EP1088902A1 - Process for manufacturing aging-resistant aluminium killed steel strip - Google Patents

Abstract

In order to provide a cost-effective and time-saving method for producing aging-resistant strips consisting of an aluminum-calmed steel, in which a strip is first produced in a conventional manner by rolling and the rolled strip is continuously annealed, the still heated strip is then wound into a coil and that a strip wound in a coil is cooled to room temperature, the strip cooled in the coil being finally treated.

Description

The invention relates to a method for generating aging-resistant tapes from one aluminum-cooled steel. Such steel strips are as hot or cold strips for the production of cold-formed Components such as body parts and the like are used.

In the course of their manufacture, the steel strips usually to improve their properties, after being rolled and hot rolled in the usual way any subsequent cold rolling required have been produced, an annealing treatment in one Subjected to continuous annealing furnace. Following this The strip often becomes an annealing treatment Surface finishing, such as one Hot-dip galvanized. Then it is cooled and subjected to skin pass rolling until it finally closes wound into a coil for further processing becomes.

A problem with the one summarized above The procedure is that the so generated Tape in practice not the required Resistance to aging. The premature aging The result of the tape is that the tape already deteriorated so shortly after its manufacture Forming properties that its Further processing becomes difficult or even impossible.

One way to eliminate the Sensitivity to aging from made of aluminum Steel strips is the strip, after it has been continuously annealed, finished and has been cooled to undergo a hood annealing and only after this hood annealing dressage and wrap into a coil. Because of the Intermediate hood annealing process is this However, the procedure is costly and time-consuming.

It has therefore been attempted to make tapes with little Aging potential from steels of the type in question in a continuous process without bell annealing through a controlled, specific cooling process following To generate cooling. However, these attempts have themselves did not lead to the desired result if the Annealing treatment with an aging treatment has been combined.

The object of the invention is a Cost-effective and time-saving procedure to produce aging-resistant, from a soothed Steel existing tapes.

This task is based on the above explained prior art by a method for Create aging resistant tapes from one aluminum-soaked steel solved, in which initially in a band is usually produced by rolling, in which the rolled strip is continuously annealed, in which the still heated strip is then wound into a coil, where the coil wound into a coil Room temperature is cooled and at which in the coil cooled band is finally trained.

Preferably the tape is following the Continuous annealing before finishing it Leaving the surface finishing facility in the warmed state is wound into the coil. This leads the inventive method to particularly good Results if the tape in the course of Surface finishing is hot-dip galvanized.

Unlike the prior art, this is believed and then optionally finished tape, if it is the continuous annealing furnace or the Has left surface finishing facility at The procedure according to the invention is not separate cooled, but in a warm state to a coil wrapped. In the coil, the band slowly cools down until it Has reached room temperature. Only then will the tape subjected to skin pass rolling.

It has been found that an inventive produced band from Al-calmed steel as well is resistant to aging like a tape, which additionally to the continuous annealing treatment and if necessary performed surface finishing of a hood annealing has been subjected. Surprisingly, this could can only be achieved by the tape under Taking the temperature to which it is in the continuous annealing furnace or in the surface finishing facility, for example, the hot-dip galvanizing device has been wrapped and then in sufficient is slowly cooled to room temperature for a long time.

For a controlled, rapid cooling afterwards the annealing or surface treatment and one with it combined aging treatment can inventive method of operation are also dispensed with, like the bonnet glow. This makes it possible with the Invention an aging-resistant tape from one aluminum-stabilized steel at low cost and Manufacturing time.

If the surface finish includes hot-dip galvanizing, see above is the one present at the end of the galvanizing process Temperature of the tape well suited for that winding the coil in accordance with the invention in direct connection to the surface finishing.

It is essential that, as mentioned, the tape is taken along its temperature at the end of the annealing or Surface finishing is wound into the coil and thus wound into a tight bundle at room temperature cools down. The temperature when reeling the annealed or surface-finished strip into a coil between 150 ° C and 350 ° C. If adhered to this temperature range for the winding temperature certainly achieved that long after the Production of the tape according to the invention its good Properties are present, so that the tape in processed essentially unaffected by its age can be.

When cooling the coil in air is an optimal one Temperature curve until the room temperature is reached guaranteed. Of course, cooling can but also in other surrounding media that ensure a comparable course of cooling.

The invention is described below with reference to Exemplary embodiments explained.

Diagrams 1 to 9 show the respective Different values related to the winding temperature Characteristics of from different aluminum-rolled steel, cold-rolled and trained tapes.

The strips B _A , B _B , B _C were produced from steels A, B, C with the composition given in the table below in the usual manner by hot rolling and then cold rolling. steel C. Si Mn P S Al N A 0.04 0.158 0.206 0.023 0.008 0.034 0.0036 B 0.031 0.013 0.164 0.014 0.008 0.033 0.0026 C. 0.021 0.014 0.162 0.007 0.008 0.033 0.0016 (Details of the contents in% by weight)

The strips B _A , B _B , B _{C were} continuously annealed in a continuous annealing furnace. Then they were subjected to hot-dip galvanizing of their surface.

After leaving the hot-dip galvanizing device, strips B _A , B _B , B _{C became one} at different winding _temperatures WT of 50 ° C, 100 ° C, 150 ° C, 200 ° C, 250 ° C, 300 ° C and 350 ° C Coil coiled. The coil was then cooled in air to room temperature. The cooling took up to 24 hours.

The cooled strips B _A , B _B , B _C were skin-pass rolled, with skin-pass degrees between 0.3% and 1.5%.

The tapes were then heated at 100 ° C for one hour to cause artificial aging. In the tear diagram, which was created in a tear test immediately following the artificial aging, the optimally designed tapes B _A , B _B , B _C showed no elongation limit at a suitable choice of the winding _temperature WT.

In the diagrams, 1 to 9, as determined for the generated from the steel A bands B _A values of the respective characteristic are by squares, the data obtained for the generated from the steel B bands B _B values of the respective property in each case by diamonds and for the Values B _C determined from the steel C produced by the respective property are each identified by triangles. The values present after the skin pass are shown by empty squares, diamonds and triangles, while the respective values determined after the artificial aging are indicated by filled squares, diamonds and triangles.

In the diag. 1 for strips B _A , B _B , B _C , depending on the respective winding temperature WT in [° C], the yield point elongation ARe is given in [%]. It can be seen that the tapes B _A , B _B , B _C are free of stretch elongation immediately after the skin pass. However, a strip B _A wound at a winding temperature WT of 20 ° C. has an elongation limit elongation ARe of 3% in the aged state. Likewise, the tape B _B wound at this winding temperature WT of 20 ° C. has an elastic limit elongation of 2%, while it is approximately 1.5% for the tape B _C. At a winding temperature WT of at least 200 ° C, on the other hand, all tapes B _A , B _B , B _{C are} also free of yield point elongation even in the aged condition, this condition already occurring for tapes B _B and B _C at 150 ° C.

In Diag. 2 the values of the yield strength Re in [MPa] are given as a function of the winding temperature WT in [° C] for the respective bands B _A , B _B , B _C , while in Diag. 3 the values of the tensile strength Rm are shown in a corresponding manner in [MPa]. It turns out that at a winding temperature of at least 200 ° C there is no aging-related increase in the yield strength or the tensile strength of the aged strips B _A , B _B , B _C compared to the corresponding values which the strips B _A , B _B , B _C in the unaged condition after dressing.

In Diag. 4, the values of the uniform elongation Ag in [%] are given as a function of the winding temperature WT in [° C] for the respective bands B _A , B _B , B _C , while in Diag. 5 the values of the elongation at break A80 in [%] are shown in a corresponding manner. It can be seen that at a winding temperature WT of less than 150 ° C., the elongation values of the artificially aged belts B _A , B _B , B _C clearly drop compared to the elongation values that the belts B _A , B _B , B _C immediately after the skin pass have. From a winding temperature WT of at least 200 ° C, on the other hand, there is hardly any decrease in the elongation values as the strips B _A , B _B , B _{C age} . Thus, breaking elongations A80 were, for example, of 42 at coiling temperatures of 250 ° C WT wound bands B _B B _C after aging - reached 44%.

In Diag. 6, the n value is given as a function of the winding temperature WT in [° C.] for the respective bands B _A , B _B , B _C. It can be seen that at a winding temperature WT of less than 150 ° C, there is a sharp decrease in the n value in the course of aging. At winding temperatures WT of at least 200 ° C, however, there is practically no longer any influence of aging. It is noteworthy that, for example, a strip B produced from steel C and wound at a winding temperature WT of more than 250 ° C. reaches _C n values of more than 0.22.

In Diag. 7, the r value is given as a function of the winding temperature WT in [° C.] for the respective strips B _A , B _B , B _C. It can easily be seen that aging does not cause a change in the r value and, accordingly, the winding temperature WT has no influence on the r value.

Finally, as parameters for the bake hardening properties in the Diag. 8 the BH0 value and in the Diag. 9 the BH2 value is given in [MPa] over the respective winding temperature WT in [° C]. It can be seen that in the artificially aged state at winding temperatures WT of less than 150 ° C for all tapes B _A , B _B , B _C BH0 values of approx. 40-60 MPa and BH2 values of approx. 50-70 MPa can be achieved. From a winding temperature WT of at least 200 ° C, the BH0 value drops to values around 10 MPa for all tapes B _A , B _B , B _C. At these winding temperatures WT, BH2 values of approx. 20 MPa are achieved for strips B _A and B _B made from steels A and B, while RH2 values of 10 MPa are also available for strips B _C made from steel C.

It can be seen from the diagrams 1 to 9 that cold rolled in the procedure according to the invention, continuous annealed and treated strips Allow aluminum-stabilized steels to be produced, which are non-aging. This is achieved in that the Strips immediately after continuous annealing Winding temperatures of at least 150 ° C and slowly cooled in air with a cooling rate ≤ 1 ° C / min become. With this procedure, the same Properties of the tapes in the aged condition Properties that the tapes immediately after own their manufacture. The invention Tapes produced have good bake hardening potential.

By a combination of the method according to the invention with suitable hot and cold strip production processes can use steel strips of the type in question particularly excellent properties, such as lowest Yield strengths, etc. are generated.

Claims (6)

Process for producing aging-resistant strips from an aluminum-calmed steel, in which a strip is first produced by rolling in the usual way, in which the rolled strip is then continuously annealed, where the still heated strip is then wound into a coil in which the coil wound into a coil is cooled to room temperature and in which the strip cooled in the coil is finally dressed. A method according to claim 1, characterized in that the strip is surface-finished after the continuous annealing before it is wound into the coil in a still heated state after leaving the surface finishing device. A method according to claim 2, characterized in that the strip is hot-dip galvanized in the course of surface finishing. Method according to one of the preceding claims, characterized in that the temperature when winding the strip into the coil is between 150 ° C and 350 ° C. Method according to one of the preceding claims, characterized in that the cooling of the coil takes place in air. Method according to one of the preceding claims, characterized in that the cooling rate ≤ 1 ° C / min. is.

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