Properties and Applications of Industrial Metals

Posted on Jan 31, 2025 in Electromechanical Engineering

Tool Steels

Tool steels are used for manufacturing equipment or tools utilized in the transformation of other materials, such as molds, shears, and dies. They are alloyed with elements that provide hardenability and/or form carbides (Cr, Mo, V, W, etc.). Depending on the type and percentage of alloying elements and heat treatment, they are classified into different groups: hot work, cold work, and high-speed steels. In many cases, they are nitrided.

Stainless Steel

Stainless steels exhibit high resistance to corrosion, making them suitable for applications in aggressive media like marine environments, kitchen utensils, and the chemical industry. The main alloying element is chromium (Cr > 12%).

Depending on the type and percentage of alloying elements, they are divided into different groups: Austenitic, Ferritic, Martensitic, Duplex, and Precipitation-Hardening (P-H).

  • Corrosion Resistance: Martensitic < Ferritic < Austenitic < P-H < Duplex
  • Mechanical Properties: Austenitic < Duplex < Ferritic < P-H < Martensitic

Cast Iron

Cast iron is used in manufacturing parts with complex shapes due to its capability to be cast, such as hoods, engine blocks, brake discs, and machine tool beds. It has a lower melting temperature (1100-1200°C) compared to steel (1500-1600°C). All cast irons contain graphite, which provides the following properties compared to steels:

  • Low shrinkage
  • Vibration damping
  • Good sliding properties: Ideal for tool machine guides
  • Good machinability: Graphite acts as a solid lubricant
  • Bad weldability: Welding is not recommended

Depending on the morphology of graphite (flake or spheroidal), cast irons exhibit different properties.

Grey Cast Iron

  • Graphite: Flake (in sheets), interconnected
  • Low mechanical resistance (100-350 MPa)
  • Low hardness (140-280 HB)
  • Low resilience
  • High thermal conductivity: Suitable for brake discs
  • Good machinability
  • Bad weldability: Welding is not recommended

Ductile Cast Iron

  • Graphite: Spheroidal, not interconnected
  • Higher strength than grey cast iron, comparable to many steels (350-900 MPa)
  • Better resilience than grey cast iron
  • Suitable for security parts, such as brake calipers
  • Medium thermal conductivity, similar to that of steels
  • Good machinability
  • Bad weldability: Welding is not recommended

Cast Aluminum

Cast aluminum is adequate for producing complex shapes due to its good castability, making it suitable for frameworks, motor blocks, and rears. It has lower strength and greater brittleness than wrought alloys but is more cost-effective. The most employed alloys are Al-Si.

Wrought Aluminum

From low to high strength:

  • Series 3000
  • Series 5000
  • Series 6000 (age-hardened)
  • Series 2000 (age-hardened)
  • Series 7000 (age-hardened)

Magnesium

Advantages

  • Low density (ρMg = 1.738 g/cm3, ρAl = 2.7 g/cm3, ρSteel = 7.8 g/cm3)
  • Easy to form stable protective oxide coatings
  • 8th most abundant element
  • Low volumetric specific heat (cools faster, casting cycles shorter) (cMg = 1.030 J/kgK, cAl = 880 J/kgK, cSteel = 460 J/kgK, cZn = 390 J/kgK)
  • Good machinability
  • Low melting point = 650°C; no need for high energy to be cast
  • Some alloys can be strengthened by heat treating

Drawbacks

  • Not found in metallic form in nature
  • Difficult to deform (hexagonal close-packed crystal structure)
  • All extraction processes require installations for cleaning off-gases and treating wastewater, making it expensive (2.85 €/g)
  • Highly flammable
  • Alloys that obtain good corrosion resistance have other bad properties
  • Low Young’s modulus (stiffness): 45 GPa; for Aluminum: 70 GPa
  • Corrosion resistance: It forms an oxide layer, but this doesn’t prevent corrosion; parts must be coated.
  • The best corrosion-resistant alloys have the worst mechanical properties

Applications

  • Industrial applications: Electronic devices, aerospace, automotive industry, agriculture, industrial chemicals, industrial furnaces, construction, etc.
  • Due to its excellent mechanical resistance, it is used in applications where the weight of the part is a fundamental factor (helicopter gearboxes, aircraft components, etc.)
  • Other applications: Magnesium-based alloys (pressure die casting, structural applications, numerous lightweight applications like automotive, hand tools, computers, etc.)