JPH04371518A - Production of ferritic stainless steel for electric material having excellent ductility, wear resistance and rust resistance - Google Patents

Abstract

PURPOSE:To obtain the steel blank material which has corrosion resistance and excellent ductility and wear resistance by subjecting a steel specified in component compsn. to hard ' rolling, then to reheating under specific conditions, followed by nitric acid electrolysis. CONSTITUTION:The compsn. of the steel is specified, by weight %, to 0.12% C, <=1.0% Si, <=1.0% Mn, 15 to 20% Cr, <=1.0% Ni, <=0.3% Al, <=0.003% O, <=0.04% P, <=0.03% S, <=0.1% N, and the balance Fe and unavoidable impurities. This steel is subjected to finish annealing, then to cold rolling at >=10%. The steel is thereafter subjected to reheating for 10 seconds to 10 minutes in a 500 to 750 deg.C range. Further, the scale on the surfaces is removed by executing nitric acid electrolysis. At least one kind of 0.002 to 0.01% B, <=0.01% Ca and <=0.2% REM as hot workability improving elements and at least one kind of respectively <=0.5% V, Nb and Ti as corrosion resistance improving elements are incorporated at need into the above-mentioned steel.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a method for producing ferritic stainless steel, which is suitable for use as a material for electrical materials, particularly as a center core material for floppy disks used as magnetic recording media. .

0002

2. Description of the Related Art Conventionally, a floppy disk used as a magnetic recording medium has a metal disk-shaped center core attached to the center of the disk for the purpose of preventing reading shake. The properties necessary for this center core material are: ■ It must be ferromagnetic so that it can be used for magnetic chucking; ■ It has excellent wear resistance because the claws that determine the position during driving rub against the surface of the center core in the initial stage of driving. (Hv220 or higher),■
When press forming the center core into the shape shown in Figure 1, to prevent cracking, the elongation of the material must be at least 5%;
It is required to have corrosion resistance comparable to that of US 430, and (1) to have excellent secondary processability. In addition, as a recent trend, this type of material has become more demanding in terms of wear resistance and ductility, and it is essential that it can be manufactured at a cost as low as or lower than that of SUS 430.

[0003] Conventionally, so-called hard-rolled materials, which are SUS 430 made hard by finishing cold rolling (hereinafter referred to as "hard rolling"), have been used as center core materials that are required to have the above-mentioned properties. It's here. However, with this method of just performing hard rolling, it is necessary to perform finish rolling of at least 20% or more in order to obtain the target level of hardness, and cracking during processing due to decreased ductility has been a problem. That is, SUS 430
It is difficult to achieve both the contradictory properties of hardness and elongation with materials that are simply hard-rolled, and parts manufacturers that actually use these materials are having problems with high defective rates. There is. From such a thing,
Regarding this type of material, there has been a desire to develop a new material that has excellent ductility and wear resistance.

[0004] In order to solve such problems, conventionally, Japanese Patent Application Laid-Open No. 19570/1983 and Japanese Patent Application Laid-open No. 1-25914 have been proposed.
In Publication No. 4 etc., Si of SUS 430 composition steel,
Attempts have been made to improve wear resistance and ductility from the viewpoint of alloy composition by increasing the amount of Ni added. In other words, increasing the amount of Si added increases the hardness of the material itself, and also increases the hardness of the material itself.
The idea is to improve the toughness, which decreases due to the addition of i, by adding Ni. However, with this method, conventional steel SUS 430
Compared to conventional SUS 430, it is a high-alloy material (particularly with the addition of Ni), which makes it more expensive, and in order to obtain the desired hardness through finish rolling, it is necessary to perform hard rolling like normal SUS 430, so it still lacks elongation.

[0005] From this, in order to produce a center core material that has excellent ductility and wear resistance and is inexpensive, a method that does not involve hard rolling is disclosed in JP-A-63-14387 and JP-A-63-169330. -169335 are proposed. These known technologies are high-strength, high-ductility stainless steels consisting of a composite structure of ferrite and martensite, which is produced by adjusting the ratio of hard martensite and soft ferrite to the total volume appropriately. By doing so, the objective was to obtain the desired hardness and ductility. However, although these composite structure stainless steels are hard and ductile compared to single-phase ferrite, they are difficult to control due to the narrow quenching and annealing temperature range, and it is difficult to make them highly alloyed. As a result, the elongation is lowered and there is a problem that it is more expensive than ordinary SUS 430.

[0006]

[Problem to be solved by the invention] From the above,
Recently, there has been a growing demand for a material that has excellent ductility, wear resistance, and rust resistance, and is also less expensive than SUS 430. That is, the object of the present invention is to create a material with better ductility, wear resistance, and rust resistance than ever before, specifically, a material with hardness Hv≧250, elongation El≧5%, and SU
The object of the present invention is to establish a manufacturing technology that provides a material for electrical materials, particularly a ferritic stainless steel for magnetic disk floppy disk center cores, which satisfies the condition of having rust resistance comparable to that of S430.

[0007]

[Means for Solving the Problems] As a result of intensive research to achieve the above object, the present inventors found that after hard rolling of 10% or more, 50%
By going through the manufacturing process of reheating for 10 seconds or more and 10 minutes or less in the temperature range of 0 to 750 degrees Celsius, and then applying nitric acid electrolysis, it is inexpensive and can be made from SUS 430.
It was discovered that a ferritic stainless steel having moderate corrosion resistance, excellent ductility and wear resistance, and sufficient characteristics as a material for a center core can be obtained, and the structure of the present invention was conceived.

That is, the present invention provides C: 0.12 wt% or less, Si: 1.0 wt% or less, Mn: 1.0
wt% or less, Cr: 15-20 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%
Below, B is further added as an element for improving hot workability as necessary.
:0.002~0.01wt%, Ca:0.01wt%
The following contains REM: 0.2 wt% or less, and at least one selected from V, Nb, and Ti, each of which is 0.05 wt% or less as a corrosion resistance improving element,
After finish annealing the steel, the balance of which is Fe and unavoidable impurities, and after hard rolling of 10% or more of the steel with the above-mentioned composition to achieve the above purpose, the steel is heated at 500°C ~
This method involves a manufacturing process characterized by performing a reheating treatment in a temperature range of 750 °C for 10 seconds or more and 10 minutes or less, and then further performing nitric acid electrolysis. It has corrosion resistance comparable to SUS 430,
Moreover, it is a method for producing ferritic stainless steel, which has sufficient properties as a material for electrical materials, especially as a material for floppy disk center cores, with excellent ductility, wear resistance, and rust resistance.

In the present invention, the reason why the composition of the steel as a starting material is limited as described above will be explained below. C: C is an element that increases hardness and wear resistance in a small amount. However, the content of C lowers rust resistance, and when it exceeds 0.12 wt%, it lowers ductility, resulting in poor secondary workability and hardness, which inhibits press formability. Therefore, in the present invention, the C content is set to 0.12 wt% or less. Si: Si is an element that forms ferrite at high temperatures and is added as a deoxidizing agent, but if it is added in excess of 1.0 wt%, it will cause edge cracking during hot rolling and reduce the yield of the product. Since the toughness decreases with the addition of C, its content was set to 1.0 wt% or less. Mn: Mn is an element that generates austenite at high temperatures, and is an element that generates martensite when cooled (quenched) after high-temperature heat treatment. Also, this Mn
If added in an amount exceeding 1.0 wt%, it is harmful to hot workability and causes the appearance of retained austenite, so the content is set to 1.0 wt% or less. Cr: It is necessary to add at least 15 wt% or more of Cr to ensure corrosion resistance comparable to that of SUS 430. On the other hand, adding more than 20 wt% will increase the cost, make it hard, and reduce ductility. The amount ranged from 15 to 20 wt%. Ni: Like Mn, Ni is an element that forms austenite and is an effective element for improving corrosion resistance.
If added in excess of wt%, the cost would be higher than SUS 430, so the content was set to 1.0 wt% or less.

B, Ca, REM: B, Ca, RE
M is an element that improves hot workability. In particular, B is an element that significantly increases 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 almost negligible below 0.002wt%, and when it exceeds 0.01wt%, it causes problems such as brittleness, deterioration of oxidation resistance at high temperatures, and increased scale formation. The range was 0.002 to 0.01 wt%. Also, C
0.01wt% for a, 0.01wt% for REM.
If it exceeds 2 wt%, hot embrittlement will occur and the yield will be significantly impaired, so this content should be set as the upper limit. V, Nb, Ti: V, Nb, and Ti are elements that are each effective in improving hot workability, and are particularly effective in improving corrosion resistance. However, these elements are 0
．． If each exceeds 0.05 wt%, hardness control becomes difficult, so the upper limit of each content is 0.05 wt%. Al: Al is added as a deoxidizing agent, but 0.3w
If Al is added in excess of t%, secondary workability deteriorates due to the scattering of inclusions, so the amount of Al added was set to 0.3 wt% or less. O: Since O forms oxide-based nonmetallic inclusions and reduces the cleanliness of steel, which causes processing cracks, the upper limit of its content was set at 0.003 wt%. Further, since it is preferable that the value be lower, no lower limit is set. P: P reduces toughness when added in a large amount, so
The upper limit of the amount added was set to 0.04 wt%. S: Since S causes a decrease in corrosion resistance, it is preferable that the content is small. In particular, if the content exceeds 0.03 wt%, the corrosion resistance deteriorates significantly, so the upper limit of the content should be set at 0.03 wt%.
It was set as wt%. N: N is an effective element for adjusting the hardness of steel, but if it is added in a large amount, it becomes hard, reduces elongation, deteriorates secondary workability, and becomes hard, reducing press formability. . Therefore, in the present invention, the amount of N is set to 0.1wt%.
The following was made.

Next, in the manufacturing method of the present invention, the steel having the above-mentioned composition is subjected to finish annealing through treatments such as hot rolling according to a conventional method, and then cold rolled by 10% or more (
hard rolling). The reason why the rolling reduction ratio was set to 10% or more in hard rolling after final annealing is as follows.
In order to obtain the desired hardness with the above component system, at least 10
This is because a rolling reduction rate of % or more is required.

Next, the hard-rolled steel material as described above is subsequently subjected to a reheating treatment, preferably in an ammonia decomposition gas or argon atmosphere. The heating temperature range for this reheating treatment is from 500℃ to 750℃.
The reason for this range is that at temperatures below 500°C, no ductility improvement effect is observed, while at temperatures above 750°C, hardness decreases as ductility improves, so this temperature range was selected. Also,
In this reheating treatment, the holding time at the heating temperature was set at the target temperature for 10 seconds to 10 minutes. In the following, this is because if the temperature exceeds 750°C for a time exceeding 10 minutes, the hardness decreases as the ductility improves, and the corrosion resistance deteriorates significantly.

[0013] The steel material that has been hard rolled and reheated as described above is then further subjected to nitric acid electrolytic treatment. Regarding the conditions for this nitric acid electrolytic treatment, it is preferable that the temperature be 80 DEG C. or less, the amount of electricity be 1 to 50 C/dm2, and the nitric acid concentration be 1 to 30%. That is, if the treatment temperature exceeds 80° C., nitric acid evaporates significantly and puts a load on the tank. Further, if the amount of electricity is less than 1 C/dm2, the harmful oxide film on the surface cannot be sufficiently removed by nitric acid electrolysis, and if it exceeds 50 C/dm2, the surface becomes rough. Regarding nitric acid concentration, 1%
This is because if it is less than 30%, nitric acid electrolysis will not be carried out sufficiently, and if it exceeds 30%, the surface will become noticeably rough.

As explained above, the material having the above-mentioned steel composition is subjected to final annealing, hard rolling, reheating treatment, and then subjected to nitric acid electrolysis to remove surface scale, thereby degrading the corrosion resistance. Ferritic stainless steel for electric pickling tanks with excellent ductility, wear resistance, and rust resistance can be produced without any corrosion. That is, steel No. in Table 1. Figure 2 shows the results of a reheating test held for 90 seconds on a 30% rolled material of No. 1 steel. Reheating temperature is 5
At temperatures above 00°C, 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, making it impossible to satisfy the hardness condition exceeding 250Hv. From this, in reheating treatment, 5
It has been found that heating at temperatures between 00 and 750°C brings the hardness and elongation to the desired levels.

[0015]

[Example] Steel with the composition shown in Table 1 was melted in a vacuum high-frequency furnace to obtain a 30 kg small steel ingot, and this steel ingot was heated at 1250°C for 1
After heating for several hours, it was made into a 4mm thick hot-rolled plate, then annealed at 800℃ for 4 hours, and then heated at 10℃/
The sample was cooled to 700° C. at a rate of 1 h, and then left to cool in the atmosphere to obtain a hot-rolled annealed plate. This hot rolled annealed plate was shot blasted and then pickled to remove surface scale.
It was cold rolled to a thickness of 0.3 mm. After that, the cold-rolled plate was heated in a temperature range of 850 to 1100℃ for 3
After heating for 0 seconds, it was air cooled. The material produced in this way is subjected to hard rolling of 10% or more, then reheated at various temperature ranges and holding times, and then heated to 10C/dm.
Nitric acid electrolysis was carried out in a 10% nitric acid solution at 20°C using the electricity amount of 2, and the effects of hard rolling conditions and reheating conditions on hardness, elongation, and corrosion resistance were investigated. Further, the finished annealed plate thus produced was press-formed into the shape shown in FIG. 1, and the defective rate and each condition were investigated. The elongation evaluation is based on JIS 13.
The hardness was measured by a tensile test using a No. B test piece, and the hardness was measured using a micro Vickers (load: 500 g).
It was evaluated from Furthermore, the rust resistance was evaluated using a salt spray test (3
The rusting area ratio was relatively evaluated by applying 10 cycles of 5°C, 16 hours of spraying, 8 hours of moistening. The results are summarized in Table 1 and Tables 2-1 and 2-2, and Figures 2 and 3.

[0016]

[Table 1]

[0017]

[Table 2-1]

[0018]

[Table 2-2]

As shown in these results, the ferritic stainless steel manufactured according to the manufacturing conditions of the present invention has
It is clear that this material fully satisfies the required properties as a material for electrical materials, especially as a center core material for floppy disks.

[0016]

Effects of the Invention As explained above, according to the present invention, steel having a predetermined composition can be treated in sequence of hard rolling, reheating treatment, and nitric acid electrolysis, thereby achieving excellent ductility and wear resistance. , ferritic stainless steel for electrical materials, which also has excellent rust resistance, can be manufactured at low cost.

[Brief explanation of drawings]

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

FIG. 2 is a graph showing the relationship between rolling reduction and hardness.

FIG. 3 is a graph showing the relationship between rolling reduction and elongation.

Claims (2)

[Claims] [Claim 1] C: 0.12 wt% or less,
Si: 1.0 wt% or less, Mn: 1.0 wt% or less, Cr: 15~
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: 0.03w
t% or less and N: 0.1 wt% or less,
After final annealing, steel with the balance consisting of Fe and unavoidable impurities is subjected to cold rolling of 10% or more, and then heated to 500°C.
A ferritic stainless steel for electrical materials with excellent ductility, wear resistance, and rust resistance, which is characterized by being reheated in a temperature range of ~750°C for 10 seconds or more and 10 minutes or less, and then subjected to nitric acid electrolysis. manufacturing method. [Claim 2] C: 0.12 wt% or less,
Si: 1.0 wt% or less, Mn: 1.0 wt% or less, Cr: 15~
20 wt%, Ni: 1.0 wt% or less,
O: 0.003 wt% or less, P: 0.04 wt% or less, S: 0.03 wt% or less, and Ni: 1
．． 0 wt% or less, Al: 0.3 wt%
Below, O: 0.003 wt% or less, P: 0.
04wt% or less, S: 0.03wt% or less, and N
: 0.1 wt% or less, and as an element for improving hot workability, B: 0.002 to 0.01 wt%, Ca:
Contains at least one selected from 0.01 wt% or less and REM: 0.2 wt% or less, and at least one selected from V, Nb, and Ti each as a corrosion resistance improving element of 0.05 wt% or less, and the remainder is After final annealing, steel consisting of Fe and unavoidable impurities is subjected to cold rolling of 10% or more, then reheated at a temperature range of 500°C to 750°C for 10 seconds or more and 10 minutes or less, and then subjected to nitric acid electrolysis. A method for manufacturing ferritic stainless steel for electrical materials, which has excellent ductility, wear resistance, and rust resistance.