Claims:WE CLAIM:

1. A sinter mixer tool composition consisting essentially by weight of about 1.4 – 1.6% Carbon, 11.0-13.0% Chromium, about 0.7 – 1.2% Molybdenum, 1.1% (max) Vanadium, about 0.6% (max) of each of Silicon and Manganese, about 0.3% (max) of Nickel, about 0.03% each of Sulphur and Phosphorus and the balance essentially iron.

2. The sinter mixer tool composition as claimed in claim 1, wherein the said chemical composition of the alloy consist of elements that provide wear resistant carbide forming elements and further heat treatment is provided in a manner to produce a matrix strong enough to sustain impact and provides breakage and chipping resistance.

3. The sinter mixer tool composition as claimed in claim 2, wherein the heat treatment includes hardening & tempering cycles as under:

Heat Treatment
Hardening (Air/Oil Quenching) Tempering
1000-1050OC 500-550OC

4. The sinter mixer tool composition as claimed in claim 3, wherein the hardening & tempering cycles provides a hardness of 56-60 HRC.

5. A sinter mixer tool employing the composition and the heat treatment as claimed in any of the preceding claims.

Dated: this 26th day of March, 2018.
, Description:SINTER MIXER TOOL COMPOSITION AND THE TOOL THEREOF

FIELD OF INVENTION:

The present invention relates to a sinter mixer tool made of steel alloy containing high carbon high chromium which can be used as mixing tool having a high hardness and the high performance sinter mixer tool thereof for intensive sinter mixer of steel plant sinter machines

BACKGROUND OF INVENTION:

The mixer tools (straight blade, scrapper tool, bottom plate also termed as end disc) of intensive sinter mixer are subjected to severe wear under moderately low stress & impact from the aggressive sinter mix, which contains iron ore fines (-10mm), coke fines (-3mm), limestone (-3mm) and return sinter (-5mm). The aggressive nature of the mix causes severe wear on these tools resulting in extremely poor life. Although the nominal life of these tools is somewhere between 2 and 3 months when these tools progressively wears out, the life is reduced even to 2-4 weeks if the tools chip off due to impact from oversized particles that may eventually be present along with the charge mix. The frequent replacement of these tools due to their poor performance does not only result in increased cost of components but also in reduced availability of mixer leading to decreased sinter machine productivity. Sometimes, in case on non availability of WC-cladded tools, the alternatives (carbon steel weld overlayed with suitable MMAW (manual metal arc welding) electrodes that have been tried has resulted in extremely poor life and therefore has not been considered suitable for use.
A hard-facing composition should have optimum wear resistance, the coating produced on the metal substrate should exhibit good corrosion resistance, very low coefficient of friction in wear applications and have a matrix capable of being hardened by heat treatment.
The sintered wear parts herein can be easily produced with respect to the available prior arts and are excellent in the mixing performance, wear resistance and workability.

SUMMARY OF THE INVENTION:
It is thus the object of the invention to provide a high carbon and high chromium steel composition capable of being of being heat treated to possess requisite service requirements for sinter mixer tools.
An attempt was made for designing and developing high performance materials for mixer tools that possess superior wear resistance along with adequate strength & toughness. The materials chosen were based on high Carbon (C), high Chromium (Cr) grade of tool steel and have been heat treated to possess adequate wear & impact resistance as an alternative to Tungsten Carbide (WC) cladded tools over alloy steel base.
These and other objects will more clearly appear when taken in conjunction with the following disclosure and the appended claims.
The mixer tools (straight blade, cutting tool for scrapper, bottom plate) of intensive sinter mixer are subjected to severe wear under moderately low stress & impact from the aggressive sinter mix, which contains iron ore fines (-10mm), coke fines (-3mm), limestone (-3mm) and return sinter (-5mm). The aggressive nature of the mix causes severe wear on these tools resulting in extremely poor life. The frequent replacement of these tools due to their poor performance does not only result in increased component cost but also in reduced availability of mixer leading to decreased sinter machine productivity.

An attempt was made for designing and developing high performance materials for mixer tools that possess superior wear resistance along with adequate strength & toughness. The materials chosen were based on high Carbon (C), high Chromium (Cr) grade of tool steel family and have been heat treated to possess adequate wear & impact resistance as an alternative to costly, imported (OEM), Tungsten Carbide (WC) cladded tools over alloy steel base. The alternative (carbon steel weld overlayed with suitable MMAW (manual metal arc welding) electrodes that have been tried, have resulted in extremely poor life and therefore have not been considered suitable for use.

The experimentations (field trials) with high-C, high-Cr sinter mixer tools have not only resulted in comparable life to WC-cladded tools but have also been found an extremely cost effective, superior performance and indigenously developed alternative. Increased machine availability thereby increasing sinter machine productivity is also envisaged with the regular use of suitably heat treated high-C high-Cr tool steel grade sinter mixer tools.

BRIEF DESCRIPTION OF ACCOMPANYING DRAWING:

Fig 1, illustrates sinter mixer tools in accordance with the present invention.

DETAIL DESCRIPTION OF THE INVENTION:

Material design and fabrication for wear parts for steel plant applications suffers from the contradictory requirements that these components are encountered during service. The wear behaviour of steel plant components does not only depend on the intrinsic material characteristics but also on the attributes of the external environment that are present around them during their service life. One of the important attribute of external environment is the nature and aggressiveness (constituents, morphology and the way of interaction with the components) of abrasive and erosive media that these components are subject to.

To combat wear in industries, use of several materials and fabrication techniques have been reported which includes high-Cr iron alloys, ceramics & cermets, tool steel grades that are fabricated using several techniques including casting, forging, sintering, surface engineering techniques and employing different bulk surface heat treatments. All these materials are characteristics of a combination of wear resistance with varying degree of strength and toughness properties and are chosen to be used for specific application depending upon the service requirements of the component under consideration.

Of the several material design and fabrication techniques, tool steel family of alloys offers unique capabilities of sustaining moderately high strength and toughness requirements alongside the necessary wear resistance. The material designers optimally select and tweak with the composition and processing technique including heat treatment that can provide the required combination of bulk mechanical and surface properties.

Although the use of tool steel grades have been envisaged for several wear parts, the high-C high-Cr grade of steels have not been reported for use as sinter mixer tools.

Considering the service requirements of sinter mixer tools which includes provisions for adequate strength and toughness along with superior wear resistance, the alloys based on high-C high-Cr grade of steel were chosen and was suitably heat treated to result in a component that offers breakage resistance from the sinter mix (the aggressive charge materials which these tools are encountered with) alongside the wear resistance which prevents machine downtime by avoiding frequent replacements due to wear & tear.

The chemical composition of the alloy was chosen to consist of elements that provide wear resistant carbide forming elements and the heat treatment was employed in a manner to produce a matrix strong enough to sustain impact and provides breakage and chipping resistance.

The chemical composition high-C high-Cr sinter mixer tool material is as follows:

C Si Mn Cr Mo V S P Ni Fe
1.4-1.6 0.6
max. 0.6
max. 11.0-13.0 0.7-1.2 1.1
max. 0.03
max. 0.03
max. 0.3
max. Balance

The hardening & tempering cycles were finalised based on the final hardness levels and micro structural constituents that were desired to be achieved. It was ensured that heating during hardening was very slow and final quenching temperature was achieved in a staged manner by providing appropriate soaking times at intermediate & final temperature levels followed by quenching/cooling in air or appropriate media (oil). The tempering (single, double or triple) was carried out at temperature with a view to achieving not only the desired hardness levels but also the optimum combination of carbides and matrix structure.

The heat treatment cycles for high-C high-Cr grade of tool steel has broadly been based on the following:

Heat Treatment Hardness
Hardening (Air/Oil Quenching) Tempering HRC
1000-1050OC 500-550OC 56-60

USEFULNESS OF THE INVENTION:

The experimental sinter mixer tools have been tried at the intensive sinter mixer of machine #2 of Sinter Plant (SP-III) of Bhilai Steel Plant (BSP). The performance has been found comparable or better than the currently used tools. This is a cost effective, high performance, indigenously developed solution for wear prevention and control in raw material processing in iron and steel industry.

INDUSTRIAL APPLICABILITY:

Based on the encouraging results in regard to the performance, these newly developed tools can be used across all the intensive sinter mixers and nodulisers in SAIL. Besides, it can also be used as wear parts in intensive sinter mixer of other steel plant sinter machines in India and abroad.

Although the foregoing description of the present invention has been shown and described with reference to particular embodiments and applications thereof, it has been presented for purposes of illustration and description and is not intended to be exhaustive or to limit the invention to the particular embodiments and applications disclosed. It will be apparent to those having ordinary skill in the art that a number of changes, modifications, variations, or alterations to the invention as described herein may be made, none of which depart from the spirit or scope of the present invention. The particular embodiments and applications were chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such changes, modifications, variations, and alterations should therefore be seen as being within the scope of the present invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.