SU1679272A1 - Method for determination of content of hydrogen in molten steel in ladle - Google Patents

Abstract

The invention relates to metallurgy and can be used for the rapid determination of hydrogen in liquid steel during its smelting. The aim of the invention is to increase the reliability of the determination of the hydrogen compound. Liquid metal is bubbled with bubbles of inert gas, gas is sampled under the bucket lid or with a submerged bell at a pressure of 20-400 mm of water. Art. and determine the hydrogen content in it, followed by recalculation of it for the hydrogen content in the liquid steel based on the Siverts law. In order to exclude the possibility of distortion of the result due to the accidental ingress of hydrogen from the outside of the sample, along with the determination of hydrogen in the sample stream, the nitrogen content is determined, compared with the maximum possible nitrogen content in the bubbling gas bubbles, which are determined previously for the specific conditions of purge . Here, for conversion to the hydrogen content in steel, the values of those hydrogen contents in the gas sample are used, at which the nitrogen content values in the gas sample are less than the maximum possible nitrogen content in the emerging gas bubbles, 1 h. the item f., 2 tab. cl

Description

The invention relates to the field of metallurgy, mainly to steelmaking and the production of steel castings, but can also be used to determine the content of hydrogen in any liquid metal.

The purpose of the invention is to increase the reliability of the determination of hydrogen content.

The nitrogen content in the gas sample, corresponding to azo-y in steel, taking into account kinetic difficulties in isolating it into argon bubbles, for steels that are not doped with nitrogen, is relatively low, and the upper level of its values is easy

predict in advance. Therefore, exceeding this level will indicate insufficient flushing of the trapped gas with a closed volume into which this gas is trapped, or a leak in the devices for taking and transporting a sample of gas. When sampling a gas while maintaining a positive pressure under the bucket lid or receiver-bell, for example, by increasing the flow rate of the sparging argon gas, the leakage of these devices cannot cause the gas sample to flow from the surrounding space.

The prerequisites underlying the invention are as follows.

about 1 yu j go

The equilibrium nitrogen content of argon bubbles that pops up from the metal, like hydrogen, with the nitrogen content of the metal is related according to the Siverts law:

N - KN VP KN MX N-Rovsch

100

(one)

where KN is the Siverts coefficient, which is numerically equal to the solubility of nitrogen in this steel at its pressure in the gas phase equal to 1 atm;

{%, №} equally - the equilibrium content of nitrogen in the inert gas after leaving the metal;

Ptotch - the total pressure of the gas phase above the metal.

Studies show that if for hydrogen the assumption of equality of the actual and equilibrium contents in most cases is close to the truth, then the nitrogen content in the sparging gas (e.g. argon) at the exit from the metal is only 10-30 due to its lower diffusion mobility. % of the equilibrium value, ie:

{M2} fact (0.1-0.3) {No.} ravn (2)

The nitrogen content in the finished steel in most cases corresponds to the ratio

N,% (0,) KN. (3)

For non-alloyed steels and structural alloyed steels with a low (less than 5%) content of alloying elements, 04-0.05,% atm 1 / at casting temperatures. Taking this into account, from expressions (1) - (3) we conclude that the nitrogen content in the gas sample, caused by the transfer of nitrogen from the metal to the emerging argon bubbles, should be in the range of 0.1-1.2%.

The presence of nitrogen in excess of 1.2% in the gas sample indicates either insufficient washing of the free space under the bucket cover or receiver-bell from the air originally enclosed in them, or the trapping of air from the atmosphere while trapping the gas sample for analysis.

Taking a sample of gas from under the bucket cover or receiver-bell while maintaining a slight excess pressure under them (20-400 mm of water. Art.) Prevents air from entering the gas sample.

The nature of the change in the nitrogen content in the current gas sample can serve as information about the source of nitrogen entering the sample.

If, when sampling, taken with a vacuum under the bell or under the bucket lid, the nitrogen content is reduced and

is established at a stable level in the range of 0.1-1.2%, this indicates that the flushing of the internal volume of the trapping device by the gas emerging from the metal is completed, the gas sample is not distorted by diluting the air and reacting with it. In this case, the result of the analysis of the gas sample for hydrogen corresponds to the content of hydrogen in the metal according to Siverts law.

0 If after a decrease in the nitrogen content and stabilization at the level of 0.1–1.2%, a short-term surge in the nitrogen content is observed with a clear tendency to repeat the subsequent decrease, a seizure has occurred.

5 air under the lower edge of the bell or under the bucket cover. In this case, in the case of gas extraction by a bell, it is necessary to somewhat increase the depth of the bell or to switch to sampling at a positive pressure.

0 under the bell. In order to obtain a representative measurement, it is necessary to wait again for the reduction of the nitrogen content to a stable level of 0.1-1.2%

If the nitrogen content in the gas sample until the installation of the bucket cover or receiver bell is reduced, but stably established at a level that lies substantially above the level corresponding to the nitrogen content in the steel, then

0 assume leaky installation of the bucket cover or the presence of a crack in the receiver-bell, as well as a leak in the sample transportation path. Getting

5 representative analysis of hydrogen is possible in this case only when switching to a sample of gas under positive pressure.

Positive pressure limits under

The bucket cover or receiver bell when sampling in the present invention is dictated by the following conditions. With an overpressure of less than 20 mm water. v.: the guarantee of eliminating the sticking of air at the local exposure of the edges of the bell immersed in the melt due to fluctuations of the melt surface or air leaks under the bucket cover disappears. With an overpressure of over 400

0 mm water Art. additional deepening of the bell into the metal by more than 60 mm is necessary, which adversely affects its durability. When gas is taken out from under the bucket cover, it becomes difficult to seal the cover.

5 In addition, a further increase in pressure does not give any advantages in terms of avoiding contamination of the sample gas.

The determination of the hydrogen content in the liquid steel according to the proposed method is carried out as follows.

In advance, the maximum possible nitrogen content in the argon bubbles {metal, M2} max emerging from the metal is derived from the formula derived from (1):

.Mmax SO

{%, No.} Max ON

to&

(four)

where ohm is the upper limit of the ratio of the actual nitrogen content in the emerging argon bubbles to the equilibrium content, which was detected in advance for the adopted variant of the gas collection device and the purge mode empirically;

 - the maximum possible nitrogen content in the analyzed steel under the accepted conditions of its smelting;

KN is the Siverts coefficient, which is numerically equal to the solubility of nitrogen in the steel produced under a pressure of 1 atm at a typical casting temperature.

Immediately at the time of the determination of hydrogen, the gas collection device is immersed through the slag to the metal or the bucket is covered with a lid, the metal is purged with an inert gas, and part of the gas to be collected is sent to the gas analyzers. The analysis of the gas for hydrogen or nitrogen is carried out either by chromatographic means, with discrete output of the results of the analysis, or on instruments of continuous action.

In a typical case, the nitrogen content in the gas sample is lowered to the level below {%, M2} max, and then stabilized. At this point, the hydrogen content in the gas sample is measured according to the hydrogen analyzer values and the hydrogen content is calculated by the formula -

HSH ° L - V US / o- 2Ur ... (with

Irlj, - 1 × 6 ° 1IP;

where robshch. 1 atm, since taking into account the dilution or overpressure in the gas collection device due to the smallness of these values has almost no effect on the result.

In the case of unstable analysis of nitrogen in the gas sample, the immersion depth of the bell-device should be increased by 30-50 mm into the melt, the stabilization of the nitrogen analysis should be again below {%, no} max and a new calculation of the hydrogen content in the gas sample should be made hydrogen content in the metal.

In the case of obtaining a stable background on the nitrogen content in the gas sample, the level of which is however significantly higher than {%, M2} max, it is necessary to increase the flow rate of argon supplied to the lance of the gas trap unit, switch to a positive gas sample in the gas extraction path and repeat

The above steps are typical for

PRI me R 1. In a 40-ton electric furnace, steel grade SHKh15 was smelted with refining in a furnace under an oxidizing furnace, then under a reducing slag. Siverts coefficients for this steel: at 1550 ° С Kn 2.0., 039; at 1600 ° С ,,, 040. Nitrogen content

10 finished steel with this technology - up to 0,008%. For sparging metal with argon, a lined tuyere immersed to a depth of about 0.5 m was used with a nozzle diameter of 2 mm. For trapping

15 flue gases used a bell-type device with a diameter of 0.3 m. It was experimentally established in advance that a maximum of 30 was possible for selected purge conditions. Consequently, {%,

20 Hr} max 1.2%. Gas samples were analyzed on a chromatograph.

Before casting at a temperature of metal 1560 ° C, the hydrogen content in steel in the ladle was measured using the proposed method.

25 The hydrogen content in the current gas sample after immersion of the bell into the working position increased from 60 to zero to 7.0% in 60 s. The nitrogen content in the sample for the same time dropped to a stable level of 0.85%,

30 which is less than the maximum possible level of 1.2% in argon bubbles. Hydrogen content in liquid steel

, 0.10 3V-y 1,, 3 10 4% 35 The control sampling of five metal samples with their subsequent analysis on a vacuum melting apparatus gave an average result of 5.1.10 4%.

Example 2. In a 100-ton electric furnace

4 smelted steel grade 40X single slag process, with deoxidation in the ladle during the release.

The nitrogen content in the finished steel is up to 0.007%. Siverts coefficients for this

45 steel,% atm 1/2: at 1550 ° C, 25 10 3, 043; at 1600 ° С, 044.

The maximum possible level of nitrogen in the argon bubbles at

50, 30 is 0.8%.

Before pouring in the ladle at a metal temperature of 1580 ° C, the hydrogen content was measured by the proposed method. To imitate the formation of a crack in the bell (oo), the le receiver was pre-drilled a hole in it with a diameter of 5 mm.

60 seconds after the bell was immersed in the working position, the nitrogen content in the gas samples dropped to 8% and

it has stabilized. This level is much higher than {%, no} max, which is equal to 0.8%, therefore, the sample is contaminated with air. The hydrogen content in the gas sample did not rise above 1.0%, which is much lower than expected and indicates oxidation of hydrogen in the sample with oxygen air,

The vacuum in the gas sampling path at the time of determining the hydrogen content is co pflt 30 f iM water. Art.

 .. pi supply of argon to the device is approximately threefold - up to 5 l / min. In the path azotor :. ugg sank pressure 80 mm of water. Art. Over the next 30 seconds, the results of the analysis of hydrogen increased to 2.8% and did not change further, while the analysis of nitrogen stabilized by 0.5%, which is less than {%, No. 2} max. Content of hydrogen sulfide in liquid steel, 2.3 10 3 - 1.0 3.85 10 4%

The control sampling of five metal samples with their subsequent analysis on a vacuum melting apparatus gave an average result of 3.7.

EXAMPLE 3 Under the conditions of Example 1, a series of experiments was conducted to determine the optimal limits of positive pressure in a gas sampling device while trapping a sample of off-gas. The results are shown in Table. one.

Tabl, 1, the following notation is accepted: Dissipated positive pressure under the bell; {N2} max - the maximum possible nitrogen content in the gas sample, based on the nitrogen content in the metalp at а 0.3; {№} fakg - nitrogen content of the gas sample after 1.0-2.0 min from the beginning of the determination of the w / w: H} - hydrogen content in the metal, calculated from the gas analyzer readings on the hydrogen content in the gas sample; H Counter the content of hydrogen in the metal according to the results of the analysis of control samples. metal by vacuum melting.

From the results presented in Table 2, it can be seen that the reliability of the method for determining the hydrogen content in liquid steel is further increased with positive pressure under the lid or immersed bell equal to 20-400 mm of water. S., (experiment 3-8). In addition, the results of experiments show that with an excess pressure under the bell less than 20 mm of water, art. and. due to pressure fluctuations caused by the EU: by blowing argon bubbles from the depth of the metal, periodic air inflow under the bell is not eliminated through its damage. This leads to a distortion of the air analysis. With a pressure over 400 mm waters. Art. there are difficulties of another

kind; The deeply submerged edges of the bell are hit hard by the wave nature of the motion of the sparged metal, which leads to its destruction.

As an example, the determination of hydrogen by a known method can serve as experience 3 in Table. 1. The decrease of the analysis for hydrogen in the metal by 1, due to the ingress of air into the gas sample in this experiment

0 would go unnoticed without controlling the nitrogen in the gas sample and the result of the analysis would mistakenly be taken for true. Such an error (underestimation of the analysis) is unavoidable with any unnoticed violation of the tightness of the gas collection device if a gas sample is taken with a vacuum under it. An error is also inevitable in case of insufficient washing of the gas extraction path by the gas sample being caught, i.e.

0 while fixing the hydrogen content in the analyzed gas before establishing the ratio {no.} Fact {no.} Max.

A quantitative assessment of the increase in the reliability of the determination of hydrogen in molten steel based on the analysis of the exhaust gas during the bubbling of steel with argon can be made from the results of laboratory experiments conducted at the stage of its development and the development of the proposed variant of this method. The experiments were carried out on a metal mass of 40 kg at a temperature of 1600 ± 20 ° С, with a purge of the deoxidized metal with argon through the bottom of the crucible at a rate of about 1 l / min, with the capture of waste

5 gas quartz bell with a diameter of 60- 80 mm and an analysis of it in 90 s from the beginning of the capture on the chromatograph at fixed intervals. In parallel with the sampling of gas, samples were taken

0 metal with their subsequent analysis for hydrogen by the method of vacuum melting. The results of the determination of hydrogen in the gas phase were considered reliable if their difference from the analysis of the metal sample did not exceed

5 0 .. Generalized experimental data are given in Table. 2

Thus, it follows from the above data that the proposed method for determining hydrogen in molten steel allows

It is more reliable to determine hydrogen than a known method, since in the latter the control of the purity of a sample of gas taken for analysis is not provided at all. In addition, the sampling of gas under positive

5, which is also not provided for in the known method, permits, in the course of the determination of hydrogen, to correct the errors of determination and reduces the requirements for tightness of the getter.

The duration of the determination of hydrogen in a metal in the known method and in the proposed case is the same, since the determination of nitrogen in a gas sample is carried out in parallel with its analysis for hydrogen. However, when deviations from the normal course of the determination (weak gas sample flow, delayed flushing of the gas extraction path, air leakage, etc.), according to a known method, an incorrect result is obtained for hydrogen in the metal, and the proposed method allows Appropriate measures to correct the course and, with some delay, produce the correct result.

Since the same gas sample is analyzed in the known method and in the proposed hydrogen content under identical conditions, the hydrogen content in the gas is determined with the same accuracy. The improvement made by the proposed method is to control the representativeness of the sample of gas through the additional determination of its nitrogen content, i.e. in the control (through nitrogen in the gas) the eligibility of using the obtained analysis of hydrogen in the gas sample to calculate the hydrogen content in the metal according to Siverts law. In addition, improvement consists in eliminating the errors introduced by the initial or gas leakage device by eliminating air leaks in the gas sample by creating a positive pressure under the gas collection device.

The use of the method for determining the hydrogen content in the liquid steel makes it possible to more extensively introduce rapid analysis of steel for hydrogen before the steel is cast. This allows the hydrogen content in the metal to be included in the smelting passport and, therefore, assigned after rolling to

billets of each heat optimal mode anti-flock heat treatment.

In the foundry industry, the introduction of the method can contribute to the implementation of measures to improve the quality of steel castings.

Claims (2)

Claim 1. Method for determining hydrogen content in liquid steel in a ladle, including bubbling steel with inert gas bubbles, such as argon, trapping pop-up gas bubbles under the bucket lid or immersed bell, taking a sample of gas and determining its hydrogen content and then recalculating it to hydrogen in liquid steel on the basis of Siverts law, characterized in that, in order to increase the reliability of the determination of hydrogen content, in the gas sample stream, along with hydrogen, soda nitrogen bursting and gas analyzes are taken for conversion to the hydrogen content for which the ratio {N2,%} ON 100 KU where {N2,%} is the nitrogen content in the gas sample; CTN is the maximum value of the ratio of the actual nitrogen content in the bubbling argon to equilibrium with the metal with the purge mode selected;  - maximum nitrogen content in steel,%; KN is the Siverts coefficient for nitrogen, ½ atm 1/2. 2. A method according to claim 1, characterized in that the sampling of gas is carried out with a positive pressure under the bucket lid or with a dipping bell equal to 20-400 mm of water. Art. Table 1 Determination of hydrogen in a gas sample without taking into account the nitrogen content in it (a known method) Determination of n hydrogen in the gas sample provided Mfont 4 feWc (proposed way) Definition of N p hydrogen sample gas provided (“D ZJpctKT - zJMaKC and positive pressure in the gas extraction path (the proposed method) On two experiments, due to air leaks, the condition was not met . Condition f К2} й {N2} achieved on all experiences Max