DE10003720A1 - Production of roller bearing elements comprises using a block of continuous cast material having a high degree of purity with fine carbide deposits and having a high fine granularity - Google Patents

Abstract

Production of roller bearing elements comprises using a block of continuous cast material having a high degree of purity with fine carbide deposits and having a high fine granularity. The block is heated without deformation and without diffusion annealing to a temperature of 1150-1180 [deg] C and molded to a seamless tube before being cut into blanks. The heat deformation is carried out in several stages with intermediate heating to approximately 900 [deg] C, the last heat deformation stage being at 790-900 [deg] C. Cooling is carried out in air so that a lamella perlite structure with a hardness of 270HV30 is produced.

Description

The invention relates to a method for producing rolling bearing elements such as Outer and inner ring made of hardening roller bearing steel according to the generic term of claim 1.

A generic method is known from DE 39 10 959 A1. In this process, a blank is made

• - heated to a first austenitizing temperature of about 1150 ° C and at transformed this temperature
• - then cooled in gas to ambient temperature, so that a lamellar pearlite structure arises
• - roughly machined
• - To a second below the first austenitizing temperature Austenitizing temperature is heated and at this temperature for formation a homogeneous austenite with finely dispersed carbides
• - Quenched in oil, salt or water so that a hardness of at least 64 HRC arises, and
• - Finished to a rolling bearing element, the blank according to his Cooling in gas in the lamellar pearlitic state roughly processed and is heated to the second austenitizing temperature immediately thereafter.

The blank is preferably cooled in gas in the range from 900 to 650 ° C. at a rate of approximately 40 ° C./min. The heating to the second austenitizing temperature takes place at about 840 ° C. with a holding time of about 20 minutes. After quenching, the blank is tempered at 160 to 240 ° C with a holding time of 1 to 2 hours. This process, which runs as a hot forging process via a forging process, has not been used on an industrial scale, despite the advantage of eliminating soft annealing. The reasons given are:

• - At that time there were no tools with sufficient tool life for the Rough machining of the hard blanks available,
• - There was difficulty in the required rapid cooling after the last one Process forming must be adhered to reliably
• - There was only inadequate starting material for the blank.

A large number of producers have therefore taken a different path, namely that the production of a hot-worked pipe as a blank. The following are about this known method known.

Starting from the pig iron via the LD steel mill and a ladle furnace and ladle degassing or alternatively starting from the E steel mill, a ladle furnace and ladle degassing and in special cases via a remelting steel mill, a block is cast, which is rolled on a roughing mill to a tube round. This round tube is preferably formed into a hot-finished tube using the Assel method (see Stahlrohr-Handbuch 10th Edition, Vulkan-Verlag, Essen 1986 , pages 141-143).

A disadvantage of this method is that the tube round used is close to dimension must be the hot-finished pipe and one to cover the delivery program A large number of rolled or forged tubular round material is required. The Assel-Straße is the preferred plant for the production of roller bearing tubes, but also other tube production systems, such as push bench systems or Pipe continuous lines are used - always using preformed and diffusion annealed feed.

It is also known, instead of a casting block (ingot), a continuous casting block (bloom) - predominantly in rectangular format - to generate and this over a rolling or To transform the forging process into a tube round. Alternatively, instead of one Rectangular format produced a continuous casting, with this continuous casting block rolled or forged after separation (see La Revue Métallurgie, IT, April 1989, pages 344-350). According to the prior art, the degree of deformation is such chosen that a forging or rolling degree of λ = 5 is achieved. The  The mentioned rolling or forging process is always a diffusion annealing upstream to the segregations resulting from the casting process and coarse To largely reduce or reduce carbide deposits. All mentioned Manufacturing processes for the primary material are expensive because they are large, capital-intensive Plants for the forming are needed and the material is moved several times. Since the bars have to be divided again and again by the stretching, falls too a corresponding amount of scrap material. Any additional work and Transport step means a risk of generating more or intensifying Errors whose elimination increases costs.

In DE-PS 37 38 858, reference is made to the fact that the hot-rolled front pipes before the reduction of their inner and outer diameters to the desired final dimensions by means of cold pilgrims or cold drawing a long-term annealing process (GKZ) be subjected to the lamellar cementite embedded in the structure to transform globular cementite. This long-term glow forms comparatively thick layers of scale on the outer and inner surface of the Front pipes and the edge zones are heavily decarburized. The front pipes are therefore peeled for their outer diameter, with the outer layers of scale be removed. Following this peeling, the front pipes are processed, i. H. they are pickled, separated or greased. After the cold pilgrimage or cold drawing are the tubes as so-called rods in magazines of a multi-spindle machine (6 or 8 spindles) is inserted and a rolling bearing ring is machined from it. The Rings are then remunerated. H. hardened and tempered. Because with this Heat treatment the rings scale and warp, the ring must open Gauge blocks are ground. The assembly then takes place at the rolling bearing manufacturer a rolling bearing by joining the outer and inner ring, rolling elements and Cage, cover plates if necessary.

It has already been proposed to reduce the manufacturing costs in the preliminary stages (DE 195 20 833 A1), the continuous casting material in the as-cast state and without To supply heat treatment (diffusion annealing) to a pipe production plant.

Another step in this direction was the elimination of long-term annealing (GKZ- Annealing) by controlled final rolling in a certain temperature range given degrees of deformation, which comes very close to TM rolling  (DE 195 13 314 A1). As an alternative to the previously known parting of the rings in the train The machining of cold pilgered or cold drawn pipes can be done by Hot cutting a so-called pipe ring are generated (WO 95/29777). All The suggestions listed lead to a cost reduction in the production of Rolling rings.

Disadvantageous when proposing a regulated end rolling as a replacement for the Long-term annealing (GKZ) is the high power requirement for forming at lower ones Temperatures what is required in the design of the rolling unit and Drive power must be taken into account. Furthermore, it is difficult for larger cross-sectional volumes, d. H. larger outside diameters or wall thicknesses Narrow temperature windows required for the controlled final rolling over the entire Set the cross section to ensure that it is safe to manufacture.

The object of the invention is a method for producing roller bearing elements to indicate where, while retaining the benefit of a discontinuation Soft annealing or a complex TM rolling on a large industrial scale and reliable Rolling bearing elements such as outer and inner rings can be produced inexpensively can.

This task is based on the generic term in conjunction with the characterizing features of claim 1 solved. Advantageous further training are the subject of subclaims.

According to the teaching of the invention, a block of continuous casting material is used as a blank high degree of purity with fine carbide precipitations and high fine grain generates and an insert length of the block without any deformation, d. H. in the Cast state and without heat treatment (diffusion annealing) at first Austenitizing temperature in the range of 1150 ° -1180 ° C heated. By means of a Pipe production plant z. B. push bench, the block becomes a seamless, hot-formed tube and this divided into individual pipe rings. The Hot forming takes place in several stages with intermediate heating to approximately 900 ° C, with the last hot forming step in the range of 790-900 ° C and then the cooling takes place in still air. In the tube is through this  The procedure is a lamellar pearlite structure with a hardness of at least 270HV30 generated.

The investigation of the results of different process routes has shown that the structure of the starting material is of central importance. Only if in Starting material already has a fine grain with fine carbide deposits one guarantees that with the elimination of soft annealing after the second Austenitization treatment produces a structure that is favorable for the rolling bearing elements becomes. The second aspect is to be seen in process security, because with that proposed method on both a TM rolling and a controlled Cooling after the last hot deformation stage is dispensed with. The inexpensive Aspect is to be seen in the fact that the hot-rolled pipe is divided Rohring is generated, so the waste of expensive material as a result of machining Machining is low.

The cutting is preferably a hard saw or a hot cutting without cutting, the hot cutting at a temperature of at most 800 ° C and with a Cooling takes place in still air. The warm separation has the advantage that it does possible residual stresses in the hot-rolled pipe are reduced.

Further features, advantages and details of the invention result from the method example according to FIG. 1 explained below.

According to the invention, a continuous casting raw material with the dimension 240 mm is produced from the steel 100 Cr6 with a high degree of purity as well as fine grain and fine carbide precipitates. The insert length of approx. 800 mm is heated in the cast state, ie without heat treatment (diffusion annealing) in a rotary hearth furnace to a drawing temperature of 1160 ° C and rolled on a tube ram bench system to tubes with the dimensions 38 × 7.5 mm. Hot forming is carried out in several stages, starting with punching, stretching and creating a billet in the push bench. After being laid down, the slug has an average temperature of 550 ° C. The billet is reheated to about 900 ° C in a walking beam furnace and then rolled in a stretch-reducing mill to the final dimension mentioned. The hot-rolled pipe leaves the plug-in reducing mill at a temperature of around 800 ° C. Then cool down to room temperature on a cooling bed in still air. The structure of such a tube produced according to the invention is shown in FIG. 2. The fine-lamellar pearlite structure with a hardness of 330HV30 can be clearly seen.

The hot-rolled pipe is divided into individual, identical pipe rings either by hard saws at almost room temperature or by hot cutting at a temperature below 800 ° C. The pipe rings produced in this way are machined by hard turning, which means fine or very fine turning with a small grinding allowance for the running surface, end faces, chamfers, etc. This is followed in a known manner by the final heat treatment, which consists of hardening and tempering. The pipe rings are heated to 850 ° C and held for about 20 minutes. This is followed by quenching, preferably in oil, so that a hardness of 65 HRC is achieved. The resulting structure is shown in Fig. 3. It is characterized by a fine-needle martensite with evenly distributed, very fine carbides. After tempering for two hours at 180 ° C, the hardness is 62 HRC. A ring produced in this way with such a homogeneous fine-needle martensite structure with fine carbide deposits ensures a high fatigue strength of the roller bearing elements.

After the final heat treatment, the pipe rings are ground and finished together with the rolling elements, if necessary, cages to form a rolling bearing assembled.

Claims (8)

1. A method for producing rolling bearing elements such as outer and inner ring from hardening rolling bearing steel, in which a blank

• - is heated to a first austenitizing temperature in the range of 1150-1180 ° C and formed.
• - is cooled to ambient temperature after forming.
• - machined
• - Then heated to a second austenitizing temperature in the range of 840 to 860 ° C and held at this temperature for at least 15 min
• - is quenched in oil, salt or water to give a hardness of at least 63 HRC and
• - heat treated at a temperature in the range between 160-240 ° C and held for at least one hour
• - and finally finished to a rolling bearing element by grinding and / or honing,

characterized in that the ingot produces a block of continuous casting material with a high degree of purity with fine carbide precipitates and a high degree of granularity, and heats an insert length of the ingot to the first austenitizing temperature in the range of 1150-1180 ° C without any deformation, ie in the as-cast state and without heat treatment (diffusion annealing) is transformed into a seamless, hot-finished tube by means of a tube production system and this is divided into individual tube rings, the hot-forming being carried out in several stages with intermediate heating to approximately 900 ° C and the last hot-forming stage being in the range from 790-900 ° C and thereafter cooling takes place in still air, so that a lamellar pearlite structure with a hardness of at least 270HV30 is created in the tube. 2. The method according to claim 1, characterized, that the cutting is hard sawing the hot-rolled pipe.   3. The method according to claim 1, characterized, that the cutting is a non-cutting warm cut. 4. The method according to claim 3, characterized, that hot cutting at a temperature of 800 ° C or less with a followed by cooling in still air. 5. The method according to any one of claims 1 to 4, characterized, that the raw outer ring through hard saws and the associated raw Inner ring is generated by hot cutting. 6. The method according to claim 5, characterized, that the raw outer ring is also produced by hot cutting. 7. The method according to any one of claims 1 to 6, characterized, that machining involves hard turning the cut Pipe rings is. 8. The method according to claim 7, characterized, that hard turning is a fine or very fine turning with a small grinding allowance is.