EP0906453B1 - Relaxation-resistant steel spring - Google Patents

Abstract

The invention concerns a very strong steel spring having a bright surface which is free from residual dirt, the spring also being resistant to relaxation at high operating temperatures. A spring of this type is produced from a steel wire of the following composition: between 0.45 and 0.85 wt % carbon; between 0.2 and 1.60 wt % silicon; between 0.3 and 1.50 wt % manganese; between 0.4 and 1.2- wt % chromium; the remainder being iron and unavoidable impurities. The wire is austenitized and then treated isothermally at temperatures ranging from 450 to 650 DEG C. The wire is then drawn to a tensile strength of between 1600 and 2300 N/mm<2> at a contraction in area when breaking of at least 40 %. The wire is cold formed to produce a spring and is then stress-free annealed at temperatures ranging from 200 to 350 DEG C.

Description

The invention relates to a steel spring operating at relatively high working temperatures has a good resistance to relaxation.

Feathers are known to consist of patented drawn spring steel wires made of unalloyed carbon steels. Such springs are essentially free of scale and residual dirt particles, but are suitable for operating temperatures of Can only be used to a limited extent above 80 ° C. The use is made with greatly reduced Working voltages, their compensation only over a higher application mass the spring can be done, as is known from economic but also brings considerable disadvantages for design reasons. Regarding springs show the relaxation behavior at higher operating temperatures from oil-quenched and tempered unalloyed spring steel and valve spring wires same disadvantages. In addition, as a result of the final oil tariff Surface with scale or residues of other residues release the spring function and in sensitive work areas such as automatic transmissions and fuel injection systems in motor vehicles to significant malfunctions or the complete failure of such units being able to lead.

To increase the relaxation behavior at higher working temperatures the use of springs made of CrV, SiCr and SiCrV alloy spring steel wires already known in practice. This allows limit temperatures of 160 ° C realize. These alloyed steels also require an oil tempering. So there are the same disadvantages as with springs made of unalloyed Spring steels on., I.e. here, too, remains of Tinder, which loosened, due to the spring function, highly sensitive to failures technical systems can lead. Another major disadvantage is in the fact that the martensitic structure created during the remuneration is extraordinary sensitive to pickling or surface treatment, which is associated with hydrogen diffusion in the spring material. The so-called hydrogen embrittlement, as used in pickling or electrolytic Coating occurs, leads to premature failure of the spring element and thus the functional fatigue of complicated and expensive mechanisms. In addition to these functional disadvantages, the springs of this material group are liable a major technological disadvantage. After reshaping Such spring elements must have a relaxation annealing without delay Undergo. If delays occur here, form residual stress cracks leading to the premature breakage of the spring element or elements to lead.

Austenitic springs are used to eliminate these disadvantages stainless spring wires, for example of the grade X 12 CrNi 17.7. As a result of the much higher Alloy expenditure and the technological peculiarities however arise unacceptably high material costs for the Spring elements.

A wire is known from JP-A-2057637 which austenitizes and isothermally kept at 250-500 ° C and then deformed into a spring becomes. The holding temperature of 250-500 ° C leads to a so-called Bainite coating with a low ductile bainite structure. A subsequent pulling process as used to increase tensile strength would be desirable in itself, at this level Technology not possible.

From GB-A-2210299 and EP-A-368638 it is also known Springs made of oil-hardened spring steel, made of tempered steel too shape or springs formed from the uncured wire compensate.

The invention has for its object a high-strength increased operating temperatures relaxation-resistant wire springs with scale and residual dirt-free surface and relative to create low material costs.

This object is achieved with the features of Claim 1 solved.

Pretailored embodiments result from the Dependent claims.

The invention is described below using two exemplary embodiments explained in more detail.

Example 1:

A relaxation-proof and heat-resistant tension spring with the following dimensions: Wire diameter 3.6 mm Spring body diameter 41.5 mm Unstretched length L _o 268 mm Tensioned spring length L ₁ 384 mm L2 570 mm is made of 8 mm Ø rolled steel with the following composition: 0.68 Weight percent carbon 1.48 Weight percent silicon 0.52 Weight percent chrome 0.65 Weight percent manganese and steel typical accompanying elements.

This rolled steel is austenitized at 900 ° C, isothermally converted at 540 ° C and then cold drawn to 3.6 mm. A strength Rm of 1900 N / mm ^{2 is} achieved. This wire is formed fully automatically into a tension spring with the above-mentioned dimensions and then annealed at 300 ° C for one hour with low stress. Relaxation loss after testing for L2 at 145 ° C
one hour: 4.8%

Example 2:

Another example relates to the manufacture of a helical compression spring. From a rolled steel 5.5 mm Ø with a composition as in Example 1, an analog heat and cold drawing treatment is carried out on the tension spring and a compression spring for a fuel injection pump with the following spring data is generated: Wire diameter 1.4 mm outer diameter 7.3 mm Unstretched length 25.4 mm Relaxation test at L ₂ = 15.4 mm and 150 ° C
twelve hours: 3.5%

Claims (5)

1. High-strength, relaxation-resistant steel spring produced from a steel wire with the composition

   a) 0.45 to 0.85 weight percent of carbon

   0.2 to 1,60 weight percent of silicon

   0.3 to 1.50 weight percent of manganese

   0.4 to 1.2 weight percent of chromium

   and selectably also

   b) 0.05 to 0.30 weight percent of vanadium additional constituent and/or

   c) 0.005 to 0.05 weight percent of titanium,

   0.01 to 0.02 weight percent of niobium and/or tantalum

   0.05 to 0.5 weight percent of molybdenum

   d) and/or with complete or partial substitution of the elements chromium and silicon by
      0.003 to 0.01 weight percent of boron

   e) and the balance iron and unavoidable additional constituents,
   wherein the said steel wire has been

   f) austenitised and then isothermally thermally treated in the temperature range between 450 and 650°C,

   g) subsequently drawn to a tensile strength of 1600 to 2300 N/mm² with a contraction of at least 40% in breakage,

   h) cold-formed into a spring and

   i) subsequently stress-free annealed in the temperature range of 200 to 350°C.
2. Steel spring according to claim 1, characterised in that it has a helical form.
3. Steel spring according to claim 1 or 2, characterised in that the mean spring core diameter is equal to or less than quadruple the wire diameter.
4. Steel spring according to one of claims 1 to 3, characterised in that it has been shot-peened for increase in service life.
5. Steel spring according to one of claims 1 to 4, characterised in that it has been preset by deformation beyond the elastic limit selectably at room temperature and/or at temperatures up to 400°C.