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CUTTING TOOLS
Sandvik Coromant – The impact of alignment on steel turning processes What do an ancient Roman war strategy and Sandvik Coromant’s ISO P steel turning grades have in common, and how can this help increase your machine shop’s output? Rolf Olofsson, Product Manager at Sandvik Coromant, explores how the coating and substrate of carbide grades can make a huge difference in the efficiency and productivity of steel turning processes. A common misconception in the metal working industry is that machining steel is simple. Experienced machinists know that turning ISO P steel is anything but. First among many concerns is the breadth of materials in the ISO P classification, which range from ductile low-carbon steels to high-alloyed. Secondly, the hardness of different steels ranges significantly from one end of the spectrum to the other. The type of application varies and so do machining conditions in workshops. Evidently, steel turning is challenging and given all variables, the task of selecting a grade to cater to the wide range of properties exhibited by ISO P steels is even more daunting.
Grade of all trades
Sandvik Coromant has launched two new ISO P steel turning insert grades, GC4415 and GC4425.
For any such grade, fracture resistance is paramount – as is a cutting edge capable of delivering the hardness needed to resist plastic deformation induced by the extreme temperatures present in the cutting zones. Moreover, the grade must be equipped with a coating that can prevent flank wear, crater wear and edge build-up. Importantly, the coating must also adhere to the substrate; if it does not stick, the substrate is exposed, leading to rapid failure. Given this array of demands, it is crucial to understand the structure of a steel turning grade in order to make an informed decision when picking one for your application.
Structure of a carbide insert All carbide grades contain a cemented carbide core, also known as a substrate. The substrate defines the toughness and strength of the grade. Resistance to plastic deformation can also be attributed to it. The cemented carbide substrate is usually covered by a few layers of coating such as titanium carbonitride (TiCN), alumina (Al2O3), titanium nitride (TiN) that give the insert its edge toughness, adhesion and wear resistance properties. The recipe for superior resistance to different kind of wears – flank, crater and edge build-up; adhesion to substrate; and improved tool life – lie in the microscopic details that go into designing the coating layer.
Roman shield wall In conventional alumina coating, crystal growth direction is random. If the growth in
AMT DEC 2021
All carbide grades contain a cemented carbide core, or substrate, which defines the toughness and strength of the grade.
the coating layer can be controlled to ensure all crystals line up in the same direction, it results in superior wear resistance. To help you understand the power of crystal alignment, let’s consider an example from Roman history. When the ancient Roman legions went on a siege, they frequently deployed a shield wall — the Testudo
formation. In this formation all shields were aligned and tightly packed avoiding any vulnerable gaps. The shield wall helped the Romans resist oncoming aggression while advancing. The alignment of crystals in a coating layer works in a similar way: the closely packed uni-directional crystals act as a shield and
