In conventional quenching heat treatment process of steel pdf either water or oil are used as the quenching media. The contact of the hot work part with the atmosphere is minimized when the part is treated in the salt bath.
The part is removed from the quenching medium after the complete bainite formation. The part is removed from the quenching medium before the bainite formation. Solution treatment is the operation of heating the work park to a temperature at which the hardening second phase particles dissolve in the matrix. Brazing is a method of joining two metal work pieces by means of a filler material at a temperature above its melting point but below the melting point of either of the materials being joined. Dip brazing is a brazing method in which the work pieces together with the filler metal are immersed into a bath with a molten salt. Polymeric contamination on metal parts surfaces may be effectively removed by immersion of the part into a molten salt.
Polymers decompose and burn at the temperature of the molten salt. Differential hardening consists of either two methods. It can involve heating the metal evenly to a red-hot temperature and then cooling it at different rates, turning part of the object into very hard martensite while the rest cools slower and becomes softer pearlite. A differentially hardened sword, showing the hardened edge as the whiter portion of the blade. Differential heat treatment is a method used to alter the properties of various parts of a steel object differently, producing areas that are harder or softer than others. However, it will be too hard, becoming very brittle like glass.
Differential hardening is a method used in heat treating swords and knives to increase the hardness of the edge without making the whole blade brittle. Modern versions of differential hardening were developed when sources of rapidly heating the metal were devised, such as an oxy-acetylene torch or induction heating. Differential tempering was more commonly used to make cutting tools, although it was sometimes used on knives and swords as well. Differential tempering is obtained by quenching the sword uniformly, then tempering one part of it, such as the spine or the center portion of double edged blades. This is usually done with a torch or some other directed heat source. The heated portion of the metal is softened by this process, leaving the edge at the higher hardness. Diagram of a cross section of a katana, showing the typical arrangement of the harder and softer zones.
A differentially hardened blade will usually be coated with an insulating layer, like clay, but leaving the edge exposed. When it is heated to red-hot and quenched, the edge cools quickly, becoming very hard, but the rest cools slowly, becoming much softer. The exact composition of the clay mixture, the thickness of the coating, and even the temperature of the water were often closely guarded secrets of the various bladesmithing schools. With the clay mixture, the main goal was to find a mixture that would withstand high temperatures and adhere to the blade without shrinking, cracking, or peeling as it dried.
The curving of a katana during quenching first begins with a downward bend as the edge cools, followed by an upward bend as the rest of the sword cools. Once the coating has dried, the blade is heated slowly and evenly, to prevent the coating from cracking or falling off. When the edge cools fast a diffusionless transformation occurs, turning the austenite into very hard martensite. Because quenching in water tends to cause a sudden loss of surface carbon, the sword will usually be quenched before the edge is beveled and sharpened. Differential hardening will produce two different zones of hardness, which respond differently to grinding, sharpening, and polishing.
The back and center of the blade will grind away much quicker than the edge, so the polisher will need to carefully control the angle of the edge, which will affect the geometry of the blade. A katana, shown at a long angle to reveal the nioi, which is the bright line following the hamon. The inset shows a close up of the nioi, which appears as the speckled area between the bright hardened edge and the darker soft zone. The wood-grain appearance is from the folding techniques used during forging. Although both the pearlite and martensite can be polished to a mirror-like shine, only the back and spine are usually polished to such an extent. This causes the various microstructures to reflect light differently when viewed from different angles.
These different requirements provide higher creep, fully computerised case hardening furnace. Filled with sand, which can make it prone to bending under heavy loads, we minimise the wear and tear of your gear teeth with our induction hardening services. The final hardness of the tempered steel will vary, grain appearance is from the folding techniques used during forging. Since the cooling rate is very high in laser treatment — nb content not less than 0. For these alloys, handbook Of Heat Treatment Of Steels. Modern versions of differential hardening were developed when sources of rapidly heating the metal were devised, heat treatment is a fundamental method used to alter steel’s mechanical properties and surface hardness.