Method for producing a tubular semi-finished product

Abstract

The invention relates to a method for producing a seamless, hot-rolled tubular semi-finished product, which includes the following steps: a) consisting of the following as a percentage by weight: and optionally a) production of a billet from a steel alloy consisting of iron and impurities and accompanying elements from smelting, where the Mn / S ratio is between 3.3:1 and 30:1 by weight; b) cutting the billet into blocks; c) forming a hollow block at a temperature of at least 1,000°C by punching the block with a punching press and then lengthening it by reducing its wall thickness and outer diameter by oblique rolling, or by simultaneously punching and lengthening the block by an oblique rolling process using an internal pin; d) lengthening the hollow block in the hot state at a temperature of at least 750°C; e) final rolling without using an internal pin and at a temperature of 850°C to 1200°C to set the final geometry of a tubular semi-finished product, where the final rolling is carried out after an optional intermediate heating step, and the final post-rolling temperature is between 740°C and 1150°C.

Description

[0001] The invention relates to a method for producing a seamless and hot-rolled tubular semi-finished product.

[0002] EP 1 264 912 A1 discloses a free-cutting steel with good machinability when machined with a carbide tool. This steel is produced from an alloy which essentially has the following composition by weight percent: C 0.05-0.8%, Si 0.01-2.5%, Mn 0.1-3.5%, O 0.0005-0.01%, S 0.01-0.2%, Al 0.001-0.020%, Ca 0.0005-0.02% and may optionally contain Cr up to 3.5%, Mo up to 2.0%, Cu up to 2.0%, Ni up to 4% and B 0.0005-0.01%. Additionally, it may contain up to 0.2% Nb, up to 0.2% Ti, up to 0.5% V, up to 0.04% N, up to 0.5% Ta, up to 0.5% Zr, and up to 0.02% Mg; the remainder is iron and impurities resulting from the fusion process. Furthermore, additions of Pb, Bi, Se, Te, Sn, and Ti are possible.

[0003] For further technological background, reference is made to EP 2 006 396 A2, JP 2000 034538 A and EP 2 135 962 A1.

[0004] The machinability of steels can be improved by adding lead, phosphorus, and especially sulfur. High-sulfur steels are widely used as solid material and are referred to as free-cutting steels, particularly due to their good machinability. However, this improved machinability comes at the cost of negatively impacting mechanical properties and significantly reducing hot formability. This makes hot forming of pipes considerably more difficult. In particular, a higher sulfur content can also lead to brittleness, such as red fracture or hot fracture. This brittleness is especially problematic in pipe manufacturing.

[0005] A key difference between pipe manufacturing and solid material production is the drilling process. This exposes material defects and weaknesses more readily than simply applying external force, leads to less welding of defects, and promotes crack formation and propagation. Compared to solid material, pipes have less material in their cross-section. Therefore, when cracks occur, especially under tensile stress, they are less effectively compensated for. This increases the likelihood of the material tearing or breaking.

[0006] For seamless, hot-formed tubes, sulfur contents are therefore usually set to a maximum of 0.05 wt.%, which enables tube production using conventional alloy concepts and manufacturing processes while maintaining good tube quality. At the same time, this significantly reduces machinability compared to higher sulfur contents. Consequently, machining operations on seamless, hot-formed tubes with low sulfur content, such as turning, result in higher machining costs relative to the material removed, compared to high-sulfur solid material. This is primarily due to poorer chip formation, more frequent process and equipment malfunctions, shorter tool life, and sometimes rougher surface finishes on the machined workpieces. There is a trade-off between good machinability and good hot-forming properties.The invention is based on the objective of demonstrating a method for producing a seamless, hot-rolled, tubular semi-finished product with an increased sulfur content, particularly suitable for machining. The steel alloy used for the semi-finished product is intended to prevent or reduce manufacturing and quality problems resulting from poor hot-forming properties through a special alloying concept. Furthermore, a defined level of good mechanical properties is to be achieved despite the negative influence of sulfur on these properties. Material weaknesses caused by large oxide inclusions, which negatively affect machinability, especially tool life, are to be reduced. Overall, the semi-finished product is intended to be very well suited for machining and, in particular, to possess very good machinability.

[0007] A method for producing such a semi-finished product is the subject of claim 1.

[0008] The tubular semi-finished product produced by the process, which is seamless and hot-rolled and intended for machining, consists of the following steel alloy, where all values ​​are in weight percent: C 0,04 - 0,48 And max. 0.60 min 1,10 - 2,90 S 0,10 - 0,40 Al 0,002 - 0,060 That 0,0001 - 0,02 O max. 80 ppm and optional V max. 0,5 N max. 0,15 Pb max. 0,1 P max. 0,1 B max. 0,01 N+P max. 0,2 Bi max. 0,1 yourself max. 0,07 it max. 0,2 us max. 2 With max. 0,8 Nb max. 0,3 IT max. 0,5

[0009] Residual iron as well as smelting-related impurities and accompanying elements, wherein the ratio of Mn to S is 3.3:1 to 30:1 wt.%. Accompanying elements include all additives that are not alloyed and result, for example, from a scrap content. They are commonly found in the production of secondary steel, e.g., electrical steel. Alternatively, the use of primary steel in the process according to the invention is also possible.

[0010] A key feature of the invention is the reliable and suitable binding of sulfur to improve the hot-forming properties of the semi-finished product. This binding is achieved in particular by alloying with manganese, which has a high affinity for sulfur and forms manganese sulfide. To ensure reliable binding, a minimum Mn content of 1.1 wt.% is specified. Furthermore, a Mn to S ratio of at least 3.3:1 wt.% and a maximum of 30:1 wt.% is specified. Excessive manganese content leads to hardening of the steel and reduces machinability. The manganese content is therefore limited to a maximum of 2.9 wt.% Mn, preferably to a maximum of 1.8 wt.% Mn.

[0011] The binding of the sulfur ensures that no harmful levels of low-melting iron sulfides (melting point approx. 1200°C) occur, which could cause hot fracture during the pipe manufacturing process. In particular, the formation of low-melting eutectics can lower the melting point to below 1000°C and cause red fracture. Iron sulfide is deposited especially along the grain boundaries. This further weakens the material and promotes intergranular fracture. By contrast, alloying with manganese within the aforementioned limits preferentially forms high-melting manganese sulfides (melting point approx. 1600°C). The proportion of iron sulfides in the sulfides present is a maximum of 6%, preferably a maximum of 3%.

[0012] In the core of a billet, or in near-surface areas of the billet or semi-finished product, manufacturing-related variations in sulfur content and sulfide composition may occur without the billet as a whole deviating from the specified proportions or content ranges.

[0013] An important aspect of the process according to the invention is that the billet material is suitably deoxidized. Oxygen, in particular by modifying the manganese sulfides, can improve machinability. However, with excessively high oxygen content, producing high-quality pipes is not possible, due in part to defects. The oxygen content is therefore limited to a maximum of 80 ppm and preferably a maximum of 60 ppm. Aluminum is used as the key element for this purpose and is added to the melt for deoxidation. Silicon and manganese also have a deoxidizing effect, but with a significantly lower affinity for oxygen than aluminum.

[0014] Additionally, the melt undergoes a calcium treatment, which modifies the oxides, particularly the aluminum oxides. A gas purge partially removes the compounds, achieving an Al content of 0.002–0.060 wt.%. A minimum Al content remains in the material due to the process. Limiting the Al content is necessary because an excessively high Al value can introduce material defects during casting, which is detrimental to hot forming in pipe production. Furthermore, this would promote the formation of larger aluminum oxide clusters, which are also undesirable and, for example, increase tool wear during machining due to their high hardness. Therefore, the Al content of all alloys according to the invention can be limited to a preferred range of 0.002–0.020 wt.%.

[0015] Calcium treatment modifies oxides present in the material, particularly aluminum oxide. Specifically, calcium aluminates are formed. The calcium can be added in various ways, for example, as calcium-silicon wire. Calcium oxides have the beneficial property of improving chip breakage. The negative impact on tool wear is reduced because the number of wear-promoting hard aluminum oxides is significantly decreased. A certain proportion of calcium-treated oxides can therefore remain in the material. During gas purging of the alloy, a large proportion of the inclusions are flushed out. Calcium aluminates are easier to flush out compared to untreated aluminum oxides. Overall, this also allows for improved control of the aluminum content. Calcium also influences the formation of manganese sulfides.A combination of manganese sulfides with calcium leads to an increase in the size of the inclusions, which also positively influences machinability. Additionally, elongation of the sulfides during the hot rolling process is reduced at these inclusions. A combination of the sulfur with calcium aluminates or with calcium is also possible. The calcium content remaining in the material is in the range of 0.0001–0.02 wt.%. Since high calcium contents complicate the production of semi-finished materials, particularly in continuous casting, the calcium content is preferably 0.0005–0.01 wt.%. Lead also contributes to improved machinability. Lead improves chip breakage and has a lubricating effect between the workpiece and the tool. Due to its toxic properties, the lead content is limited to a maximum of 0.1 wt.% and is preferably a maximum of 0.035 wt.%.

[0016] Carbon, as a key element, increases the strength of steel. Therefore, the minimum content is specified at 0.04 wt.%. Excessive carbon content, however, significantly increases tool wear, which is why an upper limit of 0.48 wt.% is specified.

[0017] Silicon increases strength and, in particular, yield strength. At the same time, weldability is hardly affected. However, silicon reduces ductility and machinability. The content is limited to a maximum of 0.60% by weight. The Si content can be specified as 0.20 to 0.60% by weight. This is particularly advantageous for free-cutting steels with higher requirements for mechanical properties, which are welded after machining.

[0018] Phosphorus and nitrogen improve machinability, particularly chip breakage. These elements have an embrittlement effect on the material and impair its mechanical and technological properties as well as its hot-forming properties. Therefore, the content is limited to a maximum of 0.1 wt.% phosphorus and 0.15 wt.% nitrogen. Particularly for tubes with special requirements regarding mechanical properties, the content is preferably a maximum of 0.025 wt.% phosphorus and 0.05 wt.% nitrogen. The combined content of phosphorus and nitrogen must not exceed 0.2 wt.%. Alternatively, boron can be added as an alloying element, which also has an embrittlement effect. Among other things, boron increases strength, which can lead to increased tool wear and negatively affects hot formability. Therefore, the boron content is limited to a maximum of 0.01 wt.% and preferably a maximum of 0.002 wt.%. While general manufacturability with boron contents above these ranges is possible with the inventive method, it is not advantageous.

[0019] Bismuth, tellurium, and / or selenium can be alloyed with the steel to further improve machinability. This effect is due, among other things, to their enrichment in or near manganese sulfides. However, at higher proportions, these elements reduce hot formability. Therefore, the contents are limited to a maximum of 0.1 wt.% bismuth, 0.07 wt.% tellurium, and 0.2 wt.% selenium. Higher tellurium contents can increase the likelihood of surface defects. Therefore, the tellurium content is preferably limited to a maximum of 0.03%. Due to the reduced hot formability, selenium contents up to 0.12% are preferable.

[0020] Alloys particularly suitable for the invention are listed in Table 1, wherein all alloys listed in the table (all values ​​in wt.%, except O) contain Al 0.002–0.060; Ca 0.001–0.02; O max. 80 ppm; and optionally P max. 0.1; Pb max. 0.1; N max. 0.15; Bi max. 0.1; Te max. 0.07; Se max. 0.2; B max. 0.01; Ni max. 2; Cu max. 0.8; Nb max. 0.3; Ti max. 0.5; N+P max. 0.2; the remainder being iron and melting-related impurities and accompanying elements, wherein the Mn / S ratio is in the range of 3.3:1 to 30:1. The semi-finished product produced according to the process preferably has the following mechanical properties: Re min. 190 MPa; Rm min. 310 MPa, A min. 7 %.

[0021] The production of tubular semi-finished products begins with the provision of continuously cast or pre-formed billets with different cross-sectional geometries, with round billets being preferred, made from one of the aforementioned steel alloys. A billet is divided into smaller blocks. This division into blocks can be carried out in the cold or hot state.

[0022] For further processing, the blocks are heated to a temperature of 1100°C–1400°C. The blocks are then perforated using a punch press, creating a hollow block. This hollow block is then elongated by skew rolling, reducing both the wall thickness (WD) and the outer diameter. Alternatively, the block can be perforated using an internal die. Various roll geometries and numbers of skew rolls (two or three) can be used. Different guiding devices, such as guide rails, guide discs, or guide rollers, can also be employed. During the aforementioned processes, the material maintains a minimum temperature of 1000°C.

[0023] The elongated hollow block is then further lengthened while still warm at a minimum of 750°C. This can be achieved using the push bench method, in which the perforated hollow block is stretched on a mandrel bar as an internal tool by stands arranged in series with non-driven rollers, or a linear rolling mill with an internal tool and driven stands, also known as a continuous pipe mill, or its further developments such as the Multi-stand Plug Mill or Multi-stand Pipe Mill (MPM), in which the internal tool is guided in a controlled manner. A varying number of rolls can be used per stand. Adjusting the roll angle during the rolling process is possible, depending on the process. Due to the material composition, particularly the near absence of FeS, lower temperatures can also be used. Brittleness, especially red brittleness, does not occur.Temperatures immediately after lengthening the hollow billet in the pusher, continuous tube rolling mill, and the described further developments in the range of 900–1130 °C are preferable. However, a minimum temperature of 750 °C must never be undercut during the rolling process.

[0024] Alternatively, the plug rolling process can be used. In this process, the hollow block is rolled onto a plug bar with a rolling plug, supported against a backing, using work rolls. Further alternatives for elongation include skew rolling mills, such as a skew mill, die mill, or planetary skew rolling mill with 3 or 4 rolls and a controlled internal die. Even with these alternatives, the specified minimum temperature of 750°C must not be undercut.

[0025] The final geometry is achieved in a final rolling process without internal dies at a material temperature of 850–1200 °C, preferably 900–1100 °C, at the start of the process. A stretch-reducing mill, a reduction mill, or a sizing mill can be used for this purpose. The preceding intermediate product can optionally be preheated. Inductive reheating within the process is also possible. The final rolling temperature after final forming is in the range of 740–1150 °C, preferably 800–1070 °C. Finally, the tubular semi-finished products are cooled, for example, on a cooling bed. Cooling can be carried out to room temperature; alternatively, an intermediate step such as heat treatment and / or straightening can be performed before final cooling to room temperature.

[0026] Surface temperature deviations are possible at all production stages, e.g. at the pipe ends or contact surfaces such as rollers or cylinders, whereby the average temperature over the intermediate product must not fall below or exceed the stated values.

[0027] At the material level, the combination of material analysis, hot forming, and temperature control results in a fine distribution of manganese sulfides within the material. During rolling, manganese sulfides elongate in the rolling direction. Smaller pipe dimensions generally exhibit greater elongation of the manganese sulfides. A certain degree of curvature is usually retained by the elongated manganese sulfides. This curvature decreases with the degree of elongation of both the manganese sulfides and the pipe. Manganese sulfides may exhibit reduced elongation or retain a spherical shape when they are present in conjunction with other elements, such as calcium.

[0028] The process according to the invention, with its alloy concept, enables production at comparatively lower temperatures, thereby saving energy and reducing CO2 emissions. At the same time, the process becomes more resistant to disruptions, as cooler hollow blocks or intermediate products can also be manufactured without red fracture. Despite the high sulfur content, the mechanical properties of the semi-finished product are good in the process according to the invention.

[0029] Vanadium can be added to further improve the mechanical properties. Vanadium refines the grain structure, leading to improved strength and toughness, while simultaneously reducing machinability. Vanadium contents should not exceed 0.5%. Optionally, a V-range of 0.06–0.17% can be used, combining improved mechanical properties with very high machinability.

[0030] The mechanical properties of particularly suitable alloys, based on tensile tests at room temperature (RT), are given in Table 1 and according to the dependent claims. The tensile tests can be performed according to European Standard EN 10002-1 or International Standard ISO 6892-1. The top and bottom surfaces of the specimens can be machined or unmachined, i.e., corresponding to the pipe surfaces. Flat specimens are typically used. The alloys can optionally be manufactured with a specified impact energy in joules. The impact energy for the alloys specified in the claims can be determined using the method according to European Standard EN 10045-1 or International Standard ISO 148-1. Longitudinal Charpy indentations and a V-notch (KV) were used for this determination. A distinction is made between a range up to 12 mm WD and a range from 12 mm WD upwards with respect to wall thickness (WD).

[0031] With regard to the aforementioned variants of semi-finished products due to the different steel alloys and mechanical properties, it should be emphasized that these mechanical properties refer to the hot-rolled condition and that different properties can be achieved by modifying the tubular semi-finished product, e.g., by heat treatment such as hardening, tempering, stress-relief annealing, and / or cold drawing, as is known in the art.

[0032] As a result of the steel alloy used for the semi-finished product according to the invention and the manufacturing process, improved chip formation, improved tool life, and overall improved machinability are achieved. The lubricating effect of the sulfur is retained in the steel alloy used for the semi-finished product according to the invention. The steel alloy used for the semi-finished product according to the invention, or the method for producing seamless, hot-rolled tubular semi-finished products, allows for adjustments to higher values ​​of the machining parameters, e.g., cutting speed, feed rate, and depth of cut. Faster machining is possible, thereby reducing manufacturing costs. The proportion of rejects, e.g., due to equipment or process malfunctions, is reduced.

[0033] In a further development of the invention, the tubular semi-finished product is cold-drawn. For this purpose, the tube surface is prepared, e.g., by pickling, and a lubricant is applied to improve the sliding properties. To enable the tubular semi-finished product to be inserted into a drawing die, the outer diameter at one end of the pre-tube is reduced to a dimension below the drawing die. Depending on the dimensions, this forming at one end of the pre-tube is optionally carried out with preheating.

[0034] The pre-tube is then drawn through the drawing die with or without an internal tool / drawing mandrel, whereby the tube dimensions are changed along the entire length of the tubular semi-finished product. The lubricant reduces friction with the drawing die. The result of this drawing process is a long product in the form of a tubular semi-finished product, manufactured by hot rolling and subsequent cold forming.

[0035] Due to the improved quality and formability resulting from the optimized inclusion morphology of the material, the cross-sectional reduction can be the same as that of non-sulfurized variants. Target cross-sectional reductions are in the range of 15-45% per draw.

[0036] The hot-rolled or hot-rolled and drawn tubular semi-finished product is usually straightened after the manufacturing process.

[0037] The hot-rolled or hot-rolled and drawn tubular semi-finished product can be modified in shape by at least one cold forming or cold working operation. Optionally, this process can also be carried out in a heated state or after prior heat treatment. The long product can be divided into semi-finished products of the required length by cutting, in particular sawing. These semi-finished products are then machined, at least partially, in a further manufacturing step, with respect to their surface finish. Machining processes, especially those involving cutting, typically with geometrically defined cutting edges, such as turning, milling, or drilling, are particularly noteworthy. This machining is generally performed to join the products with other components.

[0038] The tubular semi-finished product is essentially rotationally symmetrical due to the machining process. "Essentially" means that rotational symmetry exists at least in a longitudinal section of a surface, preferably in a predominant part of the length of the semi-finished product. Therefore, a tubular semi-finished product that, for example, has a transverse bore, is also essentially rotationally symmetrical within the meaning of the invention.

[0039] An example of a machined tubular product made from this semi-finished material are sleeves and spacer rings. These are short, cylindrical components, possibly with shoulders, essentially rotationally symmetrical, machined with varying wall thicknesses.

[0040] Another application involves coupling sleeves for various uses, such as threaded anchors and reinforcements. Coupling sleeves are cylindrical components of varying lengths and wall thicknesses with an internal thread. The inner diameter and thread dimensions are matched to a mating part (rod, anchor, etc.). The exterior of these sleeves is either machined or left unmachined. Some coupling sleeves are provided with tapers, shoulders, and bores.

Claims

1. A method for producing a seamless and hot-rolled tubular semi-finished product by means of the following steps: a) manufacturing a billet from a steel alloy, the composition of which consists, in weight percent, of C0.04 - 0.48Simax. 0.60Mn1.10 - 2.90S0.10 - 0.40Al0.002 - 0.060Ca0.0001 - 0.02Omax. 80 ppm and optionally Vmax. 0.5Nmax. 0.15Pbmax. 0.1Pmax. 0.1Bmax. 0.01N+Pmax. 0.2Bimax. 0.1Temax. 0.07Semax. 0.2Nimax. 2Cumax. 0.8Nbmax. 0.3Timax. 0.5 residual iron as well as melt-related impurities and accompanying elements, wherein the ratio of Mn to S is 3.3:1 to 30:1 in wt.%; b) separating the billet into blocks; c) forming the block into a hollow block at a temperature of at least 1,000 °C by punching using a punch press and subsequent elongation, reducing the wall thickness and outer diameter by means of skew rolling, or by simultaneously punching and elongating the block using a skew rolling process with the use of an internal mandrel; d) lengthening of the hollow block in the warm state at a temperature of at least 750 °C; e) final rolling without an inner mandrel and at a temperature of 850 °C to 1200 °C for adjusting the final geometry of a tubular semi-finished product, wherein the final rolling is carried out after an optional intermediate heating step and wherein a final temperature after rolling is in the range of 740 °C to 1150 °C.

2. The method according to claim 1, characterized in that the lengthening of the hollow block in the warm state is carried out according to one or more of the following methods: push bench method, pipe continuous method, multi-stand pipe mill method or another linear rolling process with driven rolls and internal tooling, plug rolling method, method using a wood chip mill, die shear mill or planetary skew mill.

3. The method according to claim 1 or 2, characterized in that immediately after lengthening the hollow block in the warm state, the temperature is in a range of 900-1130 °C.

4. The method according to any one of claims 1 to 3, wherein a lubricant is applied to the surface of the tubular semi-finished product and the outer diameter of one end of the tubular semi-finished product is reduced, either cold or by preheating to a temperature of preferably at least 800 °C, to a diameter smaller than the inner diameter of a drawing die, and in a subsequent step, the tubular semi-finished product is reduced in diameter, whereby the tubular semi-finished product with the end, reduced in diameter, is inserted into, gripped and subsequently drawn through the drawing die with or without an internal tool.

5. The method according to any one of claims 1 to 4, characterized in that the drawing is repeated one or more times with one or more drawing dies of decreasing diameter.

6. The method according to any one of claims 1 to 5, characterized in that the hot-rolled and optionally cold-drawn, tubular semi-finished product is formed by at least one subsequent cold or semi-warm forming process.

7. The method according to any one of claims 1 to 6, characterized in that it comprises a machining manufacturing step with a geometrically defined cutting edge.

8. The method according to any one of claims 1 to 7, characterized in that the following steel alloy is used to manufacture the billet: C0.14 - 0.22Simax. 0.60Mn1.10 - 2.90S0.10 - 0.14Al0.002 - 0.060Ca0.0001 - 0.02Omax. 80 ppmVmax. 0.5Pmax. 0.1Pbmax. 0.1Nmax. 0.15N+Pmax. 0.2Bimax. 0.1Temax. 0.07Semax. 0.2Nimax. 2Cumax. 0.8Nbmax. 0.3Timax. 0.5 and optionally Bmax. 0.01 residual iron as well as melt-related impurities and accompanying elements, wherein the ratio Mn to S is 7.9:1 to 29:1 in wt.%, wherein the tubular semi-finished product is adjusted to the following mechanical properties: yield strength Remin. 250 MPatensile strength Rmmin. 420 MPaelongation at break A5min. 9 % wherein optionally the Charpy-V longitudinal impact energy KV is 24 J at 20 °C for wall thickness up to 12 mm Charpy-V longitudinal impact energy KV is 16 J at 20 °C for wall thickness above 12 mm, wherein the mechanical properties Re, Rm, A5 are determined according to European Standard EN 10002-1 and the Charpy-V longitudinal impact energy KV is determined using the method according to European Standard EN 10045-1.

9. The method according to any one of claims 1 to 7, characterized in that the following steel alloy is used to manufacture the billet: C0.14 - 0.22Simax. 0.60Mn1.10 - 2.90S0.14 - 0.27Al0.002 - 0.060Ca0.0001 - 0.02Omax. 80 ppmVmax. 0.5Pmax. 0.1Pbmax. 0.1Nmax. 0.15N+Pmax. 0.2Bimax. 0.1Temax. 0.07Semax. 0.2Nimax. 2Cumax. 0.8Nbmax. 0.3Timax. 0.5 and optionally Bmax. 0.01 residual iron as well as melt-related impurities and accompanying elements, wherein the ratio Mn to S is 4.1:1 to 20.7:1 in wt.%, wherein the tubular semi-finished product is adjusted to the following mechanical properties: yield strength Remin. 250 MPatensile strength Rmmin. 420 MPaelongation at break A5min. 9 %, wherein optionally the Charpy-V longitudinal impact energy KV is 24 J at 20 °C for wall thickness up to 12 mm Charpy-V longitudinal impact energy KV is 16 J at 20 °C for wall thickness above 12 mm, wherein the mechanical properties Re, Rm, A5 are determined according to European Standard EN 10002-1 and the Charpy-V longitudinal impact energy KV is determined using the method according to European Standard EN 10045-1.

10. The method according to any one of claims 1 to 7, characterized in that the following steel alloy is used to manufacture the billet: C0.31 - 0.48Simax. 0.60Mn1.10 - 2.90S0.10 - 0.14Al0.002 - 0.060Ca0.0001 - 0.02Omax. 80 ppmVmax. 0.5Pmax. 0.1Pbmax. 0.1Nmax. 0.15N+Pmax. 0.2Bimax. 0.1Temax. 0.07Semax. 0.2Nimax. 2Cumax. 0.8Nbmax. 0.3Timax. 0.5 and optionally Bmax. 0.01 residual iron as well as melt-related impurities and accompanying elements, wherein the ratio Mn to S is 8.5:1 to 29:1 in wt.%, wherein the tubular semi-finished product is adjusted to the following mechanical properties: yield strength Remin. 350 MPatensile strength Rmmin. 480 MPaelongation at break A5min. 7 %, wherein optionally the Charpy-V longitudinal impact energy KV is 9 J at 20 °C for wall thickness up to 12 mm Charpy-V longitudinal impact energy KV is 7 J at 20 °C for wall thickness above 12 mm, wherein the mechanical properties Re, Rm, A5 are determined according to European Standard EN 10002-1 and the Charpy-V longitudinal impact energy KV is determined using the method according to European Standard EN 10045-1.

11. The method according to any one of claims 1 to 7, characterized in that the following steel alloy is used to manufacture the billet: C0.14 - 0.22Simax. 0.60Mn1.10 - 1.80S0.27 - 0.40Al0.002 - 0.060Ca0.0001 - 0.02Omax. 80 ppmVmax. 0.5Pmax. 0.1Pbmax. 0.1N B N+P Bi Te Se Ni Cu Nb Timax. 0.15 max. 0.01 max. 0.2 max. 0.1 max. 0.07 max. 0.2 max. 2 max. 0.8 max. 0.3 max. 0.5 and optionally Bmax. 0.01 residual iron as well as melt-related impurities and accompanying elements, wherein the ratio Mn to S is 3.3:1 to 6.7:1 in wt.%, wherein the tubular semi-finished product is adjusted to the following mechanical properties: yield strength Remin. 345 MPatensile strength Rmmin. 490 MPaelongation at break A5min. 20 %, wherein optionally the Charpy-V longitudinal impact energy KV is 24 J at 20 °C for wall thickness up to 12 mm Charpy-V longitudinal impact energy KV is 16 J at 20 °C for wall thickness above 12 mm, wherein the mechanical properties Re, Rm, A5 are determined according to European Standard EN 10002-1 and the Charpy-V longitudinal impact energy KV is determined using the method according to European Standard EN 10045-1.

12. The method according to any one of claims 1 to 7, characterized in that the following steel alloy is used to manufacture the billet: C0.14 - 0.22Si0.20 - 0.60Mn1.10 - 1.70S0.10 - 0.14Al0.002 - 0.060Ca0.0001 - 0.02Omax. 80 ppmVmax. 0.5Pmax. 0.1Pbmax. 0.1Nmax. 0.15N+Pmax. 0.2Bimax. 0.1Temax. 0.07Semax. 0.2Nimax. 2Cumax. 0.8Nbmax. 0.3Timax. 0.5 and optionally Bmax. 0.01 residual iron as well as melt-related impurities and accompanying elements, wherein the ratio Mn to S is 7.9:1 to 17:1 in wt.%, wherein the tubular semi-finished product is adjusted to the following mechanical properties: yield strength Remin. 345 MPatensile strength Rmmin. 490 MPaelongation at break A5min. 20 %, wherein optionally the Charpy-V longitudinal impact energy KV is 24 J at 20 °C for wall thickness up to 12 mm Charpy-V longitudinal impact energy KV is 16 J at 20 °C for wall thickness above 12 mm, wherein the mechanical properties Re, Rm, A5 are determined according to European Standard EN 10002-1 and the Charpy-V longitudinal impact energy KV is determined using the method according to European Standard EN 10045-1.

13. The method according to any one of claims 1 to 7, characterized in that the following steel alloy is used to manufacture the billet: C0.16 - 0.23Si0.20 - 0.60Mn1.10 - 1.70S0.10 - 0.14Al0.002 - 0.060Ca0.0001 - 0.02Omax. 80 ppmV0.06 - 0.17Pmax. 0.1Pbmax. 0.1Nmax. 0.15N+Pmax. 0.2Bimax. 0.1Temax. 0.07Semax. 0.2Nimax. 2Cumax. 0.8Nbmax. 0.3Timax. 0.5 and optionally Bmax. 0.01 residual iron as well as melt-related impurities and accompanying elements, wherein the ratio Mn to S is 7.9:1 to 17:1 in wt.%, wherein the tubular semi-finished product is adjusted to the following mechanical properties: yield strength Remin. 430 MPatensile strength Rmmin. 600 MPaelongation at break A5min. 17%, wherein optionally the Charpy-V longitudinal impact energy KV is 25 J at 20 °C for wall thickness up to 12 mm Charpy-V longitudinal impact energy KV is 17 J at 20 °C for wall thickness above 12 mm, wherein the mechanical properties Re, Rm, A5 are determined according to European Standard EN 10002-1 and the Charpy-V longitudinal impact energy KV is determined using the method according to European Standard EN 10045-1.

14. The method according to any one of claims 1 to 7, characterized in that the following steel alloy is used to manufacture the billet: C0.04 - 0.14Simax. 0.45Mn1.10 - 1.60S0.26 - 0.34Al0.002 - 0.060Ca0.0001 - 0.02Omax. 80 ppmVmax. 0.5Pmax. 0.1Pbmax. 0.1Nmax. 0.15N+Pmax. 0.2Bimax. 0.1Temax. 0.07Semax. 0.2Nimax. 2Cumax. 0.8Nbmax. 0.3Timax. 0.5 and optionally Bmax. 0.01 residual iron as well as melt-related impurities and accompanying elements, wherein the ratio Mn to S is 3.3:1 to 6.2:1 in wt.%, wherein the tubular semi-finished product is adjusted to the following mechanical properties: yield strength Remin. 215 MPatensile strength Rmmin. 350 MPaelongation at break A5min. 9 % wherein optionally the Charpy-V longitudinal impact energy KV is 24 J at 20 °C for wall thickness up to 12 mm Charpy-V longitudinal impact energy KV is 16 J at 20 °C for wall thickness above 12 mm, wherein the mechanical properties Re, Rm, A5 are determined according to European Standard EN 10002-1 and the Charpy-V longitudinal impact energy KV is determined using the method according to European Standard EN 10045-1.

15. The method according to any one of claims 1 to 7, characterized in that the following steel alloy is used to manufacture the billet: C0.14 - 0.22Simax. 0.60Mn1.10 - 1.80S0.26 - 0.34Al0.002 - 0.060Ca0.0001 - 0.02Omax. 80 ppmVmax. 0.5Pmax. 0.1Pbmax. 0.1Nmax. 0.15N+Pmax. 0.2Bimax. 0.1Temax. 0.07Semax. 0.2Nimax. 2Cumax. 0.8Nbmax. 0.3Timax. 0.5 and optionally Bmax. 0.01 residual iron as well as melt-related impurities and accompanying elements, wherein the ratio Mn to S is 3.3:1 to 6.9:1 in wt.%, wherein the tubular semi-finished product is adjusted to the following mechanical properties: yield strength Remin. 250 MPatensile strength Rmmin. 420 MPaelongation at break A5min. 9 % wherein optionally the Charpy-V longitudinal impact energy KV is 24 J at 20 °C for wall thickness up to 12 mm Charpy-V longitudinal impact energy KV is 16 J at 20 °C for wall thickness above 12 mm, wherein the mechanical properties Re, Rm, A5 are determined according to European Standard EN 10002-1 and the Charpy-V longitudinal impact energy KV is determined using the method according to European Standard EN 10045-1.