Spring makers have worried about the distinction of spring products with similar dimension. For the solution of this problem, We have already developed steel wire for spring that develops golden color at the low-temperature annealing process and acquired a reputation. In the mean time, there are great demand for products with various colors especially black color, in the market. So, this paper reports our development of steel wire for springs that acguires black color during low-temperature annealing. The summary is descrived below.: (1) In a low-temperature annealing process, copper that exists as copper plating on stainless steel wire and zinc that exists as zinc-chromium alloy plating on copper plated stainless steel wire diffuse in the deposit to exhibit a brown color tone while chromium is oxidized to exhibit dark gray color tone. The overlap of these color tones exhibits a beautiful black color tone. (2) Mechanical properties are not deteriorated by the above platings.
Low-cycle fatigue tests were carried out on spring steels at room temperature under a triangular strain wave form to obtain basic information about low-cycle fatigue behavior of springs. The results obtained are summarized as follows: (1) Cyclic softening behavior was observed under cyclic straining with plastic strain component. (2) Fatigue life properties and cyclic deformation properties of spring steel are the same as those which obtained by extrapolating properties of tempered steels for machine structural use to higher level of hardness. (3) Estimation method of low-cycle fatigue lives from tensile properties is proposed by modifying Manson's Universal Slope Method. (4) Total damage under incremental step tests becomes 1 to 1.8 at failure. Miner's cumulative rule is applicable to fatigue life estimation under straining of randon amplitudes. (5) Total damage is very small compared with 1 at failure, when stress controlled fatigue tests are carried out after a part of strain controlled test with plastic strain component. Cyclic softening by strain cycling promotes fatigue damage due to stress cycling.
In this study, mechanical and fatigue properties of the duplex (austenitic-ferritic) stainless steel wire (SSW) after drawing were invesitigated and compared with SUS304 SSW. Further, the notch samples were made with the duplex SSW after drawing, and a fatigue crack generated at the notch root was observed by means of SEM after interruption of test at halfway. The main results are as follows: 1) The duplex SSW after drawing shows the excellent fatigue and toughness properties as compared with SUS304 SSW. 2) Stress concentration at the fatigue crack tip is relaxed by the α phase that has low strength when fatigue crack propagate and propagation of fatigue crack is arrested by the γ phase that has high strength. From this result, maximum fatigue strength of the duplex SSW might be attained, if it has proper volume fraction as a microstructural component.
Surface flaws on valve springs in automobile engines are one of the crucial factors which affect the fatigue life of valve springs together with harmful non-metallic inclusions and surface decarburization. Through the fatigue tests of high tensile strength springs and nitrided springs with artificial longitudinal flaws, the influence of surface flaws on fatigue lives were investigated. Fatigue lives of both springs lowered as the depth of flaws increased, however, in this experiment, when flaw depth was not deeper than 0.05mm, no lowering of each fatigue strength was recognized. It was considered as this reason, that the large compressive residual stress of the surface layer effectively suppressed propagation of fatigue crack.
This study was aimed to examine the anodic polarization curve under various applied stresses and the state of pit formation for the high carbon steel S60C with different surface hardness in corrosive solution. The main results obtained are summerized as follows. 1) The specimen with higher surface hardness indicate the increase rate of anodic current becomes larger with increasing applied stress. 2) When the specimens have a higher surface hardness and formed unstable surface stractures due to deviation of Cementite, the possibility becomes more larger that the fracture may be caused by corrosion phenomenon.
Beryllium Copper is a well known precipitation hardening alloy that is widely used as a spring material in a variety of applications including electric, electronic, and electromechanical components. In order to realize the optimum properties for a given application, proper heat treatment is necessary after forming. Age hardening at 315°C for 2 hours provides maximum strength and is well suited for most applications. Other applications may call for a different heat treatment. Maximum spring bend limit and fatigue life are achieved below 315°C, while electrical conductivity and stress relaxation are increased above 315°C. This paper reports the effect of various ageing treatments on Beryllium Copper in terms of tensile properties, electrical conductivity, fatigue life, stress relaxation, and spring characteristics such as spring bend limit.
Spring limits, contact resistance and solderability after cold rolling and aging treatments on four surface treatments of thin plates made of Cu-Ni-Sn alloys are investigated. The results are as follows; 1) Spring limits are strongly affected by aging treatments. The preferred treatment condition is 523-623K, for 30min. 2) Surface properties are improved by pretreatments after active flux or pickle. 3) Mechanical properties after cold rolling are not influenced by surface treatments. 4) Contact resistance and solderability are strongly affected by cold rolling or aging treatments, due to the formation of tin oxide film on the surface.
The Leaf Spring consists of several leaves. Its load-deflection curve shows hysteresis because of the friction between leaves. Since this hysteresis loop affects the driving comfort and stability of vehicle, this is one of the most important factor for designing leaf spring. In this paper, the effects of type of eye, eye diameter, and edge shape of No. 2 leaf to the friction on histeresis loop were experimentally studied. It was found that combining berlin eye of No. 1 leaf with curved edge of No. 2 leaf can control the increase of dynamic spring-rate under the low deflection area. It was also realized that this effect can improve the driving comfort of vehicle.
It is afraid that increasing the strength of oil-tempered steel wire for valve springs might result in a loss of workability, fatigue strength and creep resisitance. The committee, therefore, investigated the effects of the chemical composition, wire strength, annealing condition, residual stress induced by shot peening, etc., on the mechanical properties of wires and valve springs. The material used for this study was made of the conventional oil-tempered high tension steel wire (JIS G 3566) by increasing its carbon level to the JIS-prescribed upper limit and adding some vanadium. It was then made into two specimens by tempering to tensile strength levels of 2, 000 and 2, 100MPa, respectively. For the purpose of comparison, two other specimens were made of conventional oil-tempered wire (JIS G 3566) by tempering to strength levels of 1, 900 and 2, 000MPa, respectively. In conclusion, high-tension steel wire of this study has been found to possess equal workability with improved fatigue strength, and better creep resistance, when compared with the standard steel wire (JIS G 3566), thus demonstrating the superiority of high-tension steel wire for valve springs. To further improve fatigue strength and creep resistance, it has been found more important to make changes in chemical compositions, and to make further improvements in shot peening process and in other surface-treating technologies, rather than only increasing the tensile strength of the wire.
There were many evaluation methods of corrosion fatigue endurance properties of suspension springs, depending on spring manufacturers, as many factors affect the properties. Therefore, it has been desired to standardize the evaluation methods. This committee performed theoretical studies as well as experiments on corrosion fatigue. A new evaluation method is recommended on the basis of the experimental results that crack length evaluated from residual fatigue life is a good parameter to compare corrosion fatigue performances of suspension springs relatively.