Frequently asked questions

When it comes to spring steel, frequently the same questions arise. Therefore we have decided to gather them here and to answer them on the following pages from different perspectives. We do this to the best of our knowledge, however no responsibility is taken for the correctness of this information. If you have suggestions for improvement or further questions, we will be happy to receive them at info[at]stahlbecker[dot]de.
We wish you an enjoyable read, yours Stahl-Becker

Choice of material

How do you recognize stainless spring steel strips?

Merely from looking at the material, it is hardly possible to distinguish stainless spring steel from hardened and tempered spring steel strips. Even the test with a magnet is not one hundred per cent reliable, since stainless spring steel is also slightly magnetic because of the cold rolling process. A simple way of finding out the properties of the material is to drip ammoniumcopperchloride on the metal sheet. If a rubiginose spot appears shortly afterwards, it is a carbon quality.
 

Is it possible to convert the hardness of a material into its tensile strength?

Conversion tables exist, but they basically only contain approximative values. Please find a conversion table here.

Is spring steel magnetic?

All carbon spring steels are magnetic. The stainless spring steel with the material-no. 1.4310 is also slightly magnetic, in spite of being stainless. In this case the magnetism is generated by the cold rolling process.

What is the appropriate tensile strength for my purpose?

High tensile strengths are frequently used, if the component will undergo only minor mechanical processing and a high strength is required for the employment of the material. If the component still has to be mechanically processed or folded, annealed strips are frequently used and the component is hardened after the processing. If the component is to be of stainless material, the lowest available tensile strength is 1100-1300 N/mm².

What is the difference between stainless and normal spring steel?

In addition to the corrosion and acid resistance the major difference between the two materials is the way in which the spring properties are achieved: With carbon steels, the designated resilience is achievd by heat treatment, with the stainless alternative through the cold rolling process.

Mechanical processing

How much can spring steel be bent or folded?

Only the european technical standard for stainless spring steel strips indicates the bending radius with which the strip can be bent. Please find the respective table in our data sheet "spring steel strip 1.4310".
 
In the european standard EN 10270-3 for stainless wire the minimum bending radius, with which damages to the wire mustn't occur, is defined by the bending test (chapter 6.4.5: wire is bent in a U around a mandrel with a specific diameter):
- 3 to 6,5 mm wire diameter: mandrel diameter >= 2 x wire diameter
- more than 6,5 mm wire diameter: mandrel diameter >= 3 x wire diameter
 
For carbon-material there is no specification in the codes.

Is it possible to drill spring steel?

Because of its high tensile strength, spring steel is not predestined to be drilled, but - it is possible. In general cobalt-drills are recommended. You should keep the drilling speed low and use a cooling liquid.

Thermal joining and cutting processes

Can spring steel be lasered?

All spring steels sold by Stahl-Becker are laser compatible and are cut on laser machines by our customers. For very thin sheets YAG-lasers are used frequently.

Can spring steel be welded?

Stainless spring steel can be welded. For the material 1.4310 the literature ("Stahlschlüssel"/"Key to steel", 1998, Verlag Stahlschlüssel Wegst GmbH, ISBN 3-922599-14-1) indicates the welding material with the material-number 1.4302.

Carbon qualities like for example C75S are ill-suited for welding. The higher the carbon concentration of the material, the worse it is to weld.

Heat treatment

Has spring steel to be hardened?

Not necessarily. Stainless spring steel is already "hardened" during the production process. Carbon steels, like for example C75S, exist both as hardened & tempered and as annealed version. The annealed material can be heat treated subsequently to the production of the designated parts.

Technical characteristics

What does elongation mean?

Basically, elongation means "extension relative to the initial length".

 

Elongation (at fracture) A80

The elongation at fracture states how much a sample was elongated in the test until it broke and refers to its initial length. A80 => initial length 80 mm.
 

What does Re yield point mean?

The stress, at which the yielding starts, without having increased the applied stress any further (if the stress even declines again, there is a lower yield point ReL and an upper yield point ReH). The yield point defines the transition from elastic to plastic transformation.

What does Rp strain mean?

With some materials the yield point (that is the transition from elastic to plastic transformation) cannot be clearly defined. In the area of spring steel this is true for the stainless products. In these cases the strain Rp 0,2% is indicated as an alternative to the yield point. It indicates  the stress with which the remaining strain stays at 0,2% after release of the pressure. For this, a parallel is drawn to Hooke's straight line (the Hooke's straight line is the one that depicts the elastic elongation during the tensile test in the stress-strain-diagram) in distance of 0,2% remaining strain. The stress at the point of intersection corresponds to the alternative yield point Rp0,2.
 

What does tensile strength Rm mean?

The tensile strength Rm indicates the limit, at which the steel tears under pressure, thus it's maximum tensile stress. The tensile strength is determined by the tensile test. The tensile strength is denominated with the abbreviation Rm. It is calculated with the quotient of maximum tensile force and the initial diameter of the sample (N/mm²). It is the maximum of the stress-strain-curve.

What indicates the E-module respectively the rigidity modulus?

The E-module is the mathematical tension that an elastic strain of 100% would cause (average E-module of steel: 216.000 N/mm²). The E-module is also the proportionality factor of tension and strain:

 

Tension = E-module times strain (Hooke's law)

 

The rigidity modulus (also shear modulus or torsion modulus) is a material constant, describing the linear elastic deformation of a component due to transverse stress or shear force (http://en.wikipedia.org/wiki/Shear_modulus).