One of the challenges that we, as a spring manufacturer, have little influence on is the combination of the demanded lifespan and the conditions under which the spring is required to function. Depending on the system requirements, we first assess which material is sufficiently resistant to corrosion and whether this is useable in the application. At the same time Alcomex decides, within the specified temperature range, whether the chosen material still has sufficient mechanical properties to function. Finding the right combination for this is often a difficult task.
The various literature makes material specifications available. The most common are:
|Material||Active ingredient||Normal temperature range|
|Carbon steel (C75, C85, C100)||1.1248 / 1.1269 / 1.1274||[-40°C tot +120°C]|
|Inox (301, 316, 17-7 PH)||1.4310 / 1.4401 / 1.4568||[-150°C tot +250°C]|
|Inconel (X750, 718, 625, 600)||2.4669 / 2.4668 / 2.4856 / 2.4816||[-200°C tot +550°C]|
|Hastelloy (C4, C276)||2.4610 / 2.4819||[-100°C tot +500°C]|
|MP35N||Body implantable||[-200°C tot +320°C]|
|Beryllium copper||2.1247||[-190°C tot +160°C]|
|Phosphor bronze||2.1020||[-190°C tot +80°C]|
|Brass||2.0321||[-190°C tot +120°C]|
Material and surface treatment as a solution
After the first screening, the application of the spring is examined. It may so happen that the work environment of the spring is such corrosive that certain materials simply “dissolve”. The strength of springs and spring products is largely determined by the thickness of the wire in relation to the tensile strength [N/mm2]. The thickness of the wire and tensile strength have an effect on the spring constant, thus the functioning of the spring, and in addition the lifespan is influenced. Issues can often be solved by choosing a different material. But be aware, for cost-driven applications, often this is too expensive, since certain, more exotic materials are simply not available in wire or narrow strip.
Often surface treatment can be chosen as an alternative solution for a specific medium. The most common surface treatments are: galvanising, phosphating, nickelling, chroming, powder-coating, tinning and silvering/gilding. All of these surface treatments add specific properties to the spring, as a result of which the lifespan is extended and the product made suitable for the application, with the principle that the mechanical properties are not being adversely affected.
Hydrogen embrittlement in spring materials
The application of surface treatments is not without risk and if implemented incorrectly, this may lead to embrittlement of the materials. This phenomenon is called hydrogen embrittlement and occurs in all cases where hydrogen is able to develop on the surface of the steel. The effect of hydrogen embrittlement on steel is that the steel will break at a much lower tensile strength than usual, despite the steel showing enormous durability properties during normal lifespan tests. Hydrogen embrittlement could be caused by processes for surface treatments and occurs when springs are exposed to non-oxidising acids or cathodic cleaning and coating. Remark: leaf springs that have hardened after moulding are sensitive to this.
The risk of embrittlement is reduced as the tensile strength and hardness are diminished. Generally, embrittlement does not occur on steel with a tensile strength of < 1000 N/mm ² or a hardness of < 30 Vickers. Most of the hydrogen can be removed by an additional thermal treatment (continuous warming). The thickness of the material determines the temperature and the duration of this thermal treatment:
Material thickness < 3 mm 170°C – 180°C, 5 hours
Material thickness < 12 mm 190°C – 210°C, 4 hours
The implementation of surface treatments is hardly ever without risk. Alcomex always carries out these treatments in consultation with specialised partners, in order to guarantee the quality of our spring products and solutions.
By: Marco Dekker | Head of Research & Development
Do you have a specific challenge regarding high temperatures or corrosion? Get in contact with us!