Brazing concept

Abstract

The present invention relates to an intermediate product for joining and coating by brazing comprising a base metal and a blend of boron and silicon, said base metal having a solidus temperature above 1040 C., and the intermediate product has at least partly a surface layer of the blend on the base metal, wherein the boron in the blend is selected from a boron source, and the silicon in the blend is selected from a silicon source, and wherein the blend comprises boron and silicon in a ratio of boron to silicon within a range from about 3:100 wt/wt to about 100:3 wt/wt. The present invention relates also to a stacked intermediate product, to an assembled intermediate product, to a method of brazing, to a brazed product, to a use of an intermediate product, to a pre-brazed product, to a blend and to paint.

Claims

1. A blend for brazing of joints in products of base metals and/or for coating of products of base metals, which base metal has a solidus temperature above 1040 C., which blend consists of: a boron source selected from the group consisting of boron, B.sub.4C, B.sub.4Si, NiB, and FeB; and a silicon source selected from the group consisting of silicon, FeSi, SiC, and B.sub.4Si; and at least one binder selected from the group consisting of polyesters, polyethylene, polypropylene, polyvinyl alcohol, polyvinyl acetate, and polystyrene, wherein boron and silicon of the blend are present in a ratio of boron to silicon within a range from about 3:100 wt/wt to about 100:3 wt/wt, and wherein the amount of binder in the blend is 35.7% to 55.5% by weight of the total composition.

2. The blend according to claim 1, wherein the blend is a paint.

3. A blend for brazing of joints in products of base metals and/or for coating of products of base metals, which base metal has a solidus temperature above 1040 C., which blend consists of: a boron source selected from the group consisting of boron, B.sub.4C, B.sub.4Si, NiB, and FeB; and a silicon source selected from the group consisting of silicon, FeSi, SiC, and B.sub.4Si; and at least one binder selected from the group consisting of polyesters, polyethylene, polypropylene, polyvinyl alcohol, polyvinyl acetate, and polystyrene, wherein boron and silicon of the blend are present in a ratio of boron to silicon within a range from about 3:100 wt/wt to about 100:3 wt/wt, and wherein the silicon source has a particle size less than 250 m, and wherein the amount of binder in the blend is 35.7% to 55.5% by weight of the total composition.

4. A blend for brazing of joints in products of base metals and/or for coating of products of base metals, which base metal has a solidus temperature above 1040 C., which blend consists of: a boron source selected from the group consisting of boron, B.sub.4C, B.sub.4Si, NiB, and FeB; and a silicon source selected from the group consisting of silicon, FeSi, SiC, and B.sub.4Si; and at least one binder selected from the group consisting of polyesters, polyethylene, polypropylene, polyvinyl alcohol, polyvinyl acetate, and polystyrene, powders of the base metal having a solidus temperature above 1040 C., wherein boron and silicon of the blend are present in a ratio of boron to silicon within a range from about 3:100 wt/wt to about 100:3 wt/wt, and wherein the amount of binder in the blend is 35.7% to 55.5% by weight of the total composition.

5. An intermediate product for joining and/or coating by brazing comprising plates and/or parts of products of a base metal and a blend, said base metal having a solidus temperature above 1040 C., wherein the intermediate product has a surface layer formed from the blend on at least part of a surface of the base metal, wherein the blend consists of: a boron source selected from the group consisting of boron, B.sub.4C, B.sub.4Si, NiB, and FeB, a silicon source selected from the group consisting of silicon, FeSi, SiC, and B.sub.4Si, and at least one binder selected from the group consisting of polyesters, polyethylene, polypropylene, polyvinyl alcohol, polyvinyl acetate, and polystyrene, wherein boron and silicon of the blend are present in a ratio of boron to silicon within a range from about 3:100 wt/wt to about 100:3 wt/wt, and wherein the amount of binder in the blend is 35.7% to 55.5% by weight of the total composition.

6. The intermediate product according to claim 5, wherein the base metal has a thickness <1 mm and the blend is applied on the base metal in an average amount less than 2.9 mg/mm.sup.2.

7. The intermediate product according to claim 5, wherein the base metal has a thickness >1 mm.

8. The intermediate product according to claim 5, wherein the surface layer is applied as a powder of the blend or by a deposition selected from spray deposit, physical vapor deposition, or chemical vapor deposition.

9. The intermediate product according to claim 5, wherein the base metal is selected from the group consisting of iron based alloys, nickel based alloys, chromium based alloys, and copper based alloys.

10. The intermediate product according to claim 5, wherein the base metal comprises from about 15 to about 22 wt % chromium, from about 8 to about 22 wt % nickel, from about 0 to about 3 wt % manganese, from about 0 to about 1.5 wt % silicon, optionally from about 1 to about 8 wt % molybdenum, and balanced with iron.

11. The intermediate product according to claim 5, wherein the surface layer of the blend is provided on at least one side of a plate or the surface layer of the blend is on both sides of a plate.

12. The intermediate product according to claim 5, wherein the base metal and the surface layer have been exposed to a temperature higher than the solidus temperature of the formed brazing alloy and lower than the solidus temperature of the base metal, and a layer of the brazing alloy has been formed on the base metal surface.

13. The intermediate product according to claim 5, wherein the plates are cut, formed, pressed or combinations thereof before the application of the surface layer, after the application of the surface layer or after forming the brazing alloy on the surface of the base metal.

14. A stacked intermediate product for brazing comprising an intermediate product according to claim 5, wherein the plates are stacked such that the surface layers of the plates are either in contact with a base metal or with another surface layer on another plate.

15. The stacked intermediate product according to claim 14, wherein the stacked plates have no surface layers, single surface layers, double surface layers, and/or combinations thereof.

16. An assembled intermediate product for brazing comprising one or more intermediate products according to claim 5, wherein at least one intermediate product has a thickness >1 mm, and wherein the assembled intermediate product has at least one surface layer in contact with a surface of at least one base metal or in contact with at least one surface layer before brazing, and after brazing brazed joint(s) is (are) obtained.

17. A stacked brazed product obtained by brazing a stacked intermediate product according to claim 14, wherein the stacked intermediate product is brazed at a temperature below 1250 C., in a furnace in vacuum, in an inert gas, in a reducing atmosphere, or combinations thereof forming brazed joints of brazing alloy between the stacked plates or between contact surfaces of the assembled intermediate product, which brazing alloy is formed in a melting process of the base metal and the blend, and the brazing alloy in melted form has been transported by capillary forces to the area of the joint mainly from neighboring areas.

18. An assembled brazed product obtained by brazing an assembled intermediate product according to claim 16, wherein the assembled intermediate product is brazed at a temperature below 1250 C., in a furnace in vacuum, in an inert gas, in a reducing atmosphere, or combinations thereof forming brazed joints of brazing alloy between the stacked plates or between contact surfaces of the assembled intermediate product, which brazing alloy is formed in a melting process of the base metal and the blend, and the brazing alloy in melted form has been transported by capillary forces to the area of the joint mainly from neighboring areas.

19. A method of brazing a product, which method comprises the following steps: (i) applying a blend on plates or parts of products of a base metal, said base metal having a solidus temperature above 1040 C., wherein the blend consists of: a boron source selected from the group consisting of boron, B.sub.4C, B.sub.4Si, NiB, and FeB, and a silicon source selected from the group consisting of silicon, FeSi, SiC, and B.sub.4Si, wherein boron and silicon of the blend are present in a ratio of boron to silicon within a range from about 3:100 wt/wt to about 100:3 wt/wt. and at least one binder selected from the group consisting of polyesters, polyethylene, polypropylene, polyvinyl alcohol, polyvinyl acetate, and polystyrene, wherein the amount of binder in the blend is 35.7% to 55.5% by weight of the total composition, (ii) obtaining an intermediate product according to claim 5; (iii) optionally exposing the obtained intermediate product in step (ii) to a temperature higher than the solidus temperature of a brazing alloy formed in a molding process of the base metal and the blend and lower than the solidus temperature of the base metal, and forming a layer of the brazing alloy on the base metal surface; (iv) assembling or stacking the product from step (ii) or step (iii) with one or more products according to step (ii) or step (iii), or assembling or stacking the product with one or more parts having no blend of silicon and boron, and forming an assembled product or a stacked product; (v) brazing the assembled or stacked product from step (iv) to a temperature below 1250 C. in a furnace in vacuum, in an inert gas, in a reducing atmosphere or combinations thereof; and (vi) obtaining a brazed product.

20. The method according to claim 19, wherein the brazed product obtained in step (vi) is provided with a joint(s) obtained by forming a brazing alloy in a melting process of the base metal and the blend, and transporting by capillary forces the brazing alloy in melted form to the area of the joint mainly from neighboring areas.

21. The method according to claim 19, wherein step (iv) the product from step (ii) or step (iii) is brazed to a base metal having thickness >1 mm, or brazed to a base metal having a thickness <1 mm, or brazed to one or more intermediate products according to claim 7.

22. The method according to claim 19, wherein the base metal has a thickness <1 mm and the blend is applied on the base metal in an average amount less than 2.9 mg/mm.sup.2 calculated on silicon and boron.

23. The method according to claim 19, wherein the product from step (ii) or step (iii) is cut, formed, pressed or combinations thereof obtaining plates.

24. The method according to claim 19, wherein the obtained brazed product is selected from the group consisting of heat exchangers, plate reactors, parts of reactors, parts of separators, parts of decanters, parts of pumps, and parts of valves.

25. A brazed product obtained by the method according to claim 19, wherein joint(s) of the brazed product is (are) obtained by a brazing alloy, which brazing alloy is formed in a melting process of the base metal and the blend, and the brazing alloy in melted form has been transported by capillary forces to the area of the joint mainly from neighboring areas.

26. The brazed product obtained by the method according to claim 19, wherein elements found in the brazing alloy apart from the base metal elements are Si, B and optionally C, and wherein the base metal has a solidus temperature above 1040 C.

27. A pre-brazed product for brazing comprising plates and/or parts of products of a base metal having a solidus temperature above 1040 C., which pre-brazed product is obtained by applying a surface layer formed from a blend on a surface of at least one of the plates and/or the parts of products of the base metal, which blend consists of: a boron source selected from the group consisting of boron, B.sub.4C, B.sub.4Si, NiB, and FeB, a silicon source selected from the group consisting of silicon, FeSi, SiC, and B.sub.4Si, and at least one binder selected from the group consisting of polyesters, polyethylene, polypropylene, polyvinyl alcohol, polyvinyl acetate, and polystyrene, wherein the amount of binder in the blend is 35.7% to 55.5% by weight of the total composition, wherein boron and silicon of the blend are present in a ratio boron to silicon within a range from about 3:100 wt/wt to about 100:3 wt/wt, wherein the base metal and the surface layer has been exposed to a temperature higher than the solidus temperature of a brazing alloy formed in a molding process of the base metal and the base metal and the blend and lower than the solidus temperature of the base metal, and an obtained layer of the brazing alloy is on a surface of at least one of the plates and/or the parts of products of base metal.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is showing a circular pressed plate use in the Examples.

(2) FIG. 2 is showing a graph of Approximation.

(3) FIG. 3 is showing a diagram wherein the measured width as a function of applied amount (g/3500 mm.sup.2) with trend lines.

(4) FIG. 4 is showing another diagram in which calculated filled area of the braze joint based on the measured width as a function of applied amount (g/3500 mm.sup.2) with trend lines.

(5) FIG. 5 is showing another diagram in which the % of the tensile tested samples where the joint was stronger or the same as the than the plate material as a function of applied amount of blend (gram per 3500 mm.sup.2)

(6) FIG. 6 is showing picture of one of the samples after joining.

DETAILED DESCRIPTION OF THE DRAWINGS

(7) FIG. 1 is showing a circular pressed plate, which is 42 mm in diameter and 0.4 mm thick, made of stainless steel type 316L. The pressed plate had two pressed beams V and H, each app 20 mm long. Beam V or v stands for left beam and beam H or h stands for right beam, and v and h are used in Examples 5 and 9.

(8) FIG. 2 shows approximation 1 which is based on a cross section of a brazed test sample. The cross section in FIG. 2 shows the pressed beam in the top of FIG. 2. In the bottom of FIG. 2 is the flat, earlier applied plate. In the capillary between the beam and the flat surface a joint is created. To estimate the amount of braze alloy created in the joint following approximations and calculations have been made. It has been estimated that the volume in the center of the joint is negligible. Therefore, the created braze alloy volume for joints with a width, i.e. width B of 1.21 mm or less, are set to zero. On the outer sides of the beam, i.e. ((XB)/2), formed braze alloy has been accumulated. Thus, the brazing alloy in melted form has been transported by capillary forces to the area of the joint mainly from neighboring areas forming the volumes braze alloy of the triangles.

(9) According to FIG. 2, it is possible to calculate an area by estimate that two triangles are formed on each side of the centre of the joint. The angle in the triangle is measured to app. 28. The total measured width is called X and the center width, B. The total area (A) of the two triangles are therefore A=2(((XB)/2)((XB)/2)tan()))/2, i.e. for FIG. 2 A=2(((X1.21)/2)((X1.21)12)tan(28)))/2. The total created volume of braze alloy, which had flown to the crevices, would be the area times the length of the two beams. Some of the formed braze alloy does not flow to the crevices and is left on the surface. FIG. 3 is showing a diagram wherein the measured width as a function of applied amount (g/3500 mm.sup.2) with trend lines. The results of the fillet test are shown in table 8 and 9 of Example 5 and in FIG. 3. The trend lines of FIG. 3 are base on Y=KX+L. The results of the measured widths and the estimated areas are illustrated in the diagrams of FIG. 3. The applied amounts, see Tables 8 and 9, were from 0.06 gram/3500 mm.sup.2 to 0.96 gram/3500 mm.sup.2, which correspond to from app 0.017 mg/mm.sup.2 to 0.274 mg/mm.sup.2, to be compared with app 1.3-5.1 mg of blend per mm.sup.2 used in Example 2.

(10) The trend line Y=KX+L for the blend were measured, Y is the joint width, K is the inclination of the line, X is the applied amount of blend and L is a constant, see FIG. 3. Thus, the width of braze joint:
Y(width for A3.3)=1.554+9.922(applied amount of blend A3.3)
Y(width for B2)=0.626+10.807(applied amount of blend B2)
Y(width for C1)=0.537+8.342(applied amount of blend C1)
Y(width for F0)=0.632+7.456(applied amount of blend F0)

(11) As observed from FIG. 3 blends A3.3 out of blends A3.3, B2, C1, D0.5, E0.3 and F0 give the highest amount of braze alloy in the joint as a function of applied amount of blend. Sample F0 did not give any substantial joints below 0.20 gram per 3500 mm.sup.2.

(12) FIG. 4 is showing another diagram in which calculated filled area of the braze joint based on the measured width as a function of applied amount (gram/3500 mm.sup.2) with trend lines. The trend line Y=KXL for the blend were measured, Y is the area, K is the inclination of the line, X is the applied amount of blend and L is a constant, see FIG. 4.
Y(area for A3.3)=4.361(applied amount of blend A3.3)0.161
Y(area for B2)=3.372(applied amount of blend B2)0.318
Y(area for C1)=2.549(applied amount of blend C1)0.321
Y(area for F0)=0.569(applied amount of blend F0)0.093

(13) A rough estimation on the created volume based on the diagram in FIG. 4 for e.g. an amount of 0.18 gram per 3500 mm.sup.2, excluding sample F0, due to no braze joints and sample D0.5 due to too little data, gives a value for the samples for created volume of braze alloy in the joint between the two beams, see below.
Volume(A3.3)=0.63length 40(202)=25.2 mm.sup.3
Volume(B2)=0.30length 40(202)=12.0 mm.sup.3
Volume(C1)=0.12length 40(202)=4.8 mm.sup.3
Volume(E0.3)=0.10length 40(202)=4.0 mm.sup.3

(14) FIG. 5 is showing another diagram in which the % (percent) is the success rate of the tensile tested samples where the joint was stronger or the same as the plate material as a function of applied amount of blend, i.e. gram per 3500 mm.sup.2. When the plate was stronger than the joint, resulting in a split of the joint, the result was set to zero. For the samples that the joint were stronger than the plate material the difference in results was not statistical significant.

(15) In the picture of FIG. 6 is one of the samples shown after joining. The picture shows that there is a formed joint between the two pieces. The joined sample is from Example 10.

(16) The invention is explained in more detail in by means the following Examples and the Examples are for illustrating the invention and are not intended to limit the scope of invention.

EXAMPLES

(17) The tests in these Examples were made to investigate if silicon, Si, were able to create a braze ally when silicon was applied on the surface of a test sample of base metal. Also different amounts of boron, B, were added since boron can decrease the melting point for braze alloys. Boron can also change the wetting behavior of braze alloys. Properties of the tested blends were also investigated. In the Examples wt % is percent by weight and atm % is percent of atoms.

(18) If nothing else is stated the test samples of base metal for all tests were cleaned by dish washing and with acetone before samples of the blends of silicon and boron were added to the test samples.

Example 1: Preparation of Samples of Blends of Silicon and Boron to be Tested

(19) Test sample No. C1 was prepared by blending 118.0 gram of crystalline silicon powder particle size 325 mesh, 99.5% (metal basis) 7440-21-3 from Alfa Aesar-Johnsson Matthey Company, with 13.06 gram of crystalline boron powder particle size 325 mesh, 98% (metal basis) 7440-42-8 from Alfa Aesar-Johnsson Matthey Company and 77.0 gram of Nicorobraz S-30 binder from Wall Colmonoy in a Varimixer BEAR from Busch & Holm producing 208 gram of paste, see sample C1. All test samples were produces following the same procedure as test sample C1. The samples are summarised in Table 2.

(20) TABLE-US-00002 TABLE 2 Sample Boron Silicon S-30 Binder Total Weight No. [gram] [gram] [gram] [gram] F0 0.00 124.7 73.3 198 E0.3 4.30 123.9 72.1 200 D0.5 6.41 121.2 75.0 203 C1 13.06 118.0 77.0 208 B2 24.88 104.5 72.81 202 A3.3 11.46 22.9 19.3 54.0

(21) Samples G15, H100, I66 and J was prepared the same way as samples F0, E0.3, D0.5, C1, B2 and A3.3 with the exception that another binder was used, the binder was Nicorobraz S-20 binder from Wall Colmonoy. The test samples are summarised in Table 3.

(22) TABLE-US-00003 TABLE 3 Sample Boron Silicon S-20 Binder Total Weight No. [gram] [gram] [gram] [gram] G15 0.37 2.24 3.1 5.7 H100 4.19 0 5.3 9.5 I66 1.80 2.70 5.5 10.0 J 2.03 2.02 5.0 9.0

(23) The samples are also calculated to show ratio, percent by weight and percent by atoms, these are shown in Table 4

(24) TABLE-US-00004 TABLE 4 Blend Ratio Amount Amount Sample [wt/wt] [wt %] [atm %] No. Boron Silicon Boron Silicon Boron Silicon F0 0 100 0 100 0 100 E0.3 3 100 3 97 8 92 D0.5 5 100 5 95 12 88 C1 10 100 9 91 21 79 B2 19 100 16 84 33 67 A3.3 33 100 25 75 46 54 G15 17 100 14 86 30 70 H100 100 0 100 0 100 0 I66 66 100 40 60 63 37 J 100 100 50 50 72 28
Measure of Binder (Polymeric and Solvent) Content in the S-20 and S-30 Binder.

(25) Also the content of dry material within the gels was tested. Samples of S-20 and S-30 were weight and thereafter placed in an oven for 18 hours at 98 C. After the samples had been taken out of the oven they were weight again. The results can be found in Table 5.

(26) TABLE-US-00005 TABLE 5 Polymeric Before After proportion Sample [gram] [gram] [wt %] S-20 199.64 2.88 1.44 S-30 108.38 2.68 2.47

Example 2: Brazing Tests

(27) When testing braze fillers of the prior art, the weight of the applied braze filler is 2.0 gram which correspond to 0.2 gram of silicon. Since blends of silicon and boron were to be tested similar amounts of silicon and boron in the tested compositions were used. The braze filler contains 10 wt % silicon, therefore 0.2 gram of blends of silicon and boron were applied on the test samples. The test samples were circular test pieces having a diameter of 83 mm and a thickness of 0.8 mm and the test pieces were made of stainless steel type 316L. Since it was not expected that 0.2 gram of braze blend would correspond to 2 gram of braze alloy because a formed braze alloy may first be created from the base metal and the braze blend, before it would flow, and that silicon and boron might only diffused into the base metal or even not melt the base metal a higher amount 0.4 gram was also tested. All samples were brazed in a vacuum furnace at 1210 C. for 1 hour. Double tests were used. Meaning, two weights, double test samples and six different blends, 226=24 samples, i.e. F0, E0.3, D0.5, C1, B2 and A3.3. The blends were applied on a circular area having a diameter of app 10 to 14 mm, i.e. a surface of 78 to 154 mm.sup.2 or app 1.3-5.1 mg of blend per mm.sup.2.

Results

(28) It was clearly observed that the test pieces of the base metal had melted and some type of melts were created. It was also observed that the melts in some aspects appeared as a braze alloy with flow. Without measuring the size of the wetting it appeared that an increased amount boron in the blends resulted in better wetting. However it was also seen that for most samples the whole thickness had melted and a hole was created in the middle of the test piece. For the 0.2 gram samples five out of twelve test pieces had holes, and for the 0.4 gram pieces ten out of twelve.

(29) One conclusion is therefore that it is not possible to change from a braze filler paste or the like and apply spots or lines with comparative equal amounts of blends of silicon and boron, since the blends of silicon and boron will melt a hole in the base metal if the test sample is thin, in this case 0.8 mm. If thicker test samples are used no holes might appear, but, ditches might be created in the base metal. This could be prevented or be improved by adding base metal as e.g. powder in silicon and boron blends. If only silicon is applied, i.e. sample F0, the result appear to have less flow and wetting properties than the other samples wherein both silicon and boron are applied.

Example 3: New Applying Procedure

(30) In this Example the test plates were prepared for all fillet tests, corrosion tests and the tensile tests at the same time. From Example 2 it was concluded that the blends of silicon and boron it could be a risk to apply the blend in dots or lines on thin walled plates. Therefore, new test samples, i.e. test plates, were used for application of the different the blends of Si and B for the fillet tests, corrosion tests, and the tensile tests.

(31) Accordingly, the new test samples were plates made of stainless steel type 316L. The size of the plates were 100 mm wide, 180 to 200 mm long and the thickness were 0.4 mm. All plates were cleaned by dish washing and with acetone before application of samples of the blends of Si and B. The weight was measured. On each plate a part measured as 35 mm from the short side was masked.

(32) The different test blends A3.3, B2, C1, D0.5, E0.3, F0, G15, H100, and I66 were used. The test plates were painted with the blends on the unmasked surface area, which surface area had the size of 100 mm35 mm. The binder was S-30. After drying for more than 12 hours in room temperature the masking tape was removed and the plate weight was measured for each plates. The weight presented in Table 6 below is the eight of the totally amount of the blends on the area of 100 mm35 mm=3500 mm.sup.2=35 cm.sup.2.

(33) TABLE-US-00006 TABLE 6 Weight of blend Weight of Si + B Ratio blend + dried without Weight of Test Plate B:Si binder binder blend per area No. [wt/wt] [gram] [gram] [mg/cm.sup.2] A3.3 33:100 0.0983 0.0959 2.74 B2 19:100 0.0989 0.0965 2.76 C1 10:100 0.1309 0.1277 3.65 D0.5 5:100 0.1196 0.1166 3.33 E0.3 3:100 0.0995 0.0970 2.77 H100 100:0 0.1100 0.1073 3.07 I66 66:100 0.0900 0.0878 2.51

Example 4: Corrosion-Bend Test of the Samples

(34) From the test plates were slices cut out having width of 35 mm, meaning an applied surface area of 35 mm35 mm. Onto this surface area was a circular pressed plate placed, see FIG. 1, which press plate had a size of 42 mm in diameter and 0.4 mm thick made of stainless steel type 316L. The test samples were brazed 1 hour at 1210 C. The tested plates for the corrosion tests had applied blend samples A3.3, B2, C1, D0.5, E0.3, H100, I66 and J, see Table 4.

(35) The samples were tested according to corrosion test method ASTM A262, Standard Practices for Detecting Susceptibility to inter-granular Attack in Austenitic Stainless Steels. Practice E-Copper-Copper Sulfate-Sulfuric Acid. Test for Detecting Susceptibility to Inter-granular Attack in Austenitic Stainless Steels, was selected from the test method. The reason for selecting this corrosion tests were that there is a risk that boron might react with chromium in the steel creating chromium borides, mainly in the grain boundaries, and then increases the risk for inter-granular corrosion attack, practice in the standard were used, boiling 16% sulfuric acid together with copper sulfate in 20 hours and thereafter a bend test, according to chapter 30 in the standard.

Results from the Corrosion Test and Sectioning of the Test Samples

(36) The test pieces were bent tested according to the corrosion test method in chapter 30.1. None of the samples gave indications of inter granular attack at the ocular investigation of the bended surfaces. After the ASTM investigation the bended test samples were cut, ground and policed and the cross section was studied in light optical microscope in EDS, i.e. Energy Dispersive Spectroscopy. The results are summarized in Table 7.

(37) TABLE-US-00007 TABLE 7 Ocular investigation of surface for corrosion Results of metallurgical investigation of the cracks when bended cross sectioned corrosion tested samples Sample according to the ASTM and bent tested test samples. SEM-EDS result No. test of cracked phase A3.3 No cracks No corrosion A surface layer of app. max 8 m with a few cracks. The phase that had cracked had a high Cr and B content, most probably a chromium boride phase. B2 No cracks No corrosion A surface layer of app. max 8 m with a few cracks. The phase that had cracked had a high Cr and B content, most probably a chromium boride phase C1 No cracks No corrosion or cracks D0.5 No cracks No corrosion or cracks E0.3 No cracks No corrosion A surface layer of app. max 60 m with a few cracks. The phase that had cracked had a high Si content generally <5 wt % H100 No cracks Corroded surface and joint I66 No cracks No corrosion A surface layer of app. max 12 m with a few cracks. The phase that had cracked had a high Cr and B content, most probably a chromium boride phase J No cracks No corrosion A surface layer of app. max 20 m with a few cracks. The phase that had cracked had a high Cr and B content, most probably a chromium boride phase

Comments

(38) Apparently when adding high amounts of boron, as for sample H100, J, I66, a fragile phase was formed on the surface, most probably a chromium boride phase, increasing with the amount of boron. A fragile phase was not seen in the H100 sample, most probably due to the corrosion on the surface. Also the amount of borides increased with the amount of boron, meaning it has to be taken into consideration that the corrosion properties might decrease when adding high amounts of boron, as for sample H100 that was attacked in the corrosion test. The negative effect with boron can be decreased by using thicker base metals and/or longer diffusion times. It is then possible to dilute boron in the base metal. Also for the normal amount of boron as for A3.3 and B2 a thinner fragile surface layer was formed. It was seen that for the low amount of boron in the samples, sample E0.3, a quite thick fragile surface layer, with a high silicon content generally >5 wt % of silicon, was formed with a different characteristic than for the fragile surfaces for A3.3, B2, H100, I66 and J. The negative effect with silicon can be decreased by using thicker base metals and/or longer diffusion times. It is then possible to dilute silicon in the base metal.

Example 5: Fillet Test of the Samples

(39) From test samples made according to Example 3, slices of the plates was cut out with the width of 35 mm, meaning an applied surface of 35 mm35 mm. Onto this surface was placed a circular pressed plate, see FIG. 1, 42 mm in diameter and 0.4 mm thick, made of stainless steel type 316L. The pressed plate had two pressed beams, each app 20 mm long. The samples were brazed at app 1 hour at app 1200 C.

(40) The results from the fillet test show that there were the amounts of braze alloy found in the joint area created between the flat surface area onto which surface area the blends were applied, which flat surface area was in contact with a pressed beam in the test sample seen in FIG. 1. The amount of braze alloy was calculated by an approximation, see FIG. 2, by calculate an area by estimate that two triangles are formed on each side of the centre of the joint. In the middle part there is no or very small amounts of additional formed brazing alloy. The two triangles can be measured by measuring the height (h) and the base (b), the total area of the two triangles are summing up to (h)(b) since there are two triangles. The problem with this calculation is that the height is hard to measure. Therefore we use the following equation for calculating of the two triangle areas:
A=((XB)/2)((XB)/2)tan

(41) A is total area of the two triangles, X is the total width of the formed joint, B is the part of the formed joint where the volume of the formed brazing alloy in the center of the joint is negligible. Thus, the base of each triangle is (XB)/2. The height is calculated by measuring the angle , which is the angle between the tangents of the pressed beam to the base.

(42) To calculate the volume of the total created volume of the formed braze alloy that had flown to the crevices, would be to measure the length of the two beams, i.e. each beam is 20 mm, and multiply the length and the total area.

(43) The area of two triangles is the estimated area after brazing in Table 8 and 9. The volume is the volume of the formed brazing alloy on one of the beams. The results from the fillet test are shown in table 8 and 9, and in FIG. 3. In Table 8 and in Table 9 v and h stand for v=left beam and h=right beam.

(44) TABLE-US-00008 TABLE 8 Applied binder Estimated Area Sample Si + B Width after brazing Volume No. [gram] [mm] [mm.sup.2] [mm.sup.3] A3.3x-1v 0.06 2.69 0.29 5.8 A3.3x-1h 0.06 2.58 0.25 5.0 A3.3-1v 0.10 2.23 0.14 2.8 A3.3-1h 0.10 2.31 0.16 3.2 A3.3-2v 0.14 3.38 0.63 12.6 A3.3-2h 0.14 3.19 0.52 10.4 A3.3-3v 0.09 1.92 0.07 1.4 A3.3-3h 0.09 1.85 0.05 1.0 B2X-1v 0.18 2.12 0.11 2.2 B2X-1h 0.18 2.50 0.22 4.4 B2X-2v 0.15 2.31 0.16 3.2 B2X-2h 0.15 2.31 0.16 3.2 B2-1v 0.10 1.96 0.07 1.4 B2-1h 0.10 1.92 0.07 1.4 B2-2v 0.24 3.23 0.54 10.8 B2-2h 0.24 3.23 0.54 10.8 B2-3v 0.16 2.77 0.32 6.4 B2-3h 0.16 2.69 0.29 5.8 B4v 0.11 1.35 0.00 0 B4h 0.11 1.35 0.00 0 Measured valued for the fillet test, samples A3.3 - B2/B4

(45) TABLE-US-00009 TABLE 9 Applied binder Estimated Area Sample Si + B Width after brazing Volume No. [gram] [mm] [mm.sup.2] [mm.sup.3] C1X-1v 0.22 2.50 0.22 4.4 C1X-1h 0.22 2.69 0.29 5.8 C1X-2v 0.33 3.08 0.46 9.2 C1X-2h 0.33 3.27 0.56 11.2 C1-1v 0.13 1.46 0.01 0.2 C1-1h 0.13 1.46 0.01 0.2 C1-2v 0.15 1.96 0.07 1.4 C1-2h 0.15 2.08 0.10 2.0 C1-3v 0.14 1.54 0.01 0.2 C1-3h 0.14 1.62 0.02 0.4 D0.5-1v 0.19 2.54 0.23 4.6 D0.5-1h 0.19 2.50 0.22 4.4 D0.5-2v 0.12 1.08 0.00 0 D0.5-2h 0.12 1.08 0.00 0 D0.5-3v 0.14 2.04 0.09 1.8 D0.5-3h 0.14 2.04 0.09 1.8 E0.3-1v 0.13 1.15 0.00 0 E0.3-1h 0.13 1.15 0.00 0 E0.3-2v 0.21 2.31 0.16 3.2 E0.3-2h 0.21 2.31 0.16 3.2 E0.3-3v 0.10 1.35 0.00 0 E0.3-3h 0.10 1.35 0.00 0 F0-1h 0.45 2.69 0.29 5.8 F0-2v 0.25 1.08 0.00 0 F0-2h 0.25 1.35 0.00 0 F0-3v 0.96 2.96 0.41 8.2 F0-3h 0.96 3.08 0.46 9.2 Measured valued for the fillet test for samples C1 to F0

(46) The results of the measured widths and the estimated areas are presented in the Tables 8 and 9, and illustrated in the diagrams of FIG. 3. The applied amounts, see Tables 8 and 9, were from 0.06 gram/3500 mm.sup.2 to 0.96 gram/3500 mm.sup.2, which correspond to from app 0.017 mg/m.sup.2 to 0.274 mg/mm.sup.2, to be compared with app 1.3-5.1 mg of blend per mm.sup.2 used in Example 2.

(47) The trend line Y=KX+L for the blend were measured, Y is the joint width, K is the inclination of the line, X is the applied amount of blend and L is a constant, see FIG. 3. Thus, the width of braze joint:
Y(width for A3.3)=1.554+9.922(applied amount of blend A3.3)
Y(width for B2)=0.626+10.807(applied amount of blend B2)
Y(width for C1)=0.537+8.342(applied amount of blend C1)
Y(width for F0)=0.632+7.456(applied amount of blend F0)

(48) As observed from the diagram blends A3.3 out of blends A3.3, B2, C1, D0.5, E0.3 and F0 give the highest amount of braze alloy in the joint as a function of applied amount of blend. Sample F0 did not give any substantial joints below 0.20 gram per 3500 mm.sup.2.

(49) The trend line Y=KXL for the blend were measured, Y is the area, K is the inclination of the line, X is the applied amount of blend and L is a constant, see FIG. 4.
Y(area for A3.3)=4.361(applied amount of blend A3.3)0.161
Y(area for B2)=3.372(applied amount of blend B2)0.318
Y(area for C1)=2.549(applied amount of blend C1)0.321
Y(area for F0)=0.569(applied amount of blend F0)0.093

(50) A rough estimation on the created volume based on the diagram in FIG. 4 for e.g. an amount of 0.18 gram per 3500 mm.sup.2, excluding sample F0, due to no braze joints and sample D0.5 due to too little data, gives a value for the samples for created volume of braze alloy in the joint between the two beams, see below.
Volume(A3.3)=0.63length 40(202)=25.2 mm.sup.3
Volume(B2)=0.30length 40(202)=12.0 mm.sup.3
Volume(C1)=0.12length 40(202)=4.8 mm.sup.3
Volume(E0.3)=0.10length 40(202)=4.0 mm.sup.3

(51) Also blends with higher proportion of boron were tested e.g. sample G15, H100, I66 and J. All tested samples did work quite similar to blend A3.3 and B2 regarding the created braze alloy volume. However the metallurgical cross section of the brazed samples showed that the amount of borides was greater and for sample H100, i.e. pure boron, also brittle high chromium phases were found on the surface where the blend earlier was applied. The hard phases were most probably chromium borides, which decreases the chromium content in the surrounding material, decreasing the corrosion resistance. This may be an issue when good corrosion resistance is wanted but is not an issue for non-corrosive environment. The effect of boron could be decreased by changing the heat treatment and or by using a thicker base metal that can absorb a greater amount of boron. For a thicker material 1 mm this effect in the surface will also be less severe since the proportion of the surface volume compared to the base metal volume is much less than for a thin material <1 mm or <0.5 mm. The chromium borides could be an advantage if better wear resistance is wanted. The metallurgical investigation also showed that for sample F0, i.e. pure silicon, a thick brittle silicon containing phase was found, with a thickness of >50% of the plate thickness for some areas in the investigated sample. The similar phase was also found in the joint. Cracks were found in this phase, with a length >30% of the plate thickness. Such cracks will decrease the mechanical performance of the joined product and can be initiating points for corrosion and or fatigue cracks. The average measured hardness of the phase was over 400 Hv (Vickers). This brittle phase is probably much harder to decrease, compared to the by boride phase, using thicker base metal or a change in heat treatment. Still for thicker base metal this effect can be less severe.

Example 6: Tensile Test of Brazed Joint

(52) The original applied test plates were sliced into slices. The size of the sliced samples was app 100 mm wide, 180 to 200 mm long and the thickness 0.4 mm. The applied area for each slice was then 10 mm times 35 mm=350 mm.sup.2. On the applied area a thicker part, 4 mm, of stainless steel type 316L was placed covering 30 mm of the total 35 mm applied surface. The ticker part was placed at the end of the slice leaving 5 mm of applied surface not covered by the thick plate. By doing this a decrease in the plate material strength due to the applied blend would be detected when tensile testing if the joint is stronger than the plate. The thicker plate was also wider than the 10 mm slices. All test samples were brazed at app 1200 C. for app 1 hour.

(53) After brazing the thick part was mounted horizontally in a tensile test machine. The braze slice was firmly bent to 90 to a vertical direction. The samples were mounted so that they could move in horizontal direction. The samples were then loaded and the braze joint were split.

Results

(54) When the plate was stronger than the joint, so that the joint were split, the result was set to zero. For the samples that the joint were stronger than the plate material the difference in results was not statistical significant. The results are shown as percent (%) of the tested samples where the joint were stronger than or the same as the plate as a function of applied amount, meaning that the joint was not split when tested. The results are summarized in Table 10 and in the diagram of FIG. 5.

(55) TABLE-US-00010 TABLE 10 Blend of A3.3-1 B2-1 C1-1 D0.5-1 Si + B Success Rate Success Rate Success Rate Success Rate [gram] [%] [%] [%] [%] 0.0600 100 0.0910 100 0.0989 83 0.1092 100 0.1196 0 0.1309 50 0.1399 100 0.1402 50 0.1428 0 0.1500 100 0.1548 67 0.1558 100 0.1800 100 0.1850 50 0.2200 100 0.2417 100 0.3000 100 0.3300 100

Example 7

(56) To establish the relationship between applied amount and the risk for burn through the plates, new tests were performed. For all tests blend B2, see Table 6, was used. To blend B2 was binder S-30 added. The test pieces which were tested were circular having a thickness of 0.8 mm and having a diameter of 83 mm. The base metal in the test plates were stainless steel type 316. For all samples the blend was applied in the center of the test sample. The applied area was 28 mm.sup.2, i.e. circular spot having a diameter of 6 mm. All test samples were weight before and after application, and the results are summarized in Table 11. Thereafter the test samples were placed in a furnace at room temperature for 12 hours. The samples were weight again.

(57) The test samples were all put in a furnace and were brazed at 1210 C. for app 1 hour. During brazing only the outer edges of each sample were in contact with the fixture material, keeping the plate center bottom surface not in contact with any material during brazing. The reason for keeping the plate center bottom surface free of contacts is that a collapse or a burn through might be prevented if the center material is supported from below by the fixture material.

(58) Applied amount and burn through results for the 0.8 mm samples are summarized in Table 11.

(59) TABLE-US-00011 TABLE 11 Blend of Calculated Blend of Si + B and Blend of amount of Si + B and additional wet Si + B and Blend of additional wet binder additional dried Si + B without Burn Sample binder S-30 S-30 binder S-30 binder through No. [gram] [mg/mm.sup.2] [mg/mm.sup.2] [mg/mm.sup.2] [1] or [0] 1 0.020 0.714 0.464 0.453 0 2 0.010 0.357 0.232 0.226 0 3 0.040 1.429 0.928 0.905 0 4 0.030 1.0714 0.696 0.679 0 5 0.050 1.786 1.161 1.132 0 6 0.060 2.143 1.393 1.359 0 7 0.070 2.500 1.625 1.585 0 8 0.080 2.857 1.857 1.811 0 9 0.090 3.214 2.089 2.037 0 10 0.100 3.571 2.321 2.264 0 11 0.110 3.928 2.554 2.491 1 12 0.120 4.285 2.786 2.717 1 13 0.130 4.642 3.018 2.943 1 14 0.150 5.357 3.482 3.396 1 15 0.170 6.071 3.946 3.849 1 16 0.190 6.786 4.411 4.302 1 17 0.210 7.500 4.875 4.755 1 18 0.230 8.214 5.339 5.207 1 19 0.280 10.000 6.500 6.339 1 20 0.290 10.357 6.732 6.566 1

(60) The tests show that there is a burn through between sample 10 and 11 for a plate having a thickness of 0.8 mm. Sample 10 has 2.264 mg/mm.sup.2 applied amount of blend and sample 11 has 2.491 mg/mm.sup.2. For joining plates having thickness less than 1 mm, there is a risk with an amount within the range from about 2.830 mg/mm.sup.2 to about 3.114 mg/mm.sup.2 for burning through the plates, the amount in the middle of this range is 2.972 mg/mm.sup.2. Therefore, for a plate having a thickness less than 1 mm an amount of less than 2.9 mg/mm.sup.2 would be suitable for avoiding burning through the plate.

Example 8

(61) In Example 8a braze joint between two pressed heat exchanger plates are made in three different ways. The thickness of the heat exchanger plates are 0.4 mm.

(62) In the first and second test samples an iron based braze filler with a composition close stainless steel type 316 were used, see WO 2002/38327. The braze filler had an increased amount of silicon to about 10 wt %, an amount boron to about 0.5 wt % and a decreased amount of Fe of about 10.5 wt %. In the first test sample the braze filler was applied in lines and in the second test sample the braze filler was applied evenly on the surface. In both cases the filler was applied after pressing.

(63) After brazing test sample 1 showed that the braze filler applied in lines was drawn to the braze joints. Some of the braze filler did not flow to the braze joint and therefore increased the thickness locally at the applied line. For test sample 2 the braze filler flowed to the braze joints, however some on the braze filler remained on the surface and increased the thickness. In test samples 1 and 2 the amount of braze filler corresponds to an amount of app 15 wt % of the plate material.

(64) In test sample 3 A3.3 blend was used, see Table 6. The blend was applied before pressing evenly on the plate. The blend was applied in an amount that would create braze joint with similar sizes as for test samples 1 and 2.

(65) Test sample 3 was applied with a layer having a thickness corresponding to a weight of app 1.5 wt % of the plate material. By applying blend A3.3 a braze alloy was formed from the base metal, and the formed braze alloy flow to the braze joints. Accordingly, the thickness of the plate decreased since more material was drawn to the braze joint than added blend on the surface.

Example 9: Tests with Different Si-Sources and B-Sources

(66) The tests which were performed in Example 9 were to investigate alternative boron-sources and silicon-sources. B1 end B2, see Table 6, was selected as reference for the test. The alternative sources were tested with their ability to create a joint. For each experiment either an alternative boron-source or an alternative silicon-source was tested. When using an alternative source the other element influence was assumed to be zero, meaning that it was only the weight of boron or silicon in the alternative component that was measured, see Table 12. For the reference blend B2, the weight ratio between silicon and boron is 10 gram to 2 gram summing up to 12 gram. Each blend was mixed together with S-30 binder and the blend was applied on a steel plate according to Example 1. All samples were brazed a vacuum furnace at 1210 C. for 1 hour.

(67) TABLE-US-00012 TABLE 12 Added Added Corresponding Corresponding Alter- Amount Amount Amount Amount native [Si] [B] [Si] [B] Sample source [gram] [gram] [gram] [gram] SiB SiB 10.0 2.0 10.0 2.0 SiB.sub.4C B.sub.4C 10.0 2.6 10.0 2.0 SiFeB FeB 10.1 12.5 10.1 2.0 FeSiB FeSi 30.2 2.0 10.1 2.0 SiNiB NiB 10.1 13.0 10.1 2.0

(68) The trend line Y=KX+L for blend B2 was measured, Y is the joint width, K is the inclination of the line for B2, X is the applied amount of blend and L is a constant for no applied amount of blend B2, see FIG. 3. Thus, the width of braze joint Y=0.626+10,807(applied amount of blend).

(69) In Table 13 v and h stand for v=left beam and h=right beam as in Example 5.

(70) TABLE-US-00013 TABLE 13 Joint Joint Measured Applied Amount Calculated Width Y Width Sample [gram] [mm.sup.2] [mm.sup.2] SiB.sub.4C - v 0.22 3.0 2.69 SiB.sub.4C - h 0.22 3.0 2.88 SiFeB - v 0.26 3.4 1.73 SiFeB - h 0.26 3.4 1.73 FeSiB - v 0.29 3.8 2.1 FeSiB - h 0.29 3.8 2.1 SiNiB - v 0.39 4.8 2.69 SiNiB - h 0.39 4.8 2.88

(71) The results in Table 13 show that it is possible to use B4C, NiB and FeB as alternatives source to boron. When NiB were used the created amount was less than for pure boron however NiB could be used if an Ni alloying effect is wanted.

Example 10: Tests of Base Metals

(72) In Example 10 a large number of different base metals were tested. All tests except for the mild steel and a NiCu alloy were tested according to test Y.

(73) For test Y two circular pressed test pieces with a thickness of app 0.8 mm were place onto each other. Each sample had a pressed circular beam. The top faces of the beams were placed towards each other creating a circular crevice between the pieces. For each sample the B2 blend with binder S-20 were applied with a paint brush. The weight of the added amount was not measured since the applying was not homogenous when applying with the paint brush. A picture of one of the samples after joining is presented in FIG. 6.

(74) The mild steel samples and the NiCu samples were applied in the same way, but for mild steel according to the tests made in example 5 fillet test and for the NiCu test with two flat test pieces. The samples except for the NiCu were brazed in a furnace at app 1200 C., i.e. 1210 C., for 1 h in vacuum atmosphere furnace. The NiCu sample was brazed at app 1130 C. for app 1 h in the same vacuum furnace. After brazing a joint was formed between the pieces for all made test and a flow of created braze alloy made of the base metal, to the joint was also observed for all tested samples. The results are shown on Table 14.

(75) TABLE-US-00014 TABLE 14 After Base After Brazing metal Cr Fe Mo Ni Cu Brazing Flow of Sample [wt [wt [wt [wt [wt Mn Created Brazing No. %] %] %] %] %] [wt %] joint? Alloy? 1 0.3 99 0.2 Yes Yes 2 21 0.6 16 62 0.4 Yes Yes 3 22 0.7 16 59 1.6 Yes Yes 4 0.6 1.9 29 68 0.2 Yes Yes 5 21 4.4 13 58 Yes Yes 6 19 5.0 9.0 63 0.4 Yes Yes 7 15 5.5 17 60 0.3 Yes Yes 8 1.1 5.6 28 63 0.6 0.4 Yes Yes 9 19 6.2 2.6 70 1.7 0.4 Yes Yes 10 33 32 1.7 33 0.4 0.6 Yes Yes 11 27 33 6.5 32 1.1 1.4 Yes Yes 12 27 36 3.4 32 1.0 1.4 Yes Yes 13 24 44 7.2 23 0.3 1.5 Yes Yes 14 20 48 4.3 25 1.1 1.2 Yes Yes 15 19 50 6.3 25 0.2 Yes Yes 16 20 54 6.5 19 0.6 0.4 Yes Yes 17 29 64 2.4 3.5 Yes Yes 18 28 66 2.2 3.5 Yes Yes 19 0.3 1.1 66 31 1.6 Yes Yes 20 0.17 99.5 0.3 Yes Yes

(76) The results in Table 14 show that braze alloys are formed between the blend and the base metal for each sample 1 to 20. The results show also that joints were created for each tested sample.

(77) The examples show that boron was needed to create substantial amount of braze alloy, could fill the joints and also create strength in the joints. The examples also showed that boron was needed for the microstructure, since a thick fragile phase was found for the samples with no boron.