheless, there are situations where improved mechanical performance is required for more demanding operating conditions. The influence of Silicon Carbide (SiC) reinforcement, Magnesium (Mg) addition and ageing on hardness, tensile behaviour and fracture properties of stir-cast Al–Si eutectic composites was studied in this work. The composites were prepared at 2 and 4 wt

AISI 1040 steel which is also known as plain medium carbon steel has wide range of applications especially in structural applications. This study investigated the effects of different heat treatment methods, such as annealing, normalizing, and hardening on the mechanical and microstructural properties of AISI 1040 steel. The results are analyzed statistically using the statistical tool to determine the optimum set of heat treatment parameters to obtain superior combination of hardness and impact energy. Heat treatment temperatures of 900, 925, and 950 degrees C and holding times of 1, 1.5, and 2 h were used in the study. The hardness and impact energy were evaluated using Vickers microhardness and Charpy impact tests, while microstructural changes were analyzed through SEM. Full factorial method was used to conduct the experiments. Regression equations are generated to predict the hardness and impact energy of the heat treated samples. Results showed that increase in the austenitization temperature has resulted in grain coarsening, reducing the hardness but improving impact energy. Oil quenched hardening resulted in the highest hardness (245 HV), whereas annealing provided superior toughness (38 J), and normalizing offered balanced properties. Optimal heat treatment conditions for superior combination of hardness and impact energy were identified for each processes. For annealing the optimum heat treatment temperature and time were found to be 900 degrees C and 2 h, whereas for normalizing the optimum parameters were determined to be 902 degrees C and 2 h. In the case of oil quenched hardening heat treatment the optimum parameters were found to be 912 degrees C and 2 h to get good combination of mechanical properties.

Deep Rolling (DR) is a versatile cold work-inducing surface treatment technique particularly employed for enhancing the mechanical performance of engineering components. However, the realized benefits are wholly governed by the complex interactions of processing parameters associated with the type and initial state of the material. This necessitates material-specific investigation on the influence of deep rolling process parameters to achieve the desired level of enhancement in material performance. In the present study, the influence of chosen rolling load, roller size, number of tool passes, and initial surface state of the workpiece on achieved surface roughness and hardness are investigated. Deep rolling operation is performed using a custom-built ball tool on pre-machined AISI 1040 steel specimens. The surface roughness (R-a and R-z parameters) is measured using the contact-type surface profilometer and surface hardness test is performed using the Vickers microhardness tester. The results showed a significant reduction in surface roughness from the machined state of N8 grade to N4 grade or lower after deep rolling. However, the attained enhancement in surface finish, strictly relied on the initial surface roughness of the workpiece. The highest level of 88.63 % reduction in roughness after deep rolling is observed when the initial surface roughness is largest within considered cases. Further, the surface topography micrographs observed through optical microscopy does confirm the smoothened surface due to flattened peaks of machined marks after deep rolling. Further, a notable increase of 64.23 % is observed in surface hardness with set deep rolling process parameters when initial surface roughness is largest. However, the impact of initial surface roughness is found to be marginal as the largest variation in hardness after deep rolling is about 18 % for considered cases. This indicates, the enhanced surface hardness largely relied on deep rolling process parameters at least for the parameters assumed in this study. Nevertheless, the findings evidence the effectiveness of the process for enhancing the surface finish and hardness of machined AISI 1040 steel especially when initial surface roughness is large. The study indicate deep rolling with a custom-built tool can be effectively employed on chosen material to smoothen the machined surface within assumed conditions. In the future, a statistical analysis can be performed to identify the optimum combination of process parameters that may be readily employed to realize the highest level of benefits from deep rolling of AISI 1040 steel.

Aluminum alloys require improved surface performance to satisfy the demands of today’s aerospace, automotive, marine, and structural applications. This paper compares three key surface hardening methods: diffusion-assisted microalloying, thermomechanical deformation-based treatments, and composite/hybrid reinforcing procedures. Diffusion-assisted Zn/Mg enrichment allows for localized precipitation hardening but is limited by the native Al2O3 barrier, slow solute mobility, alloy-dependent solubility, and shallow hardened depths. In contrast, thermomechanical techniques such as shot peening, surface mechanical attrition treatment (SMAT), and laser shock peening produce ultrafine/nanocrystalline layers, high dislocation densities, and deep compressive residual stresses, allowing for predictable increases in hardness, fatigue resistance, and corrosion performance. Composite and hybrid reinforcement systems, such as SiC, B4C, graphene, and graphite-based aluminum matrix composites (AMCs), use load transfer, Orowan looping, interfacial strengthening, and solid lubrication effects to enhance wear resistance and through-thickness strengthening. Comparative evaluations show that, while diffusion-assisted procedures are still labor-intensive and solute-sensitive, thermomechanical treatments are more industrially established and scalable. Composite and hybrid systems provide the best tribological and load-bearing performance but necessitate more sophisticated processing approaches. Recent corrosion studies show that interfacial chemistry, precipitate distribution, and galvanic coupling all have a significant impact on pitting and stress corrosion cracking (SCC). These findings highlight the importance of treating corrosion as a fundamental design variable in all surface hardening techniques. This work uses unified tables and drawings to provide a thorough examination of strengthening mechanisms, corrosion and fatigue behavior, hardening depth, alloy suitability, and industrial feasibility. Future research focuses on overcoming diffusion barriers, establishing next-generation gradient topologies and hybrid processing approaches, improving strength ductility corrosion trade-offs, and utilizing machine-learning-guided alloy design. This research presents the first comprehensive framework for selecting multifunctional aluminum surfaces in demanding aerospace, automotive, and marine applications by seeing composite reinforcements as supplements rather than strict alternatives to diffusion-assisted and thermomechanical approaches.

This work investigated the effect of different types of tempering on the hardness, impact toughness and microstructure of normalized and biodegradable-quenched 42CrMo4 steel. Specimens were normalised initially then hardened using green oil quenchants such as Pinnay oil, Karanja seed oil and blended oil (Equal volume percentage of Pinnay and Karanja seed oil) then subjected to single stage tempering process. Surface response methodology was used to obtain optimised conditions from single stage tempering process to carry out other types of the tempering processes such as multiple and step tempering processes. Grey relational analysis was used to select the tempering process that yield best balanced property condition. The two steps tempering process with hardness of 36 HRC, impact toughness of 56 Joules and with grey relational grade of 0.7 was considered as the process to get optimal mix of hardness and impact toughness in 42CrMo4 steel.

AISI 4340 steel is widely used in aerospace, automotive, and energy applications due to its high strength and toughness, which can be tailored through heat treatment. This study investigates the influence of annealing, normalizing, and oil quenching parameters on the microhardness and impact energy of AISI 4340 steel and develops regression-based predictive models to describe these relationships. Heat treatments were performed at 900, 925, and 950 degrees C for 1, 1.5, and 2 h, and mechanical properties were analyzed using Vickers microhardness and Charpy impact tests. Statistical analysis through ANOVA and response surface optimization identified the most influential factor as temperature, contributing over 90 % to microhardness and 60-80 % to impact energy variation. Optimal parameters were found to be 908.7 degrees C/2 h for annealing, 905 degrees C/1.75 h for normalizing, and 912.55 degrees C/2 h for oil quenching, yielding microhardness values of 221 HV, 270 HV, and 506 HV, and impact energies of 45 J, 51 J, and 33 J, respectively. The composite desirability indices (D) were 0.5991, 0.5759, and 0.7894, confirming balanced optimization between microhardness and impact energy. The regression models (R2 = 85-99 %) demonstrate strong internal consistency within the studied parameter range. These results provide quantitative insight into the temperature-time-property relationship in AISI 4340 steel and support optimized heat treatment design for structural applications.

This study investigates the effects of magnesium (Mg) content, silicon carbide (SiC) reinforcement, and aging temperature (AT) on the ultimate tensile strength (UTS) and Brinell hardness number (BHN) of eutectic Al-Si composites using a full factorial experimental approach. The analysis reveals that increasing Mg content from 0 wt% to 1.5 wt% significantly enhances UTS, likely due to solid solution strengthening and improved particle reinforcement. Similarly, a rise in SiC content up to 4 wt% leads to a notable increase in UTS, indicating effective matrix reinforcement. AT is crucial, with the highest UTS achieved at 100 °C; however, overaging at 200 °C results in reduced strength due to precipitate coarsening. Interaction plots demonstrate a synergistic effect between Mg and SiC, where higher levels of both contribute to a more substantial increase in UTS. The results also show that while both Mg and SiC improve UTS, their effects are optimized with appropriate aging conditions, although overaging diminishes these benefits. Analysis of variance (ANOVA) highlights that AT, Mg, and SiC each significantly impact UTS and BHN, with SiC having the greatest effect of 47.92% on hardness and AT having the greatest effect of 36.58% on the UTS. The interaction between SiC particles and AT is particularly influential on BHN. These findings emphasize the importance of carefully optimizing processing conditions to enhance the mechanical properties of eutectic Al-Si composites.

Recent progress in metal matrix composites (MMCs) has led to significant research efforts aimed at refining reinforcement methods and processing techniques and enhancing material properties. Incorporating reinforcements has notably improved both mechanical strength and tribological performance while addressing issues such as porosity and particle agglomeration. This study investigates the impact of copper reinforcement (1–4 wt.%) on the tribological characteristics of A356 alloy under both as-cast and heat-treated conditions. The process of heat treatment involved age hardening, where the composites were solution heat treated (SHT) at 535 °C for 2 h, followed by rapid quenching and aging at 100 °C and 200 °C. The results demonstrate that increasing the copper content enhances the composite’s mechanical properties. Specifically, heat treatment promoted the redistribution of the Al2Cu intermetallic phase during peak aging, leading to improved hardness and wear resistance. Wear testing demonstrated that heat-treated composites exhibited significantly better wear resistance than their as-cast counterparts, with improvements of 50–60% under lower loads and 80–90% under higher loads. Among the tested samples, A356 alloy reinforced with 4 wt.% copper showed the lowest wear rate across all the applied loads, along with a reduced coefficient of friction and enhanced load-bearing capacity, minimizing material deformation. Additionally, aging at 100 °C resulted in the greatest hardness and the lowest wear rate in comparison to untreated A356 alloy. These findings underscore the viability of copper-reinforced A356 composites for applications demanding enhanced mechanical characteristics and wear resistance.

This study investigates the effect of sliding parameters on the dry sliding wear behavior of (silicon carbide) SiC-reinforced (aluminum silicon) Al-Si eutectic metal matrix composites (MMCs) with 1.5 wt% of magnesium (Mg). The composites were fabricated by incorporating varying amounts of SiC particles into the aluminum-silicon matrix to improve wear resistance. A comprehensive wear analysis was conducted under different sliding speeds, normal loads, sliding distances, and SiC reinforcement contents. The Taguchi method was used to optimize the wear performance, with signal-to-noise (SN) ratios employed to assess the influence of each sliding parameter. The findings show that wear rate is mainly influenced by SiC content (32.04%), normal load (30.98%), and sliding speed (10.99%), while the coefficient of friction (COF) is largely affected by normal load (38.51%), SiC content (34.46%), and sliding distance (23.51%). The study also reveals that the addition of SiC reinforcement improves the wear resistance of the developed composite. The findings suggest that optimizing these parameters can significantly reduce wear, making these composites suitable for advanced engineering applications where high wear resistance is critical.

This study investigates the mechanical properties of Al6061-TiB2-fly ash reinforced monolithic and hybrid composites, fabricated using the stir casting technique. The experiment involved the preparation of both monolithic composites by varying TiB2 (3-6 wt%) and hybrid composites by varying TiB2 (1-3 wt%) and fly ash (3-5 wt%) within the Al6061 matrix. Preheated reinforcement particles were introduced to the matrix alloy under controlled stirring conditions to ensure proper dispersion. Mechanical testing was conducted on the fabricated composites to evaluate their hardness and tensile strength. The results indicate that the hybrid composites exhibit superior mechanical properties compared to the base Al6061 alloy and the monolithic composites. The hardness of the hybrid composites A1T3F (Al6061 + 1%TiB2 + 3% fly ash) and A3T5F (Al6061 + 3%TiB2 + 5% fly ash) were significantly improved, reaching 134 HV and 146 HV, respectively, compared to 74 HV for the base alloy. The tensile strength of the hybrid composites also exceeded that of the monolithic composites, demonstrating the synergistic reinforcement effect of TiB2 and fly ash. However, attempts to incorporate higher levels of reinforcement (TiB2 5% and fly ash 7%) were unsuccessful due to agglomeration issues. The results indicate that the hybrid composites provide a cost-effective solution with enhanced mechanical properties, making them a more economical and efficient alternative to monolithic composites reinforced solely with TiB2.

This study explores the combined influence of magnesium (Mg) alloy content (0-1.5 wt%) and silicon carbide (SiC) (0-4 wt%) on the mechanical and tribological properties of stir-cast Al-Si composites. The uniform dispersal of SiC within the alloy matrix is confirmed by the microstructural analysis, contributing to improved material properties. The mechanical characterization revealed that hardness and ultimate tensile strength (UTS) increased with the addition of Mg and SiC. Specifically, for unreinforced Al-Si composites, UTS values increased from 158.8 MPa to 191.3 MPa and further to 217.8 MPa as Mg content rose from 0 to 1.5 %. In SiC-reinforced composites, UTS improved significantly, reaching 207 MPa with 2 % SiC and 217.8 MPa with 4 % SiC at 1.5 % Mg. Wear tests conducted under varying loads (15-45 N) and speeds (150-450 RPM) demonstrated that wear rates consistently decreased with increasing Mg and SiC contents. These results emphasize the combined effect of Mg and SiC in significantly enhancing the wear resistance and mechanical properties of Al-Si matrix composites, making them appropriate for high-performance applications.

Polymer composites reinforced with natural fibers provide sustainable alternatives to synthetic materials, thanks to their biodegradability, low cost, and favorable strength-to-weight ratio. However, their hydrophilic nature leads to moisture absorption and mechanical degradation over time. The study examines the effect of alkaline fiber treatment and nanoclay incorporation on the water absorption and mechanical properties of coir fiber-reinforced epoxy composites. The compression molding method is used to fabricate composites using 20, 30, and 40 wt% untreated and treated coir fibers with varying nanoclay contents (0, 2, and 4 wt%). Water absorption tests reveal that the combination of treated fibers and nanoclay reduces water uptake by up to 35 % compared to untreated composites. Mechanical testing reveals a steady increase in tensile strength with rising fiber content. With fiber treatment and the addition of nanoclay, the tensile strength increases from 57.75 MPa to 97.02 MPa, while the flexural strength improves from 78.31 MPa to 114.24 MPa under the same conditions. The C3N2 composite, comprising 40 wt% alkaline-treated coir fiber and 4 wt% nanoclay, retains over 91 % of its tensile properties and 93 % of its flexural properties after soaking. In contrast, composites with untreated coir fiber show a declining trend in strength retention with increasing fiber content. SEM analysis confirms enhanced bonding between the matrix and fiber interface, accompanied by reduced microstructural degradation. The findings demonstrate the potential of using surface modification and nanofillers to improve the resilience and mechanical integrity of natural fiber composites in harsh environments.

AISI 4140 steel is one of the important category in the steels with wide range of applications including but not limited to automotive, general machinery, oil and gas industry. In the current study, an effort is made to understand the effects of heat treatment parameters, such as heat treatment temperature and holding time, on the mechanical properties of AISI 4140 steel, and to optimize these parameters to obtain the superior combination of mechanical properties. The three important heat treatments which are used in this study are annealing, normalizing and oil quenching. The heat treatment parameters such as temperature and time are varied at three different levels of 900, 925, and 950 °C, and 1, 1.5, and 2 h respectively. Using the full factorial method, total 9 experiments were carried out with all the possible combination of temperature and time as the variants. In each of the tests, hardness and impact energy values were evaluated using appropriate tests, while microstructural changes were analyzed through a scanning electron microscope (SEM). The results obtained through statistical analysis have shown that combination of 900 °C with 2 h for annealing, 919 °C with 2 h for normalizing and 944 °C with 1 h for oil quenching as the optimum combination of heat treatment parameters for superior combination of hardness and impact energy. Results showed that increasing temperature led to grain coarsening, reducing hardness but improving impact energy. Regression equations generated in this study which have R square value more than 90% may be used to predict the hardness and impact energy for any value of temperature and time which is within the range of values considered for this study.