Papers by Keyword: Spring Steel

Abstract: 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 (a_hml), the crack depths (a₂₅, a₅₀) that reduce the fatigue limit of non-SP smooth materials by 25% and 50%, and the crack depths (a_hml) that can be detected using non-destructive inspection (NDI) are evaluated. The residual stress affects a_hml: the larger the residual stress, the larger a_hml will be. The aspect ratio also affects a_hml. Because both SP and SSP exhibit a_hml> (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 (a_NDI1, a_NDI2) > (a₂₅, a₅₀), the crack depths of and cannot be detected using NDI.

Abstract: A new method for a fast analysis of heavily deformed, multicomponent ferritic/pearlitic steels microstructure based on XRD measurements had been developed. Its practical application has been examined and proven during wire rod production of a high-strength eutectoid non-alloyed steel grade containing 0.81 weight percent carbon. For individual technological conditions, the lattice strains and their anisotropy were analysed quantitatively by means of fast X-ray diffraction measurements and correlated with the results of comprehensive mechanical testing. Obtained relationships between the microstructure characteristics and mechanical properties were described using physically based models and used to establish a material specific database for prediction of the mechanical properties from X-ray diffraction data. Depending on the deformation state different parameters have to be applied for the material’s macroscopic properties prediction. Additionally, the fast microstructure analysis can provide more detailed information in the case of deviations from the as-required material’s properties due to technological aberrations.

Abstract: The heat treatment after cold forming is used to decrease the residual stresses of springs, but the mechanical characteristics of the spring steel wires alters, too. This presentation describes the influence of the heat treatment technology (oven equipment, temperature, duration,…) to the properties and quality of helical compression springs made from oil hardened and tempered spring steel wire.

Abstract: In order to investigate the interior-induced fatigue crack propagation behavior of high cleanliness valve spring steel (JIS SWOSC-V), rotating bending fatigue tests were performed for various kinds of specimens with different hardness or surface finishings. The harder specimen with higher compressive residual stress showed longer fatigue life. The electrochemical polished specimen pre-treated with shot peening showed almost same fatigue life as the shot-peened specimen in spite of the difference in surface roughness. After fatigue tests, fracture surfaces were observed using a scanning electron microscope (SEM) to evaluate the fatigue fracture mechanism. Most specimens failed in surface-induced fracture mode due to high cleanliness; however, some specimens failed in interior-induced fracture mode in the very high cycle regime. Although non-metallic inclusions were not observed at interior fatigue crack initiation sites, 2 types of significant microstructures (with smooth surface or granular surface) were observed. EBSD analysis, profile analysis and computational simulation using a fracture surface topographic analysis (FRASTA) method were performed to investigate the mechanism of the interior-induced fatigue fracture caused by the microstructure at defect without any inclusion.

Abstract: 50CrV4 spring steel is a tough, shock resisting, shallow hardening chromium vanadium steel having high fatigue and impact resistance in the heat treated condition. It is used extensively in gears, pinions, springs, shafts, axles, pins, bolts, etc., which require high modulus of resilience. The alloy was realised through conventional melt route of electric arc furnace (EAF) followed by ESR. The application of the alloy is limited to a section thickness of 15mm [1]. Hence obtaining optimum mechanical properties becomes a challenging task. In this study, the hardening as well as tempering operations were limited to 15mm thickness. The samples from the alloy were subjected to hardening at 860°C for 1.25 h. and oil quenching to room temperature followed by tempering at four different temperatures of 250, 300, 370 & 450°C for 3 h. each with oil quenching to room temperature. It was found that the alloy exhibited good combination of strength and ductility when tempered at 450°C. Microstructural study revealed the presence of fine tempered lath martensite along with the presence of a very small amount of delta ferrite along prior austenitic grain boundaries.

Abstract: The paper deals with the qualitative, quantitative, and phase analyses of particles that were found during the metallographic analysis of a cracked spring washer made of silicon spring steel 38Si7, with the aim of ruling out the client’s suspicion of possible initiation of graphitization in the course of the heat treatment. The problem is solved via metallographic analysis using light microscopy, scanning electron microscopy including EDS microanalysis of the chemical composition and EDS line analysis.

Abstract: Surface decarburization of spring steel 60Si2MnA heated under A_C1 temperature and in temperature range of A_C3-G was investigated. The results show that under the A_C1 temperature, pearlite spheroidization and surface decarburization were carried out simultaneously and had a mutual promotion relationship. In the temperature range of A_C3-G, decarburized layer consisted of complete and partial decarburization, and the complete decarburized depth increased but the partial decarburized depth just a small change with the increase of heating time. Besides, when heating temperature was 790 °C, functional relation between the total decarburized depth, the complete decarburized depth and the heating time follows the formula of and , respectively.

Abstract: To solve the heavy vehicle leaf spring material issues, developed heavy vehicle leaf spring with a new material. This article focuses on technical solutions and new materials, materials testing trial and material properties, structure and toughening mechanism of tissue material analysis, leaf spring using new materials bench and road tests. The test results show that the new material with high strength, high ductility and excellent manufacturability. And fewer leaf spring meet material requirements, such as the high stress, high-performance and high reliability fatigue. The development of leaf spring using new materials has high fatigue properties, and it uses for liberation series replacement truck leaf spring.

Abstract: The microstructure and mechanical properties of the four spring steels with different Si content treated by Q-I-Q-T process were studied by metallographic microscope, MTS, impact testing machine and X-ray stress analyzer. The results show that the tensile strength and yield strength is first increased and then decreased with the increase of Si content, the volume fraction of retained austenite and elongation are fist decreased and then increased when the Si content is less than 2.1%, and the microstructure become finer and homogeneous. When Si content reaches 2.1%, the comprehensive properties of 60Si2CrVA spring steel is the best.

Abstract: A high number of cycles sustained before failure, under cyclic loading application, is one of the key performance requirements of springs. Heat and surface treating of the spring steel can have a significant influence on its fatigue life. The main purpose of heat treating is to achieve a tempered-martensitic microstructure with appropriate surface hardness, in order to increase the fatigue limit of the spring. The heat treatment aims to an end martensitic formation from an initial ferritic/perlitic microstructure through the steps of heating, quenching and tempering. This study shows that the correct parameters chosen for each of these steps for 56SiCr7 steel can result to an appropriate microstructure, and therefore increase the steel surface hardness up to approximately 550-600 HV. With the aid of optical microscopy, the thickness of the decarburized surface layer is determined, in order to distinguish between the core and surface microstructure hardness of heat treated steel. Surface treatment, through shot-peening, induces compressive residual stresses on the surface of the steel, thus increasing the hardness by at least 204 HV, compared to the raw material, and doubling the number of cycles to failure. Vickers micro-hardness measurements conducted on a cross-section, at different depths from the surface of the steel, show the trend of hardness increasing towards its core, and verify the dependence of the surface hardness of the steel on heat treatment.