JPH0254740A - Steel material and tube for absorption thermal apparatus having excellent corrosion resistance - Google Patents

Abstract

PURPOSE:To obtain the title steel material having excellent corrosion resistance to an LiBr water soln. of high temp.-high concn. by using a steel having the compsn. contg. specific amounts of one or more kinds among P, Cr, Ni, etc., as a steel material or a steel tube material to be brought into contact with an LiBr water soln. and removing oxidized scale on the surface. CONSTITUTION:A steel contg., by weight, <0.25% C, 0.20 to 3.0% Si, <1.0% Mn and one or more kinds among 0.05 to 0.15% P, 0.25 to 11.5% Cr and 0.05 to 10.0% Ni or furthermore contg. one or more kinds among 0.020 to 0.10% S, 0.01 to 0.5% V, 0.005 to 0.5% Ti and 0.005 to 0.5% Nb is manufactured by a vacuum melting method; the slab is subjected to hot forging or hot rolling to manufacture a steel plate. After the removal of the oxidized scale on the surface by sand blasting, the steel plate is worked into a tube material to form into a steel material and a steel tube used in the environment of the salt of LiBr, etc., by which Fe, P, Ni, Cr, etc., on the surface of the steel are brought into reaction with LiBr to form a passivation film by the reaction prevent and to improve the corrosion resistance to LiBr.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a steel material used in absorption heat equipment that uses a salt solution such as an aqueous lithium bromide solution, and a steel material manufactured using the steel material. This relates to the pipe body. Examples of the above-mentioned absorption heat equipment include absorption chillers, absorption chillers and hot water machines, absorption heat pumps, etc., but the key is to transfer heat by utilizing changes in refrigerant partial pressure due to absorption concentration of salt solution. Any device that can perform this is covered by the present invention, regardless of the detailed mechanism of the device or the type of salt. Therefore, in the following explanation, the case of an absorption refrigerator using an aqueous lithium bromide solution will be taken up as a representative example, but the technical scope of the present invention is not interpreted to be limited by this.

[Prior Art] Absorption chillers are becoming popular as low-cost and small-sized equipment to replace so-called compressor-type chillers, and with the expansion of solar heat utilization devices, absorption chillers are becoming more popular, especially in absorption heating and cooling systems for air conditioning in buildings. There is a tendency for it to be used more widely, mainly in the fields of

As the constituent material of such absorption chillers, general-purpose materials with excellent weldability and low cost, such as mild steel plates such as SM materials (rolled steel materials for welded structures) and SS materials (rolled steel materials for shell structures), are used. Therefore, welding materials with the same composition have been used.

By the way, the most basic concept of an absorption refrigerating machine is as shown in FIG. Evaporator 2, absorber 3.
Regenerator 4. The basic configuration is a heat exchanger 5, which is piped via valves and pumps. The cross-sectional view is a single effect type, and even if it is a double effect type or other modified type, there are problems similar to those described below. That is, the salt solution used in such an absorption refrigeration system is relatively concentrated, and is particularly concentrated inside the regenerator 4 and in the infusion piping from the regenerator 4 to the absorber 3 (including the pipe passing through the heat exchanger 5). There is a considerably concentrated salt solution inside, and among these, the inside of the regenerator 4 and the piping toward the heat exchanger 5 reach a considerably high temperature.

Salt solutions of such high concentration, especially at high temperature and high concentration, are highly corrosive, and it is desirable to take measures that take this into consideration.

For example, as a countermeasure when using a concentrated aqueous solution of lithium bromide, it has been considered to add lithium hydroxide or various chromates and molybdates as corrosion inhibitors.

However, the corrosion inhibitors mentioned above have a weak anticorrosion effect,
In the former case, there is a risk of leakage of a toxic concentrated salt solution due to pitting corrosion or sometimes general corrosion, and in the latter case, the heat exchanger 5 may suffer from contamination or deterioration of the salt solution or the formation of scale. As a result of problems such as a decline in heat transfer performance within the device, it becomes impossible to continue using the device. In the former case, there is a risk not only of liquid leakage but also of sudden damage.

For this reason, the use of stainless steel, which is said to have good corrosion resistance, was considered, and it was confirmed that it is effective in preventing general corrosion, but on the contrary, it increases the depth of pitting corrosion. In addition, the fear of stress corrosion cracking has been newly pointed out, and the use of stainless steel must be said to be an improvement in terms of highly dangerous corrosion damage. Therefore, the present inventors conducted various studies in order to investigate the cause of such increased risk due to the use of stainless steel. According to the study, Cr and Ni, which are thought to contribute most significantly to the corrosion resistance of stainless steel, surprisingly show resistance to pitting corrosion against salt solutions and stress resistance at the required content levels in stainless steel. It was found that this caused a significant deterioration in corrosion cracking resistance. Therefore, when developing technology to improve corrosion resistance in this field, including absorption refrigerators that use high-temperature, high-concentration lithium bromide aqueous solutions, the approach is to select appropriate materials from among those conventionally known as corrosion-resistant materials. Therefore, the technical matters that were conventionally known as means for improving corrosion resistance have to be brought back to the drawing board. In addition to starting from the point of classifying elements into elements that exhibit the

[Problems to be Solved by the Invention] The present invention has been made under such circumstances, and is intended to be used in absorption heat equipment such as absorption refrigerators.
Various studies were conducted with the aim of developing a steel material that can exhibit excellent resistance to general corrosion, pitting corrosion, and stress corrosion cracking when used in areas that come into contact with salt solutions (particularly at high temperatures and high concentrations).

[Means for Solving the Problems] The steel material of the present invention that has achieved the above objects contains: C: 0.25% or less, Si: 0.20 to 3%, Mn: 1% or less, and P. 1f selected from the group consisting of: 0.05-0.15% Cr: 0.25-11.5% Ni: 0.05-10%! ! The basic gist is that it contains two or more types, and the remainder is composed of Fe and unavoidable impurities. Also, for this component composition,
Furthermore, 1 selected from the group consisting of S: 0.020-0.10% V: 0.01-0.5% Ti: 0.005-0.5% Nb: 0.005-0.5% A steel material containing one or more species is also provided as the steel material of the present invention. These steel materials can be used as constituent materials in the above-mentioned absorption heat equipment, such as container wall materials, tube sheet materials, pipe materials, smoke pipe materials, and other materials such as piping and valves, as well as co-metal welding. It is also possible to apply it as a welding material.

[Function] The reason for adding various alloying elements to the steel material of the present invention and the reason for setting the amount of addition will be explained.

22 Rainbows and Sandals JC is an element necessary to ensure strength, but if its content is too high, ductility and toughness will deteriorate, and it will also have a negative effect on weldability. The upper limit was set at 25%.

Si: 0.20-3% Si is an element essential for improving pitting corrosion resistance and general corrosion resistance in a high-temperature, high-concentration lithium bromide aqueous solution.
In order to obtain this effect, it is necessary to add 0.20% or more. On the other hand, if it exceeds 3%, the effect is saturated and workability deteriorates.

Mn: 1% or less Mn is effective in deoxidizing and desulfurizing during steel manufacturing, increasing strength, and improving weldability, but it is the most important harmful element that increases general corrosion and pitting corrosion. Therefore, the upper limit was set at 1%. Further, it is more preferable to keep the content to 0.5% or less.

P: 0.05-0.15% P is generally contained as an impurity, but according to the research of the present inventors, it is extremely effective in improving the pitting corrosion resistance of steel materials against high-temperature, high-concentration lithium bromide aqueous solutions. It was revealed that the element is shown in the figure. And to get that effect 0
．． It was also found that addition of 0.5% or more was necessary. However, when added in excess of 0.15%, there is a tendency to deteriorate toughness and weldability, and particularly to promote hot cracking during welding.

Cr: 0.25-11.5% As mentioned above, containing Cr at the stainless steel level (usually 12% or more) improves pitting corrosion resistance and stress corrosion cracking resistance in high-temperature, high-concentration lithium bromide aqueous solutions. Therefore, the inventors conducted various studies and found 1.
I learned that it should be kept below 1.5%, but 11
．． When it is less than 5%, it shows remarkable effects on general corrosion resistance and pitting corrosion resistance, and is an essential element for improving corrosion resistance.

In order for such an effect to be recognized in Cr, 0.25
% or more is required.

Ni: 0.05 to 10% Ni is an element that exhibits a remarkable effect on improving both general corrosion resistance and pitting corrosion resistance, and the effect of improving general corrosion resistance is particularly remarkable. However, if it is less than 0.05%, these effects will not be exhibited, while if it is added excessively, the susceptibility to stress corrosion cracking will increase, so 10% is set as the upper limit.

As mentioned above, P, Cr, and Ni are elements that exhibit almost the same effects, and if one of these is blended, the above effect can be obtained, but if two or more of these are blended, the effect will be greater than when each is added alone. A particularly remarkable effect is shown in comparison.

S・0.020-0.10% S is generally contained as an impurity, but it is an effective element in improving general corrosion resistance under the conditions of a high-temperature, high-concentration lithium bromide aqueous solution environment. That's what I found out.

In order for S to exhibit the above effects, it is necessary to add 0.020% or more, but since excessive addition causes deterioration of toughness, weldability, workability, etc., 0.10% is set as the upper limit. It has been confirmed that the effect of adding S is particularly remarkable when added in combination with P.

V: 0.01 to 0.5% It was also found that these three elements exhibit the same general corrosion resistance improvement effect as S, and also exhibit the pitting corrosion resistance improvement effect within the above range. However, if the content of any element exceeds 0.5%, the effect will be saturated and the toughness will deteriorate, so 0.5% is set as the upper limit.

As mentioned above, S, V, Ti, and Nb are elements that exhibit almost the same effects, and if one of these is blended, the above effect can be obtained, but if two or more of these are blended, each element can be added alone. A particularly remarkable effect is shown compared to other cases.

The important basic elements in the present invention are as described above, but other elements may be included as long as they do not adversely affect the expression of their effects. Examples of such elements include Cu, AI, M.

Ca, REM, etc. are shown.

As mentioned above, steel materials with the above composition are used as various structural materials in absorption type thermal equipment, and exhibit pitting corrosion resistance, general corrosion resistance, and stress corrosion cracking resistance on the side that comes into contact with high-temperature, high-concentration salt solutions. However, it has been found that it is better to remove this black crust before using the steel material, rather than using it with the black crust (oxide film) generated during the rolling process still attached to the surface of the steel material. The reason for this is not fully understood, but the components in the steel, especially Fe, P, Ni, Cr, etc., react with salt (for example, LiBr) when they come into contact with a salt solution, forming a reaction product film, and this film It is thought that this is because it has regenerating ability itself and acts as a passivation film, thereby exhibiting superior corrosion resistance. Further, the following may be considered as the reason why the presence of black scale (oxide film) has an adverse effect on corrosion resistance.

■A corrosion battery is formed between the black crust and the base iron.

■ Black scale generally has a negative potential and therefore positively polarizes the isthmus and promotes the occurrence of pitting corrosion.

■Black scale generally contains many lattice defects and therefore tends to become a starting point for pitting corrosion.

[Example Example 1] A steel having the composition shown in Table 1 was produced by vacuum melting, and hot forged and hot rolled to a length of 160 mm.
After making a steel plate of x 3~6mmt, 70mm x 70
It was cut out to a size of mm. After descaling by shot blasting, the central part of the sample piece was remelted by TIG (without using a filler rod). This simulated welding applies welding residual stress and serves as a stress corrosion cracking test piece in the solution immersion experiment described below. Regarding the steels of the present invention in the table, the first group refers to those that satisfy the conditions of claim (1), and the second group refers to those that satisfy the conditions of claim (2).

The sample obtained above was mixed with 65%-LiBr+2000ppm-
Li2Cry4+0.02N-LiOH aqueous solution (20
The specimens were immersed in 0°C for 500 hours, and the following tests were carried out: (1) calculation of corrosion rate, (2) measurement of maximum pitting depth, and (2) confirmation of the presence or absence of stress corrosion cracking.

For (2), the test piece after immersion was cathodically electrolyzed in a 10% aqueous ammonium dihydrogen citrate solution to remove scale, and the weight change before and after immersion was calculated. For (2), it was measured using a depth gauge, and for (2) This was done by visual observation.

The test results are shown in Table 2. The "corrosion rate" in the table is an evaluation item for general corrosion resistance.

Example 2 In Example 1 described above, TIG treatment was performed before the test, and therefore, an oxide film formed at 710 hours (remelt time) was attached to the sample surface.

In Example 2, for the purpose of demonstrating the effect of claim (3), the sample used in Example 1 was picked up, shot peened again after TIG treatment, and the oxide film was completely removed. ■ Corrosion rate, ■ Pitting corrosion, ■
Stress corrosion cracking was evaluated.

All test conditions and evaluation methods are the same as in Example 1. The test results are shown in Table 2.

(a) The effect of the steel material of the present invention is remarkable.

(b) In particular, it is clear that the pitting corrosion resistance is significantly improved.

Therefore, the corrosion resistance of the steel material of the present invention can be improved by contacting it with an absorbing liquid such as an aqueous lithium bromide solution in a state in which the oxide film has been removed to cause the reaction product to react.

Comparison m (A-1) to (A-t 1) (7) The relationship between the component composition and the test results will be described separately.

(A-1,) Mn exceeds the upper limit condition, and P and Cr.

Since the selective essential component of Ni did not satisfy the lower limit condition, both general corrosion resistance and pitting corrosion resistance were poor.

(A-2) Since Mn complied with the upper limit condition, pitting corrosion resistance was slightly improved compared to (A-1) (however, the evaluation itself is marked with an x), p, C
Since r and Ni did not satisfy the lower limit conditions, the overall corrosion resistance was as low as that of (A-1).

(A-3) Regarding the three components P, Ni, and Cr, Cr satisfied the requirements of the present invention, but Mn was added in large excess, C was large, and St was small. Therefore, the pitting corrosion resistance was poor, and the general corrosion resistance was also poor.

(A-4) Since it contains a lot of Cr and is equivalent to stainless steel, the stress corrosion cracking resistance was evaluated poorly. In terms of maximum pitting depth, there is still some difficulty in general corrosion resistance, which is very good and pitting corrosion occurs less frequently, so once pitting corrosion occurs, corrosion current tends to concentrate there. It's for a reason.

(A-5) Compared to (A-4), Cr was further increased, and not only the stress corrosion cracking resistance was evaluated poorly, but the maximum pitting depth was also poor.

(A-6) It is the same as (A-1) that Mn is large and P, Cr, and Ni do not satisfy the lower limit condition, and St also slightly does not satisfy the lower limit condition, causing general corrosion and porosity. Both food received poor reviews.

(A-7) Stress corrosion cracking occurred because Ni exceeded the upper limit condition.

(A-8) Corrosion resistance was low because Mn was high and P, Ni, and Cr were low.

(A-9) Since P exceeded the upper limit, weld cracking occurred when thermal stress was applied by the TIG method.

(A-10) Since the Si content exceeded the upper limit, workability decreased, and cracks occurred during hot forging, for example.

(A-11) Since S exceeded the upper limit, workability decreased and rolling cracks occurred during cold rolling.

Compared to these comparative steels, the steel of the present invention satisfied the conditions of the present invention in both Group 1 and Group 2, and therefore was given excellent evaluations in all items.

[Effect of the invention] The steel of the present invention has the above-mentioned composition, so that
Shows excellent effects in all areas: general corrosion resistance, pitting corrosion resistance, and stress corrosion resistance.

Therefore, it can provide excellent corrosion resistance to absorption type thermal equipment that uses high-temperature, high-concentration salt solutions such as lithium bromide aqueous solution, and can guarantee long-term operational stability of these thermal equipment. It became like that.

[Brief explanation of the drawing]

FIG. 1 is a conceptual diagram of an absorption refrigerator. 1... Condenser 2... Evaporator 3...Absorber 4...Regenerator 5...Heat exchanger Around the time

Claims (3)

[Claims] (1) Contains C: 0.25% (meaning by weight %, same below) or less Si: 0.20-3% Mn: 1% or less, P: 0.05-0.15% Cr: 0 .25-11.5% Ni: 0.05-10% Contains one or more selected from the group consisting of the following, with the remainder consisting of Fe and unavoidable impurities. Excellent corrosion resistance. Steel materials for absorption type heat equipment. (2) Contains C: 0.25% or less Si: 0.20-3% Mn: 1% or less, P: 0.05-0.15% Cr: 0.25-11.5% Ni: Contains one or more selected from the group consisting of 0.05-10%, further S: 0.020-0.10% V: 0.01-0.5% Ti: 0.005-0 .5% Nb: 0.005 to 0.5% An absorbent with excellent corrosion resistance characterized by containing one or more selected from the group consisting of the following, with the remainder consisting of Fe and inevitable impurities. Steel materials for type thermal equipment. (3) It is formed into a tubular shape using the steel material according to claim (1) or (2), and the oxide film on the surface is removed, so that it can react with a salt solution for absorption heat equipment in an operating environment. A pipe for an absorption type thermal equipment, characterized in that it is configured to form a product film.