FORM 2
THE PATENTS ACT 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
PROVISIONAL SPECIFICATION
(See Section 10; rule 13)
TITLE OF THE INVENTION High Tensile Speroidal Graphite with superior ductility.


APPLICANTS
TATA MOTORS LIMITED, an Indian company
Having its registered office at Bombay House,
24 Homi Mody Street, Hutatma Chowk,
Mumbai 400 001 Maharashtra, India

INVENTORS
Mr. Udayan Pathak and Mr. Vikas M Shingade
both Indian National of TATA MOTORS LIMITED
an Indian company having its registered office
at Bombay House, 24 Homi Mody Street, Hutatma Chowk,
Mumbai 400 001 Maharashtra, India
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the invention and the manner
in which it is to be performed

FIELD OF INVENTION:
The present invention deals with High Tensile Speroidal Graphite with superior ductility more particular to the base metal chemistry of Spheroidal Graphite iron (S.G. Iron) and operating ranges of critical process parameters to obtain superior combination of strength and ductility for automotive components. This invention deals with the contents of different elements in the iron. To obtain desired superior combination of strength and ductility contents of different elements should be maintained in the limits mentioned. Secondly, to ensure consistency in mechanical properties critical process parameters are also required to be controlled in specific range. With the use of this chemistry and control over process parameters it is possible to achieve superior tensile strength with improved ductility.
BACKGROUND OF INVENTION:
S.G, Iron is widely used for supporting bracketeries. Use of S.G. iron for automotive
applications is restricted only by it's reduced ductility with increased tensile strength.
As per IS 1865 for SO iron with tensile strength 500Mpa, elongation is 7 % min with
pearlite-ferrite matrix. To achieve elongation 12% min, tensile strength would be
dropped to 370MPa (min.) with ferritic matrix (Ref. IS 1865: 1991).
With current invention it is possible to achieve tensile strength of 510-550MPa and
elongation 12% min with ferritic matrix.
As per current practices and standards, alloying elements in the following range are
added to achieve tensile strength in the range of 500-550MPa with elongation 7%
min.
C: 3.2-3.75%, Mn: 0.2-0.8%, Si: 1.8-2.75%, Mg: 0.015-0.06%, S: 0.015 max,
Ni: 0.4 max, Cu: 0.4 max. Cr: 0.4 max, Fe: Balance.
Controlling process within specified range is equally important to realize combination
of high tensile strength and elongation.

Critical processes are:
1. Tapping of molten metal from melting furnace to ladle.
2. Magnesium (Mg) treatment temperature.
3. Maximum holding time for molten metal after Mg treatment. 4. Pouring temperature of Mg treated liquid metal into mold.
OBJECT OF THIS INVENTION:
1. The main object of this invention is to define upper and lower limits for
alloying elements in SG Iron to achieve tensile strength of 510-550MPa with
elongation 12% min. This would ensure the matrix to be ferritic.
2, Second objective of this invention is to define operating range for critical
process
parameters.
SUMMARY OF INVENTION:
The present invention describes contents of various alloying elements in SG Iron to
ensure tensile strength of 510-550MPa and elongation of 12% min. Chemical
composition of SG Iron is 3.5 - 3,7% C, 0.2 - 0.4% Mn, 2.4 - 2.8% Si, 0.02-0.06%
Mg, 0.015% S (max), 0.01 - 0.04% P, Fe-balance.
Secondly, critical process parameters should be controlled within limits mentioned as
below.
a. Tapping of molten metal from melting furnace to ladle: 1480-1500°C
b. Magnesium (Mg) treatment temperature: 1420-1440°C
c. Maximum holding time for molten metal after Mg treatment: 20 minutes
d. Pouring of Mg treated liquid metal into mold: 1400-1420°C

DETAILED DESCRIPTION OP INVENTION:
1. Charge mix should contain Steel Scrap 45-50% by weight and foundry returns
should be less than 50%, Chemical composition of melt should be maintained as
below:
C: 3.5-3.7%, Mtv. 0.2^0.4%. Si\ 2.4-2.8%, Mg'. 0.02-0.06%, S". 0.015 max P: 0.04 max, Ni: Nil, Cu: Nil, Cr; Nil, Fe: Balance
2. lapping temperature should be maintained within 1480-1500°C. If tapping temperature exceeds 1500°C, there is increased chance of oxidation of alloying elements at surface. This results in heterogeneity of composition which results in non uniform mechanical properties of casting. This oxidation of alloying elements at surface can be more detrimental for castings like axles which are relatively larger.
3. Magnesium treatment temperature is important and should be controlled in narrow range i.e. between I420-1440°C. Treating melt with magnesium at higher temperature reduces shelf life of treated melt and nodularising effect feds out in lesser time. Treatment of melt by magnesium at lower temperatures impairs risk of poor treatment.
4. fATcct of magnesium can be realized effectively, if treated metal is poured into mold in less than 20min after magnesium treatment. After 20 mirt, nodularising effect of magnesium feds out, and mechanical properties of casting could be
\Y\feY\OY.
5. While pouring liquid metal into mold, pouring temperature should not be more
than I420°C. This is to ensure magnesium remains active and nodularising effect
is realized. After following above mentioned steps, and maintaining chemistry of
melt in mentioned limits, it is possible to achieve superior mechanical properties
of S.G. iron. UTS can be achieved as high as 510-550 MPa, elongation 12-18%
and hardness 170-185BHN.

Table 1: Mechanical properties measured on test pieces from separately cast test samples (Rcf: IS1865 :1°91)

Grade Minimum
Tetfette
Strength,
MPtt1) Miaimum
0.2 Perctnt
Proof Stmi,
MPa Etaihgft
tiont
Ftrctnta)
SG 900/2 900 600 2
SGWO/2 800 480 2
SG 700/2 700 420 2
SG 600/3 SG 500/7 SG 450/10 600
500 450 370 320 310 3
7 10
SG 400/15 SG 400/18 400
400 250
250 15 18
SG 350/22 350 220 22
Tabic 2: [ensile properties of SO Iron (conventional available grades) grades with tensile strength 500MPa & 550MPa.

Grade
550/6
500/7

Tensile Strength (MPa)
604-675
600-660

Elongation (%) Hardness (BHN) Micro structure-Matrix
7,1-10.4 195-132 Ferrite: 25-35% Pearlite: 65-75%
7.0-10,0 190-215 Ferrite: 35-40% Pearlite: 60-67%

Table 3: Chemical Composition for SG Iron (conventional available grades) grades with tensile strength 500MPa & 550MPa I Elements
SG Iron grades
500/7
Carbon %
3.58-3.69
Silicon % Manganese %
550/6 3~.6T7
2.45-2.65
2,4-2.7
0.25-0,33
0.26-0.32

Phosphorus %
Sulphur % Copper % Magnesium % iron

0.011-0.018
0.004-0.013
0.43-0.57
0.034-0.047 Balance

0.016-0.025
0.004-0.011
0.36-0.49
0.036-0.044
Balance

Tabic 4: 'Tensile strength properties for Super Cast 510
Grade [Tensile
Strength (MPa)
5Uf-550~~
Super Cast 510

Elongation (%) Hardness (BHN) Microstructure-Matrix
12-18 170-185 Fetrfte: 90-95% Pearlite: 5-8%

Table 5: Chemical composition for Super Cast 510. Elements

Carbon %
Silicon %
Manganese % Phosphorus %
Sulphur % Copper % Magnesium % Iron

3.5-3.7 Z4-2T
0.2-0.4
0.01-0.04 0.015 max. "0.0
(T62-'O06~ Balance