Materials Science Chapter 2

Chapter 2: Nature of Materials

• Spreading salt on ice causes the ice to melt due to the lowering of the freezing point of water
  • At a salt composition of 10%, the temperature at which ice will start melting is lower than 0°C
  • The eutectic temperature of the ice and salt combination is the lowest temperature at which the mixture will freeze
• Ceramic materials are classified into five classes
• Two common ceramic materials used in Civil Engineering structures are
  • Not specified in the text, but examples include brick, concrete, and ceramics
  • They are inorganic solids
• The four types of organic solids used in engineering applications are
  • Not specified in the text, but examples include polymers, plastics, and rubbers
• Properties of 15 metals, including lead, zirconium, sodium, and others, can be found in a table
  • Properties include crystal structures, atomic radius, atomic mass, and atomic packing factor

Chapter 3: Steel

Steel Production

• Steel production involves three phases: reducing iron ore to pig iron, refining pig iron to steel, and forming the steel into products
• The materials used to produce pig iron are coal, limestone, and iron ore
• The iron is magnetically extracted from the waste, and the extracted material is formed into pellets and fired
• Reduction of the ore to pig iron is accomplished in a blast furnace
• The molten iron, with an excess of carbon in solution, collects at the bottom of the furnace

Iron-Carbon Phase Diagram

• The iron-carbon phase diagram shows the relationship between steel properties and carbon content
• The diagram extends only to 6.7% carbon, which corresponds to 100% iron carbide
• Pure iron undergoes two transformations as temperature increases: ferrite (BCC) to austenite (FCC) at 912°C, and austenite to delta ferrite (BCC) at 1394°CHere are the study notes in markdown format:

Iron-Carbon Phase Diagram

• Carbon goes into solution with ferrite at temperatures between 400°C and 912°C
• Solubility limit is very low, with a maximum of 0.022% at 727°C
• At temperatures below 727°C, ferrite and iron carbide coexist as two phases
• From 727°C to 1148°C, solubility of carbon in austenite increases from 0.77% to 2.11%

Eutectoid Reaction

• Occurs when carbon content is 0.77% and temperature is 727°C
• Results in formation of pearlite, a two-phase material consisting of ferrite and iron carbide
• Ferrite has 0.022% carbon, and iron carbide has 6.7% carbon
• Forms as thin plates, with a lamellae structure

Hypoeutectoid and Hypereutectoid Alloys

• Hypoeutectoid alloys: carbon content less than 0.77%, formed below 727°C
• Hypereutectoid alloys: carbon content greater than 0.77%, formed above 727°C

Properties of Steel

• Ferrite has low strength but is ductile
• Iron carbide has high strength but is brittle
• Combining ferrite and iron carbide in different proportions alters mechanical properties of steel
• Increasing carbon content increases strength and hardness, but reduces ductility
• Modulus of elasticity of steel does not change with carbon content

Heat Treatment of Steel

• Annealing: refines grain, softens steel, removes internal stresses, and increases ductility
• Normalizing: similar to annealing, but with faster cooling rate
• Hardening: heating above transformation range, then quenching to form martensite
• Tempering: heating to improve ductility and toughness of hardened steel

Steel Alloys

• Alloying agents can improve hardenability, corrosion resistance, machinability, ductility, and strength
• Examples of alloying agents include aluminum, sulfur, chromium, nickel, copper, manganese, silicon, molybdenum, and vanadium

Structural Steel

• Used in hot-rolled structural shapes, plates, and bars

• ASTM specifications define grades, types, and classes of structural steel

• Examples of structural steel grades include ASTM A7 and ASTM A992### Steel Classification and Properties

• ASTM steel specifications identify the yield strength, while in other specifications, the term grade indicates requirements for both chemical compositions and mechanical properties.

• The Unified Numbering System (UNS) is based on chemical composition, using a letter to identify the broad class of alloys and a five-digit number to define specific alloys within the class.

• Table 3.2 summarizes the designations, properties, and composition of ASTM structural steel.

Steel Types and Applications

• A36, A53 Gr.B, A500, A501, A529, A572, and A618 are types of structural steel used in various applications.
• High-strength low-alloy steel is used for structural applications, such as bridges and buildings.
• Corrosion-resistant steel is used for structural applications exposed to environmental factors.

Sectional Shapes

• W, HP, M, S, C, MC, and L shapes are commonly used in structural applications.
• Figure 3.9 illustrates these structural cross-sectional shapes.
• Shapes are designated by a letter, followed by two numbers separated by an asterisk, indicating the nominal depth and weight per linear unit length.

Specialty Steels

• High-performance steels (HPS) are special products with optimum combinations of properties required for cost-effective, safe, and durable structures.
• HPS 50W and HPS 70W are weathering steels with corrosion barriers that reduce maintenance needs.
• HPS 70W has stronger tensile properties than traditional steel used for bridge construction, allowing for reduced material usage.