JP2010174341A - Oxidization inhibitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an oxidization inhibitor capable of effectively inhibiting scales formed on a surface of a heat-treated steel material when applied to the steel material prior to the heat treatment such as hot forging. <P>SOLUTION: The oxidization inhibitor contains at least one chosen from magnesium carbonate, sodium chloride or a mixture of magnesium carbonate and sodium chloride so as to inhibit formation of scales on the surface of the steel material subjected to a heat treatment such as hot forging. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an oxidation inhibitor applied to a steel material subjected to heat treatment.

  When heat treatment such as hot working is performed in a heating furnace in a manufacturing process of a steel material, the steel material is usually heated in an environment where oxygen exists in the atmosphere or the like. When the steel material is heated in such a situation, an oxide film such as iron oxide is formed on the surface of the steel material. Such an oxide film is generally referred to as “scale”.

  The scale generated on the surface of the steel material is generally harder than the steel material itself, so if the scale remains on the surface of the steel material, the lubrication action during hot working is hindered and the frictional resistance increases. , The weight increase of steel materials after heat treatment and poor formation are likely to occur. Moreover, the scale produced | generated on the surface of steel materials bites into the surface at the time of processing of steel materials, and becomes a factor of damage, or becomes a factor which damages the surface of a processing tool. If the tool surface is damaged, the tool life will be shortened, increasing the cost of the tool, or if the damage on the tool surface is transferred to the surface of the hot-worked steel product, There is also a problem that the quality of the product deteriorates. Furthermore, since the scale is more fragile than the steel material, if the scale on the surface of the steel material is peeled off, the steel material itself becomes thin and thin or thin, which may cause a decrease in yield, or the scale that is peeled off in the form of sand may cause If it collects in the furnace, there are problems that it takes time and cost to remove it, and the heating furnace is damaged. In addition, the scale accumulated in the heating furnace may adhere to the surface of the steel product and cause the product quality to deteriorate.

  In this way, scale generation causes loss of not only steel materials and products but also tools and heating furnaces used in the manufacturing process and subsequent processes. Suppression of generation and efficient removal of scale have been a challenge.

  As a method for suppressing the generation of scale, for example, at least the first stand of the hot finish tandem rolling process, one or more of calcium carbonate, sodium carbonate and potassium carbonate may be used. A method for preventing wrinkles on a steel material due to a scale generated by a secondary scale by rolling while supplying a lubricant containing a lubricant composition in a predetermined ratio or more to the steel material (see Patent Document 1), titanium A method for preventing generation of an oxide film generated during hot working by applying a carbide composed of a mixture of silicon carbide and boron carbide as an antioxidant on the surface of the alloy material (see Patent Document 2), softening By using an antioxidant containing multiple glass frit with different points, it prevents dent wrinkles (roller marks) generated on the surface of the steel pipe due to scale. And a method (see Patent Document 3) are known that.

  On the other hand, as a method of removing the generated scale, an apparatus that mechanically removes the scale from the steel material by hitting a hammer facing the end face of the billet that has been heated and taken out is subjected to hot forging (Patent Document) 4) is known.

JP-A-9-276922 Japanese Patent Laid-Open No. 10-140233 JP 2007-314875 A JP 2004-268126 A

  However, as described in Patent Document 1, the technique of using lubricating oil for the purpose of suppressing scale generation in the heating process of steel materials is a burden on the work site and the surrounding environment in terms of odors and disposal generated during heating. However, it is not preferable. Moreover, since the silicon carbide and boron carbide used as antioxidants are very high-hardness carbides as in the technique described in Patent Document 2, if they cannot be completely removed before processing into steel, There is a risk of causing damage to the surface of the processing tool or steel (and product). Further, when an antioxidant containing glass frit is used as in the technique described in Patent Document 3, since the glass frit melts and spreads on the surface of the steel material after the heat treatment, the glass from the steel material is processed before the subsequent processing. It takes a lot of work to remove.

  On the other hand, as described in Patent Document 4, when using a device that mechanically removes the scale by hitting the surface of the steel material, the cost required for the device, a decrease in productivity due to an increase in the process, or the steel material Problems such as deformation and difficulty of complete removal of the scale are conceivable.

  In view of the problems as described above, the present invention mainly provides an oxidation inhibitor that can be easily used during the heat treatment of a steel material and can suppress the generation of scale on the surface of the steel material with high efficiency. To do.

  The oxidation inhibitor according to the present invention is applied to the surface of a steel material before heat treatment, and contains any one of magnesium carbonate, sodium chloride, or a mixture thereof. is there.

  That is, the oxidation inhibitor of the present invention comprises only magnesium carbonate, only sodium chloride, only a mixture of magnesium carbonate and sodium chloride, or a mixture of these and other substances. Magnesium carbonate and sodium chloride are substances that have not been used for the purpose of being applied to the surface of a steel material to be heat-treated so as to suppress its oxidation and suppress the formation of scale. According to the present inventors' research, by applying the oxidation inhibitor of the present invention to the surface of the steel material, the mechanism of action is not necessarily clear, but it is possible to generate scale on the surface of the steel material during the heat treatment. It was revealed that it can be suppressed with extremely high efficiency. Therefore, it is possible to avoid problems such as removal of oxidation inhibitors remaining on the surface of steel materials, harmful effects on heating furnaces and processing tools, or troubles, costs and damage to steel materials when removing scales generated by striking steel materials. Can be avoided. In addition, with the oxidation inhibitor of the present invention applied to the surface of steel material, especially magnesium carbonate and sodium chloride do not remain on the surface of steel material due to sublimation by heat treatment, so the antioxidant is removed from the surface of steel material. There is no need for time and effort.

  In the present invention, it is desirable to contain magnesium carbonate or sodium chloride or a mixture thereof as an aqueous solution in the oxidation inhibitor so that the oxidation inhibitor can be uniformly and uniformly applied to the surface of the steel material. .

  The oxidation inhibitor of the present invention can further contain a water-soluble compound other than magnesium carbonate or sodium chloride. Such water-soluble compounds include metals such as anhydrous magnesium sulfate, potassium chloride, calcium chloride, magnesium chloride, sodium carbonate, potassium carbonate, calcium carbonate that may or may be contained in salt. Water-soluble polysaccharides such as salts or dextrin, water-soluble cellulose derivatives, water-soluble compounds such as collagen and gelatin made from them, water-soluble organic compounds made from natural raw materials such as water-soluble chitosan, polyvinyl alcohol, Examples thereof include water-soluble synthetic polymer compounds such as polyvinyl pyrrolidone. In particular, when the oxidation inhibitor of the present invention contains a water-soluble organic compound or a water-soluble synthetic polymer compound made from a natural raw material, it can be dissolved in water to give viscosity and adhere to the surface of the steel material. It is suitable for keeping magnesium carbonate and sodium chloride on the steel surface because it is difficult to flow down in the state. In addition, when a water-soluble compound that does not contain nitrogen or sulfur is selected from water-soluble organic compounds or water-soluble synthetic polymer compounds made from natural raw materials, there is an advantage that no bad odor is produced during combustion. Among these water-soluble compounds, dextrin is viscous when dissolved in water, does not contain nitrogen or sulfur, can be obtained at low cost, and does not reduce the scale formation prevention effect of magnesium carbonate or sodium chloride, etc. Therefore, it is suitable for inclusion in the oxidation inhibitor of the present invention.

  According to the oxidation inhibitor of the present invention, it is possible to extremely efficiently suppress the generation of scale on the surface of the steel material so far by applying it to the surface of the steel material and performing heat treatment in a heating furnace or the like. As described above, the scale is less likely to be generated on the surface of the steel material. As a result, damage to the steel material and the tool due to the scale can be prevented, and the yield of the steel material and the quality of the product are improved without causing the skin material to become thin. In particular, since the oxidation inhibitor of the present invention contains at least one of magnesium carbonate and sodium chloride, its working mechanism is not clear, but the steel pipe is heated by various tests conducted by the present inventors. It is proved that the formation of scale on the surface of the steel pipe is extremely effectively suppressed even if it is used for the above, and these compounds do not leave oxidation inhibitor components on the surface of the steel or in the furnace by sublimation by combustion. In view of this, the environmental load is extremely small, the antioxidant does not need to be removed from the steel surface after the heat treatment, and the cost is also excellent.

Schematic which shows the forge processing process of the steel materials performed by apply | coating the oxidation inhibitor which concerns on one Embodiment of this invention. The figure which compares and shows the photograph of the state of the steel material surface when not apply | coating the case where the oxidation inhibitor of the embodiment is apply | coated about the steel material surface after the forging process. The figure which shows the process of the test for measuring the amount of scales produced | generated on the outer surface of a steel pipe. The figure which shows the time-dependent change of the furnace temperature in the same test. The figure which shows the amount of scale production at the time of apply | coating the dextrin aqueous solution contained in the sample used for the test to the steel material surface with a graph. The figure which compares and shows each scale amount obtained as a result of performing the same test about Example 1-3 and Comparative Example 1-6 with a graph. The figure which compares and shows each scale amount obtained as a result of performing the same test about Example 2-7 with a graph. The figure which compares and shows the state of the steel pipe during heating in the furnace in the same test about Example 2-7 with a photograph.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  This embodiment is an oxidation inhibitor applied to a test steel pipe made of steel (carbon steel). As an example, 6.1 g of sodium chloride (equivalent to 7.5 cc) is dissolved in 160 g of an aqueous dextrin solution. . The aqueous dextrin solution is obtained by dissolving 20.8 g of water-soluble dextrin (hereinafter simply referred to as “dextrin”) in 139.2 g of water (13 wt% dextrin aqueous solution). On the other hand, since sodium chloride is commercially available, it contains at least 97% by weight or more of sodium chloride. In addition, anhydrous magnesium sulfate, magnesium chloride, calcium chloride, magnesium carbonate, calcium carbonate, etc. are included as trace components. It is contained at a ratio of 3% by weight or less. However, the details of the composition of these trace components in the salt used in this embodiment are unknown.

  As described above, the main component of sodium chloride is sodium chloride, which is the main component of the oxidation inhibitor in the present embodiment. And dextrin is used in order to raise the adhesion performance of salt (sodium chloride) to the surface of a steel pipe by giving viscosity to an oxidation inhibitor.

  Here, comparing the case where the steel pipe coated with the oxidation inhibitor of the present embodiment is hot-treated and the case where the steel material not coated with the oxidation inhibitor is hot-treated, the presence or absence of scale generation or various The test conducted about the difference in the quality of the steel pipe after the hot treatment due to the difference will be described.

  FIG. 1 is a schematic view showing a hot forging process for the steel pipe 1. As illustrated in the figure, in this hot forging process, the steel pipe 1 having a predetermined size is inserted in a vertical posture with the lower end side supported between a pair of dies 21 and 21 in the hot forging device 2. The upper end side is firmly held by the grips 22 and 22. And hot forging is performed by inserting the punch 23 along the dice | dies 21 and 21 from the lower end part, and pressing it upwards, heating the steel pipe 1. FIG. In this test, when the oxidation inhibitor of this embodiment is applied to the surface of the steel pipe 1, particularly the lower end 1x (in the case of this test, the area of the lower end of the steel pipe having a longitudinal dimension of about 10 m is about 30 cm) and heated. Then, it was examined how a slip mark (grip mark) was generated in a portion held by the grip 22 when heated without applying anything.

  FIG. 2 shows a comparison of photographs of the surface of the steel pipe 1 after hot forging as described above, particularly a portion held by the grip 22. FIG. 2A shows a case where an oxidation inhibitor is not applied to the surface of the steel pipe 1 as usual. In this case, a slip mark 1 a due to the grip 22 is clearly generated intermittently in the circumferential direction on the surface of the steel pipe 1. When the steel pipe 1 is hot-forged, the sliding trace 1a is caused by the generation of an oxide film (scale) at the time of heating at the surface of the lower end 1x of the steel pipe 1 and the tool surface heated by the forging. Because a large forging load acts due to increased frictional resistance due to the intervening scale, the normal gripping force that grips the steel pipe at a part sufficiently away from the end face grips the forging load without being fully supported. This is caused by the occurrence of slippage in the part. On the other hand, FIG. 5B shows a case where the oxidation inhibitor of the present embodiment is applied to the surface of the steel pipe 1. The oxidation inhibitor may be applied to the surface of the steel pipe 1 by brushing or spraying, or may be applied by immersing the corresponding part of the steel pipe 1 in the oxidation inhibitor. In this case, the generation of the slip trace 1a as shown in FIG. This clearly shows that when an oxidation inhibitor is applied to the surface of the lower end 1x of the steel pipe 1, almost no scale is generated.

  Thus, by heat-treating the steel pipe (steel material) surface-coated with the oxidation inhibitor of the present embodiment containing sodium chloride as a main component, the oxide film previously formed on the surface of the steel material is used. Scale can be effectively suppressed. In particular, in this embodiment, since salt is mixed with the dextrin aqueous solution, the salt easily adheres to the steel material surface due to the viscosity of the dextrin, and the effect of suppressing oxidation on the steel material surface can be improved. As described above, the so-called “skinning” of the steel material caused by the scale generation by the heat treatment hardly occurs, and the quality and yield of the steel product can be improved. In addition, the salt, dextrin and water contained in the oxidation inhibitor of the present embodiment hardly remain on the surface of the steel material after the heat treatment by sublimation, evaporation or combustion during the heat treatment of the steel material. Odors and dangerous gases are not generated by heating, so that they harden like conventional oxidation inhibitors and remain on the steel surface, resulting in product quality degradation, tool damage, residue removal, The problem that the physical removal of the scale is necessary does not occur, and it can be used at a low cost and safely in the steel processing site.

  In addition, this invention is not limited to embodiment mentioned above. For example, instead of the oxidation inhibitor of the present embodiment, a saline solution containing no dextrin can be used as the oxidation inhibitor, and sodium chloride (preferably salt powder) not dissolved in water is used as the oxidation inhibitor. Even if it uses, the production | generation suppression effect of a scale can be acquired. Furthermore, the oxidation inhibitor of the present invention is not limited to those containing sodium chloride as a main component, and those containing magnesium carbonate as a main component can be applied, and they can contain other compounds. Various modifications can be made without departing from the spirit of the present invention. Various examples of the oxidation inhibitor according to the present invention will be referred to in the items of the following examples.

  Here, various examples according to the present invention and various comparative examples are applied as samples to the surface of a steel pipe (a carbon steel base pipe, a part of which is cut out from the steel pipe used in the above-described embodiment) and tested. The test conducted about how the scale was generated on the surface of the steel pipe heated in the furnace and then cooled will be described.

  In this test, as shown in FIG. 3 using photographs, (1) various samples are applied to the surface of the steel pipe by brushing, and (2) the steel pipe is set to 35 at a set temperature of 1100 ° C. in a test furnace. (3) Cooling and weighing the steel pipe (weighing 1), then (4) peeling the scale attached to the surface of the steel pipe and weighing the weight of the steel pipe (weighing 2) Is going on. Then, as the weight of the scale {= (Weighing 1) − (Weighing 2)} generated by the weight decrease before and after removal of the scale, the amount of scale generated on the outer surface of the steel material due to the difference in the samples is compared. In addition, the photograph of the steel pipe in the step (2) is a picture of the steel pipe immediately after being taken out from the test furnace. In the steel pipe of this photograph, the part that appears whitish is the surface of the steel material that is red-hot, and the part that appears blackish on the surface of the steel material is the scale. The state of the steel pipe heated in the test furnace in this manner is the same as the state of the end of the steel pipe that is actually heat-forged as in the above-described embodiment (the same applies to the photograph of FIG. 8 described later). Is).

  Here, the used steel pipe has an outer diameter of 88.5 mm, a thickness of 10 mm, a height of 100 mm ± 3 mm, and a weight of 1840 g. Each sample applied to the steel pipe was obtained by collecting 5 g from a compound equivalent to 7.5 cc dissolved in 160 g of a dextrin aqueous solution (13 wt% dextrin aqueous solution). The set temperature in the furnace during the heat treatment is 1100 ° C. (maximum 1100 ° C.), but as shown in FIG. 4, the temperature is temporarily increased by placing the steel pipe in the furnace heated to 1100 ° C. It is falling.

  In addition, about the effect which it has on the scale production | generation suppression by the dextrin contained in a sample, the result investigated beforehand according to the process mentioned above is shown in FIG. That is, the scale amount of the outer surface of the steel material when nothing was applied to the surface of the steel pipe was about 20 g (left side of the bar graph in the figure), whereas only the above dextrin aqueous solution was applied to the surface of the steel pipe. In this case, the scale amount was about 13 g (right side of the bar graph in the figure). From this, even if it is only dextrin aqueous solution, it can be said that it has a certain scale formation inhibitory effect.

Next, the sample used for the test will be described. Each sample is common in that 7.5 cc equivalent amount of the following compound is dissolved in 160 g of dextrin aqueous solution and 5 g of the sample is applied to the surface of the steel pipe as described above. The compounds included in each of the following Examples and Comparative Examples are sodium, magnesium, potassium chlorides or carbonates, and are compounds that may or may be included in sodium chloride.
(Example 1) Salt 6.1g
(Example 2) 6.1 g of sodium chloride
(Example 3) 3.8 g of magnesium carbonate
(Comparative example 1) Sodium carbonate 5.3g
(Comparative example 2) Calcium chloride 4.3g
(Comparative Example 3) Calcium carbonate 2.3 g
(Comparative Example 4) 5.4 g of potassium chloride
(Comparative Example 5) Potassium carbonate 5.1 g
(Comparative Example 6) Magnesium chloride 2.2 g

  These examples and comparative examples were applied as samples to the surface of the steel material, and the amount of scale generated on the outer surface of the steel material by the above-described test process is shown as a graph in FIG. From the figure, it is clear that in the case of Example 1-3, the amount of scale generated is much smaller than that in Comparative Example 1-6. Specifically, the salt dextrin aqueous solution (Example 1) and the sodium chloride dextrin aqueous solution (Example 2) both have a scale generation amount of about 11 g, compared with the case where only the dextrin aqueous solution shown in FIG. 5 is applied. However, in the case of magnesium carbonate dextrin aqueous solution (Example 3), a very good scale formation inhibitory effect of about 4 g was observed. In contrast to these examples, in each comparative example, the amount of scale produced was the same as when only the dextrin aqueous solution was applied, or more scale was produced than when nothing was applied. Since these scales are extremely thick and uniformly formed on the surface, it is considered that when these various salts are used, a chemical reaction that promotes oxidation of the carbon steel surface acts. However, details are unknown. However, it was confirmed that magnesium carbonate, sodium chloride, and sodium chloride containing sodium chloride as a main component have a remarkable scale formation suppressing effect.

Accordingly, Examples 4-7 were prepared by changing the formulation of a mixture of sodium chloride (NaCl) and magnesium carbonate (MgCO ₃ ) in an aqueous dextrin solution. As described above, the scale generation amount was measured and compared. Below, the compounding ratio (weight ratio) of sodium chloride and magnesium carbonate in Example 4-7 is shown by the ratio of the weight of magnesium carbonate with respect to the weight of both mixture. That is, Example 2 is 0% magnesium carbonate (100% sodium chloride), and Example 3 is 100% magnesium carbonate.
(Example 4) Magnesium carbonate 20%
(Example 5) Magnesium carbonate 40%
(Example 6) Magnesium carbonate 60%
(Example 7) Magnesium carbonate 80%

  In FIG. 7, the scale amount produced | generated on the outer surface of a steel pipe after apply | coating the sample of Example 2-7 to a steel pipe and heating is shown as a graph. As is clear from the figure, Example 2 and Example 3 are slightly different from the test results of FIG. 6, but the amount of scale generated on the outer surface of the steel material decreases as the proportion of magnesium carbonate increases. It is recognized that Moreover, in FIG. 8, the photograph which image | photographed the state of the steel pipe immediately after taking out from a test furnace after apply | coating and heating the sample of Example 2-7 is shown side by side. In these photographs, the part that appears whitish is the surface of the steel material that is red hot, and the part that appears partially black on the surface of the steel material is the scale. As can be seen from these photographs, it can be seen that the larger the proportion of magnesium carbonate in the sample, the smaller the amount of scale produced.

  Also from the above results, by applying to the surface of the steel pipe, the oxidation inhibitor of the present invention that can suppress the scale generated after the heat treatment of the steel pipe includes magnesium carbonate, sodium chloride, or these It can be said that it is very effective to contain a mixture.

  Since the present invention can suppress the generation of scale by applying to the surface of the steel material in the heat treatment of the steel material, in the heat treatment process for the steel material such as hot forging of the steel material or manufacturing of a hot tool. It can be used suitably.

1. Steel pipe (steel material)
1x: Lower end 1a ... Slip wound 2 ... Forging device 21 ... Die 22 ... Grip 23 ... Punch

Claims (4)

An oxidation inhibitor applied to the surface of the steel before heat treatment,
An oxidation inhibitor comprising any one of magnesium carbonate, sodium chloride or a mixture thereof. The oxidation inhibitor according to claim 1, wherein the magnesium carbonate or sodium chloride or a mixture thereof is contained as an aqueous solution. The oxidation inhibitor according to claim 1 or 2, further comprising a water-soluble compound other than the magnesium carbonate or sodium chloride. The oxidation inhibitor according to claim 3, wherein the water-soluble compound is dextrin.

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