metallography low alloy steel

1. George Vander Voort
Director, Research and Technology
Buehler Ltd.
Lake Bluff, IL 60044 USA

2. Microstructure of wrought iron (Fe – 0.07% C – 0.06% Mn – 0.2% Si - 0.16% P
– 0.02% S) etched with 2% nital revealing slag stringers and ferrite (alpha)
grains and grain boundaries. Original at 500X.
Wrought Iron

3. Electrical iron (<0.02% C) etched with 2% nital revealing a ferrite grain
structure.
Electrical Iron

4. Surface of electrical steel specimen showing large sub-surface ferrite grains. Tint etched
with Klemm’s I. The grain orientations are random (note the random distribution of
colored ferrite grains). Original at 100X. Viewed with crossed polars + sensitive tint.
Motor Lamination Steel

5. 4% Picral 2% Nital
Low-carbon sheet steel (Fe – 0.05% C – 0.08% Mn – 0.20% Si) etched with picral and nital.
Picral reveals the fine cementite particles and patches of pearlite. Nital reveals the ferrite
grain boundaries and the pearlite patches, but the fine cementite particles are hard to see,
especially if the are at grain boundaries. Originals at 500X.
1008 Carbon Steel – As-Rolled

6. 4% Picral 2% Nital
Low-carbon sheet steel etched with picral and nital. Picral reveals the fine cementite
particles and patches of pearlite. Nital reveals the ferrite grain boundaries and the pearlite
patches, but the fine cementite particles are hard to see, especially if the are at grain
boundaries. Originals at 500X.
1008 Carbon Steel - Annealed

7. 4% Picral 2% Nital
Microstructure of hot-rolled Fe – 0.11% C – 0.85% Mn – 0.21% Si etched with picral
and nital. Picral reveals the cementite and pearlite, but not the ferrite grain boundaries.
Nital reveals the ferrite grain boundaries and the pearlite, but the fine cementite
particles are difficult to see. Originals at 500X.
1010 Carbon Steel – As-Rolled

8. As-rolled high-strength, low-alloy (HSLA) steel strengthened with Nb revealing a duplex
ferrite grain size distribution. Microstructure is ferrite and pearlite. Specimen etched
sequentially with 4% picral and 2% nital. Originals at 200X (left) and 500X (right).
HSLA – Duplex Grain Structure

9. Ferrite-pearlite microstructure of 1018 carbon steel furnace cooled from 900 °C (1650 °F)
and etched with 4% picral (which does not reveal the ferrite grain boundaries). The
hardness was 117 HV. Compare the hardness and interlamellar spacing of the air cooled
(next slide) and furnace cooled specimens. Some small cementite particles can be seen.
P
F
1018 Carbon Steel, Full Anneal
20 µm 10 µm

10. Ferrite-pearlite microstructure of 1018 carbon steel air cooled from 900 °C
(1650 °F) and etched with 4% picral (which does not reveal the ferrite grain
boundaries). The hardness was 135 HV.
1018 Carbon Steel, Normalized
10 µm
20 µm

11. As-quenched low-carbon (lath) martensite and ferrite in 1018 carbon steel water quenched
from 900 °C (1650 °F). The hardness was 356 HV in the center and 465 HV at the edge of
the bar. These pictures were from near the outer surface, but grain boundary and
Widmanstätten ferrite (WF) can be seen even in the outer region due to the low
hardenability of 1018. The specimen was etched with 2% nital. A manganese sulfide (S)
particle can be seen; note the black oxide at each end of the sulfide.
WF
S
WF
WF
20 µm 10 µm
1018 Carbon Steel, Water Quenched, Surface

12. Tempered low-carbon (lath) martensite in 1018 carbon steel water quenched from
900 °C (1650 °F) and tempered at 204 °C (400 °F). The hardness was 350 HV in the
center and 436 HV at the edge of the bar. These pictures were from near the outer
surface in an area of almost 100% martensite. The specimen was etched with 2%
nital.
1018 Carbon Steel, Q + T (204 °C) - Surface
20 µm 10 µm

13. Tempered low-carbon (lath) martensite and ferrite in 1018 carbon steel water
quenched from 900 °C (1650 °F) and tempered at 204 °C (400 °F). The hardness was
350 HV in the center and 436 HV at the edge of the bar. These pictures were from
near the center in an where there is considerable grain boundary Widmanstätten
ferrite. The specimen was etched with 2% nital. Compare these images to those in the
previous slide.
WF
20 µm 10 µm
1018 Carbon Steel, Q+T (204 °C) - Center

14. Tempered low-carbon (lath) martensite in 1018 carbon steel water quenched from 900 °C
(1650 °F) and tempered at 538 °C (1000 °F). The hardness was 230 HV in the center and
256 HV at the edge of the bar. These pictures were from near the outer surface in an area
of almost 100% martensite. The specimen was etched with 2% nital.
1018 Carbon Steel, Q+T (538 °C) - Surface
20 µm 10 µm

15. Tempered low-carbon (lath) martensite and ferrite in 1018 carbon steel water
quenched from 900 °C (1650 °F) and tempered at 538 °C (1000 °F). The
hardness was 230 HV in the center and 256 HV at the edge of the bar. These
pictures were from near the center. Note that the grain boundary ferrite is not
as distinct as in the specimens in the as-quenched and in the quenched and
tempered at 203 ° C conditions. The specimen was etched with 2% nital.
20 µm 10 µm
1018 Carbon Steel, Q+T (538 °C) - Center

16. 4% Picral 2% Nital
Microstructure of hot-rolled Fe – 0.16% C – 1.26% Mn – 0.22% Si – 0.15% Cr etched with
picral and nital. Picral reveals the cementite and pearlite, but not the ferrite grain
boundaries. Nital reveals the ferrite grain boundaries and the pearlite, but the fine
cementite particles are difficult to see. Originals at 500X.
1019 Mod. Carbon Steel

17. Microstructure of hot-rolled X42 line-pipe steel etched sequentially with 4% picral and 2%
nital revealing a severely “banded” (layered) structure of ferrite and pearlite. The hot
working axis is horizontal. Originals at 100X (left) and 500X (right). The arrow (right
image) points to a highly elongated MnS (manganese sulfide) inclusion.
X42 Line Pipe Steel, As-Rolled

18. Microstructure of hot-rolled ASTM A572 plate steel steel etched sequentially with 4%
picral and 2% nital revealing a weakly “banded” (layered) structure of ferrite and
pearlite. The hot working axis is horizontal. Originals at 200X (left) and 500X (right).
ASTM A572 Plate Steel,As-Rolled

19. Microstructure of hot-rolled ASTM A588 plate steel steel etched sequentially with 4%
picral and 2% nital revealing a moderately “banded” (layered) structure of ferrite and
pearlite. The hot working axis is horizontal. Originals at 200X (left) and 500X (right).
ASTM A588 Plate Steel,As-Rolled

20. Microstructure of hot-rolled Fe – 0.23% C – 0.85% Mn – 0.22% Si revealing a moderately
banded structure of ferrite and pearlite. Originals at 500X. The hot working axis is
horizontal. The arrow (right picture) points to a large MnS inclusion. Note that it is quite
malleable and has been highly elongated by hot rolling.
4% Picral 2% Nital
1026 Carbon Steel, As-Rolled

21. 4% Picral 2% Nital
Microstructure of hot-rolled Fe – 0.31% C – 0.84% Mn – 0.29% Si steel revealing a
banded ferrite-pearlite structure (hot rolling direction is horizontal). The arrows point to
some of the highly elongated MnS inclusions. Originals at 500X.
1030 Carbon Steel, As-Rolled

22. As-Rolled 1040 Carbon steel (Fe – 0.4% C – 0.75% Mn) etched sequentially with 4%
picral and 2% nital revealing a fine structure of approximately half ferrite and half
pearlite. Originals at 200X (left) and 500X (right). The fine grain size is due to proper
control of the finishing temperature (temperature of bars at the last mill stand).
1040 Carbon Steel, As-Rolled

23. Normalized (871 °C, 1600 °F for 1 hour, air cool) 1040 carbon steel (Fe – 0.4% C –
0.75% Mn) etched sequentially with 4% picral and 2% nital revealing a fine structure
of approximately half ferrite and half pearlite. Originals at 200X (left) and 500X
(right). The structure is slightly finer than the as-rolled structure.
1040 Carbon Steel, Normalized at 871 °C

24. Microstructure of annealed 1040 carbon steel (0.40% C – 0.68% Mn – 0.12% Si)
revealing ferrite and pearlite. Originals are at 1000X.
4% Picral 2% Nital
1040 Carbon Steel, Full Anneal

25. Ferrite-pearlite microstructure of 1045 carbon steel furnace cooled from
900 °C (1650 °F) and etched with 4% picral (which does not reveal the
ferrite grain boundaries). The hardness was 166 HV. Compare the
hardness and interlamellar spacing of the air cooled (next slide) and
furnace cooled specimens.
1045 Carbon Steel, Full Anneal
20 µm 10 µm

26. Ferrite-pearlite microstructure of 1045 carbon steel air cooled from 900 °C (1650
°F) and etched with 4% picral (which does not reveal the ferrite grain boundaries).
The hardness was 192 HV.
1045 Carbon Steel, Normalized
20 µm 10 µm

27. As-quenched mixed low-carbon and high-carbon martensite in 1045 carbon steel
water quenched from 900 °C (1650 °F). The hardness was 596 HV in the center and
743 HV at the edge of the bar. These pictures were from near the outer surface,
where the structure is nearly all martensite, except for a few small dark patches of
pearlite. The specimen was etched with 2% nital.
P
20 µm 10 µm
1045 Carbon Steel – As Quenched, Surface

28. As-quenched martensite and pearlite in 1045 carbon steel water quenched from 900
°C (1650 °F). The hardness was 596 HV in the center and 743 HV at the edge of the
bar. These pictures were from near the center where the structure is nearly half
pearlite (P), with some grain boundary ferrite (F), and martensite (M). The specimen
was etched with 2% nital.
P
F
M
1045 Carbon Steel, As-Quenched, Center
20 µm 10 µm

29. Tempered mixed low-carbon and high-carbon martensite in 1045 carbon steel water
quenched from 900 °C (1650 °F) and tempered at 204 °C (400 °F). The hardness was
436 HV in the center and 605 HV at the edge of the bar. These pictures were from near
the outer surface in an area of 100% martensite. The specimen was etched with 2%
nital.
1045 Carbon Steel, Q+T (204 °C) - Surface
20 µm 10 µm

30. Tempered martensite and pearlite in 1045 carbon steel water quenched from 900
°C (1650 °F) and tempered at 204 °C (400 °F). The hardness was 436 HV in the
center and 605 HV at the edge of the bar. These pictures were from near the center
in an where there is martensite (M), considerable pearlite (P) and a very small
amount of grain boundary Widmanstätten ferrite. The specimen was etched with
2% nital. Compare these images to those in the previous slide.
P
M
1045 Carbon Steel, Q+T (204 °C) - Center
20 µm 10 µm

31. Tempered mixed low-carbon and high-carbon martensite in 1045 carbon steel water
quenched from 900 °C (1650 °F) and tempered at 538 °C (1000 °F). The hardness was
251 HV in the center and 280 HV at the edge of the bar. These pictures were from near
the outer surface in an area of almost 100% martensite. The specimen was etched with
2% nital.
1045 Carbon Steel, Q+T (538 °C) - Surface
20 µm 10 µm

32. Tempered martensite, pearlite and ferrite in 1045 carbon steel water quenched from 900 °C
(1650 °F) and tempered at 538 °C (1000 °F). The hardness was 251 HV in the center and
280 HV at the edge of the bar. These pictures were from near the center in an area
containing martensite (M), pearlite (P) and ferrite, including Widmanstätten ferrite (WF)
and grain boundary ferrite (GBF). The specimen was etched with 2% nital.
GBF
WF
M
P
1045 Carbon Steel, Q+T (538 °C) - Center
20 µm 10 µm

33. 4% Picral 2% Nital
Microstructure of hot-rolled Fe – 0.68% C – 0.84% Mn – 0.33% Si revealing a nearly
fully pearlitic structure. Originals at 1000X.
1070 Carbon Steel, As-Rolled

34. Microstructure of hot-rolled eutectoid Fe – 0.80% C – 0.21% Mn – 0.22% Si revealing a
pearlitic structure where some of the lamellae are resolvable at the original magnification of
1000X. Etched with 2% nital.
1080 Mod. Carbon Steel, As-Rolled

35. Fine pearlitic structure in normalized (780 °C, 1436 °F – 1 h, air cool) 1080 steel (Fe – 0.8%
C – 0.75% Mn) etched with 4% picral. Some of the lamellae are resolvable. Original at
1000X.
1080 Carbon Steel, Normalized at 780 °C

36. Coarse pearlitic structure in isothermally annealed (780 °C, 1436 °F – 1 h,
isothermally transformed) 1080 steel (Fe – 0.8% C – 0.75% Mn) etched with 4%
picral. All of the lamellae are resolvable. Original at 1000X.
1080 Carbon Steel, Isothermally Annealed

37. Coarse pearlitic structure, with some spheroidization of the cementite, in slow cooled (780
°C, 1436 °F – 1 h, furnace cool) 1080 steel (Fe – 0.8% C – 0.75% Mn) etched with 4%
picral. All of the cementite particles are resolvable. Original at 1000X.
1080 Carbon Steel, Spheroidized

38. Ferrite-pearlite microstructure of 1095 carbon steel furnace cooled from 900 °C (1650
°F) and etched with 4% picral revealing a fully pearlitic matrix with a coarse
interlamellar spacing. The hardness was 225 HV. Compare the hardness and
interlamellar spacings of the air cooled and furnace cooled specimens and compare the
amount of pearlite and ferrite with the 1018 and 1045 specimens.
1095 Carbon Steel, Full Anneal
20 µm 10 µm

39. Ferrite-pearlite microstructure of 1095 carbon steel air cooled from 900 °C (1650 °F)
and etched with 4% picral revealing a fully pearlitic matrix with a fine interlamellar
spacing. The hardness was 296 HV. Compare the hardness and interlamellar spacing of
the air cooled and furnace cooled specimens and compare the amount of pearlite and
ferrite with the 1018 and 1045 specimens.
1095 Carbon Steel, Normalize
20 µm 10 µm

40. As-quenched high-carbon plate martensite and retained austenite in 1095 carbon steel
water quenched from 900 °C (1650 °F). The hardness was 863 HV and the specimen was
through hardened. The austenitizing temperature is much higher than recommended
and dissolved all of the cementite, depressing the martensite start and finish
temperatures, which lead to the presence of excessive retained austenite. The prior-
austenite grain size was also enlarged, as high-carbon steels are not aluminum killed
(graphite will form). The specimen was etched with 2% nital.
1095 Carbon Steel, WQ (900 °C)
20 µm 10 µm

41. Tempered high-carbon plate martensite and retained austenite in 1095 carbon
steel water quenched from 900 °C (1650 °F) and tempered at 204 °C (400 °F).
The hardness was 776 HV. This tempering temperature is too low to stimulate
transformation of the retained austenite, but in may stabilize it somewhat. The
specimen was etched with 2% nital.
1095 Carbon Steel, WQ + T (204 °C)
20 µm 10 µm

42. Tempered high-carbon plate martensite and retained austenite in 1095 carbon steel
water quenched from 900 °C (1650 °F) and tempered at 538 °C (1000 °F). The hardness
was 375 HV. The retained austenite was transformed by the temper (and it would be
best to repeat the temper). The specimen was etched with 2% nital.
1095 Carbon Steel, Q + T (538 °C)
20 µm 10 µm

43. Condition 1018 1045 1095
900 °C, Furnace Cool 117 166 225
900 °C, Air Cool 135 192 296
900 °C-Water
Quench
456 (S)
356 (C)
743 (S)
596 (C)
863
900 °C-WQ-Temper
at 204 °C
436 (S)
350 (C)
605 (S)
436 (C)
776
900 °C-WQ-Temper
at 204 °C
256 (S)
230 (C)
280 (S)
251 (C)
375
Notes: The 1095 specimen was through hardened.
S = surface and C = center

44. Microstructure of as-rolled Fe – 1% C binary alloy etched with Beraha’s sodium molybdate
reagent to color cementite. The arrow points to proeutectoid cementite that precipitated on
a prior-austenite grain boundary before the eutectoid reaction (austenite forms ferrite and
cementite in the form of lamellar pearlite). Magnification bar is 10 µm long.
Fe – 1% C, As-Rolled

45. Microstructure of spheroidize annealed W1 water-hardening tool steel etched with Beraha’s
sodium molybdate reagent to color the cementite. Note that the ferrite was also colored, in
this case. Spheroidization of the cementite lowers the hardness and makes the steel more
ductile for cold forming and easier to machine. Magnification bar is 5 µm long.
AISI W1 Carbon Tool Steel, Annealed

46. Annealed Fe – 1.15% C steel with a coarse lamellar pearlite microstructure and some
large globular cementite particles. Heat treatment was: 800 °C (1472 °F) – 1 h,
furnace cool. Etched with 4% picral. Original at 1000X. Black spots are inclusions.
W1 Carbon Tool Steel, 1.15% C, Full Anneal

47. 4% Picral 2% Nital
Microstructure of as-rolled Fe – 1.31% C – 0.35% Mn – 0.25% Si high-carbon water
hardenable tool steel. Note the Widmanstätten intragranular cementite that precipitated as
pro-eutectoid cementite before the eutectoid reaction. Originals at 1000X.
W1 Carbon Tool Steel, 1.3% C, As-Rolled