Materials
General Information
All of the various materials which are shown in Table 12 are used by Bauer in the manufacturing of CB precision disc springs. The finished disc springs are manufactured from coil, sheet or forgings (depending upon the size and quantity of the springs involved) but only coil and sheet are used for disc springs which are made by cold stamping processes.
No classification of these raw materials based upon their avaiability has been made due to the fact that, even though they are shown as commonplace materials in DIN 17221 or DIN 17222, their actual market availability in the required thicknesses or in small quantities can sometimes cause considerable, if not totally impossible, purchasing conditions.
Many of the materials which are used for elevated temperatures and/or corrosion resistance are not generally available for immediate delivery to particular customer specifications and, therefore, require prolonged lead times meaning that considerations regarding the extended delivery times required for these types of disc springs must always be included in any form of product planning.
Table 12 gives chemical compositions with tolerances for each element in the melt analyses of various materials. When a compositional analysis of individual disc springs must be undertaken, the permissible chemical deviations from these particular values (as allowed by the DIN) must be taken into consideration. Unspecified background elements are permitted provided they do not in any way effect the mechanical or hardening properties of the base material and must not adversely compromise the performance of the finished disc spring product.
In Table 13 are listed the material properties associated with the various materials in their annealed, cold worked and/or heat treated condition. The thickness and production route of the raw material influence where the tensile strength is in the range of values listed. The values given are only a guide, as in a spring they can be higher or lower than the range of values. Usually a production batch can be expected to be within half of the given range of tensile strengths.
When operating at the maximum listed temperatures thermal relaxation needs to be considered, the amount of which is dependent on the highest stress which is occuring. It is also important to remember that, with increasing temperatures, the strength of the material (as well as the modulus of elasticity) will decrease. Corrosion resistant and high temperature disc spring materials have somewhat reduced strengths at ambient temperature when compared to standard disc spring steels. Should an identical disc spring load and deflection be required in a corrosion resistant or high temperature disc spring as is available at ambient temperature in a standard carbon steel disc spring, an entirely new design is required. In the majority of instances, the lowered strength value of the special material is compensated for by a reduced overall unloaded free height of the finished disc spring.
Spring Steels
Ck 67 (1.1231), Ck 75 (1.1248), 50 CrV 4 (1.8159) and 51 CrMoV 4 (1.7701) are, according to DIN 17221 and DIN 17222, special purposesteelswhich, in the heat treated condition, may be used for the forming of all types of spring parts. The materials Ck 67 (1.1231) and Ck 75 (1.1248) may only be used for DIN 2093 disc springs with a material thickness t < 1.25 mm.
The materials 50 CrV 4 (1.8159), and 51 CrMoV 4 (1.7701), are acceptable for all DIN disc springs. The alloying elements make it possible to use greater material thicknesses, which when heat treated, develop an even micro-structure across the whole cross section of the disc spring. Additionally, the alloying increases the relaxation resistance of the spring.
As a general rule, it is more advantageous to use the austempering heat treatment process on the above materials than conventional hardening and tempering. In austempering the springs are raised to the austenitising temperature and then quenched in a salt bath. By holding at a certain temperaure for a specific period of time, a transformation takes place to the so called bainitic microstructure. The process also results in less distortion and there is negligible volume change of the parts. The bainitic structure exhibits an especially good "toughness". As additional tempering of the disc spring is unnecessary, energy savings in manufacturing are realised.
High Temperature Spring Steels
48 CrMoV 6 7 (1.2323), X 30 WCrV 5 3 (1.2567), X 35 CrMo 17 (1.4122) and X 22 CrMoV 12 1 (1.4923) may all be used for the manufacturing of disc springs which are to be subjected to elevated temperatures (Table 13). The chemical compositions of these particular materials provide sufficient stability for use over the respective temperature ranges specified in the table.
The materials 48 CrMoV 67 (1.2323) and X 30 WCrV 53 (1.2567) are not corrosion resistant materials. The materials X 35 CrMo 17 (1.4122) and X 22 CrMoV 12 1 (1.4923) are only moderately corrosion resistant in spite of their Chromium and Molybdenum components. This occurs as a result of the hardening and tempering heat treatment procedures which cause a chrome carbide dispersion in these particular materials. In those areas in the material which are lacking in Chromium, there is incomplete build up of the passivation necessary for good corrosion resistance.
Non-Rusting or Stainless Spring Steels
X 12 CrNi 17 7 (1.4310 or SAE 301/302 Stainless Steel), X 5 CrNiMo 17 12 2 (1.4401) and X 7 CrNiAI 17 7 (1.4568 or Armco 17-7 PH Stainless Steel and AMS 5528 and 5529) are defined by the DIN 17224 Standard as non-rusting spring steels which exhibit good resistance to chemical corrosion.
The spring properties of these materials are obtained through cold rolling of the raw material and/or by heat treatment of the finished parts.
The materials X 12 CrNi 17 7 (1.4310) and X 5 CrN i Mo 17 12 2 (1.4401) are work-hardenable metals. As a general rule, these particular materials are only available in material thicknesses up to 2.00 mm. At approximately 100 degrees Celcius (212 degrees Fahrenheit) under tensile stresses there is a pronounced degredation of the work-hardened strength of these materials. Therefore, these materials are not suitable in excess of that temperature.
Disc springs can be manufactured from X 7 CrNi Al 17 7 stainless steel (DIN 1.4568) in thicknesses up to 2.5 mm (or, in the case of large production quantities to 3.0 mm). In addition to some work-hardening this material requires age- hardening at 480 degrees Celcius (890 degrees Fahrenheit), which makes it possible to have hot strength up to a temperature of about 350 degrees Celcius (662 degrees Fahrenheit). The increase in the strength of the material which is obtained by means of age-hardening provides an advantage in that, for the same final strength, the work hardening required is considerably reduced in comparison to either X 12 CrNi 17 7 (1.4310)
or X 5 CrNiMo 17 122 (1.4401). This also improves the corrosion resisting properties of this material.
The material X 7 CrNiAI 17.7 (1.4568 or Armco 17-7 PH stainless steel), when thicker than about 2.5 mm or 3.0 mm, is always in the annealed condition. The required hardness of the finished disc spring is obtained by means of a double age- hardening.
The first heat treatment takes place at a temperature of 760 degrees Centigrade and results in a chromecarbide precipitation, preferably at the grain boundaries. This effect produces a marked reduction in the material's corrosion resistance. Disc springs should only be held in the intermediate condition prior to final age-hardening and must never be de-greased in any sort of acidic medium.
In the annealed condition, the materials X 12 CrNi 17 7 (1.4310) and X 5 CrNiMo 17 122 (1.4401) are virtually non-magnetic. Because of the work-hardening process, the material X 12 CrNi 17 7 (1.4310) will become more or less strongly magnetizeable, while
X 5 CrNiMo 17 122 (1.4401) remains virtually non-magnetic in use; X 7 CrNiAI 17 7 (1.4568) is magnetizeable in the soft condition and becomes more magnetic through work-hardening.
High Temperature Materials with very
NiCr 19 NbMo (2.4668), NiCr 15 Fe 7 TiAI (2.4669) and NiCr 20 Co 18 Ti (2.4969) are all nickel based alloys. Duratherm 600 is a cobalt based alloy. All of these materials are age hardenable and receive their strength through hardening of the mixed crystal structure, additives from strongly diffusion-inhibiting elements and stable precipitate. Through work hardening prior to heat treat, higher strength values than are shown in Table 13 can be achieved in these materials. These materials are not only useable at relatively high temperatures and non scaling, they also offer outstanding corrosion resistance. Because of their high chrome and nickel content, they are completely rust resistant and virtually impervious to aggressive chemical mediums.
The corrosion resistance of a particular material is not entirely dependant upon the corrosive medium involved; the temperatures in which the products are working, the stresses which are present in the materials and the atmospheric conditions involved also contribute to the degree of corrosion resistance which can be obtained. As a result, we strongly recommend that our technical staff be contacted for an in-depth analysis of the particular application whenever disc springs are to be used in any corrosive enviroments.
As is shown in Table 13, these particular materials may be used in applications which require performance very near the point of absolute zero. These materials are also completely non-magnetic above the Curie-temperature but become ferro-magnetic just below Curie-temperature.
Non-magnetic and Corrosion Resistant
CuBe 1.7 (2.1245) and CuBe 2 (2.1247) are, according to the DIN 17 670 standard, age-hardenable, wrought low alloy copper based materials. As a general rule, disc spri ngs which are man ufactured from these particular materials are produced from coil or sheet in the half-hardened condition and receive their final strength from a final heat treatment or "age-hardening". Copper Beryllium is especially noted for its characteristic agehardening response and the resultant favorable values of strength and elasticity. Copper Beryllium disc springs may be used to temperatures which are very close to Absolute Zero and, throughout the temperature range, are completely non-magnetic and exhibit very good thermal and electrical conductive properties. These materials also exhibit excellent corrosion resistance in many corrosive mediums. However, when used for disc springs, the significantly lower modulus of elasticity of the copper beryllium alloys when compared to standard spring steel must be taken into consideration.
Non-magnetic, Light Weight Material
TiAI 6 V 4 (3.7165 or 6AI4V Titanium Alloy) is a wrought Titanium alloy used primarily in the aerospace industry. With a density of 4.45 kg/dm3, 6 Al 4 V Titanium is only one half the weight of standard spring steel, whose density is approximately 7.85 kg/dm3. Because of its non-magnetic and corrosion resistant properties in many corrosive mediums, this material is not restricted to use solely in aerospace applications. For the manufacturing of precision disc springs, 6 Al 4 V Titanium may be obtained in the form of coil, plate or forgings.
In the annealed and scale-free condition, this particular material exhibits a tensile strength Rm' minimum, of 890 N/mm2 and an 0.2% proof stress of at least 820 N/mm2. The 6 Al 4 V Titanium strength which has been shown in Table 13 was obtained by means of age-hardening. The modulus of elasticity is considerably reduced in comparison to the modulus of standard spring steels, and this must be taken into consideration when designing disc springs in Titanium alloy. For an equivalent outside and inside diameter disc spring in 6 A1 4 V Titanium, when compared to a disc spring in standard spring steel, the material thickness of the Titanium spring must be approximately 22% thicker than the spring steel equivalent in order to achieve a similar disc spring load and deflection.
Download here Table 12 pdf:
table_12.pdf
Download here Table 13 pdf:
table_13.pdf