JPS581052A - Austenitic welded structure for high temperature service - Google Patents

Abstract

PURPOSE:To provide a titled welded structure which consists of weld metal contg. austenitic structural steel as well as C, Si, Mn, Ni, Cr, Mo, etc. respectively at prescribed ratios and consisting of the balance Fe, and which has superior creep rupture ductility and strength at high temps. CONSTITUTION:The intended austenitic welded structure is obtained by consisting the same of austenitic structural steel contg., by weight %, 32-38% Ni, and 21-25% Cr and the weld metal of the following compsn.: Said weld metal is formed of 0.02-0.075% C, 0.1-1.5% Si, 2-3% Mn, 32-38% Ni, 21-25% Cr, 1-1.6% Mo, 0.1-1% Nb, 0.1-1% Ti and/or Zr and the balance Fe and impurities. This welded structure is used conveniently in high temp. parts of particularly >=600 deg.C in chemical plants and power generation plants.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an austenitic welded structure for high temperature use, and more specifically, an austenite welded structure having excellent high-temperature ductility and high-temperature strength, which is conveniently used in high-temperature parts of chemical plants and power plants, particularly at temperatures of 600 C or higher. Related to system welded structures.

Incoloy 800 [C: o, o
s %°, Cr: 20%, Ni: 32%,
Incoloy 138 is used to manufacture welded structural parts using structural steel of T 180.3%, At:O, '3% (weight)].
(Cr: 28%, Ni: 38%, Mo: 4%, W:
1%, Fe: balance), Inconel 182 (Cr: 15%,
Ti: 0.5%, Nb: 2%, Mn: 7%, Fe: 8%
, Nl: balance), Inconel 112 (Cr: 20%, MO
: 8%, (Nb+Ta):3]5%, Fe nia%,
Nl: Regret] I'm sorry / Coweld A (Cr: 15%, N
b: 2%, MO: 1.5%, Fe2 8%, Ni:
Welding rods such as However, the high-temperature creep strength of the weld metal produced using these welding rods is comparable to or lower than that of structural steel, the high-temperature ductility is low, and there is a drawback that embrittlement due to structural changes is significant when exposed to high-temperature conditions. . In addition, thermal stress acts on the structure at high temperatures, and because there is a large difference in the coefficient of thermal expansion between the welding rods and Incoloy 800 structural steel due to the difference in composition, the thermal stress generated in the weld metal part also increases. This is extremely inconvenient as a weld metal because it becomes large and becomes a major factor in the occurrence of cracks.

On the other hand, in order to avoid this phenomenon, attempts have been made to use weld metals that have the same coefficient of thermal expansion as the structural steel base material, especially co-metallic welding rods that have the same composition as the structural steel. Since it contains all titanium and aluminum, these oxides are formed and impair the fluidity of the molten metal, making it easy to cause welding defects.If titanium and aluminum are excluded, it lacks strength at high temperatures, so it cannot be used as a welding material. .

An object of the present invention is to provide an austenitic steel welded structure that has excellent creep rupture ductility and strength at high temperatures and can prevent high stress generation.

In view of the various drawbacks of conventionally known weld metals for austenitic steel, the present inventors have conducted research on many metals in order to achieve the above object, and as a result, have developed an extremely excellent and highly practical weld metal and the weld metal. A friend who finds austenitic welded structures welded with metal.

According to the present invention, in weight %, N1:32-38% and (
, r: 21-25%, and the following composition, i.e., C: 0.02-0.02% by weight.
075%, 8i; 0.1-1.5%, Mn: 2-3%,
Ni: 32-38%, Cr: 21-25%, MO: 1-
1.6%, Nb, 0.1-1%, TI and/or Zr
: 0.1 to 1%, with the remainder consisting of PE and impurities to provide a welded structure.

The welded structure according to the present invention is suitable as a structure used for, for example, a chemical plant reformer tube or a heat exchanger tube for a boiler, and is a welded structure in which the structural steel is, for example, Incoloy 800, which is widely used as an austenitic steel. provided in the form of

Honjitsu qo structural austenitic steel is an Fe alloy containing 3-2 to 38% by weight and 21 to 25% by weight of Nl and Cr, respectively, which form the austenitic structure, and other trace components, such as 0.1% by weight. The following C, 1% by weight
si, o, 1s to 0.6% by weight of Ti and 0,1
Those containing 5 to 0.6% by weight of Aj are preferred.

Further, in the weld metal used in the present invention, C is added to improve high-temperature strength, but the content is 0.02~
It is 0.075% by weight. If there is too much C, the workability and high-temperature ductility will be reduced, which is disadvantageous, and if it is too little, the desired high-temperature strength cannot be obtained. Si and Mn are contained in an amount of 0.1 to 1.5% by weight and 2 to 3% by weight, respectively, for the purpose of deoxidizing and desulfurizing during melting and welding.

It was confirmed that the presence of this amount is not only sufficient to obtain the effect and achieve the purpose, but also has the advantage that hot cracking phenomenon does not occur in the weld metal. In addition, Nl and Cr are the main components that coexist to form the austenite structure, and Ni: 32 to 38, respectively.
Weight% and Cr: It is necessary to contain 21 to 25% by weight. By making these contents equivalent to the coefficient of thermal expansion of structural steel, the generation of thermal stress can be reduced as much as possible. If the amount of Nl is too low, the sigma phase will precipitate during long-term use at high temperatures due to the presence of Mo+Nb, Tl, and Zr, and if it is too large, the columnar crystals will become coarse and hot cracking will occur. This is undesirable because it tends to occur and the ductility decreases. Further, sufficient oxidation resistance can be obtained with the amount of Cr within the above range.

MO strengthens the austenite matrix, and some of it precipitates as carbides, so it has the effect of improving high-temperature strength and strengthening grain boundaries. It will be done. If the amount is too large, the workability and oxidation resistance will be reduced, and the sigma phase will be likely to precipitate, which is disadvantageous. If the amount is too small, the above-mentioned inherent properties will not be realized. Nb is 0.1 to 1% by weight in the weld metal
Contain. When the amount of Nb precipitated as a carbide is within this range, a sufficient effect of improving high-temperature strength can be obtained, and the effect of improving high-temperature ductility can be obtained by lowering the amount of welding oxygen. If the amount is too small, sufficient effects cannot be obtained, and if the amount is too large, the processability will deteriorate, which is undesirable. fcTl and/or 7. r is 0.
By containing 1 to 1% by weight, part of it acts as a deoxidizing agent, lowering the amount of oxygen in the weld metal and improving high-temperature ductility, and the rest precipitates as MC type carbide in the weld metal. This suppresses the precipitation of MzsCa type carbides at grain boundaries, resulting in improved strength and ductility. T
If the amount of i is too large, weldability will be poor and welding defects such as weld cracks and inclusions will easily occur. Moreover, if it is too small, the above effects will be insufficient. In this case, when only one of them is contained, it is preferably 0.1 to 0.5% by weight. However, more favorable results can be obtained by using 0.1 to 0.3% by weight of both.

The weld metal of the present invention is a PE gold alloy containing each of the above-mentioned metals in specific range amounts, and therefore the remainder is substantially composed of PE, but in trace amounts that do not limit the predetermined effects of the weld metal of the present invention. There is no problem in the presence of impurities.

The present invention particularly provides niobium, molybdenum,
It is characterized by containing specific amounts of titanium and zirconium, and it provides excellent high-temperature strength and ductility to welded structures made of Incoloy 800 as a structural steel, and significantly reduces the occurrence of thermal stress. It's something you get.

Hereinafter, the present invention will be explained in more detail using examples.

Examples 1 to 4 and Comparative Examples 1 to 5 Welding metals having the respective compositions shown in Table 1 were welded using Incoloy 800 as the austenitic structural steel, and each sample was tested. In the table, weld metal sample shop 1
is the conventionally known Inconel 116, wholesalers 2 to 5 are also conventional weld metals, and wholesalers &6 to 9 are those of the present invention. In addition, the numerical values of the components in the table are weight %. t
700C', 800C of fc base material (Incoloy 800)
, and the coefficient of thermal expansion at 900C is 17.
5X10-6/℃, 18. Ox 10-6/'C118
, 5X10-'/C, and the thermal expansion coefficients of Examples 1 to 4 were also the same as that of the base material.

Welding is performed using a welding current of 150A (DC) and a voltage of 21 to 23V.
The welding was performed at a welding speed of 1 s o m/min.

[Fisco cracking rate]

Figure 1 shows the flask cracking rate of each weld metal.

As is clear from the figure, the cracking rate of samples &1 to 5 is 22~
25%, whereas the cracking rates of the welded structures made by the products of the present invention are all 15% or less, which is excellent.

[Creep rupture test]

A creep rupture test was conducted on each weld metal at 800C. FIG. 2 shows the results obtained regarding the relationship between creep rupture time and stress. Further, the aperture after creep rupture at 800tZ' and 1000 hours is shown in FIG.

From the figure, it can be seen that the creep rupture strength of conventional weld metal is lower than the average value of Incoloy 800, which is the base metal, but that of the molten metal of the present invention is almost the same as the average value of Incoloy 800. Recognize.

Regarding creep rupture ductility, conventional weld metal 0800
C, the aperture value at 1000 hours is less than 10%, whereas that of the weld metal according to the present invention is J! 66 and A7
The ductility is 15% for 48 and 20% for 9, which is much higher than the conventional one. Weld metal cannot be expected to have the same ductility as the base metal, but ideally it should have more than half the ductility of the base metal, and if we focus on the occurrence of cracks due to embrittlement during use, the ductility should be at least 10%. or more ductility is required. Considering from this point of view, the ductility of the base metal is about 40%, whereas all the weld metals of the present invention have a ductility of 10% or more, and Yas. 8 and 9 have particularly satisfactory ductility.

As described above, the weld metal of the present invention has a coefficient of thermal expansion equivalent to that of austenitic structural steel, and also has excellent weldability, and structures welded with such weld metal have significantly improved high-temperature It has creep rupture strength and creep rupture ductility, making it extremely practical.

[Brief explanation of the drawing]

Figure 1 is a bar graph showing the fisco cracking rate, Figure 2 is a bar graph showing the fisco cracking rate.
Figure 3 is a graph showing the relationship between creep rupture time and stress at 800C for weld metal.
Creep at 000 hours. It is a bar graph showing the fracture aperture. Atsushi / Illustrated Osen NO.

Claims (1)

[Claims] 1. In weight%, Ni: 32-38% and Cr: 21-2
Austenitic structural steel containing 5% and the following composition,
That is, in weight%, C: 0.02 to 0.075%, Si
: 0.1-1.5%, Mn: 2-3%, Nl: 32-3
8%, Cr: 21-25%, MO: 1-1.6%, Nb
:0.1~1%, Ti and/or Zr:0.1~1
%, and a weld metal with the balance consisting of Fe and impurities. 2. Structural steel, in weight%, C: 1% or less, Sl: 1%
Below, Nl: 32-38%, Cr: 21-25%, Tj
The high temperature austenitic welded structure according to claim 1, wherein the austenitic welded structure for high temperatures is an Fe alloy steel containing: 0.15 to 0.6% and At: 0.15 to 0.6%. 3. Weld metal is C: 0.02 to 0.075 in weight%
%, Si: 0.5-1%, Mn: 2.3-2.7%, N
i: 32-35%, Cr: 22-24%, MO: 1.2
~1.5%, Nb: 0.2-0.6%, Ti: 0, 1
~0.3%, Zr: 0.1~0.3%, and the remainder Fe! The high temperature austenitic welded structure according to claim 1, characterized in that: