20120140504012

International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –
6480(Print), ISSN 0976 – 6499(Online) Volume 5, Issue 4, April (2014), pp. 111-118 © IAEME
111
BEND CRACKING BEHAVIOR OF HYDROGENATED LOW STRENGTH
STRUCTURAL STEEL UNDER DIFFERENT HEAT TREATMENT
CONDITIONS
Amjad Saleh El-Amoush1
and Salman A. Al-Duheisat2
1
Al-Balqa Applied University, College of Engineering, Materials and Metallurgical Eng,
Al-Salt 19117, P. O .Box 7181, Jordan
2
Faculty of Engineering Technology, Al Balqa Applied University
P.O. Box 15008, Amman – Jordan
1. ABSTRACT
The bend cracking behavior of the low strength structural steel type A36 was studied under
cathodic charging in three-point bend system. Different heat treatments regimes were applied to the
material in order to obtain various grain sizes. The test results revealed that the low-angle grain
boundaries in a structural steel samples of small grain size are less susceptible to hydrogen damage
than those of the high-angle grain boundaries associated with large grains. Furthermore, it was found
that the type and amount of hydrogen cracking depend on the grain size. Intergranular cracking (IG)
was found to occur in the structural steel samples having both smaller and larger grain sizes. The
amount and number of hydrogen cracks were found to increase with increasing the grain size. It was
observed from the test results that the increase charging time resulted in an increase of a number of
hydrogen cracks on the surface of the structural steel samples.
Keywords: Three-Point Bending, Structural Steel Type A36, Hydrogen Charging.
2. INTRODUCTION
Low strength structural steel type A36 is the principal steel for building constructions, bridges
and other structural uses. However, this material must be used carefully in structures exposed to
hydrogen. The combined action of stress and hydrogen environment may result in the so-called
environmentally assisted cracking. Hydrogen effect is greater near room temperature and decreases
INTERNATIONAL JOURNAL OF ADVANCED RESEARCH IN ENGINEERING
AND TECHNOLOGY (IJARET)
ISSN 0976 - 6480 (Print)
ISSN 0976 - 6499 (Online)
Volume 5, Issue 4, April (2014), pp. 111-118
© IAEME: www.iaeme.com/ijaret.asp
Journal Impact Factor (2014): 7.8273 (Calculated by GISI)
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© I A E M E

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with increasing strain rate and hydrogen content or a charging rate [1]. It is well known that the
hydrogen cracking changes from transgranular to intergranular with increasing yield strength.
Environmental hydrogen cracking occurs when the material is being subjected to a hydrogen
atmosphere. Improper use of cathodic protection for corrosion protection results in absorbing and/or
adsorbing hydrogen into the structural steel. The effect strongly depends on the stress imposed on the
steel and it is maximum at around room temperature. This may lead to the structural failure of the
steel. The failure of steel by hydrogen is resulted from different propagation crack modes such as
transgranular cleavage, brittle intergranular, quasi-cleavage. Some researchers found that the
hydrogen degrade mechanical properties of steel without changing a fracture mode [2].
The effect of grain structure on the hydrogen cracking has been investigated by a numerous
researchers. The tendency to induce hydrogen cracking in purified iron and in Fe-Ti alloys decreases
with decrease in grain size [3-5]. The increase in ferrite grain size has enhanced toughening as well
as embrittling (beyond a certain limit of hydrogen content) of the low alloy steel under the charging
conditions [6]. The heavy-strain working after hydrogenation of Ti-6Al-4V Alloy composites
produces a non-homogeneous microstructure containing such as micro bands, shear bands and
lamellar boundaries. Moreover, it was found that a small increment of dislocation pile-up sources has
an important role in inducing dense dislocation walls and cells during in the early stages of
deformation of the material [7]. The effect of microstructure on the hydrogen embrittlement of steel
was studied by a numerous investigators [8-11].
The susceptibility to hydrogen embrittlement was observed to be closely related to the
microstructural state. Intercritical annealing at relatively low temperatures of hydrogenated dual-
phase microalloy steel exhibited quasi-cleavage fracture with some ductile dimpling. While, the
mode of fracture of the quenched hydrogenated steel from higher intercritical annealing temperatures
was predominantly intergranular fracture along prior austenite grain boundaries and cracking of
martensite laths [12].
The aim of this paper is to investigate the cracking behavior of the low strength under
cathodic charging in three-point bend system. The steel specimens with different grain sizes were
obtained by varying the heat treatment conditions.
3. EXPERIMENTAL PROCEDURE
Bend experiments were conducted on a structural steel sheet of 1mm thickness. The chemical
composition of the investigated material was analyzed using an energy dispersive X-ray (fig. 1).
Table 1 lists the elemental composition of the structural steel used in this investigation. A number of
specimens were cut from this material with dimensions of 10cm long and 1 cm wide.
Different heat treatment temperatures and holding times were applied to the steel specimens
in order to obtain different grain sizes. Table 2 lists the heat treatment temperatures and times for
obtaining different grain sizes.
The three-point bend system developed in the laboratory consists of a holder (metal block) in
which the specimens were supported at the ends and bents into a glass chamber (contained an
electrolyte and anode) by forcing a steel punch (equipped with a screw driven) against it at a point
halfway between the end supports as shown in figure 2.

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Figure 1: EDX analysis of A36 structural steel investigated.
Table 1: Chemical composition of A36 structural steel investigated, (wt%)
C Mn Si Al Cu Ni Mo P S
0.19 1.21 0.23 0.025 0.005 0.022 0.01 0.028 0.01
Figure 2: Schematic of the experimental set-up used for three-point bending during cathodic
hydrogen charging
The specimen with the metal block holder was made the cathode (graphite anode). The
electrolytic solution contained 75% (volume) methanol, 22.4% (volume) distilled water, 2.6%
(volume) sulphuric acid and 10mg.l-1 arsenic trioxide to inhibit hydrogen recombination at the

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surface. A constant current density of 25mA.cm-2 was applied for different times. Since hydrogen-
charged bend specimens were too ductile to bent to fracture in the bend test fixture, they were
deformed during cathodic hydrogen charging.
4. RESULTS AND DISCUSSION
It is well known that grain refinement improves resistance to hydrogen cracking (13-16), but
no quantitative data relating measured hydrogen content to grain size and associated mechanical
properties have been obtained. There have been attempts to explain why alloys of small grain size are
less prone to hydrogen damage. The concentration of hydrogen required to saturate grain boundaries
with a monolayer of hydrogen at various grain sizes was calculated and found that, by decreasing
grain size from 100 to 10µm, the hydrogen coverage on grain boundaries with 10ppm of available
hydrogen would decrease from saturation level to only about one site in ten covered (17). However, it
was found that an increase of grain size from 10 to 160 µm raised the threshold stress intensity of an
AISI 4340 steel from 20 to 30 MN m(-3/2)
and the amount of hydrogen cracking increased (18).
Metallographic examination of steel specimen with small grain size which had been
cathodically hydrogen charged during bending showed that cracking occurred mainly along the grain
boundaries i.e. intergranular cracking as can be seen from figure 3. It is believed that the more
disordered and high-energy grain boundaries occluded a higher amount of hydrogen. Thus the
presence of hydrogen increased the ease of cracking in these regions, either by building up localized
pressure or by reducing the cohesion force.
Figure 3: Intergranular and few transgranular cracks observed in a bent structural steel specimen
having a small grain size (i.e. 22 µm)
The surface of the steel specimen with larger grain size (i.e. 55µm) which had been
cathodically hydrogen charged during bending is shown in the figure 4. It is clearly seen from this
figure that the amount of intergranular cracking increased with grain size and the crack path is mostly
intergranular. However, in contrast to the steel specimen having smaller grain size, the former
specimen with larger grain size exhibits few transgranular cracks.

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Figure 4: Intergranular cracks observed in a bent structural steel specimen having a larger grain size
(i.e. 55 µm)
This shows that the low-angle grain boundaries, found in specimens of small grain size, were
less susceptible to hydrogen damage than the high-angle boundaries associated with large grains.
Bending of the steel specimen with larger grain size (i.e. 160µm) during cathodic hydrogen charging
reveals large and thick intergranular cracks (Fig. 5).
It is believed that specimens with small grains exhibited a certain amount of texture, with low
mismatch between grains, whereas specimens heated to higher temperatures and/or for longer periods
of times showed a larger extent of grain growth. Due to the high migration rate of the high-angle
grain boundaries, the eventual microstructure consisted of grains with a large degree of mismatch
separated by such high-angle grain boundaries. These grain boundaries have a high energy and the
distortion along them is greater, so more hydrogen is trapped in them than in the low-angle ones.
Figure 5: Intergranular cracks observed in a bent structural steel specimen having a larger grain size
(i.e. 160 µm)

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It was observed from the test results that the increasing charging time resulted in an increase
of a number of hydrogen cracks on the surface of the steel specimens. Figures 6(a) and (b) show the
surface micrographs of the steel specimens with small grain size which had been cathodically
hydrogen charged during bending for 12 and 24 hours respectively. The results showed that the
hydrogen cracks formed in the specimens charged for shorter charging time, initiated in groups
mainly along grains and they are relatively small, however, in the specimens charged for longer time,
hydrogen cracks were connected to each other and propagated along and across the grains and
therefore they are larger than those in the specimens charged for shorter time.
(a)
(b)
Figure 6: Micrographs of surface of the structural steel specimens of with small grain size (i.e. 22
µm) hydrogen charged during bending for (a) 12 hrs, (b) 24 hrs charging
Since with increasing time of charging, the grain boundaries are saturated more quickly and
hydrogen cracks formed at grain boundaries of the steel specimens and then connected and
propagated along the slip lines. This may explain why hydrogen induced cracks have been found to
propagate transgranularly when the steel specimen charged for longer time during bending.
The effect of the charging time on the number of hydrogen cracks formed was examined for
the steel specimens with small grain size which had been cathodically hydrogen charged during
bending for different charging times up to 24 hours. The crack density n, which is defined as the
number of surface cracks per unit area, are counted on a fixed area of 0.3 mm2, which was randomly

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marked on each specimen. The results of this semiquantitative study of the hydrogen cracks are
shown in figure 7. It should be noted that in the hydrogen-charged steel specimens with large grain
size, the initial transgranular cracks observed in the charged specimens having small grain size were
not presented. Instead, large hydrogen cracks along the grains were observed.
Figure 7: Effect of the charging time on the number of hydrogen cracks formed for the bent
structural steel specimens having a small grain size (i.e. 22 µm)
From the test results it was observed that the length of the hydrogen cracks increased with
increasing the charging time. Accordingly, the effect of the charging time on the crack length was
also examined for three steel specimens with large grain size which had been cathodically hydrogen
charged during bending for 3, 10 and 24 hours respectively. The results are shown in figure 8. The
above results showed that the hydrogen cracks initiated in groups along grains when the specimens
charged for shorter charging time, however, in the steel specimens charged for longer time, these
cracks were connected to each other as discussed above.
Figure 8: Effect of grain size on the length of hydrogen crack formed for the bent structural steel
specimens hydrogen charged during bending for (a) 3 hrs, (b) 10 hrs, (c) 24 hrs

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5. CONCLUSIONS
The low-angle grain boundaries in the bent steel specimens of small size are less
susceptible to hydrogen cracking than are the high-angle grain boundaries. Therefore the high-
angle grain boundaries associated with large grains provide an easy path for crack propagation.
Intergranular cracking is more likely to occur with larger grain sizes and its amount and length
increase with grain size.
6. REFERENCES
1. ASM Handbook. Vol. 11 Failure Analysis and Prevention. ASM International, 1986.
2. C. D. Beachen : Metall. Trans. 3 (1972), 437.
3. I M. Bernstein and B. B. Rath: Metall. Trans., 4 (1973), 1545.
4. I M. Bernstein : Metall. Trans., 1 (1970), 3143.
5. I M. Bernstein and A. W. Thompson: Int. Met. Rev., 21 (1976), 269.
6. S. K. Singh and B. Sasma : ISIJ international, Vol. 39 (1999), No. 4, pp. 371-379.
7. Naoya Machida, Masafumi Noda, Kunio Funami and Masaru Kobayashi, Materials
Transactions, Vol. 45, No. 7 (2004) 2288-2294.
8. I. M. Bernstein, R. Garber and G. M. Pressouyre, in “Effects of Hydrogen on Behaviour of
Materials”, edited by A. W. Thompson and I. M. Bernstein (TMS, New York, 1976) p. 27.
9. D. A. Ryder, T. Grundy andT. J. Davies, in Proceedings of 1st International Conference on
Current Solutions to Hydrogen Problems in Steels, Washington, DC, November 1982, edited
by C. G. Interrante and G. M. Pressouyre (ASM, Metals Park, 1982) p. 272.
10. P. Lacombe, M. Aucouturier andJ. Chene, in “Hydrogen Embrittlement and Stress Corrosion
Cracking”, edited by R. Gibala and R. F. Hehemann (ASTM, Metals Park, 1984) p. 79.
11. T. Alp, B. Dogan andT. J. Davies,J. Mater. Sci. 22 (1987) 2105.
12. T. Alp, F.I. Iskanderani and A.H. Zahed, J. of Materials Science, Springer, Vol. 26 (1991)
5644-5654.
13. M. Martinez-Madrid, S.L. Chan and J.A. Charles, Mater. Sci. Techn., Vol. 1 (1985),
p. 454.
14. A.W. Thompson and I.M. Bernstein, in Advances in Corrosion science and technology, Vol.
7, (ed. M.G. Fontana and R.W. Staehle), 53-175, 1980, New York, Plenum Press.
15. I.M. Bernstein and A.W. Thompson, Int. Met. Rev., Vol. 21 (1976), pp. 269-287.
16. W.M. Cain and A.R. Troiano, Pet. Eng., Vol. 37 (1965), pp. 37, 78.
17. J.K. Tien, in Effect of Hydrogen on Behavior of Materials, (ed. A.W. Thompson and I.M.
Bernstein), 1976, pp. 305-321.
18. W.W. Gerberick and A.G. Wright, in Environmental Degradation of Engineering Materials in
Hydrogen, (ed. Louthen et al.), 1981, pp. 183-206, Blacksburg, Va, Virginia Polytechnic
Institute.
19. Asst. Prof. Samir A. Al-Mashhadi, Asst. Prof. Dr. Ghalib M. Habeeb and Abbas Kadhim
Mushchil, “Control of Shrinkage Cracking in End Restrained Reinforced Concrete Walls”,
International Journal of Civil Engineering & Technology (IJCIET), Volume 5, Issue 1, 2014,
pp. 89 - 110, ISSN Print: 0976 – 6308, ISSN Online: 0976 – 6316.
20. Salman A. Al-Duheisat and Amjad Saleh El-Amoush, “An Investigation of the Cracking Path
of a Hydrogenated Tin Brass Heat Exchanger Tube”, International Journal of Civil
Engineering & Technology (IJCIET), Volume 5, Issue 3, 2014, pp. 202 - 208, ISSN Print:
0976 – 6308, ISSN Online: 0976 – 6316.

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