Engineering Material - APS

APS, ME
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1. Mechanical Properties of materials

Tensile test: $F-\Delta L​$,Dumbbell

1.1 Elasticity/Stiffness

  • $\sigma_p$ : proportional limit, MPa
  • $\sigma_e$ : elastic limit
  • $E$ : Elastic Modulus, $1.9-2.2\times10^5$MPa
    • $E=\dfrac{\sigma}{\varepsilon}$, $\sigma=\dfrac{F}{S_0}$, $\varepsilon=\dfrac{\Delta L}{L}$
    • stress/strain

1.2 Strength

must at static, anti deformation,fracture

  • $\sigma_s$ : yield strength
    • low-carbon steel : see
    • $\sigma_{r0.2}$high-carbon steel : 0.2% Residual elongation, conditional yield strength
    • out of work condition, the size change
  • $\sigma_b$ : ultimate tensile strength

1.3 Plasticity

  • Elongation /Cauchy strain

    $\delta=\dfrac{L-L_0}{L_0}\times 100\%$

    • 5%

  • Shrinkage of the Section

    $\psi=\dfrac{S_0-S}{S_0}\times100\%$

1.4 Hardness

  • Brinell Scale : HB S/W

    • Soft : low-carbon steel, non-ferrous alloy
    • Hardened steel sphere/ alloy sphere
    • $HB=0.102\dfrac{F}{S}$

  • Rockwell Scale : HR B/C/A, hard to soft

    • 120 degree diamond spheroconical : C/A
    • steel sphere : B

  • Vickers hardness

    • thin, component
    • a right pyramid with a square base136 degree

1.5 Impact test

Impact energy : $A_k=G(H_1-H_2)$

Impact toughness : $a_k=A_k/S$

1.6 Fatigue strength

$\sigma_{-1}$

  • $10^7$ : steel
  • $10^8$ : non-ferrous alloy

2. Metal crystal structure and crystallization

  • crystalline
  • noncrystaliine

2.1 Crystal structure

The atoms/ions/molecule of the crystal are periodically arranged according to a certain geometric law.

  • Ordered sort
  • Anisotropy (Isotropic)
  • fixed melting point

2.2 Unit cell

  • lattice 晶格
  • lattice parameters

  • bode-centered cubic structure, bcc, chromium, alpha-iron(<912 degree)
  • face-centered cubic structure, fcc, copper, gamma-iron(912<<1394)
  • hexagonal close-packed structure, hcp, sliver

  • number of atoms per cell
  • APF, the atomic packing factor, =Sum of atomic volumes/Volume of cell.
  • CN, the coordination number配位
  • closed-packed plane
  • closed-packe direction

2.3 Crystal Defect

  • point defecet

    • vacancy
    • interstitial atom
    • impurity atom

  • linear defect

    • edge dislocation
    • screw dislocation
    • the more, the strength down

  • planar defect

    • grain boundary
    • subgrain boundary
    • Polycrystalline : real material
      • grain
      • grain boundary

2.4 Crystallization

2.4.1 Thermodynamic conditions

  • $T_0$ : melting temperature
    • $<T_0$ start nucleation
  • $T_n$ : real,
  • $\Delta T=T_0-T_n$
  • $\Delta T+\Delta G_v>latent heat$

2.4.2 Progress

  • nucleation
    • homogeneous nucleation
    • heterogeneous nucleation : Impurity
    • Size->control
      • $\Delta T$ : pos
      • impurity : neg
      • vibration : neg
  • growth
    • closed-packed plane
    • like tree

2.4.3 Casting

  • chill zone : $\Delta T$, impurity
  • columnar zone : grow in the direction, that t changes the most
  • central zone : $\Delta T$

3. Binary alloy and Phase Diagrams

  • alloy system : 2 (more) element
    • components / elements
    • compounds

3.1 Phase Structure

  • Solid solution
    • interstitial solid solution
    • substition solid solution
    • Hardness, strength$\uparrow$
  • Compound
    • Non-metallic compound
    • matallic compound

3.2 Binary phase diagram

3.2.1 Isomorphous phase diagram

  • liquidus

  • solidus

  • freezing range

    • Lever rule

  • interdendritic seregation晶内偏析

  • homogenization heat treatment退火扩散

  • Equilibrium crystallization 平衡结晶

    • Thermodynamic equilibrium

3.2.2 Eutectic phase diagram

eutectic reaction

  • E : eutectic point
  • CED : solidus, 3 phase

  • CF,DG: solvus, secondary phases

  • Eutectoid reaction

4. Iron carbon alloy

  • carbon steel
  • cast iron

4.1 Phase diagram

  • Ferrite : alpha-iron, solid solution

    • strength, hardness so-so low, plasticity toughness so-so high

  • Austenite : gamma-iron, solid solution

    • hardness low, plasticity high

  • Cementite : $Fe_3C$, compound

  • AECF : solidus

  • ECF : eutectic line

  • PSK : eutectoid line

  • A : iron melting point

  • D : $Fe_3C$ melting point ss

  • C : $L=^{1148^\circ}Le(A_E+Fe_3C)$

  • S : $A=^{727^\circ}P(F+Fe_3C)$

    • $Le’=(P+Fe_3C_{II}+Fe_3C)$

4.2 Carbon steel

4.2.1 Impurity

  • :star: :star: Mn manganese : $\downarrow$ brittleness, $\uparrow$hardness, strength
  • :star:Si silicon : $\downarrow$ plasticity, toughness, $\uparrow$ hardness, strength
  • :no_entry::no_entry: S sulfur : $\uparrow$ brittleness, high T
  • :no_entry: P phosphorus : $\uparrow$ brittleness, low T

4.2.2 Classification

  • <0.25 : low carbon steel, 15, Q235
  • 0.25-0.6 : medium carbon steel, 45

  • 0.6 : high carbon steel, T10, T12

  • structural steel : low medium

  • tool steel : high

  • $Q$ : structural steel, $\sigma_s=235MPa$

  • 45 : good structral steel, 0.45% C
  • T12 : tool steel, 1.2%
  • ZG230-450 : minial,$\sigma_s/\sigma_{r0.2}=230MPa,\sigma_b=450MPa$

5. Metal plastic deformation and recrystallization

5.1 Single crystal plastic deformation

  • [Main] Slip

    • Shear stress
    • inside
    • the distance = distence between the atoms
    • along closed-packed plane and closed-packed direction
    • slip direction $\uparrow$, plasticity$\uparrow$

  • twinning

    • when slip hard

5.2 Polycrystal plastic deformation

defend more> single

  • grain boundary
  • grain finer
  • defect less
  • inside stress

5.3 Influence of Metal

  • structure
    • Fibrous tissue 纤维组织
    • Substructure : linear defect
    • Texture : Anisotropy
  • Capability
    • Working hardening :
      • hardness,strength $\uparrow$, plasticity,toughness$\downarrow$
      • linear defect $\uparrow$
  • Residual internal stress
    1. Macro, deformation
    2. grain, uneven deformation, flaw
    3. linear defect, vacancy, working hardening

5.4 High T influence

  • recovery
    • h.s little$\uparrow$, p little$\downarrow$
    • remove 1.2 residual internel stress
    • Stress relief annealing
  • recrystallization
    • recrystallization temperature
    • recrystallization annealing
  • grain growth

6. Heat treatment of steel

when solid, heating, holding, cooling to change structure

6.1 Critical temperature

  • Lag
  • calefaction
  • refrigeration

6.2 Heating

6.2.1 Austenitizing

  • P$\rightarrow$A, $Fe_3C\rightarrow$A,
  • crystallizatioin$\rightarrow$ growth$\rightarrow Fe_3C$ dissolved $\rightarrow$ Homogenization

6.2.2 Control grain size

  • T, t : pos
  • Speed : neg
  • C : neg
  • alloy
    • Al, Ti : neg
    • Mn, P : pos

6.3 Cooling

Supercooled austenite : under A1 austenite

  • continuous cooling transformation

  • isothermal transformation

  • Time-Temperature-Transformation [Eutectoid steel]

    • P Pearlite : A1-650

    • S Sorbite : 650-600

    • T Troostite : 600-550

    • B Bainite: 550-Ms

    • M Martensite : Ms-Mf

  • Continuous-Cooling-Transformation [Eutectoid steel]

    • P : Ps-Pf
    • M : under Ms

  • CCT right down of TTT

6.4 Normal heat treatment

  • Annealing : heating, holding, stove cooling

    • lowen strength for cutting
    • remove residual inherent stress avoiding fracture
    • refine grain for next
    • full / partial : less eutectoid
    • spheroidizing : over eutectoid
    • diffusion / relief /recrystallization : casting

  • normaling : GSP + 30-50, air cooloing

    • uniformize / homogenize structure & hardness
    • remove residual inside stress
    • for next step

  • quenching : Ac1/ Ac3, get martensite, water cooling for carbon steel, oil for alloy steel

    • hardenability : ability get M, $v>v_k$

  • tempering : under A1, holding, M+Ar

    • after quenching

    • remove residual inside stress

    • 150-250 tempered M, 60 HRC

    • 350-500 tempered T, 40 HRC

    • 500-650 tempered S, 30 HRC

    • temper brittleness

      1. avoid this T
      2. fast cooling

6.5 Surface treatment

  • surface quenching
    • face : h.s
    • inside : p.t
  • chemical heattreatment
    • carburizing : after normaling
    • nitriding : after mill, >carburizing
    • carbonitriding

7. Alloy steel

add alloy, eutectic point right move, S,E left move

  • carbon steel : not good enough at strength, hardenability, stability after normaling

7.1 With iron

  • increase A area : Ni, Mn, Co, help get A
  • decrease A area : Cr, V, B

7.2 Strengthening

  • Solid solution strengthening : add alloy, defend slip
  • Dispersion strengthening : unsolved in base body
  • Working hardening : add resistance of
  • Grain boundary strengthening

7.3 Alloy structural steel

  • structure steel + Mn + V + Cr

    • bridge
    • s.p.t $\uparrow$
    • low T cutting
    • melding
    • anti corrosion
    • Q345

  • Carburized steel + Cr +Mn+Ni +B

    • Gear
    • surface h. resist wear
    • inside enough s.p.t
    • variable force
    • 20Cr

  • Quenched and tempered steel +Mn+Si+Cr

    • axis

    • high h. good p.t

    • 40Cr

  • Spring

    • 65, 60SiMn

7.4Tool steel

  • Cutting tool steel : W,V
    • hardness
    • wear resistance
    • Red hardness
    • low alloy tool steel : 9SiCr
    • high speed steel : W18Cr4V
  • Die steel
    • cold-working die steel : 9SiCr
    • hot-working die steel : 5CrMnMo

7.5 Special steel

  • Stainless steel + Cr Ni
  • Refactory steel and oxidation-resistant steel + Cr+Mo+W+V

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