JPS6277444A - Corrosion resistant alloy - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a Fe-Cr-Ni corrosion-resistant alloy that has excellent corrosion resistance at high temperatures.

By adding a certain amount of Nb and N to an austenitic corrosion-resistant alloy based on iron and containing Ni-0R, it has high-temperature corrosion resistance that can withstand use at high temperatures, especially in harsh environments exceeding 700°C. The present invention relates to corrosion-resistant alloys.

[Conventional technology]

In cement production, red-hot cement clinker fired in a kiln is rapidly cooled by heat exchange on a plate-shaped grate having ventilation holes in a quenching cooler. The material of this great plate is J Engineering S.
Ni-0 equivalent to 5CH-13 (AC knee HE)
R-series austenitic cast steel is used.

[Problem that the invention seeks to solve]

In recent years, the great plate in the quenching cooler has been
As operating conditions become more severe, problems arise in corrosion resistance at high temperatures, and materials with this composition are difficult to use for long periods of time, so there is a strong demand for materials with excellent corrosion resistance at high temperatures.

[Means for solving problems]

Therefore, the inventors of the present invention have conducted extensive research to improve the high-temperature corrosion resistance of +Ni-0r austenitic alloys by adding various elements.

It has been confirmed that corrosion resistance at high temperatures can be sufficiently enhanced by adding a certain amount of Nb and N in combination to Ni-0r as the main additive element.

That is, the present invention is 2% by weight, and C: 0.1 to 0.7%.
.

Si: 0.3-2%, Mn: 0.3-2%, Cr: 1
5-30%, Ni mini full 20. Nl): 0.3~
2.5 chi.

It is a Ni-0r austenitic corrosion-resistant alloy characterized by containing 0.05 to 0.5 N and the remainder being Fe.

[action, effect]

The alloy of the present invention has better corrosion resistance at high temperatures than conventional materials.

In particular, it has excellent sulfide corrosion resistance, so when applied to actual products, it has the excellent property of significantly reducing erosion caused by high-temperature oxidation and sulfide corrosion.

[Reason for limiting the composition of the cast steel of the present invention]

The reasons for limiting the components of the two corrosion-resistant alloys according to the present invention will be explained in detail below.

C: In addition to improving the castability of cast steel, it forms primary carbides in the coexistence with Nb, and is necessary to increase mechanical strength at high temperatures. Less than 0.1 inch.

Since the strength decreases significantly at high temperatures and the metal structure becomes unstable, at least 0.1% or more is required. Moreover, if it exceeds 0.7%, secondary carbides with Cr will precipitate and the toughness will be significantly impaired, so the upper limit is set at 0.7%.

Si: Also plays a role as a deoxidizing agent during melting.

It is an element that improves the castability of cast steel, but if it is added in less than 0.3%, the effect is weak, and if it is added in excess of the necessary amount, it is effective in improving oxidation resistance, but the high-temperature strength is significantly reduced. Taking into consideration oxidation resistance and corrosion resistance at high temperatures, the upper limit is 2.

Mn2 Similar to the above-mentioned Si, Mn plays a role as a deoxidizing agent and is also effective as an element that fixes S (sulfur) in molten steel and renders it harmless, but if added in large quantities.

0 as it will reduce strength and corrosion and oxidation resistance at high temperatures.
．． Limit 3-2%.

In the coexistence with Cr:Ni, the metal structure of the @ steel is austenitized, and it has a remarkable effect of increasing the strength, corrosion resistance, and strength at high temperatures. The effect increases as Or increases, and in order to fully exhibit strength, oxidation resistance, and corrosion resistance especially at high temperatures of 700"C or higher, it is necessary to add at least 15%. However, it is necessary to add more than 15%. If added, the metal structure becomes unstable, so the upper limit is set at 30%.

N1: As mentioned above, N1 is an effective element in coexisting with Cr to form an austenitized structure in cast steel, stabilizing the structure, and increasing strength at high temperatures and acid resistance and corrosion resistance.

If less than 7% is added, the structure will become unstable. Even if it is added in excess of 15%, the increase in strength at high temperatures is not so remarkable. Although Ni itself does not have acid resistance or corrosion resistance, it indirectly contributes to the stability of the film and increases the acid resistance and corrosion resistance. However, considering economic efficiency, the upper limit is set at 20%.

The greatest feature of the cast steel of the present invention is that in addition to the above-mentioned elements, a certain amount of Nb and N are added in a composite manner. Although the combined addition of these elements dramatically improves the strength and corrosion resistance at high temperatures, the absence of any one element does not provide the same effect.

Nb: A strong carbide-forming element that increases high-temperature strength and
For high temperature corrosion, especially high temperature sulfide corrosion.

It has a significant effect. And to get that effect.

At least 0. % addition is necessary. On the other hand, if it is added in excess, the high-temperature strength will be reduced, and in consideration of sulfide corrosion resistance, the upper limit is set at 2.5%.

Note that Wb usually includes unavoidable Ta. Ta is Nl
), so when Ta is included, the total of Nl) and Ta should be [1.3 to 2.5%].

N: In the form of solid solution N, N is dissolved in the matrix to make the metallographic structure deficient in austenite, and is effective in increasing high-temperature strength by participating in the formation of nitride carbides with Nb and Or. If it is less than 0.5%, the effect will be weak, and if it exceeds 0.5%, the precipitation of carbide will be significant, and the nitride will become coarser, resulting in worse deterioration, so it is limited to 0.05 to 0.5%.

In addition, impurities such as sp may be present within the range normally allowed for this type of cast steel.

〔Example〕

Next, one embodiment of the present invention will be specifically described. 1st
The table is an example of the chemical composition (% by weight) of various cast steels used in the present invention and this test.

Table 1 In Table 1, steel type Nα1 is SC! Conventional alloys of H-13, steels iNα2 and N[L3 are comparison alloys for the present invention, steel types Nα4. Nα5. and Nα6 are examples of corrosion-resistant cast steel of the present invention.

The high-temperature tensile test was conducted in accordance with the regulations of JIS G 0567 at temperatures of 80°C and 1°C.

On the other hand, for high-temperature corrosion tests, samples were embedded in a corrosive medium made by adding 20% of reagent-grade anhydrous sodium sulfur (Na2S04) to ordinary cement clinker pulverized into 100 to 150 mesh at a temperature of 800°C. C, 900°C
After holding at 1000''C for 100 hours, evaluation was made by measuring the corrosion loss per unit surface area.

In addition, a grate plate was actually manufactured using the newly invented alloy Nα4 and used in actual operation, and compared with one made from a conventional material (N(Ll)).

Table 2 Table 2 shows the results of high temperature tensile tests of the various alloys shown in Table 1.

The steel types Nα in Table 2 correspond to the steel types in Table 1.

As can be seen from Table 2, the corrosion-resistant cast steel of the present invention has significantly improved tensile strength at high temperatures as well as corrosion resistance.

FIG. 1 is a line graph showing the results of a corrosion test for the alloys shown in Table 1. Note that the corrosion weight loss in FIG. 1 is the value obtained by subtracting the weight difference between the sample before and after the test by the surface area of the sample. As can be seen from FIG. 1, the corrosion-resistant cast steel of the present invention has extremely excellent corrosion resistance at high temperatures.

Figure 2 shows Ugly 1 (conventional alloy) and N14 (conventional alloy) shown in Table 1.
The results of fabricating a great plate using the alloy of the present invention and subjecting it to actual operation are shown in a bar graph. In addition, the second
The great plate weight loss (%) in the figure is the value obtained by multiplying the difference in weight of the great plate before and after the test by the weight before the test by 100. Figure 2 Karareka 6-
4-Uni 9 The corrosion-resistant cast steel of the present invention has been found to have sufficiently excellent corrosion resistance through actual operation.

〔Effect of the invention〕

As described above, the corrosion-resistant cast steel of the present invention has both high strength and high corrosion resistance at high temperatures of 700°C or higher. Moreover, it is extremely useful not only for the above-mentioned great plates but also for members that require high strength and high corrosion resistance in high temperature regions.

[Brief explanation of drawings]

Figure 1 is a line graph showing the high-temperature corrosion test results for conventional alloys, comparative alloys, and the alloy of the present invention. Figure 2 is the weight of the great plate as a result of field testing of the manufactured great plates using the conventional alloy and the alloy of the present invention. It is a bar graph showing the decrease.

Claims (1)

[Claims] In weight%, C: 0.1-0.7%, Si: 0.3-2%
, Mn: 0.3-2%, Cr: 15-30%, Ni: 7
~20%, Nb:0.3-2.5%, and N:0.0
A corrosion-resistant alloy characterized by containing 5 to 0.5% of Fe, with the remainder consisting of Fe.