TITLE:
A high Chromium-vanadium Cast Iron material for tube mill liners and similar applications.
FIELD OF INVENTION:
This invention relates to a high chromium-vanadium cast iron material, composition with a higher combination of hardness and impact resistant properties, a high wear resistance, and a stable morphology.
The invention also relates to a method for producing high chromium-vanadium cast iron material and revels its various mechanical and physical properties.
BACKGROUND OF INVENTION:
Generally tube mill fails because of failure of liner plates due to number of progressive elongation of micro cracks present in the vicinity of rod like continuous chromium carbides along the dendritic grain boundaries in the matrix of tempered martensite and their further fast propagation through carbide networks. The continuous distribution of rod-like M7C3 carbide in matrix makes toughness lower than that of discontinuous distribution. Vanadium additions to high chromium cast iron modify carbides morphology from continuous to discontinuous chunk or even

granular type and favors martensitic transformation with vanadium carbide precipitation in austenite. These phase transformation makes microstructure finer and imparts higher hardness and impact strength combination which is highly suitable for parts experiencing wear as well as impact action simultaneously. With an increase in vanadium content, impact toughness increases while hardness decreases. For an optimum content of vanadium, hardness and impact toughness values are optimum which can suit well for application in component like tube mill liner. Therefore, it was proposed to develop a new high chromium-vanadium cast iron with improved hardness, impact strength, wear resistance and more stable morphological changes in the alloy matrix to meet the requisite coal pulverizing strength requirement for tube mill liner and similar other applications.
In CN103981429A teaches, a high-chromium wear-resistant lining and a preparation method was explained. Wherein the percentage composition for the above alloy was given as: C: 2.2-2.6wt%, Mn: 0.4-0.8wt%, Si: 0.6- 1.2wt%, Cr: 14-16wt%, Al: 0.016- 0.04wt%, Cu≤0.2wt%, P≤0.014wt%, Re: 0.02-0.1wt%, Mo: 0.1-0.15wt%; balance: Fe. This material was claimed to have hardness HRC: 64-72, impact toughness: 8-10J/cm2 and long life about: 40000 - 44000 hours.

In CN103966498A direct, a high-chromium white iron abrasion resistant materials and manufacturing methods was described. The composition of this white cast iron was given as: 3.60wt% - 4.20wt% of C, 22.0wt% - 26.0wt% of Cr, 0.80wt% -1.20wt% of Si, 0.60wt% - 1.00wt% of Mn; 0.50wt% - 0.70wt% of Mo, 0.20wt% -0.30wt% of V, 0.10wt% - 0.20wt% of Ti, 0.10wt% - 0.20wt% of B, the balance being Fe. The mechanical properties were mentioned as hardness: 60-64HRc and impact energy: ≥3J.
In CN103757516A relates, a wear-resisting white cast iron and a preparation method was stated. The chemical composition claimed are: 2.9-3.3wt% of C, 4.5-5.5wt% of Mn, 6.0- 7.2wt% of Cr, 0.45-0.70wt% of B, 0.50wt% of Si, 0.05wt% of S, 0.05wt% of P and the balance of Fe by mass fraction. The microstructure was found as carbide-off and isolated distribution network. Mechanical properties were evaluated as hardness: 61-63HRC and impact toughness: 8-10J/cm2
In CN1068598A teaches, a method for manufacturing rare earth alloyed white cast iron liner was described, wherein the main raw materials were used as the ratio of P08, 50% of pig iron, scrap 30%, recycled iron 18%, manganese 1.5-2%, and additional material amount of rare earth alloy 0.7-1.2% & silicon, copper 0.8-1%.

The mechanical properties were given as hardness: 40-55 HRc, impact energy: upto 10J/cm2. The service life was claimed upto 10000hours.
OBJECTS OF INVENTION:
An object of the present invention is to propose a high chromium-vanadium cast iron material for tube mill liners and similar other applications.
Another object of the invention is to propose a high chromium-vanadium cast iron, wherein melt temperature, tapping temperature and the pouring temperature have to be decided.
Another object of the invention is to propose a high chromium-vanadium cast iron, wherein moulding and casting methods have to be selected.
Another object of the invention is to propose a high chromium-vanadium cast iron, wherein constituents for sand moulding have to be selected.
Another object of the invention is to propose a high chromium-vanadium cast iron, wherein mould preparation method is to be decided.

Yet another object is to propose a high chromium-vanadium cast iron, wherein heat treatment cycles are to be selected.
Another object of the invention is to propose a high chromium-vanadium cast iron, wherein heat treatment scaling resistance has to be evaluated.
A further object is to propose a high chromium-vanadium cast iron, wherein a very good combination of hardness and impact toughness properties has to be achieved.
A further object is to propose a high chromium-vanadium cast iron, wherein a high abrasion wear resistance has to be achieved.
A further object is to propose a high chromium-vanadium cast iron, wherein a microstructure of uniform distribution of globular and/or chunk like carbides in matrix of martensite is to be developed.

BRIEF DESCRIPTION OF THE INVENTION:
This invention relates to a high chromium-vanadium cast iron material, composition of which has C: 2.4wt%- 2.8wt%, Si: 1wt% Max., Mn: 0.5wt% - 1.5wt%, Ni: 0.5wt% Max., Mo: 0.6wt% Max., S: 0.06wt% Max., P: 0.06wt% Max., Cr: 22wt%-28wt%, Cu: 1wt% Max., V: 0.35wt% - 0.65wt%, and the balance being Fe.
In accordance with the invention there is also provided a method for producing high
chromium-vanadium cast iron material and its properties analysis which comprising
the steps of:
subjecting “CO2 – sand moulding” to the step of its preparation,
subjecting high chromium-vanadium iron to the step of melting,
subjecting the melt to the step of pouring into the prepared sand mould
subjecting the casting to the step of its hardening and temperting heat treatments
and its scaling evaluation thereafter,
subjecting the “heat treated casting” to the step of various mechanical and physical
testing like Radiography Testing (RT), chemical analysis, hardness measurement,
impact testing, abrasion wear testing, microscopy and EDX analysis

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
Fig. 1: Heat treatment cycles for high chromium-vanadium cast iron material
Fig. 2: Wear testing set up in testing condition.
Fig. 3: Microstructure of high chromium-vanadium cast iron material at 200X
magnification
Fig. 4: SEM image and EDX spectrum of high chromium-vanadium cast iron
material at 200X {(a) & (b)} and 1000X {(c)} magnifications
DETAILED DESCRIPTION OF THE INVENTION:
According to the present invention, a new high chromium-vanadium cast iron was developed with a good combination of hardness and impact toughness properties and better wear property. The material was casted using induction melting and sand casting methods successfully. After the applicable heat treatment, a very low scaling was observed on the casting surfaces. This shows a high scaling resistance of this material till higher temperature (upto 960 Deg. C) and atmospheric air condition. Radiography Testing (RT) on the above castings ensured a uniformity within the matrix. This implies a smooth flow of melt in mould cavity and no casting

defects in casting matrixes. Subsequent to this, various samples were made from the casting based on characterization, hardness measurement, impact testing and abrasion wear testing requirements. Hardness and impact test results have shown a very good combination of hardness and impact strength values. Abrasion wear test result has revealed a very high wear strength. The optical microscopy and Scanning Electron Microscopy (SEM) have shown a very stable morphology in the casting matrix. Energy Dispersive X-ray Spectroscopy (EDX) on the casting sample has revealed vanadium and chromium carbides precipitations in the matrix. Therefore, the above high chromium-vanadium cast iron was evaluated and found to have a promising stable morphology and requisite mechanical properties applicable for tube mill liners and similar other applications.
A high chromium-vanadium cast iron block was casted using induction melting and sand casting methods successfully. In this process, Moulding was made by CO2-Sand Moulding method wherein silica sand with sodium silicate binder was packed using jolt squeeze technique. The mould was hardened by passing CO2 gas through it. Finally, the mould wall was painted using spirit base zircon paint and spirit base graphite paint. The melt was heated till a temperature from 1650 Deg. C to 1700 Deg. C, tapped from 1580 Deg. C to 1600 Deg. C and poured in the mould

at temperature from 1420 Deg. C to 1500Deg. C. The composition considered for the casting grade is given in Table-1. After successful casting, the compositions of cast iron grade was analyzed through Spark Emission Spectroscopy (SES) method and found within the required range as per the Table-2. Subsequent to this, the casting was heat treated as per the hardening and tempering cycles given in Fig-1. The casting was observed with a negligible scaling. This shows that the casting material is highly scaling resistant till 960 deg. C temperature. A Radiography Testing of the casting block passed it with Class-1 category which shows a zero defect in the matrix. Thereafter, the casting block was cut and various samples were made for hardness survey, impact test, abrasion wear test and characterization. Hardness tests on prepared samples from the cast iron block was carried out. The hardness test was carried out in Vickers' scale using 10Kg load. The equivalent hardness value in Rockwell 'C' scale is given in Table-3. Hardness test result shows that the material has achieved a very high hardness in the range of 57 to 62 HRc. An impact test was carried out on charpy un-notched test samples made from the above cast iron block. The test result is indicated in Table-4. The impact value shows the material has achieved a very good toughness property which ranges from 40 to 60 J/cm^2. Higher impact value with higher hardness is very much favorable for tube mill liner to ensure its higher

service life. An abrasion wear test (Fig. 2) was conducted as per the standard (ASTM G 65) and the results of which show a high wear resistance in which the material wear loss was evidenced from 8.0 to 13.0 mg/minute. The samples for characterization were polished and etched with Villela's etchant. The microstructures was examined and analyzed on the polished and etched samples through optical microscopy, Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray spectroscopy (EDX) methods. Microstructure of casting material in Fig. 3 shows globular MC type carbides and chunk like M7C3 carbides uniformly distributed in the martensite matrix having a trace of retained austenite which generally contributes better combination of hardness and impact values. A very low value of retained austenite was further confirmed through X-Ray diffraction method. Globular and chunk like uniform carbides precipitates distribution in the matrix of martensite is highly favorable for imparting a better combination of higher hardness and impact toughness properties. Therefore, morphology of casting material is highly consistent with the above favorable combination of hardness and impact toughness properties. SEM images and EDX spectrums of high chromium-vanadium cast iron material are shown in Fig. 4. The SEM image and EDX spectrum in Fig. 4 confirm the globular MC type carbide as vanadium carbide and

modified chunk like M7C3 type carbide as chromium carbide distribution with vanadium content in the matrix of casting material. More uniform distribution of carbides and vanadium presence in the matrix of the above high chromium-vanadium cast iron has imparted the best combination of hardness and impact strength.


WE CLAIM:
1. A high chromium-vanadium cast iron material, composition of which has C:
2.4wt%- 2.8wt%, Si: 1wt% Max., Mn: 0.5wt% - 1.5wt%, Ni: 0.5wt% Max., Mo:
0.6wt% Max., S: 0.06wt% Max., P: 0.06wt% Max., Cr: 22wt%-28wt%, Cu: 1wt%
Max., V: 0.35wt% - 0.65wt%, and the balance being Fe.
2. A method for producing high chromium-vanadium cast iron material comprising
the steps of:
a) selection of casting method and mould preparation,
b) melt preparation method and selection of melting, tapping and pouring
temperatures,
c) heat treatment of the castings and evaluation of scaling thereafter
3. The method as claimed in claim 2, wherein the casting method used is sand
casting in which molding method used is “CO2 sand molding”.

4. The method as claimed in claim 2, wherein the said step of moulding was made by CO2-sand moulding method wherein silica sand with sodium silicate binder was packed using jolt squeeze technique followed by CO2 gas pass through it and thereafter an application of spirit base zircon paint and spirit base graphite paint on the wall of mould cavity.
5. The method as claimed in claim 2, wherein the said melt was heated to a temperature from 1650 Deg. C to 1700 Deg. C using an induction melting process.
6.The method as claimed in claim 2, wherein the said melt is tapped from 1580 Deg. C to 1600 Deg. C in a lip pouring ladle and poured in the mould at temperature from 1420 Deg. C to 1500 Deg. C.
7. The method as claimed in claim 2, wherein the hardening and tempering cycles for which are as following: a) Hardening: Heat @ 30 Deg. C/hr till 960 Deg. C, hold at 960 ± 15 Deg. C for 10 hrs and forced air cool to room temperature and b) Tempering: Heat @ 30 Deg. C/hr till 295 Deg.C, hold at 295 + 15 Deg. C for 7 hrs and air cool to room temperature.

8) A high chromium-vanadium cast iron material of claim 1, wherein the material has a very good scaling resistance during heat treatment up to 960 Deg. C temperatures.
9) A high chromium-vanadium cast iron material of claim 1, wherein the material has a very good combination of hardness form 57 to 62 HRC and impact toughness from 40 to 60J/cm^2.
i
10) A high chromium-vanadium cast iron material of claim 1, wherein the material has a very good abrasion wear resistance means wear rate of weight loss ranges from 8.0 to 13.0 mg/minute (tested as per ASTM G 65).
11) A high chromium-vanadium cast iron material of claim 1, wherein the material has macrostructure of a uniform distribution of globular MC type vanadium carbides and chunk like M7C3 type chromium carbides in the matrix of martensite with a trace of retained austenite and vanadium content in it.