HIGH PERFORMANCE SINTER PLANT GRATE BARS

TECHNICAL FIELD
[0001] The present disclosure, in general, relates to sinter plants. More particularly, the present disclosure relates to a grate bar and a method of making the molten steel for grate bars.

BACKGROUND
[0002] Background description includes information that may be useful in understanding the present disclosure. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed subject matter, or that any publication specifically or implicitly referenced is prior art.
[0003] Integrated steel plants generate many types of wastes at different stages of the processing. In an example, generation rate of Linz Donawitz (LD) steel slag is 150-180 kg per ton of crude steel. Such LD steel slag which is residual waste material remaining after the refining of pig iron is highly rich in phosphorous usually it is not used properly in steel plants. Accordingly, utilization of such waste is an environment friendly cost saving technique.

OBJECTS OF THE DISCLOSURE
[0004] Some of the objects of the present disclosure, which at least one embodiment herein satisfy, are listed herein below.
[0005] It is a general object of the present disclosure to utilize waste such as LD steel slag in an environment friendly cost saving technique.
[0006] It is an object of the present disclosure to provide a method of making the molten steel from the waste, such as LD steel slag, for producing grate bars.
[0007] It is another object of the present disclosure to provide grate bars produced from molten steel made from the waste such as LD steel slag.
[0008] These and other objects and advantages of the present invention will be apparent to those skilled in the art after a consideration of the following detailed description taken in conjunction with the accompanying drawings in which a preferred form of the present invention is illustrated.

SUMMARY
[0009] This summary is provided to introduce concepts related to a grate bar and a method of making the molten steel for grate bars. The concepts are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.
[0010] The present disclosure relates to a grate bar comprising the following composition by weight. The grate bar includes Carbon 1.6 to 1.8 %, Chromium 20-22 %, Nickel 3.5- 4.5 %, 0.5 % < Phosphorus < 0.5-1.5% %, and remainder being Iron, Manganese, Silicon and Molybdenum
[0011] In an aspect, the hardness of the grate bar is 390-440 BHN.
[0012] In an aspect, the wear rate is 0.00003 to 0.000025 mm3/N-mm at wear rate 30N to 50N.
[0013] In an aspect, the composition of the grate bar further comprising, by weight, Chromium Carbide ~ 20-25%, Iron Chromium with complex phosphide ~ 5 %, and remainder being Ferrite.
[0014] The present disclosure relates to a method of making molten steel for grate bar. The method includes charging high phosphorus pig iron (HPPI), along with various ferro alloys, including ferro chrome, ferro manganese, ferro silica, ferro nickel and Ferro Molybednum, in an induction furnace.
[0015] In an aspect, the HPPI, by weight, comprises manganese 1- % max, Silicon 1-2 % max, Carbon 3.5 – 4.0%, and Phosphorus 1.0 -1.5%.
[0016] Various objects, features, aspects, and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components.
[0017] It is to be understood that the aspects and embodiments of the disclosure described above may be used in any combination with each other. Several of the aspects and embodiments may be combined to form a further embodiment of the disclosure.
[0018] The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS
[0019] The illustrated embodiments of the subject matter will be best understood by reference to the drawings, wherein like parts are designated by like numerals throughout. The following description is intended only by way of example, and simply illustrates certain selected embodiments of devices, systems, and methods that are consistent with the subject matter as claimed herein, wherein:
[0020] FIG. 1A illustrates optical microstructures of investigated grate bar samples containing 0.05 wt. % of phosphorus (P);
[0021] FIG. 1B illustrates optical microstructures of investigated grate bar samples containing 0.5 wt. % of phosphorus (P);
[0022] FIG. 1C illustrates optical microstructures of investigated grate bar samples containing 1.1 wt. % of phosphorus (P);
[0023]
[0024] FIG. 2 illustrates the effect of phosphorous addition on hardness of the grate bar samples;
[0025] FIG. 3A illustrates the variation in the wear volume with the track distance of all three samples at 10 N applied load;
[0026] FIG. 3A illustrates the variation in the wear volume with the track distance of all three samples at 30 N applied load;
[0027] FIG. 3C illustrates the variation in the wear volume with the track distance of all three samples at 50 N applied load; and
[0028] FIG. 4 illustrates variation in wear rate of all three samples with applied load.
[0029] The figures depict embodiments of the disclosure for purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the disclosure described herein.

DETAILED DESCRIPTION
[0030] The detailed description of various exemplary embodiments of the disclosure is described herein with reference to the accompanying drawings. It should be noted that the embodiments are described herein in such details as to clearly communicate the disclosure. However, the amount of details provided herein is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.
[0031] It is also to be understood that various arrangements may be devised that, although not explicitly described or shown herein, embody the principles of the present disclosure. Moreover, all statements herein reciting principles, aspects, and embodiments of the present disclosure, as well as specific examples, are intended to encompass equivalents thereof.
[0032] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises”, “comprising”, “includes” and/or “including,” when used herein, specify the presence of stated features, integers, steps, operations, elements and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and/or groups thereof.
[0033] It should also be noted that in some alternative implementations, the functions/acts noted may occur out of the order noted in the figures. For example, two figures shown in succession may, in fact, be executed concurrently or may sometimes be executed in the reverse order, depending upon the functionality/acts involved.
[0034] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which example embodiments belong. It will be further understood that terms, e.g., those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
[0035] Embodiments explained herein pertain to a grate bar and a method of making the molten steel, made from LD steel slag, for producing grate bars. As mentioned above, the integrated steel plants generate many types of wastes at different stages of the processing. For example, generation rate of LD steel slag is 150-180 kg per ton of crude steel. LD steel slag which is residual waste material remaining after the refining of pig iron is highly rich in phosphorous usually ground dumped . In this project work our aim is to utilize this phosphorous to make high chromium high phosphorous cast steel, which can be used for the manufacturing of grate bars.
[0036] Grate bars are used for making sinter plant moving beds. The grate bars material must be highly wear resistant, because the grate bars have to handle iron ore fine particles that are subjected to the sintering process and operate under the conditions of the cyclic effect of high-temperature gas flow. the temperature during sintering reaches 1100-1200°C. Such combination of process condition makes them susceptible to premature failure due to wear and high temperature oxidation/corrosion. Usually, high chromium cast steel having chromium content up to 28 wt % is used for grate bar application. In these materials, chromium carbides which are present in the austenite matrix enhances hardness and wear properties.
[0037] In the disclosure described herein, two new alloys are developed having modified chemistry and their microstructure, hardness and wear properties are compared with conventional high chromium cast steel used for grate bars. Basically, in the modified alloys, Cr / C ratio has been decreased and deliberate addition of phosphorus has been done. Characterization techniques used in this study are simple optical microscope, hardness tester and wear test set-up. Results showed that due to addition of phosphorous, grate bars recorded higher hardness and wear properties even on lowering the chromium content from 28 wt% to 21 wt%. Also at same chromium content (21wt%) wear properties and hardness of the grate bar sample improved by increasing phosphorous content. The reason for the improvement in wear properties and hardness is refined microstructure and formation of fine dispersion of complex phosphides along with carbides in the matrix.
Experimental Procedure:
[0038] In an experimental procedure, three grate bar samples, one existing and other two having modified composition, were taken. The composition of all three samples is given in the following Table 1:
Sample
Carbon Chromium Nickel Phosphorous
Existing sample 1 1.1 – 1.3 wt. % 26-28 wt% 4 wt % 0.05 wt% max
Sample 2 1.8 wt% 22wt% 4 wt % 0.5 wt%
Sample 3 1.8 wt% 22wt% 4 wt % 1.1 wt %

[0039] For microstructural investigation, the samples were sectioned in proper size and prepared further by grinding paper followed by polishing. Finally, samples were etched using 2 vol% nital solution. An optical microscope was used to study the microstructure. Hardness of the samples were measured by Brinell Hardness. To perform the wear test, all three samples were cut in pieces of dimension 12×12×20 mm³. Wear test was carried out on a pin –on –disc type wear testing machine The test was carried out against 240 grade grit paper under different applied loads 10N, 30N and 50N. The rotating speed of the disc was 300 rpm, which gave a linear speed of 1.570 m/s. The test duration time was 30 minute for each specimen. The samples were weighted before and after the wear test using 1mg precision digital scale to determine the weight loss. Finally wear volume was calculated by multiplying wear (in micro-meter) with cross section area of the samples.
[0040] The present disclosure proposes a grate bar comprising the following composition by weight. The grate bar includes Carbon 1.6 to 1.8 %, Chromium ~ 20-22%, Nickel 3.5- 4.5 %, Phosphorus ~ 0.5 -1.5%, and remainder being Iron, Manganese, Silicon and Molybednum.
[0041] In an aspect, the hardness of the grate bar is 390-440 BHN.
[0042] In an aspect, the wear rate is 0.00003 to 0.000025 mm3/N-mm at wear rate 30N to 50N.
[0043] In an aspect, the composition of the grate bar further comprising, by weight, Chromium Carbide ~ 20-25%, Iron Chromium with complex phosphide ~ 5 %, and remainder being Ferrite.
[0044] The present disclosure further proposes a method of making molten steel for grate bar. The method includes charging high phosphorus pig iron (HPPI), along with various Ferro alloys, including, ferro chrome, ferro manganese, ferro silica, ferro nickel and Ferro Molybednum, in an induction furnace.
[0045]
[0046] In an aspect, the HPPI, by weight, comprises manganese 1 % max, Silicon 1-2 % max, Carbon 3.5-4.0 %, and Phosphorus 0.5-1.5%.
Results and Discussions
Microstructure
[0047] FIG. 1A illustrates optical microstructures of investigated grate bar samples containing 0 wt. % of phosphorus (P); FIG. 1B illustrates optical microstructures of investigated grate bar samples containing 0.5 wt. % of phosphorus (P); and FIG. 1C illustrates optical microstructures of investigated grate bar samples containing 1.1 wt. % of phosphorus (P).
[0048] The existing grate bar samples (shown in FIG. 1A) microstructure consists of M23C6 carbides in the ferrite matrix whereas the microstructure of grate bar samples (FIGS. 1B and 1C) of modified chemistry consists of complex phosphides along with M23C6 carbides embedded within the ferrite matrix. Some phosphides also present at grain boundary because phosphorous segregates into areas, which solidify late in the freezing process. Furthermore, grain refinement was also observed in the microstructure as phosphorous content was increased.
Hardness
[0049] Phosphorous addition altered the microstructure characteristics of the grate bars and affected its properties. FIG. 2 shows the effect of phosphorous addition on hardness of the grate bar samples. It seems that hardness values are increased by increasing phosphorous content. This increase is related to the reinforcement of the matrix with the hard complex phosphide phase, which are harder than chromium carbide. The refinement obtained by phosphorous additions may have also contributed to increase hardness.
Wear Properties
[0050] Grate bars are highly susceptible to wear under operating condition. One of the aim of this work is to enhance the wear resistance of high chromium cast steel by modifying the chemistry. FIG. 3A illustrates the variation in the wear volume with the track distance of all three samples at 10 N applied load; FIG. 3A illustrates the variation in the wear volume with the track distance of all three samples at 30 N applied load; and FIG. 3C illustrates the variation in the wear volume with the track distance of all three samples at 50 N applied load.
[0051] From the graph of wear volume vs track distance, it can be seen that the sample which has higher hardness value has less wear volume as compared to the samples of lower hardness value at a particular applied load. The wear volume vs track distance graph also illustrates that wear volume increases with increasing applied load. This is reasonable due to the increase in applied shear stress over the worn surface by increasing the applied load.
[0052] FIG. 4 shows variation in wear rate of all three samples with applied load. Wear rate is defined as the wear volume per unit sliding distance. From the graph, it can be observed that wear rate at a particular load is more for that sample which has lower hardness and vice versa because the sample having the lower hardness will degrade more and as a result more wear volume will occur. Additionally, from the same graph one more thing can be observed that on increasing applied load wear rate increases. This is also due to the more degradation of the samples on increasing applied load.

TECHNICAL ADVANTAGES
[0053] The present disclosure provides grate bars having modified composition showing higher hardness and good wear properties as compared to standard material even on decreasing chromium content.
[0054] The present disclosure provides, on increasing the phosphorous level, hardness and wear properties for the grate bars improved even at same chromium content.
[0055] The present disclosure proposes addition of Phosphorous to cause an increase in the hardness due to reinforcement of the matrix with hard complex phosphide phase.
[0056] The present disclosure provides a modified grate bar having higher hardness value showed better wear resistance properties as compared to the standard grate bar sample having lower hardness value.
[0057] Furthermore, those skilled in the art can appreciate that the above description does not provide specific details of the manufacture or design of the various components. Those of skill in the art are familiar with such details, and unless departures from those techniques are set out, techniques, known, related art or later developed designs and materials should be employed. Those in the art can choose suitable manufacturing and design details.
[0058] Further, the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. It will be appreciated that several of the above-disclosed and other features and functions, or alternatives thereof, may be combined into other systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may subsequently be made by those skilled in the art without departing from the scope of the present disclosure as encompassed by the following claims.
[0059] It will be appreciated that variants of the above-disclosed and other features and functions, or alternatives thereof, may be combined into many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.

We claim:

1. A grate bar comprising the following composition by weight:
Carbon 1.6 to 1.8 %,
Chromium 20-22 %,
Nickel 3.5 to 4.5 %,
0.5 % < Phosphorus < 1.5%, and
Remainder being Manganese, Silicon and Molybednum, and Iron.

2. The grate bar as claimed in claim 1, wherein hardness of the grate bar is 390-440 BHN.
3. The grate bar as claimed in claim 1, wherein wear rate is 0.00003 to 0.000025 mm3/N-mm at wear rate 30N to 50N.
4. The grate bar as claimed in claim 1, wherein the composition of the grate bar further comprising, by weight, Chromium Carbide ~ 20-25%, Iron Chromium with complex phosphide ~ 5 %, and remainder being Ferrite.
5. A method of making molten steel for grate bar, the method comprising:
charging high phosphorus pig iron (HPPI), along with various Ferro alloys, including Ferro Chrome, Ferro Nickel, Ferro Manganese, Ferro Nickel, Ferro Molybdenum, in an induction furnace.
6. The method as claimed in claim 5, wherein the HPPI, by weight, comprises manganese 1% max, Silicon 1-2 % max, Carbon 3.5-4.0 %, and Phosphorus 1.0-1.5 %.