DE102022114337A1 - Method for producing a seamless precision steel tube, such precision steel tube and corresponding manufacturing system - Google Patents

Abstract

The invention relates to a method for producing a cold-finished seamless precision steel tube with desired dimensions, it is envisaged that this method comprises the following steps: (i) hot rolling a steel having the following composition in% by weight: C: to 0.25, in particular 0.06 to 0.22, Mn: 0.30 to 2.0, Si: up to 0.60, and optionally further Cr: up to 0.60, in particular up to 0.35, Ni: up to 0.80, Mo: up to 0.10, V: up to 0.15, Nb: up to 0.06, Ti: up to 0.06, Al: up to 0.060, Cu: up to 0.60, N: up to 0.02, S: up to 0, 02 and P: to 0.025, the balance being iron and unavoidable impurities to obtain a seamless steel pipe therefrom, (ii) subsequently optionally heat treating the seamless steel pipe, (iii) subsequently cooling the seamless steel pipe and then cold finishing the cooled seamless Steel pipe for producing the seamless precision steel pipe with the desired dimensions including a desired inner diameter DI, the cold finishing comprising cold drawing of the cooled seamless steel pipe in one or more cold drawings, wherein to reduce surface defects on an inner surface of the seamless steel pipe which determines the inner diameter DI during cold production, In addition to cold drawing, a fine machining of the inner surface takes place, in which a 100 µm to 2000 µm thick surface layer of the inner surface is removed chemically and / or by machining. The invention further relates to a corresponding cold-finished seamless precision steel pipe and a corresponding system for producing a cold-finished seamless precision steel pipe desired dimensions.

Description

The invention relates to a method for producing a cold-finished seamless precision steel tube with desired dimensions as well as a corresponding cold-finished seamless precision steel tube and a corresponding system for producing a cold-finished seamless precision steel tube with desired dimensions.

Corresponding cold-finished seamless precision steel tubes are also used as HPL tubes, among other things. They are primarily used as lines in hydraulically or pneumatically operated systems (HPL pipe: hydraulic and/or pneumatic line pipe). Assembly is usually carried out using detachable or permanent connections. During the operation of hydraulic systems, changes in the speed and pressure of the flowing medium occur under operating conditions. The changes in speed create pressure surges that are superimposed on the internal pressure. The pipeline is usually subject to swelling stress. When designing, the stress under operating conditions must be taken into account.

In addition to being used as hydraulic or pneumatic lines of various dimensions, cold-finished seamless precision steel tubes can also be used as a preliminary product in the production of hydraulic cylinders and as a transport line for fluid media such as liquids and gases.

The document EP 2 044 228 B1 describes the production of a seamless precision steel tube as a preliminary product for hydraulic cylinders with the following manufacturing steps: (i) hot rolling a steel with the following composition: 0.06 to 0.15% by weight carbon, 0.30 to 2.5% by weight Mn, 0 .10 to 0.60% by weight of Si and optionally one or more of the following elements: Cr, Ni, Mo, V, Nb, N and Al, the balance iron and unavoidable impurities at a temperature above Ac3 to make a seamless steel pipe obtained, (ii) subsequently a heat treatment of the seamless steel pipe to obtain a multi-phase structure, (iii) subsequent quenching of the seamless steel pipe and subsequent cold finishing of the cooled seamless steel pipe by cold drawing to produce the seamless precision steel pipe with the desired dimensions, and (iv) a subsequent stress treatment to improve the isotropic impact strength and (v) straightening the seamless precision steel tube thus obtained. Furthermore, this document describes a corresponding seamless precision steel tube, which is characterized by improved isotropic toughness at low temperatures, as well as further processing into a hydraulic cylinder that can also be used at very low temperatures. In this context, the document also mentions the fatigue cycles of the cylinder during its life.

Particularly when used as an HPL pipe, it is desirable that the cold-finished seamless precision steel pipe can be used at a higher continuous pressure, i.e. can be subjected to a higher continuous pressure. This can be made possible by increasing the fatigue strength of this pipe. With regard to a large number of cold-finished seamless precision steel tubes, it is desirable if the spread of the fatigue strength values is significantly limited, as this enables a more precise prediction of the pressure load levels. In the application, a higher working pressure can then be achieved with the same pipe geometry.

Increasing the fatigue strength of such precision steel tubes results in additional potential for lightweight construction or higher performance of corresponding hydraulically driven machines.

It is the object of the invention to provide measures for providing a seamless precision steel tube that has high fatigue strength.

The problem is solved according to the invention with regard to the method for producing a cold-finished seamless precision steel pipe by the features of claim 1, with regard to the cold-finished seamless precision steel pipe by the features of claim 7 and with regard to the system for producing a cold-finished seamless precision steel pipe by the features of claim 11. Preferred embodiments of the invention are specified in the subclaims, which can each represent an aspect of the invention individually or in combination.

1. (i) Warmwalzen eines Stahls, der die folgende Zusammensetzung in Gewichts-% aufweist: C: bis 0,25, insbesondere 0,06 bis 0,22, Mn: 0,30 bis 2,0, Si: bis 0,60, und optional weiterhin Cr: bis 0,60, insbesondere bis 0,35, Ni: bis 0,80, Mo: bis 0,10, V: bis 0,15, Nb: bis 0,06, Ti: bis 0,06, Al: bis 0,060, Cu: bis 0,60, N: bis 0,02, S: bis 0,02 und P: bis 0,025, wobei der Rest Eisen und unvermeidliche Verunreinigungen sind, um daraus ein nahtloses Stahlrohr zu erhalten,
2. (ii) darauf folgend optionale Wärmebehandlung des nahtlosen Stahlrohrs,
3. (iii) darauf folgendes Abkühlen des nahtlosen Stahlrohrs und anschließendes Kaltfertigen des abgekühlten nahtlosen Stahlrohrs zur Erzeugung des nahtlosen Präzisionsstahlrohrs mit den gewünschten Dimensionen inklusive eines gewünschten Innendurchmessers D_I, wobei das Kaltfertigen ein Kaltziehen des abgekühlten nahtlosen Stahlrohrs in einem oder mehreren Kaltzügen umfasst, wobei zur Reduktion von Oberflächenfehlern an einer den Innendurchmesser D_I bestimmenden Innenoberfläche des nahtlosen Stahlrohrs bei der Kaltfertigung, zusätzlich zum Kaltziehen, eine Feinbearbeitung der Innenoberfläche erfolgt, bei der eine 100 µm bis 2000 µm dicke Oberflächenschicht der Innenoberfläche chemisch und/oder spanenden abgetragen wird.

In the method according to the invention for producing a cold-finished seamless precision steel tube with desired dimensions, it is provided that this method includes the following steps:

1. (i) hot rolling a steel which has the following composition in% by weight: C: up to 0.25, in particular 0.06 to 0.22, Mn: 0.30 to 2.0, Si: up to 0.60, and optionally further Cr: up to 0.60, in particular up to 0.35, Ni: up to 0.80, Mo: up to 0.10, V: up to 0.15, Nb: up to 0.06, Ti: up to 0.06 , Al: up to 0.060, Cu: up to 0.60, N: up to 0.02, S: up to 0.02 and P: up to 0.025, the balance being iron and unavoidable impurities in order to obtain a seamless steel pipe,
2. (ii) subsequent optional heat treatment of the seamless steel pipe,
3. (iii) subsequent cooling of the seamless steel pipe and subsequent cold-finishing of the cooled seamless steel pipe to produce the seamless precision steel pipe with the desired dimensions including a desired inner diameter D _I , wherein the cold-finishing comprises cold drawing of the cooled seamless steel pipe in one or more cold drawings, whereby for Reduction of surface defects on an inner surface of the seamless steel pipe that determines the inner diameter D _I during cold production, in addition to cold drawing, a fine machining of the inner surface is carried out, in which a 100 µm to 2000 µm thick surface layer of the inner surface is removed chemically and / or by machining.

It has been found that surface defects, such as cracks, on the inner surface of the seamless steel pipe, which - based on the corresponding surface normal - penetrate the steel significantly further than a critical depth, which can be roughly estimated at around 20 to 45 µm reach into it, has a negative effect on the fatigue strength of this pipe. The origin of at least some of these surface defects lies in the hot rolling process preceding cold production in the production of the cold-finished seamless precision steel tube. During cold production by pure cold drawing, a fatigue strength of the precision steel tube is usually achieved that corresponds to approximately 0.3 times the axial tensile strength of the steel.

If a 100 µm to 2000 µm thick surface layer of the inner surface is removed chemically and/or by machining through fine machining as part of cold production, the existing surface defects are eliminated or at least their depth expansion is decimated in such a way that the cold-finished seamless precision steel pipe shows a fatigue strength that is above 0.4 times the axial tensile strength of the steel.

According to a preferred embodiment of the invention, the precision machining is honing and/or peeling and/or burnishing. This results in average roughness values Ra of significantly less than one micrometer (< 1 µm).

It is advantageously provided that the fine machining is carried out by chemical removal by pickling. Staining is the treatment of changing the surface using a stain or a stain. For metal and especially steel surfaces, pickling is mainly done by etching using aggressive chemicals, usually acids or alkalis. In this case, the fine machining is carried out by chemical removal, i.e. etching, or more precisely, initial etching.

The fine machining of the inner surface can take place before the cold drawing or the first of the cold drawings and/or between two cold drawings and/or after the cold drawing or the last of the cold drawings.

The fine machining of the inner surface is preferably carried out before cold drawing or the last of the cold drawings. If there are several cold drawings, the fine machining is carried out before the first of the cold drawings or between two cold drawings. Alternatively, the fine machining of the inner surface then takes place in particular after the cold drawing or the last of the cold drawings.

• - ein Wanddicke zu Außendurchmesser-Verhältnis d/D_A des kaltgefertigten nahtlosen Präzisionsstahlrohrs von d/D_A ≤ 0,2, insbesondere d/D_A ≤ 0,02, und/oder
• - ein Rohrlänge zu Außendurchmesser-Verhältnis L/D_A von L/D_A > 5

eingestellt wird, wobei L die Rohrlänge, d die Wanddicke und D_A den Außendurchmesser des kaltgefertigten nahtlosen Präzisionsstahlrohrs beschreiben. Derartige Dimensionen schließen die typischen Rohre für Hydraulikzylinder und die Rohre für Kraftstoffleitungen von Kraftfahrzeugen regelmäßig aus.According to a further preferred embodiment of the invention it is provided that through cold finishing

• - a wall thickness to outside diameter ratio d/D _A of the cold-finished seamless precision steel pipe of d/D _A ≤ 0.2, in particular d/D _A ≤ 0.02, and/or
• - a pipe length to outside diameter ratio L/D _A of L/D _A > 5

is set, where L describes the pipe length, d the wall thickness and D _A describes the outer diameter of the cold-finished seamless precision steel pipe. Such dimensions regularly exclude the typical pipes for hydraulic cylinders and the pipes for fuel lines in motor vehicles.

It is advantageously provided that the cold-finished seamless precision steel tube has an inner surface machined by the fine machining in such a way that the precision steel tube shows a fatigue strength which corresponds to 0.46 to 0.49 times the axial tensile strength of the steel. Such a high fatigue strength comes quite close to the maximum expected fatigue strength. The maximum expected fatigue strength is around 0.5 times the axial tensile strength of the steel.

In the cold-finished seamless precision steel pipe according to the invention made of a steel which has the following composition in% by weight: C: up to 0.25, in particular 0.06 to 0.22, Mn: 0.30 to 2.0, Si: up to 0 .60, and optionally further Cr: up to 0.60, in particular up to 0.35, Ni: up to 0.80, Mo: up to 0.10, V: up to 0.15, Nb: up to 0.06, Ti: up 0.06, Al: to 0.060, Cu: up to 0.60, N: up to 0.02, S: up to 0.02 and P: up to 0.025, the balance being iron and unavoidable impurities, and the precision steel pipe having an inner diameter D _I determined by a If the inner surface is determined, it is envisaged that existing cracks or other structures of surface defects in this inner surface, based on a surface average level, extend into the steel to a maximum depth of 45 µm.

The surface average level is well known in connection with the description of the roughness of a surface and, for sufficiently smooth surfaces, coincides with the level of the surface surrounding the structures of the surface defects. For example, an average roughness value R _A is defined as the roughness parameter on the profile, which indicates the average distance of a measuring point - on the surface - to a center line. This center line intersects the actual surface profile within a corresponding reference distance in such a way that the sum of the profile deviations in a plane parallel to the center line is distributed over the length of the measuring distance. In other words, this center line is the surface average level with respect to the selected measuring section. The surface average level with respect to the surface results analogously from the roughness parameters on the surface. The roughness on the surface is standardized in ISO 25178.

As already mentioned, it has been found that surface defects, such as cracks, on the inner surface of the seamless steel pipe, which - based on the corresponding surface normal - are significantly deeper than a critical depth, which can be roughly estimated at around 20 to 45 µm , reaching into the steel, has a negative effect on the fatigue strength of this pipe. It is therefore preferred that existing cracks or other structures of surface defects in this inner surface, based on a surface average level, extend into the steel to a maximum depth of only 25 μm.

The cold-finished seamless precision steel pipe is in particular a cold-finished seamless precision steel pipe produced by the above-mentioned manufacturing method.

According to a preferred embodiment of the cold-finished seamless precision steel pipe according to the invention, the cold-finished seamless precision steel pipe has an inner surface with a corresponding surface quality that has been finely machined by chemical and/or machining.

• - ein Wanddicke zu Außendurchmesser-Verhältnis d/D_A des kaltgefertigten nahtlosen Präzisionsstahlrohrs von d/D_A ≤ 0,1, insbesondere von d/D_A ≤ 0,02, und/oder
• - ein Rohrlänge zu Außendurchmesser-Verhältnis L/D_A von L/D_A > 5 auf.

According to a further preferred embodiment of the invention, the cold-finished seamless precision steel pipe has a pipe length L, a wall thickness d, an outer diameter D _A , and

• - a wall thickness to outside diameter ratio d/D _A of the cold-finished seamless precision steel pipe of d/D _A ≤ 0.1, in particular of d/D _A ≤ 0.02, and/or
• - a pipe length to outside diameter ratio L/D _A of L/D _A > 5.

In particular, it is envisaged that the cold-finished seamless precision steel tube has an inner surface finely machined such that the precision steel tube exhibits a fatigue strength which corresponds to 0.46 to 0.49 times the axial tensile strength of the steel.

In the plant according to the invention for producing a cold-finished seamless precision steel pipe with desired dimensions, which comprises the following means: (a) Means for hot rolling a steel having the following composition in% by weight: C: up to 0.25, in particular 0.06 up to 0.22, Mn: 0.30 to 2.0, Si: up to 0.60, and optionally further Cr: up to 0.60, in particular up to 0.35, Ni: up to 0.80, Mo: up to 0, 10, V: up to 0.15, Nb: up to 0.06, Ti: up to 0.06, Al: up to 0.060, Cu: up to 0.60, N: up to 0.02, S: up to 0.02 and P : to 0.025, the balance being iron and unavoidable impurities to obtain a seamless steel pipe, (b) optionally heat treatment means for subsequent heat treatment of the seamless steel pipe, (c) cooling means for subsequent cooling of the seamless steel pipe and (d) Cold manufacturing means for subsequent cold finishing of the cooled seamless steel pipe to produce the seamless precision steel pipe with the desired dimensions including a desired inner diameter D _I , wherein the cold finishing includes cold drawing of the cooled seamless steel pipe in one or more cold drawings, it is provided that the cold manufacturing means to reduce surface defects on an inner surface of the seamless steel pipe that determines the inner diameter D _I during cold production, a fine machining agent for fine machining of the inner surface by chemical and / or machining, which is in particular designed to remove a 100 µm to 2000 µm thick surface layer. The fine processing means for fine processing of the inner surface by chemical removal is in particular a pickling device. The fine processing means for fine machining of the inner surface by metal removal is in particular a machine tool for honing and/or peeling and/or rolling the inner surface.

The system for producing a cold-finished seamless precision steel tube is in particular a system for carrying out the previously described method for producing a cold-finished seamless precision steel tube with desired dimensions. The preferred embodiments of the invention mentioned in connection with this method should also apply accordingly to the system in question.

• 1 eine schematische Darstellung eines Oberflächenprofils der Innenoberfläche eines nahtlosen Präzisionsstahlrohrs beim Kaltfertigungsschritt des erfindungsgemäßen Herstellungsverfahrens.

The invention is explained below by way of example with reference to the accompanying drawing, whereby the features shown below can represent an aspect of the invention both individually and in combination. It shows:

• 1 a schematic representation of a surface profile of the inner surface of a seamless precision steel tube in the cold manufacturing step of the manufacturing method according to the invention.

The 1 shows a sectional view of a pipe wall of a seamless precision steel pipe in the area of its inner surface during the cold manufacturing step in a schematic representation. In addition to a flat base level of the inner surface, which has not yet been finely machined, it has numerous structures of surface defects in the form of crack structures, i.e. the structures of cracks. In the example, these extend up to 140 µm into the steel material. However, the majority of cracks extend less than 80 µm into the material. Other possible surface defects, such as inclusions on the surface, are not shown.

In addition to the corresponding surface profile of the inner surface, a removal limit of material removal from the inner surface is also entered as part of a fine machining (as a dash-dot line), in which a 150 µm thick surface layer of the inner surface is removed chemically and/or by machining. This removal limit is determined by the finely machined inner surface of the cold-finished seamless precision steel tube. It is clearly visible that the surface defects have been completely removed by appropriate removal. The structure of the finely machined inner surface will therefore only be determined by the roughness, which is determined by the fine machining and possibly subsequent machining processes.

In addition to the surface profile and the removal limit, a surface average level of the inner surface before fine machining is shown as a dotted line.

The cold-finished seamless precision steel pipe considered here is an HPL pipe. The steel used in the example has the following composition in% by weight: C: up to 0.25, in particular 0.06 to 0.22, Mn: 0.30 to 2.0, Si: up to 0.60, and optionally further Cr: up to 0.60, especially up to 0.35, Ni: up to 0.80, Mo: up to 0.10, V: up to 0.15, Nb: up to 0.06, Ti: up to 0.06, Al: to 0.060, Cu: to 0.60, N: to 0.02, S: to 0.02 and P: to 0.025, the balance being iron and unavoidable impurities. The tensile strength Rm is in the range 340 to 690 MPa.

The fatigue strength of the cold-finished seamless precision steel tube achieved by the measures according to the invention is in the range from 153 MPa to 339 MPa.

QUOTES INCLUDED IN THE DESCRIPTION

This list of documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 2044228 B1 [0004]

Claims (11)

Process for producing a cold-finished seamless precision steel tube with desired dimensions, this process comprising the following steps: - hot rolling a steel having the following composition in% by weight: C: to 0.25, in particular 0.06 to 0.22, Mn: 0.30 to 2.0, Si: up to 0.60, and optionally further Cr: up to 0.60, in particular up to 0.35, Ni: up to 0.80, Mo: up to 0.10, V: up to 0.15, Nb: up to 0.06, Ti: up to 0.06, Al: up to 0.060, Cu: up to 0.60, N: up to 0.02, S: up to 0.02 and P: up to 0.025, where the rest is iron and unavoidable impurities in order to obtain a seamless steel pipe, - subsequently optional heat treatment of the seamless steel pipe, - subsequent cooling of the seamless steel pipe and subsequent cold finishing of the cooled seamless steel pipe to produce the seamless precision steel pipe with the desired dimensions including a desired inner diameter D _I , wherein the cold finishing comprises cold drawing of the cooled seamless steel pipe in one or more cold drawings, wherein in order to reduce surface defects on an inner surface of the seamless steel pipe which determines the inner diameter D _I , a fine machining of the inner surface is carried out during cold production, in addition to cold drawing in which a 100 µm to 2000 µm thick surface layer of the inner surface is removed chemically and/or by machining. Procedure according to Claim 1 , characterized in that the chip-removing fine machining is honing and/or peeling and/or burnishing. Procedure according to Claim 1 or 2 , characterized in that the fine machining of the inner surface takes place before the cold drawing or the last of the cold drawings. Procedure according to Claim 1 or 2 , characterized in that the fine machining of the inner surface takes place after the cold drawing or the last of the cold drawings. Procedure according to one of the Claims 1 until 4 , characterized in that through cold finishing - a wall thickness to outside diameter ratio d/D _A of the cold-finished seamless precision steel pipe of d/D _A ≤ 0.2, in particular d/D _A ≤ 0.02, and/or - a pipe length Outer diameter ratio L/D _A is set from L/D _A > 5, where L describes the pipe length, d describes the wall thickness and D _A describes the outer diameter of the cold-finished seamless precision steel pipe. Procedure according to one of the Claims 1 until 5 , characterized in that the cold-finished seamless precision steel pipe has an inner surface machined by the fine machining such that the precision steel pipe exhibits a fatigue strength corresponding to 0.46 to 0.49 times the tensile strength of the steel. Cold-finished seamless precision steel tube made of a steel which has the following composition in% by weight: C: up to 0.25, in particular 0.06 to 0.22, Mn: 0.30 to 2.0, Si: up to 0.60, and optionally further Cr: up to 0.60, in particular up to 0.35, Ni: up to 0.80, Mo: up to 0.10, V: up to 0.15, Nb: up to 0.06, Ti: up to 0.06 , Al: up to 0.060, Cu: up to 0.60, N: up to 0.02, S: up to 0.02 and P: up to 0.025, the balance being iron and unavoidable impurities and the precision steel pipe having an inner diameter D _I , which is determined by an inner surface in which existing cracks or other structures of surface defects in this inner surface extend into the steel to a maximum depth of 45 µm based on a surface average level. Cold-finished seamless precision steel pipe Claim 7 , characterized in that the cold-finished seamless precision steel tube has an inner surface with a corresponding surface quality that has been finely machined by chemical and/or machining. Cold-finished seamless precision steel pipe Claim 7 or 8th , characterized by a pipe length L, a wall thickness d, an outside diameter D _A , and - a wall thickness to outside diameter ratio d/D _A of the cold-finished seamless precision steel pipe of d/D _A ≤ 0.2, in particular of d/D _A ≤ 0 .02, and/or - a pipe length to outside diameter ratio L/D _A of L/D _A > 5. Cold-finished seamless precision steel pipe according to one of the Claims 7 until 9 , characterized in that the cold-finished seamless precision steel pipe has an inner surface machined by fine machining such that the precision steel pipe exhibits a fatigue strength corresponding to 0.46 to 0.49 times the axial tensile strength of the steel. Plant for producing a cold-finished seamless precision steel tube with desired dimensions, this plant comprising the following means: - Means for hot rolling a steel having the following composition in% by weight: C: up to 0.25, in particular 0.06 to 0, 22, Mn: 0.30 to 2.0, Si: up to 0.60, and optionally further Cr: up to 0.60, in particular up to 0.35, Ni: up to 0.80, Mo: up to 0.10, V : up to 0.15, Nb: up to 0.06, Ti: up to 0.06, Al: up to 0.060, Cu: up to 0.60, N: up to 0.02, S: up to 0.02 and P: up to 0.025 , the rest being iron and unavoidable impurities in order to obtain a seamless steel pipe, - optionally heat treatment means for subsequent heat treatment of the seamless steel pipe, - cooling means for subsequent cooling of the seamless steel pipe and cold finishing means for subsequent cold finishing of the cooled one seamless steel pipe for producing the seamless precision steel pipe with the desired dimensions including a desired inner diameter D _I , the cold finishing comprising cold drawing of the cooled seamless steel pipe in one or more cold drawings, the cold production means for reducing surface defects on an inner surface of the which determines the inner diameter D _I Seamless steel pipe in cold production, a fine machining agent for fine machining of the inner surface by chemical and / or machining, which is in particular designed to remove a 100 µm to 2000 µm thick surface layer.

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