Machining

The answer, of course, has to do with the fact that steel is the most commonly machined material in the 21st century.  As is well known, our material is not only extremely resilient, resistant and therefore universally applicable - it can also be excellently machined.  However, only if it has been appropriately alloyed beforehand and its microstructure has been optimized by cold forming.

On the one hand, the machinability of steel depends heavily on its internal crystalline structure and the cooling lubricant used during the forming process.  On the other hand, it depends on its chemical composition, because certain alloyed elements have a lasting effect on the machining properties of a material.

The best-known representatives of easily machinable steels are free-machining  steels with grades such as N1.4305, 1.4104 and 1.4005 according to DIN EN 10088-3 or AISI 303, 430F and 416 according to ASTM A582. Three alloy elements are particularly important in their production.

• Lead: Lead is often added to low-alloy free-machining steels. The metal melts even at low temperatures and thus forms a protective lubricating film between the tool and the chips.  This reduces the frictional forces that occur and thus tool wear.  It also contributes to good chip breaking.
• Sulfur: The element sulfur forms manganese sulfides in the material and thus increases the melting point.  This in turn leads to chips that break faster and thus to a better surface quality of the workpiece.
• Phosphorus: In low concentrations, phosphorus ensures that chips break more easily and thus a higher surface quality. However, phosphorus is only reluctantly added to the alloy because it embrittles the material.

However, not only phosphorus worsens the material properties.  Lead and sulfur are also mostly undesirable in steels because they reduce its strength and corrosion resistance.  The choice between a steel that is as durable as possible and its machinability is therefore always a compromise and is largely determined by the intended use.

At this point you are  probably asking yourself why you should value the machinability of steel at all.  Why not just take the sturdiest one and drill, mill or grind a little longer?

The simple answer is: Because it's just not practical.  After all, poorly machinable steel leads to extremely high wear on the tools, reduces their service life and increases maintenance costs - so it costs you a lot of time and money.  In addition, the results are more than unsatisfactory, because poorly machinable steel produces a poor surface quality.

In comparison, steel that is easy to machine...

• reduces the cutting forces: If only little force is required for the cutting process, your tools will last longer and have to be replaced less often.
• produces optimal chips: Chips that are too coarse can hinder the production process because workpieces often have to be reworked.  Good machinability avoids this problem.
• ensures a long service life: where machines have to be serviced less often, they can work longer - and longer service lives mean more economical work.
• forms smooth surfaces: the surface quality of easily machinable steel is significantly better after forming and thus ensures higher quality end products.

The advantages of easily machinable steel cannot be denied.  In the end, as already mentioned, it is primarily the intended use that decides on your optimal material.  But how do you find out which steel is right for you?