Bendability of Stainless steel 431Grade supplied by Jindal Stainless Steel prepared by Dr. R. Narayansamy, (Retd. Professor, National Institute of Technology,Tiruchirappalli - 620 015) Chief Metallurgist, Balaji Super Alloys,karamadai-641104, Coimbatore, Tamil Nadu, India.

1. Metallurgy of Stainless Steels
Dr. R. Narayanasamy,
B.E.,M.Tech.,M.Engg.,Ph.D.,(D.Sc.),
FIIM,FIEI,MIWS,MPMAI,MISTE.
Professor,
Department of Production Engineering,
National Institute of Technology,
Tiruchirappalli- 620 015 ,
Tamil Nadu, India.
E-mail: narayan@nitt.edu, narayan10455@yahoo.co.in
3/4/2022 1

2. Solidification structure showing dendrites
which have grown in to the melt

3. Physical Metallurgy
• Ferritic grades show ferrite solidification and are annealed at
low temperature, typically 750 – 1000°C, to avoid ferrite grain
growth.
• For some grades, particularly those which are not stabilized,
there is a risk of partial austenitization, and subsequent
martensite formation on quenching, if the annealing
temperature is too high.

4. Thermo Calc. is
a software.
Using this one,
phases can be
identified

5. Physical Metallurgy
Thermo Calc. is a
software.
Using this one,
phases can be
identified

6. Microstructure of an as-welded duplex
stainless steel with grain boundary and
Wildmanstatten austenite

7. Experimentally determined TTT diagrams for conditions
causing a 50% reduction in impact toughness for
austenitic grades

8. Experimentally determined TTT diagrams for conditions
causing a 50% reduction in impact toughness for two
duplex grades

9. Ternary diagram typically used for classification of the
oxide inclusions in stainless steels

29. • Mn+S MnS
• MnS is usually present in the form of lamellar
shape. This affects the transverse ductility.
• To improve the transverse ductility, MnS
should be in the form of small and spherical
shape.
• MnS is usually treated with Calcium. This is
not effective. Better treat with Cerium.
Sulfide Inclusions

30. • When treated with
Cerium, MnS is
available in the form
of small spherical
shape.
• This improves a lot in
transverse ductility.
Sulfide Inclusions
MnS particle: (a&b) – SEM image (c-f) - TEM
image with various magnification.

31. • This type of Ferrite grains offer more
resistance to thinning in the thickness
direction.
• Reason: This improves the R value and
formability.
Pan cake type of ferrite grains
Microstructure: Pan cake
type of ferrite grain

32. Pan cake type of ferrite grains
Yield locus plot
R > 1
R < 1

33. By control:
• Cold rolling variables
• Annealing parameters and
• Hot rolled coiling temperature
You can get/improve the pancake type of grain
size.
Pan cake type of ferrite grains

34. Pan cake type of ferrite grains

35. • V + C VC
• Nb + C NbC
• V + N VN
• Nb + N NbN
• Titanium is also added along with Nb.
• The small addition of V and Nb helps in forming
stronger and stable carbonitrides.
• This small and spherical shaped,stable
carbonitirdes does not affect formability.
Microalloying addition
V and Nb
Carbonitrides

36. Microalloying addition

37. • Rate of Heating and Cooling.
• Amount of Prior deformation
• Temperature and Time
• Initial Grain Size
• Composition or Purity
• Amount of Recovery
Annealing parameters

38. • Boron should be added in ppm level.
• B + C BC
• B + N BN
Boron
Boron Carbides and
Nitrides are formed

39. • This Boron addition strengthens the grain
boundaries.
• Phosphides formed at the grain boundary
promotes embrittlement. This is prevented by
the addition of Boron.
Boron

40. • Ferrite grain size should be lower than 21μm.
• Lower the grain size, higher is the ‘n’ – value.
n – value:
• Finer the grain size, n-value increases.
• Where, n- value is the strain hardening exponent
and d is the average grain diameter.
• As n-value increases, the uniform strain before
plastic instability increases.
• Thus, the stretchability in forming limit diagram
(FLD) increases.
Grain Size

41. Grain Size
n - value
%
uniform
elongation
•During forming, Coarse grain
size will produce orange peel
effect.
•Because of non uniform
deformation.
•Because of coarse grain, stress
pattern will vary from one grain
to another grain during
deformation.

42. Grain Size
Orange peel effect, which is nothing
but rough surface finish due to coarse
grain size.

43. • Small addition of Al and Ti forms smaller oxide
inclusions
• Al3 + 02 Al2O3
• Al2O3 is a stable oxidized inclusions
• Ti + N TiN
• Ti + C TiC
• Titanium with Oxygen will form TiO2
(In Mild steel during presence of Nb and V)
• Thus, Carbon is killed. There is no free Carbon
(or) Nitrogen (or) Oxygen is available in the steel.
Addition of Al and Ti

44. • Like in I.F. steel, carbon should be in ppm
level.
• In Al killed EDDQ steel, Carbon level is 0.08%
• Si should be less than 0.2%. Si is a dexoidizer.
• Mn should be less than 0.45%.
• FeS promotes hot shortness
• Fe+S FeS.
• This FeS is usually precipitated along grain boundaries
Other elements

45. • Phosphorous reacts with Fe
P+Fe FeP (Iron Phosphate is formed)
• This promotes cold shortness, because it is
very brittle.
• S and P should be less than 0.015 % each.
Other elements

46. Deformation
Percentage
Other elements

47. Calcium aluminate should be eliminated in
the laddle during steel making.

48. Yield point phenomenon or elongation
• Yield point elongation develops stretcher
strain defect

49. Residual stresses
• Compressive stress – Fatigue life increases.
Improves forming
Life increases
Example: Shot peening

50. • Tensile stress – Results in cracking (stress
corrosion cracking)
Residual stresses

51. Stress corrosion cracking in deep drawn cup/ flow
formed cup in the case of austenitic stainless steel
It shows stress
corrosion cracking

52. Forming Limit Diagram (FLD)

53. Combined FLD for BA, CA and CR SS 430 grade steel
sheet of 1.3 mm thickness

54. Combined forming, fracture and wrinkling limit
diagram

55. Other Studies
• SEM – Fractography to study the fracture surface
• XRD – Dislocation denisty, lattice strain and residual
stresses
• TEM – Minute details about grain boundary- second
phase particles like NbC and NbN or Nb carbonitrates
(Example I.F. steel)
• Texture study – Bulk XRD texture – To study about the
texturing (preferred orientation of grains) before and
after the deformation.
• Micro texture/EBSD – To study about the grain
orientation and to quantitatively evidence the grain
size

56. Orientation distribution function (ODF) and Pole figures
of SS 430 cold rolled sheet before annealing – X-ray bulk
texture

57. Orientation distribution function (ODF) and Pole figures
of SS 430 cold rolled sheet after annealing – X- ray bulk
texture

58. Micro texture/EBSD
Different orientation of ferrite grains
Plane orientation
EBSD of Ferrite grains

59. Acknowledgement
• Acknowledge my co-workers:
Dr.K.Sivaprasad, M.Tech., Ph.D.
Assistant Professor,
Department of Metallurgical and Materials Engineering,
NIT-Trichy.
Mr.S.Vigneshwaran, Research Scholar, NIT-Trichy.
for his very much kind help for preparing the slides for M/s.Jindal steels, Hisar.

60. Thank you very much for your kind
patience
Dr.R.Narayanasamy, Professor.
E-mail : narayan@nitt.edu