JPS597345B2 - High-strength alloy steel with excellent high-temperature corrosion resistance and high-temperature oxidation resistance - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an alloy steel that exhibits excellent corrosion resistance and oxidation resistance in high-temperature corrosive or oxidizing atmospheres, and has significantly high high-temperature strength.

Conventionally, for example, in the production of skid rails for steelmaking heating furnaces that use heavy oil as fuel, boiler devices, and other parts that require particularly high heat resistance, for example,
(a) 25% Cr-20% Ni-Fe alloy, (b) 30
%Cr-22%Ni-Fe alloy, (c) 28%Cr-F
Alloys such as e alloy, (d) 50% Cr-50% Ni alloy, and (e) 27% Cr-20% Fe-Co alloy are used.

In this case, skid rails and boiler diffusers made of conventional alloys are exposed to high-temperature corrosion or high-temperature oxidation atmospheres that contain compounds generated by oxidation of components such as V and S contained in heavy oil during combustion. Become. Although all of these conventional alloys exhibit relatively good corrosion resistance and oxidation resistance under the above-mentioned severe usage conditions, they still do not have satisfactory properties, and they also do not have the above-mentioned (a)--
The Fe-based alloy shown in (C) does not have sufficient high temperature strength, and the N
I-based and Co-based alloys have higher high-temperature strength than the Fe-based alloys, but their high content of expensive alloying elements makes them unavoidable, and therefore their range of use is limited. There are problems such as being limited and lacking in practicality. From the above-mentioned viewpoints, the present inventor has made it possible to obtain an alloy steel that has higher high-temperature strength and also has better high-temperature corrosion resistance and high-temperature oxidation resistance at a lower cost.
As a result of research, the composition of alloy steel was determined by weight percent.
C: 0.01-006%, Si: 0.1-3%, Mn 0.05-2%, Cr: 28-38%, Co2 105-7%, Ni: 21-32%, Ti: 0.01 to 2%, N: 0.01 to 095%, Mo: 1 to 5%, Fe and unavoidable impurities: the remainder, this alloy steel has extremely high high temperature strength and can withstand harsh high temperatures. They found that it exhibits excellent corrosion resistance and oxidation resistance in corrosive and high-temperature oxidation atmospheres.

This invention was made based on the above knowledge, and the reason why the component composition range was limited as described above will be explained below.

(a) C The C component includes Cr, T, which forms a solid solution in the matrix at high temperatures, and
i, and MO etc. to form MC type, M23C6 type,
It has the effect of forming carbides such as M7C3 type, strengthening the grains and grain boundaries, and improving mechanical properties at high temperatures as well as weldability and castability. If the content is less than 0.01%, the desired effect cannot be obtained; on the other hand, if the content exceeds 0.6%, carbide precipitation will be excessive and high temperature toughness will deteriorate, as well as acid resistance. The content was determined to be 0.01 to 0.6% since the chemical properties of the elements also deteriorated.

(b) Si The Si component, along with Cr, has the effect of improving oxidation resistance at high temperatures, and further improves the fluidity of the molten metal to improve castability, as well as having a deoxidizing effect. If the content is less than 0.1%, the desired effect cannot be obtained, while if the content exceeds 3%, the toughness and weldability may decrease in relation to the Cr content. Therefore, its content was determined to be 0.1 to 3%.

(c) Mn The Mn component has the effect of stabilizing the austenite matrix by forming a solid solution with Ni, and also has a deoxidizing effect, but if its content is less than 0.05%, it may not be as desired. However, if the content exceeds 2%, the high temperature oxidation resistance and toughness will decrease, so the content was set at 0.05 to 2%.

(d) The CrCr component has the effect of imparting excellent high-temperature oxidation resistance, high-temperature corrosion resistance, and high-temperature strength to alloy steel, but if its content is less than 28%, the desired effects cannot be obtained. On the other hand, if the content exceeds 38%, it will not only be extremely difficult to dissolve in the atmosphere.
Since castability and weldability also deteriorate, the content was set at 28 to 38%.

(2) CO The CO component improves high-temperature strength by solid solution in the base material, and works together with other alloy components to mutually improve oxidation resistance and sulfidation resistance at high temperatures. It has the effect of preventing cracking during cooling and improving hot workability.

However, if the content is less than 1.5%, the desired effects cannot be obtained, so it is necessary to contain more than 1.5%, but even if the content exceeds 7%, the effect will be more pronounced. No improvement in effectiveness was observed, and on the contrary, hot workability began to show a decreasing tendency, so considering economic efficiency, the content was reduced to 1.
．． It was set at 5-7%. r) The NiNi component has the effect of stabilizing the austenitic matrix, improving its oxidation resistance together with Cr, and further improving the resistance to reducing atmospheres, but if its content is less than 21%, the austenitic matrix becomes indestructible. It becomes stable and the desired effect cannot be obtained in the above-mentioned action, and on the other hand, even if it is contained in an amount exceeding 32%, no further improvement in high temperature strength and oxidation resistance can be obtained.
The content was determined to be 21 to 32% in consideration of economic efficiency.

→ Ti The Ti component has the effect of suppressing grain growth in the austenite matrix, but if its content is less than 0.01%,
If the content exceeds 2%, the production of oxides will increase and the oxidation resistance will deteriorate, so the content should be reduced to 0.01 to 2%. %.

0N In the alloy steel of this invention, the Cr content is relatively high at 28 to 38% to improve high temperature corrosion resistance and high temperature oxidation resistance. However, the N component is dissolved in the austenite matrix, stabilizes the austenite matrix, and strengthens the matrix as a solid solution.
has the effect of forming nitrides and further improving high-temperature strength, but if the content is less than 0.01%, the desired effect cannot be obtained, while if the content exceeds 0.5%, the desired effect cannot be obtained. If it is contained, the amount of nitrides becomes too large and becomes brittle, so the content is set at 0.01 to 0.5%.

(i) MO The MO component contains solid solution in the austenite matrix to strengthen it, significantly improve high-temperature corrosion resistance and high-temperature oxidation resistance, and further coexist with Cr, N, etc. Forms double nitrides such as Cr, MO)2N, which has the effect of significantly improving high-temperature strength, but if the content is less than 1%, the desired effect cannot be obtained, whereas if the content exceeds 5%, the desired effect cannot be obtained. When this happens, the austenite matrix becomes unstable and the formation of intermetallic compounds such as σ phase becomes noticeable.
Since the high-temperature toughness decreases, the content is set at 1 to 5%.

Next, the alloy steel of the present invention will be explained through examples and in comparison with comparative examples. Invention alloy steels 1 and 2, each having the final composition shown in Table 1, comparative alloy steel having a composition obtained by removing MO from the composition of the invention alloy steel, and conventionally known CO-based alloys (hereinafter referred to as (referred to as conventional alloy)
was melted in the air using a high frequency furnace and cast into skid rails each weighing approximately 70 kg.

Next, test pieces for a corrosion resistance test, an oxidation resistance test, a compression test, and a creep rupture test were taken from each of the skid rails, and each test was conducted under the conditions shown below.

The corrosion resistance test was conducted by measuring the relationship between test time and corrosion weight loss (descaling) in a C heavy oil combustion atmosphere maintained at a temperature of 1200°C. The measurement results are shown in FIG. As shown in the figure, the alloy steel of the present invention exhibits superior high-temperature corrosion resistance compared to the comparative alloy steel that does not contain MO, and it is clear that it exhibits even better high-temperature corrosion resistance when compared with the conventional alloy. The oxidation resistance test was carried out by measuring the relationship between test time and oxidation weight loss in an air atmosphere maintained at a temperature of 1200°C.

The measurement results are shown in FIG. As shown in the figure, in the oxidation resistance test at high temperatures, as well as in the corrosion resistance test at high temperatures, the alloy steels 1 and 2 of the present invention were extremely superior to the comparative alloy steels and conventional alloys. Shows high temperature oxidation resistance. In addition, the compression test was performed using a high-speed compression testing machine, and the deformation resistance (true strain ε 10.1, strain rate 7-10/Sec ) He did it by asking.

The results are shown in FIG. As shown in the figure, alloy steels 1 and 2 of the present invention exhibited superior deformation resistance at temperatures on the lower end of the test temperature range, compared to comparative alloy steels and conventional alloys, and particularly at relatively low N contents. The high inventive alloy steel 2 shows significantly better deformation resistance over the entire test temperature range and it is clear from these results that the inventive alloy steel has very high high temperature strength. Furthermore, a creep rupture test was carried out in the atmosphere at a temperature of 982° C. under a load of 3, and the rupture life and elongation were measured.

The measurement results are shown in Table 2. As is clear from the results shown in Table 2, the alloy steel of the present invention, particularly the alloy steel 2 of the present invention, has superior high-temperature strength compared to comparative alloy steels and conventional alloys.

As mentioned above, the alloy steel of the present invention has extremely excellent high-temperature strength, high-temperature corrosion resistance, and high-temperature oxidation resistance. When it does, it exhibits excellent performance.

[Brief explanation of the drawing]

Figure 1 is a curve diagram showing the results of a corrosion resistance test, Figure 2 is a curve diagram showing the results of an oxidation resistance test, and Figure 3 is a curve diagram showing the relationship between test temperature and deformation resistance in a compression test.

Claims (1)

[Claims] 1 C: 0.01-0.6%, Si: 0.1-3%, Mn: 0.05-2%, Cr: 28-38%, Co: 1.5-7 %, Ni: 21 to 32%, Ti: 0.01 to 2%, N: 0.01 to 0.5%, Mo: 1 to 5%, Fe and unavoidable impurities: the remainder (more than % by weight). A high-strength alloy steel with excellent high-temperature corrosion resistance and high-temperature oxidation resistance.