Steel, method for producing same, and method for processing steel

Abstract

The invention relates to a steel, in particular in the form of steel sheet, which has the following composition: 0.02 - 0.1 wt.% carbon; 0.01 - 0.1 wt.% silicon; 0.60 - 2.00 wt.% manganese; > 0 and ≤ 0.01 wt.% aluminum; 0.01 - 0.30 wt.% copper; 0.01 - 0.60 wt.% nickel; 0.01 - 0.30 wt.% chromium; 0.005 - 0.050 wt.% niobium; 0.005 - 0.050 wt.% titanium; 0.0005 - 0.0050 wt.% sulfur; 0.001-0.005 wt.% calcium; ≤ 0.0050 wt.% oxygen; ≤ 0.010 wt.% nitrogen; ≤ 0.02 wt.% phosphorus; 0-0.0050 wt.% magnesium; 0-0.0060 wt.% vanadium; 0-0.15 wt.% molybdenum. The remainder: iron and production-related impurities. The invention further relates to a method for producing and a method for processing the steel.

Description

[0001] The invention relates to a steel, in particular in the form of steel sheet, which is suitable for processing by welding, in particular high-energy welding, and to a method for producing and a method for processing the steel.

[0002] In steels of this type known from use, the mechanical properties deteriorate due to energy input during welding in a heat-affected zone, particularly the toughness, which is significantly reduced. Often, even with an energy input of 2-5 kJ / mm, the mechanical properties typically required for such steels cannot be achieved.

[0003] The invention is based on the object of creating a steel of the type mentioned at the outset which, after processing by welding, in particular high-energy welding, has sufficiently good mechanical properties.

[0004] According to the invention, this object is achieved by a steel having the following composition: 0.02 - 0.1 wt% C, 0.01 - 0.1 wt% Si, 0.60 - 2.00 wt% Mn, > 0 and ≤ 0.01 wt% Al, 0.01 - 0.30 wt% Cu, 0.01 - 0.60 wt% Ni, 0.01 - 0.30 wt% Cr, 0.005 - 0.050 wt% Nb, 0.005 - 0.050 wt% Ti, 0.0005 - 0.0050 wt% S, 0.0002 - 0.0050 wt% Ca, 0.0005 - 0.0050 wt% O, ≤ 0.010 wt% N, ≤ 0.02 wt% P, 0 - 0.0050 wt% Mg 0 - 0.0060 wt% V 0 - 0.15 wt% Mo Rest: Fe and manufacturing-related impurities.

[0005] The steel according to the invention has a comparatively high toughness, in particular a notched impact toughness, up to an energy input of more than 20 kJ / mm. It has further been shown that, thanks to its chemical and microstructural properties, the steel after welding has a comparatively low number of martensite / austenite components and a comparatively small austenite grain size compared to known steels in a heat-affected area of ​​the welding, i.e. in an area in which welding affects the mechanical properties of the steel, even with high heat input. Advantages of the mechanical properties of the steel are already apparent from an energy input of > 2 kJ / mm, in particular > 3.5 kJ / mm. The steel has proven particularly advantageous for processing with energy inputs of > 5 kJ / mm, in particular > 8 kJ / mm, particularly preferably > 10 kJ / mm.

[0006] The steel is advantageously a micro-alloyed steel produced by thermomechanical rolling, in particular in the form of steel sheet, commonly referred to as "TM steel".

[0007] In one embodiment of the invention, the steel, after processing by welding with an energy input of 3.5 to 30 kJ / mm, preferably with an energy input of 3.5 to 25 kJ / mm, has an impact energy of at least 75 J, preferably at least 100 J.

[0008] Advantageously, the steel, after processing by welding with an energy input of 3.5 to 7 kJ / mm, has an impact energy of at least 150 J, preferably at least 190 J.

[0009] Preferably, after processing by welding with an energy input of 7 to 15 kJ / mm, the steel has an impact energy of at least 100 J, preferably at least 130 J.

[0010] In a particularly preferred embodiment of the invention, the steel, after processing by welding with an energy input of 15 to 25 kJ / mm, preferably 15 to 30 kJ / mm, has an impact energy of at least 75 J, preferably at least 100 J.

[0011] All impact energy values ​​given above for steels processed by welding refer to a determination of a fusion line of the weld seam formed during welding using a Charpy impact test at -40 °C, in particular in accordance with DIN EN ISO 148-1:2017. They are preferably an average of results from at least three impact tests each.

[0012] In a particularly preferred embodiment of the invention, the weld intended for determining the above-mentioned impact energy is oriented longitudinally to the rolling direction and carried out at a preheating temperature of 125 °C to 250 °C. The weld shape is preferably a HV weld with a steep flank. The sample direction is preferably transverse to the rolling direction. The sample positions are preferably the top side, middle side, or bottom side of the sheet.

[0013] Submerged arc welding is ideally used, but another welding process is also conceivable. In particular, welding is carried out in accordance with DIN EN 10225-1:2019, although in this case, an energy input of > 5 kJ / mm²< may be required, deviating from the standard.

[0014] The energy input is conveniently calculated using the formula Q = k ⋅ U ⋅ I v ⋅ 10 − 3 be calculated, where Q = heat input [kJ / mm] k = thermal efficiency, U = applied arc voltage [V], I = welding current [A], v = welding speed [mm / s]

[0015] In a further embodiment of the invention, the steel has a notch impact energy of at least 75 J, preferably at least 100 J, after treatment by means of physical welding simulation of the coarse grain zone with an energy input of 3.5 to 30 kJ / mm.

[0016] Advantageously, after treatment by physical welding simulation of the coarse-grain zone with an energy input of 3.5 to 7 kJ / mm, the steel has an impact energy of at least 150 J, preferably at least 190 J. Preferably, after treatment by physical welding simulation of the coarse-grain zone with an energy input of 7 to 15 kJ / mm, the steel has an impact energy of at least 100 J, preferably at least 130 J.

[0017] In a particularly preferred embodiment of the invention, the steel, after treatment by means of physical welding simulation of the coarse grain zone with an energy input of 15 to 30 kJ / mm, has an impact energy of at least 75 J, preferably at least 100 J.

[0018] All the above-mentioned values ​​of the impact energy of the steels treated by means of physical welding simulation of the coarse grain zone refer to a determination by means of a Charpy impact test at - 40 °C or at - 20 °C, in particular according to the standard DIN EN ISO 148-1:2017, whereby a determination at - 40 °C is preferably carried out for a welding simulation with only a single cycle, but a determination at - 20 °C is carried out for a welding simulation with two cycles.

[0019] For welding simulation, a T max of 1350 °C is advantageously provided. When performing two cycles, the second cycle is carried out at a T max of 750 to 775 °C, preferably 775 °C. The single-cycle welding simulation is used to simulate the welding of the coarse-grained zone, while the two-cycle welding simulation is used to simulate the welding of the coarse-grained zone superimposed on the intercritical zone.

[0020] The notched bar impact values ​​are preferably an average of results from at least 3 of the notched bar impact tests.

[0021] In one embodiment of the invention, the energy input values ​​specified above refer to a treatment using physical welding simulation of the coarse grain zone by converting the desired energy input into a t8 / 5 time. For this purpose, the following two formulas are calculated, and the higher value is used as the t8 / 5 time to input the desired energy: 3D heat conduction: t 8 / 5 = 6700 − 5 ⋅ T V ⋅ Q ⋅ 1 500 − T V − 1 800 − T V ⋅ F 3 2D heat conduction: t 8 / 5 = 4300 − 4,3 ⋅ T V ⋅ 10 5 ⋅ Q 2 d 2 ⋅ 1 500 − T V 2 − 1 800 − T V 2 ⋅ F 2 , where Tv = preheating temperature [°C], F 3 , F 2 = seam factor for three- or two-dimensional heat dissipation, d = sheet thickness

[0022] The above-mentioned formulas (1), (2) and 3 are mentioned in the technical rule SEW 088:2017-10 (SEW 088 Supplement 1:2017-10; SEW 088 Supplement 2:2017-10 Weldable unalloyed and low-alloy steels - Recommendations for processing, especially for fusion welding).

[0023] The temperature control corresponding to the respective welding process was determined using the calculation method according to Hannerz: Hannerz's equation: T − T 0 = A 300 ∗ B ∗ t ∗ exp − A 600 ∗ e ∗ B ∗ T max − T 0 2 ∗ t , where A = t 8 / 5 ∗ (500 - T 0 ) 2< (800 - T 0 ) 2< , B = 1300 - 2 T 0 , T max = peak temperature (°C), T 0 = initial temperature (°C), e = Euler number t 8 / 5 = cooling time from 800 °C to 500 °C (s) (Source: Hannerz, NE, "Idealized thermal cycle forweld heat affected zone simulation of steel", Perdue Thermal Physical Property Handbook)

[0024] To avoid the formation of embrittling martensite / austenite components, the steel has a comparatively low content of silicon and aluminum.

[0025] Silicon is provided in such a concentration that oxygen is sufficiently bound by the silicon (Si deoxidation) despite the low aluminum content and the associated comparatively low Al deoxidation. The stated minimum silicon content of 0.01 wt.% is required to achieve sufficient Si deoxidation. Alternatively or in addition, Mg, Ca, or Ti deoxidation could be provided.

[0026] Since aluminum and silicon are highly soluble in ferrite, carbon is increasingly displaced from the ferrite into the austenite during the phase transformation, significantly reducing the driving force for cementite precipitation. Residual austenite is indirectly stabilized thanks to the increased carbon content. To avoid martensite / austenite components, the steel according to the invention contains a maximum content of 0.01 wt.% aluminum and 0.10 wt.% silicon.

[0027] Niobium in this steel is used primarily to prevent recrystallization at low rolling temperatures due to solute drag and / or deformation-induced precipitates. The specified minimum content of 0.005 wt.% niobium is intended to ensure the formation of NbC for deformation-induced precipitates. To avoid coarse primary precipitates, the alloy contains a maximum of 0.050 wt.% niobium.

[0028] Titanium leads to the formation of high-temperature-stable precipitates that withstand even high temperatures during welding and inhibit temperature-induced growth of austenite grains in the heat-affected zone ("pinning"). A maximum of 0.050 wt.% titanium is advantageously provided to prevent coarse primary precipitates. The composition contains at least 0.005 wt.% titanium to promote the formation of complex particles and ensure sufficient nitrogen binding, particularly to prevent aging effects. Thanks to the titanium content, the steel according to the invention also advantageously complies with the EN 10025-4 standard, which provides for other nitrogen-binding alloying elements with a low aluminum content.

[0029] The alloy according to the invention contains at least 0.02 wt.% carbon and at least 0.60 wt.%, preferably at least 1 wt.% manganese, so that the steel achieves the required minimum strength. The steel contains at most 0.1 wt.%, preferably at most 0.05 wt.% carbon, to avoid the formation of hard phase regions.

[0030] Manganese is provided in a maximum content of 2.00 wt.%, preferably 1.70 wt.%, in order to prevent an austenite-stabilizing effect and to avoid the formation of martensite / austenite components.

[0031] The minimum contents of 0.01 wt% copper, 0.01 wt% nickel and 0.01 wt% chromium are intended for mixed crystal strengthening.

[0032] The maximum content of 0.3 wt.%, preferably 0.1 wt.%, copper and 0.6 wt.% nickel, preferably 0.4 wt.% nickel, particularly preferably 0.2 wt.% nickel, contributes to reducing austenite stabilization and thus to avoiding martensite / austenite components.

[0033] Chromium is provided in the steel in a maximum content of 0.30 wt.%, preferably 0.10 wt.%, in order to avoid the formation of Cr carbides, which have an embrittling effect.

[0034] The minimum contents of 0.0005 wt%, preferably 0.001 wt%, of sulfur, 0.0002 wt% calcium and 0.0005 wt% oxygen are intended for the formation of complex particles.

[0035] The maximum contents of 0.0050 wt.%, preferably 0.0040 wt.%, sulfur and 0.0050 wt.% oxygen are intended to maintain a required level of purity. The specified maximum oxygen content also serves to improve castability.

[0036] Calcium is intended to be used in a maximum content of 0.0050 wt.%, as it has a detrimental effect on the mechanical properties after the titanium and oxygen have set.

[0037] A maximum nitrogen content of 0.010 wt.% prevents aging effects.

[0038] Phosphorus is provided at a maximum of 0.02 wt.% to avoid grain boundary fracture, especially temper embrittlement.

[0039] Magnesium can be added to promote the above-mentioned magnesium deoxidation. The maximum Mg content of 0.0050 wt.% is intended to prevent the formation of embrittling magnesium oxide particles.

[0040] The steel may contain vanadium as a microalloying element. To prevent the formation of coarse primary precipitates, a maximum content of 0.0060 wt.% V is recommended.

[0041] Molybdenum can be added for solid solution strengthening. A maximum Mo content of 0.15 wt.% is recommended to prevent the formation of embrittling carbides.

[0042] In one embodiment of the invention, the steel has a preferably fine-grained, bainitic microstructure, preferably with an average grain size of <15 µm, preferably <14 µm, and / or a proportion of large-angle grain boundaries of >50%, preferably >60%. The specified grain sizes are expediently determined by SEM-EBSD (backscattered electron diffraction in a scanning electron microscope), with the value preferably referring to the mean of the area-weighted distribution of the circle-equivalent diameter at a tolerance angle of 5°.

[0043] The steel preferably contains non-metallic inclusions comprising CaTiOs compounds and Al2O3, MgO, and / or MnS components. The inclusions comprise agglomerates in which the Al2O3, MgO, and / or MnS components are embedded in a matrix of the CaTiOs compound. The components of the inclusions are conveniently determined using SEM-EDX (energy-dispersive X-ray spectroscopy in a scanning electron microscope).

[0044] The inclusions are preferably present in a particle size range of 0.5 - 5 µm. Thanks to the agglomerates, the number of non-metallic inclusions in the size range of 0.5 to 2 µm, which are formed from the Al 2 O 3 , MgO, and MnS components and are not embedded in the agglomerates of the CaTiOs compound, is significantly reduced and bound into a few larger inclusions with sizes of 2 to 5 µm, which are formed by the agglomerates of the CaTiOs compound.

[0045] In a particularly preferred embodiment of the invention, the ratio of the density of particles of non-metallic inclusions having a size of 0.5 to 2 µm to the density of particles of non-metallic inclusions having a size of 2 to 5 µm is less than 5, preferably less than 3.

[0046] The steel is advantageously in the form of a cast and preferably rolled semi-finished product, preferably as a slab or sheet.

[0047] In a particularly preferred embodiment of the invention, the steel is a welded structural steel, in particular a steel construction and / or offshore structural steel, particularly preferably a wind turbine. It is preferably part of a foundation of an offshore wind turbine or a drilling platform. The steel is expediently used in a welded structure, in particular a steel construction and / or offshore structure, preferably in a wind turbine.

[0048] The aforementioned process for producing the steel is characterized by a process in which Si deoxidation occurs. The steel is expediently cast using a continuous casting process. A resulting semi-finished product, in particular a slab, is preferably thermomechanically rolled.

[0049] In one embodiment of the invention, casting is carried out in such a way that the semi-finished product, in particular the slab, is formed with a thickness of 300-600 mm, preferably 450-550 mm. Preferably, the semi-finished product, in particular the slab, is formed with a length of 1000-5200 mm, particularly preferably 2000-4500 mm.

[0050] The semi-finished product, in particular the slab, is expediently reheated in a furnace to a temperature greater than the NbC solubility temperature. Reheating is preferably carried out to a temperature between 1100 and 1250 °C, preferably between 1150 and 1200 °C.

[0051] In one embodiment of the invention, the semi-finished product formed, in particular the slab, is thermomechanically rolled in at least two rolling phases, wherein the degree of deformation after the first rolling phase is preferably > 0.20, particularly preferably > 0.25.

[0052] The final rolling temperature is preferably 750 to 850 °C.

[0053] Preferably, rolling is carried out to a final thickness of 60 to 200 mm, preferably 65 to 150 mm, particularly preferably 70 to 120 mm.

[0054] In one embodiment of the invention, after rolling, accelerated cooling takes place at a cooling rate of at least 2 K / s. This cooling rate is preferably used to cool to a temperature of no more than 600 °C, possibly down to room temperature.

[0055] In one embodiment of the invention, the resulting semi-finished product, in particular a sheet rolled from the slab, is welded and preferably retains a sufficiently high notched impact strength, in particular the aforementioned notched impact energy values. Welding is expediently carried out with an energy input of up to 30 kJ / mm, preferably an energy input of > 3.5 kJ / mm, preferably > 7 kJ / mm, particularly preferably an energy input of > 15 kJ / mm. According to the invention, the resulting semi-finished product is even particularly suitable for welding with an energy input of > 20 kJ / mm, in particular > 25 kJ / mm.

[0056] The invention is explained in more detail below using exemplary embodiments and the attached tables.

[0057] Table 1 shows the composition of steels A, B, C, and D according to the invention. Steels E, F, and G have a conventional composition and serve as a reference. The compositions are given in wt. %.

[0058] Table 2 lists the rolling parameters used to produce the steels.

[0059] Mechanical properties of the produced sheets, namely results of tensile tests, hardness measurements, impact tests and fracture mechanics (Crack Tip Opening Displacement, CTOD) are shown in Table 3.

[0060] To test the steels, overlay welds were performed on 80 mm thick steel sheets. A submerged arc welding machine ("SAW welding machine") used to perform the actual welds (overlay and multi-pass welds) consists of several components: a UniWeld tool carrier with a Subarc-5 control system as a SAW double-head welding system with power sources of one OERLIKON TRE1004 AC and one SAF Starmatic 1000DC.

[0061] The welds were performed using the OE SD3 electrode and the OP 121TT flux (both from LincolnElectric).

[0062] Table 4 shows the results of a Charpy impact test according to DIN EN ISO 148-1, which was carried out as a standard test using a pendulum impact tester to determine the impact energy.

[0063] The impact test was carried out on a sheet metal surface at a fusion line of a weld seam of a build-up weld at -40 °C under different energy inputs, which are given in kJ / mm.

[0064] The energy input was determined using the above-mentioned formula 1. In submerged arc welding, for example, the thermal efficiency k = 1.

[0065] For the sheets from Heat A, produced according to rolling table 2, and for those from Heat E, produced according to rolling table 9, several single-layer build-up welds were performed under the various energy inputs listed in Table 4. Three measurements were taken, the individual values ​​of which are given, and the average of the individual values ​​is given.

[0066] The results show that the notch impact energies of the welded sheet formed from the inventive melt A are significantly higher than those of the sheet from the reference melt E. The differences in the notch impact energies between the sheet made from the inventive steel compared to those made from the reference steel increase with increasing energy input during welding.

[0067] Table 5 shows the results of notched bar impact tests on sheets with actual multi-layer welds, with an energy input of 5 kJ / mm along a fusion seam formed in the center of the sheet during the multi-layer welds at -80 °C. Notched bar impact tests were conducted on a sheet produced from the inventive melt A according to rolling plate 2 and on a sheet from the reference melt G, which was produced according to rolling plate 10. The notched bar impact energies for the sheet produced from the inventive steel are significantly higher than those for the sheet made from the reference steel.

[0068] Table 5 also shows the results of notched bar impact tests on sheets with actual multi-layer welds, with an energy input of 7 kJ / mm along a fusion seam formed in the center of the sheet during the multi-layer welds at -80°C. Notched bar impact tests were conducted on a sheet produced from the inventive melt B according to rolling plate 5 and on a sheet from the reference melt F, which was produced according to rolling plate 10. Even with an energy input of 7 kJ / mm, it is evident that the notched bar impact energies for the sheet produced from the inventive steel are significantly higher than those for the sheet made from the reference steel.

[0069] Further impact energies were determined using a physical welding simulation of the coarse grain zone, which is explained below.

[0070] To conduct the Charpy impact test according to DIN EN ISO 148-1 on a material treated by a physical welding simulation, a sample blank with a length of at least 55 mm in the transverse direction of the sheet and a cross-sectional area of ​​10 mm x 10 mm (rolling direction x normal direction) was first taken from the ¼ sheet thickness layer of the test material. The welding simulations were carried out using a Gleeble 3800 hot forming simulator and the QuickSim 2 software (version 2.5.8011.33152). In preparation, these notched-bar impact blanks were

[0071] A pair of thermocouples was spot-welded to a side surface of a standard specimen (without a notch) at a distance of 27.5 mm from the end face. The prepared specimens were placed in the hot forming simulator and clamped with minimal tension between the designated copper dies, centered at the thermocouple position. During the test, the current required for resistance heating was flowed through these dies, and control was provided by the welded thermocouples.

[0072] The temperature control corresponding to the respective welding process was determined using the above-mentioned integrated calculation method according to Hannerz (Formula 4).

[0073] The input parameters were T max = 1350 °C (second cycle 775 °C or 750 °C), T 0 = 100 °C and t8 / 5 = 40 s, 60 s, 200 s, 300 s, or 500 s (if the second cycle has a T max < 800 °C, then proportionally). Cooling was controlled up to a minimum temperature of 350 °C. After the welding simulation, the thermocouples were removed, a 2 mm deep V-notch was made at this point, and the length of the specimens was shortened to 55 mm if necessary.

[0074] Finally, the standard test of the weld-simulated samples was carried out using a pendulum impact tester to determine the impact energy.

[0075] The energy input values ​​given below refer to a treatment using physical welding simulation of the coarse grain zone by converting the desired energy input into a t8 / 5 time using formulas 2 and 3 given above.

[0076] A preheating temperature Tv of 200 °C and a weld factor of 0.9 (F 1 and F 2 ) are conveniently assumed for simulating a multi-layer weld. The sheet thickness d was assumed to be 80 mm.

[0077] Tables 6 and 7 show the results of notched bar impact tests on various sheets produced from heats A to G and from various rolled plates 1 to 11, which were treated for welding simulation as described above.

[0078] Table 6 shows the impact test results with a t8 / 5 time of 500 s, corresponding to an energy input of 35 kJ / mm, for one cycle at 1350 °C, with a t8 / 5 time of 300 s, corresponding to an energy input of 27 kJ / mm, for one cycle at 1350 °C, with a t8 / 5 time of 200 s, corresponding to an energy input of 22 kJ / mm, both for one cycle of 1350 °C and for two cycles, the first cycle being carried out at 1350 °C and the second cycle at 775 °C.

[0079] Table 7 shows the impact test results with a t8 / 5 time of 60 s, corresponding to an energy input of 7 kJ / mm, both for one cycle of 1350 °C and for two cycles, the first cycle being carried out at 1350 °C and the second cycle at 750 °C, and with a t8 / 5 time of 40 s, corresponding to an energy input of 5 kJ / mm, both for one cycle of 1350 °C and for two cycles, the first cycle being carried out at 1350 °C and the second cycle at 775 °C.

[0080] For the sheets produced from the steels according to the invention, significantly higher impact energies are obtained for all energy inputs, both for the one and the two cycles as well as for the mean values ​​from the tests.

[0081] The results of microstructural analyses are shown in Table 8. The proportion of large-angle grain boundaries in the sheets made from the steels according to the invention is lower than in the sheets made from the reference steels, except for the sheet from melt C after rolling plate 6, but is > 50% for all sheets. Furthermore, the particle density of particles with a diameter of 0.5 µm - 2 µm is lower in the sheets made from the steels according to the invention than in those made from the reference steels, and the particle density of particles with a diameter of 2 µm - 5 µm is higher in the sheets made from the steels according to the invention than in those made from the reference steels. Accordingly, the ratio of the particle densities of particles with a diameter of 0.5 µm - 2.0 µm to those with a diameter of 2 µm - 5 µm is lower for the sheets made from the steels according to the invention than for those made from the reference steels.These results show that in the sheets made of the steel according to the invention, thanks to the agglomerates, the number of non-metallic inclusions in the size range of 0.5 to 2 µm, which are formed from the Al2O3, MgO and MnS components and are not embedded in the agglomerates of the CaTiO3 compound, is reduced.

Claims

1. Steel, in particular TM steel, which has the following composition: 0.02 - 0.1 wt% carbon, 0.01 - 0.1 wt% silicon, 0.60 - 2.00 wt% manganese, > 0 and ≤ 0.01 wt% aluminum, 0.01 - 0.30 wt% copper, 0.01 - 0.60 wt% nickel, 0.01 - 0.30 wt% chromium, 0.005 - 0.050 wt% niobium, 0.005 - 0.050 wt% titanium, 0.0005 - 0.0050 wt% sulfur, 0.0010 - 0.0050 wt% calcium, ≤ 0.0050 wt% oxygen, ≤ 0.010 wt% nitrogen, ≤ 0.02 wt% phosphorus, 0 - 0.0050 wt% magnesium 0 - 0.0060 wt% vanadium 0 - 0.15 wt% molybdenum Rest: iron and manufacturing-related impurities.

2. Steel according to claim 1, characterized by at least one of the following contents: < 0.05 wt% carbon, 1.00-1.70 wt% manganese, ≤ 0.1 wt% copper, ≤ 0.4 wt% nickel, preferably ≤ 0.2 wt% nickel ≤ 0.10 wt% chromium, > 0.001 wt% oxygen, 0.001 - 0.0040 wt% sulfur.

3. Steel according to claim 1 or 2, characterized bya preferably fine-grained, bainitic microstructure.

4. Steel according to one of claims 1 to 3, characterized by an average grain size of < 15 µm, preferably < 14 µm.

5. Steel according to one of claims 1 to 4, characterized by a proportion of large angle grain boundaries > 50%, preferably > 60%.

6. Steel according to one of claims 1 to 5, characterized by non-metallic inclusions, preferably complex agglomerates, which have a matrix of a CaTiOs compound and Al2O3, MgO and MnS components embedded therein.

7. Steel according to one of claims 1 to 6, characterized by that a ratio of the density of particles of non-metallic inclusions in the size range of 0.5 to 2 µm to the density of particles of non-metallic inclusions in the size range of 2 to 5 µm is less than 5, preferably less than 3.

8. Steel according to one of claims 1 to 7, characterized by thatthe steel, in particular a steel construction steel, is in the form of a cast and preferably rolled semi-finished product, preferably as a slab or as a sheet, wherein the steel is preferably an offshore construction steel, particularly preferably for use for a foundation of an offshore wind turbine or for a drilling platform.

9. Steel according to one of claims 1 to 8, characterized by thatthe steel, after treatment by means of physical welding simulation of the coarse grain zone with an energy input of 3.5 kJ / mm to 30 kJ / mm, preferably with an energy input of > 7 kJ / mm, particularly preferably with an energy input of > 15 kJ / mm, has an impact energy of at least 75 J, preferably at least 100 J, particularly preferably at least 130 J, wherein the respective impact energy is determined by means of a Charpy impact test at -40 °C or at -20 °C, in particular in accordance with the standard DIN EN ISO 148-1:2017, wherein preferably at -40 °C for a welding simulation with only a single cycle and at -20 °C for a welding simulation with two cycles.

10. Steel according to one of claims 1 to 8, characterized by thatthe steel, after processing by welding, has an impact energy of at least 75 J, preferably at least 100 J, particularly preferably at least 130 J in a heat-affected zone of welding or with an energy input of 3.5 kJ / mm to 30 kJ / mm, preferably with an energy input of > 7 kJ / mm, particularly preferably with an energy input of > 15 kJ / mm, wherein the respective impact energy is determined on a fusion line of the weld seam formed during welding by means of a Charpy impact test at -40 °C, in particular in accordance with the standard DIN EN ISO 148-1:2017.

11. A process for producing steel, in particular TM steel, in which the steel is formed with the following composition: 0.02 - 0.1 wt.% carbon, 0.01 - 0.1 wt.% silicon, 0.60 - 2.00 wt.% manganese, > 0 and ≤ 0.01 wt.% aluminum, 0.01 - 0.30 wt.% copper, 0.01 - 0.60 wt.% nickel, 0.01 - 0.30 wt.% chromium, 0.005 - 0.050 wt.% niobium, 0.005 - 0.050 wt.% titanium, 0.0005 - 0.0050 wt.% sulfur, 0.0010 - 0.0050 wt.% calcium, 0.0005 - 0.0050 wt.% oxygen, ≤ 0.010 wt.% nitrogen, ≤ 0.02 wt% phosphorus, 0 - 0.0050 wt% magnesium 0 - 0.0060 wt% vanadium 0 - 0.15 wt% molybdenum Rest: iron and manufacturing-related impurities.

12. Method according to claim 11, characterized by that is cast in the continuous casting process to form a semi-finished product, in particular a slab.

13. Method according to claim 11 or 12, characterized by thatthe semi-finished product formed, in particular the slab, is heated to a temperature between 1100 and 1250 °C, preferably between 1150 and 1200 °C.

14. Method according to one of claims 11 to 13, characterized by that the semi-finished product formed, in particular the slab, is thermomechanically rolled in at least two rolling phases, wherein the degree of deformation after the first phase is preferably > 0.

20.

15. Method according to one of claims 11 to 14, characterized by that the semi-finished product formed, in particular a sheet rolled from the slab, is welded, in particular with an energy input of 3.5 kJ / mm to 30 kJ / mm, preferably with an energy input > 7 kJ / mm, particularly preferably with an energy input > 15 kJ / mm.

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