DE3101850A1 - METHOD FOR PRODUCING ALUMINUM-COATED STEEL SHEETS OF LOW STRETCH LIMIT AND HIGH OXIDATION RESISTANCE - Google Patents

Description

SHIP ν. FÜNER STREHL SCHÜBE L-HOPF EBBINGHAUS FINCK

MAPIAHILFPIAIZ 'J Λ 3, MONCHPN OO POSTAnl-iESSH: POSTFACH OBOlfiO, D-HOOO MUNICH B? I

NISSHIN STEEL COMPANY, LTD.

At? .OI ¹ WOi thSIONAL ΗΓΙ'ΗΓ.ΗΙ NIAliVlri. HKIfJWC THl EUROHEAN ΡΑΙΙ.ΝΓ CH-ItCt

KARL LUDWtO SCHIFF {1ÖÜ4-1O70)

DlPL. CMEM. DR. ALEXANDER v. FIVE DIPLES. ING. F ¹ ETER STREHL

DtF ¹ L-CHEM. DR. URSULA SCHÜBEL-HOPF

DtPL. INQ. DIETER EBBINQHAU 5 DR. ING DIETER FINCK

TELEPHONE (OBO) 48SO64 TELEX 6-23 668 AURO D TELEGRAMS AUROMARCPAT MUNICH

DEA-21639

January 21, 1981

METHOD OF MANUFACTURING
ALUMINUM COATED
STEEL PLATES FROM LOWER
STRONG LIMIT AND HIGHER
OXIDATION RESISTANCE

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The invention relates to a method for producing with | molten aluminum coated steel sheets having einej low yield strength and a low rate of oxidation [Klobuk yield indicate when subjected to temperatures of an oxidation at high tempeh. !

So far, steel sheets coated with molten aluminum have been used (hereinafter referred to simply as "aluminum-coated steel sheets") for uses in which heat resistance and corrosion resistance were needed, mostly from cold rolled sheets of unskilled steels (rimmed steels) made with low carbon content. However, it is known that aluminum-coated steel sheets, the ! made of sheet metal on the basis of non-killed steel substrates ! have been made, suffer a deterioration in quality

due to the quench aging, which is caused by the rapid cooling development is caused during the coating, whereby the material is hardened.

• The main measures taken to prevent ; the deterioration mentioned above can be taken,

ι are:

(1) Use of substrate sheets made of a steel ^from which carbon and nitrogen, j
\ that cause deterrent aging as much as possible

j have been removed;

(2) Addition of a carbide-forming element such as Titanium to fix carbon and nitrogen, which cause quench aging, in the substrate material;

(3) causing overaging of the aluminum-coated

Sheets in which quench aging has occurred; and so forth.

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However, step (1) is not economical in the case j when the steel sheets are coated with a hot dip coater; device for in-1-line annealing with a non-oxidizing Furnace coated, although they are carried out in the usual steel production by the application of decarburization annealing can be.

The step (2) is economical in and of itself, but has the disadvantage that when used against steels with a low carbon content, as they are exclusively in the usual converter processes, a considerable amount Amount of titanium must be used and the highly oxidizable titanium generates a not small amount of oxide inclusions, causing a deterioration in the surface quality of the Product is achieved. In the final analysis, this measure is therefore neither economically nor technically advantageous.

Measure (3) is economical. However, this treatment enhances the iron-aluminum alloy layer, which has poor formability even if the aluminum coating was carried out under conditions conducive to the formation of the i

Control Fe-Al alloy layer. As a result of this treatment, even if the property of the substrate material is improved, the formability of the aluminum-coated layer is reduced ^! worsens. i

From Japanese Patent Publication No. 35532/76 ^: A method for producing aluminum-coated steel sheets is known which comprises the following steps: j Hot rolling of a steel consisting essentially of the following components: 0.001-0.020% carbon , £ 0.05 % silicon, 0.05-0.40% manganese, 0.10-0.30% chromium, 0.03 0.40 % effective titanium (amount of titanium minus titanium in the \ oxide form), whereby the Amount of titanium at least four times ^: the percentage of (C + N) is £ 0.006 % nitrogen,,

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60.020% oxygen and the balance iron and inevitable incidental impurities at a temperature of at least; 800 ⁰ C, \

Cold rolling the hot winding at a reduction of 40 % or more, annealing the rolled sheet at 800 to 95O ⁰ C and immersing the sheet in an Al-Si alloy ^{bath (^ 10% silicon) at 640 to 700 0} C for a period of up to 10 minutes; th.;

The aluminum-coated steel sheet produced by this method has a yield strength of 13-17 kg / mm ² \ and an elongation at break from 44 to 47% in the state of a cold-rolled sheet of 0.8 mm thickness. Today, however, there is an increasing demand for materials that are easier to mold. '

The invention is based on the idea, the three below; to apply the measures described in order to obtain improved aluminum-coated steel sheets which have good formability together with a low yield strength and, moreover, a small increase in weight in the case of high-temperature oxidation result.

(1) Decrease in the content of C and O in the substrate steel sheet by applying a vacuum degassing treatment and previous deoxidation with aluminum in the stage of steelmaking and thereby brought about a reduction in Titanium content, which is required to fix C and N and control of the formation of oxides.

(2) Reduction of the manganese content, which increases the yield strength and addition of chromium, which lowers the yield strength.

(3) Promote agglomeration and growth of the failed Ti carbide by winding up the finished machined

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th hot roller at a temperature of about 700 ⁰ C, whereby hardening is prevented by the formation of carbide of the titanium, which has been added to the substrate material. The agglomeration of Ti carbide is further promoted by heating the cold-rolled steel sheet to a temperature of about 850 ⁰ C or higher when it is passed through a hot dip coating apparatus for 1ine in-annealing treatment with a non-oxidizing furnace (this device is commonly referred to as an NOF-type coater in Japan).

In addition, the invention is characterized in that the The high-temperature oxidation resistance of the material is increased by the combined addition of titanium and chromium. That means, that the oxidation weight increase is significantly reduced at high temperatures due to the decarburization of the substrate, rials and is further improved by adding titanium. The reasons for this are as follows:

(1) By decarburizing or adding titanium, the purity becomes _; of the iron material is improved and the aluminum from the aluminum layer diffuses easily into the iron substrate and an Al diffusion layer is formed which has excellent high temperature oxidation resistance

(2) The Ti in the material diffuses toward the! Surface and forms a layer enriched in Ti un- | below the Al diffusion layer when the material is high;

i is exposed to temperatures and thus prevents the

tere diffusion of Al into the interior, whereby the decrease j

the Al concentration in the surface layer is delayed

is bound as well as the oxygen that is in the iron;

has penetrated. i

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According to the invention, a method for the production of molten aluminum-coated steel sheets with a low yield strength and high resistance to high-temperature oxidation is thus provided, which comprises the following steps: Production of a steel whose chemical composition consists essentially of 0.001-0.02 % Carbon,
0.05-0.30 % manganese,
0.05 - 0.50 % chromium,
0.01-0.10% aluminum and
0.10-0.50 % titanium

with the titanium content being at least ten times the percentage of carbon and the remainder being iron and inevitable incidental impurities, by normal converter refining and vacuum degassing, conversion into a plate shape by casting and spreading into plates or by conventional continuous casting, continuous hot-rolling the slab and winding at a temperature of at least 700 ⁰ C, cold rolling the resulting hot winding according to the usual pickling, heating the cold-rolled sheet at a temperature of at least 850 ⁰ C, and coating the sheet with molten aluminum by means of a hot-dip -Coating device for in-1-line spraying with a non-oxidizing furnace.

In a preferred embodiment, the contents for the individual components are 0.001-0.010 % carbon, 0.05-0.20 % manganese, 0.07-0.45 % chromium, 0.02-0.05 % aluminum and 0.15 - 0.40% titanium, the titanium content being at least twenty times the percentage of carbon.

In a further preferred embodiment, the carbon content is 0.001-0.007 %, the manganese content 0.10-0.17 %, the chromium content 0.07-0.42%, the aluminum content 0.03-0.041 % _t and the titanium content 0, 19 - 0.23 %, with the titanium content min-

1 30047/0522

is at least thirty times the percentage of carbon, the temperature for winding up the hot winding is approximately 720 to 730 ^° C. and the heating temperature for the coating is in the range from approximately 860 to 900 ^° C.

The reasons for the numerical stated in the main claim Limitations are given below.

The lower the carbon content, the more the quench aging effect is reduced. It is therefore desirable to reduce the carbon content as much as possible. However, it is not easy to reduce the carbon content to a percentage below 0.001% even when using a modern steelmaking process in which vacuum degassing is used. If the effect can be achieved, the process is not economical. Thus, the lower limit of the carbon content is set at 0.001%. The definition of the upper limit at 0.020 % has its own! The reason is that if the carbon content is above this limit, the amount of titanium which is added to prevent the undesirable aging quenching effect caused by the carbon would have to be increased in an uneconomical manner.

The reason for setting the manganese content at 0.05 to! 0.30 % is the difficulty of obtaining a steel whose Mn content is below 0.05 % in the usual steelmaking process. If the Mn content exceeds 0.30% , the steel becomes hard and thus has a high yield strength.

The reason for setting the chromium content at 0.05 to 0.50 % is that chromium in an amount less than 0.05 % does not give a sufficient effect of lowering the stretching ratio and, on the other hand, a chromium content more than lowers 0.50 % also has this effect.

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S ζ ~ 310185Q s

Aluminum is used for deoxidation of the molten steel, and is particularly relevant in the present process \ an important role as a material for Vordesoxidierung, ^WEL; ches prevents the waste of Ti. From this point of view, the lower limit of the Al content was given as 0.01%. However, if the Al is added in an amount of more than 0.10 % , the surface properties and formability of the steel sheet obtained are deteriorated.

The following is the reason for limiting the Ti content; to 0.10 to 0.50% and ten times the carbon content. If the Ti content is less than 0.10 %, then! the effect of improving the high-temperature oxidation resistance as indicated by the oxidation weight increase becomes insufficient although the yield strength is sufficiently low. On the other hand, if the Ti content exceeds 0.50%, the material becomes hard and loses its low yield strength property although the oxidation weight gain becomes smaller. Is the Ti content; below the ten times the carbon content, the \ binding of carbon with titanium is not sufficient, ^whereby: an increase in the yield strength and an increase in
Oxidation weight gain, thereby eliminating the benefits of the invention.

In the process according to the invention, Si, P and S may be present as inevitable impurities to the extent that
is normal and common in such steels. Nitrogen and
Oxygen can be present to the extent without inconvenience; be, which is usually achieved in the vacuum degassing process. ;

The reason for fixing the winding ^{temperature to at least 700 °} C. is that at a lower temperature, the softening of the material, which is due to the agglomeration

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and the growth of the Ti precipitate, which is formed by bonding the carbon with Ti, is insufficient, and thus one of the features of the invention is lost. Further, it is required that the cold-rolled sheet must be heated to at least 850 ⁰ C in the aluminum coating line before it enters the coating bath, i to impart a glowing effect to the cold-rolled plate so that the Ti precipitate further agglomerated to form larger particles and thus softens the material.

In the method according to the invention, the composition of the Substrate steel only differs from substrate steels in this way of the method of the aforementioned Japanese Patent Publication No. 35532/76 that the steel of the present Invention contains aluminum, which was intentionally added. The procedure, however, is completely different from the method of the patent mentioned.

In the following, the invention will be explained in detail on the basis of experimental results.

Steel samples, the compositions of which are given in Table 1: were obtained by converter refining and vacuum degassing manufactured. The blocks were a flat rolling mill and continuous | subjected to thorough hot rolling and the rolled products were 'at different temperatures, which are indicated, j

wound up and there were hot windings with a thickness of 2.5 mm! obtain. After normal pickling, the hot windings * were rolled into cold-rolled sheets of 0.8 mm thickness. The cold-rolled sheets produced in this way were heated to different temperatures and coated with aluminum (60 g / m ² ) by means of a hot dip coating device for in-1ine annealing! treatment (in practice a modified Sendzimir device) J Gen with a non-oxidizing furnace under the usual Bedingun-. The coated aluminum panels were subjected to a Mate \

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Hold and subjected to an oxidation test. The results: (mechanical properties and oxidation weight increase) are given in the same table. The material tests were carried out on samples that were prepared in accordance with JIS (Japanese
Industry standard) Z-2201 No. 5 and cut out in the direction of rolling. The oxidation test consisted of five repeated runs of a cycle in which the
Samples were each kept at 830 ^° C. in the atmosphere for 48 hours and subsequently cooled to room temperature. ^!

In Table 1, Samples D, E and F fall within the composition range of the invention, and F is within the invention with respect to the heating temperature before coating. The table shows that only materials are obtained which both relate to
excellent in moldability and oxidation resistance
are when all three factors of the composition of the substrate j steel, the winding temperature and the coating temperature j for meet the conditions defined according to the invention.

A comparison of samples A and B shows that a decrease in the Mn content leads to a decrease in the yield strength with wearing. A comparison of B and C shows that the addition of Ti i

i also contributes to reducing the yield strength. Of the

Comparison of C and F shows that the combined addition of Ti
and Cr also contributes to lowering the yield strength .;

Table 2 shows the mechanical properties of the aluminum coated steel sheet samples obtained by producing the
Steels with the specified compositions and their treatment in the manner described above were produced.

In accordance with this table, it should be noted that
Cr is effective in reducing yield strength when it is present in an amount of about 0.05 to 0.50%.

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Table 3 shows the mechanical properties and the weight increase in oxidation of the aluminum-coated steel sheet j samples were prepared by manufacturing of steels with \ the compositions indicated and their treatment in the manner described above. It can be seen from this table that when the addition of Ti is 0.1 % or more and the Ti content is more than ten times the amount of carbon, the effects of lowering the yield strength and increasing the weight j due to oxidation are obtained. As can be seen from sample G, the yield strength increases again when the Ti content exceeds the value of 0.5%.

Table 4-2 gives the results of the same tests that were carried out as described above on samples prepared in the above-mentioned manner from steels with the compositions shown in Table 4-1. This table shows that at a winding temperature of; less than 700 ⁰ C the softening of the material is not sufficient and that with a heating temperature before the coating! from 850 ^° C. or above the softening is remarkable.

Preferred embodiments of the invention are described below. <

Example ! _

Blocks having compositions shown in Table 5 as Sample No. 1 and No. 2 were vacuum degassed of molten steel produced in an LD converter was obtained, thereby reducing the contents of C and O, and subsequently the composition was adjusted by j Addition of iron alloys such as ferrochrome, j Ferrotitanium, Ferromanganese, etc. The blocks were made into sheets of j rolled and the sheets were hot rolled to 2.5 mm thick j

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hot windings under the conditions given in Table 6; After pickling, the hot windings were cold-rolled to 0.8 mm thick sheets. The cold-rolled sheets were ' coated with aluminum by means of a hot dip coating

i device for in-1 ine-Gllih treatment with a non-oxidie!

producing furnace (modified Sendzimir device) among the in i Table 6 specified conditions. The mechanical properties and the increase in oxidation weight of the aluminum-coated in this way Steel sheets which were tested in the manner described above are shown in Table 6 represents. Both sheets show excellent properties - low ones Tensile strength and high oxidation resistance at ho-; hen temperatures.

B is ρ ie 1

Panels with compositions shown in Table 5 as Sample No. 3 ^ and No. 4 were given by continuous casting obtained after the melting indicated in Example 1. The panels became aluminum-coated steel sheets after Process described in Example 1 processed. The mechanical properties and the test results of the thus obtained Steel panels tested according to the procedure described in Example 1 are shown in Table 6. These sheets have excellent properties that match the properties of the sheets according to Example 1 are comparable.

The products according to the invention are suitable for the production of parts j of complicated shape, which at high temperatures | such as exhaust gas treatment devices for machines with internal combustion. J

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TABLE 1

σ
cn
ro

PT * - Chemical composition Mn 0 Ti Cr Al Winding
temperature
at the hot
rolling Temp. Of
cold
rolled
Sheets Mechanical own
societies YP
kg / mm * El
'■% Weight
increasing
at Oxi Remarks A.
B. C. 0.27
0.15 0 - - 0.03
0.04 ( ⁰ C) at the Be
layers
( ⁰ C) TS
kg / mm ² 22nd
19th 49
49 dation
(g / m ² ) C. 0.007
0.006 0.13 0 .21 - 0.04 570
560 870
880 34
33 15th 51 182
138 Comparative
stole
Il D. 0.007 0.13 0 , 23 0.11 0.04 710 890 31 16 48 78 Il E. 0.006 0.11 , 20 0.14 0.03 550 890 32 15th 51 49 M. F. 0.004 0.12 , 23 0.13 0.04 730 810 31 13th 53 47 M. 0.005 720 890 31 43 Invention
more appropriate
stole

TS: tensile strength

YP: yield strength El: elongation

TABEL

j rehearse C h e m i watch together settlement U) Al Mechanical properties El
% ι
1
i
Notes j
I.
I.
I. ^A. C. Mn Ti Cr 0.03 TS
Kg / mm YP
Kg / mm ² 47 Comparative 1
Stole ! B. 0.00? 0.14 0.19 - 0.05 32 16 48 Comparative:
Stole ; C. 0.006 0.15 0.22 0.03 0.04 31 15th 51 ι
Invention
moderate steel D. 0.004 0.17 0.20 0.0? o.o4 31 13th 52 Inventiveness
moderate steel E. 0.005 0.15 0.18 0.16 0.05 32 13th 51 Invention
moderate steel "F. 0.004 0.13 0.19 0.30 0.03 31 14th 49 Inventiveness
moderate steel G 0.007 0.14 0.22 0.42 0.05 32 14th 46 Comparative
stole 0.004 0.11 0.19 0.58 32 17th

TS: tensile strength YP: yield strength El: elongation

TABEL

C h e m i s before Zusa mmense payment (%) Mechanical properties El Weight to Remarks rehearse TS YP % assumed
oxidation C. Ti Cr Ti / C Kg / mm ² Kg / mm ² g / m ² Comparative
stole A. 0.016 0.13 0.11 8th 19th 118 Inventive
moderate steel B. 0.011 0.12 0.1Λ 11 32 16 .8th 61 Comparative
stole C, 0.007 0.08 0.12 11 33 17th 52 92 Inventiveness
moderate steel D. 0.006 0.18 0.11 30th 30th 13th 50 LQ Inventiveness
moderate steel E. 0.007 0.23 O.I5 33 32 1* Zj.9 39 Inventiveness
moderate steel F. 0.006 0.3 ^ 0.12 57 33 17th ⁵⁷ Comparative
stole G 0.017 O.56 0.10 33 38 2k 69

TS: tensile strength YP: yield strength El: elongation

CX) cn O

TABLE 4-1

Si

Cr

Al

Ti

Ti / C

0.006 0.02 0.12 0.008 0.006 0.10 0.02? 0.21 35

TABLE 4-2

Hot whale
worked z-condition Temperature of
cold rolled Mechanical properties El
% Weight
increase Remarks Endbear
processing
Temp.
( ⁰ O Winding
lung
Temp.
(° c; Sheets at the Be
layers
( ⁰ O TS
Kg / mm YP
Kg / mm ² at
oxidation
g / m ² Comparative
stole 850 680 905 33 18th h ₅ 89 Comparative
stole 830 650 890 33 17th 101 Comparative
stole 8 ^ 0 730 810 32 15th 52 76 Inventiveness
moderate steel 850 720 860 31 13th 53 ^ 7 Inventiveness
moderate steel 860 730 880 30th 13th 39

TS: tensile strength YP: yield strength El: elongation

TABLE 5

ο
cn
K)

sample C. Si C h e mi watch sa mines set too ng (%) Al 0 Ti Ti / C 1 0.007 0.02 Mn P. S. Cr 0.028 0 .19 27 2 0.006 0.03 0.12 0.009 0.C09 0.11 0.034 0 .21 35 3 0.008 0.04 0.11 0.008 0.007 0.10 Ο.Ο38 0 .20 25th 4th 0.007 0.05 0.13 0.009 ο.οοβ 0.14 0.041 .22 31 0.12 0.008 0.007 0.09

TABLE .6

sample Hot rolling be
conditions Temperature of
kait-rolled
Sheets at the Be
sen icht
( ⁰ O Mechanical properties j Weight gain
! would take 1
2
3
4th Endbear- winding-
processing temp.
^te r ^e c) co ! oxidation
TS YP El!
Kg / mm ² Kg / mm ² % I g / m ² 850 730
830 730
840 720
860 730 900 31 13 50; 46
880! 30 12 51! 48
i ■ I
890 I 30 13 52 I 39
880; 31 I3 51 I 54
; j

OO LT. CD

TS: tensile strength YP: yield strength El: elongation

Claims (2)

1 ichen a - us 0.001 - 0.02 0.05 - 0.30 0.05 - 0.50 0.01 0.10 0.10 0.50 Patent claims Process for the manufacture of molten aluminum coated steel sheets with low yield strength and high resistance to high temperature oxidation, characterized by the production of a steel, the chemical composition of which is essentially Carbon, Manganese, Chrome,! Aluminum and Ti tan, where the titanium content is at least ten times the percentage of carbon and the remainder of Iron and unavoidable accidental impurities! is available through normal converter refining and vacuum de- | gassing, transferring into a plate shape by casting and spreading into plates or by the usual continuous; Pouring, continuous hot rolling of the plate and coiling at a temperature of at least 700 ⁰ C, cold rolling the resulting hot winding according to the usual j pickling, heating the cold-rolled sheet at a, temperature of at least 85O ⁰ C, and coating the sheet with molten aluminum j by means of a hot-dip-coating-apparatus for in-1-line annealing treatment with one ^! non-oxidizing furnace. 2. The method according to claim 1, characterized in that the: carbon content 0.001 - 0.010%, the manganese content 0.05 - ^! 0.20 %, the chromium content 0.07-0.45 %, the aluminum content 0.02-0.05% and the titanium content 0.15-0.40% , the titanium content being at least twenty times the carbon content . 130047/0522 Process according to claim 2, characterized in that the carbon content 0.001-0.007%, the manganese content 0.10- ^: 0.17 %, the chromium content 0.07-0.42%, the aluminum content 0.03-0.041% and the titanium content 0.19 - is 0.23%, the titanium content is at least thirty times the carbon content, the temperature during the winding of the coil in the range of 720 is to 730 ⁰ C, and the heating temperature is in the coating is in the range 860-900 ⁰ C. 130047/0522