EP0761826B1 - Method for manufacturing ODS seamless pipes - Google Patents

Description

The invention relates to a method for producing seamless tubes Materials according to the preamble of claim 1, which by mechanical deformation in combination with a recrystallizing heat treatment a strongly stretched coarse grain structure form.

Such materials are dispersion-strengthened metals, metal alloys or intermetallic phases due to their excellent mechanical Properties at high temperatures, especially for thermal and mechanically highly stressed components are used. An important Group of these materials are the so-called ODS super alloys Iron, nickel or cobalt based, in which oxide particles are used as dispersoids be used. The ODS superalloys expand that Temperature range from heat-resistant materials to around 1350 ° C.

All these materials have in common that they are their good ones High temperature properties, especially their good creep resistance, through the Achieve an elongated coarse grain structure. For training this coarse grain structure must be the materials with a high degree of deformation are mechanically formed and a subsequent annealing treatment for Be subjected to recrystallization. Through this directional recrystallization the materials show a fair amount depending on the alloy and the type of production pronounced directional dependence of the mechanical properties, for example the high temperature creep resistance. The best Strength properties are always in the direction of the main forming direction, that is, observed parallel to the extension of the structure. In the directions orthogonal to So far, these materials have only shown this main forming direction comparatively unfavorable strength values at high temperatures.

The largest mechanical pipe is inside Stress in the circumferential direction. The material stress in The circumferential direction is twice as high as that in the pipe longitudinal direction. For Inner pressure pipes that are exposed to high temperatures are available therefore the materials mentioned with an elongated coarse grain structure then if it is ensured that the high structural extension in Pipe circumferential direction is set to the heat resistance potential of this Make full use of materials.

So far, seamless tubes made from the materials mentioned, for example by deep hole drilling from bar material or by hot extrusion with or without subsequent cold reduction, such as pipe drawing or Pipe pilger step rollers manufactured. The disadvantage of these methods, however, lies in that the main forming direction lies in the axial direction of the tube and hence the strong structural extension or structural orientation in this Direction is the highest with a relatively low strength claimed pipe circumferential direction is connected.

In "Development of Ferritic ODS Tubes for Heat Exchangers Operating Above 1100 ° C", B. Kazimierzak, JM Prignon et al., "Structural Applications of Mechanical Alloying", ASM, Ohio (1990), pages 137-145, a hot extrusion process is disclosed Manufacture of seamless pipes from ODS materials described, which show the desired elongated structure in the pipe circumferential direction.
A disadvantage of this method is that its successful application depends on a large number of parameters. The process, especially the temperature control, must be controlled within very narrow limits in order to obtain the grain stretching in the circumferential direction in a reproducible manner. This makes the process complex and expensive.

In addition, the process limits the pipe formats that can be generated via the maximum available pressing forces of industrial extrusion presses both strongly up as well as down. The main disadvantage of this However, the method is that only relatively thick-walled tubes are produced can what for pipes in Tube bundle heat exchangers or simply for reasons of increased Material costs, despite the optimized structure, often no technical or economically satisfactory pipe manufacturing allowed. Today, hot extrusion can be used with or without downstream cold processing process tubes with outside diameters Produce between 25 and 40 mm with wall thicknesses between 2.5 and 5 mm.

The object of the present invention is to provide a method for the production of seamless pipes from ODS materials, in which a strongly stretched structure in Pipe circumferential direction is oriented, which is a good simple Reproducibility of these microstructures guaranteed and with that too thin-walled pipes with wall thicknesses below 2.5 mm over a large one Diameter range can be produced.

The object is achieved by a method according to claim 1.

The cup-shaped or tubular starting part is on a conventional press on a mandrel and by means of a or preferably several spinning rollers in one or more overflows in the Outside diameter reduced. This reduces the wall thickness and at the same time increases the length of the outlet cup or outlet sleeve, which creates a tubular body. In this way, pipes are with Wall thicknesses between 0.3 and 2.5 mm and diameters in the range from 20 to 450 mm producible.

The kinematics of the cylinder pressure rolling process is such that the material flow takes place almost exclusively in the axial direction during the forming. To parts The tangential must be obtained with an inside diameter that is as accurate as possible Material flow (material flow in the pipe circumferential direction) by coordinating the Dimensions of the output part on the pressure rollers used and Number of overflows can be reduced to a minimum.

It was completely surprising to the person skilled in the art that despite the fact that the material flow in the cylinder pressure rolling mainly in the axial direction takes place, the tubes which are produced by the method according to the invention become an elongated coarse grain structure after recrystallization annealing have, which runs in the pipe circumferential direction. This is done through simple Application of the cylinder pressure rolling within the known Process limits without the use of additional or without complex Optimization of individual process parameters achieved, so that a good one Reproducibility of the pipes by the method according to the invention is guaranteed.

The inventive method also has the advantage that high Cross-sectional reductions per pass rolling pass as well as high Total cross-sectional decreases without heating and without Intermediate annealing steps can be achieved. This was particularly the case with Application of the process is not expected for ferritic ODS materials, since these materials show a brittle-ductile transition behavior, so that such Forming materials usually always at least 60 - 100 ° must be preheated to ensure crack-free parts after forming to surrender. The fact that the inventive method practically in all Materials can be applied at room temperature without the workpiece and mandrel need to be preheated, there is one economical production and excellent reproducibility of the pipes. The good reproducibility affects both the good dimensional accuracy as well the metallurgical quality with regard to that stretched in the pipe circumferential direction Coarse grain structure after recrystallization annealing.

In addition to recrystallization annealing, you can choose between individual Deformation steps also intermediate annealing in the form of relaxation or Recuperation glows are inserted.

In particular, the oxides of one or several metals from the group yttrium, aluminum, lanthanum, cerium and zircon proven.

A variant of a material that can be used according to the invention is that solidifying particles in the material so that the material reactive metallic additives are added during processing of the material and / or during a heat treatment in the corresponding oxide, nitride or carbide particles are converted.

In particular, those based on iron, nickel or cobalt have proven themselves as metal alloys.
Those with the composition have been found to be iron-based alloys
6-30% by weight Cr, 0-10% by weight Al, 0-2% by weight Ti,
0-10% by weight Mo, 0-10% by weight W, 0-10% by weight Ta, 0.1-2% by weight of one or more oxides from the group Y, Al, La, Ce and Zr, as well as Fe as the balance and as nickel-based alloys those with the composition 6-38% by weight Cr, 0.1-7% by weight Al,
0-2% by weight Ti, 0-5% by weight Mo, 0-5% by weight W, 0-5% by weight Ta, 0.1-2% by weight of one or more oxides from the group Y, Al, La, Ce and Zr, and Ni as the rest, in particular proven.

In the following, the invention is illustrated by examples and figures explains:

Figur 1

Querschliff von einzelnen Abschnitten des nach Beispiel 1 hergestellten Rohres in 16-facher Vergrößerung

Figur 2

Querschliff von einzelnen Abschnitten des nach Beispiel 2 hergestellten Rohres in 16-facher Vergrößerung

Show it:

Figure 1

Cross section of individual sections of the tube produced according to Example 1 in 16-fold magnification

Figure 2

Cross section of individual sections of the pipe produced according to Example 2 in 16-fold magnification

EXAMPLE 1:

Mechanical alloying was carried out in the sequence of steps from an ODS alloy with the chemical composition 19% by weight Cr, 5.5% by weight Al, 0.5% by weight Ti, 0.5% by weight Y ₂ O ₃ and the rest of Fe the powder raw materials, hot isostatic compression of the powders, subsequent hot forming by round forging, drilling the forged cylinder and finally overturning the inner and outer jacket surfaces, a sleeve-shaped blank with an inner diameter of 60 mm and a wall thickness of 5 mm was made. This blank was formed on a conventional 3-roll CNC spinning machine in only two overflows with the same inside diameter from the initial wall thickness to an end wall thickness of 1.25 mm. The pipe manufactured in this way showed excellent surface quality and dimensional accuracy. It was then examined for cracks using the dye penetration method. Finally, the tube was recrystallized in air at a temperature of 1380 ° C for one hour. A very thin and firmly adhering Al ₂ O ₃ layer formed during this annealing. A metallographic examination of the annealed tube revealed a coarse-grained recrystallization structure with a high structural extension in the tube circumferential direction corresponding to FIG. 1.

EXAMPLE 2:

A hollow format was produced from an ODS alloy of the same composition as in Example 1 by mechanical alloying of the powder starting materials, hot isostatic pressing and subsequent conventional hole pressing. From this blank, a sleeve-shaped blank with an inner diameter of 60 mm and a wall thickness of 5 mm was subsequently produced by overturning. The blank obtained in this way has a fine-grained structure. It was formed from the initial wall thickness of 5 mm to an end wall thickness of 0.7 mm in just three overflows by spinning. This corresponds to an overall degree of deformation of 84% relative cross-sectional decrease, which was achieved without heating and without intermediate annealing.
The tube was then examined for cracks using both the dye penetration method and the eddy current test. The tube was subsequently recrystallized in air at 1380 ° C. for one hour. The microstructure shown in FIG. 2 was formed.

Claims (7)

1. Method of manufacturing seamless pipes, which have an extremely elongated grain structure in pipe circumferential direction, from metallic materials which are strengthened with oxide and/or carbide particles and which through mechanical transformation combined with a recrystallizing heat treatment form a coarse extremely elongated grain structure,
   characterized in
   that a cup- or bush-shaped starting part in a non-recrystallized state is brought by flow-turning according to DIN 8583, Group 2.1.1.3.2.2. with a degree of transformation of at least 30% and with conventional measures to minimize the tangential flow of material into the desired tubular shape and that the material is recrystallized in a coarse-grained manner by an intermediate annealing between individual deformation steps or by a final annealing upon completion of deformation.
2. Method of manufacturing seamless pipes according to claim 1, characterized in that the strengthening particles are oxides of one or more metals from the group yttrium, aluminium, lanthanum, cerium and zirconium.
3. Method of manufacturing seamless pipes according to claim 1, characterized in that the strengthening particles are formed from reactive metallic additives, which during the processing of the material and/or during a heat treatment are converted into the corresponding oxide, nitride or carbide particles.
4. Method of manufacturing seamless pipes according to claim 1, characterized in that, as a metal alloy, an iron-, nickel- or cobalt-based dispersion strengthened alloy is used.
5. Method of manufacturing seamless pipes according to claim 4, characterized in that the alloy comprises 6 - 30 wt.% Cr, 0 - 10 wt.% Al, 0 - 2 wt.% Ti, 0 - 10 wt.% Mo, 0 - 10 wt.% W, 0 - 10 wt.% Ta, 0.1 - 2 wt.% of one or more oxides of the metals from the group Y, Al, La, Ce and Zr, the rest being Fe.
6. Method of manufacturing seamless pipes according to claim 4, characterized in that the alloy comprises 6 - 38 wt.% Cr, 0.1 - 7 wt.% Al, 0 - 2 wt.% Ti, 0 - 5 wt.% Mo, 0 - 5 wt.% W, 0 - 5 wt.% Ta, 0.1 - 2 wt.% of one or more oxides of the metals from the group Y, Al, La, Ce and Zr, the rest being Ni.

Images