Spring Steel Research Articles

Formation Mechanism of Large CaO-SiO2-Al2O3 Inclusions in Si-Deoxidized Spring Steel Refined by Low Basicity Slag

Formation Mechanism of Large CaO-SiO2-Al2O3 Inclusions in Si-Deoxidized Spring Steel Refined by Low Basicity Slag

In-situ warm shot peening on Ti-6Al-4V alloy: Effects of temperature on fatigue life, residual stress, microstructure and mechanical properties

Shot peening (SP) is a matured surface enhancement technique to improve fatigue strength and fatigue lives of cyclically loaded metallic components at room temperature. In order to achieve enhanced beneficial effects beyond SP’s conventional performance, SP has been attempted at elevated temperatures or under tensile stress loading on spring steel with some success. In this work, SP on α/β Ti-6Al-4V alloys has been carried out when they were heated at elevated temperatures up to 400 °C. The effects of such in-situ warm SP on fatigue life of Ti-6Al-4V at different temperatures have been evaluated and correlated with respective development in compressive residual stress distribution, microstructure and hardness. The optimum in-situ warm SP condition was achieved at 100 °C after a trade-off between compressive residual stress relaxation and enhanced grain refinement, both of which are affected by thermal softening but to different degrees.

Fatigue failure of SUP-9 spring steel

The SUP-9 is a widely used steel for the construction of springs due to its resistance to permanent deformation and quick vibration relief. Spring steels are subjected to heat treatment to improve their fatigue life. In this paper, the heat treatment procedure to improve the endurance limit of the SUP-9 is reported. The process of heat treatment was carried out to investigate its effect on Brinell and Rockwell hardness metrics. The endurance limits of steel before and after heat treatment were also measured. The heat treatment procedure reported in this paper resulted in an increased harness and endurance limit due to a change in the microstructure of the specimen. The test results showed that Brinell hardness and endurance limit increased by 50% and 20% respectively after heat treatment.

Research on performance of rigid-hoop-reinforced multi-DOF soft actuator

In order to improve the bearing capacity of soft actuators, this article presents the development of the rigid-hoop-reinforced (spring or steel hoop) multi-DOF soft actuator. The actuator is composed of a rotary module with spring reinforcement on the silicone rubber-based body and a bending module with steel hoop reinforcement on the body. Compared with fiber-reinforced actuators, the bearing capacities of rigid-hoop-reinforced actuators made of 65Mn spring steel are improved. The radial and the axial bearing capacity for the bending module and the rotary module is raised by 29.6%, 28.2%, 30.6%, 49.6% respectively; under the same pressure, the spring-reinforced interval increases the maximum rotary angle of the rotary module, the steel hoop-reinforced interval increases the maximum bending angle of the bending module; with the same reinforcement type, the bending module with reinforcement interval of 10 mm has good bending characteristics that the bending angle changes with the pressure gently; the lower the hardness of silicone rubber base body, the better the adaptability and flexibility of the actuator, and the higher the hardness, the greater the bearing capacity of the actuator. Due to the above advantages, the rigid-hoop-reinforced multi-DOF soft actuator can be applied to medical devices which need high load-carrying capacity.

Influence of load ratio on torsion very high cycle fatigue of high‐strength spring steel in the presence of detrimental defects

AbstractThe influence of mean shear stress on torsion very high cycle fatigue (VHCF) for internal inclusion‐initiated fracture is investigated. Ultrasonic torsion fatigue tests are performed at load ratios R = −1, 0.1, and 0.35 with high‐strength spring steel SWOSC‐V featuring an increased number of nonmetallic inclusions. Based on Murakami and Endo's parameter model, an equation predicting the torsion fatigue limit in the presence of detrimental defects is rendered. Stress biaxiality is considered using a ratio of torsion to axial fatigue strength of τa/σa = 0.86. Considering the load ratio sensitivity according to ([1 − R]/2)α, the value for α is experimentally determined to be 0.550. A fine granular area (FGA) is generated at an artificial surface defect in a fully reversed cyclic torsion test in vacuum. Measured growth rates in the FGA were 10−14–10−12 m/cycle, and the formation of the FGA consumed 98% of the VHCF lifetime.

Effects of the Ultrasonic Assisted Surface Rolling Process on the Fatigue Crack Initiation Position Distribution and Fatigue Life of 51CrV4 Spring Steel.

In this paper, the effects of the fatigue crack initiation position (FCIP) on fatigue life are discussed. Different modified gradient fields (MGFs) are prepared on the surface of 51CrV4 spring steel components by an ultrasonic assisted surface rolling process (USRP). Subsequently, the fatigue behaviour of steels with different FCIPs is systematically studied. The results show that the fatigue life of steels first exhibits an increasing tendency and then a decreasing tendency with increasing distance between an FCIP and the surface. When an FCIP shifts from the surface of the sample to the interior, the fatigue crack initiation resistance on the interior is greater than that on the surface, which leads to an increase in fatigue life. However, when the FCIP further shifts towards the centre of the specimen, the stress triaxiality experienced by the fatigue source gradually increases, which results in a peak in the curve of FCIP versus fatigue life. The magnitude of this peak fatigue life is related to the change in the stress triaxiality. Moreover, according to focused ion beam-high-resolution transmission electron microscopy (FIB-HRTEM) microstructural analysis near FCIPs, under a higher stress triaxiality, the crack tip area is subject to greater stress constraints, making the multiplication and movement of dislocations in this area more difficult, resulting in the decrease in movable dislocation density. This decrease in dislocation density leads to an increase in the stress concentration and accelerates the crack growth rate, decreasing the fatigue life. Therefore, the significant change in fatigue life is controlled by the MGF and stress triaxiality.

Effect of Hardening and Tempering on the Microstructure and Mechanical Properties of the Tapered-Forged Leaf Spring Steel

The sharp side of a steel axe is often broken. This part is usually forged into a tapered shape until the front edge is thin and sharp. The purpose of this study was to determine the effect of tempering on the structure and hardness of a steel axe made of AISI 5160 leaf spring steel which has undergone a forging and hardening process. The as-received samples were obtained from a commercial market after undergoing a forging process to reduce their thickness from 10 mm to 5.5 mm in the base part and 1 mm in the front edge part. The hardening process was carried out by heating the samples at a temperature of 850 °C followed by rapid cooling in an isorapid oil. The samples were then tempered with tempering temperatures of 300 °C, 350 °C, and 400 °C. The hardness of the tempered samples was evaluated using a Vickers microhardness tester in three different locations; the base, the middle, and the front edge of the tapered samples. To analyze the property change, the microstructure of the tempered samples was observed using SEM and EDS. The result showed that the hardness of the samples decreased with the increase in tempering temperature. The hardness of the front edge was higher than that of the middle and base part of the tempered samples. The faster cooling rate inside the thinner part was responsible for the higher hardness. The microstructure showed that the martensitic structure that emerged after the hardening process turned into fine tempered martensitic and secondary carbides. The size and amount of carbides increased with increasing tempering temperature

Improving the cycle fatigue life of spring steel by a novel thermal cycling process

A novel thermal cycling process was applied on the 65Mn spring to improve the cycle fatigue life. Results demonstrate that the cycle fatigue life after the thermal cycling process was improved from 3 times to 14 times, with an improvement of 470%. The fine, equiaxed grains were observed on the fracture surface. Moreover, the prolongation of cracks was prevented by the high density of interfaces, and the slipping and rotating between the grains consumed the applied energy during the cycling process, contributing to the improvement of cycle fatigue life.

Effect of the Depth of Decarburized Layer in SKL15 Tension Clamp on Fatigue Strength

The surface of a quenched and tempered spring steel may have a decarburized layer from which the carbon component has been reduced. The fatigue strength of the decarburized layer is low compared to the base metal, which can easily develop fatigue cracks. Recently, fatigue failure was reported in the tension clamp (SKL 15) of the DFF-300 rail fastening system during use on one urban transit route in South Korea. As a result of measuring the depth of the decarburized layer of the SKL 15 tension clamp where the fatigue failure occurred, a decarburized layer thinner than the manufacturer’s maximum allowable decarburized layer was found in one of the eight tension clamps. To check the depth of the decarburized layer where the fatigue crack may have initiated, the decarburized layer was assumed to be the initial crack, and fatigue crack initiation was assessed based on the linear elastic fracture mechanics. The manufacturer’s maximum allowable decarburized layer depth of 0.2 mm may result in fatigue cracks.

Prediction of Fatigue Limit of Spring Steel Considering Surface Defect Size and Stress Ratio

Surface defects decrease the fatigue limit of metals. In this study, the effects of surface defects on the fatigue limit of high-strength spring steel specimens were investigated. Several equations to predict the fatigue limit of specimens with surface defects were evaluated. Specimens with a semicircular slit with depths ranging from 30 to 400 µm were prepared. The Vickers hardness of the specimen was approximately 470 HV. Bending fatigue tests were performed at stress ratios ranging from −2 to 0.4. The fatigue test results showed that the fatigue limit decreased with an increase in the slit depth. Moreover, the maximum defect size that resulted in a decrease in the fatigue limit was dependent on the stress ratio. On comparing the predicted fatigue limits with the experimental results, it was confirmed that the predictions made based on the modified El-Haddad model were in good agreement with the experimentally obtained data. Thus, this model can be used to evaluate the fatigue limit of high-strength steels containing small surface defects with different stress ratios.

Vibration-Based Locomotion of an Amphibious Robot

In this research, an innovative robot is presented that can move both on land and water thanks to a vibration-based locomotion mechanism. The robot consists of a U-shaped beam made of spring steel, two low-density feet that allow it to stand on the water surface without sinking, and a micro-DC motor with eccentric mass, which excites vibrations. The robot exhibits stable terrestrial and aquatic locomotion based on the synchronization between body vibrations and the centrifugal force due to the eccentric mass. On the one hand, in aquatic locomotion, the robot advances thanks to floating oscillations and the asymmetric shape of the floating feet. On the other hand, the terrestrial locomotion, which has already been demonstrated for a similar robot, exploits the modes of vibration of the elastic beam. In this study, the effect of different excitation frequencies on the locomotion speed in water is examined by means of experimental tests and a numerical model. A good agreement between experimental and numerical results is found. The maximum locomotion speed takes place when the floating modes of vibration are excited.

Effect of nonmetallic inclusions on localized corrosion of spring steel

Certain inclusions in high-strength 60Si2Mn-Cr spring steel result in poor resistance to localized corrosion. In this work, to study the effect of inclusions on the localized corrosion behavior of spring steel, accelerated corrosion tests were performed by immersing spring steel in 3wt% FeCl3 solution for different times. The results show that severe corrosion occurred in areas of clustered CaS inclusions. Sulfide inclusions containing Ca and Mg induced the strongest localized corrosion susceptibility. For the case of (Ca,Mn,Mg)S inclusions, the ability to induce localized corrosion susceptibility is ranked as follows: MgS > CaS > MnS. Moreover, CaS, (Ca,Mn)S, and (Ca,Mn,Mg)S inclusions were mainly responsible for inducing environmental embrittlement.

Experimental investigation on Hydrogen embrittlement of EN47 Spring steel

Carbon steel is one of the significant engineering materials used in industrial and automotive sector. Most of the engineering metals are susceptible to hydrogen embrittlement (HE). It is an inherent phenomenon, which will occur during the course of service life and leads to pre mature failure of the component. In view of this, an experimental study was conducted to investigate the failure behavior of EN47 in a hydrogen simulated environment. The immersion type hydrogen charging method was adopted. The effect of HE was explored through conventional tensile testing. Experimentations were carried out according to ASTM E8 Standards. The tensile behavior of spring steel and effect of hydrogen interaction with materials was studied. The treated test material experience brittle to ductile transition exhibiting mixed mode fracture morphology on fracture surfaces, often considered being confirmation of failure through HE. Hydrogen charging causes the samples to become brittle, and reduced the plastic deformability. From the test results it can be interfered that the hydrogen charged specimen exhibits loss of ductility and also reduced the ultimate strength.

The effect of the grain size on the cycle life of spring steel 50 CrMnV

Most of the breakdown of machine parts and metal products during operation is fatigue-related due to the impact of load cycling during operation, which often leads to serious financial losses, and sometimes even fatalities. Therefore, the issues of increasing cycle life are relevant. In this work, we propose a method for predicting the cycle life of spring-type steel: the expected cycle life of steels 50CrMnV and 60SiCr in the range of 105-106 cycles can be preliminarily estimated using the equation depending on the grain size. The method allows predicting the cycle life and significantly reducing the time of its evaluation for steels such as 50CrMnV and 60SiCr by eliminating long-term fatigue tests. In addition, it also allows choosing the best performance from process treatments for the cycle life parameter without long labor-intensive fatigue tests.

Cyclic Behavior of Beam-Column Connections in Precast Structures

The performance of precast concrete structures is greatly influenced by the response of beam–to-column connections. In this study, a new moment resisting precast concrete beam-column connection detail with post-tensioning bolts, made out of high yield strength spring steel, has been experimentally investigated as an alternative to the conventional precast moment resisting connections. Precast specimens and an aseismic monolithic reference specimen have been tested under reverse cycling loads. The contribution of the mild steel in the connection region to the flexural moment capacity, and to the initial pre-stressing force on post-tensioning bolt have been the main test variables. The moment capacity, stiffness, energy dissipation capacity and the residual displacement performance of the precast connections have been compared with those of the aseismically detailed monolithic connection. The conducted tests reveal that the connection detail with steel corbel along with the post-tensioning bolt and mild steel has superior performance properties as compared to the companion precast specimens.

Simulation and experimental investigation of tool wear rate in dry and near-dry EDM process

Purpose Many engineering applications in this era require new age materials; however, some classic alloys like spring steel are still used in critical applications such as aerospace, defense and automobile. To machine spring steel material, there exist various difficulties such as rapid tool wear rate, the rough surface formation of a workpiece and higher power consumption. The purpose of this paper is to address these issues, various approaches in addition to electrical discharge machines (EDM) are used such as dry EDM (DEDM) and near dry EDM (NDEDM). Design/methodology/approach This study focuses on these two approaches and their comparative analysis with respect to tool wear during machining of spring steel material. For this study, current, gap voltage, cycle time and dielectric medium pressure are considered input variables. This study shows that the near dry EDM approach yields better results. Hence, the thermo-electrical model for this approach is developed using ANSYS workbench, which is further validated by comparing with experimental results. This thermo-electrical model covers spark radius variation and formation of temperature profile due to electric discharge. Transient thermal analysis is used to simulate the electric discharge machining. Findings It is observed from this study that discharge environment parameters such as debris concentration and fluid viscosity largely influences the dielectric fluid pressure value. Experimental results revealed that NDEDM yields better results in comparison with DEDM as it shows a 25% lesser tool wear rate in NDEDM. Originality/value The range of predicted results and the experimental results are in close agreement, authenticating the model.

Effect of austenitizing temperatures on the microstructure and mechanical properties of AISI 9254 steel

Abstract In this study, the effect of austenitizing temperatures and low-temperature isothermal heat treatment (below martensite start temperature) on the microstructure and mechanical properties of AISI 9254 high silicon spring steel has been investigated. Experimental studies show that ultra-fine carbide-free bainite, tempered martensite and carbon enriched retained austenite could be observed in isothermally heat-treated samples where the as-received sample consisted of fine pearlite. A high tensile strength of ~2060 MPa, a total elongation of ~8 %, and absorbed energy of 105 J were achieved in a commercial high-Si steel by austempering below the Ms temperature. A good combination of strength and ductility has been obtained in prolonged austempering below the martensite start temperature (225 °C) from an austenitizing temperature of 870 °C.

Characteristic flow behaviour prediction and microstructure analysis of a commercial Si–Cr micro-alloyed spring steel under isothermal compression

This article explores the characteristic flow behaviour and microstructure analysis of Si–Cr spring steel under various compression conditions by a Gleeble 3500 facility. To better simulate the abrupt and complex compression during the hot forming process, three compression strain rates (0.01 s−1, 0.1 s−1, and 1 s−1) and four compressive temperatures (850, 900, 950 and 1000 °C) were selected. The outcomes exhibit the intragranular dislocation cells and pile-up along the subgrains were formed during the dynamic recovery (DRV) progress. The dynamic recrystallisation (DRX) of the experimental steel arose with a higher value of the compression temperature. On this basis, a strain-compensated constitutive model considering the compression activation energy and a linear correlation between the Z parameter and DRX grain size are both established according to the strain-stress curves. The constitutive model is further verified by the multiple sets of hot deformation data and exhibits a good agreement between experimental and predicted points with an excellent correlation coefficient of 0.986 and a low relative error of 5.41%, indicating the reliability of the constitutive model throughout the entirety of the hot deformation process.

Valorization of Coal Gangue and Vanadium-titanium Slag into Glass-ceramic Coating for Oxidation Resistance of 60Si2Mn Spring Steel at High Temperature

Valorization of Coal Gangue and Vanadium-titanium Slag into Glass-ceramic Coating for Oxidation Resistance of 60Si2Mn Spring Steel at High Temperature

Study on the Corrosion Resistance of 39SiCrVTiA High strength and high toughness spring steel

39SiCrVTiA spring steel is heat-treated and compared with the existing high-strength spring steels 60Si2CrVA and SAE9254 for electrochemical impedance spectroscopy (EIS), polarization curve and slow strain rate testing (SSRT). The test results of electrochemical impedance spectroscopy (EIS), polarization curve show that the corrosion resistance of 60Si2CrVA was the best, followed by that of SAE9254 and 39SiCrVTIA.However, the test results of the SSRT test show that the three spring steels in 5% NaCl solution possess high SCC susceptibility. The SCC susceptibility of 39SiCrVTiA steel is slightly lower and the stress corrosion ability is better than the other two steels which may be related to its containing Ti, V elements and lower carbon content.