Edge Hardening

The cutting edge is the most important part of a cutting tool. Therefore preparation of the cutting edge is done with expert engineering design and outstanding workmanship for tools of the highest quality. Tronex cutters, like all top quality cutting tools, have cutting edges which are induction hardened. The result is that Tronex cutters have edges that are exceptionally hard and edges that are resharpened. Many lower quality cutting tools are only case hardened which results in much lower cutting edge performance. What are these two hardening methods and why is induction hardening used in producing Tronex tools?

INDUCTION HARDENING is a precision process conducted entirely within the Tronex factory. A high grade, high carbon content steel is used as base material for the tool. After machining the tools are individually placed in the middle of an electrical coil carrying a very high frequency current. This current which induces a deep heat at about 900°C in the highly localized area of the cutting edges. The cutting edges are then rapidly cooled with a water or oil quench which immediately transforms this small localized area into a steel structure which is exceptionally hard. In fact the edges are so hard that they have become brittle. The tools must be tempered, by heating to around 200°C, to relieve stresses from the hardening process and to produce cutting edges which are not only hard, but hard and tough. Toughness is the ability to resist brittle fracture or sharp impact loads. The localized area of induction hardening can be seen on the backside of Tronex tools as light colored half moons or fans which surround the entire length of the cutting edges. This is not visible (although it is still there) on tools with Optimum Flush Cut edges. These tools have undergone another careful machining process to secure this ultimate in flush cutting. The process achieves very hard edges, 63 to 65 on the Rockwell C Scale, with a depth of 2 to 3 mm to allow resharpening, even multiple resharpening.

CASE HARDENING is usually a three step process. First the tool, made of low carbon steel, is surrounded by carbon to increase the carbon content on its surface, or outer case. The tools are then heated to a temperature of around 870°C, followed by an oil or water quench. This process imparts an elevated hardness to the cutting edges of the tool (as well as the rest of the tool). But this hardness is seldom over 55 on the Rockwell C scale. And because this hardness is literally only skin deep, sharpening such tools is impossible. Why are some cutting tools made this way? Because they can be stamped from low grade material and case hardened in large, bulk quantities.

How do tools with these differently hardened edges compare? The actual number of cuts which a tool can perform before getting a dull is determined by the specific material being cut and by the force being applied. But for the same material and same force, tools with induction hardened edges will last 5 to 10 times longer than tools which are only case hardened. Generally speaking, a resharpened induction hardened tools get only 2/3 the number of cuts it got on the first go-round. On its second resharpening it will only get 2/3 the number of cuts it got on the second go-round. A case hardened tool must be thrown away when it no longer cuts.