Surface hardening of steel | flame, induction, laser beam, case hardening and nitriding скачать в хорошем качестве

Surface hardening of steel | flame, induction, laser beam, case hardening and nitriding

Case hardening, also known as surface hardening, is a process used to increase the wear resistance of steel components by hardening only the outer layer while keeping the core tough. This is particularly applied to gears, guide rails, crankshafts, and camshafts. There are several methods of case hardening, including flame hardening, induction hardening, laser hardening, carburizing, and nitriding. In flame hardening, a burner flame is passed over the surface, heating the steel to the austenitizing temperature. Immediately afterward, quenching with water induces a martensitic transformation in the material. Flame hardening is relatively simple but challenging for small or complex parts due to the large heat-affected zone. Additionally, the hardening depth is less precisely controllable compared to other methods. Induction hardening is based on electromagnetic induction, where a high-frequency alternating current is passed through a copper coil (the inductor). This creates eddy currents in the workpiece, generating rapid and localized heating at the surface. Quenching is typically done with water or through self-quenching via the cooler core of the material. The hardening depth can be controlled by adjusting the frequency of the alternating current—higher frequencies result in shallower hardened layers. The advantages of induction hardening include short heating times, minimal oxidation, and reduced distortion. However, it requires a significant tooling investment, making it ideal for mass production. Laser hardening involves heating the workpiece surface with a high-power laser beam to just below the melting temperature. The heat is applied very precisely and rapidly, preventing unnecessary heating of adjacent areas. Quenching occurs through self-cooling. Due to the high energy density of the laser, distortion is minimal, and oxidation can be prevented under a shielding gas. This method is particularly suitable for hardening difficult-to-reach areas or small, precisely defined surfaces. Carburizing is used when low-carbon steels need a hardened outer layer. The steel is exposed to a carbon-rich environment, such as a gas furnace or a molten salt bath, and heated for several hours. Through diffusion, the carbon enriches the surface layer, making it hardenable. The component is then quenched to induce a martensitic structure. After carburizing, tempering is often required to relieve internal stresses. This process provides high wear resistance and durability, making it particularly suitable for gears and drive shafts. Nitriding, also known as nitriding hardening, involves exposing special nitriding steels to a nitrogen-rich atmosphere. The nitrogen atoms diffuse into the surface and react with alloying elements such as aluminum, chromium, molybdenum, vanadium, or titanium to form hard and wear-resistant nitrides. This process takes place at relatively low temperatures of around 500 °C, preventing distortion. The resulting compressive stresses improve the fatigue strength of the component. Nitrided layers are very thin (0.1 to 1 mm) but offer excellent hardness and corrosion resistance. However, the process is time-consuming, often requiring several days. 00:00 Surface hardening 01:19 Flame hardening 02:21 Control of the hardening depth 02:49 Advantages and disadvantages of flame hardening 04:00 Induction hardening 04:23 electromagnetic induction 05:08 Quenching 05:38 Controlling the hardening depth (skin effect) 06:37 Advantages and disadvantages of induction hardening 07:28 Laser beam hardening 08:47 Case hardening 09:52 Carburising and quenching 11:02 Nitriding