DE102008004371A1 - Component, in particular a motor vehicle component, made of a dual-phase steel - Google Patents

Abstract

The invention relates to a component, in particular a motor vehicle component, made of a steel with a dual-phase structure of martensite / bainite and ferrite, wherein the component is formed of a solid rod material having a component thickness of at least 2.5 mm.

Description

The Invention relates to a component, in particular a motor vehicle component, from a steel with a dual phase structure of martensite / bainite and Ferrite.

State of the art

A essential limitation of the utilization of high-strength materials given on the one hand by their mechanical properties, on the other hand by their machinability. For highly stressed components in vehicle construction such. B. diesel injection components are above all the cyclic resistance and the economic Machinability, d. H. formability, machinability and weldability significant. An increase the cyclic resistance, d. H. a higher vibration resistance and higher Toughness, usually goes with the addition of expensive alloying elements or with a complex heat treatment and a limitation the machinability and weldability associated.

investigations have shown that the fatigue strength of steels is not just a function the static strength is, but also of the internal structure being affected. Usually have high-strength steels a martensitic or a bainitic structure, combined with a restricted Toughness.

Though let yourself the cyclic resistance of such steels by introducing residual compressive stresses in the surface z. B. by Autofrettage still increase, but the suitability These materials due to the only moderate plastic deformation behavior for one limited such production step. Due to the moderate toughness characteristics have these high strength steels Furthermore a low tolerance inner notches, d. H. Material defects, and outer notches due to the geometry or Processing errors on.

possibly due to their chemical composition are suitable steels known from practice so-called dual-phase steels, but which due to their cooling behavior only as sheet metal materials suitable for cold rolling find application.

Disclosure of the invention

Technical task

task The invention is for mechanically highly stressed, in particular by internal pressures cyclically claimed components and in particular motor vehicle components to provide an advantageous material education.

Technical solution

The Task is based on the generic term in conjunction with the characterizing Characteristics of claim 1 solved. Advantageous developments are the subject of dependent claims.

To The teaching of the invention is called in the task Target by an embodiment of a device, in particular a Motor vehicle component made of a steel with a dual phase structure of martensite / bainite and ferrite, which consists of a solid rod material with a component thickness of at least 2.5 mm is formed reaches.

Advantageous effects

It has surprisingly shown that previously known only as sheet metal steels with a dual-phase structure from martensite / bainite and ferrite contrary to previous assumptions material-immanent advantages are also applicable to components, which from a stronger Solid rod material are formed.

Under Solid rod material is understood to be an output component, which is a wall thickness which is greater than in cold rolling suitable sheet material, wherein the material properties also in the middle of the wall thickness good by external cooling are adjustable, and usually at most 2 mm.

It It was found that the advantageous properties of the steel according to the invention also with components of a rod material with a thickness of at least 10 mm and in particular highly stressed components with a wall thickness be achieved by at least 25 mm.

at an inventively designed Component is advantageously an increase in cyclic resistance, especially the fatigue strength and the toughness, without the addition of expensive alloying elements or the implementation complex heat treatments realized, bringing the operational capability of the material steel z. For example Components in diesel injection systems such as nozzles, injectors or high-pressure pumps and accumulator increased is. With components according to the invention, in contrast to conventional toughen hence in the future expected requirements, for example diesel engines injection pressures of up to 3000 bar, fulfilled become.

By Utilization of the previously not considered Potentials in the chemical composition of medium-alloyed steels and an optimization of the heat treatment can steels according to the invention are produced, that meet such extreme requirements. Draw these steels through strength over 1100M Pa and a dual-phase structure from martensite / bainite and ferrite and exhibit despite their high Strength a good shapeability and thus a suitability for the autofrettage.

The component strength and the chemical composition of material may vary depending on the application predefined mechanical properties in the middle of the device be set.

By the choice of alloying elements and their proportions can be the structure such conversion amounts be designed that without big Heat treatment measures only by defined cooling or cooling off in air at room temperature after forging the desired Properties are achieved.

By the microstructure The notch sensitivity is reduced and thus the strength increased under cyclic load.

by virtue of the restricted chemical composition ensures weldability, and by optimizing the steelmaking or rolling process can be applied to a heat treatment be dispensed with the subsequent component production line.

The Invention allows the production of mechanically and / or cyclically highly stressed Components with rod material components not previously available property combinations as well as by the possible Elimination of a heat treatment to set the desired Material properties a reduction the value chain.

One Component according to the invention is particularly suitable as a fuel injection component of a motor vehicle, which is designed for the injection of both diesel and gasoline can be.

A such fuel injection component can be forged and machined. Represent component.

in the The following are preferred chemical compositions of a Device according to the invention described, wherein the components each in% by weight.

Embodiments of the invention

at advantageous embodiments a device according to the invention, this has a C content of at least 0.18% and at most 0.25%, an Si content of at least 0.2% and at most 1.1%, an Mn content of at least 1% and at most 2%, a P content of at most 0.025%, an S content of at most 0.025%, a Cr content of at least 1.2% and at most 1.7%, a Mo content of at least 0.2% and at most 0.4%, a Ni content of at least 0.1% and at most 0.6%, a Cu content of at most 0.3%, a Nb content of at most 0.15%, a V content of at most 0.2%, a Ti content of at most 0.05%, an Al content of at most 0.03% and an N-content of at most 0.025% on.

The chemical composition of two advantageous dual-phase steels with microalloying properties Table 1 can be found. Chemical element C Si Mn P S Cr Not a word Ni Cu Nb V Ti al N Steel 1 0.22 0.24 1.69 0.02 0.02 1.66 0.32 0.17 0.21 0.1 0.03 0.03 0.02 0,017 Steel 2 0.19 0.4 1.12 0.01 0.01 1.22 0.31 0.55 0.2 0.09 0.16 0.03 0.01 0,014 Min values 0.18 0.2 1.0 Max Max 1.2 0.2 0.1 Max Max Max Max Max Max Max values 0.25 1.1 2.0 0,025 0,025 1.7 0.4 0.6 0.3 0.15 0.2 0.05 0.03 0,025 All data in% by weight Table 1

By The choice of chemical composition is used in steels Group 1 a very transformative Behavior adjusted, in which even after slower or more moderate Cooling from an austenitizing temperature, for example after forging, a complete one martensitic structure is present. By varying the cooling rate and, if necessary the occasion treatment can the strength of the basic texture from fine-grained Martensite in the range of about 1200 to approx. 1500 MPa be comparable to a hardness from 400-460 HV10.

at toughen Group 2 is characterized by a slightly different chemical composition achieved that for a larger area cooling rates Dual-phase microstructure consisting of ferrite and bainite. The strengths are between 1000 and 1100 MPa (300-350 HV10).

For the described steels can through minor changes in the chemical composition and by suitable cooling the hot forming heat targeted microstructure conditions and Strengths can be adjusted without requiring additional heat treatments become.

by virtue of the microstructure These materials have a very high despite their high strength high ductility. By the limited Alloy element content, the materials are weldable and are characterized by a low residual stress due to the conversion inertia after welding out. This property combination is rather uncommon for steels. Because of the high strength In addition, there is a very good cyclic resistance of the materials guaranteed which is further improved by the ductile, fault tolerant structure.

by virtue of The phase components ferrite and bainite have the dual phase structures described in comparison with tempered steels equal strength advantageously also sufficient workability.

Claims (8)

Component, in particular motor vehicle component, made of a steel with a dual-phase structure of martensite / bainite and ferrite, characterized in that it is formed of a solid rod material having a component thickness of at least 2.5 mm. Component according to claim 1, characterized by a component strength of at least 5 mm, in particular of at least 10 mm or at least 25 mm. Component according to claim 1 or 2, characterized in that its Baüelementstärke and chemical material composition in dependence of predefined for the application mechani is selected in the middle of the device's properties. Component according to one of claims 1 to 3, characterized by a C content of at least 0.18% and at most 0.25%, an Si content of at least 0.2% and at most 1.1%, an Mn content of at least 1% and at most 2%, a P content from at most 0.025%, an S-content of at most 0.025%, a Cr content of at least 1.2% and at most 1.7%, a Mo content of at least 0.2% and at most 0.4%, a Ni content of at least 0.1% and at most 0.6%, a Cu content from at most 0.3%, a Nb content of at most 0.15%, a V content of at most 0.2%, a Ti content of at most 0.05%, an Al content of at most 0.03% and an N content of at most 0.025%. Component according to claim 4, characterized by a C content of at least approximately 0.22%, an Si content from at least approximate 0.24%, an Mn content of at least approximately 1.69%, a P content of at least nearly 0.02%, an S content of at least approximately 0.02%, a Cr content from at least approximate 1.66%, a Mo content of at least approximately 0.32%, a Ni content of at least approximately 0.17%, a Cu content of at least approximately 0.21%, an Nb content from at least approximate 0.1%, a V content of at least approximately 0.03%, a Ti content from at least approximate 0.03%, an Al content from at least approximate 0.02% and an N content of at least approximately 0.017%. Component according to claim 4, characterized by a C content of at least approximately 0.19%, an Si content from at least approximate 0.4%, an Mn content of at least approximately 1.12%, a P content from at least approximate 0.01%, an S content of at least approximately 0.01%, a Cr content of at least nearly 1.22%, a Mo content of at least approximately 0.31%, a Ni content of at least approximately 0.55%, a Cu content of at least approximately 0.2%, an Nb content from at least approximate 0.09%, a V content of at least approximately 0.16%, a Ti content from at least approximate 0.03%, an Al content of at least approximately 0.01%, and an N content from at least approximate 0.014%. Component according to one of claims 1 to 6, characterized that it is heat treated is. Component according to one of claims 1 to 7, characterized it is a fuel injection component of a motor vehicle forms.