What are the main types of corrosion of mold steel

　　The phenomenon that the mold steel is gradually damaged under the action of external media is called corrosion, and there are basically two forms of corrosion, chemical corrosion and electrochemical corrosion. The corrosion encountered in the actual production is mainly electrochemical corrosion, chemical corrosion does not produce current, only in the corrosion process to form a certain corrosion product. This corrosion product is generally covered on the surface of the metal to form a film, so that the metal and the medium are isolated.

　　Die steel

　　Electrochemical corrosion is an important and common form of metal corrosion, which is caused by the difference of electrode potentials between different metals or different metal slots. This kind of galvanic cell corrosion is generated between microscopic structures, so it is also called microcell corrosion. Electrochemical corrosion is characterized by the presence of dielectrics, potential connectivity or contact between different metals, metal microzones or phases, and corrosion currents.

　　The corrosion failure forms of die steel in industrial production are various. Under the action of different steel materials under different loads and different media environments, the corrosion forms of 51 mold materials are mainly classified as follows:

　　1. General corrosion

　　A large area of uniform corrosion occurs on the exposed surface of the steel material, which reduces the effective force area of the component and its service life, but is less harmful than local corrosion.

　　2. Intergranular corrosion

　　Corrosion along the boundary of the product, resulting in the destruction of the connection of the grains. This kind of corrosion is the most harmful, it can make the gold brittle or lose strength, lose the metal sound when knocking, easy to cause sudden accidents. The corrosion is the main corrosion form of austenitic stainless steel, which is due to the difference between the product boundary area and the composition or stress in the crystal, resulting in a significant reduction of the electrode potential in the product boundary area.

　　2. Stress corrosion

　　Metal cracking occurs under the combined action of corrosive media and tensile stress (external stress or internal stress). The fracture mode is mainly intergranular, but also transgranular, which is a dangerous low stress brittle fracture, often occurs in chlorination and alkaline atmosphere oxides or other water-soluble media stress corrosion, in many equipment accidents accounted for a considerable proportion.

　　3. Point corrosion

　　Point corrosion is a form of corrosion failure that occurs in a local area of the metal surface. After the formation of point corrosion, it can develop rapidly to the deep and finally penetrate the metal. Point corrosion is very harmful, especially to various containers is extremely unfavorable. After the occurrence of point corrosion, it should be polished or painted in time to avoid deepening corrosion. The cause of point corrosion is that the passivation film on the metal surface is locally damaged under the action of the medium. Or in the media containing chloride ions, the material surface defects and non-metallic inclusions can cause point corrosion.

　　4. Corrosion fatigue

　　The failure of metals under corrosive media and alternating stress is characterized by corrosion pits and a large number of cracks. Significantly reduce the fatigue strength of steel, resulting in premature fracture. Corrosion fatigue is different from mechanical fatigue, it does not have a certain fatigue limit, with the increase of the number of cycles, the fatigue strength has been declining.