FAQ: Materials and Finishes Guide

Materials

4140 Chromoly Steel

4140 steel (often referred to as "chromoly") is a steel alloy that contains:

  • 0.80–1.10% Chromium (Cr)
  • 0.15–0.25% Molybdenum (Mo)
  • 0.38–0.43% Carbon (C)
  • 0.75–1.00% Manganese (Mn)
  • ≤0.035% Phosphorus (P)
  • ≤0.040% Sulfur (S)
  • 0.15–0.35% Silicon (Si)

This composition gives it exceptional strength, wear resistance, and toughness. When oil quenched and tempered, 4140 can reach a hardness of HRC 28-32 and a tensile strength of approximately 180,000 psi, making it suitable for high-stress applications. However, it has lower inherent corrosion resistance compared to stainless steel and often requires protective coatings to prevent rust. Its machinability is more challenging due to its higher carbon content, necessitating specialized tools and techniques.

416 Stainless Steel

416 Stainless Steel is a martenistic stainless steel which is magnetic and able to be hardened through heat treatment for high tensile and creep strength; however, it has moderate corrosion resistance compared to other stainless steels. It is generally used in applications where high strength and wear resistance are required. 416 Stainless Steel has a composition of:

  • ≤0.15% Carbon (C)
  • 13% Chromium (Cr)
  • ≤1.25% Manganese (Mn)
  • ≤1.0% Nickel (Ni)
  • ≤0.60% Molybdenum (Mo)
  • ≤0.060% Phosphorus (P)
  • ≤1.0% Silicon (Si)
  • ≥0.15% Sulfur (S)

416 Stainless Steel offers the best machinability of all stainless steel. This superior machinability comes from its high Sulfur content, making it especially suitable for high-speed machining operations. 416 Stainless Steel can be heat-treated to a hardness of HRC 26-32.

Finishes

Black Oxide ("Blued")

Black Oxide ("Blued") surface finish is a conversion coating for ferrous materials, stainless steel, copper and copper-based alloys, zinc, and powdered metals. It is used to add mild corrosion resistance. Chemically, black oxide is Fe3O4 (aka, magnetite) while red oxide (aka, rust) is Fe2O3. Hughes Precision uses a hot black oxide coating process which utilizes a hot bath of sodium hydroxide (NaOH), nitrates, and nitrites at elevated temperatures of around 280-290°F to convert the steel surface into black oxide. Fresh black oxide is porous, so oil is applied to the surface of the heated part which seals the porosity.

Unfinished

Just what it says, no finish, leaving the product finishing to you.