KR100821329B1 - Carburizing alloy steel excellent in high-temperature strength - Google Patents

Abstract

A carburizing alloy steel is provided to improve strength and erosion-resistant characteristics of the carburizing alloy steel under the high temperature condition while reducing the content of nickel. A carburizing alloy steel comprises 0.2 to 04 weight percent of carbon, 2.0 or less weight percent of silicon, 2.0 or less weight percent of manganese, 0.04 or less weight percent of phosphorus, 0.04 or less weight percent of sulfur, 23 to 29 weight percent of chrome, 5 to 8 weight percent of nickel, 0.1 to 5.0 weight percent of niobium, remainder of Fe, and inevitable impurities. The carburizing alloy steel has creep rupture strength of 50N/mm2 or above. The carburizing alloy steel further comprises 0.05 to 0.1 weight percent of Rem.

Description

Carburizing alloy steel excellent in high-temperature strength

The present invention relates to a carburizing heat-resistant alloy steel with excellent high temperature durability. Specifically, the composition of the Jig & Tray alloy, which is currently manufactured by SCH13 using sand casting method, is improved to improve high temperature strength, oxidation resistance, and lifespan. It is about super heat resistant alloy.

In order to go through the carburizing process for various industrial parts such as automobile parts, carburizing fixtures (Jig) or trays are used to fix and move these parts in the carburizing furnace. Because of the environment, these carburizing fixtures (Jig) or trays (Tray) require considerable durability. For this reason, there are certain standards for the composition of the alloys used for industrial fixtures and trays.

For example, 13 SCH and 21 SCH are commonly used for carburizing as a material standard of JIS, which is a Japanese industrial standard. The composition table for these alloy steels is shown in Table 1 below.

[Reference Table 1]

In fact, in the industry, a jig and a tray of a carburizing heat treatment furnace have been manufactured by sand casting using the SCH13 alloy described above. As can be seen in Table 1 above, chromium (Cr) and nickel (Ni) are the main components of the alloy steel mainly used in the heat treatment furnace for carburizing process. As a result, production cost reduction is a hot topic in appliances and components made of various metals.

Cr, Ni and Nb mainly used for the SCH13 species in November 2007 the present application price is shown in Table 2 below. However, Cr is injected into the state of "Fe-Cr" when casting in an electric furnace, "Fe-Cr" means that iron and chromium are present in the metal together.

[Reference Table 2]

Therefore, there is a need for the development of alloy steel that can reduce the added amount of expensive Ni while maximizing the strength of the existing SCH 13 alloy steel under a high temperature of 900 ° C. or higher.

As to solve the above problems,

An object of the present invention is to provide a high-strength alloy to improve the high temperature strength and high temperature oxidation resistance while reducing the content of Ni compared to 13 SCH.

In order to achieve the above technical problem,

Carburizing alloy steel excellent in high temperature durability according to the present invention,

In weight percent,

C: 0.2 to 0.4%,

Si: 2.0% or less,

Mn: 2.0% or less,

P: 0.04% or less,

S: 0.04% or less,

Cr: 23 to 29%,

Ni: 5-9%, including below,

The balance consists of Fe and unavoidable impurities.

In addition, the carburizing alloy steel having excellent high temperature durability according to the present invention may further include Nb: 0.1 to 0.5% and a small amount of rare earth metal.

From the structural features of the present invention described above,

The present invention improves the high temperature strength and high temperature oxidation resistance by reducing the Ni component and suggesting an alloy containing Cr as a main component in manufacturing heat-resistant materials such as jigs and trays used in heating furnaces and incinerators.

In addition, the present invention provides a small amount of Nb and Nb and rare earth metals that can actively add cheaper Cr and selectively add more expensive but lesser strength while satisfying the high temperature strength and high temperature oxidation resistance required for such materials. The cost can be reduced by the addition.

Hereinafter will be described the specific content for the practice of the invention. 'SCH' used below is a term used when naming alloy steel standardized in the Japanese JIS standard.

The point of the component phase of the heat-resistant alloy steel according to the present invention is to actively add Cr to secure the base material strength under the lowest Ni content, and to add a small amount of Nb and Nb and rare earth metals for further strength improvement.

Hereinafter, the reason for component limitation of the carburizing alloy steel of this invention is demonstrated. All units are weight percent.

C: 0.2 to 0.4%

Carbon is an element that plays an important role in improving the strength of steel as a reinforcing alloy element of Fe. It is mainly present as carbide, which is a small hard particle in the alloy, which combines with elements such as Cr, Mo, W, and Nb to form carbides. And improves hardness. It is preferable to contain C or more than 0.2% in order to obtain the strength required for use in carburizing jigs or trays. However, as the carbon component increases, the strength increases, but the carbon component serves to reduce toughness and oxidation / corrosion resistance, and in particular, when it is added more than 0.5%, the oxidation resistance and corrosion resistance greatly decreases, and therefore, it is preferable to limit the concentration to within 0.5%.

Si: 2.0% or less

Si improves carbonization and oxidation resistance, increases resistance to nitrogen absorption at high temperatures, and resistance to hot cracking. Also added to improve the flowability of all cast heat-resistant alloys. As long as it does not form a compound such as SiO ₂ , it does not have a great influence on the mechanical properties, but it is preferable to limit the addition amount to within 2% since the toughness and plastic working characteristics are lowered when the addition exceeds 2%.

Mn: 2.0% or less

Some of the Mn is employed in the river, and some combines with S to form MnS, which reduces the amount of S in the river, thereby reducing the weaker FeS. Although it improves the workability at high temperature, it is limited to within 2% because it inhibits acid resistance and oxidation resistance.

P and S: 0.04% or less

S and P are very fragile and form a low melting point FeS and Fe3P to reduce the strength and impact reduction, so it needs to be adjusted to 0.04 or less.

Cr: 23 to 29%

Cr increases the austenite region when added more than 13% and forms a carbide which is inexpensive and does not cause brittleness even if a large amount is added, thereby greatly improving the strength, and also serves to improve oxidation resistance and emulsion resistance. In addition, in the present invention, there is one purpose to actively increase the amount of Cr added instead of minimizing the content of Ni, so that the minimum amount of Cr added to minimize the effect of reduced Ni was 23%.

On the other hand, if the amount of Cr added is very sigma phase is formed at high temperature it is preferable to control within 29% increase.

Ni: less than 5 to 8%

Ni plays a role in reinforcing the base because the structure of the steel is refined and well-used in austenite and ferrite. And addition to the mixture of iron and chromium increases the ductility and high temperature strength, thereby increasing the resistance to carbonization and nitriding. However, the minimum content should be more than 5% in order to improve the properties through the addition of other elements within the range that does not cause deterioration in order to reduce the cost of Ni raw materials.

Nb: less than 0.1 to 0.5%

 If it is less than 0.1%, the effect of Nb addition is not obtained, and when 0.1% or more is added, the strength and oxidation resistance increase as the amount of Nb added increases. However, even if the addition of more than 0.5% Nb does not have a significant difference as much as the addition amount, rather if the addition amount is large, the oxidation resistance and weldability is reduced, so the addition amount of Nb is adjusted to contribute to the characteristics improvement by adding around 0.5%.

Rem: 0.05 to 0.1%

 Rare Earth Elements (REM) is a generic term for rare earth metals and refers to alloys of single or two or more lanthanides such as cerium (Ce), lanthanum (La), and yttrium (Y). These rare earth metals are thinner, harder, and more protective than Cr to form oxide films, which improve oxidation resistance and contribute to creep fracture strength. In addition, by increasing the reaction speed also plays a role in contributing to the formation of more microstructure. In order to improve the oxidation resistance and reinforcing effect, it was adjusted to contribute to the improvement of the characteristic at 0.05-0.1%.

<Experimental data>

First of all, for the sake of understanding, the heat-resistant alloy steel according to the present invention is named 'SCF13 series', and the base alloy is 'SCF13S', and the alloy steel in which Nb is added to the base alloy is 'SCF13N', and Nb and rare earth elements are added to the base alloy. The added alloy steel is called "SCF13NR".

The physical properties were measured while adjusting the respective component ratios of the improved heat resistant alloy steel according to the present invention. The measuring method is to measure the Tensile Strength, Yield Strength, and Elongation by applying a continuous load to the specimen at high temperature. Was measured.

The creep rupture strength of SCF13S was as shown in [Table 3] below.

[Reference Table 3]: Creep fracture strength according to the components of the invention alloy steel SCF13S

  As can be seen from the above table, in the case of SCF13S, the invention alloy steel, the breaking strength cannot be used significantly lower than that of the existing SCH13 in the Ni content of 4%, and the breaking strength is superior to the existing SCH13 at 5% or more. However, in the Ni content of 8%, the breaking strength did not show any difference even if the Ni content was increased.

Subsequently, the creep rupture strength of SCF13N was shown in [Table 4].

[Table 4]: Creep fracture strength according to the components of the invention alloy steel SCF13N

 The above table shows a significant increase in breaking strength when a small amount of Nb is added.

In addition, creep rupture strength according to the components of the SCF13NR was measured as shown in [Table 5].

[Table 5]: Creep breaking strength according to the components of the invention alloy steel SCF13NR

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The above table shows that the breaking strength of SCF13NR added with a small amount of rare earth element (0.05 or 01%) was significantly increased compared to SCF13N.

In conclusion, the heat-resistant alloy steel according to the present invention can obtain excellent breaking strength even by reducing the Ni content compared to the existing SCH13 species, and proves that the breaking strength can be further improved by adding a small amount of Nb and rare earth elements.

Hereinafter, the measured physical properties of the present invention and the physical properties of SCH13 were compared to prepare a table.

As described above, the alloy steel according to the present invention has tensile strength (tensile strength) and yield strength (yield strength) under the same conditions of 930 degrees Celsius or less (carburizing furnace temperature condition of automotive parts), even though less Ni is added. ), Elongation and Creep Rupture were found to be higher.

Although the preferred embodiments of the present invention have been described above, the technical spirit of the present invention is not limited to the above-described preferred embodiments, and various high temperature durability is excellent in a range without departing from the technical spirit of the present invention specified in the claims. It may be implemented as an alloy steel for carburization.

Claims (3)

In weight percent, C: 0.2 to 0.4%, Si: 2.0% or less, Mn: 2.0% or less, P: 0.04% or less, S: 0.04% or less, Cr: 23 to 29%, Ni: less than 5-8%, Nb: from 0.1 to less than 0.5%, The balance consists of Fe and unavoidable impurities, Carburized alloy steel with excellent high temperature durability with creep rupture strength of 50 N / mm2 or more. delete The method of claim 1, Rem: Carburizing alloy steel having excellent high temperature durability, further comprising 0.05 to 0.1%.