FIELD OF THE INVENTION
The present invention relates to a process for production of sulphur bearing crank shaft
quality (CSQ) steel grades with consistent sulphur content in a selective narrow band. More
particularly, the present invention relates to developing a standard operating practice for re-
sulphurisation of alloy steel to achieve consistency in sulphur recovery so as to limit sulphur
content within desired narrow band. The process of the invention is directed to developing a
standard practice for steel re-sulphurisation and optimisation of slag composition at Vacuum
Arc Degasser (VAD), favouring controlling sulphur in a narrow band ranging from 0.022% to
0.033%. The crank shaft quality (CSQ) steel grades with desired consistently controlled
narrow band sulphur content achieved by following the process comprising grade specific
optimization of ladle addition comprising initial deoxidation by silicon manganese, lowering
Aluminium addition, deferring iron pyrite addition toward secondary refining treatment in
VAD at later stage at specific temperature range of 1575°C - 1585°C followed by degassing
up to 100 torr, modified flux and de-oxidation practice to achieve a low basicity, low
sulphide capacity slag to arrest further de-sulphurisation and improve re-sulphurisation
with higher sulphur recovery. The process of the invention on one hand stabilize sulphur
content in alloy steel grade in desired narrow band and on the other hand favor reducing
the aluminium consumption by about 30% due to modified deoxidation practice, reduce VAD
treatment time by about 25% by achieving consistent sulphur recovery and avoiding
multiple processing of heat for re-sulphurisation. The present invention thus having the
potential for wide industrial application in alloy and special steel making plants to cater to a
variety of end application for the consistently controlled sulphur content in narrow band of
crank shaft quality and other variants of alloy steel having definite sulphur to cater to
automobile and other industries using such grades.
BACKGROUND OF THE INVENTION
It is known in the art of steel making and ladle refining of alloy steels that making of crank
shaft quality alloy steel grades for application in auto sector having the process route
comprising Electric Arc Furnace (EAF) - Vacuum Arc Degassing (VAD) - Bottom Pouring
(BP)/ Continuous Casting (CC). It is also known in the art that auto sector grades of steel
require sulphur in a specific range to improve machinability during processing of forged and
annealed steel billet/bars. In order to maintain sulphur in a narrow band, suitable flux and
deoxidation practice has been designed to achieve a low basicity, low sulphide capacity slag
to minimize de-sulphurisation during refining operation and to improve re-sulphurization
(higher sulphur recovery).The steel is primarily refined in EAF and tapped in ladle along with
pet coke, de-oxidiser (aluminium), SiMn and iron pyrites. The normal practice leads to wide
variation of sulphur analysis due to variation in oxygen potential, slag analysis and
treatment time in vacuum refining unit. The steel is again re-sulphurised in VAD by addition
of either iron pyrites or sulphur cored wire for adjustment of sulphur in specified band by
repeated addition leading to higher treatment time and hence adding to cost of processing,
resulting in poor productivity and increased cost of steel products. Conventional process
also suffers from the limitation of increased consumption of the aluminium as de-oxidant
and inconsistency in variation of sulphur content in the processed and refined steel. Normal
practice of ladle addition, involve addition of Aluminium (~2.0 kg/t), Iron Pyrite (~1.0 kg/t)
and with grade specific pet coke during tapping, flux addition before start of VAD treatment
comprising average addition of Lime 700kg, Dolomite 225kg providing a slag characteristics
having slag basicity (CaO/SiO2) of 3.03 and slag sulphide capacity in the range of 0.009.
The existing process thus failed to consistently maintain a narrow band of low sulphur
content in CSQ steel grade to thereby being unable to meet the requirements of the end
application in the automobile sector.
There has thus been a need in the art to produce the CSQ alloy steels with consistent
narrow band of low sulphur content by modifying the process steps having suitable flux
addition and de-oxidation practice designed to achieve a low basicity, low sulphide capacity
slag to minimize de-sulphurisation during refining operation and to improve re-
sulphurization (higher sulphur recovery) in order to consistently maintain sulphur level in a
narrow band. Also considering control on variable sulphur recovery in re-sulphurised steel
having sulphur addition at different stages of refining, resulting in wide variation because of
variation in oxygen content, slag composition and refining time, standardization of steel
refining stage and conditions such as oxygen content, slag composition, temperature and
further treatment found to be very important parameters to control, to achieve consistent
sulphur recovery in narrow band.
OBJECTS OF THE INVENTION
It is thus the basic object of the present invention to develop a crank shaft quality alloy
steel grade having a composition comprising consistently controlled narrow band sulphur
content in said steel grade in a faster, reliable and cost effective manner.

A further object of the present invention is to developing a process for production of said
CSQ steel grade with sulphur consistently maintained in a narrow band, preferably 0.022%-
0.033%, following the process route Electric Arc Furnace (EAF) - Vacuum Arc Degassing
(VAD) - Bottom Pouring (BP) / Continuous Casting (CC), wherein suitable flux addition and
de-oxidation practice designed to achieve a low basicity, low sulphide capacity slag to
minimize de-sulphurisation during refining operation and to improve re-sulphurization
(higher sulphur recovery).
A still further object of the present invention is directed to developing crank shaft quality
alloy steel grade having a composition having a consistent narrow band sulphur wherein the
process for it production avoids re-sulphurisation in ladle and VAD at initial stage of refining
by iron pyrites or sulphur cored wire additions and eliminates repeated addition for
adjustment of sulphur in specified band leading to higher treatment time and higher cost of
processing.
A still further object of the present invention is directed to a process for developing crank
shaft quality alloy steel grade having a composition with consistent narrow band sulphur
wherein the process involves ensuring consistent sulphur recovery by standardization of
steel refining stage and controlling the important parameters including oxygen content, slag
composition, temperature and treatment time and the like.
A still further object of the present invention is directed to a process for developing crank
shaft quality alloy steel grade with consistent narrow band sulphur wherein the modified re-
sulpharisation practice for sulphur bearing steel can be utilized in any steel melting shop
with minor modifications of flux and de-oxidation practice and selection of suitable
temperature range after deep degassing based on the specific grade.
A still further object of the present invention is directed to a process for developing crank
shaft quality alloy steel grade having a composition with consistent narrow band sulphur
wherein the deoxidation step ensure substantial saving of aluminium and SiMn as the de-
oxidants during ladle addition and thus saving on input costs.
A still further object of the present invention is directed to a process for developing crank
shaft quality alloy steel grade having a composition with consistent narrow band sulphur
wherein re-sulphurisation of steel has been shifted from existing ladle and initial addition in

VAD to addition of iron pyrite at later stage of secondary refining after deep degassing in
VAD at selective temperature range followed by selective vacuum degassing.
A still further object of the present invention is directed to said process for developing crank
shaft quality alloy steel grade having a composition with consistent narrow band sulphur
wherein modified flux addition and de-oxidation practice help reducing the VAD treatment
time by about 25%.
A still further object of the present invention is directed to said process for developing crank
shaft quality alloy steel grade having a composition with consistent narrow band sulphur
wherein sulphur recovery is consistently achieved in the range of 10% - 20%, avoiding
multiple processing of heat for re-sulphurisation.
A still further object of the present invention is directed to said process for developing crank
shaft quality alloy steel grade having a composition with consistent narrow band sulphur
wherein heats made with modified ladle addition, flux addition, de-oxidation and
methodology of sulphur addition practice for steel re-sulphurisation and optimisation of VAD
slag composition, has resulted in reduced standard deviation in sulphur analysis at different
stages of refining from 0.013% to 0.003%, indicating improved control on variation of the
sulphur content in resulting steel composition.
SUMMARY OF THE INVENTION
Thus according to the basic aspect of the present invention there is provided a process for
consistent control of sulphur in re-sulphurised steel comprising:
ladle addition during taping of steel from EAF to ladle carried out without re-sulphurisation;
selective flux and de-oxidation such as to achieve low slag basicity in the range of 1.75 to
2.25 for basic lined ladle refractory, low sulphide capacity slag in the range of 0.004 to
0.006 to arrest further de-sulphurisation and improved re-sulphurisation; and re-
sulphurisation of steel at later stage of secondary refining.
A further aspect of the present invention is directed to a process for consistent control of
sulphur in re-sulphurised steel wherein said slag comprises:

CaO: 30.0 to 40.0 preferably 35.0 %;
SiO2: 15.0 to 25.0 preferably 20.0 %;
Al2O3: 15.0 to 22.0 preferably 18.0 %;
MgO: 18.0 to 23.0 preferably 20.0 %;
A still further aspect of the present invention is directed to a process for consistent control
of sulphur in re-sulphurised steel comprising addition of iron pyrite at later stage of
secondary refining after deep degassing in VAD at 1575°C to 1585°C followed by mild
degassing up to 100 torr.
A still further aspect of the present invention is directed to said process for consistent
control of sulphur in re-sulphurised steel comprising ladle de-oxidation involving selective
additions comprising Aluminium 1.0 to 1.5 kg/t, SiMn 4.0 to 5.0 kg/t and Pet coke as per
grade.
According to a yet another aspect of the present invention is directed to said process for
consistent control of sulphur in re-sulphurised steel comprising flux addition before start of
VAD treatment comprising Lime 8.0 to 10.0 kg/t, Dolomite 2.0 to 2.5 kg/t and Quartz Sand
1.0 to 2.0 kg/t.
A still further aspect of the present invention is directed to a process for consistent control
of sulphur in re-sulphurised steel comprising reduction in VAD treatment time by 25.0 to
35.0 % by way of consistent sulphur recovery in the range of 10% to 20% and avoiding
multiple processing of heat for re-sulphurisation.
Present invention and its objects and advantages are described in greater details with
reference to the following non limiting accompanying examples.
DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE
ACCOMPANYING EXAMPLE
The present invention is directed to developing a standardized process for consistent control
of sulphur within a narrow band, preferably 0.022% to 0.033%, in the crank shaft quality
alloy steel grades, selectively modifying the stages of flux addition and deoxidizing stage as

well as deferring the iron pyrite(FeS) addition in secondary refining stage at specified
temperature range in EAF-VAD-BP/CC route, with reduced treatment time and lower
processing costs through selective consistently higher sulphur recovery in the range of 10%
to 20% and avoiding multiple processing of heats for re-sulphurisation.
Importantly, the present invention adopts a modified ladle operation comprising flux
addition and deoxidation carried out at selective timing and temperature in order to develop
a standard operating practice for re-sulphurisation of steel to achieve consistency in sulphur
recovery within a narrow band, comprising
- Optimization of ladle addition during tapping of steel from EAF to ladle
(grade specific);
- Modification of flux and de-oxidation practice to achieve a low basicity, low sulphide
capacity slag to arrest further de-sulphurisation and improve re-sulphurisation
(higher sulphur recovery);
- Standardisation of methodology of re-sulphurisation of steel at specific refining stage
and temperature.
The conventional ladle addition as well as flux and de-oxidation carried out in selectively
modified manner in order to maintain sulphur in a narrow band, said flux and de-oxidation
practice has been designed to achieve a low basicity, low sulphide capacity slag to minimize
de-sulphurization during refining operation and to improve re-sulphurization with higher
sulphur recovery. Also the iron pyrites addition is deferred down the process at later stage
of secondary refining at selective temperature followed by vacuum degassing at selective
pressure below atmospheric.
The objects and advantages of the present invention and its manner of implementation is
described in further details with reference to the following non limiting illustrative example:

EXAMPLE 1;
Industry scale trial of modified steel making practice according to the present invention has
been carried out in 50t heat size at the Alloy Steels Plant of the applicants and the process
standardization established successfully for production of sulphur bearing heats. The heats
made with modified ladle addition, flux addition, de-oxidation and methodology of sulphur
addition practice with improved economy, productivity and consistent quality.
For desired achievement of consistent composition in sulphur bearing crank shaft quality
(CSQ) steel grades with controlled sulphur in a narrow band preferably in the range of
0.022% - 0.033%, the standardized process route adopted through Electric Arc Furnace
(EAF) -.Vacuum Arc Degassing (VAD) - Bottom Pouring (BP)/ Continuous Casting (CC), in
steel melting shop in steel plant comprising the steps of:
a. Tapping of primarily refined steel from EAF into ladle;
b. Implementing modified ladle addition pattern comprising adding Aluminium: ~1.5
kg/t, SiMn: 4-6 kg/t, Iron Pyrite :Nil, and pet coke :as per grade requirement;
c. Implementing flux addition practice Before start of VAD Treatment comprising adding
Quartz sand about 1.5 kg/t, lime about 10 kg/t, Dolomite about 5.0 kg/t in order to
achieve desired slag composition/characteristic with desired low basicity in the range
of 1.75 to 2.25 and preferably 2.0 and slag sulphide capacity in the range of 0.004 to
0.006 and preferably 0.005;
d. Re-sulphurisation of steel shifted from ladle addition and initial addition in VAD to
addition of iron pyrite in the range of 0.4 to 1.1 kg/t depending upon the last sulphur
analysis in VAD at later stage of secondary refining after deep degassing in VAD at
1575°C - 1585°C in medium carbon steel grade 40Cr4 Ty-C (Indian Standard having
specification C: 0.40-0.45%, Mn: 0.70-1.0%, P: 0.035%, S: 0.022-0.033%, Si:
0.10-0.35%, Cr:0.90-1.1%) followed by degassing up to 100 torr, to minimize de-
sulphurization during refining operation and to improve desired re-sulphurisation i.e.
consistent higher sulphur recovery in the range of 10-20%. Similar practice will be
applicable for other grades like 42Cr4Mo2, 42CrMo4, 20MnCr5 etc.

e. Bottom pouring/continuous casting at the end of ladle treatment ensuring desired
consistent narrow band of sulphur content in the final refined CSQ/alloy steel
product;
The above stated standardized process has been put on industry scale trial with modified
practice/parameters in 50t heat size at Alloy Steels Plant of the applicants, which has been
successfully carried out to produce sulphur bearing heats. The heats made with modified
ladle addition, flux addition, de-oxidation and methodology of sulphur addition practice has
resulted in the following benefits:
Development of standard practice for steel re-sulphurisation and optimisation of VAD slag
composition, reduced standard deviation in sulphur analysis at different stages of refining
obtained as 0.013% in conventional practice as shown in accompanying Table-I, and which
reduced to 0.003% with consistent control of sulphur according to the present invention, in
a narrow band to meet customer's specification as of the invention as illustrated in the
accompanying Table II.
Table-I: Variation in sulphur analysis at different stages before innovation

It is thus possible by way of the present invention to developing auto sector grades of steel
with sulphur in a specific range to improve machinability during processing of forged and
annealed steel billet/bars. In order to develop a standard operating practice for re-
sulphurisation of steel to achieve consistency in sulphur recovery in a narrow band as well
as to maintain sulphur in a narrow band in resulting alloy steel grade, suitable flux and de-
oxidation practice has been designed to achieve a low basicity, low sulphide capacity slag to
minimise de-sulphurisation during refining operation and to improve re-sulphurisation with
higher sulphur recovery. The process of producing the narrow band sulphur containing alloy
steel achieved reduction in VAD treatment time by ~ 25% along with consistent sulphur
recovery in the range of 10% - 20% and avoiding multiple processing of heat for re-
sulphurisation. The process also ensured reduction in aluminium consumption by 30 % by
modification of initial de-oxidation practice in ladle during tapping. The re-sulphurised crank
shaft quality (CSQ) alloy steel grade with effectively and consistently controlled narrow
band sulphur contents produced following the standard process according to the present
invention is thus having prospects of wide industrial application to cater to auto sector as
well as similar other application requiring similar strength properties as well as
fabrication/machining requirements for components produced from such steel grade.
Advantageously, modified re-sulpharisation practice for sulphur bearing steel can be utilized
in any steel melting shop with minor modifications of flux and de-oxidation practice and
selection of suitable temperature range after deep degassing based on the specific grade,
favoring wide scale application of the process according to the present invention.
WE CLAIM:
1. A process for consistent control of sulphur in re-sulphurised steel comprising:
Ladle addition during taping of steel from EAF to ladle carried out without re-sulphurisation;
selective flux and de-oxidation such as to achieve low slag basicity in the range of 1.75 to
2.25, low sulphide capacity slag in the range of 0.004 to 0.006 to arrest further de-
sulphurisation and improved re-sulphurisation; and re-sulphurisation of steel at later stage
of secondary refining.
2. A process for consistent control of sulphur in re-sulphurised steel wherein said slag
comprise:
CaO: 30.0 to 40.0 preferably 35.0 %;
SiO2: 15.0 to 25.0 preferably 20.0 %;
Al2O3: 15.0 to 22.0 preferably 18.0 %;
MgO: 18.0 to 23.0 preferably 20.0 %;
3. A process for consistent control of sulphur in re-sulphurised steel as claimed in anyone of
claims 1 or 2 comprising addition of iron pyrite at later stage of secondary refining after
deep degassing in VAD at 1575°C to 1585°C followed by mild degassing up to 100 torr.
4. A process for consistent control of sulphur in re-sulphurised steel as claimed in anyone of
claims 1 to 3 comprising Aluminium 1.0 to 1.5 kg/t, SiMn 4.0 to 5.0 kg/t and Pet coke as
per grade.
5. A process for consistent control of sulphur in re-sulphurised steel as claimed in anyone of
claims 1 to 4 comprising flux addition before start of VAD treatment comprising Lime 8.0 to
10.0 kg/t, Dolomite 2.0 to 2.5 kg/t and Quartz Sand 1.0 to 2.0 kg/t.
6. A process for consistent control of sulphur in re-sulphurised steel as claimed in anyone of
claims 1 to 5 comprising reduction in VAD treatment time by 25.0 to 35.0 % by way of
consistent sulphur recovery in the range of 10% to 20% and avoiding multiple processing of
heat for re-sulphurisation.
7. A process for consistent control of sulphur in re-sulphurised steel substantially as herein
described and illustrated with reference to the accompanying examples.

The invention relates to developing a standard operating practice for re-sulphurisation of alloy steel, e.g. crank shaft quality (CSQ) steel grades to achieve consistency in sulphur recovery in the range of 10% to 20% so as to limit sulphur content within a narrow band from 0.022% to 0.033%. The standard practice for steel re-sulphurisation and optimisation of slag composition achieved involve treating steel in EAF-Vacuum Arc Degasser (VAD)-BP/Continuous casting (CC) route, grade specific optimization of ladle addition comprising lower Aluminium addition, deferring addition of iron pyrites at later stage of secondary refining after deep degassing in VAD at 1575°C - 1585°C for medium carbon steel grades and grade specific pet coke addition, modified flux and de-oxidation practice to achieve a low basicity, low sulphide capacity slag to arrest further de-sulphurisation during refining treatment and improve re-sulphurisation. The aluminium consumption reduced by about 30% and VAD treatment time by about 25% while achieving consistent sulphur recovery and avoiding multiple processing of heat for re-sulphurisation.