carbon steel and plastics examples

Low carbon steel (0.07-0.15%C)

• Automobile body parts

• Wire and wire products (nails and rivets)

Mild carbon steel (0.15-0.3%C)

Structural plates and sections, stampings, forging, seamless tubes, boiler plates

Medium carbon steel (0.3-0.6%)

• forgings and automotive components including:

  • Shafts

  • axles

  • gears

  • crankshafts

High carbon steel (0.6-1.25%C)

• high strength spring materials and wires

• Cutting tools

• Punches

• Dies

• Industrial knives

Ultra high carbon steel (1.25-2%C)

• highly tempered non-industrial purpose knives, punches and axles

Explain how the chemical composition of mild carbon steel contributes to its mechanical properties in the context of two industrial applications

Mild-carbon steel is a hypoeutectoid alloy (meaning it contains less carbon than the eutectoid composition of 0.76%), containing approximately 0.15-0.3% carbon. This low carbon content results in a microstructure dominated by ferrite with small regions of pearlite. Ferrite is a soft, ductile phase of iron, while pearlite is a lamellar mixture of ferrite and cementite (Fe3C) that provides moderate strength. Because mild-carbon steel contains a high proportion of ferrite and limited cementite, it exhibits high ductility and toughness but low hardness and strength compared to higher-carbon steels.

These mechanical properties make mild carbon steel suitable for industrial applications where formability and impact resistance are important. For example, it is used ins tructural plates and sections that require good ductility for shaping and welding and in seamless tubes or boiler plates, where toughness and resilience under repeated loading at room temperature make it a reliable material for pressurised or structural environments.

Explain how the chemical composition of medium carbon steel contributes to its mechanical properties in the context of two industrial applications

Medium carbon steel is a hypoeutectoid alloy with a carbon content of approximately 0.30-0.60%. This higher carbon content compared to mild steel produces a microstructure with less ferrite and a greater proportion of pearlite, where pearlite is a lamellar structure of soft, ductile ferrite and hard, brittle cementite (Fe3C).

The increased cementite content in medium carbon steel improve strength, hardness and wear resistance making it suitable for applications under impact or rubbing forces. The remaining ferrite in the structure still provides moderate ductility and toughness, allowing the material to absorb repeated loading without failure.

These properties make medium carbon steel ideal for mechanical components such as axles, gears and crankshafts, which require high strength for heavy loads, surface hardness for resistance to wear, and resilience under cyclic stresses, especially in high-temperature or dynamic environments like gearboxes and engines.

Explain how the chemical composition of high-carbon steel contributes to its mechanical properties in the context of two industrial applications

High-carbon steel contains approximately 0.60–1.25% carbon and may be classified as either a hypoeutectoid or hypereutectoid alloy, depending on its exact carbon content. In hypereutectoid steel, the microstructure at room temperature consists of very strong pearlite and additional cementite at the grain boundaries, with very little ferrite present. Pearlite is a lamellar structure of ductile ferrite and hard, brittle cementite (Fe₃C).

The high carbon content increases the cementite fraction, which significantly improves the strength, surface hardness, and wear resistance of the steel. These properties make it suitable for applications under repeated heavy loading, friction, or impact. However, the reduced ferrite content results in lower ductility and toughness, meaning the steel is more brittle and less resistant to fracture under shock loads.

Despite this trade-off, high-carbon steel is ideal for high-strength spring materials, cutting tools, and industrial punches or knives, where very high strength, hardness, and wear resistance are essential, even if some ductility is sacrificed.

Polyethylene (PE, LDPE, HDPE, PETE, PET)

Plastic containers

Water pipes

Cable insulation

Polypropylene

Laboratory equipment

Electronics products

Automobile products

Polypropylene characteristics

Resists corrosion and chemicals.

Impermeable, electrical insulator

ABS

Automotive body parts (bumper bars)

Household electronics and electrical appliances

Business equipment

PLA

Biodegradable food containers

Medical impants

Automobile interiors

PVC

Automobile parts

Electronics and electrical equipment

Water/waste drainage pipe

Furniture

Nylon

Gears

Rollers and guides

Bearings

Wear pads

ABS characteristics

Flexible

Strong

Impact resistant

Cheap

PLA characteristics

100% biodegradable

High tensile strength and ductility

PVC characteristics

durable, good chemical resistance. Excellent electrical insulation.

Nylon characteristics

Very sturdy material

Very high wear and abrasion resistance

High tensile and compressive strength

One of the most durable plastics

Fire resistant but easily melts

Hygroscopic (absorbs water)