JP2002249846A - Steel having excellent pitting resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a steel which has more excellent pitting resistance. SOLUTION: The steel has a composition containing, by mass, <=0.20% C, <=2.0% Si, >0.3 to 3.5% Mn, <=0.10% P, <=0.02% S, 0.005 to 0.10% Al and 0.002 to 0.50% Sb, and in which the above Mn, P and Sb are contained also so as to satisfy the following inequality of 0.003Mn%+0.02P%<=Sb%, and the balance Fe with inevitable impurities.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a deep drawing material suitable for use in outer panels, inner panels, members, undercarriage parts, wheels, and the like of automobiles, and more particularly, to steel sheets such as welds and hemmed parts. The present invention relates to a steel material having excellent resistance to perforation in a joint portion.

[0002]

2. Description of the Related Art In recent years, as automobiles have been reduced in weight from the viewpoint of energy saving and the like, the thickness of automotive steel sheets has tended to become increasingly thinner. However, on the other hand, when such a reduction in thickness is achieved, the margin after corrosion is reduced, which is disadvantageous from the viewpoint of perforation resistance. Automotive steel sheets used in such situations are usually
After being assembled on an automobile body, electrodeposition coating is performed as a measure against rust. However, even when such a rust-preventive treatment is applied, the steel sheet surface is exposed without sufficient sneaking of the electrodeposition coating at the steel sheet joining part such as a welded part or a hemmed part. Mud, snow-melting salt, etc. stay in this area, so corrosion progresses from this area,
There was a problem that perforated corrosion easily occurred. Furthermore, with the recent increase in strength of steel sheets, a large amount of Mn is added.
Also had the problem of promoting this corrosiveness more and more.

Conventionally, measures to improve the puncture resistance of steel materials such as steel sheets for automobiles have been taken by methods such as surface treatment represented by zinc plating,
A method of adding components such as P, Cu, Cr, and Ni is known. For example, JIS G 3125 states that P, C
Corrosion resistant steel materials are standardized by adding u, Cr and Ni. JP-A-2-22416 discloses a technique for improving the perforation resistance by forming a dense rust layer by adding P and Cu, and JP-A-56-139655 discloses a technique.
A technique of forming an intermetallic compound of Cu and Sb by adding Sb or the like to P and Cu and improving the puncture resistance is disclosed in JP-A-10-251797 and JP-A-11-174.
No. 5 discloses a structural steel containing P, Ni, Mo, and Sb, and a technique for improving corrosion resistance and seawater corrosion resistance in an environment where salt flies. Further, Japanese Patent Application Laid-Open No. Sho 61
JP-A-117249, JP-A-63-203747 and JP-A-2-50940 disclose a technique for improving corrosion resistance by adding Cr, and JP-A-11-172378 discloses that Al and Cr are added. Each discloses a technique for improving corrosion resistance.

[0004]

However, even with the above-mentioned prior art, the perforation resistance is still not sufficient.
In addition, each had the following problems. That is, JIS G 3125, JP-A-2-22416, JP-A-56-139655, and JP-A-63-139655.
The technology disclosed in JP 203747 has a problem that the inclusion of Cu causes deterioration of surface properties and an increase in cost, and is difficult to separate when recovered as iron resources.
Also, JIS G 3125, JP-A-10-25179
No. 7, JP-A-11-1745 discloses Ni.
However, there is a problem that the processability is deteriorated and the cost is increased due to the above. Also, JIS G 3125, JP-A-61-117249, JP-A-63-203747.
And Japanese Patent Application Laid-Open No. Hei 2-50940,
Since Cr is contained, there is a problem that it is easily corroded in an environment where Cl ⁻ ions are present. Therefore, an object of the present invention is to provide a steel material which does not have the above-mentioned problems of the prior art and further improves the puncture resistance.

[0005]

Means for Solving the Problems In order to achieve the above object, the inventors have conducted detailed studies from the aspect of steel composition for improving the puncture resistance. As a result, it has been found that by setting the composition of steel in an appropriate range, a sufficient effect can be obtained even with a relatively simple component system, and the present invention has been accomplished. The summary configuration is as follows.

(1) In mass%, C: 0.20% or less, Si: 2.
0% or less, Mn: more than 0.3 to 3.5%, P: 0.10% or less,
S: 0.02% or less, Al: 0.005 to 0.10%, Sb: 0.002 to
0.50%, and the content of Mn, P, and Sb satisfies the following formula: 0.003 Mn% + 0.02P% ≦ Sb%, with the balance being Fe and unavoidable impurities. Steel material with excellent porosity.

(2) In addition to the components described in (1), Ti: 0.02 to 0.50%, Nb: 0.001 to 0.50%,
Mo: 0.01 to 1.0%, V: 0.001 to 0.50%, B: 0.0001
A steel material having excellent perforation resistance, characterized by containing one or two or more selected from 0.0050%.

(3) The steel material having excellent puncture resistance according to the above (1) or (2), which has a surface treatment layer on at least a part of its surface.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The reasons for limiting the composition of the steel material according to the present invention to the above ranges will be described below. C: 0.20% or less C is an element which lowers the workability of the steel sheet and adversely affects the corrosion resistance. Therefore, the upper limit is set to 0.20%, preferably less than 0.15%. If the C content is excessively reduced, the production cost increases and the welding strength decreases. Therefore, the lower limit is preferably made 0.001%.

Si: 2.0% or less Si is an element effective for increasing the strength and improving corrosion resistance in addition to deoxidation in steel making. However, if it is contained excessively, the ferrite phase becomes brittle and the structure becomes rough, and the surface treatment property deteriorates. Therefore, the upper limit is made 2.0%. Preferably, it is contained in the range of 0.01 to 1.5%.

Mn: more than 0.3 to 3.5% Mn is an element effective for deoxidation and desulfurization in steel making and also for increasing strength. To achieve this effect, 0.3
% Is required, but if the content exceeds 3.5%, the formation of rusting points such as MnS, MnO, etc. has a significant adverse effect on corrosion resistance (perforation resistance). Therefore, Mn
The amount is more than 0.3 to 3.5%, preferably 0.4 to 3.5%.

P: 0.10% or less P is an element effective for increasing the strength. However, a large amount of P reduces toughness due to segregation, or P dissolves in the dew formed in the concave portions on the steel surface. Therefore, it is necessary to limit the content to 0.10% or less since a local battery is formed and the perforation resistance is reduced. If the P content is excessively reduced, the production cost increases. Therefore, the lower limit is preferably set to 0.005%.

S: 0.02% or less S is present as sulfide-based inclusions by combining with elements such as Mn in steel. This sulfide-based inclusion easily causes a potential difference between the sulfide-based inclusion and the ground iron, and is likely to be a rusting point. Therefore, the S content is
Limit to 0.02% or less. The preferred content is 0.006
%, More preferably 0.003% or less. Also,
If the S content is excessively reduced, the production cost increases and burrs on the shear end face increase, so the lower limit is preferably made 0.0006%.

Al: 0.005 to 0.10% Al is useful for deoxidation and denitrification in steel making. At least 0.005% is necessary. However, if contained in an excessive amount, the toughness and the perforation resistance decrease. 0.
The range is 005 to 0.10%. The preferred content is 0.
It is in the range of 01-0.05%.

Sb: 0.002 to 0.50% Sb is an element that is particularly useful for improving the puncture resistance. Sb
If the content is less than 0.002%, sufficient puncture resistance cannot be obtained, while if it exceeds 0.50%, the effect is saturated and no further effect is obtained, which is uneconomical. Therefore, the Sb content is 0.00
The range is 2 to 0.50%, preferably 0.008 to 0.02%.

0.003 Mn% + 0.02 P% ≦ Sb% Mn and P have an adverse effect on the puncture resistance.
With the Sb content of Mn% + 0.02P% or more, the puncture resistance can be improved. The reason for this is that Mn-based inclusion MnS,
When MnO or P dissolves in condensed water and becomes a rusting point,
Acts as inhibitors of these reactions, and MnS, Mn
It is believed that this has the effect of suppressing the dissolution of O and P and reducing the rusting action. If the contents of Mn, P, and Sb are within the range satisfying the above expression, the puncture resistance is improved.

Ti: 0.02 to 0.50% Ti is an element fixing C, N and S, if necessary.
0.02% or more can be contained, but if it exceeds 0.50%, the workability deteriorates, so the content is made in the range of 0.02 to 0.50%.

Nb: 0.001 to 0.50% Nb is an element for fixing C and N, and is 0.000% if necessary.
More than 1% can be contained, but if it exceeds 0.50%, the workability deteriorates, so it is contained in the range of 0.001 to 0.50%.

Mo: 0.01 to 1.0% Mo is an element which improves the corrosion resistance, and is used in an amount of 0.1 to 1.0%, if necessary.
Although it can be contained at least 01%, even if it exceeds 1.0%, no further effect is obtained and saturation occurs.
It is contained in the range of 01 to 1.0%.

V: 0.001 to 0.50% V, like Ti and Nb, can contain 0.001% or more as an element for fixing C, N, and S, if necessary. Since workability deteriorates, 0.001
It is contained in the range of 0.50%.

B: 0.0001 to 0.0050% B is useful for improving ductility, but if contained excessively, on the contrary, ductility is reduced. Therefore, B is contained in the range of 0.0001 to 0.0050% as necessary.

[0022] The steel material of the present invention shall be composed of Fe and unavoidable impurities in addition to the above components. The inevitable impurities include Ni: 0.3% or less, preferably 0.02% or less, and Cr: less than 0.5%, preferably 0.03%.
Hereafter, Cu: 0.2% or less, preferably 0.04% or less, N: 20
Even if it contains 0 ppm or less, preferably 150 ppm or less, O: 100 ppm or less, preferably 70 ppm or less, and Ca: 0.01% or less, preferably 0.003% or less, it does not inhibit the porosity resistance. Each may be contained in the above range.

The steel material of the present invention includes those having a surface treatment layer formed on at least a part of the surface of the steel material. Specific examples of the surface treatment layer are as follows. That is, as a metal coating layer, a metal plating layer of Al, Ni, Zn, Sn or the like or Al-S
i, Ni-Co, Zn- Al, Zn-Fe, Zn-Ni, alloy plating layer such as Zn-Fe-Al, also a composite coating layer, Zn-SiO ₂
And a dispersion plating layer of Zn—SiO ₂ —resin or the like.
Among them, those containing a metal that is electrochemically lower than Fe, such as Zn, are suitable surface treatment layers that have a large effect of improving corrosion resistance. In the case of Zn-based plating, the time until rusting of steel material becomes longer due to the sacrificial corrosion protection effect of Zn against Fe and the corrosion resistance of Zn itself, so the time until the occurrence of perforation increases and the product life is increased It is possible to do. In general, corrosion resistance can be improved by increasing the amount of plating. However, since the steel material of the present invention has good perforation resistance even without a plating layer, the amount of plating can be reduced. Therefore, when further corrosion resistance is required, the amount of plating applied may be adjusted according to the required corrosion resistance performance. In addition, as the surface treatment layer, in addition to those described above, enamel-based, acrylic-based coating film formed, a chemical conversion treatment such as a zinc phosphate coating or chromate on the plating layer, or further on the upper layer A coating film is also included.

Next, a method for producing the steel material of the present invention will be described. Note that the steel material of the present invention is mainly intended for steel sheets such as hot-rolled sheets, cold-rolled sheets, and those subjected to surface treatment such as plating. Molten steel of the above composition, converter, electric furnace,
It is melted by a known method such as a vacuum melting furnace, and is made into a steel material (slab) by a continuous casting method or an ingot making method. The steel material is then heated or directly hot-rolled without heating to obtain a hot-rolled sheet. The heating temperature in the hot rolling is not particularly limited, but is preferably in the temperature range of 1000 to 1300 ° C. The finish rolling temperature is 800 ℃ or more,
The winding temperature is preferably set to 500 ° C. or higher. This is because, if the finish rolling temperature is lower than 800 ° C., the deformation resistance increases, the load on the rolling mill increases, and the crystal grains become coarser significantly, deteriorating the mechanical properties of the steel sheet. On the other hand, if the winding temperature after hot rolling is less than 500 ° C., the shape of the steel sheet deteriorates and the workability deteriorates. However, in order to achieve a high r value, etc., two-phase area rolling or α
When zone rolling is performed, the finishing temperature and the winding temperature may be outside the above ranges.

The hot rolled sheet obtained by hot rolling is used as it is, or after hot rolling, further cold rolled and annealed to be a cold rolled sheet. When a cold-rolled sheet is used, the hot-rolled sheet obtained by hot rolling is cold-rolled after pickling, and then annealed. The rolling reduction of the cold rolling is desirably 50 to 95% from the viewpoint of obtaining a uniform cold work structure. The annealing method may be either continuous annealing or batch annealing,
Continuous annealing is preferred from the viewpoint of productivity and control of the cooling rate.

The hot-rolled sheet or cold-rolled sheet thus manufactured can be used as it is. However, in order to further increase the corrosion resistance, the steel material is subjected to a surface treatment, and the above-mentioned metal coating layer, coating film, etc. May be formed and used. When surface treatment is performed on the surface of the hot-rolled sheet, it is preferable to perform surface treatment after removing an oxide layer such as black scale by pickling. For forming the metal coating layer, any method such as hot-dip plating, electroplating, PVD (physical vapor deposition), CVD (chemical vapor deposition), sol-gel, thermal spraying, and mechanical plating can be applied. . As the metal coating layer, in order to form a zinc-based plating layer, which is preferable from the viewpoint of corrosion resistance, any of the above-described hot-dip plating method, electroplating method, PVD method, and the like can be applied. An alloying treatment may be performed. Further, the coating film may be formed by any method such as a roll coater method, a spray coating method, an electrodeposition coating method, and a powder coating method.

[0027]

Next, the present invention will be described based on embodiments.
Steels having the component compositions shown in Table 1 were melted in a vacuum melting furnace, and slabs were formed by continuous casting. Heat these slabs to 1150 ° C, finishing temperature 900-950 ° C, winding temperature 550-650 ° C
Hot rolled into a 3.5 mm hot rolled sheet. Next, these hot-rolled sheets were pickled in a 10% by mass aqueous hydrochloric acid solution at 80 ° C. to remove scale on the surface of the steel sheet, and then the sheet thickness was reduced to 0.
It was cold rolled to 6 mm. The obtained cold-rolled sheet was subjected to alkaline electrolytic degreasing treatment to remove the rolling oil adhering to the surface, and further, in a 5 vol% H ₂ -N ₂ atmosphere (dew point −30 ° C.)
After heating and holding at 850 ° C. for 40 seconds, annealing for cooling at a rate of 30 ° C./s was performed. The obtained hot-rolled sheet, cold-rolled sheet, and those obtained by subjecting these sheet surfaces to a metal coating surface treatment were used as test materials. Here, as the treatment of the metal film, Zn plating was performed by a hot-dip plating method or an electroplating method, and an alloying treatment was further performed on a part of the metal coating. Some of these test materials were subjected to a zinc phosphate treatment, followed by a 20 μm-thick cationic electrodeposition coating, and the perforation resistance was evaluated by a perforation test shown below.

Pore resistance test Salt spray (JISZ2371) 2 hours → drying (60 ° C)
The cycle of 4 hours → wet (50 ° C., RH 95%) 2 hours was defined as one cycle, and after repeating this cycle 60 times, the maximum corrosion depth was measured to evaluate the puncture resistance. In addition, about the test piece which performed the zinc phosphate treatment and the electrodeposition coating, before the test, make a cut reaching the ground iron with a cutter knife,
After the test, the maximum corrosion depth (thickness reduction value) of the damaged part was measured, and the puncture resistance was evaluated. From the results of the test, when the test piece without plating was used, the reduction in thickness was 0.4 mm.
If less than ○ (good) and 0.4 mm or more × (poor), and the test piece with plating is used, the thickness reduction value is considered in consideration of the merit that the original thickness can be reduced. 0.3
未 満 (good) for less than 0.3 mm and × for 0.3 mm or more
(Poor) was evaluated. Tables 2 and 3 show the obtained test results. As is clear from these tables, the invention examples
Although the piercing resistance was exhibited, the comparative example was inferior in this property.

[0029]

[Table 1]

[0030]

[Table 2]

[0031]

[Table 3]

[0032]

As described above, according to the present invention,
A steel material having excellent puncture resistance can be provided. Further, according to the present invention, without plating, with plating, in any state,
A steel material having good puncture resistance can be provided. Therefore, for example, when the present invention is applied to a steel material for an automobile, it is possible to improve fuel efficiency by making the steel material thinner and lighter. In addition, the amount of steel used can be reduced and the life of the steel can be extended, greatly contributing to the protection of the global environment.

Claims (3)

[Claims] 1. In mass%, C: 0.20% or less, Si: 2.0% or less, Mn: more than 0.3 to 3.5%, P: 0.10% or less, S: 0.02% or less, Al: 0.005 to 0.10%, Sb: 0.002 to 0.50%, and wherein Mn, P, and Sb satisfy the following formula: 0.003 Mn% + 0.02P% ≦ Sb%, and the balance consists of Fe and unavoidable impurities. Steel with excellent drilling properties. 2. In addition to the components described in claim 1, Ti: 0.02 to 0.50%, Nb: 0.001 to 0.50%, Mo: 0.01 to 1.0%, V: 0.001 to 0.50%, B: A steel material having excellent puncture resistance, characterized by containing one or more kinds selected from 0.0001 to 0.0050%. 3. The steel material having excellent puncture resistance according to claim 1, wherein the steel material has a surface treatment layer on at least a part of its surface.