WO2015044120A1

WO2015044120A1 - Method for the hot forging of a seamless hollow body of material that is difficult to form, in particular of steel

Info

Publication number: WO2015044120A1
Application number: PCT/EP2014/070208
Authority: WO
Inventors: Rolf Kümmerling; Antonio Sergio Medeiros Fonseca; Thomas Schlothane; Robert Koppensteiner; Rupert Wieser
Original assignee: Vallourec Deutschland Gmbh; Gfm Gmbh
Priority date: 2013-09-25
Filing date: 2014-09-23
Publication date: 2015-04-02
Also published as: EP3049200A1; BR112016003146B1; CN105592954A; EP3049200B1; DE102013219310A1; BR112016003146A2; CN105592954B

Abstract

The invention relates to a method for the hot forging of a seamless hollow body of material that is difficult to form. It is proposed that the hot forging is performed with a degree of forming, with respect to the cross section to be formed, in the forging section with ln(AO/A1) of less than 1.5 and a method-related form changing rate of less than 5/s, where AO is defined as the local cross-sectional area of a hollow body to be forged in m² and A1 is defined as a local cross-sectional area of the finished hollow body in m² and the form changing rate is defined as the maximum rate of the hollow body to be forged in m/s with respect to the outside diameter of the finished-forged hollow body in m.

Description

Method for hot forging a seamless hollow body from heavy

deformable material, in particular steel

The invention relates to a method for hot forging a seamless

Hollow body made of difficult to deform material, in particular of steel, according to the preamble of claim 1. In particular, the invention relates to a produced by hot forging tube made of a difficult to deform material.

After the invention of the brothers Mannesmann from a heated block to produce a thick-walled seamless hollow block pipe, there have been various proposals to stretch this hollow block pipe in the same heat in another hot work stage. Key words are the well-known Kontiwalz-, Stoßbank-, Stoppfenwalz- and Pilgerschrittverfahren. All the above methods have different dimensions and dimensions

Materials their advantages, whereby there are also overlaps. For the medium size range from 5 "to 18", the continuous and plug rolling process is used, for the size range up to 26 "the pilgrim stepping method is used.With thicker walls in the range of> 30 mm, the continuous and stopper rolling process are less suitable, while the pilgrimage process is has no wall thickness problems, but is slower in the production cycle.

Characteristic of the production of seamless tubes from a heated block by hot rolling are the three steps punching - stretching - reducing rolls.

The disadvantage of all these methods are the more or less long

Changeover times for dimensional changes and high production costs for small batches that require frequent retooling. With the method disclosed in the international patent application WO 2006/045301 A1, these disadvantages have been eliminated, in which the hitherto known second and third forming step characterized by rolling (draw rolls and

Reduzierwalzen) is replaced by a forming step in the form of a

Radialschmiedeprozesses using an inserted into the hollow block inner tool and at least two on the lateral surface of the hollow block acting forging jaws a forging machine, wherein the hollow block clocked in the phase of the idle stroke of the forging jaws is rotated and moved axially. Depending on the type of control, the rotation and the axial feed of the hollow block can take place simultaneously or with a time offset.

With this method, which is very efficient and is also of interest for small lot sizes, tubes with a circumference of more than 500 mm and lengths of more than 4000 mm can be produced very advantageously. However, it has been shown that the method is not optimally designed for the forging of difficult-to-form materials. Under hard-workable materials, metallic materials, especially steels, understood that at the forming temperature, ie the forging temperature, a yield point of more than 150 MPa determined at 0.3 logarithmic strain and a

Have a rate of deformation of 10 / s. By way of example, these are steels with chromium contents of more than 5.0% by weight, duplex steels, nickel-base alloys or refractory metals.

Usual forging temperatures are depending on the material to be forged at least 70% of the respective melting temperature of the material. By way of example, the forging temperature of the Inconel 718 material is at least 850 ° C.

During forging can be difficult to form materials due to the very high forming forces applied after a short time to abrasive wear and caking on the formed as a forged mandrel inner tool or hot welding of the inner tool with the

Hollow block come. This leads either to a termination of the forging process or at least to faulty inner pipe surfaces and a significantly shorter service life of the forging mandrel. As a result, the efficiency of the forging process is significantly restricted in difficult-to-form materials.

International patent application WO 2009/006873 A1 discloses a forging mandrel made of a heat-resistant material for hot forging tubes with high wear resistance and high dimensional stability, in which the mandrel body has a layer which reduces the heat input into the mandrel body and which has a Thermal conductivity has significantly lower than that of the mandrel body. Due to the lower heat input into the mandrel main body remains this

dimensionally stable and wear-resistant. In addition, the forge can be a

Have internal cooling for cooling during forging or the

Blacksmith's mandrel is cooled externally between forging operations. Of the

Mandrel body is on a support rod, also called mandrel, attached, with the mandrel body in the phase of the idle stroke in the hollow block can be moved axially or rotated. With the known forging method and the well-known forging mandrel, however, sufficiently long service life of the forging mandrel and consistently high quality of the inner surface of the tube can not yet be ensured in materials which are difficult to form. Furthermore, German Patent Application DE 10 2012 107 375 A1 already discloses a device for forging a hollow body with forging tools arranged centrally and symmetrically about a forging axis. To increase the service life of the forging mandrel, it is provided that a rotary drive can be controlled via a control device as a function of the rotational position of the forging mandrel relative to the forging tools.

The object of the invention is an improved method for producing a seamless hot-finished metallic hollow body by hot forging

This is also the case when forging difficult-to-form materials with a yield point at a forming temperature of more than 150 MPa at 0.3

logarithmic expansion and a rate of deformation of 10 / s, realized a high quality of the inner surface of the hollow body with improved service life of the forging mandrel. This object is based on the preamble in connection with the

characterizing part of claim 1 solved. Advantageous developments are the subject of dependent claims. According to the teachings of the invention, this object is achieved by a method for hot forging a seamless hollow body made of difficult-to-form material, in particular steel, having a yield point at forming temperature of more than 150 MPa determined at 0.3 logarithmic strain and a

Forming rate of 10 / s by means of hot forging, which is characterized in that the hot forging is carried out with a forming degree in the forged section with ln (A0 / A1) of less than 1, 5 and a process-related strain rate of less than 5 / s, A0 as a local cross-sectional area of a hollow body to be forged in m ² and A1 as a local cross-sectional area of the finished hollow body in m ² and the

Deformation rate as maximum speed of the hollow body to be forged in m / s based on the outer diameter of the finished forged hollow body in m are defined. The service life of the forging mandrel can advantageously be improved by using a forging mandrel made of a material having a strength of at least 700 MPa at 500 ° C.

Advantageously, hot forging is characterized by the fact that the hollow body located at the forging temperature has a forging mandrel attached to a mandrel as an internal tool, by means of a forging axis arranged symmetrically and drivable in the radial strokes acting on the shell surface of the hollow body and the forging mandrel

Schmiedebacken a forging machine is formed into a tube with a tube circumference of on average at least 500 mm and a length of at least 4000 mm, the hollow body clocked in the phase of the idle stroke of the

Forging jaws turned and moved axially.

The proposed method has the advantage that now hollow body made of difficult to transform materials with optimum inner surface can be produced economically, at the same time significantly increased service life of the forging mandrel.

It has surprisingly been found in experiments that the relative to the reshaped cross section degree of deformation and the process-related strain rate during forging in combination with a heat-resistant mandrel material are the quality and durability determining quantities, the specified limits for the degree of deformation and the rate of deformation are to be adhered to the local adiabatic

Heating and shear banding, material flow instabilities and local

Material overstresses that show up as cracks can be reliably avoided.

The proposed forging process is particularly effective and qualitatively favorable if, depending on the pipe diameter to be forged, two, four or more forging jaws are used, which act in a plane synchronously on the lateral surface of the hollow block.

The inserted as an internal tool in the hollow block forging mandrel can in principle be arranged freely movable in the hollow block. For better distribution, in particular the thermal load, but it is advantageous to rotate the forging mandrel in the phases of idle strokes and / or to move in the same direction or opposite to the axial feed of the hollow block.

It is particularly advantageous if the forging mandrel is rotated by means of a controller or a controller and / or moved in the axial direction, because it is then possible to specifically homogenize the thermal and mechanical load of the forging mandrel. The axial mandrel speed is either constant or variable.

In order to achieve the goal of the most even heat distribution in the forging mandrel, the rotation of the forging mandrel should be so large that in the following forging stroke the loads act on a region of the forging mandrel, which were without or with little impact in the previous forging. In this case, the direction of rotation of the forging mandrel can be selected equal to or different from the direction of rotation of the hollow block. An unequal direction of rotation is advantageous, since thereby the relative movements between the surfaces of

Forging mandrel and hollow block are larger and thus heat welding of the workpiece with the forging mandrel can be better prevented.

Optionally, according to the invention, the forging mandrel may additionally be provided with a coating consisting of a ceramic, for example Tungsten carbide, and having a layer thickness of at least 0.02 mm and a maximum of 0.2 mm has a surface hardness of at least 900 HV0.1 at room temperature. It is known that mandrels have a coating for thermal insulation. However, the coating according to the invention relates to a tribologically acting layer, which by its thickness in the area mentioned both the necessary

However, abrasion resistance also achieves heat welding of the hollow block on

Blacksmith's mandrel obstructed. The layer is still thin enough to do so

To avoid spalling of the coating due to the different thermal expansion compared to the base material under the thermal cyclic load.

Especially in the case of large degrees of stretch (> 4) and small wall thickness (<30 mm), in the case of materials which are difficult to form to avoid hot welding, it may still be necessary to place in the forging process before starting the forging process

Forming zone between forging mandrel and hollow block a separating and / or

Lubricant is introduced.

Here, the release agent and / or lubricant may be applied to the inside of the hollow block before the start of the radial forging process and / or the

Forging mandrel is lubricated at least in the area of the forging jaws acting on it before or during forging.

If the release and / or lubricant applied to the inside of the hollow block, should, in order to achieve a sufficient effect on the

Inner surface of the hollow block amount of not less than 40 g / m ² .

Furthermore, it may be advantageous for equalizing the thermal load when the forging mandrel makes an alternating forward and backward rotation relative to the workpiece. In particular, it turns out that at a same

Direction of rotation of the forging mandrel and the hollow block of the forging mandrel a twice as high rotation step between the Umformhüben is advantageous than uneven direction of rotation. This is because the contact surface of the forging jaw and thus the contact surface on the mandrel is always slightly asymmetrical to the longitudinal axis of the forging jaw and thus the lubricant is more easily pressed into the incoming zone and stripped from the mandrel. This is at the same direction of rotation significantly larger (about twice as large) rotation step of the mandrel necessary to bring the release agent and / or lubricant in the forming zone.

Due to the asymmetry mentioned, positioning and controlling the mandrel not only relative to the hollow block, but also relative to the forging plane to equalize the thermal load of importance.

In an advantageous development of the invention, the minimum turning step of the forging mandrel in the idle stroke phase should satisfy the following condition: min DSD = 0.32 x DSH, where min DSD is the minimum turning step in angular degree of

Forging mandrel and DSH is the turning step in angular degree of the hollow block. It has been found that the width of the contact zone of the forging mandrel is significantly lower than that of the forge. Falling below the above limit leads to investigations on massive thermal stresses on the mandrel, which usually lead to plugs and thus to a failure of the process.

Increasing the mandrel rotation beyond the minimum reduces the

Overlap of the mandrel contact zones between two forming strokes or completely avoids overlapping. This homogenizes the thermal load on the circumference and it can get more new release / lubricant in the forming zone between mandrel and workpiece.

In the experiments it has also been found that the forging mandrel is thermally stressed by two influences before contact during forging. On the one hand by the radiation load through the warm workpiece and on the other hand by the introduced in the contact zone with the forging mandrel amount of heat. This flows axially in the forging mandrel into those areas of the mandrel that were not yet in contact with the hollow block. If these mandrel areas then enter the forming zone, the contact and thus surface temperatures are higher than in the mandrel areas, which were previously forged. The thermal loads can be adjusted by the variability of the mandrel speed such that equalization of the introduced heat sufficiently reduces the maximum temperature of the mandrel surface to prevent plastic deformation or premature wear of the forge mandrel. The average mandrel speed should satisfy the following conditions GDmin <GD <GDmax, where GDmin = GEx (HL / DL) and GDmax = GAx (HL / DL), where DL = mandrel length in m, HL = hollow block length in m, GD = mean absolute velocity of the mandrel in m / s, GE = inlet velocity of the mandrel

Hollow blocks in the forging machine in m / s and GA = discharge speed of the hollow block into the forging machine in m / s.

In a further advantageous embodiment of the invention, the forging mandrel can be solid or designed as a hollow body.

In a further advantageous embodiment of the invention it is provided that the forging mandrel during the forging from the inside and / or between the

Forging is cooled from the outside to further reduce the thermal load.

In order to ensure sufficient mechanical stability in the forging of difficult-to-form materials, even with hollow bodies as a forging mandrel, the wall thickness should be at least 9% for an internal cooling and at least 15% of the outside diameter of the forging mandrel for external cooling.

In order to ensure adequate cooling of the forging mandrel in the case of internal cooling, the forging mandrel should advantageously have a minimum length that is dependent on the outside diameter of the hollow block and the forged tube and is calculated as follows: L min = (ADH-ADF) / TAN (20 × PI / 180) with ADH =

Outer diameter hollow block in m, ADF = outer diameter forged tube in m and Lmin is the minimum working length of the mandrel in m.

In the case of external cooling of the forge - mandrel during forging breaks, the forging mandrel should have a length calculated as follows:

Hollow block length in m, MH = mass of the hollow block in kg and MD =

Heat-absorbing mandrel mass in kg.

In a further advantageous embodiment of the method, it is provided that forging a forging mandrel is used, which has a conicity of at least 1: 1000, with the larger diameter at the mandril end of the Forging mandrel. Compliance with the specified conicity is necessary because the forged workpiece cools behind the forming zone such that a

Shrinking the forged part at the spine relative moving and

Peel off the spine would prevent.

Furthermore, the use of a slightly conical forging mandrel increases the clearance between the forged finish tube and the inner tool, so that the deduction of the finished tube is facilitated by the inner tool. However, the conicity must be low, otherwise the wall thickness over the length seen in

would change in an improper way.

A further advantageous embodiment of the invention therefore provides that in terms of compliance with the tolerance requirements for inner or outer diameter and wall thickness of the hollow body, which by the conicity of

Forging mandrel diameter conditional geometric deviation of the hollow body during forging is compensated by adjusting the stroke of the forging hammers.

In order to ensure a trouble-free method of forging mandrel in the hollow block is also provided according to the invention that a forging mandrel is inserted into the hollow block whose diameter was chosen so that a game between hollow block and forging mandrel adjusts, which satisfies the following condition: min SP = 0 , 0012 x (1 + HL), where min SP, that minimum game in the

Diameter between forging mandrel and hollow block in m and HL represent the length of the hollow block in m.

The inner diameter and the inner contour over the length of the forged hollow body are determined essentially by the geometry of the inner tool, preferably in the form of a cylindrical dome.

With the method according to the invention can be with a corresponding

Forming of the forging tools and / or a special control of the strokes of the forging hammers and the axial movements of the forging mandrel in addition to outside and inside round tubes also produce axisymmetric tubes, for example, as rectangular or square hollow body, even the used hollow block may have a corresponding geometry, so that the necessary forming work during forging of the finished part can be reduced to a minimum. Furthermore, the cross sections of both the hollow block used and the forged hollow body can change over the length.

By way of example, the use of a diameter-graduated dome is conceivable with which, for example, stepped or / and conical cylinders with thickened ends can be produced over the length. Depending on the type of gradation and the production of several stepped cylinder from a hollow block would be possible. The

Separation of the cylinder would then take place after the forging process.

In a further advantageous embodiment of the invention, it is provided that the hollow block is not formed as a hollow body open on both sides, but on one side has a bottom. This results in comparison to a hollow body open on both sides to a performance improvement in forging and is also advantageous if the finished part should also have a bottom.

The finished forged hollow body is after the usual adjustment steps, such as cutting to length, visual inspection, marking, etc. either immediately deliverable or is still subjected to a heat treatment and / or non-destructive testing. The heat treatment may be normalizing or tempering. Depending on the straightness requirement, straightening is required. Likewise, with appropriate delivery requirements, over-sanding or other suitable chip removal of the outer surface may be necessary to eliminate the small bumps caused by the forging process.

Based on schematic representations, the inventive method will be explained in more detail.

Show it:

Figure 1 shows the inventive method in a schematic representation, im

Longitudinal section with an engaged hollow block and

2 shows a section in the direction A - A in Figure 1. 1 shows the method according to the invention in a schematic representation in a longitudinal section with a hollow block 1 to be forged having an initial cross-sectional area AO, which enters the forging machine from the left and leaves the forging machine on the right as a ready-to-use tube 2 with a local cross-sectional area A1.

The forging takes place with a degree of deformation in the forging section in the forged section with ln (A0 / A1) of less than 1/5 and a process-related rate of deformation of less than 5 / s, the rate of deformation being the maximum tool speed in m / s relative to the outer diameter of the finished forged hollow body is defined in m.

In the forging area on the outside in this embodiment, four forging jaws 3, 3 ', 3 ", 3"' and on the inside a cylindrical forging mandrel 4 together. The forging mandrel 4 is made of a material having a strength of at least 700 MPa at 500 ° C and is held in place by a support rod 5, but may alternatively be axially moved back and forth during the forging process and / or rotated. The direction of rotation of the forging mandrel can be in the direction of rotation of the hollow block or opposite.

Not shown is the means for controlling the mandrel or hollow block movement and for the lubrication of the forging mandrel 4. In the present example, the forging mandrel 4 is designed as a solid body with a taper of more than 1: 1000 and is cooled only from the outside.

The rotary arrow 6 and the axial arrow 7 are intended to illustrate that during the

Leerhubes the forging jaws 3 to 3 "', the hollow block 1 is rotated and pushed further axially and the forging mandrel can also be rotated and moved axially.

Each forging jaw 3 to 3 "'has in longitudinal section a predominantly conically shaped inlet section 8 and a subsequent smoothing section 9. The inlet section 8 can also be slightly convexly curved. As seen in cross-section (see Figure 2), all the forging jaws 3 to 3 "'have a concave curvature, as a rule, the curvature is a circular arc whose radius is greater than the current radius of the part to be forged.

The movement arrows 10 shown in FIGS. 1 and 2 are intended to illustrate the radial stroke of the respective forging jaw 3 to 3 "'.

LIST OF REFERENCE NUMBERS

1 hollow block

2 ready to use pipe

3, 3 ', 3 ", 3"' forged brick

4 thorn

5 handrail

6 rotary arrow

7 axial arrow

8 inlet section

9 smoothing part

10 motion arrow

A0 local cross-sectional area hollow block A1 local cross-sectional area finished tube

Claims

Patent claims

1 . Method for hot forging a seamless hollow body made of material that is difficult to form, in particular made of steel, having a yield point at a forming temperature of more than 150 MPa determined at 0.3 logarithmic strain and a rate of change of 10/s by means of hot forging, characterized in that the hot forging with a degree of deformation in the forging section based on the cross section to be formed with ln(A0/A1) of less than 1.5 and a process-related deformation rate of less than 5/s, where A0 is the local cross-sectional area of a hollow body to be forged in m ² and A1 is the local cross-sectional area of the finished one Hollow body in m ² and the rate of deformation as the maximum speed of the hollow body to be forged in m / s based on the outer diameter of the finished forged hollow body in m are defined.

2. The method according to claim 1, characterized in that a forging mandrel made of a material with a strength of at least 700 MPa at 500 ° C is used.

3. The method according to claim 1 or 2, characterized in that the on

Forging temperature hollow body with a forging mandrel inserted therein attached to a mandrel rod as an internal tool, by means of symmetrically arranged around a forging axis and drivable in the sense of radial working strokes, acting on the outer surface of the hollow body and the forging mandrel

Forging jaws of a forging machine are formed into a tube with an average tube circumference of at least 500 mm and a length of at least 4000 mm, the hollow body being clocked in the phase of the idle stroke

Forging jaws are rotated and axially displaced.

4. The method according to claim 3, characterized in that the forging mandrel moves freely with the hollow block in the phase of the idle stroke.

5. The method according to claim 3, characterized in that the forging mandrel is additionally rotated and / or axially moved in the phase of the idle stroke.

6. The method according to claim 5, characterized in that the forging mandrel is moved in the same direction as the axial feed of the hollow block during forging.

7. The method according to claim 5, characterized in that the forging mandrel is moved in the opposite direction to the axial advance of the hollow block during forging.

8. Method according to one of claims 5 to 7, characterized in that the travel speed of the forging mandrel is kept constant in the axial direction or is set variably.

9. The method according to claim 8, characterized in that the average axial mandrel speed satisfies the following conditions:

GDmin < GD < GDmax, where GDmin = GE x (HL/DL) and GDmax = GA x (HL/DL), with DL = mandrel length in m, HL = hollow block length in m, GD = average

Absolute speed of the mandrel in m/s, GE = inlet speed of the

Hollow block in forging machine in m/s and GA = outlet speed of the hollow block in forging machine in m/s.

10. The method according to one of claims 5 to 9, characterized in that the forging mandrel is rotated and / or moved in the axial direction by means of a control or regulation during the idle stroke.

1 1. The method according to claim 10, characterized in that the forging mandrel is rotated so far during the idle stroke that in the following forging stroke the forging jaws act on an area of the forging mandrel on which the forging jaws had little or no influence in the previous forging stroke.

12. The method according to claim 10 and 1 1, characterized in that the forging mandrel is rotated in the same or unequal direction to the direction of rotation of the hollow block.

13. The method according to claim 12, characterized in that the forging mandrel performs an alternating forward and backward rotation in relation to the hollow block.

14. The method according to one of claims 5 to 13, characterized in that the rotation step of the forging mandrel (angular degree) in the phase of the idle stroke satisfies the following condition: min DSD = 0.32 x DSH, where min DSD is the minimum rotation step of the forging mandrel and DSH is the rotation step of the hollow block.

15. The method according to any one of claims 1 to 14, characterized in that the forging mandrel during forging from the inside and / or between the

Cooled from the outside during forging processes. 16. The method according to claim 15, characterized in that at one

Internal cooling of the forging mandrel has a minimum length, which is calculated as follows: L min = (ADH-ADF)/TAN(20 x PI/180) with ADH= outer diameter of hollow block in m and ADF= outer diameter of forged in m. 17. Method according to one of claims 1 to 16, characterized in that the forging mandrel is designed as a hollow body, the wall thickness being at one

Internal cooling is at least 9% and with external cooling at least 15% of the outer diameter of the forging mandrel. 18. The method according to claim 15, characterized in that at one

External cooling, the forging mandrel has a minimum length, which is calculated as follows: HL = hollow block length in m, MH = mass of the hollow block in kg and MD = heat-absorbing mandrel mass in kg 19. Method according to one of claims 1 to 18, characterized in that for For forging, a forging mandrel is used which has a taper of at least 1:1000 over its length, with the larger diameter at the end of the forging mandrel on the mandrel rod side.

20. The method according to claim 19, characterized in that with regard to compliance with the tolerance specifications for inside or outside diameter and

Wall thicknesses of the hollow body, which are due to the conicity of the

Geometric deviation of the hollow body caused by the forging mandrel diameter is compensated for during forging by adjusting the stroke of the forging hammers.

21. The method according to one of claims 1 to 20, characterized in that for forging, a forging mandrel is inserted into the hollow block, the diameter of which is selected so that there is play between the hollow block and

Forging mandrel sets which meets the following condition: min SP = 0.0012 x (1 + HL), where min SP represents the minimum play in the diameter between forging mandrel and hollow block in m and HL represents the length of the hollow block in m.

22. The method according to any one of claims 1 to 21, characterized in that before the start of the forging process in the forming zone between the forging mandrel and

Hollow block a release agent and / or lubricant with a dry amount of at least 40 g / m ² based on the inner surface of the hollow block is applied.

23. The method according to claim 21, characterized in that a separating and / or on the inside of the hollow block before the start of the radial forging process

Lubricant is applied.

24. The method according to claim 21 and 23, characterized in that the

Forging mandrel is provided with lubrication at least in the area of the forging jaws acting on it before and / or during forging.

25. The method according to any one of claims 1 to 24, characterized in that a wear-reducing coating is additionally applied to the forging mandrel before the forging operation.

26. The method according to claim 25, characterized in that the coating consists of a ceramic.

27. The method according to claim 26, characterized in that the ceramic

Tungsten carbide is.

28. The method according to any one of claims 25 to 27, characterized in that the coating is applied to the forging mandrel with a thickness of at least 0.02 mm and a maximum of 0.2 mm and with a surface hardness of at least 900 HV0.1 at room temperature.