Steel alloy with high energy absorption capacity and tubular steel product

Abstract

The present invention relates to a steel alloy with high energy absorption capacity and good formability, comprising beside inevitable impurities due to smelting and iron the following components in weight percent: C 0.05-0.6% Sum of Cr+2*Ti+3*(Mo+V+Nb)+4*W=2-7%,
wherein the structure of the steel alloy comprises beside martensite portions of 10-40 Vol.-% retained austenite, wherein the energy absorption capacity expressed by the product of tensile strength (Rm) and uniform strain (Ag) is higher than 12,000 MPa % and the steel alloy has a minimal tensile strength of 1000 MPa. In addition, the invention relates to a steel tube product with high energy absorption capacity and good formability, which is characterized in that it at least partially consists of such a steel alloy.

Claims

1. Steel tube product with high energy absorption capacity, characterized in that it at least partially comprises a steel alloy with high energy absorption capacity, comprising, besides inevitable impurities and iron, the following components in weight percent: C 0.05-0.6% Sum of Cr+2*Ti+3*(Mo+V+Nb)+4*W=2−7%, wherein the structure of the steel alloy comprises besides martensite 10-40 Vol.-% retained austenite, wherein the energy absorption capacity expressed by the product of tensile strength (Rm) and uniform strain (Ag) is higher than 12,000 MPa % and the steel alloy has a minimal tensile strength of 1,000 MPa; wherein the chromium content is in the range from 2-7%; and wherein the steel tube product is heat treated by a quenching and partitioning heat treatment.

2. Steel tube product according to claim 1, characterized in that the steel tube product forms at least a part of a perforation gun, wherein the steel tube product has a plurality of locally limited sections of reduced wall thickness.

3. Steel tube product according to claim 1, characterized in that the steel tube product forms at least a part of a drill tube.

4. Steel tube product according to claim 1, characterized in that the steel tube product is a steel tube product for a motor vehicle.

5. Steel tube product according to claim 1, characterized in that the steel tube product forms at least a part of an airbag gas pressure vessel with at least two longitudinal sections of different outer circumference, wherein the outer circumference of a longitudinal section is smaller by at least 5 percent than the outer circumference of at least one of the other longitudinal sections.

6. Steel tube product according to claim 1, characterized in that the steel tube product contains 10-40 Vol.-% retained austenite of film-shaped or polyhedron-shaped retained austenite.

7. Steel tube product according to claim 1, characterized in that the structure has 15-35 Vol.-% retained austenite.

8. Steel tube product according to claim 1, characterized in that the steel tube product has a metallic coating which protects against corrosion at least at its outer surface.

9. Steel tube product according to claim 1, characterized in that the steel tube product is at least a part of a structural component of a motor vehicle.

10. Steel tube product according to claim 6, characterized in that the 10-40 Vol.-% retained austenite consists of polyhedron-shaped retained austenite.

11. Steel tube product according to claim 7, characterized in that the structure contains 20 to 35 Vol.-% retained austenite.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the enclosed figures, embodiments of steel tube products according to the present invention are schematically shown. Herein shows:

(2) FIG. 1: a schematic depiction of a steel tube product in the embodiment as airbag gas pressure vessel;

(3) FIG. 2: a schematic depiction of a steel tube product in the embodiment as hollow carrier of a perforation gun;

(4) FIG. 3: a schematic depiction of a steel tube product in an embodiment as stabilizer; and

(5) FIG. 4: a schematic depiction of a steel tube product in an embodiment as drill tube.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(6) In FIG. 1 an embodiment of the steel tube product 1 according to the invention as gas pressure vessel, in particular airbag gas pressure vessel, is shown. The steel tube product 1 comprises a tube element 10. In the embodiment shown in FIG. 1 the tube ends 101 are tapered or pulled in. The taper of the tube ends 101 can be produced by cold forming. The tube ends 101 in the depicted embodiment each have a diameter D.sub.1 which is smaller than the diameter D.sub.0 of the tube element 10 in its central area 102. The diameter of the tube ends 101 can also be different. In the embodiment shown in FIG. 1 the steel tube product 1 has a combustion chamber 4, in which an igniter 12 as well as the further pyrotechnical components are provided. At the one tube end 101 the combustion chamber 14 is closed by a disc 17 which is welded thereto. To the combustion chamber 14 the cold gas storage 15 follows. This is separated from the combustion chamber 14 by the membrane 11, which can also be referred to as burst disc. The cold gas storage 15 is in the central area 102 of the tube element 10, which has the larger diameter D.sub.0. The cold gas storage 15 is followed by the Diffusor 13. In FIG. 1 a filling hole 16 is shown in the area of the diffusor 13. The tube end 101 of the diffusor 13 is welded with a disc 17, that means is closed thereby.

(7) In the cold gas storage 15, for example, a pressure of 580 bar may prevail. In the combustion chamber 14 the pressure may increase, for example, from 580 bar to 1,200 bar upon ignition of the igniter. The steel tube product 1 according to the invention can reliably withstand this pressure due to its properties without having to fear brittle fracture or expansion of a brittle crack.

(8) FIG. 2 shows a schematic view of a further embodiment of the steel tube product 1, which is a perforation gun. The perforation gun 1 comprises a tube element 10, which can also be referred to as hollow carrier. The tube element 10 is preferably a seamless tube element. In the tube element 10 locally limited areas 100 with a reduced wall thickness are provided. The locally limited areas 100 each have a circular area. The areas 100 are distributed over the length of the tube element 10. In the tube element 10 an ignition unit 18 with ignition charges is inserted. The explosive material of the ignition charge is ignited by the ignition unit 18 and thereby on the one hand the areas 100 of the tube element 10 are opened and on the other hand the surrounding material, for example rock, is perforated.

(9) In FIG. 3 a further embodiment the steel tube product 1 is shown. In this embodiment the steel tube product 1 is a stabilizer. The stabilizer 1 comprises in the depicted embodiment a tube element 10, the ends 101 of which each are attached to a connection component 2. As can be derived from FIG. 3, the tube ends 101 are connected to the connection components 2 via a connection point 19, for example by a welding seam.

(10) In FIG. 4 a further embodiment of the steel tube product 1 is shown. In this embodiment, the steel tube product 1 is a drill tube, in particular a drill pipe. The drill tube 1 comprises in the depicted embodiment a tube element 10, at the tube ends 101 of which threads are provided. As shown at the left tube end 101, this thread can be an external thread or as shown at the right tube end 101 be an internal thread, which is provided into the widened tube end 101. However, also other shapes of drill tubes can be used. For example, at one of the tube ends 101 drilling projections or knives can be provided. Via the thread several tube elements 10 can be attached to each other and thus a long drill tube 1 can be build.

(11) With the present invention a number of unexpected advantages can be achieved. On the one hand by alloying of carbide-forming elements according to the invention, which according to general understanding should further reduce the austenite content to be expected by the expected carbide formation, and a temperature control, which contrary to expectation specifically suppresses bainite formation and carbide formation, the austenite content is significantly increased. The increased usage of silicon, which leads to worse surfaces in the hot forming, can be omitted according to the invention.

(12) With the present invention thus a novel material group of the high strength Q&P steels is provided, which excellently can be used for tubes. In particular steel products, in particular tubes, can be manufactured, which have a high strength with simultaneous high ductility. In particular the steel products according to the invention have a higher energy absorption capacity compared to conventional heat treatment tubes. Due to the low yield strength ratio of the steel alloy a better formability is achieved. Due to the low content or the absence of silicon in the steel alloy a better surface quality of the steel product is achieved. In particular, with the steel alloy according to the invention also after hot working a coating of the surface, for example galvanizing, is possible.

(13) Finally due to the low proportion of alloying elements the costs for the steel alloy are low.

REFERENCE NUMBERS

(14) 1 steel tube product 10 tube element 101 tube end 102 central area 11 membrane 12 igniter 13 diffusor 14 combustion chamber 15 cold gas storage 16 filling hole 17 disc 100 area of reduced wall thickness 18 ignition unit 19 connection point 2 connection component