FIELD OF THE INVENTION
The present invention relates to fine grained austenitic manganese steel rolled plates
and a process for its production. More particularly, the present invention is directed
to providing austenitic manganese steel rolled plates of thickness 12 mm or less with
fine grained austenitic microstructure without carbide precipitation and a process for
its production with improved yield. The production process involves optimization of
chemistry and rolling parameters as well as post rolling treatment for achieving
desired grain size with improved mechanical properties. The product obtained is a
cost effective variety of austenitic manganese steel with improved yield, adopting
specialized toughening treatment for rolled plates involving online heat treatment
and also favouring elimination of problems relating to bending, straightening or
buckling.
BACKGROUND OF THE INVENTION
It has been observed in the field of production of conventional manganese steel
rolled plates in steel industry, there existed a number of problems relating to
achieving improvement in mechanical properties, workability and yield. Though the
higher carbon level was required to stabilize the austenite in manganese steels, it
segregates to the grain boundaries as carbides and the hot workability is
deteriorated due to the transition of deformation behavior by slip deformation. There
was thus a need to develop a austenitic structure free from carbide precipitate at
grain boundaries that are detrimental to the strength and ductility. The control on
other alloying elements such as Si, P, S, Al, Cr were also critical to avoid problems
relating to promoting desired grain size and improved strength and ductility,
improved toughness, hot workability, surface quality and avoiding crack, tearing or
other hot rolling defects.
Apart from suitable designing of alloy chemistry, there has been need for optimizing
process parameters in developing manganese steels with improved mechanical
properties and in particular fine grained austenitic manganese steels rolled plates
which would on one hand ensure the above desired fine grained structure avoiding
carbide precipitation and on the other hand enhanced mechanical properties with
improved surface qualities achieved through control on rolling parameters and post

rolling treatment including online toughening treatment directed to avoid rolling
defects and operational problems while improving yield and reducing cycle time in a
cost effective manner.
OBJECTS OF THE INVENTION
The basic object of the present invention is thus directed to providing fine grained
austenitic manganese steel plates and a process for its production involving selective
alloy composition and selective control on process parameters for teeming, limiting
ingot size, soaking, hot rolling, heat treatment and the like, so as to achieve desired
fine grained austenitic microstructure, improved mechanical properties, improved
surface quality.
A further object of the present invention is directed to providing fine grained
austenitic manganese steel plates wherein the process for its production would be
having improved yield.
A still further object of the present invention is directed to providing fine grained
austenitic manganese steel plates wherein the process for its production involves
teeming temperature selectively maintained to achieve fine grain structure, uniform
dispersion of carbide, minimize chemical segregation and avoid other related casting
defects.
A still further object of the present invention is directed to providing fine grained
austenitic manganese steel plates wherein the process for its production involves
bottom pouring during ingot casting process which ensured improved surface quality
of subsequent rolled products obtained thereof.
A still further object of the present invention is directed to providing fine grained
austenitic manganese steel plates wherein the process for its production involves
ingots are subjected to hot transfer to soaking and then to rolling with
controlled/optimized timing of teeming finish through soaking to rolling mill such that
to avoid surface cracks and hot tearing during rolling.

A still further object of the present invention is directed to providing fine grained
austenitic manganese steel plates wherein the process for its production involves
selective heating and soaking temperature regime for hot rolling of ingots/slab in
blooming/ plate mill to avoid hot tearing and surface cracks in rolled products.
A still further object of the present invention is directed to providing fine grained
austenitic manganese steel plates wherein the process for its production involves
maintaining selectively maintaining draft/reduction per roll pass in blooming/plate
mill to eliminate roll breakage and edge tearing problems.
A still further object of the present invention is directed to providing fine grained
austenitic manganese steel plates wherein the process for its production involves
toughening treatment using on line water quenching of rolled slabs in finishing area
of blooming mill and online forced air quenching of rolled plates are carried out to
eliminate bending/buckling problem experienced in the conventional process while
ensure retaining 100% austenite at room temperature free of carbide precipitation
along grain boundaries.
SUMMARY OF THE INVENTION
The basic aspect of the present invention is thus directed to providing fine grained
austenitic manganese steel plates comprising C 1.0-1.05%, Mn 12.5-12.7%, Si 0.30-
0.50%, P 0.060-0.067%, S 0.01% Max, Cr 0.20% Max & Al 0.010% max. and
having a plate thickness of up to 12 mm.
A further aspect of the present invention is directed to said fine grained austenitic
manganese steel plates which comprises
Yield strength in the range of 38-44 Kg/Sq. mm;
Ultimate tensile strength in the range of 92-102 Kg/Sq.mm;
Elongation in the range of 40-55 %;
Reduction in area in the range of 42-48 %; and
Hardness in the range of 185-210 BHN.

A still further aspect of the present invention is directed to a process for the
manufacture of fine grained austenitic manganese steel plates comprising (A)
improving the yield following the steps of selectively providing the teeming
temperature, ingot size along with modified disposition of the teemed ingot for
rolling and application of bottom pouring technique (B) selectively providing heating
and soaking temperature regime for rolling in blooming mill and plate mill (C)
selectively providing rolling draft schedule for rolling ingots to slabs in blooming mill
and slabs to plates in plate mill and (D) toughening treatment of hot rolled
austenitic manganese product involving on line heat treatment.
A still further aspect of the present invention is directed to a process for the
manufacture of fine grained austenitic manganese steel plates wherein said step (A)
comprises (i) maintaining the teeming temperature in the range of 1440°C to
1455°C, (ii) selectively restricting ingot size to 2.35 T only accompanied with bottom
pouring for improved surface quality of the rolled products and (iii) subjecting the
ingots to hot transfer comprising teeming finish to charging finish time in soaking pit
in the range of 4.5 hrs. to 6.5 hrs.
A still further aspect of the present invention is directed to a process for the
manufacture of fine grained austenitic manganese steel plates wherein said step (B)
comprises of maintaining the soaking temperature at 1080-1090°C and prior to
soaking , the hot ingots were held at 800°C for 1 hour/200mm followed by raise to
1000°C with holding for 1hr/100mm and thereafter subjected to soak temperature
with soaking preferably for about 1 hr/100mm in the blooming mill and in the plate
mill, the soak temperature for the slabs was kept between 1140°C to 1180°C with
soak time preferably of about 1.2 minutes per mm thickness.
A still further aspect of the present invention is directed to a process for the
manufacture of fine grained austenitic manganese steel plates wherein selection of
rolling draft for improved rollability comprise of selective low draft of 20-30 mm only
per pass for rolling ingots to slabs in blooming mill and the draft was optimized to
10-20mm per pass for rolling slabs to plates in plate mill.

A still further aspect of the present invention is directed to a process for the
manufacture of fine grained austenitic manganese steel plates comprising
toughening treatment of hot rolled austenitic manganese product to avoid bending
and straightening problems of hot rolled product including on line water quenching of
rolled slabs in blooming mill and on line air quenched of rolled plates below 12 mm in
plate mill.
BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES
Figure 1: is the chart showing the comparative impact value of austenitic manganese
steel according to the invention compared to other existing equivalent grades.
DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE
ACCOMPANYING FIGURES
The present invention is directed to providing austenitic manganese steel rolled
plates of thickness 12 mm and below with fine grained austenitic microstructure
without carbide precipitation and a process for its production. It involves (a)
development of optimized chemistry, (b) improvement in yield by 15% through
change in teeming temperature, ingot size, modified disposition of the teemed ingot
for rolling and application of bottom pouring technique (c) optimization of heating &
soaking temperature regime for rolling and draft for rolling ingots to slabs and slabs
to plates & (d) specialized toughening treatment of hot rolled austenitic manganese
product involving online heat treatment necessitating no need of extra toughening
treatment for the rolled plates below 12 mm and for rolled slabs.
(a) Development of optimised Composition of the Austanitic Manganese
steel according to the present invention :
The composition of austenitic manganese steel according to the present invention
involved maintaining C 1.0-1.05%, Mn 12.5-12.7%, Si 0.30-0.50%, P 0.060-
0.067%, S 0.010% Max, Cr 0.2% Max & Al 0.010% max. which is achieved through
experiments based on following considerations:
Carbon forms interstitial solid solution of austenitic iron and contributes towards the
strain hardening capacity of the austenitic manganese steel. As carbon content is

increased, it becomes difficult to retain all the carbon in solid solution leading to
reduction in tensile strength and ductility. While carbon levels below 1% cause yield
strength to decrease, carbon exceeding 1.2% though improves abrasion resistance
but lowers the ductility. For higher levels of carbon, though the stability of the
austenite phase is enhanced but, it segregates to the grain boundaries as carbides
and the hot workability is deteriorated due to the transition of deformation behaviour
by slip deformation. Hence, carbon (C) contents of 1.0-1.05% was selected in
combination with Mn level of 12.5-12.7% to obtain an austenitic structure free from
carbides at grain boundary that are detrimental to strength and ductility.
Manganese is an austenitic stabilizer and sharply depresses the austenite-ferrite
transformation thus helping to retain 100% austenite at room temperature after
water quenching treatment. It enhances the depth of hardening of steels and
improves wear resistance in the presence of carbon. Manganese content of 12%-
14% has no effect on yield strength but does improve tensile strength and ductility.
The maximum tensile strength is attained with 12.5%-12.7% manganese contents
combined with improved ductility of the developed steel grade meeting the critical
application requirements. Mn content in the developed steel composition is thus
maintained at 12.5%-12.7%.
Silicon enhances fluidity and hence, a minimum of 0.1% is necessary and good
fluidity is observed at 0.3% and above. It is a solid solution strengthening element
that increases yield strength by reducing the grain size. Silicon plays a crucial role in
changing the hardness and Fe3C phase morphology from acicular to chunky. The
toughness decreases when the silicon content exceeds 0.6% with increasing carbon
content. Also, high silicon contents produce poor surface of the rolled product due to
silicon oxide. When silicon content exceeds 0.6%, the de-oxidizing effect is saturated
and the weldability gets deteriorated. Considering the above, silicon contents are
preferably maintained at 0.3-0.5% in this steel.
Phosphorus is a deleterious element in manganese steels. It lowers toughness with
increasing phosphorus content in these steels. In cast products, it leads to
embrittlement which is further influenced by the cast section thickness, carbon,
silicon & other alloy element content. Phosphorus increases crack susceptibility
during removal of risers as well as during welding operation. Increasing content of
this element affects toughness even at high temperature. Cracking and tearing

occurs during hot rolling due to lowered toughness at levels of 0.07% and above
caused by eutectic phosphide formation at grain boundaries. Practically, low levels
of P necessitates use of manganese metal that increases the cost & hence, with out
deteriorating the rollability P of 0'.060-0.067% selected for improved hot workability,
improved yield with reduced cost of this steel.
Sulphur reacts with manganese to form coarse manganese sulfide that causes
defects such as flange cracks in the hot rolled product. It thus affects the directional
properties of the rolled product. Hence, S needs to be kept as low as possible and is
generally maintained at a maximum of 0.010% .
Chromium in small amounts enhances the strength of the austenite matrix and
controls the precipitation of Fe3C carbides at grain boundaries improving wettability.
It is detrimental to toughness and' highly sensitive to cast section size variation with
smaller sections exhibiting satisfactory toughness compared to the larger cast
sections. Also, the austenizing temperature needs to be increased for increase in
chromium for the given carbon content for total carbon solution. Excess chromium
content also impairs hot ductility and leads to higher strength affecting
machinability. Hence, Cr is restricted to a maximum of 0.2%.
Aluminium content in these steels has a considerable influence on the shape and
distribution of the phosphides. Phosphides occur as large particles on grain
boundaries for a residual aluminium content of 0.02% containing 0.08% phosphorus
in manganese steel compared to reduced amount of phosphides imparting improved
ductility and toughness when residual aluminium levels are increased to 0.08%-
0.15%. Increased aluminium levels enhance the machinability of the manganese
steels. However, further increase in aluminium content leads to segregation on grain
boundaries of columnar crystals during solidification forming low melting inter-
metallic compound Fe2Ai5 with melting point of 1170°C and below this temperature,
aluminium fixes with nitrogen to form coarse nitrides along the grain boundaries
which weaken the structure that necessitates use of other elements like boron,
titanium, zirconium, lanthanum and cerium for raising the temperature of the inter-
metallic compound to 1300°C. Also, aluminium levels of 0.03% were found to affect
the hot workability and no hot workability problems observed for aluminium levels
below 0.01%. Considering the above stated deleterious affect of aluminium, it is
preferred to be kept at a maximum of 0.01%.

(b) Improvement in yield b'y 15% have been achieved through :
(i) teeming temperature maintained within 1440°C-1455°C: High teeming
temperatures promote large grain size and alloy element segregation that are
detrimental to strength and ductility in manganese steels. Along with temperature,
the segregation tendency in this steel increases with increasing cast thickness and
carbon content affecting the toughness property. Segregation has a profound
influence on the wear properties. Higher the segregation lower is the wear resistance
of the manganese steel. With increased teeming temperatures over 1460°C, the
problem of segregation and hot tearing tendency of ingots during rolling were
observed. Reducing teeming temperature reduces the order of dispersion of carbide
in the matrix. At 1450°C, the carbides are less dispersed in the matrix. The teeming
temperature of 1400°C-1450'°C promotes uniform dispersion of carbide particles
within the structure and further lowering of the temperature diminishes the fluidity
and lead to casting defects. Teeming temperature of less than 1460°C were found to
prevent excessively coarse grain size and minimize chemical segregation and other
related casting defects. Also, the teeming temperature affects the hot tear resistance
of this steel at high phosphorus content. Hence, the teeming temperatures are kept
at 1440°C-1455°C that resulted in improved performance of the ingot during rolling
with out any hot tearing problems.
(ii) Ingot size is restricted to 2.35T and application of bottom pouring
technique applied for production of high quality ingot : Manganese steel is the
most difficult material to roll because of its poor hot workability causing multiple
clinking during rolling and increased risk of roll failure. For rolling, the ingot size
should be as small as possible to minimize segregation that influences strength and
ductility. Ingots weighing 4.02 T and 3.65T were taken up for rolling but resulted in
hot tearing during rolling. Accordingly, ingot size was tried with 2.35T which resulted
in no hot tearing and the ingot was restricted to 2.35T only for manganese steel.
Earlier, top pouring was carried out that caused poor surface on the rolled products
as well as sticker formation that reduced hot tearing resistance of this steel during
rolling. Considering the above, the process of casting was switched over to bottom
pouring that lead to improved"surface quality of the rolled products.

(iii) Modified disposition oflteemed ingots to soaking pits for rolling:
It is observed that with slow cooling of ingots after teeming, the segregation
tendency increases with carbide precipitation. It was also noticed that ingots that
were piled when subjected to heating and soaking in soaking pits suffered from
cracks & hot tearing problem. Considering this problem, after teeming followed by
solidification, the hot ingots are then transferred to the soaking pits to make them
ready for rolling. It is further observed that higher transfer time of the solidified
ingots to the soaking pits, leads to higher was the hot tearing problem caused by
large columnar crystals, higher grain size and carbide precipitation. The ingots were
subjected to hot transfer i.e. teeming finish to charging finish time in soaking pits
from 4.5 hrs - 6.5 hrs to the rolling mill. This time was optimized as it was observed
that there were problems of surface cracks & tearing if teeming finish to charging
finish time exceeded 6.5 hrs.
(c) Optimizing heating & soaking temperature regime for rolling and
development of modified draft schedule for rolling ingots to slabs and slabs
to plates
(i) Modified design of Heating & soaking regime :
IN BLOOMING MILL : Hot workability problems of the ingots rolled to slabs observed
when soak temperatures were maintained at 1140°C -1200°C. Further increase in
temperature aggravated the hot tearing of the rolled product. Considering this
problem, the soak temperature was modified to 1080°C-1120°C and to ensure proper
soaking holding at 1000°C was increased. Hot tearing was reduced but could not be
eliminated. It was observed that the amount of phosphorus in steel was found to
play a vital role on selection of soaking temperature. For P content of 0.060% &
below, the soak temperature was maintained at 1120C as there were no hot
workability problems for temperatures up to 1120C. For P content of 0.060-0.067%,
temperature was maintained at 1080-1090C with no incidents of cracking of the
rolled slabs from the ingots'. Prior to soak temperature, the hot ingots were held at
800°C for 1 hour/200 mm followed by raise to 1000°C with holding for 1 hr/100mm
and then to soak temperature with soaking for 1 hr/100mm. Absence of intermediate
holding also lead to cracks that lead to optimization of the heating & soaking
regimes. The process of manufacturing involved conversion of hot bottom poured
ingots of 2.35 tons to intermediate rolled slabs of 70 mm to 90 mm thickness with

width of 430mm - 450 mm by following the optimized heating and soaking regime to
produce slab free from defects.
IN PLATE MILL : Application of soak temperature exceeding 1200°C led to cracks in
the slabs rolled. The soak ternperature for the slabs was kept between 1140°C to
1180°C with soak time of 1.2 minutes per mm thickness that resulted in crack
elimination in the rolled plates.
(ii)Optimized selection of rolling draft for improved rollability :
IN BLOOMING MILL : Application of draft of 30-40 mm during rolling led to roll
breakages & edge crack formation in the rolled product. To take of this issue, the
rolling process was optimized through selection of low draft of 20 mm -30 mm only
per pass. It was observed that, once this draft exceeded the values, the rolling load
showed increased current exceeding 6KA with tripping of the mill. The application of
this draft along with decreasing water during rolling process helped in achieving
currents of 4-4.5 KA. The roll pass schedule that was established involves rolling in
32 passes for producing 70 mm thick slab & 29 passes for 90 mm thick slab from
500 mm ingot with reduction of only 20 mm per pass. This process minimize roll
breakage incidents & eliminate edge cracking of the rolled slabs.
IN PLATE MILL : The so obtained rolled slabs from blooming mill were cut to
requisite length by gas cutting and subjected to cross rolling in the Plate Mill for
produce 5 mm to 30 mm thick plates. The draft was optimized to 10-20 mm per pass
for rolling rolled slabs to plates in the plate mill. The so obtained rolled slabs were
cut to requisite length by gas cutting and subjected to cross rolling in the 3 Hi
reversing Plate Mill for produce 5 mm to 30 mm thick plates.
(d) Development of specialized toughening treatment of rolled austenitic
manganese plates to avoid bending & straightening problems in the rolled
product
The purpose of heat treatment! for manganese steel is to retain 100% austenite at
room temperature with all the carbon dissolved in it. The process involves heating
the product to fully austenitic condition i.e. above the carbon solubility line Acm by
about 10°C-35°C followed by rapid quenching in water. It was found that the

temperature range from 871°C to 315°C that is more critical leading to carbide
precipitation if slow cooled in the range.
(i) On line quenching of rolled slabs in blooming mill : The process of
toughening treatment of rolled slabs of this steel was time consuming & affecting the
production and quality of the rolled slabs. There were bending problems in the rolled
slabs for non-uniform cooling and straightening was difficult. A new process was
developed that involved on line quenching of rolled slabs in the finishing area of the
blooming area. This on line water quenching system developed involved laminated
water flow from top and bottom of the slab after the slab crosses the bloom shear
that eliminated the bending tendency.
(ii) On line quenching of rolled plates of 12 mm & below thickness in plate
mill : Initially, all the plates irrespective of the thickness used to be subjected to
heat treatment in a roller hearth annealing furnace with the plates moving from one
zone to other with temperature in the initial zone maintained at 1000°C followed by
1050°C in soak zone with immediate quenching using compressed air and water that
used to take 14 -18 minutes for heat treatment of each plate. There used to be
buckling problems in plates of thickness 12 mm & below. Considering the high time
involved in heat treatment &, the quality problems in the rolled plates, on line
quenching system through forced air cooling up to 12 mm thick plates was
developed just after rolling that could eliminate heat treatment after microscopic
examination of the samples that revealed no carbide precipitation along the grain
boundaries.
The mechanical properties achieved in the resulting hot rolled steel products i.e. fine
grained austenitic manganese steel plates up to 12 mm thick according to the
present invention are as follows:
Yield strength in the range of 38-44 Kg/Sq. mm;
Ultimate tensile strength in the range of 92-102 Kg/Sq.mm;
Elongation in the range of 40-55 %;
Reduction in area in the range of 42-48 %; and
Hardness in the range of 185-210 BHN.

The I -Zod impact strength of 16.8 Kgm for the developed steel grade in comparison
with other existing steels grades for similar application are shown in the
accompanying Figure 1.
It is thus possible by way of the present invention to developing fine grained
austenitic manganese steel plates free of carbide precipitates along grain boundaries
having higher yield strength, ductility and impact strength enabling advantageous
use in various industrial applications.

We Claim:
1. Fine grained austenitic manganese steel plates comprising C 1.0-1.05%, Mn
12.5-12.7%, Si 0.30-0.50%, P 0.060-0.067% , S 0.01% Max, Cr 0.20% Max
& Al 0.010% max. and having a plate thickness of up to 12 mm.
2. Fine grained austenitic manganese steel plates as claimed in claim 1
comprising:
Yield strength in the range of 38-44 Kg/Sq. mm;
Ultimate tensile strength in the range of 92-102 Kg/Sq.mm;
Elongation in the range of 40-55 %;
Reduction in area in the range of 42-48 %; and
Hardness in the range of 185-210 BHN.
3. A process for the manufacture of fine grained austenitic manganese steel
plates as claimed in anyone of claims 1 or 2 comprising (A) improving the
yield following the steps of selectively providing the teeming temperature,
ingot size along with modified disposition of the teemed ingot for rolling and
application of bottom pouring technique (B) selectively providing heating and
soaking temperature regime for rolling in blooming mill and plate mill (C)
selectively providing rolling draft schedule for rolling ingots to slabs in
blooming mill and slabs to plates in plate mill and (D) toughening treatment
of hot rolled austenitic manganese product involving on line heat treatment.
4. A process for the manufacture of fine grained austenitic manganese steel
plates as claimed in claim 3 wherein said step (A) comprises (i) maintaining
the teeming temperature in the range of 1440°C to 1455°C, (ii) selectively
restricting ingot size to 2.35 T only accompanied with bottom pouring for
improved surface quality of the rolled products and (iii) subjecting the ingots
to hot transfer comprising teeming finish to charging finish time in soaking pit
in the range of 4.5 hrs. to 6.5 hrs.
5. A process for the manufacture of fine grained austenitic manganese steel
plates as claimed in anyone of claims 3 or 4 wherein said step (B) comprises

of maintaining the soaking temperature at 1080-1090°C and prior to soaking ,
the hot ingots were held at 800°C for 1 hour/200mm followed by raise to
1000°C with holding for 1hr/100mm and thereafter subjected to soak
temperature with soaking preferably for about 1 hr/100mm in the blooming
mill and in the plate mill, the soak temperature for the slabs was kept
between 1140°C to 1180°C with soak time preferably of about 1.2 minutes
per mm thickness.
6. A process for the manufacture of fine grained austenitic manganese steel
plates as claimed in claim 5 comprises of selection of rolling draft for
improved rollability in blooming mill through selective low draft of 20-30 mm
only per pass for rolling ingots to slabs and the draft was optimized to 10-
20mm per pass for rolling slabs to plates in plate mill.
7. A process for the manufacture of fine grained austenitic manganese steel
plates as claimed in anyone of claims 1 to 6 comprising toughening treatment
of hot rolled austenitic manganese product to avoid bending and straightening
problems through on line water quenching of rolled slabs in blooming mill and
on line air quenching of rolled plates below 12 mm in plate mill.
8. Fine grained austenitic manganese steel plates and a process for the
manufacture of fine grained austenitic manganese steel plates substantially as
herein described and illustrated with reference to the accompanying figures.


ABSTRACT

The present invention is directed to providing fine grained austenitic manganese
steel plates without carbide precipitation comprising C 1.0-1.05%, Mn 12.5-12.7%,
Si 0.30-0.50%, P 0.060-0.067%, S 0.01% Max, Cr 0.20% Max and Al 0.010%
max. and having a plate thickness of up to 12 mm. The developed steel grade is
having improved yield strength, ductility and impact properties. A process for
production of the above steel grade is disclosed involving (A) improving the yield
following the steps of selectively providing the teeming temperature, ingot size
along with modified disposition of the teemed ingot for rolling and application of
bottom pouring technique (B) selectively providing heating and soaking temperature
regime for rolling in blooming mill and plate mill (C) selectively providing rolling draft
schedule for rolling ingots to slabs in blooming mill and slabs to plates in plate mill
and (D) toughening treatment of hot rolled austenitic manganese product involving
on line heat treatment.