JP2015219134A - Chemical-element-analysis sample preparation method and device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and device for rapidly preparing a sample having no breaking or crack that is appropriate for analysis from a steel ingot that is collected from molten steel and is in a high-temperature red-heat state.SOLUTION: First, of a steel ingot collected from molten steel and supplied in a high-temperature red-heat state to a preparation device, an unnecessary part that is not analyzed is previously isolated by a cutting mechanism. Then, the remaining part of the sample is cooled to 100°C or less by a cooling mechanism, while the cooling rate is controlled in response to the steel type and chemical composition of the sample so that the hardness of the sample after the completion of the cooling is 400 or less in Vickers hardness.

Description

  In the steelmaking operation, the solidified ingot is collected from molten steel in the middle of refining, and after preparing a sample for component analysis by machining, the concentration of elements contained in the sample is analyzed, and the analysis result is referred to The present invention relates to a quick and reliable elemental analysis sample preparation method applicable to a series of steps to be reflected in the component adjustment operation of molten steel.

  In order to obtain the desired performance, steel materials are designed with alloys that add appropriate amounts of various elements to the steel. When steel with the same performance is actually manufactured based on the design, Product performance is stabilized by managing the concentration of each element within a certain range. Furthermore, analysis of molten steel components is performed during refining, the concentration of the target element is confirmed, and the results are adjusted accordingly, so that not only accurate analysis results but also analysis values must be waited for. From the viewpoint of reducing production volume and energy loss due to, rapid analysis is indispensable.

  Therefore, if the concentration of the contained element can be analyzed quickly and accurately during the refining process in the steelmaking process for producing steel having the desired performance by adding various elements, appropriate components will be based on the analysis results. By performing the adjustment, it becomes possible to manufacture steel having stable performance at low cost and low environmental load.

  In such a process, an analysis sample preparation apparatus is used to quickly prepare an analysis sample. In the elemental analysis sample preparation device, a steel ingot receiving device, a cutting device, a polishing device, a cooling device, a transport device, etc. are comprehensively controlled by a sequencer. A sample for gas analysis is dispensed.

  For example, in Patent Document 1, a plurality of samples used for different types of analysis, for example, luminescence analysis and gas analysis, can be produced simultaneously, and a tapered sample can be easily and reliably grasped and conveyed. An analytical sample preparation apparatus capable of reliably performing the above is disclosed. In this apparatus, the temperature of the steel ingot collected from the molten steel and supplied in a hot red hot state is first lowered from 1000 ° C. to 800 ° C. by cutting, and then to 400 ° C. by rapid cooling completely immersed in cooling water. It is disclosed that the temperature is lowered to 300 ° C. by descent and further grinding with a grindstone, again cooled rapidly to 30 ° C., or air mixed with water is blown and gradually cooled from 300 ° C. to 200 ° C., and then cooled to 30 ° C. by rapid cooling. Has been.

  Patent Document 2 discloses a component in steel that is rapidly cooled to a temperature slightly higher than the martensitic transformation start temperature, for example, 400 ° C., and then rapidly cooled to room temperature, in the case of low carbon steel, and gradually cooled in the case of high carbon steel. A method for processing an analytical sample is disclosed.

  Further, in Patent Document 3, a steel ingot equipped with two cooling devices and received at 900 ° C. to 1000 ° C. is first rapidly cooled to about 400 ° C. to 600 ° C. with a first cooling device, and then the gate is cut by a cutting device. A preparation method and apparatus are disclosed in which a sample that has been separated and cooled to 200 ° C. to 300 ° C. by natural temperature drop after cutting is cooled in two stages to about 20 ° C. to 50 ° C. by a second cooling device.

  In any of these techniques and apparatuses, the steel ingots that have been charged are cooled by a combination of rapid cooling and natural cooling, and the mechanism of the apparatus is complicated. Furthermore, none of these prior arts provide a method for appropriately controlling the cooling rate in accordance with the chemical composition of the steel.

  On the other hand, in the steelmaking process, steels of various types, that is, components, are mixed and melted. For example, in the case of high carbon steel and alloy steel for mechanical structure, even if the sample preparation device according to the prior art is applied, For steel types that are hardened and hardened by cooling, cutting and punching cannot be performed, processing can be performed, but the desired dimensional accuracy cannot be obtained, cracks and chips in the analytical sample due to burning cracks, etc. There was a problem. Of course, even if a sample containing such a defect is subjected to analysis, an accurate result cannot be expected.

  In the actual work, for steel types that are hardened by rapid cooling and harden, the operator intervenes and manually prepares the sample based on experience and intuition, but again the work becomes complicated, In addition to the time required, process variations were unavoidable, and it was necessary to collect steel ingots again due to improper cooling, which caused process loss.

JP-A-9-166530 JP-A-9-152391 JP-A-10-311782

  It is an object of the present invention to provide a method and an apparatus for quickly preparing a sample suitable for analysis free from cracks and chips from a high temperature red hot ingot collected from molten steel.

  As a result of various investigations, the present inventor has optimized the cooling conditions in accordance with the steel type, that is, the chemical composition of the steel when cooling the hot ingot in the analysis sample preparation. The present inventors have found a quick and reliable sample preparation method applicable to analysis, and have completed the following present invention.

(1) For the steel ingot collected from the molten steel and supplied to the elemental analysis sample preparation device in a 700-800 ° C. red-hot state, first, unnecessary portions not subjected to analysis are separated by a cutting mechanism, and then cooling is completed. The upper limit Vcr [° C./sec] of the cooling rate is determined as a function of the steel type and chemical composition of the steel ingot so that the hardness of the steel ingot afterwards becomes 400 or less in terms of Vickers hardness. A method for preparing an elemental analysis sample, wherein the sample is cooled to 100 ° C. or less by a cooling mechanism while controlling the temperature.

(2) The elemental analysis sample preparation method according to (1), wherein the cooling rate is equal to or less than Vcr [° C./second] represented by the formula (1).
Vcr = a * exp (b * Ceq.) (1 expression)
here,
Ceq. = [C] + [Si] / 24 + [Mn] / 5 + [Cr] / 5 + [Mo] /2.5+ [Nb] / 3 + [V] / 5 + [Cu] / 10 + [ Ni] / 18 (2 sets)
a = 420 ± 50
b = −6.2 ± 0.3
It is.

(3) The elemental analysis sample preparation method according to (1) or (2), wherein the cooling rate is 0.8 * Vcr or more and Vcr or less with respect to the upper limit Vcr of the cooling rate.

(4) A receiving part that receives a 700 to 800 ° C. red hot ingot collected from molten steel, a cutting part that cuts an unnecessary part that is not used for analysis of the steel ingot, and the steel ingot after cutting The cooling rate is determined from the steel type of the steel ingot and the predicted component value so that the cooling of the steel ingot after cooling and water cooling and / or air cooling and the hardness of the steel ingot after cooling is 400 or less in terms of Vickers hardness. The calculation unit, the control unit for controlling the cooling unit so as to cool the steel ingot after cutting from 700 ° C. to 100 ° C. at the cooling rate, and the steel ingot after completion of cooling are suitable for elemental analysis. A sample preparation device for elemental analysis, comprising a processing section for processing into properties.

(5) The sample preparation apparatus for elemental analysis according to (4), wherein the upper limit of the cooling rate determined by the calculation unit is determined by the equation (1).
Vcr = a * exp (b * Ceq.) (1 expression)
here,
Ceq. = [C] + [Si] / 24 + [Mn] / 5 + [Cr] / 5 + [Mo] /2.5+ [Nb] / 3 + [V] / 5 + [Cu] / 10 + [ Ni] / 18 (2 formulas) a = 420 ± 50
b = −6.2 ± 0.3
It is.

(6) The steel ingot is sampled from the molten steel and supplied to the elemental analysis sample preparation device in a red hot state of 700 to 800 ° C., and the steel ingot is cooled at a constant cooling rate from 700 ° C. to 100 ° C. (4) or the elemental analysis sample preparation apparatus according to (5).

  According to the present invention, in steelmaking operation, a solidified ingot is collected from molten steel in the middle of refining, a sample for component analysis is prepared by machining, the element concentration contained in the sample is analyzed, and the analysis result is referred to Rapid and reliable elemental analysis sample preparation that can be applied to a series of processes to be reflected in the component adjustment operation of molten steel becomes possible. As a result, in steelmaking operations where steels of various types, that is, steels of various components are mixed and melted, for example, high-carbon steels and alloy steels for machine structural use, even steel types that harden and become hard due to rapid cooling are analyzed by elemental analysis. Using the preparation device, it is possible to quickly prepare a sample suitable for analysis without cracks or chips, leading to efficient operation.

It is a block diagram of the configuration of the elemental analysis sample preparation apparatus of the present invention. It is a graph which shows the relationship between the cooling rate and carbon equivalent in which the Vickers hardness Hv of a sample is set to about 400. It is a graph which shows a cold stamping process evaluation result (a relationship between sample hardness and a carbon equivalent).

  Hereinafter, an example of an embodiment of an elemental analysis sample preparation method according to the present invention will be described.

  Steel ingots extracted from molten steel are of various dimensions, but are generally cylindrical bodies with a diameter of about 25 mm to 40 mm and a length of about 50 mm to 70 mm. The steel ingot taken out from the sampler at the steelmaking site is transported to the analysis site by air transportation or the like in a hot red hot state.

  The temperature of the steel ingot immediately after acceptance is about 700 ° C. to 800 ° C., but in order to prepare an analytical sample at about room temperature in the shortest possible time using this preparation device, A portion containing a cavity defect (so-called “shrinkage nest”) formed at the time of solidification or solidification, that is, an unnecessary portion that is not used for analysis is separated in advance by a cutting mechanism so as to make the sample volume as small as possible.

  Thereafter, the sample is not cracked or chipped by cutting, polishing, cutting, punching, or the like necessary for preparation of the analysis sample, that is, the hardness of the sample after completion of cooling is a predetermined value suitable for processing. Cooling while controlling the cooling rate according to the steel type so as to be below the value. When the cooling rate is too high, the hard martensite phase fraction increases, the hardness of the sample increases, and the processing is hindered. The hardness suitable for processing depends on the specifications of the analytical sample preparation device and the tool, but the present inventors have prepared a high hardness sample punching device provided in a commercially available analytical sample preparation device, and after completion of cooling. The relationship between the hardness of the sample and the quality of processing was investigated.

  As a result, the inventors have found that an analysis sample having no cracks or chipping can be obtained even in cold working by setting the hardness of the sample to 400 or less in terms of Vickers hardness, and the present invention has been achieved.

  The steel ingot temperature after receiving and cutting is 700 ° C., and cooling is performed while controlling the sample temperature up to 100 ° C. in order to avoid martensitic transformation of the steel in the cooling process as much as possible. Here, combining rapid cooling and gradual cooling may require a mechanism for keeping the sample warm and heating in gradual cooling in order to obtain the required hardness, which complicates the apparatus mechanism. Therefore, in this invention, it controls to a substantially constant cooling rate from 700 degreeC to 100 degreeC.

  The critical cooling rate Vcr [° C / sec] at which the Vickers hardness of the steel ingot after cooling is about 400 differs depending on the C concentration (wt%) contained in the sample and other element concentrations. Is given as a function of In the present invention, this function, that is, a relational expression between element concentration and Vcr is obtained in advance. Specifically, it can be determined from the relationship with the hardness of the obtained sample by appropriately changing the cooling rate in the manner of creating a continuous cooling transformation diagram (CCT diagram) of steel.

  When preparing an elemental analysis sample from a steel ingot collected in the refining process, Vcr is obtained by substituting the predicted component value into the above relational expression. The predicted component value is obtained, for example, by taking into account the subsequent refining action based on the immediately preceding analysis result.

  In the present invention, the cooling rate is controlled to Vcr or less, but in view of the requirement for rapid sample preparation, it is preferably set to a value as close to Vcr as possible, and preferably set to 0.8 * Vcr or more. . More preferably, it is 0.9 * Vcr or more.

  According to the present invention, for example, even when the composition changes due to the addition of an alloy during refining, it is possible to set the fastest cooling rate at which an elemental analysis sample free from cracks and chips can be adjusted with certainty.

  Next, the elemental analysis sample preparation apparatus of the present invention will be described based on the configuration block diagram shown in FIG.

(1) Receiving part The steel ingot in a high-temperature red hot state collected from molten steel is received in a preparation device, and the steel ingot is transferred to a gripping mechanism (such as an air chuck with a linear guide) that conveys it to a predetermined place where preparation is performed.

(2) Cutting part The steel ingot received at the receiving part is cut at a gate or a part containing a cavity defect (so-called “shrinkage nest”) formed when solidifying, that is, an unnecessary part not subjected to analysis.

(3) Cooling part The steel ingot after cutting at the cutting part is cooled by water cooling and / or air cooling and / or standing to cool.

(4) Calculation part When cooling a steel ingot, a cooling rate is determined from the component prediction value of a steel ingot so that the hardness of the steel ingot after completion of cooling will be 400 or less in terms of Vickers hardness. As shown in FIG. 1, it may be installed in the elemental analysis sample preparation apparatus, or a computer or the like that manages the analysis value may have the calculation function, that is, the calculation unit may be independent from the apparatus.

(5) Control unit The cooling unit (3) is controlled so that the steel ingot after cutting is cooled from 700 ° C to 100 ° C at the cooling rate determined by the calculation unit (4). Specifically, a necessary means is selected from each cooling means mounted on the cutting part, and the steel ingot is cooled for a necessary time. If the operation sequence pattern that obtains a desired cooling rate is previously registered and registered, and the system selects the same pattern, the function of the control unit can be simplified as in the conventional preparation apparatus.

(6) Processed portion The steel ingot after cooling is processed into properties suitable for the elemental analysis sample. For example, in the case of a spark discharge emission analysis sample, the cut surface of the steel ingot is cut or polished. If it is a sample for gas analysis, if necessary, first cut or polished the cut surface of the steel ingot, then transported again to the cutting unit, cut to a desired thickness to produce a slice piece, This is punched. The punching function may be installed in the preparation device, or the slice piece may be discharged out of the preparation device and processed by a separate punching device. Since the steel ingot is cooled to a temperature lower than 100 ° C. at the time of processing in the processing section, a clean analysis surface can be obtained without being significantly oxidized by the heat of the steel ingot itself. Therefore, particularly in gas analysis, it is possible to prepare a sample suitable for analysis of oxygen in addition to carbon, sulfur, and nitrogen that have been conventionally performed.

A CCT diagram was created for 11 types of steels having a carbon equivalent Ceq. Of 0.34 to 0.96 determined by the equation (2). From the relationship between the cooling rate and the hardness of the obtained sample, The cooling rate at which the Vickers hardness Hv was about 400 was determined.
Ceq. = [C] + [Si] / 24 + [Mn] / 5 + [Cr] / 5 + [Mo] /2.5+ [Nb] / 3 + [V] / 5 + [Cu] / 10 + [ Ni] / 18 (2 sets)
However, [C], [Si], etc. on the right side of Equation (2) are the concentrations [wt%] in steel of elements such as C and Si, respectively.

The relationship between the cooling rate thus obtained and the carbon equivalent Ceq. Is shown in FIG. Since a good correlation was observed between the two, Ceq. Was determined from Eq. (2) from the chemical composition of any steel, and the upper limit Vcr of the cooling rate was determined from the approximate curve indicated by the broken line in FIG. [° C / sec] is obtained. This approximate curve was expressed by the following equation (1);
Vcr = a * exp (b * Ceq.) (1 expression)
Here, the values of the coefficients a and b on the right side of the equation (1) were 418 and −6.16, respectively.

  Therefore, 26 types of molten steel having a carbon equivalent Ceq. Of 0.17 to 1.03 were separately prepared, a steel ingot (bomb sample) was collected, and the cooling rate was appropriately changed to be cooled from 700 ° C. to 100 ° C. Then, after finally cooling to room temperature, a slice piece having a thickness of 3 mm was produced. This slice piece was cold punched to a diameter of 7 mm using a high hardness sample punching device CSP type manufactured by Estec to prepare a sample for gas analysis. The results are summarized in FIG.

  In the case of punching a slice piece obtained by cooling at a speed equal to or less than Vcr obtained by substituting Ceq. Of each steel ingot into the equation (1) (black circle in FIG. 3, example of the present invention) The Vickers hardness of the slice piece was 400 or less, and no cracks or chips were found in the punched sample. On the other hand, when a slice piece obtained by cooling at a speed exceeding Vcr is punched out (open circle in FIG. 2, comparative example), the Vickers hardness of the slice piece exceeds 400. Chipping was observed.

Claims (6)

  For the steel ingot collected from the molten steel and supplied to the elemental analysis sample preparation apparatus in a red hot state of 700 to 800 ° C., first, unnecessary portions not subjected to analysis are separated by a cutting mechanism, and then the cooling after completion of cooling. The upper limit Vcr [° C./sec] of the cooling rate is determined as a function of the steel type and chemical composition of the ingot so that the hardness of the ingot is 400 or less in terms of Vickers hardness, and the cooling rate is controlled below the Vcr. However, the element analysis sample preparation method characterized by cooling a sample to 100 degrees C or less by a cooling mechanism. The elemental analysis sample preparation method according to claim 1, wherein the cooling rate is equal to or less than Vcr [° C./second] represented by the formula (1).
Vcr = a * exp (b * Ceq.) (1)
here,
Ceq. = [C] + [Si] / 24 + [Mn] / 5 + [Cr] / 5 + [Mo] /2.5+ [Nb] / 3 + [V] / 5 + [Cu] / 10 + [ Ni] / 18 (2)
a = 420 ± 50
b = −6.2 ± 0.3
It is.   The elemental analysis sample preparation method according to claim 1 or 2, wherein the cooling rate is 0.8 * Vcr or more and Vcr or less with respect to the upper limit Vcr of the cooling rate. A receiving part for receiving a 700 to 800 ° C. red hot ingot collected from molten steel;
A cutting part for cutting an unnecessary part not subjected to the analysis of the steel ingot;
A cooling section for cooling the steel ingot after cutting by water cooling and / or air cooling;
An arithmetic unit that determines a cooling rate from the steel type and component predicted value of the steel ingot so that the hardness of the steel ingot after cooling is 400 or less in Vickers hardness,
A control unit for controlling the cooling unit so as to cool the steel ingot after cutting from 700 ° C. to 100 ° C. at the cooling rate;
A sample preparation apparatus for elemental analysis, comprising: a processing section for processing the steel ingot after completion of cooling into properties suitable for elemental analysis. The sample preparation apparatus for elemental analysis according to claim 4, wherein the upper limit of the cooling rate determined by the calculation unit is determined by equation (1).
Vcr = a * exp (b * Ceq.) (1)
here,
Ceq. = [C] + [Si] / 24 + [Mn] / 5 + [Cr] / 5 + [Mo] /2.5+ [Nb] / 3 + [V] / 5 + [Cu] / 10 + [ Ni] / 18 (2) a = 420 ± 50
b = −6.2 ± 0.3
It is.   The steel ingot is sampled from molten steel and supplied to the elemental analysis sample preparation apparatus in a red hot state of 700 to 800 ° C., and the temperature of the steel ingot is cooled at a constant cooling rate from 700 ° C. to 100 ° C. The elemental analysis sample preparation apparatus according to claim 4 or 5.

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