KR102176332B1 - Steel having excellent high temperature corrosion resistance and creep resistance - Google Patents

Abstract

Disclosed is a steel material excellent in high temperature corrosion resistance and creep resistance. An aspect of the present invention, the steel material having excellent high temperature corrosion resistance and creep resistance is weight %, carbon (C): 0.17 to 0.25%, chromium (Cr): 19 to 22%, nickel (Ni): 31 to 35%, Manganese (Mn): 1.5% or less, silicon (Si): 1.2% or less, 1.5 to 2.5% of the sum of one or two selected from niobium (Nb) and vanadium (V), tungsten (W): 1 to It contains 3%, rare earth (REM): 0.1-0.4%, yttrium (Y): 0.1-0.5%, aluminum (Al): 0.1-0.2%, remaining Fe and inevitable impurities.

Description

Steel having excellent high temperature corrosion resistance and creep resistance {STEEL HAVING EXCELLENT HIGH TEMPERATURE CORROSION RESISTANCE AND CREEP RESISTANCE}

The present invention relates to a steel material used in a rapid cooling section roll used in a region where a steel sheet is rapidly cooled.

In general, the cold rolling process is a process performed to satisfy various conditions such as final thickness, hardness, roughness, shape control, etc. after pickling the hot-rolled material.It belongs to the final stage of the production process of steel products. It is one of the very important processes for determining product quality.

In this cold-rolling process, there is a rapid cooling zone to improve the strength of a cold-rolled steel sheet heated to a high temperature for the purpose of manufacturing a high-strength steel sheet, and the rapid cooling zone is a section in which the cold-rolled steel sheet is rapidly cooled by spraying cooling water from a nozzle. to be. The temperature of the cold-rolled steel sheet introduced into the rapid cooling zone is high, and the cold-rolled steel sheet is rapidly cooled to a moderate temperature in order to secure physical properties such as strength. At this time, the cold-rolled steel sheet is transferred in the rapid cooling zone by means of a rapid cooling section roll, and since these rolls are in continuous contact with the medium-temperature steel sheet, the lower part of the roll is maintained at a constant temperature, but the roll The upper part of the nozzle is subjected to thermal shock due to repeated heating and cooling, such as being rapidly cooled by scattering and falling of coolant periodically sprayed from the nozzle. In addition, these rolls are exposed to a corrosive environment by splashing and dropping cooling water, and also to a creep environment that takes a long load at 400~500℃.

As described above, in consideration of the conditions applied to the rapid cooling zone roll, heat-resistant steel having excellent thermal shock characteristics has been used as a material of the roll in the prior art. For example, in Non-Patent Document 1, C: 0.07 to 0.16% by weight, Cr: 19 to 22%, Ni: 31 to 35%, Nb: 0.6 to 1.6%, Mn: 1.5% or less, Si: 1.2% The following steel types (KHR32C) are disclosed, and these materials have excellent elongation properties against occurrence of cracks due to rapid contraction and expansion.

However, since the heat-resistant steel as described above has excellent elongation, the occurrence of cracks can be minimized, but on the other hand, it has a disadvantage in that its strength is low and deformation is well caused by stress generation due to repeated heat loads.

http://www.kubotametal.com/alloys/heat_resistant/KHR32C.pdf

An aspect of the present invention is to provide a steel material having excellent high temperature corrosion resistance and creep resistance.

One aspect of the present invention is, by weight %, carbon (C): 0.17-0.25%, chromium (Cr): 19-22%, nickel (Ni): 31-35%, manganese (Mn): 1.5% or less, Silicon (Si): 1.2% or less, and 1.5 to 2.5% by the sum of one or two selected from niobium (Nb) and vanadium (V), tungsten (W): 1 to 3%, rare earth (REM): 0.1 Provides a steel material with excellent high temperature corrosion resistance and creep resistance including ~0.4%, yttrium (Y): 0.1 ~ 0.5%, aluminum (Al): 0.1 ~ 0.2%, remaining Fe and inevitable impurities.

The steel material provided by the present invention has excellent high-temperature corrosion resistance and creep resistance, and thus can be preferably applied to a rapid cooling zone roll.

Usually, for the purpose of securing excellent physical properties such as strength of cold rolled steel sheet, a process of rapid cooling is performed in the rapid cooling zone during the cold rolling process. At this time, the rapid cooling zone roll is used to transport the cold rolled steel sheet within the rapid cooling zone. Is installed. In the rapid cooling zone, the heating and cooling of the cold-rolled steel sheet are repeated, and the steel material for manufacturing the rapid cooling zone roll according to these conditions can sufficiently absorb the thermal shock conditions, as well as high-temperature corrosion resistance and creep resistance. Should be.

Conventionally, heat-resistant steel was mainly used as a steel material for rapid cooling zone rolls, and these heat-resistant steels have excellent elongation and thus less cracking, but have a problem in that they are well deformed due to stress generation due to repeated heat loads due to their low strength.

Accordingly, the inventors of the present invention closely studied a solution to the above problem, and as a result, the component composition of the steel material that was used for the manufacture of the existing rapid cooling zone roll includes yttrium (Y), aluminum (Al), etc. It was confirmed that a steel material having excellent crack resistance and deformation resistance as well as high temperature corrosion resistance and creep resistance can be obtained through control of additional components, etc., and the present invention was completed.

Hereinafter, a steel material having excellent high temperature corrosion resistance and creep resistance, which is an aspect of the present invention, will be described in detail.

The steel according to the present invention is in weight%, carbon (C): 0.17 to 0.25%, chromium (Cr): 19 to 22%, nickel (Ni): 31 to 35%, manganese (Mn): 1.5% or less, silicon (Si): 1.2% or less, 1.5 to 2.5% of one or two selected from niobium (Nb) and vanadium (V), tungsten (W): 1 to 3%, rare earth (REM): 0.1 to 0.4% , Yttrium (Y): 0.1-0.5%, aluminum (Al): 0.1-0.2%.

Here, the content of chromium (Cr), nickel (Ni), manganese (Mn) and silicon (Si) in consideration of the cost aspect and strength maintenance aspect maintains the component range of the steel material applied to the existing rapid cooling zone roll ( See Non-Patent Document 1).

In the steel material as an aspect of the present invention, the reason for controlling the components as described above will be described in detail (hereinafter, in weight %).

C: 0.17~0.25%

Carbon (C) is an essential element that affects strength improvement, and if its content is less than 0.17%, the strength improvement effect is insignificant. On the other hand, if the content exceeds 0.25%, the strength increases sufficiently, but rather the elongation decreases and the possibility of cracking increases, and there is a problem that the weldability becomes poor when welding with a roller shaft, which is not preferable.

1.5~2.5% of the sum of one or two of Nb and V

Niobium (Nb) and vanadium (V) are elements that combine with carbon (C) or nitrogen (N) to form carbides or nitrides, and these carbides or nitrides contribute to improving tensile strength, yield strength, and high temperature strength. Therefore, it is necessary to add one or two or more of these elements.

At this time, if the sum of the niobium (Nb) and vanadium (V) content is less than 1.5%, the effect of enhancing the strength due to precipitation strengthening and particle refinement is insignificant, whereas if it exceeds 2.5%, the above-described effect is saturated, but rather the elongation It is not desirable because it can reduce.

W: 1-3%

Tungsten (W), together with the Nb and/or V, is an element that contributes to improving the high-temperature strength, and if the content is less than 1%, the effect of improving the tensile strength at high temperature is insignificant. On the other hand, when the content exceeds 3%, the strength improvement by W is sufficient, but the elongation decreases to increase the risk of cracking, and there is a problem that the weldability is also poor during welding.

REM: 0.1~0.4%

Rare earth (REM) is added to prevent a decrease in elongation due to concern about a decrease in elongation due to the addition of Nb, V, or W, which contributes to the high-temperature strength improvement. For this purpose, it is necessary to add rare earths in an amount of 0.1% or more, but if the content exceeds 0.4%, there is a concern that the strength increases excessively. The rare earth metals include La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.

In the present invention, commercially available rare earth metals may be used, wherein the composition of the rare earth metal is based on the total weight% of the rare earth, cerium (Ce): 48 to 54%, neodymium (Nd): 13 to 17%, lanthanum (La ): 24 to 28% and praseodymium (Pr): 13 to 17%.

In the present invention, it is preferable to contain the sum of the total content of the rare earth metals in the range of 0.1 to 0.4%.

Y: 0.1~0.5%

Yttrium (Y) is an element that aims to improve strength without lowering the elongation due to the refining effect of metal grains.If the content of Y is less than 0.1%, it is difficult to obtain the effect of the addition of Y as described above. If the amount exceeds 0.5%, the elongation and strength are rather lowered, and there is a very disadvantageous problem in terms of cost.

Al: 0.1~0.2%

Aluminum (Al) is an element that aims to improve corrosion resistance and creep resistance at high temperatures.If the content of Al is less than 0.1%, it is difficult to obtain the effect of the addition of Al, whereas if the content exceeds 0.2%, it is difficult to obtain high temperature. Corrosion resistance is excellent, but there is a problem that the elongation sharply decreases and creep resistance decreases.

The rest is composed of Fe and unavoidable impurities.

A steel material that satisfies the above-described component composition has not only excellent crack resistance and deformation resistance, but also excellent high temperature corrosion resistance and creep resistance.

Hereinafter, the present invention will be described in more detail through examples. However, it should be noted that the following examples are for illustrative purposes only and are not intended to limit the scope of the present invention. This is because the scope of the present invention is determined by matters described in the claims and matters reasonably inferred therefrom.

( Example )

Scrap iron and various alloying elements were melted in an air furnace to melt and cast a steel material having a component composition as shown in Table 1 below, and the injection temperature was set at 1550°C during casting to prepare a final metal cooling zone roll.

For each of the prepared rapid cooling zone rolls, a test piece having a width of 50 mm x a length of 50 mm x a thickness of 10 mm was prepared, and then a high temperature corrosion test and a creep test were performed, and the results are shown in Table 1 below.

In the high-temperature corrosion test, after exposure to a heat treatment furnace in an atmospheric atmosphere at 500° C. for 300 hours, the oxide thickness on the surface of the test piece was measured. When the thickness of the oxide scale is less than 20 μm, it is excellent (○), and the thickness of the oxide scale is 20 In the case of ~200㎛, it was classified as normal (△), and if the thickness of the oxide scale exceeded 200㎛, it was classified as defective (X).

The creep test measured the breaking time when a stress of 270 MPa was applied at 500°C. When the breaking time exceeded 130 hours, it was excellent (○), and when the breaking time was 100 to 130 hours, it was normal (△), and the breaking time was If it is less than 100 hours, it is classified as defective (X).

division C Cr Ni Mn Si Nb V W REM Y Al High temperature corrosion resistance Creep
characteristic Invention Example 1 0.2 20 33 One 0.8 One 0.5 1.5 0.2 0.1 0.1 ○ ○ Invention Example 2 0.2 20 33 One 0.8 One 0.5 1.5 0.2 0.1 0.15 ○ ○ Invention Example 3 0.2 20 33 One 0.8 One 0.5 1.5 0.2 0.1 0.2 ○ ○ Comparative Example 1 0.2 20 33 One 0.8 One 0.5 1.5 0.2 0.1 - × x Comparative Example 2 0.2 20 33 One 0.8 One 0.5 1.5 0.2 0.1 0.05 △ △ Comparative Example 3 0.2 20 33 One 0.8 One 0.5 1.5 0.2 0.1 0.21 ○ △ Comparative Example 4 0.2 20 33 One 0.8 One 0.5 1.5 0.2 0.8 0.24 ○ △ Comparative Example 5 0.2 20 33 One 0.8 One 0.5 1.5 0.2 0.9 0.3 ○ ×

As shown in Table 1, the rapid cooling zone rolls of Inventive Examples 1 to 3, which satisfy all the component conditions proposed in the present invention, have excellent high-temperature corrosion resistance and creep resistance.

On the other hand, Comparative Examples 1 to 5 did not satisfy the alloy composition proposed by the present invention, and thus showed inferior high temperature corrosion resistance and/or creep characteristics.

Claims (2)

In% by weight, carbon (C): 0.17 to 0.25%, chromium (Cr): 19 to 22%, nickel (Ni): 31 to 35%, manganese (Mn): 1.5% or less, silicon (Si): 1.2% Below, 1.5 to 2.5% of one or two selected from niobium (Nb) and vanadium (V), tungsten (W): 1 to 3%, rare earth (REM): 0.1 to 0.4%, yttrium (Y ): 0.1~0.5%, Aluminum (Al): 0.1~0.2%, Steel material with excellent high temperature corrosion resistance and creep resistance containing the remaining Fe and inevitable impurities.
The method of claim 1,
The rare earth (REM) is based on the total weight% of the rare earth, cerium (Ce): 48 to 50%, neodymium (Nd): 13 to 15%, lanthanum (La): 24 to 26% and praseodymium (Pr): 13 to Steel material with excellent high temperature corrosion resistance and creep resistance, including 15%.