JPS5954453A - Continuous casting method of steel - Google Patents

Abstract

PURPOSE:To obtain a billet having less defects such as segregation or the like by maintaining the temp. in a slab and a cooling rate in a secondary cooling zone until solidification within a specified range to decrease the rate of bulging and maintaining the temp. for a while after exerting a specified pressure. CONSTITUTION:The average internal cooling rate (CR) in about 1/4 from the surface from right under a casting mold until the completion of solidification is regulated in accordance with the formula determined from a liquidus line temp. and time to diffuse thoroughly carbon and phosphorus and to set the rate of bulging in the central part at about <=0.5mm. so that the concn. of phosphorus is decreased down to a substantially harmless level. Compressive strain is applied in about 0.1-1.5% thickness direction in a point of about <=20% unsolidification rate, by which the solidification shrinkage hole is eliminated, and the accumulation of hydrogen, etc. is prohibited; at the same time, the molten metal is held for about >=15min at about >=1,200 deg.C to diffuse thoroughly carbon and phosphorus. An uneconomical breakdown stage is eliminated by the above-mentioned method and the high temp. feeding to the succeeeding stage is made possible.

Description

DETAILED DESCRIPTION OF THE INVENTION This invention provides a carbon residue t! Alloy addition from 1, hot saw↓! Jj A9- is applied to orientation, toughness, strength, weldability, cold workability, ml corrosion 1t I: and resistance 1
'i''4, !-1, high-grade ril'4, which is provided for limited use with J'j, 1iil's weight; 1□ and relates to a casting method.

One of the factors that inhibits this continuous casting ratio is segregation. Especially the thickness is 11 plates (7) f: 'I' for J'? ■
Conventionally, countermeasures against segregation pair 1 "r'L that degrade 'rI" have been taken against center segregation and V-shaped segregation.
Mac [1 (lGt analysis).The main pair; Cutting or supporting on a surface to prevent the addition of concentrated molten steel due to parunong!: Prevent JII.
(2) The person described in Japanese Patent Application Laid-Open No. 57-62804 711-
．． ．． As shown in FIG. Special Publication No. 44-2441, Special Publication No. 53-1
As shown in J in Japanese Patent No. 12247, there is no (i.
Leave C solid solution steel L >>, make a slab and use it for use
, l, press 2 and especially the center jII contraction hole and the center 1
(4) Proposals to eliminate the 1' and 11 segregations, (4) 3jf, the same organization's trade reform 2, and the JJ+j plan to measure segregation and dispersion using electromagnetic stirring are well known.

The feature of these Jl industries is that both Q and L prevent the formation of the central part 4Ji'iiV, or obtain a healthy JulJ piece by F for slabs that follows the solidification shrinkage of the central part.

However, with these methods alone, it has become impossible to ensure the performance of steel (4), which is becoming increasingly severe, especially for thick steel plates. In the production of "Steel +", which is difficult to obtain, one method is to cool it once; charge the steel sheet into a heating furnace and roll it in a thermal cracking process (called breakdown).
The reality is that after that, soaking and diffusion treatment is performed at a certain temperature.

In the present invention, Nagisa et al., despite the elimination of center segregation due to NH countermeasures during continuous casting, the usability characteristics of the thick steel plate are sufficiently high.
The causes of these unsatisfactory usage characteristics are not only due to so-called macro segregation called central segregation, but also due to andrite tree spacing, etc. It was discovered that this phenomenon is caused by the segregation of impurity elements such as phosphorus, carbon, and sulfur in microscopic regions between crystals (hereinafter referred to as microsegregation and storage). At this point, I put this point on the tree. (Based on the Sung Dynasty, the following sections will be explained in 1.゛.

In addition, in the following theory], in the previous knowledge of lAl- (which worsens the expedient compensation of X++"d I made from four pieces), 1ζ1 uniform diffraction element is Phosphorus, charcoal - (he, 1l) 1 is stirred, and when these elements solidify, 11ii! Analysis II and old 1 are consistent, and the :l]/u maki 1 direction after coagulation is also the same, so phosphorus' I will explain the analysis using a representative.

In addition, manganese, silicon, etc. also precipitate in 111i during solidification, but elements with a concentration of 71% have sharper quality characteristics. Phosphorus, carbon% 41
It is less common than f-yellow and less harmful than Q, and the countermeasures against soil phosphorus in A can almost make it harmless, so it does not reach the same level as A! The effect is the same.

Figure 1 shows the low temperature toughness (-
(Charpy at iQ℃:
It is expressed in rugi (kg・m). ) shows the relationship between 111'f and the finished product phosphorus content 4j -+1t of the steel plate. [:/, I
Inside is the one that was just cast (A) and in addition to that
The low-temperature toughness values of two types of 3 (1 plates) of (b), which were subjected to hot uniform thermal expansion 1t+, are also shown.

Breakdown according to this figure - High? 17j, the low-temperature toughness of the soaked-diffusion treatment is outstanding, and the phosphorus content in the vortex is low. It can be seen that it has excellent low-temperature toughness. The present inventors carried out a more detailed experimental investigation into the cause of this, and found that, as shown in Figure 2, even if the same lymph layer is present, the phosphorus microscopic ( It was found that there was a difference in the form of till analysis. Figure 2 (a) shows the rolled slab of &'5 under pressure 1)jj
', This is a diagram showing the phosphorus segregation in the center of the J corner of the 11th plate using the corrosion method, and Figure 2 (1)) shows the same t
After the ta piece was broken down as described above, it was subjected to W warm-temperature diffusion treatment to obtain a thickness β! It is a diagram showing phosphorus segregation in the center of the thickness of the interplate using a similar method. In the figure, the black part is the phosphorus segregation area.

From now on, we will continue to roll thick steel plates (a
), even though the center 114 segregation has disappeared, the micro-segregation has spread over the ITE and remains wide and long. On the other hand, breakdown - high temperature soaking treatment (interval plate (+3)
This shows that the width is narrower and shorter than the micro-segregation zone t. These 1. “11 plates micro-biased (
11 parts of H and
・Break 7゛un soaked and diffused material (b) and phosphorus content 1i- reduced to 50 ppm and 1.61J bond remaining.
-l1 Each of the extended monthly charges (C) is shown in Figure 3. That's it-・ε゛re's 214 old f! ) The 1j・1\ range of the leaked low temperature toughness value is shown in Figure 4.02111:3
As is clear from the figure and Fig. 4, although sufficient low +74 'l゛・vJ properties were not obtained for the wood, #
; + (+)) was able to obtain a sufficiently satisfactory low temperature gel IJ property value. Incidentally, reducing the phosphorus content to 50 ppm is still not sufficient.

In other words, 1. It is reported that the lower the phosphorus content in the micro-segregation part of the I.1.1 plate, the lower the low-temperature toughness value.

The present invention was made without this knowledge.
・R (7L in both processes, ': /i=' to expand the log 11 to "11) I, 7th Miku a 1 I 1 υr Ir
I: Also, the macro old and t also soaked and expanded by 4, and 1'
1j-wise (l:i! CU'J piece without analysis +1!I, :', "promotes the method of i 7.)" 1, below. Noto'', -ri 1: Yes.

(')', for it'd board, Eite [11'', for A, line A,
(4) In the continuous casting of general carbon steel for commercial use and steel with alloy additions as necessary, in the secondary cooling zone from just below the mold at the point of completion of solidification (1/4 groove from the surface layer of the 011 piece) The average cooling rate (CR) at the second thickness position is c R=(T, -130o)/l<0.2 (here, CR
is the average cooling rate (℃/5ec), 'r, is the liquidus line 1'1
11. (degrees or t is time).A method for continuous casting of steel.

(2) For continuous casting of general carbonite 1 for plates, Sakae steel, wire rod phase, etc., and steel with alloy additions as necessary, J.
Then, the average cooling rate JOf(CR) of 1 toy at a thickness of 174 or more from the Iljl table piece in the secondary cooling zone at υ solidification completion point from just below the 1Jj type, CR= (TL-1300)/l< 0.2 (here CR
is the average cooling rate (°C/see), r14 is the liquidus method + 1 degree or t is time), and the unsolidified rate of the slab is 20
■(Continuous casting method of 13) characterized by maintaining the amount of bulging at 0.5 or less in the secondary cooling zone of 13% or less.

(3) In the continuous casting of steel for 61'i plates, for strips i+'t/f"1, for pure utilization etc. of general carbon +1ii, and with alloy additions as necessary, 6!, 'J,!'CQ
In the secondary cooling zone up to the solidification completion point ((I
J piece f (!, 1/4 thickness lr from layer), upper J!, 7-
7+a) The average cooling rate ((month) at y position is C[l ('f't, 1300)/l<0.2 (where C1, Q, J average cooling rate (℃/5ec), T, 4.j
:*The phase line temperature is also set to t (LIL'l' 1ill), and the second stage of the slab is not heated;
``In the case of a bandage, the parunong'' d is kept at 0.5 rym or less, and the unsolidified rate of the cast slab is at least 0.1% or more in the two-phase region consisting of a solid phase and a liquid phase with a coefficient of 20 or less. J, 1
．． A method for continuous casting of gold of 5 inches or more, characterized by applying shrinkage strain in the J'J direction of IJ.

(4) In continuous casting of general carbon steel for J++4 plates, strips ((・I, etc.) and steel with alloy additions as necessary, the casting process is performed from just below the mold to the solidification completion point. In the next cooling zone, 1/4 J5' or more from the surface of the slab /,'
7mi (near iFi average cooling rate (Crt), CR=(TL-1300)/l minus (1,2(here CR
is the average cooling rate (℃/r4ec), '[' r, ki
above the liquidus line/ζt is time), and the unsolidified rate of the slab is 2.
The amount of bulging is set to 0 in the secondary cooling zone after 0.
A compressive strain in the thickness direction of at least 0.1 coefficient or more and 1.5 inches or less is maintained in the two-phase castle consisting of the same phase and liquid phase, where the solidity of the slab is maintained at 5 or less and the solidity of the slab is 2 () or less. Then, approximately 1/2 of the groove area of both slabs subjected to compressive strain in the thickness direction is maintained at a temperature between 1^1 A-line temperature (Tg) and 1200℃ for at least 15 minutes. That! A method of continuous skillful use of steel with one feature.

According to the present invention, there is no macro-segregation as well as substantially harmful micro-segregation.
Also, the steel keplake down with alloy additions as required is capable of producing a product substantially free of harmful segregation without soaking Iv or scattering treatment. In the present invention, in the secondary cooling zone area up to the solidification completion point, 19.
The limit of the average cooling rate (CR) of 1/4 thickness or more from j is defined as C0.2℃/see. In particular, because the carbon and phosphorus did not diffuse sufficiently, the concentration of carbon and phosphorus in the microscopic (fta) area near the center of the slab was high, and the usage characteristics of the plate could not be satisfied. If the cooling rate LW (CR) is lower than this, the Ti element will be sufficiently diffused at 11.1' below 1/4F!
It has been reduced to the level of 1 steel plate + 1'& satisfaction - Jurul novel. In Naokohi, ;C1 piece j1 (1mi1
/4 thickness or more
1 cooling rate (11 cooling is sufficient, but 1/4 J!i'
From the perspective
If there is a row P1 in which / does not occur, ζ・, 11, - should be gradually cooled from before. , it is 171 most interesting because it lowers the swampy log Buddha in the center of Hayabusa. In addition, the redundant night is given four consecutive times until the fixed point (
J: 'Q', i)'+'D recuperation from uncoagulated bath port J
This is because it waits for v1.

Next, it is necessary to suppress the bulging amount to 0°5 or less in the 1"↓"I region with an unsolidified rate of 20 or less.111) The mountains are as follows.

Keep it cool enough until the solidification is completed, and expand it.
) Oka's distribution is still tri-I-, unsolidified, and 20
In the case of gold bulging in an area of 1-1, the concentrated molten steel in the solid area +(i is sucked, and the remaining molten steel in the central area is
'f) Since the quality θ'1 degree increases, the previous expansion 11
The segregation concentration becomes better regardless of the 7L effect. It goes without saying that it is desirable to eliminate Parunong wind in order to prevent this negative effect, but this fruit;
Close to fit:. Therefore, the present inventors measured all the changes in solute concentration at the center of the thickness by varying the pulse song jd, and found that a substantially virgin phosphorus concentration that satisfies the usage characteristics of steel sheets with bulging of 0.5 mm or less is now possible. :) It all depends on what you found out.

Here, the method of supporting the slab is based on the solidified powder Il.
In order to keep it cool until the cleaning section (%i (ti', j of 71 shells)
In order to reduce the i'jll property and suppress the bulging amount f to 0.5 mm or less, the current support method using rolls has a small rrf capability, and it is recommended to use a surface support method or a group of segment rolls arranged densely and in a staggered manner. desirable.

LE in #'j thickness direction of 0.1% or more just before the next time
By applying shrinkage strain (hereinafter referred to as downstream), the so-called solidification shrinkage pores disappear and the solute elements are prevented from moving to the surface of the solidification shrinkage pores and agglomerating through self-diffusion due to the subsequent sensible heat of the slab, and hydrogen It is also necessary to prevent IX [1] from accumulating in the solidification shrinkage pores.

At this time, if the L level is less than 0.1, there is no downstream effect. Furthermore, at a high JE lowering ratio, a large tensile strain occurs at the 0〈 solid interface, causing inner +111 cracks. The limit pressure 5λ resulting from this internal crack is the pressure of the pressure being reduced).

Although it depends on the profile, the actual j-χ result that the inventor should have obtained is C91.
, Section 1 and 5! 1; Eroto it arises. j7'ko,
The four shoulders 1 speed of solidification 1 and 2 and the heat retention period are regulated by the self-sensible heat of the slab thickness center i'jj (υ
This is to ensure sufficient diffusion. (At the time of Ll, slow cooling is in charge: Keep it at a high temperature.) If the time is long, it takes more effort.1. I'll call you.

The following is an example of Honjo 4 no Hi hlji; 171y, Vero.

Casting is 1Jff curve f, I;, 12 with 10.51FT radius.
Continuous casting/use, XJ method, thickness 280mm x ri 1
1.0 to 1.2n ray n using 900 constant cast J1 gold
It was carried out in Shibuzou Renj↓(.For this casting, υ, depending on the spacing, pre-treatment of hot iron, removal of iron)f treatment and Ca,
A surface support device I!fi: is installed at a distance of approximately 3 m from directly below the VJ type in the continuous casting machine using the blind #1i (1) process. In addition, an air/water spray nozzle is placed in the secondary cooling zone after the surface support device directly under the mold.One strand is further separated by approximately 3.3 nt from the Me4buscus. 1- for length δ of 5 m
1. A specially devised device that allows surface support of the Q'J piece and Ichikawa Shita! ']: was installed, and at the rear of this surface support device, a heat insulating section capable of keeping the hot slab chip warm was installed. The remaining strands are up to the normal length, and the slab is supported by rolls.

In order to compare the effects of the present invention, the strands were made in different amounts, but all the v11 production parameters such as iL'2J production speed and casting temperature were made the same.

Table 1 shows the invention examples, comparative soft examples, ladle components, 3.
y, qVp disputes, macro segregation, micro (i:j analysis, internal cracks, surface cracks, etc.) are shown.

In this table, 0) to φ) are conventional examples ('D to φ) are examples of the present invention.

Conventionally, there is no 1 tari: i+- is also 1/4 Jv of the Z piece, and the 31' uniform cooling rate from the liquidus temperature to 1300℃ (
CR) is as large as 0.25℃, /F e C or more, so Miku (1 level ii'f' f + lIi is the highest phosphor i pitch ("n1aX)" and Kj (shitaame deku) is more than 4 units. When using a steel plate, it is impossible to create a vortex Jj' = -j at any time.

Furthermore, if the unsolidified rate is 20 width 1, the π'i b・(λ) is large, and the center 111i analytical finger I is jJ't −I black segregation. The central segregation index is 140 or more for these applicable steel types.
(I diverted because I don't have L).

In addition, rl+, ・f at the head loading with an uncoagulated rate of 20 cm or more
In the case of q) and (4) in which the reduction rate Ql) exceeded 1.5-, internal division J occurred in both cases and it could not be used.

On the other hand, the slab Hi bottom was not performed ■), ((Rino((4)
Not only does the center segregation index deteriorate, but there is also a V
Shape segregation and solidification shrinkage pores were observed.

In addition, there is a solid phase 1 in the slab 17'2 thickness ij 1%.
．． Ti! A, the maximum phosphorus concentration in the micro-neighborhood group is high, and the maximum phosphorus concentration in the micro-neighborhood is high, and the temperature between the temperatures from ~1°C to 1200°C is 15 minutes (i). :, r 7 things I was satisfied with; I couldn't do it.

On the other hand, among the examples of the present invention, ■ and ■ are examples of the invention of item 1. It was prepared by average cooling to 1j degree (CR) gold to less than 0.2'C/'see. As a result, the maximum phosphorus concentration (Pmax) in the micro-segregation became 0.15% or less, and accordingly, the central segregation index representing the macro-segregation i became 0.5 or less.

Furthermore, as shown in Invention Example (2), when all casting was carried out under the conditions of the second invention with the bulging kept at 0.5 mm or less, the center 1i74 analysis score became 0, and PmaX also became low.

In addition, when a reduction is applied to the two-phase region under the conditions of the third invention as shown in Example ③ of the present invention, the central segregation score is 0, which is good, and at the same time, the micro (lif + analysis becomes more elaborate, and the Pnl
ax also decreased.

In the case of wheat, if the retention time in the high temperature range is prolonged after solidification under the conditions of the invention in Section 4 as shown in the example of the present invention ~ [Phase],
Furthermore, PmaX decreased. (Comparing the present invention example ■ Tori p) In addition, the present invention example with a large compressive strain (However) has the highest phosphorescence in the micro-segregation part! ;Prnax further decreases -j" and toga! i, + “,
The surface properties of the finished product after L-b rolling of R'i copper plate or piano glue 1, qy4.5'' (knee or ?) alloy, etc.) 1 There is no interval L'JI in both the So form and 4J quality, ', 1: lζ (Le f, 1 Use of f shi! 1゛ is sufficiently 1'I: ~ JiL
L It:. In addition, the billet and bloom &, I: of j'1me 1!4mi j and strip i6 and j river are divided into 11 pieces of slab type and made in 1 lip ~, but the problem of segregation, (・swivel shrinkage hole) There wasn't any.

In accordance with the present invention as described hereinafter, the adverse effects of diffraction, which is an unavoidable and life-changing defect of the 11.1 piece, can be avoided in the manufacture of the 1'4 sheet, which has conventionally been used in various ways. Total reduction - going to /ζ unpa: f/? Not only is it possible to omit the high-temperature soaking/diffusion process, but also it is possible to omit the high-temperature soaking/diffusion process in the present invention. It became possible to charge slabs at a crystallized rate, resulting in energy savings of +13 and labor savings of 11, which had great benefits.

[Brief explanation of drawings]

Figure 1 shows the low-temperature toughness value of the R joint. @ When the fishing pieces of (a) and -t are further subjected to high-temperature soaking and diffusion treatment 3-I.1, the steel plate in (b) has a 1η phosphorus thickness close to 1/2 thickness 11) 11 analysis; Mar III
! 1. l'l: Schematic diagram revealed by law, Figure 3 is ii4iK Humin+-+ 111:l InohirojVSminnoifl
Figure 4 shows the relationship between the analytical thickness and the phosphorus concentration measured by the X-ray microanalyzer. be. Patent Applicant Shinto J Hon Steel Co., Ltd. (0) )

Claims (4)

[Claims] (1) For talk board, i, 1:Hip:'I, f~material, etc.-
Remaining coal fu: 11., 1. In continuous casting of steel with alloy additions as necessary, the thickness of the slab at a thickness of 1/4 or more from the surface layer in the secondary cooling zone from just below the mold to the point of completion of solidification. The average cooling rate (CR) is defined as CR=(TL-1300)/l<0.2 (where CR is the average cooling rate ('C/5ee), T+, U: liquidus temperature or t is time). A continuous steel casting method characterized by: (2) In continuous 'Ij'd manufacturing of general carbon 61+i and steel with alloy additions as necessary, such as for steel plates, long steel, wire use, etc., secondary cooling zone from directly below the mold to the point where the solidification light ends. The average cooling rate (CR) at a thickness of 1/4 or more from the surface of the plate is calculated as follows: CR = (Tr, 1300)/l × 0.2 (here, CR is the average cooling rate IA ((°C/see) ), TL is the liquidus temperature or t is the time), and the amount of nitrogen is set to 0 in the secondary cooling zone where the solidity rate is 20% or less.
．． It is characterized by K・If: 'p'+ below 5 tmn (continuous casting of calligraphy j'3J, <direction l). (3) For steel plates, 2) shi, I; iApril 1, ll: 1I
J (・j use,・wo-residual coal fu)1・・il :l',-
Continuation of copper with fine additions if necessary &,! j
In J/let, mold 11g, 1/4 from the surface of the slab in the secondary cooling zone in the coagulation point trench from below)
The average cooling rate (crt) at the thickness position is CR=(TL-1300)/l<0.2 (here, C1l
is the average cooling rate (°C/5ee), TL is the liquidus temperature, or t is the time), and the amount of bulging is maintained at 0.5 or less in the secondary cooling zone where the unsolidified rate of the slab is 20 inches or less. ,
In addition, the slab has a two-phase structure consisting of a solid phase and a liquid phase with a ratio of not more than 20%. A continuous steel casting method characterized by applying #t'+ strain. (4) General carbon for steel plates, Φ drawings, gland use, etc. (In continuous casting of steel with moe and alloy addition as necessary, nails,
The average cooling rate (CR) at the corner position (more than i/48 r from the surface layer of the 5 pieces) is cR = (T, -1300)/l × 0.2 (here, CRi
Yo average? <7 cooling rate (℃/5ec), T t, tj,
'liquid phase + i, J temperature phase - 1) time) and maintain the amount of bulging at less than 0.5 degrees in the secondary cooling zone where the solid flow is less than 2 degrees. , and the two-phase structure consisting of the unr: h; t: 1e・] phase with a solidity of 20% or more and a liquid phase of the μ'3 piece has at least o, 1% or more and 1.5% or less in the thickness direction. A compressive strain is applied, and then a compressive strain is applied in the thickness direction, and the corner area of +u) 4 pieces is 2.14 between the solidus temperature (T8) and 1200'C.
Hold for at least 15 minutes at a temperature of 'l': f
A method of announcing a series of bean paste j1 as a sign.