FI125290B - Method of manufacturing a steel pipe and steel pipe - Google Patents

Description

METHOD FOR MANUFACTURE OF STEEL TUBE AND STEEL TUBE FIELD OF THE INVENTION

The present invention relates to high-strength steel tubes with excellent workability and to processes for their manufacture.

More particularly, the invention relates to a method for producing a steel tube as defined in the preamble of independent claim 1.

More particularly, the invention relates to a steel tube as defined in the preamble of independent claim 10.

The invention relates to such a method of making steel tubes, comprising the step of providing a parent tube, a heating step of heating the parent tube, a heat reduction step after the heating step, wherein the diameter of the parent tube is

Objective of the Invention

The steel tubes used in the automotive industry must be of high strength in order to make structures as thin as possible, resulting in lighter vehicle structures, which in turn leads to material and fuel savings. At the same time, automotive parts, many of which are made of steel tubes, have complex shapes and must also be able to absorb collision energy. This requires that the steel pipes must be both highly malleable and at the same time high strength.

Until now, this well-known problem has been solved by improving workability at the expense of other goals by using higher material thicknesses and using low strength steel. Alternatively, the parts are designed to include simpler shapes to reduce the flexibility requirements.

It is an object of the invention to provide a method for producing a high-strength steel tube having both better ductility and high strength, and to provide a high-strength steel tube having both better ductility and high strength.

Brief Description of the Invention

The method of the invention is known from the definitions of independent claim 1.

Preferred embodiments of the method are defined in the dependent claims 2 to 9.

The steel tube of the invention is known from the definitions of independent claim 10, respectively.

Preferred embodiments of the steel tube are defined in the dependent claims 11-26.

The process for producing a steel tube according to the invention comprises the step of providing a parent tube containing 0.05-0.25% C, 2.0% or less Si, 0.25-2.5% Mn, 2.5% or less Al, 2.0% or less Cr, 1.0% or less Mo, 0.3% or less Ti + Nb + V, and Fe, unavoidable impurities and residual content in the mouth, and having a manganese equivalent of 1.3 to 3.9 as determined by the following formula (1)

The method of producing the steel tube according to the invention further comprises the step of heating the parent tube to a temperature in the range (Ac3-50) to 1280 ° C.

The process for producing a steel tube according to the invention further comprises a step of heat reduction after the heating step, wherein reducing the diameter of the parent tube is performed to form a hot rolled steel tube, wherein the step of

The process for producing a steel tube according to the invention further comprises the step of cooling the hot-rolled steel tube to a temperature below 300 ° C, wherein the cooling step is performed after the hot reduction step, and the hot-rolled steel tube is cooled at 5 ° C / min.

Correspondingly, the steel tube of the invention containing Fe, inevitable impurities and residual contents is also known to contain, by weight, 0.05-0.25% C, 2.0% or less Si, 0.25-2.5% Mn, 2.5 % or less Al, 2.0% or less Cr, 1.0% or less Mo, 0.3% or less Ti + Nb + V, and has a manganese equivalent of 1.3 to 3.9 as defined by the following formula (1)

This advantageous manganese equivalent combined with a controlled cooling step at a temperature range of 300-500 ° C after a controlled heat reduction machining step results in a high ductility and high strength multiphase steel tube where carbon can be substantially purified from , martensite, bainite, and possibly residual austenite.

Said ferrite base is soft and highly malleable, suggesting that the deformation could concentrate on the soft ferrite and that, therefore, cracking could easily occur at the edges susceptible to tensile stress during the shaping. Even with this highly customizable ferrite base, the steel tube can be successfully shaped near edges, holes or openings without cracks or fractures at the cutting edge.

The present invention provides a steel tube with surprisingly good workability, elongation, and high strength properties, as described below in this specification. Furthermore, based on impact strength measurements, the steel tube appears to exhibit tough fracture behavior, suggesting that the steel tube of the invention has a very wide range of industrial applications, e.g.

List of figures

Figure 1 is a flowchart of the method of the invention,

Figure 2 is a flowchart of a first preferred embodiment of the method of the invention,

Fig. 3 is a flowchart of another preferred embodiment of the method of the invention,

Figure 4 illustrates an experimental arrangement for a curry extension test.

DETAILED DESCRIPTION OF THE INVENTION

The invention relates to a method of making a steel tube, and to a steel tube.

First, the method for making the steel tube and the preferred and alternative embodiments of the method will be explained in more detail.

The method comprises the step of providing a parent tube containing 0.05-0.25% C, 2.0% or less Si, 0.25-2.5% Mn, 2.5% or less Al, 2.0% or less Cr, in mass, 1.0% or less Mo, 0.3% or less Ti + Nb + V, and Fe, unavoidable impurities and residual content of a, and having a manganese equivalent of 1.3 to 3.9 as determined by the following formula (1)

In this process, a manganese equivalent of from 1.3 to 3.9 is necessary to achieve the desired mechanical properties. If the manganese equivalent is less than 1.3, the multi-phase microstructure of the steel tube will not be achieved to achieve the objectives of the invention. On the other hand, if the manganese equivalent is greater than 3.9, the hardening is too strong, which results in poorer formability.

The method further comprises the step of heating the parent tube to a temperature in the range (C3-50) ° C to 1280 ° C.

Preferably, but not necessarily, the heating step is accomplished, at least in part, by induction heating, which provides a high heating rate in a continuous production line.

The method further comprises a hot reduction step after the heating step, wherein the reduction of the parent tube diameter is performed to form a hot rolled steel tube from the parent tube, wherein the hot reduction step is terminated such that the temperature of the hot rolled steel is higher than 1 ° C.

In other words, the hot reduction machining step may include some shaping at a temperature below Ar3.

The hot reduction machining step is preferably, but not necessarily, terminated such that the temperature of the hot rolled steel tube exceeds (Ar3-50) ° C at the end of the hot reduction machining step. In this way, the malleability of the steel tube can be assured, in particular, the increased yield strength which would be detrimental to the malleability is avoided.

The limit is defined as (Ar3-50) ° C, because in some cases the results are not substantially different when comparing the results obtained with the heat reduction end temperature cut-off (Ar3-50) ° C or Ar3.

During the hot reduction step, the diameter of the parent tube decreases and changes occur in the microstructure of the steel, which has a positive effect on the mechanical properties of the steel in the mother tube.

The parent tube may be a welded steel tube or a seamless steel tube. Usually, standard length parent tubes are used, and using this same size, it is possible to achieve many end product sizes by varying the reduction ratio. The reduction ratio is defined as:

Preferably, the diameter of the parent tube is reduced by 5% or more during the hot reduction step to achieve the mechanical properties of the invention. Preferably, but not necessarily, the diameter of the parent tube is reduced by 10% or more during the hot reduction step. The diameter reduction performed during the hot reduction machining step provides a fine microstructure which results in a combination of high strength and high elongation at break. Reducing the diameter also increases impact resistance due to the finer microstructure. The heat reduction machining step is preferably performed by rolling the parent tube.

The method further comprises the step of cooling the hot-rolled steel tube to a temperature below 300 ° C, wherein the cooling step is performed after the hot reduction machining step, and wherein the hot-rolled steel tube is cooled in the cooling step at a temperature below 500 ° C / sec. The cooling step may be carried out using air cooling, such as free air cooling in the temperature range of 500-300 ° C. The cooling steps are carried out after the heat reduction machining step, without cooling below (Ar3 -50) ° C, between the two steps.

The cooling step can be performed using water cooling and at a cooling rate above 10 ° C / sec at temperatures above 500 ° C. In the case where cooling at temperatures above 500 ° C is carried out at a cooling rate above 10 ° C / sec, it is preferable to use a parent tube having a manganese equivalent of 1.3 to 2.0 in order to achieve the desired mechanical properties. This preferred embodiment results in fine-grained ferrite, which results in excellent workability of the steel tube.

Water cooling is preferably, but not necessarily, initiated within 5 seconds after the completion of the heat reduction step.

The cooling step can be performed using air cooling, such as free air cooling at temperatures above 500 ° C. Thanks to the favorable manganese equivalent, free-air cooling at temperatures above 500 ° C also results in surprisingly good mechanical properties. Amazingly, during the slow air cooling, virtually no perlite was formed in the microstructure, and a very low yield steel tube was provided. In the case where cooling at temperatures above 500 ° C is carried out with free air cooling, it is preferable to use a parent tube having a manganese equivalent of 2.0 to 3.9 in order to obtain the desired mechanical properties. In addition, cooling with free air at temperatures above 500 ° C results in harder secondary phases such as martensite, which increases strength.

The criteria for upper and lower limits for chemical elements in the parent tube are as follows (the chemical element concentrations are by weight):

The upper limit for carbon, C, is set at 0.25% because a higher concentration would reduce the workability and weldability. The lower limit for carbon, C, is set at 0.05% because it is difficult to achieve high tensile strength at lower concentrations without blending other expensive alloying elements.

The upper limit for silicon, Si, is set at 2.0% because a higher concentration would result in a poor quality steel tube surface. The lower limit for silicon, Si, is preferably set at 0.01% so that Si is even available as a desulfurizing agent.

The upper limit for manganese, Μη, is set at 2.5%, since higher concentrations would lead to harmful midline filtration of manganese and carbon. The lower limit for manganese, Mn, is set at 0.25% to achieve desirable strength in some cases.

The upper limit for aluminum, AI, is set at 2.5%, since a higher concentration would make it difficult to drain the steel billet.

The upper limit for aluminum, Al is preferably, but not necessarily, set at 1.5%. The lower limit for aluminum, Al, is preferably set at 0.02% to provide enough aluminum to function at least as an oxygen scavenger.

The upper limit for chromium, Cr, is set at 2.0%, since chromium has a strong effect on carbon equivalent (CEV), resulting in reduced weldability, and, in addition, high chromium content can lead to a streaky structure which impairs ductility. The upper limit for chromium is preferably, but not necessarily, set at 1.4% to avoid these drawbacks. The lower limit for chromium is preferably, but not necessarily, set at 0.1% to achieve the desired hardening of the steel tube.

The upper limit for molybdenum, Mo, is set at 1.0%. Preferably, the upper limit for molybdenum is set at 0.5%, since molybdenum adversely affects the hot rolling of the parent tube during the hot reduction step by increasing the strength at high temperature. The lower limit for molybdenum, Mo, is preferably, but not necessarily, set at 0.05% because the favorable molybdenum doping delays perlite formation during the cooling step at temperatures above 500 ° C. For this reason, molybdenum doping may be advantageous, especially when cooling at temperatures above 500 ° C is achieved using slow air cooling.

The total concentration of the combination of titanium, Ti, niobium, Nb, and vanadium, V, is set at 0.3%. These microalloying elements increase yield strength and give the steel tube a finer granularity, which can also contribute to providing a highly malleable steel tube. The total concentration of the combination of titanium, Ti, niobium, Nb, and vanadium, Y, is preferably, but not necessarily, 0.01-0.08%.

The steel tube may also contain nickel, Ni, copper, Cu and boron, B.

Boron B may not be needed, but if it is alloyed, the upper limit for boron B is set at 0.009%. Boron can be doped to increase hardening, especially when the other doping level is low, which otherwise results in a manganese equivalent too low.

Nickel, Ni, may not be needed, but if nickel, Ni, is alloyed, its upper limit is set at 1.0%. Ni can be mainly doped due to the possible presence of copper, Cu, and in some cases may be doped to improve the toughness of the steel tube. In order to operate as described, the lower limit for nickel is preferably set at 0.05%.

Copper may not be needed, but when copper, Cu, is alloyed, its upper limit is set at 1.0%, since higher content adversely affects hot workability. The mass concentration of copper is preferably, but not necessarily, selected to be less than half the mass content of nickel, Ni, i.e., Cu (%) <Ni (%) / 2.

A first preferred embodiment of the method comprises the step of providing a parent tube containing 0.05 to 0.14% C, 0.4% or less Si, 0.5 to 1.5% Mn, 0.7% or less Cr, 0 , 01 -0.5% Mo, 0.009% or less B%, and 0.22% or less Ti + Nb + V.

Another preferred embodiment of the method comprises the step of providing a parent tube containing 0.05-0.25% C, 2.0% or less Si, 0.5-2.5% Mn, 2.0% or less Cr, 0.01-0, in mass. , 1% Mo, 0.009% or less B, and 0.22% or less Ti + Nb + V.

The steel tube and the preferred and alternative embodiments of the steel tube will be explained in more detail below.

The steel tube contains Fe, unavoidable impurities, residual contents, and additionally contains 0.05-0.25% C, 2.0% or less Si, 0.25-2.5% Mn,

2.5% or less AI

2.0% or less Cr, 1.0% or less Mo, 0.3% or less Ti + Nb + V.

The manganese equivalent of a steel tube is 1.3 to 3.9 as defined by the following formula (1)

The basics of upper and lower limits of the parent chemical elements are given in the detailed description of the method.

The diameter of the steel tube may vary depending on the production equipment. The diameter of the steel tube is preferably, but not necessarily, 20 to 200 mm, most preferably 30 to 150 mm. The steel tube profile is preferably circular because the reduction ratio of the circular steel tube is equal at each point of the tube cross-section.

The steel tube has a yield strength (Rpo?) Of more than 250 MPa and a breaking strength (Rm) of more than 450 MPa.

The steel tube preferably has a yield strength (Rpo, 2) of more than 300 MPa and a tensile strength (Rm) of preferably 550 to 1200 MPa.

Excellent adaptability is characterized by a number of mechanical properties such as yield, n-value, curve-to-prediction ratio, and various types of elongation measurements. The steel tube according to the invention can achieve excellent values in most of these measurements, as shown in Table 3. Consideration of these properties together with the strength of the steel tube is also essential.

The steel tube yield ratio (Rpo, 2 / Rm) is preferably, but not necessarily, less than 0.65, preferably less than 0.6, more preferably less than 0.55. The extremely low yield ratio (Rpo ^ / Rm) provides a very good formability of the steel tube, as the steel tube can undergo a high degree of deformation beyond its high strength before it reaches tensile strength. On the other hand, due to the low yield ratio, the final steel part made of steel tube has an energy absorbing capacity after it is made of steel tube.

Preferably, but not necessarily, the bending strength component of the steel tube is greater than 0.08, preferably greater than 0.10. A high n-value indicates excellent elasticity. In practical shaping situations, a high n-value will result in a steady-state stress gradient, i.e., local thinning in the high-tension regions will be reduced compared to lower n-values.

The steel tube also has excellent elongation-related properties, the elongation at break (A5) is greater than 8%, preferably more than 20%, and the uniform elongation (Ag) is greater than 5%, preferably more than 10%.

Further, taking into account the strength, the product between the elongation at break (A5) and the yield strength (Rm) of the steel tube is at least 15,000, preferably at least 17,000, even more than 20,000.

Part of the steel tube preferably, but not necessarily, has a microstructure containing more than 30% ferrite, more than 5% martensite and / or bainite and less than 20% residual austenite.

Most preferably, the entire steel tube has a microstructure containing more than 30% ferrite, more than 5% martensite and / or bainite and less than 20% residual austenite.

Based on the coarse microstructure measurements in Table 3, the steel tube may preferably have a microstructure containing more than 80% main phase (ferrite) and more than 10% secondary phases (martensite and / or bainite and possibly residual austenite). Microstructure measurements were performed by etching the steel tube sample and subsequent image processing.

According to a preferred embodiment of the steel tube, the manganese equivalent is 2.0 to 3.9 as defined by formula (1). In this embodiment, it is preferred, but not necessary, to use a more detailed composition. According to this embodiment, the steel tube may contain by weight: 0.05-0.25% C, 2.0% or less Si, 0.5-2.5% Mn, 2.0% or less Cr, 0.01-0.1% Mo, 0.009% or less B, and 0.22% or less Ti + Nb + V.

In this preferred embodiment, the yield strength (Rpo, 2) of the steel tube is preferably, but not necessarily, 400 to 700 MPa. In this preferred embodiment, the elongation (A5) of the steel tube is preferably, but not necessarily, more than 8%, preferably more than 10%.

In the most preferred embodiment, the manganese equivalent of the steel tube is 1.3 to 2.0 as defined by formula (1). In this embodiment, it is preferred, but not necessary, to use a more detailed composition. According to this embodiment, the steel tube may contain by weight: 0.05-0.14% C, 0.4% or less Si, 0.5-1.5% Mn, 0.7% or less Cr, 0.01-0. 5% Mo, 0.009% or less B, and 0.22% or less Ti + Nb + V.

In this preferred embodiment, the yield strength (Rpo, 2) of the steel tube is preferably, but not necessarily, from 300 to 500 MPa. This preferred embodiment may also result in a steel tube having an elongation at break (A5) of greater than 15%, preferably greater than 20%.

examples

The steel compositions shown in Table 1 were subjected to a heating step, followed by a hot reduction step to form a hot rolled steel tube from the parent tube, and a cooling step following the heat reduction step. All samples were cooled over a temperature range of 500-300 ° C at a cooling rate below 5 ° C / s.

The columns "Diameter of the tube (mm)" and "Thickness of the tube (mm)" in Table 2 show the dimensions of the tube.

Table 2 also shows the production parameters (Reduction (%), Heating temperature (° C), Temperature before heat reduction (° C), Temperature after heat reduction (° C), and Temperature before cooling (° C)). Also shown is whether the temperature after heat reduction (° C) is higher than Ari or higher than Ar3.

Table 3 shows the obtained properties (Rpo, 2, Rm, A5, Ag, Rpo, 2 / Rm, Rm * A5, carrion expansion ratio (%), n value, Charpy V (-40 ° C), and microstructure compositions.

Karri shoulder expansion ratio measurements were performed for some steel tubes. The test conditions were in accordance with SFS EN ISO 8493. The end of the tube cut from the tube was expanded by a conical mandrel until the tube edge was broken. The experimental arrangement is illustrated in Figure 4. The steel tube ring was measured from the end of the steel tube in the initial stage (D) and just before the fracture (Du). The withdrawal ratio (%) was calculated from these two measurements D and Du according to the following formula:

Curve Shoulder Expansion Ratio (%) = Post-Test Maximum Outer Diameter Dn (mm) - Original Tube D (mm) Original Tube D (mm)

Steel 1

It is determined that for steel 2, about 730 ° C is the temperature at which the conversion of austenite to ferrite is initiated (Ar 3). All examples were produced by heat reduction with an end temperature above Ar3.

As shown in Table 3, steel 1 resulted in steel tubes having a yield strength (Rpo, 2) of 0.2% in the range of 405 to 431 MPa.

As shown in Table 3, steel 1 resulted in steel tubes having a tensile strength (Rm) of 793 to 815 MPa.

As shown in Table 3, steel 1 resulted in steel tubes having a yield ratio (Rpo, 2 / Rm) in the range of 0.50 to 0.53.

As shown in Table 3, for steel 1, steel tubes with an elongation at break (A5) of 21.2 to 21.9% and even elongation (Ag) at 11.2 to 12.1 were obtained, both of which are excellent results.

Steel 2

For steel 2, it is determined that the temperature at which the conversion of austenite to ferrite is initiated (Ar 3) is about 745 ° C. All examples except Experiment 1, Experiment 7, and Experiment 30 were produced by heat reduction whose end temperature T exceeded Ar 3. Exemplary tests 1, 7 and 30 were produced by heat reduction with a termination temperature of Ar3> T> Ar1, resulting in a lower tensile strength (Rm) which in turn increases the yield ratio. As shown in Table 3, for example, Test 30, which has the lowest heat reduction end temperature T of the test matrix at 690 ° C, yields the lowest tensile strength (Rm) of 671 MPa.

As shown in Table 3, steel 2 resulted in steel tubes with yield strength (Rpo, 2) in the range of 350-488 MPa.

As shown in Table 3, steel 2 resulted in steel tubes having a tensile strength (Rm) in the range of 728-957 MPa.

As shown in Table 3, steel 2 resulted in steel tubes having a yield ratio (Rpo ^ / Rm) in the range of 0.45 to 0.61.

As shown in Table 3, steel 2 resulted in steel tubes having a elongation at break (A5) in the range of 20.9 to 31.2% and also a flat strain (Ag) in the range of 11.1 to 16.8, both of which are excellent results.

As shown in Table 3, for steel 2, the result was steel tubes with a high n-value, which means very good workability, given the level of strength.

For most of the samples measured, the n value exceeded 0.10 or even 0.12.

As shown in Table 3, steel 2 resulted in steel tubes having a Charpy V toughness crack behavior of more than 50 J / cm 2 at -40 ° C as measured by a 10 * 3 mm test seam of the steel tube of the invention. Impact strength results are better at a higher reduction ratio and most preferably have a reduction ratio above 30%.

As shown in Table 3, steel 2 resulted in steel tubes having a cone expansion ratio (%) of more than 10%, even more than 20%. The results are surprisingly good considering the very low yield ratio of the steel tube in question.

Table 1: Test compositions

Table 2: Production parameters

Table 3: Properties obtained and microstructure composition

M = main phase (essentially ferrite), S = secondary fascia (containing martensite + bainite + possibly residual austenite)

It will be obvious to a person skilled in the art that, with the advancement of technology, the basic idea of the invention can be implemented in various ways. The invention and its embodiments are therefore not limited to the above examples, but may vary within the scope of the claims.

Claims (26)

A method for producing a steel tube, characterized in that the method comprises the step of providing a parent tube containing by weight: 0.05-0.25% C, 2.0% or less Si, 0.25-2.5% Mn, 2.5% or less Al 2.0% or less Cr, 1.0% or less Mo, 0.3% or less Ti + Nb + Y, and Fe, unavoidable impurities and residual content of a, and having a manganese equivalent of 1.3 to 3.9 as defined by according to formula (1) a heating step for heating the parent tube to a temperature in the range of (A C3 - 50) ° C to 1280 ° C, a heat reduction step after the heating step and wherein reducing the diameter of the parent tube to form a hot rolled , preferably above (Ar3 -50) ° C, and a cooling step for cooling the hot-rolled steel tube to a temperature below 300 ° C, whereby the cooling step is performed after the hot reduction step, and wherein the hot-rolled steel tube is cooled at 5 ° C to 500-300 ° C. 2. Förfarande enligt patentkrav 1, kännetecknat av, att man utför reducttionen av diametern så, att man i freductor onsb earb ethnings steg reducerar moderrörets diameter 5% eller mera, fördelaktigt 10% eller mera. Method according to claim 1, characterized in that the diameter reduction is carried out by reducing the diameter of the parent tube by 5% or more, preferably by 10% or more, in the heat reduction step. 3. Förfarande enligt patentkrav 1 eller 2, kännetecknat av, att man utför avkylningssteget med hjälp av luftkylning, t.ex. friluftskylning, inom tempurområdet 500-300 ° C. Process according to Claim 1 or 2, characterized in that the freezing step is carried out using air cooling, such as free air cooling, at a temperature in the range of from 500 to 300 ° C. 4. Förfarande enligt något av patentkraven 1 till 3, kännetecknat av, att man utför avkylningssteget med hjälp av vattenkylning och med en avkylningshastighet som 10 ° C / s vid tempurer över 500 ° C. Method according to one of Claims 1 to 3, characterized in that the cooling step is carried out using water cooling and at a cooling rate exceeding 10 ° C / sec at temperatures above 500 ° C. 5. Förfarande enligt patentkrav 4, kangnetecknat av, att manganese equivalent of 1,3-2,0 definierad enligt formel (1). Process according to Claim 4, characterized in that the manganese equivalent is between 1.3 and 2.0 as defined by formula (1). 6. Förfarande enligt patentkrav 4 eller 5, kännetecknat av, att man i framställningssteget framställer et moderrör, som i mass innehåller 0.05 - 0.14% C, 0.4% eller mindre Si, 0.5 - 1.5% Mn, 0.7% eller mindre Cr, 0.01 -0.5% Moer, 0.009% eller mindre B, and 0.22% eller mindre Ti + Nb + Y samt Fe, oundvikliga föroreningar and resthalter. A process according to claim 4 or 5, characterized in that the step of providing comprises providing a parent tube containing 0.05 to 0.14% C, 0.4% or less Si, 0.5 to 1.5% Mn, 0, 7% or less Cr, 0.01-0.5% Mo, 0.009% or less B, and 0.22% or less Ti + Nb + V and Fe, inevitable impurities and residues. 7. Förfarande enligt något av patentkraven 1 till 3, kännetecknat av, att man utför avkylningssteget med hjälp av luftkylning, t.ex. friluftskylning, vid tempurer som överstiger 500 ° C. Process according to one of Claims 1 to 3, characterized in that the cooling step is carried out using air cooling, such as free air cooling, at temperatures above 500 ° C. 8. Förfarande enligt patentkrav 7, kännetecknat av, att manganequivalen 2,0 - 3,9 definierad med hjälp av formel (1). Process according to Claim 7, characterized in that the manganese equivalent is from 2.0 to 3.9 as determined by formula (1). 9. Förfarande enligt patentkrav 7 eller 8, kangnetecknat av, att man i framställningssteget framställer et moderrör, som i mass innehåller 0.05-0.25% C, 2.0% eller mindre Si, 0.5-2.5% Mn, 2.0% eller mindre Cr, 0.01-0.1% Mo, 0.009% eller mindre B, och 0.22% eller mindre Ti + Nb + V samt Fe, oundvikl föroreningar och resthalter. Method according to Claim 7 or 8, characterized in that the step of providing comprises providing a parent tube containing 0.05-0.25% C, 2.0% or less Si, 0.5-2.5% Mn, 2.0% by weight. or less Cr, 0.01-0.1% Mo, 0.009% or less B, and 0.22% or less Ti + Nb + V and Fe, inevitable impurities and residues. 10. Et stålrör, som innehåller Fe, oundvikliga föroreningar och resthalter, kännetecknat av, att det ytterligare innehåller i mass above 0.05 - 0.25% C, 2.0% eller mindre Si, 0.25 - 2.5% Mn, 2.5% eller mindre Al 2.0% eller mindre Cr, 1.0% eller mindre Mo, 0.3% eller mindre Ti + Nb + V, och vars manganese equivalents 1.3 - 3.9 definierad med hjälp av feljande formel (1 ) 10. A steel tube containing Fe, unavoidable impurities and residual contents, further characterized by the following pulp contents of 0.05 to 0.25% C, 2.0% or less of Si, 0.25 to 2.5% Mn, 2, 5% or less Al 2.0% or less Cr, 1.0% or less Mo, 0.3% or less Ti + Nb + V, and having a manganese equivalent of 1.3 to 3.9 as determined by the following formula (1) 11. Stålrör enligt patentkrav 10, kännetecknat av, att - en del av stålröret har en microstructur som innehåller ove 30% ferrit, ove 5% martensit och / eller bainit, och under 20% restorationit, och - dess sträckgräns (Rpo, 2 / Rm) Business mindre vote 0.65. Steel tube according to Claim 10, characterized in that a portion of the steel tube has a microstructure containing more than 30% ferrite, more than 5% martensite and / or bainite, and less than 20% residual austenite, and has a yield ratio (Rpo ^ / Rm) of less than 0. 65. 12. Stålrör enligt patentkrav 10 eller 11, tiltneck av, att dess flytgräns vid 0.2% (Rpo.i) överstiger 300 MPa. Steel tube according to Claim 10 or 11, characterized in that the yield strength (Rpo, 2) of 0.2% is greater than 300 MPa. 13. Stålrör enligt patent krav 12, tilt gearnat av, att dess draghållfasthet (Rm) Överstiger 450 MPa, fördelaktigt 550-1200 MPa. Steel tube according to one of Claims 9 to 12, characterized in that it has a yield ratio (Rp0 / Rm) of less than 0.65, preferably less than 0.6, more preferably less than 0.55. Steel tube according to Claim 12, characterized in that it has a tensile strength (R m) greater than 450 MPa, preferably 550 to 1200 MPa. 14. Stålrör enligt något av patentkraven 9 till 12, kännetecknat av, att dess sträckgräns (Rpo, 2 / Rm) up to 0,65, fördelaktigt allre 0,6, mer fördelaktigt allre 0,55. 15. Stålrör enligt patentkrav 10, tilt technat av, att det i mass innehåller 0.05-0.14% C, 0.4% eller mindre Si, 0.5-1.5% Mn, 0.7% eller mindre Cr , 0.01-0.5% Mo, 0.009% eller mindre B, and 0.22% eller mindre Ti + Nb + Y. Steel tube according to Claim 10, characterized in that it contains, by weight, 0.05 to 0.14% C, 0.4% or less Si, 0.5 to 1.5% Mn, 0.7% or less Cr, 0.01-0.5% Mo, 0.009% or less B, and 0.22% or less Ti + Nb + V. 16. Stålrör enligt patentkrav 15, kännetecknat av, att dess manganese equivalent of 1,3 - 2,0 definierad med hjälp av formel (1). Steel tube according to Claim 15, characterized in that it has a manganese equivalent of from 1.3 to 2.0 as defined by formula (1). 17. Stålrör enligt patent krav 15 eller 16, inclination angle, att dess flytgräns vid 0.2% (Rpo, 2) and 300 - 500 MPa. Steel tube according to Claim 15 or 16, characterized in that it has a 0.2% yield strength (Rpo, 2) of 300 to 500 MPa. 18. Stålrör enligt något av patentkraven 15 till 17, kännetecknat av, att dess sträckgräns (Rpo, 2 / Rm) up to 0,60, fördelaktigt mindre up to 0,55. Steel tube according to one of Claims 15 to 17, characterized in that it has a yield ratio (Rpo, 2 / Rm) of less than 0.60, more preferably less than 0.55. 19. Stålrör enligt något av patentkraven 15 till 18, kännetecknat av, att dess brottöjning (As) margin 15%, fördelaktigt margin 20%. Steel tube according to one of Claims 15 to 18, characterized in that it has a elongation at break (A5) of more than 15%, preferably more than 20%. 20. Stålrör enligt patentkrav 10, rotation technique, att de mass innehåller 0.05-0.25% C, 2.0% eller mindre Si, 0.5-2.5% Mn, 2.0% eller mindre Cr, 0.01 -0.1% Mo, 0.009% eller for all B, and 0.22% eller for all Ti + Nb + V. Steel tube according to Claim 10, characterized in that it contains 0.05 to 0.25% C, 2.0% or less Si, 0.5-2.5% Mn, 2.0% or less Cr, 0.01- 0.1% Mo, 0.009% or less B, and 0.22% or less Ti + Nb + V. 21. Stålrör enligt patentkrav 20, kännetecknat av, att dess manganese equivalent of 2,0 to 3,9 definierad med hjälp av formel (1). Steel tube according to claim 20, characterized in that it has a manganese equivalent of from 2.0 to 3.9, as determined by formula (1). 22. Stålrör enligt patent krav 20 eller 21, turning angle, att dess flytgräns vid 0.2% (Rpo, 2) and 400 - 700 MPa. Steel tube according to Claim 20 or 21, characterized in that it has a yield strength (Rpo, 2) of 0.2% to 400 to 700 MPa. 23. Stålrör enligt något av patentkraven 19 till 21, kännetecknat av, att dess sträckgräns (Rpo, 2 / Rm) up to 0,60, fördelaktigt mindre up to 0,55. Steel tube according to one of claims 19 to 21, characterized in that it has a yield ratio (Rpo, 2 / Rm) of less than 0.60, more preferably less than 0.55. 24. Stålrör enligt något av patentkraven 20 till 23, kännetecknat av, att dess brottöjning (As) margin 8%, fördelaktigt margin 10%. Steel tube according to one of Claims 20 to 23, characterized in that it has an elongation at break (A5) of more than 8%, preferably more than 10%. 25. Stålrör enligt något av patentkraven 10 till 23, kännetecknat av, att en del av stålröret haren microstruktur, som innehåller över 80% ferrit och över 10% martensit och / eller bainit, och möjligen restorationit. Steel tube according to one of Claims 10 to 23, characterized in that part of the steel tube has a microstructure containing more than 80% ferrite and more than 10% martensite and / or bainite, and possibly residual austenite. Steel tube according to one of Claims 10 to 25, characterized in that it has a bending strength (n-value) of greater than 0.08, preferably greater than 0.10. Ett förfarande för att tillverka et stålrör, kännetecknat av, att förfarandet omfattar ett framställningssteg för att framställa et moderrör, Finnish I mass innehåller: 0,05 - 0,25% C, 2,0% eller mindre Si, 0,25 - 2,5 % Mn, 2.5% eller mindre Al, 2.0% eller mindre Cr, 1.0% eller mindre Mo, 0.3% eller mindre Ti + Nb + Y, samt Fe, oundvikliga föroreningar och resthalter, och varnish manganese equivalent of 1,3 - 3.9, definierad enligt feljande formel (1) et upphettningssteg för att upphetta moderröret till en tempur inom området (ÄC3 - 50) ° C - 1280 ° C, that varreduktionsbearbetningssteg, som man utför efter upphettningssteget och i wolf man utför reduction mod för att utat. , varvid man avslutar variations in temperature control, temperature control, temperature control, variations in temperature, temperature control, temperature control (An -50) ° C, temperature control at 300 ° C, the color of the manifold is then set at 5 ° C / s and the temperature is between 500 and 300 ° C. 26. Stålrör enligt något av patentkraven 10 till 25, kännetecknat av, att dess deformationshärdningsexponent (n-warp) överstiger 0.08, fördelaktigt överstiger 0.10.