Knowledge

Molybdenum (Mo)

Molybdenum is a white malleable metal. Mo powder can be obtained by reducing the oxide of molybdenum with carbon, and then pressed into blocks, sintered and forged. The melting point of molybdenum is as high as 2620°C, which can reduce the tendency of steel to overheat. Molybdenum has high deformation resistance and, like nickel, can promote the distribution of sulfides in a pasty form on the grain boundaries. According to Goodrich's data, when the molybdenum content in molybdenum steel exceeds 1%, and according to Dumas' data, when it exceeds 3-4%, a brittle substance of fog-like (μ phase) molybdenum dioxide (MoO₂) will decompose at forging temperature. Molybdenum steel containing 0.7% C and 2-15% Mo has no special difficulty in hot working deformation. These steels can be quenched when cooled in air, and it is necessary to pay attention to prevent the formation of cracks during cooling.                                               

Tungsten (W)

Tungsten is a strong carbide-forming element that forms stable tungsten carbide WC (containing 6.1% C) and W₂C with carbon.

Tungsten has a very high melting point (3370°C) and a hardness slightly lower than that of chromium. Pure tungsten is also easy to forge. Tungsten does not affect forgeability in a hot state, but tungsten steel consumes more energy and has higher deformation resistance during forging.                                                

Vanadium (V)

Vanadium is a grayish-white malleable metal with a melting point of 1720°C. Vanadium can promote the formation of fine-grained structures in steel, thereby enhancing its ductility. For instance, high-speed steel containing 3 to 5% vanadium and 18% tungsten can be forged smoothly even when the carbon content exceeds 1.5%.                                                

Copper (Cu)

Once copper enters steel, on the one hand, it dissolves in ferrite; on the other hand, it may also precipitate along the grain boundaries, existing as free copper. When the copper content in steel is less than 0.4%, the steel's electrical resistance increases with the increase of its solubility in the ferrite solid solution. Additionally, when steel contains 0.15 to 0.25% copper, it can enhance the steel's resistance to atmospheric corrosion. If copper is added to stainless steel, it can also increase its resistance to acid corrosion. When forging at 1050°C, even if the copper content in the steel is around 0.2%, surface cracking may occur due to the oxidation of the steel surface, with the result that the free copper beneath the oxide layer melts.                                                  

Boron (B)

Boron can refine the grains of steel, dissolve in γ and α solid solutions, and react with iron to form Fe₂B. This boron iron compound remains stable even at high temperatures.

Adding a very small amount of boron (about 0.002%, or 20 grams per ton of steel) to steel can increase the hardenability depth by 1.5 to 5 times and improve the mechanical properties of the steel. However, when the boron content in steel exceeds 0.005 or 0.007%, it can cause processing cracks during high-temperature forging.                                                  

Sulfur (S)

Sulfur has an extremely adverse effect on the plasticity of steel. It exists in steel in the form of compounds and eutectics.

Sulfur in steel can form various sulfides, such as FeS, MnS, (FeS·MnS), CrS, MoS₂, ZrS₂, TiS, NiS, CoS, and other compounds. The most harmful form in steel is the low-melting-point eutectic of FeS·Fe (melting point 950°C), which forms a network distribution around the primary grains.

Steel with a higher sulfur content can withstand plastic deformation when forged at white-hot temperatures of 1000~1200°C. The reason is that intense annealing at high temperatures can eliminate the network distribution of iron sulfide.                                                 

Phosphorus (P)

Phosphorus is one of the elements that cause severe segregation in steel. It diffuses into ferrite to form a solid solution, promoting grain coarsening and having a significant impact on hot working. It can easily lead to surface cracking and cracking in castings. In steels containing phosphorus and nitrogen:

When P > 0.06%, the nitrogen content should be N < 0.012%.

When N > 0.16% and P > 0.045%, the steel becomes sensitive to aging and fracture.

 

If you have any question, demand, new parts need to be developed or improve your supply chain, please feel free to contact us info@castings-forging.com