WO2007065380A2

WO2007065380A2 - Method of production of high-strength low-alloyed steel pipes

Info

Publication number: WO2007065380A2
Application number: PCT/CZ2006/000086
Authority: WO
Inventors: Zbysek Novy; Libor Kraus; Jozef Zrnik; Stanislav Nemecek
Original assignee: Comtes Fht S.R.O.
Priority date: 2005-12-06
Filing date: 2006-12-06
Publication date: 2007-06-14
Also published as: EP1984527B1; CZ299495B6; EP1984527A2; CZ2005756A3; WO2007065380A3

Abstract

A method of production of high-strength low-alloyed steel pipes including a thermomechanical treatment and/or an intercritical heat treatment, where the pipes are produced first by hot rolling or hot extrusion, upon which follows a cooling process and, finally, drawing and/or forming with internal pressure and/or bending of pipes. The thermomechanical treatment process includes hot rolling or hot extrusion with finish forming temperature between 600 and l,000°C and subsequent controlled cooling with delay of maximum 50 sec in the temperature range of 700 to 4500C and the delay of at least 120 sec in the temperature range of 450 to 350°C. The hot rolling or hot extrusion process is followed by the following sequence: a cooling process, intercritical heat treatment with the maximum temperature between 770 and 850°C; upon soaking at this temperature, there is controlled cooling with the delay of max. 50 sec in the temperature range of 700 to 450°C and a delay of at least 120 sec in the temperature range of 450 to 350°C.

Description

Method of production of high-strength low-alloyed steel pipes

Field of the Invention

The invention concerns a method of production of high-strength low-alloyed steel pipes by drawing, extrusion, rolling or by combination of these steps from steels with controlled multi-phase microstructures.

Prior Art

According to similar solutions, which have been known up to this day, the object of the invention as described in the document no. US 2003116238 concerns high strength steel tubes with excellent material formability produced for hydroforming and similar forming processes. Chemical composition of the tube material is listed in weight per cent: 0.0005 - 0.30 % C, 0.001 - 2.0 % Si, 0.01 - 3.0 % Mn and appropriate amounts of alloying elements if needed. The balance consists of iron and unavoidable amount of additional elements.

However, the solution as described in this document does not specify the technological process which would ensure formation of required microstructure in the material and the required propertis.

According to the document no. US 2003051782, the steel tube composition is as follows: 0.05 - 0.3 % C, 1.8 - 4 % Mn. The material with silicon and aluminium is rolled to reduce its diameter, where the overall diameter reduction is no less than 20% and the finish rolling temperature in diameter-reduction rolling is no higher than 800°C. The microstructure obtained in this fashion consisting of martensite and/or bainite or even ferrite was achieved as a product of deformed austenite transformation.

The solution consists in a material for tubes with tensile strength above 1,000 MPa and excellent three-point bending properties. The chemical composition of the steel tubes as described in this document may additionally contain at least one of the following group of elements: Cu, Ni, Cr and Mo or at least one of the following group of elements: Nb, V, Ti and B or at least one element of the group of rare earth metals and Ca.

However, the solution as described in this document does not specify the technological process, which would guarantee the formation of required microstructure and the required propertis.

Summary of the Invention

A method of production of high-strength low-alloyed steel pipes from a material containing impurities in the amounts of 0.03 wt. % S max., 0.03 wt. % Pmax., 0.08 wt. % Cu max., 0.08 wt. % Al max. and also containing 0.10 to 0.45 wt. % C, 1.2 to 2.5 wt. % Mn, 1.2 to 2.5 wt. % Si with the balance of Fe and minute amounts of trace elements and, preferably, containing microalloying elements Nb, V, Ti. The pipes are produced by drawing, extrusion, rolling or combination of these processes from steels with multi-phase microstructure.

The essence of the solution consists in the fact that the pipes are produced by a

thermomechanical treatment and/or intercritical heat treatment,

where the hot rolling process or hot extrusion process for manufacturing of pipes is performed first and then the cooling and final drawing and/or forming by internal pressure and/or bending of pipes is performed. An alternative solution involves thermomechanical treatment, consisting in hot rolling or hot extrusion, where the finishing temperature is between 600 and I₅OOO⁰C.

Controlled cooling is the next process where the delay in the temperature range of 700 to 45O⁰C is no more than 50 seconds and the delay in the range of 450 to 350⁰C is at least 120 sec.

Another alternative solution consists in the following sequence: hot rolling or hot extrusion, cooling, intercritical heat treatment with the maxium temperature between 770 and 850°C. Upon soaking at this temperature, controlled cooling is applied with delay in the temperature range of 700 to 450°C of no more than 50 sec and the delay in the temperature range of 450 to 35O⁰C is at least 120 sec.

Another alternative solution consists in the following sequence: hot rolling or hot extrusion, cooling, drawing and intercritical heat treatment with the maximum temperature in the range of 770 to 850⁰C.

Upon soaking at this temperature, controlled cooling is applied with delay in the temperature range of 700 to 450⁰C of no more than 50 sec and the delay in the temperature range of 450 to 350⁰C is at least 120 sec.

The advantage of this solution lies in the possibility to obtain high-strength tubes with high plasticity required for cold forming, e.g. drawing and/or bending and/or hydroforming

(forming with internal pressure). With this solution it is possible to achieve the required multiphase microstructure with excellent properties either by means of thermomechanical treatment or intercritical heat treatment. , _;

The available choice between the above alternatives represents another advantage. It is because in some plants it is not possible to perform thermomechanical treatment. Moreover, in some applications drawing has to be carried out before the processing for the required microstructure. hi the latter case, the microstructure development can be achieved with the intercritical heat treatment.

Examples of the Ivention Embodiment

Example 1

A steel containing 0.03 wt. % S max., 0.03 % P max., 0.08 % Cu max., 0.08 % Al max., 0.10 to 0.45 wt. % C, 1.2 to 2,5 wt. % Mn, 1.2 to 2,5 wt. % Si, with the balance of Fe and minute contents of trace elements and microalloying elements: Nb, V, Ti, has been used for making high-strength low-alloyed steel pipes with wall thickness of 2 mm. .

The pipes were made from steels with multiphase microstrucrures by means of rolling, controlled cooling and subsequent drawing.

hi this example, thermomechanical treatment has been used for production of pipes. This process involved hot rolling with finishing temperature between 800 and 900⁰C.

Next process was controlled cooling with 25 sec delay in the temperature range of 700 to

45O⁰C and 300 sec delay in the 450 - 350⁰C temperature range.

The processing is concluded with a single-pass drawing, i.e. without interstage annealing.

This fact (preferable advantage) is a result of high plasticity of material that has been achieved owing to the multi-phase structure of the steel. The controlled multi-phase structure of the material has been achieved during the thermomechanical treatment. Example 2

A steel containing 0.03 wt. % S max., 0.03 wt. % P max., 0.08 wt. % Cu max., 0.08 wt. % Al max., 0.10 to 0.45 wt. % C, 1.2 to 2,5 wt. % Mn, 1.2 to 2,5 wt. % Si, with the balance of Fe and minute contents of trace elements and microalloying elements: Nb, V, Ti, has been used for making high-strength low-alloyed steel pipes with wall thickness of 2 mm.

The pipes were made from steels with multiphase microstructures by means of rolling, drawing and intercritical heat treatment.

In this example, the procedure used for the tube production consisted in the procedure involving the sequence of hot rolling or hot extrusion, cooling, drawing and intercritical heat treatment with heating to 800°C.

Upon soaking at this temperature, controlled cooling is applied with delay in the temperature range of 700 to 450°C of 15 sec and the delay in the temperature range of 450 to 350°C is

400 sec.

A pipe produced in this fashion can be used for forming by internal pressure, which requires that the material shows high plasticity. The required amount of plasticity has been obtained by the intercritical heat treatment, which produced the multiphase microstructure.

Industrial Utility

The proposed solution is practically usable in production of transport vehicles, in particular cars, buses and rail vehicles.

Claims

1. A method of production of high-strength low-alloyed steel pipes from a material containing impurities in the amounts of 0.03 wt. % S max., 0.03 % P max., 0.08 % Cu max., 0.08 % Al max. and also containing 0.10 to 0.45 wt. % C, 1.2 to 2.5 wt. % Mn, 1.2 to 2.5 wt. % Si with the balance of Fe and minute amounts of trace elements and, preferably, containing microalloying elements Nb, V, Ti, where the pipes are produced by drawing, extrusion, rolling or combination of these processes from steels with multi-phase microstructure, characterized in that the manufacturing procedure includes thermomechanical treatment and/or intercritical heat treatment, where the pipes are produced first by hot rolling or hot extrusion, then the cooling process follows and the production is concluded with drawing and/or forming by internal pressure and/or bending.

2. A method of production of high-strength low-alloyed pipes of claim 1,

chracterized in that the thermomechanical treatment process includes hot rolling or hot extrusion with finish forming temperature between 600 and 1 ,000°C and subsequent controlled cooling with delay of maximum 50 sec in the temperature range of 700 to 450°C and the delay of at least 120 sec in the temperature range of 450 to 350°C.

3. A method of production of high-strength low-alloyed steel pipes of claim 1,

characterized in that the hot rolling or hot extrusion process is followed by the following sequence: a cooling process, intercritical heat treatment at the maximum temperature between 770 and 850⁰C, upon soaking at this temperature, there is a following controlled cooling with the delay of 50 sec in the temperature range of 700 to 450°C and a delay of at least 120 sec in the temperature range of 450 to 350°C.

4. A method of production of high-strength low-alloyed steel pipes of claim 1,

characterized in that the hot rolling or hot extrusion process is followed by the following sequence: a cooling process, drawing, intercritical heat treatment where the maximum temperature is between 770 and 850⁰C, upon soaking at this temperature, there is controlled cooling with the delay of max. 50 sec in the temperature range of 700 to 450⁰C and a delay of at least 120 sec in the temperature range of 450 to 350⁰C.