DE102009052994A1 - Ferritic stainless steel and steel sheet for heating pipes or heat pipes, and heating pipe or heat pipe and high-temperature system for recovering exhaust heat - Google Patents

Abstract

A ferritic stainless steel is provided for heat pipes of high temperature exhaust gas heat recovery systems which, expressed in percentage by weight, contains: from 16 to 32% Cr, at most 0.03% C, at most 0.03% N, at most 3% Si, at most 2% Mn, not more than 0,008% S, from 0 (no additive) to 0,3% Al, and at least one of the following: not more than 0,7% Nb, not more than 0,3% Ti, not more than 0,5% Zr and at most 1% V, and optionally at least one of the following: at most 3% Mo, at most 3% W and at most 3% Cu, at most 0.1% Y, at most 0.1% REM (rare earth metal), and at most 0 , 01% Ca, balance being Fe and unavoidable impurities, and satisfying the following formula (1), formula (2) and formula (5): Cr + 3 (Mo + Cu) ≧ 20 ... ( 1) Cr + 3 (Si + Mn + Al - Ti) ≧ 20 ... (2) 0.037 {(C + N) / (V + Ti + 0.5Nb + 0.5Zr)} + 0.001 ≰ 0.01 ... (5)

Description

Background of the invention

Field of the invention

The The present invention relates to stainless steel and steel sheets for use with heat pipes containing the heat of vaporization use of water, as well as on the existing heat pipe and a high-temperature system for recovering exhaust heat, that contains this heat pipe.

State of the art

Recently became a high-temperature system for the recovery of exhaust gas heat implemented in a practical application to the heat recover from engine exhaust gases at high temperatures be released when driving by vehicles, and these as an energy source to use for vehicles to increase fuel efficiency Increase vehicles. In general, a heat exchanger used to recover the exhaust heat, the heat exchange between the exhaust heat and cooling water or any other heat medium is used; and as a method to efficient heat exchange to realize, in particular, a heat exchanger with a means of transferring heat, called Heat pipe can be called, for use in high-temperature systems for the recovery of exhaust gas heat mentioned in vehicles etc.

1 FIG. 11 shows an example of a conventional arrangement of an exhaust pipe including a high-temperature exhaust heat recovery system disposed in the exhaust pipe of a vehicle. In many cases, the exhaust heat recovery system is located behind the underfloor converter, as in this illustration. The heat recovered by the high-temperature exhaust heat recovery system is actually used to warm the engine cooling water when the vehicle starts running, and to heat the interior in winter; and this helps improve fuel efficiency in gasoline vehicles, diesel vehicles, hybrid vehicles, etc., and conserve the batteries therein.

2 schematically shows the principle of a heat pipe.

[0th Initial state]

The heat pipe 10 is a metallic, closed hollow vessel with pure water sealed therein in a vacuum (at most 100 Pa); and the inside of the hollow vessel forms a liquid phase region 11 and an area of free space 12 ,

[1. Heating / cooling condition]

If the place of the heating pipe 10 indicating the liquid phase area 11 (Heating zone) is heated with exhaust gas, the water in the liquid phase region 11 evaporated. The vaporization is an endothermic reaction, and therefore, the site can efficiently absorb the heat of the exhaust gas. More specifically, most of the heat energy of the exhaust gas is transferred to the water vapor as latent heat of vaporization (heating). If part of the scope of free space 12 (Cooling area) of the heat pipe 10 is cooled with cooling water or the like, then condenses the water vapor on the inside of the cooled hollow vessel of the heat pipe, and the condensed water returns to the liquid phase region 11 back. The condensation is an exothermic reaction and therefore the energy corresponding to the latent heat of the water vapor is released and released to the cooling water (cooling). The cooling water that has absorbed the heat energy is heated and used as hot water. The cycle of heating and cooling takes place continuously, thus realizing efficient heat exchange utilizing the latent heat of vaporization of water.

Reference Patent 1 discloses a high-temperature system for recovering exhaust heat of the "heat pipe" type. 3 schematically shows the part of the system. This includes an area 22 , in which exhaust gas flows, and a cooling area 32 in which cooling water 31 flows; and calottes or tubes 23 are parallel to each other in the heating area 22 arranged. Between the adjacent calottes 23 is one to the calotte 23 soldered heat collecting lamella 24 arranged. The exhaust gas is directed so that it passes through the heat collecting lamella 24 passes. Both ends of each tube 23 are with the upper tube manifold (steam flow path) and the lower manifold (liquid return path) connected, causing the heating zone 22 with the cooling zone 32 connected is; and the tubes 23 and the manifolds are charged with water and sealed after creating the vacuum, as described above. A valve 33 for switching the operating mode, which is able to open and close the liquid return path, is in the lower region of the cooling region 32 arranged. If water in the pipe 23 by exhaust gas in an open state of the valve 33 is heated to switch the operating mode (heat recovery mode), then circulates the water in a cycle of boiling (vapor) → condensation (condensed liquid), and regains the exhaust gas heat of the exhaust gas. In many cases, the tube is 23 formed so that it has a flat shape to increase its specific surface area and reduce the Ausströmungswiderstand of the exhaust gas as much as possible; and in general, the tube is formed by pressing a stainless steel sheet having high resistance to heat and corrosion. In many cases, the temperature is in the heating area 22 introduced exhaust gas due to the catalytic effect of the catalyst increases, and is often 800 ° C and more. The material temperature of the heating area 22 is highest when the valve is 33 is for switching the operating mode in a closed state (heat absorption mode), and presumably reaches a temperature range of 600 ° C to 900 ° C.

On This way, the heat pipe is up to a temperature range heated by 900 ° C, and therefore it must be made of a Material with excellent heat resistance (creep resistance, fatigue resistance at high temperatures, fatigue resistance at heat) and also formed excellent high temperature corrosion resistance be. In addition, it has to be excellently workable, weldable and solderable be. It is also important that it is cost effective. Taking into account all of these requirements currently assumed that stainless steel as the material of Heat pipes is most suitable.

Reference Patent 2 discloses a heat pipe formed of a stainless steel containing 14-27% by weight of Cr. contains.
Reference Patent 1: JP-A 2007-327719
Reference Patent 2: JP-A 7-243784

One however, a heat pipe formed of stainless steel may be one have large amount of hydrogen within it was generated in the early stages of the journey. As a result Various investigations have determined that the internal pressure often can exceed 1 Mpa due to the hydrogen produced. In such a case, the heat pipe should be a pressure vessel be under strict legal conditions. For the simple use as popular or widespread It is system for recovering exhaust heat desirable, a high temperature recovery system of exhaust heat to construct, in which the internal pressure of the heat pipe does not exceed 1 MPa.

additionally Represents the generation of hydrogen within the heat pipe a risk factor because it increases the efficiency of heat transfer to reduce the cooling water, and in addition a risk factor because they make the system more excessive Can expose stress; and therefore this may be a possible reason system damage and serious accidents.

One Ferritic stainless steel compares with austenitic stainless steel Steels have a lower coefficient of thermal expansion on, and is therefore advantageous in terms of resistance against thermal fatigue in heating and cooling cycles. In addition, a ferritic stainless steel compares with austenitic steels a lower hydrogen diffusion coefficient on, and is therefore beneficial to within a hollow body to discharge generated hydrogen from the system. Furthermore is a ferritic stainless steel generally cheaper as austenitic steels. Negative, however, is that ferritic steel austenitic steels in general concerning high-temperature oxidation resistance, heat resistance, Corrosion resistance, etc. is inferior.

Summary of the invention

It is an object of the present invention to develop a ferritic stainless steel which is of a type of ferritic stainless steels, which normally have the above-mentioned advantages, which has the property of securely preventing in hollow vessels constituting a heat pipe , the pressure increase is caused by the formation of hydrogen in their use, which has a high-temperature oxidation resistance and a high heat resistance, which are high enough to use it in a temperature range of 600 ° C to 900 ° C, and a corrosion resistance and having Ni brazing capability suitable for heat pipes; and a popular or widespread high-temperature system for the recovery of exhaust heat of the type "heat pipe" to construct.

In order to achieve the above object, the invention provides a ferritic stainless steel for heat pipes of high temperature exhaust heat recovery systems, expressed in percentage by mass, from 16% to 32% Cr, at most 0.03% C, at most 0.03% N, not more than 3% Si, not more than 2% Mn, not more than 0,008% S, from 0% (no additive) to 0,3% Al, and containing at least one of the following: not more than 0,7% Nb, not more than 0,3% Ti, at most 0.5% Zr, at most 0.03% N, with a balance of Fe and unavoidable impurities, and which satisfies all of the following formulas: Formula (1), Formula (2), Formula (5), and satisfies at least one of the following formulas: Formula (3) and Formula (4). The invention also provides the ferritic stainless steel which also contains one of the following: at most 3% Mo, at most 3% W, and at most 3% Cu. The ferritic stainless steel may further contain at least one of the following: at most 0.1% Y, at most 0.1% REM (rare earth metal, rare earth metal), and at most 0.01% approx. Cr + 3 (Mo + Cu) ≥ 20 (1) Cr + 3 (Si + Mn + Al - Ti) ≥ 20 (2) Ti + Al ≤ 0.05 (3) Nb≥Ti + Al (4) 0.037 {(C + N) / (V + Ti + 0.5Nb + 0.5Zr)} + 0.001 ≤ 0.01 (5)

In In the formulas (1) to (5), the location of the atomic symbol is represented by Value of the content of the corresponding element, expressed in mass percent, replaced, and the location of an element not added to the steel is replaced by 0 (zero).

The invention also provides a ferritic stainless steel sheet for heat pipes formed of the steel mentioned above, and one having a grain size of # 100 to # 800 according to JIS R6001: 1998 has ground or polished surface, or that has a ground or polished surface HL according to Table 14 in JIS G4305: 2005 having.

The Invention also provides a heat pipe that constructs is by placing a hollow vessel from one of the above mentioned steel existing steel material or steel sheet is formed and has a thickness of 0.5 mm to 1 mm, whereupon Water is filled in there and it is sealed, around a liquid phase area and an area free To make room in it.

Preferably, the hollow vessel has an inner surface having a grain size of # 100 to # 800 JIS R6001: 1998 ground or polished surface, or has a ground or polished surface HL according to Table 14 in JIS G4305: 2005 on. The invention also provides a high-temperature exhaust heat recovery system having the above-mentioned heat pipe mounted at a position where the material temperature moves in a range of 600 to 900 ° C.

According to the Invention can increase the internal pressure in a stainless Steel heat pipe produced by the generation caused by hydrogen in the heat pipe and there is problematic, can be significantly reduced. By use the heat pipe can be a popular or widespread High temperature system for the recovery of exhaust gas heat be realized at low cost, resulting in further dissemination of systems for the recovery of exhaust heat contributes in vehicles etc.

Brief description of the drawings

1 FIG. 10 is a schematic diagram showing an example of an arrangement of an exhaust pipe having a high-temperature exhaust heat recovery system installed in the exhaust pipe of a vehicle.

2 is a conceptual representation, which shows schematically the principle of a heat pipe.

3 Fig. 10 is a schematic view showing an example of a conventional high temperature exhaust heat recovery system.

4 Fig. 10 is a schematic view showing the construction of a hydrogen generating test apparatus.

5 Fig. 12 is a view schematically showing the structure of the components of a test piece for a hydrogen continuity test.

6 Fig. 12 is a view schematically showing the structure of a hydrogen passage test test apparatus.

7 is a view explaining a corrosion test method.

Description of the preferred embodiments

In order to prevent the pressure increase in a heat pipe from being caused by the generation of hydrogen, it is first necessary to understand its mechanism. After the vacuum is generated, a heat pipe is charged with pure water and sealed, and therefore, only pure water and the metal of the heat pipe (hollow vessel) exist within it. The generation of hydrogen within the heat pipe is caused by the oxidation of the heat pipe (hollow vessel) forming metal with water (water vapor). The reaction can be represented essentially as follows: xM + yH ₂ O → M _x O _y + yH ₂ ↑ where M is a metal, and x and y are coefficients, respectively.

• (i) Material, das kaum Wasserstoff erzeugt
• (ii) Material, durch das Wasserstoff leicht hindurchtritt.

The investigations of the inventor of the present invention have proved that the hydrogen generated within a heat pipe passes through the material of the heat pipe (hollow vessel) to penetrate to some extent to the outside. Accordingly, for reducing the pressure increase caused by generation of hydrogen within the heat pipe, it is effective to use one of the following two materials in the construction of the heat pipe.

• (i) Material that hardly generates hydrogen
• (ii) material through which hydrogen easily passes.

in the Difference to austenitic steels are ferritic Steels with respect to (ii) naturally quite well suited. Accordingly, it is important to be ferritic Steels with respect to (i) to improve.

• [1] Die Stahlzusammensetzung umfasst Cr, Si und Mn, jeweils in der unten angegebenen Spanne, und erfüllt folgende Formel (2): Cr + 3(Si + Mn + Al – Ti) ≥ 20 (2)

Considering the above (i), it is important to increase the resistance of the stainless steel constituting the heat pipe to the water vapor oxidation. Stainless steel may exhibit increased resistance to water vapor oxidation when coated with a dense layer of Cr ₂ O ₃ . As a means for this, the inventors of the present invention found that the use of the following method [1] is extremely effective for a ferritic steel and that the use of the following methods [2] or [3] is preferable. In the invention, the following [1] is used, and if desired, one or both of the following [2] and [3] is used.

• [1] The steel composition includes Cr, Si and Mn, each in the range given below, and satisfies the following formula (2): Cr + 3 (Si + Mn + Al - Ti) ≥ 20 (2)

• [2] Die Stahlzusammensetzung umfasst Y, REM (rare earth metal, Seltenerdmetall) und Ca, jeweils in der unten angegebenen Spanne.

In order to prevent the generation of hydrogen when using heat pipes, it is effective to add Cr, Si and Mn to a ferritic steel, which has the effect of inhibiting the growth of oxidation scale at 600 to 900 ° C, respectively, in the below specified range. The addition of Al is also effective. However, when the steel includes Ti, it has been found that the generation of hydrogen increases due to the oxidation of Ti. Ti may be added as an element for fixing C and N in the steel as described below, and therefore it is particularly important in the invention to control the Ti content of the ferritic stainless steel of the invention. As a result of various investigations, the inventors found that for the reduction of hydrogen production, the above-mentioned formula (2) must be satisfied.

• [2] The steel composition includes Y, REM (rare earth metal) and Ca, each in the range given below.

• [3] Das Stahlblech weist eine polierte bzw. geschliffene Oberfläche auf.

These elements have the effect of high-temperature oxidation resistance of a ferritic rust free steel and cause a reduction in hydrogen production.

• The steel sheet has a polished or ground surface.

A ferritic stainless steel can easily form a poorly protective oxidation scale (red scale) having Fe ₂ O ₃ as a main component in a low-oxygen atmosphere of high humidity at 500 to 600 ° C. A heat pipe is often exposed to this environment in a cycle of heating up to the highest operating temperature and cooling to ordinary temperatures, in which the oxidation reaction of red scale formation can often be problematic because it generates a large amount of hydrogen. The inventors of the present invention found that it is extremely effective for this problem to previously apply a work stress to the surface layer of the ferritic stainless steel sheet exposed to the above-mentioned environment. Accordingly, Cr, Si, Mn and Al can easily diffuse into the surface layer of the steel sheet in a middle temperature range of 500 to 600 ° C, whereby a protective dense oxidation layer could be formed quickly to prevent the formation of red scale on the steel sheet.

In order to form a work load in the surface layer, a method such as shot peening, polishing or the like may be used;
but in the invention polishing is used as a suitable method for mass production on a large scale. The investigations of the inventors of the present invention have clarified that the application of stress to a depth of 50 μm or similar to the surface layer may be sufficient for these purposes. For this purpose, the steel sheet may be processed to be one having a grain size of # 100 to # 800 according to JIS R6001: 1998 has ground or polished surface, or that has a ground or polished surface HL according to Table 14 in JIS G4305: 2005 having.

Of the Steel to which this invention is directed is preferably a steel (ferritic single-phase steel) whose composition is so designed is that he is not so much an austenitic at a high temperature Phase as possible forms (as little as possible forms an austenitic phase). A steel that has a composition having an austenitic at a high temperature easily Phase forming is undesirable, because when in the matrix just below the oxidation layer covering the steel one At chromium poor layer forms, then the chrome-poor proportion can locally forming an austenitic phase at a high temperature, and therefore can be a barrier to the diffusion of hydrogen form. In addition, if that turns into steel this can Type formed at a high temperature austenitic phase in Cooling is converted into a martensitic phase, in steel the further problem of reducing fatigue strength at ordinary temperatures and at high temperatures due to hydrogen embrittlement.

The alloying elements are described below. In this specification, "%" means "mass percent" unless otherwise specified. Cr is an important alloying addition to give the stainless steel the necessary corrosion resistance and oxidation resistance. In order to give the steel a safe oxidation resistance to water vapor at 600 to 900 ° C, at least 16% Cr is needed, and the steel (the composition of the steel) must satisfy the following formula (1): Cr + 3 (Mo + Cu) ≥ 20 (1)

If For example, no Mo and Cu are added to the steel in the places of Mo and Cu a 0 (zero) is inserted, and Cr must stand alone for at least 20% in the formula (1).

If the content of Cr is higher, then the stability of the ferrite higher, causing a delay of Formation of a poor layer and delay the austenitic transformation in the low-Cr layer leads if she trains herself. Even better is the salary at least 18%, and even better at least 20%, Cr if the above-mentioned polishing or previous oxidation treatment on the steel was not performed. On the other hand can the Cr content of more than 32% optionally the workability and the resistance to embrittlement of the steel at 475 ° C severely worsen. Accordingly, the Cr content moves in a range not exceeding 32%.

C and N are elements for increasing the high-temperature strength, in particular the creep resistance of the steel; however, when in the form of solid sols, they can bind hydrogen in the steel and form methane and ammonia, thus posing a risk factor by reducing the high temperature strength, toughness, and hydrogen permeability of the steel. Because C and N are austenite forming elements They can also be a risk factor by forming one out tenitic phase at high temperatures. In this case, the steel may have a problem of reducing the hydrogen permeability in the Cr layer and reducing the fatigue strength due to oxygen embrittlement, as mentioned above. Accordingly, the steel preferably has a lower C content and a lower N content as much as possible. As a result of various investigations, both C and N are acceptable in an amount of 0.03% each. However, in order to sufficiently reduce the total amount of C in solid solution and N in solid solution (hereinafter referred to as "amount of C + N in solid solution") in the steel, it is important that the steel has the following formula ( 5) in terms of the content of Nb, Ti, Zr and V which bind easily to C and N: 0.037 {(C + N) / (V + Ti + 0.5Nb + 0.5Zr)} + 0.001 ≤ 0.01 (5)

In of Formula (5), the left-most component represents an index representing the amount of C + N in solid solution in the ferritic stainless steel indicating the composition according to the Invention. If the steel does not satisfy formula (5), The durability of the formed from this steel heat pipe can be clearly be lower because of the resistance of the steel to thermal fatigue can be low at high temperatures.

Si is an element for increasing the oxidation resistance and the Resistance of the steel to red tinder, and works in order to prevent the generation of hydrogen. additionally This is an element that has a stabilizing effect on ferrite Has. The Si content is particularly effective at least 0.18%; However, too much Si may possibly increase the thermal conductivity of the steel deteriorate and the formation of defects in the surface of the steel, and can therefore be a risk factor for the significant deterioration of manufacturability and weldability of steel. Accordingly, the Si content is one Limited to a maximum of 3%.

Mn is an element that serves to resist the resistance of stainless steel to increase against scaling of scale, and is effective in preventing the generation of the Hydrogen within the heat pipe formed from the steel caused pressure increase. However, too much Mn may be reduce the toughness of the steel; therefore, the Mn content is limited to a maximum of 2%.

S is an additive that has some negative effects on hot workability and the sweat-resistant high-temperature crack resistance of steel, and can be a starting point for one be abnormal oxidation in the steel. Therefore, the S content is preferable as low as possible; and his upper limit is 0.008 Fixed mass percent: even better is the S content not more than 0.005 mass%.

Nb, Ti, Zr, and V act to fix C and N, thereby reducing the amount of C in solid solution and N in solid solution in the steel. In addition, they also work to improve the high temperature strength of ferritic stainless steel by improving the precipitation by fine distribution of their carbides and nitrides in the steel. Al shows an effect of improving the oxidation resistance of the steel and an effect of reducing hydrogen production by the steel. In order to obtain these effects in the invention, at least one of the following is added to steel: at most 0.7% Nb, at most 0.3% Ti, at most 0.5% Zr and at most 1 V. In particular, at least one of the following is preferable added: 0.001 to 0.7% Nb, 0.005 to 0.4% Ti, 0.001 to 0.5% Zr, and from 0.05 to 1% V. Al is added to the steel optionally in an amount of at most 0.3% added. If Al is added, its content is most effectively between 0.03 and 0.3%. However, special attention should be paid to the addition of Al and Ti. One reason is that Ti can be a risk factor for the production of hydrogen as described above. This problem can be solved by controlling the composition such that the above formula (2) is satisfied. Another reason is that Al and Ti are a risk factor for the deterioration of the brazeability of the steel. Most components of a heat pipe are put into practice by brazing; However, when the content of Ti and Al in the ferritic stainless steel is high, Ti and Al can form an oxidation layer under heat during brazing, even under conditions of low oxygen partial pressure, which reduces the ability to braze the steel (in particular, the wettability of the steel) a brazing material). As a result of detailed investigations, this problem can be solved by controlling the composition to satisfy at least one of the following formulas (3) and (4): Ti + Al ≤ 0.05 (3) Nb≥Ti + Al (4)

As already mentioned above, the steel must at least Nb, Ti, Zr and V, while satisfying the formula (5), in that around the amount of C + N in solid solution in it completely to reduce.

Not a word, W and Cu are all elements for increasing high-temperature strength stainless steel through solid solution hardening. In the Invention can be a method, a large amount of C and N to increase the strength of the steel, not be used, and therefore in a case where the Strength of the steel is in the foreground, preferably at least Mo, W or Cu added to the steel. additionally especially Mo and Cu have the effect, formation and growth from pitting or pitting through the dew condensation to delay dew point corrosion caused in the exhaust gas. The Adding at least one of the two, Mo or Cu, can extend the range of Cr content (that is, it can be the lowest Limit further), which is necessary to the formula (1) fulfill. In case that at least one of Mo, W and Cu is added, these are preferably controlled so that the Mo content is at most 3%, the W content at most 3% and the Cu content is not more than 3%. Yet It is more effective if the content of Mo, W and Cu at least each 0.1%. Y, REM (rare earth metal) and Ca have the effect of binding S, which is harmful for the resistance of the steel opposite the flaking of tinder suppress it the thickening of S in the scale / base interface, and have the effect, the density of the damaged areas in the oxidation layer reduce, thereby strengthening the oxidation layer, whereby the oxidation resistance of the steel is greatly increased can be. Accordingly, in the invention optionally at least one of these substances can be added to the steel. One too big Addition of these elements can not only harden the steel material too much, but may also be surface defects in the production cause the steel, resulting in an increase in production costs leads. The result of various investigations is that these elements, if added, are preferably so controlled or that the Y content is at most 0.1%, the REM content is at most 0.1%, and the CA content is 0.01% or less. Even more effective to add at least one of the following to the steel: from 0.0005 to 0.1% Y, from 0.0005 to 0.18)% REM and from 0.0005 up to 0.01% approx.

At the Stainless steel melting can be Ni, P, B, Mg and others may be added, for example, from the raw material and from the adhering to the walls of the melting device Deposits come from. The acceptable range is up to to 0.6% for Ni, up to 0.05% for P, up to 0.01% for B, and 0.005% for Mg.

at the production of a heat pipe using the Ferritic stainless steel is first a stainless steel sheet Steel having the above-described predetermined composition, according to a manufacturing process for a conventional one prepared ferritic stainless steel sheet; then a sheet metal part, which has been cut out of the steel sheet, shaped and welded into a hollow vessel, and then the hollow vessel is evacuated and then charged with pure water. Another method is also applicable in which a welded steel tube from the steel sheet is formed, or a seamless steel tube from the steel blank or the steel ingot is formed, and the steel tubes processed into a hollow vessel become.

The Technique of "feeding with pure water" means that the hollow vessel into which the water is filled is sealed by welding or fusion welding becomes. When the wall thickness of the hollow vessel is too small, the vessel could hardly have a sufficient durability. If she is too high, can on the other hand, the hydrogen diffusion path through the wall of the Hollow vessel be long because hydrogen through has to penetrate the thick wall, and that is detrimental to the reduction of the internal pressure of the hollow vessel. Due to the increase in the heat transfer path through the Steel material can affect the thermal resistance of the steel material increase, which is detrimental to an efficient Heat exchange based on the latent evaporation energy of steam is. As a result of various investigations is the Wall thickness of the heat pipe preferably in a range from 0.5 mm to 1 mm.

Example 1:

Steels shown in Table 1 (each 30 kg) were melted, hot rolled, annealed, pickled, cold rolled and finish annealed in accordance with a manufacturing method of a conventional ferritic stainless steel sheet in a vacuum melting furnace, whereby cold rolled annealed pickled steel materials (sample materials) were prepared have a thickness of 1.0 mm, whose finish stain no. 2D, defined in Table 14 in JIS G4305: 2005 , represents.

Hydrogen Production Test

test pieces for the hydrogen production test of 10 mm × 50 each mm × 1.0 mm were cut out of each sample material. These were divided into two groups; and the sheet surface the one in a group was the final one according to No. 2D as such, while those in the other group have one with # 400 dry polished surface was. The cut edges of all test parts all were polished # 600.

4 schematically shows the arrangement of the hydrogen generating test apparatus used here. A test piece is inserted into the quartz tube, and this is inserted into an electric heater. The quartz tube is shielded or insulated from the outside world by a suitable quartz cover. However, an encapsulated thermocouple housed in a quartz protective tube is inserted into the quartz tube to measure the temperature around the sample. A Pyrex ^® tubing is connected to the quartz tube, and the Pyrex tube is connected to a vacuum pump and a tank of clean water. The quartz tube, the quartz cover, the pyrex tube and the quartz protective sheath are connected to each other by lapping (lapped joints), and the air impermeability is further enhanced by a vacuum lubricant. At the beginning all valves (A to D) are closed.

First only the valve D is opened at normal temperature. In this step, the pipe between the valves C and D with filled about 30 ml of pure water. Then the valve D closed again. Then the vacuum pump is operated, the valve B is opened and the quartz tube is evacuated, and then the valve A is opened and the pressure is measured. After the pressure has been lowered to 1 Pa, the valve B is closed. Then the valve C is opened. At this time will be the pure water between the valves C and D, passed through the pyrex tube into the quartz tube. Since it is energetic in The vacuum is sucked, gets almost all the water that is in the pipe C-D remained close to the test piece.

Then, the inside of the quartz tube is heated by the electric heater. Monitored by the encapsulated thermocouple, the temperature within the quartz tube is maintained at 600 ° C or 800 ° C. The pressure change during the test, in which the temperature is kept at 600 ° C or 800 ° C for 10 hours, is monitored, and from the pressure change at the time after 10 hours, the rate of hydrogen production by the sample surface per unit time and surface unit is calculated. Those samples whose rate of hydrogen production after 10 hours is at most 1.0 × 10 ^-6 mol / (h · cm ² ) are determined to be those having the property of restricting the internal pressure increase in a real heat pipe to a highest 10 kPa. Therefore, samples whose hydrogen production rate after 10 hours is at most 1.0 × 10 ^-6 mol / (h · cm ² ) are considered good (as effective in reducing hydrogen production), while those whose hydrogen production rate is above this range considered inferior (as ineffective in reducing hydrogen production). The results are shown in Table 2.

When Reference values in Table 2 are the speed data Hydrogen production of each sample under the same evaluation criteria as shown previously, after being at 600 ° C for 1 hour was held.

Hydrogen permeation test, investigation on brazeability

5 schematically shows the structure of a test body for the hydrogen permeation test. The components formed from a test material are plate (two) and calottes (four). The calottes are formed by pressing, and the dimensions of their outer shape are about 100 mm (length) × 30 mm (width) and 5 mm (height). In 5 The width and height of the cap are exaggerated compared to their length. Two holes are made in the bottom of each calotte, and the interior of a calotte communicates with that of the adjacent calotte by connecting pipes attached to the holes. The connecting tube is made from a 1/2 inch tube of SUS 310S by flattening it. The distance between the two connected by the connecting tubes calotte is 8 mm. The two middle calottes are joined together to form a bag. The lateral dome is covered by a plate. A hole is made in the center of the plate to be attached to the test piece, and hydrogen gas is introduced into the test piece through the hole. These components are "braded" with a nickel-based brazing material (BNi-5) and brazed, and thus the test body is made. The soldered part is hermetically sealed to prevent leakage of gas therethrough. The soldering is carried out in a vacuum oven and the vacuum brazing conditions are as follows: the pressure is 1 Pa, the brazing temperature at 1175 ° C, the heating time from room temperature to the brazing temperature is 2 hours, and the soaking time at soldering temperature is 30 minutes.

6 schematically shows the structure of a test device for hydrogen penetration. The test body in 6 is exaggerated in the direction of its height (in the direction of lamination or in the direction of its stratification). The test piece is placed in an electric heater. Hydrogen gas from a hydrogen production unit is directed into the interior of the test body by means of the 1/2 inch tube of SUS 310S soldered to the test body. First, the inside of the test piece is evacuated by the vacuum pump to an internal pressure of 1 Pa. While the valve Y is closed, the valve X is opened, and hydrogen gas from the hydrogen generating unit is led into the interior of the test body, and when the pressure within the test body becomes higher than 100 kPa, the valve X is closed. Accordingly, hydrogen gas having a hydrogen partial pressure of more than 120 kPa is enclosed within the test body. Then, the electric heater is heated and the test piece therein is kept at 800 ° C. While being maintained at 800 ° C, the pressure change within the test body is monitored; and from the pressure change at the time when the pressure is 100 kPa (ie, at the time when the hydrogen partial pressure is 100 kPa), the rate of hydrogen permeation is calculated. Then, the value of the rate of hydrogen permeation is divided by the surface area of the portion exposed to the internal atmosphere of the four calottes and two plates consisting of the test material, giving the rate of hydrogen permeation per unit time and per unit area. Hydrogen can also penetrate into other components than those made of the test material existing inside the furnace (a part of the 1/4-inch pipe and the connecting pipe); the surface area of the other non-test material components is sufficiently smaller than the surface of the test material, and hydrogen penetration by other components than the test material can be ignored.

Those samples in which the rate of hydrogen peroxide penetration, determined in the manner indicated above, is at least 1.0 x 10 ^-9 mol / (h · cm ² · Pa ^1/2 ) are determined to be those having the property of limit the increase of the internal pressure in a real heat pipe to at most 10 kPa, provided that the rate of hydrogen production by the samples measured according to the measuring method described above is at most 1.0 × 10 ^-6 mol / (h · cm ² ) , Accordingly, the samples in which the rate of hydrogen permeation is at least 1.0 x 10 ^-9 mol / (h · cm ² · Pa ^1/2 ) are found to be good (as effective for increasing hydrogen permeation), while those their rate of hydrogen permeation is less than this range, as poor (as ineffective for increasing hydrogen permeation) can be determined.

The Samples with a soldering failure could be due to steam leakage by the "braded" part during evacuation no vacuum and could therefore be found in the Hydrogen permeation test can not be tested. Accordingly the brazeability of the samples was determined as follows: Those samples that have a predetermined degree of vacuum could be detected as good (with good brazeability); the others are considered bad (with poor brazeability) determined.

The Results are shown in Table 2.

corrosion test

The corrosion test is conducted in accordance with a test in which an exhaust gas condensing environment is simulated; and an overview of the test procedure is in 7 shown. Specifically, a test piece of 25 mm × 70 mm is cut out of each test material; its surface is # 400 dry-polished, and its edges are # 600 dry-polished; and this is heat-treated at 800 ° C for 10 hours to prepare a corrosion test piece. The composition of the simulated condensed water is shown in the table in the Annex to 7 shown. The corrosion test piece is placed between a vertical electric heater and a water tank filled with simulated condensed water in such a manner that it can be reciprocated between the two and subjected to 50 heating and immersion cycles, one cycle including: holding in the heater at 350 ° C for 6 minutes (including a soaking time of about 1 minute) → cooling outside the heater for 7 minutes (the temperature of the test piece, not higher than 100 ° C) → immersing the lower one Partly, 20 mm of the test piece in the simulated condensed water for 1 minute → drying in air for 10 min (for the condensation of the components in the liquid). Then, the test piece is kept in a thermo-hygrostat at 30 ° C and 80% RH for 2000 hours, and after holding, the maximum corrosion depth of the corroded pores formed in the test piece is measured using an optical microscope Focus depth method measured. If the maxi If the corrosion depth in this test method is more than 0.8 mm, there is a possibility that the dome portion of the heat pipe formed from the test piece may be so corroded that it has been exposed to an exhaust fouling environment of a vehicle for 15 years Through hole, even if a plate thickness of 1 mm is assumed, which is the largest strength, which is intended for heat pipes for vehicles. Accordingly, the samples whose maximum depth of corrosion is 0.8 mm in this test are rated as good (have a high corrosion resistance) and the others as poor (have low corrosion resistance).

The results are shown in Table 2. Table 2 No. Speed of hydrogen production Hartlöteignung Speed of hydrogen permeation 800 ° C Corrosion test 2000 h 800 ° C, after 10 h 600 ° C, after 10 h 600 ° C, after 1 h # 400 2D # 400 2D # 400 2D Samples of the invention A1 Good Good Good Good Good Good Good Good bad A2 Good Good Good Good Good Good Good Good bad A3 Good Good Good Good Good Good Good Good bad A4 Good Good Good Good Good Good Good Good bad A5 Good Good Good Good Good Good Good Good bad A6 Good Good Good Good Good Good Good Good bad A7 Good Good Good Good Good Good Good Good bad A8 Good Good Good Good Good Good Good Good bad A9 Good Good Good Good Good Good Good Good bad A10 Good Good Good Good Good Good Good Good bad Comparative samples B1 bad bad Good Good Good Not measurable Good Good bad B2 bad bad Good Good Good Not measurable bad Good bad B3 Good Good Good Good Good Not measurable bad Good bad B4 Good Good Good Good Good Not measurable bad Good bad B5 Good Good Good Good Good Good bad Good bad Speed of hydrogen production B6 bad bad Good Good Good Good bad Good bad B7 Good Good Good Good Good Good bad Good bad

As from Table 2, all samples of the invention good results in all test points. In particular, it should be noted that the samples, in the surface by polishing a Tension was introduced in the initial phase of heating in a medium temperature range of about 600 ° C fast could form a protective oxidation scale, and that their rate of hydrogen production in time after one hour at 600 ° C decreases.

Accordingly These samples could have a more stable effect of prevention Hydrogen production in the initial phase of the beginning of use show a heat pipe.

in the Contrary to these, samples B2 to B7 had the formula (1) do not meet, a bad corrosion resistance on; and the samples B1, B2 and B6 which do not satisfy the formula (2), a high hydrogen production rate at 800 ° C on what is in the maximum end temperature range of heat pipes lies. Samples B1 to B4 having the formula (3) and the formula (4) did not meet, had a bad brazing ability on.

Example 2:

Heating / cooling cycle durability test

Using a cold-rolled annealed steel sheet (# 400 dry-polished steel sheet) from samples A1 to A3 and B6 and B7 in the table having a thickness of 0.8 mm, the heat pipe (calotte 23 ) of a high-temperature system for recovering exhaust heat produced. The heating method used herein comprises introducing a hot gas into the heat collection lamella 24 from an external gas burner. The system was subjected to a test of 2,000 cycles of heating / cooling, in which one cycle comprised: 1. Circulating coolant (water) heating for 5 minutes → 2. Further heating for 5 minutes, stopping the coolant circulation. 3. Coolant circulation and Heating stopped for 5 minutes. The temperature of the heat pipe was in step 1 heating with circulating coolant approx. 400 ° C, in step 2 of heating, wherein the coolant circulation was stopped about 800 ° C, and from 100 to 200 ° C in the cooling step 3 ; and in this cycle, the system is not corroded by dew condensation. After the heating / cooling cycle test, the system was disassembled, and the components of the dome 23 were examined in color for the presence or absence of damage. As a result, no damage was done in the dome 23 found, which was formed from the samples A1 to A3. In contrast, the dome pointed 23 formed from the samples B6 or B7 which do not satisfy the formula (5), due to the large content of C + Ni solid solution through the sheet running damage.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• JP 2007-327719 A [0009]
• JP 7-243784 A [0009]

Cited non-patent literature

• - JIS R6001: 1998 [0016]
• - JIS G4305: 2005 [0016]
• - JIS R6001: 1998 [0018]
• - JIS G4305: 2005 [0018]
• - JIS R6001: 1998 [0034]
• - JIS G4305: 2005 [0034]
• - JIS G4305: 2005 [0050]

Claims (7)

A ferritic stainless steel for heat pipes of high-temperature systems for recovering exhaust gas heat, which, expressed in percentage by mass, comprises: from 16 to 32% Cr, at most 0.03% C, at most 0.03% N, at most 3% Si, at most 2% Mn, not more than 0,008% S, from 0 (no additive) to 0,3% Al, and at least one of the following: not more than 0,7% Nb, not more than 0,3% Ti, not more than 0,5% Zr and not more than 1% V, the balance being Fe and unavoidable impurities, and satisfying the following formula (1), formula (2) and formula (5), and satisfying at least one of the following formula (3) and formula (4): Cr + 3 (Mo + Cu) ≥ 20 (1) Cr + 3 (Si + Mn + Al - Ti) ≥ 20 (2) Ti + Al ≤ 0.05 (3) Nb≥Ti + Al (4) 0.037 {(C + N) / (V + Ti + 0.5Nb + 0.5Zr)} + 0.001 ≤ 0.01 (5), wherein in the formulas (1) to (5), the location of the atomic symbol is replaced by the value of the content of the corresponding element expressed in percentage by mass, and the location of an element not added to the steel is replaced by 0 (zero). The ferritic stainless steel for heat pipes according to claim 1 which also at least one the following includes: maximum 3% Mo, maximum 3% W and at most 3% Cu. The ferritic stainless steel for heat pipes according to claims 1 or 2, which moreover contains at least one of the following: 0.1% Y, at most 0.1% REM (rare earth, rare earth metal), and at most 0.01% approx. A sheet of ferritic stainless steel for heat pipes, which made of steel one of Claims 1 to 3 is formed, and one with a Grit # 100 to # 800 according to JIS R6001: 1998 ground or polished surface, or a ground or polished surface according to HL according to the table 14 in JIS G4305: 2005. A heat pipe for a high temperature system for the recovery of exhaust heat, which produced is made by a hollow vessel made of a steel material one of the steels of one of claims 1 to 3 is formed and has a thickness of 0.5 to 1 mm, whereupon Water is channeled there and then closed to in this way, a liquid phase region and a region to form in it. A heat pipe for a high temperature system for the recovery of exhaust heat, which produced is made by a hollow vessel made of a steel material one of the steels of one of claims 1 to 3 is formed and has a thickness of 0.5 to 1 mm, and that as inner surface one with a grain of # 100 to # 800 according to JIS R6001: 1998 ground or polished surface, or a ground or polished surface according to HL according to the table 14 in JIS G4305: 2005, whereupon water enters there and which is then closed so as to form a liquid phase region and to form an area of free space therein. A high temperature recovery system of exhaust heat, which is the heat pipe according to claim 5 or 6, which is mounted in a position at the the temperature of the material from 600 ° C to 900 ° C enough.