RU2027986C1 - Method of determination of content of carbon in pig iron - Google Patents

Abstract

FIELD: foundry. SUBSTANCE: technological sample is cast without extraction of graphite. It is subjected to graphitization annealing at temperature 940-1120 C. Value of elongation of sample is measured and content of carbon in pig iron is found by it. For speed-up of annealing liquid pig iron intended for casting of technological sample is injected with additive containing graphitization elements. EFFECT: enhanced authenticity of determination of carbon content during smelting. 2 cl

Description

 The invention relates to foundry and can be used to determine the carbon content in cast iron mainly during melting.

 The carbon content of cast irons is one of the main factors affecting the casting and mechanical properties. Therefore, the control of carbon in cast irons during melting and the adjustment of its content are of great importance.

 To obtain a given grade of cast iron, it is sufficient to provide the required carbon content, and the content of other elements, in particular silicon, can be adjusted according to the size of the bleached process sample for bleaching.

 Various methods are used to determine the carbon content.

 Chemical-analytical methods are widely used. Their basis is the burning of a sample of pig-iron shavings on a boat in a tubular furnace using the AN-7529 device. Burning is carried out in a stream of oxygen, which greatly speeds up the process.

However, the resulting CO _{2 is} absorbed by the solution located in the electric cell, which changes the emf of the indicator system of the pH meter. The total analysis time from the moment of pouring the sample to obtain the finished result is, as a rule, at least 10 minutes. The analysis is carried out in a separate room by special laboratory assistants. For these reasons, the method is of limited use for monitoring along the course of smelting and adjusting the composition of cast iron by carbon.

 Some enterprises use the thermographic method for determining the carbon content from the cooling curve of cast iron, which records the temperature of liquidus and solidus. Cast iron is poured into the single-use rod probe, the temperature of which is continuously measured using a low-inertia thermocouple. The cooling curve is recorded on the potentiometer bar chart. The location of the bends at critical points (solidus and liquidus) determine the carbon and silicon contents. Analysis duration approximately 3 minutes. The advantage of the method is that the measurement is carried out by the smelter directly at the smelter.

 The disadvantages of the method are the need to produce special probes with thermocouples (usually disposable), as well as high requirements for the accuracy of instruments and thermocouples.

 Spectral methods are widely used to determine the content of carbon and other elements. Modern multichannel quantometers foreign and domestic (DFS-51, DFS-61) allow you to determine the carbon content and a number of other elements within a minute, without taking into account the time for sample preparation: pouring, cooling, transportation and grinding.

 A necessary condition for determining the carbon content by the spectral method is to obtain a technological sample without graphite, i.e., all carbon must be in a bound state.

 The disadvantages of the method are the use of complex and expensive appliances, well-equipped rooms, qualified service, as well as the necessary expensive and usually scarce standards. Therefore, this method is advisable to apply in the conditions of mass-production.

 The purpose of the invention is to determine the carbon directly at the smelter, in the exclusion of complex, expensive equipment and standards and special maintenance personnel.

 The method for determining the carbon content, including the casting of a technological sample without emissions of graphite, is carried out by the magnitude of the elongation of the sample subjected to graphitizing annealing.

 In the method adopted for the prototype, after casting the sample without graphite, it is transported to the room where the spectral devices, such as a quantometer, are located, the surface is ground and the content of carbon and other elements is determined from the spectrum.

 In the present invention, after casting a technological sample without graphite, it is cooled to ambient temperature, the length is measured (or fixed), it is graphitized annealed, it is cooled to ambient temperature and the length (or elongation) is measured. The elongation is determined by the carbon content.

 In a cast sample, all carbon is in a bound state. After graphitizing annealing, the sample consists of a metal base and graphite. The release of carbon in the form of graphite causes an increase in sample volume. The elongation of the sample is greater, the higher the carbon content in cast iron.

 The cooling rate of the technological sample during its solidification should be such that, for any composition of cast iron, the release of graphite is eliminated. This condition is satisfied by the solidification of the sample in a metallic form, in particular copper.

The optimum temperature of graphitizing annealing is 940-1120 ^о С. The temperature below 940 ^о С significantly prolongs the graphitization process, and above 1120 ^о С it leads to deformation of the sample and its melting. Increasing the temperature by ¹⁰ ° C is almost twice the rate of graphitization increases and reduces the disintegration time of cement by 1.25 times.

 The optimal length of the technological sample is 50-120 mm. A shorter length significantly increases the relative measurement error of the length, and a larger one makes it difficult to obtain a sample. The optimal cross-section (diameter) of the sample is 2-5 mm. A smaller cross-section reduces the time of graphitization, but complicates the process of obtaining samples. A larger cross section facilitates this process, but increases the graphitization time and the likelihood of graphite precipitation during sample solidification.

 For cast irons with a low content of elements that accelerate graphitization (for example, silicon), and a high content of elements that slow down graphitization (for example, manganese and chromium), an additive should be added to liquid cast iron intended for filling the technological sample. A graphitizing modifier, for example, FS75 ferrosilicon, in the amount of 0.3-0.8% by weight of cast iron in the sampler, can be recommended as the basis for such an additive. Graphitizing modifier reduces the time and / or temperature of graphitizing annealing.

EXAMPLE 1. Using a sampler, cast iron is cast into a copper mold with a density of 4 mm in diameter and a length of 100 mm for a technological sample. 20 hours after pouring, the sample is removed from the mold and cooled in water to ambient temperature. The length of the sample measured with a micrometer is 98.05 mm. Place the sample in a laboratory furnace with 1080 ^{° C,} it was kept for 4 minutes, cooled in water at ambient temperature. Again, measure the length of the sample. It is equal to 100.35 mm. The elongation is 2.30 mm (2.36%). According to the graph constructed on the basis of experimental data, in the axes: elongation of the sample (%) and carbon content (%), the carbon content is determined to be 3.49%. The total time from pouring the sample to obtaining the result is 5 minutes. Chemical analysis shows the carbon content of cast iron is 3.51%.

PRI me R 2. In the sampler is placed a stabilizing additive (0.5% FS75 of the weight of the metal in the sampler). The sampler is filled with cast iron, then it is poured into a copper mold with a cavity with a diameter of 4 mm and a length of 50 mm for a technological sample. After 20 seconds, the sample is removed from the mold, cooled in water to ambient temperature, a measuring device is installed and its length is fixed. Place the sample in a laboratory furnace with 1040 ^{° C,} held for 3 minutes and cooled in water at ambient temperature. Again install the sample in the measuring device and determine the elongation of 0.534 mm (1.09%). The graph determines the carbon content of 2.69%. The total time from pouring the sample to obtaining the result is 4.5 minutes. Chemical analysis shows the carbon content of cast iron 2.67%.

 The proposed method allows the smelter to determine the carbon content directly at the smelter during the smelting process, does not require expensive instruments and equipment, special personnel. The method is simple, reliable and provides sufficient accuracy of ± 0.03% for practice in the production of cast iron castings.

Claims (2)

1. METHOD FOR DETERMINING THE CARBON CONTENT IN CAST IRON mainly along the melting process, including casting a technological sample without graphite emissions, characterized in that the sample is subjected to graphitizing annealing at 940 - 1120 ^° C and the carbon content is determined by the magnitude of the elongation of the sample.  2. The method according to claim 1, characterized in that when casting a technological sample, an additive containing graphitizing elements is introduced into it.