Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
  • B23K35/22—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by the composition or nature of the material
  • B23K35/24—Selection of soldering or welding materials proper
  • B23K35/30—Selection of soldering or welding materials proper with the principal constituent melting at less than 1550°C
  • B23K35/3053—Fe as the principal constituent
  • B23K35/308—Fe as the principal constituent with Cr as next major constituent
  • B23K35/3086—Fe as the principal constituent with Cr as next major constituent containing Ni or Mn
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
  • B23K35/02—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by mechanical features, e.g. shape
  • B23K35/0222—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by mechanical features, e.g. shape for use in soldering or brazing
  • B23K35/0233—Sheets or foils
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
  • B23K35/02—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by mechanical features, e.g. shape
  • B23K35/0222—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by mechanical features, e.g. shape for use in soldering or brazing
  • B23K35/0244—Powders, particles or spheres; Preforms made therefrom
• • 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
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/34—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of 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
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
• • 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
  • C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
• • 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
  • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F28—HEAT EXCHANGE IN GENERAL
  • F28D—HEAT-EXCHANGE APPARATUS, NOT PROVIDED FOR IN ANOTHER SUBCLASS, IN WHICH THE HEAT-EXCHANGE MEDIA DO NOT COME INTO DIRECT CONTACT
  • F28D9/00—Heat-exchange apparatus having stationary plate-like or laminated conduit assemblies for both heat-exchange media, the media being in contact with different sides of a conduit wall
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F28—HEAT EXCHANGE IN GENERAL
  • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
  • F28F21/00—Constructions of heat-exchange apparatus characterised by the selection of particular materials
  • F28F21/08—Constructions of heat-exchange apparatus characterised by the selection of particular materials of metal
  • F28F21/081—Heat exchange elements made from metals or metal alloys
  • F28F21/082—Heat exchange elements made from metals or metal alloys from steel or ferrous alloys
  • F28F21/083—Heat exchange elements made from metals or metal alloys from steel or ferrous alloys from stainless steel
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F28—HEAT EXCHANGE IN GENERAL
  • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
  • F28F21/00—Constructions of heat-exchange apparatus characterised by the selection of particular materials
  • F28F21/08—Constructions of heat-exchange apparatus characterised by the selection of particular materials of metal
  • F28F21/089—Coatings, claddings or bonding layers made from metals or metal alloys
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K2101/00—Articles made by soldering, welding or cutting
  • B23K2101/04—Tubular or hollow articles
  • B23K2101/14—Heat exchangers
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K2103/00—Materials to be soldered, welded or cut
  • B23K2103/02—Iron or ferrous alloys
  • B23K2103/04—Steel or steel alloys
  • B23K2103/05—Stainless steel

Definitions

• the present invention relates to a brazing material comprising:
• Si Silicon
• Manganese (Mn) Manganese
• the invention relates to a use of a brazing material according to the above for brazing together article of stainless steel.
• the invention relates to a heat exchanger made from plates from austenitic stainless steel being brazed with a brazing material according to the invention.
• Brazing is a commonly used and well-known method for joining articles by melting a metal or alloy having a lower melting point than the material of the articles to be joined.
• Common examples of brazing are joining copper articles by a copper- phosphorous brazing material and articles of stainless steel by a copper brazing material.
• the brazing material has a lower melting point than the material to be joined, that the wetting between the molten brazing material and the material to be brazed is good, that the brittle phases are kept at a minimum, that it does not entrain too much into the base material and weaken it or make its melting point decrease such that the base material melts during the brazing cycle or make important elements of the brazing material migrate from the base material to the brazing material, hence altering the properties of the base material. For example, if Nickel (Ni) would migrate from the base material to the brazing material, there is a risk that the base material would not be austenitic after the brazing.
• Silver (Ag) as a brazing material, at least in part, and, having general knowledge of the Silver (Ag) price, it is not difficult to comprehend that omission of Silver (Ag) will make a large difference on the prize of the brazing material.
• Another common brazing material is Nickel and Nickel based alloys, which also are a relatively costly.
• Brazed heat exchangers have been used for a long time; usually, such heat exchangers comprise a number of heat exchanger plates provided with a pressed pattern of ridges and grooves adapted to keep the plates on a distance form one another under formation of interplate flow channels for media to exchange heat.
• the plates will contact one another in crossing points between the ridges and grooves of neighboring plates, and in order to keep the plates together, the plates are brazed to one another in these crossing points.
• a common material of the heat exchanger plates is austenitic stainless steel, e.g. 316 or 304 stainless steel, and a common brazing material is copper.
• the heat exchanger plates are usually brazed in a furnace under vacuum or a controlled atmosphere. Copper brazing of stainless steel plates is a very efficient and reliable method for joining the heat exchanger plates, but in some applications, the copper brazings are not sufficient. For example, copper is sensitive to some chemicals (e.g. ammonia) and if tap water is heated by the heat exchanger, copper ions may be dissolved into the tap water, especially if the water to be heated contains salts.
• some chemicals e.g. ammonia
• EP 1 347 859 One example of an Iron (Fe) based brazing material according to the prior art is disclosed in EP 1 347 859.
• Si melting point depressant
• Another example of an Iron (Fe) based brazing material is found in
• a brazing material comprising:
• Nickel 12.5-14.5% Nickel (Ni);
• the content of Molybdenum (Mo) may be 1.9- 2.2 %.
• the percentage of Nickel (Ni) may be 13.1-13,3 %.
• Chromium (Cr) may be 18.0-18.2 %. This percentage also mimics the Chromium (Cr) content of the base material to be brazed.
• the percentage of Silicon (Si) may be 7.5-8.2 %. In some embodiments of the invention, the percentage of Silicon (Si) may be 7.8-8.0%.
• the percentage of Manganese (Mn) may be 4.0-5.5%.
• the erosion may be even more reduced if the percentage of Manganese (Mn) is 5.0-5.5% or 5.1-5.3%.
• the percentage of Boron (B) may 0.9-1.2%. In order to further reduce the formation of chromium borides, the percentage of Boron (B) may be 1.0-1.1%.
• the brazing material may be used for brazing together article of austenitic stainless steel, especially of the type 304 or 316.
• One example of articles suitable to be brazed is heat exchanger plates.
• Fig. la is a graph showing DTA-TGA curves for several different brazing materials according to the present invention.
• Fig. lb is a graph showing a DTA-TGA diagram for one brazing material having a composition according to the present invention
• Fig. 2 is three graphs showing the main effects for erosion as a function of percentage of Silicon, Manganese and Boron;
• Fig. 3 is a scatterplot showing erosion vs. brazing temperature minus liquidus temperature, i.e. superheat, for different brazing materials.
• the brazing material according to the invention contains:
• Nickel 12.5-14.5% Nickel (Ni);
• brazing material constituents all cooperate to give the desired properties. It is hence not possible to amend the percentage of one constituent and foresee the effect on the brazing material as a whole, concerning e.g. melting point, corrosion resistance, erosion and strength.
• Iron Iron is used for two reasons: the first reason is that it is a low cost metal and the second reason is that it will make a brazing material mimicking the base material to be brazed (in this case 316 or 304 stainless steel);
• Nickel (Ni) will give the brazing material its austenitic properties. If less Nickel than defined above is used, the risk of excessive formation of ferritic phases in the brazing joint is increased. Also, there will be a risk that Nickel in the base material will migrate to the brazing joint during the brazing process, hence increasing the risk of formation of ferritic phases in the base material. If more Nickel than defined above is used, the cost of the brazing material will increase.
• Chromium (Cr) content will give the brazing joint its corrosion resistance
• Chromium also works as a ferrite stabilizer - by adding an amount of Chromium to the brazing material that about equals the amount of Chromium in the material to be brazed, the base material composition is mimicked.
• Molybdenum (Mo) will also increase the corrosion resistance of the brazing material. If less Molybdenum than defined above is used, the corrosion resistance will decrease. Molybdenum is an expensive metal - hence, the cost of the brazing material will increase if more Molybdenum is used. Moreover, Molybdenum is a ferrite stabilizer, and the used level is tailored to mimic the austenitic base material to be brazed.
• Manganese (Mn) is a constituent that reduces the erosion of the base material, i.e. the material being joined by brazing.
• the Manganese will evaporate during the brazing process, at least to some extent, and excessive amounts of manganese is added to the brazing material, the evaporated Manganese will foul the interior of the brazing furnaces in which the brazing is performed.
• the Manganese will reduce erosion significantly, without causing too much fouling of the furnace interior or the vacuum pumps used to pump out gas from the furnace in case it is desired to use vacuum during the brazing.
• Manganese is an austenite stabilizer, and will to some extent counteract the melt depressant Silicon, which is a ferrite stabilizer. In the prior art, the austenite stabilizing properties seem to be neglected, just like its erosion reducing properties. Also, the interaction between the Silicon and the Manganese properties when it comes to ferrite/austenite formation are not mentioned in conjunction with brazing material.
• Silicon (Si) is added for reduction of the melting temperature. It also increases the wettability of the brazing material to the base material. If less Silicon than defined is used, the melting point of the brazing material is not decreased sufficiently, while more Silicon than defined above will give a weaker brazing joint, due to formation of brittle Silicide phases. Moreover, the erosion of the base material increases with large amounts of Silicon.
• Boron (B) is also added for depressing the melting point.
• B Boron
• the Boron may react with the other constituents of the brazing material and the base material to form borides, primarily chromium borides, which are very brittle and hence decreases the strength of the brazing joints. Increased amounts of Boron will worsen the corrosion properties. However, in the amounts defined above, the boride formation and corrosion resistance have turned out to be within acceptable limits.
• the liquidus temperature should be below 1170 degrees C.
• a liquidus temperature of 1190 degrees C may, however, be acceptable in some cases.
• the brazing material has a liquidus temperature of less than 1 170 degrees C, e.g. 1 160 degrees C.
• the brazing material entrains the base material and lowers its melting temperature, such that the base material melts, are acceptable.
• Fig. 1 a DTA-TGA measurements for the brazing alloys G74, G71, G72 and G69 are shown. As can be noted, the melting temperatures for these materials ranges from 1092 degrees C (for G74) to 1133 degrees C (for G69) it can further be noted that there is a distinct DSC peak at 1092 degrees C for the G72 brazing material, indicating that one component of the brazing material will start to melt that the rest of the brazing material.
• Fig. lb DTA-TGA measurements for the brazing alloy Gl 18 is shown. As can be noted, this material is completely melted at 1160 degrees C, and there is also a slight peak at 11 15 degrees C, indicating that some of the material melts at this temperature.
• the erosion i.e. the phenomenon that the brazing material, or at least the melting point depressants thereof, has a minimum (it is desired with an as low erosion as possible) for 3-5.5% Manganese.
• Silicon in amounts of more than 9% rapidly increases erosion.
• Fig. 2 Plots of erosion as a function of Silicon, Manganese and Boron percentages are shown. As can be seen, the erosion increases rapidly above 8-9% Silicon, while Manganese percentages above 3% decrease the erosion. When it comes to the content of Boron, the results are indecisive.
• Fig. 3 a scatterplot showing erosion ratio on the X-axis and the difference between brazing temperature and melting temperature is shown.
• the brazing alloys G71 and G74 stand out when it comes to low erosion.
• G72 has similar Mn content as G71, the higher Si content in G72 seems to increase the erosion rate.
• the erosion ratio is defined as (ho-hi)/ho, wherein ho is the material thickness before brazing and hi is the undissolved material thickness after brazing.
• Another effect of addition of Manganese is that the solidus and liquidus temperatures of the brazing material after the brazing cycle will be higher than the solidus and liquidus temperatures under a brazing cycle. This is due to the Manganese, which has liquidus lowering properties, vaporizing during the brazing operation, meaning that if the brazed article is reheated after the brazing, it must be heated to a higher temperature before the brazing joints melt. The vaporized Manganese will not entrain into the base material; rather, it will leave the furnace in which the brazing is performed through the vacuum pumps usually deployed to evacuate the furnace. The Boron, which as mentioned also has some liquidus lowering properities, will also to some extent leave the brazing material, since it will migrate into the base material during the brazing cycle, hence increasing the solidus and liquidus temperatures of the brazing material.
• a brazing material In order to manufacture a brazing material according to the invention, it is preferred to blend alloys containing some or all of the desired metals of the brazing material according to the invention, and/or elemental metal, and melt the blend to form a uniform alloy containing all the desired elements in the desired percentages. It should be noted that vaporizing of the Manganese during the blending and consecutive melting of the brazing material can be avoided if the melting is performed in a protective atmosphere rather than under vacuum. Once melted and blended, the alloy is poured into one or several molds and allowed to solidify to form ingots of brazing alloy. It should be noted that in some cases, it might be suitable to use rather small molds for obtaining small ingots, since there might be a small risk that the elements of the brazing alloy might separate during the solidification in the mold.
• the ingots After the ingots have solidified, they are crushed. In order to even out possible differences between the compositions of the ingots, a batch of powder may be mixed. The powder is then mixed with a binder to form a paste.
• More common methods of forming a powder are, however, water or gas atomization.
• the brazing material is made in form of ribbons or foils, e.g. by melt spinning.
• the excellent properties of the G 118 braze material come at a price - the melting temperature of this brazing material is considerably higher than for prior art brazing materials.
• Iron based brazing materials having a considerably lower melting temperature than the base material to be brazed.
• the brazing temperature has been kept slightly above the melting temperature of the brazing material.
• the prime reason for this approach has been to reduce erosion of the base material, which, as mentioned above, results due to melting point depressant migrating into the base material such that its melting temperature decreases.
• brazing material of the invention and high brazing temperatures, i.e. above 1200 degrees C, preferably above 1230 degrees C, brazing joints exhibiting high strength, limited corrosion due to entrainment of melting point depressant into base material and excellent corrosion resistance at a reasonable price have been achieved.
• a suitable brazing process for brazing articles of austenitic stainless steels with the brazing material according to the invention may e.g. comprise:
• brazing material on or in close vicinity of portions to be brazed to one another;
• Cooling the furnace such that the brazing material solidifies and the brazed articles may be removed from the furnace.
• One reason for the excellent result of the combination between the brazing method of Swedish patent application 1351284-3 and the brazing material according to the present invention may be the high temperature - by placing the brazing material such that no brazing material is located between the surfaces to be brazed to one another, the diffusion bonding between the surfaces to be brazed increases (due to the parts coming in close contact with one another), and diffusion brazing increases with increasing temperature.
• the brazing joint has a strength exceeding the theoretical strength of the brazing material. Tests have shown that this might be due to the diffusion or trans liquid phase bonding process - if the items to be joined are located very close to one another during the brazing process, the base material of the items to be joined will start to migrate into one another, such that a metallic bond is formed without or with minimal melting of the base material. This also reduces the amount of brittle phases (e.g. nickel silicides and chromium borides) in the j oint.
• brittle phases e.g. nickel silicides and chromium borides

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
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• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• General Engineering & Computer Science (AREA)
• Ceramic Products (AREA)
• Pressure Welding/Diffusion-Bonding (AREA)

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• 2015
  • 2015-10-06 WO PCT/EP2015/072972 patent/WO2016055430A1/en not_active Ceased
  • 2015-10-06 EP EP15777665.9A patent/EP3204185B1/en active Active
  • 2015-10-06 KR KR1020177012343A patent/KR20170071526A/ko not_active Withdrawn
  • 2015-10-06 SE SE1750386A patent/SE542232C2/en unknown
  • 2015-10-06 CN CN201580054700.1A patent/CN106794555A/zh active Pending
  • 2015-10-06 US US15/517,426 patent/US20180236611A1/en not_active Abandoned
  • 2015-10-06 JP JP2017518500A patent/JP2017534462A/ja active Pending
  • 2015-10-06 CN CN202010541750.5A patent/CN111673314A/zh active Pending

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