FORM 2
THE PATENT ACT 1970
&
The Patents Rules, 2003
PROVISIONAL / COMPLETE SPECIFICATION (See section 10 and rule 13)

1. TITLE OF THE INVENTIONGrey Cast Iron Alloyed with Manganese for sheet metal forming dies for automotive applications.
2. APPLICANT(a) NAME . MAHINDRA & MAHINDRA Ltd.(b) NATIONALITY. Indian company registered under the Companies Act 1956(c) ADDRESS . R&D Centre, Auto Sector89, M.I.D.C,Nashik-422007, Maharahstra State, India
3. PREAMBLE TO THE DESCRIPTION
PROVISIONALThe following specification describes the invention. COMPLETEThe following specification^^ particularly descrihes^tftelnvention and the manpeF-flfwhich it is to be ^-performed.
4. DESCRIPTION (Description starts fror n page 2)
5. CLAIMS: N.A
6. DATE AND SIGNATURE: Given at the end of last page of specification.
7. ABSTRACT OF THE INVENTION: N.A


Title: Grey Cast Iron Alloyed with Manganese for sheet metal forming dies for automotive applications.
Technical Field: The present invention relates to cast iron compositions and the heat treatment for the same. More particularly the present invention is related to the compositions to be used for draw dies for manufacturing the automotive stampings.
Prior Art: Different types of tooling like dies for drawing, trimming, re-striking, blanking are used in automotive sheet metal forming process. The material for these tools is required to have the strength level of about 300 Mpa while the surface hardness in the functional areas required" ranges from HRC 45 to 50, where HRC means the Rockwell Hardness number on C scale. These draw dies are presently manufactured from chromium-molybdenum (Cr-Mo) type alloy gray cast iron. These dies are sand cast & subsequently machined to required shape. They are then flame hardened in the functional areas by using air cooling. A typical composition of these Cr-Mo type alloy Grey Cast Irons is shown in following Table 1 as a representative of the compositions used in the prior art.

Elements % C % Si % Mn % S % P %Cr %Mo
Max Max
Cr-Mo G CI 2.6- 1.7- 0.6- 0.15 0.20 0.3- 0.35
3.2 2.2 0.9 0.5 -0.5
Rest is iron.

2

The alloying element additions of chromium (Cr) & molybdenum (Mo) are done predominantly for two purposes,
1) To give required strength to dies during forming operation
2) For increasing the hardenability to produce required hardness of HRC 45-50 by flame hardening, using air as quenching media.
Particularly in absence, or presence in low percentages of the alloying element molybdenum in such compositions leads to low hardenability and the desired results as described above cannot be obtained consistently even with increased severity of quenching (e.g. use of water mist instead of plane air blast). At the same time Mo being very expensive material the cost of the compositions with Mo as alloying element is high. Thus the cost of the tools manufactured using these compositions becomes high leading to higher cost of the components manufactured with them. Secondly Mo having higher density than iron (Fe) is prone to segregation during the process of solidification of the melt, during casting. This segregation leads to variation in the hardness achieved on the surface, when subjected to flame hardening process leading to uneven wear of the tool during the use. This reduces the effective life of the tool. It is also observed that even though the Cr-MO alloys can give high hardenability, the hardness and strength mentioned above is required only in the 10% surface depth of the tool for its effective function.
Summary of the Invention: The objective of the present invention is to eliminate the deficiencies in the prior art as mentioned above.

Hence, the first objective of the present invention is to reduce the cost of the castings by replacing expensive alloying element molybdenum by inexpensive manganese and hence reducing the cost of the components manufactured; keeping the hardness and the strength of the castings to the required values mentioned above in the 10% of the surface depth.
Another objective of the present invention is to achieve uniformity in the surface hardness of the above-mentioned tools, thereby improving the life of the same.
The present invention, "Grey Cast Iron Alloyed with Manganese for sheet metal forming dies for automotive applications", comprises of optimization of the casting process and the chemical cornoosition of gray cast iron alloyed with manganese. Mist cooling system is used to enhance the severity of quench and to obtain flame-hardening response to produce strength & hardness in cast dies which is equivalent to gray cast iron containing Mo as a major alloying element. The surface hardness of this Mn alloyed Cast Iron is within the range of 45 to 50 HRC and the strength is 300 MPa achieving wear resistance & strength properties required by the draw dies. The performance of such dies in actual production environment is also found satisfactory & similar to Mo containing gray Cast Iron.
Advantages of the Present Invention:
1. Expensive Molybdenum addition is eliminated.
4

2. Mn having density closer to Iron shows reduced tendency for segregation as compared to Molybdenum during casting process.
Description of the Present Invention:
Typical chemical composition for sand cast alloyed gray C.I. with molybdenum content; a representative of those used for automotive draw dies in the prior art, is shown in table 1

Elements % C % Si % Mn % S Max % P Max %Cr %Mo
Cr-Mo G CI 2.6- 1.7- 0.6- 0.1 0.20 0.3- 0.35-
3.2 2.2 0.9 5 0.5 0.5
Rest is iron.
The elements like C, Si, S, & P originate either from the basic raw material used like pig iron or steel scrap & or are controlled to get required casting processing characteristics. Thus these elements are part requirement of basic cast iron family & have more role related to casting process.
The purpose of additions of Cr & Mo as alloying elements is for achieving the required strength level & producing surface hardness after flame hardening.
During flame hardening the functional surface is heated with the help of Oxy-acetylene flame to above austenitising temperature (840-860 Deg. C) & quenched in suitable media to get hard surfaces. Due to higher hardenability, of Cr-Mo type alloy gray cast iron, it is possible to get the hard surfaces by air cooling during flame hardening.

In present invention the Molybdenum content of 0.35-0.50% is eliminated and Manganese content is increased to 1-1.9 %. The new alloy chemistry as a representative of the chemical compositions of this invention is shown in table 2,

Elements % C % Si % Mn % S Max % P Max %Cr %Mo
Mn- G CI 3.0- 1.7- 1.5- 0.1 0.20 0.2- NIL
3.2 2.1 1.9 5 0.4
Rest is iron.
Manganese is abundantly available & is less expensive than molybdenum. Sulphur combines with Mn in preference to iron to form manganese sulphide. This replaces the ferrous sulphide,-which would have been formed and impaired the physical properties of the cast iron. For this, the Mn content sufficient would be 1.7 times that of the sulpher content due to the ratio of the molecular weighs of Mn and S. It is also known that it is necessary to keep the Mn content above this value to a small extent i.e. by +0.3% to 0.5%. Mn content above this value can be treated as an alloying element. However increase in the Mn content above the value of 1% can lead to pin holes in the casting as experienced in the prior art.
However, mechanical properties of gray cast iron are influenced by foundry practice, particularly proper use of inoculants, superheat and cooling rate in the casting, though the composition has its roll in obtaining the same.
The effect of Mn on strength, hardness, microstructure & solidification characteristics like shrinkage, porosity & segregation,
6

on different cross sections (50X100 mm, 75X100 mm, 100X100 mm &. 150X100 mm.) at three Mn contents viz. 0.96%, 1.35% & 1.75 %, keeping base chemistry same was investigated. The carbon equivalent (C.E.) was kept between (3.73 to 3.77). It was observed that the required strength, (300 MPa) & microstructure (Predominantly Pearlitic with Ferrite & carbide < 5%) and surface hardness after flame hardening & mist cooling of 45 to 50 HPX are achieved in all the section sizes studied. Also no abnormal shrinkage, porosity, segregation was observed at any point in above sections. Inoculation was used in the casting process using the commonly available inoculants according to the manufacturers recommendations. Super heat of melt~& cooling rate were controlled as mentioned bellow. The required eutectic cell count (100 cells/CM2) over area greater than 2cm2 & graphitisation (Graphite-predominantly Type A size 3 to 5 as per IS 7754) with traces of Type D & E) was observed with Mn % values those used in the above experiments, which are higher than the optimal recommended (1.7X %S +0.3% to 0.5%) in the prior art. The high Mn% is primarilv to aid higher hardenability response during flame hardening & has no deterioration effect on as cast strength measured on std. 30 mm cast test piece.
Thus all the difficulties mentioned above for using Mn as an effective alloying element are overcome by this invention using combination of chemistry as mentioned above and the process summarized as follows.
1. Increasing the Mn content to (1 to 1.9 %) and eliminating Mo to reduce the cost.
7

2. Using C.E. in the range (3.56 to 3.83) (C.E. is carbon equivalent of the cast iron. C.E. = C% + l/3*Si%).
3. Use of inoculation during the casting process with standard available inoculants on market (e.g. Ferro-silicon superseed or ELKM GARGI)
4. Controlling the superheat of the melt. (1480 to 1550 deg. C)
5. Controlling the cooling rate of the casting between 30deg C/min. to 100 deg C/min.
6. Increasing the severity of the quenching operation by using air blast with water mist for quenching, with 5% to 10% water v/v, As the Manganese alloyed gray Cast iron has lower hardenability than the molybdenum containing grade.
The dies with new alloy chemistry the casting process described above & mist cooling process for flame hardening gives equivalent properties & die performance in actual production set up as compared to the Cr-Mo type gray cast irons used for the above application in prior art.
Detailed descriptions of the preferred embodiment are provided herein; however, it is to be understood that the present invention may be embodied in various forms. Therefore, specific details disclosed herein are not to be interpreted as limiting, but rather as a basis for the claims and as a representative basis for teaching one skilled in the art to employ the present invention in virtually any appropriately detailed system, structure or matter.
Dated this 23rd day of August 2006 Kiran Joshi
(Agent for the applicant)
8