Method for joining metal parts

Abstract

A method for joining a first metal part with a second metal part, the metal parts having a solidus temperature above 1000 C. The method includes applying a melting depressant composition on a surface of the first metal part, the melting depressant composition including a melting depressant component that includes phosphorus and silicon for decreasing a melting temperature of the first metal part; bringing the second metal part into contact with the melting depressant composition at a contact point on said surface; heating the first and second metal parts to a temperature above 1000 C.; and allowing a melted metal layer of the first metal component to solidify, such that a joint is obtained at the contact point. The melting depressant composition and related products are also described.

Claims

1. A method for joining a first metal part with a second metal part, the metal parts having a solidus temperature above 1000 C., the method comprising the steps of: applying a melting depressant composition on a surface of the first metal part, the melting depressant composition comprising: a melting depressant component that comprises phosphorus and silicon for decreasing a melting temperature of the first metal part; and optionally, a binder component for facilitating the applying of the melting depressant composition on the surface; bringing the second metal part into contact with the melting depressant composition at a contact point on said surface; heating the first and second metal parts to a temperature above 1000 C., said surface of the first metal part thereby melting such that a surface layer of the first metal part melts and, together with the melting depressant component, forms a melted metal layer that is in contact with the second metal part at the contact point; and allowing the melted metal layer to solidify and form a joint at the contact point, the joint comprising at least 50 wt % metal that, before the heating, was part of any of the first metal part and the second metal part, wherein the melting depressant component comprises less than 10 wt % metallic elements.

2. The method according to claim 1, wherein the phosphorus originates from a phosphorus compound selected from at least any of the following compounds: Mn.sub.xP.sub.y, Fe.sub.xP.sub.y and Ni.sub.xP.sub.y.

3. The method according to claim 1, wherein the silicon originates from any of elemental silicon and silicon of a silicon compound selected from at least any of the following compounds: silicon carbide, silicon boride and ferrosilicon.

4. The method according to claim 1, wherein the melting depressant component comprises any of at least 25 wt %, at least 35 wt % and at least 55 wt % phosphorus and silicon.

5. The method according to claim 1, wherein phosphorus constitutes at least 10 wt % of the phosphorus and silicon content of the melting depressant compound.

6. The method according to claim 1, wherein silicon constitutes at least 55 wt % of the phosphorus and silicon content of the melting depressant compound.

7. The method according to claim 1, wherein the first metal part comprises a thickness of 0.3-0.6 mm and the applying of the melting depressant composition comprises applying an average of 0.02-1.00 mg phosphorus and silicon per mm.sup.2 on the surface of the first metal part.

8. The method according to claim 1, wherein the first metal part comprises a thickness of 0.6-1.0 mm and the applying the melting depressant composition comprises applying an average of 0.02-2.0 mg phosphorus and silicon per mm.sup.2 on the surface of the first metal part.

9. The method according to claim 1, wherein the surface has an area that is larger than an area defined by the contact point on said surface, such that metal in the melted metal layer flows to the contact point when allowing the joint to form.

10. The method according to claim 9, wherein the area of the surface is at least 3 times larger than the area defined by the contact point.

11. The method according to claim 9, wherein the area of the surface is at least 10 times larger than a cross-sectional area of the joint.

12. The method according to claim 1, wherein any of the first metal part and the second metal part comprises a plurality of protrusions that extend towards the other metal part, such that, when bringing the second metal part into contact with said surface, a plurality of contact points are formed on said surface.

13. The method according to claim 1, wherein the first metal part comprises one of: >50 wt % Fe, <13 wt % Cr, <1 wt % Mo, <1 wt % Ni and <3 wt % Mn, >90 wt % Fe, >65 wt % Fe and >13 wt % Cr, >50 wt % Fe, >15.5 wt % Cr and >6 wt % Ni, >50 wt % Fe, >15.5 wt % Cr, 1-10 wt % Mo and >8 wt % Ni, >97 wt % Ni, >10 wt % Cr and >60 wt % Ni, >15 wt % Cr, >10 wt % Mo and >50 wt % Ni, >70 wt % Co, >80 wt % Cu, and >10 wt % Fe, 0.1-30 wt % Mo, 0.1-30 wt % Ni and >50 wt % Co.

14. The method according to claim 2, wherein the silicon originates from any of elemental silicon and silicon of a silicon compound selected from at least any of the following compounds: silicon carbide, silicon boride and ferrosilicon.

15. The method according to claim 2, wherein the melting depressant component comprises any of at least 25 wt %, at least 35 wt % and at least 55 wt % phosphorus and silicon.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the invention will now be described, by way of example, with reference to the accompanying schematic drawings, in which

(2) FIG. 1 is a cross-sectional view of a first and a second metal part where a melting depressant composition is applied intermediate the parts,

(3) FIG. 2 shows the metal parts of FIG. 1 during heating,

(4) FIG. 3 shows the metal parts of FIG. 1 when a joint is formed,

(5) FIG. 4 is a cross-sectional view of a first and a second metal part where a melting depressant composition is applied intermediate the components and when the second metal part abuts the first metal part,

(6) FIG. 5 shows the metal parts of FIG. 4 during heating,

(7) FIG. 6 shows the metal parts of FIG. 4 when a joint is formed,

(8) FIG. 7 shows metal parts when a joint is formed and where the parts have been pressed towards each other during the forming of the joint,

(9) FIG. 8 is a view corresponding to FIG. 7, where material from both metal parts have melted and formed the joint,

(10) FIG. 9, corresponds to FIG. 1 and shows distribution of a contact point between the metal parts,

(11) FIG. 10 shows an area of the contact point between the metal parts,

(12) FIG. 11, corresponds to FIG. 3 and shows distribution of a joint between the metal parts,

(13) FIG. 12 shows a cross-sectional area of the joint,

(14) FIG. 13 shows a pressed plate that is used in a number of examples that described how two metal parts may be joined,

(15) FIG. 14 is a photo of a cross-section of a joint between the plate shown in FIG. 13 and a flat plate,

(16) FIG. 15 shows a diagram where a measured joint width is plotted as a function of an applied amount of melting depressant composition, including trend lines,

(17) FIGS. 16-20 show a cross section of a joint investigated in an SEM, (scanning electron microscope), and locations of electron scanning,))) and

(18) FIG. 21 is a flow chart of a method for joining a first and second metal part.

DETAILED DESCRIPTION

(19) FIG. 1 shows a first metal part 11 and a second metal part 12 where a melting depressant composition 14 is arranged on a surface 15 of the first metal part 11. The second metal part 12 is, at a contact point 16, in contact with the melting depressant composition 14 on the surface 15. For the illustrated second metal part 12, a first protrusion 28 is in contact with the melting depressant composition 14 at contact point 16 while a second protrusion 29 is in contact with the melting depressant composition 14 at another contact point 116. The first metal part 11 is made of a metallic element, such as an iron-based alloy. More examples of suitable metallic elements the first metal part 11 may be made of are given below. The second metal part 12 is also made of a metallic element, which may be the same metallic element that as the first metal part 11 is made of. In FIG. 1 the first metal part 11 and the second metal part 12 are not yet joined.

(20) Five planes P1-P5 are used for describing how the first metal part 11 and the second metal part 12 are joined. The first plane P1 defines the surface of the melting depressant composition 14. The second plane P2 defines the surface 15 of the first metal part 11, which is an upper surface 15 of the first metal part 11. This means that the melting depressant composition 14 has a thickness that corresponds to the distance between the first plane P1 and the second plane P2 (the surface 15). It should be noted that the thickness of the melting depressant composition 14 is greatly exaggerated in the illustrated figures. The real thickness, i.e. the amount of the melting depressant composition 14 on the surface 15 as well as the composition of the melting depressant composition 14, is discussed in detail below.

(21) The third plane P3 defines a surface layer 21 of the first metal part 11, where the surface layer 21 extends from the surface 15 and to the third plane P3 which is located in the first metal part 11. Thus, the thickness of the surface layer 21 corresponds to the distance between the second plane P2 (the surface 15) and the third plane P3. The fourth plane P4 defines a lower surface of the first metal part 11. The thickness of the first metal part 11 corresponds to the distance between the second plane P2 and fourth plane P4. The first metal part 11 has also a lower layer 22, which is a part of the first metal part 11 that does not include the surface layer 21 and which extends from the third plane P3 to the fourth plane P4. The fifth plane P5 defines a base line of the second metal part 12, where the first protrusion 28 and second protrusion 29 protrudes from the base line in a direction towards the first metal part 11.

(22) The illustrated shapes of the first metal part 11 and the second metal part 12 are just exemplifying shapes and other shapes are equally conceivable. For example, the metal parts 11, 12 may have curved shapes, such that the planes P1-P5 do not have the form of flat, two-dimensional surfaces, but instead the form of curved surfaces. In particular planes P2 and P3 must not be sharp lines but may represent gradual transitions.

(23) FIG. 2 shows the metal components 11, 12 when they are heated to a temperature above which the melting depressant composition 14 causes the surface layer 21 to melt and form a melted metal layer 210. The temperature is still below a melting temperature of the materials in the first metal part 11 and in the second metal part 12. In brief, when heating the metal parts 11, 12, phosphorous and optionally silicon that is comprised in the melting depressant composition 14 diffuses into the first metal part 11 and causes it to melt at a temperature that is lower than the melting temperature of the material in the first metal part 11 (and of the second metal part 12). The melting depressant composition 14 is applied on the surface 15 at amounts that causes the surface layer 21 to melt and form the melted metal layer 210. Thus, the amount of melting depressant composition 14 is chosen so that phosphorous diffuses only into the surface layer 21 (too much phosphorous might melt the entire first metal part 11). Suitable compositions and amounts of the melting depressant composition 14 are described in the examples below. Metal in the melted metal layer 210 then flows, typically by capillary action, towards the contact point 16 (and to other, similar contact points such as contact point 116).

(24) FIG. 3 shows the metal components 11, 12 when all melting depressant composition 14 have diffused into the first metal part 11 and when metal in the melted metal layer 210 has flown towards the contact point 16 where a joint 25 now is formed. The joint now comprises metal that previously was part of the first metal part 11. As may be seen, the melting depressant composition 14 is no longer present on the surface 15 of the first metal part 11 since it has diffused into the first metal part 11 and, typically, to some extent into the second metal part 12. Since the joint 25 is formed from metal from the first metal part 11, the first metal part 11 is now at least locally slightly thinner than before the heating. As may be seen, the first metal part 11 now has an upper surface 15 that is not located at the second plane P2. Instead, the upper surface is now closer to the fourth plane P4. Generally, not all metal in the melted metal layer 210 flows towards the contact point 16 to form the joint 25, but some remains as an upper surface of the first metal part 11 and solidifies there simultaneously with the solidification of the joint 25. The solidification takes place when the temperature is decreased but also prior a decrease of the temperature, e.g. because the phosphorous in the melting depressant composition gradually diffuse into and mix with the material of the first metal part 11. The physical process behind the melting of the metal in the first metal part 11 as well as the subsequent solidification is similar with the melting and solidification process that occur during brazing. However, compared to conventional brazing there is a great difference in that the melting depressant composition 14 comprises no or very small amounts of filler metal; instead of using a filler metal for creating the joint 25, metal from the first metal part 11 is used for creating the joint 25. Optionally, as will be described, metal from the second metal part 12 may be used for creating the joint 25,

(25) FIGS. 4-6 corresponds to FIGS. 1-3 with the difference that the second metal part 12 is pressed into the melting depressant composition 14 to such an extent that it is basically in contact with or abuts to the first metal part 11 (some small amounts of the melting depressant composition 14 is still typically present between the metal parts 11, 12).

(26) FIG. 7 corresponds to FIGS. 3 and 6 with the difference that the first metal part 11 and the second metal part 12 have been pressed towards each other during the forming the joint 25. As a result the second metal part 12 has at the location of the joint 25 sunk into the melted metal layer 210 of the first metal part 11.

(27) FIG. 8 corresponds to FIG. 7, where material from both the first metal part 11 and the second metal part 12 have melted and formed the joint 25. In practice, this is typically what happens during the forming the joint 25, especially if the first metal part 11 and the second metal part 12 are made of the same material, since the second metal part 12 also is in contact with the melting depressant composition.

(28) Before the heating the second metal part 12 has an outer contour defined by line L2. During heating, a surface layer of the second metal part 12 forms a melted surface layer, where the metal of this layer flows to the contact point 16 and forms a joint 25 there. The melted surface layer of the second metal part 12 is represented by the layer between line L2 and line L1, where line L1 defines a boundary where the metal of the second metal part 12 has not been melted.

(29) It should be noted that there is no real sharp boundary between metal of the first metal part 11 and the second metal part 12 that is melted respectively is not melted. Instead, there is a gradual transition from melted to not melted.

(30) FIG. 9 corresponds to FIG. 1 and shows a distribution of the contact point 16 between the first metal part 11 and the second metal part 12. FIG. 10 shows the same metal parts 11, 12 but from above and in the first plane P1. FIG. 9 is a cross-sectional view as seen along line A-A in FIG. 10.

(31) As may be seen, the contact point 16 has a distribution over the melting depressant composition 14 on the first metal part 11 that is significantly larger than a distribution of the melting depressant composition 14 on the surface 15. The distribution of the contact point 16 has an area A2 that is significantly smaller than an area A1 of the melting depressant composition 14 on the surface 15. The area A1 comprises the area the A2. The area A1 extends between two lines L3, L4 that are located at a respective side of the contact point 16. Line L3 is located between the contact point 16 and the other contact point 116, since melted metal of the first metal part 11 generally flows towards the closest contact point. The area A1 of the surface 15 on which the melting depressant composition 14 is applied is at least 10 times larger than the area A2 defined by the contact point 16. The area A1 may be defined as an area of the surface 15 on which melting depressant composition 14 is applied and from which area A1 metal is drawn to the form the joint 25. The area A2 may be defined as the area of the contact point 16, i.e. the area of contact between the melting depressant composition 14 and the second metal part 12, optionally including an area of contact (if any) between the first metal part 11 and the second metal part 12 at the contact point 16. The area A1 is generally at least 10 times larger than the area A2.

(32) FIG. 11 corresponds to FIG. 3 and shows a cross-sectional area A3 of the joint 25. The area A1 of the surface 15 on which the melting depressant composition 14 is applied is at least 3 times larger than the cross-sectional area A3 of the joint 25. FIG. 12 shows the same metal parts 11, 12 but from above and in the second plane P2. FIG. 11 is a cross-sectional view as seen along line A-A in FIG. 12.

(33) As may be seen, the joint 25 has a cross-sectional are A3 that is significantly smaller than the area A1 of the melting depressant composition 14 on the surface 15. As before, the area A1 may be defined as an area of the surface 15 on which melting depressant composition 14 is applied and from which area A1 metal is drawn to form the joint 25. The cross-sectional area A3 of the joint 25 may be defined as the smallest area the joint 25 has between the first metal part 11 and the second metal part 12. The cross-sectional area A3 may have the shape of a curved surface. Obviously, the areas A1 and A2 may have the shape of curved surfaces, depending on the respective shape of the first metal part 11 and the second metal part 12.

(34) Depending on the shape of the metal parts to be joined the area on which the melting depressant composition is applied may be substantially equal to the area of a joint that is subsequently formed.

(35) A number of experiments and examples are now presented for describing suitable materials for the first metal part 11, the second metal part 12, the composition of the melting depressant composition 14, which amounts of melting depressant composition 14 should be used, suitable temperatures for the heating, for how long heating shall be done etc. Thus, the results of these experiments and examples are used for previously described entities like the first metal part 11, the second metal part 12, the melting depressant composition 14, the contact point 16, the joint 25 etc., i.e. all previously described entities may incorporate the respectively related features described in connection with the experiments and examples below. In the following the melting depressant composition is referred to as a blend. Metal part may be referred to as parent metal.

(36) A number of suitable melting depressant compositions, i.e. melting point temperature depressant compositions, have been tested. The active component in the melting depressant composition is phosphorous (P). Compounds of phosphorous have been selected as the source for phosphorous. The compounds include Fe.sub.3P, NiP and Mn.sub.3P.sub.2, where Mn.sub.3P.sub.2 is a mixture of MnP and Mn.sub.2P. Other compounds that include phosphorous may be used just as wellthey only have to be verified in respect of their usefulness and in respect of the result they provide, in a similar manner as done for the for Fe.sub.3P, NiP and Mn.sub.3P.sub.2 and outlined below.

(37) The Fe.sub.3P, also called iron phosphide, is a conventional compound that was obtained from the company Alfa Aesar, with a CAS (Chemical Abstracts Service) number of 12023-53-9 and MDL (Molecular Design Limited) number of MFCD00799762.

(38) The Mn.sub.3P.sub.2, also called manganese phosphide, is a conventional compound that was obtained from the company Alfa Aesar, with a CAS (Chemical Abstracts Service) number of 12263-33-1 and MDL (Molecular Design Limited) number of MFCD00064736.

(39) The NiP, also called nickel phosphorus, is a conventional compound that was plated on a metal part to be joined. The metal part to be joined is also referred to as a base metal or base material, The plating was done by performing a conventional nickel phosphorus plating method, as done by, for example, the company Brink Frnicklingsfabriken AB in Norrkping, Sweden

(40) For some the of the examples Si, or Silicon, was used. The silicon is a conventional compound that was obtained from the company Alfa Aesar, is referred to as silicon powder, crystalline, 325 mesh, 99.5% (metals basis), with CAS 7440-21-3 and MDL MFCD00085311.

(41) When looking on the atomic compositions of compounds, by applying the atomic weights and by using conventional calculation techniques it may be determined that

(42) Fe.sub.3P comprises 16 wt % P (phosphorous) and Mn.sub.3P.sub.2 comprises 27 wt % P. When nickel plating, approximately 11-14 wt % P are comprised in the NiP layer.

(43) A binder was used for applying the Fe.sub.3P and the Mn.sub.3P.sub.2 on metal parts to be joined. The binder (polymeric and solvent) is a binder sold by Wall Colmonoy under the name of Nicorobraz S-20 (S-20). A sample of the binder was placed on a metal plate and dried at 22 C. for 24 h. The weight of the sample was 0.56 g before drying and 0.02 g after drying. Thus, 3.57 wt % of the binder are components that remain after drying. A melting depressant composition was prepared where Mn.sub.3P.sub.2 and Si form a melting depressant component (melting point temperature depressant component) and where were the binder S-20 form a binder component. The preparation was done by first mixing Mn.sub.3P.sub.2 with Si and then by adding and mixing the binder S-20. Two variants of the melting depressant composition with different amounts of Si was prepared, referred to as A1Mn.sub.3P.sub.2 (A1) and B1Mn.sub.3P.sub.2 (B1), as shown in table 1.

(44) TABLE-US-00001 TABLE 1 X: A1 Mn.sub.3P.sub.2 B1 Mn.sub.3P.sub.2 X: 10.00 g 10.00 g Si 4.07 g 6.15 g Sum X and Si 14.07 g 16.15 g X:Si 2.46:1 1.63:1 S-20 16.80 g 15.98 g Tot sum 30.87 g 32.13 g

(45) The compositions A1 and A2 were applied on flat, circular test pieces of stainless steel type 316 L (SAE steel grade) and with a diameter of 42 mm in diameter.

(46) On every test piece another piece of a different material, 254 SMO (SAE steel grade), was placed. This other piece is shown in FIG. 13 and has the form of a circular, pressed plate 150, which is 42 mm in diameter and has a thickness of 0.4 mm The pressed plate 150 has two pressed beams v and h, each approximately 20 mm long. When the piece with the beams was placed on the flat piece, contact points were formed where the beams of piece 150 abut the other, flat piece.

(47) The pieces, i.e. that flat circular piece and the pressed plate, are referred to as a sample, and several samples were heat treated for 2 hours in vacuum at different temperatures for each sample. Table 2 shows which amounts of the compositions that were used for the samples.

(48) For samples A1:1 to A1:3 and samples B1:1 to B1:3 the heat treatment comprised holding the samples in a temperature of 1120 C. for 2 hours at vacuum.

(49) For samples A1:4 to A1:6 and samples B1:4 to B1:6 the heat treatment comprised holding the samples in a temperature of 1140 C. for 2 hours at vacuum.

(50) A1 indicates composition A1 Mn.sub.3P.sub.2 while B2 indicates composition B1 Mn.sub.3P.sub.2. The numbers after A1 respectively B2 indicates different samples, as presented in Table 2. In this table is the weight of the sample is presented, which includes the weight of the melting depressant component and the weight of the dry binder component.

(51) TABLE-US-00002 TABLE 2 Dry binder + melting depressant Sample component (g) A1:1 0.22 A1:2 0.13 A1:3 0.14 A1:4 0.33 A1:5 0.1 A1:6 0.16 B1:1 0.19 B1:2 0.09 B1:3 0.16 B1:4 0.16 B1:5 0.34 B1:6 0.14

(52) After the heat treatment the samples were allowed to cool to a room temperature (22 C.) and it was observed that the two pieces of the sample were joined along the lengths of the beams of the pressed plate 150, i.e. the sample has joints along the beams. The samples were cut across the joints at two sections and each joint was measured at its broadest section X, which is illustrated in FIG. 14. The results are presented in Table 3 and illustrated in the diagram of FIG. 15, where the width of the joint is plotted as a function of the applied amount of melting depressant composition.

(53) TABLE-US-00003 TABLE 3 applied Sample amount (g) width (m) A1-2 0.13 1640 A1-2 0.13 1610 A1-3 0.14 2070 A1-3 0.14 2240 A1-1 0.22 2961 A1-1 0.22 3050 B1-2 0.09 1240 B1-2 0.09 1220 B1-3 0.16 2010 B1-3 0.16 1600 B1-1 0.19 2170 B1-1 0.19 2290 A1-5 0.1 1831.9 A1-5 0.1 1810.1 A1-6 0.16 2195.01 A1-6 0.16 2202.28 A1-4 0.33 3107.34 A1-4 0.33 2993.13 B1-6 0.14 1470.32 B1-6 0.14 1661.94 B1-4 0.16 1832.65 B1-4 0.16 1810.9 B1-5 0.34 3264.29 B1-5 0.34 3237.96

(54) Metallurgical investigations were then made for the joints. This was done by analyzing the cut cross sections of the joints in a so called SEM-EDX, which is a conventional and commercially available scanning electron microscope with X-ray detector. FIG. 16 illustrates the locations of three measurements for sample A1-6 and Table 4 shows the results of the measurements.

(55) TABLE-US-00004 TABLE 4 Spectrum Label (chemical substance) Spectrum 1 Spectrum 2 Spectrum 3 C 3.04 2.86 2.95 Si 0.40 2.40 1.52 P 1.43 0.76 Cr 16.11 18.00 17.33 Mn 1.50 1.63 1.35 Fe 62.90 50.54 51.15 Ni 13.88 18.00 20.76 Mo 2.17 5.16 4.17 Total 100.00 100.00 100.00

(56) The investigations shows that the joints comprise at least 90 wt % metal that, before the heating, was part of any of the first metal part and the second metal part, i.e. the pieces of the sample. This is readily determined since Mn and P together represent less than 2.2 wt %.

(57) Similar investigations were also made for sample B1-6. FIG. 17 illustrates the locations of three measurements for sample B1-6 and Table 5 shows the results of the measurements.

(58) TABLE-US-00005 TABLE 5 Spectrum Label (chemical substance) Spectrum 1 Spectrum 2 Spectrum 3 C 2.87 2.86 2.77 Si 0.43 2.58 0.42 P 0.17 1.76 Cr 18.75 16.72 16.61 Mn 0.00 2.41 1.46 Fe 50.56 50.18 63.19 Ni 21.70 18.90 13.63 Mo 5.53 4.58 1.91 Total 100.00 100.00 100.00

(59) Investigations shows that the joints comprises at least 90 wt % metal that, before the heating, was part of any of the first metal part and the second metal part, i.e. the pieces of the sample. This is readily determined since Mn and P together represent less than 4.2 wt %,

(60) In a next test pieces of type 316 stainless steel, referred to as 316, with a diameter of 42 mm were applied with three different melting depressant compositions (one composition on a respective piece): i) Mn.sub.3P.sub.2, ii) NiP plated on 316 and iii) NiP plated on 316 together with Si as melting point depressants. The thickness of the plated NiP is 50 m. 0.15 g Si was applied by conventional painting. On every piece a pressed piece similar to that of FIG. 13 of type 254 SMO was placed. The pieces form samples that were heat treated for 2 hours in vacuum at 1120 C. Joints were formed between the pieces.

(61) Table 6 shows an analysis of a cut cross section of the joints by using SEM-EDX for the sample with 50 m NiP plating. From the result it appears that the joint comprises at least 20 wt % metal that, before the heating, was part of any of the piece (first metal part) or second piece (second metal part). FIG. 18 shows the location of the measurements in the joint.

(62) TABLE-US-00006 TABLE 6 Spectrum Label (chemical Spec- Spec- Spec- Spec- Spec- Spec- substance) trum 10 trum 5 trum 6 trum 7 trum 8 trum 9 O 0.91 1.48 0.67 1.20 0.99 2.34 Si 0.32 0.26 0.29 0.18 P 1.07 9.60 0.95 14.41 1.06 10.84 Cr 7.42 8.83 7.64 17.99 7.78 13.27 Mn 0.61 0.51 0.43 Fe 33.22 23.11 33.69 20.17 33.60 23.03 Ni 56.01 54.25 55.61 40.95 55.06 46.83 Mo 1.06 1.86 1.16 4.77 1.33 3.25 Total 100.00 100.00 100.00 100.00 100.00 100.00

(63) Table 7 shows an analyze of a cut cross section of the joints by using SEM-EDX for the sample with 50 m NiP plating where app 0.15 g amount of Si has been applied (painted) on the plated surface. From the result it appears that the joint comprises more metal in comparison with the test where no Si was used. A higher amount of Si would most likely increase the amount of metal in the joint that comes from the test pieces. FIG. 19 shows the location of the measurements in the joint.

(64) TABLE-US-00007 TABLE 7 Spectrum Label (chemical Spectrum Spectrum Spectrum substance) 11 12 13 C 7.44 6.41 6.34 O 1.48 1.71 1.06 Si 2.22 1.99 2.43 P 5.76 8.83 0.48 Cr 11.13 12.33 9.47 Mn 0.39 0.51 0.00 Fe 30.33 26.57 38.80 Ni 38.70 38.19 40.10 Mo 2.54 3.46 1.33 Total 100.00 100.00 100.00

(65) Table 8 shows an analysis of a cut cross section of the joints by using SEM-EDX for the sample with Mn.sub.3P.sub.2. The Mn.sub.3P.sub.2 has been mixed 50 wt:50 wt with S-20 binder but no Si is used. An amount of 0.2 g (after drying of the binder component) was applied. From the result it appears that the joint comprises at least 80 wt % metal that before the joining was part of the products that were joined. FIG. 20 shows the location of the spectrum 1 measurements in the joint.

(66) TABLE-US-00008 TABLE 8 Spectrum Label (chemical substance) Spectrum 1 Spectrum 2 O 2.28 Si 0.29 0.31 P 6.33 7.23 S 0.54 Cr 21.70 22.65 Mn 1.08 1.40 Fe 51.93 46.63 Ni 12.02 12.19 Mo 6.65 6.78 Total 100.00 100.00

Method

(67) With reference to FIG. 21 a flow chart of a method for joining a first and second metal part is illustrated. The metal parts may be made of different materials as described above.

(68) In a first step 201 the melting depressant composition is applied on the surface of one of the metal parts (here the first metal part). The application per se may be done by conventional techniques, e.g. by spraying or painting in case the melting depressant composition comprises a binder component, and by PVD or CVD in case not binder component is used.

(69) A next step 202 the second metal part is brought into contact with the melting depressant composition at a contact point on the surface. This can be done manually or automatically by employing conventional, automated manufacturing systems.

(70) In a next step 303 the metal parts are heated to a temperature which is above 1000 C. The exact temperature can be found the examples above. During the heating a surface of at least the first metal part melt and, together with the melting depressant component, forms a melted metal layer that is in contact with the second metal part at the contact point between the first metal part and the second metal part. When this happens, metal of the melted metal layer flows towards the contact point.

(71) A final step 204 the melted metal layer is allowed to solidify, such that a joint is obtained at the contact point, i.e. the metal that has flown to the contact point solidifies. The solidification typically includes decreasing temperature to normal room temperature. However, solidification also occurs during the physical process of redistribution of components (phosphorous and optionally silicon) in the joint area, before a temperature is decreased.

(72) From the description above follows that, although various embodiments of the invention have been described and shown, the invention is not restricted thereto, but may also be embodied in other ways within the scope of the subject-matter defined in the following claims. Various melting depressant compositions can also be combined with various metals for the metal parts.