Field of the Invention
This invention relates to a coated electrode with improved austemperability. More particularly, this present invention relates to the coated electrode with improved austemperability in which weld metal can be converted to Austempered ductile iron by isothermal heat treatment. This invention relates tothe coated electrode with improved austemperability wherein the number of small ductile iron castings can be joined to make big size and then converted to Austempered ductile iron. This invention also relates to the coated electrode with improved austemperabilityhavingadvantages of low cost, good recycling capacity, excellent castability, a wide range of mechanical properties, safety and reliability. Background of the invention and the related Prior Art
The conventional covered are weldingelectrode has a solid, round rod as core wire and this coatedwith a single kind of mixed flux. When this wire is of particularly large diameter, the working characteristics of the electrode are poor, showing drop form transfer. It is due to a great surface tension developing at the globule formed at the wire tip. In consequence, the composition of deposit steel changes, leaving

blow-holes and coarsened pattern of bead waves; thus it is impossible to gain a beautiful appearance of weld.
In an effort to eliminate these defects of conventional electrodes, various attempts have been made. For instance, 'a double-coated electrode with claimed superiority in working characteristic was proposed. But this type of electrode has the drawback that it is hard to manufacture, consequently uneconomical.
The other document JP2011156588 discloses a welding electrode for FCD conventionally includes Fe-Ni type core wire and graphite flux and its maximum strength is limited at 440 N/mm2allowing to apply only for repair work; color tone of weld is different from that of a mother material so that a repair mark gets remarkable damaging appearance and impairs reliability of the product; and no electrode is available for weld bonding of materials among FCD 450-800 each other. The core wire of the welding electrode is made of ductile cast iron and coated with flux in two layer structure so that outside flux emits carbon dioxide and inside flux emits fluorine gas. The inside flux is a gel type flux which is a mixture of a liquid flux and an inoculation agent incorporated with elements necessary to increase strength of bonding zone.
According to the document US3036205when the electrode is partitioned in the
cross-section by flux into several compartments, the surface tension acting on each
globule forming from such subdivided section becomes vastly smaller and the
globule making an idea spray-particle transfers to the base metal, resulting in

good working. characteristic, arc stability, fine appearance of deposit metal and other favourable effects.
The document US3235405 states the fluorspar (calcium fluoride) or sodium fluoride operates as a flux or scouring agent which combines with various oxides liberated during deposition to form a highly effective slag cover which eliminates and excludes oxygen from the weld deposit. Potassium and barium fluorides can also be used for this purpose.The metallic deoxidizers, for example, may be selected from the following list of such agents or any. other effective metallic deoxidizing agents which are compatible with flux, core metal and parent metals.
According to the invention stated in the document US8372222a system and method for producing locally austempered ductile iron includes a computer program for closely controlling the heating and cooling of an iron part or workpiece. The process allows for the austempering of a relatively low cost iron workpiece to produce significantly higher, quality end products. The locally austempered regions may be formed to a substantial controlled depth.
The document GülcanToktas. and AlaaddinToktas. (2006) illustrates an investigation was performed to examine the influence of the matrix structure on the impact properties of a 1.03% Cu, 1.25% Ni and 0.18% Mo pearlitic ductile iron. Specimens were first homogenized at 925 °C for 7 h and a fully ferritic structure was obtained in all ductile iron samples. Then, various heat treatments were

applied to the homogenized specimens in order to obtain pearlilic/ferritic, pearlitic. tempered martensitic, lower and upper ausferritic matrix structures. The unnotchedcharpy impact specimens were tested at temperatures between - 80 °C and + 100 °C; the tensile properties (ultimate tensile strength, 0.2% yield strength and elongation) and the hardnesses of the matrix structures were investigated at room temperature. The microstructures and the fracture surfaces of the impact specimens tested at room temperature were also investigated by optical and scanning electron microscope. The results showed that the best impact properties were obtained for the ferritic matrix structure that had the lowest hardness, yield and tensile strength. Ductile iron with a lower ausferritic matrix had the best combination of ultimate tensile strength, percent elongation and impact energies of all structures.
In this study the effect of the austempering parameters on structure and mechanical properties of specimens made from 75 mm ductile iron Y-block with the composition of 3.5% carbon, 2.5% silicon, 1.1% nickel. 0.6% copper, 0.23% molybdenum, and 0.3% manganese was studied: The austempering carried out at 315 and 350 °C for 30, 60, 120, 180, 240, and 360 min. The results showed that the austempering times for optimum mechanical properties of austempered materials at 315 and 350 °C were 240 and 180 min, respectively. The results also indicated that austempering at 350 °C, in comparison with austempering at 315 °C. results in higher ductility and toughness and lower strength and hardness. It was also noticed

that in a Y-block, the best mechanical properties are achieved near the bottom of the Y-block which has been stated in document of patent application Mahmoud HeydarzadehSohi and A.BahramiVahdat(2004).
None of these above patents, however alone or in combination, disclose the present invention. The invention consists of certain novel features and a combination of parts hereinafter fully described, illustrated in the accompanying drawings, and particularly pointed out in the appended claims, it being understood that various changes in the details may be made without departing from the spirit, or sacrificing any of the advantages of the present invention.
Summary of the invention
This invention relates to a coated electrode with improved austemperability. More particularly, this present invention relates to the coated electrode with improved austemperabilityin which weld metal can be converted to Austempered ductile iron by isothermal heat treatment. This invention relates tothe coated electrode with improved austemperability wherein the number of small ductile iron castings can be joined to make big size and then converted to Austempered ductile iron. This invention also relates to the coated electrode with improved austemperabilityhavingadvantages of low cost, good recycling

capacity, excellent castability, a wide range of mechanical properties, safety and reliability.
Detailed description of the invention
For the purpose of facilitating an understanding of the invention, there is illustrated in the preferred embodiment thereof, from an inspection of which, when considered in connection with the following description, the invention, its construction and operation, and many of its advantages should be readily understood and appreciated.
The principal object of the invention is to provide a coated electrode with improved austemperability.
The object of the invention is to provide the coated electrode with improved austemperabilityin which weld metal can be converted to Austempered ductile iron by isothermal heat treatment.
The object of the invention is to provide the coated electrode with improved austemperability wherein the number of small ductile iron castings can be joined to make big size and then converted to Austempered ductile iron.

The other object of the invention is to provide the coated electrode with improved
austemperabilityhaving advantages of low cost, good recycling capacity,
excellent castability, a wide range of mechanical properties, safety and
reliability.
The other object of the invention is to provide the coated electrode with improved
austemperability wherein the high yield strength of Austempered ductile iron is
650-1300MPa.
The other object of the invention is to provide the coated electrode with improved
austemperability wherein the ultimate tensile strength of Austempered ductile
iron is 800-1600MPa.
The other object of the invention is to provide the coated electrode with improved
austemperability wherein charpy impact toughness of Austempered ductile
ironis 128 MPa.
The other object of the invention is to provide the coated electrode with improved
austemperability wherein fatigue strength of Austempered ductile iron is
302MPa.
The other object of the invention is to provide the coated electrode with improved
austemperabilityhaving a ductility of 4-16%.
The other object of the invention is to provide the process for converting ductile
iron to Austempered ductile iron which comprises a) Austenitization is done at
850-910°C for 30 min, b) the heating is done for 2 hours, c) austempering is

performed at 250-450°C for 5 min, and d) the heating is done for 4 hours. e) air cooling to room temperature to avoid the formation of martensite.
The novel features that are considered characteristic of the present invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and its method of operation, together with additional objects and advantages thereof, will best be understood from the following description of certain specific embodiments.
Austempered ductile iron (ADI) is a new and very promising engineering material with duplex matrix microstructure of bainitic ferrite and retained austenite and graphite nodules. The material is now of great interest for its low production cost, good recycling capacity, excellent castability and a wide range of mechanical properties such as high yield strength (650-l300MPa) and ultimate tensile strength (800-1600MPa), good ductility (4-16%), good fatigue strength, excellent wear resistance and high fracture toughness (120J). Due to the attractive mechanical properties and low production cost, ADI is now widely used in different commercial applications such as automotive, agricultural, earth moving machinery, railways and structural applications.
For ADI initial material is selected from as-cast ductile iron (DI) which is converted to ADI by two steps isothermal heat treatment process: austenitization
and austempering. Austenitization is done at 850-910°C for 30min -2 h holding
time and austempering is performed at 250-450°C for 5 min- 4 h holing time

followed by air cooling to room temperature to avoid the formation of martensite.
Till today ADI is mostly used as cast product. However, in order to provide more design flexibility and more use of low cost potential material (ADI) as well as for repairing the casting defects in producing ADI, or in joining several small casings to make a large component that could not, perhaps, have been cast as a single piece; the importance of welding DI which could be later converted to ADI, cannot be overridden. It is well known that cast iron is difficult to weld-the most common problem being cracking. But a thorough understanding of the metallurgy involved with DI, it could be possible to avoid cracking and develop sufficient joint strength. Although numbers of coated electrodes (which consists of solid wire with mineral coating and used in manual metal or shielded metal arc welding process) such as ENi-CI, pure nickel (90-97%), stainless steel (Fe-Cr-Ni) and ENiFe-CI etcare available commercially (Table 1) for welding DI, the weld metal produced with these electrodes can not be converted to ADI by isothermal heat treatment due to poor austemberability of the elements present in the electrodes.


Thus the problem of commercially available electrodes for welding DI is that these electrodes after welding cannot be converted to ADI by isothermal heat treatment due to poor austemperability of the weld deposits. Thus we have developed coated electrode with improved austemperability for welding DI and weld metal can be converted to ADI by isothermal heat treatment. As a result no.s of small DI castings can be joined to make big size and then converted to ADI. Also any defects present in DI castings can be repaired using the developed electrode and then converted to ADI. Therefore development of electrode will facilitate maximum exploitation of such low cost high potential engineering material such as ADI in different applications.
For minimizing the cost of the developed electrode we have used lesser amount of Ni (0.6%) which is very costly alloying element, as shown in Table 2, without compromising the joint quality. After welding DI and successfully converted to ADI, joint shows optimum mechanical properties [100% joint efficiency (yield strength > 690MPa,. Ultimate Tensile Strength > 910MPa), charpy impact toughness (128 MPa) and fatigue strength (302MPa). The chemical composition of the developed electrode is given in Table 2


Numerous objects, features and advantages of the present invention will be readily apparent upon a reading of the following detailed description of embodiments of the present invention when taken in conjunction with the accompanying drawings. However, the drawings employed herein are for the purpose of descriptions and should not be regarded as limiting. Advantages over the prior art
The coated electrode with improved austemperabilityproposed by the present invention has the following advantages over the prior art:
a) It is cost effective.
b) It has the characteristics of, convenient use, high efficiency.
c) It is economical in maintenances.
While the invention has been described in terms of what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention needs not be limited to the disclosed embodiment. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims which are to be accorded with the broadest interpretation so as to encompass all such modifications and similar structures.

We claim:
1) Acoated electrode with improved austemperability which contains the ingredient as described in table 2.
2) Thecoated electrode with improved austemperability as claimed in claim 1 which contains the ingredient more preferably as described in table 3.
3) The coated electrode with improved austemperability as claimed in claim 1 wherein the high yield strength of Austempered ductile iron is 650-1300 MPa.
4) The coated electrode with improved austemperability as claimed in claim 1 wherein the ultimate tensile strength of Austempered ductile iron is 800-1600 MPa.
5) The coated electrode with improved austemperability as claimed in claim 1 wherein charpy impact toughness of Austempered ductile iron is 128 MPa.
6) The coated electrode with improved austemperability as claimed in claim 1 wherein fatigue strength of Austempered ductile iron is 302MPa.
7) The coated electrode with improved austemperability as claimed in claim 1 wherein the number of small ductile iron castings can be joined to make big size and then converted to Austempered ductile iron.

8) The coated electrode with improved austemperability as claimed in claim 1 wherein more preferably yield strength of Austempered ductile iron is > 690MPa
9) The coated electrode with improved austemperability as:,claimed in claim 1 wherein more preferably Ultimate Tensile Strength of Austempered ductile iron is > 910MPa.
10) A process for converting ductile iron toAustempered ductile iron which comprises a) Austenitization is done at 850-910°C for 30 min, b) the heating is done for 2 hours, c) austempering is performed at 250-450°C for 5 min, and d) the heating is done for 4 hours. e) air cooling to room temperature to avoid the formation of martensite.