JPS6254065A - Low c-cr-mo steel used under damp steam - Google Patents

Abstract

PURPOSE:To obtain the titled low C-Cr-Mo steel excellent in EC resistance and welability and having moderate strength and toughness by specifhing a composition consisting of C, Si, Mn, Cr, Mo, Cu, Ni and Fe. CONSTITUTION:The low C-Cr-Mo steel excellent in weldability and showing superior EC resistance when used under damp steam of a feed water heater for nuclear power plant or the like can be obtained by providing a composition consisting of, by weight, 0.02-0.14% (preferably <=0.13%) C, 0.45-0.90% Si, 0.30-0.80% Mn, 0.70-1.60% Cr, 0.40-0.70% Mo, 0.02-0.5% (preferably 0.16-0.30%) Cu, 0.02-0.5% (preferably 0.16-0.30%) Ni and the balance essentially Fe except inevitable impurities and further containing, if necessary, 0.005-0.08% Al. The above steel is refined after regulation into prescribed components and is subjected to rolling, forging, etc., by the ordinary method, to which normalizing-and-tempering or annealing treatment is applied to form a steel material.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) This specification relates to a new low C-Cr-Mo steel for use in wet steam applications, particularly in feed water heaters for nuclear power generation equipment or similar applications. We present the results of our research and development on the above-mentioned types of steel, whose chemical compositions have been adjusted so that they can be used appropriately even in environments where they are attacked by erosion and corrosion (abbreviated as B and C), which are unique to the application. This is what I am trying to propose.

Wet steam and high-temperature condensed water, or high-temperature condensed water itself, which are usually below 250°C, are simply collectively referred to as "wet steam", and these high-temperature gas-liquid two-phase flows or high-temperature water flows are collectively referred to as "wet steam". Due to high-speed flow, the inner surface of the body of a closed vessel such as a feedwater heater for nuclear power generation equipment such as a light water reactor becomes B.

When attacked by C0, the corrosion products caused by B and C1 circulate within the reactor system, resulting in the activation of the entire system, and the reduction in reliability due to E, C, and damage to the feed water heater itself. There are concerns. .

As a means to eliminate these problems, first from a design perspective, the flow velocity of the fluid in the metal body in the system should be lowered by increasing the diameter of the feed water heater body and the diameter of the piping system.
From a material standpoint, it is conceivable to use steel types with better B and C1 resistance.

In the former case, lowering the flow velocity of the system fluid leads to larger equipment, which leads to an increase in the amount of steel used, which in turn leads to an increase in material and construction costs, so it is better to prevent this kind of harm from the material perspective. is requested.

(Prior art) As a result of analyzing and examining a large number of conventional knowledge and research results regarding E and C, JIS G410 shown in Table 1 was developed.
G4109SC (commonly known as 11/4%Cr-1/2%Mo-
3/4% S1 steel), heat treatment (normalizing and tempering, hereinafter abbreviated as N-T) and annealing, hereinafter abbreviated as A), and mechanical properties (N- For T steel and A steel, within the standard range of high strength level and low strength level, respectively, the C content is specifically regulated to 0.15 to 0.17%, which is near the upper limit of the standard, and heat treatment is also restricted to N-T. High C-11/4%Cr-1/2 with limited high strength level
Following the conclusion that %Mo-3/4 -11/4%Cr-1/2%Mo-3/4%S1 steel has been uniquely adopted in Japan as the steel material for the feed water heater as a measure to enhance the safety of nuclear power generation equipment. be.

One of the reasons why this type of net with a C content of 0.15% or more is applied is that it has a resistance to 8. This is mainly due to the fact that it is necessary to impart hardness to steel to ensure C1 properties.
In addition to this, the standards for SCMV-3, especially N-T steel, are high, such as high tensile strength (for example, tensile strength of 53 kgf/
mm2 or more).

However, today the resistance of feed water heaters for nuclear power generation equipment is E and C.
, In Japan, as a measure to improve the properties, we mainly deal with materials, using high-grade high C-11/4%Cr-1/2%Mo-3/4%S.
Although there is a tendency to adopt i steel, on the other hand, high C-11/4%Cr-1/2%Mo-3/4 as mentioned above
The use of %Si steel has many problems due to its poor weldability as shown below.

In other words, the feed water heater is shaped like a huge container with a diameter of about 2 ms and a length of about 10 m. First, the body plate is made by bending a steel plate into a cylindrical shape and welding the longitudinal direction, and then several of these cylindrical pieces are connected by circumferential welding. After the tube plate, tubes, and various other members are further assembled inside this cylinder by welding or the like, end plates are welded to both ends. In such welding assembly, high C
-11/4%Cr-1/2%Mo-3/4%Si steel has a weld hardenability index, C equivalent (C+Si/24+Mn/6+
Ni/40+Cr15+Mo/4+V/14) is, for example, 0.72%, and the welding susceptibility index, PCl4 value (C
+Si/30+Mn/20+Cu/20+Ni/60
+Cr/20+Mo/15+V/10+5B) is, for example, 0.32%, so it is a steel that is prone to welding cracks, so when welding, preheating and postheating should be carried out to avoid welding cracks. Particularly careful and at the same time stress-relieving annealing after welding, usually 5tress Reli
eving, or SR for short. ) must also be carried out at extremely high temperatures for a long period of time.

However, careful preheating means raising the temperature of the area to be welded to around 250°C using a gas burner, for example, and therefore not only affects the welding work environment (not only does it reduce welding efficiency, but the energy consumption of the gas burner is also significant). , resulting in great disadvantages.

(Problems to be Solved by the Invention) In this way, for the construction of current feed water heaters for nuclear power generation equipment, in order to save energy, improve the work environment, and improve efficiency, it is necessary to use Cr- The development of Mo steel is extremely important.

Resistance to wet steam 8. The essential conditions are that it has C1 properties and has strength and toughness suitable for feed water heaters. In addition, this resistance B.

Regarding C0 properties, the high C-11/4 that has been used so far
%Cr-1/2%Mo-3/4%Si steel is by no means perfect, and in consideration of the lifespan of the container and the safety of operation, further improvements are desperately needed.

That is, the purpose of this invention is to provide resistance to E and C under wet steam.
It is an object of the present invention to provide a steel composition with excellent zero properties and excellent weldability.

First, it is clear from the calculation formulas for the C equivalent and PGI1 value mentioned above that in order to improve weldability, it is sufficient to reduce the C content, but in such a case, the hardness of the steel naturally decreases, so the E resistance, C. It is usually assumed that the quality deteriorates.

Rather than improving weldability without impairing B, C and resistance, it is desired to further improve B and C0 resistance, and also improve weldability. It is common knowledge among those skilled in the art that reducing C content is inherently inappropriate for improving C1 property, and in fact, reducing C content can improve resistance to 8. There are no examples of attempts to improve C1 properties.

On the other hand, this problem was considered to be an insurmountable problem in terms of economic efficiency under the current state of technology, and the reality was that the compromises mentioned above had to be made.

(Means for Solving the Problems) The inventors have purposely tried to find a more advantageous solution to the above-mentioned problems, and have particularly focused on improving the C content and trace alloying elements of this steel type in terms of E resistance, C resistance, weldability, As a result of systematic and fundamental research into the essence of the relationships that should affect mechanical properties, we discovered an unexpected fact: this type of Cr-Mo steel has B resistance,
Regarding the C0 property, ■ it becomes better when the C content is reduced to 0.14% or less, ■ it is significantly improved by the simultaneous addition of trace amounts of Cu and Ni, ■■, ■. We discovered that in each case, excellent performance was achieved even at low strength levels.

All of these facts can be said to be unexpected findings that contradict conventional technical common sense or academic concepts.

The inventors applied these findings to steels used under wet steam conditions, such as the feedwater heaters mentioned above, and improved the ε resistance, C1 resistance, and weldability, which were considered difficult in such applications as mentioned above. This resulted in improvements in both aspects all at once.

This first invention contains c:o, 02 to 0.14% by weight (
(hereinafter simply expressed in %), Si: 0.45 to 0.90%,
Mn: 0.30-0.80%, Cr: 0.70-1.6
0% and Mo: 0.40 to 0.70%, with the remainder excluding inevitable impurities and having a substantially Fe composition as a basic component,
In addition, Cu is an element that contributes to increasing strength through solid solution hardening.
By making the composition contain 0.02 to 0.5% of N1 and N1 at the same time, the weldability and resistance 8. This achieved improvement in C6 properties.

Further, in this second invention, C: 0.02 to 0.14% by weight (
(hereinafter simply expressed in %), Si: 0.45-0.90%
,! +In: 0, 30-0.80%, Cr: 0.7
0 to 1.60%, Mo: 0.40 to 0.30%, C
u: o, 02-0.5%, Ni: 0.02-0.5
% and Al: 0.005 to 0.08%, and the remainder is essentially Fe, excluding inevitable impurities, to improve the ε resistance.
, improved C8 properties and weldability.

In addition, the C content, which is an important component among the above, is particularly set at 0.02 to 0.13%, and the same <Cu and Ni contents are set at 0.16 to 0.30%, respectively, as expected in each of the inventions. The present invention includes embodiments limited to areas where the above effects can be further enhanced.

(for I) The reasons for limiting the above component ranges are as follows.

The C content is the most important requirement in this invention, reducing weld hardenability and weld crack sensitivity, lowering the preheating temperature of welding, omitting postheating, and lowering the stress relief annealing temperature.
Furthermore, in order to achieve excellent B and C0 resistance, particularly breaking through conventional ideas, the content must be limited to 0.14% or less. From the point of view of weldability, the lower the C content, the better, but it is necessary to use steel at room temperature and temperatures up to about 250°C, which is required for steel used in wet steam environments such as feed water heaters for nuclear power generation equipment. Since at least 0.02% is necessary to obtain strength and toughness in the range, the lower limit is set at 0.02%.

In particular, the Cr-Mo steel having the composition according to the present invention has a remarkable feature in that when the C content is reduced as described above, even if it is a very small amount, the welding flaw sensitivity is significantly improved. The upper limit of content is 0.14% to 0.
A reduction to 13% can significantly improve weld susceptibility without causing a significant drop in strength levels, so the C content is preferably up to 0.13%, more preferably up to 0.11%. good.

Next, Si is an element effective in increasing strength at room temperature and at very high temperatures. In this invention, in order to fully exhibit the desired effect, it is necessary to strictly limit the C content, so it is expected that the strength will decrease accordingly, and in order to maintain the specified strength, the minimum S1 content is 0.45% is required, and from the viewpoint of strength, the more the better, up to 0.90%, but if it exceeds 0.90%, the toughness of the weld heat affected zone deteriorates, so 0.45 to 0. Limited to 90%.

Mn needs to be 0.30% or more in order to give strength and ductility to steel, but in steel with the composition of this invention, Cr and Mo make a large contribution to ensuring strength, so Mn is not necessary in terms of strength. There is no need to use a large amount, rather 0.80
If it exceeds 0.30% to 0.80%, the welding hardenability will increase and cause problems.

Both Cr and Mo are treated by E,
It is an important element that increases resistance to C0. In order to provide excellent ε resistance and C8 properties for applications such as feed water heaters for nuclear power generation equipment, the steels with the compositions of these inventions must contain at least 0.70% and 0.40% of Cr and MO, respectively.
is necessary. Considering the purpose of improving ε resistance and C1 property, the larger the amount of Cr and Mo, the greater the effect.
If it exceeds 60%, and if Mo exceeds 0.70%, there is a concern that workability and weldability will deteriorate. Therefore, Cr
The content is 0.70-1.60%, and the MO is 0.40%.
~0.70%, respectively. Note that Cr not only contributes to the formation of a high-strength structure as an element that improves hardenability, but also has a solid solution strengthening effect.
On the other hand, MO is a precipitation-hardening element, which precipitates fine carbides during tempering treatment, both of which also contribute to an increase in strength, and as a result, the above-mentioned effects are appropriately exhibited within their respective limits.

Next, Cu: 0.02-0.5%, Ni: 0.02-0.
The reason for containing both at the same time at 5% is that the B, C, resistance to high flow rate wet steam can be further significantly improved. This effect is due to CuO, 0.02% or more, Ni0.
At 0.02% or more, the effect becomes more pronounced when combined than when each of them is used alone, so it is necessary to use them together. Epsilon resistance
.

In terms of improving C0 properties, the more Cu and Ni there are, the better; however, if either one exceeds 0.5%, weldability will be significantly reduced, so the upper limit of each content should be set at 0.5%.
And so. Resistance B and C due to simultaneous addition of Cu and Ni.

In order to further improve the welding properties, it is preferable to set it to 0.16% or more, and the higher the amount up to 0.5%, the greater the effect, but on the other hand, in terms of welding susceptibility, In fact, less is better, and each content is preferably 0.30% or less.

In other words, in order to maximize B resistance, C1 properties, and weldability, it is practically desirable to limit C to 0.13% or less, and to contain both Cu and Ni at 0.16 to 0.30%. .

Cu and Ni are elements that originally have a solid solution strengthening effect and improve hardenability, and by including them in combination, the strength is greatly increased. Since strength can be improved by Cu and Ni in this way, it is possible to reduce the C content in terms of strength, and the content of Cu and Ni can improve B resistance.
, it is also useful for improving C0 properties. That is, Cu
When Ni and Ni are contained together, they themselves improve the ε resistance and C0 property and also help increase the strength.The increase in strength makes it possible to reduce the C content, so this also improves the E. C.
This will contribute doubly to improving sexual performance.

Furthermore, the reason why Al is contained in the range of 0.005 to 0.08% is that Al is particularly useful for improving toughness based on the grain refining effect by forming AIN. These effects are clearly expressed at 0.005% or more and become significant at first as the amount increases, but they are saturated at about 0.08%, so they are limited to 0.005 to 0.08%.

In each of these inventions, unavoidable impurities contained in a normal steel manufacturing process are acceptable. That is, the general limit for S and P is preferably 0.025% or less in order to increase the susceptibility of the welded part to high temperature cracking. On the other hand, N is contained in the normal steelmaking process.
, 0020-0.0150% is acceptable, but 0.0
If it exceeds 150%, the properties of the steel ingot will deteriorate due to the occurrence of blowholes, etc., and the weldability will also deteriorate, so it is preferably within the above range.

Furthermore, steel with the above composition is used for parts used under wet steam, and as mentioned above, it has B, C, resistance, weldability, strength, toughness, etc., and is suitable for the above-mentioned applications that require these properties. It is valuable and economical.

In other words, this invention exhibits effects in terms of both quality and economy only when used for the above-mentioned purposes.

The reasons for limiting the steel composition, uses, etc. of each invention have been explained above, but the steel of this invention is produced by melting with the above-mentioned composition adjustment, and then subjected to a rolling or forging process by a conventional method, and then sintered. It is produced as a steel material by conditioning and subsequently tempering or annealing, the heat treatment being limited to the two types mentioned above.

Note that normalizing here refers to air cooling after heating to AC 3 points or higher (for example, if the plate thickness is less than 100111+Q, it is just air cooling!
Air cooling or forced cooling for extremely thick materials of 00n++n or more)
Tempering is a process of AC heating and then air cooling, and annealing is a process of heating to a temperature above the ACI point and then slowly cooling. Normalized and tempered materials usually have a ferrite-pearlite structure and may contain bainite. Annealed materials usually have a pearlite-in-ferrite structure.

To be sure, we will mention feedwater heaters for nuclear power generation equipment as a typical example of equipment used under wet steam. The fact that it can be annealed is a major feature, and has high value as described below.

In other words, steel that has undergone annealing heat treatment is less sensitive to thermal cycles such as stress relief annealing after welding, and has less variation in structure and mechanical properties than steel that has undergone normalizing and tempering treatments. .

Therefore, when considerable temperature variations are expected, such as during stress-relief annealing of large welded structures, it is necessary to It may be more desirable to use annealed steel rather than tempered steel.

Despite these characteristics of annealed steel, conventionally only normalized and tempered steel has been used in feed water heaters for nuclear power generation equipment, and there has been no movement to use annealed steel until now. The main reason for this was that annealed steel had lower strength than tempered steel, and was thought to have significantly lower E, C, and resistance. However, as a result of intensive research without being bound by conventional fixed ideas, the inventors found that even if the composition according to the present invention is subjected to annealing heat treatment, the resistance to E, C, and properties are extremely high, and it is possible to reduce C. Weldability was sufficiently improved, and it was also confirmed that the steel had appropriate strength and toughness as steel for feed water heaters for nuclear power generation equipment.

(Examples) Now, in order to further clarify the constituent elements of each of the inventions as described above and specifically demonstrate the special effects of each invention, examples will be described below.

The chemical composition of the test steel is shown in Table 2.

Symbols No. 1 to 3 in the table are the first invention steels, and symbol N
o, 4 to 13 are the second invention steels, and symbol No. 14.
15 is a commercially available high C-11/4%Cr-1/2%Mo- that has been used in feed water heaters for nuclear power generation equipment as a representative example of equipment used under wet steam in Japan.
This is 3/4% Si steel, which corresponds to so-called conventional steel, and has a C content of 0.16 to 0.17%, which is much higher than the upper limit of 0.14% according to the present invention.

Symbol No. 16 to 18 will be shown later in N-T-3.
All of R material, N-T material, and A-5R material have E.
C. The effect of the trace amounts of Cu and N1 on improving the properties of each of these inventions is such that the upper limit of the C content according to each of these inventions is 0.
．． This is a so-called comparative steel which shows that it cannot be obtained if it exceeds 14%, and among these, the symbol Nα16.17 is a comparative steel that was used for the weldability test.

Furthermore, symbol No. 19.20 has a Cr content that does not meet the lower limit of this invention, and symbol No. 21.22 has Cr, Mo
These are comparative steels in which both amounts exceed the upper limits of the respective ranges of the present invention, thus exhibiting inferior E resistance, C1 properties, or weldability.

Table 2: These steels are commercially available. Symbol No. 14.15
With the exception of the conventional steel, 100 kg steel ingots were melted using a small high-frequency induction heating vacuum melting furnace and hot rolled to a plate thickness of 30 mm using a small rolling mill. The heat treatment after rolling was not limited to the normalizing and tempering treatments conventionally applied to steel materials for feed water heaters for nuclear power generation equipment, but annealing was also performed.

Note that the normalizing treatment referred to here is C, which is charged into a heating furnace at 930°C, held for one hour, extracted, and left to cool in the atmosphere. The tempering treatment conditions were 660°C x 1 hour.

In addition, for annealing heat treatment, the steel plate is charged into a heating furnace at 930°C, held for 1 hour, and then slowly cooled in the furnace by adjusting the cooling rate of the steel plate to an average of 0.8°C/min between 800 and 400°C. It is something that makes you

Steel plates always undergo stress relief annealing after welding and assembly, so both normalized and tempered materials and normalized materials undergo an additional 6
45℃ x 1h, however, 67 in the case of Nα15 and Nα16
0°C x 3h, 690°C x for No, 17 and Nα18
A stress relief annealing (SR) of 11 hours was applied and the test was carried out. However, it goes without saying that test materials that have not undergone stress relief annealing were used for the weldability tests.

Using these test materials, we first conducted tensile tests and V-Charpy impact tests at room temperature and 250°C to confirm that each invented steel has appropriate strength and toughness as steel used in feedwater heaters for nuclear power generation equipment. It was verified by doing this. The appropriate strength and toughness mentioned here are:
For example, in terms of tensile strength, it is approximately 40 kgf at room temperature.
/mm2 or more, and considering that the feed water heater is heated to about 150℃, it is desirable to maintain 40kgf/mm2 or more even at 250℃, which is higher than that, and the absorbed energy at 0℃ Considering the usage conditions, approximately 2.1 kgf-m or more is sufficient.

For tensile testing, diameter 5mm, parallel part 30mm, gauge length 2
A 2 mm V notch Charpy specimen was used for the impact test.

Furthermore, the effect of improving weldability, which is one of the objectives of each of the inventions, was investigated using representative test materials. JIS for weldability test
Using the diagonal Y-shaped weld warpage test method specified in Z 3158, the warpage prevention preheating temperature was determined.

Next, E with high-speed high-temperature water was carried out on representative test materials.
The method of C0 test will be described. As shown in Fig. 1, the test piece was a disk with a diameter of 9 mm and a thickness of 10++ mm and a width of 3 mm.

A groove with a depth of 5m+n is cut in the shape of a cross. In the test, a nozzle with a diameter of 1 mm was passed through the intersection of the grooves from the top.
℃, high-temperature, high-pressure water simulating reactor water containing 5 ppb or less of oxygen was sprayed at a high flow rate of 10m/s for 500 hours, E.
This was done by examining the weight loss of the test piece due to C0.

Test results based on the above test method are shown in Table 3, FIG. 21, and FIG.

Figure 2 shows the relationship between tensile strength and C content at room temperature and the relationship between crack prevention preheating temperature during welding and C content using steel belonging to the composition of the second invention, conventional steel, and comparative steel. It is.

According to Table 3, each of the invented steels exhibits sufficiently high tensile strength and toughness at room temperature and 250°C to be suitable for the above-mentioned uses, and C content is required to improve ε resistance, C0 property, and weldability. It is clear that even if it is reduced, there is no problem in terms of strength. In addition, there is no problem in changing the normalizing and tempering treatment conventionally applied to steel for feedwater heaters to an annealing treatment that is difficult to increase strength, and in terms of strength, the C content can be significantly reduced compared to the conventional method. This knowledge is completely new.

Next, FIG. 2 shows the relationship between welding susceptibility and C content for steels whose Cr and Mo contents fall within the range of the second invention.

From FIG. 2, conventional steels No. 14, No. 15, and comparative steel No. 15 having a C content exceeding the upper limit of the second invention are shown.
, 16, the crack prevention preheating temperature is 150 to 200°C, but if the C content is limited to 0.14% or less according to the second invention, the preheating temperature can be lowered to 125°C or less,
Furthermore, if the amount of C is limited to 0.13% or less and the content of Cu and Ni is limited to 0.30% or less, the temperature can be further reduced to 100° C. or less.

Symbol No. 11 and No. 6 and No. 12 and No. 13
A comparison of the welding prevention preheating temperatures reveals that, in the case of this steel type, trace amounts of Cu and Ni have a large effect on welding susceptibility, contrary to expectations under the general state of the art, and that both of their contents are 0. By limiting the content to 30% or less, the crack prevention preheating temperature can be lowered by 25°C compared to the case where the content is more than 0.30% and 0.50% or less. Also, the first invention steel No.
, 1 to 3, the crack prevention preheating temperature is also 100°C or less.

In other words, in order to prevent weld cracks, conventional steel needed to be preheated to a high temperature of at least 150 to 200°C, but it is only necessary to preheat to a temperature of 125°C or less (
The amount of C is 0.13% or less, and the amount of Cu and Ni is 0.16 to 0.
．． 3% steel can be preheated to 100°C or less, which can be said to be a dramatic improvement in welding work.

Next, E resistance, C0 resistance and C
, Regarding the relationship with U and N+ content, as well as lower C and Cu
It can be seen that the combined addition of Ni and Ni is extremely effective in improving this property. The combined addition of Cu and Ni is effective in improving this property, and the more Cu and Ni there are, the greater the effect, but in order for Cu and Ni to exhibit this property improvement effect, the C content must be 0. It is clear from comparison with Comparative Steel Nos. 16 to 18 that the limit of 14% or less is essential. This type of Cu-Mo steel has a low C content of 0.1 as the steel for feed water heaters.
It has been found that significant improvement can be achieved by limiting the content to 4% or less, or by simultaneously adding small amounts of Cu and N1, preferably at least 0.16% of each.

Furthermore, to explain the relationship between E, C and resistance and c, Cu and N1 content which are important requirements of this second invention using FIG. Steel symbol No. 14 and 15, comparative steel symbol Nα18
From the comparison, it is clear that reducing the amount of C to 0.14% or less and adding Cu and Ni in combination is effective in improving the ε resistance and C1 property. The resistance of this type of Cr-Mo steel is E and C.

In other words, as steel for feed water heaters, the C content is reduced to 0.
It has been found that significant improvement can be achieved by limiting the content to 14% or less, or by simultaneously adding trace amounts of Cu and N1, preferably by adding 0.16% or more of each.

Further, in Table 3, 0, 5Cr-0,5Mo steels (symbols No. 19, No. 20), 21/4Cr-1Mo steels whose Cr and/or Mo content is outside the scope of each invention
Looking at steels (symbols No. 21', No. 22), the former has insufficient ε and C1 resistance due to the small amount of Cr, and E and C: become problems when used under wet steam. Also, the latter has a high welding susceptibility index <250℃
It can be seen that this requires preheating, which is accompanied by great difficulty in operation. On the other hand, each invented steel has a resistance of 6. C0
It has excellent properties as a steel used under wet steam conditions.

(Effects of the Invention) As described in detail above, according to the present invention, the preheating temperature during welding can be reduced to about 125°C or considerably lower, which reduces the risk of damaging the working environment and Since less energy is required for preheating, energy costs can be reduced, and of course, the E and C0 resistance against wet steam are extremely excellent, so the life of the container can be extended. . In particular, the present invention can be used with remarkable effects in feed water heaters for nuclear power generation facilities.

[Brief explanation of the drawing]

Figure 1 is a perspective view of the E and C1 specimens, and Figure 2 is a comparison showing the tensile strength of the steel composition of the present invention and the effect of reducing the preheating temperature necessary to prevent cracking during welding with respect to C content. The graph, Figure 3, shows resistance to 6. 1 is a comparison graph summarizing the influence of components in steel on C0 property.

Claims (1)

[Claims] 1. C: 0.02-0.14% by weight Si: 0.45-0.90% by weight Mn: 0.30-0.80% by weight Cr: 0.70-1.60 Weight% Mo: 0.40 to 0.70% by weight, Cu: 0.02 to 0.5% by weight, and Ni: 0.02 to 0.5% by weight, and the remainder is substantially Fe except for inevitable impurities. The composition is
Endurance E. C. A low C-Cr-Mo steel that is used under wet steam and is characterized by excellent weldability and weldability. 2. The low C-Cr-Mo steel according to claim 1, wherein the C content is 0.13% by weight or less, and the Cu and Ni contents are each 0.16 to 0.30% by weight. 3. C: 0.02-0.14% by weight Si: 0.45-0.90% by weight Mn: 0.30-0.80% by weight Cr: 0.70-1.60% by weight Mo: 0. Contains 40-0.70% by weight, Cu: 0.02-0.5% by weight, Ni: 0.02-0.5% by weight, and Al: 0.005-0.08% by weight, with the remainder containing unavoidable impurities. Except for this, the composition is essentially Fe, and the E. C
．． A low C-Cr-Mo steel that is used under wet steam and is characterized by excellent strength and weldability. 4. The low C-Cr-Mo steel according to claim 3, wherein the C content is 0.13% by weight or less, and the Cu and Ni contents are each 0.16 to 0.30% by weight.