Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel

Definitions

• the invention relates to an iron-nickel-chromium-silicon alloy with improved life and dimensional stability.
• Austenitic iron-nickel-chromium-silicon alloys with different nickel, chromium and silicon contents have long been used as heating conductors in the temperature range up to 1100 ° C.
• this alloy group is standardized in DIN 17470 (Table 1) and ASTM B344-83 (Table 2). There are a number of commercially available alloys listed in Table 3 for this standard.
• the lifetime is increased by a higher chromium content, since a higher content of the protective layer forming element chromium Time delays at which the Cr content is below the critical limit and form other oxides than Cr 2 O 3 , which are, for example, iron-containing oxides.
• EP-A O 531 775 is a heat-resistant austenitic heat-deformable
• Nickel alloy of the following composition (in% by weight):
• EP-A-0 386 730 describes a nickel-chromium-iron alloy with very good oxidation resistance and high temperature resistance, as desired for advanced heat conductor applications, starting from the known NiCr6015 heating conductor alloy and making significant modifications to the composition Improvements in performance could be achieved.
• the alloy differs from the known material NiCr6015 in particular in that the rare earth metals are replaced by yttrium, that it additionally contains zirconium and titanium, and that the nitrogen content is specially adapted to the contents of zirconium and titanium.
• WO-A 2005/031018 discloses an austenitic Fe-Cr-Ni alloy for use in the high-temperature range, which has essentially the following chemical composition (in% by weight): Ni 38-48% Cr 18-24% Si 1, 0-1, 9% C ⁇ 0.1% Fe remainder.
• Diffusion creep are all influenced by the creep, except for the dislocation creeping by a large grain size in the direction of greater creep resistance.
• the dislocation creep does not depend on the grain size.
• the production of a wire with a large grain size increases the creep resistance and thus the dimensional stability. For all considerations, grain size should therefore also be taken into account as an important influencing factor.
• the task is therefore to design an alloy that has a much lower nickel content than NiCr6015 and therefore significantly lower costs
• c) has a high electrical resistivity in conjunction with the smallest possible change in the ratio of heat resistance / cold resistance with the temperature (temperature coefficient et).
• iron-nickel-chromium-silicon alloy with (in wt .-%) 34 to 42% nickel, 18 to 26% chromium, 1, 0 to 2.5% silicon and additions of 0, 05 to 1% Al, 0.01 to 1% Mn, 0.01 to 0.26% lanthanum, 0.0005 to 0.05% magnesium, 0.01 to 0.14% carbon, 0.01 to 0, 14% nitrogen, max. 0.01% sulfur, max. 0.005% B, balance iron and the usual process-related impurities.
• This alloy due to its special composition, has a longer service life than the alloys of the prior art with the same nickel and chromium contents. In addition, increased dimensional stability or sagging can be achieved than the prior art alloys with 0.04 to 0.10% carbon.
• the spreading range for the element nickel is between 34 and 42%, whereby, depending on the application, nickel contents can be given as follows:
• the chromium content is between 18 and 26%, although here too, depending on the area of use of the alloy, chromium contents can be given as follows:
• the silicon content is between 1.0 and 2.5%, whereby, depending on the field of application, defined contents within the spread range can be set:
• the element aluminum is provided as an addition and in amounts of 0.05 to 1%. Preferably, it may also be adjusted in the alloy as follows:
• the subject of the invention preferably assumes that the material properties specified in the examples are essentially set with the addition of the element lanthanum in contents of 0.01 to 0.26%. Depending on the field of application, defined values in the alloy can also be set here:
• Carbon is added to the alloy in the same manner, at levels between 0.01 and 0.14%. Specifically, contents can be adjusted in the alloy as follows:
• magnesium is one of the addition elements in levels of 0.0005 to 0.05%. Specifically, it is possible to adjust this element in the alloy as follows:
• the elements sulfur and boron may be given in the alloy as follows: sulfur max. 0.005% boron max. 0.003%.
• the alloy may further include calcium at levels between 0.0005 and 0.07%, especially 0.001 to 0.05% or 0.01 to 0.05%. If the effectiveness of the reactive element lanthanum alone should not be sufficient to produce the material properties set out in the problem, the alloy may further comprise at least one of the elements Ce, Y, Zr, Hf, Ti with a content of 0.01 to 0, 3%, which can also be defined supplements as needed.
• oxygen-affinity elements such as La, Ce, Y, Zr, Hf, Ti improve the lifetime. They do this by incorporating them into the oxide layer and blocking the diffusion paths of the oxygen there on the grain boundaries. The amount of elements available for this mechanism must therefore be normalized to the atomic weight in order to be able to compare the amounts of different elements among each other.
• the alloy may contain 0.01 to 0.3% of one or more of the elements La, Ce, Y, Zr, Hf, Ti, respectively
• the alloy may have a phosphorus content between 0.01 to 0.20%, in particular from 0.005 to 0.020%.
• the alloy may contain between 0.01 to 1.0% of one or more of the elements Mo, W, V, Nb, Ta, Co, which may be further limited as follows:
• impurities may still contain the elements copper, lead, zinc and tin in amounts as follows:
• the alloy according to the invention is to be used for use in electric heating elements, in particular in electrical heating elements which require high dimensional stability and low sagging.
• a concrete application for the alloy according to the invention is the use in furnace construction.
• Tables 1 to 3 reflect - as already mentioned at the beginning - the state of the art.
• Tables 4a and 4b are industrially molten iron-nickel-chromium-silicon alloys according to the prior art T1 to T7, one on a laboratory scale Prior art molten alloy T8 and a plurality of bench scale inventive experimental alloys V771 to V777, V1070 to V1076, V1090 to V1093 melted to optimize the alloy composition.
• the heat conductor life test is carried out on wires with a diameter of 0.40 mm.
• the wire is clamped between 2 power supply lines at a distance of 150 mm and heated by applying a voltage up to 1150 0 C.
• the heating at 1150 0 C takes place in each case for 2 minutes, then the power supply is interrupted for 15 seconds.
• the burning time is the addition of the "on" times during the life of the wire
• the relative burning time tb is the indication in% related to the burning time of a reference batch.
• the sagging behavior of heating coils at the application temperature is investigated in a sagging test. This is on heating coils, the sagging of the helices of the Horizontal captured after a certain time. The lower the sag, the greater the dimensional stability or creep resistance of the material.
• T1 and T2 are alloys with about 30% nickel, about 20% Cr and about 2% Si. They contain rare earth (SE) additions in this case, cerium misch metal, which means that SE consists of about 60% Ce, about 35% La and the rest Pr and Nd. The relative burning time is 24% or 35%.
• SE rare earth
• the example T3 is an alloy with about 40% nickel, about 20% Cr and about 1.3% Si. It contains rare earth (SE) additions in this case, cerium misch metal, which means that SE is about 60% Ce, about 35% La, and the balance is Pr and Nd. The relative burning time is 72%.
• SE rare earth
• the examples T4 to T7 are alloys with about 60% nickel, about 16% Cr and about 1, 2 - 1, 5% Si. They contain rare earth (SE) additions in this case, cerium mischmetal, which means that SE is about 60% Ce, about 35% La and the rest Pr and Nd.
• SE rare earth
• cerium mischmetal which means that SE is about 60% Ce, about 35% La and the rest Pr and Nd.
• the relative burning time is in the range of about 100 to 130%.
• Tables 4a and 4b contain a number of alloys melted on a laboratory scale.
• the laboratory-scale melted prior art alloy T8 is an alloy of 36.2% nickel, 20.8% Cr, and 1.87% Si.
• SE rare earth
• Cerium misch metal which means that SE is and was about 60% Ce, about 35% La and the rest Pr and Nd, apart from the Ni, Cr, and Si contents, melted to the same specifications as the large-scale batches.
• the batches according to the prior art T1 to T8 are thus directly comparable.
• the relative burning time of T8 is 53%.
• the Ni content is about 36%, the Cr content about 20% and the Si content about 1, 8%.
• the additions to Ce, La, Y, Zr, Hf, Ti, Al, Ca, Mg C, N were varied. These batches can therefore be compared directly with the prior art alloys T8, thus serving as a reference alloy for optimization serves.
• Fig. 1 shows a graph of the relative burning time tb and the potential PwE for the different alloys indicated in Tables 4a and 4b.
• Range A typical content of active elements
• range B possible content of active elements
• range C too high content of active elements.
• PwE is between 0.11 (T2 and T4) and 0.15 (T6 and Jl).
• V1090 and V1072 which did not add cerium misch metal, ie, Ce and La, but Y instead, show a lower relative burn time than T8, although V1090 at 0.10 has a slightly lower PwE but V1072 at 0, 18 has a higher PwE. Y does not appear to work as well as Ce and / or La, so replacement of SE by Y leads to a deterioration over the prior art. Further additions of Zr and Ti (V1074) or Zr and Hf (V1092, V1073, V1091, V1093) in different proportions have succeeded in achieving the service life of T8 again.
• V771 to V777, V1070, V1071 have all been melted with cerium mischmetal, V1075 contains only La.
• the experimental melts V1075 and V777 achieved the highest relative burning time of about 70% of these experimental melts.
• the PwE of V777 is significantly larger at 0.36 than in V1075 at 0.20, which is at the limit of the PwE of the prior art alloys.
• a similar good burning time was achieved with V777 with a combination of 0.06% Ce, 0.02% La, 0.03% Zr and 0.04% Ti.
• V775 with 0.07% Ce and 0.03% La, 0.05% Y and 0.03% Hf with a PwE of 0.30 only has a relative burning time of 46%, indicating that additional doses of Y and Zr to Ce and La are not as effective.
• Figure 2 is a plot of relative burn time and PwE to illustrate the previously described.
• Figure 2 shows the relative burning time of the alloys T1 to T8 according to the prior art as a function of the nickel content.
• the straight lines limit the scattering band in the relative burning time into which the alloys of the prior art fall as a function of the nickel content.
• the trial alloy V1075 with the addition of the best acting element La. Their life is well above the scattering range.
• Table 4b summarizes sagging along with the grain size of the wires.
• the alloys of the prior art T1 to T8 show sagging between 4.5 and 6.2 mm at comparable grain sizes between 20 and 25 microns.
• Figure 3 shows a plot of nickel content. However, this does not seem to be decisive for sagging.
• Figure 4 shows a plot of the alloys T1 to T8 and the experimental alloys over the C content. Since the experimental alloys have different particle sizes, they were divided into 2 classes: particle sizes from 19 to 26 ⁇ m and particle sizes from 11 to 16 ⁇ m. The alloys T1 to T8 and the trial alloys with a grain size of 19 microns to 26 microns, the comparable Grain sizes all show a similar sagging in the range of 4.5 to 6.2 mm. The experimental alloys, which have a particle size of 11 to 16 microns and a carbon content less than 0.042% have a larger Sagging of about 8 mm, as it is to be expected due to the smaller grain size. The experimental alloys with a grain size of 11 to 16 microns and a carbon content of greater than 0.044% unexpectedly show a lower sagging of 2.8 to 5 mm.
• Figure 5 shows a plot of the alloys T1 to T8 and the experimental melts over the N content.
• Figure 6 shows a plot over the sum C + N. It illustrates once again how C + N significantly reduce sagging.
• a higher C- or N-content thus reduces sagging so much that the sagging-enhancing effect of a smaller grain size is not fully compensated.
• the trial alloys have all been subjected to a standard heat treatment.
• the alloy V777 shows the lowest sagging of all alloys. It has the highest C content and an N content in the upper third. A high C content therefore seems to be particularly effective in reducing sagging.
• Nickel contents below 34% degrade the lifetime (relative burning time), the electrical resistivity and the ct value too much. Therefore, 34% is the lower limit for the nickel content. Too high nickel contents cause higher costs due to the high nickel price. Therefore, 42% should be the upper limit for the nickel content.
• Too low Cr contents mean that the Cr concentration falls too fast below the critical limit. That is why 18% Cr is the lower limit for chromium. Too high Cr contents deteriorate the workability of the alloy. Therefore, 26% Cr is the upper limit.
• a minimum content of 0.01% La is necessary to obtain the oxidation resistance-enhancing effect of La.
• the upper limit is set at 0.26%, which corresponds to a PwE of 0.38. Larger values of PwE are not meaningful as explained in the examples.
• AI is needed to improve the processability of the alloy. It is therefore necessary a minimum content of 0.05%. Too high contents in turn affect the processability.
• the Al content is therefore limited to 1%.
• a minimum content of 0.01% C is necessary for good dimensional stability or low sagging. C is limited to 0.14% because this element reduces oxidation resistance and processability.
• N A minimum content of 0.01% N is necessary for good dimensional stability or low sagging. N is limited to 0.14% because this element reduces oxidation resistance and processability.
• Mg a minimum content of 0.001% is required as this improves the processability of the material.
• the threshold is set at 0.05%, so as not to soften the positive effect of this element.
• the levels of sulfur and boron should be kept as low as possible, since these surface-active elements affect the oxidation resistance. It will therefore max. 0.01% S and max. 0.005% B is set.
• Copper is heated to max. 1% limited as this element reduces the oxidation resistance.
• Pb is set to max. 0.002% limited because this element reduces the oxidation resistance. The same applies to Sn.
• a minimum content of 0.01% Mn is required to improve processability.
• Manganese is limited to 1% because this element reduces oxidation resistance.
• Table 4b Continuation: Relative burning time tb and composition of test batches (batch number starts with V) and prior art batches (T1 to T8). All data in% by weight.

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