Some examples of magnetic and non-magnetic steels

1. Magnetic Steels

These steels exhibit ferromagnetism (strong attraction to magnets, ability to retain magnetism) due to their body-centered cubic (BCC) crystal structure (stabilized by iron-rich compositions, low nickel, and specific heat treatment).

A. Carbon Steel (Plain Carbon Steel)

• Key Examples:
  • 1018 Steel (low carbon: 0.18% C)
  • A36 Steel (mild carbon: 0.25-0.29% C)
  • 1045 Steel (medium carbon: 0.45% C)
  • C1095 Steel (high carbon: 0.95% C)
• Why Magnetic: Carbon atoms are small enough to fit into iron’s BCC lattice without disrupting magnetic domain alignment.
• Applications:
  • 1018 Steel: Machinery parts (bolts, shafts), automotive brackets, and sheet metal.
  • A36 Steel: Construction beams, bridges, and structural framing (the “workhorse” of building materials).
  • 1045 Steel: Gear shafts, axles, and hydraulic components (balances strength and ductility).
  • C1095 Steel: Knife blades, springs, and piano wire (high hardness from carbon content).
• Test Tip: A fridge magnet will stick firmly to all these—try a common nail (1018) or a steel I-beam (A36).

B. Ferritic Stainless Steel

• Key Examples:
  • 430 Stainless Steel (16-18% Cr, <0.75% Ni)
  • 409 Stainless Steel (10.5-11.75% Cr, <0.5% Ni)
  • 444 Stainless Steel (17-19% Cr, 1.75-2.5% Mo, <0.5% Ni)
• Why Magnetic: High chromium content (no nickel) stabilizes the BCC ferrite structure, preserving iron’s ferromagnetic traits. Corrosion-resistant but less durable than austenitic grades.
• Applications:
  • 430 Steel: Kitchen sinks, dishwasher tubs, automotive trim, and appliance panels (affordable, rust-resistant for household use).
  • 409 Steel: Exhaust systems, catalytic converters, and marine hardware (resists high temperatures and exhaust gases).
  • 444 Steel: Chemical storage tanks, water heaters, and desalination equipment (enhanced corrosion resistance from molybdenum).
• Test Tip: A magnet will cling strongly to a 430 stainless steel kitchen spoon or a car’s exhaust pipe.

C. Martensitic Stainless Steel

• Key Examples:
  • 410 Stainless Steel (11.5-13.5% Cr, <0.6% Ni)
  • 420 Stainless Steel (12-14% Cr, <0.75% Ni)
  • 440C Stainless Steel (16-18% Cr, 0.5-1.0% Mo, <0.75% Ni)
• Why Magnetic: Heat treatment (quenching and tempering) transforms the structure into BCC martensite, which is ferromagnetic. Harder and more wear-resistant than ferritic grades.
• Applications:
  • 410 Steel: Valve stems, pump parts, and industrial fasteners (balances strength and corrosion resistance).
  • 420 Steel: Surgical scissors, hunting knives, and food processing blades (sharp, easy to sanitize).
  • 440C Steel: High-end cutlery (e.g., some kitchen knives), ball bearings, and aerospace components (extreme hardness and edge retention).
• Test Tip: A magnet will stick to a 420 stainless steel pocket knife or surgical forceps.

2. Non-Magnetic Steels

These steels are primarily austenitic stainless steels, which have a face-centered cubic (FCC) crystal structure (stabilized by nickel and chromium). The FCC structure prevents magnetic domain alignment, resulting in paramagnetism (weak, temporary attraction to strong fields only).

A. Austenitic Stainless Steel (Most Common Non-Magnetic Steels)

• Key Examples:
  • 304 Stainless Steel (18-20% Cr, 8-12% Ni)
  • 316 Stainless Steel (16-18% Cr, 10-14% Ni, 2-3% Mo)
  • 321 Stainless Steel (17-19% Cr, 9-12% Ni, titanium-stabilized)
  • 347 Stainless Steel (17-19% Cr, 9-13% Ni, niobium-stabilized)
• Why Non-Magnetic (Annealed State): Nickel (8-14%) stabilizes the FCC structure, where iron atoms are arranged too tightly for magnetic dipoles to align uniformly.
• Critical Note: Cold working (bending, stamping, rolling) can create tiny martensite regions, leading to weak, temporary magnetism (e.g., a bent 304 stainless steel bracket may slightly attract a magnet). This fades if the steel is annealed (heat-treated to restore FCC structure).
• Applications:
  • 304 Steel: Food processing equipment (stainless steel bowls, sinks), chemical tanks, and architectural cladding (the most widely used stainless steel globally).
  • 316 Steel: Marine hardware (boat railings, propellers), medical implants (screws, plates), and pharmaceutical equipment (resists saltwater and harsh chemicals via molybdenum).
  • 321 Steel: Jet engine components, furnace parts, and high-temperature pipelines (titanium prevents corrosion at 800-1000°C).
  • 347 Steel: Nuclear reactors and pressure vessels (niobium enhances stability under extreme heat and radiation).
• Test Tip: A standard fridge magnet will NOT stick to an annealed 304 or 316 steel object—try a new stainless steel cooking pot, a hospital grade surgical tray, or a boat’s 316 stainless steel railing.

B. Other Non-Magnetic Alloys (Specialty Steels)

• Example: 2205 Duplex Stainless Steel (austenitic-ferritic hybrid: 21-23% Cr, 4.5-6.5% Ni, 2-3% Mo)
  • Magnetic Trait: Weakly magnetic (ferrite phase contributes slight attraction, but austenite dominates). Often classified as “low-magnetic” for applications where magnetism must be minimized.
  • Application: Offshore oil rigs, desalination plants, and chemical processing (combines high strength and corrosion resistance).

Category	Examples	Magnetic?	Key Trait	Common Use Case
Carbon Steel	1018, A36, 1045	Yes	Iron-carbon alloy (BCC structure)	Construction beams, bolts
Ferritic Stainless	430, 409	Yes	High Cr, low Ni (BCC ferrite)	Kitchen sinks, exhaust pipes
Martensitic Stainless	410, 420, 440C	Yes	Heat-treated BCC martensite	Knife blades, surgical tools
Austenitic Stainless	304, 316, 321	No (annealed)	High Ni/Cr (FCC austenite)	Food equipment, medical implants
Duplex Stainless	2205	Weakly	Austenitic-ferritic hybrid	Offshore structures

Practical Takeaway

The easiest way to identify magnetic vs. non-magnetic steel is with a simple magnet:

• Sticks firmly: Carbon steel, 430/410 stainless steel (magnetic).
• No stick (or weak stick): 304/316 stainless steel (non-magnetic, unless cold-worked).

These examples highlight how steel’s magnetic behavior is engineered for specific needs—from magnetic rebars (A36) that enable structural inspections to non-magnetic 316 implants that avoid MRI interference.