DESC:FIELD
The present disclosure relates to ferritic ductile iron, particularly ferritic ductile iron having adequate Brinell Hardness Number for manufacturing wheel hubs.
DEFINITION
As used in the present disclosure, the following term is generally intended to have the meaning as set forth below, except to the extent that the context in which it is used indicates otherwise.
Ferritic Ductile Iron is an iron alloy composed of primarily iron, carbon and silicon, and having a body-centered cubic crystal structure.
Microstructure: Microstructure is a small scale structure of a material, defined as the structure of a prepared surface of material as revealed by an optical microscope above 25X magnification.
BHN (Brinell Hardness Number) is the measurement of hardness, of a material, calculated from the size of an impression produced on the material under load by a hard steel ball.
HV (Vickers Pyramid Number) is a measure of the hardness of a material, calculated from the size of an impression produced on the material under load by a pyramid-shaped diamond indenter.
BACKGROUND
Ductile iron is an alloy composed of iron, nodule-shaped graphite and silicon, which makes the material ductile, and capable of withstanding temperature of 1350F (730C°). Further, ductile iron has excellent corrosion resistance, tensile strength, and yield strength. More specifically, the minimum value of tensile strength of ductile iron is 60,000 psi, while the minimum value of yield strength of ductile iron is 40,000 psi.
Of all the various types of ductile iron, ferritic ductile iron offers high impact resistance and good machinability without the need for being cast by a heat treatment processes. Generally, the yield strength to tensile strength, i.e., Ys/Ts ratio of ferritic ductile iron lies between 55% and 65%.
The above mentioned characteristics make ferritic ductile iron suitable for manufacturing metallic elements, particularly, automotive elements, more particularly wheel hubs. However for casting a wheel hub, the desired hardness factor is at least 250 BHN (Brinell Hardness Number) which is a stark contrast to the hardness factor of ferritic ductile iron which only ranges between 147 and 155 BHN. To manufacture a wheel hub having hardness of at least 250 BHN, cast iron could be used. However, cast iron is a poor choice for making wheel hubs due to its brittleness and significantly less tensile strength and yield strength.
There is therefore felt a need for ferritic ductile iron having Brinell Hardness Number greater than 250 BHN.
OBJECTS
Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows:
It is an object of the present disclosure to ameliorate one or more problems of the prior art or to at least provide a useful alternative.
An object of the present disclosure is to provide ferritic ductile iron having Brinell Hardness Number greater than 250 BHN.
Another object of the present disclosure is to provide ferritic ductile iron for casting metallic elements, especially wheel hubs.
Another object of the present disclosure is to provide ferritic ductile iron, which has relatively better machinability for manufacturing elements like wheel hubs without being heat treated, and yet provides a desired hardness factor.
Other objects and advantages of the present disclosure will be more apparent from the following description, which is not intended to limit the scope of the present disclosure.
SUMMARY
The present disclosure envisages ferritic ductile iron, comprising:
i. silicon in the range of 3 wt% to 5 wt%;
ii. carbon in the range of 2 wt% to 4 wt%;
iii. manganese in the range of 0.1 wt% to 0.5 wt%;
iv. phosphorous in the range of maximum 0.05 wt%;
v. magnesium in the range of 0.01 wt% to 0.1 wt%;
vi. cerium in the range of 4 wt% to 5 wt%;
vii. sulphur in the range of maximum 0.1 wt%; and
viii. balance wt% of iron;
wherein the Brinell Hardness Number of the ferritic ductile iron is greater than 250 BHN.
In one embodiment, the ferritic ductile iron preferably comprises:
i. silicon in the range of 3.5 wt% to 4.3 wt%;
ii. carbon in the range of 3.5 wt% to 4.3 wt%;
iii. manganese in the range of 0.1 wt% to 0.3 wt%;
iv. phosphorous in the range of maximum 0.02 wt%;
v. magnesium in the range of 0.03 wt% to 0.06 wt%;
vi. cerium in the range of 4.15 wt% to 4.5 wt%;
vii. sulphur in the range of maximum 0.03 wt%; and
viii. balance wt% of iron.
In yet another embodiment, the ferritic ductile iron more preferably comprises:
i. 3.12 wt% of carbon;
ii. 4.2 wt% of silicon;
iii. 0.28 wt% of manganese;
iv. 0.016 wt% of phosphorous;
v. 0.047 wt% of magnesium;
vi. 4.57 wt% of cerium;
vii. 0.027 wt% of sulphur; and
viii. balance wt% of iron.
In one embodiment, the iron content comprises pearlite and ferrite in the range of 1:99 and 10:90.
In another embodiment, the iron content comprises pearlite and ferrite in the range of 5:95.
In an embodiment, Vicker Hardness Number of the ferritic ductile iron ranges between 235-275 HV. In another embodiment, Brinell Hardness Number of the ferritic ductile iron ranges between 200-260 BHN.
The present disclosure also envisages a process of manufacturing ferritic ductile iron having Brinell Hardness Number greater than 250 BHN. The process comprises the steps of:
i. making a mould with green sand and a pattern, the mould having a gating system;
ii. melting iron;
iii. carburizing the molten iron to induce carbon in the range of 2 wt% to 4 wt% therein, and treating the carbon induced molten iron with silicon, manganese, phosphorus, magnesium, cerium, sulphur to induce the carbon induced molten iron with silicon in the range of 3 wt% to 5 wt%, manganese in the range of 0.1 wt% to 0.5 wt%, phosphorous in the range of maximum 0.05 wt%, magnesium in the range of 0.01 wt% to 0.1 wt%, cerium in the range of 4 wt% to 5 wt% and sulphur in the range of maximum 0.1 wt%;
iv. pouring the molten, carburized and treated iron in the mould for casting;
v. cooling of casting and knocking out; and
vi. degating.
The present disclosure further envisages ferritic ductile iron, prepared by the following steps of:
i. melting iron in a mould;
ii. carburizing the molten iron to induce carbon in the range of 2 wt% to 4 wt% therein;
iii. treating the carbon induced molten iron with silicon, manganese, phosphorus, magnesium, cerium, sulphur to induce the carbon induced molten iron with silicon in the range of 3 wt% to 5 wt%, manganese in the range of 0.1 wt% to 0.5 wt%, phosphorous in the range of maximum 0.05 wt%, magnesium in the range of 0.01 wt% to 0.1 wt%, cerium in the range of 4 wt% to 5 wt% and sulphur in the range of maximum 0.1 wt%;
iv. pouring the molten, carburized and treated iron in the mould and casting; and
v. cooling the casted molten iron to form ferritic ductile iron having Brinell Hardness Number greater than 250 BHN.
DETAILED DESCRIPTION
Embodiments are provided so as to thoroughly and fully convey the scope of the present disclosure to the person skilled in the art. Numerous details are set forth, relating to specific components, and methods, to provide a complete understanding of embodiments of the present disclosure. It will be apparent to the person skilled in the art that the details provided in the embodiments should not be construed to limit the scope of the present disclosure. In some embodiments, well-known processes, well-known apparatus structures, and well-known techniques are not described in detail.
The terminology used, in the present disclosure, is only for the purpose of explaining a particular embodiment and such terminology shall not be considered to limit the scope of the present disclosure. As used in the present disclosure, the forms "a,” "an," and "the" may be intended to include the plural forms as well, unless the context clearly suggests otherwise. The terms "comprises," "comprising," “including,” and “having,” are open ended transitional phrases and therefore specify the presence of stated features, integers, steps, operations, elements, modules, units and/or components, but do not forbid the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The particular order of steps disclosed in the method and process of the present disclosure is not to be construed as necessarily requiring their performance as described or illustrated. It is also to be understood that additional or alternative steps may be employed.
When an element is referred to as being "mounted on," “engaged to,” "connected to," or "coupled to" another element, it may be directly on, engaged, connected or coupled to the other element. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed elements.
The present disclosure envisages ferritic ductile iron. The ferritic ductile iron is, in a preferred embodiment, solution strengthened ferritic ductile iron (SSF DI). The ferritic ductile iron (SSF DI) comprises:
i. silicon in the range of 3 wt% to 5 wt%;
ii. carbon in the range of 2 wt% to 4 wt%;
iii. manganese in the range of 0.1 wt% to 0.5 wt%;
iv. phosphorous in the range of maximum 0.05 wt%;
v. magnesium in the range of 0.01 wt% to 0.1 wt%;
vi. cerium in the range of 4 wt% to 5 wt%;
vii. sulphur in the range of maximum 0.1 wt%; and
viii. balance wt% of iron.
The ferritic ductile iron, so formed by the above composition, has Brinell Hardness Number greater than 250 BHN.
SSF DI has a uniform matrix of ferrite which provides uniform hardness throughout the matrix leads to ease of machining and saves manufacturing cost and time. The unique composition of SSF DI with addition of higher silicon content increases the strength of steel without requiring heat treatment to be performed thereon.
In one embodiment, the solution strengthened ferritic ductile iron (SSF DI) preferably comprises:
i. silicon in the range of 3.5 wt% to 4.3 wt%;
ii. carbon in the range of 3.5 wt% to 4.3 wt%;
iii. manganese in the range of 0.1 wt% to 0.3 wt%;
iv. phosphorous in the range of maximum 0.02 wt%;
v. magnesium in the range of 0.03 wt% to 0.06 wt%;
vi. cerium in the range of 4.15 wt% to 4.6 wt%;
vii. sulphur in the range of maximum 0.03 wt%; and
viii. balance wt% of iron.

In yet another embodiment, the solution strengthened ferritic ductile iron (SSF DI) more preferably comprises:
i. 3.12 wt% of carbon;
ii. 4.2 wt% of silicon;
iii. 0.28 wt% of manganese;
iv. 0.016 wt% of phosphorous;
v. 0.047 wt% of magnesium;
vi. 4.57 wt% of cerium;
vii. 0.027 wt% of sulphur; and
viii. balance wt% of iron.
In one embodiment, the iron content comprises pearlite and ferrite in the range of 1:99 and 10:90.
In another embodiment, the iron content comprises pearlite and ferrite in the range of 5:95.
The ferritic ductile iron (SSF DI), of the present disclosure, exhibits a relatively high ratio of yield strength to tensile strength, i.e., Ys/Ts ratio of 80%. The ferritic ductile iron SSF DI displays medium to high mechanical properties, and excellent tensile strength, yield strength and elastic limit, without requiring any heat treatment process for casting a part, thereby saving machining cost and time.
In an embodiment, Vicker Hardness Number of the ferritic ductile iron ranges between 235-275 HV. In another embodiment, the Brinell Hardness Number of the ferritic ductile iron ranges between 200-260 BHN.
Further, the ferritic ductile iron, of the present disclosure, has tensile strength of at least 600 MPa, yield strength of at least 470MPa and % elongation of at least 10%. These characteristics are beneficial while manufacturing various types of metallic elements, particularly automotive elements, more particularly wheel hubs that require significantly higher hardness factor, yet need to be ductile enough for ease in machinability.
In a preferred embodiment, the ferritic ductile iron (SSF DI) can be casted for manufacturing metallic elements such as steering knuckle, gear carrier, differential case, bearing carriers and other casting products as well, apart from wheel hubs.
The present disclosure also envisages a process of manufacturing ferritic ductile iron having Brinell Hardness Number greater than 250 BHN. The process comprises the steps of:
i. making a mould with green sand and a pattern, wherein the mould has a gating system;
ii. melting iron;
iii. carburizing the molten iron to induce carbon in the range of 2 wt% to 4 wt% therein, and treating the carbon induced molten iron with silicon, manganese, phosphorus, magnesium, cerium, sulphur to induce the carbon induced molten iron with silicon in the range of 3 wt% to 5 wt%, manganese in the range of 0.1 wt% to 0.5 wt%, phosphorous in the range of maximum 0.05 wt%, magnesium in the range of 0.01 wt% to 0.1 wt%, cerium in the range of 4 wt% to 5 wt% and sulphur in the range of maximum 0.1 wt%;
iv. pouring the molten, carburized and treated iron in the mould for casting;
v. cooling of casting and knocking out; and
vi. degating.
The present disclosure further discloses ferritic ductile iron prepared by the following steps of:
i. melting iron in a mould;
ii. carburizing the molten iron to induce carbon in the range of 2 wt% to 4 wt% therein;
iii. treating the carbon induced molten iron with silicon, manganese, phosphorus, magnesium, cerium, sulphur to induce the carbon induced molten iron with silicon in the range of 3 wt% to 5 wt%, manganese in the range of 0.1 wt% to 0.5 wt%, phosphorous in the range of maximum 0.05 wt%, magnesium in the range of 0.01 wt% to 0.1 wt%, cerium in the range of 4 wt% to 5 wt% and sulphur in the range of maximum 0.1 wt%;
iv. pouring the molten, carburized and treated iron in the mould and casting; and
v. cooling the casted molten iron to form ferritic ductile iron having Brinell Hardness Number greater than 250 BHN.
The present disclosure is further described in light of the following experiment which is set forth for illustration purpose only and not to be construed for limiting the scope of the disclosure.
Experiment 1: Preparation of ferritic ductile iron (SSF DI) of hardness greater than 250BHN:
The solution strengthened ferritic ductile iron - SSF DI-1 is prepared, wherein the composition of the solution strengthened ferritic ductile iron is as follow:
i. 3.12 wt% of carbon;
ii. 4.2 wt% of silicon;
iii. 0.28 wt% of manganese;
iv. 0.016 wt% of phosphorous;
v. 0.047 wt% of magnesium;
vi. 4.57 wt% of cerium;
vii. 0.027 wt% of sulphur; and
viii. balance wt% of iron.
The results of tensile strength, yield strength and elastic limit of the SSF DI-1 are summarized in table 1.
Table-1
S.no. Tensile strength (MPa) Yield strength (MPa) Elastic limit (%)
1. 648.7 585.9 12.8
2. 642.9 602.0 11.1
Inference: SSF DI-1 exhibits a high Ys/Ts ratio of 80% as against 55% to 65% of conventional ductile iron. SSF DI-1 shows medium to high mechanical properties and excellent tensile strength, yield strength and elastic limit, and eliminates any heat treatment required for machining. SSF DI-1 has a uniform matrix of ferrite which provides uniform hardness throughout the matrix, which leads to ease of machining and saves manufacturing cost and time. Therefore, the unique composition of SSF DI with addition of Silicone increases the strength of steel without heat treatment.
Experiment 2: Casting of solution strengthened ferritic ductile iron (SSF DI):
SSF DI -1 of experiment 1 is casted into a multiple cavity mould for a wheel hub of the car wheel axle and hardness is measured at six different locations of the part for four cavities of the casting. The results of hardness value in HV (hardness scale: Vickers) of the SSF DI-1 parts are summarized in table 2.
Table-2
Location 1 Location 2 Location 3 Location 4 Location 5 Location 6
Cavity 1 255 255 269 269 255 255
Cavity 2 255 255 255 269 255 241
Cavity 3 241 255 255 255 255 241
Cavity 4 241 255 255 241 255 255
Inference: The hardness of SSF DI-1 is uniform throughout the part. SSF DI-1 has uniform matrix of ferrite which provides uniform hardness throughout the matrix, which in turn leads to ease of machining and saves manufacturing cost and time. Further, casting a light weight wheel hub with SSF DI-1 meets the functional requirements, and saves weight by approximately 1.6 kgs per axle.
The foregoing description of the embodiments has been provided for purposes of illustration and not intended to limit the scope of the present disclosure. Individual components of a particular embodiment are generally not limited to that particular embodiment, but, are interchangeable. Such variations are not to be regarded as a departure from the present disclosure, and all such modifications are considered to be within the scope of the present disclosure.
TECHNICAL ADVANCEMENTS
The present disclosure described herein above has several technical advantages including, but not limited to, the realization of ferritic ductile iron having Brinell Hardness Number greater than 250BHN, that:
• does not require heat treatment, thereby leading to cost saving and time saving;
• exhibits a high Ys/Ts ratio;
• has enhanced tensile strength, yield strength and elastic limit;
• has lower density;
• has relatively high and uniform hardness spread across the matrix, to facilitate ease of machining, and save manufacturing cost and time;
• has uniform ferritic matrix (<10% Pearlite) formed across the cross-section, irrespective of cooling rates in different cross-section of the part, leading to uniform properties all over the casting helping in stress distribution; and
• reduces weight of the manufactured part, thereby contributing to fuel economy and sustainability of planet.
The embodiments herein and the various features and advantageous details thereof are explained with reference to the non-limiting embodiments in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
The foregoing description of the specific embodiments so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.
The use of the expression “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the disclosure to achieve one or more of the desired objects or results.
The numerical values mentioned for the various physical parameters, dimensions or quantities are only approximations and it is envisaged that the values higher/lower than the numerical values assigned to the parameters, dimensions or quantities fall within the scope of the disclosure, unless there is a statement in the specification specific to the contrary.
While considerable emphasis has been placed herein on the components and component parts of the preferred embodiments, it will be appreciated that many embodiments can be made and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. These and other changes in the preferred embodiment as well as other embodiments of the disclosure will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation.
,CLAIMS:WE CLAIM:
1. Ferritic ductile iron, comprising:
i. silicon in the range of 3 wt% to 5 wt%;
ii. carbon in the range of 2 wt% to 4 wt%;
iii. manganese in the range of 0.1 wt% to 0.5 wt%;
iv. phosphorous in the range of maximum 0.05 wt%;
v. magnesium in the range of 0.01 wt% to 0.1 wt%;
vi. cerium in the range of 4 wt% to 5 wt%;
vii. sulphur in the range of maximum 0.1 wt%; and
viii. balance wt% of iron;
wherein the Brinell Hardness Number of the ferritic ductile iron is greater than 250 BHN.
2. The ferritic ductile iron as claimed in claim 1, wherein the ferritic ductile iron preferably comprises:
i. silicon in the range of 3.5 wt% to 4.3 wt%;
ii. carbon in the range of 3.5 wt% to 4.3 wt%;
iii. manganese in the range of 0.1 wt% to 0.3 wt%;
iv. phosphorous in the range of maximum 0.02 wt%;
v. magnesium in the range of 0.03 wt% to 0.06 wt%;
vi. cerium in the range of 4.15 wt% to 4.5 wt%;
vii. sulphur in the range of maximum 0.03 wt%; and
viii. balance wt% of iron.
3. The ferritic ductile iron as claimed in claim 1, wherein the ferritic ductile iron more preferably comprises:
i. 3.12 wt% of carbon;
ii. 4.2 wt% of silicon;
iii. 0.28 wt% of manganese;
iv. 0.016 wt% of phosphorous;
v. 0.047 wt% of magnesium;
vi. 4.57 wt% of cerium;
vii. 0.027 wt% of sulphur; and
viii. balance wt% of iron.
4. The ferritic ductile iron as claimed in claim 1, wherein the iron content comprises pearlite and ferrite in the range of 1:99 and 10:90.
5. The ferritic ductile iron as claimed in claim 1, wherein the iron content comprises pearlite and ferrite in the range of 5:95.
6. The ferritic ductile iron as claimed in claim 1, wherein Vicker Hardness Number of the ferritic ductile iron ranges between 235-275 HV.
7. The ferritic ductile iron as claimed in claim 1, Brinell Hardness Number of the ferritic ductile iron ranges between 200-260 BHN
8. A process of manufacturing ferritic ductile iron of hardness greater than 250 BHN, said process comprising the steps of:
i. making a mould with green sand and a pattern, said mould having a gating system;
ii. melting iron;
iii. carburizing the molten iron to induce carbon in the range of 2 wt% to 4 wt% therein, and treating the carbon induced molten iron with silicon, manganese, phosphorus, magnesium, cerium, sulphur to induce the carbon induced molten iron with silicon in the range of 3 wt% to 5 wt%, manganese in the range of 0.1 wt% to 0.5 wt%, phosphorous in the range of maximum 0.05 wt%, magnesium in the range of 0.01 wt% to 0.1 wt%, cerium in the range of 4 wt% to 5 wt% and sulphur in the range of maximum 0.1 wt%;
iv. pouring the molten, carburized and treated iron in the mould for casting;
v. cooling of casting and knocking out; and
vi. degating.
9. Ferritic ductile iron of hardness, prepared by:
i. melting iron in a mould;
ii. carburizing the molten iron to induce carbon in the range of 2 wt% to 4 wt% therein;
iii. treating the carbon induced molten iron with silicon, manganese, phosphorus, magnesium, cerium, sulphur to induce the carbon induced molten iron with silicon in the range of 3 wt% to 5 wt%, manganese in the range of 0.1 wt% to 0.5 wt%, phosphorous in the range of maximum 0.05 wt%, magnesium in the range of 0.01 wt% to 0.1 wt%, cerium in the range of 4 wt% to 5 wt% and sulphur in the range of maximum 0.1 wt%;
iv. pouring the molten, carburized and treated iron in the mould and casting; and
v. cooling the casted molten iron to form ferritic ductile iron having Brinell Hardness Number greater than 250 BHN.

Dated this 02nd day of July, 2022

_______________________________
MOHAN RAJKUMAR DEWAN, IN/PA – 25
of R.K.DEWAN & CO.
Authorized Agent of Applicant

TO,
THE CONTROLLER OF PATENTS
THE PATENT OFFICE, AT CHENNAI