METHOD FOR PRODUCING STEEL SHEETS, STEEL SHEET AND USE THEREOF

Abstract

A method for producing steel sheets, in particular for body shell sheets of vehicles, in which a steel alloy of a desired composition is melted, poured, and then rolled into sheet form, the steel alloy being an interstitial free steel (IF steel) and after the rolling, the steel sheet being annealed and dressed and then provided with a metallic anti-corrosion coating by means of an electrolytic process or by means of vapor deposition, wherein in order to achieve a low Wsa value with the narrowest possible spread, a niobium content of >0.01% by weight, preferably >0.011% by weight, is added to the alloy of the steel.

Claims

1. A method for producing steel sheets, in particular for body shell sheets of vehicles, comprising. melting an interstitial free steel (IF steel) alloy of a desired composition adding a niobium content of >0.01% by weight to the steel alloy in order to achieve a low Wsa value with a narrowest possible spread; pouring the steel alloy, and rolling the steel alloy into sheet form; and annealing and dressing the steel sheet after the rolling.

2. The method according to claim 1, wherein the IF steel has the following analysis in % by weight: TABLE-US-00001 C 0.001-0.015 Si 0.01-0.5 Mn 0.02 to 0.5 P max. 0.1 S max. 0.05 Al 0.01 to 1.0 Nb 0.011 to 0.15 Ti 0.01 to 0.4 optionally containing one or more of the following elements: up to max. 100 ppm boron and/or up to 0.4% by weight vanadium and/or up to 0.4% by w eight zirconium; a remainder composed of iron and smelting-dictated impurities.

3. The method according to claim 1, wherein the IF steel has the following analysis in % by weight: TABLE-US-00002 C 0.001 to 0.020 Si 0.01 to 0.7 Mn 0.02 to 1.5 P max. 0.15 S max. 0.05 Al 0.015 to 1.0 Nb 0.02 to 0.15 Ti 0.01 to 0.2 optionally containing one or more of the following elements: up to max. 100 ppm boron and/or up to 0.4% by weight vanadium and/or up to 0.4% by weight zirconium, and or up to 0.5% by weight hafnium, and/or up to 0.5% by weight tungsten, and/or up to 0.5% by weight tantalum; a remainder composed of iron and smelting-dictated impurities.

4. The method according to claim 1, comprising, after the dressing, providing the steel sheet with a metallic anti-corrosion coating using an electrolytic process or vapor deposition.

5. The method according to claim 4, comprising applying the metallic anti-corrosion coating to the steel sheet electrolytically or using a CVD or PVD process, the wherein the metallic coating is selected from tire group consisting of: zinc-chromium, zinc-nickel, zinc-magnesium, zinc-titanium, zinc-calcium, zinc alloys with zirconium, hafnium, cerium, and mixed metals or metals composed of rare earths

6. The method according to claim 1, comprising using skin-pass rolls with a roughness (Ra) of 1.6 to 3.3 m.

7. The method according to claim 1, wherein a degree of dressing is between 0.5 and 0.75%.

8. The method according to claim 1, wherein the alloy fulfills to the following condition: N*(TiNb)*S*10{circumflex over ()}6, the product being greater than 1.

9. The method according to claim 1, comprising annealing the steel sheet at a heating rate between 5 K/s and 30 K/s.

10. A steel sheet produced according to the method of claim 2.

11. A method of using the steel sheet according to claim 10, comprising using the steel sheet to form body shell components of motor vehicles and/or buildings.

12. A steel sheet produced according to the method of claim 3.

13. A method of using the steel sheet according to claim 12, comprising using the steel sheet to form body shell components of motor vehicles and or buildings.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The invention will be explained by way of example based on several drawings. In the drawings:

[0025] FIG. 1: shows the comparison of long undulation in dressed IF steel in the uncoated state according to the prior art (through example 48) versus the Wsa values that are improved according to the invention, respectively before and after deformation (starting from example 49);

[0026] FIG. 2: shows the relationship between the niobium content in the base material (dressed IF steel) and the measured Wsa values in the deformed state; uncoated;

[0027] FIG. 3: shows the comparison of long undulation in dressed IF steel in the uncoated state and in the electrolytically galvanized state after deformation;

[0028] FIG. 4: shows the alloy according to the invention in the form of a table;

[0029] FIG. 5: is a table showing a preferred alloy range;

[0030] FIG. 6: is a table showing a particularly preferred alloy range.

[0031] FIG. 7: is a table showing several exemplary embodiments; according to the invention and comparison examples.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] FIG. 1 shows a conventional IF steel, which has been produced and processed according to the prior art (through example 48). The considerable spread of the Wsa values in the course of the deformation is readily apparent. Starting from example 49, die examples are IF steels according to the invention with considerably improved Wsa values and a clearly reduced spread. It is clear that with the invention, the values can be reliably kept approximately at or below 0.30 m. In this case, the light-colored bars are the Wsa values for the non-deformed state and the black bars are the values for the deformed state.

[0033] FIG. 2 clearly shows the relationship between the niobium content in the base material (IF steel) and the measured Wsa values in the dressed, uncoatcd steel in the deformed state. With an increasing Nb content, not only does the Wsa value decrease, but there is also a significant drop in the spread.

[0034] According to the invention, a niobium content of >0.02% by weight (200 ppm) is set in the alloy. According to the invention, the niobium content is preferably set to 0.021 to 0.15% by weight, more preferably to 0.021 to 0.10% by weight, and even more preferably to 0.021 to 0.05% by weight. With these values, it is possible to achieve extremely good Wsa values.

[0035] FIG. 3 shows that the change in the Wsa value is almost unaffected by the galvanization process.

[0036] Through the use of suitable skin-pass rolls, it is possible to reduce the undulation values of the metallically coated strip in the non-deformed state to a low level. This improvement is no longer present, however, in the deformed state.

[0037] The degree of dressing is between 0.5 and 0.75%.

[0038] Through the addition of Nb, it was possible to achieve the fact that little or no increase in the Wsa values occurred due to the deformation.

[0039] Particularly after the deformation, the IF steels produced according to the invention exhibit considerably better properties than conventional IF steels according to the prior an.

[0040] According to the invention, the IF steel can have the alloy composition according to FIG. 4 (all values in percent by weight):

[0041] Preferably, the IF steel has the composition according to FIG. 5:

[0042] A particularly preferable range of the IF steel is shown in FIG. 6:

[0043] The remainder is respectively composed of iron and smelting-dictated impurities.

[0044] FIG. 2 shows the corresponding measured relationship in the IF steel, which indicates the Wsa values after deformation plotted over the niobium content In this case, a steady improvement of the Wsa value is apparent as the Nb content increases. This relationship presumably also exists in additions of niobium to the alloy beyond 0.03% by weight. But the ranges according to the invention on the one hand permit a sufficient reduction of the Wsa value and on the other hand, prevent unwanted hardening effects in die base material, which would lead to a reduction in the deformability.

[0045] For a low long undulation in the non-deformed state and subsequently in the deformed state, the roll roughness (Ra) for the dressing procedure is set to values of between 1.6 and 3.3 m in order to be able to maintain the roughness values in the strip that are required by the customer. A further reduction of the Wsa values is possible by reducing roll roughness values, but would require a reduction of the customer's roughness specifications.

[0046] All conventional metallic coating materials according to the prior art can be used as the coating material in the electrolytic depositing process. These particularly include, but are not limited to, zinc alloys.

[0047] In the invention, it is advantageous that by taking steps within the alloy concept in the steel, it is possible to successfully set the Wsa value to a very low level in a very stable way.

[0048] The following examples should demonstrate the positive influence of the niobium content on the formation of the Wsa value level in the formed component (measured in Marciniak specimens with 5% deformation) and should differentiate it from other influences.

[0049] In the examples for the coating variants Z listed below, strip speeds and depositing conditions have also been indicated for the sake of completeness. They all lie within the parameters that are customary according to the prior art, but have no significant influence on the Wsa values in the deformed state.

[0050] FIG. 1: Examples of Wsa values measured in IF steels according to the prior art (through example 48) and according to the present invention (starting from example 49)

[0051] It has turned out that it is advantageous to comply with the following condition.

N*(TiNb)*S*10{circumflex over ()}6

[0052] with the proviso that

[0053] with pure zinc coatings (Z), the product is >1 and with zinc-magnesium coatings (ZM), the product is >2.

[0054] According to the invention, it is thus possible to ensure that rougher deposits are formed. This results in a better deformability without having a negative influence on the strength.

[0055] FIG. 2: shows the relationship between the Nb content in the steel and die Wsa values after deformation.

[0056] FIG. 3: shows Wsa values in the uncoated steel and after electrolytic galvanization.