COMPONENT MADE OF B-ZR ALLOYED STEEL

Description

[0001] The invention relates to a component with a steel component, in which the steel is alloyed with, among other things, boron (hereinafter also "B"). In particular, the invention relates to a fastening element such as a screw or a nut.

[0002] For steel components, especially high-strength and ultra-high-strength components, boron is often used as a cost-effective alloying element to improve through-hardenability. Boron-alloyed steels are described, for example, in WO 2021 / 009705 A1 and WO 2008 / 142275 A2.

[0003] EP 3 078 758 A1 describes a steel wire for bolts, consisting of C: 0.20 to 0.35%; Si: 0.01% or more; Mn: 0.3 to 1.50; P: more than one and 0.020% or less; S: more than 0% and 0.020% or less; Cr: 0.10 to 1.5%; Al: 0.01 to 0.10%; B: 0.0005 to 0.005%; N: 0.001% or more; and at least one element of Ti: 0.02 to 0.10% and Nb: 0.02 to 0.10%, the balance being iron and unavoidable impurities, wherein when a proportion of a B content at D 0 / 4 in the steel wire for bolts is 100%, where D 0 is a diameter of the steel wire for bolts, a ratio of a B content at a surface of the steel wire for bolts is 75% or less on average, and a difference between a maximum value and a minimum value of the ratio is 25% or less.

[0004] However, components made of boron-alloyed steels, such as screws or nuts, often show a decrease in hardness in the edge area after heat treatment, in particular an isothermal heat treatment in a salt bath to achieve a bainitic structure, especially to a depth of up to 300 µm below the surface, which limits the applicability for high-strength and ultra-high-strength products, such as high-strength and ultra-high-strength screws.

[0005] Typically, steels containing boron are alloyed with additional titanium and aluminum to keep the boron in the dissolved state and prevent it from precipitating as nitrides, carbides, carbonitrides, silicides, or oxides. However, this is not sufficient to reduce the hardness inhomogeneity in the edge region described above.

[0006] The present invention is therefore based on the object of reducing the hardness loss in the edge region of components made of boron-alloyed steels.

[0007] This object is achieved by a component with a component made of steel according to claim 1 and a method for production according to claim 14. Further features, embodiments and advantages emerge from the dependent claims, the description and the figures.

[0008] One aspect of the invention relates to a component with a component made of steel, wherein the steel 0.30 - 0.50 wt% C, 0.05 - 1.3 wt% Mn, 0.001 - 0.015 wt% P, 0.001 - 0.015 wt% S, 0.01 - 0.8 wt% Si, 0.3 - 1.5 wt% Cr, 0.005 - 0.40 wt% V, 0.0008 - 0.0050 wt% B, 0.02 - 0.35 wt% Al, 0.0001 - 0.0200 wt% N, 0.01 - 0.08 wt% Ti, and 0.0030 - 0.0800 wt% Zr; optionally 0.01 - 0.20 wt.% Mo, 0.01 - 0.50 wt.% Ni, 0.01 - 0.50 wt.% Cu, 0.001 - 0.010 wt.% Ca, 0.01 - 0.10 wt.% Bi, 0.01 - 0.30 wt.% Co, 0.01 - 0.06 wt.% Nb, 0.01-0.40 wt.% Pb, 0.01-0.10 wt.% Se, 0.01-0.10 wt.% Te, 0.01-0.3 wt.% W, 0.01-0.04 wt.% As, 0.01-0.20 wt.% Ta, 0.01-0.20 wt.% Ce, 0.01-0.50% by weight Sn, 0.01-0.40% by weight Sb, 0.01-0.20 wt% Hf, and / or one or more lanthanides, each in an amount of 0.01-0.02 wt%, the remainder iron and unavoidable impurities, each unavoidable impurity ≤ 0.01 wt%.-% and wherein the component part has a steel surface and the B content (boron content) in the steel at a depth of 5 - 60 µm is ≥ 80% of the B content in the steel at a depth of 500 µm, the depth being measured perpendicular to the steel surface.

[0009] A further aspect of the invention relates to a method for producing a component with a steel component, comprising the steps: Providing the steel with the above-mentioned composition, then forming a component with a component made of the steel and optionally heat treating it.

[0010] Surprisingly, the composition according to the invention, in particular the zirconium added to the B-containing steel, in combination with the other alloying elements in the component according to the invention with a steel component, counteracts the loss of hardness in the edge region, especially when the steel component is heat-treated. Another surprising advantage of the component according to the invention with a steel component is the improved resistance to hydrogen embrittlement. Surprisingly, significantly higher strengths can be achieved in this way.

[0011] Particularly in fasteners, which usually exhibit high and frequently dynamic axial stresses, improving the hardness in the edge region and also reducing hydrogen embrittlement are particularly advantageous, since the fasteners, which can be screws or nuts, for example, are essential for many assemblies. A failure of a fastener can have drastic consequences for humans or machines, such as in the case of a bridge screw, a chassis screw, an engine head screw, or the like. The invention can thus also relate to a vehicle, an engine, a cylinder head, a chassis assembly, or a battery assembly with a component according to the invention, in particular a fastener.

[0012] In a preferred embodiment of the invention, the component has a steel component, the steel consisting of the following components: 0.30 - 0.50 wt% C, 0.05 - 1.3 wt% Mn, 0.001 - 0.015 wt% P, 0.001 - 0.015 wt% S, 0.01 - 0.80 wt% Si, 0.3 - 1.5 wt% Cr, 0.005 - 0.40 wt% V, 0.0008 - 0.0050 wt% B, 0.02 - 0.35 wt% Al, 0.0001 - 0.0200 wt% N, 0.01 - 0.08 wt% Ti, and 0.0030 - 0.08 wt% Zr; optionally 0.01 - 0.20 wt% Mo, 0.01 - 0.50 wt% Ni, 0.01 - 0.50 wt% Cu, and / or 0.0010 - 0.0100 wt% Ca; and the remainder iron and unavoidable impurities, wherein the component part has a steel surface and the B content in the steel at a depth of 5 - 60 µm is ≥ 80% of the B content in the steel at a depth of 500 µm, the depth being measured perpendicular to the steel surface, each impurity being present in ≤ 0.01 wt%.

[0013] Further preferably, the steel can optionally 0.01-0.10 wt% Bi, 0.01-0.30 wt% Co, 0.01-0.06 wt% Nb, 0.01-0.40 wt% Pb, 0.01-0.10 wt% Se, 0.01-0.10 wt% Te, 0.01-0.3 wt% W, 0.01-0.04 wt% As, 0.01-0.20 wt% Ta, 0.01-0.20 wt% Ce, 0.01-0.50 wt% Sn, 0.01-0.40 wt% Sb, 0.01-0.20 wt% Hf, and / or one or more lanthanides, each in an amount of 0.01-0.02 wt%.

[0014] The invention further preferably relates to a component with a component made of steel, wherein the steel 0.30 - 0.48 wt% C, 0.2 - 1.3 wt% Mn, 0.001 - 0.015 wt% P, 0.001 - 0.015 wt% S, 0.01 - 0.70 wt% Si, 0.3 - 1.4 wt% Cr, 0.005 - 0.38 wt% V, 0.0010 - 0.0050 wt% B, 0.02 - 0.30 wt% Al, 0.0010 - 0.0180 wt% N, 0.012 - 0.07 wt% Ti, and 0.0040 - 0.0600 wt% Zr; optionally 0.01 - 0.18 wt% Mo, 0.01 - 0.45 wt% Ni, 0.01 - 0.40 wt% Cu, and / or 0.0010 - 0.0090 wt% Ca; and the remainder iron and unavoidable impurities, wherein the component of the component has a steel surface and the B content in the steel at a depth of 5 - 60 µm is ≥ 80% of the B content in the steel at a depth of 500 µm, wherein the depth is measured perpendicular to the steel surface. Preferably, the steel consists of the above-mentioned components. Each impurity is present in ≤ 0.01 wt%.

[0015] In a further preferred embodiment, the invention relates to a component with a component made of steel, wherein the steel 0.30 - 0.46 wt% C, 0.3 - 1.3 wt% Mn, 0.001 - 0.015 wt% P, 0.001 - 0.015 wt% S, 0.01 - 0.60 wt% Si, 0.3 - 1.3 wt% Cr, 0.005 - 0.35 wt% V, 0.0012 - 0.0050 wt% B, 0.02 - 0.25 wt% Al, 0.0020 - 0.0150 wt% N, 0.014 - 0.060 wt% Ti, and 0.0050 - 0.0500 wt% Zr; optionally 0.01 - 0.16 wt% Mo, 0.01 - 0.40 wt% Ni, 0.01 - 0.30 wt% Cu, and / or 0.0010 - 0.0080 wt% Ca; and the remainder iron and unavoidable impurities, wherein the component of the component has a steel surface and the B content in the steel at a depth of 5 - 60 µm is ≥ 80% of the B content in the steel at a depth of 500 µm, the depth being measured perpendicular to the steel surface. Preferably, the steel consists of the above-mentioned components. Each impurity is present in ≤ 0.01 wt%.

[0016] In the most preferred embodiment of the invention, a component comprising a steel component is provided, wherein the steel 0.34 - 0.42 wt% C, 0.45 - 0.90 wt% Mn, 0.001 - 0.015 wt% P, 0.001 - 0.015 wt% S, 0.02 - 0.50 wt% Si, 0.60 - 1.00 wt% Cr, 0.08 - 0.25 wt% V, 0.0012 - 0.0050 wt% B, 0.02 - 0.25 wt% Al, 0.0025 - 0.0090 wt% N, 0.015 - 0.060 wt% Ti, and 0.0050 - 0.0500 wt% Zr; optionally 0.01 - 0.16 wt% Mo, 0.01 - 0.40 wt% Ni, 0.01 - 0.30 wt% Cu, and / or 0.0010 - 0.0060 wt% Ca; and the remainder iron and unavoidable impurities, wherein the component of the component has a steel surface and the B content in the steel at a depth of 5 - 60 µm is ≥ 80% of the B content in the steel at a depth of 500 µm, wherein the depth is measured perpendicular to the steel surface. Preferably, the steel consists of the above-mentioned components. Each impurity is present in ≤ 0.01 wt%.

[0017] More preferably, the steel according to the above compositions may also optionally 0.01-0.10 wt% Bi, 0.01-0.30 wt% Co, 0.01-0.06 wt% Nb, 0.01-0.40 wt% Pb, 0.01-0.10 wt% Se, 0.01-0.10 wt% Te, 0.01-0.3 wt% W, 0.01-0.04 wt% As, 0.01-0.20 wt% Ta, 0.01-0.20 wt% Ce, 0.01-0.50 wt% Sn, 0.01-0.40 wt% Sb, 0.01-0.20 wt% Hf, and / or one or more lanthanides, each in an amount of 0.01-0.02 wt%.

[0018] According to the invention, a component with a component made of steel, wherein the steel 0.30 - 0.50 wt% C, 0.05 - 1.3 wt% Mn, 0.001 - 0.015 wt% P, 0.001 - 0.015 wt% S, 0.01 - 0.8 wt% Si, 0.3 - 1.5 wt% Cr, 0.005 - 0.40 wt% V, 0.0008 - 0.0050 wt% B, 0.02 - 0.35 wt% Al, 0.0001 - 0.0200 wt% N, 0.01 - 0.08 wt% Ti, and 0.0030 - 0.0800 wt% Zr; optionally 0.01 - 0.20 wt.% Mo, 0.01 - 0.50 wt.% Ni, 0.01 - 0.50 wt.% Cu, 0.0010 - 0.0100 wt.% Ca, 0.01-0.10 wt% Bi, 0.01-0.30 wt% Co, 0.01-0.06 wt% Nb, 0.01-0.40 wt% Pb, 0.01-0.10 wt% Se, 0.01-0.10 wt% Te, 0.01-0.3 wt% W, 0.01-0.04 wt% As, 0.01-0.20 wt% Ta, 0.01-0.20 wt% Ce, 0.01-0.50 wt% Sn, 0.01-0.40 wt% Sb, 0.01-0.20 wt% Hf, and / or one or more lanthanides, each in an amount of 0.01-0.02 wt%, the remainder iron and unavoidable impurities, preferably consists of these components, wherein each impurity ≤ 0.01 wt.%.

[0019] With the above-mentioned preferred and particularly preferred steel compositions, the loss of hardness in the edge region of the components can be particularly effectively reduced. Furthermore, hydrogen embrittlement of the steel is significantly reduced.

[0020] The components Mo, Ni, Cu, and Ca are optional, meaning they may not be present independently of one another, or, if present, they may be present independently of one another in the steel in the specified amounts of, for example, 0.01-0.20 wt% Mo, 0.01-0.50 wt% Ni, 0.01-0.50 wt% Cu, and / or 0.0010-0.0100 wt% Ca. In a preferred embodiment, the components Mo, Ni, Cu, and Ca are present independently of one another in the steel. It is thus preferred that the steel contains 0.01 - 0.20 wt% Mo, 0.01 - 0.50 wt% Ni, 0.01 - 0.50 wt% Cu and / or 0.0010 - 0.0100 wt% Ca, more preferably 0.01 - 0.16 wt% Mo, 0.01 - 0.40 wt% Ni, 0.01 - 0.30 wt% Cu and / or 0.0010 - 0.0080 wt% Ca.

[0021] The components Bi, Co, Nb, Pb, Se, Te, W, As, Ta, Ce, Sn, Sb, Hf, and / or lanthanides may also optionally be included in the steel, meaning they may be included or not included independently of one another. If included, they may be included independently of one another, preferably in the specified amounts.

[0022] Zirconium is a microalloying element in the steel of the component according to the invention, meaning it exerts an effect even in very small amounts, especially below 0.05 wt.%. Boron, titanium, and vanadium are also microalloying elements. In the composition according to the invention, zirconium interacts with the other alloying elements, for example, vanadium.

[0023] According to the invention, the B content in the steel at a depth of 5 - 60 µm is ≥ 80%, preferably ≥ 90%, of the B content in the steel at a depth of 500 µm (micrometers), with the depth being measured perpendicular to the steel surface. This means that the B content at any point at a depth of 5 - 60 µm is ≥ 80% of the B content in the steel at a depth of 500 micrometers. In other words, over the depth range of 5 - 60 µm, the minimum B content in the steel at a depth of 5 - 60 µm is ≥ 80% of the boron content in the steel at a depth of 500 µm, preferably ≥ 90%, particularly preferably ≥ 95%.

[0024] The boron content refers to the concentration of boron in weight percent, based on the total weight of the steel. Since the value of, for example, ≥ 80% is a relative value of two B contents, the B content does not have to be expressed in weight percent, but can also be expressed in volume or atomic percent, for example.

[0025] The B content is determined according to the invention using GDOES (Glow Discharge Optical Emission Spectroscopy) (apparatus: GDA 750 HR from Spectruma Analytik GmbH). The surface of the sample material (steel) is ablated using an Ar plasma, and the sample atoms are brought into the gas phase (cathode sputtering) and then quantitatively determined spectroscopically. In this way, the B content is measured spectroscopically at every depth, for example, over a depth range of 0 - 500 µm. The measurement result is a so-called B depth profile. In this way, the B content is determined at every depth, for example, over a depth range of 0 - 500 µm. The ratio is then determined by dividing the B contents at a specific depth (e.g. 10 µm) and at a depth of 500 µm, thus determining the percentage value, which according to the invention is ≥ 80%.

[0026] Furthermore, according to the invention, the boron content in the steel at a depth of 140-220 µm is preferably ≥ 80% of the boron content in the steel at a depth of 500 µm. At both the depth of 5-60 µm and the depth of 140-220 µm, the boron content is independently preferably ≥ 90%, further preferably ≥ 95%, further preferably ≥ 98%, even more preferably ≥ 100%, most preferably 100-1000% of the boron content of the steel at a depth of 500 µm, with the depth being measured perpendicular to the steel surface. For example, if the boron content (B concentration) in the steel is 0.0030 - 0.0033 wt% at a depth of 5 - 60 µm and 0.0033 wt% at a depth of 500 µm, that would be 90.9% - 100%.

[0027] The other chemical elements in the steel are measured, as usual, using conventional optical emission spectrometry on the surface of a cross-section of the steel component (so-called product analysis). The stated weight percentages of the chemical elements in the steel are based on the total weight of the steel.

[0028] Investigations of the alloy composition of known boron steels within the scope of the invention showed that there is a reduction in boron content in the edge region compared to the boron content at greater depths. Without being bound by the invention, it is assumed that the low or reduced drop in boron concentration in the edge region according to the invention leads to a surprisingly small drop in hardness in the edge region of the steel component and to a surprising reduction in hydrogen embrittlement in the edge region. This is attributed to a combination of the inventive amounts of zirconium and the other alloying elements, for example, vanadium.According to the invention, in addition to the composition of the steel, the heat treatment or tempering at the end of the manufacturing process, in particular a salt bath tempering, which leads to these advantageous properties in the edge region of the steel component in the component according to the invention, is advantageous for the low or non-existent drop in the boron concentration.

[0029] The edge area is understood to be the area at a depth of 0 - 300 micrometers, measured from the steel surface.

[0030] According to the invention, the zirconium in particular, in combination with the other alloying elements, counteracts the decrease in hardness in the edge region and leads to a reduction in hydrogen embrittlement in the edge region.

[0031] For the purposes of the invention, an impurity is understood to mean an element present in an amount of ≤ 0.01 wt.%. The steel contains unavoidable impurities, each in an amount of ≤ 0.01 wt.%.

[0032] Furthermore, it was found within the scope of the invention that the hardness drop in the edge region of the components can be particularly effectively reduced if the ratio of (Zr + Ti + Al) to N is in a range from 2.7 to 150, more preferably 2.8 to 130, particularly preferably 3 to 100. The respective weight percentages of Zr, Ti, Al, and N are used in the aforementioned formula.

[0033] The component according to the invention with a component made of steel is preferably a fastening means, particularly preferably selected from the group consisting of screws, nuts, rivets, bolts and chains.

[0034] A steel component within the meaning of the invention can be understood in particular to mean that at least a portion of the component, i.e., a volume region, is made of steel. It is preferred that the steel component constitutes ≥ 80 wt.%, more preferably ≥ 90 wt.%, particularly preferably ≥ 95 wt.% of the component. This means that the component consists of ≥ 80 wt.%, more preferably ≥ 90 wt.%, particularly preferably ≥ 95 wt.% steel. This allows particularly good mechanical strength of the component, in particular of the fastening means, to be achieved. In order to increase mechanical strength, it is particularly preferred if the steel component is made in one piece. "Integral" can be understood in particular to mean that at least the one-piece part has been created in a forming process and / or is continuous.

[0035] The component according to the invention, in particular a screw, is preferably a high-strength or ultra-high-strength component, preferably with strengths ≥ 800 MPa (so-called high-strength components), particularly preferably over 1200 MPa, further preferably ≥ 1400 MPa (so-called ultra-high-strength components), particularly preferably 1200-1900 MPa, in particular 1400-1900 MPa. Strength classes according to ISO 898-1 in the version valid in January 2021. Preferred high-strength and ultra-high-strength components are high-strength or ultra-high-strength screws, nuts, chain drives, formed components, and / or structural components. Further or alternatively, the component according to the invention, in particular the high-strength or ultra-high-strength component, is preferably a welded component, an additively manufactured component, or a case-hardened component.

[0036] In a further preferred embodiment, in the component according to the invention with a steel component, the component or the steel is heat-treated, a so-called tempering, for example by salt bath tempering, in order to establish a preferred microstructure. In a preferred embodiment, the microstructure of the steel is ≥ 70 vol. %, more preferably ≥ 80 vol. %, particularly preferably ≥ 90 vol. % bainitic and / or martensitic, in particular after tempering such as heat treatment. The proportion of the microstructure in volume percent can be determined, for example, in microscopic images of micrographs, since the areas reflect the volumes on average over several micrographs. For this purpose, the areas are determined in several micrographs and the arithmetic mean is calculated. Since the densities of the microstructures of the steel are relatively similar, it is also preferred that the microstructure of the steel is ≥ 70 wt. %, more preferably ≥ 80 wt.-%, particularly preferably ≥ 90 wt.% bainitic and / or martensitic. Also preferably, the proportion of austenite (residual austenite) is ≤ 20 vol.% or wt.%, in particular ≤ 10 vol.% or wt.%. These microstructures impart particularly high strength and toughness to the component according to the invention. They can be subjected to high and frequently dynamic axial stress. Before tempering, the microstructure of the component according to the invention is preferably ≥ 90 vol.% ferritic and / or pearlitic. Preferably, the microstructure of the component according to the invention is ≥ 90 wt.% ferritic and / or pearlitic before tempering.

[0037] The component according to the invention is further preferably a formed component. A formed component is understood, in particular, to be a component that has been formed by means of a forming step, in particular a cold forming process. Reducing hydrogen embrittlement is particularly advantageous for a formed component without heat treatment, because formed components already exhibit a certain degree of brittleness due to the accumulated forest dislocations (e.g., two or more dislocations that collide transversely or perpendicularly with each other on different slip planes).

[0038] An above-mentioned structural component within the meaning of the invention exists in particular when the component is a load-bearing component. This structural component has, in particular, two load introduction sections, which advantageously have load-introducing structures, such as mounting recesses or openings, and a transmission area arranged between the load introduction sections, which can and / or does transmit a load, in particular a bending load and / or tensile load, from one load introduction section to the other load introduction section.

[0039] The improvement in resistance to hydrogen embrittlement is attributed to, without being bound by the invention, the fact that additional bonding points for diffusible hydrogen are created in the component in the microstructure, in particular a heat-treated microstructure of the steel, in particular by precipitation-forming elements such as Al, Cu, Mo, V, Zr, Ti, B with C, N, O, Si and / or due to the microstructure adjusted by heat treatment.

[0040] As described above, the component according to the invention with a component made of steel is, in a preferred embodiment, a fastening means. The fastening means according to the invention can in particular be force-fitting fastening means, such as screws, bolts or nuts. Force-fitting fastening means are characterized in particular by the fact that they have a threaded portion for clamping or fastening, in particular with an external thread or an internal thread. For example, the threaded portion can therefore be an external thread or an internal thread. Advantageously, this threaded portion is introduced into a component of the fastening means which is made of steel. The fastening means can expediently have a shank region. This shank region can be formed adjacent to the threaded portion and / or a drive region, in particular a head, of the fastening means.Preferably, the shaft portion can be threadless and / or formed as a cylindrical section. The diameter of the shaft can be greater than, less than, or equal to the thread diameter in the threaded section. The screws are advantageously high-strength or ultra-high-strength screws.

[0041] In a particularly preferred embodiment of the invention, the component is a high-strength or ultra-high-strength screw. A high-strength screw is understood to be a screw with a tensile strength of at least 800 MPa. High-strength screws are, for example, screws of strength classes 8.8, 10.9, and 12.9. In particular, the strength classes of the invention correspond to ISO 898-1 in the version valid as of January 2021. An ultra-high-strength screw is understood to be a screw with a tensile strength, in particular of at least 1200 MPa and / or advantageously of at least 1400 MPa. Ultra-high-strength screws include screws in strength classes 12.8, 12.9, 14.8, 14.9, 15.8, 15.9, 16.8, 16.9, 17.8, and 12.8U, 12.9U, 14.8U, 14.9U, 15.8U, 15.9U, 16.8U, and 17.8U. A high-strength screw is a screw that is at least high-strength, but can also be ultra-high-strength.Preferably, it is a high-strength or ultra-high-strength screw with a strength of over 1000 MPa. The screw may have a head with tool engagement surfaces, wherein these tool engagement surfaces, in particular, form an internal or external hexagon.

[0042] The invention also relates to a method for producing the component according to the invention. For production, the individual alloying elements are first added to a steel in a known manner. The method according to the invention for producing a component with a steel component comprises the following steps: Providing a steel having the composition described above, then forming a component with a component made of the steel and optionally heat treating it.

[0043] The method according to the invention for producing a component with a steel component comprises, in a preferred embodiment, the following steps: a) providing a steel having the composition described above b) rolling, in particular thermomechanical rolling of the steel c) producing a wire or a bar of the steel, d) optionally GKZ annealing, e) wire drawing, f) forming and g) optionally heat treating.

[0044] The above steps are carried out in the specified order. Each step further processes the product obtained from the immediately preceding step.

[0045] The preferred method according to the invention has the advantage of a resource-saving and cost-efficient process route, since, for example, a rolled wire rod can be processed directly without the need for intermediate GKZ annealing. In this way, a ferrite-pearlite microstructure can be achieved in the rolled wire rod state by means of TM rolling (thermomechanical rolling). Thermomechanical rolling is preferably carried out in step b). Thermomechanical rolling is particularly preferred in which the material is rolled with a final forming temperature in a range of Ar 3 - 50 °C and + 100 °C, where Ar 3 in the Fe-C diagram is referred to as the austenite-proeutectoid transformation temperature. Particularly preferably, a microstructure predominantly consisting of ferrite and pearlite is produced, in particular with an average secondary grain size of 8 or finer according to ASTM E112.

[0046] GKZ annealing (annealing for spheroidal cementite) refers to heating with the aim of forming spheroidal cementite. In step d), the optional GKZ annealing, it is preferred that the steel is annealed for 6-10 hours, preferably 7-9 hours, for example 8 hours, at a holding temperature of 700-750 °C, for example 735 °C. Subsequently, cooling is preferably carried out to below 100 °C, particularly preferably below 50 °C, in particular to room temperature. Annealing (heating) advantageously produces a microstructure of ferrite and spheroidal cementite.

[0047] Further steps may follow the forming and / or optional heat treatment, in particular a tempering step, in which the known tempering processes for steels are suitable. Alternatively or additionally, a tempering step may preferably also take place during and / or simultaneously with the heat treatment step. In other words, the tempering and heating can take place together in a single step. The optional heat treatment and / or tempering in step g) is preferably salt bath tempering, particularly preferably at a temperature of 200-450°C for 10 minutes to 3 hours.

[0048] After rolling in step b), in particular thermomechanical rolling, and before heat treatment in step f), the microstructure of the steel component is predominantly ferritic-pearlitic, bainitic, and / or a mixed microstructure. Preferably, the microstructure of the steel is ≥ 80 vol.%, particularly preferably ≥ 90 vol.% ferritic-pearlitic, bainitic, and / or a mixed microstructure. After heat treatment, the microstructure of the component, in a preferred embodiment, is predominantly martensitic and / or bainitic, as described above. In a preferred embodiment, the microstructure of the steel component in the component according to the invention is ≥ 70 vol.%, more preferably ≥ 80 vol.%, particularly preferably ≥ 90 vol.% bainitic or martensitic, as described above.Furthermore, it is preferred that the structure of the steel in the edge region, in particular the region from the surface of the steel component to a depth of 15 µm, preferably up to 12 µm, particularly preferably up to 10 µm, measured perpendicular to the surface of the steel component, is predominantly ferritic and / or pearlitic, preferably ≥ 80 vol.%, particularly preferably ≥ 90 vol.% ferritic and / or pearlitic. The steel below the above-mentioned depths, ie below a depth of 15 µm, preferably below a depth of 12 µm, particularly preferably below a depth of 10 µm, preferably has the structure described above, ie preferably ≥ 70 vol.%, further preferably ≥ 80 vol.%, particularly preferably ≥ 90 vol.% bainitic or martensitic.

[0049] In a preferred embodiment of the invention, the steel component in the edge region, in particular at a depth of 30-100 µm, preferably 50-150 µm, measured from the surface perpendicular to the surface of the steel component, has a Vickers hardness of ≥ 350 HV 0.3, more preferably ≥ 400 HV 0.3, particularly preferably ≥ 430 HV 0.3, in particular ≥ 450 HV 0.3.

[0050] In a further preferred embodiment of the invention, the steel component has a Vickers hardness at a depth of 30-100 µm, preferably 40-120 µm, particularly preferably 50-150 µm, measured from the surface perpendicular to the surface of the steel component, that is less than 150 HV 0.3 below the Vickers hardness HV 0.3 of the steel component at a depth of 300-400 µm, in particular at a depth of 400 µm, particularly preferably at a depth of 1 / 4 of the diameter of the steel component. This describes the reduced hardness drop in the edge region of the steel compared to the core region, which is preferred according to the invention.More preferably, the steel component has a Vickers hardness of less than 100 HV 0.5, more preferably less than 60 HV 0.5, in particular less than 30 HV 0.5, at a depth of 30 - 100 µm, preferably 40 - 120 µm, particularly preferably 50 - 150 µm, measured from the surface perpendicular to the surface of the steel component, which is less than 30 HV 0.5, below the Vickers hardness HV 0.5 of the steel component at a depth of 300 - 400 µm, likewise measured from the surface into the depth of the steel component, perpendicular to the surface of the steel component, in particular at a depth of 400 µm, particularly preferably at a depth of 1 / 4 of the diameter of the steel component.

[0051] The invention also relates to a component with a steel component, obtainable by the method according to the invention. Advantageously, the component and / or the steel component can also have the aforementioned features with regard to the method.

[0052] It is understood that the features mentioned above and those to be explained below can be used not only in the specified combinations, but also in other combinations or alone, without departing from the scope of the present invention. The advantages of features or combinations of several features mentioned are merely exemplary and can be used alternatively or cumulatively. The combination of features of different embodiments of the invention or of features of different patent claims is possible, deviating from the selected references to the patent claims.

[0053] The invention is further explained below with reference to the figures. Fig. 1 shows the hardness curve in the edge area of a screw according to the invention. Fig. 2 showed the hardness curve in the edge area of a state-of-the-art screw.

[0054] In Fig. 1 The hardness of the steel depends on the edge distance, measured perpendicular to the surface, of a screw according to the invention and it can be seen that there is only a slight decrease in hardness.

[0055] In Fig. 2 The hardness profile of the steel in the edge region of a bainitic heat-treated B-alloy screw is shown, using a conventional B-alloy steel. It can be seen that there is a significant hardness drop in the edge region, combined with a greater depth of hardness drop, measured perpendicular to the surface of the screw.

[0056] The above example according to Fig. 1 and the comparison example according to Fig. 2 thus shows the advantageous effect of the steel composition according to the invention in the component with a steel component.

Claims

1. Component with a constituent made of steel, characterized in that the steel comprises 0.30 - 0.50 wt.-% C, 0.05 - 1.3 wt.-% Mn, 0.001 - 0.015 wt.-% P, 0.001 - 0.015 wt.-% S, 0.01 - 0.8 wt.-% Si, 0.3 - 1.5 wt.-% Cr, 0.005 - 0.40 wt.-% V, 0.0008 - 0.0050 wt.-% B, 0.02 - 0.35 wt.-% Al, 0.0001 - 0.0200 wt.-% N, 0.01 - 0.08 wt.-% Ti, and 0.0030 - 0.0800 wt.-% Zr; optionally 0.01 - 0.20 wt.-% Mo, 0.01 - 0.50 wt.-% Ni, 0.01 - 0.50 wt.-% Cu 0.0010 - 0.0100 wt.-% Ca, 0.01-0.10 wt.-% Bi, 0.01-0.30 wt.-% Co, 0.01-0.06 wt.-% Nb, 0.01-0.40 wt.-% Pb, 0.01-0.10 wt.-% Se, 0.01-0.10 wt.-% Te, 0.01-0.3 wt.-% W, 0.01-0.04 wt.-% As, 0.01-0.20 wt.-% Ta, 0.01-0.20 wt.-% Ce, 0.01-0.50 wt.-% Sn, 0.01-0.40 wt.-% Sb, 0.01-0.20 wt.-% Hf, and / or one or more lanthanides, each in an amount of 0.01 - 0.02 wt.-%; the rest iron and unavoidable impurities, wherein each unavoidable impurity is ≤ 0.01 wt.-% and wherein the constituent of the component has a steel surface and the B content in the steel at a depth of 5 - 60 µm ≥ is 80% of the B content in the steel at a depth of 500 µm, wherein the depth is measured perpendicular to the steel surface.

2. Component according to claim 1, characterized in that the B content in the steel at a depth of 5 - 60 µm is ≥ 90%, preferably ≥ 95%, of the B content in the steel at a depth of 500 µm.

3. Component according to claim 1 or 2, characterized in that the B content in the steel at a depth of 140 - 220 µm is ≥ 80 % of the B content in the steel at a depth of 500 µm, wherein the depth is measured perpendicular to the steel surface.

4. Component according to one of the preceding claims, characterized in that the B content in the steel at a depth of 140 - 220 µm is ≥ 90%, preferably ≥ 95%, of the B content of the steel at a depth of 500 µm.

5. Component according to one of the preceding claims, characterized in that the steel consists of the specified components.

6. Component according to one of the preceding claims, characterized in that the steel comprises 0.30 - 0.46 wt.-% C, 0.3 - 1.3 wt.-% Mn, 0.001 - 0.015 wt.-% P, 0.001 - 0.015 wt.-% S, 0.01 - 0.60 wt.-% Si, 0.3 - 1.3 wt.-% Cr, 0.005 - 0.35 wt.-% V, 0.0012 - 0.0050 wt.-% B, 0.02 - 0.25 wt.-% Al, 0.0020 - 0.0150 wt.-% N, 0.014 - 0.060 wt.-% Ti, and 0.0050 - 0.0500 wt.-% Zr; optionally 0.01 - 0.16 wt.-% Mo, 0.01 - 0.40 wt.-% Ni, 0.01 - 0.30 wt.-% Cu, and / or 0.0010 - 0.0080 wt.-% Ca; the rest iron and unavoidable impurities, preferably consists of it.

7. Component according to one of claims 1 to 5, characterized in that the steel consists of 0.30 - 0.50 wt.-% C, 0.05 - 1.3 wt.-% Mn, 0.001 - 0.015 wt.-% P, 0.001 - 0.015 wt.-% S, 0.01 - 0.8 wt.-% Si, 0.3 - 1.5 wt.-% Cr, 0.005 - 0.40 wt.-% V, 0.0008 - 0.0050 wt.-% B, 0.02 - 0.35 wt.-% Al, 0.0001 - 0.0200 wt.-% N, 0.01 - 0.08 wt.-% Ti, and 0.0030 - 0.0800 wt.-% Zr; optionally 0.01 - 0.20 wt.-% Mo, 0.01 - 0.50 wt.-% Ni, 0.01 - 0.50 wt.-% Cu, 0.0010 - 0.0100 wt.-% Ca, 0.01-0.10 wt.-% Bi 0.01-0.30 wt.-% Co, 0.01-0.06 wt.-% Nb, 0.01-0.40 wt.-% Pb, 0.01-0.10 wt.-% Se, 0.01-0.10 wt.-% Te, 0.01-0.3 wt.-% W, 0.01-0.04 wt.-% As, 0.01-0.20 wt.-% Ta, 0.01-0.20 wt.-% Ce, 0.01-0.50 wt.-% Sn, 0.01-0.40 wt.-% Sb, 0.01-0.20 wt.-% Hf, and / or one or more lanthanoid(s), each in an amount of 0.01 - 0.02 wt.-%; the rest iron and unavoidable impurities, wherein each impurity is ≤ 0.01 wt.-%.

8. Component according to one of the preceding claims, characterized in that (Zr + Ti + Al) / N is in a range from 2.7 to 150, preferably from 3 to 100.

9. Component according to one of the preceding claims, characterized in that the steel constituent has a Vickers hardness at a depth of 30 - 100 µm, preferably 40 - 120 µm, particularly preferably 50 - 150 µm, measured from the surface perpendicular to the surface of the steel constituent, which is less than 150 HV 0.3, preferably less than 100 HV 0.3, particularly preferably less than 60 HV 0.3, in particular less than 30 HV 0.3 below the Vickers hardness HV 0.3 of the steel constituent at a depth of 400 µm.

10. Component according to one of the preceding claims, characterized in that the component is a fastening means, preferably selected from the group consisting of screws, nuts, rivets, bolts and chains.

11. Component according to one of the preceding claims, characterized in that the steel makes up at least 90 wt.-% of the component and / or the component has a tensile strength according to ISO 898-1:2021 of ≥ 800 MPa, preferably ≥ 1400 MPa.

12. Component according to one of the preceding claims, characterized in that the structure of the steel is bainitic and / or martensitic after tempering ≥ 90 vol.-%.

13. Component according to one of the preceding claims, characterized in that the structure of the steel without tempering is ≥ 90 vol.-% ferritic-pearlitic.

14. Method of manufacturing a component according to one of the preceding claims, comprising the steps of - Providing a steel with a composition according to one of claims 1 - 3 - Forming a component with a constituent from the steel and - optionally heat treatment.

15. Method according to claim 14, characterized in that the method comprises the steps of a) Providing a steel with a composition according to one of claims 1 - 8, b) Rolling, in particular thermomechanical rolling of the steel, c) Producing a wire or bar of steel, d) Optionally heating to 700 - 750 °C for 6 - 10 hours, e) Wire drawing, f) Reshaping and g) Optionally heat treatment and / or tempering, in particular salt bath tempering.