JPH06271935A - Production of high carbon cold rolled steel sheet small in anisotropy - Google Patents

Abstract

PURPOSE:To provide the method for producing a high carbon cold rolled steel sheet small in a dimensional change at the time of heat treatment such as hardening and tempering. CONSTITUTION:At the time of subjecting steel having a compsn. contg. 0.35 to 1.40% C, 0.10 to 0.70% Si and 0.20 to 1.5% Mn and contg., as necessary, one or more kinds among Mo, Cr, Ni and B to hot rolling, the hot rolling is finished at the Ar3 point or above, and it is cooled from the same temp. to a coiling temp. at >=30 deg.C/sec and is coiled in the temp. range of 550 to 700 deg.C. After descaling, it is annealed at 600 to 680 deg.C and is subjected to cold rolling at >=40% draft, annealing and skin pass rolling to produce the high carbon cold rolled steel sheet small in anisotropy. In this way, the plane anisotropy of the dimensional change caused by hardening and tempering is made small, the dimensional correction after hardening is eliminated and its productivity is increased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a high carbon cold-rolled steel sheet having a small dimensional change during heat treatment such as quenching and tempering.

[0002]

2. Description of the Related Art High carbon cold-rolled steel sheets are used for chain parts, gear parts, clutch parts and the like. These are manufactured by forming each target product shape and then hardening it by heat treatment such as quenching and tempering. Therefore, the material steel plate of each of the above products is required to be soft and easy to work before forming. In addition, the product after processing and heat treatment has high strength mechanical properties such as wear resistance, fatigue resistance, impact resistance, etc., and dimensional accuracy after quenching and tempering (the dimensional change is as small as possible or the dimensional change However, the anisotropy is required to be small).

Japanese Patent Application Laid-Open No. 03-24233 discloses a method for producing a high-carbon thin steel sheet having high strength and high toughness. This is because “high carbon thin steel sheet with C, Si, Mn, P, Cu, Al and Ni specified is tempered at a relatively high temperature after quenching, resulting in excellent impact resistance and wear resistance after heat treatment and excellent manufacturability. It makes it possible to manufacture steel sheets with excellent workability. " On the other hand, almost no study has been made on the technology for ensuring the dimensional accuracy after quenching and tempering, and for those requiring high-accuracy dimensions, machining was performed after heat treatment. In this case, since the high carbon steel plate has a high hardness after heat treatment, it takes a long processing time, and the working tool is consumed so much that productivity and cost are hindered.

[0004]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned conventional problems and provides a method for producing a high carbon cold-rolled steel sheet having a small anisotropy of deformation during heat treatment such as quenching and tempering. The purpose is to do.

[0005]

In order to achieve the above object, the present invention provides C: 0.35 to 1.4% by weight and Si:
0.10 to 0.80%, Mn: 0.20 to 1.5%, or, if necessary, Cr: 1.5% or less, Mo: 0.
50% or less, Ni: 1.20% or less, B: 0.0030
% Or less, Al: 0.0030% or less, at the time of hot rolling a steel having a composition that the balance substantially consists of iron, when hot rolling is completed at an Ar ₃ point temperature or higher, winding It is cooled to a temperature of 30 ° C./sec or more, wound in a temperature range of 550 to 700 ° C., and subsequently descaled to 600 to 680.
Annealing at a temperature between ℃, cold rolling at a cold rolling rate of 40% or more,
This is a method for producing a high carbon cold-rolled steel sheet having small anisotropy, which is characterized by annealing and pressure regulation.

The constitutional requirements of the present invention will be described in detail below.
First, the experimental facts found that the deformation anisotropy after quenching and tempering becomes small by combining the annealing condition after hot rolling and the cold rolling condition will be described. The high carbon cold-rolled steel sheet of the present invention is obtained by subjecting a steel ingot to hot rolling, spheroidizing annealing, and then 1
Or two or more cold rollings with intermediate annealing
If necessary, temper rolling is performed. Specifically, C: 0.5
0%, Si: 0.18%, Mn: 0.80%, Al:
A 0.035% hot-rolled steel sheet having a thickness of 4.0 mm was descaled and then ground in accordance with the subsequent cold rolling reduction. This steel plate 5
Annealing is performed at 50 to 730 ° C. for 5 hours, and cold rolling rate is 0 to 8
670 ℃ after adjusting to 0.80mm thickness by cold rolling 0%
× Annealing was performed for 3 hours. 100mm after temper rolling of 2%
After punching into φ, holding at 850 ° C. for 50 minutes, quenching in oil at 40 ° C., and tempering at 400 ° C. for 50 minutes, dimensional change in the circumferential direction was measured. The difference between the maximum change amount and the minimum change amount in the circumferential direction is represented by ΔD. The reason is that if there is no anisotropy in the plane even if there is a dimensional change due to heat treatment, the dimensions before heat treatment should be adjusted in advance. ΔD in Figure 1
The relationship between the hot-rolled sheet annealing conditions and the cold rolling reduction rate was shown. As is clear from the figure, the anisotropy of dimensional change after quenching and tempering is affected by the annealing temperature and cold rolling reduction, and there is an optimum temperature range for the annealing temperature, which is 600-680 ° C.
It can be seen that the anisotropy becomes smaller when the cold rolling reduction rate is increased to 40% or more at the temperature. Therefore, as a condition that the dimensional change after quenching and tempering is small, the annealing temperature is 600 to 680.
A combination of ℃ and cold rolling reduction of 40% or more was specified. A preferable range is an annealing temperature of the hot rolled sheet of 630 to 670 ° C., and a cold rolling reduction is 50% or more.

As described above, the combination of hot-rolled sheet annealing and cold-rolling conditions reduces the in-plane anisotropy of dimensional changes due to quenching and tempering. On the other hand, the recrystallization annealing temperature immediately before temper rolling does not affect the quenching anisotropy so much and may be within the range generally used.

Next, the steel composition constituting the present invention will be described. C is an important element that controls the quenching hardness when used as a final product. Therefore, at least 0.35
%is necessary. On the other hand, if the amount of C is too large, cracking occurs during quenching, so 1.4% was made the upper limit. If the Si content exceeds 0.80%, ferrite tends to be solid solution strengthened and the steel sheet tends to become brittle, so the upper limit is 0.80%.
Specified in. The lower bound need not be specified. Mn is an element that enhances hardenability, but if Mn is too high, it is an element that promotes segregation of P that deteriorates impact properties after quenching and tempering and hydrogen embrittlement. Therefore, the Mn content is specified to be 1.5% as an upper limit. .
The lower limit is 0.2% in order to secure hardenability.

In addition, one or more of Cr, Mo, Ni, B and Al are added as required. It has been conventionally known that Cr is an element that improves hardenability and at the same time improves wear resistance due to carbide precipitation. 1.5%
If this value is exceeded, this effect will be saturated, so when adding 1.
Add up to 5%. It is known that Mo raises the coarsening temperature of austenite during quenching and at the same time enhances the softening resistance by quenching and tempering. However, 0.50%
The above additions saturate the effect. In the present invention, 0.50% or less is added if necessary. It is known that Ni is an element effective in strengthening in a solid solution and at the same time, an element enhancing toughness. Even in the method of the present invention, when toughness is particularly required, it is added within the range of 1.5% or less. B is conventionally known as an element that enhances hardenability. In the present invention as well, in order to enhance the hardenability, 0.0030 is added if necessary.
% Or less is added. It is known that Al is added as a deoxidizer. Even with the method of the present invention, 0.080
If necessary, it is added in the range of not more than%.

Steel having such a composition is melted in a converter or an ordinary melting furnace such as an electric furnace, and a slab is produced by a continuous casting machine or a steel ingot-segmenting rolling. The slab will be surface-cleaned as needed. Next, it is hot rolled to produce a hot rolled steel strip. Among the hot rolling conditions, the finishing temperature and the cooling conditions after rolling have a great influence on the in-plane anisotropy of quenching strain. When the finishing temperature is below the Ar ₃ point temperature, the in-plane anisotropy of strain due to quenching and tempering becomes large. Further, since the shape of the hot-rolled steel sheet deteriorates and the unevenness of the material due to the non-uniform cooling increases, the finishing temperature needs to be the Ar ₃ point temperature or higher.
Cooling conditions after hot rolling are also important. If the cooling rate from the finishing temperature to the coiling temperature becomes slower, the in-plane anisotropy of the dimensional change due to quenching and tempering increases, so the average cooling rate from the hot rolling finishing temperature to the coiling should be 30 ° C / sec or more. There is. A preferable range is 35 ° C./second or more.

The hot rolled sheet is subjected to spheroidizing treatment of carbide after descaling by pickling or the like. This carbide spheroidizing annealing temperature is 6
It is necessary to carry out at 00 to 680 ° C. The preferred range is 63
It is 0-670 degreeC. The spheroidized steel sheet is cold rolled. As described above, the cold rolling rate also greatly affects the in-plane anisotropy of the shape change due to quenching and tempering, and a reduction rate of 40% or more is required. The preferable range is 50% or more for the same reason. Thus, in the high carbon cold-rolled steel sheet, the reason why the anisotropy becomes small by the combination of the hot rolling conditions, the annealing conditions, and the cold rolling reduction is not clear, but by these, a preferable texture is formed. It is estimated to be because.

The annealing temperature differs depending on whether the next step is cold rolling or temper rolling. When cold rolling is performed next, it is necessary to perform at 600 to 680 ° C. as in the case of spheroidizing annealing.
When it is subjected to temper rolling, it does not impair the characteristics of the present invention no matter how many times it is annealed if it is recrystallized. This temper rolling rate may be a degree that is usually performed. If necessary, the temper-rolled steel sheet is slit and supplied to customers.After processing such as punching, it is quenched and tempered to adjust to desired properties.
The steel sheet manufactured by the method of the present invention has a small in-plane anisotropy of shape change due to quenching and tempering, and does not require dimensional modification after heat treatment, or may be a little modified, and has the effect of increasing productivity. large.

[0013]

EXAMPLE A steel plate having a composition shown in Table 1 was manufactured under the manufacturing conditions shown in the same table, a 150 mmφ disk was punched out, the diameter change was measured, and after heating for 850 ° C. × 50 minutes, 400 ° C. ×
It was tempered for 55 minutes, the diameter of the disk was measured, and the difference between the longest diameter and the shortest diameter was evaluated as the quenching / tempering strain. In Examples A to I-1 and 2 within the scope of the present invention, the dimensional difference in the circumferential direction is small even if the steel type is changed. On the other hand, the small number -3 is the same as the examples of the present invention until hot rolling, but one or both of the spheroidizing annealing temperature and the cold rolling reduction ratio are examples outside the scope of the present invention, but which steel type Also, the anisotropy of dimensional change in the circumferential direction due to quenching and tempering is large. C-4 is an example in which only the hot rolling condition is out of the scope of the present invention, but it can be seen that this also has a large in-plane anisotropy of dimensional change.

[0014]

[Table 1]

[0015]

[Table 2]

[0016]

As described in the above examples, by specifying the hot rolling conditions, the spheroidizing annealing temperature, and the cold rolling rate, it is possible to reduce the in-plane anisotropy of the dimensional change due to quenching and tempering. If the hot rolling condition, the spheroidizing annealing condition, or the cold rolling reduction falls outside the scope of the present invention, the anisotropy of dimensional change becomes large. This is an industrially very useful technique because it requires no dimensional maintenance after quenching only by molding in a low hardness state before heat treatment.

[Brief description of drawings]

FIG. 1 is a drawing for explaining the influence of spheroidizing annealing temperature and cold rolling ratio on in-plane anisotropy of dimensional changes after quenching and tempering.

Claims (1)

[Claims] 1. C: 0.35-1.4% by weight%, S
i: 0.10 to 0.80%, Mn: 0.20 to 1.5
%, If necessary Cr: 1.5% or less, Mo: 0.50
% Or less, Ni: 1.20%, B: 0.0030% or less,
Al: 0.080% or less steel containing one or more kinds is subjected to hot rolling, descaling, annealing, cold rolling, and temper rolling. The rolling finishing temperature is set to an Ar ₃ point temperature or higher, and the temperature from the end of hot rolling to the winding is cooled at 30 ° C./sec or more, and 550 to 50
High carbon cold with small anisotropy, which is characterized in that it is wound in a temperature range of 700 ° C, the annealing temperature before cold rolling is set to 600 to 680 ° C, and the rolling reduction of cold rolling is set to 40% or more. Manufacturing method of rolled steel sheet.