The relationship between fatigue life and inclusions and the defect sensitivity of oiltempered Si-Cr steel wire have been investigated by rotating-bending fatigue tests and observations of fracture surfaces. The results show that fatigue failure occurs at the number of respetitive test cycles of 10⁸ despite no failure occurs at the 10⁷ cycles, fatigue failure progresses in the perpendicular direction to the principal stress after microcracks appear along the plane of shearing stress in the case that the tested wire has relatively long fatigue life, and smaller inclusions can more lengthen fatigue life of the wire.

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As the diameters of suspension springs become smaller due to reduction of the weight of motor cars and increase of the stress levels of the coil springs, cold formed springs have come to draw attention. In contrast to the hot formed springs, however, there are few materials appropriate for cold formed springs.
The only steel available so far is SAE9254, but its application to a spring in a higher stress level is substantially impossible for lack of sag resistance. SAE9254 has a long history as an oil tempered wire for springs. And of some elements to improve the sag resistance, we selected vanadium, for vanadium is known to have no direct effect on heat treatment of the steel. The addition of vanadium into SAE9254 was found to enhance both sag resistance and corrosion fatigue resistance of coil springs for automotive suspension.
The most prominent effect of vanadium is seen in the refinement of austemite grains upon heat treating. The grain size diminishes from No. 9.5 to No. 12. This refinement of the grains is supposed to be responsible for the improvement of sag resistance by 25% as well as corrosion fatigue resistance.

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Many studies have been caried out for the stress problem of coil springs by many investigators. Few analysis, however, have been performed for the coil springs using the wire of noncircular nor rectangupar cross section except the egg shaped cross section for which the simplified design formulas are proposed by H. O. Fuchs.
Concerning the analytical methods for the spring with the wire of arbitrary cross section, the conformal mapping method and the finite element method are available. But the former is difficult in determining the mapping function for the arbitrary cross section and the latter is costly for its use of large computers and FEM programs.
In this paper, the ‘Fourier expansion collocation method’ are presented and the analytical results are compared with the experimental ones. It is clarified that the stress analysis of the coil springs with arbitrary wire cross section can be carried out by the new method with sufficient accuracy for practical use.

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The deformation and strength of generalized curved rods are examined in order to apply for the design of springs. The analysis by three-dimensional elasticity has considerable error because of neglecting the cross-sectional deformation. In this study, a rod is regared as one-dimensional Cosserat's continuum which has bending, torsional and axial rigidities.
Curvature and torsion which are connected with the principal axes are defined and strain energy is described by the variation of these values. Through the principle of virtual work, the fourth order simultaneous differential equations are derived as fundamental equations and the equations for the boundary conditions are also obtained.
In these approaches, we used the tensorial relation of differential geometry for the general curves. In the analysis, strain energy by the distortion and shearing deformation are not counted. Nonlinear terms are neglected and the analysis is based on the infinitesimal theory, but we think the finite deformation theory will be able to introduce on the line of this theory. Simple special cases are analyzed to verify above equations and analytical solutions are obtained in closed forms.

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SMA springs (coil springs of shape memory alloy) show some characteristics including material nonlinearity, temperature dependency, and hysteresis different from those of usual metal springs: so that SMA springs can not be designed by using the traditional design formula as it is.
This paper studies dynamic properties of SMA springs on the basis of the governing equation of usual springs and introduces a design formula of SMA springs by taking account of twisting test results of element wires and loading test results of SMA springs. The design system of SMA springs based on the computer-aided data base has been developed; so that can now calculate characteristics by loading in acting state of springs and hysteresis which are difficult to be shown by making drawings.

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High strength, unchanged ductility, good impact properties and superior fatigue behavior were produced in Mn-Cr-B spring steel (SUP 11A) by modified ausforming in which reductions in thickness up to 50% in the temperature range from 880°C to about 720°C were followed by rapid quenching into martensite. Observations of fracture surfaces by electron microscope have disclosed the existence of partial intergranular fracture along the prior austenite grain boundary in conventionally heat-treated steel. The modified ausformed steel, however, does not involve such the intergranular fracture at all but transgranular fracture entirely even at the sub-zero temperature in the impact test as well as at room temperature. Refinement of martensite laths, the improvements in the shape, the alignment and the distribution of carbides in matrices, and the refined subgrains tempered at higher temperature tempering, and so on, seemed to give beneficial effects on strengthening and toughening of the steel.

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Thermal and transformation stresses occur during quenching steel and cause crack, strain and so on. The former is due to ununiform cooling and the latter is due to transformation expanding. Specially, as to spring steel with over 0.5% carbon, quenching crack is easily occured by transformation stress. This paper is concerned with the numerical analyses of temperature and transformed structure during quenching under variable cooling condition. This analysis is the first step to make the distribution of stress and strain clearly after quenching.
This main conclusions are summarized as follows:
(1) When the coolant that the heat transfer coefficient is varied by surface temperature of material is used, the large slope of temperature occurs instantly within material.
(2) As the heat transfer coefficient varies rapidly, the cooling curve bends immediately. The bent point of the temperature in center is higher than that of surface. Therefore, on quenching of material with low hardenability, the inverse hardening may happen.
(3) If the coolant with high cooling ability is used in the range of martensite transformation temperature, the opportunity of transformation will differ time at each location of material.

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Nowadays, phenomena concerning cylindrical springs designed to be under high stress are such that failure of cylindrical springs starts from the outside of the cylinder coil and the fatigue life of such springs is shorter than that of traditionally designed springs. The springs designed to be under high stress have larger pitch angles than those of traditional springs. The above phenomena show that Wahl's equation can not calculate proper design conditions of such modern springs.
This paper describes an analysis of cylindrical springs by taking account of pitch angles which can so far be ignored in traditional spring design and shows the clear relationship between specifications of a spring and its stress. This paper also demonstrates that the maximum principal stress of the coil outside is greater than that of the coil inside as spring stress is higher and that the fatigue life of springs designed under high stress may be inferred from fatigue test results of traditionally designed springs by assessment of S-N curves in terms of the maximum principal stress.

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In this paper, the cause of the discrepancy between the theoretical results and the experimental results on the pitch working process is studied.
1) Considering the factors which are missed or ignored in the former theory proposed by the authors, modified relations between the pitch of coils and the stroke of pitching tools are derived, which still holds linearity. The effects of the factors mainly appear in the segment of the graphs. For the inclinations of these, the factors effect only slightly.
2) The observation of the coiling curve shows that in the case of larger spring indices, the unexpected deformation of wire occurs and the contact condition between wire and tools changes. From these results of the observation, the tendency of the experimental results can be qualitatively explained. In general, the application of the theoretical results must be limited in the case of small spring indices and small pitching stroke.

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In this paper, we describe an experimental study on working characteristics of coil ends when rotating coil is cut off with abrasive cut-off wheel. The summary of experimental results is shown as follows:
1) Coil can be cut off at higher infeed rate in case of regular revolution and lower revolution.
2) Abrasive wear amount of cut-off wheel increases as infeed rate increases. The increment of the wear becames larger as coil revolution increases.
3) Inclination of coil outside face is within Grade 2 of JIS B2707 in case of low infeed rate (f<10mm/min).
4) Considering the working accuracy, coil had better be cut off with thick wheel at low infeed rate (f<10mm/min) and coil revolution of 40-75rpm. Considering the cost, grade of wheel had better be higher and coil revolution less then 30rpm.

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The Committee of Strength of Flat Spring has been in activities for five years to perform various joint tests and accumulation of data with regard to the flat springs and to establish a method of feature evaluation test thereof.
The activities contain the examination of flat springs in thicknesses popular in the present market and in 0.05mm expecting the future trend, report on the results and suggest a feature evaluation method.

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It is known that an adequate control of non-metallic inclusions (nmi) is one of the key factors for modern spring materials to ensure their advanced fatigue performances. The research activities including questionnaire due to this committee have revealed that the microscopic testing method in the Japanese Industrial Standard (JIS) is not enough valid for the assessment of spring steels from fatigue point of view, while the method is most widely used for quality control purposes in steel making industries.
In view of obtaining a common basis for the establishment of a new method of evaluation particularly applicable to nmi in the spring steels, a round robin test was undertaken to compare several existing microscopic methods using two heats of SAE 9254 steels with different nmi levels. Analyses of the results was resumed as in the following:
(1) method by JIS is not adequate for very low levels of nmi besides the lack of informations about the size,
(2) a commercial method known as Michelin's can evaluate both size and quantity of nmi and would be a practical one if the procedure is well standardized,
(3) method D by ASTM is effective but cannot result in a single value: it is difficult and requires long time for operation,
(4) another commercial method called Bekaert's seems to be a good one and would be also effective if well standardized but scarcely known at present,
(5) method M by VDEh cannot give a single value but seems possible to become so if some modifications and simplification are applied, and
(6) automatic image analysers used for evaluation of nmi needs more improvement to be practiced to materials with very low level of nmi like spring steels.

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