JPS5817811B2 - Fukashiboriseino Sugretakouchiyouriyoreienkohanno Seizouhouhou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention provides a material with excellent deep drawability and a tensile strength of 40 to 50k.
The present invention relates to a method for manufacturing g1mA class cold-rolled high-strength steel sheets.

Recently, there has been an increasing demand for cold-rolled steel sheets that have high strength and excellent deep drawability.

For example, there is a trend that pollution safety is becoming more important in the manufacturing of automobiles, and it is preferable to ensure safety while minimizing the increase in weight of each device. High-strength cold-rolled steel sheets that allow the use of thin steel sheets are also required for exterior panels.

However, conventional steel plates with a strength of 40 to 50 kg/1st grade have poor deep drawability, making it difficult to form parts that require severe processing conditions.

Table 1 shows the composition of conventional 40-50 Yu/1st grade cold rolled steel sheet,
The Lankford value (hereinafter referred to as π value), which is used as one of the measures of strength and deep drawability, is shown.

As is clear from Table 1, the n value of conventional cold-rolled steel sheets is 1.4.50 ky/=1.4.50 ky/=4.4 for grade 4.
2, the n value tends to decrease as the strength increases, and the deep drawability is lower than that of soft cold rolled steel sheets.

It's quite inferior.

The purpose of this invention is to produce a cold-rolled steel sheet that has a tensile strength of 40 to 50 ky/m4 class and has far better deep drawability than conventional steel sheets of this class. .

The above objective is achieved by specifying the composition of the steel that is the raw material for cold-rolled steel sheets and producing cold-rolled steel sheets under specific manufacturing conditions (hot rolling, cold rolling, and annealing conditions). be done.

That is, this invention provides: (i) C: 0.02% or less, s;:o, 5 to 2.0
%, Mn: 0.2 to 1,0 ratio, P: 0.030 ratio or less,
S: 0.030 or less, Sol, Affl: 0.020
~0.100%, Zr:.

Steel consisting of 0.05 to 0.30%, balance iron and unavoidable impurities, and Z r (%) / C (%) of 5 to 7.5, is rolled at a finishing temperature of A, at r3 points or more. (2) C: 0.02. Hot rolled at a temperature of Ar below 1 point, pickled, then cold rolled at a cold rolling rate of 40% or above, and then annealed at a recrystallization temperature of Ac of 3 points or below. (2) C: 0.02 % or less, Si: 0.5-2.
0%, Mn: 0.2 to 1.0 ratio, P: 0.030 ratio or less, S: 0.030 ratio or less, 5olJV: 0.02
0-0.100%, Zr: 0.05-0.30%, Cr
: 0.01 to 0.15%, the balance consists of iron and unavoidable impurities, and the steel has a Zr (%) / C (%) of 5 or more,
The gist is a method for manufacturing a cold-rolled steel sheet that is rolled and annealed under the same conditions as in (1) above.

First, the reason why the material steel composition was determined as described above will be explained.

The strength of C increases as the content increases, but in the present invention,
The increase in strength is due to solid solution hardening of Si and Mn, and the C and N dissolved in solid solution during hot rolling are replaced by Zr and Cr.
This improves deep drawability.

Therefore, in order to make solid solution hardening of Si and Mn effective, and to reduce the required amount of Zr and Cr to fix solid solution C and N, and to make it economical, the upper limit of C was set to 0.02.
%.

As mentioned above, Si is included as a solid solution hardening element to increase strength, but if it is less than 0.5%, the degree of strengthening will be small, and if it exceeds 2.0%, it will be difficult to strengthen after cold rolling or annealing. It not only impairs deep drawability but also tends to cause embrittlement.

Mn is also added to increase the strength of the material, but adding an appropriate amount □ increases the strength without significantly impairing deep drawability.

If it is less than 0.2%, depending on the amount of S and O in the steel, there is a risk of embrittlement during hot rolling, while if it contains excessive Mn, it will not only significantly deteriorate the deep drawability of the material, but also Deteriorates impact properties after deep drawing.

Therefore, the optimum range of Mn is O', 20 to 1. of
b.

Within this range, steelmaking workability is also good.

Both P and S are components that are unavoidably contained in steel manufacturing.

P increases the strength of steel, but if contained excessively, it deteriorates the impact properties after deep drawing.

Also, since S causes hot embrittlement, both elements are 0.0
It was set to 30% or less.

Al is necessary as a deoxidizing agent, and if the amount is small, silicon oxide inclusions are generated in steels containing Si such as the steel of the present invention, impairing the cleanliness and ductility of the steel sheet.

On the other hand, if Al is excessive, alumina in the steel will increase, impairing cleanliness and causing surface flaws.

Therefore, the M content is 0.020 to 0 as Sol-M.
．． There were 100 people in charge.

Zr is an important additive component in manufacturing the steel sheet according to the present invention.

Although Zr does not contribute to an increase in strength, it has the effect of fixing solid solution N, C, etc. that degrade deep drawability as ZrN and ZrC during hot rolling.

However, if Zr is less than 0.05%, the above-mentioned effect cannot be sufficiently exhibited unless the amount of C is considerably low.

On the other hand, excessive content not only unnecessarily increases the recrystallization temperature during annealing, but also is unfavorable for annealing operations and is uneconomical, so the upper limit was set to 30%.

The above Zr is expressed as Zr(%)/C(
%) is 5 or more.

Since Zr and C combine in an atomic ratio of 1:1, Z
Calculating from the atomic weights of r and C, the weight ratio of Zr/C is 8 (!:).

Therefore, in order to completely fix the solute carbon during hot rolling,
Z r (%)/C.

It is desirable to set (department) to 8 or higher.

However, if the ratio of Zr(%)/c(%) is 5 or more,
Considerable effects can be expected compared to steels with lower ratios.

This means that Zr(%)/C(
This is well supported by the relationship between the ratio of b) and the R value.
.

When z r (%)//C (%) is 5, the R value is approximately 1.
57, and when Z r (%)/C (%) is 7.5, the R value is about 1,60, showing an R value superior to that of conventional cold rolled steel sheets.

Further, since the content of N is usually considerably lower than the amount of C, the amount of Zr is sufficient to fix the solid solution C.

If there is, it is thought that solid solution N is also fixed.

Further, if Zr (%)//C (%) is 5 or more, a considerable effect can be expected in fixing solid solution N.

FIG. 1 is a graph showing the relationship between the Zr/C value and the R value in cold-rolled steel sheets.
0.60%, Mn: 0.50%, P: 0.014%,
S: 0.009 section, N2: 0.0030 section,) J:
They were obtained by varying the amount of Zr based on 0.040 steel, and hot rolling, cold rolling, and annealing were all performed within the scope of the present invention.

Cr is also an effective component for improving the deep drawability of cold rolled steel sheets.

As mentioned above, the deep drawability is significantly improved even when Zr is added alone, but if an appropriate amount of Cr is added together with Zr, the deep drawability is further improved.

The lowest amount that produces that effect is 001, while 0.1
．． If it exceeds 5%, the deep drawability of the steel plate will be impaired (Table 2 4)
When adding Cr, the content was set to 0.01 to 0.15% (as in 0 kg class comparative materials (1), (2) and 50 kg class comparative materials (2)).

Next, the reasons for limiting the manufacturing conditions will be described.

If the hot-rolling finishing temperature is lower than the Ar3 point, the structure of the hot-rolled sheet will become mixed grains, which will significantly impair the deep drawability after cold rolling annealing, so it is essential that the finishing temperature be at the Ar3 point or higher.

In addition, if the winding temperature is higher than the Ar1 point, the scale of the hot rolled sheet will become thicker, which will not only impair pickling properties but also cause problems such as unevenness of the material in the longitudinal direction of the coil.
It is necessary to wind it at a temperature below Ar1 point.

The reason why the cold rolling rate is set to 40% or more is that if the cold rolling rate is smaller than that, the sheet passability in cold tandem rolling will deteriorate, and the structure will become coarse during annealing, resulting in poor deep drawability. .

The annealing temperature needs to be higher than the recrystallization temperature to ensure good deep drawability, and if it exceeds the A c 3 point, the orientation of the recrystallized grains will become random and the deep drawability will deteriorate. Point or less.

As mentioned above, this invention makes it possible to manufacture cold-rolled steel sheets with high strength and excellent deep drawability by combining a specific composition and hot rolling, cold rolling, and annealing conditions. be.

The properties of the cold rolled steel sheet produced by the method of the present invention are as follows:
Specific test results are shown along with those of comparative materials.

Table 2 shows 40J/rtaN class cold rolled steel sheets and 50J/rtaN class cold rolled steel sheets.
The chemical composition and mechanical test results of kg/ma class cold rolled steel sheets are shown.

The test materials were manufactured as follows. Refining steel in a converter,
After further vacuum degassing treatment, various alloying elements were added to obtain a steel ingot having the composition shown in Table 2.

After blooming this steel ingot, it was charged into a heating furnace and heated to 1250°C
After soaking for 3 hours, the finishing temperature was 880℃ and the winding temperature was 65℃.
After hot rolling at 0°C to a plate thickness of 3.2 mm, further cold rolling at a cold rolling rate of 75 to a thickness of 0.8 mrn, recrystallization annealing was performed at a temperature of 750°C for 5 hours, and finally 1.2
% temper rolling was performed.

As shown in Table 2, the cold-rolled steel sheets produced by the method of the present invention have high strength and deep drawability that far exceeds that of conventional cold-rolled steel sheets. This can fully meet the demands of industry and other industrial fields.

[Brief explanation of the drawing]

Figure 1 shows the ratio of Zr and C content (Z, -/
It is a graph showing the relationship between C)') and the π value.

Claims (1)

[Claims] 1 c: o, o 2% or less, S i: 0.5 to 2.
0%, Mn: 0.2-1.0%, P: 0.030 or less, S: 0.030 or less, 5oAl! ,AA? :0.
020-0.100%, Zr: 0.05-0.30%,
The balance consists of iron and unavoidable impurities, z r (%) /
A steel having a c (%) of 5 to 7.5 is hot rolled under the conditions of a finishing temperature of Ar 3 points or more and a coiling temperature of Ar 1 point or less, and after pickling, cold rolling at a cold rolling ratio of 40 or more. and then annealing at a temperature higher than the recrystallization temperature and lower than Ac3. 2 c: o, o2% or less, Si: 0.5-2.
0%, Mn: 0.2 to 1.0, P: 0.030 or less, S: 0.030 or less, Sol! , IU: 0.0
20-0.100%, Zr: 0.05-0.30%, C
r:0.01~0.1! 5%, the balance is iron and unavoidable impurities, and Z r (%) / C (a) is 5 or more, hot rolled under the conditions of a finishing temperature of 3 points or more Ar and a coiling temperature of 1 point or less. A method for producing a high-strength cold-rolled steel sheet with excellent deep drawability, which is characterized in that after pickling, cold rolling is carried out at a cold rolling reduction of 40 inches or more, and then annealing is performed at a temperature above the recrystallization temperature and below Ac 3 points.