DE102020004685A1 - Process for producing a surface-treated solid component from a steel material and such a component - Google Patents

Abstract

The invention relates to a method for producing a surface-treated solid component from a quench-hardenable steel material, in which the steel material is formed to shape the component, if necessary heated and cooled from a temperature above the austenitization temperature faster than the lower critical cooling rate, in particular than the upper critical cooling rate is quenched and subjected to surface treatment, with tempering of the quenched part only after surface treatment and below a temperature of 260°C.

Description

The invention relates to a method for producing a surface-treated solid component from a quench-hardenable steel material, in which the steel material is formed to shape the component, is quenched during case hardening from a temperature above the austenitization temperature by cooling faster than the lower critical cooling rate, and is subjected to a surface treatment is, as well as such a solid component.

Such components are of course well known from numerous applications, for example the automotive industry, in order to form the mechanical systems of higher functionality and structural components and their arrangements from them.

In order to achieve the desired strength of, for example, above 800 MPa, the components are usually made of steel, in particular so-called QT steels (Quenching and Tempering). They gain their hardness through rapid quenching from a temperature above _Ac 3 or a temperature at which there is at least partial austenitization. After rapid cooling/quenching, tempering occurs at temperatures typically greater than 500°C to increase ductility by relieving residual stresses generated during quenching. During tempering, the very hard but also very brittle microstructure created by lattice changes during tempering is made ductile again. After annealing, the parts are typically given their final shape by machining and subsequent smoothing, and are then surface-treated, for example by applying a coating galvanically, and if necessary subjected to another heat treatment or hot drying.

Despite many years of practice and a procedure that usually works well, a functionality that is less than desired can occasionally be observed, especially in the case of the application of moving components.

The invention is therefore based on the object of further developing a method of the type mentioned at the outset in such a way that a satisfactory compromise between the effort involved in the method and satisfactory functionality of the component in the application is achieved.

This object is achieved from a procedural point of view by a further development of the method of the type mentioned at the outset, which is essentially characterized in that the quenched part is only tempered after the surface treatment and below a temperature of 260°C.

In the context of the invention, it was recognized that by postponing the time of tempering until after the surface treatment while simultaneously carrying out the same at significantly lower tempering temperatures than usual, on the one hand a satisfactory tensile strength or hardness of the component can be achieved while at the same time avoiding negative effects on the surface layer, for example due to very thin oxide layers.

More preferably, the tempering temperature in the process is kept below 254°C, preferably below 248°C, more preferably below 242°C, and/or above 180°C, preferably above 188°C, in particular above 194 °C maintained.

In the method, the duration of the tempering is more preferably kept to less than 12 hours, preferably less than 10.4 hours, more preferably less than 9.6 hours, and/or more than 1 hour, preferably more than 2 hours, in particular more than 4 hours.

More preferably, in the method after quenching, no more heat treatment with temperature increase of the part to over 300° C. is carried out.

More preferably, no further heat treatment with temperatures above 260° C., in particular above 250° C., is carried out in the method after the quenching and/or after the surface treatment.

In the method, the part is also preferably machined before the surface treatment, and the part is optionally smoothed.

In the method, the surface treatment is more preferably carried out by means of a galvanically or otherwise applied coating of the part.

More preferably, in the method after the annealing there is no polishing with material removal of a thickness of more than 400 nm, preferably more than 200 nm, in particular more than 100 nm of the outer surface layer of the part.

In terms of device technology, the invention relates to a solid component made of an at least partially coated steel material, with a yield point of greater than obtained via case hardening 1040 MPa, preferably greater than 1070 MPa, in particular greater than 1100 MPa, an at least partially bainitic and/or martensitic structure with an elongation at break of less than 14% and in particular a surface with a coefficient of friction (ISO 16047) of less than 0.12 at least in some areas , preferably as 0.08, in particular as 0.06.

In the case of the solid component, the microstructure is more preferably formed by a heat treatment/tempering that takes place after hardening and cooling faster than the lower, in particular than the upper, critical cooling rate at a temperature of greater than or equal to 188° C. and/or less than 280° C. and for a period of greater than 40 minutes and/or less than 12 hours.

More preferably, the surface of the solid component is at least partially formed from the layer formation itself and its subsequent heat treatment at a temperature of greater than or equal to 188° C. and/or less than 254° C. and for a period of greater than 40 minutes and/or less than 12 hours, in particular formed without subsequent polishing with material removal of more than 400 nm.

More preferably, in the case of the solid component, the steel has a carbon content of less than 0.32% by weight, preferably less than 0.28% by weight, in particular 0.24% by weight.

In the case of the solid component, the coating is more preferably a galvanically applied coating or a coating applied in some other way by immersion in a coating bath or by spraying.

More preferably, the invention relates to a solid component, which is a component that is in variable surface contact with a mating surface of another component during use and/or during the assembly of which a surface area comes into variable surface contact with a mating surface.

More preferably, the invention relates to a solid component that is produced according to one of the method aspects described above.

In terms of device technology, the invention also relates to a system for producing a solid component according to one of the aforementioned method aspects with a first heat treatment device for quench-hardening the component, a surface treatment device for surface treatment of the component and a second heat treatment device for tempering the surface-treated component and with an actuation of the second heat treatment device to temperatures below 260°C and in terms of time after the actuation of the surface treatment device.

The advantages of the system according to the invention result from the advantages of the method according to the invention.

With regard to the steel composition, in addition to the already preferred upper limits, compositions with a carbon content of no greater than 0.24% by weight are also used, but preferably with a carbon content of at least 0.12, preferably at least 0.14, in particular at least 0.16% by weight. It preferably contains at least 0.2, preferably at least 0.28, in particular at least 0.36 and/or at most 0.8, preferably at most 0.72, in particular at most 0.64% by weight of silicon.

Furthermore, preferably at least 1.2, preferably at least 1.36, in particular at least 1.52% by weight manganese is contained, and this element with preferably less than 2.1% by weight, more preferably with less than 1.9% by weight. %, in particular with less than 1.84% by weight. Furthermore, chromium is preferably contained as a steel component, in an amount of in particular greater than 1.2% by weight, preferably greater than 1.36% by weight, in particular greater than 1.48% by weight, but preferably less than 2 wt%, more preferably less than 1.88 wt%, especially less than 1.78 wt% chromium. Another preferred alloying element is nickel, with preferably at least 0.04% by weight, more preferably at least 0.06% by weight, in particular at least 0.08% by weight and/or at most 0.4% by weight, more preferably less than 0.36% by weight, in particular less than 0.23% by weight.

As a further preferred alloy component, molybdenum is provided in an amount of preferably at least 0.15, more preferably at least 0.18, in particular at least 0.22% by weight, but preferably not more than 0.5, more preferably not more than 0. 45, especially not more than 0.4% by weight.

Niobium and/or titanium can be included in a small amount, such as in the range of 0.01 to 0.1% by weight.

Sulfur with preferably less than 0.016% by weight can be provided as a further alloying component, but the sulfur content is particularly preferably well below 0.01% by weight, namely not greater than 0.006% by weight, in particular not greater than 0.003% by weight.

Furthermore, the steel preferably contains (in each case) less than 0.05% by weight, in particular less than 0.02% by weight, of boron, phosphorus, copper and/or aluminum.

With regard to the coating thicknesses, thicknesses of at least 4 μm, in particular at least 6 μm and/or at most 22 μm, in particular at most 20 μm, are preferred.

With regard to the mechanical properties, the tensile strength of the component is greater than 1380 MPa, preferably greater than 1400 MPa, in particular greater than 1440 MPa, and/or a yield point R _p0.2 of greater than 1040 MPa, more preferably than 1070 MPa, in particular than 1100MPa. The elongation at break (A5) is also greater than 8%, preferably greater than 10%, but preferably less than 14%, in particular less than 12%.

The invention is described below using exemplary embodiments.

A ball joint is to be manufactured, and the description will be given by way of example of the ball of the ball joint.

The starting steel material is provided and a blank is forged by cold forming or alternatively by hot forming, the outer circumference of which takes on the desired spherical shape.

A bainitic steel with 0.2% by weight of carbon, 0.44% by weight of silicon, 1.6% by weight of manganese, 1.3% by weight of chromium, 0.12% by weight of nickel, 0. 24 wt.% Molybdenum used.

The part is tempered and brought to and held at a temperature of 920°C. After rapid cooling in e.g. water, the part is quench-hardened, alternatively it could also be quenched with the medium air or oil, for example. A first heat treatment device is used for this purpose.

Contrary to the usual procedure, the part is not initially tempered after quenching. Rather, it is machined, e.g. by a CNC machine, to create the final spherical shape and then surface-treated.

In this exemplary embodiment, the surface treatment is carried out by galvanically applying a coating, e.g. a ZnNi coating. A surface treatment device is used for surface treatment.

Only then is the component tempered, in this exemplary embodiment at 240° for 6 hours. This relieves the internal stresses of quench hardening combined with a gentle surface treatment with possibly reduced formation of nano-oxide layers. The coefficient of friction (static friction) of the coated surface is 0.05. The layer thickness of the coating itself is 10 μm in this exemplary embodiment. Tempering takes place by means of a second heat treatment device, which is preferably a different device from the first heat treatment device.

Furthermore, hydrogen is also effused during this heat treatment and thus the risk of hydrogen embrittlement is avoided without resorting to an additional heat treatment.

The time between quench hardening and tempering is 8 hours in this embodiment. During this period, both the mechanical post-treatment by machining and possibly a smoothing process and the application of the coating takes place, which in this exemplary embodiment preferably takes place at room temperature or at temperatures at least preferably less than 60°C, in particular less than 40°C.

The qualitative structure of a temperature curve used for the manufacturing process of the component is in 1 represented in a time-temperature diagram. Conventional methods, on the other hand, work with higher tempering temperatures and/or at least one additional heat treatment and coating that is only carried out later.

In a second exemplary embodiment, again illustrated using the example of a ball of a ball joint with a diameter in the range of 25 to 40 mm, as in the first exemplary embodiment, the same procedure is followed as in the first exemplary embodiment with regard to the timing of the work steps.

Instead of the galvanically applied coating, in this exemplary embodiment the coating is carried out using a spraying method with a commercially available product such as Geomet®321. Tempering takes place at a temperature of 255°C over a period of 1 hour.

In both exemplary embodiments, after the quench hardening, only an additional heat treatment of tempering takes place with the component already coated.

In addition, the surface of the components was checked optically for traces of nano-oxide layers. It was found that with existing mechanical properties such as a yield point R _p0.2 of more than 1040 MPa, in the exemplary embodiments even more than 1100 MPa, nano-oxide layers are also avoided. Accordingly, no relevant abrasive polishing work is required on the component.

The invention is not limited to the above exemplary embodiments. Rather, the features of the above description as well as the following claims can be essential individually and in combination for the implementation of the invention in its various embodiments.

Claims (16)

Method for producing a surface-treated solid component from a quench-hardenable steel material, in which the steel material is deformed to shape the component, if necessary heated and cooled from a temperature above the austenitization temperature faster than the lower critical cooling rate, in particular than the upper critical cooling rate is quenched and subjected to a surface treatment, characterized in that the quenched part is only tempered after the surface treatment and below a temperature of 260°C. procedure after claim 1 wherein the tempering temperature is maintained below 254°C, preferably below 248°C, more preferably below 242°C, and/or above 180°C, preferably above 188°C, especially above 194°C is held. procedure after claim 1 , in which the duration of the tempering is kept below 12 hours, preferably below 10.4 hours, more preferably below 9.6 hours, and/or above 20 minutes, preferably 1 hour, more preferably above 2 hours, in particular above 4 hours . Method according to one of the preceding claims, in which, after quenching, no heat treatment is carried out with the temperature of the part being raised above 300°C. Method according to one of the preceding claims, in which after the quenching and/or after the surface treatment no further heat treatment with temperatures above 260°C is carried out apart from this tempering. Method according to one of the preceding claims, in which the part is machined before the surface treatment, and the part is optionally smoothed. Method according to one of the preceding claims, in which the surface treatment is carried out by electroplating or otherwise applying a coating to the part. Method according to one of the preceding claims, in which, after the annealing, there is no more polishing with material removal of a thickness of more than 400 mm, preferably more than 200 mm, in particular more than 100 mm of the outer surface layer of the part. Solid component made of an at least partially coated steel material, with a yield point obtained via case hardening of greater than 1040 MPa, preferably greater than 1070 MPa, in particular greater than 1100 MPa, an at least partially bainitic and/or martensitic structure with an elongation at break of less than 14%, in particular less than 12% and in particular a surface with at least in some areas a coefficient of friction (ISO 16047) of less than 0.12, preferably less than 0.08, in particular less than 0.06. solid component claim 9 , in which the structure is treated by heat treatment/tempering at a temperature of greater than or equal to 188°C and/or less than 280°C and/or less than 280°C and for a period of more than 40 min and/or less than 12h. solid component claim 9 or 10 , the surface of which is formed from the layer formation itself and its subsequent heat treatment at a temperature of greater than or equal to 188°C and/or less than 254°C and for a period of greater than 40 minutes and/or less than 12 hours, in particular without a subsequent polishing process with material removal of more than 400 nm is formed. Solid component according to one of claims 9 until 11 , in which the steel has a carbon content of less than 0.32% by weight, preferably 0.28% by weight, in particular 0.24% by weight. Solid component according to one of claims 9 until 12 , in which the coating is an electroplated coating or otherwise coating applied by immersion in a coating bath or spraying. Solid component according to one of Claims 1 until 9 , which is a component in use that is in variable surface contact with a mating surface of another component. Solid component after a claims 9 until 14 , Prepared by a method according to any one of Claims 1 until 8th . System for producing a solid component according to a method according to one of Claims 1 until 8th , with a first heat treatment device for quench-hardening the component, a surface treatment device for surface treatment of the component and a second heat treatment device for tempering the surface-treated component, and with a sequence control that controls actuation of the second heat treatment device to temperatures below 260°C and time after actuation of the surface treatment device.

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