Spring Steel Research Articles

Correlation between Tetragonality and the Residual Stress in Cryotreated Spring Steels

Correlation between Tetragonality and the Residual Stress in Cryotreated Spring Steels

EFFECT OF STRESS RELIEVING TREATMENT ON HELICAL COMPRESSION SPRING MADE OF SPRING STEEL WIRE

Helical springs are one of the various forms of mechanical springs that are frequently used in car and mechanical systems. During the operation of cold coiling of helical springs, residual stresses are generated in spring. These stresses are relieved by stress relieving treatment, which is carried out just after the coiling. In stress relieving slight dimensional changes occurs. As per design of springs the wire diameter, coil diameter, number of turns and modulus of rigidity of spring wire play an important role. In these studies, experimental investigation is carried for change in outer diameter and change in no. of turns due to stress relieving. Experimentation is carried out on helical compression spring made of spring steel wire. Springs of wire diameter 1.2 mm, 2.3, mm, 3.0 mm and 4.0 mm are were studied.

Analytical and experimental investigation on a NiTiNOL circular ring-type vibration isolator with both stiffness and damping nonlinearities

Vibration isolators with both stiffness and damping nonlinearities are expected to exhibit the advantages of broad-band and high-efficiency vibration isolation. A NiTiNOL circular ring is used to implement a novel type of high-static-low-dynamic-stiffness vibration isolator with nonlinear damping. The nonlinear restoring and damping force of the NiTiNOL circular ring is fitted by a restoring force surface method, and the dynamic equation of the isolator under a harmonic base excitation is established. A harmonic balance method is applied to determine the steady-state responses and the displacement transmissibility. The analytical outcomes are numerically confirmed by the direct integration of the dynamic equation. The restoring and damping force measurement experiment and the vibration isolation experiment on both the NiTiNOL and the spring steel circular ring-type isolators are performed, and the experimental results validate the analytical results. For the NiTiNOL circular ring with an obvious material nonlinearity, the restoring force surface model achieves higher accuracy than the elliptical integral method with a linear damping assumption. The errors in predicting the restoring and damping force and the displacement transmissibility are below 0.89% and 1.78%, respectively. Compared with the spring steel circular ring with the same dimensions and preload, the NiTiNOL circular ring-type isolator exhibits a stronger high-static-low-dynamic-stiffness characteristic, together with a larger damping ratio due to the energy consumption of the phase transition. Thus, the NiTiNOL circular ring-type isolator demonstrates a better vibration isolation performance with a broader frequency band and a higher dissipation efficiency.

Reliability Evaluation of 0.57wt.% Carbon Steel for Springs with Different Types of Shot Peening

Springs acting as suspension systems can damaged by external collisions, such as those with stones. Corrosion pitting occurs in the damaged areas, and cracks will initiate and fracture. However, the allowable corrosion pitting size can be increased by inducing residual stresses via shot peening. In this study, residual stresses are induced through shot peening (SP) and stress shot peening (SSP). Then, the harmless crack depth (ahml), the crack depths (a25, a50) that reduce the fatigue limit of non-SP smooth materials by 25% and 50%, and the crack depths (ahml) that can be detected using non-destructive inspection (NDI) are evaluated. The residual stress affects ahml: the larger the residual stress, the larger ahml will be. The aspect ratio also affects ahml. Because both SP and SSP exhibit ahml> (a25, a50), (a25, a50) can be rendered harmless. Hence, (a25, a50) can secure the safety and reliability of the steel via SP and SSP. Because both SP and SSP exhibit (aNDI1, aNDI2) > (a25, a50), the crack depths of and cannot be detected using NDI.

Characteristic Flow Behavior and Processing Map of a Novel Lean Si Spring Steel for Automotive Stabilizer Bars

The spring steel for automotive stabilizer bars has a great responsibility in that its quality directly affects the stability, safety, and comfort of vehicle operation. The isothermal thermal compression behavior of a novel lean Si spring steel that was used to manufacture an anti-roll bar was investigated with a DIL805A/D quenching thermal dilatometer in this research. A hyperbolic sine type of constitutive model was established, and hot processing maps were produced to evaluate the experimental steel’s hot workability properties. The experimental results suggest that dynamic recrystallization (DRX) preferentially occurs at a low strain rate and high thermal processing temperature, while the processing maps of the experimental steel are susceptible to strain. The instability regions increase as the strain increases. The processing maps’ stable and instable domains should be decided upon comprehensive analysis of the instability criterion, power dissipation efficiency, and strain rate sensitivity index. The optimum parameters of hot processing for the experimental steel at various strains are that the deformation temperature of 1000–1150 °C and the strain rate of 0.1, approximately.

Evolution Mechanism of MgO–Al2O3–SiO2–CaO Inclusions During Continuous Casting of Si‐Killed Spring Steel

Controlling inclusions is essential for producing high‐quality spring steels. In continuous casting (CC), the thermodynamic equilibrium between the steel and inclusions changes with the reoxidation and temperature reduction of molten steel, resulting in the compositional transformation of the inclusions. Herein, the evolution mechanism of the inclusions during CC is investigated through industrial trials and thermodynamic analyses. Three types of oxide inclusions are classified in the steel, namely, Al2O3–SiO2, CaO–Al2O3–SiO2, and MgO–CaO–Al2O3–SiO2, whereby MgO–CaO–Al2O3–SiO2 is the main type. The average mass content of Al2O3 in the inclusions is 15–21% at the end of vacuum degassing. The number density of the inclusions increases because of the reoxidation of molten steel. The reoxidation and temperature decrease result in the further reaction among Si, Al, Mg, and O in steel, thereby increasing the melting point of the inclusions. Moreover, the inclusions evolve during CC. The mass fractions of CaO and MgO decrease, that of Al2O3 increase, and that of SiO2 hardly change. Compared to reoxidation, temperature plays a leading role in the inclusion evolution. Finally, the details of the inclusion evolution are illustrated by thermodynamic calculations.

Effect of Slag Adjustment on Inclusions and Mechanical Properties of Si-Killed 55SiCr Spring Steel

The effects of the Al2O3 content and basicity of CaO–SiO2–Al2O3–10 wt.% MgO refining slag on inclusions removal in 55SiCr spring steel were investigated. The viscosity of slag was studied using a viscometer, while the microstructure investigation involved using a water-quenching furnace and a Fourier-transform infrared spectrometer. The influence mechanism of the slag adjustment on inclusions was explored through thermodynamic calculations and kinetic analysis. The results indicated that the viscosity of the molten slag increased gradually with the content of Al2O3 increasing due to it increasing the degree of polymerization of the slag network structure, especially the [AlO4]5− and [Si-O-Si] structures. In contrast, the viscosity of molten slag experienced the opposite pattern, with the basicity of molten slag increasing. This was due to the fact that Ca2+ can significantly reduce the degree of polymerization of a slag network structure, especially the percentages of the [SiO4]4−, [AlO4]5− and [Si-O-Si] network structures. Finally, the changes in physical properties and structure of slag significantly affected the removal effect of the inclusions in molten steel. As a result, the number, size distribution, composition distribution and morphology of the inclusions displayed significant changes when the content of Al2O3 increased from 3 wt.% to 12 wt.% and the basicity of the slag gradually increased from 0.5 to 1.2.

Application of Honeycomb Structures in Key Components of Space Deployable Structures

The reed structure is the key component in the foldable space deployment mechanism. In the aerospace industry, weight loss occupies a pivotal position. The use of lightweight structure can achieve significant savings in launch costs and improve load efficiency. Aiming at the lightweight requirements of the space deployment mechanism, this paper discusses the substitution effect of the honeycomb topology on the reed structure in the space deployment structure. Firstly, the column structure of the honeycomb is equivalent to an orthotropic cylindrical block-shell structure. According to the bending theory of an orthotropic cylinder, the expanded honeycomb structure equivalent to an orthotropic cylindrical block-shell structure is deduced. Then, the exact expression of the reverse bending moment was obtained, and the bending moment-curvature curve during the folding process was drawn. The bending moment-curvature characteristics during the folding process are simulated by finite element numerical simulation. By proposing the index of unit mass for analysis and comparison, the results show that compared with the common spring steel structure, the honeycomb structure has better mechanical properties per unit mass and has a certain substitution effect on the reed structure.

A design of underwater soft gripper with water pressure sensing and enhanced stiffness

AbstractIn this paper, a hydraulic soft gripper for underwater applications is designed to provide a solution for improving the gripping force as well as the sensing capability of the soft gripper. The soft gripper is made of silicone and has an integrated semi-circular hydraulic network inside. To enhance the rigidity and grasping performance of the soft gripper, we have integrated a restriction layer consisting of a spring steel plate in the soft gripper. Meanwhile, to enhance the sensing capability of this soft gripper, we have designed a water pressure sensor based on resistance strain gauges and integrated it on the spring steel plate. Before fabrication, we determined the structural parameters of the soft gripper by geometric analysis. Then we experimentally evaluated its pressure-bearing capacity, bending performance, the role of spring steel plates, and the accuracy of the sensor.The experimental results show that the spring steel plate improves the gripping force of the soft gripper, the sensor also has high accuracy, and the built four-finger gripping system has good adaptability to objects of different shapes and weights.Compared with the existing solutions, this solution takes a simpler structural form while improving the gripping force and sensing ability of the soft gripper, and integrates the issues of improving the gripping force and sensing ability. The spring steel plate used in this paper not only improves the gripping force of the soft gripper but also provides a stable and reliable platform for installing sensors.

Enhanced Spring Steel’s Strength Using Strain Assisted Tempering

Spring steels are typical materials where enhancement of mechanical properties can save considerable mass for transport vehicles, in this way the consumption of fuel or electric energy can be decreased. A drastic change in both the resulting microstructure and mechanical properties could be achieved due to the inclusion of strain into the tempering process after quenching. The strain assisted tempering (SAT) technology was applied, i.e., the process of quenching and following a sequence of tempering operations alternating with strain operations. After the first tempering, controlled deformation by rotary swaging was carried out with a strain of 17% (strain rate is about 120 s−1). Considerably higher strength parameters after SAT compared to conventional quenching and tempering (QT) technology were nevertheless accompanied by enhanced notch toughness at the same time by the decrease of elongation and reduction of area. However, by optimizing the process it is was also possible to achieve acceptable values for those parameters. Remarkable differences are visible in resulting microstructures of compared samples, which were revealed by metallographic analysis and X-ray diffraction measurement. While the standard microstructure of tempered martensite with transition carbides was observed after QT processing, carbideless islands with nanotwins occurred in martensitic laths after SAT processing.

On the low temperature creep controlling mechanism in a high strength spring steel

Despite of the well-known fact that high strength steels are exhibiting low temperature creep deformation, its rate controlling mechanism is yet to be understood. The strain hardening theory and the exhaustion creep model were proposed almost seven decades ago to unravel the low temperature creep mechanism in a single phase homogeneous isotropic material. However, their applicability to low temperature creep deformation in a technical material like a modern high strength steel is still a matter of investigation owing to their nature of multi-phase, in-homogeneous, and an-isotropic behavior. The authors have grabbed this chance to experimentally validate the exhaustion creep model based on low temperature creep tests of the SAE 9254 spring steel. The ultimate tensile strength and yield strength σe of SAE 9254 were determined in a temperature range of 298K≤T≤353K at a constant strain rate of 2.5∙10−4s−1. Low temperature creep deformation behavior was studied at the above-mentioned temperatures T at a constant stress σ=1634MPa, and at stresses 1071MPa≤σ≤1634MPa at a constant temperature T=353K for a duration of 1hr, respectively, at each condition. The retained austenite quantity was determined prior and post low temperature creep testing by means of X-ray diffraction. A reworked exhaustion creep model well describes the stress σ and temperature T dependency of low temperature creep deformation behavior in SAE 9254. Consequently, our hypothesis of a low temperature creep rate controlling mechanism reads: Low temperature creep strain is predominantly contributed by dislocation glide in the retained austenite phase. The reduction in creep rate with time can then be attributed to the exhaustion of this specific deformation mechanism by strain induced martensitic transformation of the retained austenite.

Influence of Austenitisation Time and Temperature on Grain Size and Martensite Start of 51CrV4 Spring Steel

51CrV4 spring steel is a martensitic steel grade that is heat treated by quenching and tempering. Therefore, austenitisation is an important step that influences steel properties. The main goal of austenitisation is to obtain a single-phase austenite structure that will transform into martensite. We studied the influence of austenitisation parameters on grain growth and martensite transformation temperatures. The samples were quenched from different austenitisation temperatures (800–1040 °C) and were held for 5, 10 and 30 min. The martensite start transformation temperatures (MS) were determined from dilatometric curves, and the hardness was measured using the Vickers method. The microstructure of the samples and the size of the prior austenite grains were characterised using optical microscopy. The increase in the size of the prior austenite crystal grains increases the MS temperature. However, this trend is visible up to 960 °C, where the results start to deviate. High temperatures, 960 °C and above, cause both grain growth and increased carbide dissolution along with chemical homogenization of the steel. The added influence of strong solute diffusion caused a big deviation in the results. The stability of carbides during austenitisation were evaluated with scanning electron microscopy (SEM) and thermodynamic calculations of equilibrium phases using the Thermo-Calc program. MC-type vanadium carbides are stable up to 956 °C under equilibrium conditions, but the SEM results show that they were present in the microstructure even after annealing at 1040 °C. This means that crystal growth is slowed down, which is positive, and that the austenite contains less carbon, so the hardness is lower.

Role of Si in the Oxide Nucleation and Growth Mechanisms of 60Si2Mn Spring Steel: Experimental and First-Principles Study

Role of Si in the Oxide Nucleation and Growth Mechanisms of 60Si2Mn Spring Steel: Experimental and First-Principles Study

C-Shaped Bidirectional Stiffness Joint Design For Anthropomorphic Hand

In this letter, we propose a C-shaped bidirectional stiffness joint for an anthropomorphic hand. The spring steel piece is used to connect the knuckles with inner concave C-shape as a rotational joint. The finger is bent by the tendon driven with low stiffness and reset by its own elasticity. The reverse bent has high stiffness with the C-shaped structure of the spring steel piece. The model of the designed joint is deduced, and the load-bearing capacity is analyzed. Meanwhile, the finite element simulation of the maximum bending moment of this joint is implemented. Then, an experimental platform was built to test a single finger, and the C-shaped joint was found to be 36 times larger than the maximum bending moment of the rectangular section joint. Finally, a prototype anthropomorphic hand was developed and the effectiveness of the C-shaped joint-based anthropomorphic hand was verified through various gesture, grasping and load bearing experiments.

Effect of Deoxidizing and Alloying Routes on the Evolution of Non-Metallic Inclusions in 55SiCr Spring Steel

Compared to the conventional deoxidation process with Al or Si-Mn for 55SiCr spring steel production, the possibility of using a Si-Ca-Ba compounded deoxidizer to control the behavior of non-metallic inclusions in spring steel was explored in this study. The effect of the addition sequence of deoxidizer and alloys into molten steel on the morphology, size, and composition of the inclusions was emphatically studied at 1873 K (1600 °C) using a high-temperature electric resistance furnace. The results indicate that adding alloy first can form less harmful inclusions in steel, which are roughly spherical and smaller than 3 μm in diameter, and its inclusion evolution path is MnO-SiO2-Al2O3→CaO-SiO2-Al2O3 and CaO-Al2O3-MgO. While adding deoxidizer first, the inclusions in steel are harmful due to its mostly irregular geometry and relatively large size over 5 μm. The inclusion evolution path is Fe-O→CaO-Al2O3(-SiO2) and CaO-Al2O3-MgO. The formation and evolution mechanism of inclusions under different addition sequences were discussed. In addition, the solubility limits of MgO from refractory into steel were studied to inhibit its corrosion by molten steel.

Microstructures and Mechanical Properties of an Ultrahigh‐Strength and Ductile Medium‐Carbon High‐Silicon Spring Steel

Herein, the microstructure and mechanical properties of medium‐carbon high‐silicon spring steel are studied, which is alloyed and/or microalloyed with Cr, Mo, Ni, Cu, Nb, and V, and subjected to various austenitizing and tempering processes. The steel has a mixed microstructure consisting of fine lath martensite, nanoscale cementite, ε‐carbide, and an amount of retained austenite (10.4 vol%). At room temperature, the steel exhibits ultrahigh tensile strength (2002 MPa) and yield strength (1775 MPa) with total elongation of 11.1%, while a good toughness is obtained characterized by Charpy impact energy as 38 J. The ultrahigh strength of this steel is attributed to the dislocation and precipitation strengthening, while the excellent total elongation is closely associated with the retained austenite. In addition, tempered martensite embrittlement is found in this steel when tempered at 450 °C. This is due to the retained austenite decomposition and cementite coarsening along the prior austenite grain and martensite laths.

Experimental investigations on waist supportive passive exoskeleton to improve human comfort

An exoskeleton is a mechanism that works as an external skeleton to assist the human body in daily tasks, rehabilitation, and strengthening. A lot of active exoskeletons have been developed in order to provide assistance to the human body while walking or running. However, developing an unpowered exoskeleton can reduce the human efforts while running is something that requires more attention. The goal is to create a lower limb assistive exoskeleton that will allow people to run while spending as little energy as possible and which is affordable and can be worn easily. The design is entirely mechanical (passive), which means it does not rely on any external electrical energy inputs.This article discusses the design and testing of waist supportive passive exoskeleton for human comfort. Exoskeleton was designed by using silicon-chromium spring steel for manufacturing of leaf spring. The leaf spring was with 50 mm width and 1 mm thick. Total weight of the exoskeleton was 1.5 kg. The stiffness of leaf spring was 56.19 Nm/rad. It has been observed that the proposed design is more comfortable to human beings while running. Composite Materials can be used for manufacturing of various parts of the passive exoskeleton to reduce its overall weight and enhance Mechanical Properties.

Effect of Vanadium on the Microstructure and Mechanical Properties of 2100 MPa Ultra-High Strength High Plasticity Spring Steel Processed by a Novel Online Rapid-Induction Heat Treatment

Advanced automotive industries generate large demand for the next generation of high strength and high toughness spring steels. Vanadium-containing 55SiCrV spring steels subjected to rapid-induction heating treatment can fulfil such requirements. However, the effect of vanadium microalloying under online rapid-induction heat treatments is rarely reported. A comparative study of the microstructure and tensile properties of 55SiCr and 55SiCrV spring steel wires subjected to a novel online rapid induction heat treatment has been demonstrated herein. It is found that the tensile strength of the 55SiCr spring wire decreases with the decrease in the wire speed in online rapid-induction heating, and the plasticity increases. Whereas, the tensile strength of the 55SiCrV steel wire increases with the decrease in the wire speed with the retained high plasticity, which is attributed to the strengthening effect of the dislocations. Through the optimized rapid-induction heating/cooling thermal cycles and intermediate-temperature tempering treatment, the tensile strength of the 55SiCrV steel wire approaches 2106 MPa with total elongation of 9.7%. Compared with the 55SiCr spring steel, the addition of V in 55SiCrV spring steel changes the strengthening and toughening mechanisms via the grain refinement and enhancement in the hardenability and tempering resistance. The finely dispersed V-containing secondary phases are rarely found in the matrix, which indicates that the precipitation effect stemming from the addition of V is not the dominant strengthening factor in the online rapid-induction heat process. The proposed novel online rapid-induction heat treatment provides a promising pathway for the mechanical property improvement of the spring steel.Graphical

A new, flexible tool concept for rotary die stretch bending

Mitigating manufacturing risks for profile-type parts formed using stretch bending operations is a considerable challenge in the industry, due to the investments required to manufacture the tooling for these processes. Traditionally such tooling has been made by solid steel blocks machined to the desired shape. This paper introduces a new tool concept for stretch bending processes, utilizing an adjustable multipoint supported flexible spring steel plate as a bend die, applied on a double rotary turntable stretch bender. The capability of the tool is investigated through a proof-of-concept experiment, assessing whether the tool design is capable of creating bends with the same quality as bends made using traditional solid steel dies. Overall, the experiment shows promising results as it allows for creating a large variation of bending shapes with good dimensional quality with low tooling investment, although the interface between the spring steel plate end and the aluminum profile creates some minor scuffing marks. The initial investigation found a pooled standard deviation of 0.25mm over 3 bend shapes with 3 samples for each, which is promising for further development. In industrial applications, the proposed tool would enable cost-efficient experimenting using production-intent tooling in the early product development phase, which could also be utilized for pre-production qualification processes, low volume manufacturing and multi-variant products.

Influence of Austenitisation Temperature and Time on Martensitic and Isothermal Bainite Phase Transformation of Spring Steel

The influence of austenitisation temperature and time on the martensitic and isothermal bainite transformation of 51CrV4 spring steel was analysed. Based on the analysis of dilatometric curves, the martensite start temperatures (MS) were determined at different austenitisation temperatures (800–960 °C) and austenitisation times (5–30 min). At a temperature of 800 °C, a partial austenitic transformation occurred, and undissolved chromium carbides were present in the matrix. At higher temperatures, the austenitic transformation was complete, and the temperature MS increased with the austenitisation temperature. The temperature of the isothermal phase transformation has a stronger effect on the bainite transformation, which has different effects on the stability of the austenite and the diffusion processes. The microstructure of isothermal bainite transformation samples at 330, 430 and 520 °C was characterised by optical microscopy and dilatometric curves. Lower bainite was formed at a bainitic transformation temperature of 330 °C, and a combination of upper and lower bainite was characterised at a transformation temperature of 430 °C. In the samples transformed at 520 °C, a smaller proportion of lower bainite formed in addition to the upper bainite and martensite. Some allotriomorphic ferrite formed along the boundaries of the austenitic grains.