SE465321B - PROCEDURES FOR PREPARING ZINC ALLOY PLATED TITANETETED STEEL PLATE AND USING ITS SAME - Google Patents

Description

465 521 of Zn alloy sheet steel using vacuum vapor deposition has therefore been proposed and used (see for example JP-A-61-195965). According to this procedure plated cold-rolled steel strip with zinc on one side or both sides by vacuum vapor deposition and heat treated then for alloying at 250-350 ° C for 1 to 15 hours in one non-oxidizing or slightly reducing atmosphere in a batch working annealing furnace.

At the same time used for the production of steel sheet for deep drawing aluminum (Al) -sealed steel and Ti-sealed steel. With Al- sealed steel sheet, Zn alloy sheet steel can be produced by vacuum vapor deposition and heat treatment in accordance with the known process described above. With Ti-sealed steel plate however, a problem occurs in that it formed the alloy layer is inferior in pulverization durability and easily peeled off.

For standard deep drawing purposes, Al-sealed steel sheet is sufficient. In recent times, however, more and more is required complicated shaping. For such purposes, Ti-sealed steel, which have better machinability and formability, be used. Zinc- alloy-plated steel sheet made of Ti-sealed steel sheet must therefore be given good pulverization resistance.

We have conducted investigations to determine the cause to the inferior pulverization resistance of Zn alloy-plated steel sheet made of Ti-sealed sheet steel and focused our attention on the structure of the lated plating layer. As a result of our research, we have found that in Ti-sealed steel very brittle is formed intermetallic compounds of iron (Fe) and Zn when the Zn- plated steel sheets are heated to temperatures outside one specific temperature range and that this specific temperature tour range varies depending on the Ti content. This temperature thus exceeds 320 ° C when the Ti content is 0.05% and exceeds rises 260 ° C when the Ti content is 0.3%. Then well a layer of 465 324 i brittle intermetallic compound formed is deterioration of pulverization resistance inevitable regardless of the alloying conditions under which the plated steel sheet treated. We have thus found that in the foregoing said problem can be solved by holding off the substrate Ti-sealed steel sheet at a low temperature set in relative to the Ti content during the vacuum vapor deposition and heats the plated steel sheet in a non-oxidizing atmosphere, preferably in a batch heat treatment in annealing furnace, at a temperature within the temperature range of which Fe content in the formed alloy layer is within one predetermined area.

The present invention relates to a process for the preparation of of zinc alloy-plated steel sheet with very good depth drawability, which includes setting the temperature of the Ti-sealed steel sheet, substantially consisting of C 10.0%, Si <0.05%, Mn: 0.15-0.85%, Ti: 0.05- 0.30%, P§0.02%, S§0.02%, Al§0.05% and the rest Fe, to a temperature within a range T (° C), which is defined as l80§T§-240xW + 292, where W (%) is the Ti content of the substrate of steel sheet, and Zn plating of the sheet steel by vacuum evaporation deposition and subsequent keeping of the plated steel the plate for alloying the zinc plating layer and the steel sub- at 220-320 ° C for 1-50 hours depending on Ti halten.

In the present description, the percentage (%) refers to the weight.

Sealed steel for the production of sheet steel suitable for deep drawing is a low-carbon steel, the C content of which is usually is not more than 0.01%. The silicon (Si) content should preferably be be lower than 0.15%, because with a Si content exceeding 0.15% adhesion of the plating layer is unsatisfactory posing. Mangen (Mn), an element that improves steel strength, should preferably be included in the range 0.15-0.85%.

When the Mn content is lower than 0.15%, unsatisfactory results are obtained. 465 321 positioning strength. On the other hand, the strength of the steel not further by an Mn content exceeding 0.85%.

The Ti content of Ti-sealed steel for the production of steel for traction is usually 0.05-0.30%. Ti is an element that binds C in steel and improves the machinability of the steel and is considered to be required in an amount of at least about four times the content of C. This element also binds nitrogen (N), which is a purification in the steel. Ti is therefore included in an amount exceeding 0.05 % or more taking into account the N content. On the other hand, is obtained no benefit corresponding to the increase in the cost if the Ti content exceeds 0.3%.

Phosphorus (P), sulfur (S) and Al can be included as impurities in an amount of §0.02%, §0.02% resp. §0.05%. These amounts are the same as the usual pollution levels in ordinary carbon steel.

The Ti-sealed steel sheet described above is held at a temperature. temperature T (° C) defined as 180§T§-240xW + 292 dependent on the Ti content W (%) and then subjected to plating with Zn by vacuum vapor depositionï At the vacuum vapor deposition, whereby Zn vapor condenses on the surface of the steel strip and forms a plating layer, the temperature rises the turn of the steel sheet with a maximum of 40 ° C. About the temperature at the steel substrate (T) of Ti-sealed steel exceeds that temperature which is defined as l80§Tš-240xW + 292, which depends on the Ti content W (%), before being subjected to vacuum vapor deposition falls below the vacuum vapor deposition temperature of the steel sheet to reach one temperature, at which brittle intermetallic compounds formed due to the temperature rise caused by the the condensation heat of the Zn steam. Thus, the pulverized the resistance of the formed alloy layer to deteriorate.

The upper limit of the substrate temperature varies depending on the Ti content as described above. Specifically, when 465 s21g¿ '~ The Ti content is 0.3%, it is not higher than 220 ° C, calculated according to the above formula, and when the Ti content is 0.05% is not higher than 280 ° C. The substrate temperature must thus adjusted so that it does not exceed the upper limit as defined by the above formula, before vacuum steam deposition.

If the substrate temperature is too low, the adhesion is off the Zn plating layer formed is poor. The lower limit is 180 ° C, which is the same as in the case of ordinary carbon steel as not contains Ti.

The steel strip plated with Zn by vacuum vapor deposition heat treated for alloy. The formed alloy layer should preferably contain 8-12% Fe. If the Fe content is lower than 6%, unalloyed 07-Zn remains on the surface of the plating layer. and affects the coatability, weldability, etc. of it plated steel plate. If the Fe content exceeds 14%, it deteriorates the pulverization resistance of the alloy layer.

As an annealing device, a batch operating annealing oven is used. In the alloy treatment with a batch working annealing furnace, the steel sheets are usually heated in a non-oxidizing atmosphere to prevent oxidation of the steel strip (or plate). The heating can be performed with a band in the form of a roll, a tight roll or an open one roll.

The heating temperature and time can be varied accordingly accordance with the intended coating weight and average Fe content, but the heating temperature must be 30 ° C lower than the alloy temperature of Zn-plated Ti-free steel plate. The upper limit of the heating temperature varies depending on the Ti content. It is 280 ° C when the Ti content is 0.3% and is 320 ° C when the Ti content is 0.05%. If the heating temperature the temperature exceeds the above upper limit deteriorates pulverization resistance, since a brittle alloy 465 321 layers are formed. If, on the other hand, the heating temperature is below the above temperature range, the Zn- the plating layer not well. Heating for a shorter time than one hour does not raise the substrate temperature sufficiently and satisfactory heating can not be carried out. On the other the side lowers heating for more than 50 hours vitality.

It is possible to carry out the heating continuously with by means of an annealing furnace provided with a continuous plating line, but the heating conditions differ the conditions used with a batch of annealing ningsugn. Use of a batch operating annealing furnace is preferred because the temperature control is easy to implement.

The temperature rise rate and the cooling rate are not specifically limited and these conditions are determined by consideration of the functional characteristics of ordinary people in industry use batch annealing furnaces.

The following is a general explanation of the attachments the drawings.

Fig. 1 is a diagram showing the areas of the substrate plate. temperature and Ti contents in substrate steel within which brittle Fe-Zn intermetallic compounds do not form at the interface between the steel substrate and the plating layer when the substrate plated with Zn by vacuum vapor deposition.

Fig. 2 is a graph showing the areas of treatment. temperature and time within which the average Fe content in the alloy layer can be adjusted to 8-12.0%.

The invention is described in the following specifically with the aid of test results, processing examples and comparison examples.

O 465 s21ß: 'ïi We plated standard Ti-sealed steel strips containing 0.05- 0.3% Ti with Zn by vacuum vapor deposition using a continuous vacuum vapor deposition apparatus as set forth in Nisshin Gino No. 51,1954, 1984, with various substrate temperatures tours.

The other process conditions were as follows: Steel strip: 0.8 mm thick and 1200 mm wide Ti-sealed steel strip Treatment speed: 80 m / min.

Pressure in the deposition chamber: 0.01 torr Alloy temperature: 270 ° C.

We thus investigated the relationship between Ti content of substrate the steel and the substrate temperature to obtain a layers which did not contain intermetallic compounds.

The results are summarized in Fig. 1.

Fig. 1 shows the ranges of substrate temperature and Ti content in substrate steels within which the formation of Fe-Zn intermetallic compounds do not occur at the interface between the substrate and the plating layer. In the drawing, the solid represents line a the upper limit temperatures below which brittle Fe-Zn- intermetallic compounds are not formed. The line is expressed by the relationship T = -240xW + 292 (° C), where T is the substrate temperature in ° C and W is the Ti content in%. The solid line b represents lower limit temperatures above which the adhesion of it formed plating layer is satisfactory. The temperature is constant 180 ° C independent of the Ti content.

The Zn-plated steel strips prepared as described above (not yet alloyed) were kept at different temperatures below different times and the Fe contents in the formed alloy layers was measured. It turned out that there is a connection between Ti content and the upper limit temperature. The results are taken in Fig. 2. 465 521 i'f! Fig. 2 is a diagram showing the areas for heat treatment. temperatures and times within which the average The Fe content of the alloy layer can be adjusted to 8-12.0%.

In the drawing, the area surrounded by dashed lines is it area within which the Fe content of the formed alloy layer is between 8% and 12%. As can be seen from this figure, the band is heated to 320 ° C when the Ti content is 0.05% and up 280 ° C when the Ti content is 0.3%. For those skilled in the art, it is possible to determine the upper limit temperature for Ti levels between 0.05% and 0.3% of this figure. Fe content in the medical The layer of Ti-sealed steel sheet is between 8% and 12% when the Zn-plated steel sheet is heated to 220-320 ° C depending on the Ti content.

In Fig. 2, the area surrounded by solid lines is that area known for Al-sealed steel. The sloping line the bottom left side is known to those skilled in the art.

Examples and comparative examples The Ti-sealed steel strips described above containing 0.05% and 0.3% was plated with Zn on both sides by vacuum evaporation. deposition, as described above, under different conditions listed in Table 1.

The Zn-plated steel strip rollers heat-treated in this way was laid for alloying in a batch annealing furnace in an atmosphere consisting of 3% H2 and 97% N2 and with a dew point (D.P.) of -25 ° C under the temperature and time conditions see in table l.

The surface condition and pulverization resistance of those on alloyed in this way the alloyed Zn-plated steel sheets was examined. The pulverization resistance was assessed by bending of test pieces with a radius of curvature of 3 times the thickness of the sheet up to 180 ° C (6x bending) and examination whether peeling of the plating layers belonged 465 321 COW room or not on the inside.

The results are summarized in Table 1. The expressions that used in Table 1 has the following meanings: Regarding the surface condition: Good: homogeneous alloy was formed.

Zn-remaining: 77-Zn remained.

Regarding the pulverization resistance: Good: no pulverization occurred.

Bad: pulverization occurred.

Poor adhesion: the plating layer was easily peeled off.

The asterisk-denoted values are outside the conditions as defined in the claim.

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Claims (2)

ff 465 321; PATENT REQUIREMENTS A process for producing zinc alloy-plated titanium-sealed steel sheet, which comprises Zn-plating the steel sheet by vacuum vapor deposition and then heating the plated steel sheet to alloy the applied zinc layer, characterized in that the use of titanium-sealed sheet is used. steel, consisting essentially of Cs0.01%, Si Ss0.02%, Als0.05% and the remainder Fe, sets the temperature of the steel sheet to a temperature within a temperature range T (° C), which is defined as 180 = T = -240xw + 292, where W (%) is the Ti content of the steel sheet substrate, the steel sheet undergoes Zn plating by vacuum vapor deposition and then keeps the plated steel sheet for alloying the zinc plating layer and the steel substrate at 220-320% 3 for 1-50 hours depending on The ten content in the steel substrate. Use of the zinc alloy plated titanium-sealed steel sheet produced by the process according to claim 1 for deep drawing.