Spherodization of high carbon steel.

Spheroidizing is a form of heat treatment for iron-based alloys, commonly carbon steels, in order to convert them into ductile and machinable alloys. It is conducted at temperatures that are slightly below the eutectoid temperature (temperature at which the solution is a solid solution rather than liquid), followed by a slow cooling process.

The resulting spheroidite structure is a microstructure that contains sphere-like cementitie particles. Spheroidite is known as the most ductile and machinable form of steel. This article will look into the technique and applications of spheroidizing process.

Technique of Spheroidizing
Spheroidizing of high carbon steel is a method of prolonged heating at a temperature below the eutectoid temperature. By heating at this temperature pearlite, which is the lowest energy arrangement of steel, gets converted to ferrite and cementite. The graphite content of steel assumes a spheroidal shape after spheroidizing and after prolonged heating the pearlite layers are broken down and spherical lumps of cementite, or spheroidite, are formed.

The structures in spheroidite are one thousand times larger than those of pearlite and are spaced further apart. This means the spheroidite steel is extremely ductile. However, the process of spheroidizing does consume a lot of energy.

Hardening & Tempering of Knife Steel.

Hardening is a way of making the knife steel harder. By first heating the knife steel to between 1050 and 1090°C (1922 and 1994°F) and then quickly cooling (quenching) it, the knife steel will become much harder, but also more brittle.

To reduce the brittleness, the material is tempered, usually by heating it to 175–350°C (347–662°F) for 2 hours, which results in a hardness of 53–63 HRC and a good balance between sharpness retention, grindability and toughness.

Tempering should be carried out within a reasonable time after hardening, preferably within an hour or so. It is of vital importance that the blade should be allowed to cool to room temperature before tempering is started. The transformation to martensite will otherwise be interrupted and the hardening results may be impaired.

A higher tempering temperature will yield a somewhat softer material with higher toughness, whereas a lower tempering temperature will produce a harder and somewhat more brittle material

Source: http://www.smt.sandvik.com/en-in/products/strip-steel/strip-products/knife-steel/hardening-guide/purpose-of-hardening-and-tempering/

Special Tempre Strips – As rolled hard

These are basically as rolled hard steel strip. To achieve a desired hardness, an annealed material of suitable thickness is taken and rolled down to the required thickness, to achieve that required hardness. After rolling, the material is pinch passed and final annealing is not required. To choose the correct thickness (for reduction to the desired thickness) is a matter of expertise.
Grades: This strip is available in low, medium & high carbon grades.

Applications: It is suitable for components where formability is limited. It saves the extra annealing cost. The strip is directly punched & formed and if required sent for heat treatment.