DE19834361A1 - Precision deep-drawn case-hardened component, especially a roller bearing and motor component e.g. a needle bearing, sleeve or bush, is made from a cold rolled strip of steel with specified titanium, nitrogen and low aluminum contents - Google Patents

Abstract

A precision deep drawn, case hardened component, made from a cold rolled strip of steel with specified titanium, nitrogen and low aluminum contents, is new. A precision deep drawn, case hardened component is made from a cold rolled strip of composition 0.04-0.14 % C, <= 0.10 % Si, 0.20-0.90 % Mn, <= 0.025 % P, <= 0.015 % S, <= 0.080 % Al, 0.006-0.015 % N, 0.015-0.060 % Ti, <= 0.15 % Cu, <= 0.10 % Ni and balance Fe and has a wall thickness uniformity of less than 0.1 %, a surface roughness Ra of less than 0.25 microns and a core hardness of 150-300 HV 1. An Independent claim is also included for production of the cold rolled strip described above by hot rolling a slab at above 980 deg C, coiling the resulting strip at 600-750 deg C, cold rolling with 30-65 % deformation, recrystallization annealing at \} 730 deg C and optionally skin pass rolling.

Description

Field of application of the invention

The invention relates to a cold-formed, precision deep-drawn, case-hardened tes component, in particular roller bearing and engine component that consists of a cold tape is made. The invention also relates to a method for Her position of the cold strip.

Background of the invention

For the production of rotationally symmetrical, cold-formed components from According to the state of the art, deep-drawing steel strip is an aluminum-calmed, Fine-grain steel is used, which after forming anisotropies in shape of lobes. According to the relevant standards, e.g. B. DIN 1623, DIN 1624 or new DIN-EN 10 130 "Cold-rolled flat products made of white For this purpose, an Al-killed steel is used for cold forming steels beat, which can also be optionally alloyed with titanium.

The chemical composition is regulated according to Table 2, i.e., for example, the deep-drawing quality FePO4 (former designation St 14 or St 4 fully calmed) is produced with the following analysis, whereby the remaining elements mentioned in this standard differ only insignificantly:

The so-called vertical anisotropy as a ratio of true width form Change to true change in thickness in a specimen with uniaxial tension stress is detailed under A1 (terms, abbreviations and designations) described. With regard to austenite or ferrite grain sizes, shape and distribution nothing else is mentioned (EN 10 130).

In this context, the person skilled in the art is also aware that the Elements carbon, phosphorus, sulfur, silicon, manganese so low should be kept as possible in order to guarantee good deep-drawability.

A peculiarity of this steel is that in the fully calmed structure it is with customary Al additions when rolling from the slab to the hot strip up to a so-called pancake structure forms with the cold strip, which is directly related to Aluminum nitride precipitates is related. This Alumi Nium and nitrogen atoms are partly dissolved and partly on grain limits of austenite as Al nitrides, this process diffusion and is temperature dependent. Is used for capacity reasons when rolling the warm If the band cools down quickly, Al nitride precipitates on the grain borders are not yet fully completed. During the subsequent cold rolling and heating during the recrystallization annealing of the cold strip, these separate Aluminum nitride completely at the deformed ferrite crystal boundaries because the recrystallization temperature is higher than the precipitation temperature of the Aluminum nitrides. In other words, recrystallization does take place, however their grain boundary orientation depends on the deposited aluminum triden. The result is a flat, non-globular ferrite grain, called a pancake Structure. The grain boundaries oriented in the rolling direction now promote the end formation of a so-called orange peel after the deep-drawing process. Is this Orange peel on roller bearing components in the area of a raceway, this is what leads to this to undesirable noise generation during rolling contact due to increased roughness.

Another disadvantage of this aluminum-killed steel strip produced in this way is that it is anisotropic, i.e. H. Has direction-dependent properties.

For example, when deep drawing it tends to form tips with different amounts of material wall thicknesses in the tip. This in turn means that you can either Loss of material due to cutting off the tip or differences in wall thickness must accept with the non-cutting precision end part.

Summary of the invention

The object of the present invention is therefore to provide case-hardened precision components, such as needle bearings, sleeves or bushings with optimal properties to produce properties.

According to the invention, this object is achieved according to the characterizing part of claim 1 in that the cold strip has the following composition:

carbon 0.06-0.14% silicon ≦ 0.10% manganese 0.40-0.90% phosphorus ≦ 0.025% sulfur ≦ 0.015% aluminum ≦ 0.080% nitrogen 0.006-0.015% titanium 0.020-0.060% copper ≦ 0.15% nickel ≦ 0.10% rest Iron,

a wall thickness equality of <1 ‰ and a surface roughness of R _a

<0.25 µm and has a core hardness of 150-300 HV 1.

The drawn parts according to the invention produced therefrom, that is to say precision deep-drawn ones ner rolling bearing parts, differ from the cold strip St 4 after the previous one State of the art mainly in that the aluminum content is down sets and additionally Ti in the stoichiometric ratio to the nitrogen content in the Steel is alloyed, with sufficient martensite formation in use hardened surface, a core strength of 150-220 HV, fine-grained, only low running noise induced the track topography and the symmetrical wall thickness ratios exist.

The associated process for producing the cold strip is characterized by this from that from the cast steel over a slab at more than 980 ° C Hot strip is produced, the end temperature of the coiler when winding the Coils is around 600-750 ° C, the subsequent cold forming with a Deformation degree of 30 to 65% takes place before a recrystalline at a maximum of 730 ° C lizing cold strip final annealing takes place and the cold strip is optionally removed is then trained. This sequence of procedural steps is safe put that the typical pancake structure of an aluminum-killed steel is avoided and isotropic properties are given to the component.

The advantages of the steel composition of the invention and the exact Coordination of hot rolling, cold rolling and annealing conditions are that the forming properties in all directions, d. h., in longitudinal, transverse and Diagonal direction are almost the same. In other words, it is a long way off using isotropic cold strip. The advantages of these isotropic properties of the Cold strip in the manufacture of the precision components are such that in the non-cutting A very even flow of material is given in the shaping process. Through this tools and machines are essential for a uniform flow of material during forming less stressed and disadvantageous wall tapers during the forming process Borders drawn in the radius avoided due to favorable R values. With the Refined secondary grain size means a reduction in the roughening of the Surfaces, so that with a Ra ≦ 0.4 µm in the raceway area of Rolling bearing parts reduce the noise when rolling over in running operation and speeds above 1 500 µ / min are given.

The invention is explained in more detail using the following exemplary embodiment.

Brief description of the drawings

Show it:

Fig. 1 shows a needle barrel shown in perspective

Fig. 2 shows a deep-drawn bowl without ear formation

Fig. 3 is a deep-drawn cup having earing

Detailed description of the drawings

The needle bushing shown in Fig. 1 and denoted by 1 has a radial section 2 with an annular profile, which merges at one end into a radially inwardly directed rim 3 , and is closed by a bottom 4 at the other end. Between the elevation 5 is provided with a bottom 4 and the board 3 guided needle rollers 7 roll on in a cage 6, being arranged at the open side of the needle bushing 1 nor a lip seal. 8 Such needle bushings 1 close bearings on shafts ends. The preliminary stage of the finished needle sleeve 1 is shown in FIG . The cup 9 shown there, produced by a multi-stage drawing process, is free of tips, while the cup 10 shown in FIG. 3 has a considerable amount of tip formation.

A killed steel with the following composition:

0.08% carbon
0.06% silicon
0.60% manganese
0.020% phosphorus
0.010% sulfur
0.030% aluminum
0.009% nitrogen
0.050% titanium
0.10% copper
0.05% nickel
Remainder iron

is melted in a corresponding melting metallurgical unit and then cast into a slab. This slab becomes with With the help of a hot rolling process, a hot strip is produced whose wall thickness is a multiple of the later thickness of the cold strip. The rolling of the Hot strip takes place at 1000 ° C in a homogeneous austenite area. The reel temperature when winding the so-called coil of titanium-stabilized steel after hot rolling takes place at 750 ° C. After the coil has cooled down the hot strip is descaled and subjected to a pickling process. Afterward becomes the desired in a cold rolling mill through a shaping process Thickness of the cold strip set, with a degree of deformation of 30 to 65% The aim is to achieve the lowest degree of cold forming in this area Ear formation is to be expected. After this cold rolling process, the cold strip is made a so-called cold strip final annealing at 700 ° C for recrystallization threw. The end result of this cold strip annealing is a grain with a Secondary grain size 7 with a globular structure and fine-grain cementite distribution. In this way there is high isotropy, i. H. a direction independence of the Tape properties given. A generally customary skin-pass process follows, d. H. a slight re-rolling of the strip to stabilize it Stretch limit.

Such a coil with dimensions of, for example, 100 × 1.10 mm is now being delivered to the metalworking industry for further processing. A precision needle bearing bushing is made from this 1.10 mm thick cold strip produced by a multi-stage molding process, the end dic ke is then 0.90-0.010 mm, d. H. the wall thickness was reduced by approx. 15% duced with a square or over-square draw ratio.

This needle bearing bushing is now subjected in a known manner to case hardening in a continuous furnace at about 900 ° C., with a carbon content of 0.8% being set in an edge layer of the component after about 2 hours. The needle barrel 1 carburized in this way is then quenched in an oil bath to increase the hardness (case hardening), the edge hardness after carburizing being 700 + 140 HV. Then the needle barrel is subjected to a cleaning process. This component with high dimensional accuracy is now immediately ready for use without further reworking such as grinding and honing the raceway, as long as the rolling elements (needles, balls with and without cage) are inserted and the end face is closed by flanging the open side of the sleeve.

List of reference symbols

1

Needle sleeve

2

Radial section

3rd

Board

4th

floor

5

Elevation

6th

Cage

7th

Bearing needle

8th

Lip seal

9

Bowl

10

Bowl

Claims (2)

1. Cold-formed, precision deep-drawn, case-hardened component, insbesonde re roller bearing and engine component, which is made from a cold strip, characterized in that the cold strip has the following composition:
carbon 0.04-0.14% silicon ≦ 0.10% manganese 0.20-0.90% phosphorus ≦ 0.025% sulfur ≦ 0.015% aluminum ≦ 0.080% nitrogen 0.006-0.015% titanium 0.015-0.060% copper ≦ 0.15% nickel ≦ 0.10% rest Iron, has an equality of wall thickness of <1 ‰ and a surface roughness R _a <0.25 µm and has a core hardness of 150-300 HV 1. 2. A method for producing the cold strip according to claim 1, characterized in that records that from the cast steel over a slab at more than 980 ° C a hot strip is produced, the coiling temperature of which when opening winding the coil is around 600-750 ° C, the subsequent cold forming takes place with a degree of deformation of 30 to 65%, before at a maximum of 730 ° C a recrystallizing cold strip final annealing takes place and the cold strip is given If necessary, it is finally trained.