BMEE209L: Module 5

Question 1

Purpose of annealing

Answer 1

to eliminate effects of cold working

Question 2

Process Annealing

Answer 2

1. Heat to 550ºC - 650°C
2. Hold for recrystallisation
3. Cool slowly

Question 3

What is austenitizing?

Answer 3

Heating to form homogenous FCC γ-austenite

Question 4

Why do we austenitize?

Answer 4

1. Austenite is often the parent phase for phase transformations
2. To reset the effects of cold working by removing any previous microstructures for better phase transformations
3. Creates uniform microstructure

Question 5

Full Annealing

Answer 5

1. Austenization
2. Slow Cooling in furnace (coarse pearlite)

Question 6

Normalization

Answer 6

1. Austenization
2. Rapid cooling in air (fine pearlite)

Question 7

Annealing is used in __________carbon steel

Answer 7

low

Question 8

Spheroidizing is used in ____________ carbon steel

Answer 8

high

Question 9

Purpose of Spheroidizing

Answer 9

To make the material more machinable (more easily cut, shaped, drilled)

Question 10

Spheroidizing

Answer 10

1. Heat to 697ºC
2. Cementite becomes large spherical structures
3. Final Structure: Spheroidite –> soft ferrite matrix with spheroidal Fe3C

Question 11

Purpose of Austempering

Answer 11

To get bainite, a perfect combination of ductility and toughness unlike martensite which is brittle

Question 12

Austempering

Answer 12

1. Austenitize
2. Quench below TTT curve nose to 300 - 400°C
3. Hold isothermally until austenite turns into bainite

Question 13

Purpose of Martempering

Answer 13

to avoid cracks and residual stress

Question 14

Martermpering

Answer 14

1. Austenitize
2. Rapidly quench to just above Ms (Martensite start)
3. Hold
4. Rapidly cools in air –> martensite forms
5. Tempering done to reduce brittleness

Question 15

Jominy-end quench test

Answer 15

1. Austenize cylindrical sample
2. Spray water at one end
3. Cooling gradient forms
4. Measure hardness along the length

Question 16

Diffusionless Transformation

Answer 16

Involves phase change that occurs without the long-range diffusion of atoms across the materials but rather the homogenous movement of many atoms resulting in a change in crystal structure

Question 17

How do you temper materials?

Answer 17

Re-heat at 150°C to 650°C

Question 18

Surface hardening by localized heating

Answer 18

1. Rapidly heat surface to above A3 (temp at which ferrite forms upon cooling)
2. Core stays below A1
3. Surface –> Martensite and Core–>Ferrite + Pearlite

Question 19

Carburizing

Answer 19

1) Add carbon to surface
2) Heat to above A3 (900°C to 950ºC)
3) Carbon diffuses into austenite
4) Quench and Temper
5) Surface = High-C Martensite
Core = Ductile ferrite

Question 20

Nitriding

Answer 20

1) Keep material in ammonia atmosphere
2) Add nitrogen
3) Heat below A1
4) Hard nitrides produced on the surface

Question 21

Cyaniding

Answer 21

Steel immersed in liquid cyanide

Question 22

Carbonitriding

Answer 22

use gases containing (CO and NH3) to diffuse N and C