JPH0254415B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial application field) New low C-Cr for use under wet steam
-With regard to Mo steel, this specification specifically refers to erosion and corrosion (abbreviated as EC), which is specific to applications in feedwater heaters for nuclear power generation facilities or similar products.
This paper attempts to propose the results of research and development related to the above-mentioned types of steel, the composition of which has been adjusted so that it can be used appropriately even in environments where it is attacked by steel. Wet steam and high-temperature condensed water, or high-temperature condensed water itself, which are usually below 250°C, are collectively referred to here as "wet steam", and these high-temperature gas-liquid two-phase flows or high-speed flows of high-temperature water flows are collectively referred to as "wet steam". Due to E.
When attacked by C., there are concerns that corrosion products caused by EC may circulate within the reactor system, causing activation damage to the entire system, and reducing reliability due to EC damage to the feedwater heater itself. Ru. As a means to eliminate these problems, first of all, from a design perspective, the flow velocity of the fluid throughout the system should be lowered by increasing the diameter of the feed water heater body and the diameter of the piping system, and from the viewpoint of materials, it should be It is conceivable to adopt a steel grade with better properties. In the former case, lowering the flow rate of fluid in the system leads to larger equipment, increasing the amount of steel used, and ultimately reducing material costs.
Rather, it is required to prevent this type of damage from occurring in terms of materials, since this will lead to an increase in construction costs. (Conventional technology) As a result of analyzing and examining a large amount of conventional knowledge and research results regarding EC, the JIS standard shown in Table 1 was
G4109, SCMV-3 (commonly known as 1 1/4wt% (hereinafter simply expressed as %) Cr-1/2%Mo-3/4%Si
chemical composition of steel), heat treatment (two types: normalizing and tempering (hereinafter abbreviated as NT) and annealing (hereinafter abbreviated as A)) and mechanical properties (NT steel and A steel), Among the standard ranges for high strength and low strength levels, the C content is specifically regulated to 0.15% to 0.17%, which is near the upper limit of the standard.
High C- with high strength level with heat treatment limited to N-T.
1 Following the conclusion that 1/4%Cr-1/2%Mo-3/4%Si steel is a steel with excellent EC resistance suitable for feed water heaters, its properties were actually confirmed through experiments. In this way, this high C-1 1/
4% Cr-1/2% Mo-3/4% Si steel was uniquely adopted in Japan as a steel material for the feed water heater as a measure to further enhance the safety of nuclear power generation equipment.

[Table] The reason why this type of steel with a C content of 0.15% or more is applied is mainly because it is necessary to impart hardness to the steel in order to ensure EC resistance. In addition to this, we also ensured the high tensile strength (for example, tensile strength of 53 kgf/mm ² or more) of SCMV-3, especially for NT steel. However, today the durability of feedwater heaters for nuclear power generation equipment is
In Japan, as a measure to improve EC properties, we use high-grade high C-1 1/4%Cr-1/2Mo to deal exclusively with materials.
-Although there is a tendency to adopt 3/4% Si steel, on the other hand, high C-1 1/4% as mentioned above
The use of Cr-1/2Mo-3/4%Si steel has many problems due to poor weldability as shown below. In other words, the feed water heater has a diameter of approximately 2 m and a length of approximately
It is a huge container-like object that is 10 meters long. 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-1
1/4%Cr-1/2Mo-3/4%Si steel has the following properties: weld hardenability index, C equivalent (C+Si/24+Mn/
6+Ni/40+Cr/5+Mo/4+V/14) is, for example, 0.72%, and the welding susceptibility index, P _CM value (C+Si/30
+Mn/20+Cu/20+Ni/60+Cr/20+Mo/15
+V/10+5B) is, for example, 0.32%, making it a steel that is prone to welding cracks. Therefore, when welding, preheating and postheating must be carried out very carefully to avoid welding cracks. Stress relief annealing after welding (usually
It is called Stress Relieving, or SR for short. ) must also be carried out at extremely high temperatures for a long period of time. However, careful preheating here usually means using a gas burner to raise the temperature of the area to be welded to about 250℃, which not only makes the welding work environment worse, but also reduces welding efficiency and consumes significant energy by the gas burner. , resulting in great disadvantages. (Problems to be Solved by the Invention) In this way, energy saving, working environment,
In order to improve efficiency, it is extremely important to develop Cr-Mo steel that is less susceptible to welding. The essential conditions are that it has EC resistance against wet steam, and that it has strength and toughness suitable for use in feed water heaters. In addition, this E.
C. With regard to sex, the high C-1 used so far
1/4% Cr - 1/2% Mo - 3/4% Si steel is by no means perfect, and in consideration of the lifespan of the container and operational safety, further improvements are desperately needed. There is. In other words, the purpose of this invention is to provide resistance under wet steam.
The objective is to provide a steel composition with excellent EC properties and excellent weldability. First, it is clear from the calculation formulas for C equivalent, P _CM , etc. that the C content should be reduced in order to improve weldability, but in that case, the hardness of the steel will naturally decrease, so the EC resistance will deteriorate. It is usually assumed that Rather than improving weldability without compromising EC resistance, we have further improved EC resistance,
Moreover, it is desired to improve weldability, and it is common knowledge among those skilled in the art that reducing the C content is inherently inappropriate for improving EC resistance. There are no examples of attempts to improve EC resistance by reducing the amount. 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 difficult problem, and have particularly focused on improving the C content and trace alloying elements of this steel type to improve its EC resistance, weldability, and mechanical properties. As a result of systematic and fundamental research into the essence of the relationship between Furthermore, we discovered that the simultaneous addition of trace amounts of Cu and Ni significantly improved the performance, and that in each case, excellent performance was achieved even at low strength levels. did. 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 steel used under wet steam conditions, such as in the feed water heater, and solved the above-mentioned challenges in such applications.
This resulted in improvements in both EC resistance and weldability all at once. Herein, the first invention is as follows: C: 0.02% to 0.14%, Si: More than 0.50% to 0.90%, Mn: 0.30% to 0.80%, Cr: 0.70% to 1.60%, Mo: 0.40% to 0.70. % or less, Cu: 0.02% or more and 0.50% or less and Ni: 0.02% or more and 0.50% or less, the remainder consists of Fe and inevitable impurities,
Characterized by excellent EC resistance and weldability,
It is a low C-Cr-Mo steel used under wet steam,
Next, the second invention is as follows: C: 0.02% to 0.14%, Si: 0.50% to 0.90%, Mn: 0.30% to 0.80%, Cr: 0.70% to 1.60%, Mo: 0.40% to 0.70. % or less, Cu: 0.02% or more and 0.50% or less: Ni: 0.02% or more and 0.50% or less and Al: 0.005% or more and 0.08% or less, the remainder consists of Fe and inevitable impurities,
Characterized by excellent EC resistance and weldability,
This is a low C-Cr-Mo steel used under wet steam conditions. In addition, in the first invention and the second invention, the C content, which is an important component among the above, is particularly reduced to 0.02%.
It also includes embodiments in which the Cu and Ni contents are each limited to 0.16% or more and 0.30% or less, respectively, to further enhance the desired effects of each invention. (Function) The reasons for limiting the above component ranges are as follows. The C content is the most important requirement in this invention, and it reduces weld hardenability and weld crack susceptibility, lowers the welding preheating temperature, eliminates postheating, lowers the stress relief annealing temperature, and has excellent EC resistance. In order to break through conventional ideas about sexuality and realize it,
Must be limited to 0.14% or less. From the point of view of weldability, the lower the C content, the better. Since at least 0.02% is necessary to obtain strength and toughness in the temperature range, the lower limit is set at 0.02%. In particular, the Cr-Mo steel having the composition according to the present invention exhibits 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 susceptibility is significantly improved. A reduction in the amount from the upper limit of 0.14% to 0.13% can significantly improve the weld flaw susceptibility without causing a significant decrease in the strength level, so the C content is preferably up to 0.13%, more preferably up to 0.11%. It is better to control Next, Si is an effective element for increasing strength at room and 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 Si content is required. It is necessary to exceed 0.50%,
In terms of strength, the higher the content up to 0.90%, the better; however, if it exceeds 0.90%, the toughness of the weld heat affected zone deteriorates, so it is limited to over 0.50% and up to 0.90%. Mn requires 0.30% or more 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. It is not necessary to use it; in fact, if it exceeds 0.80%, the weld hardening property increases and problems arise, so it is limited to a range of 0.30 to 0.80%. Both Cr and Mo are important elements that increase the resistance to EC due to high flow rates of wet steam. In order to provide excellent EC resistance for applications such as feed water heaters for nuclear power generation equipment, steels with the compositions of these inventions require at least 0.70% and 0.40% of Cr and Mo, respectively. Considering the purpose of improving EC resistance, the larger the amount of Cr and Mo, the greater the effect, but if Cr exceeds 1.60%, and Mo exceeds 0.70%.
There is a concern that workability and weldability will deteriorate in any case. Therefore, the Cr content is limited to a range of 0.70% to 1.60%, and the Mo content is limited to a range of 0.40% to 0.70%. 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;
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% or more 0.50%, Ni: 0.02% or more
The reason for containing both at the same time within the range of 0.50% is that the EC resistance against wet steam at a high flow rate can be further significantly improved. This effect is
If Cu is 0.02% or more and Ni is 0.02% or more, the effect becomes more pronounced when combined than when each of them is used alone, so they must be used together. In terms of improving EC resistance, 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 of these contents was set at 0.5%.
In order to further improve the EC resistance by simultaneous addition of Cu and Ni, it is preferable to add each to 0.16% or more, and up to 0.50%, the greater the effect, but on the other hand, it is difficult to weld. In terms of sensitivity, less is better, and each
It is desirable that it be 0.30% or less. In other words, to maximize EC resistance and weldability, C
It is practically desirable to limit the content of Cu 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 inclusion of Cu and Ni is also useful for improving EC resistance. In other words, when Cu and Ni are contained together, they themselves improve EC resistance and help increase strength, and their increased strength makes it possible to reduce C content, which also improves EC resistance. This will make a double contribution. Furthermore, in the second invention, 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 AlN. Their effect is 0.005
% or more, and becomes noticeable at first as the dose increases, but saturates at about 0.08%, so 0.005 to 0.08
%. For each of these inventions, unavoidable impurities contained in a normal steel manufacturing process are acceptable. That is, the general limit for both 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 content of 0.0020% to 0.0150% is allowed in the normal steelmaking process, but if it exceeds 0.0150%, the properties of the steel ingot will deteriorate due to the occurrence of blowholes, etc., and weldability will also deteriorate, so it should be within the above range. It is preferable. Furthermore, steel with the above composition can be used in parts that are used under wet steam, and as mentioned above, it has EC resistance, weldability, strength, toughness, etc., and it is valuable only when it is applied to the above applications that require these properties. It is 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 welded with the above-mentioned composition adjustment, then subjected to a rolling or forging process by a conventional method, and then sintered. The steel material is produced by tempering and subsequent 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 100 mm, simply air cooling,
For extra-thick materials of 100 mm or more, it is a process of air cooling or forced cooling. Tempering is a process of heating to Ac ₁ point or less and then air cooling, and annealing is a process of heating to Ac of ₃ points or more and then slowly cooling. It is processing. Normalized and tempered materials usually have a ferrite/pearlite structure,
It may also contain bainite. Annealed materials usually have a ferrite + pearlite structure. To be sure, we mention feedwater heaters for nuclear power generation equipment as a typical example of equipment used under wet steam. Namashi”
The fact that it can be used even if it is used is a major feature, and has particularly 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 than steel that has undergone normalization and tempering, and its structure and mechanical properties may change. few. Therefore, in cases where considerable temperature variations are expected, such as during stress relief annealing of large welded structures, it is necessary to It is 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 EC resistance. However, as a result of intensive research without being bound by conventional fixed ideas, the inventors found that even if annealing heat treatment is performed using the composition according to the present invention, the EC resistance is extremely high, low C is possible, and weldability is sufficiently improved. Moreover, it was 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 this 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 the symbols
Nos. 4 to 13 are the second invention steels, and Nos. 14 and 15 are commercially available steels that have been used in feed water heaters for nuclear power generation equipment as representative examples of equipment used under wet steam in Japan. C-1 1/4%Cr-1/
It is a 2Mo-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. Symbols No. 16 to 18 will be explained later.
If the effect of each of these inventions on improving the EC resistance of the SR material, NT material, and A-SR material by trace amounts of Cu and Ni exceeds the upper limit of 0.14% of the C content according to each of these inventions. It is a so-called comparison steel that indicates that it will no longer be possible to obtain it, and the symbol
Nos. 16 and 17 are comparative steels used for weldability tests. Further, in symbols No. 19 and 20, the amount of Cr is less than the lower limit of this invention, and in symbols No. 21 and 22, the amount of Cr and Mo both exceed the upper limit of the range of each of these inventions, and thus the EC resistance or This is a comparative steel showing inferior weldability.

【table】

[Table] These steels are commercially available with symbols No. 14 and 15.
With the exception of the conventional steel, 100Kg steel ingots were melted using a small high-frequency induction heating vacuum melting furnace and hot-rolled to a thickness of 30mm 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 facilities, but annealing was also performed. Note that the normalizing treatment referred to here involves charging the material into a heating furnace at 930°C, holding it for one hour, extracting it, and allowing it to cool in the atmosphere. The tempering treatment conditions were 660°C x 1h. In addition, for annealing heat treatment, the material is charged into a heating furnace at 930℃.
After holding for 1 hour, the cooling rate of the steel plate in the furnace is 800-400℃.
The temperature is gradually cooled at an average rate of 0.8°C/min. Steel plates always undergo stress relief annealing after welding and assembly, so both normalized and tempered materials are further heated at 645°C for 1 hour, except for No. 15 and No. 16 at 670°C for 8 hours. , No. 17 and No. 18 were subjected to stress relief annealing (SR) at 690°C for 11 hours and subjected to testing. However, it goes without saying that the test materials that have not undergone stress relief annealing were used for the weldability tests. Using these test materials, we first confirmed that each invented steel has appropriate strength and toughness as steel used in feedwater heaters for nuclear power generation equipment at room temperature and
This was verified by conducting a tensile test at 250°C and a V-Sharpie impact test. In addition, the appropriate strength and toughness mentioned here, for example, in terms of tensile strength, should be about 40Kgf/mm ² or more at room temperature, and should be higher considering that the water is heated to about 150℃ by a water heater. Similarly, at 250℃, 40Kgf/
It is desired that the absorption energy be maintained at ^2.1 Kgf·m or more, considering the usage conditions at 0°C. For tensile testing, diameter 6mm, parallel part 30mm, gauge length
A 25 mm round bar specimen was used, and a 2 mm V-notched pea specimen was used for the impact test. Furthermore, the effect of improving weldability, which is one of the objectives of this invention, was investigated using representative test materials. For the weldability test, we used the diagonal Y-shaped weld warpage test method specified in JIS Z 3158, and determined the warpage prevention preheating temperature. Next, we will describe the method of EC testing using high-speed, high-temperature water on representative test materials. The test piece was a disk with a diameter of 9 mm and a thickness of 10 mm, with a width of 3 mm, as shown in Figure 1.
A groove with a depth of 5 mm is cut in the shape of a cross. For 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 nuclear reactor water at 150℃ and less than 5 ppb of oxygen was sprayed at a high flow rate of 10 m/s for 500 hours.
This was done by examining the weight loss of the test piece due to EC. Test results based on the above test method are shown in Table 3, Figures 2 and 3.

[Table] Figure 2 shows the tensile strength and C
It shows the relationship between the content and the relationship between the crack prevention preheating temperature during welding and the C content. 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 uses, and the C content is reduced to improve EC resistance and weldability. However, it is clear that 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 feed water 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, for steels whose Cr and Mo contents fall within the range of this second invention, the relationship between weld fray sensitivity and C content is determined as follows.
As shown in the figure. From FIG. 2, it can be seen that the crack prevention preheating temperature of conventional steels No. 14 and No. 15 and comparative steel No. 16, which have a C content exceeding the upper limit of the second invention, is 150 to 200°C. According to this second invention, the C content is reduced to 0.14.
% or less, the above preheating temperature can be lowered to 125°C or less, and furthermore, if the C amount is limited to 0.13% or less, Cu and Ni
If each is limited to 0.30% or less, the temperature will increase further by 100℃.
It can be reduced to below. A comparison of the crack prevention preheating temperatures of No. 11 and No. 6 and No. 12 and No. 13 reveals that a trace amount of Cu and Ni are welded in this steel type, contrary to expectations based on the general state of the art. By limiting their contents to 0.30% or less, the preheating temperature for preventing cracking can be lowered by 25°C compared to when they are more than 0.30% and 0.50% or less. Further, the crack prevention preheating temperature of the first invention steel Nos. 1 to 3 is also 100°C or less. In other words, in order to prevent weld cracking, conventional steels had to be preheated to a high temperature of at least 150 to 200°C, whereas it is only necessary to preheat to 125°C or less at most, and in particular, the C content is 0.13% or less, Cu and Ni amount
Steel with a content of 0.16 to 0.3% can be preheated to 100°C or less, which can be said to be a dramatic improvement in welding work. Next, the relationship between EC resistance and C, Cu, and Ni contents, which are important requirements of the first invention, will be compared with conventional steel symbols No. 14 and 15.
It can be seen that the combined addition of Cu and Ni is extremely effective in improving this property. To improve this characteristic
Combined addition of Cu and Ni is effective, and Cu and Ni
The larger the amount, the greater the effect, but in order for Cu and Ni to exhibit this property improvement effect, C
It is clear from comparison with Comparative Steel Nos. 16 to 18 that it is essential to limit the content to 0.14% or less. this species
The EC resistance of Cu-Mo steel is reduced by lowering the C content, that is, by limiting the C content to 0.14% or less as steel for feed water heaters, and by simultaneously adding small amounts of Cu and Ni, preferably at least 0.16% each. It was found that there was a significant improvement. Furthermore, the relationship between EC resistance and C, Cu, and Ni contents, which are important requirements of this second invention, is explained in the third section.
To explain using a diagram, the second invention steel symbol No. 4, 5
and 9, conventional steel symbols No. 14 and 15, comparative steel symbol No.
In comparison with 18, the amount of C was reduced to 0.14% or less, and Cu
It is clear that the combined addition of Ni and Ni is effective in improving EC resistance. The EC resistance of this type of Cu-Mo steel is improved by lowering the C content, that is, by limiting the C content to 0.14% or less as steel for feed water heaters, and by simultaneously adding trace amounts of Cu and Ni, preferably 0.16% each. It has been found that the addition of the above results in a significant improvement. Furthermore, in Table 3, 0.5Cr-0.5Mo steel (symbol No. 19, No. 20) and 21/4Cr-1Mo steel (symbol No. 21,
Regarding No. 22), the former has insufficient EC resistance due to the small amount of Cr, and EC becomes a problem when used in humid steam, and the latter has a high welding susceptibility index at 250°C. It can be seen that this requires preheating, which is accompanied by great difficulty in operation. On the other hand, each invention steel has both EC resistance and weldability as described above, and has excellent properties as a steel used under wet steam. (Effects of the Invention) As described in detail above, according to the present invention, the preheating temperature for welding can be set to about 125°C or considerably lower, and there is less risk of damaging the working environment. Since less energy is required for preheating during welding, energy costs can be reduced, and of course, the EC resistance against wet steam is extremely excellent, so the lifespan of the container can be extended. can. 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]

FIG. 1 is a perspective view of an EC test piece, and FIG. 2 is a comparative graph 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. Figure 3 is a comparison graph summarizing the effects of steel components on EC resistance.

Claims (1)

[Claims] 1 C: 0.02wt% or more and 0.14wt% or less, Si: More than 0.50wt% and up to 0.90wt%, Mn: 0.30wt% or more and 0.80wt% or less, Cr: 0.70wt% or more and 1.60wt% The following contains Mo: 0.40wt% or more and 0.70wt% or less, Cu: 0.02wt% or more and 0.50wt% or less, and Ni: 0.02wt% or more and 0.50wt% or less, and the remainder consists of Fe and unavoidable impurities, and has EC resistance.
A low C-Cr-Mo steel for use under wet steam, characterized by excellent strength and weldability. 2. The low C—Cr—Mo steel according to claim 1, wherein the C content is 0.13 wt% or less, and the Cu and Ni contents are each 0.16 wt% or more and 0.30 wt% or less. 3 C: 0.02wt% to 0.14wt%, Si: More than 0.50wt% to 0.90wt%, Mn: 0.30wt% to 0.80wt%, Cr: 0.70wt% to 1.60wt%, Mo: 0.40wt % or more and 0.70wt% or less, Cu: 0.02wt% or more and 0.50wt% or less, Ni: 0.02wt% or more and 0.50wt% or less, and Al: 0.005wt% or more and 0.08wt% or less, the remainder being Fe and unavoidable impurities. EC resistance
A low C-Cr-Mo steel for use under wet steam, characterized by excellent strength and weldability. 4 The C content is 0.13wt% or less, and the Cu and Ni contents are each 0.16wt% or more and 0.30wt% or less,
Low C—Cr—Mo steel according to claim 3.