Modified Draft Indian Standard METHODS FOR CHEMICAL ANALYSIS OF STEELS

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1 Doc: MTD 4( 4850) For Comments Only Modified Draft Indian Standard METHODS FOR CHEMICAL ANALYSIS OF STEELS Part 20 DETERMINATION OF CARBON AND SULFUR BY INFRA RED ABSORPTION METHOD (FOR CARBON TO 5.0% AND SULFUR TO 0.35%) [Third Revision of IS 228 (Part 20)] ICS Not to be reproduced without the permission of Last date for receipt of BIS or used as STANDARD comments is 16 June 2009 FOREWORD (Formal clauses will be added later on) For the purpose of deciding whether a particular requirement of this standard is complied with, the final value, observed or calculated, expressing the result of a test or analysis, shall be rounded off in accordance with IS 2:1960 `Rules for rounding off numerical values (revised). The number of significant places retained in the rounded off value should be the same as that of the specified value in this standard. 1. SCOPE This standard (Part 20) describes the method for determination of carbon in the range from to 5 percent and sulfur from to 0.35 percent in steel and iron. 2. SAMPLING The samples shall be drawn and prepared as prescribed in the relevant Indian Standards. 3 QUALITY OF REAGENTS Unless specified otherwise, analytical grade reagents or reagents procured from the instrument manufacturers shall be applied for test. 4. DETERMINATION OF THE CARBON AND SULFUR 4.1 Outline of the method The sample is burnt with accelerator at high temperature in a flow of oxygen in a high frequency induction furnace. The oxygen flow serves both as oxidizing agent and as system carrier gas. Carbon in the sample is converted to carbon dioxide and sulfur to sulfur dioxide. These are carried by oxygen stream into the non dispersive infra red absorption analyzer where these gases are measured quantitatively. 4.2 Reagents i) Oxygen: Purity 99.9 percent (purified by passing through magnesium per chlorate and soda asbestos) ii) Accelerators: Tungsten, copper or tin with low carbon and sulphur (below %) 1

2 iii) Trap materials: Ascarite for removing traces of carbon dioxide and anhydrone, particle size less than 1.5 mm, for removing moisture. iv) Crucibles: Ceramic crucibles of dimensions suitable for the furnace which can withstand thermal shock and high temperature and having low consistent carbon and sulfur contents. v) Standard samples: The standard samples of steel and iron of known carbon and sulphur, preferably in the same range as the sample are to be used for calibration. b) Apparatus: An automatic carbon and sulfur analyzer consisting of a high frequency induction furnace precision flow regulator and tandem IR detectors. Oxygen gas is passed into the induction furnace. This oxygen stream carries the evolved gases, namely, carbon dioxide and sulfur dioxide due to combustion of the sample. After passing through the moisture and dust filters, the gas is passed through precision flow regulator and the regulated gas is conveyed to the non dispersive infra red detector arranged in tandem. Sulfur is measured as sulfur dioxide in the first IR cell. Carbon is measured as carbon dioxide while gases flow through both the low and high range IR cells. The low carbon range features a greater resolution carbon content as a result of the longer path length of the IR cell. For high carbon range, the IR cell has a shorter path length. Depending on the types of samples and concentration ranges, the low or high carbon IR cell should be selected for analysis. as Some of such units may have facilities for recording the sample weight and display of blank weight corrected results in terms of percentage or ppm of carbon and sulfur. Follow the detailed instruction manuals for the operation of the instrument. i) High precision balance for weighing 0 to 100 gm with a accuracy of 0.1 mg. 5. PROCEDURE 5.1 Equipment Preparation: Turn on the instrument and allow sufficient time to stabilize the system. Change dust filters, reagents as required. Clean the furnace chamber and test the furnace and analyzer for absence of leaks. Fix the parameters like analysis time, sample identity, etc. 5.2 Crucible preparation: For Ultra low carbon (< 0.01% ) and ultra low sulfur (< 0.005%) preheat the ceramic crucibles in a flow of oxygen in a furnace at 1000 deg C for 2 hours or 1200 deg C for 15 minutes. Cool and remove these crucibles and store them in a desiccator. For samples containing greater then 0.01% C and 0.005% S, the crucibles can be used as such. The crucibles should always be handled using forceps only. 5.3 Sample preparation: It is preferable to have all samples and standards in the form of small blocks, chips or wires. The samples have to be filed to remove surface contamination, cut / broken into small pieces of approximately 1 gm, washed in acetone and dried. Blank determination: For Carbon ( < 0.01%) in steel Transfer high purity tungsten and tin mixture accelerator (approximately equal in weight to that of the sample being tested) into a preheated crucible. Load the crucibles in the induction furnace and run the analysis cycle. The output of the IR detector are converted to percentage carbon and sulfur respectively and used for blank correction. If provision exists, enter these values into the memory for automatic blank corrections during further analysis. Repeat the blank run in order to ensure good precision. 2

3 For Sulfur ( < 0.005%) in iron Transfer high purity tungsten and tin miuxture accelerator (approximately equal in wight to that of the sample being tested) along with one gram of (-6 to + 20 mesh) high purity iron chip accelerator into a preheated crucible. Load the crucibles in the induction furnace and run the analysis cycle. The output of the IR detectors are converted to percentage carbon and sulfur respectively and used for blank correction. If provision exists, enter these values into the memory for automatic blank corrections during further analysis. Repeat the blank run in order to ensure good precision. For Carbon ( > 0.01%) in steel and iron Transfer high purity tungsten metal accelerator (approximately equal in weight to that of the sample being tested) into a ceramic crucible.. Load the crucibles in the induction furnace and run the analysis cycle. The output of the IR detector are converted to percentage carbon and sulfur respectively and used for blank correction. If provision exists, enter these values into the memory for automatic blank corrections during further analysis. Repeat the blank run in order to ensure good precision. For Sulfur ( %) in iron and steel Transfer high purity tungsten metal accelerator (approximately equal in weight to that of the sample being tested) into a ceramic crucible. Load the crucibles in the induction furnace and run the analysis cycle. The output of the IR detectors are converted to percentage carbon and sulfur respectively and used for blank correction. If provision exists, enter these values into the memory for automatic blank corrections during further analysis. Repeat the blank run in order to ensure good precision. 5.5 Calibration Weigh about one gram of sample as per 5.3 and transfer into the crucible. Depending on the carbon and sulfur contents and the types of samples to be analysed select the IR cell ie low carbon or high carbon and sulfur. Generally any automatic carbon / sulfur analyzer has no. of channels and each channel can be assigned for different concentration ranges and types of samples. The relevant accelerators to be added depending on the sample types and concentration ranges are given in the Annex 1. Add the necessary accelerator and the sample to the crucible and insert the crucible into the furnace. Run through the analysis cycle. Adjust the output of the IR detectors to the standard values after deducting blanks for carbon and sulfur. Repeat the calibration procedure with the same standard and proceed further only, if consistent results are obtained. If multi point calibration facility is available in the instrument, additional standards may be used. 5.6 Analysis of the sample Select the channel depending the sample type and concentration range to be measured. Run the sample to be as per procedure given in 5.5. Apply corrections for blank, if it is not done automatically done by the instrument. Repeat the analysis to check the consistency of the results. Validation Data Carbon ( to 0.005%) in steel Sample id Certified value Obtained value Leco ppm ±

4 Std. Dev 0.37 Leco ± Std. dev 0.56 Carbon (2-4 %) in iron Sample id Certified value Obtained value Leco ± Std. Dev 0.03 Leco ± Std. dev 0.03 Sulfur ( %) in iron and steel Sample id Certified value Obtained value Leco ±

5 Std. Dev Bramer Standard CSN ± Std. dev Leco ± Std. Dev Leco ± Std. Dev Precision The precision of analysis should be with in 10%. 5

6 ANNEX 1 Sample Type Concentration range Accelerator to be added C&S in plain carbon steel and <0.01% C and % Tungsten accelerator S Ultra low sulphur in cast iron < 0.005% S Iron chip along with tungsten accelerator Ultra low carbon in steel < 0.01% C High purity tungsten/tin mixture 6