EP1974065A1

EP1974065A1 - Galvanized rolling-hardened cold-rolled flat product and process for producing it

Info

Publication number: EP1974065A1
Application number: EP07703609A
Authority: EP
Inventors: Peter Dr. Biele; Ralph Dipl.-Ing. Goecke; Peter Dipl.-Ing. Klauke; Markus Dipl.-Ing. Lohe
Original assignee: ThyssenKrupp Steel AG
Current assignee: ThyssenKrupp Steel Europe AG
Priority date: 2006-01-11
Filing date: 2007-01-03
Publication date: 2008-10-01
Also published as: US20100159276A1; DE102006001628A1; CA2634527A1; WO2007082786A8; CN101454464A; KR20080085028A; WO2007082786A1

Abstract

A flat product according to the invention which has been produced from a low-alloy steel containing iron and unavoidable impurities together with (in % by weight) up to 0.45% of C, up to 2.20% of Si, up to 2.50% of Mn, up to 0.12% of P, up to 0.025% of S, up to 2.0% of Al, up to 0.15% of Ti, up to 0.09% of Nb, a total of up to 1.0% of Cr and Mo, up to 0.2% of V and up to 0.005% of B and has been cold-rolled to a thickness of 0.1-4 mm and is in the rolling-hardened state has a tensile strength of 700-1000 MPa and is coated with a zinc layer which has been applied by electrolytic galvanization and has a layer thickness of up to 12 µm. The cold-rolled flat product of this type provides a steel sheet or strip which has not only a particularly high strength but also a high corrosion resistance. In addition, the invention provides a process for producing such a flat product.

Description

GALVANIZED ROLLED COLD-ROLLED FLAT PRODUCT AND METHOD FOR THE PRODUCTION THEREOF

The invention relates to a cold-rolled flat product produced from a low-alloy steel, provided with a galvanizing, such as cold strip or cold-rolled sheet, of high strength and a method for its production.

In the steel processing industry there is a demand for cost-effective steel sheets which are suitable for applications which are of high strength and which are of low importance, while the extensibility and deformability of the respectively processed sheet is of minor importance. An example of such an application are profiles from which doors and gates are made. In particular, steel sheets of the type in question are required for the production of lamellar profiles from which rolling doors, shutters or similar components are assembled.

Another example of the use of steel sheets of the type in question is the transmission or coupling construction, in which cost-effective steel sheets of low weight and high strength required in terms of maximum weight savings, especially for the production of simple-shaped, but highly stressed in use parts become. A method which enables the production of such steel sheets is described in JP 200589853 A. According to this known method, from a low alloy steel containing (in mass%) 0.15-0.25% C, up to 0.25% Si, 0.3-0.9% Mn, up to 0.025% P, 0.005% S, up to 0.08% Al, 0.008% N, up to 0.07% Ti, up to 0.006% B and the balance iron and unavoidable impurities, first produces a hot strip whose microstructure contains certain perlite and Zementitanteile and ferrite grains of a certain size. This hot strip is then rolled without annealing at cold work rates of at least 50% to cold strip. By further processing the strip thus obtained without recrystallizing annealing downstream of the cold rolling, at the time of its processing into the respective component, it has the high strength which has occurred in the course of cold rolling by work hardening of the steel. This condition of "roll hard", non-recrystallizing annealed cold rolled sheet material is also referred to in the jargon as "full hard".

In order to impart the required corrosion resistance to the rigid-hard metal sheets used in the field of building construction, such sheets are today usually provided with a hot-dip galvanizing system. This has the advantage that a high thickness of the zinc coating can be reliably produced even on the relatively uneven, highly-bonded cold-rolled substrate. In addition, high throughput can be achieved in today's hot-dip galvanizing plants. However, this economic advantage is offset by the disadvantage that the delivered in the full-hard state sheets in the course of hot dip galvanizing prior to their entry into the zinc bath at least at its temperature must be heated, which is typically in the range of 475 ⁰ C.

Although this temperature is significantly lower than the recrystallization temperature of the respective steel, this heating acts like a tempering. The heating to the zinc bath temperature therefore results in a decrease in the strength of the cold strip delivered in the full-hard state via the hot-dip galvanizing. Full hard cold strips, which are provided with a hot-dip galvanizing, accordingly have typical strengths, which are in the range of 500 - 700 MPa.

Although an attempt has been described in JP 10176253 A to minimize the decrease in strength occurring in the course of hot-dip galvanizing by the fact that the section of the steel strip entering the zinc bath only reaches the required level prior to its entry into the bath by a closely concentrated inductive heating Temperature is brought. However, the required apparatus and control engineering effort is so considerable that the known method proves to be uneconomical in practice.

Based on the above-described prior art, the invention was based on the object to provide a cold-rolled, flat-rolled steel flat product which is in a roll-resistant, full-hard state and has, in addition to a particularly high strength, a high corrosion resistance. In addition, a method for producing such a flat product should be specified.

With respect to the product, this object has been achieved according to the invention by a cold-rolled flat product, the a low-alloyed steel which, in addition to iron and unavoidable impurities (in% by weight) up to 0.45% C, up to 2.20% Si, up to 2.50% Mn, up to 0.12% P, up to 0.025% S, up to 2.0% Al, up to 0.15% Ti, up to 0.09% Nb, in total up to 1.0% Cr and Mo, up to 0.2% V and up to 0.005% B, which has a thickness of 0.1 - 4 mm which is in the hard-rolled state and has a tensile strength of 700-1000 MPa and which is coated with a zinc layer, which is applied by electrolytic galvanizing and has a layer thickness of up to 12 microns.

In a corresponding manner, the above-mentioned object with respect to the method has been achieved by the fact that, according to the invention, a hard-cold galvanized cold-rolled flat product with a strength of 700-1000 MPa is thereby produced,

-that of a steel, in addition to iron and unavoidable impurities (in wt .-%) up to 0.45% C, up to 2.20% Si, up to 2.50% Mn, up to 0.12% P, up to 0.025% S, up to 2.0% Al, up to 0.15% Ti, to 0.09% Nb, in total up to 1.0% Cr and Mo, up to 0.2% V and up to 0.005% B, a hot strip is produced,

-that a cold-rolled flat product having a thickness of 0.1 - 4 mm is cold-rolled from the hot strip with a degree of deformation of more than 30%,

and

in that the cold-rolled flat product is subjected to electrolytic galvanizing in the hard-rolled state which is applied to the cold-rolled flat product up to 12 microns thick zinc layer.

According to the invention, a non-annealed cold-rolled flat product made of a steel of a given composition, such as cold strip or cold-rolled sheet, in the hard-rolled state, having a tensile strength of at least 700 MPa at an elongation of less than 1%.

(Tensile strength ~ yield strength), coated in an electrolytic galvanizing plant with a zinc coating. Surprisingly, it has been found that the zinc coating produced in the course of the electrolytic deposition on the full-hard cold strip despite its unevenness is continuous and thickness, uniformity and density reaches a sufficient for the respective purpose corrosion resistance of the invention produced and produced cold strip or sheet safely ensured. At the same time, it has been found that in the course of electrolytic galvanizing, the cold-rolled flat product according to the invention at least maintains the strength achieved after cold rolling, and even increases in strength, so that for bandings and sheets produced and produced according to the invention, strengths of more than 700 MPa typically more than 800 MPa, could be ensured on a regular basis. Surprisingly, it has also been found in this context that the high strength of the flat material according to the invention, which may even be increased by the electrolytic galvanizing, does not impede its further deformation, which is possible within the scope of its minimized extensibility. For example, simply shaped profile elements, such as slats for roller shutters or roller shutters, can be produced from products according to the invention by means of edging, bending or roll profiling. produce, which not only due to their small material thickness have a low weight and ensure good thermal insulation, but also have a particularly high rigidity and a correspondingly high Beulfestigkeit due to their particularly high strength. This combination of properties makes products according to the invention particularly suitable for applications in which the respective component is exposed to large-area loads, for example due to wind or comparable loads.

Depending on the particular applications, cold-rolled steel or sheet metal according to the invention can be made available with a thickness which is 0.1-3 mm, and for typical applications its thickness can be in the range of 0.1-1.0 mm, in particular up to 0.8 mm.

The corrosion-protective effect of the zinc layer present on cold-rolled flat products according to the invention can thereby be reliably ensured that the zinc layer is at least 2 μm thick. Typical layer thicknesses are 2.5 μm, 7.5 μm or 10 μm. A preferred layer thickness range is accordingly in the range of 2 to 10 .mu.m, in particular 4 to 8 .mu.m.

In addition to the electrolytically deposited zinc layer according to the invention, cold-rolled full-hard steel materials according to the invention can carry on the zinc layer at least one further coating, such as a coating, a powder coating or comparable layers.

A particularly high work hardening and, consequently, particularly high strength values can be achieved by correspondingly high, achieved in the course of multi-stage cold rolling if necessary obtained degrees of deformation can be achieved. In this regard, it may be desirable for the degree of cold working achieved during cold rolling to be at least 50%.

To demonstrate the effect of the invention is first in a conventional casting-rolling plant from a (in wt .-%) 0.034% C, 0.023% Si, 0.24% Mn, 0.009% P, 0.006% S, 0.037% Al, 0.031 Cr , 0.0029 Mo, 0.0004% Ti, 0.001% V, 0.001 Nb and the remainder of iron and other unavoidable impurities containing low alloy steel cast a thin slab and hot rolled from a hot strip. From this hot strip then a 0.35 mm thick cold strip was produced at a degree of cold deformation of 82%, the tensile strength in the non-annealed, hard-rolling state was 841 MPa.

The full-hard material produced in this way was then coated on both sides with a zinc layer in a conventional electrolytic strip coating plant, the thickness of which was 7.5 μm. The tensile strength of the full-hard material after electrolytic galvanizing was still 841 MPa.

The thus obtained electrolytically galvanized, hard-cold rolled strip was then provided with a color coat. By roll profiling it could be easily deformed into slats for roller shutters, which are characterized by a high dent resistance in addition to a low weight and good thermal insulation property.

Claims

PATENT APPLICATIONS

1. cold rolled flat product,

- which is made of a low-alloyed steel containing, in addition to iron and unavoidable impurities (in% by weight) up to 0.45% C, up to 2.20% Si, up to 2.50% Mn, up to 0.12% P, up to 0.025 % S, up to 2.0% Al, up to 0.15% Ti, up to 0.09% Nb, in total up to 1.0% Cr and Mo, up to 0.2% V and up to 0.005% B,

- which has a thickness of 0.1 - 4 mm,

- Is in the hard rolling condition and it has a tensile strength of 700 - 1000 MPa and

- Which is covered with a zinc layer, which is applied by electrolytic galvanizing and has a layer thickness of up to 12 microns.

2. Cold-rolled flat product according to claim 1, characterized in that it is 0.1 - 3 mm thick.

3. cold rolled flat product according to claim 2, characterized in that it is 0.1 - 1.0 mm thick.

4. Cold rolled flat product according to one of the preceding claims, characterized in that the zinc layer is at least 2 .mu.m thick.

5. Cold-rolled flat product according to claim 4, characterized in that the zinc layer is 2-10 μm, in particular 4-8 μm, thick.

6. Cold rolled flat product according to one of the preceding claims, characterized in that it carries at least one further layer on the zinc layer.

7. A method for producing a hard-rolled galvanized cold-rolled flat product having a strength of 700 - 1000 MPa,

- of a steel containing not only iron and unavoidable impurities (in% by weight) up to 0.45% C, but also 2.20% Si, up to 2.50% Mn, up to 0.12% P, up to 0.025% S, up to 2.0% Al, up to 0.15% Ti, up to 0.09% Nb, in total up to 1.0% Cr and Mo, up to 0.2% V and up to 0.005% B, producing a hot strip,

- In which is cold-rolled from the hot strip with a degree of deformation of more than 30% cold-rolled flat product having a thickness of 0.1 - 4 mm, and

- In which subjected to the cold rolled flat product in the hard rolling state of an electrolytic galvanizing in which the cold-rolled flat product is applied with a zinc layer up to 12 μm thick.

8. Method according to one of the preceding claims, characterized in that the cold-rolled flat product is cold-rolled to a thickness of 0.1-1 mm.

9. Method according to one of claims 7 or 8, characterized in that the thickness of the zinc layer is at least 2 .mu.m.

10. A process according to any of claims 7 to 9, wherein the thickness of the zinc layer is 4-8 microns.

11. A process according to any one of claims 7 to 10, wherein a further layer is applied to the zinc layer.

12. The method according to any one of the preceding claims, d a d u c h e c e n e c e e s, which reached during the cold rolling

Cold deformation is at least 50%.