Metallurgy

Understanding metal structure and properties:

Crystalline Structure:

Crystal Systems:
- Face-centered cubic (FCC): Aluminum, copper, nickel
- Body-centered cubic (BCC): Iron (ferrite), chromium
- Hexagonal close-packed (HCP): Titanium, magnesium

Why Structure Matters:
- FCC: Generally ductile, good formability
- BCC: Higher strength, less ductile
- Structure affects: strength, ductility, thermal behavior

Grain Structure:
- Metals are polycrystalline
- Grain boundaries affect properties
- Finer grains = higher strength
- Heat treatment affects grain size

Phase Diagrams:

Iron-Carbon Diagram:
Foundation for steel metallurgy:
- Ferrite: Soft, magnetic, low carbon
- Austenite: FCC, high temperature
- Cementite: Iron carbide, hard
- Pearlite: Ferrite + cementite layers

Key Points:
- Eutectoid (0.76% C, 727C)
- Phase transformations with temperature
- Explains heat treatment response

Other Systems:
- Aluminum-copper (age hardening)
- Copper-zinc (brass)
- Titanium alloys

Mechanical Properties:

Tensile Properties:
- Yield strength (elastic limit)
- Tensile strength (ultimate)
- Elongation (ductility)
- Reduction of area

Hardness:
- Resistance to indentation
- Related to strength
- Brinell, Rockwell, Vickers scales

Toughness:
- Energy absorption
- Impact resistance
- Charpy/Izod testing
- Temperature dependent

Fatigue:
- Cyclic loading failure
- Below static strength
- Endurance limit (steels)
- Design consideration

Modifying properties through thermal processing:

Steel Heat Treatment:

Annealing:
- Heat above transformation, slow cool
- Softens material
- Relieves stress
- Improves machinability

Normalizing:
- Heat above transformation, air cool
- Refines grain structure
- Improves uniformity
- Moderate properties

Hardening:
- Heat to austenitizing temperature
- Quench (water, oil, air)
- Forms martensite (hard, brittle)
- Temperature and time critical

Tempering:
- Reheat hardened steel below transformation
- Reduces hardness and brittleness
- Increases toughness
- Balance properties for application

Hardenability:
- Ability to form martensite
- Jominy end quench test
- Alloy effects
- Section size considerations

Non-Ferrous Heat Treatment:

Aluminum Age Hardening:
- Solution treatment (dissolve precipitates)
- Quench (retain supersaturation)
- Aging (precipitate formation)
- Natural or artificial aging

Common Tempers:
- T4: Solution treated, naturally aged
- T6: Solution treated, artificially aged
- Affects strength and ductility

Titanium:
- Alpha/beta alloy treatments
- Stress relief critical
- Atmosphere protection required

Surface Hardening:

Carburizing:
- Add carbon to surface
- Deep cases possible
- Low-carbon steels
- High surface hardness, tough core

Nitriding:
- Add nitrogen to surface
- Lower temperatures
- Wear resistance
- Minimal distortion

Induction Hardening:
- Selective surface heating
- Rapid quench
- Local hardening
- Good control

Understanding weld zone behavior:

Weld Zones:

Fusion Zone:
- Melted and solidified
- Solidification structure
- Composition from base + filler
- Solidification cracking risk

Heat Affected Zone (HAZ):
- Base metal affected by heat
- Not melted
- Property changes
- Often weakest region

Base Metal:
- Unaffected by heat
- Original properties
- Design basis

Solidification:

Grain Growth:
- Epitaxial growth from base
- Columnar grains toward centerline
- Affects properties and cracking
- Welding parameters influence

Segregation:
- Alloying elements concentrate
- Centerline segregation
- Can cause cracking
- Affected by welding speed

HAZ Issues:

Grain Growth:
- Overheating coarsens grains
- Reduces toughness
- Especially in low-carbon steels

Phase Transformations:
- Similar to heat treatment
- Cooling rate matters
- Martensite possible in HAZ
- Preheat and interpass control

Hydrogen Cracking:
- Cold cracking in HAZ
- Hydrogen from moisture
- Low-hydrogen practices
- Preheat requirements

Material-Specific:

Carbon Steels:
- Carbon equivalent affects weldability
- Preheat above certain CE
- Low-hydrogen essential for higher CE

Stainless Steels:
- Sensitization (carbide precipitation)
- Low carbon grades (L grades)
- Ferrite content for cracking resistance
- Heat input control

Aluminum:
- Porosity from hydrogen
- Hot cracking susceptibility
- Strength loss in HAZ
- Filler metal selection

Nickel Alloys:
- Crack sensitive
- Strict cleanliness
- Low heat input
- Post-weld stress relief

Metallurgy expertise in manufacturing careers:

Career Paths:

Materials Engineer:
Material selection and application:
- Material specifications
- Failure analysis
- Process development
- $75,000-$110,000

Metallurgist:
Deep materials expertise:
- Laboratory analysis
- Process metallurgy
- Research and development
- $70,000-$105,000

Welding Engineer:
Welding and joining:
- Procedure development
- Failure investigation
- Process optimization
- $75,000-$110,000

Quality Engineer:
Materials quality:
- Specification compliance
- Inspection methods
- Material testing
- $65,000-$95,000

Skills Development:

Fundamentals:
- Phase diagrams
- Heat treatment principles
- Mechanical testing
- Welding metallurgy basics

Advanced:
- Failure analysis
- Corrosion mechanisms
- Specialty alloys
- Process metallurgy

Testing Knowledge:
- Tensile testing
- Hardness testing
- Impact testing
- Metallography

Education:

Paths:
- Metallurgical engineering degree
- Materials science degree
- Related engineering with metallurgy focus
- Technical programs with metallurgy courses

Certifications:
- AWS CWI/CWE for welding focus
- ASNT for NDT
- Professional Engineer (PE)

Industries:
- Aerospace (critical materials)
- Automotive
- Power generation
- Oil and gas
- Heavy equipment
- Metal fabrication

Metallurgical knowledge underpins quality and performance across manufacturing.