M-Steel offers particular benefits in hard part turning, Ovako says

Hard on the heels of hard part turning

A new test program now shows that M-Steel can offer particular benefits in hard part turning, as Göran Nyström, executive vice-president group marketing and technology at Ovako explains.

M-Steel is a low alloyed, or non-alloyed, machinability-treated steel. Over 30 years it has proven its ability to achieve significant reductions in machining costs. M-Steel has been used as a successful replacement for conventional steel by hundreds of component manufacturers in the automotive and general engineering industries – its benefits are especially apparent in automated turning and drilling processes. This has been confirmed by independent tests, with machining costs reduced by up to 30% or better in some cases.

The M-Steel treatment can be applied to almost any steel grade. The aim is to modify and control non-metallic inclusions in the steel to maximise machinability.

The hard, non-metallic inclusions found in conventional steel can cause considerable wear of machine tools whereas the M-Steel treatment transforms them into softer, calcium containing inclusions. The main role of these inclusions is to aid machinability as they create a beneficial protective layer between the tool and the chip interface that very significantly reduces tool wear, with a consequent increase in tool life.

Furthermore, the sulphur content is also optimised for the best possible machinability. At the same time, the M-treatment is designed to balance machining performance against other vital properties such as hardenability, impact toughness, tensile and fatigue strength.

The M-Steel production process is about much more than just the calcium treatment – it is tightly controlled from raw material through melt, to casting, hot rolling and the final heat treatment. This ensures consistent machinability from cast to cast, meaning that machines can be run with fixed high cutting rates and predictable tool change intervals from one production run to another. This repeatability is crucial for automated machining processes.

When conventional steel is replaced by M-Steel it is possible to lower machining costs by up to 30%, boosting both productivity and profitability. This is achieved by its ability to facilitate faster run times through higher cutting speeds, more predictable and longer tool lives, and easier chip formation.

The hard facts

Hard part turning is gradually removing the need for grinding and separate, more expensive heat treatment. It is often the critical last machining process in the production of highly-stressed steel components such as those used in automotive transmissions.

Defined generally as the turning of steel with a hardness greater than 45 HRC, the process removes the final layers of the metal from the workpiece in order to produce the required surface finish and geometry. The most frequent alternative to hard part turning is grinding, which is both costly and reduces operating production efficiency.

Hard part turning is particularly demanding on the super hard PCBN (polycrystalline cubic boron nitride) tools developed to machine case-or induction-hardened steel. This is where M-Steel can offer particular benefits.

Swerea Kimab, an independent test institute, conducted an investigation that compared two case hardened steels with approximately the same basic alloying properties and higher sulphur levels: conventional steel (152A) and M-Steel (20NiCrMo2-2).

Test pieces were then case hardened to surface hardness 58 - 65 HRC and hard part turned using PCBN inserts at different cutting speeds. The investigation looked at the wear mechanisms of the insert edges, the surface finish achieved and also the chip formation.

The major conclusion of the study was that M-Steel proved to be, by far, the easiest-to-machine steel, with a potential doubling of tool life.

The reason for this improvement is linked to the protective deposits that form on the rake face during machining. While in conventional steel, hard non-metallic inclusions cause considerable tool wear, the M-Steel treatment will change their composition so that they instead form a protective film between the tool and chip interface.

Cool and calculated

To optimise the success of the M-Steel concept, we work closely with customers to advise on machine settings, choice of tools and quality assurance through machining tests that ensure the correct material grade and dimensional characteristics are selected for a given application.

This knowledge is now available through the M-Steel Calculator, based on Ovako’s Steel Navigator platform. This digital tool guides customers in identifying the right machine settings based on the steel properties they wish to achieve and the cutting tools they plan to use.

To use the M-Steel Calculator a customer simply has to enter the relevant information for their cutting tool and workpiece material. They are then presented with specific information on machine power, chip stream and the expected surface quality.

The calculator will also establish the difference between these parameters when using M-Steel and a conventional steel. This will normally be a saving of up to 30% in production cost without losing any of the improvement in machining quality.

Ovako www.ovako.com/Products/M-Steel/