Effect of Titanium Addition on Behavior of Medium Carbon Steel

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Journal of Minerals and Materials Characterization and Engineering, 2012, 11, 1108-1112

Published Online November 2012 (http://www.SciRP.org/journal/jmmce)

Effect of Titanium Addition on Behavior of

Medium Carbon Steel

Hoda S. El-Faramawy, Saeed N. Ghali*, Mamdouh M. Eissa

Steel Technology Department, Central Metallurgical R & D Institute (CMRDI), Cairo, Egypt

Email: *[email protected]

Received July 10, 2012; revised August 15, 2012; accepted August 31, 2012

ABSTRACT

This work aims at investigating the influence of titanium addition on behavior of medium carbon steel. Three types of

medium carbon steel with different titanium content and one reference steel titanium free were produced in 100 kg in-

duction furnace. Titanium addition was increased up to 0.230%. The produced steels were forged at start temperature

1150˚C. Forging process was finished at temperatures 900˚C, 975˚C, and 1050˚C. Microstructure examination and

hardness measurement were carried out for forged steels. Mechanical properties and impact measurements were carried

out for quenched tempered steels. Ti addition was found to have significant influence on refinement of grains and in-

crease of ferrite/pearlite ratio. It was also, observed that grain size decreases as finishing temperature of forging process

decreases. Both Ti addition and lowering finishing forging temperature have positive effect on hardness. In addition,

results indicated that addition of titanium has significan t effect on the mechanical properties and toughness.

Keywords: Titanium; Refinement; Ferrite; Pearlite; Forging

1. Introduction

Mechanical properties of steels are strongly connected to

their microstructure obtained after heat treatments that are

generally performed in order to achieve a good hardness

and/or tensile strength with sufficient ductility [1].

Microalloyed steels have been developed for many

years and are widely used in modern industry. It is well

known that microalloyed high-strength low-alloy steels

are essentially carbon low-alloy steels that contain small

additions of alloying elements such as Nb, V, or Ti [2-6].

These elements act as solution atoms or precipitation to

suppress the recrystallization and grain growth of auste-

nite. Microalloying of carbon steels is widely used in

practice. At the same time, little attention has been given

to medium carbon steels containing vanadium, niobium

and titanium.

The obtained fine grain microstructure can enhance the

mechanical properties of steels obviously. In addition,

multimicroalloying can lead to the formation of carbide

and nitride particles which can further influence on the

mechanical properties of steels [7-10].

Due to the high price of niobium and vanadium, the

development of titanium microallo yed steels seems to be

attracted and get more attention recently.

Steel alloyed with titanium alone esp ecially the forma-

tion mechanism of TiC precipitation during different

processes and its effect are seldom studied in carbon

steel.

This work aims at investigating the influence of tita-

nium additions in medium carbon steels on mechanical

properties and also investigation of the effect of finishing

forging temperatures on grain refinem ents.

2. Experimental

Four steels with different titanium contents were melted

in induction furnace of capacity 100 kg and cast in sand

mold. Complete chemical analysis has been carried out

for all cast steels. Ingots with diameter 90 mm were hot

forged to about 40 mm square. The ingots were reheated

up to 1200˚C and hold to 30 min then start forging.

Starting forging temperature was 1150˚C while forging

process was ended at temperatures 900˚C, 975˚C, and

1050˚C for the four steels. Microstructure examination

and hardness measurements were carried out after for-

ging process. Ferrite/pearlite ratios were measured using

software Paxit program for forged steels. The forged bars

—which ended at 975˚C—were reheated up to 960˚C for

1 hour and water-coo led followed by tempering at 260˚C

for 30 min. The mechanical properties were measured for

tempered steels. The standard V-notch Charpy specimens

samples (10 mm × 10 mm × 55 mm, notch depth 2 mm)

was prepared to investigate the influence of the titanium

addition on impact toughness at 25˚C for tempered steels.

*Corresponding author.

H. S. EL-FARAMAWY ET AL. 1109

3. Results

The melted steels have the chemical composition given

in Table 1. The microstructure examination of forged

steels at finishing temperatures 900˚C, 975˚C, and 1050˚C

is given in Figures 1-3 respectively.

It is clear that the grain size decreases as titanium con-

tent increases at finished forging temperature 900˚C as

illustrated in Figure 1. This can be attributed to the pre-

sence of titanium forming titanium carbides and/or tita-

nium nitrides on the austenite grains th at retard the grains

growth and hence grain of ferrite decrease. The same re-

sults observed at finishing forging temperatures 975˚C

and 1050˚C as shown in Figures 2 and 3. However, it

was observed that for the same steel, the grain size in-

crease by increasing the finishing forging temperature.

This can be due to the grain growth of austenite phase

during forging process and hence the ferrite and pearlite

grain size increase. Also, it may be due to the solubility

of titanium in austenitic phase increase as temperature

increases leading to decrease of TiC formation which

suppress the growth of austenitic grains.

The microstructure examination show that the fer-

rite/pearlite ratio increases by increasing titanium content.

This can be attributed to the formation of titanium car-

bides and consequently the free carbon is decreased

leading to the increase of ferrite/pearlite ratio.

Table 1. Chemical composition of melted steels.

Chemical composition (%)

Type C Si Mn P S Cr Ti

T0 0.301 0.108 1.13 0.040 0.030 0.4010.0015

T1 0.277 0.083 1.01 0.030 0.013 0.4040.0485

T2 0.275 0.104 1.04 0.033 0.019 0.4140.0997

T3 0.296 0.110 1.02 0.034 0.015 0.4090.2300

(a) (b)

Figure 1. Microstructure of forged steels at finishing forg-

ing temperature 900˚C ((a) reference steel 0.0015%Ti, (b)

0.0485%Ti, (c) 0.0997%Ti, (d) 0.230%Ti)—X400.

However the finished forging temperature has little in-

fluence on the ferrite/pearlite ratios as illustrated in Ta -

ble 2.

It is clear fromTable 2 that ferrite percentage increases

from 10% to 12% as titanium content increases from

0.0015% to 0.2300%. While, th ere is little change in fer-

rite/pearlite ratio that results from finishing temperatures

of forging.

(a) (b)

Figure 2. Microstructure of forged steels at finishing forging

temperature 975˚C ((a) reference steel (b) 0.0485%Ti, (c)

0.0997%Ti, (d) 0.230%Ti)—X400.

(a) (b)

Figure 3. Microstructure of forged steels at finishing forg-

ing temperature 1050˚C ((a) reference steel (b) 0.0485%Ti,

Table 2. Show ferrite percentage of different Ti steel grades

at different finishing forging temperature.

Ferrite (%) at temperature (˚C)

Type 900 975 1050

Ti 0 68.28 65.02 63.13

Ti 1 69.46 70.94 69.12

Ti 2 73.53 71.78 70.01

Ti 3 78.21 76.95 75.12

H. S. EL-FARAMAWY ET AL.

1110

The results show that the hardness increases by in-

creasing titanium content for each finishing forging tem-

peratures and increases by decreasing the finishing of

forging temperature as illustrated in Figure 4. Theref ore,

it is clear that the main controlling parameter for hard-

ness is the grain refinement.

Titanium content has great influence on mechanical

properties of steels, where it was noticed that the yield

and ultimate tensile strength increase by increasing tita-

nium content but elongation decreases as given in Figure

5. This can be attributed to the effect of grain refinement

of titanium.

Impact toughness is of importance for the evaluation

of the resistance capability of steel against the crack ini-

tiation and rupture. In general, it is of significant evi-

dences that the additio n of low alloy element (such as V,

Ti, and Ni , etc.) [11-12].

Titanium is used to retard grain growth and thus im-

prove toughness as it is clear from Figure 6.

Ti Content, %

0.00 0.05 0.10 0.15 0.20 0.25

Hardness, HV

100

120

140

160

180

200

220

240

260

900 oC

975 oC

1050 oC

Figure 4. Variation of hardness with titanium content at

different finishing forging temperatures.

Figure 5. Yield, ultimate tensile strength and elongation of

tempered steels with different titanium content.

The relation between the solubility products of car-

bides and nitrides as a fun ction of temperature illustrated

by Aronsson [13] is given in Figure 7. From this figure,

it is clear that the solubility product of TiC in austenitic

phase increases by increasing temperature from 770˚C to

1050˚C.

From the results given in this figure the solubility of

titanium at this temperature range can be calculated and

is given in Table 3. From this table, it is clear that the

solubility of titanium increases by increasing temperature.

Consequently, TiC will decreases by increasing tem-

perature in the austenitic phase. As, there is a direct ef-

fect of TiC on the formed ferrite grain size, therefore by

decreasing temperature the ferrite grain size decreases.

The actual atomic mole fraction of Ti and its solubility

product of four types of steels is given in Table 4.

Ti content, %

0.00 0.05 0.10 0.15 0.20 0.25

Impact Energy, J

Figure 6. Impact energy of tempered steels at different tita-

nium content.

Figure 7. Solubility products of carbides and nitrides in

austenite as a function of temperature [13].

H. S. EL-FARAMAWY ET AL. 1111

Table 3. The predicted solubility and solubility product of

Temp K 10000/T(K) Intercept mic

TiC with temperature according to Aronsson [13].

Solubility Solubility (S) Ato

product (S2) (mole fraction) %

1173 8.525149 2.8807 0.317188 0.563194

1248 8.012821 2.8807 0.471245 0.686473

1323 7.558579 2.8807 0.607835 0.779638

1073 9.319664 2.8807 0.078277 0.27978

1053 9.496676 2.8807 0.025049 0.15827

1044 9.578544 2.8807 0.000432 0.02078

1043 9.587728 2.8807 –0.00233 -

able 4. Actual solubility and solubility product of investi-

Type Ti mole Fraction Solubility product

gated steels.

Ti 0 0.0017 2.972E-06

Ti 1 0.0559 3.124E-03

Ti 2 0.1148 1.318E-02

Ti 3 0.2644 6.992E-02

Figure 7 and Table 3 show that the formation of TiC

the grain growth is re-

4. Conclusions

nium has great influence on grain

[1] N. Mebarki, D. Delagnes, P. Lameise, F. Delimas and C.

Levaillant, “Ricrostructure and

Mechanical Prpered Martensitic

function in temperature of austenitic phase. Solubility

of Ti decreases by increasing temperature as indicated

from decreasing of solubility and solubility product. The

solubility of Ti at 770˚C equal zero that is mean that any

Ti content must form TiC. At 800˚C the solubility is

0.27978% atom. This means that any titanium content

less than 0.2797% atomic present as soluble and start to

form TiC by decreasing temperature. This means that the

grain refinement is controlled at stage of cooling above

and near to Ac3, Ti & C content.

Actually, this study shows that

ricted as finishing forging temperature decreased (from

1050˚C to 900˚C). But, Ti content has positive effect on

grain refinement at high temperature (up to 1050˚C). The

later need to more investigation in future work.

The addition of tita

refinement and hence has positive effect on hardness,

mechanical properties, and impact toughness. The grain

refinement increases as finished forging temperature de-

creases fro m 1050˚C to 900˚C passing through 975˚C.

Ferrite/pearlite ratio increase as titanium content in-

ease from 0.0015% to 0.2300%. The finishing forging

temperature has little negative influence on ferrite/pear-

lite ratio. The precipitation of TiC is took place in tempe-

rature above an d close to Ac3.

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