5B

• Steel is the most suitable building material among metallic material.
• Types of Steel:

  1. Mild Steel
  2. High Carbon Steel
  3. High Tensile Steel
• MILD STEEL

  Also known as low carbon or soft steel. It is ductile, malleable; tougher and more elastic than wrought iron.
• Mild steel is used in the form of rolled sections, reinforcing bars, roof coverings and sheet piles and in railway tracks.
• HIGH CARBON STEEL is also known as hard steel. It is used for reinforcing cement concrete and pre stressed concrete members. It can take shocks and vibrations and is used for making tools and machine parts.
• HIGH TENSILE STEEL is also known as high strength steel and is essentially a medium carbon steel.
• High tensile steel is used in pre stressed concrete construction.
• The carbon content in high tensile steel is 0.6-0.8%, manganese 0.6%, silicon 0.2%, Sulphur 0.05%.
• The carbon content in high carbon steel varies from 0.55 to 1.50%.
• The pressure of carbon in steel gives high degree of hardness and strength.
• Silicon is often added to molten metal to remove oxygen and diminish blow holes. In structural steel, it rarely exceeds 0.25%. Silicon up to 1.75% appears to increase both ultimate strength and elastic limit without decreasing ductility.
• Phosphorus is considered to promote enlargement of the grains and thus produce brittleness. The ductility of low-carbon steel decreases slightly by the presence of 0.3-0.5% phosphorus
• Sulphur readily combines with iron to form iron sulphide (FeS) which, when present in iron or steel, has a tendency to segregate and form brittle networks at the grain boundaries.
• Manganese has a very powerful affinity for sulphur, it is possible to relieve red shortness by adding sufficient quantity of manganese to the molten metal to combine with sulphur.
• Manganese increases the tensile strength, hardenability and dilutes the effect of sulphur.
• Copper increases resistance to corrosion when present in small percentage.
• Arsenic has a tendency to raise the strength and brittleness.
• Non-metallic impurities are mechanically suspended in the metal and are often called slag.
• Heat treatment influences the solubility relations of the constituents, changes the crystallization either with respect to form or degree of aggregation and introduces or relieves internal stresses in the metal.
• Martensite is the chief constituents of hardened steel and is fibrous or needle like structure.
• ANNEALING is a general term used for heating and slow cooling of metal, glass and any other material.
• NORMALIZING consists in heating steel above critical range and cooling rapidly in air, but at rate slower than the critical cooling rate.
• Mechanical working involves many stages of hot working and may or may not include eventual cold working.
• The most important methods of hot working steel are:

  • hot rolling
  • hammer forging
  • hydraulic and mechanical press forging
  • hot extrusion.
• The principle methods of cold working steel are:

  • cold rolling
  • cold drawing
  • cold extrusion.
• The cold working methods are used to provide increased strength, accurate dimensions, and bright and scale free surfaces.
• Surface characteristics of steel bar:

  • Plain
  • Deformed
• PROPERTIES OF GOOD STEEL AND ENHANCING EFFECTIVENESS

  • Carbon content should not exceed 0.25%.
  • Sulphur content should not exceed 0.05%.
  • Phosphorus content should not exceed 0.05%.
  • Low-alloy steel, mechanical strengthening, and heat treatment.
  • Mechanical strengthening methods:
  • Drawing
  • Stretching
  • Twisting
• cold drawing is a process of strengthening steel bars after rolling.
• Mechanical testing steel:

  • Tension Test
  • Torsion Test
  • Charpy V Notch Impact Test
  • Bend Test
  • Hardness Test
  • Ultrasonic Testing
• Test specimens for mechanical test:

  • Bar
  • Tube
  • Wire
  • Flat section
  • Notched bar
• Tension Test determines yield strength, ultimate strength, elongation, and reduction of area. Test performed at temperatures between 10°C and 35°C.
• Torsion Test determines shear modulus of structural materials. Used in the design of members subjected to torsion.
• Charpy V Notch Impact Test is used to measure the toughness of the material or the energy required to fracture a V-notched simply supported specimen.
• The standard specimen in charpy v notch impact test is 55 × 10 × 10 mm with a V notch at the center of one side.
• Bend Test evaluates the ability of steel, or a weld, to resist cracking during bending.
• Hardness Test is a test wherein an indenter is forced into the surface of material with a specified load magnitude and rate of application.
• Rockwell Hardness Test is used for steel surface layers which incorporates 10 kg as its preliminary load and have larger total loads
• Rockwell Superficial Hardness Test is used for very thin steel or thin surface layers which incorporates smaller preliminary and total loads.
• Ultrasonic Testing is a non destructive method for detecting flaws in materials.