JP2009285675A - Overlaying method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a two-layer overlaying method for fully suppressing production of bead crack. <P>SOLUTION: In the two-layer overlaying method in which different kinds of metal are overlayed in two layers on the surface of a base material 1, a material suitable for desired surface reforming is selected as an overlaying material for forming the overlay layer 7 of the second layer and a material having a higher melting point and a tensile strength higher than the overlay layer of the second layer is selected as an overlay material for forming the overlay layer 6 of the first layer. Since the overlay layer 6 of the first layer has a higher strength, a crack is hardly caused in the overlay layer 6 of the first layer even when thermally affected in overlaying of the second layer, and as a result, the bead crack for the entire overlay layer 5 is prevented. Meantime, a desired surface reforming effect is secured by the overlay layer 7 of the second layer. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a two-layer overlaying method for depositing dissimilar metals in two layers on the surface of a substrate.

  In order to modify the surface, depositing a dissimilar metal on the surface of the base material has been widely performed. For example, even in a cast iron cylinder head constituting an automobile engine, the valve seat portion is built up. (For example, refer to Patent Document 1). By the way, when it builds up on the substrate surface, cracks (bead cracks) often occur in the built-up layer. This is influenced by internal stress (residual stress) generated in the build-up layer. In particular, the thicker the build-up thickness, the higher the residual stress and the easier the bead cracking occurs.

  Therefore, conventionally, in order to prevent the occurrence of the above-described bead cracking, in the one described in Patent Document 1, measures are taken to relieve the residual stress generated in each layer by depositing different types of metals in two layers on the surface of the substrate. Is adopted.

JP 2008-12564 A

  However, in the countermeasure described in Patent Document 1 described above, the same material (Cu-based alloy) is built up in the first layer and the second layer. There was a risk that cracks were induced in the built-up layer of the eyes and the cracks spread over the whole, which was insufficient as a countermeasure against bead cracks.

  The present invention has been made in view of the above-described conventional problems, and the object of the present invention is to provide a two-layer overlaying method that can sufficiently suppress the occurrence of bead cracking.

It is known that metal breakdown is usually caused by tensile stress. The present invention has been made paying attention to this point, and performs a two-layer overlay by selecting a material having a higher tensile strength than the second-layer overlay material as the first-layer overlay material. It is characterized by. In this way, when the two-layer build-up is performed, the strength of the first build-up layer is high, so that it is difficult for the first layer to crack even under the influence of heat during the second layer build-up. As a result, bead cracking of the entire overlay layer is prevented.
In the following, some aspects of the present invention will be illustrated and described in terms of items.

  (1) In a two-layer overlaying method in which different types of metal are deposited on the surface of a base material in two layers, a material suitable for the desired surface modification is selected as the second-layer overlay material, and the first layer meat 2. A two-layer overlay method characterized by selecting a material having a higher melting point and a higher tensile strength than the second-layer overlay material.

  In the two-layer overlay method described in the item (1), a material having a higher melting point and a higher tensile strength than the second-layer overlay material is selected as the first-layer overlay material. When the first layer is built up, the first layer is melted to prevent the components of the first layer and the second layer from being mixed, the strength reduction of the first layer is suppressed, and the second layer is built up. Even under the influence of heat at the time, cracks do not occur in the first layer. Further, since the material suitable for the desired surface modification is selected as the second overlay material, the required quality is not sacrificed.

  (2) The ratio of the build-up thickness of the 1st layer and the 2nd layer is set to 2: 8-8: 2, The 2-layer build-up method as described in the (1) term characterized by the above-mentioned.

  In the present invention, the build-up thickness of the first layer and the build-up thickness of the second layer can be widely changed. However, if one of the build-up layers becomes extremely thick, the residual stress increases and In order to prevent bead cracking with certainty, it is desirable to keep it in the range of 2: 8 to 8: 2 as described in the item (2).

  (3) The two-layer structure according to (1) or (2), wherein the base material is a cast iron cylinder head base material for an internal combustion engine, and a surface as a build-up target is a valve seat portion. Overlaying method.

  Although the build-up object of this invention is arbitrary, it becomes useful toward the build-up with respect to the valve seat of a cast iron cylinder head base material as described in the item (3).

  (4) The build-up material for the second layer is a Cu-based alloy, and the build-up material for the first layer is one selected from a Ni-based alloy, a Co-based alloy, and an austenitic stainless steel. The two-layer overlaying method according to item (3).

  The valve seat portion of the cast iron cylinder head base material is generally overlaid with a Cu-based alloy for the purpose of improving wear resistance, and the Cu-based alloy is added to the second layer as described in (4). When selecting as a build-up material, if Ni-base alloy, Co-base alloy, austenitic stainless steel, etc. are selected as the build-up material for the first layer, the requirements of the present invention are satisfied in terms of melting point and tensile strength. To be.

  (5) The two-layer overlay method according to any one of (1) to (4), wherein the overlay is performed using a laser as a heat source.

  In the two-layer overlaying method described in the item (5), since so-called laser cladding is performed using a laser as a heat source, the component dilution from the base material to the first layer can be minimized, and the first layer The risk of inadvertent decline in strength can be avoided.

  According to the two-layer cladding method according to the present invention, it is possible to sufficiently suppress the occurrence of bead cracking in the cladding layer, and it is possible to sufficiently ensure the surface modification effect. There is something great.

  The best mode for carrying out the present invention will be described below with reference to the accompanying drawings.

  FIG. 1 and FIG. 2 show one embodiment of the two-layer overlay method according to the present invention. In the present embodiment, build-up processing (cladding processing) of a dissimilar metal is performed on the valve seat portion 2 of a cast iron cylinder head (base material) 1 for an internal combustion engine. A laser overlay system using the apparatus 3 is employed. The laser cladding apparatus 3 includes a laser processing head 4 that irradiates a laser beam toward the valve seat portion 2 and discharges metal powder (building material). At the time of overlaying, the laser processing head 4 is scanned along the valve seat portion 2, whereby an after-mentioned overlay layer 5 is continuously formed in an annular shape on the valve seat portion 2.

  In this embodiment, the build-up process for the valve seat portion 2 is performed in two steps by changing the type of the build-up material (metal powder). More specifically, as the build-up material used in the second step, a material having desired wear resistance required for the valve seat portion 2, for example, a Cu-based alloy is selected. On the other hand, the build-up material used in the first step is a material having a higher melting point and a higher tensile strength than the build-up material used in the second step, such as a Ni-base alloy, a Co-base alloy, and austenitic stainless steel. Is selected.

  By performing the build-up process in two steps as described above, the valve seat portion 2 has two layers including the first build-up layer 6 and the second build-up layer 7 having different component compositions. A built-up layer 5 having a structure is formed (FIG. 2). In this case, the two-step build-up processing is performed so that the ratio of the thickness of the first build-up layer 6 and the second build-up layer 7 falls within the range of 2: 8 to 8: 2. The By accommodating the thicknesses of the first and second build-up layers 6 and 7 in the above-described ratio, the residual stress generated in the build-up layers 6 and 7 accompanying the build-up processing in each step is relieved. The occurrence of cracks in each of the overlay layers 6 and 7 is prevented. In addition, since a material having a melting point higher than that of the second layer is selected as the first layer, the first layer 6 is melted when the second layer is built. This suppresses mixing of the first layer and second layer components, and suppresses the strength reduction of the first overlay layer 6. In addition, since the tensile strength of the first overlay layer 6 is high, even if it is affected by heat during the overlay process in the second step of forming the second overlay layer 7, the first overlay The layer 6 is hardly cracked, and as a result, the entire bead crack of the built-up layer 5 is prevented. In addition, since the second build-up layer 7 has desired wear resistance, the surface modification effect of the valve seat portion 2 of the cylinder head 1 is sufficient. Particularly in the present embodiment, since the cladding layer 5 is formed by the laser cladding method, component dilution from the base material (cast iron cylinder head) 1 with respect to the first cladding layer 6 is minimized. As a result, the strength of the first build-up layer 6 is not inadvertently reduced.

  In the above-described embodiment, laser cladding is performed by using the laser processing head 4 having a function of irradiating a laser beam and discharging a metal powder. Of course, laser cladding may be performed using a laser processing apparatus that is independently provided with a powder supply head to be discharged. Further, this laser overlay may be replaced with an arc overlay method such as MIG, TIG, or plasma.

  For the valve seat portion 2 of the cylinder head 1 shown in FIG. 1, the low-melting point Cu-base alloy, general-purpose Cu-base alloy, Ni-base alloy, C0 of the component system shown in Table 1 are used as the first layer build-up material. Five types of base alloy and austenitic stainless steel are selected, and the general-purpose Cu-based alloy is selected as the second layer build-up material, and a semiconductor laser is used and the processing conditions shown in Table 2 are used. Laser overlay processing of the second layer (first step) and the second layer (second step) was performed, and after the overlay processing, the presence or absence of bead cracking was observed on the entire circumference of the valve seat portion 2.

  In Table 1, the observation result of the bead crack about each case is appended. From this, bead cracking was observed in case 1 in which a low melting point Cu-based alloy was selected as the first layer build-up material and in case 2 in which a general-purpose Cu-based alloy was selected, and in particular, case 1 in which a low melting point Cu-based alloy was selected. In the case of, bead cracking is remarkably generated. On the other hand, Ni-base alloy, C0-base alloy, and austenitic stainless steel with higher melting point and higher tensile strength than the second-layer overlay material (Cu-based alloy) are selected as the first-layer overlay material. In all cases 3 to 5, the bead crack was zero (0), and it was revealed that the material selection of the first layer greatly affects the occurrence of the bead crack.

  As shown in FIG. 3, a plurality of cast iron specimens 10 having a shape simulating the valve seat portion 2 (FIG. 1) of the cylinder head 1 are prepared, and in the concave grooves 11 of the specimen 10 as shown in FIG. Laser build-up processing was performed in two steps, and a first build-up layer 12 and a second build-up layer 13 were laminated. Here, as the build-up material for forming the first build-up layer 12, the Ni-based alloy of the case 3 in Table 1 is the same as the build-up material for forming the second build-up layer 13. Each Cu-based alloy in the case of Table 1 was selected. And among the processing conditions shown in Table 2, the processing speed and the amount of powder are changed, and the ratio of the thickness t1 of the first overlay layer 12 to the thickness t2 of the second overlay layer 13 (T1: t2) was changed to 2: 8, 5: 5, and 8: 2, and the presence or absence of a bead crack was observed after build-up processing.

  As a result, no bead cracking was observed in the build-up portion of each specimen 10, and according to the method of the present invention, the build-up thickness of the first layer and the build-up thickness of the second layer were widened. It became clear that it could be changed.

It is a mimetic diagram showing one embodiment of the two-layer build-up method concerning the present invention. It is sectional drawing which expands and shows the built-up state with respect to the valve seat part of the cylinder head shown in FIG. It is sectional drawing which shows the specimen used for the Example of this invention performed by changing the build-up thickness of the 1st layer and the 2nd layer.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Cylinder head 2 Valve seat part 3 Laser build-up apparatus 4 Laser processing head 5 Build-up layer 6 1st build-up layer 7 2nd build-up layer

Claims (5)

  In the two-layer overlay method in which different types of metal are deposited on the surface of the base material in two layers, a material suitable for the desired surface modification is selected as the second-layer overlay material, and the first-layer overlay material is selected. A two-layer overlaying method, wherein a material having a higher melting point and a higher tensile strength than the second-layer overlay material is selected.   The ratio of the build-up thickness of the 1st layer and the 2nd layer is set to 2: 8-8: 2, The 2-layer build-up method of Claim 1 characterized by the above-mentioned.   3. The two-layer overlay method according to claim 1, wherein the base material is a cast iron cylinder head base material for an internal combustion engine, and a surface to be overlayed is a valve seat portion.   The second-layer cladding material is a Cu-based alloy, and the first-layer cladding material is one selected from a Ni-based alloy, a Co-based alloy, and an austenitic stainless steel. Item 4. The two-layer overlay method according to Item 3.   The two-layer overlaying method according to any one of claims 1 to 4, wherein the overlaying is performed using a laser as a heat source.

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