Alloying Elements in Tool Steels for Molds

Mold steel is a type of tool steel used to manufacture various forming tools, including cold work, hot work, and plastic mold steels.

What elements are used to manufacture mold steel?

Major Alloying Elements: Carbon (C), Silicon (Si), Manganese (Mn), Phosphorus (P), Sulfur (S), Nickel (Ni), Chromium (Cr), Molybdenum (Mo), Aluminum (Al), Tungsten (W), Vanadium (V), Cobalt (Co).
Minor Alloying Elements: Titanium (Ti), Niobium (Nb), Copper (Cu), Aluminum (Al).
Non-metallic Elements: Nitrogen (N), Boron (B).

Effects of Various Alloying Elements on Mold Steel

1. Carbon
It is the main alloying element, increasing hardening properties and wear resistance. Compared with other alloys, carbides are formed after austenite solid solution during hardening treatment. Alloys with high carbon content are more likely to cause deviation during steel casting, resulting in coarse carbides, which have a negative impact on toughness, ductility, machinability and weldability.

2. Silicon (Si)
Advantages: Enhanced hardening ability, wear resistance, and improved elastic limit.
Disadvantages: Reduced electrical conductivity, toughness, thermal conductivity, polishability.

3. Manganese (Mn)
Advantages: Deoxidation effect in smelting, easy to combine with sulfur to form manganese sulfide, improve machinability, help to improve the yield point and tensile strength.

4. Phosphorus(P)
Disadvantages: The solidification process of the steel ingot easily leads to coarse segregation and secondary segregation during stress annealing after forging, which seriously affects the homogeneity of the material. Increased temper brittleness, poor toughness and low forging ratio.

Non-negative effects: In Austenitic stainless steel, phosphorus can improve yield strength and assist in the precipitation-hardening process with nickel and chromium.

5. Sulphur (S)
Disadvantages: Sulfur forms iron sulfide with iron, which makes it easy to segregate during the solidification process of the copper ingot, seriously affecting the network sulfide surrounding the grain boundary during hot forging. Sulfur easily combines with manganese to form manganese sulfide, which is an impurity that affects the purity, reduces the toughness of the material, has poor welding adhesion, and is also prone to cracking. The mirror polishing is poor, the texture etching uniformity is poor, and hair-like spots are easy to appear on the mold surface. The surface coating such as Chard chromiurm plated and Electroless Ni-plated affect its coating effect.

6. Chromium (Cr)
Increasing the hardening energy (oil cooling or air cooling) can easily result in too high a Martensite content, which has a negative impact on impact strength (toughness). It easily forms chromium carbide (M7C3) with carbon, which improves wear resistance, increases toughness, and resists hydrogen embrittlement. It has touch resistance (stainless steel series) when it contains more than 13% chromium (Gr). Too high chromium content will relatively reduce thermal conductivity, electrical conductivity, polishability, and the effect of discharge scratching and chemical etching.

7. Nickel(Ni)
Nickel does not form carbides with carbon eutectic and is a single alloying element. It has good touch resistance, is easy to polish, is not prone to scratching and etching, has improved toughness, has high temperature corrosion resistance and high temperature strength above 600°C (good ductility), has poor machinability, is easy to stick to the tool, is not easy to remove chips, has low thermal expansion and low thermal conductivity.

8. Molybdenum(Mo)
Molybdenum is usually dissolved in solid solution with other alloys to form alloy carbides (M6C), which strengthen the base hardness and improve the hardening ability. In hot working steel, it has resistance to temper softening, corrosion resistance, high temperature heat melting and thermal erosion, resistance to temper brittleness, and improves yield strength and tensile strength. Improve machinability and high temperature strength of high speed steel (M-35, M-42, M-45, M-50, M-52). 8.

9. Vanadium(V)
Vanadium is added during secondary refining to inhibit grain coarsening during the solidification process of the steel ingot and strengthen the formation of carbides. In the subsequent heat treatment, the austenitic ironization time must be sufficient to participate in the solid solution to increase the solid solution ratio of carbides, prevent grain coarsening, and achieve its ultimate hardening ability.
The carbide hardness of vanadium carbide (MC) is HV 2600~3200, and it has high resistance to adhesion and general abrasive wear, resistance to tempering softening and good high-energy strength, and good cutting tool edge toughness (not easy to chip corners)

10. Tungsten (W)
Tungsten is also the main element for strengthening carbide formation. The hardness of its carbide (MC) can reach HV: 2250~3200. It can improve hardening energy, red-hot hardness, high-temperature strength, and resistance to temper softening. It is generally added to hot steel and high-speed steel. It has hysteresis ability and strong saturation magnetism, and is used to be added to magnetic materials.

11. Cobalt(Co)
Cobalt does not participate in the carbon eutectic and therefore does not form carbides. Inhibits grain growth at high temperatures, has good high temperature hardness maintenance capability, and has good high temperature strength and high temperature thermal wear resistance. Improve hardening ability and strengthen base hardness and creep strength. It also has excellent saturation capacity and thermal conductivity and is used in advanced magnetic materials and alloys.

12. Niobium (Nb)
Strengthen carbide forming ability, increase base hardness and resist chemical corrosion, have high temperature strength and creep strength, improve fracture toughness and wear resistance. In recent years, trace amounts of niobium (Nb) have been added to cold work tool steels to improve their mechanical properties.