Method for measuring total mass of oxide skin on surface of carbon steel rod

Abstract

The invention relates to the technical field of metallurgy, in particular to a method for measuring the total mass of oxide skin on the surface of a carbon steel rod, which comprises the following steps: S1, taking a plurality of samples from a cooled rolled product, and measuring the average thickness of the oxide skin layer on the surface of the sample; s2, measuring chemical components of oxide skin on the surface of the sample, and calculating the mass ratio of oxygen to iron in the oxide skin; s3, calculating the density of the oxide skin according to the chemical components, measured in the step S2, of the oxide skin on the surface of the sample; s4, according to the average thickness obtained through measurement in the step S1 and the results obtained through calculation in the step S2 and the step S3, the diameter of the rolled product is subtracted by the thickness of the steel layer which becomes the oxide skin layer; and S5, according to the average thickness measured in the step S1, the results calculated in the step S3 and the results calculated in the step S4, the total oxide skin mass on the surface of the rolled product with the nominal diameter D per ton is calculated. The determination method is simple to operate, convenient to calculate, low in labor intensity and environment-friendly.

Description

Technical Field

[0001] The invention relates to the technical field of metallurgy, and in particular to a method for measuring the total mass of oxide scale on the surface of a carbon steel rod. Background Art

[0002] In the production process of metal materials, in order to improve the mechanical properties and other properties of the metal materials, a heating-cooling heat treatment process is usually carried out on them; and due to the different application scenarios of different metal materials and equipment constraints, the requirements for their material, shape, mechanical strength, corrosion resistance, etc. are also different, and the heat treatment process will be different. During the rolling process of carbon steel, the steel will be heated to a high temperature of more than 700°C; steel heated to a high temperature in the atmosphere will generate oxide scale (oxide) caused by surface oxidation during the heating period. The generation of oxide scale will make the surface of the steel rough and affect the appearance quality of the steel; at the same time, it will also have a certain impact on the dimensional accuracy of the steel; in addition, if the oxide scale is pressed into the metal, it will have a certain impact on the mechanical properties and performance of the steel. In severe cases, it may even cause the steel to become scrap, reduce the qualified rate of the steel, and increase the production cost of the steel. Therefore, in the past, after the heat treatment of the steel, the oxide scale would be removed by pickling and shot peening. However, different steel grades have different elemental compositions, and the hot rolling processes used are also different. The morphology, composition, and size of the oxide scale obtained under different hot rolling processes are different. The sampling and testing of the oxide scale during the rolling process are the final results. It is difficult to continuously track the structure and characteristics of the oxide scale, and it is impossible to provide effective guidance for the parameters of the straightening and pickling processes. At the same time, according to the relevant standards for evaluating the quality of rolled carbon steel, among the quality indicators for controlling rolled circular sections, the amount of oxide scale (oxide) on the metal surface is one of the important indicators for evaluating the quality of rolled circular sections. Therefore, studying and characterizing the cross-sectional structure and characteristics of the oxide scale on the surface of rolled carbon steel has always been the focus of research and development personnel.

[0003] It is known that a method for determining the total oxide scale quality on the surface of high and low carbon steels has been disclosed in the prior art (Quantitative determination of the total oxide scale quality, descaling ability and residual oxide on the surface of high and low carbon steels: GA-03-16, BEKAERT.MBUSC.BK-spec:GA-03-16. May 1994, page 9), which is used to measure the total oxide scale quality on the surface of rolled products produced on a high-speed wire rod mill. In this production process, the rolled products are water-cooled when leaving the last rolling mill of the finishing mill group, and then formed into coils on a conveyor belt and cooled with air by a jet fan. After cooling, samples are taken and the total oxide scale quality on the surface of the rolled products is measured.

[0004] The measurement method known in the prior art is to heat a hydrochloric acid solution with a mass concentration of 0.15 g / cm3 to no more than 50 degrees Celsius, then add the inhibitor at a rate of 0.5 g / dm3, and then place 3-5 previously weighed samples with a length of 90-100 mm in the prepared solution at the same time. Before weighing the samples for etching, it is necessary to take into account the amount of oxide scale that falls off during the sample preparation (cutting). At the final stage, the etched samples are cleaned, dried and reweighed.

[0005] It is known that the total scale mass on the measured sample is determined by mathematical calculation. For example, the methodology of Kobe Steel (Japan) is based on experience:

[0006]

[0007] Among them, ε 0 is the critical deformation level before spalling on the surface of the rolled product; γ0 is the fracture energy of the oxide scale in smooth contact; χ is the roughness index of the contact surface; h is the thickness of the oxide scale; and E is the Young's modulus of the oxide scale.

[0008] The above methods all require a large amount of experimental operations, high labor intensity, and the use of special laboratory equipment, resulting in high measurement costs. At the same time, during the experiment, environmentally harmful reagents are also used, which is not environmentally friendly. In addition, the above methods have a small scope of application and can only be used to determine the total scale mass on the surface of a rolled circular section of carbon steel with a specific chemical composition and / or a specific diameter.

[0009] The purpose of the present invention is to provide a method for measuring the total mass of oxide scale on the surface of a carbon steel rod, so as to solve the problems of the existing measuring methods in the prior art, such as small application scope, high labor intensity and unfriendly environment. Summary of the invention

[0010] The purpose of the present invention is to provide a method for measuring the total mass of oxide scale on the surface of a carbon steel rod, so as to solve the problems of the existing measuring methods in the prior art, such as small application scope, high labor intensity and unfriendly environment.

[0011] The technical solution of the present invention is: a method for measuring the total mass of oxide scale on the surface of a carbon steel bar, comprising the following steps:

[0012] S1. Take several samples from the cooled rolled product and measure the average thickness of the oxide layer on the surface of the samples by metallographic analysis;

[0013] S2. Determine the chemical composition of the oxide scale on the surface of the sample and calculate the mass ratio of oxygen to iron in the oxide scale;

[0014] S3, calculating the density of the oxide scale according to the chemical composition of the oxide scale on the surface of the sample measured in step S2;

[0015] S4, calculating the diameter of the rolled product minus the thickness of the steel layer that becomes the oxide scale layer according to the average thickness of the oxide scale layer on the sample surface measured in step S1, the mass ratio of oxygen to iron in the oxide scale calculated in step S2, and the oxide scale density calculated in step S3;

[0016] S5, calculating the total mass of oxide scale on the surface of one ton of rolled product with a nominal diameter of D according to the average thickness of the oxide scale layer on the sample surface measured in step S1, the oxide scale density calculated in step S3, and the diameter of the rolled product calculated in step S4 minus the thickness of the steel layer that becomes the oxide scale;

[0017] The calculation formula for the total mass of oxide scale on the surface of one ton of rolled steel with a nominal diameter of D is:

[0018]

[0019] Where M scale It is the total mass of oxide scale on the surface of one ton of rolled steel with a nominal diameter of D, in kilograms per ton (kg / t); h scale is the average thickness of the oxide layer on the surface of the rolled product, in meters; ρ scale is the density of the oxide scale, in kilograms per cubic meter; d is the diameter of the rolled steel minus the thickness of the steel layer that has become the oxide scale, in meters; D is the nominal diameter of the rolled product, in meters.

[0020] Preferably, the chemical composition of the oxide scale on the surface of the sample includes rust, magnetite and hematite; wherein, calculated by mass percentage, the mass ratio of rust in the chemical composition of the oxide scale on the surface of the sample is 63-84%, the mass ratio of magnetite is 15-35%, and the mass ratio of hematite is 1-2%.

[0021] Preferably, the method for determining the chemical composition of the oxide scale on the surface of the sample includes: inductively coupled plasma spectroscopy, automatic X-ray spectroscopy using a reference sample, and metallographic analysis after special etching of transverse microgrooves.

[0022] Preferably, the expression for the mass ratio of oxygen to iron in the oxide scale on the surface of the sample is:

[0023]

[0024] Where K is the mass ratio of oxygen to iron in the oxide scale; m0 is the mass percentage of oxygen in the oxide scale; m Fe is the mass percentage of iron in the oxide scale; m FeOis the mass percentage of rust in the oxide scale; m Fe3O4 is the mass percentage of magnetite in the oxide scale.

[0025] Preferably, the calculation formula of the oxide scale density is:

[0026]

[0027] In the formula, ρ scale is the density of the oxide scale, in kilograms per cubic meter; ρ FeO is the density of rust stone, which is 5745 kg per cubic meter; ρ Fe3O4 is the density of magnetite, which is 5170 kilograms per cubic meter.

[0028] Preferably, the diameter of the rolled product minus the thickness of the steel layer that becomes the oxide scale layer is expressed by an equation; the equation is:

[0029]

[0030] In the formula, ρ Fe is the density of iron, 7874 kg per cubic meter; d is the diameter of the rolled product minus the thickness of the steel layer that has turned into oxide scale, in meters.

[0031] Compared with the prior art, the advantages of the present invention are:

[0032] (1) The present invention provides a method for determining the total mass of oxide scale on the surface of a carbon steel bar. The method determines the total mass of oxide scale on the surface of a rolled product by determining the average thickness of the oxide scale on the surface of the rolled product and the actual chemical composition of the oxide scale on the surface. The method is simple to operate and convenient to calculate. It does not require a large amount of experimental operation, has low labor intensity, and does not require the use of chemical reagents that are harmful to the environment. At the same time, the method does not need to rely on the cooling process of the rolled product after deformation and heating, and has a wide range of applications. It solves the problems of the existing measurement methods in the prior art, such as small application range, high labor intensity, and environmental unfriendliness.

[0033] (2) The present invention provides a method for determining the total mass of oxide scale on the surface of a carbon steel bar. When using this method to determine the total mass of oxide scale on the surface of a rolled product, it is only necessary to take a sample and determine the average thickness of the oxide scale layer on the surface of the sample and the actual chemical composition of the oxide scale on the surface. The total mass of the oxide scale on the surface of the rolled product can be calculated using expressions (1)-(4). There is no need to consider the type of steel to which the rolled product belongs, nor the cooling process after heat treatment of the rolled product. This allows the determination method to be used to determine the total mass of oxide scale on the rolled circular cross section of carbon steel of any chemical composition and diameter, thereby expanding the scope of use of the determination method.

[0034] The present invention will be further described below in conjunction with the accompanying drawings and embodiments:

[0035] Figure 1 The present invention is a flow chart of the method for determining the total mass of oxide scale on the surface of a carbon steel rod. DETAILED DESCRIPTION

[0036] The present invention is further described in detail below in conjunction with specific embodiments:

[0037] like Figure 1 As shown, a method for measuring the total mass of oxide scale on the surface of a carbon steel bar comprises the following steps:

[0038] S1. Take several samples from the cooled rolled product and measure the average thickness of the oxide layer on the surface of the sample by metallographic analysis. scale .

[0039] Metallographic analysis is one of the important means of experimental research on metal materials. Metallographic analysis can be used to study the structure of metal materials and the relationship between the structure and other chemical components, such as the relative number of various inclusions and surface oxides in the structure, grain size, shape and distribution, etc. Metallographic analysis can also be used to study the microstructural changes of metal materials during heat treatment, thereby optimizing the heat treatment process.

[0040] S2. Determine the chemical composition of the oxide scale on the surface of the sample and calculate the mass ratio of oxygen to iron in the oxide scale, K.

[0041] When the steel wire is produced in the rolling mill, it will be water-cooled after forming the final size, and then it will be rolled into a coil on a roller conveyor belt through a coiling cone and cooled; there are many kinds of post-rolling cooling process methods, such as air cooling, pile cooling, wind cooling, water cooling, spray cooling, etc.; different steels use one cooling method or a combination of two or more cooling methods according to their steel type and performance requirements, for example, air cooling (two-stage cooling) or after water cooling treatment, it is rolled into a coil and cooled in calm air (single-stage cooling), etc.

[0042] It is known that rust (FeO) has the least adhesion to the metal surface and is most easily removed mechanically from the surface of the cooled rolled product. Therefore, when the oxide scale on the surface of the rolled product is mainly composed of rust, it is most beneficial for the production and further processing of the rolled product. In the process of continuous cooling of the rolled product, in order to form an oxide scale almost entirely composed of rust on the surface of the rolled product, it is necessary to accelerate the cooling of the metal within a certain temperature range, that is, within the temperature range of 570-400°C, the cooling rate of the metal must be at least 100°C / second; at a slower cooling rate, the rust will decompose into magnetite (Fe3O4) and metallic iron, and then magnetite and hematite will appear in the oxide scale. Therefore, in order to retain the components of rust on the surface of the rolled product and prevent the decomposition of rust, the metal needs to be cooled at an accelerated rate. However, in the actual production process, it is almost impossible to achieve an actual cooling rate of more than 100°C / second in the temperature range of 570-400°C, so the surface scale of the rolled product is usually composed of rust (63-84%), magnetite (15-35%) and hematite (1-2%), and in the surface scale, the content of rust is in the range of 63-84%, the content of magnetite is in the range of 15-35% and the content of hematite does not exceed 2%. Since the content of hematite is only 1-2%, this oxide only exists in trace amounts and will not significantly affect the total mass of the surface scale of the rolled product. Therefore, in the process of calculating the total mass of the surface scale of the rolled product, it is not necessary to consider the influence of the formation of hematite on its results.

[0043] The chemical composition of the oxide scale on the surface of rolled products and the content of each component in the chemical composition can be detected by inductively coupled plasma spectroscopy, automatic X-ray spectroscopy using reference samples, metallographic method after special etching of transverse microgrooves, etc. Among them, when using inductively coupled plasma spectroscopy to determine the chemical composition of the surface oxide scale, instruments such as gas analyzers and plasma spectrometers can be used. At the same time, this method has the advantages of simultaneous determination of multiple elements and a wide linear range; it can simultaneously determine the main, secondary and trace elements, and is suitable for direct analysis of solid, liquid and gaseous samples. It is an ideal method for laboratory element analysis. The method of using an automatic X-ray diffractometer with a reference sample to determine the chemical composition of the oxide scale on the surface of rolled products is also an important method in the current methods for material composition analysis and chemical state research.

[0044] According to the measured chemical composition of the surface oxide scale of the rolled product, the mass ratio of oxygen to iron in the surface oxide scale can be calculated. The mass ratio of oxygen to iron in the surface oxide scale is calculated by the following expression:

[0045]

[0046] Where K is the mass ratio of oxygen to iron in the oxide scale; m0 is the mass fraction of oxygen in the oxide scale; m Fe is the mass fraction of iron in the oxide scale; m FeO is the mass fraction of rust in the oxide scale; m Fe3O4 Mass fraction of magnetite in oxide scale.

[0047] By substituting the chemical composition of the surface oxide scale obtained by measurement into expression (2), the mass ratio of oxygen element to iron element in the surface oxide scale can be calculated.

[0048] S3, according to the chemical composition of the oxide scale on the sample surface measured in step S2, calculate the density of the oxide scale, ρ scale ;

[0049] Since the content of magnetite in the surface oxide scale is determined by the actual cooling rate of the rolled product within the temperature range of 570-400℃, the actual ratio of rust and magnetite in the surface oxide scale of different steels or the same steel treated with different post-rolling cooling processes is different; according to the actual ratio of rust and magnetite, the density of the oxide scale obtained is also different; therefore, when the average thickness of the oxide scale layer on the surface of the rolled product is the same, the weight of the surface oxide scale is not exactly the same.

[0050] The density of the surface oxide scale can be calculated through the chemical composition of the oxide scale (rust and magnetite content) formed on the surface of the rolled product obtained in step S2; thus, the weight of the surface oxide scale of one ton of rolled product can be determined when the average thickness of the surface oxide scale layer is known.

[0051] The density of the oxide scale is determined by the following expression:

[0052]

[0053] In the formula, ρ scale is the density of the oxide scale in kilograms per cubic meter (kg / m 3 );ρ FeO The density of rust stone is 5745 kg / m 3 );ρ Fe3O4 is the density of magnetite, which is 5170 kilograms per cubic meter (kg / m 3 );m FeO is the mass fraction of rust in the oxide scale; m Fe3O4 is the mass fraction of magnetite in the oxide scale.

[0054] By inserting the result of the chemical composition of the surface oxide scale measured in step S2 into expression (3), the mass ratio of oxygen element to iron element in the surface oxide scale can be calculated.

[0055] S4. Based on the average thickness of the oxide scale layer on the sample surface measured in step S1, the mass ratio of oxygen to iron in the oxide scale calculated in step S2, and the oxide scale density calculated in step S3, the diameter of the rolled product minus the thickness of the steel layer that becomes the oxide scale, d, can be calculated.

[0056] The diameter of the rolled steel minus the thickness of the oxide scale is determined by the following equation:

[0057]

[0058] In the formula, ρ Fe is the density of iron, 7874 kg per cubic meter; d is the diameter of the rolled product minus the thickness of the steel layer that has become the oxide layer, in meters; K is the ratio of oxygen to iron in the oxide layer; ρ scale is the density of the oxide scale of a specific chemical composition, expressed in kilograms per cubic meter; h scale It is the average thickness of the oxide layer on the surface of the rolled product, measured in meters; D is the nominal diameter of the rolled product, measured in meters.

[0059] The above equation can be written in the form of a quadratic equation as follows:

[0060]

[0061] Substitute the result obtained in step S1 and the results calculated in steps S2 and S3 into equation (5); at the same time, through the discriminant: △ = b 2 After -4ac, the root of the square equation can be determined and calculated, and the rolling diameter minus the thickness of the steel layer that has been converted into oxide scale can be calculated.

[0062] S5. According to the average thickness of the oxide scale layer on the sample surface measured in step S1, the oxide scale density calculated in step S3, and the diameter of the rolled product calculated in step S4 minus the thickness of the steel layer that becomes the oxide scale, the total oxide scale mass on the surface of one ton of rolled product with a nominal diameter of D can be calculated.

[0063] The total mass of oxide scale on the surface of one ton of rolled steel with a nominal diameter of D is determined by the following expression:

[0064]

[0065] Where M scale It is the total mass of oxide scale on the surface of one ton of rolled steel with a nominal diameter of D, expressed in kilograms per ton (kg / t); D is the nominal diameter of the rolled product, expressed in meters.

[0066] Substituting the result measured in step S1, the result calculated in step S3 and the result calculated in step S4 into expression (1), the total mass of the oxide scale on the surface of one ton of rolled steel with a nominal diameter of D can be calculated. Under the conditions of a metallurgical enterprise, a steel grade with a diameter of 5.5-11.0 mm and a carbon content of 0.05-0.87% (mass percentage) is selected as the rolled product to be tested, and sampling is performed; the average thickness of the oxide scale layer on the surface of the sample is measured by metallographic analysis, and the chemical composition of the oxide scale layer on the surface of the sample is determined by inductively coupled plasma spectroscopy or other methods, and the total oxide scale mass of the oxide scale on the surface of the circular cross-section rolled product is calculated by the above expression and equation, and the experimental data results calculated by the above method are compared with the experimental data results obtained by the existing experimental method relying on the post-rolling cooling process. The comparison results show that the calculated data are highly consistent with the experimental data, that is, the error of the calculated total oxide scale mass does not exceed ±3%.

[0067] Since the data calculated by the above method under the production conditions of a typical high-speed rolling mill are highly consistent with the experimental data obtained, it can be seen that the above calculation method is also applicable under other production conditions and can achieve the same effect. It can be seen that the above method can be used to determine a series of quality indicators of rolled round steel, that is, to determine the quality of the oxide scale (oxide) on the surface of the metal material.

[0068] Therefore, using the calculation method provided in this application, the total scale mass on the surface of a rolled circular section of any diameter can be determined by determining the average thickness of the scale layer and by determining the actual chemical composition of the surface scale, without considering the type of steel described in the rolled product and the cooling method of the rolled product after deformation and heating.

[0069] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with this technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the scope of protection of the present invention. For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic features of the present invention. Therefore, no matter from which point of view, the embodiments should be regarded as exemplary and non-restrictive. The scope of the present invention is limited by the attached claims rather than the above description, and it is intended to include all changes within the meaning and scope of the equivalent elements of the claims in the present invention.

Claims

1. A method for determining the total mass of oxide scale on the surface of a carbon steel bar, characterized in that: The following steps are involved: S1. Take several samples from the cooled rolled product and measure the average thickness of the oxide layer on the surface of the samples by metallographic analysis; S2. Determine the chemical composition of the oxide scale on the surface of the sample and calculate the mass ratio of oxygen to iron in the oxide scale; S3, calculating the density of the oxide scale according to the chemical composition of the oxide scale on the surface of the sample measured in step S2; S4, calculating the diameter of the rolled product minus the thickness of the steel layer that becomes the oxide scale layer according to the average thickness of the oxide scale layer on the sample surface measured in step S1, the mass ratio of oxygen to iron in the oxide scale calculated in step S2, and the oxide scale density calculated in step S3; S5, calculating the total mass of oxide scale on the surface of one ton of rolled product with a nominal diameter of D according to the average thickness of the oxide scale layer on the sample surface measured in step S1, the oxide scale density calculated in step S3, and the diameter of the rolled product calculated in step S4 minus the thickness of the steel layer that becomes the oxide scale; Among them, the calculation formula for the total mass of oxide scale on the surface of one ton of rolled steel with a nominal diameter of D is: Where M scale It is the total mass of oxide scale on the surface of one ton of rolled steel with a nominal diameter of D, in kilograms per ton (kg / t); h scale is the average thickness of the oxide layer on the surface of the rolled product, in meters; ρ scale is the density of the oxide scale, in kilograms per cubic meter; d is the diameter of the rolled steel minus the thickness of the steel layer that has become the oxide scale, in meters; D is the nominal diameter of the rolled product, in meters.

2. A method for measuring the total mass of oxide scale on the surface of a carbon steel rod according to claim 1, characterized in that: The chemical composition of the oxide scale on the surface of the sample includes rust, magnetite and hematite; wherein, calculated by mass percentage, the mass ratio of rust in the chemical composition of the oxide scale on the surface of the sample is 63-84%, the mass ratio of magnetite is 15-35%, and the mass ratio of hematite is 1-2%.

3. A method for measuring the total mass of oxide scale on the surface of a carbon steel rod according to claim 2, characterized in that: Methods for determining the chemical composition of the oxide scale on the surface of the sample include: inductively coupled plasma spectroscopy, automatic X-ray spectroscopy using reference samples, and metallographic analysis after special etching of transverse microgrooves.

4. A method for measuring the total mass of oxide scale on the surface of a carbon steel rod according to claim 2, characterized in that: The expression for the mass ratio of oxygen to iron in the oxide scale on the surface of the sample is: Where K is the mass ratio of oxygen to iron in the oxide scale; m0 is the mass percentage of oxygen in the oxide scale; m Fe is the mass percentage of iron in the oxide scale; m FeO is the mass percentage of rust in the oxide scale; m Fe3O4 is the mass percentage of magnetite in the oxide scale.

5. A method for measuring the total mass of oxide scale on the surface of a carbon steel rod according to claim 4, characterized in that: The calculation formula of the oxide scale density is: In the formula, ρ scale is the density of the oxide scale, in kilograms per cubic meter; ρ FeO is the density of rust stone, which is 5745 kg per cubic meter; ρ Fe3O4 is the density of magnetite, which is 5170 kilograms per cubic meter.

6. A method for measuring the total mass of oxide scale on the surface of a carbon steel rod according to claim 5, characterized in that: The diameter of the rolled product minus the thickness of the steel layer that becomes the oxide scale layer is expressed by an equation; the equation is: In the formula, ρ Fe is the density of iron, 7874 kg per cubic meter; d is the diameter of the rolled product minus the thickness of the steel layer that has turned into oxide scale, in meters.

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