DE3101850C2 - Process for the production of molten aluminum coated, low carbon steel sheets with low yield strength and high resistance to high temperature oxidation - Google Patents

Abstract

A process is described for producing molten aluminum coated steel sheets having good formability and high resistance to oxidation at elevated temperatures. The process comprises making a steel containing 0.001-0.020% carbon, 0.05-0.30% manganese, 0.05-0.50% chromium, 0.01-0.10% aluminum and 0.10-0 Contains 50% titanium, the titanium content being at least ten times the percentage of carbon, the steel is formed into a hot winding at a winding temperature of at least 700 ° C, the hot winding is subsequently cold-rolled and the cold-rolled sheet is coated by Heating to a temperature of at least 850 ° C. by means of a hot dip coating device for in-line annealing treatment with a non-oxidizing furnace.

Description

0.001 to 0.02% carbon.
0.05 to 030% manganese.
0.05 to 0.50%
0.01 to 0.10%

0.10 to 0.5%
Remainder iron

Chrome.
Aluminum.
Titanium and

30th

0.001 to 0.01% carbon.
0.05 to 0.20% manganese.
0.07 to 0.45%
0.02 to 0.05%

0.15 to 0.40%
Rest of Risen

Chrome.
Aluminum,
Titanium and

and the titanium content is at least twenty times the carbon content will.

4. The method according to claim I or 2. characterized.

d.ili a steel for the production of the steel sheet, its chemical composition

0.001 to 0.007% carbon,
0.10 to 0.17% manganese,
0.07 to 0.42% chromium,
0.03 to 0.041% aluminum.
0.15 to 0.23% titanium and
Remainder iron

and the titanium content is at least thirty times the carbon content is used,
that the sheet is wound up at a temperature of 720 to 730 ^{0 C and}

that a heating temperature of 860 to 900 ⁰ C is maintained when coating with aluminum.

and the one following converter refining is still subjected to vacuum degassing.

that the wound sheet is cold-rolled after a conventional pickling treatment and
that the cold rolled sheet is heated again to a temperature of at least 850 ⁰ C, after which the coating is carried the sheet with geschmol- (I) zenem aluminum by the heated sheet passed through a nonoxidizing furnace and is then passed through the hot dipping bath.

2. The method according to claim 1, characterized in that that the hot rolling is carried out up to a thickness of (2) 2.5 mm, after which after the normal pickling the hot windings are rolled out to cold-rolled sheets of 0.8 mm thickness and (3) then be treated further.

3. The method according to claim I or 2. characterized in that for the production of the steel sheet a steel, its chemical composition

The invention relates to a method of manufacture of low carbon steel sheets coated with molten aluminum with low yield strength and high resistance to high temperature oxidation.

So far, steel sheets coated with molten aluminum (hereinafter simply as »Aluminum-coated steel sheets«) for purposes of use, with soft heat resistance and corrosion resistance were needed, mostly from cold-rolled sheets made from unskilled steels produced with low carbon content. However, it is known that aluminum-coated steel sheets that have been made from sheets of unskilled steels, suffer a deterioration in quality due to the quench aging caused by the rapid cooling during the coating thereby hardening the material.

The essential measures taken to prevent the above deterioration are:

Use of substrate blocks. which have been made of a steel from which Carbon and nitrogen that reduce aging cause have been removed as far as possible;

Addition of a carbide-forming element, for example titanium, in order to fix carbon and nitrogen in the substrate material;
Effect of aging of the aluminum-coated sheets, etc.

However, step (I) is not economical in that Case when the steel sheets with a hot dip coating device can be coated for in-line annealing treatment in a non-oxidizing furnace, although they are carried out in the usual steel production Application of decarburization annealing can be carried out.

Here and in the following, in-line annealing treatment is to be understood as meaning that the heated sheet is passed through a non-oxidizing oven and then passed through the hot dip bath. So it will modified a so-called Sendzimir system, as described in the "Handbook of Metal Surface Treatment", Kin / oku Hyomen Gijutsu Binran, page 490. This plant shows an oxidation furnace, a Reduction furnace and a cooling zone.

Step (2) is economical in and of itself, shows

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however, the disadvantage. that when applying opposite Steels with a low carbon content, which are only used in conventional converter processes be obtained, a considerable amount of titanium must be used. The highly oxidizable titanium generates a significant amount of oxide inclusions, causing deterioration in surface quality of the product is achieved. In the end, this measure is therefore neither economical still technically advantageous.

Measure (3) is economical. However, this treatment increases the iron-aluminum alloy layer, which has poor formability even when the aluminum coating under conditions which control the formation of the Fe-Al alloy layer. Thus, through this Treatment, if the property of the substrate material is also improved, the formability of the aluminum-coated Shift deteriorated.

From Japanese Patent Publication No. 35 532/76 there is a method for producing Aluminum-coated steel sheets known, which comprises the following steps:

Hot rolling of a steel consisting essentially of the consists of: 0.001 to 0.020% carbon, <0.05% silicon. 0.05 to 0.40% manganese. 0.10 to 0.30% chromium. 0.03 to 0.40% effective titanium (amount of titanium minus titanium in the oxide form), where the amount of titanium is at least four times the percentage of (C + N). <0.006% nitrogen. <0.020% Saucitoff and the remainder iron and unavoidable accidental cleansing in one Temperature of at least 800 "C, cold rolling of the hot sheets with a reduction of 40% or more. Annealing the rolled sheet at »00 to 950 ° C and immersing the sheet in an Al-Si alloy bath (<10% silicon) at 640 to 700 ° C for a period of time of up to 10 minutes.

The aluminum-coated steel sheet produced by this process has a tensile strength of 130 to 170 N / mm ² and an elongation at break of 44 to 47% in the state of a cold-rolled sheet 0.8 mm thick. Today, however, there is an increasing demand for materials that are easier to mold.

In DE-AS 22 58 286 objects coated with aluminum or aluminum alloys are made from Mild steel with a low carbon content, usually less than 0.1%, which at 815 C against Underlayer oxidation resistant are described. The carbon content is in the preamble of the claim 1 as »usually below 0.1%«, but gives the preferred composition according to claim 3 and according to the embodiment in column 8 a carbon content of 0.05 % By weight. The reduction of the carbon content is already a considerable problem in itself. Therefore, if it was even assumed that a carbon content of "0.001 to 0.02%". like him for that The present invention is defined by digsgm prior that is grasped by technology, this is by metallurgical Point of view not tenable. Ms already creates difficulties, the carbon content of steels reduce less than 0.05%.

According to US-PS J9 05 780 the Triigcrstahl of contain about 0.5 to about 3% chromium. As stated below, the reason for tlie down is the Chromium content specified as 0.05 to 0.50%. In this

ίο

Chromium has a reducing effect on the elasticity. However, if the chromium content exceeds 03%, this effect disappears. DE-AS 22 58 286 thus gives no teaching about the importance of the chromium content with regard to the stretching ratios for the purpose of the present invention, although the addition of chromium in steel is described, namely in a range from 03 to 3%.

In addition, the steel according to US-PS 39 05 780 should contain 0.8 to 3.0% aluminum, while the steel to be used in accordance with the present invention. an aluminum content of Should have 0.01 to 0.1%.

In column 3 of US-PS 39 05 780 are in lines 10 to 21 reasons given for the lower limits for chromium and aluminum, and it is also on the lines 22 to 27 state that a minimum silicon content of 0.4% is essential.

The last two references do not provide any information about the process steps involved in present invention are to be applied. According to the present invention, the hot rolled Sheets or strips are wound up before their temperature drops to 700 ° C. According to the status of Technique, the hot roll was wound at a temperature below 700 ° C or the RUIe was wound at a temperature not lower than 800'C as disclosed in Japanese Patent Publication No. 35 532/76. With the commonly used coating devices (Sendzimir devices) with continuous cold rolling and hot dipping, the final temperature is hot Rolling usually below 700'C. Therefore, if it is suggested, the hot rolling at

J) a temperature of not less than 700'C quit, additional measures are required. It is obvious, however, that it is easier and is more economical. the hot rolling temperature before finishing at a temperature vos: not less than

w 70O ¹⁵ C than keep the final temperature at a temperature of not less than 800 ° C / u.

Furthermore, the cold-rolled sheet must be heated to a temperature of at least 850 "C. Before of the present invention was in Japanese

■ <"■ Patent Publication No. 35 532/76 a method described in which the cold-rolled sheet was not heated to temperatures of at least 850'C. the Effect of heating the cold rolled sheet to a temperature of at least 850C is in the

'"Tables 4-1 and 4-2 made clear.

The invention is therefore based on the object of a streckbrrcs. easily deformable sheet steel with aluminum coating produce, so a low carbon content having steel sheets with good

i 'malleability, low yield strength and high durability against high temperature oxidation.

This object is achieved as can be seen from the preceding claims.
This solves the problem

(1) Decreasing the content of C and O in the substrate steel sheet by using a stainless steel degassing tank and prior deoxidation with aluminum in the steelmaking stage and reduction thereby brought about of the titanium hall, which is required to fix C and N. and governance of education of oxides;

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(2) Reduction of the manganese content, which the Yield strength increased, and addition of chromium, which reduces the yield strength;

Is prevented (3) promoting the agglomeration and growth of the precipitated Ti carbide by Aufwikkein the finished hot RoHe at a temperature of about 700 ⁰ C, whereby curing by formation of carbide of 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 line apparatus for in-annealing treatment in a non-oxidizing furnace.

The method according to the invention is further characterized in that the high-temperature oxidation resistance The material is increased by the combined addition of titanium and chromium. That means that the Oxidation weight gain at high. Temperatures is significantly reduced due to the decarburization of the Substrate material and is further improved by adding titanium. The reasons for this are as follows:

1I) By the decarburization or addition of titanium becomes improves the purity of the ferrous material. The aluminum diffuses from the aluminum layer easily into the iron substrate, and an Al diffusion layer is formed which is excellent Has high temperature oxidation resistance.

(2) The Ti in the material diffuses toward the surface and forms one enriched in Ti Layer below the Al diffusion layer if the material is exposed to high temperatures, thus preventing the further diffusion of Al into the interior, thereby decreasing the Al concentration delay in the surface layer! is bound as well as the oxygen that is in the iron has penetrated.

The reasons for the numerical restrictions are given below.

The lower the carbon content, the more the quenching aging effect becomes decreased. That is why it is desirable to use the C-Gchalt as much as possible. However, it is not easy to calculate the carbon content as a percentage of less than 0.001%, even when using a modern steelmaking process, in which vacuum degassing is used. If the effect can be achieved, so it is Process not economical. Thus, the lower limit of the carbon content is set at 0.001%. The reason for setting the upper limit at 0.020% is that when the carbon content is above this limit the amount of titanium needed to prevent the undesirable effect caused by dark carbon Quenching aging effect is added in uneconomical Would have to be increased wisely.

The reason for setting the manganese content at 0.05 to 0.30% is the difficulty in obtaining steel. acs ^r .en Mn content below O.C5% is in the usual steelmaking process. If the Mn content exceeds 0.30%, the steel becomes hard and thus has a large elongation.

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

Aluminum is used to deoxidize the molten material

Steel is used and plays an important role as materia, especially in the method according to the invention! for the pre-deoxidation. which prevents the waste of Ti. From this point of view, the the lower limit of the Al content is specified as 0.01%.

However, if the Al is more than 0.10% added, the surface properties and formability of the obtained steel sheet become worsened.

The following is the reason for limiting the Ti content to 0.10 to 0.50% and ten times of the carbon content. Is the Ti content less than 0.10%. so there will be the effect of improving the high-temperature oxidation resistance. as indicated by the increase in weight of oxidation, not sufficient, although the elongation; stiffness is sufficiently low. On the other hand, if the Ti content exceeds 0.50%, it becomes Material hard and loses its property of low yield strength, although the oxidation weight increase becomes less. If the Ti content is below ten times the carbon content, then If the bond between the carbon and titanium is insufficient, this increases the yield strength and an increase in oxidation weight gain, thereby providing the benefits of the invention be eliminated

In the process according to the invention, Si. P and S to be present as inevitable impurities to the extent that normal unc ¹ is üb'ich in such steels. Nitrogen and oxygen can be present without inconvenience to the extent that is usually achieved in the vacuum degassing process.

The reason for fixing the winding temperature to at least 700 ° C is that at a 4, lower temperature the softening of the material, which is due to the agglomeration and the growth of the Ti precipitate, which is formed by bonding of the carbon with Ti becomes, is not sufficient 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 Aluniinium coating distance before egg enters the coating bath to impart a glowing effect to the cold-rolled plate so that the Ti-Niederschla.n further agglomerated to larger Particles and thus the material softens.

In the method according to the invention, the composition is of the substrate steel only thereby different from the substrate steels of the process according to the Japanese Patent Publication No. 35 532/76 mentioned earlier that the steel of the present invention Contains aluminum which has been added on purpose. The procedures, however, are completely different from each other.

b5 The invention is detailed below explained on the basis of experimental results.

Steel samples, the compositions of which are given in Table 1, were obtained by converter refining

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liiul \; ikiium-l.; ili '.: sun;' ! 1 (. ¹ IL ¹ CU ¹ Ml Ι), ι · IiIoAc> \ ■ Ii .! F ■ a I l; i \ s; i 'χlt.in_ ^ uiul koniiuiiicrlii ίκ · ιη i I, ιHu, ii / ·. ■ subject, ιπκ! the :: rolled products were ι different rcmperaluren. di. N; i.-fi the γ> ιί ■ ι:, ιI <_ ■ π pickling, the hot sheets / ιι cold-rolled ν mi os nm thicknesses were rolled out. The cold-rolled sheets produced in this way were aiii different lc'ii |) eraiurcn eri.itz: utiil coated with aluminum (hi) i; in ') iiiitiel ·. e: no 1 leilJtaueh-Hosehichumgsvorrichtuiii! for in-liiiL · (iiiih treatment in a nicliti) \ idiereiuleii oils (practically a modified Sencl / imir device) under the usual conditions. The aluminum-coated ion sheets were subjected to a Maienaltesi and an oxidation test. The results (see mechanical properties and oxidation (weight / unahine) are given in the same table. The material

ICSis WlIfUCM ii'iii iVi'ibCü uiirchpv'iihr ;. d: C J.'C "i; i! ' 'Y-J!

Regulation JIS (Japanese Industrial Standard) / -22Ol> No. 5 and cut out in the direction of rolling. The oxide ion test includes five repeated passes of a cycle in which the samples are each heated to 830 C in an atmosphere for 4K Hours were held and subsequently on room; -, temperature were cooled.

In Table I, Samples D., E and F fall within the compositional range of the invention, and E is within the invention with respect to the temperature before coating. The table shows that.! only then in Materials are obtained that are both related to the Excellent moldability and oxidation resistance are if all three factors of the composition of the substraht steel. the winding temperature and the viewing temperature the invention meet specified conditions.

The comparison of samples Λ and B results. that a decrease in the Mn content leads to degradation contributes to the yield strength. A comparison of B and C shows that the addition of Ti also reduces -ίο contributes to the yield strength. Comparison of C and F shows that the combined addition of Ti and Cr also contributes to reducing the yield strength.

Table 2 shows the mechanical properties of the aluminum-coated steel sheet samples, welehe by producing the steels with the specified compositions and treating them in the were prepared as described above.

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

Table 3 shows the mechanical properties and the weight gain upon oxidation of the aluminum-coated steel sheet samples which were produced by producing the steels with the specified compositions and treating them in the manner described above. From this table it appears that are at a Ti-addition of 0.1% or more and at a Ti-content of more than ten times the amount of carbon to the effects of reducing the Mreckfestigkeit and animal (lew ichtszun.ihme achieved by oxidation As with the sample (i is to be taken.) The yield strength increases again when the IiC 'exceeds the value of 0.3'! O.

I'.ibelle 4-2 gives the results of the same tests. which were carried out as described above with samples which are in the above - \ rt were made from steels with the compositions given in Table 4-1. From this table result: it turns out that with a winding temperature of less .ils 700 C does not soften the material is sufficient and that at a heating temperature before the coating of 850 C or above Softening is remarkable.

Preferred embodiments of the invention are described below.

Example I.

Blocks; ΐ;: ί together

ck'hc

indicated as Samples No. I and No. 2 by vacuum degassing of molten steel. tier was made in an I.D converter, whereby the contents of C and O have been reduced, and subsequently the composition was adjusted by adding iron alloys such as Ferrochrome. Ferrotitsn. Ferromanganese etc. The Blocks were rolled into sheets and the sheets were rolled into 2.5 mm thick hot sheets under the conditions given in Table 6. After pickling, the hot sheets were cold rolled to 0.8 mm thick sheets. The cold-rolled sheets were loaded with aluminum by means of a I hot dip charging device for annealing treatment in a non-oxidizing oven (modified Sendzimir device) under those given in table b Conditions. The mechanical properties and the oxidation weight gain of the thus obtained Aluminum-coated steel panels tested in the manner described above are shown in Table b shown. Both sheets show excellent properties - low and high yield strength Oxidation resistance at high temperatures.

Example 2

Panels having compositions shown in Table 5 as Sample No. 3 and No. 4 were prepared continuous casting obtained according to the melting indicated in Example I. The panels were processed into aluminum-coated steel sheets according to the method described in Example 1. the mechanical properties and the test results ^ r thus obtained steel sheets, which were tested according to the method described in Example 1, are in Table 6 given. These sheets have excellent properties. those with the properties of Sheets according to Example 1 are comparable.

The products according to the invention are suitable for the production of parts with a complicated shape that are used in high temperatures are used, such as exhaust gas treatment devices for machines with internal combustion.

Chemical composition Mn Ti 9 Al Wick 31 01 850 marriage l-igen- D. 10 Remarks ι lung . ·? C. tempe- SF Weight ί rature Temp. Mechanis increase ι Table 1 at the the cold stocks at Oxi i Per composition (%) love- rolled ZF (%) dation I. ben 0.27 - 0.03 rolling Sheets 49 I. 0.15 - Cr 0.04 ( ⁰ C) at the Be (N / mm ² ) 49 ) 0.007 0.13 0.21 0.04 570 layers 220 51 Reference steel ι 0.006 0.13 0.23 0.04 560 190 48 (g / nr) Comparison steel t 0.007 0.11 0.20 0.03 710 ( ⁰ C) (N / mnr) 150 51 182 Reference steel 0.006 OJ 2 0.23 0.04 550 870 340 160 53 138 Comparison steel 0.004 Tensile strenght. 730 880 330 150 78 Comparison steel Λ 0.005 Extension wedge - 720 890 310 130 49 Inventive B. Strain. - 890 320 47 moderate steel C. Table 2 - 810 310 43 D. 0.11 890 310 E. 0.14 F. 0.13 7.F = SF = ύ -

Samples Chemical Composition (%) C Mn Ti

Cr

Al

Mechanical properties

ZF SF D

(N / mnr) (N / mnr) (%)

Remarks

A 0.007 0.14 0.19 Cr - 0.03 * 20 160 SF D. 47 Comparison steel ί ο 0.006 0.15 0.22 0.03 0.05 ■! 10 150 48 Comparison steel H C 0.004 0.17 0.20 0.07 0.04 310 130 (N / mm ³ ) (%) 51 Inventiveness 0.11 190 45 moderate steel D 0.005 0J5 0.18 0.14 0.16 0.04 320 130 160 49 52 Inventive moderate steel E 0.004 0.13 0.19 0.12 0.30 0.05 310 140 170 48 51 Inventive 0.11 130 52 moderate steel F 0.007 0.14 0.22 0.42 0.03 320 140 49 Inventiveness f ■ ^: 0.15 140 50 moderate steel 1 G 0.004 0.11 0.19 0.58 0.05 320 170 46 Comparison steel S. VF = tensile strength. 0J2 170 49 SF = yield strength. D = elongation. 0.10 240 41 I. Table 3 Si Samples chemical Composition (%) Mechanical properties Weight Remarks C. Ti Ti / C ZF increase
at Oxi S. dation (N / mm ² ) (g / m ² ) A 0.016 0.13 8th 340 118 Comparison steel B 0.011 0.12 11th 320 61 Inventiveness moderate steel U C 0.007 0.08 11th 330 92 Comparison steel % D 0.006 0.18 30th 300 48 Inventiveness ■ Ä moderate steel S. E 0.007 0.23 33 320 39 Inventiveness moderate steel F 0.006 0.34 57 330 57 Inventiveness 1 moderate steel G 0.017 0.56 33 380 69 Comparison steel ZF = tensile strength SF = yield strength. D = elongation.

11th

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12th

Table 4-1 Si ( ⁰ C) Mn P S. Cr (N / mm ^! L (%) Al Ti Ti / C C. 0.02 680 0.006 0.10 180 44 0.027 0.21 35 0.006 650 170 45 Table 4-2 Ileißwalz conditions
Finishing- Aul'wick-
temp. lungs temp. 730 0.12 0.008 Mechanical properties
ZF SF D 150 49 Weight
increase
at Oxi
dation Remarks ( ⁰ C) 720 (N / mm ² ) 130 52 (g / nr) 850 730 Temperature of
cold rolled
Sheets at
Coating 330 130 53 89 Comparison item 830 ( ⁰ C) 330 101 Comparison steel 840 905 320 76 Comparison steel 850 890 310 47 Inventiveness
moderate steel 860 810 300 39 Inventiveness
moderate steel 860 880

ZF = tensile strength. SF = yield strength. D = elongation.

Table 5

Sample Chemical Composition (%) C Si Mn

Al

Ti

1 0.007 0.02 Table 6 0.12 CC) 0.009 0.009 0.11 0.028 0.19 27 2 0.006 0.03 sample 0.11 730 0.008 0.007 η in 0.034 0.2! 35 3 0.008 0.04 0.13 730 0.009 0.006 0.14 0.038 0.20 25th 4th 0.007 0.05 1 0.12 720 0.008 0.007 0.09 0.041 0.22 31 2 730 3 : Hot rolling conditions
Finishing- winding-
processing temp. lungstcmp. Temperature of
cold rolled
Sheets at
Coating Mechanical
ZF properties
SF D. Weight to
assumed
oxidation 4th ( ⁰ C) co (N / mm ² ) (N / mm ² ) (%) (g / m *) ZF =
SF =
D = 350 900 310 130 50 46 830 880 300 120 51 48 840 890 300 130 52 39 860 880 310 130 51 54 Tensile strenght.
Yield strength.
Strain.

Claims (1)

31 Ol Patent claims: 1- A process for the production of molten aluminum coated steel sheets having a low carbon content and having a low yield strength and high resistance to high-temperature oxidation, in which first a steel sheet containing carbon, manganese, chromium. Aluminum and titanium as well as iron with the inevitable incidental impurities and a titanium content that is at least ten times the percentage of carbon, by normal converter refining, conversion into a plaite form by casting and spreading into plates or by conventional continuous casting and continuous hot rolling of the plate and the rolling stock is wound up at a temperature of at least 700 ^° C., which is then coated by dipping into molten aluminum, characterized in that, that a steel is used for the production of the steel sheet, its chemical composition essentially> 5 15th