JPS5953660A - Heat resistant cast steel with superior carburizing resistance and superior creep rupture strenegth at high temperature - Google Patents

Abstract

PURPOSE:To obtain the titled heat resistant cast steel most suitable for use as the material of a member for a high temp. apparatus such as a reformer tube by specifying the composition of Ni-Cr-Mn-N-Nb steel. CONSTITUTION:This heat resistant cast steel consists of, by weight, 0.25-0.75% C, <=2.0% Si, 5-20% Mn, 20-30% Cr, 15-40% Ni, 0.01-0.40% N, 0.3-2.0% Nb and the balance Fe. The steel may further contain 0.5-3.0% Cu and/or 0.01-1.0% Al. The steel can be provided with especially superior carburizing resistance without deteriorating the creep rupture strength at high temp. as compared to a conventional HP material contg. Nb or the like.

Description

[Detailed Description of the Invention] For use in tubes, etc.
1. Concerning heat-resistant Φl steel with excellent high-temperature creep rupture strength.

For ethylene cracking tubes in the petrochemical industry, welded assemblies of one white tube and a bent tube manufactured by nail f construction are used.
A welded assembly of a straight pipe with d and a turn (Φ)f and a retractor is used for the tube. For these applications, mill heat steel materials containing Ni and Cr are generally used, and ABTMHK40 material and UP material are typically used.

In recent years, with the rise in operating temperatures, further improvements in high-temperature properties are required for this type of milling material. There is one.

Therefore, if the month corresponding to this is f, 1, the HP profit is Nb,
Products to which W, MO, etc. are added have also been developed and are currently in practical use. However, in view of the ever-increasing temperature of the operating environment and the heavier fuel gas, cracking tubes and rift A-mer tubes have been developed not only to improve their high-temperature properties, but also to improve their performance. There is a strong demand for improved carburization resistance under high pressure conditions.

In view of these circumstances, the present invention aims to provide a material suitable for high-temperature equipment members such as the above-mentioned cracking tubes and former tubes, which have a carburization resistance of 8 or higher. A new type of N that can improve carburization resistance to RLJ without reducing breaking strength.
We have succeeded in developing i-Cr-Mn-N-Nb heat-resistant cast steel.

That is, the heat-resistant cast steel 1ql1, C0,25~0.
75, Si 2.0 or less, Mn 5-20. , Or 2
0-30, Ni 15-40, NO, 01-0.40
, Nb O, each II contains 3 to 2.0, and the remainder is substantially F
Furthermore, in addition to the above components, for the purpose of further improving carburization resistance, Cu
O,5-3,0, AeO,0]-1,0 or 1
- It is characterized by containing two types of each weight.

Below, the characteristics of the constituent elements constituting the heat-resistant cast steel of the present invention and the reason for limiting the range of the constituent elements will be explained in detail.

CO, 25-0.75% In addition to improving the castability of Cil''1 cast steel, it forms primary carbonitrides and pyrooxides in the coexistence with Nb, Cr, and N, which will be described later, and improves the creep rupture strength. Improve!a, do it.

Therefore, it is necessary to contain at least 0.25% or more. However, although its effect increases as c-1 increases, if it is contained in an excessively large amount, the toughness after use will be significantly lowered due to excessive precipitation of secondary carbides, and at the same time, weldability will also deteriorate. Upper limit.

Si 2.0 or less In addition to acting as a deoxidizing agent during the melting of cast steel, Si
Effective in improving carburization resistance. Since weldability will be impaired if a large amount of 1 is contained, the upper limit is set at 2.0.

Mn 5-20% Mn stabilizes the austenite phase, and a particularly important effect is its contribution to improvement of carburizability.

If the ratio is less than 5%, the effect is small, while if it exceeds 20%, the ductility of the material deteriorates and weldability is significantly impaired.

Cr 20-30% Cr has the effect of making the metal structure ausbunite in coexistence with Mn and later N1, and improving high temperature strength and oxidation resistance. In particular, in order to obtain the required strength and oxidation resistance in a high temperature range of 1000° C. or higher, the F- content must be at least 20 V. Such an effect li is strengthened as the r content increases, but if the r content increases too much, the NrEj properties after use will drop significantly, so a ratio of 30 is set as the upper limit.

As shown in the old 15th to 40th Niid l description, an element that coexists with Or and Mn to maintain an austenitic structure, provides structural stability, and is effective in ensuring carburization resistance, oxidation resistance, and high-temperature strength. It is. In order to obtain good oxidation resistance and high temperature strength in the high temperature range of ]000℃ or higher, it is necessary to
This inclusion is required. Upper n[:Special('L 1clIqj will improve as the number of states containing it increases, but if 40% is introduced, the effect of addition will be saturated and it will be disadvantageous in terms of redness, so the upper limit is set at 40%.

N O,01~0.40N is in the form of solid solution nitrogen, stably strengthening the austenite phase containing Mn, and is also involved in the formation of nitrides and free nitrides with Nb and Or, and this compound is 319 By dispersing and precipitating in groups, the crystal grains become fine 7, grain growth is inhibited, and creep rupture strength is increased. In order to actively exhibit this effect, the content of 11 should be M-〇, Ol-chi or more. However, if the N content is too large, excessive 1'+ of nitrides and carbonitrides will appear and become coarse, resulting in a decrease in weldability. Let lj, 0 be the 2nd limit.

Nb O, 3-2. o% Nb has the effect of increasing creep rupture strength.

In order to achieve this effect, it is necessary to contain I soil at 0.3%. However, if the content is too large, the creep rupture strength will decrease, so 2.0
The upper limit is %. In addition, +iJJ usually accompanies Ta, which is an element with the same effect as this, but in that case, l'T
If the total with a is 0.3 to 2.0, it's fine. The heat-resistant rF steel of the present invention basically contains at least the following components, with the remainder Cj essentially consisting of Fe.

By the way, in the present invention, for the purpose of further improving the carburization resistance of the heat-resistant cast steel, one or both of the following Cu and Ae may be incorporated in place of Fe.

Cu 0.5-3.0% Cu does not change the material properties due to the basic chemical components mentioned above, and also has its ill? It is an effective additive element for improving carbon chloride. In this case, the amount added is 0.5
Can you withstand below the level? There is no noticeable improvement in J coal I/1゛, and on the other hand, if it is added in excess of 3.0'%, it causes deterioration of weldability due to a decrease in ductility, which is not desirable.
In addition to being effective in improving the oxidation resistance of 0.01 to 1.0 Ae, it is also an effective element in improving the carburization resistance of the ribs. In that case, adding Cu in combination shows a more significant improvement effect.

In the present invention, which aims to improve carburization resistance, the content of K i+ is set to at least 0.01% or more in order to achieve the desired improvement effect by adding Ae. As the content increases, the carburization resistance +1 improves.

However, the amount of Ae added is 1. If the value exceeds 0, the fluidity of the molten steel will decrease and the castability will be significantly impaired, so the upper limit is set at 1.0. In addition, the content of AI is (,), 05 L
l) In the case of the following trace amounts, the effect of improving carburization resistance of Cu becomes more remarkable by adding it in combination with Cu.

The heat-resistant cast steel of the present invention may be unavoidably grooved with other impurities such as P and S when it is melted, but if there is a concave roundness within the range normally allowed for this type of steel, their presence will be prevented. harm.

Next, examples of the present invention will be listed together with comparative examples to clarify its excellent characteristics.

<Example: Each mH in a high frequency melting furnace (in the atmosphere)? Steel was melted and cast into pieces (outer diameter: 36 pieces, wall thickness: 20 mm, length: 500 m) using the centrifugal casting method. The chemical components of each of these test materials are shown in Table 1. In the sample materials, )r(a 1.2 is the comparison month, and Tigers 3 to 16 are the steel phases of the present invention.

A test piece was taken from each sample and subjected to measurement of creep rupture strength and carburization resistance TT. The results are shown in Table 2.

The details of each test are as follows.

[■] Creep rupture strength' JIS Z 22't'2 standard 9Kj. k
DA'L, (A) Temperature 093°C1 Load 1.9 K9f
The experiment was carried out under two conditions: temperature: 850°C, load: 7i', and filtration at 7.3°C.

CIl, l] Carburization resistance test specimens (diameter 12mm, length 6mm) were kept at a temperature of 1100°C for 300 hours in a fixed carburizing agent (Teguza KG 30, containing BaCO3), and then the surface of the specimen was 1m deep
Chips were collected from the layer at the age of 10 years old and the layer 1 to 2 depths from the surface, and the amount of C was analyzed to determine the increase in Cj) J Table 1
Chemical composition (wt) of test materials Table 2 Test results As is clear from the test results in Table 2 above, the cast steels of the present invention (test samples 3 to 16) had It was introduced that it has creep rupture strength equivalent to that of Nb-containing HP powder (sample material 1), which is said to have excellent high-temperature creep rupture strength among conventional materials. The results show that the increase in Oct is half or less than that of conventional materials, and it is confirmed that this material has extremely excellent carburization resistance.

In this way, Ni-Cr-Mn-N- according to the present invention
Compared to conventional Nb-containing HP materials, Nb-based heat-resistant cast steel has lower high-temperature creep rupture strength /l','
It is characterized by being able to obtain excellent carburization resistance.

Therefore, the cast steel of the present invention can be used in many applications such as ethylene cracking tubes for the petrochemical industry that require carburization resistance and high-temperature creep rupture strength, and former tubes in reforming furnaces. Introducing -1,000℃ rolls and radiant tubes.

It can be used as a suitable material for various weighing equipment components used in high temperature ranges.

Claims (1)

[Claims] 1. G O, 25 to O,'i'52.
0 or less Mn 5 ~ 20 Cr 2Q -, - Ni '15 ~ 4O N O, 01 ~ 0,4O Nb O, 3 ~ 2.0 is engaged in each amount, and the remainder is substantially composed of Fe. Heat-resistant cast steel with excellent carburization resistance and high-temperature creep rupture strength. 2, GO, 25~0.75Si
2.0 or less Mn 5 ~ 20 Cr 20 - 3O Nj Co5 ~ 4O N O, 01 ~ 0.4O Nb O, 3 ~ 2.0 and Cu O, 5-3, 0, AI? 0.01-1.0 -J11i and two types are included in each city, the remainder is substantially Fe
A heat-resistant cast pot with excellent try carburizing properties and high-temperature creep rupture strength.