JPS61145439A - Method for measuring alloying degree of alloyed molten zinc plated steel plate - Google Patents

Abstract

PURPOSE:To measure an alloying degree with good accuracy and to enhance the automatic control accuracy of the alloying degree, by measuring the temp. of a steel plate at a predetermined point and allowing X-rays to be incident to the surface of the steel plate to measure the diffraction X-ray intensity of a surface alloy phase. CONSTITUTION:At a predetermined point after the alloying heat treatment furnace in the manufacturing line of an alloyed molten zinc plated steel plate but before a skin pass process and a leveling process, the temp. of the steel plate is measured in such a state the temp. of the alloyed molten zinc plated steel plate is set to a temp. range of + or -15 deg.C in a range of room temp. - 50 deg.C or in a range of above 50 deg.C-400 deg.C. At the same point, X-rays are incident to the surface of the steel plate to measure the diffraction X-ray intensity of the alloy phase on the surface of the steel plate. The alloying degree in an alloy phase is calculated from these measured results, the preliminarily calculated temp. of the steel plate and X-ray diffraction intensity and the corresponding relation of the diffraction X-ray intensity and the alloying degree.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for continuously measuring the degree of alloying in equipment for continuously manufacturing single-alloyed hot-dip galvanized steel sheets.

<Prior art and its problems> For example, Japanese Patent Publication No. 58-47659 discloses a method for measuring the degree of alloying of an alloyed hot-dip galvanized steel sheet. However, according to research by one of the inventors, in the technique disclosed in the publication, the measured value of the degree of alloying is strongly influenced by the basis weight. Therefore, in a continuous production facility for alloyed hot-dip galvanized steel sheets where the basis weight level inevitably changes, measurement errors due to this technique are unavoidable. Therefore, although the purpose of this technique is to control the quality characteristics of the coating layer by controlling the degree of alloying of the galvannealed steel sheet, it is hardly possible to adequately control the quality characteristics.

Therefore, the inventors developed a new technology (patent application No. 59-2409).
No. 5) was proposed to address the above-mentioned problems. This technology is based on the new knowledge that the basis weight can be measured by X-ray diffraction method, and the disadvantage of the above technology (#Publication No. 58-47659) is that measurement errors in the degree of alloying occur due to variations in the basis weight. However, even with this technology, it is installed on equipment that continuously manufactures alloyed hot-dip galvanized steel sheets, and the degree of alloying is continuously increased. It was found that the measurement accuracy was not necessarily sufficient when measuring.

In other words, a relatively large positive or negative error occurs between the alloying degree measured on actual manufacturing equipment and the alloying degree determined by chemical analysis of the same steel sheet, which is currently considered the most accurate method. It is.

Table 1 shows the true value of the degree of alloying according to the inventors' investigation, that is, the degree of alloying determined by chemical analysis, the degree of alloying measured on the manufacturing equipment (the temperature of the steel plate is 40 to 400"C), and the degree of alloying determined by cooling. The relationship between the degree of alloying measured at room temperature is shown, and the degree of alloying measured on manufacturing equipment is both lower and higher than the degree of alloying determined by chemical analysis. It is also found that the degree of alloying in the cooled state is higher than the degree of alloying in the manufacturing equipment.

Table 1 By the way, the process characteristics of general continuous manufacturing equipment for alloyed hot-dip galvanized steel sheets are that the steel sheet immediately after hot-dip galvanization is guided into a heating furnace, where the temperature of the steel sheet is raised to 500 to 650°C. This process accelerates the alloying reaction between the zinc in the plating layer and the iron in the base steel sheet, converting the plating layer into a layer consisting of an iron-zinc intermetallic compound, and then cooling by air cooling, water cooling, etc., and further forming the steel sheet. It goes through a temper rolling process that applies a light reduction of 2% or less and a leveler process before reaching the final process.

In addition, the degree of alloying of alloyed hot-dip galvanized steel sheets was measured,
When automatically controlling the alloying degree based on this, it is essential that the measured value is accurate, but it is also important that the alloying degree measurement position and the position to be automatically controlled are as close as possible. It is.

In other words, the heating energy of the heating furnace that causes the alloying reaction to proceed concurrently, that is, gas combustion energy or electrical heating energy, is generally selected as the automatic control target, but the farther the measurement position is from the heating furnace, the more Control response to changes in alloying degree is delayed, and as a result, a large number of defective products are manufactured.

Therefore, the closer the measurement position is to the heating furnace, the better; however, in general manufacturing equipment, the steel plate temperature is 500 to 650°C immediately after the steel plate leaves the heating furnace.
After that, the steel plate is cooled in stages, but the problem is that the plate temperature fluctuates depending on the steel plate thickness and heating conditions.

That is, from the research conducted by the inventors, the X-ray diffraction intensity of each alloy layer constituting the alloyed galvanized layer is
In the temperature range up to , the higher the temperature of the steel sheet, the smaller it becomes. Furthermore, it has been found that when the steel sheet temperature is at a high temperature of 450° C. or higher, the alloying reaction proceeds within a few seconds, causing a problem in that the degree of alloying changes. In other words, the degree of alloying differs depending on the steel sheet temperature process, and the degree of alloying differs between the time of measurement and the time of cooling into a product.

As mentioned above, the research conducted by the inventors has led to the conclusion that one of the causes of measurement errors in the degree of alloying is the problem related to fluctuations in steel sheet temperature. However, as can be seen from Table 1, the steel plate temperature is not the only cause of the error; that is, the degree of alloying determined by chemical analysis does not match the degree of alloying in the cooled state.

<Object of the Invention> As mentioned above, the object of the present invention is to provide a facility for continuously manufacturing alloyed hot-dip galvanized steel sheets.

Continuously measure the degree of alloying and automatically control the degree of alloying.
To provide a method for measuring the degree of alloying of an alloyed galvanized steel sheet, which can minimize the occurrence of products (defective products) that deviate from the desired degree of alloying by accurately controlling the degree of alloying of the final product. There is a particular thing.

<Structure of the Invention> The present invention provides a method for manufacturing a 5-alloyed hot-dip galvanized steel sheet,
At a predetermined point after the alloying heat treatment furnace and before the temper rolling process and the leveling process, the temperature of the alloyed hot-dip galvanized steel sheet is adjusted to room temperature to 50°C or 50°C to 40°C.
The temperature of the steel plate is measured under a controlled temperature range of ±15°C in the range of 0°C, and X-rays are incident on the surface of the steel plate at the same point as the temperature measurement point to determine the alloy phase on the surface of the steel plate. Measure the diffraction X-ray intensity of The present invention provides a method for measuring the degree of alloying of an alloyed hot-dip galvanized steel sheet.

In the laboratory, the iron concentration in the plating (chemical analysis value) was 8.
Regarding 10, 12, 14, and 16 wt% alloyed galvanized steel sheets, the temperature of the steel sheets was controlled within the range of 25°C to approximately 400°C, and the X of each Fe-Zn alloy phase was adjusted at each temperature.
Linear diffraction intensity was measured.

As a result, each diffraction intensity becomes weaker as the temperature increases.
It was found that the degree of weakening differs depending on the type of Fe-Zn alloy phase. It was also found that the diffraction angle (2θ) of each phase shifts as the temperature increases. From this, it was found that changes in plate temperature during measurement caused measurement errors.

In addition, in the laboratory, iron concentration in plating (chemical analysis value)
An alloyed hot-dip galvanized steel sheet with 12% was subjected to temper rolling and leveling, and the relationship between the rolling reduction in the range of 0.1 to 2.0% and the diffraction intensity of each Fe-Zn alloy phase in the coating layer I looked into it. As a result, it was found that the diffraction intensity of each phase changed significantly in response to changes in rolling reduction, and that the amount of change was not uniform for each alloy phase. From this, it was found that slight differences in rolling reduction due to temper rolling caused measurement errors.

Therefore, the inventors investigated various measures to minimize measurement errors due to plate temperature, temper rolling, and leveling. As a result, the steel plate temperature during X-ray diffraction intensity measurement can be controlled within a range of ±15°C around a predetermined temperature between room temperature and 50°C or lower or 400°C or lower, and the alloying degree measuring device can be tempered. It has been found that measurement errors can be minimized by installing it in the main processes of the rolling process and leveling process.

Furthermore, the relationship between plate temperature and X-ray diffraction intensity can be expressed by a certain type of function, and by measuring plate temperature and X-ray diffraction intensity, for example, the X-ray diffraction intensity at a certain temperature can be accurately estimated. It turns out it can be done.

In the present invention, when continuously measuring the degree of alloying of an alloyed hot-dip galvanized steel sheet by X-ray diffraction method, the temperature of the steel sheet at the time of measurement is kept from room temperature to 50°C or less, or from over 50°C to 400°C or less. The reason why the temperature is controlled within the range of ±15°C is as follows.

That is, according to the inventors' research, as shown in FIG. 1, the steel plate temperature and, for example, η, δ1. r.

The relationship between the X-ray diffraction peak intensity and diffraction angle of each phase of α-Fe is that when the steel sheet temperature is between 25 (room temperature) and 400°C, the X-ray diffraction peak intensity is almost inversely proportional to the temperature rise. become weak. As a result, even if the same alloyed galvanized steel sheet is measured, the measured values of the Fe concentration will be different due to the difference in the temperature of the steel sheet when the calibration curve for determining the iron concentration in the plating is created. However, from FIG. 1, it can be seen that in the range of 25 to 50°C, the degree of weakening of the X-ray diffraction peak intensity is so small that it can be almost ignored;
It can be seen that even at a steel plate temperature of 00°C or lower, the change in the X-ray diffraction peak intensity within the range of ±15°C, that is, within the range of 30°C, is minute and can be almost ignored.

According to the inventors' calculations, within the range of 50°C or less, and 50°C or more and 400°C or less, each steel plate temperature is within ±15°C.
The effect of a minute change in the X-ray diffraction peak intensity on the measured Fe concentration is within 0.3% for an alloyed galvanized steel sheet with an Fe concentration of 12%. That is, 11.7 to 12.3
% range. When the steel plate temperature exceeds the control range of ±15° C., the error in the Fe concentration measurement value increases depending on the extent to which it exceeds the control range, but the larger the control range, the easier the control becomes.

However, since the purpose of the present invention is to reduce the measurement error as much as possible, in the present invention,
Within the following range, or ± within the range of 50”0 to 400℃
Control within the range of 15°C. In addition, the reason why the temperature range of 50°C to 400°C is limited to ±15°C is because alloying progresses within a few seconds at temperatures above 450°C, and the degree of alloying at the time of measurement is different from the degree of alloying in the product. It is necessary to develop a new prediction system for the progression of alloying degree during cooling to form a product, and the inventors' experience has shown that In the measurement of This is to do so.

Furthermore, in the present invention, the installation location of the alloying degree measuring device is downstream of the alloying heat treatment furnace and upstream of the temper rolling process and the leveling process, based on the research conducted by the present inventors. This is based on the fact that it has been found that the degree of alloying changes significantly even when the reduction rate is only about 0.1% by rough rolling or leveling.

That is, in actual manufacturing equipment, the steel type, plate thickness, thermal history, etc. of the manufactured products vary. Accordingly, the rolling reduction ratio of skin pass rolling and the rolling reduction ratio by a leveler also vary within the range of 0.1 to 2.0%. Therefore, if the degree of alloying is measured downstream of these processes, the degree of alloying will be significantly different even for the same alloyed galvanized steel sheet. Therefore, in the present invention.

The measuring device is installed downstream of the alloying process and upstream of the temper rolling process and the leveling process.

In addition, the temperature of the steel plate is ±15℃ between 50℃ and 400℃.
The method of controlling the temperature within this range is to measure the temperature of the plate immediately after leaving the heating furnace with a non-contact type thermometer such as a radiation thermometer, and then adjust the cooling temperature according to the deviation between the measured temperature value and the target temperature. By providing an air cooling zone that can control the amount of air used,
±15℃ centered on any temperature within the range of 0 to 400℃
can be controlled within a range of

Further, at temperatures below 300°C, by controlling the cooling rate by changing the mixing ratio of water and air using a mist cooling method, it is possible to maintain an arbitrary temperature within a range of ±15°C. In addition, in the experience of the inventors, it has been found that when a steel plate with a temperature of 300°C or higher is rapidly cooled by mist cooling, the shape of the steel plate deteriorates, which causes an error in measuring the degree of alloying. .

Furthermore, the second feature of the invention is that the X-ray diffraction intensity and the steel plate temperature are measured simultaneously, and the X-ray diffraction intensity at a reference steel plate temperature is determined from the relational expression between the steel plate hot dust and the X-ray diffraction intensity determined in advance. The purpose is to measure the degree of alloying by correcting the X-ray diffraction intensity and inserting the corrected X-ray diffraction intensity into a relational expression between the X-ray diffraction intensity and the degree of alloying prepared at a predetermined reference steel plate temperature.

Measuring the steel plate temperature and X-ray diffraction intensity simultaneously in this way is important because, as mentioned above, the steel plate temperature varies depending on the plate thickness, alloying heating conditions, etc., and as can be seen from Figure 1. This is because the X-ray diffraction intensity also fluctuates, so it is necessary to install the X-ray diffraction device and the thermometer at the same location and take measurements at the same time.

In addition, in the experience of the inventors, the temperature distribution of the steel sheet in the width direction of the steel sheet is generally lower at both ends than at the center of the width direction. Therefore, when measuring the degree of alloying in the width direction, X-ray diffraction When the degree of alloying was measured by placing the device and the plate thermometer on the same traverse cart, the measured value of the degree of alloying in one width direction agreed well with the value measured by chemical analysis.

In addition, the relational expression between X-ray diffraction intensity and degree of alloying, that is, the calibration curve of degree of alloying, is determined at the reference steel plate temperature only once at 25°C, for example, if the reference temperature is 25°C. It is sufficient to prepare a calibration curve of

Practical example Hereinafter, the present invention will be specifically explained with reference to examples.

(Example 1) In a continuous production facility for alloyed hot-dip galvanized steel sheets, a low carbon AiL killed steel sheet (unannealed material) with a thickness of 0.7 mm and a sheet width of 1,200 mm was processed at line speed Fuji Layer Min.
A4Q in the plating bath was passed through a plating bath with a concentration of 0.15 fI amount %, and the basis weight was adjusted to 16 by the gas jet basis weight adjustment device.
Immediately after adjusting to 0 g/go (one side), heat the maximum atmospheric temperature to 800-1100 in a gas combustion type heating furnace.
℃ heat treatment to continuously produce alloyed hot-dip galvanized steel sheets with various degrees of alloying, and measure the degrees of alloying using degree-of-alloying measuring devices installed at eight locations downstream from the heating furnace. was measured. At the same time, the temperature of the steel plate at each alloying degree measuring device installation position was measured using a radiation thermometer.

The temperature of the steel plate at each measurement position was determined from 425 ± 15 °C, 375 ± 15 °C, 32
5±15℃, 275±15℃, 225℃, 15℃, 150
It was controlled at eight levels: ±15°C, 70°C 15°C, and 30±15°C. Further, the degree of alloying (ie, the iron concentration in the plating) of the various alloyed hot-dip galvanized steel sheets after manufacture was measured by atomic absorption spectrometry.

The alloying degree measuring devices installed at eight locations are X-ray diffraction devices with parallel beam optics, and the r-phase (2θ=13
9") and a-Fe (2θ=105J°), and the measured values were
℃, 275℃, 225℃, 150℃, 70℃ and 30℃
It has the function of calculating the final Fe concentration by a computer with built-in Fe concentration calibration curves created for each level of °C.

Note that the peak intensity of a-Fe (2θ = 105.8°) is determined by measuring the area weight by measuring the same intensity, as stated in Japanese Patent Application No. 59-24095. This minimizes measurement errors caused by changes in the basis weight.

On the other hand, when the steel plate temperature is not controlled at all (case 1), the temperature of the steel plate is controlled, and the reduction rate is 0.8% and 1.2% between the 7th and 8th alloying degree measurement positions. (Case?) and when temperature control is performed and leveling is performed with a rolling reduction of 0.2% between the 7th and 8th measurement positions (Case 3). The degree of oxidation was measured. For case l, the second, 5
In Case 2 and Case 3, the measurement was performed with the 8th measuring device.

In addition, to control the steel plate temperature, an air cooling chamber and a water-air mist spray nozzle are used together, and the steel plate temperature measured by a radiation thermometer is fed back, and the air amount and water-air mixing ratio are adjusted according to the measured value. This was done using a method that automatically changes the

The above measurement values and chemical analysis values are summarized in Table 2.

From Table 2, the values measured by the method of the present invention are 8-0%
, 11.0%, and 110% iron concentration kJj, the difference from the chemical analysis value is in the range of ±0.1%. It can be seen that the measurement accuracy is significantly improved compared to the case where the measured values are relatively far apart from the chemical analysis values when the chemical analysis values are not controlled. In addition, in order to minimize errors in measuring the degree of alloying, it is necessary not only to control the steel plate temperature, but also to install a degree of alloying measuring device upstream in the flow direction of the line during the leveling process and the temper rolling process. I understand that.

(Example 2) Using an electrogalvanized steel plate (plate thickness 0.8 mm, plate width 1,112 cm) with a basis weight of 60 g/m'' (one side), the maximum atmospheric temperature reached in a gas combustion type heating furnace was 800-1100
℃ heat treatment to continuously produce alloyed galvanized steel sheets with various alloying levels, and place them approximately 15 m away from the heating furnace (upstream of the temper rolling process and leveling process). An X-ray diffraction device and a radiation thermometer were installed in the cooling zone of the air chamber cooling method installed in the
Linear diffraction intensity and steel plate temperature were measured. In addition, regarding the manufactured alloyed galvanized steel sheets, the iron concentration in the plating was analyzed by atomic absorption spectrophotometry. The steel plate temperature at the X-ray diffraction intensity measurement position was in the range of 250 to 400°C.

In addition, in the xm diffractometer, alpha rays are taken out from the Or metal X-ray tube to Cr-, and
9°) and a-Fe (2θ = 105.6°), and automatically input the measured values and the steel plate temperature measured by a radiation thermometer into a computer.
Compare with the steel plate temperature-X-ray diffraction intensity calibration curve input in advance.

The degree of alloying was measured by converting it into an X-ray diffraction intensity at a standard steel plate temperature (25°C) and comparing this with an Fe concentration calibration curve prepared at a steel plate temperature of 25°C. The degree of alloying was also measured using a conventional method that does not involve inputting the steel plate temperature.

Table 3 summarizes each iron concentration measurement value by the above method and the analytical value by chemical analysis.

From Table 3, it can be seen that the values measured by the conventional method are all smaller than the chemical analysis values, and their errors are large, but the values measured by the method of the present invention have almost no difference from the chemical analysis values. I understand. In other words, a measuring device is installed upstream of the temper rolling process or the leveling process, and the X-ray diffraction intensity and the steel plate temperature are measured simultaneously, and a predetermined relational expression between the steel plate temperature and the X-ray diffraction intensity is determined. Then, the measured X-ray diffraction intensity is corrected to the X-ray diffraction intensity at the set standard steel plate temperature, and the corrected It can be seen that the accuracy of measuring the degree of alloying is significantly improved by inserting it into the relational expression and measuring the degree of alloying.

<Effects of the Invention> (1) According to the method of the present invention, the degree of alloying of an alloyed galvanized steel sheet can be measured with high accuracy. Furthermore, the accuracy of automatic control of the degree of alloying using this measured value is improved.

(2) The degree of alloying can be measured accurately no matter where the steel plate temperature is below 400°C, so the measuring device can be installed near the alloying furnace and the measurement can be carried out in a short time. The occurrence of poorly alloyed materials due to delays can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the influence of the steel plate temperature of a 1-alloyed galvanized steel sheet on the X-ray diffraction intensities of the η, δ1, r phases and the α-Fe phase during plating.

Claims (1)

[Claims] 1. In the production line for alloyed hot-dip galvanized steel sheets, at a predetermined point after the alloying heat treatment furnace and before the temper rolling process and the leveling process, the temperature of the alloyed hot-dip galvanized steel sheets is adjusted from room temperature to 50°C. Temperature range or 50℃
The temperature of the steel plate is measured in a controlled state within a temperature range of ±15°C in the range of ultra-400°C, and X-rays are incident on the steel plate surface at the same point as the temperature measurement point, Measure the diffraction X-ray intensity of the alloy phase, and determine the degree of alloying in the alloy phase from the measurement results, the steel plate temperature and X-ray diffraction intensity determined in advance, and the correspondence between the diffraction X-ray intensity and the alloying degree. A method for measuring the degree of alloying of an alloyed hot-dip galvanized steel sheet, characterized by calculating the following.