DE102008031107A1 - Steel element with claimable surface and method for its production - Google Patents

Abstract

According to the invention, a particularly wear-resistant steel component (12, 14) is provided by a method in which, starting from a shell component having a sulfur content of less than 0.01% by weight and a carbon content between 0.8% and 1.1%, a heat treatment with carbonitriding, Hardening, quenching and storage is carried out at low temperature. By the method, a particularly hard and crack-resistant surface of the component is realized.

Description

Field of the invention

The Invention is in the field of mechanical engineering and there special in the field of tribology, that is, the design of components with the goal of stability, resistance and durability of components against surface wear increase and Optimize friction parameters.

specially The invention is concerned with steel components which have an increased surface load, for example exposed when used in rolling bearings are.

In principle, such Components from as possible tough Steel grades or similar Alloys are made to both Rei friction coefficient as well as hardness and to optimize abrasion. However, this is often because of the material costs not possible or for example because the components are not for various reasons can be made homogeneous or should.

It alternatively have different types of surface designs and developed treatments that allow surfaces of steels and other alloys can be specially treated around the surface properties across from to change the properties of the respective component core.

Of the present invention is based on the object, a steel component as well as to provide a method of its production which, if possible low production costs in the area of a particularly stressed surface a big Material hardness with a low tendency to cracking and high wear resistance connect against abrasion.

The Task is according to the invention solved with the features of claim 1.

there will be in a basically known processes carbonitriding a shell component, that is, at elevated temperatures Exposed to carbon and nitrogen, leaving corresponding atoms in the surface area can diffuse.

This For example, in an ammonia-enriched hydrocarbon gas, advantageously at a temperature between 820 ° C and 930 ° C happen. The duration of a Such treatment can take between two and twelve hours depending on the temperature choice and composition of the gas as well as gas pressure vary.

Thereon the shell component can continue at a corresponding temperature for example between 820 ° C and 880 ° C (Curing temperature) be stored to a large extent conversion of ferrite into austenite (Austenitization). Then there is a deterrent this means a quick cooling, for example, up to room temperature (20 ° C), instead of at least with a cooling rate, which corresponds to the so-called first critical cooling rate, the authoritative for one martensitic hardening is.

Corresponding At least part of the austenite will be in the quenching process converted into martensite, at least in the surface area a desired one size Has hardness.

Thereon the component is stored for a time at a low temperature, at least below 0 ° C to reduce residual austenite.

There the shell component has a carbon content between 0.8% and 1.1% in Having proportions by weight, can with the appropriately formed martensitic part of a high hardness be achieved when a corresponding freezing occurs. By the preceding Carbonitriding is the carbon content, especially in the surface area high, so that the achievable by the storage at low temperature Hardness in the outdoors particularly high values (62 to 67 HRC), while below the surface layer a hardness of at least 60 HRC and a retained austenite content of less than 10% is present.

in the surface area is the transformation of retained austenite into martensite because of there increased Carbon content is not as pronounced as in the core area and must by refrigerated storage supports become.

Especially by limiting the sulfur content to less than 0.01 weight percent results in the surface area a good tenacity against stress-induced cracking.

By the overall reduced residual austenite content also results in one size Dimensional stability of the steel component, at least up to 135 ° C.

The inventive method can be advantageously configured in that between the Carbonitriding and quenching the shell at a hardening temperature between 820 ° C and At least 880 ° C Stored for 20 minutes.

The Storage time is doing so advantageously at least 20 minutes after heating, in this hardening process extensive austenitisation takes place. This will be the increased by deterrence achievable martensite.

Additionally or Alternatively, it can also be provided that between the carbonitriding and quenching the shell at a temperature between 600 ° C and At least 750 ° C stored for one hour.

Additionally or alternatively it is also possible that between carbonitriding and quenching the shell component at a temperature between 500 ° C and 750 ° C an annealing treatment is suspended.

A advantageous embodiment of the invention provides that the shell component between the carbonitriding and the following treatment step cooled to room temperature becomes.

By the interim cooling At room temperature, some martensite in the core of the component take place because there the carbon content is relatively low and the corresponding martensite start temperature higher as for the outdoor area, in which the carbon content of the component is much higher.

To quenching takes place the actual reduction of retained austenite content by a further cooling and storage of the component at a low temperature place, the advantageously below 0 ° C, particularly advantageous below -40 ° C, especially -100 ° C and occasionally advantageous even below -150 ° C.

The Component can also be using liquid nitrogen brought to its temperature and stored there to a preferably extensive conversion of retained austenite to martensite.

These Storage may last, for example, for at least one hour.

In order to it is ensured that the component is cooled to the core and correspondingly long at the cooling temperature is stored.

To Storage at low temperature, the component can be heated and to be started.

there the tempering at different temperature levels is conceivable, wherein Advantageously, the first tempering stage between 120 ° C and 200 ° C is provided. When starting on the first tempering stage the martensite goes into a cubic one Martensite referred to modification level.

moreover Further tempering stages between 200 ° C and 320 ° C are conceivable for the reduction of the residual austenite.

The Invention relates except to a method for producing a steel component also on a Steel component made according to the method described and that a retained austenite content in the area of the surface between 15% and 40%.

in the Core area, the steel component has a much lower austenite content on than in the surface area, for example, less than 10%. This will cause the surface area as a result of a tough Residual austenite content, high residual compressive stresses and a high hardness extreme wear-resistant, In addition, the component by the low sulfur content an excellent Resistance to stress-induced cracking and toughness having.

in the The invention will be described below with reference to an exemplary embodiment in a drawing shown and described below.

there shows

1 the spindle of a machine tool;

2 a spindle bearing in the form of an angular contact ball bearing;

3 a schematic process representation of the method according to the invention.

The inventive method is particularly suitable for the production of elements for rolling bearings, in particular rolling bearings for fast-moving Spindles of machine tools or other fast-moving and highly loaded Components. With such elements are particularly high demands to the wear resistance of the steel in the rolling bearing posed. In the corresponding bearings are advantageous Keramikwälzkörper (cylindrical rollers or Balls) used. It is advantageous to lubricate with grease or oil instead of.

The 1 shows a spindle 1 a machine tool not shown in detail, which is rotatably mounted in a plurality of bearings and by means of a drive 2 is driven in rotation.

There are in detail two angular contact ball bearings 3 . 4 shown, the axial movement of the spindle in the direction of the arrow 5 prevent and the spindle in the arrow 5 Support opposite axial direction. In addition, there are two angular contact ball bearings 6 . 7 shown, which is an axial movement of the spindle 1 in the direction of the arrow 8th prevent it and the spindle with it in the arrow 8th Support opposite axial direction.

In addition, the respective Schrägkugella provide ger 3 . 4 . 6 . 7 for radial support and storage. The corresponding rolling elements (balls) are designed as ceramic body.

In each case the inner and / or outer ring 9 . 10 a bearing is at least in the region of its tread, which comes into contact with the rolling elements, particularly wear-resistant.

This is closer in connection with the 2 shown. In the 1 is in addition to the angular contact ball bearings nor a radial cylindrical roller bearings 11 illustrated, will not be discussed in more detail below.

The 2 shows enlarged a single angular contact ball bearing with an outer ring 12 who has a tread 13 has, as well as an inner ring 14 who has a tread 15 for a spherical rolling element 16 having.

The treads 13 . 15 are arranged asymmetrically such that an axial relative movement in the direction of the arrows 17 . 18 prevents the two bearing rings against each other and the bearing is supported accordingly.

In addition, in the figure schematically a bearing cage 19 as well as a multi-part end shield on each end face 20 . 21 shown. The bearing is typically oil lubricated and is suitable for high speeds and exceptionally long tool life.

In the 3 is a schematic diagram of the inventive method based on time and temperatures for different process steps shown.

there The process begins at a Temp 5 temperature, which is between 820 ° C and 930 ° C lie can. The crude steel component, which is homogeneous at the beginning of the process is between 0.8 and 1.1 percent by weight carbon, 1.3 to 2 weight percent chromium, 0.2 to 1.5 weight percent manganese, 0.2 to 0.9 weight percent silicon and less than 0.01 weight percent Contains sulfur as well as other usual and unavoidable impurities and accompanying elements will be added this temperature of a carbonitriding in an ammonia enriched Hydrocarbon gas subjected, wherein in the tread (rolled over Functional surface) the carbon content at 0.9% to 1.4% and the nitrogen content is enriched to 0.05% to 0.5%. The increase of said carbon and nitrogen contents to a depth of between 1% and 6% of the corresponding component diameter in the area of the rolled over Area. The carbonitriding at the temperature Temp 5, for example, over two to twelve Hours take place and their end is by the time t1 in the diagram characterized. After that, the temperature can reach room temperature Temp 2 lowered, held there from t2 to t3 and then again be kept at a temperature Temp 4 between 820 ° C and 880 ° C until the time t4. Instead of this hardening between t3 and t4 at a temperature between 820 ° C and 880 ° C can there also a heat treatment between 500 ° C and 750 ° C respectively an annealing treatment between 500 ° C and 750 ° C made become.

The transition between the carbonitriding temperature Temp 5 and the hardening temperature Temp 4 can also be effected directly without intermediate cooling to room temperature, as indicated by the dotted line 22 is indicated.

To the At time t4, a quench is provided with a cooling rate, the first critical cooling rate for one exceeds martensitic transformation and zwartypisch to room temperature Temp 2. Here, however also a cooling off be provided to another lower temperature, too less than the room temperature can be temp 2.

To quenching, the component can be further cooled until time t5 down to a temperature of 1, which is well below room temperature, often advantageous below -40 ° C or -100 ° C, for example even at the temperature of the liquid Nitrogen can lie. At this temperature Temp 1, the component stored over at time t6 a period of time that is complete Through-cooling and after that a storage period of at least half an hour is planned.

Thereon until the time t7, the component is again up to room temperature heated to later to Time t8 to be started. The tempering to increase the toughness typically occurs at the first tempering Temp 3 in Range between 120 ° C and 200 ° C instead of.

After that the steel component is cooled down again and ready for use.

By The treatment described becomes a steel component with an extraordinary wear resistance and resilience against stress cracks in the surface area as well as a big one Hardness between 62 and 67 HRC in the surface area created.

The restriction of the sulfur content to avoid the excretion of larger sulphides, otherwise, the fracture toughness achieved by the treatment to destroy.

1

spindle

2

drive

3, 4, 6, 7

Angular contact ball bearings

5

movement direction the spindle

8th

prevented Axial movement of the spindle

9 14

inner ring

10 12

outer ring

11

Cylindrical roller bearings

13

Tread of the outer ring

15

Tread of the inner ring

17 18

prevented Relative movement of the treads

19

bearing cage

20 21

end shield

22

direct transition between carbonation and hardening temperature

Claims (11)

Method for producing a steel component ( 12 . 14 ) starting from a shell component having a sulfur content of less than 0.01% by weight of sulfur and a carbon fraction of between 0.8 and 1.1% by weight, in which at least one surface area ( 13 . 15 ) is carbonitrided, then the component quenched at least at the first critical cooling temperature and then stored at a low temperature below 0 ° C. Method according to claim 1, characterized that between carbonitriding and quenching the shell component at a hardening temperature between 820 ° C and 880 ° C stored for at least 20 minutes. Method according to claim 1 or 2, characterized that between carbonitriding and quenching, the shell component at a temperature between 600 ° C and 750 ° C is stored for at least one hour. Method according to claim 1, 2 or 3, characterized that between carbonitriding and quenching the shell component at a temperature between 500 ° C and 750 ° C an annealing treatment is suspended. Method according to one of claims 1 to 4, characterized that the shell component between the carbonitriding and the following Treatment step is cooled to room temperature. Method according to one of claims 1 to 5, characterized that the low temperature below -40 ° C, especially below -100 ° C, particularly advantageous less than -150 ° C. Method according to one of claims 1 to 6, characterized that storage at low temperature for at least one hour ongoing. Method according to one of claims 1 to 7, characterized that the shell component after storage at low temperature and heated is started. Method according to one of claims 1 to 8, characterized that the carbonitriding in an ammonia-enriched hydrocarbon gas over at least two hours. Steel component produced by the method according to one of the preceding claims 1, characterized by a Restaustinitgehalt between 15% and 40% in the surface area. Steel component according to claim 10, characterized by an Austinitgehalt in the core, which is lower than in the range of Surface.