JP3272804B2 - Manufacturing method of high carbon cold rolled steel sheet with small anisotropy - Google Patents

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]

[0002] High carbon cold rolled steel sheets are used for chain parts, gear parts, clutch parts and the like. These are manufactured by forming them into respective target product shapes and then hardening them 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 process before forming. In addition, the processed and heat-treated products have high-strength mechanical properties such as wear resistance, fatigue resistance and impact resistance, as well as dimensional accuracy after quenching and tempering. The anisotropy is small).

Japanese Patent Application Laid-Open No. 03-24233 discloses a method for producing a high-strength, high-toughness high carbon thin steel sheet. This is because the high carbon steel sheet specified for C, Si, Mn, P, Cu, Al and Ni is tempered at a relatively high temperature after quenching, so that it has excellent impact resistance and abrasion resistance after heat treatment and excellent manufacturability. And a steel sheet with excellent workability can be manufactured. " On the other hand, a technique for ensuring dimensional accuracy after quenching and tempering has been scarcely studied, and for those requiring high-precision dimensions, machining has been performed after heat treatment. In this case, the high carbon steel sheet has a high hardness after the heat treatment, so that it takes a long processing time, and the working tool is greatly consumed, which hinders productivity and cost.

[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 small anisotropy of deformation during heat treatment such as quenching and tempering. The purpose is to do.

[0005]

In order to achieve the above-mentioned object, the present invention provides a method of the present invention wherein C: 0.35 to 1.4% by weight, 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: at least one kind of 0.0030% or less, and when the steel having a composition substantially consisting of iron is hot-rolled, hot rolling is terminated at an Ar temperature of ₃ points or more, and winding is performed. It is cooled to a temperature of 30 ° C./sec or more, wound up in a temperature range of 550 to 700 ° C., and subsequently 600 to 680 after descaling.
Annealing at a temperature between ℃ and 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, characterized by annealing and pressure control.

Hereinafter, the constituent elements of the present invention will be described in detail.
First, the experimental fact that the deformation anisotropy after quenching and tempering is reduced by the combination of the annealing condition after hot rolling and the cold rolling condition is described. The high-carbon cold-rolled steel sheet of the present invention is subjected to spheroidizing annealing after hot rolling of an ingot,
Cold rolling two or more times with intermediate or intermediate annealing,
Temper rolling is performed as necessary. 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 ground in accordance with the subsequent cold rolling reduction. This steel plate
Anneal at 50 to 730 ° C. × 5 hours, cold rolling reduction: 0 to 8
0% cold rolling and adjusting to 0.80mm thickness, then 670 ℃
The annealing was performed for 3 hours. 100mm after temper rolling of 2%
It was punched into φ, kept at 850 ° C. × 50 minutes, quenched in oil at 40 ° C., and measured for dimensional change in the circumferential direction after tempering at 400 ° C. × 50 minutes. The difference between the maximum change amount and the minimum change amount in the circumferential direction is indicated by ΔD. It is thought that if there is no anisotropy in the plane even if there is a dimensional change due to the heat treatment, the dimensions before the heat treatment may be adjusted in advance. FIG. 1 shows ΔD
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 the dimensional change after quenching and tempering is affected by the annealing temperature and the rolling reduction, and there is an optimum temperature range for the annealing temperature, which is 600 to 680 ° C.
It can be seen that the anisotropy decreases as the cold rolling reduction at 40% or more is increased to 40% or more. Therefore, as a condition in which the dimensional change after quenching and tempering is small, annealing temperature: 600 to 680
A combination of at least 40 ° C. and a cold rolling reduction of 40% was specified. A preferable range is an annealing temperature of 630 to 670 ° C. of the hot rolled sheet, and a cold rolling reduction is 50% or more.

As described above, the in-plane anisotropy of the dimensional change due to quenching and tempering is reduced by the combination of the hot rolled sheet annealing and the cold rolling conditions. On the other hand, the recrystallization annealing temperature immediately before the temper rolling does not significantly affect the quenching anisotropy, and may be in a normal range.

Next, the steel composition constituting the present invention will be described. C is an important element that controls quenching hardness when used as a final product. Therefore, at least 0.35
%is necessary. On the other hand, if the C content is too large, cracks occur during quenching, so the upper limit was set to 1.4%. If the Si content exceeds 0.80%, ferrite is solid-solution strengthened and the steel sheet tends to become brittle, so the upper limit is 0.80%.
Specified. The lower limit need not be specified. Mn is an element that enhances the hardenability, but if Mn is too high, it is an element that promotes segregation of P that deteriorates the impact characteristics after quenching and tempering, and deteriorates hydrogen embrittlement. .
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 known that Cr is an element that enhances hardenability and at the same time improves wear resistance due to carbide precipitation. 1.5%
If the amount exceeds 1, the effect is saturated.
Add up to 5%. Mo is known to increase the austenite coarsening temperature during quenching, and at the same time, increase the softening resistance due to quenching and tempering. However, 0.50%
The above addition saturates the effect. In the present invention, it is added as required in a range of 0.50% or less. It is known that Ni is a solid solution, an element effective for strengthening, and an element that enhances toughness. Also in the method of the present invention, when toughness is particularly required, it is added in a range of 1.5% or less. B has been conventionally known as an element for improving hardenability. In the present invention, if necessary, 0.0030 to improve hardenability.
% Or less. It is known that Al is added as a deoxidizer. In the method of the present invention, 0.080
% If necessary.

[0010] The steel having such a composition is smelted in a conventional melting furnace such as a converter or an electric furnace, and a slab is produced by a continuous casting machine or a steel ingot-bulk rolling. The slab is surface-cleaned as needed. Next, it is hot-rolled to produce a hot-rolled steel strip. Of the hot rolling conditions, the finishing temperature and the cooling conditions after rolling greatly affect the in-plane anisotropy of quenching strain. When the finishing temperature is lower than the Ar ₃ point temperature, the in-plane anisotropy of strain due to quenching and tempering increases. In addition, the finish temperature needs to be equal to or higher than the _three- point Ar temperature since the material variation due to deterioration in the shape of the hot-rolled steel sheet and uneven cooling is increased.
The cooling conditions after hot rolling are also important. If the cooling rate from the finishing temperature to the winding temperature is slow, 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 winding needs to be 30 ° C / sec or more. There is. A preferred range is at least 35 ° C./sec.

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

The annealing temperature differs depending on whether the next step is cold rolling or temper rolling. Next, when cold rolling is performed, it is necessary to perform at 600 to 680 ° C. as in the case of spheroidizing annealing.
When subjected to temper rolling, the characteristics of the present invention are not impaired no matter how many times annealing is performed if recrystallization is performed. This temper reduction rate may be a level which is usually performed. The tempered rolled steel sheet is supplied to the customer by slitting as necessary, and after processing such as punching, it is quenched and tempered and adjusted to the 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 / tempering, and does not require or require only a small amount of dimensional correction after heat treatment, and has the effect of increasing productivity. large.

[0013]

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

[0014]

[Table 1]

[0015]

[Table 2]

[0016]

As described in the above embodiments, by specifying the hot rolling conditions, the spheroidizing annealing temperature, and the cold rolling reduction, it is possible to reduce the in-plane anisotropy of the dimensional change due to quenching and tempering. If any one of the hot rolling conditions, the spheroidizing annealing conditions, and the cold rolling reduction is out of the range of the present invention, the anisotropy of the dimensional change becomes large. This is an industrially very useful technique because it only requires molding before heat treatment with low hardness and does not require dimensional maintenance after quenching.

[Brief description of the drawings]

FIG. 1 is a drawing for explaining the effect of dimensional change after quenching / tempering on in-plane anisotropy of spheroidizing annealing temperature and cold rolling reduction.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-55-50427 (JP, A) JP-A-62-109929 (JP, A) JP-A-62-284019 (JP, A) JP-A-3-3 47922 (JP, A) JP-A-5-171288 (JP, A) JP-B-57-53418 (JP, B2) JP-B-2-19173 (JP, B2) (58) Fields investigated (Int. ⁷ , DB name) C21D 9/46 C21D 8/00-8/02

Claims (1)

(57) [Claims] 1. C: 0.35 to 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
%, Ni: 1.20%, B: 0.0030% or less,
Al: A method for producing a high-carbon cold-rolled steel sheet in which a steel containing one or more of 0.080% or less is subjected to hot rolling, descaling, annealing, cold rolling, and temper rolling. The rolling finishing temperature is set to be equal to or higher than the Ar ₃ point temperature, and the temperature from the end of hot rolling to winding is cooled at 30 ° C./sec or more.
A high anisotropy high carbon cold roll characterized by winding at a temperature range of 700 ° C., an annealing temperature before cold rolling of 600 to 680 ° C., and a rolling reduction of cold rolling of 40% or more. Manufacturing method of rolled steel sheet.