Journal of Surface Engineered Materials and Advanced Technology, 2013, 3, 283-286
http://dx.doi.org/10.4236/jsemat.2013.34038 Published Online October 2013 (http://www.scirp.org/journal/jsemat)
Effect of Carbon Content on Ti Inclusion Precipitated in
Tire Cord Steel
Yuedong Jiang1,2, Jialiu Lei1, Jing Zhang1, Rui Xiong1, Feng Zou1, Zhengliang Xue1
1Key Laboratory for Ferrous Metallurgy and Resources Utilization of Ministry of Education, Wuhan University of Science and
Technology, Wuhan, China; 2Research and Development Center of Wuhan Iron & Steel Group, Wuhan, China.
Received September 10th, 2013; revised October 4th, 2013; accepted October 20th, 2013
Copyright © 2013 Yuedong Jiang et al. This is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
ABSTRACT
The precipitation of TiN inclusion during solidification of different carbon content of 0.72%, 0.82% and 0.95% in tire
cord steel is thermodynamically studied respectively. The results show that the carbon content has obvious effect on
TiN inclusion precipitated in tire cord steel of different strength levels. With the carbon content of tire cord steel in-
creasing, the temperature before solidifying reduced grad u ally and the required activity produ ct of titanium and nitro gen
for TiN inclusion precipitation also declined gradually. With the same condition of initial Ti and N content in liquid
steel, the size of TiN inclusion precipitated in tire co rd steel of higher carbon con tent is bigg er than that of lower car bon
content. In order to control the harmful effects on processability of TiN inclusion precipitated in hypereutectoid tire
cord steel of the ultra high strength level, the measures of smelting process must be taken to further reduce the titanium
and nitrogen con tent in liquid steel.
Keywords: Hypereutectoid Tire Cord Steel; TiN Inclusion; Carbon Content; Thermodynamics
1. Introduction
The tire cord steel is a kind of high carbon steel, wh ich is
used for the production of car tyres meridian steel wire.
With the car lightening and considering the safety of the
car, the strength level of car tyre cord steel wire is im-
proving. Before the 1990s, the mainstream brands of the
tyre steel wire are SWRH62A and SWRH67A of ordi-
nary strength grade 1750 MPa. Since the 1990s, the main-
stream brands of the tyre steel wire are SWRH72A of
high strength grade 1870 MPa. Entering the 21st century,
the mainstream of the tire steel wire product is the hype-
reutectoid tire cord steel SWRH82A of the ultra high
strength level and brands of a higher strength level in
which carbon content reached 0.92% - 0.95%. In order to
control the harmful effects of titanium inclusion in hy-
pereutectoid tire cord steel on the drawing performance
of wire rod, steelmakers should take tough measures of
steelmaking and refining technology to remove the con-
tent of Ti and N in the molten steel to the limit as much
as possible. In spite of this, in the condition of current steel
production technology, the precipitation of titanium in-
clusion is still inevitable before solidifying [1]. In order
to provide theoretical guidance to control TiN inclusion
precipitated in the hypereutectoid tire cord steel of the
ultra high strength level, the effect of carbon content on
Ti inclusion precipitated in tire cord steel of different
intensity levels is studied on th e basis of thermodyn a mics
in this paper.
2. Temperature Changes in Solidifying Front
of Tire Cord Steel
The temperature in the front of solidifying (Ts − l) of liq-
uid steel is the solidification interface temperature, this
temperature value is between the solidus temperature (Ts)
and the liquidus temperature (Tl), It related with the so-
lidification rate (g) of liquid-solid two phase region. The
temperature in the front of solidifying is calculated ac-
cording to formula (1) [2]:
0
0
0
1
l
sl
ls
s
TT
TT TT
gTT


 

(1)
In formula (1) T0 is the melting point of Fe 1538˚C,
the liquidus temperature (Tl) and the solidus temperature
(Ts) are calculated according to formula (2) and formula
(3):

Effect of Carbon Content on Ti Inclusion Precipitated in Tire Cord Steel 284
153865 []8 []5 []
20 []30 []25 [ ]
1300[] 90[]80[]
l
TwCwSiw
wTi wP wS
wHwN wO
 


Mn
(2) [3]
1538175 []20 []
30[]40[ ] 280[]
575 [ ]160[]
S
TwCwSi
wMnwTiwP
wS wO
 


(3) [3]
The components of tire cord steel used for calculation
are shown in Table 1.
According to the components of tire cord steel in Ta-
ble 1 the liquidus temperature (Tl) and solidus tempera-
ture (Ts) can be calculated, as shown in Table 2. With the
increase of carbon content, the temperature difference of
liquidus and solidus become large.
The relationship between the temperature in the front
of solidifying (Ts − l) and solidification rate (g), as shown
in Figure 1.
Figure 1 shows that the temperature in the front of so-
lidifying (Ts − l) decreased along with the development of
the solidification process. When the solidification rate is
the same, the higher carbon content in the tire cord steel,
the lower the temperature in the front of solidifying.
3. Effect of Carbon Content on Ti Inclusion
Precipitated in Tire Cord Steel
Due to the solidification segregation of the solute ele-
ments during solidification process, Ti and N are enrich-
ed in the solid ifying front co ntin uou sly, wh en the activ ity
product of Ti and N is greater than the balanced activity
product of TiN precipitation, TiN inclusion will precipi-
tate according to the followi ng formula:





0291000 107.97
S
TiN TiN
GT

 
(4)
lg5.64 15220
TiN
K
T

 (5)
In formula (5), KTiN is the equilibrium activity product
of TiN precipitation, which related with the temperature
Ts - l in the front of solidifying. With the solidification
rate (g) of liquid-solid two phase region increase, tempe-
rature in the front of solidifying dropped and the value of
KTiN calculated according to formula (5) declined corre-
spondingly.
The actual activity product of Ti an d N in the solidify-
ing front is:




TiNTi N
QffwTiwN  (6)
In formula (6), fTi and fN are the activity coefficients of
Ti and N at the temperature of solidifying front, which
can be calculated according to formula (7) and formula
(8):
Table 1. Chemical composition of high carbon tire cord
steel.
Steel gradeC P S Si Mn N Ti
72A 0.720.010.008 0.2 0.5 0.0040.0006
82A 0.820.010.008 0.2 0.5 0.0040.0006
95A 0.950.010.008 0.2 0.5 0.0040.0006
Table 2. The value of Tl and Ts for tire cord steel of differ-
ent carbon content.
Steel grade Tl T
s T l - Ts
72A 1486 1386 100
82A 1480 1368 112
95A 1472 1345 127
0.2 0.4 0.6 0.8 1.0
1340
1360
1380
1400
1420
1440
1460
1480
凝固率，g
凝固前沿温度，℃
72A
82A
95A
solidification rate,(g)
tempera ture i n the f r on t of solidifying,
℃
Figure 1. Relationship between the temperature in the front of solidifying and solidification rate at different carbon content
f tire cord steel. o

Effect of Carbon Content on Ti Inclusion Precipitated in Tire Cord Steel 285


1873
lg 2557 0.365lg
Tis lTi
fT f

 (7) [4]


1873
lg32800.75 lg
Nsl N
fT f

 (8) [4]
In formula (7) and formula (8), fTi(1873) and fN(1873) are
the activity coefficients of elements Ti and N at 1873 K
respectively:



1873
lg j
Ti
Ti
f
ewj (9)



1873
lg j
N
N
f
ewj (10)
The interaction coefficients
j
Ti
e and
j
N
e at 1873 K
can be obtained by literature [5,6].
Since the solute elements in the solidifying front en-
riched during solid ification process continuously, so w[j]
can be calculated according to formula (9) and formula
(10) [7]. It can be seen that w[j] is the function of solidi-
fication rate (g).
 

1
01k
wjwjg   (11)
 


0
11
wj
wj gk  (12)
Formula (11) is used to calculate the quality percent-
age content of Ti, Si, Mn in the solidifying front and for-
mula (12) is used to calcu late the quality percen tage con-
tent of C, N, P, S in the solidifying front; w[j]0 is the ini-
tial percentage of so lute element j in liquid steel. k is the
equilibrium partition coefficients between liquid steel and
γ-Fe which can be obtained by literature [8,9].
The actual activity product QTiN of Ti and N in the so-
lidifying front of liquid steel can be calculated by for-
mula (6) - formula (12), When the actual activity product
QTiN of Ti and N in the solidifying front is greater than
that of the equilibrium activity product KTiN, TiN inclu-
sion will precipitate in the solidifying front. If the initial
Ti, N content of tire cord steel are 0.0006% and 0.004%
respectively, the temperature in the front of solidifying
and solidification rate for 72A, 82A, 95A, when TiN in-
clusion precipitated in the solidifying front are shown in
Figure 2.
Figure 2 shows that with the carbon content in tire
cord steel increase, the temperature in the front of solidi-
fying dropped when TiN inclusion precipitated during so-
lidification and the required equilibrium activity product
is also declined (Figure 2(a)). In addition, with the in-
crease of carbon content in the tire cord steel, TiN inclu-
sion is earlier to precipitate in the solidifying front (Fig-
ure 2(b)), Therefore, TiN inclusion is also more easily to
grow up.
In conclusion, the carbon content has obvious effect on
TiN inclusion precipitated in tire cord steel of different
strength levels. The higher the carbon content in molten
steel, the easier the TiN inclusion will precipitate and
grow up during solid ification process.
Therefore, in order to control the size of TiN inclusion
precipitated in hypereutectoid tire cord steel of ultra high
strength level, more strict measures of steelmaking and
continuous casting process must be taken to further re-
duce the initial titanium and nitrogen content in liquid
steel. Because the effect of N on the grown up of TiN in-
clusion is bigger than that of Ti [1], Therefore, it is par-
ticularly important to further reduce the N content in hy-
pereutectoid tire cord steel.
The Ti content in the high carbon tire cord steel in
molten steel can be reduced effectively through the fol-
lowing measures in the production practice; (1) reducing
the TiO2 content in blast furnace burden and silicon con-
tent in hot metal; (2) control of carbon conent and tem-
perature in the bof(basic oxygen furnace) endpoint; (3)
control of the amount of converter slag; (4) material con-
trol of LF(ladle furnace) refining slag and the TiO2 content
1340 1360 1380 1400 1420
-5.0
-4.5
-4.0
-3.5
-3.0
-2.5
-2.0
-1.5
凝固前沿温度，℃
lgKTiN, lgQTiN
1—lgK
TiN
72A
2—lgK
TiN
82A
3—lgK
TiN
95A
4—lgQ
TiN
(72A 、 82A 、 95A)
4
3 2 1
1440
14601480
temperat ure in the front of solidifying,℃
0.90 0.91 0.92 0.93 0.94 0.95 0.96 0.97 0.98
-5.0
-4.5
-4.0
-3.5
-3.0
-2.5
-2.0
-1.5
lgK
TiN
, lgQ
TiN
凝固率，g
1
2
3
1—lgK
TiN
72A
2—lgK
TiN
82A
3—lgK
TiN
95A
4—lgQ
TiN
(72A 、 82A 、 95A)
4
solidi fication rate,(g )
(a) (b)
Figure 2. The effect of carbon content on TiN inclusion precipitated in tire cord steel.

Effect of Carbon Content on Ti Inclusion Precipitated in Tire Cord Steel 286
in the tundish flux. The control of nitrogen in the tire
cord steel are mainly from the following several aspects:
(1) reducing the reblowing operation in endpoint; (2) us-
ing pre-melted slag to cover the liquid steel and reducing
the inspiration during converter tapping; (3) using low
nitrogen carburant; (4) control of LF refining slag and ar-
gon stirring; (5) further reducing the content of oxygen
and nitrogen in liquid steel by vacuum treatment.
4. Conclusion
(1) The temperature before solidifying (Ts − l) decreas-
ed along with the development of the solidification proc-
ess. When the solidification rate is the same, the higher
the carbon content in the tire cord steel is, the lower the
temperature before solidifying is.
(2) The carbon content has an obvious effect on TiN
inclusion precipitated in tire cord steel of different strength
levels. The higher the carbon content is in the molten
steel, the easier the TiN inclusion will precipitate and
grow up during the solid ification process.
(3) In order to control the size of TiN inclusion pre-
cipitated in hypereutectoid tire cord steel of the ultra high
strength level, more strict measures of steelmaking and
the continuous casting process must be taken to further
reduce the initial titanium and nitrogen content in liquid
steel, especially the N content.
5. Acknowledgements
The author gratefully acknowledges the financial support
for this work from the Science research plan (No.
201210321098) of Wuhan Science and Technology Bu-
reau, China.
REFERENCES
[1] J. L. Lei, Z. L. Xue and Y. D. Jiang, “Study on TiN Preci-
pitation during Solidification of Hypereutectoid Tire Cord
Steel,” Metalurgia International, Vol. 17, No. 9, 2012, pp.
10-15.
[2] I. Ohnaka, “Mathematical Analysis of Solute Redistribu-
tion during Solidification with Diffusion in Solid Phase,”
Transaction ISIJ, Vol. 26, No. 12, 1986, pp. 1045-1051.
[3] E. P. Chen, “Calculation Method and Empirical Formula
for Melting Point of Fe-Based, Ni-Based and Co-Based
Alloy,” Special Steel, Vol. 13, No. 2, 1992, pp. 25-30.
[4] J. Fu, J. Zhu and L. Di, “Research on Precipitation Regu-
larity of TiN in Micro Alloy Steel,” Acta Metallurgica Si-
nica, Vol. 36, No. 8, 2000, pp. 801-804.
[5] L. K. Liang, “Metallurgical Ther modynamics and Ki netics,”
Northeast University Press, Shenyang, 1990, pp. 30-31.
[6] Z. T. Ma and J. Dieter, “Characteristic of Oxide Precipi-
tation and Growth during Solidification of Deoxidized
Steel,” ISIJ International, Vol. 1, No. 38, 1988, pp. 46-
52.
[7] Y. Qu, “Steelmaking Principles,” Metallurgical Industry
Press, Beijing, Vol. 8, 1983, pp. 294-313.
[8] Y. Ueshima, S. Mizoguchi and T. Matsumiya, “Analysis
of Solute Distribution in Dendrites of Carbon Steel with


Transformation Solidification,” Metallurgical Tran-
saction, Vol. 17B, No. 4, 1986, pp. 845-859．
[9] P. A. Manohar, D. P. Dunne and T. Chandra, “Grai n Growt h
Predictions in Microalloyed Steels,” ISIJ International,
Vol. 36, No. 2, 1996, p. 194.
http://dx.doi.org/10.2355/isijinternational.36.194