DE1900774A1 - Inchromizing of hot strip - Google Patents

Description

JKL R. POSCHENRIEDEiI

> DR. F. BOHTTNER 10 0077 /

-IMG. H-J. MÜLLER I d U U / /

Pdtuütü

Munich bo oasis A 57

Lucile-Gnihn-Strasse 38
Telephone 443755

JDr "vdB / öh

Albright * Wilson Ltd. , Oldbury to Birmingham, Warwickshire (UK)

Inchromizing of warning tape

The present invention relates to the production of chrome-plated steel strip and relates to a process by which steel strip can be chrome-plated by a press-chrome-plated process and then significantly reduced by cold re-rolling and pressed thereon to form a porous, firmly adhering coating. "The material obtained is then subjected to a heat treatment in order to allow the chromium to diffuse into the surface of the steel substrate." An example of such a process is in the pending patent application A 55 892 VIb / 48b (P 16 21 202.5). *

Usually steel strips are produced by hot rolling the originally obtained steel to about the 2 to 2 1/2-roalige organic tea, which ultimately is desired, whereupon the steel is allowed to cool

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and him. then a reduction to the final one Thickness by Xaltnachwalzen »subject, Daran followed by a glow to a steel of to produce machinable deformability. The pre-chromium treatment process proposed so far would produce satisfactory results »if they were applied to steel belt, which one more? contains than 0.01 $ effective carbon and if only it has already been substantially reduced to the desired final thickness and annealed. In such a process, the chromium-plated tape is normally subjected to a cleaning treatment and, if a good surface quality is desired «, a reduction of a few percent through cold subject to re-rolling "

The chrome plating of a thick strip, which is followed by cold re-rolling to make it onto his "Reduce final desired thickness" would be an economical way of working because it does the Increase the production capacity of the powder overshoot and the press release of an inchroming system and would also allow a rolling step to be omitted if a product of good surface finish ^ oh condition g & wishes is. So far, however, has been found » that the results were unsatisfactory because the chromium coating produced was too thin and was too brittle to survive the essential cold re-rolling.

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It has now been found that one can obtain an inching oversize thick enough to give satisfactory results in a process SU in which thick hot rolled steel is inched and then substantially reduced by cold pass rolling when 1.5 to 20 ^, preferably 1.5 to 10 # of certain additional elements incorporated into the chromium-containing material to be pressed onto the steel strip. Such a process improves the mechanical properties of the steel compared to other chromating processes because grain growth occurs in the substrate during the heat treatment step of the chromating process. This deterioration of its mechanical properties is caused rectification would require considerable cold reduction, weloher a usual annealing ansehließt ₀ What has, however, pointed out above, this was previously impossible Sine significant reduction is the inchromierten steel by temper the surfaces »beschaffenste Improving it of the band »If the term" band "is used here, unless the context states otherwise, the meaning of both steel bands and steel sheets is to be understood ·

Accordingly, the present invention relates to a process for preparing inchromiertem steel strip with the characterizing feature that one introduced under a chromium-containing powder on a relatively thick steel strip which a total of 1.5 to 20 wt _o = $ a

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contains one or more substances of silicon, aluminum, molybdenum, niobium 'vanadium, Iitan and Phoephor, subjecting the coated substrate to a heat treatment in a non-harmful Inohromierungsatmosphäre of at least 800 ⁰ C, _r to diffuse to the chromium in the steel, and in that .man then the tape substantially reduced by Kaltnaohwalzen · the additional materials can be used alone or in combination · ϊη particular it was found that phosphorus exerts a beneficial effect when it overall in a so _Λ wrestle MengeTi & e 0.3 # of Chromium is present in the presence of one or more other additional elements.

In another respect, the invention relates to a relatively thick chrome-plated steel strip which, like is produced as described above and weloh.ee can be reduced essentially by cold re-rolling can" .

Pas inchromizing the relatively thick steel strip so that it is suitable for subsequent substantial use To be subjected to cold reduction requires the formation of a coating which is thick enough and is malleable enough to withstand the stresses of cold rolling to resist "The formation of a thick coating depends, at least in part, on that the formation of a chrome carbide barrier is kept to a minimum, which prevents the diffusion of the chrome into would complicate the substrate. Also, in order to obtain a ductile coating, the formation of chromium carbide should be requested

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be kept to a minimum · At a relatively thick steel band makes this a great a There was a problem with a thin ribbon because of the fact that it was found to be infr "age circumstance rather the total amount of the carbon present as the percentage.

Although the scope of the invention is in no way limited by any theory 1st, it is believed that the effect of additional Elements with the formation of a barrier against the change of carbon to the ear rows Surface layers of the metal be united could. This can include three mechanisms:

Ie All used in the method according to the invention Additives tend to accelerate the formation of a ferritic phase where They are present in the steel "because the carbon" has a much lower solubility in the carbon ferritic phase than in the austen! tic phase, there is a tendency for carbon from the ferritic surface clay; of the steel to migrate inward to the austenitic region.

2ο Chromium diffuses faster in errite than in Austenlt and therefore diffuses in and out faster in the presence of a ferritic accelerator delivers low concentrations of chromium deeper in the substrate, which reacts with carbon to prevent its outward migration than

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it is the case when there is no perite accelerator present iet «

3 «Gewlese used additives sipd carbide-forming elements, which quickly get into the substrate in-diffuse and deep inside carbides form. Piping carbides - form a barrier against carbon migration

Steels for treatment according to the method of Invention are normally those "which have a carbon content of at least $ 0.015, and preferably those with a carbon content of 0.036 to 0.08%, normal commercial ones can be used Steels such as strip steel or capped mild steel are used «

Usually the steel which is treated according to the method of the invention is previously treated with a Thickness of up to 6.55 zsm (0.25 inoh), even more common to the range from 0.8 to 4.5 mm (0.03 up to 0.18 inch), hot-rolled, followed by it is pickled and fed to a distributor where the chromium-containing material is placed on the belt will"

The chromium-containing material is in on the tape Powder form applied ^ preferably in a lamp « size less than about 100 British Standard meshes, and even more advantageous in one Particle size that most through a sieve of

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200 British Standard Masehen, whereby the material can be a single powdered alloy or a mixture of powdered alloys »Optionally, different alloys can be separated,. to be given to the substrate. However, the containing of the steel strip to be applied chromium material is 1.5 wt .- ^ ₄ Feie 20 preferably 1.5 bie 10 $ ew "contain £ .- ale total amount of the additives, based on the amount of chromium present.

It is highly beneficial to the additives not to be used in the form of the pure elements, but rather an alloy, often with iron, to use »chrome can also be in the form of a alloy with iron can be used, which is preferably one or more of the additional elements Can contain «Pas powder should be used in such a way reach that about 11 g of chromium, preferably between 16 and 20 g of chromium for every 0.09 m (1 eq. ft ”) of the steel strip. The chrome and Powder containing additive can be applied to at least one surface of the steel belt, although it is more common to apply it to both sides. bring, and usually be compressed by passing the tape through a set of rollers, the a pressure of more than about? Tons per running 2.5 cm (7 tons per linear inch) «,

The tape onto which the powder containing the chromium and additive has been pressed becomes a * ~ Subjected to heat treatment in a non-harmful, halogen-containing atmosphere, as below

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is carried out to put the chromium Io into the substrate to diffuse.

Although the substrate can be treated in an open or closed coil, the latter will Embodiment usually preferred because of this reduces the loss of the additional element, especially la trap with silicon and aluminum la form of their volatile halides during heat., treated.

The heat treatment is carried out in a non-harmful atmosphere, i.e. one that prevents oxidation, nitration or carburization of the strip, i.e. usually hydrogen or an inert gas accelerate ο if there are spaces in the sand during the heat treatment, for example when an open coil is used, a hydrogen ralogenate gas, usually hydrogen chloride, is usually used. If the substrate for the heat treatment is arranged with surfaces in contact, for example in a closed coil, as is preferably the case, an iron halide or other metal halide which reacts with iron during the heat treatment step to form iron halide is applied to the substrate after Pressing the powder containing chromium applied What kind of

Arrangement of the substrate for the heat treatment also, is applied feswlrö at least to 80O ⁰ O, preferably to 920 to ICOO ⁰ O, heated. Generally should

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care must be taken to ensure that, whenever possible, harmful materials are Oven must be removed before these temperatures are reached. For example, if a closed Spulenteohnik is applied, it may be desirable be able to add some other compounds to the metal halide, which will volatilize or ßioh decompose into non-harmful substances at a comparatively low temperature to the Removal by cleaning assisted, Suitable compounds include Aimaoniu halides *

If a closed coil type technique is used, the procedure is customary performed as described in the pending application A 55 892 VIb / 48b (P 16 21 202 * 5). A technique is used that leaves the substrate gaps during heat treatment has, the execution is usually carried out in the manner as it is in the adhesive application A 52 850 TO / 4813 (P 15 21 122ου) is described »

After the heat treatment has been completed, it is left to do so Cool the strip and, after washing and drying, it is subjected to a reduction during cold re-rolling.

Typical reductions according to the method of the invention range from $ 30 to $ 80, usually around 4-5 to 75 #. The strip is then commonly annealed to make it workable. The temperature,

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which the glow was carried out, and legs duration are made by the use that the incorporated Tape is to be exposed and determined by the amount of reduction to which it has been subjected is * ■. ":

Pas method according to the invention is carried out by the

the following examples are explained in more detail:

Examples ■

Powdered alloys of a particle size that passed a British Standard 200 Haschen and had compositions as shown in the table were applied to a hot-rolled normal Ran as t aiii with once "carbon content of about 0.04 /" The Pick of the substrate in each example and the amount of chromium applied in each case is given in the table. Pieces of powdered alloys were then pressed onto the substrate using a set of rollers which applied a pressure of 10 suns per running 2.5 cm (10 tons per linear inch). The coated tape was then passed through a solution of iron (chloride tetrahydrate (4> 2 ropes) and ammonium chloride (0.97 ropes) in water and dried, the tape being passed through an infrared dryer, producing a Low 4 0.09 g per n "(1 sq. ft.) of the coating was obtained" Sin 6.1 m (20 ft ") long piece of the tape was treated under a train of 454 kg (1000 lbs _o) on a mandrel with an outside diameter of about 9 om (3.5 inches)

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“Wiggled and the free end clamped to Maintain tensile stress

The coil was placed in a suitable furnace, which was then purged with hydrogen for 3 hours at 25Q ⁰ O. After this time, the temperature was increased to 40O ⁰ C over a period of 1 1/2 hours. The gas flow was continuously passed through the furnace for 10 hours in order to ensure the complete removal of harmful materials.

The bead of the obtained chrome diffusion silver ssugs and are certain mechanical properties of the tape indicated in the table. The strip was then cold rolled to the specified reduction to effect, and then annealed as indicated.

There were then certain mechanical properties examined, and the results given in the table

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Claims (2)

Ictent claims (1. / Process for the production of an inebromised steel strip, whereby a powder containing cisromium is pressed onto a steel strip and this is subjected to a heat treatment in order to allow chromium to diffuse into the substrate 1.5 to 10 wt «~ $ of one or more of the following additional elements Dämlich silicon, Aluminiuffij MolyMäa, Jiiob, vanadium _s titanium and phosphorus, and. that the substrate is reduced by. EaItnaohwalzen substantially following the Wärraebehandlung. 2. The method according to claim. I ₉ characterized by the fact that after the heat treatment the strip is reduced to 45 to 75 $> by means of Keltnaahwalaen « 3 · Method according to one of the preceding claims, characterized in that the heat treatment is carried out at a temperature in the range from 920 to 100O ⁰ O » 4 · Ancestors according to one of the preceding claims, characterized in that after the pressing of the chromium-containing powder a further coating of an iron (IX) balogenide or another metal halide on the substrate takes place, which occurs with iron under the relevant conditions during the heat treatment with the formation of iron (II) halide reacts, and that the substrate for the heat treatment step is packed with surfaces in contact. 909838 / 0826-