recrystallisation and grain growth n.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
Recrystallisation and Grain Growth PowerPoint Presentation
Download Presentation
Recrystallisation and Grain Growth

Loading in 2 Seconds...

play fullscreen
1 / 15

Recrystallisation and Grain Growth - PowerPoint PPT Presentation


  • 89 Views
  • Uploaded on

Recrystallisation and Grain Growth. Cold working: for malleable in cold and weak and brittle when heated materials – often in finishing stages of production to get clean smooth finish; to straighten (in some); to get required degree of hardness

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

Recrystallisation and Grain Growth


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
recrystallisation and grain growth
Recrystallisation and Grain Growth
  • Cold working: for malleable in cold and weak and brittle when heated materials –

often in finishing stages of production

to get clean smooth finish;

to straighten (in some);

to get required degree of hardness

  • Hot working: Increase in temperature increases interatomic spacing; decreases bond strength. Dislocations moved more easily through crystal. Becomes softer more malleable, less energy for deformation.

Carried at temperatures above RECRYSTALLISATION

slide2

Relief of stresses:At low temperatures-atoms move to positions nearer to equilibrium

Small movements-reduces local strain& stress, without change in shape

Hardness & tensile strength, as in cold worked, are high

slide3

When annealing temperature increased, at a point of temperature,

new crystals form-

at high P.E. positions,

grain boundaries.

slide4

First, small;

Then

grow gradually

slide6

Then

completely

slide7

These new crystals equiaxed

Recrystallisation temp:≈ 1/3 to ½ Tm

stages in recrystallisation
STAGES IN RECRYSTALLISATION

Recrystallisation temperature depends

on degree of cold work.

severe cold work- lower crystallisation temperature

grain growth
GRAIN GROWTH

When annealing temperature above recrystallisation, newly formed crystals continue to grow

By absorbing each other (in a cannibal fashion)

Final structure - coarse grained.

Crystal boundary moves towards centre of curvature

impurities in steel
IMPURITIES IN STEEL
  • SULPHUR, PHOSPHEROUS, SILICON, MANGANESE
  • PROPERTIES DEPEND ON THE WAY BY WHICH THESE IMOURITIES ARE DISTRIBUTED
  • EVEN DISTRIBUTION PREFERRED TO CORED
  • CORING CONCENTRATES IMPURITIES
slide11

Sulphur & Phosphorus segregate and precipitate at grain boundaries----- coring.

Silicon & Manganese evenly distributed (Even 0.3% effect is minimum)

Si- imparts fluidity, upto 0.3%- [In HCS, kept lower (decomposes to graphite)]

Mn- soluble in Austenite and Ferrite Mn3C. Increases ‘depth’ of hardening, improves strength & toughness, max 0.3%

slide13
Nitrogen-forms nitrides during manufacture.
  • Makes steel not suitable for cold working. (Fe4N brittle).
  • Possible to bring to very low (0.002%), with good processes.
slide14

HARDENING- From above A3 when cooled RAPIDLY,

HARDENS.

Degree of hardening –

on initial quenching temperature, size, constitution, properties

and temperature of quenching medium

IRON ATOMS

CARBON ATOMS

From FCC Austenite

to

BCC Tetragonal based cell on ABCD

In 10-7 seconds

By

DIFFUSIONLESS PHASE TRANSFORMATION

AB = ao/√2

slide15

UPPER CRITICAL TEMPERATURE, A3

LOWER CRITICAL TEMPERATURE, A1