JPS5811743A - Manufacture of soft cold-rolled steel plate which is excellent in aging resistance, by continuous annealing - Google Patents

Abstract

PURPOSE:To obtain a steel plate which is excellent in its strength, ductility and aging resistance, by cold-rolling hot rolled steel containing C, Si, Mn etc. in a prescribed ratio, under a prescribed condition, and annealing it continuously. CONSTITUTION:Steel consisting of 0.01-0.05% C, <=0.1% Si, 0.05-0.3% Mn, 0.02-0.1% solAl, <=0.005% N, and Fe of the remaining part is hot-rolled, and is wound at a temperature of >=650 deg.C. Subsequently, annealing is performed by dividing into a cooling velocity in a temperature area exceeding an Ar1 transformation point, a cooling velocity in a temperature area reaching a quick- cooling start temperature TQ from the Ar1, and a cooling velocity of a temperature area of TQ-200 deg.C. In case when an annealing temperature TA is <=750 deg.C, V1 is optional, and in case of TA; >=750 deg.C, V1 is <=-0.2TA+180( deg.C/sec). In case of the following temperature; Ar1-TQ, the cooling velocity is set to 40-100 deg.C/ sec. Also, in case when a temperature is TQ-200 deg.C, the cooling velocity is set to 250 deg.C/sec.

Description

[Detailed Description of the Invention] The present invention relates to the creation of a method for manufacturing a soft cold-rolled steel sheet with excellent aging resistance by continuous W8 dulling, and aims at manufacturing a soft cold-rolled steel sheet with excellent aging resistance. The aim is to provide a method that allows for

The production of cold-rolled steel sheets for drawing by continuous annealing has been well known for some time, but the reason behind the production of cold-rolled steel sheets for drawing by continuous annealing is In addition, even during rapid heating annealing after rolling, sufficient grain growth of noble crystal ferrite grains, which is preferable as a steel sheet for drawing, should be promoted, and drawing should be carried out. In order to precipitate l#KC, an interstitial solid solution element in ferrite, in a short time in order to eliminate strain aging, which is the main cause of material deterioration in steel sheets for industrial use, after annealing, ERIC is saturated during rapid cooling. Point 02 is to bring it into a solid solution state and then perform an overaging treatment using the supersaturation degree as a driving force.

However, soft cold-rolled steel sheets manufactured by continuous annealing satisfy all the requirements of low strength, high marriageability, high deep drawability, and non-aging properties of soft cold-rolled steel sheets manufactured by ordinary box annealing. K has not yet been achieved, and steel sheets for drawing are mainly products that are below intermediate grade. This is because short-time heating annealing does not allow sufficient growth of feetite grains. The dominant factor is that solid solution C in ferrite cannot be completely precipitated in the overaging treatment stage. Therefore, with the aim of manufacturing soft cold steel sheets with continuous annealing, we have developed a method to promote ferrite grain growth and a method to reduce the interstitial solid solution elements (and <vcC) in ferrite to a level where aging does not become [11]. Many studies have been made regarding this. Regarding the former, it is possible to obtain a desired material level relatively easily even with ordinary low-C steel by performing high-temperature annealing. However, regarding the latter, if we ignore the cost, there are methods such as reducing C in the steel by degassing in advance and then adding π or the like to fix the remaining C, but this method is advantageous at low cost. No technology has yet been discovered that can be used to develop this technology. This is because conventional continuous annealing cannot sufficiently precipitate solid solution C in ferrite during the overaging treatment stage.

The present invention was devised after careful consideration in view of the above-mentioned circumstances, and is intended to improve the aging resistance of soft cold-rolled steel sheets by improving the continuous annealing method without adding special K11II special elements. succeeded in improving it effectively. That is, in the present invention, the aging property is significantly improved without deterioration of the material by controlling the cooling/turning from the annealing heating temperature in one continuous annealing, and the cooling pattern is controlled. The main point is to satisfy the following conditions.

■ During the cooling process from the annealing heating temperature, the temperature inside the steel is uneven.
The cooling rate (vl) at gA above the transformation temperature is controlled under the following conditions.

When annealing temperature (Tj)>750°C, V* <-0,2Tj+180 (C/sec) When annealing temperature (Tj)<750°C, Vt is arbitrary.

■ The temperature in the steel changes from Arl to the quenching start temperature TQ (600
Any temperature in the temperature range from °C to 500 °C ) cooling rate up to K! (Vs).

The temperature should be in the range of 40°C/sec or more and 100°C/sec or less.

- Cooling rate (Vs) t' 250 for 7 seconds or more until the zone temperature reaches 200°C or less from TQ.

■ Perform overaging treatment on the steel at a temperature of 300°C or higher and 400°C or lower.

The present invention makes it possible to manufacture a cold-rolled steel sheet for drawing with excellent ductility and slow aging properties by performing continuous annealing while satisfying the above conditions. It can be applied to all general steel types for soft cold-rolled steel sheets.

Further information on each of the above requirements constituting the present invention I/Ca12
To be clear, in order to produce a cold-rolled steel sheet with excellent aging resistance through continuous annealing, K is used to supersaturate solid solution C in ferrite in the cooling groove phase from the annealing temperature, as mentioned above. Using this 1 saturation type as a driving force, the overaging treatment stage I
Attempt to precipitate solid solution C in ferrite during @i waiting time in Il#. If this degree of supersaturation is insufficient, sufficient driving force for C precipitation cannot be obtained, which not only necessitates a long overaging treatment but also makes it impossible to achieve sufficient C precipitation. First, strain aging of the annealed plate due to residual solid solution CK becomes a problem.

So, consecutive #! For #i blunt, appropriate quenching treatment is performed before overaging treatment, but at what level of supersaturated solid solute C is reached at that time, strain aging of fired M& is not slowed down by overaging treatment. Figure 1 shows the influence of the amount of C in the supersaturated bath during quenching on the aging index after overaging treatment. . In other words, the points in the figure indicate the C content of 0.015 to 0.04.
This is shown for 4 different steels, but the aging index after overaging treatment is independent of the steel composition, and the solid solute C1l during quenching is
It can be seen that under the over-aging treatment conditions, it is determined in a So-like manner.

In other words, in order to obtain an aging index (AI) <3.5kII7/-, which is at a level where strain aging is not a problem, the solid solute C1Q-breath during cooling is Q-")80XIO""' (
>138 ppm) and (>156 ppwa
), but in general, strain aging is not a problem if Ax (a, 5 to 9//-).The provisions of ``Shidam 1'' are separately specified in Figure 2. This is the place to do it.

Therefore, in order to improve the aging properties of soft cold-rolled steel sheets manufactured by continuous annealing, it is necessary to
It is necessary to control the continuous annealing heat cycle in order to make Q-'>80X10-4. In other words, the present invention is based on the above-mentioned technical concept, and the continuous annealing process is 8K.
j? Therefore, there is a novelty in defining the cooling/#turn to obtain the desired amount of supersaturated solid solution C without compromising the deterioration of the ductility of the annealed plate.

To explain in detail the reasons for specifying the cooling conditions from the following KIiM temperature (T), Figure 3 shows the Lii molten C in ferrite during continuous annealing heating and cooling for Steel 1.3 in Table 1, which will be described later. This shows the change in quantity. This third
As is clear from the figure, when soaking for 1 minute at the heating temperature, the solid solution C in ferrite does not depend on Cl1K of steel, but on Fs
- The #t so-plane value expected from the C system phase diagram is reached. However, during the cooling process (air cooling), it was found that the solid lWC in the ferrite was cooled by a significantly non-equilibrium downward movement, and this non-equilibrium cooling of 6 degrees was 1 degree different from the carbon content and processing temperature. . Therefore, in order to increase the solid solution C in the ferrite as much as possible at the time of rapid cooling, judging from the Pb-C system phase diagram,
In the humidity region above the Arl transformation temperature, the cooling rate is slowed down as much as possible to maintain a state close to the equilibrium state Ill#c, and ArI transformation is carried out.
It is considered effective to perform cooling in a non-equilibrium state (2) by increasing the cooling rate as much as possible in the humidity region below 30°C.

Figure 4 (al is the amount of solid solute C in ferrite at Ar1 (near 00°C) when cooled at a cooling rate in the range of 2.5 to b seconds from the annealing temperature, at 700°C at each cooling rate. It is clear from this figure that the amount of solid solute C at 700℃ is shown in Figure 1 when annealing is performed at high temperature. Q″
In order to obtain 80×10-', it is necessary to slow down the cooling rate.

Therefore, solid solution CtttQ″″ chanting〉80XI at 700℃
Figure 4 (b) shows the results of the cooling rate required for each annealing temperature in order to obtain O''4. speed(
vl) under the conditions of the following formula, it becomes solid fe#C at 700℃.
t can be q-1≧80X10-4.

vl(0,2Ta+180 (CIf/pl) At an annealing temperature Tj<750°C, steel with c>o, o1j hardness already has q-”>5oxto-4 at the annealing temperature, which decreases when cooled to 700°C. Therefore, the cooling rate can be set arbitrarily.

Next, the cooling rate (7 times) from Arl to the quenching start temperature (TQ) and TQ are the solid # of the ferrite at TQ.
Cfl and total elongation and yield strength after overaging treatment (1,5
Fig. 5 shows what carvings are produced when the pressure is adjusted.

Solid solution Ct at quenching start temperature TQ is Q-1≧80XIO-
'To set TQ to 500℃ or higher and from Arl to T
The cooling rate to Q must be 40° C./second or higher.

When TQ<500°C, the solid solution C in the ferrite rapidly approaches the flat-sided NK, so it is difficult to achieve optical supersaturation of C. On the other hand, regarding the changes in yield strength and total elongation when performing overaging treatment at 350°C for 2 minutes after rapid cooling (water quenching) treatment from TQ, the cooling rate from MrI to TQ once When the temperature is 100° C./second or more, the yield strength increases and the total elongation decreases significantly.

In addition, if TQ exceeds 600℃, it is possible to obtain sufficient overload strength scm, but on the other hand, the yield strength level increases and the total elongation level decreases significantly, making it undesirable as a steel plate for drawing. , cooling rate from Arl to TQ (Vs) t-4
Specified at 0℃/second or more and 100℃/second or less, and TQ is 6
The temperature range is defined as 00°C or lower and 500°C or higher.

Furthermore, the effect of the cooling rate (V,) from this rapid cooling TQ to 200° C. or less is as shown in FIG.

That is, originally, the degree of supersaturation of solid solution C in TQ was maximized in the overaging treatment.

In order to effectively act as a driving force for C precipitation, K is
i below Q! Cooling should be performed as rapidly as possible. However, if cooling is substantially performed at 250°C/paper or higher, it is possible to reduce the aging index after overaging treatment to 3.5 kgf/- or less. Therefore, cooling from TQ to a temperature of 200°C or less is specified at 250°C/sec or more.

After cooling under the above series of cooling conditions, from 300℃ to 4℃
By performing the overaging treatment at a temperature of 0.000C, it becomes possible to produce a cold rolled steel sheet having good ductility and excellent slow aging properties. Regarding the over-aging treatment conditions, there are no detailed regulations regarding the percentage, but if the temperature is less than 300°C, it will take a long time to perform a sufficient aging treatment, so it is preferable that I L < tr. Moreover, at temperatures exceeding 400° C., p+ solid solution of precipitated C becomes a problem, and conversely, the solid solution C increases, resulting in deterioration of aging properties. For these reasons, it is assumed that the overaging treatment is carried out at a temperature range of 300°C to 400°C.

The delayed annealing thermal cycle consisting of the basic constituent elements of the present invention described above is as shown in @7.

Now, as mentioned above, the present invention can be applied to all steels 111 for general soft cold rolled steel drawing, but substantially the range should be 0.010<c<0.0501. It is. This is difficult to achieve in steels with a carbon content of 0.010 or less, since even under the cooling conditions specified in the present invention, there is an optical overblast of solid solute carbon. In addition, in steels with C of 0.050 or more, it is essential to obtain sufficient ductility in practice.

Moreover, when & is contained in a large amount, it causes an increase in A-based inclusions and deteriorates ductility. Therefore, for a soft steel plate, 0.1 is specified as the upper limit that can ensure the desired ductility.

- If contained in a large amount, the Lankford value decreases, so it is necessary to specify an upper limit for the steel plate for drawing. In addition, if the lower limit is lowered too much, hot embrittlement due to B cannot be suppressed, so S removal treatment must be performed to improve the strength, leading to an increase in cost.

In addition, problems arise in steelmaking, such as poor flow of molten steel. Therefore, − is, from the above point of view, annealed at, respectively;
No overage treatment.

350°C x 2 minutes → air cooling・ ■Inventive method (Tj>750°C) T no 850°C, vl =
8℃/8, V,=50℃/8, Vm-1500℃1
5 ■ Rice method (Tj〉750℃) Tmu = 850℃, Vl =
15°C/S, Vm = 15°C/8. Vs=1
At 500/S ■ Invention method (Tj<7so℃) T no 700
℃, V, = 50℃/B, Vs = 1500℃/S ■ 78 at Tj - 700℃, Vt = 15
, Vs=1500°C/S The tensile property values and aging index of the obtained steel plate are shown in Table 2 below.

That is, as is clear from the above table, c<o, ot.

Tsuna-no-So, even if it is an invention method! However, if c<o, oso is excellent, satisfactory ductility and low yield strength as a steel sheet for drawing cannot be obtained. However, it is clear that for steels with 0.010<c<o and oso<o>, cooling by the method of the present invention significantly improves aging properties without deteriorating elongation or increasing yield gff. There is.

In the history of steel I, the material and aging after overaging treatment when the cooling conditions after phosphorus annealing were changed dramatically are shown in the following table 81! Only in this way can a material with excellent ductility and favorable aging resistance be obtained.

! 3 tables Cooling conditions based on the method of the present invention: Satisfied - ○.

Unsatisfactory - × This invention According to the present invention, the cold-rolled steel sheet for drawing which has an excellent balance of strength and ductility and also has aging resistance, as shown in the JI No. 85 tensile test piece or higher after 1.5 degrees of pressure adjustment. This invention makes it possible to accurately manufacture KL by continuous annealing, and is an industrially highly effective invention.

[Brief explanation of the drawing]

The drawings show the technical contents of the present invention, and FIG. 1 is a chart showing the relationship between the amount of solid solute C during quenching and the aging index after overaging treatment, and FIG. A! A graph showing the change in the amount of solid solute C in ferrite during the FI heating and cooling process. The third graph shows the influence of the aging index on yield point elongation recovery i+t and elongation deterioration tK after aging at 38°C for 16 days. Figure 4 shows the influence of the cooling rate (V,) from the annealing temperature to Arl on the solid solution C1K in ferrite at mu r1, the annealing temperature necessary to obtain Q-'>5oxio-a, and the cooling rate. A diagram showing the relationship between (vl) and ferrite = molten C at a temperature of 650°C (TQ)
The yield strength (1) and total elongation (k) when subjected to water-cooled backward aging based on the amount and sheep temperature are also shown in the table, and the influence of the cooling rate from Ar4 to TQt. Chart showing the cooling rate from TQ to room temperature, No. 7
The figure shows 115! of the slow ribbon annealing heat cycle according to the present invention! This is a clear diagram. Patent applicant: Nippon Kokan Co., Ltd. Inventor: Aijima Matsufuji Takashi Shimomura
Good question Vice No.
Shudo Ono
Supported by Yoshi Hosoya
HI'A cliff R
('%) Figure 5 ArljM n21? ``ty@p force let ('B/x
) Fig. 6 (11111匈所 Cumulative; ilD”l:Xη啼!片) No. 7
Figure ↑ 11, 1, 1, 1, 1, 2, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 3, 3, 3, 4, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 4, 5, 1, 2, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 4, 5, 10, 10, 10, 10, 10, 10s 100s sb 1stsssssssssssssssssss why's' Related patent applicant name (Mr. Nippon Steel Tube Co., Ltd. 4, agent 1939, Month, Day, Dispatch 6, subject of amendment - as per the paper -) 'Contents of amendment B No. 12 in the specification of the present application Page line 14 f [Rapid cooling TQ
Correct J to C quenching start temperature TQJ 0 2, page 15, line 8 l Correct ``At killed steel'' to read (At killed steel) 0 4 In the attached drawings of this application Correct Figure 5 as shown in the attached sheet.

Claims (1)

[Claims] C: 0.010 to 0.05011. i: 0.11 or less,
& : 0.05~0.30 Tatami, sel, Aj:
0.02 to 0.101, N: 0.00501 or less and the remainder consists of h'j and unavoidable impurities. The cooling rate is divided into a temperature range above the Arl transformation point, a temperature range from the Mr1 turning point to the rapid cooling start temperature TQK, and a temperature range from this TQ to 200 ° C or less, In the temperature range above the Arl transformation point, if the annealing temperature is 750'C or less, cooling is performed at an arbitrary cooling rate, and if the annealing temperature is 750'C or higher, the cooling rate is set to satisfy the formula that satisfies the following Arl transformation point. In the temperature range from 40 to TQK, the cooling rate in the temperature range from 40 to 200'C is 2.
A method for producing a soft cold-rolled steel sheet with excellent aging resistance by continuous annealing at a temperature of 50° C./se or higher. V 凰 (-0.2°rm+180℃℃/re) However, %Vl is the cooling rate in the temperature range above the Mr1 transformation point〒A is the annealing temperature