Description:FORM 2
THE PATENT ACT 1970
(39 OF 1970)
&
The Patent Rules, 2003
COMPLETE SPECIFICATION
(See Section 10 and Rule 13)

1 TITLE OF THE INVENTION :
COLD WORK TOOL STEEL BASED WEAR RESISTANT LINERS FOR STEEL PLANT SINTER MACHINE RAW MIX HOPPER AND PRODUCTION METHOD THEREOF.



2 APPLICANT (S)

Name : STEEL AUTHORITY OF INDIA LIMITED.

Nationality : Indian.

Address : Research & Development Centre for Iron & Steel,
Doranda, Ranchi, Jharkhand, India. PIN-834002.






3 PREAMBLE TO THE DESCRIPTION

COMPLETE

The following specification particularly describes the invention and the manner in which it is to be performed.

FIELD OF INVENTION

The present invention relates to cold work tool steel based wear resistant liners for raw mix hopper of sinter machine in steel plant. More particularly, the present invention is directed to developing high performance materials for mixer hopper tool steel liners that possess superior wear resistance along with adequate strength and toughness. The materials chosen was based on high Carbon (C), high Chromium (Cr) alloy from cold work tool steel family designated as AISI-D2 and have been heat treated to possess adequate wear & impact resistance as an alternative to conventionally used wear resistant liner plates. The experimental liners for lower portion of raw mix hopper of sinter machine has been manufactured with 1.5-2.0% C and 10-15% Cr cold work tool steel having additionally alloyed with 1.0-1.5% Mo, 0.8-1.2% V. The liner steel is heat treated with a quenching temperature of 1000-1050OC-0.5H followed by forced air cooling and double tempering at 500-550OC-4H has been employed which resulted in hardness in the range of 56-60 HRC. The life of Quenched &Tempered high-C, high-Cr cold work tool steel liners put on industrial trial completed 24 months and beyond in satisfactory service.

BACKGROUND OF INVENTION

The engineering systems in a complex manufacturing industry, such as an integrated iron and steel industry are composed of multitudes of machineries and other systems and structures. The components of these systems are subjected to several undesired changes and irreversible degradations during the service life which manifest through worsening of the system functions and lead to failures.

Wear in engineering industries in general and steel & mining industries in particular, as a result of the relative motion of the components in contact under the influence of load, temperature and other external conditions, is one of the three major causes of loss of materials and assemblies, the other two being fatigue & corrosion. Wear is rarely catastrophic, but it reduces operating efficiency by increasing the power losses, oil consumption, component replacement which inevitably incur increased cost to the industries. Besides, the needs for the periodic maintenance of these systems in order to avoid catastrophic failures further add to the operating costs. It is, therefore, imperative that the wear prevention and control is dealt upon with great emphasis as a solution to the maintenance problems and generating cost savings rather than allowing it to become the cause for the same.

Raw Mix Hoppers of Sinter Plant receive sinter mix from conveyors and feed it to sinter bed for sinter making. Sinter Mix contains iron ore fines (-8 mm), coke fines (-3 mm), limestone (-3 mm) and return sinter (-5 mm). Being highly abrasive in nature, the Liners of the Raw Mix hoppers are subjected to severe wear under low stress & impact conditions necessitating frequent replacements. Protective liners are installed along the entire inner surface of the Raw Mix Hopper to prevent damage of the mother equipment. Currently used liner materials include monolithic materials, such as, Mn-steel, Hot Rolled and Q&T Abrasion Resistant Plates and at some instances composite materials with hard layer over a mild steel base plate. Life of most of the monolithic materials is 6-8 months whereas composite plates are much costlier and are not of consistent qualities. Frequent replacements of these liners not only result in increased component cost but also lead to production losses.

There has been thus a need to develop high performance liner plates for raw mix hopper with sufficient wear resistance and ensuring longer service life without replacement.

OBJECTIVE OF THE INVENTION

The basic object of the present invention is directed to provide cold work tool steel based wear resistant liners for raw mix hoper of sinter machine in steel plant.

A further object of the present invention is directed to designing and developing a cold work tool steel based on high-C high-Cr heat treated (Quenched & Tempered) liners to result in a component that offers wear resistance from the raw sinter mix along with strength and toughness to ensure breakage resistance.

A still further object of the present invention is directed to develop a suitable alternative to currently used monolithic material with superior performance and competitive cost.

A still further object of the present invention is directed to develop a high performance liner material protecting the inner surface of for sinter plant raw mix hoppers from wear and other in-service deterioration of the mother equipment, ensuring longer service life and reduced down time of plant as compared to existing composite liner materials.

SUMMARY OF THE IVENTION

The basic aspect of the present invention is directed to cold work tool steel based wear resistant liners for steel plant sinter machine hopper comprising of a high C and high Cr chemical composition including :

C Si Mn Cr Mo V S P Ni Fe
1.5-2.0 0.6
max. 0.6
max. 10.0-15.0 1.0-1.5 0.8-1.2 0.03
max. 0.03
max. 0.5
max. Balance

and having hardness in the range of 56-60 HRC .

A further aspect of the present invention is directed to said cold work toll steel based wear resistant liner which is heat treated wear resistant liner having protective service life of even more than 24 months.

A still further aspect of the present invention is directed to a process for the manufacture of the cold work tool steel based wear resistant liners for steel plant sinter machine hopper as described above comprising :

i) providing the liner select chemical composition of

C Si Mn Cr Mo V S P Ni Fe
1.5-2.0 0.6
max. 0.6
max. 10.0-15.0 1.0-1.5 0.8-1.2 0.03
max. 0.03
max. 0.5
max. Balance

ii) obtaining the cold work tool steel involving the above select composition;
iii) subjecting the thus obtained cold work tool steel to quenching in the temperature range of 1000-10500C , followed by forced air cooling ; and
iv) subjecting to double tempering at 500-5500C to reach to the desired hardness range of 56-60 HRC.

A still further aspect of the present invention is directed to said process wherein said step of quenching in the temperature range of 1000-10500C is carried out for a period of 20 min. to 40 min. preferably about 30 min. followed by forced air cooling and said step of double tempering at 500-5500C was carried out for a period of 3 hrs. to 5 hrs. preferably about 4 hrs followed by air cooling.

Above and other aspects and advantages of the present invention are described hereunder in details with reference to accompanying illustrative example.

DETAILED DESCRIPTION OF THE INVENTION:

The present invention relates to cold work tool steel based wear resistant liners for raw mix hopper of sinter machine in steel plant. More particularly, the present invention is directed to developing high performance materials for mixer hopper tool steel liners that possess superior wear resistance along with adequate strength and toughness. The materials chosen was based on high Carbon (C), high Chromium (Cr) alloy from cold work tool steel family designated as AISI-D2 and have been heat treated to possess adequate wear & impact resistance as an alternative to conventionally used wear resistant liner plates.

Wear can be defined as the progressive loss of materials from the surfaces of contacting bodies in relative motion. The conditions that affect the nature and extent of wear are load, speed, temperature, dynamic loading (i.e. variation in loads during the operation), presence or absence of external particles in the system and their natures, external environment, lubrication condition, mechanical or other damages in the system and assembly. The wear mechanisms that will manifest in a given system will depend on the prevailing conditions and their proportions.

The science of wear and friction, being interdisciplinary in nature, poses great difficulties to designers and engineers in making choices toward selection of materials for wear prone components in industries. The judgment on suitability of the material is dependent on the nature and extent of wear occurring in a given set of operating conditions. It therefore becomes important for the material engineers to possess an adequate knowledge of the engineering systems, wear mechanisms and the characteristics of engineering materials in order to suggest the most appropriate materials for such applications. The considerations to be made for selection of materials sometimes contradict each other and makes it imperative for a material engineer to strike a fine balance between several surface and bulk properties. The solutions may, therefore, emanate from a wide range of materials and processing techniques and several combinations thereon which makes it necessary to have an understanding of not only the engineering systems but also of strength and limitations of different engineering materials as well as of fabrication techniques.

To combat wear in industries, use of several materials and fabrication techniques have been reported which includes tool steels & alloys, ceramics & cermets, cast irons 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 cold work tool steels have not been selected for use as sinter machine raw mix hopper liners.

Considering the service requirements of sinter machine raw mix hopper liners which includes provisions for adequate strength and toughness along with superior wear resistance, an alloy based on high-C high-Cr cold work tool steel was chosen and was suitably heat treated to result in a component that offers wear resistance from the raw sinter mix (the aggressive charge materials which these liners are encountered with) alongside breakage resistance which prevents machine downtime by avoiding frequent replacements due to wear & other failures. 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.

Example:

The high-C high-Cr grade of cold work tool steel was considered primarily for providing prolonged life by sustaining progressive wear and moderate impact. 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, heat treatment cycle and hardness of high-C high-Cr cold work tool steel raw mix hopper materials are as follows:

Chemical Composition, Elements (wt. %)
C Si Mn Cr Mo V S P Ni Fe
1.5-2.0 0.6
max. 0.6
max. 10.0-15.0 1.0-1.5 0.8-1.2 0.03
max. 0.03
max. 0.5
max. Balance

Heat Treatment Cycle
Hardening (Air/Oil Quenching) Double Tempering
1000-1050OC 500-550OC
Hardness: 58-62 HRC Hardness: 56-60 HRC

The salient aspects of present invention are as follows:

1. Diagnosing the nature and extent of wear and other service related deterioration in order to formulate the material specification for obtaining high performance liners for sinter plant raw mix hoppers.
2. A high performance liner material protecting the inner surface of for sinter plant raw mix hoppers from wear and other in-service deterioration of the mother equipment.
3. A chemical composition of the wear resistant cold work tool steel that upon employing a carefully chosen heat treatment can result in high performance liners for sinter plant raw mix hoppers.
4. A heat treatment cycle that imparts desired properties that is required for high performance liners for sinter plant raw mix hoppers.
5. The whole process cycle including a clear understanding of the service requirements based on the nature and extent of wear and other service related deteriorations; steel composition; heat treatment; machining and grinding; quality control measure that can be employed for obtaining high performance liners of sinter plant raw mix hoppers.

Usefulness of the Invention:

The life of Quenched & Tempered(Q&T) high-C, high-Cr cold work tool steel liners have already been put on industrial trial to ensure practical utility of the present advancement and completed 24 months of service after its installation in Raw Mix Hopper of Sinter machine of Applicant’s Steel Plant and continued successful service. Considering the comparative cost, time required for periodic replacement of worn out liners & the resultant production losses, and the life of currently used liner materials, use of high-C, high-Cr cold work tool steel liners favouring substantial annual cost saving of the order of INR 125 lakh.

Industrial Applicability:

High-C High-Cr grades of cold work tool steel alloys suitably heat treated to produce desired combination of bulk and surface properties can be a suitable choice for protective lining material for bulk solid handling equipment not only in iron and steel industries but also in metals, mining and minerals possessing industries.

, Claims:We Claim:

1.Cold work tool steel based wear resistant liners for steel plant sinter machine hopper comprising of a high C and high Cr chemical composition including :
C Si Mn Cr Mo V S P Ni Fe
1.5-2.0 0.6
max. 0.6
max. 10.0-15.0 1.0-1.5 0.8-1.2 0.03
max. 0.03
max. 0.5
max. Balance

and having hardness in the range of 56-60 HRC .

2.The cold work toll steel based wear resistant liner as claimed in claim 1 which is heat treated wear resistant liner having protective service life of even more than 24 months.

3. A process for the manufacture of the cold work tool steel based wear resistant liners for steel plant sinter machine hopper as claimed in claim 1 comprising :

i) providing the liner select chemical composition of

C Si Mn Cr Mo V S P Ni Fe
1.5-2.0 0.6
max. 0.6
max. 10.0-15.0 1.0-1.5 0.8-1.2 0.03
max. 0.03
max. 0.5
max. Balance

ii) obtaining the cold work tool steel involving the above select composition;
iii) subjecting the thus obtained cold work tool steel to quenching in the temperature range of 1000-10500C , followed by forced air cooling ; and
iv) subjecting to double tempering at 500-5500C to reach to the desired hardness range of 56-60 HRC.

4.The process as claimed in claim 3 wherein said step of quenching in the temperature range of 1000-10500C is carried out for a period of 20 min. to 40 min. preferably about 30 min. followed by forced air cooling and said step of double tempering at 500-5500C was carried out for a period of 3 hrs. to 5 hrs. preferably about 4 hrs. followed by air cooling.

Dated this the 25th day of March, 2023
Anjan Sen
Of Anjan Sen & Associates
(Applicants’ Agent)
IN/PA-199