Nano structured bainite
nano structure bainite
Published on: Mar 3, 2016
Transcripts - Nano structured bainite
Formed when steel is cooled rapidly enough from
Austenitizing temperature by passing the nose of the c-curve
and kept isothermally at constant temperature .
Formed at a temperature range (250-550) °c.
Based on the quenching temperature it is devided into two
1. Upper Bainite ( formed between 550-350 °c , and has a
morphology of feathery shaped ferrite).
2. Lower Bainite ( formed between temperature below 350 °c ,
and has a morphology of plate-like structure ).
Fig 1. Fig 2.
Process of formation:- Austenitization of steel at ~950 °c followed
by transfer into an oven at the low temperature say ~200 ° c to be
held there for 10 days or so.
No rapid cooling is needed ,residual stresses are avoided.
With careful alloy design, Bainite transformation can be
made possible at temperatures as low as 125 ° c.
The sample must be large enough because the time taken to reach
200 °c from the Austenization temperature is much less than that
required to initiate Bainite.
Some amount of residual Austenite is important because it
enhances the work hardening capacity of material.
Achieve strength in excess of 2.5 Gpa.
Toughness ~30 Mpa.m1/2
The Bainite obtained by low temperature
transformation is harder then ever achieved and will
have better wear resistance.
Ys/mpa Uts/mpa El./%
0.8 c 220°c 35 16 710 1865 2444 4.9
0.8 c 250°c 37 18 659 1810 2345 6.6
0.8 c 270°c 24 24 615 1658 2226 10.2
1CSi 220°c 28 36 650 1626 2488 8.1
1CSi 250°c 28 34 625 1642 2417 17.2
Yield strength were found to correlate well with the
By Mack & Bartlett :
o For a thickness ‘t’ of the ferrite plates the mean intercept
o By Langford and Cohen Strength is given by =115/L
Mpa , where ‘L’ is in micrometer.
It cannot be satisfactorily welded.
Different military industries such as
Car manufacturing such as shaft ,