JPH1060540A - Production of high carbon cold rolled steel strip - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the generation of seizing flaws in a steel strip by prescriging the conditions of annealing. SOLUTION: A hot rolled steel strip subjected to pickling and descaling is repeatedly subjected to soaking and slow cooling of executing soaking and holding for <=8Hr under heating to the Ac1 point to the Ac1 point +50 deg.C at a heating rate of 20 to 100 deg.C/Hr by using a bell-type batch annealing furnace in a gas atmosphere composed of >=75vol.% hydrogen, and the balance nitrogen and executing cooling to the Ar1 point or below at a cooling rate of <=50 deg.C/Hr for two times. In this way, the spheroidizing rate of cementite improves, and the production of a soft hot rolled steel strip is made possible. Then, it is subjected to cold rolling at 20 to 85% draft and is next subjected to finish annealing at 630 deg.C to directly below the Ac1 point by a bell-type batch annealing furnace. In this way, cold rolling strains are released to grow the crystal grains, by which a soft recrystallized texture can be obtd. As a result, the possibility of occuring seizing flaws can be solved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for high-hardness parts such as blades, washers, seat belt fittings, etc., and has a uniform shape and characteristics, and is relatively soft and has a high softness and good processing characteristics. The present invention relates to a method for manufacturing a rolled steel strip.

[0002]

2. Description of the Related Art Generally, blades, springs, washers, springs, seat belt fittings, and other mechanical parts are JIS-compliant.
The high carbon cold rolled steel strip, which is a special steel strip specified in G 3311, is used as a material, and is manufactured through processing steps such as punching, bending, pressing, and cutting, and quenching, tempering, and other heat treatment steps. In order to improve the product quality, stabilize, and reduce the manufacturing cost, it is necessary that the high-carbon cold-rolled steel strip as the material is soft, has good workability, and has excellent structure uniformity.

[0003] The high-carbon cold-rolled steel strip is manufactured by pickling a hot-rolled steel strip, then cold rolling and annealing to adjust the hardness to a desired hardness. It is required to have a predetermined hardness by heat treatment performed after processing, and to have sufficient hardness and abrasion resistance for use as a product. Therefore, annealing after cold rolling must be performed at a high temperature, and as a result, seizure flaws are likely to occur due to close contact between steel strips. There is a problem that poor quality is liable to occur due to annealing seizure due to severe surface inspection.

Conventionally, as a method for converting a high-carbon cold-rolled steel strip into a soft and easy-to-work structure, in hot rolling, rapid transformation on a run-out table is performed to complete the phase transformation, and the steel having undergone the phase transformation is completed. Using a high-carbon hot-rolled steel strip obtained by winding the strip at 500 to 620 ° C as a base material, the base material is cold-rolled at a rolling reduction of 20% or more, and then, at a point of Ac 1 point or more and 770 ° C in a bell furnace.
A method of annealing at the following temperature (Japanese Patent Laid-Open No. 58-55532), C: 0.27 to 0.90%, Si: 0.15 to
0.30%, Mn: 0.60 to 0.90%, P: 0.0
30% or less, S: 0.035% or less, steel containing normal balance of Fe and unavoidable impurities is subjected to ordinary hot rolling, and then hot-rolled steel strip obtained by pickling is used as a starting material to start high-carbon cold rolling. In the method for producing a steel strip, primary annealing is performed by holding the hot-rolled steel strip as the starting material at a temperature of 680 to 720 ° C for 15 hours or more, and then cold rolling is performed at a rolling reduction of 20 to 45%, Thereafter, a method of performing finish annealing in which the temperature is maintained at a temperature of 630 to 720 ° C. for 10 hours or more (Japanese Patent Application Laid-Open No. 61-766)
No. 19), C: 0.3% or more high carbon hot rolled steel sheet,
Intermediate cold rolling is performed at a rolling reduction of 45% or more, and then intermediate annealing is performed by box annealing.
c1 point, C: 680 to 750 ° C. when 0.8% or more
The final rolling is performed at a rolling reduction of 13% or more, and the thickness before and after the intermediate cold rolling and the thickness after the final cold rolling are respectively t ₀ , t _1, and t _2. , The logarithm ln (t ₀ /
against t _1), the logarithm ln (t ₁ of the final cold reduction ratio of rolling
/ T ₂ ) is 0.5 times or less, and final annealing is performed by box annealing at 550 to 700 ° C. for 1 to 6 hours (JP-A-3-21235).
A high-carbon hot-rolled steel strip having a chemical composition of 0.6 to 1.3%, Si: 0.5% or less, Mn: 1% or less, Cr: 1.6% or less, and the balance substantially consisting of Fe Ac 1 point to 780 ° C. in an atmosphere furnace containing 50% by volume or more of hydrogen and the balance being nitrogen
After the soaking in the temperature range of 1 hour or more, the first stage soaking / slow cooling to cool down to just below the Ar 1 point at a cooling rate of 60 ° C./Hr or less, and after soaking for 3 to 20 hours just below the Ac 1 point , 60 ° C
/ Hr at a cooling rate of not more than Ar1 point
After subjecting to a primary annealing treatment consisting of soaking and slow cooling of the step, cold rolling is performed, and then a secondary annealing treatment is performed in a temperature range from 600 ° C. to just below the Ac1 point (Japanese Patent Laid-Open No. Hei 4-202629).
And the like have been proposed.

[0005]

SUMMARY OF THE INVENTION The above-mentioned JP-A-58-55 is disclosed.
No. 532 discloses a method in which an annealing step before cold rolling is omitted, pickling is performed, then cold rolling is performed, and the subsequent annealing is performed using Ac1.
As described above, since the surface of the high-carbon cold-rolled steel strip has a bright skin as described above, as long as it is processed in a batch coil annealing furnace, it is for high-temperature annealing of more than Ac1 point.
Anneal seizure flaws occur, and it is difficult to stably produce high-carbon cold-rolled steel strip with actual production equipment. Moreover, this method is based on the premise that a high-carbon hot-rolled steel strip obtained by winding a steel strip which has been phase-transformed by rapid cooling on a hot-rolled run-out table at 500 to 620 ° C is used as a base material. But 55
If the temperature is 0 ° C. or lower, the ductility of the base material is reduced, and breakage in the pickling line in the next step or breakage during cold rolling occurs, which has a disadvantage that the operation is significantly impaired.

In the method disclosed in Japanese Patent Application Laid-Open No. 61-76619, the primary annealing temperature of a hot-rolled steel strip is 680 to 720.
° C and the Ac1 point or less, a sufficiently soft high carbon steel strip cannot be obtained.

Further, in the method disclosed in Japanese Patent Application Laid-Open No. Hei 3-21235, the intermediate annealing is performed at 680 ° C. to an Ac1 point or less.
Since it is performed for 0 to 40 hours, it is disadvantageous in terms of efficiency, and wasteful in actual production equipment. Also, Japanese Patent Application Laid-Open No. Hei 3-21235 states that "If the intermediate annealing temperature is higher than the Ac1 point, C:
In a steel of 0.6% or less, a spheroidization rate is reduced due to generation of a ferrite phase, and even when C exceeds 0.6%, part of the steel is completely austenitized, so that coarse pearlite is generated upon cooling after annealing, Again, the spheroidization rate decreases. And C: 0.3-0.8% of high carbon hot rolled steel strip,
There is a problem that the spheroidization rate cannot be reduced. Moreover, the finish annealing temperature is set to 55 by box annealing.
It is soaked at 0 to 700 ° C for 1 to 6 hours, but it is necessary to raise the annealing temperature for softening. In the high carbon hot rolled steel strip, seizure flaws are generated, so it has to be annealed at low temperature. Not get
Soft annealing of thin materials is difficult.

Further, in the method disclosed in Japanese Patent Application Laid-Open No. 4-202629, the soaking time when the annealing temperature is raised to a temperature of from Ac 1 point to 780 ° C. is set to 1 hour or more, but the upper limit is specified. Not. As described later, it is difficult to obtain spherical cementite after annealing for a long time at an Ac point or more, and it is rather deteriorated after working. Even after repeated cold rolling and annealing, the workability of a high carbon steel strip is improved. Improvement cannot be expected. Further, in coil annealing, Ac1
Above this point, a specific method for realizing short-time annealing is not disclosed, and it is impossible to stably obtain a good spheroidized structure with an actual machine.

An object of the present invention is to solve the above-mentioned problems of the prior art, to provide a high carbon cold rolled steel sheet having workability equal to or higher than that of a conventional high carbon cold rolled steel strip and having excellent crystal structure homogeneity. Steel strip,
An object of the present invention is to provide a method for manufacturing a high-carbon cold-rolled steel strip that can be manufactured at low cost while preventing the occurrence of seizure flaws.

[0010]

According to the first aspect of the present invention, C: 0.3-1.3%, Si: 0.03-0.35.
%, Mn: 0.20 to 1.50%, the balance being substantially high Fe and unavoidable impurities.
75% by volume after hot rolling, pickling and descaling
Using a bell-type batch annealing furnace in a gas atmosphere in which the hydrogen and the balance substantially consist of nitrogen and unavoidable impurities,
Ac1 point to Ac1 point + 5 at a heating rate of １００100 ° C./Hr
After heating to 0 ° C. and maintaining the soaking temperature for 8 hours or less, the first stage of soaking and slow cooling to cool to Ar 1 point or less at a cooling rate of 50 ° C./Hr or less, and Ac1 at a heating rate of 20 to 100 ° C./Hr.
After heating to a point + Ac1 point + 50 ° C and maintaining a soaking temperature of 8Hr or less, a second stage of soaking and gradual cooling to cool to an Ar1 point or less at a cooling rate of 50 ° C / Hr or less, and thereafter from 20 to 100
After the primary annealing treatment of cooling to room temperature at a temperature of ° C./Hr, cold rolling is performed at a rolling reduction of 20% or more and 85% or less, and then finish annealing is performed in a bell-type batch annealing furnace at 630 ° C. to just below Ac1 point. . Thus, the high carbon hot rolled steel strip is
Ac 1 point to Ac at a heating rate of 20 to 100 ° C./Hr using a bell-type batch annealing furnace in a gas atmosphere consisting of 5% by volume or more of hydrogen and the balance substantially consisting of nitrogen and inevitable impurities.
Heat to 1 point + 50 ° C, keep 8Hr or less soak, then 50 ° C
By repeating soaking and slow cooling twice at a cooling rate of not more than / Hr to Ar1 point or less, the spheroidization rate of cementite is improved, and a soft hot-rolled steel strip can be manufactured.
In addition, cold rolling is performed at a rolling reduction of 20% or more and 85% or less,
Next, by performing finish annealing in a bell-type batch annealing furnace at 630 ° C. to just below the Ac1 point, a soft hot-rolled steel strip having completed spheroidization is formed to a predetermined plate thickness, and the cold rolling strain is released to reduce the crystal grains. It is possible to obtain a soft, high-carbon cold-rolled steel strip that has grown.

[0011] The invention of claim 2 of the present application is characterized in that:
0.3-1.3%, Si: 0.03-0.35%, M
n: 0.20 to 1.50%, the balance being substantially F
e and hot rolling, pickling and descaling of a high carbon steel slab consisting of unavoidable impurities, followed by a bell-shaped gas atmosphere comprising 75% by volume or more of hydrogen and the balance substantially consisting of nitrogen and unavoidable impurities. Using a batch annealing furnace, 20 to 10
Heating from Ac1 point to Ac1 point + 50 ° C at a heating rate of 0 ° C / Hr and holding soaking at 8Hr or less, then cooling to Ar1 point or less at a cooling rate of 50 ° C / Hr or less, first stage soaking, slow cooling And an Ac 1 point to an Ac at a heating rate of 20 to 100 ° C./Hr.
Heat to 1 point + 50 ° C, keep 8Hr or less soak, then 50 ° C
/ Hr at a cooling rate of not more than Ar1 point
Step soaking, slow cooling, heating from Ac1 point to Ac1 point + 50 ° C at a heating rate of 20 to 100 ° C / Hr, holding at a soaking temperature of 8Hr or less, and then down to Ar1 point at a cooling rate of 50 ° C / Hr or less. The third stage of cooling, soaking and gradual cooling, is performed.
After primary annealing under the condition of cooling to room temperature at 100 ° C / Hr, cold rolling is performed at a rolling reduction of 20% or more and 85% or less, and finish annealing is performed in a bell-type batch annealing furnace at 630 ° C to just below Ac1 point. And As described above, the high-carbon hot-rolled steel strip is heated at a rate of 20 to 100 ° C./Hr using a bell-type batch annealing furnace in a gas atmosphere consisting of 75% by volume or more of hydrogen and the balance substantially consisting of nitrogen and unavoidable impurities. And Ac1
After heating to a point + Ac1 point + 50 ° C and maintaining a soaking temperature of 8Hr or less, cooling at a cooling rate of 50 ° C / Hr or less to Ar1 point or less is repeated three times to reduce the spheroidization rate of cementite. It further improves and approaches nearly 100%, and a softer hot-rolled steel strip can be manufactured. Further, by performing cold rolling at a reduction ratio of 20% or more and 85% or less, and then performing finish annealing in a bell-type batch annealing furnace at 630 ° C. to just below Ac1 point, a soft hot-rolled steel strip having completed spheroidization can be obtained. It is possible to obtain a soft high-carbon cold-rolled steel strip having a predetermined thickness, releasing the cold rolling strain and growing crystal grains.

Further, the invention according to claim 3 of the present application is characterized in that, after the primary annealing, cold rolling at a reduction ratio of 20% or more and 85% or less, and finish annealing at 630 ° C. to just below Ac1 point in a bell-type batch annealing furnace. Is repeated twice or more. As described above, after the high-carbon hot-rolled steel strip is subjected to the primary annealing treatment, the rolling reduction is 2%.
By repeating the cold rolling of 0% or more and 85% or less and the finish annealing at 630 ° C. to just below the Ac1 point in a bell-type batch annealing furnace twice or more, the final sheet thickness is small, for example, 0.3 mm in thickness. If the desired thickness cannot be obtained by one cold rolling as in the above, cold rolling should be stopped once, finish annealing should be performed under the same conditions, and then soft rolling should be performed again. The thickness of the steel sheet is set to a desired value, and the finish annealing is performed again under the same conditions to soften the steel sheet. Thus, a soft high-carbon cold-rolled steel strip having a sheet thickness of 0.3 mm can be obtained.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hot rolling of a high carbon steel slab having the above-mentioned chemical composition is performed by a usual method, and there are no particular restrictions on hot rolling conditions. It is preferably performed after the transformation. The crystal structure of the hot-rolled steel strip wound at a high temperature before the completion of the phase transformation has a structure in which coarse pearlite has developed, whereas the crystal structure of the hot-rolled steel strip wound after the completion of the phase transformation has The structure has a homogeneous structure consisting of ferrite + pearlite or fine pearlite or fine pearlite + pro-eutectoid cementite, so that segregation of the austenite phase in the primary annealing treatment is small and uneven distribution of spheroidized carbide and variation in particle size are suppressed. It is effective to do.

In the primary annealing treatment of the hot-rolled steel strip in the bell-type batch annealing furnace in the present invention, the temperature difference between the outermost periphery and the coldest point is large in the bell-type batch coil annealing. As shown, at a temperature of 0 ° C. and a pressure of 0.1 MPa, hydrogen having a thermal conductivity of about 7 times that of nitrogen and a density of about 14 times that of nitrogen is set to be 75% by volume or more in the atmosphere gas, thereby obtaining a coil width of 960 mm. As shown in FIG. 2 showing the relationship between the soaking time and the temperature difference in the coil when the coil having an outer diameter of 1847 mm, a inner diameter of 610 mm, and a weight of 18 Ton was annealed at a soaking temperature of 770 ° C., the heat transfer inside the coil was As a result, the temperature difference between the inner and outer circumferences of the coil can be reduced as compared with the conventional case mainly using nitrogen, and a bell-type batch annealing furnace can be applied.

[0015]

[Table 1]

The primary annealing treatment in an atmosphere gas comprising 75% by volume or more of hydrogen and the balance substantially nitrogen is carried out at a heating rate of 20 to
After soaking at 100 ° C./Hr from Ac1 point to Ac1 point + 50 ° C. for 8 hours or less, the first stage soaking and slow cooling step of gradually cooling to 50 ° C./Hr or less to 1 Ar or less, and heating rate of 20 to
After soaking at 100 ° C. from Ac1 point to Ac1 point + 50 ° C. for 8 hours or less, and then gradually cooling at 50 ° C./Hr or less to Ar 1 point or less, a second stage soaking and slow cooling step, and more preferably a heating rate Ac1 point to Ac1 point +5 at 20 to 100 ° C / Hr
After soaking at 0 ° C for 8 hours or less, A at 50 ° C / Hr or less
It comprises a third-stage soaking and gradual cooling step of gradual cooling to the r1 point or lower, and a cooling step of cooling to room temperature at a rate of 50 to 100 ° C./Hr.

The soaking in the first stage soaking and slow cooling step is a step in which pearlite having a hot-rolled structure is solid-dissolved in austenite, and the slow cooling after soaking is a process in which undissolved residual carbide is nucleated. This is a step of generating spheroidized carbide by precipitation of solid solution C. The reason why the heating rate is set to 20 to 100 ° C./Hr is that if the heating rate is lower than 20 ° C./Hr, the operating efficiency is poor.
When the temperature exceeds 00 ° C./Hr, the heating efficiency is deteriorated, and the temperature in the coil is likely to be uneven. Soaking temperature is from Ac1 point to Ac1
The reason for setting the temperature at the point + 50 ° C. is that if the temperature exceeds the Ac1 point + 50 ° C., undissolved carbides serving as nuclei for forming spheroidized carbide grains cannot be left, and pearlite is formed even when the cooling conditions are controlled. This is because if it is below the Ac point, it takes a long time to form cementite into a spheroid. The reason for setting the soaking time to 8 hours or less is that pearlite is likely to be formed under conditions of 8 hours or more.

The cooling rate following the first stage soaking is 50 ° C./H
When the cooling rate exceeds 50 ° C./Hr, the precipitation of solid solution C is suppressed, so that the formation of spheroidized carbide having undissolved carbide as a nucleus becomes insufficient, and a large amount of C is contained in austenite. This is because the Ar1 transformation occurs while forming a solid solution, resulting in a layered pearlite structure. The reason why the cooling ultimate temperature is set to the Ar1 point or less is that the cooling ultimate temperature is Ar
If it exceeds one point, the formation rate of spheroidized carbide is deteriorated, so that the temperature may be lower than Ar 1 point. However, if the temperature is lowered more than necessary, the processing efficiency and thermal economy when performing subsequent soaking in the subsequent stage Ar1 point to Ar
One point at -20 ° C is sufficient.

The soaking in the second-stage soaking / slow-cooling process is performed after the first-stage soaking / slow-cooling process to further improve the generation rate of spheroidized carbides, and in the third-stage soaking. The soaking in the heat and slow cooling step is a process for further improving the generation rate of spheroidized carbide after the second-stage soaking and slow cooling step, so that a soft steel strip can be manufactured. The reasons for limiting the heating rate, soaking temperature, soaking time, cooling rate, and cooling temperature in the second and third stages of soaking and slow cooling processes were described in the first stage soaking and slow cooling process. It is on the street.

The cooling rate from the Ar 1 point or lower to room temperature after the first or second stage or the first to third stages of soaking and slow cooling is set to 50 to 100 ° C./Hr because the cooling rate is less than 50 ° C./Hr. In this case, the operation efficiency is poor, and when the temperature exceeds 100 ° C./Hr, the temperature difference between the inner and outer circumferences of the coil becomes large, and the generation rate of the spheroidized carbide becomes uneven.

After the primary annealing treatment consisting of the first or second stage or first to third stage soaking and slow cooling steps, the rolling reduction is 20 to 8%.
Perform cold rolling at 5%. The high-carbon hot-rolled steel strip subjected to the primary annealing treatment has a homogeneous structure in which spherical carbide grains are uniformly dispersed in the ferrite structure, and unlike the hard and brittle structure as it is hot-rolled, it is soft and soft. It shows good workability.
Therefore, the high-carbon hot-rolled steel strip subjected to the primary annealing treatment has excellent workability in cold rolling, and can be cold-rolled to a predetermined thickness without causing troubles such as cut edges. The reason why the rolling reduction in the cold rolling is set to 20 to 85% is that if it is less than 20%, abnormal grain growth of crystal grains may occur in the subsequent finish annealing treatment, and the elongation may be significantly reduced. This is because a break may occur during cold rolling and the operation may be significantly impaired.

The finish annealing treatment after the cold rolling is a heat treatment for causing the texture formed by the cold rolling to recover and recrystallize to change the texture to a soft recrystallization texture in which work hardening is eliminated. . The finish annealing treatment is achieved by maintaining the temperature soaked at 630 ° C. to just below the Ac1 point for a predetermined time. The reason why the finish annealing temperature was set to 630 ° C. to just below the Ac1 point was 63
If the temperature is lower than 0 ° C., recrystallization and grain growth of ferrite become insufficient, resulting in insufficient softening effect. Also, Ac
If the number exceeds one point, an austenite phase is formed, and layered pearlite appears during the cooling process to become hard and may cause seizure flaws.

Unlike the primary annealing, the finish annealing is not necessarily required to be performed in a high hydrogen atmosphere, but may be performed in a nitrogen-based atmosphere. In this finish annealing treatment, the soaking time is not so important,
A soaking time of about 5 hours is sufficient. Further, the control of the cooling rate is not particularly required, and for example, natural cooling can be performed.

After the primary annealing treatment including the first and second or first to third stage soaking and slow cooling steps, the rolling reduction is 20 to 8%.
Even if cold rolling is performed at 5%, the final sheet thickness is thin, for example,
In the case of 0.3 mm or less, if the desired sheet thickness cannot be obtained by one cold rolling, the cold rolling is temporarily stopped, the finish annealing treatment is performed under the same conditions, and the softening is performed again. Cold rolling is performed to obtain a desired thickness, and finish annealing is performed.
This finish annealing treatment can be performed a plurality of times according to the thickness of the finished plate.

The reasons for limiting the components of the high carbon steel used in the present invention are as follows. C is an element having an effect of imparting strength, hardenability, wear resistance, and the like to steel. The lower the softness, the better the workability. However, if less than 0.3%, the hardenability is insufficient, and a predetermined amount after heat treatment. Hardness cannot be obtained. on the other hand,
If it exceeds 1.3%, the hardness at the stage of the hot-rolled steel strip is high, and no matter how well the cementite is spheroidized by the primary annealing treatment, elongation is deteriorated and cold rolling becomes difficult. 0.3 to 1.3%.

Si is an element to be added as a deoxidizing agent, but if it is less than 0.03%, the deoxidizing effect is not sufficient, and if it exceeds 0.35%, the deoxidizing ability is saturated, and solid solution hardening occurs. From 0.03 to
0.35%.

Mn is an element which improves the strength and hardenability and has the effect of stabilizing cementite.
If it is less than 0.2%, stable hardenability cannot be secured, and if it exceeds 1.5%, the effect of improving the hardenability is saturated and the hardness of the material is increased.
2 to 1.5%.

[0028]

EXAMPLES Example 1 Steel No. 1 having the chemical composition shown in Table 2 was used. 1-5 high carbon steel slabs
Finish plate thickness: 2mm, Finish temperature: 840 ° C, Winding temperature: 5
After hot rolling under hot rolling conditions of 90 ° C. to form a high carbon hot rolled steel strip, pickling and descaling, using a bell-type batch annealing furnace, in an atmosphere gas consisting of 99% by volume of hydrogen and the balance of nitrogen Test No. shown in Table 3. The primary annealing treatment including the first and second stage soaking and slow cooling steps of Nos. 1 to 26 was performed. Then
After cold rolling at a rolling reduction of 40%, a finish annealing at a soaking temperature of 710 ° C. and a soaking time of 6 hours was carried out in an atmosphere gas consisting of 99% by volume of hydrogen and the balance of nitrogen using a bell-type batch annealing furnace. To obtain a high-carbon cold-rolled steel strip. A test piece was cut out from each high-carbon cold-rolled steel strip, and the Vickers hardness (HV) was measured according to the Vickers hardness test method specified in JISZ 2244. For each steel type of each high-carbon cold-rolled steel strip, JIS G 3
Evaluation was made based on the softness (see Table 4) in comparison with the Vickers hardness after annealing specified for the special steel strip specified in 311. Table 3 shows the results. No seizure flaw was observed in the high-carbon cold-rolled steel strip after completion of the finish annealing.

[0029]

[Table 2]

[0030]

[Table 3]

[0031]

[Table 4]

As shown in Table 3, Test No. 1 in which the soaking temperature in the primary annealing treatment was less than Ac1 point. The high-carbon cold-rolled steel strip No. 2 has a Vickers hardness HV of 174, and is not sufficiently softened. The soaking temperature of each stage in the primary annealing process is A
Test No. c exceeding point + 50 ° C. The high-carbon cold-rolled steel strips Nos. 5 and 17 are hard with Vickers hardness HV: 215 and 160. Test No. 1 in which the soaking time of each stage in the primary annealing treatment exceeded 8 hours. 9 and 21 high carbon cold rolled steel strips
Vickers hardness HV: Hard, 194,216. Test No. 1 in which the cooling rate in the primary annealing treatment exceeded 50 ° C./Hr. The high-carbon cold-rolled steel strips 11 and 23 are also hard.
Test No. 1 in which the ultimate cooling temperature in the primary annealing treatment was Ar 1 point or more. The 12 and 24 high carbon cold rolled steel strips are also hard with Vickers hardness HV: 171 and 180.

On the other hand, in the primary annealing treatment, the soaking temperature of each stage is from Ac1 point to Ac1 point + 50 ° C., the soaking time of each stage is within 8 hours, the cooling rate is 50 ° C./Hr or less, and the cooling ultimate temperature is Test No. 1 that satisfies the conditions of the present invention just below the Ar1 point. 1, 3, 4, 6 to 8, 10, 14 to 16, 18 to
As shown in Table 3, the high carbon cold rolled steel strips of 20, 22, and 25 all have a Vickers hardness (HV) that is softer than the standard. In addition, as shown in Table 3, test No. 2
Although the heating rate and the cooling rate of each stage in the primary annealing treatment as shown in FIG. 6 do not adversely affect the hardness of the high-carbon cold-rolled steel strip at 5 ° C./Hr and 3 ° C./Hr, the production efficiency of the annealing treatment is reduced. There is no merit in energy saving.

Example 2 Steel No. 1 in Table 2 of Example 1 was used. No. 2 high carbon steel slab, finishing plate thickness: 2 mm, finishing temperature: 840 ° C, winding temperature: 590 ° C
After hot rolling under hot rolling conditions to form a high carbon hot rolled steel strip, pickling, descaling, using a bell type batch annealing furnace,
As shown in Table 5, heating rate: 50 ° C./Hr, soaking temperature:
Ac 1 point + 20 ° C, soaking time: 2 hours, cooling rate: 30
° C / Hr, cooling attainment temperature: Ar 1 point -20 ° C, first stage soaking, after slow cooling, heating rate: 10 ° C / Hr, soaking temperature: A
c1 point + 20 ° C, soaking time: 2 hours, cooling rate: 10 ° C
/ Hr, ultimate cooling temperature: Ar 1 point-10 ° C. second stage soaking and slow cooling to perform primary annealing treatment. Then, after cold rolling at a reduction of 40%, using a bell-type batch annealing furnace, in an atmosphere gas consisting of 99% by volume of hydrogen and the balance of nitrogen, finishing at a soaking temperature of 710 ° C and soaking time of 27 hours Test No. 31 high carbon cold rolled steel strips were obtained.

In order to confirm the soaking and gradual cooling effects after the third-stage soaking and gradual cooling steps in the primary annealing treatment, the first and second-stage soaking and gradual cooling were performed under the same conditions as described above. As shown in Table 6, heating rate: 10 ° C./Hr, soaking temperature: Ac 1 point +
20 ° C., soaking time: 4 hours, cooling rate: 10 ° C./Hr,
Achieved cooling temperature: Ar 1 point-10 ° C., third-stage soaking, gradual cooling, primary annealing treatment, then cold rolling at a reduction of 40%, and using a bell-type batch annealing furnace, hydrogen 99 volume %, In an atmosphere gas consisting of the balance nitrogen, soaking temperature: 7
A finish annealing treatment was performed at 10 ° C. and a soaking time of 27 hours. 32 high carbon cold rolled steel strips were obtained. After the first and second stages of soaking and gradual cooling under the same conditions as above, heating rate: 10 ° C./Hr, soaking temperature: Ac 1 point + 20 ° C., soaking time: 4 hours, cooling rate: 10 ° C./Hr, ultimate cooling temperature: Ar 1 point −10 ° C., third and fourth stage soaking, slow cooling, primary annealing, cold rolling at 40% reduction, bell-shaped batch Using an annealing furnace, in an atmosphere gas consisting of 99% by volume of hydrogen and the balance of nitrogen, soaking temperature: 71
Test annealing was performed after finishing annealing treatment at 0 ° C. and soaking time: 27 hours. 33 high carbon cold rolled steel strips were obtained. A test piece was cut out from each high-carbon cold-rolled steel strip, and Vickers hardness (H) was determined according to the Vickers hardness test method specified in JIS Z 2244.
V) was measured. Table 6 shows the results. No seizure flaw was observed in the high-carbon cold-rolled steel strip after completion of the finish annealing.

[0036]

[Table 5]

[0037]

[Table 6]

As shown in Table 6, in the primary annealing treatment, test No. 1 was subjected to first and second stage soaking and gradual cooling, followed by third stage soaking and gradual cooling. The high carbon cold rolled steel strip of Test No. 32 was subjected to the first and second stage soaking and slow cooling. 31
Spheroidization is further promoted compared to the high carbon cold rolled steel strip of
The Vickers hardness is reduced by 4 points to make it softer. However, after the first to third stage soaking and gradual cooling, test No. 4 was subjected to the fourth stage soaking and gradual cooling. In the high-carbon cold-rolled steel strip of No. 33, the spheroidization approaches nearly 100% by the third-stage soaking and slow cooling, so the effect after the fourth-stage soaking and slow cooling is reduced, and the disadvantage of prolonged time is reduced. It was confirmed that it became larger.

Example 3 In order to investigate the influence of chemical components in steel, steel N shown in Table 7 was used.
o. Each high carbon steel slab of 6 to 20 was hot rolled under hot rolling conditions of a finishing plate thickness: 2 mm, a finishing temperature: 840 ° C., and a winding temperature of 590 ° C. to form a high carbon hot rolled steel strip. After pickling and descaling the hot-rolled steel strip, using a bell-type batch annealing furnace, in an atmosphere gas consisting of 99% by volume of hydrogen and the balance of nitrogen, heating rate: 50 ° C./Hr, soaking temperature: Ac 1 point +2
0 ° C., soaking time: 2 hours, cooling rate: 30 ° C./Hr, cooling ultimate temperature: Ar 1 point, first stage soaking at −20 ° C., after slow cooling, heating rate: 10 ° C./Hr, soaking temperature : Ac 1 point + 2
Primary annealing treatment was performed by performing a second-stage soaking at 0 ° C., soaking time: 2 hours, a cooling rate: 10 ° C./Hr, an ultimate cooling temperature: Ar 1 point−10 ° C., and slow cooling. Then, after cold rolling at a reduction of 40%, a bell-type batch annealing furnace was
In an atmosphere gas consisting of volume% and the balance nitrogen, soaking temperature:
Each high carbon cold rolled steel strip was obtained by performing a finish annealing treatment at 690 ° C. and soaking time: 2 hours. A test piece was collected from each of the obtained high-carbon cold-rolled steel strips and subjected to JIS Z 224 in the same manner as in Example 1.
Vickers hardness was measured according to the Vickers hardness test method specified in 4. Table 7 shows the results. No seizure flaw was observed in the high-carbon cold-rolled steel strip after completion of the finish annealing.

[0040]

[Table 7]

As shown in Table 7, the steel Nos. 11 and 15 high carbon cold rolled steel strips
Since the addition amounts of i and Mn exceed the upper limit of the range of the present invention, the steel strip is harder than other steel strips corresponding to the present invention. In addition, steel N
o. The high-carbon cold-rolled steel strips Nos. 8 and 12 are soft because they are below the lower limits of the present invention. However, steel No. In the high-carbon cold-rolled steel strip No. 8, since the Si content is low, the fatigue strength after quenching and tempering involves the risk of property deterioration due to an increase in oxides. In addition, steel No. In the high carbon cold rolled steel strip No. 12, since the Mn content is low, the quenchability is reduced, and there is a risk that sufficient hardness cannot be obtained after quenching and tempering.

Example 4 In order to investigate the effects of the rolling reduction in the cold rolling after the primary annealing and the soaking temperature in the finish rolling after the cold rolling,
The steel No. shown in Table 7 above. No. 13 high-carbon steel slab was hot-rolled under hot-rolling conditions of a finishing plate thickness: 2 mm, a finishing temperature: 840 ° C., and a winding temperature of 590 ° C. to form a high-carbon hot-rolled steel strip, and pickling.
After descaling, using a bell-type batch annealing furnace,
In an atmosphere gas consisting of 99% by volume of hydrogen and the balance of nitrogen, heating rate: 50 ° C./Hr, soaking temperature: Ac 1 point + 30 ° C.
Soaking time: 4 hours, Cooling rate: 40 ° C./Hr, Cooling attainment temperature: Heating of the first stage at Ar 1 point, after slow cooling, Heating rate: 1
0 ° C / Hr, soaking temperature: Ac 1 point + 20 ° C, soaking time:
4 hours, cooling rate: 10 ° C./Hr, ultimate cooling temperature: Ar
One-point second-stage soaking and slow cooling were performed to perform a primary annealing treatment. Next, after the cold rolling was performed with the reduction ratio changed in the range of 20 to 87% as shown in Table 8, the finish annealing temperature was determined in an atmosphere gas consisting of 99% by volume of hydrogen and the balance of nitrogen using a bell-type batch annealing furnace. 620-720 ° C, finish annealing time 2
A one-hour finish annealing was performed to obtain a high carbon cold-rolled steel strip. A test piece was collected from each high-carbon cold-rolled steel strip and subjected to JISZ2241.
A tensile test is performed in accordance with the specified metal material tensile test method, and the yield point (YP), tensile strength (TS), and elongation (EL)
Along with JIS Z 22 as in Example 1.
Vickers hardness (HV) was measured according to the Vickers hardness test method specified in 44. Table 8 shows the results. No seizure flaw was observed in the high-carbon cold-rolled steel strip after completion of the finish annealing.

[0043]

[Table 8]

As shown in Table 8, in test No. 2 in which the rolling reduction in cold rolling was 20%. As is clear from 35,
When the rolling reduction is less than 20%, the crystal grains cause abnormal grain growth, which indicates that the elongation is reduced. Further, in test No. 1 in which the rolling reduction in cold rolling exceeded 85%. In No. 40, fracture occurred during cold rolling. For this reason, the rolling reduction in cold rolling is limited to 20 to 85%. Further, in the test No. having a finish annealing temperature of 620 ° C. In 41,
Hardness is high and elongation is significantly lower. For this reason, the finish annealing temperature needs to be 630 ° C. or higher. On the other hand, in the test No. satisfying the conditions of the present invention. 36
~ 39, 42-44, satisfactory hardness HV and elongation were obtained.

Example 5 Steel No. 3 in Table 7 of Example 3 was used. The high carbon steel slabs of Nos. 18 and 20 are hot-rolled under hot rolling conditions of a finishing plate thickness: 2 mm, a finishing temperature: 840 ° C., and a winding temperature of 590 ° C. to form a high-carbon hot-rolled steel strip, pickling and removing. After the scale treatment, using a bell-type batch annealing furnace, in an atmosphere gas consisting of 99% by volume of hydrogen and the balance of nitrogen, heating rate: 50 ° C./Hr, soaking temperature: Ac1
Point + 30 ° C, soaking time: 4 hours, cooling rate: 40 ° C / H
r, ultimate cooling temperature: soaking at the first stage of Ar1 point, after slow cooling,
Heating rate: 10 ° C / Hr, soaking temperature: Ac 1 point +20
C., soaking time: 4 hours, cooling rate: 10 ° C./Hr, cooling ultimate temperature: second-stage soaking at one Ar point, and slow cooling to perform a primary annealing treatment. Next, as shown in Table 9, the steel No. 1
The high-carbon hot-rolled steel strip of No. 8 was subjected to the first cold rolling at a reduction of 75% to a sheet thickness of 0.5 mm, and thereafter was composed of 99% by volume of hydrogen and the balance of nitrogen using a bell-type batch annealing furnace. In an atmosphere gas, as shown in Table 10, annealing temperature: 690 ° C.
Annealing time: The first finish annealing was performed for 20 hours, and as shown in Table 9, the second cold rolling was performed at a rolling reduction of 40% to a sheet thickness of 0.3 mm, and a bell-type batch annealing furnace was used. In an atmosphere gas consisting of 99% by volume of hydrogen and the balance of nitrogen, Table 1
0, annealing temperature: 690 ° C., annealing time: 20
The second finish annealing was performed for a long time to obtain a high-carbon cold-rolled steel strip. In addition, steel No. As shown in Table 9, the high-carbon hot-rolled steel strip of No. 20 was subjected to the first cold rolling at a rolling reduction of 60% to a sheet thickness of 0.8 mm, and then a bell-type batch annealing furnace was used.
In an atmosphere gas consisting of 99% by volume of hydrogen and the balance of nitrogen, as shown in Table 10, annealing temperature: 690 ° C., annealing time: 2
Perform the first finish annealing in 0 hours, as shown in Table 9,
The second cold rolling was performed at a rolling reduction of 38%, and the sheet thickness was 0.5 m.
m, and in a bell-type batch annealing furnace, in an atmosphere gas consisting of 99% by volume of hydrogen and the balance of nitrogen, as shown in Table 10, annealing temperature: 670 ° C., annealing time: 20 hours, the second finish annealing was performed. Then, as shown in Table 9, the rolling reduction was 40%.
The third cold rolling was performed to obtain a sheet thickness of 0.3 mm, and using a bell-type batch annealing furnace, in an atmosphere gas consisting of 99% by volume of hydrogen and the balance of nitrogen, as shown in Table 10, annealing temperature: 660 C., annealing time: 20 hours, a third finish annealing was performed to obtain a high carbon cold rolled steel strip. A test piece was collected from each of the obtained high-carbon cold-rolled steel strips and was subjected to JIS Z in the same manner as in Example 1.
Vickers hardness (HV) was measured according to the Vickers hardness test method specified in 2244. Table 9 shows the results. No seizure flaw was observed in the high-carbon cold-rolled steel strip after completion of the finish annealing.

[0046]

[Table 9]

[0047]

[Table 10]

As shown in Tables 9 and 10, by repeating cold rolling and finish annealing, it is possible to produce a high carbon cold rolled steel strip having a small thickness.

[0049]

According to the method for producing a high-carbon cold-rolled steel strip according to the first aspect of the present invention, a high-carbon hot-rolled steel strip is produced by using a gas comprising 75% by volume or more of hydrogen and the balance substantially consisting of nitrogen and inevitable impurities. Using a bell-type batch annealing furnace in an atmosphere, 20 to 100 ° C / H
By heating to the Ac1 point to the Ac1 point + 50 ° C. at a heating rate of r and maintaining a soaking temperature of 8 Hr or less, cooling at a cooling rate of 50 ° C./Hr or less to Ar 1 point or less is repeated twice. The spheroidization rate of cementite is improved, and a soft hot-rolled steel strip can be manufactured. In addition, reduction rate 20% or more 8
By performing cold rolling at 5% or less, and then performing finish annealing in a bell-type batch annealing furnace at 630 ° C. to just below the Ac1 point, the spheroidized soft hot-rolled steel strip is reduced to a predetermined thickness. The crystal grains grow by releasing the strain during rolling, and a soft high-carbon cold-rolled steel strip can be obtained.

The method for producing a high-carbon cold-rolled steel strip according to a second aspect of the present invention is characterized in that the high-carbon hot-rolled steel strip is formed in a gas atmosphere comprising 75% by volume or more of hydrogen and the balance substantially consisting of nitrogen and unavoidable impurities. Using a bell-type batch annealing furnace, 20 to 100 ° C / Hr
Heating from Ac1 point to Ac1 point + 50 ° C at a heating rate of 8
After holding at a soaking temperature of less than Hr, A
By repeating the soaking and slow cooling three times at or below the r1 point, the spheroidization rate of cementite is further improved to approach almost 100%, and a softer hot-rolled steel strip can be manufactured. Further, by performing cold rolling at a reduction ratio of 20% or more and 85% or less, and then performing finish annealing in a bell-type batch annealing furnace at 630 ° C. to just below Ac1 point, a soft hot-rolled steel strip having completed spheroidization can be obtained. It is possible to obtain a soft high-carbon cold-rolled steel strip having a predetermined thickness, releasing the cold rolling strain and growing crystal grains.

According to a third aspect of the present invention, there is provided a method for producing a high-carbon cold-rolled steel strip, comprising: performing a primary annealing treatment on the high-carbon hot-rolled steel strip; By repeating the finish annealing in a batch annealing furnace at 630 ° C. to just below the Ac1 point twice or more, a soft ultra-thin high-carbon cold-rolled steel strip having a thickness of 0.3 mm or less can be obtained.

[Brief description of the drawings]

FIG. 1 is a graph showing a relationship between hydrogen concentration and thermal conductivity at temperatures of 400 ° C., 600 ° C., and 800 ° C.

FIG. 2 is a graph showing a relationship between a soaking time at an atmospheric temperature of an atmosphere gas consisting of 75% of hydrogen and the balance of nitrogen and an atmosphere gas consisting of 5% of hydrogen and a balance of nitrogen, and a temperature difference in a coil.

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location C21D 9/663 C21D 9/663 A C22C 38/00 301 C22C 38/00 301S 38/04 38/04

Claims (3)

[Claims] 1. C: 0.3-1.3%, Si: 0.03
０．３0.35%, Mn: 0.20 to 1.50%,
After the high-carbon steel slab substantially consisting of Fe and unavoidable impurities is subjected to hot rolling, pickling, and descaling,
Ac 1 point to A at a heating rate of 20 to 100 ° C./Hr using a bell-type batch annealing furnace in a gas atmosphere consisting of 75% by volume or more of hydrogen and the balance substantially consisting of nitrogen and inevitable impurities.
c1 point + 50 ° C after heating to 8Hr or less
1st stage soaking, cooling down to Ar 1 point or less at a cooling rate of not more than ° C / Hr, and heating to Ac1 point to Ac1 point + 50 ° C at a heating rate of 20 to 100 ° C / Hr and soaking for 8Hr or less After the holding, a second-stage soaking and gradual cooling is performed at a cooling rate of 50 ° C./Hr or less to a point of Ar or less.
After performing a primary annealing treatment of cooling to room temperature at 100 ° C./Hr, cold rolling is performed at a rolling reduction of 20% or more and 85% or less,
Then, a finish annealing is performed in a bell-type batch annealing furnace at a temperature of 630 [deg.] C. to just below the Ac1 point. 2. C: 0.3-1.3%, Si: 0.03
０．３0.35%, Mn: 0.20 to 1.50%,
After the high-carbon steel slab substantially consisting of Fe and unavoidable impurities is subjected to hot rolling, pickling, and descaling,
Ac 1 point to A at a heating rate of 20 to 100 ° C./Hr using a bell-type batch annealing furnace in a gas atmosphere consisting of 75% by volume or more of hydrogen and the balance substantially consisting of nitrogen and inevitable impurities.
c1 point + 50 ° C after heating to 8Hr or less
1st stage soaking, cooling down to Ar 1 point or less at a cooling rate of not more than ° C / Hr, and heating to Ac1 point to Ac1 point + 50 ° C at a heating rate of 20 to 100 ° C / Hr and soaking for 8Hr or less After the holding, a second stage of soaking and cooling at a cooling rate of 50 ° C./Hr or less to an Ar 1 point or less, and 20 to 100 ° C./hr
After heating from Ac1 point to Ac1 point + 50 ° C. at a heating rate of Hr and maintaining a soaking temperature of 8 Hr or less, a third-stage soaking and gradual cooling in which the cooling rate is 50 ° C./Hr or less to 1 Ar or less is performed. After that, after performing a primary annealing treatment of cooling to room temperature at 20 to 100 ° C./Hr, cold rolling is performed at a rolling reduction of 20% or more and 85% or less, and 630 ° C. to Ac in a bell-type batch annealing furnace.
A method for producing a high-carbon cold-rolled steel strip, wherein finish annealing is performed immediately below one point. 3. After the primary annealing treatment, cold rolling with a rolling reduction of 20% or more and 85% or less and 63% in a bell-type batch annealing furnace.
3. The method for producing a high-carbon cold-rolled steel strip according to claim 1, wherein the step of finishing annealing at 0 [deg.] C. to just below the Ac1 point is repeated twice or more.