JP2016094662A - Stainless foil for resistance heating element and stainless wire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inexpensive material for resistance heating element for an electric heating heater such as seeds heater and planar heating element, excellent in various properties and more excellent in manufacturability than a nickel chromium alloy.SOLUTION: There is provided a stainless foil for resistance heating material or a stainless wire having a chemical composition containing, by mass%, C:0.080% or less, Si:1.5 to 5.0%, Mn:5% or less, P:0.050% or less, S:0.003% or less, Ni:10 to 15%, Cr:15 to 22%, Mo:3% or less, Cu:3.5% or less, N:0.2% or less, O:0.01% or less, Ti:0.05% or less with percentage of Ni/Si in a range of 3 to 7 and the balance Fe with inevitable impurities, and having average temperature coefficient of volume resistance at 20 to 600°C of 0.00100/°C or less, cold workability dependency index of the volume resistance defined by β(c)/β(A) in a range of 0.970 to 1.030 and small cold workability dependency index of the volume resistance.SELECTED DRAWING: None

Description

The present invention relates to a resistance heating element material for an electric heater used in a sheathed heater, a planar heating element, or the like.

The resistance heating element generates heat by supplying electricity to various metals, and a thin plate, foil, wire, or the like is used as the metal heating element. The sheet heating element mainly using foil material is characterized by being thin and soft and suitable for heating to curved surfaces and narrow spaces. Therefore, it is suitable for heating to curved surfaces and narrow spaces. Widely used in equipment. On the other hand, a rod-shaped heating element mainly using a wire is characterized in that it can be heated by a large current, and is widely used in various heating parts such as a sheathed heater and a hot plate. As a material for the resistance heating element, generally a material having a high electric resistance is desirable.

Various high electrical resistance materials have been used for conventional resistance heating materials. Examples of general-purpose materials include austenitic stainless steels such as SUS301 and SUS304 disclosed in Japanese Patent Application Laid-Open No. 2004-149885 (Patent Document 1) and Japanese Patent Application Laid-Open No. 2004-79247 (Patent Document 2). These steels have excellent formability and low embrittlement susceptibility to heating, and contain 17 to 18% by mass of Cr. Therefore, the volume resistivity is 0.76 μΩ · m compared to ordinary steel. high. However, the volume resistivity is small and the temperature dependence of the volume resistivity is large compared to a material that has been used as a dedicated material for a conventional electric resistance heating element described later.

Examples of the dedicated material for the electric resistance heating element include iron-chromium-based materials and nickel-chromium-based materials defined in JlS C2520 “Alloy wire and strip for electric heating”. For iron-chromium, Fe-Cr-Al alloys such as FCH1 and FCH2 are defined as wires, and for foils, for example, Japanese Patent Application Laid-Open No. 7-153556 (Patent Document 3) has similar component-based alloys. Is disclosed. Since these alloys contain 17 to 26% Cr and 2 to 6% Al, they have a feature of high volume resistivity and low temperature dependency of volume resistivity. However, since this alloy system has a ferrite single phase structure, it is difficult to essentially avoid the disadvantage of embrittlement. That is, when the use temperature is around 500 ° C., 475 ° C. embrittlement, σ embrittlement at about 700 ° C., and embrittlement due to crystal grain coarsening at 900 ° C. or higher are concerned. It was difficult to apply to resistance heating elements.

Nickel-chromium alloys include nichrome alloys such as NCH1 and NCH2 as wires. This alloy has been used most widely as a material for resistance heating elements because it has excellent workability like austenitic stainless steel and has a relatively small volume resistivity temperature dependency. However, these alloys have the problem of high production costs due to poor manufacturability. That is, since NCH1 and NCH2 have high deformation resistance at high temperature and are inferior in hot deformability, in the hot deformation process in manufacturing such as hot rolling in a plate or hot drawing in a wire, Surface defects such as surface cracks and surface defects are likely to occur. If these wrinkles remain, there is a possibility of causing problems such as breakage or disconnection of the plate in the next cold working process. In particular, in the manufacturing process of foils and thin wires, a great load of wrinkle removal may be required. there were. Furthermore, these alloys are also very expensive materials because they contain Ni in a large amount of 80% for NCH1 and 60% for NCH2.

As means for solving these problems, there is means for improving the electric resistance value of austenitic stainless steel. Although the method is different from this application, the materials used for the power resistor, the main resistor of the resistance control vehicle, the vehicle resistor, and the like described in JP-A-2003-41349 (Patent Document 4) , A material used for a radio wave watch member and a radio wave receiver described in Japanese Patent Application Laid-Open No. 2011-214154 (Patent Document 5), and the material used for these materials adds a large amount of Si to improve the electrical resistance value. It is disclosed. Since this component system has the same performance as a nickel-chromium-based material and may be inexpensive, it is promising to be applied to a resistance heating element. However, even with these materials, it is difficult to suppress the formation of surface defects in the manufacturing process, and the temperature of the volume resistivity in the temperature range required for the resistance heating element, that is, the temperature exceeding 400 ° C. It is hard to say that sufficient consideration has been given to dependencies.

In addition to the above problems, when used as a resistance heating element, it may be used as it is cold-worked or as it is drawn, and in this case, these strains are gradually recovered during use. It is also necessary that the volume resistivity does not vary greatly by processing. For example, the volume resistivity of nickel chrome-based NCH1 decreases as the cold rolling rate increases, and conversely, the volume resistivity of SUS304 increases along with the cold rolling rate. This means that in both cases where the product form is a foil material and a wire material, the characteristics differ depending on whether the material is annealed or processed. If the raw material is used, the processing strain is released during use. Therefore, it is necessary to reflect the variation in volume resistivity due to the fact that the volume resistivity varies depending on the part due to processing being applied even if an annealed material is used in the design of the product. In addition, JP 2003-41349 A (Patent Document 4) discloses a result of studying the stability of the magnetic permeability assuming a wrapping around a processing rate of about 20%, but the resistance heating element is still processed. In general, in many cases, strong processing exceeding a processing rate of 20% is often applied.

JP 2004-149885 A JP 2004-79247 A JP-A-7-153556 JP 2003-41349 A JP2011-214154A

As described above, any of the above knowledge technologies has a problem of any one of the temperature dependency of the volume resistivity and the processing strain dependency, the manufacturability as a foil or a wire, and the manufacturing cost including the material cost as a resistance heating element material. However, it is difficult to say that these are materials that satisfy these requirements at the same time.

The present invention has been devised to solve such a problem. The volume resistivity in the temperature range exceeding 400 ° C. is increased, and at the same time, the temperature dependence of the volume resistivity in this temperature range is reduced. It is an object of the present invention to clarify an effective design method for reducing the surface defects generated during hot working, and to provide a resistance heating element material that is more manufacturable and less expensive than a nickel chromium alloy.

In order to achieve the object, the material for a resistance heating element of the present invention is, in mass%, C: 0.080% or less, Si: 1.5 to 5.0%, Mn: 2% or less, P: 0.00. 050% or less, S: 0.003% or less, Ni: 10-15%, Cr: 15-22%, Mo: 3% or less, Cu: 3.5% or less, N: 0.2% or less, 0: 0.01% or less, Ti: 0.05% or less, and the ratio of Ni / Si is in the range of 3-7. If necessary, Nb: 0.04 to 0.25%, V, W and Al 1 4% or less in total, and one or more of B and REM in a total range of 0.1% or less, with the balance being Fe and inevitable impurities, and having a chemical composition of 20 to 600 ° C. The average temperature coefficient of volume resistivity is 0.00100 / ° C. or less, and the volume resistivity defined by β (c) / β (A) is a cold working rate dependency index. Is in the range of 0.970 to 1.030. Here, β (c) represents the volume resistivity at 200 ° C. of the processed material having a rolling rate or area reduction of 50%, and β (A) represents the volume resistivity of the annealed material at 200 ° C.

According to the stainless steel foil for resistance heating elements and the stainless wire according to the present invention, the volume resistivity in the temperature range exceeding 400 ° C. can be increased and the temperature dependency of the volume resistivity in this temperature range can be reduced. It is possible to provide a low-cost material for a resistance heating element that is excellent in manufacturability as compared with nickel chrome alloy, reducing surface defects generated during hot working.

The present inventors have a component system in which Si, which is effective for increasing electric resistance, is added up to 600 ° C., starting from an austenitic Fe—Cr—Ni alloy capable of significantly reducing costs from a nickel chromium alloy. The content of alloy elements effective for reducing the temperature coefficient of the volume resistivity and reducing the fluctuation of the volume resistivity when a working strain exceeding 20% was applied was examined. As a result, it was found that it is important to optimize the addition amounts of Ni and Si. That is, Ni mainly promotes a decrease in volume resistivity due to processing strain, so excessive addition causes the amount of fluctuation to be too large, and Si reduces the temperature dependence of volume resistivity in a high temperature region and also due to processing strain. It was clarified that there is an effect of suppressing the decrease in volume resistivity to some extent. Also, considering these, if the Ni / Si ratio is in the range of 3 to 7 and the content of other alloy elements is optimized, the temperature coefficient of volume resistivity at 20 to 600 ° C. is 0.00100 / ° C. or less. , Β (c) / β (A) was found to have a cold working rate dependency index of volume resistivity in the range of 0.970 to 1.030 at a working strain of 50%.

On the other hand, in order to reduce surface defects generated during hot working, it is widely known that it is effective to generate δ ferrite during hot working of a material, but in this component system, Ti, S, O was found to be very harmful. Based on the results, the inventors have found that it is possible to ensure the surface defect level of austenitic stainless steel by strictly defining the upper limit of these alloy elements, and have reached the present invention.

Hereinafter, the reason for selecting the range will be described for each of the alloy elements constituting the stainless steel foil for resistance heating elements and the stainless steel wire and the defined limiting formulas, which have low temperature dependency and processing strain dependency of the volume resistivity of the present invention. .

C is a strong austenite-forming element and is an element effective for improving the strength. However, excessive addition causes coarse Cr carbide to precipitate by recrystallization treatment, causing intergranular corrosion resistance and weldability deterioration. Therefore, C is preferably 0.080% by mass or less (excluding 0%).

Si is an alloy component effective for increasing the volume resistivity, and is an important element effective for reducing the temperature dependence of the volume resistivity up to 600 ° C. Therefore, addition of 1.5% by mass or more is necessary. I need. However, if an excessive amount of silicon exceeding 5% by mass is contained, bending workability deteriorates due to hardening. Although the reason is not clear, as described above, Si contributes to the reduction of the processing strain dependence of the volume resistivity by the combined addition with Ni, and the Si content is 1.5 to 5.0% by mass. In the range, if Ni / Si is 3 to 7, both temperature dependency and processing strain dependency can be stabilized at a low level. A more preferable range of Ni / Si is 3 to 5, and a further preferable range is 3.5 to 4.5.

Although Mn is an austenite forming element and can be expected to have the same effect as Ni, adding a large amount induces surface defects caused by the generation of blowholes even when dissolved under nitrogen pressure. It may cause trouble. In the production of foils and fine wires, bright annealing is often employed because pickling after annealing after cold working is often difficult. At this time, if Mn is contained in a large amount, the steel may be colored, and in this case, there is a high possibility of causing a quality defect in the subsequent manufacturing process. For this reason, the Mn content is desirably 5% by mass or less (not including 0%).

P is preferably low because it impairs the hot workability of the base material. However, since it is difficult to remove P by refining in the production of Cr-containing steel, excessively increasing the cost for selecting raw materials or the like is accompanied by extremely low P content. Therefore, in the present invention, the P content up to 0.050% by mass is allowed, as in the general austenitic stainless steel.

S is an element that promotes the formation of MnS. If there is a surface defect caused by MnS in the foil or wire that is the object of the present invention, the manufacturing cost is significantly increased and the possibility that the surface defect remains is denied. This is not possible, and there is a concern that durability will be reduced due to defects. For this reason, it is preferable to reduce S content as much as possible, and prescribe | regulate to 0.003 mass% or less.

Ni, like Mn, is an element necessary for maintaining austenite after annealing. It is an element that has a great influence on the cold working rate dependency of volume resistivity, which is a feature of the present invention. When the amount of Ni is less than 10% by mass, the volume resistivity increases due to strain caused by cold rolling. When the amount of Ni increases, the cold rolling rate dependency of the volume resistivity decreases. In order to solve this problem, the Ni / Si ratio may be kept in the range of 3 to 7 as described above. However, since Ni is an expensive element, the upper limit is set to 15% by mass.

Cr is a main constituent element of the passive film while slightly increasing the volume resistivity, and is an element improving corrosion resistance and oxidation resistance at high temperatures. Considering the application of the present application, it is necessary that the corrosion resistance is not easily rusted in the atmosphere, and the heat resistance is not abnormally oxidized by heating at about 800 ° C. In this component system, considering that Si is added in an amount of 1.5% by mass or more, at least 15% by mass of Cr is required to impart intended corrosion resistance and oxidation resistance. On the other hand, since Cr is also a ferrite forming element, if it is added excessively, a large amount of δ ferrite phase is generated at a high temperature. Therefore, an austenite forming element (C, N, Ni, Mn, Cu, etc.) must be added to suppress the δ ferrite phase, resulting in an increase in cost. For this reason, the upper limit of Cr content was 22 mass%.

Mo is an effective element for improving the corrosion resistance level together with Cr, and it is known that the effect of improving the corrosion resistance increases as the Cr content increases. However, if a large amount of Mo is added, δ ferrite is formed at a high temperature, so the Mo component range is preferably 3% by mass or less, and more preferably 2% by mass or less from the viewpoint of economy.

Cu is an effective element for reducing the foil rolling load and the drawing work load because it raises the stacking fault energy of the austenite phase and reduces the work hardening by reducing the cross slip interval at the time of deformation. However, excessive addition inhibits pitting corrosion resistance and hot workability, so the Cu component range is preferably 3.5% by mass or less.

N is an austenite-forming element and is an effective element for maintaining non-magnetism and obtaining high strength. However, excessive addition of N causes blowholes at the time of casting, and surface defects caused by the addition become serious in foils and wires. Considering this, the upper limit is preferably 0.2% by mass or less.

Ti is an element effective for precipitation hardening, and is effective for increasing the strength during aging treatment. However, surface flaws of the steelmaking slab are likely to be generated, and there is a problem in manufacturing. Moreover, it is easy to produce a large inclusion of TiN. In the foil or wire that is the subject of the present invention, if there is a surface defect caused by TiS or TiN, it is necessary to remove it at the time of manufacturing, and the manufacturing cost rises. The amount must be strictly defined, and the upper limit is 0.05% by mass.

O is a gas used for decarburization at the time of steelmaking blowing, but may remain in steel as inclusions by combining with metal or nonmetal. When the amount of inclusions increases, surface defects such as Ti and S are likely to be generated, and surface defects are formed in the manufacturing process of foils and wires, thereby significantly reducing the manufacturing yield. For this reason, it is necessary to specify | regulate O content exactly | strictly, The upper limit shall be 0.01 mass%.

Nb is effective for increasing the high-temperature strength, but conversely causes a decrease in hot workability due to an increase in high-temperature strength, so the appropriate range was set to 0.04 to 0.25% by mass.

V and W are effective elements for increasing the strength. However, when these elements are added excessively, the hot workability is adversely affected. Al is an effective element for increasing the volume resistivity, but excessive addition like V and W adversely affects hot workability. In addition, since these elements are ferrite forming elements, it is necessary to add them while paying attention to the deterioration of hot workability due to the formation of δ ferrite during manufacture and to embrittlement due to the formation of σ phase during use. Considering these factors, when adding one or more of V, W, and Al, it is necessary to suppress the total content to 4% by mass or less.

B is an element effective in preventing the occurrence of edge cracks in the hot-rolled steel strip caused by the difference in deformation resistance between the δ ferrite phase and the austenite phase in the hot rolling temperature range. REM is an element that fixes S in steel and enhances the deformability of the austenite phase grain boundaries, and is effective in preventing the occurrence of edge cracks in the hot-rolled steel strip. However, excessive addition of B tends to form a low melting point boride, and excessive addition of REM increases the formation of inclusions and conversely degrades hot workability. When adding, the total content was made into 0.1 mass% or less. In addition, there exist Y, Ca, Mg etc. as an element which can anticipate the effect similar to REM, Although content of these elements is not prescribed | regulated in particular, it shall add suitably according to REM as needed.

The resistance heating material may be heated to about 600 ° C. except for an industrial heating furnace. The average temperature coefficient of volume resistivity is a factor that varies depending on the amount of each alloy element added as described above, and the lower the value, the better. However, if the upper limit is strictly defined, an alloy that satisfies the upper limit is limited to an Fe—Cr—Al alloy such as FCH 2 and does not satisfy other required characteristics. Therefore, the average temperature coefficient is set to 0.00100 / ° C. or less which is the same as that of the nickel chromium alloy. This coefficient is a value obtained by dividing the volume resistivity difference between 600 ° C. and 20 ° C. by the temperature difference 580 and the volume resistivity at 20 ° C.

The cold work rate dependency index of the volume resistivity defined by β (c) / β (A) is also a factor that varies depending on the amount of each alloy element added as described above, and taking into account the average temperature coefficient, It depends mainly on the value of Ni / Si. This value is also preferably low, and the measurement error range of the volume resistivity is within 3%. Therefore, the range of this index is set to 0.970 or more and 1.030 or less equivalent to it. The rolling rate and the area reduction rate used in this definition formula are set to 50% close to general manufacturing conditions, but the processing rate according to special manufacturing conditions may be set individually.

The stainless steel having the above composition has a high volume resistivity, and a wire rod is realized as a heating element / electric resistance foil having a small volume resistivity temperature dependency and processing strain dependency.

Stainless steel having the chemical composition shown in Table 1 was melted, and a hot-rolled sheet having a thickness of 3 mm was produced by hot rolling. Thereafter, annealing and cold rolling were repeated to obtain a sheet thickness of 0.1 mm, and annealing was performed in a reducing atmosphere of 100% hydrogen at 950 to 1000 ° C. to produce an annealed foil. This foil material was rolled to 0.050 mm to produce a 50% rolled material. On the other hand, for the wire rods, the slit members of the steels C and D of the present invention and the comparative steel H are made from the 1.2 mm cold-rolled annealed plates having the same components shown in Table 1, followed by drawing and annealing the wire rods having a diameter of 0.836 mm. Manufactured. Further, this 0.836 mm diameter wire rod was drawn to a diameter of 0.59 mm to produce a cold-rolled wire rod having a surface reduction rate (cross-sectional reduction rate) of 50%. Hereinafter, a sheet material having a rolling rate of 50% and a wire material having a surface reduction rate of 50% are referred to as “50% processed material”. In addition, in the process of manufacturing 50% processed material, about the steel which detected the defect exceeding 3% of a total surface area visually, it determined with there being a problem in manufacturability.

A test piece was cut out from each annealed material and each rolled material, and the volume resistivity, the temperature dependency of the volume resistivity and the processing strain dependency were measured as follows. For measuring the volume resistivity, an electrical resistance-one-temperature characteristic test method defined in JlSC 2526 was adopted, and the volume resistivity of each test piece at each temperature was measured. The average temperature coefficient in the temperature range of 20 to 600 ° C. was determined from the measured value. As an index of the cold working rate dependency, a value obtained by dividing the volume resistivity of the 50% processed material at the test temperature of 200 ° C. by the volume resistivity of the annealed material at 200 ° C. was used. These results are shown in Table 2.

As seen in the measurement results of Table 2, A to J of the steel of the present invention has a volume resistivity of 0.9 μΩ · m or more at 20 ° C., and an average temperature coefficient in the temperature range of 20 to 600 ° C. is 0.00. 10000 / ° C. or less. Furthermore, the value change when processing strain is introduced from the value obtained by dividing the volume resistivity of the 50% processed material at the test temperature of 200 ° C. by the volume resistivity of the annealed material at 200 ° C. is less than ± 3%. On the other hand, in Comparative Steels K and L, since Si and Ni are out of the scope of the present invention, the volume resistivity at 20 ° C. is less than 0.9 μΩ · m, and the average temperature coefficient in the temperature range of 20 to 600 ° C. is also 0. It is over 40400 / ° C. In Comparative Steel L, the value change obtained by dividing the volume resistivity of the 50% processed material at the test temperature of 200 ° C. by the volume resistivity of the annealed material at 200 ° C. exceeds 5%. The characteristics related to the volume resistivity of the comparative steels M and N are the same as those of the steel of the present invention, but the production ranges of the Ti and S amounts are out of the foil, respectively, There is a manufacturing problem due to surface defects caused by inclusions in the manufacturing process. Comparative steel 0 is an alloy corresponding to nickel-chromium alloy NCH-1, but compared to the steel of the present invention, the volume resistivity of the 50% processed material at the test temperature of 200 ° C is the volume resistivity of the annealed material at 200 ° C. The divided value is large.

As described above, the resistance heating element material of the present invention has a high volume resistivity, a low volume resistivity temperature dependency, and a small volume resistivity cold work rate dependency. In addition, since it is excellent in cold workability and hot workability and has a low content of expensive Ni, a foil as a resistance heating element material in various fields where NCH1 or NCH2 nickel-chromium alloys have been used so far The expansion of the application range is expected in both forms of lines and lines.

Claims (4)

C: 0.080% or less, Si: 1.5-5.0%, Mn: 5% or less, P: 0.050% or less, S: 0.003% or less, Ni: 10-15 %, Cr: 15-22%, Mo: 3% or less, Cu: 3.5% or less, N: 0.2% or less, O: 0.01% or less, Ti: 0.05% or less, Ni / Si The ratio is 3 to 7 and the balance has a chemical composition composed of Fe and inevitable impurities, the average temperature coefficient of volume resistivity at 20 to 600 ° C. is 0.00100 / ° C. or less, β (c ) / Β (A) defined by the cold working rate dependence of the volume resistivity, wherein the volume working resistivity dependence index of the volume resistivity is 0.970 or more and 1.030 or less. Stainless steel foil or stainless wire for resistance heating elements Here, β (c) represents the volume resistivity at 200 ° C. in the processed material having a foil rolling ratio or 50% area reduction, and β (A) represents the volume resistivity at 200 ° C. of the annealed material. . Furthermore, the stainless steel foil or stainless steel wire for resistance heating elements according to claim 1, wherein Nb is contained in the range of 0.04 to 0.25%, and the volume resistivity is less dependent on the cold working rate. Furthermore, the stainless steel foil for resistance heating elements according to claim 1 or 2, wherein one or more of V, W, and Al are contained within a total range of 4% or less, and the volume resistivity has a low cold work rate dependency. Stainless wire. Furthermore, the stainless steel foil for resistance heating elements with small dependence on the cold work rate of the volume resistivity of Claim 1-3 which contains 1 or more types of B and REM in the range of 0.1% or less in total or Stainless wire.