Machinery's Handbook, 31st Edition
306 Spring Materials or blue-tempered condition. The steel is obtainable in several finishes, such as straw color, blue color, black, or plain. Hardnesses ranging from 42 to 46 RC (Rockwell C scale) are recommended for spring applications. Uses include spring clips, flat springs, clock springs, and motor, power, and spiral springs. Cold-Rolled Spring Steel, Blue-Tempered Clock Steel, SAE 1095: (0.90 to 1.05 percent carbon) This popular type should be used principally in the blue-tempered condition. Although obtainable in the annealed condition, it does not always harden properly dur- ing heat treatment as it is a “shallow” hardening type. It is used principally in clocks and motor springs. End sections of springs made from this steel are annealed for bending or piercing operations. Hardnesses usually range from 47 to 51 RC. Other materials available in strip form and used for flat springs are brass, phosphor- bronze, beryllium-copper, stainless steels, and nickel alloys. Alloy Spring Steels.— These spring steels are used for conditions of high stress, and shock or impact loadings. They can withstand both higher and lower temperatures than the high- carbon steels and are obtainable in either the annealed or pretempered conditions. Chromium Vanadium, ASTM A231: This very popular spring steel is used under condi tions involving higher stresses than those for which the high-carbon spring steels are recommended and is also used where good fatigue strength and endurance are needed. It behaves well under shock and impact loading. The material is available in diameters rang ing from 0.031 to 0.500 inch and in some larger sizes also. In square sections it is avail- able in fractional sizes. Both the annealed and pretempered types are available in round, square, and rectangular sections. It is used extensively in aircraft-engine valve springs and for springs operating at temperatures up to 425°F. Silicon Manganese: This alloy steel is quite popular in Great Britain. It is less expensive than chromium-vanadium steel and is available in round, square, and rectangular sections in both annealed and pretempered conditions in sizes ranging from 0.031 to 0.500 inch. It was formerly used for knee-action springs in automobiles. It is used in flat leaf springs for trucks and as a substitute for more expensive spring steels. Chromium Silicon, ASTM A401: This alloy is used for highly stressed springs that re- quire long life and are subjected to shock loading. It can be heat treated to higher hard nesses than other spring steels so that high tensile strengths are obtainable. The most popular sizes range from 0.031 to 0.500 inch in diameter. Very rarely are square, flat, or rectangular sections used. Hardnesses ranging from 50 to 53 RC are quite common and the alloy may be used at temperatures up to 475°F. This material is usually ordered specially for each job. Stainless Spring Steels.— The use of stainless spring steels has increased and several compositions are available all of which may be used for temperatures up to 550°F. They are all corrosion resistant. Only the stainless 18-8 compositions should be used at sub- zero temperatures. Stainless Type 302, ASTM A313: (18 percent chromium, 8 percent nickel) This stainless spring steel is very popular because it has the highest tensile strength and quite uniform properties. It is cold-drawn to obtain its mechanical properties and cannot be hardened by heat treatment. This material is nonmagnetic only when fully annealed and becomes slightly magnetic due to the cold-working performed to produce spring properties. It is suitable for use at temperatures up to 550°F. and for sub-zero temperatures. It is very corrosion resistant. The material best exhibits its desirable mechanical properties in di- ameters ranging from 0.005 to 0.1875 inch although some larger diameters are available. It is also available as hard-rolled flat strip. Square and rectangular sections are available but are infrequently used.
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