JP2017179404A - Manufacturing method of cast steel article - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a cast steel article capable of manufacturing the cast steel article excellent in heat impact resistance by reducing inclusions.SOLUTION: The manufacturing method of a cast steel article includes flowing Ar gas in a high frequency induction furnace to obtain a molten metal of the cast steel article while stirring and conducting a vacuum degasification treatment on the resulting molten metal at 100 Torr or less for 10 min. to 30 min. while stirring the same with Ar gas. A flow rate of the Ar gas while the vacuum degasification treatment is preferably 0.1 L/min. to 1.0 L/min. The cast steel article obtained by the manufacturing method has inclusion amount of less than 0.1%.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a method for producing a cast steel product having excellent thermal shock characteristics.

  In many cases, the molten metal necessary for the production of a cast product contains non-metallic inclusions such as hydrogen gas and oxides. For example, when a large amount of hydrogen gas is present in the molten metal, defects such as gas porosity are generated in the cast product, and inclusions in the cast product become inclusions in the cast product.

  Both of these defects and inclusions are the starting point for the destruction of the cast product, which greatly impairs the thermal shock resistance of the material, and is the main cause of weld cracking during welding of product assembly. . Moreover, in a use environment with repeated temperature fluctuations, it becomes a cause of short life due to the same reason.

  For this reason, it is not preferable in terms of product quality that a casting product contains a lot of hydrogen gas and non-metallic inclusions, and a method for preventing deterioration of product quality is required.

  For example, Patent Document 1 introduces an inert gas such as Ar into a molten metal in a holding furnace installed in a vacuum in order to remove non-metallic inclusions such as hydrogen gas and oxides in the molten metal. A VOD (vacuum oxygen decarburization) method is disclosed in which hydrogen and nonmetallic inclusions in a molten metal are adsorbed and removed by an inert gas finely dispersed by stirring.

  However, the method disclosed in Patent Document 1 aims to promote the reduction of inclusions while adjusting the concentration of nitrogen with high accuracy. Therefore, reflux with nitrogen gas is an essential condition.

JP2013-224461A

  This invention is proposed in view of such a situation, and it aims at providing the method of reducing the amount of inclusions and manufacturing the cast steel goods excellent in the thermal shock resistance characteristic.

  As a result of intensive studies, the present inventor maintained a predetermined condition of the molten molten steel cast while flowing Ar gas and stirring it, and performing vacuum degassing while stirring with Ar gas. The present inventors have found that the above-described problems can be solved and have completed the present invention.

  (1) According to the first aspect of the present invention, a molten molten cast steel product is obtained while flowing Ar gas in a high-frequency induction furnace while stirring, and the obtained molten metal is 10 to 30 minutes at 100 Torr or less. This is a method for producing a cast steel product having thermal shock resistance, which is held for a minute and subjected to vacuum degassing while being stirred with Ar gas.

  (2) The second invention of the present invention is the cast steel having the thermal shock characteristics according to the first invention, wherein the molten metal is stirred using Ar gas having a flow rate of 0.1 L / min to 1.0 L / min. Product manufacturing method.

  (3) The third invention of the present invention is a method for producing a cast steel product having thermal shock resistance characteristics, in which nitrogen gas is not blown in the first or second invention.

  (4) According to a fourth aspect of the present invention, in any one of the first to third aspects, the amount of inclusions contained in the cast steel product is less than 0.1%. It is a manufacturing method.

  (5) According to a fifth aspect of the present invention, in any one of the first to fourth aspects, the cast steel product includes C: 0.20 wt% to 0.50 wt%, Si: ≤ 2.00 wt%, Mn : ≦ 2.00 wt%, P: ≦ 0.040 wt%, S: ≦ 0.040 wt%, Ni: 11.00 wt% to 28.00 wt%, Cr: 23.00 wt% to 37.00 wt%, the balance Is made of Fe and inevitable impurities, and when Ni is 33.00 wt% or more, W: 1.00 wt% to 6.00 wt, Co: 2.00 wt% to 17.00 wt%, A method for producing a cast steel product having thermal shock resistance.

  (5) According to a fifth aspect of the present invention, in any one of the first to fourth aspects, the cast steel product includes C: 0.15 wt% to 0.40 wt%, Si: ≤ 0.50 wt%, Mn : ≦ 1.00 wt%, P: ≦ 0.040 wt%, S: ≦ 0.040 wt%, Fe: ≦ 10.00 wt%, Cr: 32.00 wt% to 36.00 wt%, W: 4.00 wt% ~ This is a method for producing a cast steel product having a thermal shock characteristic, containing 17.00 wt%, with the balance being Ni and inevitable impurities.

  According to the present invention, the amount of inclusions can be effectively reduced, and a cast steel product having excellent thermal shock characteristics can be manufactured.

It is a figure which shows the shape of the test piece used for a thermal shock test. It is each microscope observation image of the sample obtained by the Example and the comparative example. It is a graph which shows the result of the thermal shock test of Example 1 and Comparative Example 1. It is a graph which shows the result of the thermal shock test of Example 2 and Comparative Example 2. It is a graph which shows the result of the thermal shock test of Example 3 and Comparative Example 3.

  Hereinafter, a specific embodiment of the present invention (hereinafter referred to as “the present embodiment”) will be described in detail. In addition, this invention is not limited to the following embodiment, A various change is possible in the range which does not change the summary of this invention.

  The method for producing a cast steel product according to the present embodiment is a method for producing a cast steel product having thermal shock characteristics. Specifically, in this manufacturing method, first, Ar gas is blown in a high-frequency induction furnace and melted while stirring to obtain a molten steel product. And the vacuum degassing process is given with respect to the obtained molten metal by stirring for 10 to 30 minutes using Ar gas at 100 Torr or less.

  The vacuum degassing process can be performed using, for example, a known vacuum degassing apparatus. For example, the vacuum degassing apparatus is not particularly limited, and includes a ladle in which the molten metal is charged and a vacuum tank for removing gas components and oxides in the molten metal charged in the ladle as a vacuum state. Prepare. In addition, a blow-in port for blowing Ar gas, which is an inert gas, is provided in the lower part of the vacuum tank, and an exhaust port for exhausting the gas in the vacuum tank is provided in the upper part of the vacuum tank.

  The molten metal charged into the vacuum degassing apparatus can be obtained by melting a metal material weighed so as to be a cast steel product having a desired composition using a high frequency dielectric furnace. At this time, the melting is performed while sufficiently stirring the metal material charged in the dielectric furnace by blowing Ar gas, which is an inert gas. As described above, even when the metal material is melted to form a molten metal, the gas component such as hydrogen gas and the oxide component contained in the molten metal are more effectively removed by blowing and stirring Ar gas. can do.

  The high frequency dielectric furnace is not particularly limited, and a known one can be used.

  Next, vacuum degassing treatment is performed on the molten cast steel product obtained by melting. This vacuum degassing treatment is performed by evacuating to 100 Torr or less and holding the molten metal for 10 to 30 minutes while stirring the Ar gas.

  In addition, a high frequency dielectric furnace that is a melting furnace and a vacuum degassing treatment device are prepared, and after obtaining molten metal in the melting furnace, the molten metal is charged into a ladle of the vacuum degassing treatment device, Although vacuum degassing treatment can be performed, a vacuum degassing treatment device is provided in the melting furnace, and after melting and obtaining molten metal, the vacuum degassing treatment is performed as it is (without transferring to a ladle or the like). You may make it perform. Thus, an efficient operation becomes possible by providing the melting furnace with a vacuum degassing apparatus and performing the vacuum degassing process on the obtained molten metal as it is. Moreover, mixing of the gas component and oxide at the time of making it transfer to a ladle can also be prevented, and the cast steel article which reduced the amount of inclusions more effectively can be obtained.

  In the vacuum degassing process, the vacuum chamber is maintained at a vacuum degree of 100 Torr or less. Further, it is preferably 50 Torr or less, more preferably 30 Torr or less. Thus, inclusions can be effectively removed by maintaining the degree of vacuum at 100 Torr or less. Specifically, in the vacuum degassing process, for example, the gas in the vacuum chamber is exhausted from an exhaust port provided in the upper portion of the vacuum chamber, and the inside thereof is brought into a substantially vacuum state.

  The holding time in the vacuum state is 10 minutes to 30 minutes. Inclusions can be effectively removed by performing vacuum degassing while maintaining the degree of vacuum at 100 Torr or less for such a holding time.

  Further, in the vacuum degassing process, Ar gas is blown through a blowing port provided in the lower part of the vacuum chamber so that Ar gas is circulated in the molten metal, thereby stirring the molten metal. In this way, during vacuuming, gas components such as hydrogen gas and oxide components contained in the molten metal can be effectively removed by performing vacuum degassing while blowing Ar gas and stirring. .

  The flow rate of Ar gas is not particularly limited, but is preferably about 0.1 L / min to 10 L / min, more preferably about 0.3 L / min to 5.0 L / min, and 0.5 L / Min to about 1.0 L / min is particularly preferable. If the flow rate of Ar gas is less than 0.1 L / min, the molten metal cannot be sufficiently stirred, and gas components, oxides, and the like in the molten metal may not be removed. On the other hand, if the flow rate of Ar gas is higher than 10 L / min, the effect of removing gas components, oxides, etc. will not be enhanced further, and the life of the apparatus will be damaged by spraying from the molten metal and damaging the furnace body. May shorten and increase costs.

Here, in this method for producing a cast steel product, N ₂ (nitrogen) gas is not blown into the molten metal (not refluxed). In the vacuum degassing process, for example, when N ₂ gas is blown together with Ar gas or instead of Ar gas, it is considered that the stirring ability of the molten metal is increased, but the molten metal contains a nitrogen component. Affects the composition of cast steel products.

  In the present embodiment, specifically, C: 0.20 wt% to 0.50 wt%, Si: ≦ 2.00 wt%, Mn: ≦ 2.00 wt%, P: ≦ 0.040 wt%, S: ≦ 0.040 wt%, Ni: 11.00 wt% to 28.00 wt%, Cr: 23.00 wt% to 37.00 wt%, with the balance being Fe and inevitable impurities, and Ni: 33.00 wt% or more , A cast steel product having heat resistance containing W: 1.00 wt% to 6.00 wt% and Co: 2.00 wt% to 17.00 wt% is manufactured.

  Other composition examples include C: 0.15 wt% to 0.40 wt%, Si: ≦ 0.50 wt%, Mn: ≦ 1.00 wt%, P: ≦ 0.040 wt%, S: ≦ 0. Manufacture of cast steel products containing 040 wt%, Fe: ≦ 10.00 wt%, Cr: 32.00 wt% to 36.00 wt%, W: 4.00 wt% to 17.00 wt%, with the balance being Ni and inevitable impurities can do.

  In the manufacturing method according to the present embodiment, a molten cast steel product melted while flowing Ar gas in a high-frequency induction furnace and being stirred is held for 10 to 30 minutes while stirring with Ar gas at 100 Torr or less. Then, by performing the vacuum degassing treatment, for example, a cast steel product having the above-described composition and effectively reducing the amount of inclusions can be obtained. And since there are few inclusions in a cast steel product, there are few starting points of destruction, Therefore It becomes a cast steel product which has impact resistance and heat resistance.

  Specifically, in the cast steel product obtained by this manufacturing method, the amount of inclusions is less than 0.1%. The amount of inclusions can be measured from the area of inclusions obtained from a microscope observation image based on, for example, “Microscopic test method for nonmetallic inclusions in steel” defined in JIS G 0555.

  Moreover, as mentioned above, the cast steel product obtained by this manufacturing method has heat resistance. “Heat resistance” refers to the property of maintaining the impact resistance even in a use environment with repeated temperature fluctuations, thereby extending the life of the cast steel product. In addition, the characteristic of this cast steel product is also called a thermal shock characteristic.

This thermal shock characteristic can be carried out, for example, by the thermal shock test shown below. “Thermal shock” means that a concentration gradient is generated in an integral structure (for example, a cast steel product), and a large thermal stress is generated accordingly.
[Thermal shock test]
Using an eccentric ring as shown in FIG. 1 as a test piece, a heating cycle of heating × 20 minutes → water cooling × 15 seconds and a rapid cooling thermal cycle test are carried out, and the occurrence of cracks in the subsequent test piece is confirmed. The heating temperature in the heat cycle test can be appropriately set according to the intended use temperature of the cast steel product.

  EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples.

[Example]
Three metal materials of “SCH13” and “SCH22” of JIS standards and “NA22H” manufactured by BLAW-KNOX, USA were used. In the embodiment, a molten metal melted with Ar gas blown and stirred in a high-frequency induction furnace was held at 100 Torr or less for 10 minutes while stirring with Ar gas, and the flow rate was 0.5 L / min. The Ar gas adjusted to was blown into the molten metal and stirred to perform vacuum degassing.

  The sample was cast in a sand mold so as to have an as-cast dimension of 30 mm in diameter and 300 mm in length to obtain a cast steel product.

[Comparative example]
In the comparative example, three metal materials of “SCH13”, “SCH22”, and “NA22H” were melted, and the obtained molten metal was cast without performing vacuum degassing treatment.

  In the same manner as in Example 1, the sample was cast in a sand mold so as to have an as-cast dimension of 30 mm in diameter and 300 mm in length to obtain a cast steel product.

  Table 1 below shows the results of component analysis of the cast steel products obtained in the examples and comparative examples.

[Evaluation]
(Measurement of inclusion amount)
Based on the samples obtained in Examples 1 to 3 and Comparative Examples 1 to 3, the amount of inclusions was measured. Table 2 below summarizes the measurement results. The amount of inclusions was determined based on “Microscopic test method for nonmetallic inclusions in steel” defined in JIS G 0555. FIG. 2 is a microscopic observation image of each sample obtained in Examples and Comparative Examples.

  As shown in Table 2, in any material, the amount of inclusions in the example was reduced by 50% or more than the amount of inclusions in the comparative example.

(Thermal shock test)
The thermal shock test was done about the sample obtained in Examples 1-3 and Comparative Examples 1-3. In the thermal shock test, a test piece (eccentric ring) having the shape shown in FIG. 1 is prepared using the obtained sample, and heating and cooling are performed in the condition cycle shown in Table 3 below to generate internal thermal stress. The occurrence was observed.

  Table 4 below shows the results of the number of cracks generated with respect to the number of cycles of Example 1 and Comparative Example 1 (SCH13), and Table 5 below shows the occurrence of cracks with respect to the number of cycles of Example 2 and Comparative Example 2 (SCH22). Table 6 below shows the number of cracks generated with respect to the number of cycles of Example 3 and Comparative Example 3 (NA22H). 3 to 5 are graphs of the results shown in Tables 4 to 6.

  As shown in Tables 4 to 6 and FIGS. 3 to 5, in any of the materials, the number of cycles in which cracks occurred was large in the samples of the examples. Therefore, as in the example, the amount of inclusions is effectively increased by performing vacuum degassing treatment under predetermined conditions using a molten metal melted while flowing Ar gas in a high-frequency induction furnace while stirring. It was found that a cast steel product having excellent thermal shock resistance can be obtained.

Claims (6)

A molten molten cast steel product was obtained while flowing Ar gas in a high-frequency induction furnace and stirring. The obtained molten metal was held at 100 Torr or less for 10 to 30 minutes, and vacuum degassing while stirring with Ar gas. A method for producing a cast steel product having a thermal shock resistance with gas treatment. The method for producing a cast steel product having thermal shock resistance according to claim 1, wherein the molten metal is stirred using Ar gas having a flow rate of 0.1 L / min to 10 L / min. The method for producing a cast steel product having thermal shock resistance according to claim 1 or 2, wherein nitrogen gas is not blown. The method for producing a cast steel product having thermal shock characteristics according to any one of claims 1 to 3, wherein the amount of inclusions contained in the cast steel product is less than 0.1%. The cast steel product is
C: 0.20 wt% to 0.50 wt%, Si: ≦ 2.00 wt%, Mn: ≦ 2.00 wt%, P: ≦ 0.040 wt%, S: ≦ 0.040 wt%, Ni: 11.00 wt% -28.00 wt%, Cr: 23.00 wt%-37.00 wt% contained, the balance consisting of Fe and inevitable impurities,
Furthermore, when Ni is 33.00 wt% or more, W: 1.00 wt% to 6.00 wt, Co: 2.00 wt% to 17.00 wt% is contained. A method for producing a cast steel product having the thermal shock characteristics described in the paragraph. The cast steel product is
C: 0.15 wt% to 0.40 wt%, Si: ≦ 0.50 wt%, Mn: ≦ 1.00 wt%, P: ≦ 0.040 wt%, S: ≦ 0.040 wt%, Fe: ≦ 10.00 wt% %, Cr: 32.00 wt% to 36.00 wt%, W: 4.00 wt% to 17.00 wt%, with the balance being made of Ni and inevitable impurities. A method for producing a cast steel product having thermal shock resistance.