Machinery's Handbook, 31st Edition
Spring Materials 307 Stainless Type 304, ASTM A313: (18 percent chromium, 8 percent nickel) This material is quite similar to Type 302, but has better bending properties and about 5 percent lower tensile strength. It is a little easier to draw, due to the slightly lower carbon content. Stainless Type 316, ASTM A313: (18 percent chromium, 12 percent nickel, 2 percent mo- lybdenum) This material is quite similar to Type 302 but is slightly more corrosion resis- tant because of its higher nickel content. Its tensile strength is 10 to 15 percent lower than Type 302. It is used for aircraft springs. Stainless Type 17-7 PH ASTM A313: (17 percent chromium, 7 percent nickel) This alloy, which also contains small amounts of aluminum and titanium, is formed in a moder ately hard state and then precipitation hardened at relatively low temperatures for several hours to produce tensile strengths nearly comparable to music wire. This material is not readily available in all sizes, and has limited applications due to its high manufacturing cost. Stainless Type 414, SAE 51414: (12 percent chromium, 2 percent nickel) This alloy has tensile strengths about 15 percent lower than Type 302 and can be hardened by heat- treatment. For best corrosion resistance it should be highly polished or kept clean. It can be obtained hard drawn in diameters up to 0.1875 inch and is commonly used in flat cold-rolled strip for stampings. The material is not satisfactory for use at low temperatures. Stainless Type 420, SAE 51420: (13 percent chromium) This is the best stainless steel for use in large diameters above 0.1875 inch and is frequently used in smaller sizes. It is formed in the annealed condition and then hardened and tempered. It does not exhibit its stainless properties until after it is hardened. Clean bright surfaces provide the best corrosion resistance, therefore the heat-treating scale must be removed. Bright hardening methods are preferred. Stainless Type 431, SAE 51431: (16 percent chromium, 2 percent nickel) This spring alloy acquires high tensile properties (nearly the same as music wire) by a combination of heat- treatment to harden the wire plus cold-drawing after heat treatment. Its corrosion resis- tance is not equal to Type 302. Copper-Base Spring Alloys.— Copper-base alloys are important spring materials be- cause of their good electrical properties combined with their good resistance to corro sion. Although these materials are more expensive than the high-carbon and the alloy steels, they nevertheless are frequently used in electrical components and in sub-zero temperatures. Spring Brass, ASTM B134: (70 percent copper, 30 percent zinc) This material is the least expensive and has the highest electrical conductivity of the copper-base alloys. It has a low tensile strength and poor spring qualities, but is extensively used in flat stampings and where sharp bends are needed. It cannot be hardened by heat treatment and should not be used at temperatures above 150°F, but is especially good at sub-zero temperatures. Available in round sections and flat strips, this hard-drawn material is usually used in the “spring hard” temper. Phosphor Bronze, ASTM B159: (95 percent copper, 5 percent tin) This alloy is the most popular of this group because it combines the best qualities of tensile strength, hardness, electrical conductivity, and corrosion resistance with the least cost. It is more expensive than brass, but can withstand stresses 50 percent higher. The mate- rial cannot be hardened by heat treatment. It can be used at temperatures up to 212°F and at sub-zero temperatures. It is available in round sections and flat strip, usually in the “extra-hard” or “spring hard” tempers. It is frequently used for contact fingers in switches because of its low arcing properties. An 8 percent tin composition is used for flat springs and a superfine grain composition called “Duraflex” has good endurance properties. Beryllium Copper, ASTM B197: (98 percent copper, 2 percent beryllium) This alloy can be formed in the annealed condition and then precipitation hardened after forming at
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