Machinability of stainless steels

The world market for stainless steel long products (billets, wire rod, bars) currently stands at almost two million tonnes. More than half of these products will undergo at least one machining operation during their shaping. This machining may be limited, as in the case of forged parts, but it can also be very significant, as in the case of mechanical parts. In bar turning, machining costs account for the bulk of the cost of finished parts, leading to the following paradox: machinability is one of the most important properties required of long stainless steel products.

This machinability involves a number of parameters: the material itself, of course, but also the machine on which the material is to be processed, the cutting tools and the lubricant, to mention only the most immediate parameters. All these parameters, and in particular the material, are evolving rapidly, to such an extent that the bad reputation of stainless steels in terms of machinability is becoming increasingly unjustified.

First, we'll review a few definitions of machinability, its assessment criteria and the various machining techniques. We then examine the influence of the material's physical and metallurgical properties on its machinability, taking into account matrix-related parameters and the role of inclusions. Finally, we return to the subject of cutting tools, to show the new perspectives brought about by their rapid evolution.