Chapter 4Equilibrium Phase Diagrams and The

Iron-Carbon system

Kanchala Sudtachat

Phases

A phases is simply a form of material possessing a characteristic structure and properties.

A phases has a definable structure, a uniform and identifiable chemistry.

And distinct boundaries or interfaces that separate it from other different phases.

Equilibrium Phase Diagrams

is a graphic mapping of the natural tendencies of a material or a material system.

There are three primary variable to be considered: temperature, pressure and composition

Pressure-Temperature (P-T) diagram

Diagram maps the stable form of water for various conditions.

The region boundaries denote the melting and boiling point.

It has important to make freeze drying.

Temperature-Composition(T-C) diagram

At atmospheric pressure and variations more likely to occur in temperature and composition.

Cooling Curves

The equilibrium phase diagram is collective presentation of cooling-curve data for an entire range of alloy compositions

Solubility Studies

Can ice retain some salt in a single phase solid solution?

Can solid salt hold some water and remain a single-phase?

How much, and does the amount vary with temperature?

We called solubility limit.

Lead-tin equilibrium phase diagram

Solvus line: เส้�นแบ่�งระหว่�างของแข�งเฟส้เดี�ยว่และของแข�ง 2เฟส้

Complete solubility in both liquid and solid states

Liquidus line – เหน�อเส้�นน��เป็�นส้ารละลายในเฟส้เหลว่

Solidus line – ดี�านล�างของเส้�นน��เป็�นส้ารละลายในเฟส้ของแข�ง

Freezing range: Between the liquidus and Solidus

Partial solid solubility

At the point of max solubility, 183oC

Lead can hold up to 19.2 wt%

If T is decreased, the amount of solute that can be held in solution decreased.

Insolubility

Utilization of diagramที่��อ�ณหภู!มิ#และส้�ว่นผส้มิหน%�งๆน'�นจะบ่อกไดี�ว่�า

• The phase present เป็�นเฟส้ของอะไร –ของแข�ง?, ของเหลว่?, ของแข�งโครงส้ร�าง?

• The composition of each phase ป็ร#มิาณของแต่�ละเฟส้ ของแข�ง – ?%, ของเหลว่ ?%

• The amount of each phase presentส้�ว่นผส้มิในแต่�ละเฟส้ ในของแข�งมิ�ส้าร – A อย!� ?% ส้ารB อย!� ?%, ในของเหลว่มิ�ส้าร A อย!� ?% ส้ารB อย!� ?%

ป็ร#มิาณของแต่�ละเฟส้ ของแข�ง – ?%, ของเหลว่ ?%

Equilibrium Phase Diagrams: T-C Diagram

Equilibrium Phase Diagrams: T-C Diagram

ส้�ว่นผส้มิในแต่�ละเฟส้ ในของเหลว่–มิ�ส้าร A อย!� ?% ส้ารB อย!� ?%

a – S2 x 100%

L2 – S2

Three-phase reactions

Iron-Carbon Equilibrium Diagram

Eutectoid

Eutectic

Peritectic

Steel, compose primarily of iron and carbon

Iron-Carbon Equilibrium Diagram

a body-cubic solid that is stable down to 1394oC, know as delta-ferrite.

From 1394oC to 912oC (FCC), know as austenite.

Alpha-ferrite (BCC) below 912oC

Iron-Carbon Equilibrium Diagram

At 1495oC, a peritectic reaction. At 1148oC, a eutectic with composition of

4.3% carbon 2.11% carbon are classified by the general

term cast iron At 727oC, a eutectoid with composition of

0.77% carbon. Alloy with less than 2.11% carbon, know as steels

Steels and the simplified iron-carbon diagram

The key transition will be the conversion of austenite to the two-phase ferrite plus carbide mixture.

Steels and the simplified iron-carbon diagram

Pearlite (ferrite + cementite) Eutectoid composition (0.77%C)

Austenite0.77%C; FCC Ferrite0.02%C; BCC + Cementite6.67%C

Steels and the simplified iron-carbon diagram

Hypoeutectoid steels (ferrite + pearlite) less than eutectoid composition

Hypereutectoid steels (cementile + pearlite) greater than eutectoid composition

Cast Irons

Iron-carbon alloys with more than 2.11% Wide variety properties. Contains iron, carbon, silicon, manganese,

sulfur, phosphorous อาจที่.าให�เก#ดี Graphite หร�อ Cementite Graphite form by slow cooling Cementite form by fast cooling

Cast Irons

Cast Irons

Graphite

• เย�นต่'ว่ลงช้�าๆ• ป็ร#มิาณคาร0บ่อน C, Si ส้!ง• ใช้�เว่ลาบ่�มิต่'ว่• มิ�ส้�ว่นผส้มิของ S, P, Al, Mg, Sn, Cu, Co

Cementite

• เย�นต่'ว่ลงเร�ว่• ป็ร#มิาณคาร0บ่อน C, Si ต่.�า• มิ�ส้�ว่นผส้มิของ Ti, V, Cr, Zr, Mn, Mo

Cast Irons

Gray Cast Iron 0.5-4.0%C, 1.0-3.0%Si, 0.4-1.0%Mn ผลของ Graphite ที่.าให�

• Brittle

• Excellent compressive strength

• Excellent machinability

• Good resistance to adhesive wear

• Outstanding vibration damping

Cast Irons

White Cast Iron 1.8-3.6%C, 0.5-1.9%Si, 0.25-0.8%Mn ผลของ Cementite ที่.าให�

• Very hard & brittle

• High abrasion resistance