MMET 207 Carbon and Alloy System Designation

##xx

percent of carbon

E prefix

electric arc furnace

X prefix

experimental composition

H suffix

meets hardenability requirements (high end of acceptable range for hardenability)

B (middle of number)

Boron in steel

L (Middle of number)

lead in steel (improves machinability by making it softer)

UNS

unified numbering system (ASTM, SAE)

10xx-11xx

Carbon steels

Hot Finishing

worked at elevated temperature till final form (poor surface finish)

Cold Finished

worked at room temp (higher cost, warps when welding due to more pressure)

Weldability of Carbon Steel

>0.3% carbon equivalent, requires preheat and interpass temp control to weld (more carbon makes it harder, more brittle, which the weld will deform)

Carbon Equivalent

each material contributes to the CE, material is 1:1, while others are divided in value (CE = C% + Mn%/6…)

Hardenability

the ability to form martensite, carbon limits hardness of martensite

Aluminum (Alloying Element)

typically less than 2%, restricts grain growth, removes oxygen in steel making, aids nitriding

Sulfur and Phosphorus (Alloying Element)

< 0.5%, adds machinability, reduces weldability, ductility, and toughness

Chromium (Alloying Element)

range 0.3%-4%, increases hardenability, increases resistance to corrosion

Nickel (Alloying Element)

0.3-5%, promotes an austenitic structure, increases hardenability a little bit, increases toughness a lot

Copper (Alloying Element)

0.2-0.5%, not removed during the recycling process, too much will lower impact strength, promotes tenacious oxide film to aid atmospheric corrosion resistance

Manganese (Alloying Element)

0.3-2%, increases hardenability, combines with sulfur to reduce its adverse effects, promotes austenitic structure

Silicon (Alloying Element)

0.2-2.5%, removes oxygen in steelmaking, improves toughness, improves hardenability, improves fluidity of molten metal (lower viscosity)

Molybdenum (Alloying Element)

0.1-0.5%, promotes grain refinement, increases hardenability, improves high-temp strength

Vanadium (Alloying Element)

0.1-0.3%, promotes grain refinement, increases hardenability, forms vanadium carbides

Boron (Alloying Element)

0.0005-0.003%, added in small amount to increase hardenability

Lead (Alloying Element)

>0.3%, added to aid machinability, dangerous

Nitrogen (Alloying Element)

>0.1%, acts like carbon in strengthening

Chromium (Alloying Element)

0.3-4%, increased hardenability, corrosion resistance, flattens the nose

Nickel (Alloying Element)

hardenability, toughness

Erosion

loss of volume in the material