Title of Invention

METHOD OF MANUFACTURE OF CO2 WELDING WIRE RODS

Abstract

This invention relates to a method of manufacturing of CO2 welding wire rods by direct drawing from improved wire rod materials comprising the following steps: i) low carbon-high manganese is processed at the wire rod mill with rolling parameters having laying heat temperature (LHT), conveyor speed and mill speed to obtain a time ferrite containing microstructure and suitable mechanical properties; ii) the conveyor speed is fixed based on continuous cooling experiments carried out in a termal simulator; iii) transformation start temperature is 817°C and the finish temperature is 560°C which is then cooled under a cooling rate of 0.4°C/sec and a conveyor speed of 0.15m/sec to 0.175m/sec; iv) wire rods of diameter of 5.5mm or 0.8mm diameter without any intermediate operations of annealing and pickling.

Full Text

The invention relates to a method of manufacture of CO2 welding wire rods by direct drawing from improved wire rod materials. CO2 welding wire rod is used as a filler material for continuous welding by inert gas welding process in manufacturing industries. Carbon dioxide (CO2) welding wires are used for continuous welding in fabrication of structural components. Higher productivity levels, requirements of semi-skilled labour, and good weld quality has made CO2 welding the most sought after metal joining process, particularly in developing countries. Till recently the production of a CO2 wires of 1.2mm diameter were being produced by direct drawing from 5.5mm diameter wire rods. Major requirement of the industry of CO2 wires were 1.2mm diameter and was being met by TISCO. Meanwhile there was a substantial shift in the requirement of wire size by the end users. The growing automobile sector required more of 0.8mm wires in place of 1.2mm diameter wire for sheet metal and small component welding. With the present technology it is not possible to direct draw CO2 wire from 5.5mm to 0.8mm diameter and additional process steps of annealing and pickling is required by the wire drawers thus increasing the cost. Therefore the main object of the present invention is to produce 0.8mm diameter CO2 wires by direct drawing without the additional operation of annealing and pickling. Another object of the present invention is to develop an improved material with modification of chemistry producing direct draw quality wire rods of 1.2mm and 0.8mm. According to the present invention there is provided a method of manufacture of CO2 welding wire rods by direct drawing from improved wire rod materials comprising the following steps: i) low carbon-high manganese is processed at the wire rod mill with rolling parameters having Laying heat temperature (LHT) conveyor speed and mill speed to obtain a time ferrite containing microstructure and suitable mechanical property; ii) the conveyor speed is fixed based on continuous cooling experiments carried out in a thermal simulator; iii) transformation start temperature is 817°C and the finish temperature is 560°C which is then cooled under a cooling rate of 0.4°C/sec and a conveyor speed of 0.15m/sec of 0.175m/sec; iv) wire rods of diameter of 5.5mm is then direct drawn to 1.8mm or 0.8mm diameter without any intermediate operations of annealing and pickling. The nature of the invention, its objective and further advantages residing in the same will be apparent from the following description made with reference to the non limiting embodiments of the invention represented in the accompanying drawings: Figure 1 shows graphically the experiment results of trans- formation start and finish temperatures. Figure 2 shows microstructure at 3500 magnification. The improved material has been developed based on the following criteria: Producing steel with consistently low carbon (0.07-0.09%C) by adding low carbon silico-mzanganese, which is cheaper alternative to low carbon ferro-manganese. Eliminate re-blow in LD converter to keep N2 ppm for 0.8mm diameter wire. Control WRM processing parameters (laying head temperature, conveyor speed, and mill speed) properly to obtain a time ferrite containing mcirostructure and suitable (UTS 575 MPa) mechanical properties with minimum variation. For drawing to 1.2mm diameter wires, the rod chemistry should have a relatively leaner chemistry (C% = 0.07-0.09, Mn%l.40-1.50, N2 reduction of area (RA) > 78% , and a non-adherent scale. The specification of CO2, wire rod is given in Table 1. Table 1: Specification of CO2 welding wire rod It is important to note that nitrogen is responsible for strain ageing during drawing and hardens the stock material. For 0.8mm diameter it is essential to have a lower nitrogen level with uniform microstructure and properties over the length of the coil. The UTS should preferably less than 525MPa with RA over 78%. With the advent of more automobile industries, the requirement of 0.8mm diameter wires is expected to rise. Accordingly, the rod rolling parameters (laying head temperature mill speed, and conveyor speed) required to be adjusted to achieve the final properties. The experimental work was related to the following specific areas. Generation of continuous cooling curves for identification of transformation temperature and assessment of final microstructure using Gleeble 150 Heat balance calculation for steelmaking at LD1 using low carbon silico manganese. Strain Ageing index (SAI) determination with different nitrogen levels. Commercial heat making at LDI and rolling at WRM. Mechanical property evaluation. Drawing at customers end. The rolling parameters that include laying head temperature (LHT) and conveyor speed were fixed based on continuous cooling experiments carried out in a thermal simulator, Gleeble - 1500. A large number of Experiments (Fig-1) suggested that the transformation start temperature was 817°C and the finish temperature was 560°C when cooled under a cooling rate of 0.4°C/sec. The cooling rate of 0.4°C/sec relates to the retarded Stelmor effect with conveyor speed corresponding to 0.15m/sec. The WRM parameters were fine-tuned to obtain the desired ASTM grain size of 9-10 and ferrite fraction of 90% or higher. The Stelmor cooling was made effected by increasing the mill speed to 78m/sec with a conveyor speed of 0.15-0.175m/sec. By doing so, the volume fraction pearlite revolved around 10%. The interlammelar spacing of: the pearlite was extremely fine and could be resolved at 3500 magnificant (Fig.2) using SEM. Microstructure, mechanical and corrosion properties of wire rod: With close control of rolling parameters, a consistent microstructure with low pearlite content and fine ferrite grain size is obtained. A suitable microstructure for direct drawing draw wire rods should have 9-11% fine pearlite and ferrite grain size of 10-12µm. Large deviation in the rolling conditions bring about marked difference in the micro-structual characteristicsm which is subsequently reflected in the mechanical properties of the wire rod. By adopting proper rolling conditions the USTS obtained in most cases 525MPa, El.% ~ 38, and RA% ~ 78. The properties that have been obtained in wires for direct drawing application are given in the following table: Evaluation of Strain Ageing Index (SAI): During drawing the temperature of the wire rod rises to 100-150°C due to frictionai contact with surface of the dies, it is well established that interstitial elements like carbon and nitrogen tend to cause dynamic strain ageing and eventually increases the strength of the semi-drawn rod and affects further drawing. Tensle tests were carried out to determine the SAI of the wire rods with different nitrogen content between 42 ppm to 74 ppm. This was done to study the effect of nitrogen on drawability as a result of strain ageing. It has been established that a low carbon-high manganese chemistry for CO2 welding wire rods can be made using low carbon ( ~ 1%C) silico manganese ferro-alloy. Commercial heats are being processed with nitrogen content consistently blow 70 ppm for 1.2 mm diameter wires and below 50 ppm for 0.8 mm diameter wires. For producing 0.8 mm diameter wires, the wire rods are being processed with close control in chemistry, cleanliness and microstructure. Rods with nitrogen less than 50 ppm, UTS of around 515 MPa and RA% of 80 make suitable wire rods for direct drawing. With proper monitoring of parameters (LHT=800-820°C, CS=0.15-0.17m/min, MS-105%) at wire rod mill (WRM) the microstructure and mechanical properties have been found satisfactory for direct drawing application. Wide deviation in parameters causes property variation within the coil and from one coil to another and renders it unsuitable for direct draw application. Direct drawing trials on several heats (M37785, M37961 and M38562) were tired at customer end and was found suitable. Wires of 0.8 mm diameter and 1.2 mm diameter were drawn from 5.5 mm wire rods. The invention described hereinabove is in relation to the non-limited embodiments defined by the accompanying claims. WE CLAIM : 1. A method of manufacturing CO2 welding wire rods by direct drawing from improved wire rod materials, characterized by the steps of : attaining a lower carbon content steel through addition of low carbon silico-manganese ferroalloy; producing steel billets in the LD converters by adopting a single blow process of steel making thereby, ensuring low N2 content in steel produced; rolling billets into 5.5 mm diameter rods while controlling rolling parameters comprising mill speed, laying head temperature (LHT) and cooling rate (CR) for obtaining high volume fraction of fine grain ferrite; and drawing 1.2 mm and 0.8 mm CO2 welding wires at users end from said 5.5 mm diameter wire rods directly without any intermediate operations of annealing and pickling. 2. The method as claimed in claim 1, wherein the carbon content in steel is kept between 0.07 to 0.09 % and manganese content kept between 1.4 to 1.5 %. 3. The method as claimed in claim 1, wherein low carbon and high manganese content is achieved by adding low carbon silico manganese for producing steel. 4. The method as claimed in claim 1, wherein the nitrogen content is restricted to 70 ppm for 1.2 mm diameter wires and below 50 ppm for 0.8 mm diameter wires. 5. The method as claimed in claim 1, wherein said rolling parameters are mills speed of 78 m / sec with conveyor speed of 0.15 to 0.175 m / sec, laying head temperature 800 to 820° C, and a cooling rate of 0.4° C / sec. 6. The method as claimed in claim 5, wherein the rolling parameters are controlled for achieving mechanical property of UTS (ultimate tensile strength) ≈ 525 MPa, El % ≈ 38 % and RA ≈ 78 % for direct drawing application. 7. A method of manufacturing CO2 welding wire rods by direct drawing from improved wire rods materials, as herein described and illustrated with the help of the accompanying drawings. This invention relates to a method of manufacturing of CO2 welding wire rods by direct drawing from improved wire rod materials comprising the following steps: i) low carbon-high manganese is processed at the wire rod mill with rolling parameters having laying heat temperature (LHT), conveyor speed and mill speed to obtain a time ferrite containing microstructure and suitable mechanical properties; ii) the conveyor speed is fixed based on continuous cooling experiments carried out in a termal simulator; iii) transformation start temperature is 817°C and the finish temperature is 560°C which is then cooled under a cooling rate of 0.4°C/sec and a conveyor speed of 0.15m/sec to 0.175m/sec; iv) wire rods of diameter of 5.5mm or 0.8mm diameter without any intermediate operations of annealing and pickling.

Documents:

189-cal-2002-granted-abstract.pdf

189-cal-2002-granted-claims.pdf

189-cal-2002-granted-correspondence.pdf

189-cal-2002-granted-description (complete).pdf

189-cal-2002-granted-drawings.pdf

189-cal-2002-granted-examination report.pdf

189-cal-2002-granted-form 1.pdf

189-cal-2002-granted-form 18.pdf

189-cal-2002-granted-form 2.pdf

189-cal-2002-granted-form 26.pdf

189-cal-2002-granted-form 3.pdf

189-cal-2002-granted-reply to examination report.pdf

189-cal-2002-granted-specification.pdf