JPS59208019A - Manufacture of hot-rolled high-tension steel sheet for working - Google Patents

Abstract

PURPOSE:To manufacture the titled steel sheet by continuously casting a steel contg. specified amounts of C, Si, Mn, S and Al, hot rolling the resulting slab without lowering the temp. to the Ar3 point or below, finishing the hot rolling at a specified temp., and carrying out accelerated cooling to a specified temp. at a specified cooling rate and coiling. CONSTITUTION:A steel having a composition consisting of, by weight, 0.12- 0.25% C, <0.5% Si, 0.5-1.2% Mn, <0.015% S, 0.005-0.08% Al and the balance Fe with inevitable impurities is continuously cast, and the resulting slab is hot rolled without lowering the temp. of the slab to the Ar3 point or below. After finishing the hot rolling at (the Ar3 point + 50 deg.C)- the Ar3 point, accelerated cooling to 500 deg.C- the Ms point at >=60 deg.C/sec cooling rate and coiling are carried out to manufacture a steel sheet.

Description

DETAILED DESCRIPTION OF THE INVENTION This invention has an elongation O: of about 30 degrees, an impact*fracture surface transition temperature of about 140 degrees Celsius, and a tensile strength of 50 K9 f/
navy blue? By using hot-rolled high-strength steel sheets that are inferior in terms of processing, toughness, and strength, we effectively use the heat retained in the hot slab obtained by continuous four-piece construction to reduce energy consumption h1.
It relates to a method of manufacturing in small quantities.

Conventionally, non-thermal hot-rolled steel sheets with a tensile strength of 50 KSl'f/mt♂ or higher are hot-rolled by adding elements such as 'I'i, Nb and Y, and then coiled at 550-600°C. This type of material has been mainly known and used, but this type of material [
1 plate requires expensive additive elements, which makes it expensive, and it also lacks versatility in terms of workability, so the current situation is that it cannot meet widespread demand. I was in a bad situation.

In addition, as a non-temperature thermalized high tensile strength steel sheet, after hot-rolling full-length carbon steel, it is rapidly cooled at a temperature of 1 below the his point and coiled.
A copper plate made of two-phase copper is also known, but this copper plate also has the problems of high manufacturing cost and low yield ratio compared to 7JO, and its use is still limited to 1b11.

By the way, in recent years, from 61 points of energy saving, continuous @
The direct insertion rolling method, in which the hot slab after η゛5 (iz-8) is hot-rolled as it is without cooling or after just passing through light heating and heat insulation, has attracted attention, and many research reports have been published. 3 Therefore, attempts were made to apply the direct rolling method to the production of non-thermal hot rolled steel sheets in order to reduce costs, but it was not possible to reduce the temperature of the hot slab to below 3 Ar points. When hot rolling was performed, the austenite grains before rolling became ultra-coarse grains, so the structure after rolling also became coarse grains, resulting in a significant deterioration of workability and toughness. Like VC, continuous casting slab company Ar
The situation continued in which the steel had to be heated to -H, R below the point a, then ladle heated and rolled.

From the above-mentioned viewpoint, the present inventors developed a high-tensile copper plate with sufficient strength and excellent force 1i processing by direct rolling method f.
(Therefore, in order to find a method for manufacturing with less energy consumption, we have repeatedly conducted various tests and investigations on both the steel material composition and rolling processing methods, and as a result,
When hot IJ-rolling carbon steel with a constant component ratio, in order to control the finish temperature, cooling rate after rolling, and coiling temperature to constant values, 1, as the steel component. Without adding any special elements, the hot-rolled slab obtained by rolling and continuous casting has good workability and high strength even if the temperature is not lowered to below the Ar3 point. I came to know that it is possible to obtain a hot-rolled steel sheet that exhibits high toughness.

This invention was made based on the above findings, and includes C: 0°12 to 25%, Si: 0.50% or less, M
u: 0.50-1.2%, S: 0-015%
Below, Al: 1005-0.080%.

or further, P: 0.10% or less, N: 0.300% or less, Ca: 0.10% or less, IJ+: of the following, Fe and unavoidable impurities: remain. Ingredient composition (Hereinafter, the number representing the component ratio is weight 11)
After continuous casting of the slab and 1~
Continue hot rolling without lowering the temperature of the slab below Ar3 point, (Ar3 point + 50℃)~A
r3 point Jt degree T rolling k 'fr' After 3 completion, 500
"A hot-rolled high-strength steel plate for processing that has excellent workability, toughness, and strength by cooling at a cooling rate of 60°C/Sec or more at a cooling rate of 7JII at a temperature of C-Ms point and winding. It is characterized by the fact that it has been fully realized.

Next, in the method for manufacturing a hot-rolled high-strength steel sheet for processing according to the present invention, C, 8i, and Mn, which are components of the material strength.

S, Al, P, N, and Ca V) component composition, ffi
The reason why the K14 rolling conditions and cooling conditions were limited as described above will be explained.

A. Composition of steel (a) C The C component has the effect of strengthening steel, and is 50Kyf/fin? ? In order to obtain a high tensile strength steel plate having a tensile strength of 0.0012 or more, it is necessary to contain J1d" of 0.0012 or more.
If the C content exceeds 25 f=k, the spot weldability, which is essential for high-strength steel plates for automobiles, for example, will deteriorate, so the C content is determined to be 0.12 to 0.25%.

(b) The Si ζ5I component has f2,9. It is 9;4-, which is suitable for holding the revived high tension sword body 1 of IJL note, but its content is 0.
If the diameter exceeds 050φ, the Rin-like t<curvature properties will deteriorate due to the formation of so-called island scales.
The Sl mountain 'I'J'' 11 was determined to be 0°50% or less.

(C) In the 1~in f\'rn component (', the same bath strengthens the steel and improves the hardenability of y1'1, and also improves the ductility of the 7,:3 part by dispersing pearlite grains. The effect of improving is 8.
9 In order to obtain the necessary strength, it is necessary to contain 0.50% or more, but if the content exceeds 1.2%, a two-phase mixture of Rintemp'A-state 5.11 range will occur. Tona9, the λ4n-containing phase has a low yield ratio and increases cost.
It was estimated to be between 0.50 and 1°2.

(d,) S S produces sulfides and deteriorates workability, so it is desirable to have a small amount in terms of size, but if the content is less than 0.015%, it will affect the desired workability. Because it is possible,
The upper limit of the S content was set at 0.015%.

(C) J~l Al (sn6.A, g) Ide:1t7) De-r
l + y agent t 12"C'rT effect is also effective, but Yi's 〇ft・ is 0.005 ratio and c 1 and 1, it is impossible to expect a desu〃Song, and on the other hand it exceeds 0.080 ratio. Even if it is contained, the deoxidizing effect!!4 becomes saturated and no further effect can be expected, so the kl content should be increased from 0.005 to
It was limited to 0.080 chi.

(f) PP component (1. It has the effect of strengthening the total solid solution during relaxation and is actively added to the pot where it is necessary to further improve the strength of the pot. However, its content is 0°10
If φ is exceeded, grain boundaries become brittle, so the P content was determined to be 0.10 or less.

(!:) Similar to P, the N component also has the effect of strengthening steel in the same bath at a low cost, but if nine people are trained at 0.0300%, it will cause blisters during PLL waiting. And η1) It does not include the possibility of deterioration of the process.
i+1. ' r, t (1, cl: (Set as 00% or less.

(1ri (Σa C3I・2 minutes) Ju machining h1.', '9r: There is an effect of turning the steel due to the shape adjustment effect of inclusions, so it is necessary to press the turning even more to improve workability. If there is cold 7Ji] 'iU with 4t', but if the steel is added with 10% or more, the amount of inclusions in the steel will increase, which is opposite to the purpose of adding ijD (C Since this would result in poor workability, the gauze containing ca was determined to be 010 or less.

B. The temperature of the thermal slab cannot be lowered below Ar3 point 311.
Out) The score of the heat slab that was damaged by L.T nail 1 is 3 points ↓ So, 1'! ? What we will be looking at in the next hot sail is the tz taste that eliminates the healthy basic unit of the heating furnace, which is similar to VJ' heating, and Ar3. This is because when the temperature is lowered to a lower temperature, the metal becomes Aβf~ (the strengthening effect of -1 to 1-7% solid solution).

'-'I'F<'+!- System failure temperature (rolling finish is warm) -'1', l 101 is;
! ! Final finish applied to 81I property and O yield point rfl?
This shows the effect of degree T1 in I3], which is C: O
-16~O-2f) %-": O-1~O-2'+
5.

Mn: 0.8-1.0%, S: 0.002~
0.010%.

Al: 0.01-0.05 fissure.

N: o, o O60-Sail 0150 staff.

P: 0.020-0.080.

A steel containing 0 to 0.005 Ca and the balance being Fe was continuously cast in 2001.・Results of an investigation conducted on a 2°5 twr JI hot plate obtained by making a 4-thick slab and then heating it to below Ar 3 points without heating it to 1-12 times. It is.

From Figure gF1, the final finishing temperature (extended to 1 and the sealing temperature) is Ar3. If it is lower than H, the yield point will be extremely high due to the processing of pro-eutectoid ferrite, which will include the ferrite group and the carininity (elongation).
It can be seen that it also deteriorates. On the other hand, the final finishing temperature is (A
When the degree of depression (n, A) is higher than the point (r3 point + 50°C), the effect of turning austenite into ill J, J7 by rolling is insufficient, so the coarse grains of the phase become noticeable9, and the ductility is about 0.
It is clear that this results in deterioration of the wire performance. Therefore, the rolling end temperature should be set from (Ar 3 points + 50℃) to A
The temperature at point r3 was determined.

D. Cooling rate after the end of rolling If the cooling rate after the end of rolling is less than 60°C/Sec, the ferrite grains will become coarse, leading to deterioration of workability and toughness. ”2.

Figure 2 shows the influence of the cooling rate after rolling on the ferrite grain size, elongation, O, and toughness of a steel plate. The final finishing temperature of each (Ar 3 points + 50
The results were investigated using a 2°6-thick steel plate V with three points ranging from ℃) to Ar. It is also clear from FIG. 2 that if the cooling rate after rolling is less than 60° C./SeCi, the pre-EB characteristics deteriorate at various times. .

The upper limit of the cooling rate does not require any special restriction, but if the cooling rate becomes faster than the rod axis 1, bainite will be mixed in, so the upper limit of the cooling rate should be set at 60 to 150°/sec.
A cooling rate of

9. If the cooling rate after rolling is slow, as mentioned above, pro-eutectoid ferrite will precipitate and grow from the coarse γ grains after rolling, forming coarse ferrite grains.
2. The pearlite part, which is the second phase, also becomes thicker and deteriorates workability, so the cooling rate must be controlled to avoid exceeding the lower limit of 60C/5eCfr:'F. It is necessary to fully implement the following.

L, Accelerated cooling end temperature V (coiling temperature) The reason why the coiling temperature was set at 500 to 100°C is because if the temperature exceeds 500°C, klN will precipitate and strengthening by solid solution N cannot be expected. On the other hand, if the steel is wound at a temperature outside the Ms point, it will become a so-called duplex steel and its yield point will be too low, limiting its uses.

Furthermore, by setting the r5 winding temperature to 500°C or less, P
It is possible to prevent embrittlement due to grain boundary segregation of P.
Since it is possible to add a large amount of calories, the winding temperature can be lowered to 5.
Advantageously, the temperature is below 00°C.

In addition, in the method of this invention;
(N7 and above) In the furnace, the ingredients must be adjusted. After being cast, it is hot-rolled, but there are no special VC restrictions on starting ≤/stopping YI11-1Y degrees.
It is essential to directly roll the i'/% slab obtained with J pieces without lowering the temperature to 3 points or less as mentioned above. Here, [i-tangential pressure daughter J is [θ-tangential? This means rolling the product slab by sending it to j+i+, or charging the slab to a heating furnace and then rolling it at 1 heat or 1:ri for heat retention.

Next, let's compare all the examples of this invention according to the implementation sequence.C) lts? IJj 1, Example 1 La-1'1-6 method, C: 0.15, Si:
Q. 1 rice cake.

k'ln: 0.829:r, P: 0.015
%, S: o, o O5%.

Ae: 0.04 force, N: o, o A piece containing O62 was made into a slab with a thickness of 250 mm by rolling and casting, and then rolled under the conditions shown in Table 1. 3
゜5npa Z1! ,,'! A thermal pregnancy plate was manufactured. In addition, the Ar 3 points in (1) are 780°C, the IS room is 105°C, and the temperature is 105°C.

- &7'(-1q':"Normal heating method" in direct mode)
(1 furnace 31゛, the slab is once cooled at home, and then re-O. (1200℃) for the hot rolling staff.
The "re-7Jl heating method" refers to the method of heating the continuous casting slab to 00℃ (00℃) under three points of Ar.
For hot rolling, it is a method of heating the slab to a temperature of 11.
This is a method of rolling with rolling without lowering the temperature to below the r3 point.

And, the 71.5 nature of the board which was detailed in this way, 1 (; 0 to 7.1
Add 11, and Beniiri is also 551 years old.

C): 1.6S, KAs is clear from the results shown, method 1, which failed to produce results, has great energy savings and speed, and alternative processing has both advantages and disadvantages. High strength button 1. Compared to the normal heating method (1) when the board is (14 years old), x method (1) (1, aiming at 5 (+
1 well ζ% lj on Kri f/m iri, 5', wa, 1, not only can't be done, but also requires a thermal momme furnace for multih), υ, 1') method. ) Thermal method is Ruru Comparative method 2 is 41, some proverbial energy and (, zu-naru, but the obtained ρ
If-F: of the board is at the same level as the comparative method] and does not have L7.

[7]Comparative method 3 is a product in which the continuous beveled end slab is directly rolled, resulting in significant energy savings.

Finishing rolling temperature, cooling rate, and winding humidity all failed.

The characteristics of the steel sheet obtained are inferior to Comparative Methods 1 and 2 because the method is outside the 0 range of brightness. , 廿,
In Comparative Methods 6 to 10, any of the finishing degree, cooling rate, and winding temperature are outside the range of the present invention, and the obtained silver plates are also compared to those obtained by the method of the present invention. The characteristics are clearly inferior.

In each of the examples, steel having the composition as shown in Table 2 was cast in a conventional manner and cast into a slab of 200 m1 thickness by continuous casting, followed by heating at 3 points of Ar and lowering the temperature. Rolled directly without rolling. The rolling conditions for this removal are rolling start temperature F
5: 1000℃, finishing temperature: 800℃, cooling rate:
80°C/SeC, coiling temperature: 450°C, and the thickness of the PL plate obtained was 4.5 mm.

The results of measuring the various characteristics of the hot-rolled film prepared in this way are also shown in the second report.

As is clear from the results shown in Table 2.

Whereas methods 11 to 18 of the present invention yield high-strength steel plates having excellent warpage and toughness.

It can be seen that Comparative Methods 19 to 23, which use materials whose chemical compositions are outside the scope of the present invention, yield only steel plates with inferior workability or toughness1. According to the invention, it is possible to produce hot-rolled tensile strength sheets with excellent workability, toughness, and strength at low cost without energy-consuming needlework, and other industrially useful effects. is obtained.

[Brief explanation of the drawing]

Figure 1 shows the effect of temperature on final finish on elongation, toughness and yield point of fl'4 plate, and Figure 2 shows the effect of ferrite grain size A, elongation and toughness of lead plate after rolling. It is a diagram showing the speed change sound 1. 7th station Ar5-5o”c AYs Ar3+5oCA7
+1oo℃ maximum F: L fLL

Claims (1)

[Claims] fl, IC: 0.12 to 0.25%, 31: t
), below 50μ, hermitage: 0.50 to 1.2%, s: o, ois%% or less M: 0.005 to o, o s o, production and unavoidable impurities: rA, from After continuous casting of steel with the following chemical composition (heavily cracked) to form a slab, hot rolling is performed without lowering the temperature of the slab below Ar3 point, (Ar3 point +50
After finishing rolling at a temperature of 3 points (°C) to Ar, 500°C to M
, a method for producing a hot-rolled high-strength steel sheet for processing, the method comprising accelerated cooling at a cooling rate of 60° C./880° C. or higher to a temperature range of point s, and winding the sheet. (2) C: 0012-0.25, Si: Q. 50% or less, Mn:Q. 50 to 1.2%, S: 0°015% or less, Al: 0.005 to O8080, and further contains P20. 10% or less; N: 0.0300% or less; Ca: 0.010% or less. After continuous casting to form a slab, hot rolling was performed without lowering the temperature of the slab below Ar3 point (A13 point +50
℃)~After finishing the rolling at 3 warm points of Ar, 500'C-
A method for producing a hot-rolled high-strength copper plate for processing, comprising accelerated cooling at a cooling rate of 60° C./SeC or higher to a temperature range of Ms point, and winding.