DE3018345A1 - METHOD FOR PRODUCING A THREAD-ROLLED SINTERED CYLINDRICAL METAL PRODUCT - Google Patents

Description

The invention relates to thread-rolled metal products from sintered powder metal workpieces, in particular a method for producing thread-rolled powder metal products from sintered cylindrical powder metal workpieces.

It is known to produce threaded products from cylindrical wrought metal workpieces with the aid of a thread rolling tool to manufacture. If on a cylindrical work-

piece or molding a thread is to be rolled, it penetrates Tool in the surface of the workpiece to form the thread root. This causes the material to move radially displaced on the outside to form the tip and the outer diameter of the thread. The diameter of the workpieces used for thread rolling forged metals is common the pitch diameter of the finished thread.

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Since the material is neither removed nor compressed during thread rolling, this is an essential requirement when thread rolling, that the workpiece is no more than the correct amount of material to form the finished Thread, otherwise the tool will be overstressed could be. If the workpiece diameter is smaller than the correct amount, an incompletely formed one results Thread.

It is very important that the outside diameter of the workpiece is as accurate as possible. Since the volume of the thread is greater than the pitch diameter (head height) of an American Standard thread almost corresponds to the volume of the material displaced from below (foot height), it can be seen that the diameter of the workpiece approximates the pitch diameter of the finished thread. An incorrect one Setting the workpiece diameter is one of the most common Causes of premature tool failure.

In the case of a balanced thread, the thread volume over the pitch diameter is essentially equal to the thread volume below the pitch diameter. Typically, the diameter of a forged metal workpiece should be smaller than be the effective pitch diameter to give "room to grow" to let before the maximum allowable workpiece diameter is reached. Metal can be made to flow, but it cannot be compressed.

As already said, the workpiece dimensions must be set precisely. For example, the tolerances are the final thread dimensions are usually two to three times the dimensional tolerances of the starting workpiece. As long as the forged metal workpiece is uniform and dimensionally accurate is, thread rolling offers the great advantage that

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the precision of the original tool set-up during long run times in high-speed manufacturing can be sustained.

It is of course desirable to provide a method of thread rolling metal workpieces in which none High-precision dimensionally stable workpieces are required and with the high production rates as well as a thread-rolled Product with a good combination of physical properties can be obtained.

The object of the invention is to provide a powder metal method for producing thread-rolled metal products; a thread-rolled sintered powder metal product is also to be produced, which is metallographically characterized by such a structure that the rolled and mechanically formed threads are high-density from foot to tip on the surface and have a density of at least about 95 %, e.g. B. at least about 98 % of the effective density of the metal, and that the core of the thread below the thread turns has a porosity that is due to an average density of about .75-92 95, essentially about 80-92 % , the effective density of the metal is defined.

The invention therefore provides a method for thread rolling a cylindrical sintered powder metal workpiece, in which a sintered cylindrical powder metal workpiece is formed which has a density in the range of approx. 75-92 % of the effective density of the workpiece and a selected diameter, which is greater than the flank end diameter of a predetermined thread-rolled product to be produced therefrom and not significantly greater than the outer diameter of this product. The ge

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The selected diameter of the powder metal workpiece is due the density of the workpiece is essentially inversely related and is tuned so that an essentially fully formed thread is generated. Afterward the sintered powder metal workpiece is thread-rolled using a rolling tool with the same Thread diameter as the predetermined thread-rolled product to be produced.

The invention is explained in more detail, for example, with the aid of the drawing. Show it:

1 shows a section of a cylindrical porous sintered metal workpiece;

2 shows the section of the sintered metal workpiece after thread rolling;

Fig. 3 schematically shows a typical balanced thread in which the thread volume over the pitch diameter (head height) equals the thread volume under the pitch diameter (Foot height) is;

A-A shows a porous sintered metal workpiece in front of the Thread rolling;

Fig. 4-B shows the workpiece after thread rolling, wherein a part has broken away to form the inner structure to clarify; this is enlarged for better clarity;

5 is a macro photograph, enlarged 20 times, of a cross section of a thread rolling manufactured Powder metal product, where the high density on the threaded sections, especially the high density layer underneath the surface, and the relatively high porosity of the core of the product are ;

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FIG. 6 shows a macro photograph corresponding to FIG. 5, but in 50 times enlargement; FIG. and

Fig. 7 shows a tensile stress testing device used in Determine the shear strength of the threaded workpiece is used.

An advantage of the invention is that the sintered powder metal workpiece need not be dimensioned as precisely as a forged metal workpiece in order to produce a high quality end product. For example, the diameter of the powder metal workpiece is larger than the recommended diameter of the forged metal workpiece, i.e. larger than the pitch diameter, provided that the sintered powder metal molding used as the starting workpiece is porous and has a density between approx. 75 and 92 % the effective density of the metal.

The cold hardening and grain orientation of the powder metal workpiece correspond to those that can be achieved with forged material, but to a lesser extent as a result the reduction in porosity through compaction. A major advantage to using powder metal materials is in the elimination of embrittlement and strength-reducing porosity in areas within of the core section and at this where the stress concentration is highest.

As already mentioned with reference to forging materials after the entire thread flank has been filled in, no further deformation is permitted or tolerated; on the other hand, in the case of the powder metal workpiece, a white. tere deformation or compression achieved simply by doing this that the inner pores of the workpiece are closed further

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will. This further deformation increases the depth or the zone of compaction, thereby increasing the shear strength the thread of the powder metal workpiece is improved.

The fact that one can start with a larger diameter powder metal workpiece and thread rolling beyond the point of complete thread formation can also perform, results from the compressibility of the porous material. Thus there is a for the practical application significant advantage of the invention is that from a workpiece with low precision a High-precision thread is malleable. This allows a high degree of flexibility in the process, given the dimensions of the workpiece need not be too precise and easily within the possibilities of the powder metallurgical process without the need for secondary steps.

After the thread rolling of the sintered powder metal workpiece, the workpiece having a thread can continue are sintered to increase the strength, followed by a heat or tempering treatment, if the The material used can be tempered (e.g. carbon steel).

Fig. 1 shows a portion of a typical cylindrical powder metal workpiece 10. The workpiece is passed through the Tool 11 (see. Fig. 2) provided with a thread. Fig. 3 shows a balanced thread 12 with a neutral line 13, the head height 14 · and the same foot height 15, whereby the The neutral line runs centrally between the foot and the tip of the thread.

The invention provides a method for thread rolling a cylindrical sintered powder metal workpiece, in which a sintered cylindrical powder

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metal workpiece is formed with a density in the range of about 75-92 % of the effective density of the workpiece, which has a larger selected diameter than the pitch diameter of a predetermined thread rolling product made therefrom, which does not substantially exceed the outer diameter of that product; the selected workpiece diameter is adjusted so that a substantially fully formed thread is produced; Then the sintered powder metal workpiece is thread-rolled using a rolling tool according to the thickness of the predetermined product to be produced, whereby a thread body is produced in which the density from the core to the tip of the thread turns is at least about 95 % of the effective density of the metal and the material has a density under the thread in the range of approx. 75-92 % of the effective density of the metal.

By using a workpiece diameter that is larger than the flank end diameter, a high degree of density is ensured at the thread section. This is illustrated in FIGS. A and 4B. Fig. AA shows a sintered powder metal workpiece 16, where ^ the pitch diameter is indicated by a dashed line 17; the thread rolled workpiece 16 of Fig. AB shows the work hardened threads 18, with the flow lines 19 shown schematically, and the inner porous portion or core 20. As noted, the surface and sub-surface layer has the thread at the root and on the tip has a density of at least about 95 %, essentially at least about 98 %, of the effective density of the metal.

The macrographs of Figures 5 and 6 are 20 and 50 times, respectively enlarged cross-section through threaded powder metal workpieces in the unetched state.

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Fig. 5 shows a threaded sintered workpiece with a size of 3 / 8-16 UNC thread (UNC = standard coarse thread), which illustrates the characteristics of forming a powder metal workpiece. The original one Workpiece diameter was 8.79 mm, whereas a forged workpiece must have a pitch diameter of 8.0 mm. The final flank diameter of the finished thread of the powder metal workpiece was 8.56 mm. A workpiece diameter with an oversize of 0.38 mm resulted in a flank end diameter, which only has an oversize of 0.076 mm. This difference is explained by the compressibility of the material.

As can be seen from Fig. 6, the threads on both the feet and the tips (A) are very dense, and the inner area or thread core B of the thread has a lower porosity than the original porosity of the workpiece, which is passed through area C. is designated. The core region C has a density of about 75-92 %, essentially 80-92 %, of the effective density of the metal. Area A closest to the thread surfaces has an effective density that is greater than 95 %, typically 98 %, of the effective density of the metal. The compression takes place in the area B, in which the density lies between the extreme values A and C.

The powder metal workpiece can be made from various metal compounds, e.g. B. of steel, aluminum alloys, copper alloys such as brass and bronze, nickel-based alloys, e.g. B. Monel (TM), which consists of 60 % nickel, 37 % copper, the rest including silicon, manganese, etc.

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The invention is particularly applicable to powder metal workpieces made of steel. In the manufacture of a sintered cylindrical workpiece from steel, a steel powder mass is cold-pressed in a cylindrical pressing tool which has the dimensions suitable for the desired final size. The mass is compacted with a pressure of about 4-2-63 kg: mm and the workpiece obtained is subjected to essentially non-carburizing conditions in a non-oxidizing atmosphere, e.g. B. in cracked ammonia gas for about 20 min at a sintering temperature of about 1093-1177 ⁰ C. The sintered workpiece has a density of about 75-92 % of the effective density of the steel, usually a density of about 80 or 85-92 %.

The types of steel powder used are preferred from an economical as well as practical point of view chosen. The powder mass can be a mixture of elemental powders or have the final alloy composition.

Pre-alloyed powders, e.g. B. by atomization or atomization are generated from a liquid melt, are preferably used. To make sure that such Powders are compressible, the carbon is omitted from the composition and later prior to compaction mixed with the atomized powder. Alternatively, the carbon can be added after the workpiece is sintered is by carburizing the sintered workpiece to the desired carbon content.

The invention is applicable to a large number of steels, e.g. with steels of type 52100, low-alloy nickel-molybdenum steels, Molybdenum-manganese steels and the like. Thus, it becomes a steel for the purposes of the present invention defined as a composition containing at least approx.

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65% by weight iron, approx. 0.3-1.5% by weight carbon, remainder Steel alloy additives.

Examples of usable steels among various known steel compositions are e.g. B. k% Ni, 2 % Cu, 0.6 % C, remainder iron; 1.5 % Mo, 1 % C, remainder iron; 0.5 % Mo, 0.5 % Mn, 0.8% C, balance iron; 1.5 % Cr, 0.5 % Mo, 1.0 % C, balance iron; and 1.8 % Ni, 0.5 % Mo, 0.25 % Mn, 0.6 % C, the balance iron.

The following examples serve to illustrate the invention,

example

Sintered cylindrical powder metal workpieces with a length of 22.22 mm and a diameter of 76.2 mm were produced by the method previously explained. The cylinders, which had an average density of approx. 6.6 g / cm, esp
0.5 % Mo, remainder iron.

6.6 g / cm, consisted of 0.8 % C, 0.5 % Mn,

The cylindrical bricks were cut to size, by machining machined and dry ground so that thread rolling workpieces to produce a 3 / 8-16 UNC thread. The cut work pieces were on four different ones Ground diameters, namely 8, A- mm, 8.66 mm, 8.79 mm and 9.04 mm. The work pieces were on a reed thread rolling machine (designation :, Reed A22HB-Cylindrical The Thread Rolling Machine from Reed Rolled Thread Die Co.) provided with threads.

The machine was set up so that a completely cut out Thread was rolled in workpieces made of low-carbon forged steel, whereby the workpieces are necessary

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to the effective pitch diameter (8.40 ram) of the finished thread (3 / 8-16 UNC thread) was. The powder-metal cylinder became ^ it the same Rolled machine setting using oil as a coolant (lubricant). The details of thread rolling are known to the person skilled in the art and are not explained.

After each powder metal workpiece was thread-rolled, the workpiece was tested using the tensile tester checked according to FIG. 7, which has two internal thread jaws or clamps 20, 2.1, in both of which Ends the finished workpiece 22 is screwed in the manner shown. Then both ends of the jaws 20, 21 applied load, and the load acting in the event of breakage becomes recorded. A break occurred in the tests performed in the event of shear stress on all threads.

For further comparison, machined powder metal threads were produced in some of the powder metal workpieces, so that a comparison between machined threads and rolled threads of the powder metal workpieces was possible. The threads produced from powder metal workpieces of various diameters were measured. The measured densities were an average of the entire workpiece and are reported as the mean. Hardening is carried out by heating to 851 C and holding this temperature for 20 minutes in an endothermic atmosphere, the dew point being adjusted so that it was in equilibrium with the carbon content of the workpiece, followed by quenching in oil and subsequent tempering for 2 hours at 171 ⁰ C in air.

In the following table the data obtained are related to the dimensions and physical properties are summarized. The various powder metal threads are labeled A, B, C and D.

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TABEL

Outside ~ 0 thread
Blacksmithing
φ 8, AO mm Powder metal
work, with
cut
thread Workpiece 0 before thread rolling (density 6.56 g / cm) 8.79 mm
(C) 9.0A- mm
(D) VO Edge 0
Core-0 9.1 + 9 mm 9, A-9 mm 8, AO mm
(A) 8.66 mm
(B) 9.55 mm 9.62 mm ¹ made 8, AO mm
7.36 mm 8, AO mm
7.36 mm 8.8A- mm 9, A-O mm 8.51 mm
7, AA- mm 8.56 mm
7, A-9 mm ο
co
O Thread form fully fully 8.07 mm
7.06 mm 8, A-3 mm
7, AA- mm fully fully O
σ> cut cut not not cut seen. average density fully fully σ
σ> after this seen. cut to shape - 6.56 g / cm j '
6.80 g / cm " ³ 6.84 g / cm ³ (83.3 56) 6.75 g / cm 6.83 g / cm ^: (86, A- 56) (87.0 %) (85.8 %) (86.8 56)

average Shear strength before tempering

Average shear strength after hardening

1700 #

1760 #

2A-00 #

33OO #

2600 #

'= Forged materials have a higher shear strength than powder metal materials.

The comparison between cut and rolled powder metal threads is important.

Examination of the data in the table shows that a fully cut thread form with the Forged workpiece is achieved, the workpiece diameter was 8, A-O mm, whereas the powder metal workpieces with 8.40 mm and 8.66 mm (workpieces A and B) due to compressibility of the material still had incompletely cut thread forms. The completely cut out For powder metal workpieces, the thread form is C with a diameter of 8.79 mm and D with a Achieved a diameter of 9.04 mm. Forms of oversized Threaded workpieces had their cores broken or partially broken Tool as it would have been the case with an oversized forged workpiece.

The data relating to workpieces C and D show also the adaptability ("forgiving characteristic") of the powder metal materials. While the diameter was enlarged by 0.25 mm, the flank end diameter was only 0.05 mm, i.e. 1/5 of the diameter of the original Workpiece, larger. It has already been mentioned that the final tolerance of a forged workpiece thread is the Two to three times the initial workpiece. These results show the thread-rolled powder metal workpieces possible wide tolerance range. That is, the powder metal starting workpiece does not require precision of a forged metal workpiece.

Furthermore, the data in the table show that the density of the ■ Powder metal thread increases when thread rolling. It should be remembered, however, that the increases shown result from the elimination of porosity near the tooth surfaces themselves, while the midsections of the workpieces do not change compared to the original workpiece densities. The average density of workpieces B, C and D

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is 6.82 g / cm (86.7 %) , which is an increase over the original workpiece density of 6.56 g / cm (83.3 %) . The fact that most of this increase is due to the concentration of the removal of porosity near the thread root and the flank surface is evident from the increases in shear strength actually achieved.

As can be seen, the cut threads have a much lower shear strength, both tempered and unhardened. Thus, the thread-rolled powder metal workpieces are far superior to the machined powder metal workpieces. Thread rolling increases the shear strength in the thread rolling condition by more than 4-0 % of the shear strength achieved with machined threads, and the shear strength in the quenched and tempered condition is increased by more than 75 % of the shear strength of quenched and machined threads.

As mentioned above, when thread rolling powder metal workpieces, it is essential that the starting diameter of the workpiece is greater than the flank end diameter of the predetermined thread rolling product and not noticeably exceeding the outer diameter (i.e. the major diameter) of the predetermined product, the selected diameter of the powder metal Workpiece is inversely related to the density of the porous workpiece, which is in the range of 75-92 % of the effective density of the workpiece metal, the higher z. B. the density of the workpiece, the smaller the selected diameter, provided it is greater than the end flank diameter of the thread-rolled product, and vice versa. The workpiece diameter before the thread rolling is preferably between the flank end diameter and the outer diameter of the rolled thread.

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An approximate equation that is used in determining the initial diameter of the powder metal workpiece is applicable as follows:

Workpiece 0 = flank 0 + 2-fold thread

(100 - density%)

height

100

When producing a 3 / 8-16 thread from a powder metal workpiece with a density of 83 % of the effective density, the following workpiece diameter is selected:

Workpiece 0 = 8.40 + 2 1.12

= 8.40 + 2 x 1.12 x 0.17 = 8.40 + 0.38 = 8.78.

Please note that the calculated workpiece diameter corresponds to the same workpiece diameter that is used for the Powder metal workpiece C is specified and with which the desired Results are obtained.

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- C. J ""

example

A steel alloy, for example, which can be used in the manufacture of thread rolling products is known under the designation AISI'4660 and contains 1.8 % Ni, 0.5 % Mo, 0.25 % Mn, 0.6 % C, the remainder essentially Iron. With the exception of the carbon, the steel is produced as an atomized pre-alloyed powder with a particle size of less than 0.15 mm (100 mesh US standard). Carbon with 0.75 % wax is added, the amount of carbon being sufficient to reduce any oxides present and result in a final carbon content of approximately 0.6 % . The powder mixture produced in this way has a higher compressibility.

Powder metal workpieces are made from the powder mixture Cold pressing in a pressing tool with a compression

2
force of approx. 4-2 kp / mm, and the briquettes are sintered at approx. 1121 C for 20 min in an atmosphere of ammonia cracked gas. During sintering, the carbon diffuses quickly and evenly into the alloy, so that it becomes highly homogeneous.

High carbon materials are normally used considered too brittle to deform; however, it was observed that the porosity in the deformed area is eliminated more completely when the material is harder.

After the sintered powder metal workpiece has been produced, it is thread-rolled. The thread rolling is set up in such a way that that as far as possible a high stress, a low work cycle and fatigue failure prevented or eliminated and not up to deformability

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limit is being worked. This is achieved by performing the rolling steps in as few revolutions as possible will; less than five revolutions are preferred and less than ten revolutions are normally required .

After thread rolling, the workpiece is treated in one of the following ways:

1) The thread-rolled workpiece is hardened simply by that it is quenched from the austenitic temperature for the respective steel in oil and then for about 1-4 h is tempered at a temperature of approx. 121-204 C; or

2) the thread rolled workpiece is at a temperature of about 1093 to 1177 ⁰ C (. Eg 1121 ⁰ C) for about 20-60 min sintered again, after which a compensation takes place as indicated above.

To ensure optimal properties, is preferred the latter treatment is applied after the threads have been rolled.

Through the invention, a sintered, thread-rolled powder metal product is obtained as a finished product, which has a porous core and high-density thread, the density of the threads on the surface and in the area below the surface from the thread root to the thread tip at least about 95 %, preferably at least about 98%, of the effective density of the metal forming the sintered product, and the density of the porous core is in a range from about 75-92 %, essentially from about 80-92%. The metals used are

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Steel, aluminum alloys, copper alloys or nickel alloys, etc. Steel is preferred. A typical composition range of steel comprises at least about 65 % iron, about 0.3-1.5 % carbon, the remainder being steel alloy additives.

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Claims (1)

Claims Method for producing a thread-rolled sintered cylindrical metal product, marked by - Forming a sintered cylindrical Pililvermetall workpiece with a density in the range of approx. 75-92% of the effective density of the metal and with a chosen one Diameter which is greater than the flank end diameter of the predetermined thread-rolled to be produced therefrom Product and does not exceed the outer diameter of this product, - wherein the selected diameter of the powder metal workpiece to the density of the workpiece substantially in is inversely related and tuned so that a substantially fully formed thread is produced, and - Thread rolling the sintered powder metal workpiece using a rolling tool with the same thread diameter such as the predetermined thread-rolled product to be manufactured, - so that a thread-rolled powder metal product is produced j which has a porous core and highly compressed Has threads, - the density of the threads on the surface and in the layer lying below the surface from the foot to the tip being at least approx. 95 % of the effective rotations
and - the density of the core is in a range of approx. 75-92 % of the effective density of the metal forming the product. 2. The method according to claim 1, characterized in that that the product is renewed after thread rolling by exposure to an increased sintering temperature is sintered. 3. The method according to claim 2, characterized in that that the product consists of a heat-treatable metal, that it is tempered by heat treatment. ή ·. Method according to claim 3, characterized in that that the metal product is heat-treatable steel. 5. The method according to claim k, characterized, ·" that the steel is at least about 65 % iron, about 0.3-1-, 5 ..%. Contains carbon, the remainder being steel alloy additives. 6. Method for producing a thread-rolled sintered, th cylindrical powder metal product, .. ...._ .. marked by . - Forms from a heat-treatable steel composition. A sintered cylindrical powder metal workpiece with. , a density in the range of approx. 75-92 % of the effective density of the steel and with a "selected" purchmes ₍ ^seE v> which is greater than the flank end diameter, of a predetermined thread-rolled product made from it, and the outer diameter this product does not exceed, 030066/0623 - being the selected diameter of the powder metal workpiece is essentially inversely related to the density of the workpiece and is thus matched is that a substantially completely formed thread can be generated, and - Thread rolling of the sintered powder metal workpiece using a rolling tool with the same thread diameter as the predetermined one to be produced thread rolled product, - so that a powder-rolled thread-rolled steel product is produced, which has a porous core and high density threads, - wherein the density of the threads on the surface and in the layer lying below the surface from the foot to the tip is at least approx. 95 % of the effective density and - the density of the core is in a range of approx. 75-92 % of the effective density of the steel making up the product. 7. The method according to claim 6, characterized in that that the steel product is tempered after thread rolling. 8. The method according to claim 6, characterized in that that the steel product is sintered again after thread rolling at an increased sintering temperature and then tempered will . 9. The method according to claim 6, characterized in that 030066/0623 that the heat treatable steel contains at least approx. 65 % iron, approx. 0.3-1.5 % carbon, the remainder steel alloy components. 10. The method according to claim 9, characterized, that the workpiece diameter before thread rolling after is determined by the following approximation equation: Workpiece diameter = Flank diameter + Double thread .... (100 - density-56 ") high. _Μ = 11. A method for producing a thread-rolled sintered cylindrical powder metal product,
marked by - Molds from a heat treatable steel composition a ·;
Sintered cylindrical powder metal workpiece with a density of approx. 75-92% of the effective density of the steel and with a selected diameter which is greater than the
The flank end diameter of a predetermined thread-rolled product manufactured therefrom and does not exceed the outer diameter of this product, - wherein the selected diameter of the powder metal workpiece is essentially inversely related to the density of the workpiece and is adjusted so that an essentially fully formed thread
is produced, and . - where the selected workpiece diameter through the
the following approximation equation is determined: Workpiece diameter = Flank diameter + 2-fold thread .... (100 - density-%) high - y-öö 030066/0823 - Thread rolling of the sintered powder metal workpiece using a rolling tool with the same thread diameter like the pre-determined thread-rolled one to be produced Product, - so that a thread-rolled powder metal product is produced, which has a porous core and high density threads, - where the density of the threads on the surface and in the sub-surface layer from foot to tip is at least about 95% of the effective density of the steel and - the density of the core is in a range of approx. 75-92 % of the effective density of the steel making up the product. 12. The method according to claim 11, characterized in that that the steel product is tempered after thread rolling 13. The method according to claim 11, characterized in that that the steel product is sintered again after thread rolling at increased sintering temperature and then is remunerated. I ^. Method according to claim 11, characterized in that that the heat treatable steel contains at least approx. 65% iron, approx. 0.3-1.5 % carbon, the remainder steel alloy additives. 030066/0 15. Sintered, thread-rolled powder metal product, characterized by - a porous core and high density threads, - The density of the threads on the surface and in the layer below the surface from the foot to the tip is at least approx. 95 % of the effective density, and - The density of the porous core is in a range of approx. 75-92 % of the effective density of the metal forming the product. 16. Powder metal product according to claim 15, characterized in that that the density of the threads is at least about 98 % that the density of the core is in a range of about 80-92 % . 17. Sintered, thread-rolled powder metal product made from a heat treatable steel composition that contains at least approx. 65 % iron, approx. 0.3-1.5 % carbon, the remainder steel alloy additives,
marked by - a porous core and high density threads, - The density of the threads on the surface and in the layer lying below the surface from the foot to the tip being at least approx. 95 % of the effective density the density of the porous core is in a range of approx. 75-92 % of the effective density of the steel composition forming the product. 03-006070623 18. Powder metal product according to claim 17, characterized in that that the density of the threads is at least approx. 98 % that the density of the porous core is in a range of approx. 80-92 % . 19. Powder metal product according to claim 17, characterized in that that the sintered thread-rolled product is a quenched and tempered product. 030066/0823