Properties of 17%Cr-15%Mn-0.35%N austenitic stainless steel were investigated for its application to spring use, compared with other Cr-Ni type 301, 304 and so on.
This stainless steel has high strength and maintains its low magnetic permeability even after large amounts of cold working. Increasing of the hardness and the threshold value of spring by aging of this steel in the as rolled condition is larger and its softening start temperature is 650 to 700°C, about 200°C higher than those of type 301 steel. Decreasing rate of its hardness by so high temperature overaging as 700 to 800°C is very slow. The elevated temperature strength of this steel by short time tensile test was compared with the other Cr-Ni stainless and heat resistant steels; type 304, 310 and so on. This steel has the highest strength at the temperature range of RT to 800°C among these steels.
This stainless steel is used where high strength and low magnetic permeability are required. And also this steel is expected to be used for elevated temperature spring such as metal packings for automotive engine peripheries: cylinder head gasket, exhaustmanifold gasket, and so on.

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The spring steels have comparatively higher hardenability, therefore hardening cracks tend to occur. From the viewpoint to prevent hardening cracks, the martensite transformation behavior of four spring steels were investigated by two-step quenching method using Formastor-F.
The results obtained are follows.
1) The martensite transformation starts just below the Ms point every type spring steels.
2) The temperature difference from the Ms point to the 90% martensite transformed temperature of SUP9 is smoller than that of other spring steels (that is, SUP11A, SUP10 and SUP12). So that, when SUP9 is quenched, the martensite transformation rapidly proceeds other spring steels.

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For estimation of the nonlinear load-deflection behavior of the disk spring which is subjected to compressive load, an approximate equation presented by J. O. Almen & A. Laszlo has widely been used. Another approximate equation was also proposed by G. A. Wempner as a more accurate solution. Since these two equations are both induced from some aproximate assumptions, mechanical designers using disk springs should know the degree of errors of the above-mentioned two equations. In this paper, some numerically accurate examples for the load-deflection relation of the disk spring are obtained by applying the finite difference method to solve the fundamental differential equations of the problem of the disk spring, and they are compared with the results obtained by the above-mentioned two equations. Also experiments are carried out, and their results are compared with those by the above three theoretical methods. From results of such comparisons some prospect about the accuracy of the above-mentioned two equations can be obtained.

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This paper discusses the optimal shape for the wire corss section of a helical spring. In general, stress at the inner side of the coil is higher than that at the outer side in a helical spring with a round cross section. Therefore, weight may be saved through stress equalization effected by improving the shape of the wire cross section. Shape optimization is performed by modification of the cross-sectional shape so as to minimize the weight of the helical spring under the constraints of design stress, spring rate, coil diameter and applied load. Stress caused by torsinal moment and shear force is calculated by means of FEM, taking the effect of coil curvature into account. The shape of the wire cross section is successively modified by changing r_i, which represent the radius from the sectional center to each node on the periphery of the section. The optimized shapes are almost oval and are obtained independent of supposed initial shapes.

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Stresses in elliptical cross section coil srings become small as compared to the other springs used in practical machines in a certain aspect ratio. This article presents a simplified stress expression for designing the elliptical cross section coil springs. The stresses obtained by the present design formula are compared with those by the numerical methods. It is ascertained that the present formula is applicable to design the elliptical cross section coil springs.

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Coil springs of non circular wire cross section, such as oval and modified oval sections, have been applied to the automotive-engine valve springs recently. In such types of springs, it is particularly important to know the sectional distortion to estimate the effect on the shearing stress distribution.
In this paper, the plastic distortion of wires having elliptic and Fuchs' oval cross sections by coiling are studied theoretically and experimentally. The main results are as follows:
(1) The formulas to estimate the plastic distortion of wire cross sections by coiling are derived for elliptic and for Fuchs' oval sections.
(2) The effect of the cutting error on the profile of the cross sections is analyzed approximately.
(3) The experimental results show that the distortion for the ellipse is more remarkable than for the circle for the same spring indicies.
(4) The experimental distortion of the cross sections is larger than the theoretical one in the compressive side.

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We performed the following study to examine the influence of the residual stress distribution by shot-peening on the fatigue crack propagation life. The results we obtained are as follows;
(1) To define the threshold conditions of small crack propagation in spring steels, we proposed a method which consists of applying the hardness and stress ratio dependency to Haddad's consolidation.
(2) It is very important to raise the surface residual stress for improving the fatigue crack propagation life.
(3) Most of the fatigue crack propagation life is spent while the crack propagates from the surface to the position where the compressive residual stress is maximum.
(4) The nearer to the surface the position where the compressive residual stress is maximum, the longer fatigue crack propagation life is extended.
(5) The predicted S-N curve by this method shows good correspondence with the actual results of the rotary bending fatigue tests.

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This report refers to the development of the coil springs with wires of non circular cross section which has been applied more and more to the automotive engine valve springs and to the other springs of motor cars.
Investigation on the subject had been made by the cooperation of 9 automobile manufacturers, 13 spring makers and 6 spring wire makers in Japan from October 1988 to September 1989.
The report makes clear the recent development of the noncircular wire springs (N. C. W. S.) and the problems to be solved which are summarized as follows.
Development of N. C. W. S. in Japan:
1) The springs have been mass produced for automotive engine valve springs by some Japanese spring makers since about 1984.
The total production of N. C. W. S. in Japan is more than 3, 000, 000 springs per month in 1989.
2) The N. C. W. S. has been applied not only to the valve springs but also to the clutch springs and the automatic transmission springs.
Now some new applications of N. C. W. S. including suspension springs of cars are tried.
3) More than 18 types of N. C. W. S. with wire sections of oval, elliptic, and their modifications have been applied for patent. Some of them have been applied to the mass production.
4) The investigation shows that the wire size, the spring indices and the aspect ratio of the wire cross sections are in some range respectively for practical uses.
5) The cost of N. C. W. S. in mass production is 20-30% higher than the one for circular wire springs.
Merits of N. C. W. S. in Designing and Problems to be solved:
1) Small solid height of N. C. W. S. makes possible the compact designing of automotive parts.
2) Mass reduction of the springs are possible by the optimum designing which varies both of the shape of wire cross section and the effective turns of coils.
3) The stress variation around the wire cross section is smallest for ellipse comparing with circle and Fuchs' oval section.
4) The stress of N. C. W. S. can be analyzed with sufficient accuracy by the FEM using solid elements or by the analytical methods with two dimensional FEM or BEM, or the Fourier expansion collocation method developed by Nagaya.
But the conventional designing formulae must be derived for the practical use.
5) The effect of the inclination of wire cross section on the stress distribution must be made clear.
Problems in Production and Inspection of N. C. W. S.:
1) The torsion of the wire of coils about it's axis varies the stress distribution which is especially important for the N. C. W. S. Therefore the practical methods of measuring the torsion must be settled for each type of the sections.
2) A practical method must be established for measuring the area of the breaking section of the N. C. W. tensile specimen.
3) The detecting accuracy must be improved for the detection of the surface flaws of the non circular wires.

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