Field of Invention
The present invention relates to a process for producing alloy steel products with low
titanium level . More particularly the present invention relates to a process for producing
ball bearing/other alloy steels with titanium at a level less than 30 ppm The invention is
further related to a process for producing alloy steel products with low titanium level in
which both high and low titanium scrap may be used.
Background of the Invention
There is demand for steel having high fatigue properties. In particular the automobile
industry has a need for steel having high fatigue properties for the manufacture of ball
bearings. Titanium in steel is known to have influence on fatigue properties. The
applicants have found that steel with the desired fatigue properties can be achieved in
certain grades of alloy steels having titanium content restricted to less than 30 ppm. Such
low titanium level would provide bearing grade steel including ball bearing steels for car
industry and also for use in aerospace turbine bearings to obtain the desired fatigue
properties.
Objects of the Invention
It is the object of the present invention to provide for a process for producing low
titanium level alloy steel products including ball bearing steels for use in car industry and
also aerospace turbine bearings.
It is a further object of the present invention to use both high and low titanium scrap to
obtain low titanium in alloy steel products including ball bearing steel.
It is another object of the present invention to achieve enhanced fatigue properties of the
end product by control of titanium in steel.
Summary of the invention
Thus according to the present invention there is provided a process for producing alloy
steel products with low titanium level, the process comprising of the following steps:
i) melting of input materials;
ii) effecting decarburisation through oxygen lancing of the melt to generate foamy
slag;
iii) allowing the slag to drain;
iv) tapping in the ladle with reduced carry over slag (less than 15kg/t, preferably less
than 10 kg/t);
v) minimising arcing duration to less than 25 minutes, preferably less than 20
minutes;
vi) refining for temperature and composition adjustment.
The steps i) - iv) are carried out in the EAF while steps v) - vi) take place in the VAD of
the EAF - VAD route.
According to further aspect of the present invention there is provided a process for
producing alloy steel products with low titanium at a level less than 30ppm.
According to another aspect of the present invention both high and low titanium -
containing scrap is used.
According to another aspect of the present invention there is provided a process for
producing alloy steel products with low titanium level for attaining enhanced fatigue
properties in bearing grade steel.
Detailed Description of the Invention
The input to EAF comprises of plain carbon/alloy steel scrap, pig iron/hot metal etc. In
order to have control of titanium content, hitherto, the practice involved careful selection
of low titanium scrap and ferroalloys. Even with this the titanium content often exceeded
the specified limit causing off grade heats.
The alloy steel produced by the process of the invention has titanium level less than
30ppm even with the use of high titanium scrap. Such alloy steel is used in ball bearing
steels in car industry and also in aerospace turbine bearings to obtain the desired fatigue
properties. Steel is produced through Electric Arc Furnace (EAF), Vacuum Arc
Degassing (VAD) route. The process may be effected in conventional furnaces using
standard alloy steel making processes.
The various process steps of the invention are discussed below in greater details:
Melting of input materials ;-
Input materials including steel scrap with or without other scrap like Pig iron, Hot metal
iron, Iron carbide, etc are charged in EAF from top by swinging out roof.
The titanium content in various input scrap materials are generally as under:

Both high and low titanium scrap is used. Use of high carbon input materials like Pig
iron/Hot metal iron is to the extent of 300-400kg/t steel and preferably to the extent of
200 kg/t give better results. Power is then switched on and scrap is then melted by three
electrode arc system. When the scrap melts and attains a temperature of around 1550-
1560°C, metal sample is sent for analysis
Effecting decarburisation of the melt through oxygen lancing to generate foamy slag:-
Based on the carbon analysis and final carbon requirement, decarburisation is carried
out through oxygen lancing in the bath. Carbon boil i.e. decarburisation by carbon
oxidation of 0.3 0.4% is desired for good quality steel. Duration of oxygen lancing
is usually for 5-15 minutes at How rate of 600-800 Nm3/hr. In specific cases if the
input oi" carbon is too high or too low, the duration of oxygen lancing may vary.
Oxygen lancing is resorted to give a carbon boil and generate foamy slag in high
v^cuOOn ualn. j
Allowing the slag to drain:-
Foaming slag overflows through slag door resulting in automatic slag off. Titanium, a
highly oxidisable element, which is present in scrap as tramp element gets oxidised,
floats up to slag and eventually is removed from bath along with slag if good slag off
is done exposing more than 50% of the bath surface.
Tanning in the ladle with reduced carry over stag (less than 15 kg/t):-
The bath temperature is then raised to 1640°C and tapped in a ladle. If furnace is not
equipped with slag stopping devices, slag also comes out during tapping along with
metal stream. Carry over slag is controlled by skilled operation (through timely tilting
back of the furnace), characteristic and amount of shig in the furnace. Carry over slag
is maintained at less than 15kg/t, preferably less than lOkg/t and more preferably less
than 5kg/t.
Minimising arcing duration to less than 25 minutes;-
The metal along with carry over slag is taken to a secondary refining unit called VAD
(Vacuum Arc Degassing). In VAD, alloying and refining as well as arc heating are
carried out. Based on the VAD-IN temperature, extent of alloying and refining
requirement and grade specific VAD dispatch temperature, arcing is carried out in
VAD. In VAD operation lowest possible arcing is always attempted through measures
like maintaining proper tap temperature, ladle condition as well utilising operational
skills.. Arcing time beyond 25 minutes will be harmful from titanium reversal point of
view as titanium reversal has direct relation to arcing time in VAD. Arcing duration is
ihus preferably minimised to less than 20 and mote preferably to less than 15 minutes.
Lower the arcing time, lower will be titanium reversal and hence desired lower level
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Refining for temperature and composition adjustment:-
This rcilning in the VAD involves metallurgical processes such as deoxidation,
desulphurisation, degassing, alloying, stirring and heating. Adding of fluxes or
ferroalloys are made as per requirement. Lime is added in an amount of 300-
600kg/heat (Heat size ~ SOO.Jjs^of lime at an amount more than 400kg/heat is found
to be preferable
Finally low titanium ferrochrome is added at an amount of 20-25kg/t of the charge.
The amount of titanium in low titanium ferrochrome varies in the level of 0.05-0.06%.
After attaining the/desired chem.isuV, quality and temperature of the steel the heat is
taken for casting
Detailed description in relation to non limiting exemplary illustrations
Example 1&2
Two heats were performed as Example 1 & 2 as per the present invention. Pig iron
was used partly as input material for both the experiments. The stage wise titanium
analyses are shown in Table-1 and Table-2 for Example 1 & 2 respectively.
The output steel from EAF contains as low as 3 ppm titanium. This is due to its
removal by decarburisation through oxygen lancing. As the addition of FeCr is made
in VAD the titanium content goes up to 22-28 ppm level. This becomes possible due
to the absence of any titanium reversion from slag as most EAF slag was drained
out/retained in EAF.
Table - 1 : Chemical Analysis of steel samples at different stages of steel making
It can be seen that even use of high titanium input materials lead to production of low
titanium steel due to intensive oxygen lancing and prevention of titanium reversion
from the slag by allowing the slag to drain off.
Example 3
The heat performed as Example 3 had A2 revert scrap as part of the input materials.
Adequate decarburisation through oxygen lancing was not done. Also there was good
amount of carry over slag.
Table-3 shows the result of this heat where intensive oxygen lancing was not restored
to due to non usage of high carbon bearing materials. Although upto EAF stage the
titanium content was 5-7 ppm, the same went up to 48 ppm for same addition of FeCr
as in Examples 1 &2 .
It can be seen that absence of intensive oxygen lancing and the titanium reversion
from EAF carry over slag have lead to the high titanium content in this heat.
The effect of various input materials are shown in the following figures: (I
A
Fig-1 shows the effect of usage of A2 scrap in charge (Ti~0.024%) without high
carbon inputs, on the titanium content in steel. In most heats with greater than 15%
A2 charge, the titanium content exceeded 30 ppm.
It can be seen that even low titanium content input materials lead to high titanium
content in steel as intensive oxygen lancing and draining of carry over slag have not
been resorted to.
Fig.-2 shows the effect of increasing usage of high carbon inputs like pig iron, cast
iron and hot metal on final titanium content in steel. Beyond 25-30% usage of
PI/HM, most heats finish with less than 30 ppm titanium, due to extensive oxygen
lancing and drainage of slag inspite of high Ti content in such charge materials
compared to A2 Scrap.
Fig.-3 shows that under reducing condition, the arcing in VAD favours reversion of
titanium from slag. It can be seen that lower the arcing time in VAD, lower is the
titanium reversal.
Fig.- 4. This flow chart represents the entire process of the present invention of
producing alloy steel products with low titanium level. It starts with melting of input
materials that may be high or low in titanium content and include scrap, hot metal,
pig iron in the EAF.
The melt is decarburised through oxygen lancing which results in continuous slag
drain out
Next the tapping takes place in the ladle and carry' over slag is minimized.
The metal along with carry over slag is then transferred to VAD.
In the VAD alloying, refining and arcing are carried out - the arcing time is kept low
to minimize titanium reversal; additions of lime, ferroalloys are made as per
requirement and thus the composition is maintained.
Finally after attaining thqfdesired chemistryjrthe heat is taken for casting.
We claim
1. A process for producing alloy steel products with low titanium level, the process
comprising of the following steps:
i) melting of input materials;
ii) effecting decarburisation through oxygen lancing of the melt to generate foamy
slag;
iii) allowing the slag to drain;
iv) tapping in the ladle with reduced carry over slag (less than 15kg/t);
v) minimising arcing duration to less than 25 minutes;
vi) refining for temperature and composition adjustment.
2. The process according to claim 1 wherein the steps i) - iv) are carried out in the EAF
while steps v) - vii) take place in the VAD of the EAF - VAD route.
3. The process according to 1 for producing alloy steel products with low titanium level
wherein titanium is at a level of less than 30 ppm.
4. The process according to anyone of claims 1 to 3 wherein both high and low titanium
-containing scrap is used.
5. The process according to anyone of claims 1 to 4 wherein the high carbon input
materials are Pig iron, Hot metal Iron, Iron carbide.
6. The process according to anyone of claims 1 to 5 wherein the high carbon input
materials are added in the range of 300-400kg/t steel.
7. The process according to claim 6 wherein the high carbon input materials are added
in the level of 200kg/t steel.
8. The process according to any preceding claims wherein the oxygen lancing is done
for 5-15 minutes.
9. The process according to any one of the preceding claims wherein the oxygen
lancing is done to decarburise in the range of 0.3-0.4%.
10. The process according to any one of the preceding claims wherein the oxygen
lancing is done with a ilow rate of oxygen of 600-800NmJ /hi.
11. The process according to any one of the preceding claims wherein foamy slag
along with oxidised titanium is simultaneously allowed to drain off by exposing
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.
12. The process according to any one of the preceding claims wherein the carry over
slag is maintained at low level of less than lOkg/t by sk4tied-t>pcratwn-of timely
tilting back of the furnace. A/ ^/>
13. The process according to any one of the preceding claims wherein the carry over
slag is maintained at less than 5kg/t.
14. The process according to any one of the preceding claims wherein the arcing time
is kept below 20 minutes.
15. The process according to claim 14 wherein the arcing time is kept below 15
minutes.
16. The process according to any one of the preceding claims wherein the step of
refining for temperature and composition adjustment comprises addition 300-600
kg/hcatof lime.
17. The process according to claim 16 wherein the addition of lime is done at an
amount more than 400 kg/heat.
18. The process according to any one of the preceding claims wherein the step of
refining for temperature and composition adjustment comprises addition of
ferrochromc which has low titanium in the range of 0.05-0.06 %.
19. The process according to claim 19 wherein the said low titanium ferrochrome
used is in the level of 20 -25kg/t.

A process for producing alloy steel products with low titanium level. More particularly a process for producing ball bearing/other alloy steels with titanium at a level less than 30 ppm. The invention is further related to a process for producing alloy steel products with low titanium level in which both high and low titanium scrap may be used. The process comprises melting of input materials; effecting decarburisation through oxygen lancing of the melt to generate foamy slag; allowing the slag to drain; tapping in the ladle with reduced carry over slag (less than 15kg/t); minimizing arcing duration to less than 25 minutes; and refining for temperature and composition adjustment.