GB2531097A

GB2531097A - Method for treating plate

Info

Publication number: GB2531097A
Application number: GB1508825.5A
Authority: GB
Inventors: Sanders Ronald; Baumgart Hartmut
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2014-05-31
Filing date: 2015-05-21
Publication date: 2016-04-13
Also published as: GB201508825D0

Abstract

A method for treating a plate by applying a pattern formed from a material 6 containing at least one alloying element onto at least one surface of the plate 1. The surface of the plate 1 comprising the pattern is covered by an adequately heat-resistant contacting layer 5 and the plate is then heat treated in order to diffuse the alloying element into the plate 1. The pattern 6 may also be applied to the contacting layer 5. The plate parts (Fig 4, 14) can lie flat upon each other to form a stack (Fig 4, 15) or they can be wound into a coil 5. The pattern may be applied by spraying, intaglio or screen printing. It may also be applied to both surfaces of the plate (Fig 2 3, 7, Fig 4 17, 19). The material 6 can be in the form of a powder containing an alloying element. Heat treatment may take place in an oven or furnace 10 and potentially under vacuum or in an inert atmosphere.

Description

METHOD FOR TREATING PLATE

Description

The present invention relates to a method for treating plate.

Methods for treating plate with the objective of creating plate parts having properties that are locally modified in part regions are known.

Plate parts with locally modified properties can be created by locally alloying-in suitable alloying elements. DE 19650258 Al describes a method for laser-alloying metal parts with alloying components being added in the form of rods or wires. This method is suitable above all for alloying linear regions but not for the uniform alloying of areal regions. In addition, the use of lasers is only economical for modifying minor area components of a plate or component, but not for larger area components.

An object of the invention is to state a method for the cost-effective treating of plates, with which at least a part region with a modified alloying composition is created in any desired location of the plate.

According to a configuration of the invention, the object is solved by a method for treating plate with the steps: a) applying a pattern to at least one surface of the plate, wherein the pattern is formed from a compound containing at least one alloying element, subsequently b) heat-treating the plate in order to diffuse the alloying element into the plate, wherein at least the surface comprising the pattern is covered by a contacting layer of material that is resistant to the heat treatment.

Through the contacting layer, the plate surface is covered and during the heat treatment largely protected from undesirable reactions with the surrounding atmosphere so that elaborate methods for adjusting the atmosphere can be omitted.

s The simplest and most cost-effective way of providing the contacting layer is to likewise use a plate to be treated for this purpose.

During the heat treatment, the plate can be present in the form of a stack of plate parts of the same geometry. Accordingly, the surface of a plate to be treated can be completely covered by an adjacent plate as contacting layer.

In order to minimise the width of a gap between the surface to be treated and the adjacent plate, the plate parts should be plate-shaped. In this way, they can lie flat on one another during the heat treatment.

Alternatively, the plate can be available as a coil during the heat treatment. Accordingly, an outer layer of the coiled plate in each case can form the contacting layer for the inner layer covered by it.

Applying the pattern can be a printing-on of the compound, in particular screen printing. Screen printing is particularly suitable for plate-shaped plate parts.

Applying the pattern can be a spraying-on of the compound. This is practical in particular when working a coil since a spray nozzle that is immovable relative to the passing plate strip or only moveable transversely to the running direction of the plate strip can be used.

The pattern can be applied on both surfaces of the plate. This can be effected by applying the compound onto the front and back side of the plate using the same method in each case such as for example printing on, spraying on or the like.

It is easier to apply the compound onto only a first surface of the plate and to apply the pattern onto the opposite second surface, by bringing this surface into contact with a pattern formed on the contacting layer. In the event that the compound is applied in the form of a paste or suspension which dries or sets on the contacting layer it can be practical to establish the contact with the second surface while the compound is not yet solid, so that they in fact enter into a close contact with the second surface and during the subsequent heat treatment the alloying s element can diffuse into the plate and the contacting layer in equal parts.

The pattern can be congruently applied on both surfaces. If the alloying element is to be diffused in over the entire plate thickness, the heat treatment time can thereby shortened.

Such congruent application can be realised in a simple manner in particular with stackable plate parts in that the compound in each case is applied onto a first surface of each plate part and subsequently the plate parts are congruently layered up into a stack so that the pattern through contact with the compound applied onto an adjacent plate part is applied onto the second surface.

The compound can contain a powder of the at least one alloying element. The compound however can also contain a mixture of powders of multiple alloying elements or powder of an alloy.

Heat treatment can take place in a stationary oven, in particular a bell furnace. Especially with small batches or quantities this is more cost-effective than using continuous ovens.

Heat treatment can take place in an inert gas atmosphere or in a vacuum. The use of inert gas or vacuum is practical in particular when the contact between the plate parts or the windings of the coil is not sufficient to ensure adequate protection of the surfaces of the plate layers located opposite one another against influences of the surrounding atmosphere or when at the edges of the plates or of the coil gaps which are open towards the outside are present between the plate layers.

Further features and advantages of the invention are obtained from the following description of exemplary embodiments making reference to the attached figures. It shows: Fig. I the schematic sequence of the method for a first exemplary embodiment; Fig. 2 a schematic extractive cross section through a coil; Fig. 3 the extract from Fig. 3 following diffusion annealing; Fig. 4 a top view of a plate stack; Fig. 5 a schematic extractive cross section through the plate stack; Fig. 6 the extract from Fig. 5 following diffusion annealing.

Is Fig. I schematically shows various stages of the method according to the invention. In a first stage, shown in the left part of Fig. 1, the plate to be processed is present as a plate stripi wound into a coil 2.

The plate strip in this case consists of low-alloyed aluminium, preferably from an alloying group lxxx, with a plate thickness of 0.5 to 3.5 mm.

However, the method can also be applied to other plates, in particular low-alloyed steel sheets, preferably of an IF-steel and to other material thicknesses.

In its middle part, Fig. 1 shows the plate strip 1 that is partly unwound from the coil 2 and wound up into a new coil 5. Between the coils 2, 5 one or multiple spray nozzles 4 are arranged in order to apply a compound 6 to a first surface 3 (front side) of the strip 1 by spraying on, while said strip 1 is rewound from coil 2 onto coil 5. The spray nozzles 4 can be arranged fixed in location or be movable transversely to the running direction of the plate strip 1. The nozzles 4 are arranged in order to form on the surface 3 a pattern of regions that are covered by the compound 6 and such that are free of the compound 6.

The compound 6 contains at least one alloying element in the form of a powder which, in order to adhere to the surface 3 following the spraying, is suspended in liquid that is mixed with a binding agent if appropriate. If the plate strip I consists of aluminium, the alloying elements can be in particular copper andlor zinc. If it is a steel plate, carbon is also a consideration as alloying element.

The liquid can be volatile in order to at least largely evaporate before s the freshly sprayed surface 3 reaches the coil 5 and further evaporation is prevented in that the compound is closed in between the already existing coil 5 and the surface 3.

However, it can also be provided that the compound 6 for the major part still contains the liquid at the moment of its inclusion on the coil 5so that it continues to be plastic and closely hugs the back side of the plate strip 1 which -when passing under the spray nozzles 4 -is not coated with the compound 6.

Once the entire plate strip 1 has been recoiled into the coil 5 and in the process has been provided with the compound 6, the coil 5 as shown In the right part of Fig. I is subjected to a heat treatment in a bell furnace 10.

According to an alternatively configuration, the spray nozzles are replaced by a roller on which the pattern to be applied is pre-moulded. This pre-moulding can consist in that the roller comprises recesses in a manner known from intaglio printing, which receive the compound 6 coated onto the roller with the help of a doctor blade, while non-recessed surface regions of the roller do not receive the compound and in contact with the strip 1 transfer the compound 6 onto the surface 3 of the same.

While the nozzles 4 are primarily suitable for applying patterns with elements that are elongated in running direction of the plate strip 1. patterns can also be created with the help of the roller which comprise elements that are elongated transversely to the running direction.

In an extractive cross section through the coil 5, Fig. 2 shows the plate strip I with the applied compound 6. An edge region 9 on both edges of the plate strip Us clear of the compound 6. Between these two edge regions 9, the compound 6 can be applied in a manner covering the area.

Although the compound 6 was initially sprayed on or rolled on only on the front side 3 of the plate 1, it is now also in close contact with its back side 7. In this way, the pattern is present on both surfaces 3, 7 of the strip 1.

This method is suitable above all for patterns formed of lines which extend in the direction of the longitudinal edges of the strip 1. By transferring such linear patterns onto the back side 7 of the plate, a congruent pattern is obtained on both plate surfaces 3, 7. Here, the pattern can also consist of multiple lines of any width. It must be noted here that when winding up the plate strip I into the coil 5 the contact of the applied compound 6 with the outside 7 has to be over as full an area as possible since the pattern is otherwise not uniformly transferred onto the outside 7.

During the heat treatment in the bell furnace 10 the coil 5 of aluminium plate provided with the compound 6 is heated up and held a temperature between 200 °C and 600 °C for 10 to 60 in order to achieve diffusing in the alloying elements from the compound 6. In the case of a coil of steel plate, the temperatures must be selected higher, for example between 900 and I lOOt, ideally at 1050 °C.

During this diffusion annealing, temperature curve and time during the heating and holding are dependent on the dimensions of the coil 5 and the plate thickness. If possible these are adjusted so that a complete diffusion of the alloying elements from the compound 6 into the plate I is achieved.

Diffusion annealing can take place under air atmosphere. When the compound 6 or a sealing material applied in a manner similar to the compound 6 tightly seals intermediate spaces between windings of the plate strip I that are adjacent in the coil 5, reactions with the atmospheric oxygen remain restricted to the strip edges and in particular then have no effects on the parts produced from the annealed plate strip when on separating these parts any scaled or otherwise changed strip edges are cut away.

When, as in Fig. 2, along the edge regions 9 no compound 6 is applied and the properties of the edge regions 9 are to be adjusted in a defined manner, interfering reactions with oxygen can be avoided by using an inert gas atmosphere for example nitrogen. In individual cases, heat treatment in vacuum can also be practical.

Fig. 3 shows the extract of Fig. 2 following the diffusion annealing. A concentration increase of the alloying elements relative to the initial state is obtained through the diffusion of the alloying elements from the applied compound 6 into the s plate 1. Because of this, a diffusion region 8 is created in the plate 1. Since the pattern was congruently applied on both surfaces of the strip 3, 7, the diffusion of both plate surfaces 3, 7 takes place simultaneously. In the present example, alloying up in the diffusion region 8 was achieved within the entire plate thickness. By subjecting both plate surfaces 3, 7 to diffusion, the diffusion time compared with one-sided diffusion is shortened. In addition, the alloy concentration can be symmetrically adjusted over the plate thickness.

On the outermost winding of the coil S the compound 6 is applied only on one side. In addition, it is not covered by contacting plate on one side.

Consequently the properties of this winding differ from those of the windings located further inside. In practice, this outer wInding is rejected during the further processing of the coil 5.

The amount of the concentration and the distribution of the alloying elements in the plate determine the achievable strength and hardness increase. In the present example, an increase of strength and hardness in the diffusion region 8 is achieved while the edge regions 9 remain ductile.

In case that the bringing into contact of the still moist compound 6 on the front side 3 of the plate in the coil 5 with the back side 7 of the plate is not suitable in order to satisfactorily transfer the pattern on to the back side 7, the compound 6 can also be congruently applied onto both surfaces 3, 7 of the plate 1.

This can be achieved by congruently spraying or rolling the pattern onto both surfaces 3, 7 of the plate 1 in step Si. Here it can be advantageous to dry the compound 6 before the plate I is wound up into the coil 5. Smudging the compound 6 or undesirable transferring of the pattern onto the contact surface 3 or 7 is thus avoided.

In a second exemplary embodiment, the plate 1 is present as a stack of plate-shaped, flat, unformed plate parts of steel plate. In the first step, the compound 6 is applied onto the plate parts in the form of a pattern. To this end, a each plate part is individually placed into a screen printing machine and printed with the compound 6 on one side. In Fig. 4, one of the removed plate parts 14 is shown which is placed onto a stack 15 with the already printed plate pails 14. As in the first exemplary embodiment, the still moist compound 6 on the printed surface 17 comes S into contact with the unprinted surface 19 (back side). Here it must be noted that the printed plate part 14 preferably has a good contact with the plate part of the stack 15 located below, lying on the same in a congruent manner. In a second step, the plate stack 15 is subjected to heat treatment in a bell furnace 10.

The pattern on the plate part 14 in the top view is evident in Fig. 4. It is formed of differently shaped lines consisting of compound 6. In this exemplary embodiment, no compound 6 is applied in a region along the edges of the plate parts 14. As shown, the pattern can be formed of lines, wherein the lines can also cross or form circles. The pattern can also be formed of areas shaped in any way.

The edge region can also be covered by the pattern.

In an extractive cross section through the plate stack 15, Fig. 5 shows the compound 6 applied onto the plate parts 14. As a consequence of the stacking, the unprinted back side of a plate 14 comes in contact with the still moist compound Son the printed front side 17 of another plate 14, so that the pattern is transferred to the unprinted back side 19. In this way, the pattern is congruently present on both surfaces 17, 19 of the plate pails.

In the second step, the plate stack 15 is subjected to heat treatment in the bell surface 10. In a first step of the heat treatment, the stack 15 is heated up and held at a temperature between 900 °C and 1100 °C for 15 to 60 minutes in order to achieve the carbon from the compound 6 diffusing into the steel plate parts 14. During this diffusion annealing, temperature curve and time during the heating-up and holding are dependent on the dimensions of the stack 15 and of the plate thickness. These are preferentially adjusted so that complete diffusion of the alloying elements from the compound 6 into the plate parts 14 is achieved.

Following this, the plate stack 1&is quenched from the temperature of the diffusion annealing in the known manner. The choice of the quenching medium and of the quenching conditions depends on the steel material and the properties to be achieved.

In a second stage of the heat treatment, the stack 15 is subjected to a tempering treatment in the bell furnace 10. The tempering conditions depend in the known manner from the steel material and the properties to be achieved.

S Temperature curve and time during the heating-up and holding are dependent on the dimensions of the stack 15 and on the plate thickness.

Diffusion annealing and tempering treatment can take place under air atmosphere. Reactions with the atmospheric oxygen occur in particular along the edges of the plate parts 14 as explained above. If the properties of the edges resulting from this are unimportant since the edges are for example trimmed later on, air atmosphere can be utilised. If, as in Fig. 5, along the edge no compound 6 is applied and the properties of the edges are to be-adjusted in a defined manner, interfering reactions with oxygen can be avoided by using an inert gas atmosphere, for example nitrogen. In individual cases, heat treatment in vacuum can also be practical.

Fig. 6 shows the extract from Fig. 5 following diffusion annealing. An increase in concentration of the alloying elements relative to the initial state is obtained through the diffusion of the alloying elements from the applied compound 6 into the plate 14. Because of this, a diffusion region 18 is created in the plate 14.

Since the pattern was congruently applied onto both surfaces 17, 19 of the plate parts, both plate surfaces 17, 19 are simultaneously subjected to diffusion. In the present example, alloying up was achieved in the diffusion region 18 within the entire plate thickness. By subjecting both plate surfaces 17, 19 to diffusion, the diffusion time relative to one-sided diffusion is shortened. In addition, the alloy concentration can be symmetrically adjusted over the plate thickness.

Both exemplary embodiments are not restricted to the stated materials and alloying elements.

It is to be understood that the above detailed description and the drawings represent certain exemplary configurations of the invention but that these are only intended for explanation and should not be interpreted as being restrictive 3$ of the scope of the invention. Various modifications of the described configurations are possible without leaving the scope of the following claims and their equivalents range. In particular, this description and the figures also present features of the exemplary embodiments which are not mentioned in the claims. Such features can also occur in combinations other than those specifically disclosed here. The fad that multiple such features are mentioned together in a same sentence or in another type of context does not therefore justify the conclusion that they can only occur in the specific combination disclosed; instead it must always be assumed that of multiple such features individual ones can also be omitted or modified provided this does not put the functionality of the invention in: question.

Reference List 1 Plate strip 2 Coil 3 Front side 4 Nozzle Coil 6 Compound 7 Backside 8 Diffusion region 9 Edge region Bell furnace 14 Plate part Stack 17 Front side 18 Diffusion region 19 Back side

Claims

Patent Claims 1. A method for treating plate with the steps: a) applying a pattern onto at least one surface of the plate (1, 14), wherein the pattern is formed from a compound (6) containing at least one alloying element, subsequently b) heat treating of the plate (1 14) in order to diffuse the alloying element into the plate (1, 14), wherein at least the surface (3, 17) comprising the pattern is covered by a contacting layer of material that is resistant to the heat treatment.
2. The method for treating plate according to claim 1, wherein the contacting layer is likewise plate (1, 14) to be treated.
3. The method for treating plate according to any one of the preceding claims, wherein the plate (14) during the heat treatment is present in the form of a stack (15) of plate parts (14) of the same geometry.
4. The method for treating plate according to claim 3, wherein the plate pans (14) are plate-shaped and during the heat treatment lie flat on one another.
5. The method for treating plate according to any one of the claims I or 2, wherein the plate (1) during the heat treatment is present as a coil (2).
6. The method for treating plate according to any one of the preceding claims, wherein applying the pattern is a printing on of the compound (6), in particular intagilo or screen printing.
7. The method for treating plate according to any one of the claims I to 5, wherein applying the pattern is a spraying on of the compound (6).
8. The method for treating plate according to any one of the preceding claims, wherein the pattern is applied onto both surfaces (3, 7; 17, 19) of the plate (I, 14).
9. The method for treating plate according to claim B, wherein applying is a bringing into contact of the surface (7:19) with the pattern formed on the contacting layer.
10. The method for treating plate according to any one of the preceding claims, wherein the pattern is congruently applied onto both surfaces.
11. The method for treating plate according to any one of the preceding claims, wherein the compound (6) contains a powder of the at least one alloying element.
12. The method for treating plate according to any one of the preceding claims, wherein heat treating takes place in a stationary oven, in particular a bell furnace (10).
13. The method for treating plate according to any one of the preceding claims, wherein the heat treatment takes place in an inert gas atmosphere or in vacuum.