【DESCRIPTION】
【Invention Title】
HIGH-MANGANESE STEEL WITH SUPERIOR COATING ADHESION AND METHOD FOR MANUFACTURING HOT-DIP GALVANIZED STEEL SHEET FROM SAME
【Technical Field】
[0001] The present disclosure relates to a high-manganese steel with superior coating adhesion and a method for manufacturing a hot-dip galvanized steel sheet from the same, and more particularly, to a high-manganese steel having superior coating adhesion as well as high ductility and high strength, used for automobile bodies and structural members and prevents coating failures by minimizing formation of an oxide film on a surface thereof in a hot-dip galvanizing using the high-manganese steel, and a method for manufacturing a hot-dip galvanized steel sheet from same.
【Background Art】
[0002] As high strengthening of automobile bodies and structural materials is required in view of improvements in fuel efficiency and stability resulting from the lightening of automobiles, many kinds of high strength steels for automobiles have been developed. However, since high strengthening decreases ductility in most steel sheets, many types of steel sheets resultantly have many limitations in the processing thereof to form parts. To solve the problem of a decrease in ductility due to the high strengthening of steel sheets, many studies have been undertaken, and as a result of the studies, austenite-based high-manganese steel (see JP1992-
Page 2
259325, WO93/013233, WO99/001585, WO02/101109, and the like) has been proposed in which 5-35% by weight of manganese is contained in steel to induce twin boundary defects deformation during plastic deformation of steel, thereby remarkably improving ductility.
[0003] Then, the high-manganese steel has a problem in that the coating adhesion of the hot-dip galvanized steel may be relatively poor. That is, since hot-dipped galvanizing of a steel sheet improves corrosion resistance, weldability and paint coatability, a majority of steel sheets for automobiles are hot-dip galvanized. Then, hot-dip galvanized steel sheets which use high-manganese steel as a material to be galvanized are annealed in a nitrogen atmosphere containing hydrogen for the securing of desired material qualities and surface activation (reduction). Such an atmosphere is a reducing atmosphere with respect to matrix iron (Fe) that is a material to be galvanized but acts as an oxidizing atmosphere with respect to elements which are easily oxidizable, such as manganese (Mn), silicon (Si), aluminum (Al), and the like, in high-manganese steel. Therefore, when high-manganese steel containing a large amount of Al, Si, and the like, as well as Mn being annealed for recrystallization in such an atmosphere, alloy elements are selectively oxidized by a trace of moisture or oxygen contained in the atmosphere to form a Mn, Al, Si surface oxide layer on a surface of the matrix material (to be galvanized). Thus, when high-manganese steel containing a large amount of Al, Si, and the like is used as a material to
Page 3
be galvanized, coating failures occurs due to a surface oxide formed during an annealing process that is a pre-coating process, or even in the case that a galvanized layer is formed, the galvanized layer may be delaminated during a processing process.
[0004] To date, as publicly disclosed art related to preventing coating failures of a high-manganese and hot-dip galvanized steel sheet, there are provided 1) a plating method (Korean Patent Application Publication No. 2007-0067950) in which silicon (Si) is added to form a thin Si oxide film on a surface, thus suppressing the formation of an Mn oxide, 2) a method (Korean Patent Application Publication No. 2007-0107138) in which a 50 nm to 1000 nm of aluminum layer is deposited by a physical vapor deposition (PVD) followed by annealing to prevent the formation of an Mn oxide, and the like.
[0005] However, since in the case of method 1, Si has a higher oxidation potential than Mn to form a stable film type oxide, it is impossible to improve wettability with molten zinc. Also, since method 2 requires a vacuum deposition process followed by annealing for galvanizing, Al, a material to be galvanized, is easily oxidizable, and the deposited Al forms an oxide having poor wettability due to moisture or oxygen contained in the annealing atmosphere, method 2 may rather deteriorate galvanizability.
[0006] As described above, in the existing publicly disclosed art, when high-manganese steel containing a large amount of Mn
Page 4
is used as a plating material, since thick Mn, Al, Si oxides or composite oxides thereof formed during the annealing cause coating failures, or a galvanized layer is formed, the galvanized layer simply covers a thin oxide layer without an interfacial inhibition layer at an interface between the plating layer iron, coating delaminations in which the galvanized layer is separated from matrix iron during a processing process may occur.
【Disclosure】
【Technical Problem】
[0007] An aspect of the present disclosure may provide a high-manganese steel with superior coating adhesion, which prevents failures while satisfying requirements for high strength and ductility.
[0008] aspect also method manufacturing hot-dip galvanized sheet from above-described in are suppressed.
【Technical Solution】
[0009] According to an disclosure, include, by weight %: C: 0.3-1%; Mn: 8-25%; Al: 1-8%; Si: 0.1-3.0%; Ti: 0.01-0.2%; Sn: 0.06-B: 0.0005-0.01%, remainder being Fe unavoidable impurities.
[0010] The further at least one Ni: 2% Cr: 2.0%.
[0011] another
Page 5 a method for manufacturing hot-dip galvanized steel sheet, the may include: preparing sheet having composition including, by weight %: C: 0.3-1%; Mn: 8-25%; Al: 1-8%; Si: 0.1-3.0%; Ti: 0.01-0.2%; Sn: 0.06-and B: 0.0005-0.01%, with remainder being Fe unavoidable impurities; annealing under conditions dew point temperature of -30°C to 60°an 750°850°C; dipping annealed in hot galvanizing bath including 0.2-0.25% at 480°520°C.
[0012] The high-manganese further least one Ni: 2% Cr: 2.0% weight.
Page 6
【Advantageous Effects】
[0013] As set forth above, according to exemplary embodiments of the present disclosure, a high-manganese and hot-dip galvanized steel sheet with superior surface quality as well as with high strength and workability may be provided by preventing occurrence of coating failures due to alloy elements such as a large amount of Mn, Al, and Si.
【Best Mode】
[0014] Hereinafter, embodiments of the present disclosure will be described in detail. The may, however, embodied many different forms and should not construed as being limited to set forth herein. Rather, these are provided so that this thorough complete, fully convey scope those skilled art.
[0015] inventors have found for obtaining high-manganese steel with superior mechanical properties while preventing occurrence coating failures, compositions C, Al, Si, Ti, Sn, B, like, addition a high content manganese, need controlled within proper ranges, completed invention.
[0016] That is, confirmed from studies determination formation an annealing oxide is only suppressed by reducing atmosphere (strictly speaking, oxidizing respect alloy elements) failures due prevented,
Page 7 steel with superior coating adhesion as well strength and ductility may be obtained by adding an element capable of preventing occurrence failures setting the content in consideration synergy another added order to allow high-manganese exhibit ductility, have developed this invention.
[0017] That is, present disclosure is characterized controlling compositions steel, more particularly, C, Mn, Si, Ti, Sn, B, like, follows.
[0018] Hereinafter, reason for which components a matrix sheet are selected limited range will described. It should noted that each component expressed percentage (%) weight unless otherwise specified.
[0019] C: 0.3-1%
[0020] Carbon (C) contributing stability austenite, advantageous amount thereof increases, preferably 0.3% or so obtain effect. However, when C exceeds 1%, austenite phase greatly increases decrease workability, due transition deformation behavior slip. Therefore, upper limit 1%.
[0021] Mn: 8-25%
[0022] Mn essential
Page 8 which remarkably improves ductility while increasing strength because it induces twining when the steel is plastically deformed due to austenite phase stability. To obtain such an effect, advantageous that Mn be added in amount of at least 8%. However, exceeds 25%, high temperature decreased generate cracking a casting process, oxidation rapidly occurs reheating process for hot rolling deteriorate surface quality product, (selective oxidation) annealing followed by hot-dipped galvanizing plating properties, and production costs increase large Mn. Therefore, limited 25% or less.
[0023] Al: 1-8%
[0024] While Al typically as deoxidizer, present disclosure prevent delayed fracture. component stabilize ferrite phase, but increases stacking fault energy slip plane suppress formation ε–martensite thereby improving fracture resistance. In addition, even low, since suppresses ε-contributes minimization exhibit effect high-manganese steel, preferably 1% more. 8%, twin, decreasing deteriorating castability continuous casting,
Page 9 and also, since Al is an easily oxidizable element, surface-oxidized in annealing process followed by hot-dipped galvanizing to deteriorate wettability with molten zinc. Therefore, the upper limit of limited 8% or less.
[0025] Si: 0.1-3.0%
[0026] When silicon (Si) added alone, Si saturated form a dense film type oxide galvanizability thus it preferable that not added. However, when combination Mn, restrained Mn changed into particle oxide, thickness also decreased. In order obtain above-described effect, proper amount 1-5 times greater than Si/0.2), exceeds this range, are formed reduced cause coating failures delaminations. excessive addition preferred. 3% more, ductility high-manganese steel rapidly reduced. Also, less 0.1%, strength improvement effect low. lower 0.1% more.
[0027] Ti: 0.01-0.2%
[0028] Titanium Ti) solid-solutioned columnar grain boundary increase melting temperature Al-
Page 10 low melting point compound, thus preventing the formation of a liquid phase film at temperature not higher than 1,300°C, and has high affinity with nitrogen to act as nucleus for precipitation aluminum nitride (AlN) which is cause columnar grain boundary brittleness coarse state, strengthening boundary. However, when added amount Ti less 0.01%, there no effect, exceeds 0.2%, an excessive segregated in embrittlement. Therefore, limited 0.01-0.2%.
[0029] Sn: 0.06-0.2%
[0030] Since tin Sn) noble element does form thin oxide temperatures by itself, Sn precipitated on surface matrix annealing prior hot dip galvanizing suppress pro-oxidant such Al, Si, Mn, or like from being diffused into forming oxide, thereby improving galvanizability. 0.06%, effect distinct increase suppresses selective whereas causes shortness deteriorate workability. upper limit less.
[0031] B: 0.0005-0.01%
[0032] Boron B) solid-solutioned 1000°C creation
Page 11 movement of vacancies, thus strengthening columnar grain boundaries. However, when the added amount B is less than 0.0005%, there no effect, and exceeds 0.01%, generates a large carbides nitrides to act as nucleus for precipitation aluminum nitride help coarse nitride, thereby embrittling Also, in an aspect galvanizability, 0.01% or more, boron oxide formed by boundary saturation oxidation annealing followed galvanizing. Therefore, limited 0.0005-0.01%.
[0033] In addition above-described useful component elements, impurities may be inevitably mixed production steel. present disclosure, inevitable mixing such not limited, representative impurities, example, phosphorous (P), sulfur S) included following content ranges.
[0034] P, S: Each more 0.03%
[0035] Generally, P S are elements which steel, allowable range each less. Particularly, since segregated reduce workability forms manganese sulfide generate defects flange cracks hole expansion, amounts suppressed much possible.
[0036] addition above composition, it preferable control Ni Cr components follows. At
Page 12 least one of Ni and Cr may be added.
[0037] Ni: 0.01-2%
[0038] Since Nickel (Ni) increases the stability austenite phase in an aspect material, suppresses formation α' martensite phase. Therefore, since promotes twin high-manganese steel having even at room temperature, contributes to increase strength improvement ductility a processing steel. Also, is noble element galvanizing, not autonomously oxidized high temperatures but precipitated on surface suppress diffusion easily oxidizable elements such as Al, Mn, Si, like, Ni, reduces thickness oxide induces change composition, thus exhibiting superior wettability with molten zinc. While should added amount 0.01% or more order obtain effect, sharply progresses internal oxidation along grain boundaries cause cracking during hot rolling also production costs. upper limit limited 2%.
[0039] Cr: 0.01-2.0%
[0040] Chromium Cr) forms passive film air corrosion like Si prevents decarburization carbon temperature sheet, thereby improving formability it
Page 13 preferable that Cr be added in an amount not less than 0.01%. However, when the of is a ferrite stabilizing element increased to 2% or more, formation α' martensite phase rather promoted decrease ductility steel. Also, aspect galvanizing, added, oxide formed directly under surface prevents saturation and oxidation Mn, Si Al having poor galvanizability improve galvanizability, but large, thick composite film which main portion deteriorate wettability with molten zinc cause coating failures delamination. Therefore, upper limit limited 2%.
[0041] It has been described present disclosure superior adhesion may obtained by composition including C, Al, Si, Ti, Sn, B, like. as above, at least one Ni peeling off hot-dip galvanized steel sheet further improved. Hereinafter, reasons will detail.
[0042] The inventors observed influences on high-manganese (hereinafter briefly referred ‘base steel’) C: 0.65%, Mn: 15%, Si: 0.6%, Al: 2%, Ti: 0.1%, B: 0.001%, P: 0.017%, S: 0.0005%, remainder being substantially Fe, another trace elements such Ni, Cr, like, were
Page 14
[0043] First, in the case of high-manganese and hot-dip galvanized steel sheets which were by using, as a material to be galvanized, base noble element, such Sn, Ni, like, was not added, lot coating failures occurred.
The inventors have investigated cause confirmed that thick Mn oxide film or Al formed on portions Such thin also observed at an interface layer formed, when bend test (workability test) performed, delamination coated completely peeled off from matrix iron [0044] This is because wettability molten zinc with type annealing process reduced failures, although failure portion locally interfacial inhibition between state simply covers film.
[0045] Therefore, performed studies order solve problem found it possible produce hot dipped sheet free then 0.06-0.2%
Page 15 Sn is added to the composition of base steel. This because or thickness surface (annealing) oxide greatly changed by addition Sn. That is, since a noble element, not oxidized during high temperature annealing but precipitated on steel sheet suppress diffusion easily oxidizable elements, such as Al, Mn, Si, and like, in matrix iron, thereby decreasing changing oxide, it may be understood that exhibits superior wettability with molten zinc.
[0046] For this, preferable Sn-saturated layer forms thin film material galvanized annealing. when amount less than 0.06%, non-uniformly formed thus have difficulty preventing oxidative elements so diffuse into form Al Mn films Al-O, Mn-O) zinc poor cause coating failures.
[0047] On contrary, 0.06% more, decrease 10 nm less, change having relatively good zinc, failures
Page 16 and coating delamination do not occur.
[0048] Also, in a case where one or both of Ni: 0.01-2.0% Cr: is added to base steel, it possible produce high-manganese hot-dip galvanized steel sheet free failures galvanizing after annealing general production conditions.
[0049] This effect greater when any Ni Cr are combination than Sn alone, because thinner surface oxide formed combination. That is, noble element like Sn, precipitated on matrix suppress the diffusion Al, Mn, Si, like, iron, thereby greatly reducing thickness oxide. In order obtain above-described effect, amount should be at least 0.1% more, that case, since about 5 nm very thin due synergy effect with dipped galvanizability much superior.
[0050] Galvanizability superior particularly which contained. Since such as Ni, alone thick Al-Cr-Si-Mn-O composite film formed, but together (an internal oxide) directly under iron prevent saturation oxidation Si Al having relatively poor galvanizability, so
Page 17 thickness of the surface oxide film is decreased to 5 nm or less exhibit superior galvanizability in hot-dipped galvanizing.
[0051] That is, when an existing high-manganese steel sheet which a large amount Al and Si as well Mn are added annealed at high temperatures followed by galvanizing process, thick having two-layered structure (Al-O) Mn-poor wettability with molten zinc formed cause coating failures delamination processing but base present disclosure Sn Ni Cr alone combination steel, since relatively good gradually decreased, it possible produce hot galvanized adhesion.
[0052] When above-described advantageous characteristics dip galvanized, formation Al, Mn, oxides suppressed on improve adhesion, so that appearance may be obtained. In case where rolled cold-then general method,
Page 18 obtained, but a more preferred method for obtaining hot-dip galvanized steel sheet will be described below.
[0053] An atmosphere dew point temperature of an annealing process followed by dipped galvanizing is preferably set to range -30°C 60°C, and recrystallization 750°850°C. When the atmosphere exceeds matrix iron (Fe) as well Mn oxidized form thick oxide film, thus coating delamination occurs. On contrary, when less than selective oxidation or Si suppressed Al that main cause failures high-manganese may easily occur. Also, in order keep at lower 60plurality apparatuses removing moisture gas oxygen are required not preferred.
[0054] annealing 750it difficult secure material quality, 850softened, layer formed due surface saturation alloy element such Mn, Si, Al, like, much greater amount Sn Ni should added prevent from being formed. Therefore, exceeding
Page 19
[0055] After the steel sheet is annealed as above, dipping of steel in a hot dip galvanizing bath performed to galvanize sheet. In this regard, proper temperature at which material be galvanized dipped bath, i.e., temperature, properly 480C 520C, and concentration Al 0.2% by weight 0.25% weight. When order allow Fe matrix iron hot-preferentially react with each other, an oxide film on surface should eliminated solid-solutioned bath. However, when oxidation layer too thick or low, not eliminated, so that wettability molten zinc poor thus coating failures occur. prevent occurrence such failures, it required incoming higher. This because higher sheet, easier elimination layer. exceeds 520°excessive eluted from reacts Zn form Fe-Zn-based bottom dross Al-floating dross, portion these drosses mixed into deteriorate appearance. Therefore, exceeding
Page 20 preferred.
[0056] When an annealed steel material (sheet) is dipped in the galvanizing bath, Al bath preferentially reacts with sheet to reduce oxide film remaining on surface of and form Fe-Al-Zn-Si-Ni-based layer which a soft interfacial inhibition layer, thus playing role suppressing growth brittle Mn-intermetallic compound. In order obtain above-described advantageous effect, concentration preferably 0.2% by weight or more. Therefore, it manage at more, but when exceeds 0.25%, floating dross may be easily generated flow pattern looking like galvanized flowing down generated. upper limit limited 0.25%.
[0057] That is, according present disclosure, high-manganese Sn added annealed annealing atmosphere small amount within range badly influencing coating adhesion, then hot-dip produce free failures delamination.
【Mode for Invention】
[0058] Hereinafter, disclosure will
Page 21 in more detail with examples thereof. It is noted that the following should be not construed to limit scope of present disclosure, but rather are only exemplarily provided describe disclosure detail. The defined by claims and matters reasonably analogized from claims.
[0059] (Examples)
[0060] High-manganese steel having a composition, weight, including C: 0.65%, Mn: 15%, Si: 0.6%, Al: 2%, Ti: 0.1%, B: 0.001%, P: 0.017%, S: 0.0005%, further Sn, Ni, Cr compositions shown Table 1 was dissolved vacuum produce ingots, produced ingots were soaked at 1,100°C, hot rolled, wound 450°C. After pickling, material cold rolled reduction ratio 45% sheet width 200 mm thickness 1.2 mm.
[0061] [1]
No.
Steel Composition
Surface
(annealing)
oxide
Coating quality
Remarks
Sn
Ni
Cr
Composition
Thickness
(nm)
Coating failures
(Good 15
Bad)
Coating adhesion
(Good
15 Bad)
1
-
-
-
Al-O/Mn-O
50
Grade 5
Grade 5
Comp. Ex
2
0.05
-
-
Mn—Al-O
40
Grade 3
Grade 2
Comp. Ex
3
0.06
-
-
Mn-O
20
Grade 2
Grade 2
Example
4
0.1
-
-
Mn-O
10
Grade 1
Grade 1
Example
5
0.2
-
-
Mn-O
10
Grade 1
Grade 1
Example
Page 22
6
0.3
-
-
Mn-O
10
Grade 1
Grade 1
Comp. Ex
7
-
2.0
-
Mn—Al-O
40
Grade 3
Grade 3
Comp. Ex
8
0.06
0.01
-
Mn-O
20
Grade 2
Grade 1
Example
9
0.06
1.0
-
Mn-O
5
Grade 1
Grade 1
Example
10
0.06
1.5
-
Mn-O
5
Grade 1
Grade 1
Example
11
0.06
2.0
-
Mn-O
5
Grade 1
Grade 1
Example
12
0.06
2.5
-
Mn-O
5
Grade 1
Grade 1
Example
13
0.2
0.01
-
Mn-O
5
Grade 1
Grade 1
Comp. Ex
14
0.2
1.0
-
Mn-O
5
Grade 1
Grade 1
Example
15
0.2
1.5
-
Mn-O
5
Grade 1
Grade 1
Example
16
0.2
2.0
-
Mn-O
5
Grade 1
Grade 1
Example
17
0.2
2.5
-
Mn-O
5
Grade 1
Grade 1
Comp. Ex
18
-
-
0.3
Al-Cr-Si-Mn-O
120
Grade 5
Grade 5
Comp. Ex
19
0.06
-
0.01
Mn-O
25
Grade 2
Grade 2
Example
20
0.06
-
1.0
Mn-Cr-O
10
Grade 1
Grade 1
Example
21
0.06
1.5
Mn-Cr-O
10
Grade 1
Grade 1
Example
22
0.06
-
2.0
Mn-Cr-O
10
Grade 1
Grade 1
Example
23
0.06
-
2.5
Mn-Cr-O
40
Grade 3
Grade 2
Comp. Ex
24
0.2
-
0.01
Mn-O
5
Grade 1
Grade 1
Example
25
0.2
-
1.0
Mn-Cr-O
5
Grade 1
Grade 1
Example
26
0.2
-
2.0
Mn-Cr-O
10
Grade 1
Grade 1
Example
27
0.2
-
2.5
Mn-Cr-O
30
Grade 3
Grade 2
Comp. Ex
28
0.06
0.01
0.01
Mn-O
5
Grade 1
Grade 1
Example
29
0.06
0.01
2.0
Mn-O
5
Grade 1
Grade 1
Example
30
0.06
0.01
2.5
Mn-Cr-O
30
Grade 3
Grade 2
Comp. Ex
31
0.06
2.0
0.01
Mn-O
5
Grade 1
Grade 1
Example
32
0.06
2.5
0.01
Mn-O
5
Grade 1
Grade 1
Comp. Ex
33
0.2
0.01
0.01
Mn-O
5
Grade 1
Grade 1
Example
34
0.25
0.01
0.01
Mn-O
5
Grade 1
Grade 1
Comp. Ex
35
0.25
2.5
0.01
Mn-O
5
Grade 1
Grade 1
Comp. Ex
36
0.25
2.5
2.5
Mn-Cr-O
20
Grade 2
Grade 1
Comp. Ex
[0062] * Comp. Ex.: Comparative Example
[0063] These steel sheets were degreased and recrystallization-annealed at an annealing temperature of 800°C for 40 seconds in a reducing atmosphere including 5%
Page 23 hydrogen, with the remainder being nitrogen, and having a dew point temperature of -60°C.
[0064] The shape, thickness composition surface oxide in steel sheets produced annealed as above were observed measured by using focused ion beam (FIB) field emission-transmission electron microscopy FE-TEM), an energy-dispersive X-ray spectroscopy EDS), glow discharge GDS), etc, measurement results are shown Table 1.
[0065] Thereafter, surfaces via processes hot-dip galvanized. galvanizing treatment was performed annealing test pieces under above-described conditions, cooling sheet to 500°C, dipping bath Al concentration 0.23%, controlling adhesion amount on one 60 g/m2 air knife which is apparatus for blowing onto galvanized layer that not completely solidified control layer).
[0066] evaluation quality evaluating occurrence coating failures good bad according following references.
[0067] In order evaluate degree failures, appearance imaged measure size
Page 24 non-coated portion and the object steel sheets were graded according to following criteria.
[0068] -1st grade: No defect of coating failures
[0069] 2nd Average diameter is less than 1 mm
[0070] 3rd 1-2 mm.
[0071] 4th 2-3 [0072] 5th or more
[0073] The adhesions hot-dip galvanized evaluated by performing an OT-bend test, then a taping test external winding evaluating occurrence delamination
in layer [0074] [0075] Delamination 5%
[0076] 5- 10%
[0077] 10- 30%
[0078] not [0079] Coating failure indices adhesion high-manganese evaluation results are shown Table 1. In results, case (Samples Nos. 3-5) where added amount Sn base was 0.06-0.2% which within
Page 25 the added range defined in present disclosure, a case (Nos. 8-11, 13-16) where Ni was to base steel and amount of 0.01-0.2% which is within 19-22, 24-26) Cr 28-29, 31, 33) were combination steels each when samples annealed followed by galvanizing, since had discontinuous oxides Mn-O or Cr-at thickness not more than 20 nm, coating failures galvanizing did occur, it also possible produce hot-dip galvanized sheets free delamination processing thereof.
[0080] On contrary, No. 1) Sn steel, 2) but satisfy lower limit 0.06% 7) alone 18) continuous thick surface compositions formed are Al-oxide, composite oxide Si-with poor wettability molten zinc formed,
Page 26 occurred during galvanizing and even when coated, the coated layer was delaminated processing.
[0081] In a case (No. 6) where Sn added amount of exceeded 0.2% that is upper limit Sn, in Nos. 12 17) high-manganese steels which Ni to base steels, 2% defined present disclosure, 32 35) Cr were combination since surface oxide formed by annealing followed discontinuous Mn had thickness not more than 5 nm, coating failures did occur, it also possible produce hot-dip galvanized steel sheets free delamination processing thereof. However, hot shortness reheating for rolling, limit, internal oxidation sharply progressed generate cracking such compositions preferred.
[0082] Also, 23 27) disclosure 30 36)
Page 27 in high-manganese steels which Ni and Cr were added combination to base steels, the amount of exceeded upper limit defined present disclosure, since thick composite oxide was formed deteriorate wettability with molten zinc cause coating failures or delamination, such compositions are not preferred.
[0083] While exemplary embodiments have been shown described above, it will be apparent those skilled art that modifications variations could made without departing from spirit scope disclosure as by appended claims.
Page 28
【CLAIMS】
【Claim 1】
A high-manganese steel with superior coating adhesion comprising, by weight, C: 0.3-1%, Mn: 8-25%, Al: 1-8%, Si: 0.1-3.0%, Ti: 0.01-0.2%, Sn: 0.06-0.2%, B: 0.0005-0.01%, with the remainder being Fe and inevitable impurities.
【Claim 2】
The high-manganese steel of claim 1, further comprising, by weight, at least one of Ni: 0.01 to 2% and Cr: 0.01 to 2.0%.
【Claim 3】
The high-manganese steel of claim 1 or 2, wherein a Sn-saturated layer exists on a surface thereof.
【Claim 4】
A method for producing a hot-dip galvanized steel sheet, the method comprising:
preparing a steel sheet comprising, by weight, C: 0.3-1%, Mn: 8-25%, Al: 1-8%, Si: 0.1-3.0%, Ti: 0.01-0.2%, Sn: 0.06-0.2%, B: 0.0005-0.01%, with the remainder being Fe and inevitable impurities;
annealing the steel sheet under conditions having a dew point temperature of -30ºC to -60ºC and an annealing temperature of 750ºC to 850ºC; and
dipping the annealed steel sheet in a hot-dipped galvanizing bath comprising, by weight, Al: 0.2-0.25% at a dipping temperature of 480ºC to 520ºC.
【Claim 5】
The method of claim 4, wherein the steel sheet further
Page 29
comprises, by weight, at least one of Ni: 0.01 to 2% and Cr: 0.01 to 2.0