Alloys for mold Steel
Mold steel is a type of tool steel that is used to make various types of forming tools: cold work, hot work and plastic mold steel.
What elements can be used to make mold steel?
- Main alloys: carbon (C), silicon (Si), manganese (Mn), phosphorus (P), sulfur (S), nickel (Ni), chromium (Cr), Molybdenum (Mo), Aluminum (Mo), Tungsten (W), Vanadium(V), Cobalt (Co)
- Other trace alloys: Titanium (Ti), Niobium (Nb), Copper (Cu), Aluminum (A1).
- Non-metallic elements: Nitrogen (N) and Bromine (B)
Influence of various alloying elements on mold materials
1.Carbon
It is the main alloying element to increase the hardening performance and wear resistance. With other alloys in the hardening treatment of Wolstad ferrite solidification after the formation of carbides, alloys with a high content of carbon relative to the steel casting caused by the increased probability of offset, resulting in carbide coarseness, the toughness of the ductility, mechanical machinability, weldability has a negative impact.
2.Si-Silicon
Advantages: Enhanced hardening ability, abrasion resistance, improved elasticity limit.
Disadvantages: Reduced electrical conductivity, toughness, thermal conductivity, polishability.
3.Mn-Manganese
Advantages: smelting deoxidizing effect, easy to combine with sulfur to synthesize manganese sulfide, improve cutting performance, help to improve the yield point and tensile strength.
4.P-Phosphorus
Disadvantages: The curing process of the ingot is prone to cause coarse segregation and secondary segregation during stress annealing after forging, which seriously affects the homogeneity of the material. Increased temper brittleness, poor toughness, low forging ratio.
Its non-negative effects: Phosphorus P in Wolstadt iron-based stainless steels, which can increase the yield point strength and contain chromium (Cr) and nickel (Ni) in the precipitation hardening process contributes to the diffusion strengthening effect.
5.S-Sulphur
Disadvantages: Sulfur in iron to form iron sulfide leads to easy segregation in the copper ingot curing process, seriously affecting the hot forging molding of the mesh sulfide ring surrounded by grain boundaries. Sulfur easily combines with manganese to form manganese sulfide, which is an impurity that affects purity, reduces the material’s firmness, combines poorly with soldering, and cracks easily. Poor mirror polish, poor etching uniformity, easy to have hairline emerging spots on the surface of the mold, and surface plating such as hard chrome plated (Chard chromiurm plated) and chemical (Electroless Ni-plated) affects its coating effect.
6.Cr-Chromium
Improve hardening ability (oil or air cooling), easy to form Martensite organization, too high content has negative effect on impact strength (toughness). Chromium carbide (M7C3) is easily formed with carbon, which improves wear resistance, increases toughness, resists hydrogen embrittlement, and is resistant to contact (stainless steel system) at a Chromium (Gr) content of 13% or more. Excessive chromium content reduces thermal conductivity, electrical conductivity, polishability, electrical discharge and chemical etching effects.
7.Ni-Nickel
Nickel does not eutectic with carbon to form carbide, is a single alloying element, with good touch resistance, easy to polish, not easy to bite flower etching, improve toughness, 600 ° C or more resistance to high-temperature corrosion of touch and high-temperature strength (ductility is good), cutting is not good, easy to stick the knife, not easy to chip removal, low thermal expansion and low heat conduction.
8.Mo-Molybdenum
Molybdenum is mostly involved in solidification with other alloys to form alloy carbides (M6C), strengthen the base hardness and improve the hardening ability in the hot work steel with temper softening resistance, corrosion resistance, high temperature resistance to hot melting and hot stamping, resistance to temper brittleness, and to increase the yield strength and tensile strength. It is used in high speed steel (M-35, M-42, M-45, M-50, M-52) to improve cutting performance and high temperature strength.
9.V-Vanadium
Vanadium in the secondary refining of additives, in the solidification process of the ingot to inhibit grain coarsening, strengthen the formation of carbides, in the subsequent heat treatment of Wolstad ferrofluidization time to be sufficient to participate in solidification, in order to improve the solidification ratio of the carbide, the efficacy of the grains are not easy to coarsen, and to achieve the ultimate hardening performance.
The carbide hardness of vanadium carbide (MC) is HV 2600~3200, and has a high degree of adhesion resistance and general wear resistance, tempering softening resistance and good high source of strength, cutting tool edge toughness (not easy to chipping).
10.W-Tungsten
Tungsten is also strengthened carbide formation of the main elements, its carbide (MC) hardness up to HV: 2250 ~ 3200 can improve the hardening capacity, red hot hardness, high temperature strength, tempering softening resistance is generally added to the hot steel and high-speed steel, hysteresis ability, saturation of the magnetic properties of the strong, there is a use of magnetic materials added.
11.Co-Cobalt
Cobalt does not participate in carbon eutectic, so it does not form carbide. Inhibit grain growth at high temperature, good ability to maintain high temperature hardness, good resistance to high temperature strength and high temperature thermal wear. Improve the hardening ability and strengthen the base hardness and potential strength. It also has good magnetizing ability and thermal conductivity, and is used in high-grade magnetic materials and alloys.
12.Nb-Niobium
Enhanced carbide formation, increased base hardness and resistance to chemical attack, high-temperature strength, latent strength, increased fracture toughness and wear resistance. In recent years, cold work tool steels have been supplemented with trace amounts of Niobium (Nb) to improve their mechanical properties.
