Method for producing a tubular semi-finished product

Abstract

The invention relates to a method for producing a seamless and hot-rolled tubular semi-finished product by means of the following steps: a) producing a billet from a steel alloy consisting of, in wt. percent, and optionally residual iron as well as melting-related impurities and accompanying elements, wherein the ratio Mn to S is 3.3:1 to 30:1 in wt. percent; b) cutting the billet into blocks; c) forming the block into a hollow block at a temperature of at least 1.000°C by punching with a punch press and subsequent elongation with reduction of the wall thickness and outer diameter by skew rolling or by simultaneously punching and elongating the block by a skew rolling process using an internal mandrel; d) lengths of the hollow block in the warm state at a temperature of at least 750 °C; e) final rolling without an internal mandrel and at a temperature of 850 °C to 1200 °C, to adjust 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.

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 cemented carbide tool. This steel is made from an alloy essentially having the following composition in 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 can 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, with the remainder being iron and fusion-related impurities. Additions of Pb, Bi, Se, Te, Sn, and Tl are also possible.

[0003] The machinability of steels can be improved by adding lead, phosphorus, and especially sulfur. Highly sulfurized steels are widely used as solid materials and are referred to as free-cutting steels, particularly due to their good machinability. The improvement in machinability is accompanied by a negative impact on mechanical properties and a significantly reduced hot formability. This significantly complicates pipe production by hot forming. In particular, a higher sulfur content can also result in brittleness, such as red fracture or hot fracture. This brittleness is particularly problematic in pipe production.

[0004] A key difference between pipe production and solid material is the piercing process. This process exposes material defects and weak points more effectively than applying force only from the outside, leads to less welding of defects, and promotes the formation and propagation of cracks in the material. Compared to solid material, pipes have less material in their cross-section. If cracks occur, especially under tensile loads, they are less easily compensated for. This makes it easier for the material to tear open or break off.

[0005] For seamless, hot-formed tubes, sulfur contents of up to a maximum of 0.05 wt.% are therefore usually set for tube production using conventional alloying concepts and manufacturing processes while maintaining good tube quality. At the same time, machinability is significantly reduced compared to higher sulfur contents. This leads to higher machining costs relative to the machining volume during machining steps of seamless, hot-formed tube products with low sulfur content, such as turning, compared to high-sulfur solid material. The main reasons for this are poorer chip formation, more frequent process and system malfunctions, shorter tool life, and sometimes coarser surfaces of the machined workpieces. There is a trade-off between good machinability and good hot-forming properties.

[0006] The invention is based on the object of demonstrating a method for producing a seamless, hot-rolled tubular semi-finished product with an elevated sulfur content that is particularly suitable for machining. The steel alloy used for the semi-finished product is intended to prevent or reduce production and quality problems resulting from poorer 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 the mechanical properties. Material weaknesses resulting from large oxide inclusions, which negatively impact machinability, particularly tool life, are to be reduced. Overall, the semi-finished product is intended to be highly suitable for machining and, in particular, to exhibit very good machinability.

[0007] A process for producing such a semi-finished product is the subject of patent 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, all values ​​being 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 optionally 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] The remainder consists of iron, as well as smelting-related impurities and accompanying elements, with the Mn to S ratio being 3.3:1 to 30:1 wt.%. Accompanying elements include all additions that are not alloyed and arise, for example, from a scrap component. They are commonly found in the production of secondary steel, such as electrical steel. Alternatively, the use of primary steel is also possible in the process according to the invention.

[0010] An essential feature of the invention is to bind sulfur reliably and suitably in order to improve the hot forming properties of the semi-finished product. The binding takes place in particular by alloying manganese, which has a high affinity for sulfur and forms manganese sulfide. To ensure reliable binding, a minimum content of 1.1 wt.% Mn is specified. Furthermore, a ratio of Mn to S of at least 3.3:1 wt.% and max. 30:1 wt.% is specified. An excessively high 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] Binding the sulfur ensures that no harmful levels of low-melting iron sulfides (melting point approx. 1200°C) occur, which can cause hot fractures in the pipe manufacturing process. In particular, the formation of low-melting eutectics can lower the melting point to below 1000°C, causing red fractures. Iron sulfide deposits particularly along grain boundaries. This further weakens the material and promotes intergranular fracture. Alloying manganese within the specified limits, on the other hand, preferentially forms high-melting manganese sulfides (melting points 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 areas close to the surface of the billet or semi-finished product, different sulfur contents and a different sulfide composition may occur due to manufacturing reasons, without the billet as a whole deviating from the specified proportions or content ranges.

[0013] It is also important for the process according to the invention that the billet material is suitably deoxidized. Oxygen can improve machinability, particularly by modifying the manganese sulfides. However, if the oxygen content is too high, high-quality tube production is impossible due to defects, among other things. The oxygen content is therefore limited to a maximum of 80 ppm and preferably a maximum of 60 ppm. For this purpose, aluminum is used as the central element 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] In addition, the melt is subjected to a calcium treatment, which modifies the oxides, particularly the aluminum oxides. Gas purging partially flushes out the compounds, setting 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 lead to the introduction of material defects during casting, which in turn is detrimental to hot forming in tube production. In addition, this would promote the formation of larger clusters of aluminum oxides, which are also detrimental and, for example, increase tool wear during machining due to their high hardness. The Al content can therefore be limited to a preferred range of 0.002–0.020 wt.% for all alloys according to the invention.

[0015] Calcium treatment modifies the oxides present in the material, particularly aluminum oxide. Calcium aluminates are formed in particular. The calcium can be added in various ways, for example as calcium-silicon wire. Oxides with a calcium content have the positive property of improving chip breaking. The negative impact on tool wear is reduced because the number of wear-promoting hard aluminum oxides is greatly reduced. A certain proportion of calcium-treated oxides can therefore remain in the material. During gas purging of the alloy, the majority of the inclusions are flushed out. Calcium aluminates are easier to flush out than untreated aluminum oxides. Overall, this also enables, among other things, better control of the aluminum content. Calcium also influences the formation of manganese sulfides.Combining manganese sulfides with Ca leads to an increase in the size of the inclusions, which also positively influences machinability. Furthermore, elongation of the sulfides during the hot rolling process is reduced. Combining 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 precursor materials, particularly in continuous casting, the Ca content is preferably 0.0005–0.01 wt.%. Lead also contributes to improved machinability. Lead improves chip breaking 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, a key element, increases the strength of steel. The minimum content is therefore specified at 0.04 wt.%. Excessively high carbon content, in particular, 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 barely affected. However, silicon reduces ductility and machinability. The content is limited to a maximum of 0.60 wt.%. The Si content can be specified at 0.20 to 0.60 wt.%. This is particularly advantageous for free-cutting steels with higher mechanical properties that are welded after machining.

[0018] Phosphorus and nitrogen improve machinability, particularly chip breaking. These elements have an embrittling effect on the material and impair its mechanical and hot-forming properties. The content is therefore limited to a maximum of 0.1 wt.% P and a maximum of 0.15 wt.% N. Particularly for tubes with special requirements regarding mechanical properties, the content is preferably a maximum of 0.025 wt.% P and a maximum of 0.05 wt.% N. The total contents of P and N must not exceed 0.2 wt.%. Alternatively, boron can be alloyed, which also has an embrittling effect. Among other things, boron increases strength, which can lead to increased tool wear and has a negative effect on hot-formability. The boron content is therefore limited to a maximum of 0.01 wt.% and preferably a maximum of 0.002 wt. While generally manufacturable with boron contents above these ranges, the process according to the invention is possible, but not advantageous.

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

[0020] Alloys particularly suitable for the invention are listed in Table 1, whereby all alloys listed in the table (all values ​​in wt. %, except O) contain Al 0.002-0.060; Ca 0.001-0.02 and 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 iron and melting-related impurities and accompanying elements, whereby the ratio of Mn / S is in the range from 3.3:1 to 30:1. The semi-finished product produced by 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 various cross-sectional geometries, with round billets being preferred, made from one of the aforementioned steel alloys. Each billet is divided into smaller ingots. The division into ingots can be performed 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 pierced using a hole press. This creates a hollow block. This hollow block is then elongated using cross-rolling, reducing the wall thickness (WD) and outer diameter. Alternatively, the block can be pierced using a cross-rolling process with the aid of an internal tool. Various roll geometries and the number of cross-rollers (2 or 3) can be used. Various guiding devices, such as guide bars, guide discs, or guide rollers, can also be employed. During the aforementioned processes, the material has a minimum temperature of 1,000°C.

[0023] The elongated hollow block is then stretched again while hot at a minimum of 750°C. The push bench process is suitable for this, in which the perforated hollow block is stretched on a mandrel bar as an internal tool through stands arranged in series with non-driven rollers, or a linear rolling mill with an internal tool and driven stands, also known as the continuous pipe process, 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 different number of rolls can be used per stand. Adjusting the rolls during the rolling process is possible depending on the process. Due to the material concept, in particular because there is almost no FeS present, lower temperatures can also be used. Brittleness, in particular red brittleness, does not occur.Temperatures in the range of 900–1130 °C immediately after lengthening the hollow billet in the push bench, continuous tube rolling mill, and the described further developments are preferable. However, a minimum temperature of 750 °C must never be exceeded during the rolling process.

[0024] Alternatively, the plug rolling process can be used. In this process, the hollow ingot is rolled onto a plug rod with a rolling plug supported by abutments using work rolls. Other alternatives to elongation include a cross-rolling mill, e.g., an Assel rolling mill, a Diescher rolling mill, or a planetary cross-rolling mill with three or four rolls and a controlled internal tool. Even with these alternatives, the specified minimum temperature of 750°C must not be exceeded.

[0025] The final geometry is achieved in a final rolling process without internal tools, with the material temperature at the start of the process ranging from 850°C to 1200°C, and preferably from 900°C to 1100°C. A stretch-reducing mill, a reducing mill, or a sizing mill can be used for this purpose. The preceding intermediate product can optionally be reheated beforehand. Inductive reheating within the process is also possible. The final rolling temperature after final forming is in the range of 740°C to 1150°C, and preferably from 800°C to 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 carried out before the final cooling to room temperature.

[0026] Surface temperature deviations are possible at all production stages, e.g. at the pipe end or contact surfaces such as rollers or rolls, whereby the average temperature across 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. Manganese sulfides undergo elongation in the rolling direction during rolling. Smaller tube dimensions exhibit greater elongation of the manganese sulfides on average. The elongated manganese sulfides usually retain a certain curvature. The curvature decreases with the degree of elongation of the manganese sulfides and the tube. Manganese sulfides can exhibit reduced elongation or retain a spherical shape when combined with other elements, such as calcium.

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

[0029] To further improve mechanical properties, vanadium can be alloyed. Vanadium refines the grain, improving strength and toughness while simultaneously reducing machinability. Vanadium contents should not exceed 0.5%. Optionally, a vanadium range of 0.06–0.17% can be used, which combines improved mechanical properties with very high machinability.

[0030] The mechanical properties based on tensile tests at room temperature (RT) of particularly suitable alloys are given for the alloys in Table 1 and in the dependent claims. The tensile tests can be carried out in accordance with 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., to match the tube surfaces. Flat specimens are usually used. The alloys can optionally be manufactured with a specified notched bar impact energy in joules. The notched bar impact energy can be determined for the alloys specified in the claims using the method according to European Standard EN 10045-1 or International Standard ISO 148-1. Charpy impact test pieces in the longitudinal direction and a V-notch (KV) were used for the determination. With regard to wall thickness (WD), a distinction is made between a range up to 12 mm WD and a range from 12 mm WD.

[0031] With regard to the above-mentioned variations of the 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 state and that different properties can be achieved by modifying the tubular semi-finished product, e.g. heat treatment, such as hardening, tempering, stress relief, and / or cold drawing.

[0032] As a result, the steel alloy used according to the invention for the semi-finished product and the manufacturing process result in improved chip formation, longer tool life, and an overall improvement in machinability. The lubricating effect of sulfur is retained in the steel alloy used according to the invention for the semi-finished product. The steel alloy used according to the invention for the semi-finished product and the process for producing seamless, hot-rolled tubular semi-finished products enable the machining parameters, e.g., cutting speed, feed, and cutting depth, to be adjusted to higher values. Faster machining is possible, thereby reducing manufacturing costs. The proportion of reject parts, e.g., due to system 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 its 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 size 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-pipe is then drawn through the drawing die, with or without an internal tool / drawing mandrel, whereby the pipe 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 of the material's optimized inclusion morphology, the cross-sectional reduction can be chosen to be similar to that of non-sulfurized variants. Target cross-sectional reductions are in the range of 15-45% per pull.

[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 deformation step. Optionally, this process can also be performed in the heated state or after prior heat treatment. The long product can be divided into semi-finished products of the required length by cutting, particularly sawing. These semi-finished products are machined in a subsequent production step, at least partially with respect to the surface of the semi-finished products. Cutting processes, generally involving geometrically defined cutting edges, are particularly noteworthy as machining processes, particularly processes such as turning, milling, or drilling. Machining is typically performed to join the products to 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 along a longitudinal section of a surface, preferably along a predominant portion of the length of the semi-finished product. Therefore, a tubular semi-finished product that has, for example, 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 product are sleeves and spacer rings. These are short, cylindrical, possibly stepped, essentially rotationally symmetrical, machined components with various wall thicknesses.

[0040] Another application concerns coupling sleeves for various applications, such as threaded anchors and reinforcement. Coupling sleeves are cylindrical components of various lengths and wall thicknesses with an internal thread. The inner diameter and thread dimensions are matched to a counterpart (rod, anchor, etc.). Such sleeves are either machined or left unmachined on the outside. Coupling sleeves are sometimes provided with tapers, shoulders, and holes.

Claims

1. A process for producing a seamless and hot-rolled tubular semi-finished product by means of the following steps: a) producing a billet from a steel alloy which, in weight percent, consists of C 0,04 - 0,48 Si max. 0.60 Mn 1,10-2,90 S 0,10-0,40 Al 0,002 - 0,060 Ca 0,0001 - 0,02 O max. 80 ppm and optionally 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 The max. 0.07 See max. 0.2 Ni max. 2 Cu max. 0.8 Nb max. 0.3 Ti max. 0.5 The remainder is iron, as well as impurities and accompanying elements resulting from the smelting process, with the Mn to S ratio being 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 piercing using a piercing press and subsequent elongation with reduction of the wall thickness and the outer diameter by means of cross rolling or by simultaneous piercing and elongation of the block by a cross rolling process using an internal mandrel; d) lengthening the hollow block in the hot state at a temperature of at least 750°C; e) final rolling without an internal mandrel and at a temperature of 850°C to 1,200°C to set the final geometry of a tubular semi-finished product, wherein the final rolling takes place after an optional intermediate heating step and wherein a final temperature after rolling is in a range of 740°C to 1,150°C.

2. Method according to claim 1, characterized in thatthe lengthening of the hollow ingot in the hot state is carried out by one or more of the following processes: push bench process, continuous pipe process, multi-stand pipe mill process or another linear rolling process with driven rolls and internal tool, plug rolling process, process using an Assel rolling mill, Diescher rolling mill or planetary cross-rolling mill.

3. 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 - 1,130 °C.

4. Method according to 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 cold or with 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 by means of the drawing die by inserting the tubular semi-finished product with the end with the reduced diameter into the drawing die, gripping it and then pulling it through the drawing die with or without an inner tool.

5. Method according to one of claims 1 to 4, characterized in that the drawing is repeated one or more times with one or more drawing dies that become smaller in diameter.

6. Method according to one of claims 1 to 5, characterized in thatthe hot-rolled and optionally cold-drawn tubular semi-finished product is formed by at least one subsequent cold or warm forming step.

7. Method according to one of claims 1 to 6, characterized in that it includes a machining step with a geometrically defined cutting edge.

8. Method according to one of claims 1 to 7, characterized in that The following steel alloy is used to manufacture the billet: C 0,14-0,22 Si max. 0.60 Mn 1,10-2,90 S 0,10-0,14 Al 0,002 - 0,060 Ca 0,0001 - 0,02 O max. 80 ppm V max. 0.5 P max. 0.1 Pb max. 0.1 N max. 0.15 N+P max. 0.2 Bi max. 0.1 The max. 0.07 See max. 0.2 Ni max. 2 Cu max. 0.8 Nb max. 0.3 Ti max. 0.5 and optionally B max. 0.01 The remainder is iron as well as impurities and accompanying elements caused by the melting process, with the ratio of Mn to S being 7.9:1 to 29:1 in wt.%, whereby the tubular semi-finished product is adjusted to the following mechanical properties: Yield strength Re min. 250 MPa Tensile strength Rm min. 420 MPa Elongation at break A5 min. 9%, where optionally the Charpy V-longitudinal impact strength KV up to 12 mm wall thickness 24 J (20°C) Charpy V-longitudinal impact strength KV from 12 mm wall thickness 16 J (20°C) amounts.

9. Method according to one of claims 1 to 7, characterized in that The following steel alloy is used to manufacture the billet: C 0,14-0,22 Si max. 0.60 Mn 1,10-2,90 S 0,14-0,27 Al 0,002 - 0,060 Ca 0,0001 - 0,02 O max. 80 ppm V max. 0.5 P max. 0.1 Pb max. 0.1 N max. 0.15 N+P max. 0.2 Bi max. 0.1 The max. 0.07 See max. 0.2 Ni max. 2 Cu max. 0.8 Nb max. 0.3 Ti max. 0.5 and optionally B max. 0.01 The remainder is iron as well as impurities and accompanying elements caused by the melting process, with the ratio of Mn to S being 4.1:1 to 20.7:1 in wt.%, whereby the tubular semi-finished product is adjusted to the following mechanical properties: Yield strength Re min. 250 MPa Tensile strength Rm min. 420 MPa Elongation at break A5 min. 9%, where optionally the Charpy V-longitudinal impact strength KV up to 12 mm wall thickness 24 J (20°C) Charpy V-longitudinal impact strength KV from 12 mm wall thickness 16 J (20°C) amounts.

10. Method according to one of claims 1 to 7, characterized in that The following steel alloy is used to manufacture the billet: C 0,31 - 0,48 Si max. 0.60 Mn 1,10-2,90 S 0,10-0,14 Al 0,002 - 0,060 Ca 0,0001 - 0,02 O max. 80 ppm V max. 0.5P max. 0.1 Pb max. 0.1 N max. 0.15 N+P max. 0.2 Bi max. 0.1 The max. 0.07 See max. 0.2 Ni max. 2 Cu max. 0.8 Nb max. 0.3 Ti max. 0.5 and optionally B max. 0.01 The remainder is iron as well as impurities and accompanying elements caused by the melting process, with the ratio of Mn to S being 8.5:1 to 29:1 in wt.%, whereby the tubular semi-finished product is adjusted to the following mechanical properties: Yield strength Re min. 350 MPa Tensile strength Rm min. 480 MPa Elongation at break A5 min. 7%, where optionally the Charpy V-longitudinal impact strength KV up to 12 mm wall thickness 9 J (20°C) Charpy V-longitudinal impact strength KV from 12 mm wall thickness 7 J (20°C) amounts.

11. Method according to one of claims 1 to 7, characterized in that The following steel alloy is used to manufacture the billet: C 0,14-0,22 Si max. 0.60 Mn 1,10-1,80 S 0,27 - 0,40 Al 0,002 - 0,060 Ca 0,0001 - 0,02 O max. 80 ppm V max. 0.5 P max. 0.1 Pb max. 0.1 N max. 0.15 B max. 0.01 N+P max. 0.2 Bi max. 0.1 The max. 0.07 See max. 0.2 Ni max. 2 Cu max. 0.8 Nb max. 0.3 Ti max. 0.5 and optionally B max. 0.01 The remainder is iron as well as impurities and accompanying elements caused by the melting process, with the ratio of Mn to S being 3.3:1 to 6.7:1 in wt.%, whereby the tubular semi-finished product is adjusted to the following mechanical properties: Yield strength Re min. 345 MPa Tensile strength Rm min. 490 MPa Elongation at break A5 min. 20%, where optionally the Charpy V-longitudinal impact strength KV up to 12 mm wall thickness 24 J (20°C) Charpy V-longitudinal impact strength KV from 12 mm wall thickness 16 J (20°C) amounts.

12. Method according to one of claims 1 to 7, characterized in that The following steel alloy is used to manufacture the billet: C 0,14-0,22 Si 0,20-0,60 Mn 1,10-1,70 S 0,10-0,14 Al 0,002 - 0,060 Ca 0,0001 - 0,02 O max. 80 ppm V max. 0.5 P max. 0.1 Pb max. 0.1 N max. 0.15 N+P max. 0.2 Bi max. 0.1 The max. 0.07 See max. 0.2 Ni max. 2 Cu max. 0.8 Nb max. 0.3 Ti max. 0.5 and optionally B max. 0.01 The remainder is iron as well as impurities and accompanying elements caused by the melting process, with the ratio of Mn to S being 7.9:1 to 17:1 in wt.%, whereby the tubular semi-finished product is adjusted to the following mechanical properties: Yield strength Re min. 345 MPa Tensile strength Rm min. 490 MPa Elongation at break A5 min. 20%, where optionally the Charpy V-longitudinal impact strength KV up to 12 mm wall thickness 24 J (20°C) Charpy V-longitudinal impact strength KV from 12 mm wall thickness 16 J (20°C) amounts.

13. Method according to one of claims 1 to 7, characterized in that The following steel alloy is used to manufacture the billet: C 0,16-0,23 Si 0,20-0,60 Mn 1,10-1,70 S 0,10-0,14 Al 0,002 - 0,060 Ca 0,0001 - 0,02 O max. 80 ppm V 0,06 - 0,17 P max. 0.1 Pb max. 0.1 N max. 0.15 N+P max. 0.2 Bi max. 0.1 The max. 0.07 See max. 0.2 Ni max. 2 Cu max. 0.8 Nb max. 0.3 Ti max. 0.5 and optionally B max. 0.01 The remainder is iron as well as impurities and accompanying elements caused by the melting process, with the ratio of Mn to S being 7.9:1 to 17:1 in wt.%, whereby the tubular semi-finished product is adjusted to the following mechanical properties: Yield strength Re min. 430 MPa Tensile strength Rm min. 600 MPa Elongation at break A5 min. 17%, where optionally the Charpy V-longitudinal impact strength KV up to 12 mm wall thickness 25 J (20°C) Charpy V-longitudinal impact strength KV from 12 mm wall thickness. 17 J (20°C) 14. Method according to one of claims 1 to 7, characterized in that The following steel alloy is used to manufacture the billet: C 0,04 - 0,14 Si max. 0.45 Mn 1,10 - 1,60 S 0,26 - 0,34 Al 0,002 - 0,060 Ca 0,0001 - 0,02 O max. 80 ppm V max. 0.5 P max. 0.1 Pb max. 0.1 N max. 0.15 N+P max. 0.2 Bi max. 0.1 The max. 0.07 See max. 0.2 Ni max. 2 Cu max. 0.8 Nb max. 0.3 Ti max. 0.5 and optionally B max. 0.01 The remainder is iron as well as impurities and accompanying elements caused by the melting process, with the ratio of Mn to S being 3.3:1 to 6.2:1 in wt.%, whereby the tubular semi-finished product is adjusted to the following mechanical properties: Yield strength Re min. 215 MPa Tensile strength Rm min. 350 MPa Elongation at break A5 min. 9%, where optionally the Charpy V-longitudinal impact strength KV up to 12 mm wall thickness 24 J (20°C) Charpy V-longitudinal impact strength KV from 12 mm wall thickness 16 J (20°C) amounts.

15. Method according to one of claims 1 to 7, characterized in that The following steel alloy is used to manufacture the billet: C 0,14-0,22 Si max. 0.60 Mn 1,10-1,80 S 0,26 - 0,34 Al 0,002 - 0,060 Ca 0,0001 - 0,02 O max. 80 ppm V max. 0.5 P max. 0.1 Pb max. 0.1 N max. 0.15 N+P max. 0.2 Bi max. 0.1 The max. 0.07 See max. 0.2 Ni max. 2 Cu max. 0.8 Nb max. 0.3 Ti max. 0.5 and optionally B max. 0.01 The remainder is iron as well as impurities and accompanying elements caused by the melting process, with the ratio of Mn to S being 3.3:1 to 6.9:1 in wt.%, whereby the tubular semi-finished product is adjusted to the following mechanical properties: Yield strength Re min. 250 MPa Tensile strength Rm min. 420 MPa Elongation at break A5 min. 9%, where optionally the Charpy V-longitudinal impact strength KV up to 12 mm wall thickness 24 J (20°C) Charpy V-longitudinal impact strength KV from 12 mm wall thickness 16 J (20°C) amounts. Table 1 Tensile test (longitudinal, RT) Charpy-V longitudinal material C Si Mn S Mn-S ratio V re Rm A KV up to 12 mm WD KV from 12 mm WD min max min max min max min max min max min max min. MPa min. MPa min. % J (+20 °C) J (+20 °C) 1 0,04 0,14 0 0,6 1,1 2,9 0,10 0,14 7,9 29,0 0,5 190 310 11 27 18 2 0,04 0,14 0 0,6 1,1 2,9 0,14 0,27 4,1 20,7 0,5 190 310 11 27 18 3 0,04 0,14 0 0,6 1,1 2,9 0,27 0,4 3,3 10,7 0,5 190 310 11 27 18 4 0,14 0,22 0 0,6 1,1 2,9 0,10 0,14 7,9 29,0 0,5 250 420 9 24 16 5 0,14 0,22 0 0,6 1,1 2,9 0,14 0,27 4,1 20,7 0,5 250 420 9 24 16 6 0,14 0,22 0 0,6 1,1 2,9 0,27 0,4 3,3 10,7 0,5 250 420 9 24 16 7 0,22 0,31 0 0,6 1,1 2,9 0,10 0,13 8,5 29,0 0,5 310 460 9 17 12 8 0,22 0,31 0 0,6 1,1 2,9 0,14 0,27 4,1 20,7 0,5 310 460 9 17 12 9 0,22 0,31 0 0,6 1,1 2,9 0,27 0,4 3,3 10,7 0,5 310 460 9 17 12 10 0,31 0,48 0 0,6 1,1 2,9 0,10 0,14 7,9 29,0 0,5 350 480 7 9 7 11 0,31 0,48 0 0,6 1,1 2,9 0,14 0,27 4,1 20,7 0,5 350 480 7 9 7 12 0,31 0,48 0 0,6 1,1 2,9 0,27 0,4 3,3 10,7 0,5 350 480 7 9 7 13 0,14 0,24 0 0,6 1,1 2,9 0,10 0,14 7,9 29,0 0,06 0,17 355 440 10 25 17 14 0,14 0,24 0 0,6 1,1 2,9 0,14 0,27 4,1 20,7 0,06 0,17 355 440 10 25 17 15 0,14 0,24 0 0,6 1,1 2,9 0,27 0,4 3,3 10,7 0,06 0,17 355 440 10 25 17 16 0,14 0,22 0 0,6 1,1 1,8 0,10 0,14 7,9 18,0 0,5 345 490 20 24 16 17 0,14 0,22 0 0,6 1,1 1,8 0,14 0,27 4,1 12,9 0,5 345 490 20 24 16 18 0,14 0,22 0 0,6 1,1 1,8 0,27 0,4 3,3 6,7 0,5 345 490 20 24 16 19 0,14 0,22 0,2 0,6 1,1 1,7 0,10 0,14 7,9 17,0 0,5 345 490 20 24 16 20 0,14 0,22 0,2 0,6 1,1 1,7 0,14 0,27 4,1 12,1 0,5 345 490 20 24 16 21 0,14 0,22 0,2 0,6 1,1 1,7 0,27 0,4 3,3 6,3 0,5 345 490 20 24 16 22 0,16 0,23 0 0,6 1,1 1,8 0,10 0,14 7,9 18,0 0,06 0,17 420 600 17 25 17 23 0,16 0,23 0 0,6 1,1 1,8 0,14 0,27 4,1 12,9 0,06 0,17 420 600 17 25 17 24 0,16 0,23 0 0,6 1,1 1,8 0,27 0,4 3,3 6,7 0,06 0,17 420 600 17 25 17 25 0,16 0,23 0,2 0,6 1,1 1,7 0,10 0,14 7,9 17,0 0,06 0,17 430 600 17 25 17 26 0,16 0,23 0,2 0,6 1,1 1,7 0,14 0,27 4,1 12,1 0,06 0,17 430 600 17 25 17 27 0,16 0,23 0,2 0,6 1,1 1,7 0,27 0,4 3,3 6,3 0,06 0,17 430 600 17 25 17 28 0,04 0,14 0 0,45 1,1 1,6 0,26 0,34 3,3 6,2 0,5 215 350 - 580 9 24 16 29 0,31 0,39 0 0,45 1,2 1,8 0,10 0,2 6,0 18,0 0,5 370 530 - 790 9 16 12 30 0,14 0,22 0 0,6 1,1 1,8 0,26 0,34 3,3 6,9 0,5 250 420 9 24 16