Title of Invention | A METHOD FOR FORMING EASY TO REMOVE OXIDE SCALES FOR HIGH CARBON RODS |
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Abstract | A method to form an 'easy to remove oxide scale' during mechanical descaling of high carbon rods consists of simulating oxide scale formation of wire rod samples maintaining different thermal profile at Gleeble- 1500 and measuring the oxide composition of the wire rod samples by means of semi quantitative reitveld method by GAXRD. The samples are heated by GAXRD. The samples are heated to 1200°C and held for austenitising and cooling them to 1000°C in 20 secs. These are further cooled to 860°C at cooling rate 140°C/ sec. Different samples are cooled at different cooling rate maintaining stelmor cooling to cool them to 600°C- 550°C and finally cooling them in air. The observations at different cooling rates LHT are plotted to find a relationship between % Fe2O3 with LHT for high cooling rate and a relationship between % Fe2O3 with LHT for various cooling rates to record the best inference. |
Full Text | FIELD OF THE INVENTION: This invention relates to a method to form an 'easy to remove oxide scale' during mechanical descaling of high carbon rods. More particularly, the invention relates to a method which results formation of hematite very less during the process of wire rod rolling. BACKGROUND OF THE INVENTION: During the process of wire rod rolling, oxide scale are formed on the surface of steel wire rods. This scale should be removed before any further processing like wire drawing. Initially the descaling process was done by pickling using hydrochloric acid. Nowadays, because of stringent laws for environmental protection use of HCl is being discouraged. So, a lot of emphasis is being laid for alternate methods of descaling like mechanical descaling. Reverse bending procedure is being used today as a method of mechanical descaling in wire rod mills. Oxide layers in high carbon wire rods are not completely removed by mechanical descaling process. Formation of hematite causes poor mechanical descaling whereas magnetite and wustite are found to be non-adherent oxides. Accordingly there exists a need to find a method which enables formation of hematite very less during the process of wire rod rolling that results formation of easily removable oxide scale during mechanical descaling of high carbon rods. SUMMARY OF THE INVENTION: Oxide formation at high temperature has been thoroughly studied using Gleeble simulation and it is found that high laying head temperature (LHT) followed by faster cooling reduces the formation of hematite layer which is adherent in nature so that during mechanical descaling oxide scales are easily removed. OBJECTS OF THE INVENTION: It is therefore an object of the invention to propose a method to form an 'easy to remove oxide scale' during mechanical descaling of high carbon rods which enables the formation of adherent oxides like hematite very less. Another object of the invention is to propose a method to form an 'easy to remove oxide scale' during mechanical descaling of high carbon rods which restricts the formation of Fe2O3 to maximum around 10%. BRIEF DESCCRIPTION OF THE ACCOMPANYING DRAWINGS: Table 1: It shows the chemical composition (% wt.) of the wire rod used for the experiments. Table 2: It shows the details of thermal profiles maintained in Gleeble - 1500 Fig 1- It shows the quantitative analysis obtained from semi reitveld method to record, (a) a relationship between % Fe2O3 with LHT for high cooling rate. (b) a relationship between % FC3O4 with LHT for various cooling rates. DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT FOR THE INVENTION The chemical composition of wire rod is given in Table 1. The oxide scale formation was simulated using the Gleeble-1500. Gleeble-1500 is thermo-mechanical simulator where heat treatment or thermo- mechanical treatment can be applied to material of interest. This simulator is used in order to study the oxide formation at high temperature on wire rods. The different thermal profile maintained at Gleeble-1500 is given in Table-2. Initially the samples are heated to 1200°C and held for austenitising (rate not important) and then cool to 1000°C in 20 sec (rate not important). After that cooling from 1000° to 860° (precise cooling rate 140° C/sec) is done. Finally, different cooling rates are maintained during the rest and it is limited up to the end of stelmor cooling i.e. up to 600-550°C, then conventional forced air cooling is done. After the wire rods are rolled at high temperature (Hot rolling) the wire rods are layed and cooled to desired temperature to achieve desired microstructure and properties. This cooling is known as Stelmor cooling where air is blown from the bottom by putting some fans. After the Gleeble simulation the oxide composition of the wire rods is measured by semi quantitative reitveld method using GAXRD and the result is shown in Fig. 1 a and b. Semi quantitative reitveld method is done in X-ray diffraction machine. After getting the XRD plot for different phases present at a particular sample the relative amounts of each phase is determined by using this technique. This is done using "ExpertPro" software attached with X-ray machine. GAXRD is known as Grazing angle XRD. This is mainly used to determine the coating/thin layer/oxide layer composition. The incident beam is kept at an angle 0.5-5 degree. In Fig 1 the result of fast cooling rate is plotted. From Fig la it is evident that at lower LHT, the amount of hematite has increased significantly. The wire rods after getting rolled to desired size are layed. The temperature at which the laying process starts is known as Laying Head Temperature. At high temperature as per the oxide stability diagram only magnetite and wustite are stable. But during the cooling process, equilibrium diagram is not maintained properly and so hematite formation takes place. But at higher LHT the formation of hematite is low. From literature it is known that the formation of magnetite and wustite is favourable for mechanical descaling purpose. The variation of magnetite at different cooling rate at different LHT is shown in Fig 1 b. In Fig 1 b each data point corresponds to particular LHT followed by particular cooling rate as described in Table 2. From Fig 1 b it can be seen that at faster cooling rate the amount of magnetite is always higher compared with two other cooling rates. At high temperature as wustite and magnetite scales are dominant and as the cooling process starts the tendency to decompose of these oxides to form hematite starts. If cooling rate is maintained high then the time for formation of hematite is very less and therefore higher amount of magnetite is observed. Whereas, for slower cooling rate chance of hematite formation is high and as a result less amount to magnetite is observed. Phase transformation in oxide scale depends on various factors like availability of oxygen, cooling rate. As the complete process takes place in normal air condition so that availability of oxygen is not the critical factor. In this type of condition, only cooling rate plays important role in determining the oxide scale composition. WE CLAIM 1. A method for forming easy to remove oxide scales for high carbon rods comprising: - heating the rods to 1200°C for austenitising; - cooling them to 1000°C; - cooling them again from 1000°C to 860°C at a cooling rate of 140°C/sec; and then - further cooling to normal temperature. ABSTRACT A METHOD FOR FORMING EASY TO REMOVE OXIDES SCALES FOR HIGH CARBON RODS A method to form an 'easy to remove oxide scale' during mechanical descaling of high carbon rods consists of simulating oxide scale formation of wire rod samples maintaining different thermal profile at Gleeble- 1500 and measuring the oxide composition of the wire rod samples by means of semi quantitative reitveld method by GAXRD. The samples are heated by GAXRD. The samples are heated to 1200°C and held for austenitising and cooling them to 1000°C in 20 secs. These are further cooled to 860°C at cooling rate 140°C/ sec. Different samples are cooled at different cooling rate maintaining stelmor cooling to cool them to 600°C- 550°C and finally cooling them in air. The observations at different cooling rates LHT are plotted to find a relationship between % Fe2O3 with LHT for high cooling rate and a relationship between % Fe2O3 with LHT for various cooling rates to record the best inference. |
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440-KOL-2009-(08-02-2013)-ABSTRACT.pdf
440-KOL-2009-(08-02-2013)-CLAIMS.pdf
440-KOL-2009-(08-02-2013)-CORRESPONDENCE.pdf
440-KOL-2009-(08-02-2013)-DESCRIPTION (COMPLETE).pdf
440-KOL-2009-(08-02-2013)-DRAWINGS.pdf
440-KOL-2009-(08-02-2013)-FORM-1.pdf
440-KOL-2009-(08-02-2013)-FORM-2.pdf
440-KOL-2009-(08-02-2013)-OTHERS.pdf
440-KOL-2009-CANCELLED PAGES.pdf
440-KOL-2009-CORRESPONDENCE-1.1.pdf
440-kol-2009-correspondence.pdf
440-kol-2009-description (complete).pdf
440-KOL-2009-EXAMINATION REPORT.pdf
440-KOL-2009-GRANTED-ABSTRACT.pdf
440-KOL-2009-GRANTED-CLAIMS.pdf
440-KOL-2009-GRANTED-DESCRIPTION (COMPLETE).pdf
440-KOL-2009-GRANTED-DRAWINGS.pdf
440-KOL-2009-GRANTED-FORM 1.pdf
440-KOL-2009-GRANTED-FORM 2.pdf
440-KOL-2009-GRANTED-FORM 3.pdf
440-KOL-2009-GRANTED-SPECIFICATION-COMPLETE.pdf
440-KOL-2009-REPLY TO EXAMINATION REPORT.pdf
440-kol-2009-specification.pdf
Patent Number | 256531 | |||||||||
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Indian Patent Application Number | 440/KOL/2009 | |||||||||
PG Journal Number | 27/2013 | |||||||||
Publication Date | 05-Jul-2013 | |||||||||
Grant Date | 28-Jun-2013 | |||||||||
Date of Filing | 12-Mar-2009 | |||||||||
Name of Patentee | TATA STEEL LIMITED | |||||||||
Applicant Address | RESEARCH AND DEVELOPMENT AND SCIENTIFIC SERVICES DIVISION, JAMSHEDPUR | |||||||||
Inventors:
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PCT International Classification Number | B24B27/033; C21D9/46 | |||||||||
PCT International Application Number | N/A | |||||||||
PCT International Filing date | ||||||||||
PCT Conventions:
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