JP2583694B2 - Method for producing ferritic stainless steel for electrical materials with excellent ductility, wear resistance and rust resistance - 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 ferritic stainless steel as a material suitable for use as a material for electric materials, particularly a floppy disk center core material used as a magnetic recording medium. .

[0002]

2. Description of the Related Art Conventionally, on a floppy disk used as a magnetic recording medium, a disk called a metal disk-shaped center core is mounted at the center of the disk for the purpose of preventing read deflection. The characteristics required for this center core material are that it is ferromagnetic for use in magnet chucking, and that the claws that determine the position during driving rub against the surface of the center core in the initial stage of driving, so that it has excellent wear resistance. it (Hv220 or higher), when press forming the cell pointer <br/> Koa, for preventing cracking, elongation of the material is 5% or more, the metal powder due to rusting can cause a malfunction, SUS 430 average corrosion resistance,
Excellent secondary workability is required. In recent years, this type of material has become more demanding in terms of wear resistance and ductility, and SUS 430
It is essential that it can be manufactured at a cost as low as or less than that.

[0003] As a center core material required to have the above-mentioned characteristics, a so-called hard rolled material which has been hardened by subjecting SUS 430 to finish cold rolling (hereinafter referred to as "hard rolling") has been used. Have been. However,
With this method of only performing hard rolling, it is necessary to perform finish rolling of at least 20% or more in order to obtain a target level of hardness, and there has been a problem of cracking during processing due to reduced ductility. In other words, it is difficult to achieve both contradictory properties of hardness and elongation with a material obtained by simply rolling SUS 430 material hard, and parts manufacturers that actually use these materials have a high defect rate. It is a problem. Therefore, development of a new material having excellent ductility and abrasion resistance has been desired for this kind of material.

In order to solve such a problem, Japanese Unexamined Patent Application Publication Nos. 64-19570 and 1-259144 have conventionally disclosed a method of increasing the amount of Si and Ni added to SUS 430 component steel.
Attempts have been made to improve wear resistance and ductility in terms of alloy composition. In other words, the hardness of the material itself is increased by increasing the amount of Si added, and the toughness that is reduced by the addition of Si is reduced by Ni.
The idea is to try to improve by adding.
However, this method requires a higher alloy (especially Ni addition) and higher cost than the conventional steel SUS 430.
As in 430, it was necessary to perform hard rolling, so elongation was still insufficient.

[0005] For this reason, in order to obtain an inexpensive center core material having excellent ductility and abrasion resistance, a method in which hard rolling is not performed is disclosed in JP-A-63-14387 and JP-A-63-169330. No. 169335. These known techniques are high-strength, high-ductility stainless steels composed of a composite structure of ferrite and martensite, which appropriately adjust the ratio of hard martensite and soft ferrite to the total volume. In this way, the intended hardness and ductility are intended to be obtained. However, although these composite structure stainless steels are certainly harder and more ductile than ferrite single phases, their control is difficult due to the narrow quenching annealing temperature range, and high alloying is required. As a result, the elongation decreases, and normal SUS 43
There was a problem that it was more expensive than 0.

[0006]

SUMMARY OF THE INVENTION
Recently, there has been a further demand for a material which is excellent in ductility and abrasion resistance, is excellent in rust resistance, and is less expensive than SUS430. That is, an object of the present invention is to provide a material having more excellent ductility, abrasion resistance, and rust resistance than ever, specifically, a hardness Hv ≧ 250, an elongation El ≧ 5%, and a rust resistance comparable to that of SUS430. An object of the present invention is to establish a manufacturing technique for providing a material for electric materials satisfying the condition of having a ferrite-based stainless steel for a magnetic disk floppy disk center core.

[0007]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to achieve the above object, and as a result, after hard rolling of 10% or more with respect to a component-based material as described below,
By performing a reheating treatment in a temperature range of 0 ° C for 10 seconds or more and 10 minutes or less, and then performing nitric acid electrolysis, it is inexpensive and has the same corrosion resistance as SUS 430, and further has ductility and resistance They have found that a ferritic stainless steel having sufficient properties as a material for a center core having excellent wear properties can be obtained, and have arrived at the configuration of the present invention.

That is, according to the present invention, C: 0.12 wt% or less;
Si: 1.0 wt% or less, Mn: 1.0 wt% or less, Cr: 15 to 20 wt
%, Ni: 1.0 wt% or less, Al: 0.3 wt% or less, O: 0.
003 wt% or less, P: 0.04 wt% or less, S: 0.03 wt% or less, N: 0.1 wt% or less, and if necessary, as a hot workability improving element B: 0.002 to 0.01 wt%, Ca: 0.01 wt% %, REM: 0.2 wt% or less, and steel containing at least one selected from V, Nb and Ti of 0.05 wt% or less as a corrosion resistance improving element, the balance being Fe and unavoidable impurities. After the finish annealing, to achieve the above purpose, after hard rolling of 10% or more to the steel of the above-mentioned composition, 10 seconds or more at a temperature range of 500 ° C to 750 ° C,
After performing a reheating treatment of 10 minutes or less, it is a method that undergoes a manufacturing process characterized by further performing nitric acid electrolysis, and by performing such a method, it is inexpensive and has the same corrosion resistance as SUS 430, Moreover, the present invention is a method for producing a ferritic stainless steel having sufficient properties as a material for electric materials having excellent ductility, wear resistance and rust resistance, particularly a material for a floppy disk center core.

In the present invention, the reason why the composition of the steel as the starting material is limited as described above will be described below. C: C is an element that increases hardness and improves wear resistance in a small amount. However, the content of C lowers the rust resistance, and when it exceeds 0.12 wt%, the ductility is reduced, the secondary workability is deteriorated, the steel becomes hard, and the press formability is impaired. Therefore, in the present invention, the C content is 0.12
wt% or less. Si: Si is an element that forms ferrite at high temperatures,
It is added as a deoxidizer, but if it is added in excess of 1.0 wt%, ear cracks occur during hot rolling, resulting in poor product yield and reduced toughness. . Mn: Mn is an element that generates austenite at a high temperature, and is an element that generates martensite by cooling (quenching) after a high-temperature heat treatment. This Mn is 1.0 wt%
If added in excess of, it is harmful to hot workability,
Since the appearance of retained austenite is caused, its content should be 1.
0 wt% or less. Cr: Cr must be added in an amount of at least 15 wt% in order to ensure corrosion resistance equivalent to that of SUS430. On the other hand, if it is added in excess of 20 wt%, it increases costs and hardens and reduces ductility. The amount range was 15-20 wt%. Ni: Ni is an element that forms austenite, like Mn, and is an effective element for improving corrosion resistance. However, if added in excess of 1.0 wt%, the cost will be higher than SUS430,
The content was set to 1.0 wt% or less.

B, Ca, REM: B, Ca, REM are all hot workability improving elements. In particular, B is an element that significantly increases the strength and ductility at high temperatures even when added in a small amount, and is extremely effective in improving hot workability. However, the effect is little if less than 0.002wt%,
If it exceeds 0.01% by weight, on the contrary, it causes brittleness, and the oxidation resistance at high temperatures is deteriorated, resulting in increased scale formation. Therefore, the range is set to 0.002 to 0.01% by weight. Also, 0.01wt% for Ca and REM for
If the content exceeds 0.2 wt%, hot brittleness is caused on the contrary and the yield is remarkably impaired. V, Nb, Ti: V, Nb, Ti are effective elements for improving hot workability, and are particularly effective for improving corrosion resistance. However, if each of these elements exceeds 0.05 wt%, it becomes difficult to control the hardness.
% As the upper limit. Al: Al is added as a deoxidizing agent, but if added in excess of 0.3 wt%, the secondary workability deteriorates due to the scattering of inclusions, so the Al addition amount was set to 0.3 wt% or less. O: O forms oxide-based nonmetallic inclusions, lowers the cleanliness of the steel, and causes work cracking due to this. Therefore, the upper limit of the content is 0.003 wt%. Further, the lower the value, the better, so no lower limit is set. P: Since P reduces toughness when the amount of P added is large,
The upper limit of the amount was 0.04 wt%. S: Since S causes a decrease in corrosion resistance, it is preferable that this content is small. In particular, when the content exceeds 0.03% by weight, the corrosion resistance deteriorates remarkably. Therefore, the upper limit of the content is set to 0.03% by weight. N: N is an element effective for adjusting the hardness of steel. However, if the amount of N added is large, it becomes hard and the elongation is reduced, the secondary workability is deteriorated, the hardness is increased, and the press formability is reduced. . Therefore, in the present invention, the N amount is set to 0.1 wt% or less.

Next, in the production method of the present invention, the steel having the above composition is subjected to finish annealing through a process such as hot rolling according to a conventional method, and then to cold rolling (hard rolling) of 10% or more. ) Is applied. In the hard rolling after the finish annealing, the rolling reduction is set to 10% or more because a rolling reduction of at least 10% or more is required in order to obtain a target hardness with the above-mentioned component system.

Next, the steel material subjected to the hard rolling as described above is continuously subjected to a reheating treatment in an ammonia decomposition gas or an argon atmosphere if possible. The reason for setting the heating temperature range in this reheating treatment to be in the range of 500 ° C to 750 ° C is that the effect of improving ductility is not observed below 500 ° C, whereas the hardness decreases with the improvement of ductility above 750 ° C. Limited to the temperature range. In this reheating treatment, the holding time at the heating temperature was set to 10 seconds to 10 minutes at the target temperature. The reason is that the effect of improving the ductility is not sufficient at less than 10 seconds. If the time is 10 minutes or less, if the temperature is maintained at a temperature exceeding 750 ° C. for a time exceeding 10 minutes, the hardness is reduced and the corrosion resistance is significantly deteriorated due to the improvement in ductility.

The steel material subjected to the hard rolling and the reheating treatment as described above is further subjected to a nitric acid electrolytic treatment thereafter. Regarding the conditions of this nitric acid electrolytic treatment, the temperature is
It is preferable that the temperature is 80 ° C. or less, the amount of electricity is 1 to 50 C / dm ² , and the concentration of nitric acid is 1 to 30%. That is, when the processing temperature exceeds 80 ° C., the nitric acid is remarkably evaporated and a load is applied to the tank. If the quantity of electricity is less than 1 C / dm ² , the harmful oxide film on the surface cannot be sufficiently removed by nitric acid electrolysis,
On the other hand, if it exceeds 50 C / dm ² , the surface becomes rough. If the nitric acid concentration is less than 1%, the nitric acid electrolysis is not sufficiently performed, and if it exceeds 30%, the surface roughness becomes noticeable.

As described above, the steel having the above-described composition is subjected to hard rolling after finish annealing, reheating, and then nitric acid electrolysis to remove surface scale, thereby deteriorating corrosion resistance. A ferritic stainless steel for an electric pickling tank excellent in ductility, abrasion resistance and rust resistance can be produced without the need. That is, the steels in Table 1
FIG. 1 shows the results of a reheating test of a 30% rolled material of No. 1 steel held for 90 seconds. When the reheating temperature was 500 ° C. or higher, no decrease in hardness was observed, and an improvement in ductility was observed. On the other hand, when the temperature exceeds 750 ° C, the hardness decreases significantly,
Hardness requirements exceeding v cannot be met. From this, it was found that when the reheating treatment was performed at a temperature of 500 to 750 ° C., the hardness and elongation reached the expected levels. The results are shown in FIG.

[0015]

[Example] A 30 kg small ingot was obtained by melting a steel having the composition shown in Table 1 in a vacuum high-frequency furnace, and then heating the ingot at 1250 ° C for 1 hour to form a hot-rolled sheet having a thickness of 4 mm. , Then 800 ℃, 4
After annealing for an hour, it was cooled to 700 ° C. at a rate of 10 ° C./h, and then allowed to cool to the atmosphere to obtain a hot-rolled annealed sheet. The hot-rolled annealed plate was shot blasted and then pickled to remove scale on the surface and then cold-rolled to a thickness of 0.3 mm.
Thereafter, the cold-rolled sheet was heated for 30 seconds in a temperature range of 850 to 1100 ° C., and then air-cooled. After subjecting the material thus manufactured to hard rolling of 10% or more, after reheating in various temperature ranges and holding times, the amount of electricity of 10 C / dm ² and 20 ° C.
Nitric acid electrolysis was performed in a 10% nitric acid solution, and the effects of hard rolling and reheating on hardness, elongation, and corrosion resistance were investigated. In addition, for the final annealing plate made in this way, subjected to up-less molding, they were investigated for each of the conditions and the failure rate. The elongation was evaluated by a tensile test using a JIS No. 13B test piece, and the hardness was evaluated by a plate surface hardness measurement (500 g load) using a Micro Vickers. Furthermore, the rust resistance was evaluated by subjecting the material that was actually processed to the center core shape to 10 cycles of salt spray test (35 ° C, sprayed for 16 hours, wetted for 8 hours), and relatively evaluated the rusting area ratio. did. Table 1 summarizes the results of those in Tables 2-1 and 2-2. 2 and 3
Shows the relationship between the draft and the hardness.

[0016]

[Table 1]

[0017]

[Table 2-1]

[0018]

[Table 2-2]

As shown in these results, the ferritic stainless steel manufactured in accordance with the manufacturing conditions of the present invention is:
It is clear that the required properties as a material for electrical materials, especially floppy disk center core material, are sufficiently satisfied.

[0016]

As described above, according to the present invention, a steel having a predetermined composition is simply processed in the order of hard rolling, reheating, and nitric acid electrolysis, so that it is excellent in ductility and wear resistance. In addition, ferritic stainless steel for electrical materials having excellent rust resistance can be manufactured at low cost.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between reheating temperature, hardness and elongation.

FIG. 2 is a graph showing a relationship between a draft and a hardness.

FIG. 3 is a graph showing a relationship between a draft and an elongation.

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical display location C25F 1/06 C25F 1/06 B (72) Inventor Sadao Hasuno 1 Kawasaki-cho, Chiba-shi, Chiba Kawasaki (56) References JP-A-63-169330 (JP, A) JP-A-62-124230 (JP, A)

Claims (2)

(57) [Claims] 1. C: 0.12 wt% or less, Si: 1.0 wt%
Mn: 1.0 wt% or less, Cr: 15 to 20 wt%, Ni: 1.0 wt% or less, Al: 0.3 wt% or less, O: 0.003 wt% or less, P: 0.04 wt% or less, S: 0.03 wt% or less And N: a steel containing 0.1 wt% or less, with the balance being Fe and unavoidable impurities, subjected to cold rolling of 10% or more after finish annealing, and then 500 ° C to 750 ° C.
A method for producing a ferritic stainless steel for electrical materials having excellent ductility, abrasion resistance and rust resistance, characterized by reheating for at least 10 seconds and not more than 10 minutes in a temperature range of 10 minutes and then subjecting to nitric acid electrolysis. . 2. C: 0.12 wt% or less, Si: 1.0 wt% or less, Mn: 1.0 wt% or less, Cr: 15 to 20 wt%, Ni: 1.0 wt% or less, Al: 0.3 wt% or less, O: 0.003 wt% or less, P: 0.04 wt% or less, S: 0.03 wt% or less, N: 0.1 wt% or less, and B: 0.002 to 0.01 wt% as a hot workability improving element
%, At least one of Ca: 0.01 wt% or less and REM: 0.2 wt% or less, and 0.1% each as a corrosion resistance improving element.
A steel containing at least one selected from the group consisting of V, Nb and Ti in an amount of not more than 05 wt%, the balance being Fe and unavoidable impurities.
Ferritic stainless steel for electrical materials with excellent ductility, abrasion resistance and rust resistance characterized by reheating for 10 seconds or more and 10 minutes or less in a temperature range of up to 750 ° C and then nitric acid electrolysis Manufacturing method.