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Steel

Properties of Materials- Chapter 3

QuestionAnswer
Steel's origins Melting of steel using charcoal (1500 BC)
Types of Steel • Structural Steel (Beams, columns, pipes, bars, plates, etc) • Fastening products (Connections like bolts, nuts, washers, etc) • Reinforcing steel “rebar's” (for concrete reinforcing) • Others (structuralforms, pans, etc)
Why civil engineers should study steel as a material? Civil engineers are not responsible for the production of steel, but it is highly important for them to understand the properties of steel that can affect it’s behavior as a structural element.
Basic material required in production: • Iron Ore: Pig iron. • Coal (Coke)(Carbon): To produce iron oxides in the ore. • Limestone: Removes impurities
Cast Iron characteristics High carbon Brittle behavior Products are shaped by casting Relatively low tensile strength
Steel characteristics Low carbon content Ductile behavior Products are shaped by rolling, hammering, stretching Higher tensile strength
Steel Heat Treatment purpose Altering steel properties (hardening, softening, surface treatment, etc.)
Types of Heat treatment Annealing, normalizing, hardening, tempering
Annealing heat treatment Objectives: • Refine grains • Soften steel • Remove internal stress • Remove gases • Increase durability & toughness • Change electrical & magnetic properties
Normalizing heat treatment Same as annealing except a different rate of cooling is used to produce a uniform fine grained microstructure. Example: Structural plates.
Hardening heat treatment Cooling at a faster rate to produce a very hard and brittle material (ex: camshaft for carrying torque to rear car wheels)
Tempering heat treatment Transforming steel with undesirable brittleness to more ductile and tough steel through heating and cooling to about 40 °C followed by reheating through immersion in oil or nitrate salts. Example: Structural beam in a building
Steel Alloys Definition: Additives (materials, agents) added to steel to improve its characteristics. Properties improved: • Hardibility. • Corrosionresistance. • Mechanicability. • Ductility. • Strength.
Types of steel alloys • Low alloy: ex. High strength alloy steel • High alloy: ex. Stainless steel Note: Steel in construction are predominantly low (& medium) carbon plain steel.
Structural steel Hot-rolled structural elements (plates, bars)
How is Steel identified? – Grade: Chemical composition or yield strength or mechanical properties. – Type – Class
What is special steel (high performance steel)? Combination of materials that possess the optimum combination of material properties required to build a cost effective structure that will be safe and durable throughout their service life.
Fastening Product Bolts • Nuts • Washers • Rods
Reinforcing steel Used in cement concrete for the purpose of carrying tensile stresses since concrete has negligible tensile strength
Types of reinforcing steel • Conventional reinforcing steel • Pre‐stressed reinforcing steel
Forms of reinforcing steel • • • Plain bars Deformed bars: Good bond preventing slippage in beams & columns Wire Fabric: Economical for concrete slabs & pavements
Tension Test Determines: • Yieldpoint • Ultimate strength • Elongation • Reduction in area
Impact Test Determines: • Toughness of material
Hardness Test Determines: • Resistance of material to localized plastic deformation (dents or scratches)
Steel Tests Tension, torsion, impact, bend, hardness
Corrosion Destruction of material by electrochemical reaction to the environment (Ex: formation of rust)
What is required for corrosion to occur? • Two side electrode • Medium to move • Liquid to support the movement of electrons
How to prevent corrosion? • Barrier coating • Inhibitive primer coating • Sacrificial primers (Zinc coating)
Created by: smh02