Three classification mold steel

Core Tip: Mold can be divided into cold mold, hot die and plastic mold 3 category for forging, stamping, cutting type, die-casting and so on. Due to the different kinds of mold uses, working conditions are very complex, so the mold steel, mold manufacturing according to their working conditions, should have high hardness, strength, wear resistance, sufficient toughness, and high hardenability, quenching rigid and other process performance.

        Because of these different uses, working conditions are very complex, and therefore mold steel performance requirements are also different.

 Cold mold includes Die, drawing die, drawing die, pressure die, thread rolling die, rolling plate, cold heading and cold extrusion die molds.

There are steel cold die, according to the working conditions of their manufacturing equipment, should have a high hardness, strength, wear resistance, sufficient toughness, and high hardenability, hardened and other process performance.

Alloy analyzer for alloy tool steel such uses are generally high-carbon steel, carbon mass fraction of more than 0.80%, chromium is an important alloying elements such steel mass fraction is generally not more than 5%. But for some high wear resistance, mold steel after quenching deformation is small, the highest chromium content up to 13%, and for the formation of large carbides, the steel carbon content is also high, up 2.0% ~ twenty three%.

Higher carbon content cold die steel, most of which belong to the organization eutectoid steel or ledeburite.

Commonly used class of high-carbon low-alloy steel, high carbon high chromium steel, chromium molybdenum steel, carbon steel and other chromium tungsten Kushiro.

   Cold die [applications]: cold die for the cold state (operating temperature below 200 ~ 300 ℃) forming metals, such as Die, cold extrusion die, shear modulus and the like. Such mold under a lot of pressure, strong friction and a certain impact, therefore, requires a high hardness, wear resistance and sufficient toughness. In addition, the shape of complex, precision and large molds also requires a high hardenability and small heat deformation.

 [Chemical composition]: carbon and sulfur analyzer cold work die steel generally has a high carbon content, wC = 1.0% ~ 2.0%, to obtain a high hardness and high wear resistance. Alloying elements Cr, Mo, W, V, etc., to improve wear resistance, hardenability and tempering resistance.

[Common cold work die steel]: Crl2 steel include Cr12, Cr12MoV etc., hardenability and wear resistance of these steels is good, heat deformation small, commonly used in large-scale cold mold. In addition to the wear resistance of the steel which Crl2MoV less than Cr12 steel, the strength, toughness are good, the most widely used. Smaller size can be used cold mold low-alloy cold work die steel CrWMn, etc., may also 9SiCr cutting tool steel or bearing steel GCr15.

[Heat]: Crl2 steel belonging ledeburite should be repeated forged and annealed before processing. Cr12 steel of the final heat treatment is usually quenching and tempering, eligible tempered martensite, carbide and residual austenite, hardness 60 ~ 64HRC.

Hot die forging into, forging, extrusion and die-casting several main types, including forging die, die forging presses, stamping die, hot extrusion die and metal casting molds. Thermal deformation of the mold at work in addition to withstand enormous mechanical stress, but also to withstand repeated heating and cooling to do with, and cause a lot of thermal stress. In addition to hot work die steel should have high hardness, strength, red hardness, wear resistance and toughness, but also has good high temperature strength, thermal fatigue stability, thermal conductivity and corrosion resistance, are also required to have a high hardenability, in order to ensure that the entire section has the same mechanical properties. For the die-casting mold steel, it should have properties of the surface layer after repeated heating and cooling without causing cracks and withstand shock and erosion liquid metal stream. Such steels are generally carbon steel, carbon mass fraction of 0.30% to 0.60%, below sub-eutectoid steel, also part of the steel due to the addition of more alloying elements (such as tungsten, molybdenum, vanadium, etc.) become eutectoid or hypereutectoid steel. Commonly used types of steel are chromium-manganese steel, chrome-nickel steel, chrome tungsten steel.

Hot die (2) [Applications]: hot die is used in the form of hot metal processing, such as forging die, die casting, hot extrusion mold. Hot die work was at a relatively high impact loads, while the cavity surface to be in contact with the hot metal and friction, the local temperature up to 500 ℃, and also constantly repeated heating and cooling, often leaving the cavity due to thermal fatigue surface cracking, and called for hot work die steel with high mechanical properties and good thermal fatigue resistance at high temperatures. In addition, it must have sufficient hardenability.

[Chemical composition]: hot work die steel to carbon content, wC = 0.3% ~ 0.6%, in order to obtain mechanical properties; alloy analyzer alloying elements are Cr, Mn, Ni, Mo, W, Si, etc., in which Cr , Mn, Ni main role is to enhance hardenability; W, Mo improve tempering resistance and prevent temper brittleness; Cr, W, Mo, Si also improves the thermal fatigue resistance of the steel.

[Common hot die steel]: 5CrMnMo and 5CrNiMo is the most common hot forging die steel, which used to manufacture small and medium 5CrMnMo forging die, 5CrNiMo commonly used in the manufacture of medium-sized forging die; for the mold that the static pressure (eg die casting, extrusion molding, etc.), should be used 3Cr2W8V or 4Cr5W2VSi steel.

[Heat]: After forging die forging blanks need to be annealed to eliminate forging stress, lower hardness, in favor of cutting; to obtain uniform tempering sorbite final heat treatment of quenching, high temperature (or temperature) tempering, tempering or tempering care's body, the hardness is about 40HRC.

Plastic mold include thermoplastic and thermosetting plastic mold plastic mold. Plastic mold steel requires a certain amount of strength, hardness, wear resistance, thermal stability and corrosion resistance and other properties. In addition, it requires a good process, such as heat treatment becomes small, good processing properties, corrosion resistance, good grinding and polishing properties, good welding performance, high roughness, thermal conductivity, good working conditions and the size and shape stability . In general, the injection molding or extrusion molding die can be used hot die steel; thermoset molding and require high wear resistance, high strength cold work die steel mold can be used. Injection molding [performance requirements]: plastic mold suffered less stress and wear, the main failure in the form of the mold surface degradation, and therefore should have the following properties: ① good processing performance, pre-hardened high hardness (28 ~ 35HRC) , facilitate machining or EDM, easy to etch a variety of patterns, words and symbols; ② good polishing, to achieve a high degree of mirror surface (typically Ra value 0.1 ~ 0.012μm) after mold polishing; ③ high hardness (hardness should be more than 45 ~ 55HRC after heat treatment), good abrasion resistance, sufficient strength and toughness; ④ heat deformation small (to ensure accuracy), good weldability (easy to mold welding), etc.