Why ESR is recognized as the preferred production method for high-performance materials?
The ESR (Electro Slag Remelting) is used for the productions of special tools steels.
The starting material used for the remelting is a bar of steel obtained from conventional melting process. The bar is used as consumable electrode and has already the chemical composition of the desired material. To simplify the explanation of the refining process please find here below the ESR plant representation.
The heat required for remelting is produced by the passage of electric current (AC) between the electrode (negatively charged) and the starter plate (positively charged), located on the bottom of the copper mold. Essentially the approaching of the electrode near to the starter plate creates a short circuit thereby generating an electric arc that releases a strong heat. The heat produced by the electric arc reaches high temperatures between 1800 and 2000°C, in the bath of liquid molten slag. The electrode immersed in it begins to melt in the form of drops which, passing through the bath of slag, reacts eliminating any impurities (oxygen, sulphur, phosphorus and other undesirable elements). The liquid steel begins to touch the bottom of strike off plate and begins to solidify due to the cooled copper mold. The electrode continues to melt, creating the new material remelted ingot.
Which are the substantial differences of the material after solidification between an ingot produced with the conventional melting process and an ingot remelted with the ESR process?
By conventional melting processes, the long time of ingot solidification causes segregations, inclusions not uniformly distributed and, finally, some structure anomaly at those points in which the liquid steel is no longer able to flow during solidification.
In the ESR ingot, however, has at all times only a small amount of steel in the liquid state, for which the flow of heat and crystallization occur in a steady manner.
The crystallites grow freely and almost parallel to the ingot longitudinal natural axis. The ingot obtained by this remelting / refining process is very homogeneous and free of internal defects. The segregation of the ingot (called macro-segregations) are substantially eliminated and the segregations of crystals (called micro-segregations) are significantly reduced.
The ESR remelted material improve following mechanical characteristics:
- Improved toughness due to increased homogeneity and isotropy
- Improved creep resistance properties
- Best fatigue strength and tenacity properties as well as outstanding tensile strength
- Improved purity
This is why ESR remelting process is recognized as the preferred production method for high-performance materials that shall withstand high stresses.
KnifeSol have therefore decided to provide its customers, knives and blades, produced with ESR materials.