How to guarantee high standards of mechanical resistance on quenched and tempered materials?
Recently, we happened to have to deal with a complex request to satisfy, in terms of quality on a tree with tempered and quenched material. Today we have decided to take you into this very special case study. The reference lot is small so the starting material should be chosen from rolled bar.
Here is how we managed the required mechanical strength
To arrive at the correct solution we have made several analysis. First of all, we thought to start from a material that had the required characteristics from ready-made. Subsequently, we evaluated the possibility of carrying out the tempered and quenched treatment on a piece of cut steel. In the end, we decide to consult the reference standards. Let's take UNI EN ISO 683-2 (Alloyed steels for quenching and tempering) which describes the mechanical characteristics of the steel according to the reference diameter. From the standard we were also able to understand the size of the specimen used by the various manufacturers and suppliers of heat treatments.
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From the norm to the effective solution
The next step is to adapt the value indicated by the standard to our case. For the reference shaft with a diameter of 100 mm, the value Rm is a range between 900 and 110N / mm2. This means that the supplier must guarantee a value of 900-1000 N / mm2 from the external diameter to 12.5 mm on the radius. Tempered and quenched parts are extremely energy-intensive treated materials, therefore very expensive. Consequently, suppliers often optimize their processes and therefore market values tend towards the minimum.
In the end, to guarantee the required quality, it is necessary to start from a length of at least 105mm. This however comes with an Rm of 800-950 N / mm2. Consequently, you will understand that it is impossible to start from a commercial tempered and quenched bar. The best way is to carry out a first roughing turning obtaining a minimum stock. After that, we carry out the reclamation heat treatment on the affected areas.
Have you ever had problems managing tempered and quenched materials?