CN103572159A - Ultrahigh strength cold rolled steel sheet with superior hydrogen embrittlement resistance and manufacturing method thereof - Google Patents
Ultrahigh strength cold rolled steel sheet with superior hydrogen embrittlement resistance and manufacturing method thereof Download PDFInfo
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- CN103572159A CN103572159A CN201210249309.5A CN201210249309A CN103572159A CN 103572159 A CN103572159 A CN 103572159A CN 201210249309 A CN201210249309 A CN 201210249309A CN 103572159 A CN103572159 A CN 103572159A
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Abstract
The invention provides an ultrahigh strength steel sheet used for processing and a manufacturing method thereof. The ultrahigh strength steel sheet has tensile strength of 980-1670MPa and superior hydrogen embrittlement resistance, and comprises, by mass%: 0.05-0.17% of C, 0.2-1.5% of Si, 1.7-3.5% of Mn, less than or equal to 0.030% of P, less than or equal to 0.010% of S, 0.025-0.120% of Al, less than or equal to 0.0100% of N, 3.43*N-0.150% of Ti, and the balance iron and unavoidable impurities.
Description
Technical field
The present invention relates to super high tensile cold-rolled steel plate and manufacture method thereof that the superior tensile strength of a kind of hydrogen-embrittlement resistance is 980～1670MPa, relate in particular to a kind of manufacture method that is subject to the superior super high tensile cold-rolled steel plate of hydrogen-embrittlement resistance after the processing such as stamping or roller shaping, specifically, such as the manufacture of super-high strength steel plate suitable in being suitable for the light weights such as strengthening part of collision bumper at automobile, car door and requiring the purposes of resistance to intensity.
Background technology
Along with the lightweight of automobile, in the purposes of collision bumper, car door impact beam equal strength parts etc., by stamping or roller, be shaped and ultrahigh-strength thin steel sheet more than 980MPa is made to the situation that tube shape adopts become many.
In ultrahigh-strength steel more than 980MPa, produce this thing of hydrogen embrittlement for example known by Japanese screw TIA's " design of screw threads for fastening is with actual " advanced study and training lecture teaching material (October 18 nineteen ninety).Therefore, in ultrahigh-strength thin steel sheet, think that the hydrogen producing by the corrosion reaction under atmospheric environment also enters in steel plate, in use fragility ground destroys suddenly.And then the in the situation that of ultrahigh-strength thin steel sheet, owing to using as molding by processing such as stamping or roller shapings, so can produce be accompanied by significantly high residual stress existence, force work at the in-house hole of steel plate or crackle etc., think in more easily causing the state of hydrogen embrittlement.
But, the strengthening part ultrahigh-strength thin steel sheet of collision bumper so far, car door, for example Japanese kokai publication hei 4-268016 communique or Japanese kokai publication hei 4-365814 communique are such, main purpose be improve processibility or sinter-hardened property, as the characteristic of damaging by pressure of molding, seldom refer to being in use contemplated to the countermeasure of problem of the hydrogen embrittlement of generation, for example, visible degree in Japanese kokai publication hei 4-268053 communique etc. just.
The method that Japanese kokai publication hei 4-268053 communique is recorded is a kind of Si that adds in steel, suppresses hydrogen atom to the intrusion in steel plate, prevents thus the method for the generation of hydrogen embrittlement.But in fact, for the preventing of hydrogen embrittlement, only by adding Si, to suppress hydrogen atom be inadequate to the intrusion in steel plate, it is important that steel plate itself is pre-formed as being difficult to produce tissue, the composition of fragility for the hydrogen with respect to invading.
From preventing the viewpoint of hydrogen embrittlement, the tissue of steel, composition are studied, in the field of bar steel, for example, described in Japanese kokai publication sho 60-155644 communique, known a kind of by martensitic stucture in more than 400 ℃ tempering, Fe-C based compound is fully separated out and the method that prevents.
But such steel is different from the steel sheet of processing that carries out stamping or roller shaping etc., being wanting in of processibility.In addition, as mentioned above, for because be accompanied by the existence of residual stress or force the generation at the in-house hole of steel plate or crackle etc. of work and easily produce hydrogen embrittlement this point without any consideration.In addition, conventionally the ultrahigh-strength steel plates with the manufacture of continuous annealing method is by the lower steel of C, Mn amount is carried out after equal thermal treatment, with speed of cooling faster, be cooled to below martensitic phase height, and at 400 ℃, carry out below tempering and manufacture, but this manufacture method is a kind of manufacture method that is different from known method in bar steel completely, therefore need the different countermeasure in field a kind of and bar steel.
Technical literature formerly
Patent documentation
Patent documentation 1: Japanese kokai publication hei 4-268053 communique
Patent documentation 2: Japanese kokai publication sho 60-155644 communique
Summary of the invention
The present invention is in order to solve the problem points of above-mentioned prior art, and it is superstrength and superior ultrahigh-strength thin steel sheet and the manufacture method thereof for processing of hydrogen-embrittlement resistance of 980～1670MPa that object is to provide a kind of tensile strength.
As with solving the means of described problem, of the present inventionly to be intended to the superior super high tensile cold-rolled steel plate of hydrogen-embrittlement resistance that a kind of tensile strength is 980～1670MPa, it calculates with quality %, comprise C:0.05～0.17%, Si:0.2～1.5%, Mn:1.7～3.5%, P≤0.030%, S≤0.010%, Al:0.025～0.120%, N≤0.0100%, Ti:3.43 * N～0.150%, also comprise as required Mo≤1.0%, surplus consists of iron and inevitable impurity.
In addition, its manufacture method is characterised in that, carries out hot rolling, after pickling by usual method to having the steel billet of above-mentioned chemical composition, carry out cold rolling, when continuous annealing, with Ac3 point～1000 ℃, implement after soaking slow cooling, from more than 650 ℃ temperature, with 70 ℃/more than s speed of cooling, be cooled to below Ms point, make it produce martensitic transformation, after, reheat or with regard to former state fixedly with 150～300 ℃ of temper of carrying out 1～15min.
And then in above-mentioned manufacture method, during rolling before continuous annealing, the calendering rate of preferably establishing roughing is more than 80%, the calendering rate of establishing finish rolling is more than 90%, and it is more than 830 ℃ establishing hot precision work temperature, establishes coiling temperature and be 400～750 ℃ to carry out hot rolling.
Invention effect
Cold-rolled steel sheet of the present invention has as the collision bumper of automobile or car door impact beam equal strength parts and tensile strength and the processibility of 980 best～1670MPa, and become when using for the hydrogen embrittlement of problem and there is superior patience, aspect the lightweight of above-mentioned strength member, strengthening part etc., bringing into play superior effect.
Embodiment
Below further describe the present invention.First, the restriction reason of the chemical composition of steel of the present invention is described.
C:C is to generate martensite and is essential element for high strength, in order to obtain intensity more than 980MPa, need to have more than 0.05%, if but become many, easily produce hydrogen embrittlement.In the present invention, especially, when obtaining necessary superstrength, consider processibility and spot weldability, establish and be limited to 0.17%, but for obtaining the tensile strength of 980～1670MPa, this C amount is enough.
Si:Si strengthens the effective element of steel in order not make deteriorated ductility, add more than 0.2% in the present invention.But when surpassing 1.5%, not only its effect is saturated, and also have the load of the roller mill in cold rolling to become the problem such as large, be therefore defined as below 1.5%.
Mn:Mn is the element that improves the hardenability of steel, in order stably to obtain martensitic stucture by continuous annealing apparatus, need to have more than 1.7%.But when surpassing 3.5%, not only its effect is saturated,, and segregation change is large, tissue becomes inhomogeneous, and processibility declines, and therefore establishing 3.5% is the upper limit.
P:P is the effective element that improves ductility in order to strengthen steel, but due to easily at grain boundary segregation, easily cause embrittlement, so be made as below 0.030%.
S:S makes bendability etc. deteriorated owing to forming inclusion, so be suppressed at below 0.010%.
Al:Al adds more than 0.025% for the object of depickling, but from the viewpoint of surface texture, stipulates to be limited to 0.120% on it.
Even if N:N does not add especially, when steel processed, also can from atmosphere, invade.If this N is present in steel with solid solution condition, significantly promote embrittlement.Therefore, in the present invention, thereby form precipitate by interpolation Ti, make N innoxious.But, if N surpasses 0.0100%, need the Ti amount of adding to increase, not only cost rises, and processibility is also deteriorated, and therefore suppressing is below 0.0100%.
Ti: on the one hand, Ti is owing to being fixed as object with separating out of N, so more than need at least adding the equivalent (3.43 * N) of N, if but too much, form precipitate with the required C of the strengthening of steel, thereby therefore softening is defined as 0.150% by its upper limit.
Mo:Mo is not only in order to improve the hardenability of steel and stably obtains martensitic effective element by continuous annealing apparatus, and also has Dui Li circle to strengthen, suppress the effect of the generation of hydrogen embrittlement, adds as required.In the situation that adding, when surpassing 1.0%, effect is saturated, so be made as below 1.0%.
Below manufacture method of the present invention is described.
Although have the steel billet of above-mentioned chemical composition, cast continuously or manufacture by agglomeration method by usual method, and carrying out hot rolling, these are created conditions and are not specially limited.It should be noted that, when hot rolling, although need to be heated to be the temperature more than rolling temperature of regulation, but after casting, be temporarily cooled near normal temperature, and then heating, or in the situation that keeping high temperature, directly insert process furnace, or Direct Rolling after casting, also have no problem.Hot rolling is as long as carry out precision work with 830 ℃ of above temperature, for cooling conditions, coiling temperature afterwards, be not particularly limited, as long as usual method, for example, coolingly on average in the scope of 30～100 ℃/s, carry out, batch at 400～750 ℃.And then the total calendering rate of the roughing when making hot rolling is more than 80%, it is more than 90% making the total calendering rate of finish rolling, thereby can reduce crystallization particle diameter, can improve hydrogen-embrittlement resistance.
After hot rolling, carry out pickling, carry out cold rollingly, but cold rolling rate is for example in 25～70% degree.Then implement continuous annealing, make the steel plate of the intensity of regulation, but continuous annealing is defined as following condition.
The soaking of continuous annealing need to be more than Ac3 transformation temperature 1000 ℃ carry out below.At the temperature less than Ac3 transformation temperature, all producing ferritic structure in thermal process, be difficult to guarantee intensity.Although the existence of ferritic structure sees it is favourable from the viewpoint of hydrogen embrittlement, but practical situation are, it is difficult that the ferrite of controlling specified amount corresponding to chemical composition in equal thermal processs generates, therefore, as described later, it is generated in process of cooling easier.On the other hand, even if heat surpassing at the temperature of 1000 ℃, so long as what problem austenite one phase tissue does not have yet, even but futile effort is heated to high temperature, crystallization particle diameter also becomes greatly, causes cost rising, thus on be limited to 1000 ℃.
After soaking, slow cooling starts temperature to chilling, then starts chilling.The speed of slow cooling for example can be 1～30 ℃/s.It is substantially from the state of the tissue of austenite one phase, to start to carry out that chilling starts temperature, generates martensite and can guarantee the temperature of the intensity of regulation.Therefore, chilling starts temperature wishes for more than Ar3 transformation temperature, but from the viewpoint of hydrogen embrittlement, exists ferritic structure more favourable, therefore, as long as in the scope that can guarantee intensity, even if generate a small amount of ferritic structure, also has no problem, and is made as more than 650 ℃.It should be noted that, at this so-called a small amount of ferritic structure, refer to area occupation ratio and be calculated as below 20%.In addition, if rapidly cooling speed be 70 ℃/more than s, can obtain low temperature phase change resultant, be therefore made as lower limit.It should be noted that, about method of cooling, water quenching, water cooled rolls is cooling, air water is cooling and jet cooling etc. can, no matter its method.
Chilling proceeds to martensitic transformation to start, below temperature (Ms point), to carry out afterwards the temper of 1～15min at 150～300 ℃, is adjusted into thus the intensity of regulation.Now, as long as chilling end temp, in temper temperature range, intactly carries out constant temperature with this temperature and keeps, lower than temper temperature in the situation that, as long as reheat.The temper time, its effect almost cannot be confirmed if not more than 1min, and on the other hand, if longer than 15min, equipment gigantism, is therefore defined as the upper limit.Temper temperature is during lower than 150 ℃, and its effect does not almost have, and is therefore made as lower limit.On the other hand, the inventor confirms: when surpassing 300 ℃, separate out thicker carbide, in the hydrogen embrittlement test under the corrosive environments such as atmosphere and brine spray, grain circle occurred in the short period of time and destroy.Its reason is very not clear and definite, but thinks that hydrogen atom is gathered in this owing to adding man-hour in shaping in generation hole, the interface of carbide and mother metal, improves stress concentration, causes be full of cracks to occur.Therefore, temper temperature on be limited to 300 ℃.
After annealing, as required, in order to make shape good, can implement skin-pass, in addition, even if carry out the plating of zinc etc., process and also have no problem.
Embodiments of the invention are shown below.
(embodiment)
The steel of the chemical composition shown in table 1 is being heated to be after 1200 ℃, and under the condition of table 2, hot rolling is thickness of slab 3.0mm.After pickling, be cold rolled to thickness of slab 1.8mm, with the condition shown in table 2, carry out respectively continuous annealing.After having implemented 0.3% skin-pass, investigation mechanical characteristics and hydrogen-embrittlement resistance.Its result is as shown in table 3.
About hydrogen-embrittlement resistance, with bending radius 9R, the rectangular test film of 30mm * 150mm is carried out to U bending forming, constriction is to reaching 2R (=18mm) between plate, on surface, implement the electrodeposition-coating of thickness 20 μ m, afterwards, with cutting knife, in curved top portion, cut out slit, in the KSCN solution that the sulfuric acid rising at 0.5mol/+0.0001mol/ rises, use potentiostat to give than the current potential of the low 600mV of spontaneous potential, the time producing by crackle is evaluated.
As known from Table 3, the inventive example (No.1,2,3,6,8,13～16) shows the tensile strength of 980～1670MPa and good processibility, until the time that crackle produces is also long, more than 1000s, hydrogen-embrittlement resistance is superior.With respect to this, the continuous annealing condition of comparative example (No.4,5,7) departs from from the scope of the invention, and in addition, the chemical composition of comparative example (No.10,12) departs from from the scope of the invention, ferrite area occupation ratio becomes too high separately, cannot guarantee the intensity of regulation.On the other hand, the chemical composition of comparative example (No.9,11) departs from from the scope of the invention, until the time that crackle produces is short, is 300～500s, obvious with the difference of the hydrogen-embrittlement resistance of the inventive example.
It should be noted that, although inventive example No.6,8 is discontented with unabridged version application technical schemes 4, No.6 meets technical scheme 1,3, and No.8 meets technical scheme 1,3.
[table 1]
[table 2]
[table 3]
Table 3 test-results
(noting 1) underscore is illustrated in outside the scope of the invention.
Claims (4)
1. the superior super high tensile cold-rolled steel plate of hydrogen-embrittlement resistance that tensile strength is 980～1670MPa, is characterized in that,
With quality %, calculate, comprise C:0.05～0.17%, Si:0.2～1.5%, Mn:1.7～3.5%, P≤0.030%, S≤0.010%, Al:0.025～0.120%, N≤0.0100%, Ti:3.43 * N～0.150%, surplus consists of iron and inevitable impurity.
2. cold-rolled steel sheet as claimed in claim 1, it also contains Mo≤1.0%.
3. a manufacture method for the super high tensile cold-rolled steel plate that tensile strength is 980～1670MPa hydrogen-embrittlement resistance is superior, is characterized in that,
By usual method, to thering is the steel billet of the chemical composition described in claim 1 or 2, carry out hot rolling, after pickling, carry out cold rolling, when continuous annealing, with Ac3 point～1000 ℃, implement after soaking slow cooling, from more than 650 ℃ temperature, with 70 ℃/more than s speed of cooling, be cooled to below Ms point, make it produce martensitic transformation, after, reheat or with regard to former state fixedly with 150～300 ℃ of temper of carrying out 1～15min.
4. a manufacture method for the super high tensile cold-rolled steel plate that tensile strength is 980～1670MPa hydrogen-embrittlement resistance is superior, is characterized in that,
For the steel billet with the chemical composition described in claim 1 or 2, calendering rate with more than 80% roughing, the calendering rate of more than 90% finish rolling, 830 ℃ of above hot precision work temperature, the coiling temperature of 400～750 ℃ carries out hot rolling, after pickling, carry out cold rolling, when continuous annealing, with Ac3 point～1000 ℃, implement after soaking, slow cooling, from more than 650 ℃ temperature, with 70 ℃/more than s speed of cooling, be cooled to below Ms point, make it produce martensitic transformation, after, reheat or with regard to former state fixedly with 150～300 ℃ of temper of carrying out 1～15min.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN106795609A (en) * | 2014-10-17 | 2017-05-31 | 新日铁住金株式会社 | Drawing steel plate for tanks and its manufacture method |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| JPH0790488A (en) * | 1993-09-27 | 1995-04-04 | Kobe Steel Ltd | Ultrahigh strength cold rolled steel sheet excellent in hydrogen brittlement resistance and its production |
| JPH08134589A (en) * | 1994-11-10 | 1996-05-28 | Kobe Steel Ltd | Ultrahigh strength steel sheet excellent in hydrogen embrittlement resistance and reinforcing member made therefrom |
| CN1796588A (en) * | 2004-12-28 | 2006-07-05 | 株式会社神户制钢所 | High strength thin steel sheet having high hydrogen embrittlement resisting property and high workability |
| CN101748347A (en) * | 2008-11-28 | 2010-06-23 | 株式会社神户制钢所 | Ultrahigh-strength steel sheet excellent in hydrogen embrittlement resistance and workability, and manufacturing method therefor |
| CN102449180A (en) * | 2009-05-29 | 2012-05-09 | 株式会社神户制钢所 | High strength steel sheet having excellent hydrogen embrittlement resistance |
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- 2012-07-18 CN CN201210249309.5A patent/CN103572159B/en active Active
Patent Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH0790488A (en) * | 1993-09-27 | 1995-04-04 | Kobe Steel Ltd | Ultrahigh strength cold rolled steel sheet excellent in hydrogen brittlement resistance and its production |
| JPH08134589A (en) * | 1994-11-10 | 1996-05-28 | Kobe Steel Ltd | Ultrahigh strength steel sheet excellent in hydrogen embrittlement resistance and reinforcing member made therefrom |
| CN1796588A (en) * | 2004-12-28 | 2006-07-05 | 株式会社神户制钢所 | High strength thin steel sheet having high hydrogen embrittlement resisting property and high workability |
| CN101748347A (en) * | 2008-11-28 | 2010-06-23 | 株式会社神户制钢所 | Ultrahigh-strength steel sheet excellent in hydrogen embrittlement resistance and workability, and manufacturing method therefor |
| CN102449180A (en) * | 2009-05-29 | 2012-05-09 | 株式会社神户制钢所 | High strength steel sheet having excellent hydrogen embrittlement resistance |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN106795609A (en) * | 2014-10-17 | 2017-05-31 | 新日铁住金株式会社 | Drawing steel plate for tanks and its manufacture method |
| CN106795609B (en) * | 2014-10-17 | 2018-12-04 | 新日铁住金株式会社 | Drawing steel plate for tanks and its manufacturing method |
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