CH618468A5 - Process for surface-alloying of a substrate metal, and product of the process. - Google Patents

Description

The present invention relates to a method for surface alloying a substrate metal, preferably steel or cast iron, and to a product of the method.

Methods of the type mentioned are known, for example, from US Pat. Nos. 1 986 704.3 310 423 and 3 493 713 and from French Pat. No. 2,059,732. The surface layers formed in a known manner are each those whose connection to the substrate is limited to an intermediate layer between the substrate and the covering. The methods mentioned accordingly lead to a two-layer surface structure of the substrate consisting, on the one hand, of the unalloyed coating itself and, on the other hand, of the intermediate layer which connects to the substrate. The formation of such a structure is undesirable and should be prevented with the method according to the invention.

It is a further object of the present invention to convert the surface layer of a substrate into a form which contains a substantial portion of the substrate as a separate and different phase and / or as part of a newly formed compound.

This is achieved according to the invention in that a layer of one or more alloy components is applied to the metal surface and this is guided along a sectionally straight-line processing path past the beam of a continuously excited laser source, the power density of which is between 8 and 1600 kW / cm 2 and which in cooperation with the The rate of displacement brings the layer and a predetermined depth range of the metal beneath it to melt along a straight processing path, mixes them with one another and can be solidified again, whereby an alloy layer of the predetermined depth is formed along this path, which over its entire thickness and evenly over the entire treated surface has a composition and properties that differ from that of the underlying substrate metal.

The resulting product according to the invention is characterized in that the substrate is provided with a metal alloy layer, the main component of which comes from the substrate, the layer having the structure characteristic of melting and sudden re-hardening of metal and being harder than the substrate over its entire thickness as well as having a constant composition over the treated surface area at a given layer depth.

The invention will now be explained in detail on the basis of the description of an exemplary embodiment with reference to the drawings.

1 is a sectional view of a sheet metal substrate in a leading state of surface modification;

Figure 2 is a similar sectional view of the part after surface modification is complete;

3 is a sketch of a preferably used apparatus arrangement for carrying out the method according to the present invention;

Figures 4 and 5 are isometric views of parts undergoing surface modification;

6 and 6A ... 6D are photomicrographs of sections of a substrate subjected to surface modification;

Figures 7, 8, 9, 11, 12, 15 and 17 are concentration curves as a function of layer depth for minority components in the surface layer of workpieces treated by the method of the present invention;

Figures 10, 13, 14, 16, 18 and 19 are curves of hardness as a function of layer depth for surface layers of workpieces treated by the method of the present invention.

1 shows as the substrate a metal part 10, for example a rolled product such as sheet steel or a production part such as a valve seat made of steel. In order to increase the wear resistance of the surface, it is provided with a layer of minority components (for example chrome and manganese) in order to transform the surface layer into a high-alloy material. A predetermined depth line 16 is defined below the surface, which defines the surface layer and a proportion of the substrate material which, together with the coating 12 of minority components, gives the desired alloy. An energy-absorbing layer 14 can be placed on the substrate part as a base for the overlayer

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train 12 applied or mixed into this. An energy beam 18 is applied from a laser device and generates a melting zone 19 down to the depth line 16. By moving the substrate 10 and the beam 18 against one another, the melting zone is shifted linearly continuously or in steps as desired, and thus results in a group arrangement of such melting surface parts in chronological succession. While there is a melting zone 19 at some point, there is a very rapid heat transfer from this to the very large heat sink formed by the substrate part 10; as soon as the impinging jet 18 leaves the melting zone, it cools down and solidifies.

For the treatment of metals, a laser beam of 5 ... 20 kW is preferably left, which is focused to a circle of 0.635 ... 17.78 mm (0.025 ... 0.7 in.) Diameter or a contour of equal area, (which results in a power density between 8 and 1600 kW / cm2), paint over the surface to be modified at a speed of 0.127 ... 1.27 m / min (5 ... 50 in./min). A predetermined area of the surface layer typically remains in the molten state for 0.1 to 1.5 seconds and typically cools to a temperature below the solidus point for the corresponding alloy within 0.1 to 1.5 seconds. During the melting process, the thermal gradients already cause the minority components of the coating to mix considerably with the molten surface layer portion. It is believed that the high energy applied also causes a pressure wave that additionally mixes the components vigorously. Mixing can be further promoted by locally swinging the point of impact of the energy as set forth below with reference to FIGS. 4 and 5.

With preheated substrate, higher treatment speeds are possible; see. example 7.

FIG. 2 shows a substrate part 10 with a hardened surface layer 20 and an interface layer 22. The thickness of the layer 20 essentially corresponds to the predetermined depth line 16 (FIG. 1).

3 shows an apparatus arrangement for carrying out the method according to the invention. The workpiece 10 is clamped onto a conventional milling table, which is provided with guides and control devices which allow the workpiece to be displaced in directions lying at right angles to one another, as indicated by the double arrows 11 and 13. The x and y movements can take place simultaneously or one of them intermittently.

The energy beam 18 for the treatment described above with reference to FIG. 1 is supplied by a laser 30. This can be an embodiment according to US Pat. Nos. 3,721,915,3,702,973,3,577,096 and 3,713,030. The laser 30 operates in FIG. 3 on a beam splitter 31, which allows the beam to be divided over a number of application points via one or more beam guides 36. sequential application works at several points by using tilting mirror arrangements and rotatable beam interrupters. As indicated at 38, an adjustable mirror arrangement can be provided that picks up the laser beam from the optics and, in addition to or instead of moving the workpiece on the table 39, deflects it and at the same time allows it to oscillate, as described below with reference to FIG. 5 is.

FIGS. 4 and 5 show an isometric view of a workpiece 10 which is treated using the device of FIG. 3 according to the method of the present invention; the workpiece is provided with the coating 12/14, as described with reference to FIG. 1. The workpiece is moved in a longitudinal direction indicated by arrow 11A in FIG. 4 and arrow 118 in FIG. 5 and at the same time intermittently according to arrow 13 in FIGS. 4 and 5 to produce a series of lines lying side by side.

One of the beam lines 36 is connected to an optics unit 37, where the laser beam is shaped to heat the substrate.

During the return, the jet is switched off or machined partial areas lying next to one another during the forward run and the return on the other hand. Furthermore, the beam can be switched so that it jumps over certain surface parts of the coating 12/24 in order to produce a desired pattern from hard and non-hard surface areas.

The movements indicated by arrows 11A and 11B in FIGS. 4 and 5 typically take place at a speed of approximately 0.5 m / min (approximately 20 in / min). According to FIG. 5, however, the movement can be superimposed on a local lateral swinging out, as indicated by the waveform 1 IC above the arrow IIB. The size of the working spot in the first mode of operation shown in FIG. 4 typically coincides with the full width of lines 20A and may be considerably less than the full width of line 20B in the second mode of operation of FIG. 5; in the latter case, the vibrations of the working spot relative to the surface of the part 10 cover the entire line width while repeated energy surges are applied to the same surface zone, and as a result there is a considerably better mixing of the molten surface layer of the part 10 with the locally melted part of the coating 12 . Such gradients can also be achieved if the beam is focused on the width of line 20B by continuously changing the cross-sectional contour of the beam, for example from a straight line to a circular or from a circular to a star shape. In addition to or instead of the lateral vibrations of the beam point, longitudinal vibrations can be given to it.

The implementation of the invention will now be explained with reference to the following working examples, which, however, do not limit the invention.

example 1

Metal powder mixtures were sprayed onto the surface of metal products. These coated surfaces were then coated with a high power laser that melted and evenly alloyed the surface and powder. In this way, a considerable increase in surface hardness could be achieved. In a test, the surface of steel was given a 6.35 ... 12.7 | x (1/4 ... 1/2 mil) thick layer of manganese phosphate in accordance with AISIC 1018 using a conventional manganese phosphating process.

This optional measure of a coating with manganese phosphate causes better absorption of the laser beam. Other heat absorbing substances that can be used are zinc phosphate, aluminum oxide and carbon black. The choice also depends on the wavelength of the heat source used. Then a mixture of 6 g carbon powder (particle size 45 jx), 3 g chrome powder (10 ja) and 3 g manganese powder (45 (j.) In 40 ml isopropyl alcohol was sprayed evenly onto the manganese phosphate coating. The thickness of the loosely packed metal powder layer was 12.7 | i (1/2 mil). Then the surface of the steel was mixed with the metal powder mixture at a relative speed of 0.5 m / min (20 in./min) with a locally swinging laser beam of 11 ... 11, 5 kW coated, the laser beam a

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Rectangular contour of 2.54 x 12.7 mm (0.1 x 0.5 in.) And the long dimension was perpendicular to the direction of movement, since in this direction the local deflection to cover the entire line width (20B, Fig. 5) took place. The power density of the laser beam was therefore 34.1 ... 35.6 kW / cm2. The oscillation frequency was 690 Hz. Under these conditions the steel surface melted and alloyed evenly with the carbon, chrome and manganese powder. After melting and resolidification, the hardness to a depth of 0.127 mm (5 mil) was greater than Rockwell C 58, while the steel had a Rockwell hardness of B 93.

6 is a photomicrograph of a workpiece treated according to Example 1 at a magnification of 200 times, while FIGS. 6A, 6B, 6C and 6D are photographs taken with a scanning electron microscope at a magnification of 3500 times at depths of 51 p. (2 mil), 76 p. (3 mil), 102 | i (4 mil) or 127 (i (5 mil) depth below the surface of the workpiece in the area shown in FIG. 6.

In FIG. 6, the uninfluenced substrate is designated by 10, the alloyed surface layer by 20 and the intermediate layer, the inner boundary between the surface layer 20 and the substrate 10, by 22. Layer 20 has a finer grain structure than the substrate. 6A ... 6D show in the layer 20 a two-phase structure made of martensitic dendrites, which are surrounded by carbides in the regions between the dendrites.

7, 8 and 9 show the concentrations of minority components in the end product for carbon, chromium and manganese, as they result from the treatment according to Example 1. The curves of FIGS. 7, 8 and 9 are diagrams of the concentrations of the specified alloy components as a function of the depth of use. According to common practice, these curves are adapted to the original data points. They show an increase in the minority shares in the iron alloy. The falling part of curve 93 of curve 91 (FIG. 9) is based on the volatilization of the manganese on the surface; without this volatilization this part of the curve would correspond to the dashed part 95. If the depth of use is significantly greater (see Example 7), the surface effect is less pronounced.

10 shows hardness profiles of the end product after laser processing with local decay. The melting zone had a depth of 0.127 mm (5 mil) and in it the Rockwell hardness was C 58 to C 63, while the Rockwell hardness for the heat-affected zone of the steel was B 90 and in the steel core B 93. The depth of the heat affected zone was approximately 1.27 mm (0.05 in.).

Example 2

A sheet of steel in accordance with AISIC 1018 was provided with a 6.35 ... 12.7 | i (1/4 ... 1/2 mil) thick manganese phosphate layer according to a conventional manganese phosphating process and a small proportion of a mixture of this manganese phosphate layer 10 g aluminum powder of 45 p. Spread the particle size evenly in 50 ml of isopropyl alcohol to counteract the evolution of gas during melting. A mixture of 12 g of carbon powder (45 ml), 6 g of chrome powder (10 fi) and 6 g of manganese powder (45 fi) in 40 ml of isopropyl alcohol was then sprayed uniformly onto the aluminum powder coating 20 times; the thickness of the loose metal powder layer was then 0.38 ... 0.51 mm (15 ... 20 mil).

The coated surface was then laser treated in separate samples as described with reference to FIGS. 4 and 5. That is, the surface of a sample was hardened by melting to a limited depth to mix the minority components of an alloy with the main component derived from the substrate without local swinging out. In both cases the melting time for a given area size was 0.3 sec and the laser power was 13 ... 14 kW. When working without local swinging out, the movement speed was 1.27 m / min (50 in./min), while working with local swinging out was 0.51 m / min (20 in./min). In both cases, the power density applied for melting was 38.75 ... 46.5 kW / cm2 (250 ... 300 kW / sq.in.) Of the surface of the workpiece. When working without local swinging out, the size of the incident laser beam was 6.35 mm (0.25 in.), When working with local swinging out 2.54 x 12.7 mm (0.1 x 0.5 in.) In a rectangular shape which was stretched transverse to the direction of movement since the local swinging out took place in this direction in order to cover the entire line width (208, FIG. 5). The oscillation frequency was 690 Hz.

Figures 11 and 12 show depth profiles of the minority components in the finished product, i.e. for chrome and manganese. The upper curves for chrome and manganese were obtained with, the lower curves without local swinging out.

FIG. 13 shows hardness profiles in various end products which were treated with or without local oscillation of the laser beam. Rockwell hardness values between C 27 and C 44 were found without local swing-out, and Rockwell hardness values between C 46 and C 58 with local swing-out, in both cases to a depth of almost 0.762 mm (0.03 in.). The core steel hardness was Rockwell B 93, the hardness of the heat-affected zone Rockwell B 90. The heat-affected zone had a depth of about 1.27 mm (0.05 in.).

Example 3

The surface of a steel sheet according to AISI C 1018 was coated 6.35 ... 12.7 | x (1/4 ... 1/2 mil) thick with manganese phosphate, a small part of a mixture of 10, according to a conventional manganese phosphating process Evenly spread g of aluminum powder (45 | a particle size) in 50 ml of isopropyl alcohol on the manganese phosphate layer to counteract gas evolution during melting and then a mixture of 12 g of carbon powder (45 | i), 20 g of chrome powder (10 p.) and 8 g Tungsten powder (45 ji) in isopropyl alcohol sprayed 20 times evenly onto the aluminum powder coating; the thickness of the loose metal powder coating was 0.635 ... 0.762 mm (25 ... 30 mil). The surface of the steel sheet with the metal powder mixture was coated at 0.254 m / min (10 in / min) by a locally swinging 12 kW laser beam, the beam size of 2.54 x 12.7 mm (0.1 x 0, 5 in.), The long dimension being transverse to the direction of movement, since the local swinging out took place in this direction. The power density of the laser beam was 37.2 kW / cm2. The oscillation frequency was 690 Hz. The molten and solidified steel surface proved to be intimately alloyed with the carbon, chromium, tungsten and aluminum.

14 shows the hardness profile of the end product after the laser treatment with local swinging out, as described above. The melting zone was 1.12 mm (44 mils) deep; A Rockwell hardness of C 48 to C 53 was measured in this zone, while the Rockwell hardness of the core steel B 93 and the heat-affected zone B was 90. This heat affected zone was approximately 3.05 mm (0.12 in.) Deep.

Example 4

The surface of a gray cast iron part with approximately 0.2% by weight of chromium was coated with a 6.35 ... 12.7 [i (1/4 ... 1/2 mil) thick manganese phosphate layer according to a conventional manganese phosphating process, then one Mixture of 5 g chrome powder (10 p, particle size) in 40 ml

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Isopropyl alcohol sprayed 10 times evenly onto the manganese phosphate coating; the thickness of the loose metal powder layer was 12.7 ... 25.4 p, (1/2 ... 1 mil). The surface of the cast iron part with the chrome powder was coated at 0.76 m / min (30 in / min) with a locally swinging laser beam of 11 kW. The beam size was 2.54 x 12.7 mm (0.1 x 0.5 in.) In a rectangular shape and with a long dimension perpendicular to the direction of movement, since the local oscillation took place in this direction. The power density of the laser beam was 34.1 kW / cm2. The oscillation frequency was 690 Hz. In this way, the surface of the cast iron part was melted and intimately alloyed with the chrome powder.

Figure 15 shows the minority concentration for chromium in the finished product. The curve is adapted to the original measuring points according to conventional static practice. It shows an increase in chromium concentration in the 0.254 mm (10 mil) deep melting zone.

16 shows hardness profiles of the end product after laser processing with local decay. In the melting zone, the Rockwell hardness was C 60 to C 65, while the Rock well hardness for the part of the casting that was not laser-treated was B 95. The Rockwell hardness of the heat-affected zone was C 56 to C 61.

Example 5

The surface of a steel sheet according to AISI 4815 was provided with a 6.35 ... 12.7 (i (1/4 ... 1/2 mil) thick manganese phosphate layer according to a conventional manganese phosphating process, then chrome powder of 10 | x grain size was uniform The depth of the dense layer of chrome powder was about 0.635 mm (0.025 in.). Then coal powder of 45 μm particle size was sprinkled evenly onto the layer of chrome powder and then heavily compacted; the depth of the compressed carbon powder layer was about 0.254 mm (0.01 in.) The steel plate with the coal and chrome powder was then preheated to 482 ° C (900 ° F) and then the surface at 0.23 m / min (9 in / min) with a local sweeping 14 kW laser beam, using a protective gas shield made of 0.193 m3 / h (7 cu.ft./h) argon and 0.057 mVh (2 cu.ft./h) hydrogen. The size of the laser beam was 2.54 x 12.7 mm (0.1 x 0.5 in.) In a rectangle orm with a long dimension perpendicular to the direction of movement, because the local vibrations took place in this direction. The power density of the laser beam was 43.4 kW / cm2. The vibration frequency was 690 Hz. Under these conditions, the surface of the steel sheet melted and intimately alloyed with the carbon and chrome powder.

Immediately after the laser treatment, the steel sheet was post-treated for half an hour at 482 ° C (900 ° F). Pre and post heating were done in an oven; by

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these measures prevented the melting zone from being torn open.

Fig. 17 shows the concentration of the minority component, chromium, in the finished product. The curve is adapted to the original measuring points according to customary static practice. This curve shows a significant increase in the chromium concentration in the melting zone, which was 1.27 mm (50 mils) deep. The chromium concentration was 21% by weight to a depth of 1.27 mm (50 mil).

18 shows hardness profiles of the finished product after the laser treatment with local decay. A Rockwell hardness of C 53 to C 57 was found in the melting zone, the Rockwell hardness of the steel not detected by the laser was C 20 and the Rockwell hardness in the heat-affected zone C 30.

19 shows hardness profiles in the finished product after the laser treatment with local swinging out, the laser-treated steel plate last being held at 649 ° C (1200 ° F) for two hours and then air-cooled. The Rockwell hardness was C 55 to C 58 in the melting zone and C 25 in the heat-affected zone. The curve in FIG. 21 shows the resistance of the melting zone to high-temperature annealing.

As for the surface treatment methods, the equipment arrangement used and the products obtained, as described above, the treatment time is very short and the space, equipment and costs required are low. The disturbances in the properties of the substrate lying under the treated layer are minimal. Alloys are formed by inserting the minority alloy components into the substrate. The resulting surface layer can be single or multi-phase, as was explained above with reference to FIGS. 6A ... 6D. The surface area of the treatment layer can be continuous or discontinuous. In most cases, it has a concentration gradient of the minority components, the concentration decreasing towards the substrate, but being uniform in area within the gradient at a predetermined depth.

The invention is applicable to ferrous metals and alloys including all types of cast and steel. The element or elements to be inserted into the surface of the metal product can be applied as a powder or powder mixture or as an alloy powder or any suitable composition thereof.

As can be seen immediately, the invention is not limited to alloying the surface layer with a single brushing of the workpiece by the laser beam. After the first pass, further alloy material can be applied to the substrate together with further heat, as described above, in order to further treat the surface layer in the manner specified.

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Claims (8)

618468 2nd PATENT CLAIMS 1. A method for surface alloying a substrate metal, preferably steel or cast iron, characterized in that a layer of one or more alloy components is applied to the metal surface and this is guided along a section-wise straight-line processing path past the beam of a continuously excited laser source, the power density of which is between 8 and 1600 kW / cm2 and which, in cooperation with the displacement speed, melts the layer and a predetermined depth range of the underlying metal along a rectilinear processing path, mixes it and can be solidified again, whereby an alloy layer of the predetermined depth is formed along this path, which over their entire thickness and evenly over the entire treated surface has a composition and properties that differ from those of the underlying substrate metal. 2. The method according to claim 1, characterized in that the laser beam is deflected such that the surface to be treated is successively swept by it along a plurality of straight, laterally adjacent processing paths. 3. The method according to claim 1, characterized in that the laser beam swings back and forth transversely to its processing path while it sweeps over the surface to be treated. 4. The method according to any one of claims 1 to 3, characterized in that the beam is focused on a circle with a diameter between 0.063 and 1.78 cm or on an area of the same size but different shape, the output power of the laser beam between 5 and 20 kW and its displacement speed is between 12.7 and 127 cm / min. 5. The method according to any one of claims 1 to 3, characterized in that the power density of the laser beam is 38.8 and 46.5 kW / cm2. 6. Product of the method according to claim 1, characterized in that the substrate is provided with a metal alloy layer, the main component of which comes from the substrate, the layer over its entire thickness having the structure characteristic of melting and sudden re-hardening of metal and being harder than the substrate and, at a predetermined layer depth, has a constant composition over the treated area. 7. Product according to claim 6, characterized in that it comprises an iron substrate and the layer is an iron alloy. 8. Product according to claim 6, characterized in that the layer thickness is between 127 and 1270 p.