JPS5938366A - Heat resistant cast steel - 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 The present invention relates to a heat-resistant cast steel having excellent high-temperature creep rupture strength, thermal shock resistance, carburization resistance, etc.

ASTM has been used as ethylene cranking tube material, rifoma tube material, etc. in the petroleum engineering industry.
Cr-Ni heat-resistant cast steel, typified by HK 40 material and HP material, is used. Unfortunately, HP improving materials containing W have been developed to improve high-temperature properties. However, in order to cope with increasingly severe usage conditions, improve service life, and stabilize operations, we are improving high-temperature properties, especially high-temperature creep rupture strength, thermal shock resistance, and carburization resistance. It's twisted.

In view of the above, the present inventors have determined that Cr -N i -W
-As a result of detailed research on the effects of various gold elements on the high-temperature properties of Fe-based heat-resistant cast steel, we found that N, Ti, Af
.

Due to the combined addition of B and Cu, high temperatures, especially 100
It has been found that creep rupture strength at temperatures above 0°C, thermal shock resistance, carburization resistance, etc. can be significantly improved. The present invention has been made based on this knowledge.

That is, the present invention provides C013 to 0.6% (wt%, same hereinafter), Si 2.0% or less, Mn 2.0% or less, Cr
2O~30%, Ni30~40%, WO15~50%,
N004~0.15%, TiO,04~0.5%, Af
fo, 02-0.5%, B O, 0002-0.004
%, Cu is 3.0% or less, and the balance is substantially Fe.

The reasons for limiting the components of the present invention will be explained below.

C: 0.3 to 0.6% C not only improves the castability of cast steel, but also combines with Ti to form primary carbides, increasing creep rupture strength. This effect increases as the amount of OC increases, which requires at least 0.3%, but if it is contained in a large amount, the toughness after use will be significantly reduced due to the precipitation of secondary carbides, and weldability will also deteriorate. Therefore, the upper limit is set at 0.6%.

Si: 2.0% or less Si is a deoxidizing element for molten metal, and has the effect of improving carburization resistance as well as improving castability. However, if contained in a large amount, weldability will be impaired, so the content should be 20% or less.

Hetn:2. 0% or less Mn deoxidizes the molten metal and also fixes the impurity element S in the steel.
Although it has the effect of making it harmless, its upper limit is set at 2.0% since its content causes a decrease in oxidation resistance.

Cr: 20-30% Cr coexists with Ni, which will be described later, to make the cast steel structure an austenite structure and improve high-temperature strength and oxidation resistance. In particular, 1000
In order to maintain high strength and oxidation resistance in the high temperature range from °C to -L, it must be at least 20%.

This effect increases as the content increases, but if it is included too much, the toughness after use will decrease, so the upper limit is set at 30%.

Ni: 30-40% As mentioned above, Ni forms an austenite structure in coexistence with Cr, and is an element effective in increasing structural stability and ensuring oxidation resistance and high-temperature strength. 1000℃
In order to achieve excellent oxidation resistance and strength in the above high temperature range, a content of 30% or more is required. These high-temperature properties improve as the content increases, but when it exceeds 40%,
The effect is saturated, and further content is economically disadvantageous. Therefore, the upper limit is set at 40%.

W: O, S ~ 5.0% W has the effect of increasing high temperature strength. In order to obtain this effect, the content must be at least 0.5%, but if the content is too large, the oxidation resistance will decrease, so the upper limit is set at 5.0%.

The cast steel of the present invention contains NXTi, AlB, as well as the above elements.
The greatest feature is that it contains Cu in a composite manner. T1 combines with C and N to form carbides, nitrides, and carbonitrides, and B and Al finely disperse and precipitate these compounds to strengthen grain boundaries and improve intergranular cracking resistance. This results in significant improvements in high-temperature creep rupture strength, high-temperature thermal shock properties, long-term creep rupture strength, etc. Also,
Ti significantly increases carburization resistance as a synergistic effect with Al,
Furthermore, Cu greatly improves thermal shock resistance due to its synergistic effect with Ti and Al.

N: 0.04-0.15% While N stabilizes and strengthens the austenite phase in the form of solid solution nitrogen, it also participates in the formation of nitrides such as Ti and carbonitrides. This compound is A1. , finely disperses and precipitates in the coexistence with B, finely cracking the crystal grains and inhibiting grain growth, thereby increasing creep rupture strength and thermal shock resistance. To ensure this effect, at least 0.
However, if the content is too large, the compound will precipitate and become coarse, which will actually worsen the thermal shock resistance, so the upper limit is set at 0.15%.

Ti: 0.04 to 0.5% 1.i forms nitrides and the like to improve high temperature strength and thermal shock resistance as described above, and also enhances carburization resistance in coexistence with Al. At least 0.04% is required to achieve these effects sufficiently. The effect increases as the content increases, but if it increases too much, the precipitates become coarser and
The increase in oxide inclusions actually reduces the strength. Therefore, the upper limit is 0.5%, and if strength is particularly important, it is preferably 0.15% or less.

Al: 0.02 to 0.5% In addition to the effect of improving creep rupture strength, Al has a remarkable effect on improving carburization resistance due to its coexistence with Ti.

When emphasis is placed on improving creep rupture strength, the content is preferably 0.02 to 0.07%. In addition, especially when emphasis is placed on strengthening carburization resistance, it is preferable to set the amount above 0.07%, and as the content increases, carburization resistance improves. However, on the other hand, there is a tendency for strength to decrease, so
The upper limit is 0.5%.

In addition, Tio. When the A/containing material is subjected to an X-ray microanalyzer (EPMA) after a carburization test, an Aj'-rich layer is observed on the surface layer of the test piece. This Al lynch layer exhibits a strong carburization prevention effect.

B: 0.0002 to 0°004% In addition to strengthening grain boundaries, B contributes to improving creep rupture strength by causing fine precipitation of the Ti compound and retarding agglomeration coarsening after precipitation. The content of this dame is 0.0002%
Although the above is necessary, if the amount is increased by twisting, not only will strength increase be slow, but weldability will deteriorate, so the upper limit is set at 0.004%.

Cu: 3.0% or less CurriTi has a remarkable effect on improving thermal shock resistance in coexistence with Al. This effect increases as the content increases, or if it exceeds 3.0%, the degree of improvement in thermal shock resistance becomes slow and weldability deteriorates, so 3.0%
% or less. However, Cu has the effect of increasing carburization resistance. A preferable content to fully exhibit these effects is 0.2 to 3.0%, and a more preferable content is 0.5 to 3.0%.
It is 0%.

Of course, it is desirable that P, S, and other unavoidably mixed impurities be as small as possible, but there is no problem as long as they are within the range normally allowed for this type of steel.

Next, the present invention will be specifically explained with reference to Examples.

Example Cast steel melted in a high-frequency melting furnace (in the atmosphere) was subjected to centrifugal casting, and a cast steel pipe (outer diameter 1369×
(20 thickness x 500 pieces of length) were obtained, and test pieces were prepared from each sample and subjected to a creep rupture test, a thermal shock resistance test, and an immersion resistance test. The test results are shown in Table 2.

Fragrances 1 to 6 are comparative examples, and 101 to 107 are inventive examples. Among the comparative examples, Nof1 is a conventional HP improving material containing W (
(Does not include NXTi, Al, B, Cu, etc.)
, Nb', 2 to 5 include N, TiXAIXB, but an example in which Cu deviates from the provisions of the present invention! No. 6 is an example in which the required amount of Cu is contained, but the contents of T1 and AJ are insufficient.

The test conditions are as follows.

[I] Creep rupture test According to the provisions of JIS Z2272. However, the rupture time (Hr) was measured under two conditions: (A) temperature 1093°C and load 1.9Kgf/d, and CB) temperature 85°C and load 7.3Kgf/mi.

[II Thermal Shock Resistance Test A specimen with the shape and dimensions shown in Figure 1 (thickness: 8 mm) was heated to 90°C.
Repeat the heating and cooling operation of heating and holding at 0°CK (holding time: 30 minutes) and cooling with water. Every time this operation is repeated 10 times, the length of the crank generated on the specimen is measured. Thermal shock resistance was evaluated by the number of repetitions when the crank length reached 5 months.

In Table 2, the values in the 'Thermal Shock Resistance' column are the number of times.
The higher the number of times, the better the thermal shock resistance.

Field Carburization resistance test specimen (diameter 12 x 1 x length 60 ni) F solid carburizing agent (Tegu fKG30, containing BaCO3), temperature 130
After holding at 0°C for 300 hours, chips were collected from the 1st layer from the surface of the specimen and from the 1st to 2nd layers, and the increased C amount (~ Vt%) was determined. In Table 2, r carburization resistance and column J indicate the increased amount of C. The smaller the increase in C content, the better the carburization resistance.

Table 2 Test Results As is clear from the above test results, the present invention material (1101
-107) have good high-temperature properties that far exceed those of the conventional HP improving material 1t) in terms of high-temperature creep rupture strength, thermal shock resistance, and carburization resistance. Also, the comparative examples () f2 to f6) of the pond are conventional materials! Although they show better results than Material No. 1, they are not as good as the materials of the present invention in the overall evaluation of each property. In addition, in the welding test, the weekly Cu
Although poor welding was observed in sample material I4.5 containing the following, the material of the present invention has good weldability and poses no problem as a welded structural material.

As mentioned above, the heat-resistant cast copper of the present invention has superior high-temperature properties, especially high-temperature creep rupture strength, thermal shock resistance, carburization resistance, etc., compared to conventional W-containing HP materials. ,
Ethylene cranking tube in petrochemical industry,
It withstands harsh conditions of use as a re-former tube, and guarantees stability and durability superior to conventional paulownia wood in high-temperature applications exceeding 1000°C, such as high-quality steel-related equipment components such as hammer rolls and radiant tube materials. It is something to do.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of the shape and dimensions of a thermal shock resistance test piece in an example. Agent Patent Attorney Arata Miyazaki Department Figure 1

Claims (1)

[Claims] f+) C0.3-0.6%, Si2.0% or less, M
n 20% or less, Cr2O~30%, N130~40
%, Wo, 5-50%, NO, 04-0.15%, Ti
0.04-0.5%, AJo, 02-0.5%, BO,
Heat-resistant cast steel consisting of 0O02 to 0.004%, Cu 3.0% or less, and the remainder substantially Fe.