Carburized Steel Research Articles

Effects of (Al + N) and (Nb + Mo) Microalloying and Reduction Ratio of Cold Rolling on Abnormal Grain Growth in AISI 4121 Carburizing Steels

Effects of (Al + N) and (Nb + Mo) Microalloying and Reduction Ratio of Cold Rolling on Abnormal Grain Growth in AISI 4121 Carburizing Steels

Rapid carburizing of low-alloy steel by atmospheric-controlled induction-heating fine-particle peening and investigation of its fatigue properties

Atmospheric-controlled induction-heating fine-particle peening (AIH-FPP) was applied to low-alloy, low-carbon steel AISI 4120 to achieve rapid carburizing within minutes and enhance fatigue strength. The shot particles used during AIH-FPP were specifically created by mechanically milling a mixture of steel particles and carbon powders. The specimens were analyzed using laser microscopy, optical microscopy, X-ray diffraction for residual stress measurement, a micro-Vickers hardness tester, and an electron probe micro-analyzer. Axial fatigue tests and fracture surface analyses via scanning electron microscopy and energy-dispersive X-ray spectroscopy were also conducted. AIH-FPP effectively transferred carbon to the treated surface and facilitated its diffusion in a short period, creating a martensite layer with high hardness and compressive residual stress, which resulted in increased fatigue strength. The fatigue strength of the AIH-FPP-treated specimens was influenced by the conditions of reheating and quenching, which altered the prior austenitic grain size and stress concentration at the specimen surface. Notably, specimens treated with AIH-FPP followed by reheating and water-injection quenching exhibited fatigue strength comparable to that of conventional gas-carburized specimens, owing to the formation of a carburized layer with a small prior austenite grain size.

Influence of Aluminum on the Retained Austenite Content and Stresses in the Surface Layer of Steel after a Hybrid Low‐Pressure Carburizing Process with Metallization

The article presents a unique method of modifying the surface layer properties of low‐alloy steels. This method consists of the simultaneous saturation of the surface layer with aluminum and carbon. A hybrid heat treatment process is used, which integrates diffusion metallization with low‐pressure carburizing (LPC). An aluminum coating is applied to the surface of the steel by physical vapour deposition or slurry method to saturate the surface layer with aluminum. The steel is then annealed to create a diffusion layer and subjected to LPC. Gas quenching in nitrogen and low‐temperature tempering are performed after carburization. This surface treatment tenfold reduces the amount of retained austenite in the carburized layer. This is particularly critical for carburized steels that include austenite‐stabilizing elements, such as nickel and manganese. This causes an increase in surface hardness. It also changes the state of residual stress compared to ordinary LPC to one that is more favorable from the point of view of operation—compressive stresses are generated in the technological surface layer.

Effects of Shot Peening Pressure, Time, and Material on the Properties of Carburized Steel Shafts.

Carburized steel shafts are commonly used in industry due to their good wear resistance and fatigue life. If the surface of carburized shafts exhibits an undesired tensile stress, shot peening treatment may be required to alter the stress condition on the surface. In the present study, the effects of shot peening pressure (3-5 kg/cm2), time (32-64 s), and material (stainless steel, carbon steel, and glass) on the residual stress, retained austenite, microhardness, and surface roughness of the carburized shafts were investigated. The experimental results showed that the surface residual tensile stress was changed into compressive stress after the shot peening treatment. The shot peening effects increased with the increasing peening pressure and time. In addition, a significant decrease in the amount of retained austenite in the subsurface region was observed. Peening with different materials can affect the peening effect. Using glass pellets exhibited the best shot peening effect but suffered massive pellet fracture during processing. In overall consideration, the optimal peening parameters for carburized steel shafts for practical industrial applications involved using the stainless-steel pellets with a peening pressure of 5 kg/cm2 and a peening time of 64 s. The maximum residual stress was -779 MPa at a depth of 0.02 mm, while the highest surface microhardness was 827 HV0.1.

Fatigue life improvement by shot peening for pre‐fatigue tested carburized steel

AbstractThe effect of shot peening (SP) on pre‐fatigue tested carburized steel was investigated. Plane‐bending fatigue tests were conducted on carburized CrMo steel that was pre‐fatigue tested and treated with SP. Fatigue cracks were induced by pre‐fatigue tests with a stress amplitude of σa = 1000 MPa, and the number of the pre‐fatigue test cycles was 2.0 × 104 (L5 test) and 4.0 × 104 (L15 test). We compared the fatigue lives of the fatigue‐damaged and smooth specimens without fatigue damage treated with the same SP. The fatigue life of the L5 tested specimens with SP was longer than that of the non‐fatigue damaged smooth specimens after SP. Therefore, the fatigue cracks introduced by the L5 test can be rendered harmless by SP. Furthermore, near‐surface material properties were evaluated and the mechanisms of rendering surface cracks harmless were investigated.

Determination of Carbon Potential and Carbon Mass Transfer Coefficient During Vacuum Carburizing of Steel

Determination of Carbon Potential and Carbon Mass Transfer Coefficient During Vacuum Carburizing of Steel

THE INFLUENCE OF THE CARBURIZING PROCESS ON THE IMPACT-SLIDING WEAR BEHAVIOR OF 14NiCr14 STEEL

Weapons depend largely on the barrel. Gunpowder combustion converts chemical energy into thermal and mechanical energy. Barrels give projectiles initial speed and flight direction, and helical grooves require fast spinning for stability while moving toward the target. Due of barrel exposure to heat, high pressures, gunpowder vapors, and external impacts, this weapon element needs extensive investigation. The study discusses carburizing for surface modification in high-pressure circumstances to improve gun barrel interior line tribology. Carburizing has been detected at a depth of 960 μm from the surface, as revealed by light-optical microscope images. The microhardness test has been performed on the sample's cross section, which has a maximal hardness of 650 ± 10 HV0.05 close to the surface and 250 ± 5 HV0.05 close to the interface. At room temperature (RT), this study looked at how the carburizing process affects the impact-sliding wear performance of 14NiCr14 steel, which is widely used in the barrel extensions of guns under complex loading conditions. A series of impact-sliding wear experiments were conducted on 10 mm-diameter bearing steel balls made of 52100-grade steel, for a total of 4297 loading cycles. A 2-D contact profilometer and a light optical microscope (LOM) then examined the wear tracks that had formed on the samples. The carburized steel caused a decrease in the wear rate at the impact and sliding zones of the wear track.

AlN and Nb(C,N) Composite Precipitation Behaviors and Their Effects on Austenite Grain Growth in SCr420H High‐Temperature Carburized Gear Steel

The effects of nitrogen (N) and niobium (Nb) contents on the precipitation behaviors of AlN, Nb(C,N), and AlN‐Nb(C,N) precipitates and austenite grain growth during the pseudo‐carburizing process are investigated for the carburized steel SCr420H. The results indicate that an increase of N content from 0.011% to 0.019% leads to the emergence of fine and uniform austenite grain structure in the sample while being held at 930 °C for 6 h, which is attributed to a notable rise in the number density of AlN and a decrease in the coarsening rate of AlN. In the steel containing 0.023% Nb, the composite precipitates AlN‐Nb(C,N) play a primary role in the pinning effect on austenite grains growth. The isolated Nb(C,N) and AlN precipitates have minor pinning effects due to their very low volume fractions. Nb(C,N) cap forming on AlN substrate obeys the Shoji–Nishiyama orientation relationship. The favorable lattice matching between AlN and Nb(C,N) and accelerated coarsening rate of Nb(C,N) cap decrease hindrances to the nucleation, growth, and coarsening of Nb(C,N) on AlN substrate. Meanwhile, these simultaneous effects also suppress the same processes for the isolated Nb(C,N) in the matrix.

Real-time prediction method of carbon concentration in carburized steel based on a BP neural network

ABSTRACT Gears are key components of mechanical transmission systems. They need to be carburized and quenched to meet the requirements of internal toughness and external hardness, to obtain higher hardness and wear resistance. Heat treatment engineers can calculate carbon concentration distribution through the finite element analysis method, facing the challenge of high computational cost and high memory requirements. To solve this problem, a real-time prediction method of 1D and 2D carburizing concentration based on a Back Propagation (BP) neural network (BPNN) is proposed. First, carburizing experiments were conducted to verify the accuracy of the carburizing numerical model. Then, by establishing an accurate carburizing model, 37,800 and 177,147 1D and 2D carburizing training samples were generated using the finite element model (FEM) method, respectively. Finally, for 1D carburizing, the average relative error of the training model on the test set is 0.2911%. For 2D carburizing, the average relative error of the reconstructed BPNN model on the test set was 0.4381%, and a real-time performance evaluation was performed. The carbon concentration prediction time for each set of process parameters is only 0.12 s, nearly 175 times faster than FEM calculation, which meets the accuracy and real-time requirements for real-time prediction of carburizing carbon concentration.

Exceptional strength and wear resistance in an AA7075/TiB2 composite fabricated via friction consolidation

The friction consolidation method successfully reinforced aluminum 7075 alloy (AA7075) with high-volume fractions (12 and 24 vol%) of titanium diboride (TiB2) by high pressure and severe plastic deformation at elevated temperatures. The consolidated AMCs have a uniform dispersion of submicron- and micron-sized TiB2 particles in the AA7075 matrix, with significant refinement of the matrix grain size and the particles. The addition of TiB2 significantly increases hardness by up to 50 %, Young’s modulus by up to 62 %, and ultimate tensile strength by up to 28 % to 672 MPa, while reducing ductility by 80 %. Wear resistance of 7075/24 vol% TiB2 improves seven-fold compared to baseline, making it comparable to that of carburized steels. Microstructure-based finite element modeling provided a theoretical strength limit of ∼730 MPa for the composites and indicated that high triaxiality in conjunction with severe equivalent plastic strain in a narrow area between the TiB2 particles led to early fracture initiations, limiting the ductility.

Effect of shot peening conditions on the surface defect size rendered which is harmless in carburized steel

Effect of shot peening conditions on the surface defect size rendered which is harmless in carburized steel

A study of the effect of dual shot peening on the surface integrity of carburized steel: combined experiments with dislocation density-based simulations

A study of the effect of dual shot peening on the surface integrity of carburized steel: combined experiments with dislocation density-based simulations

Effect of ultrasonic surface rolling on the friction and wear properties of 8620H carburized steel at elevated temperatures

The surface strengthening treatment of 8620H carburized steel was carried out by ultrasonic surface rolling (USR) process, and the samples with and without the treatment were subjected to friction and wear experiments at 25°C, 100°C, and 150°C. The experimental results showed that the samples with USR treatment had higher surface hardness, lower surface roughness, deeper hardened layer depth, and higher surface residual compressive stress than the samples without USR treatment. Meanwhile, the wear degree of the samples deteriorated as the temperature increased, but the anti-wear performance of the samples with USR treatment increased by 52.9%, 29.8%, and 14.9% compared with the samples without USR treatment at 25°C, 100°C, and 150°C, respectively, indicating that the USR treatment still had a better strengthening effect at high temperatures.

Further enhancement of surface mechanical properties of carburized 9310 steel by electropulsing-assisted ultrasonic surface rolling process

9310 carburized steel experiences significant wear and spalling problems when operating under high friction and heavy loads, which severely restricts its applications in the aviation industry. Therefore, it holds great significance to further enhance the surface mechanical properties of 9310 carburized steel through suitable surface strengthening technologies. The Electropulsing-Assisted Ultrasonic Surface Rolling Process (EP-USRP) has been successfully applied to carburized 9310 steel, yielding significant improvements in surface quality, hardness, friction and wear properties, and microstructure. Systematic investigations were conducted under varying EP-USRP parameters. Regarding the electric pulse parameters, it is observed that with the increase in output voltage, surface properties such as surface roughness and surface hardness tend to first optimize and then deteriorate. After applying EP-USRP with optimal parameters, the surface roughness of carburized 9310 steel was reduced to Ra 0.154 μm, a mere 5 % of its initial value. The surface hardness experienced a substantial increase, reaching 909.2 HV, representing a notable improvement of 29.9 % compared to the original sample, with a corresponding hardening depth of 1400 μm. Moreover, the wear amount of carburized 9310 steel witnessed a remarkable reduction to 11.8 % of its initial value, accompanied by a decrease in the coefficient of friction to 43.0 %. The enhancement of carburized 9310 steel through EP-USRP is attributed to two key mechanisms: deformation hardening induced by severe plastic deformation and microstructure strengthening resulting from strain-induced martensitic transformation. Among them, the severe plastic deformation mechanism is dominant, Through these mechanisms, the proportion of small-angle boundaries in carburized 9310 steel strengthened by EP-USRP increased. Additionally, the grain size of the surface layer decreased, and the content of retained austenite in the surface layer decreased, collectively contributing to significant improvements in surface properties, as well as friction and wear performance.

Modeling surface roughness profiles generated by the belt finishing process of a 27MnCr5 carburized steel

Belt finishing is a superfinishing process that enables to reach fine surface roughness. This paper proposes a numerical model, predicting belt finishing roughness profiles of a 27MnCr5 carburized steel. It utilizes belt topographies that are then numerically deformed thanks to a specific morphological filter. A method for determining the morphological filter parameters is proposed and depends on the size of the grains. Then, the deformed topography of the belt virtually scratches the workpiece at a given depth of indentation (computed by a rough contact model). The model predicts surface roughness profiles in the steady state regime. The paper shows a reasonable agreement between experimental and numerical results. The model captures the main trends: the higher the grain size the higher the roughness of the workpiece. Computational time needed for this model is a few minutes, making it a useable solution for the industry.

Role of the martensitic microstructure in the stabilized residual stresses under cyclic loading and in the fatigue behavior of two steels

The influence of martensitic microstructure on the evolution of residual stresses during cyclic loading has been investigated using X-ray diffraction, both in martensite and in retained austenite. Different microstructures containing retained austenite fractions of 25% and 40% were obtained by vacuum carburizing applied to the 14NiCr11 steel. Additionally, other microstructures, such as quenched or tempered martensite of the 42CrMo4 steel were also studied.The results indicate that, for the same hardness and similar stabilized residual stresses in retained austenite, the greater the longitudinal residual stresses in quenched martensite, the greater the improvement in fatigue strength.From initial biaxial isotropic residual stresses, cyclic loading close to the endurance limit created anisotropic residual stress relaxation in quenched martensite and retained austenite. After cyclic loading, the longitudinal residual stresses were higher than the transverse residual stresses, regardless of the type of loading (bending in the case of 14NiCr11 carburized steel or combined bending and torsion in the case of the 42CrMo4 steel). The high level of longitudinal residual stresses after cyclic loading was correlated with the high retained austenite transformation to martensite in the case of 14NiCr11 carburized steel. The anisotropy of the stabilized residual stresses (after a few 10th of cycles) is due to the metastability of quenched martensite under cyclic loading.

Experimental study on slow tensile, fatigue, and impact on X42 steel and #20 carburizing steel

Hydrogen embrittlement is a common phenomenon in high-strength steels and presents a significant challenge in the research and development process. This study aims to analyze the mechanism of hydrogen embrittlement, investigate the causes of crack growth in steel, and conduct experiments at mesoscopic and microscopic scales to gain a deep understanding of the relationship between hydrogen embrittlement and defects in high-strength steels. The research includes a slow tensile test to study the shrinkage and ductility of X42 steel and 20# carburizing steel under air and hydrogen environments. Furthermore, fatigue testing is conducted to comparatively investigate the crack growth of CT specimens in nitrogen and hydrogen environments at different pressures. Additionally, impact testing is performed to examine the fracture of V-notched specimens in air and hydrogen at different pressures. The findings reveal that 20# carburizing steel exhibits better fracture toughness than X42 steel during the slow tensile process, and its hydrogen embrittlement sensitivity is lower. Moreover, the fatigue crack growth process of 20# carburizing steel is less affected by hydrogen embrittlement, resulting in better fatigue rupture resistance compared to X42 steel. Furthermore, the impact toughness value of 20# carburizing steel is higher than that of X42 steel in the impact toughness test. Both steels show varying effects on crack growth under different hydrogenation pressures. Importantly, the impact toughness of both steels is less affected by different hydrogenation pressures.

Fatigue damage development associated with microstructure and alloying effects in carburized steels

Fatigue damage development associated with microstructure and alloying effects in carburized steels

Surface Integrity induced by the Belt Finishing Process and Effects on the Fatigue Limit of a 27MnCr5 Carburized Steel

Among superfinishing processes, belt finishing is well known for its ability to induce compressive residual stresses and low surface roughness. Moreover, it is promoted by industry, as this process requires limited investments and is easy to handle. Combined with hard turning, precise dimensions and fine surface roughness of the parts can be ensured. Therefore, the combination of these processes could replace the grinding operation performed on automotive gear shafts for example. The article proposes to study the effects of the belt finishing operation on surface integrity of 27MnCr5 carburized steel shafts. Residual stresses and surface roughness are investigated for hard machined and belt finished samples. Afterwards, rotating bending fatigue tests are performed, and the fatigue limit of the belt-finished samples is compared with hard machined ones.

Leveraging Deep Neural Networks for Estimating Vickers Hardness from Nanoindentation Hardness.

This research presents a comprehensive analysis of deep neural network models (DNNs) for the precise prediction of Vickers hardness (HV) in nitrided and carburized M50NiL steel samples, with hardness values spanning from 400 to 1000 HV. By conducting rigorous experimentation and obtaining corresponding nanoindentation data, we evaluated the performance of four distinct neural network architectures: Multilayer Perceptron (MLP), Convolutional Neural Network (CNN), Long Short-Term Memory network (LSTM), and Transformer. Our findings reveal that MLP and LSTM models excel in predictive accuracy and efficiency, with MLP showing exceptional iteration efficiency and predictive precision. The study validates models for broad application in various steel types and confirms nanoindentation as an effective direct measure for HV hardness in thin films and gradient-variable regions. This work contributes a validated and versatile approach to the hardness assessment of thin-film materials and those with intricate microstructures, enhancing material characterization and potential application in advanced material engineering.