JPS60204833A - Manufacture of "sendust(r)" plate having superior magnetic characteristic - Google Patents

Abstract

PURPOSE:To enable the manufacture of a large-sized member and to improve the magnetic characteristics by hot rolling and cooling a hot billet contg. prescribed percentages of C, Si, P, S, sol.Al, N, O, V, Nb and Mn under prescribed conditions. CONSTITUTION:A steel contg., by weight, <=0.015% C, 4.5-12% Si, <=0.05% P, <=0.01% S, 2.5-7.5% sol.Al, <=0.008% N, <=0.008 O, 0.05-0.8% V, 0.005-0.4% Nb and <=0.5% Mn is refined. The steel is cast into a billet, the billet kept at >=1,150 deg.C is hot rolled at <=35% draft per one pass, and the resulting plate is cooled at 300-30 deg.C/hr cooling rate.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a sendust plate with excellent magnetic properties.

<Industrial Application Fields> In recent years, with the remarkable progress in powder metallurgy technology and the wide spread of electronic devices, Sendust C5t-At-Fe alloys are used as magnetic head materials and magnetic shielding materials.
However, despite K being a difficult-to-process material, demand for it appears to be increasing significantly.

<Prior art> By the way, although the Sendust mentioned above is a material with excellent magnetic properties such as extremely high magnetic permeability and specific resistance, -
However, even though it is a very brittle material, sendust containing 4.5% or more of Sit (hereinafter, % by weight) has a remarkable tendency to do so, so most of it is considered to be sintered crystals. At present, they are used only by being cast or directly cast into products with a desired wall thickness, and the possibility of using them as large-sized parts is currently closed.

However, because of Sendust's excellent magnetic properties, many studies were conducted from an early stage to explore its plastic working potential.

These studies have also attracted a great deal of attention in the sense that they aim to avoid the problems that inevitably arise with the adoption of powder metallurgy, which is almost the only means of producing practical sendust parts. Ta. Because it is manufactured using powder metallurgy
Sendust sintered parts inevitably undergo some oxidation on the powder surface during the powder manufacturing process, so
This is because Sendust itself could not exhibit its excellent magnetic properties.

Under these circumstances, recently, ``Even though sendust is said to be brittle and impossible to roll, it is possible to select one with a relatively low S1 content and heat it in an extremely narrow temperature range at high temperatures.'' There are reports stating, ``If rolling is carried out, it is possible to somehow obtain a rolled material, although unstable,'' or ``Rolling only yields a sendust plate with extremely poor toughness, which cannot be used for practical use, but the corner There have been no reports that if the steel is added and rolled at a high temperature range and at a strain rate that is considerably lower than in the practical range, it is possible to produce sendust plates that are unstable but have relatively good toughness. Even with this method, mass production of Sendust rolled plates is impossible, and there are many problems in manufacturing Sendust plates on an industrial scale, such as the need to reheat the material many times during rolling. It was something that I was dealing with.

<Purpose of the Invention> From the above-mentioned viewpoint, the present inventors have developed sendust plate material with excellent magnetic properties on an industrial scale by hot rolling, a simple process that does not require any special treatment or conditions. As a result of many years of repeated research through trial and error in order to find a method for mass production, we have come to the knowledge 1 shown below.

Findings> When an appropriate amount of V7i is added to sendust, an extremely brittle alloy, its hot workability is greatly improved without affecting its magnetic properties, and it can be applied at the same strain rate as in normal hot rolling. In addition to almost no cracking occurring during rolling, adding an appropriate amount of Nb also improves the toughness of the rolled material, so the heating temperature, rolling reduction rate, and cooling rate after finishing during hot rolling can be Be careful even when using NTF, as well as superior magnetic properties.
To efficiently mass-produce sendust plate material having good toughness sufficient for practical use on an industrial scale.

That is, in order to mass-produce high-toughness sendust plates with excellent magnetic properties by hot rolling, K is added to the alloy in an appropriate amount.
Addition.

■ Appropriate amount of addition to the alloy.

■ Ensuring the rolling temperature and limiting the rolling lid.

[Co., Ltd.] There are four important technical points, slow cooling after rolling, and we have discovered that mass production of the above-mentioned Nanodust hot-rolled sheet material is only possible when these are combined.

The above findings will be explained in more detail below.

■ Addition of ■ to the alloy When VL was added in a stoichiometrically larger amount than the trace amounts of C and N contained in the steel (sendust), the steel began to show a tendency to soften. .

This phenomenon is caused by the fact that in addition to the fact that the atoms have favorable size factors for solid solution in iron, they also tend to form carbonitrides. 5
This is thought to be due to the fact that a C, N atmosphere is formed, thereby eliminating the negative influence of the solid solution C, N atoms, which increases the 4' Eels potential for mobile dislocations. As a reminder, in this case, it is more likely that ■ is precipitated as a carbonitride, but rather that it forms a solid solution and forms a C or N atmosphere around it. be.

Of course, this kind of behavior can be expected for Tl or teeth, but contrary to expectations, these elements are too large in terms of size factor compared to Fe atoms, so the solid solubility limit in iron is small. Moreover, since it causes hardening due to solid solution, ■
Such effects were not at all as expected.

■ Difficult-to-work steel materials such as sendust are also extremely brittle, so it is necessary to improve toughness by making the structure finer. Quantitative Nbtv
Although sendust requires a relatively high temperature range for hot working, the grain growth after hot rolling and knee recrystallization is effectively suppressed, and the ferrite grain size becomes fine, improving toughness at room temperature. The result is a Sendust plate material that has improved properties and is soluble in mild cold working.

■ Ensuring the rolling temperature and limiting the amount of rolling reduction Even with an appropriate amount ■ and Sendust with Nbt added
Good hot workability is not exhibited unless the temperature is 00°C or higher, and hot workability is improved at high temperatures in the temperature range of 900°C or higher. Therefore, when forming into a plate material by regular processing, unless the rolling gt is completed at 900° C. or higher, hot ductility will be insufficient and cracks will occur.

For this purpose, the temperature U of the slab just before rolling must be 115
Whether it is direct rolling or reheat rolling of slabs, if the temperature immediately before rolling is below 1150°C, it will not be possible to ensure a finishing temperature of 900°C or higher, which is difficult to achieve in practice. It is not possible to roll the plate to a specified thickness.

Also, the amount of reduction is l? If the rolling reduction amount during rolling is as low as possible, the strain rate will decrease and the risk of cracking during rolling will be reduced, but if the appropriate amount of V and N as described above is
In sendust to which b' is added, when the reduction rate per pass exceeds 35%, the risk of occurrence of split n increases rapidly.

[Co., Ltd.] Controlled Cooling After Rolling Appropriate amounts of V and Nbt-added sendas) are cast, and rolling is performed before the temperature of the slab or steel slab falls below 1150°C, or until the temperature drops below the above temperature. If the temperature drops, reheating to 115C1℃ or higher before rolling will make it possible to obtain a plate material of the desired thickness when the rolling meets the condition that the rolling reduction rate per pass is 35 inches or less. However, when the obtained plate material is rapidly cooled after rolling, large thermal stress is generated, resulting in cracking. Furthermore, if the steel is cooled too slowly, recrystallization and grain growth will occur after rolling, and the toughness at room temperature will deteriorate due to the coarse ferrite structure.

However, if the plate material is cooled in a controlled manner within a predetermined cooling rate range for tempering or annealing after completion of rolling, the above-mentioned disadvantages will be resolved.

<Structure of the Invention> This invention has been made based on the above knowledge, and has the following characteristics: C: 0.015- or less, Si: 4-5 to 12.0
%.

P: 0.050% or less, S: 0.010% or less.

5ob-At: 2.5-7.5%, N: 0
．． 0 O8% or less.

0: 0.008% or less, V: 0.05-0.50
%.

Nb: 0.005-0.40%, Mn: O-50
, % or less of K, the remainder being substantially KFe'''
A slab or steel slab with C and a temperature of 1150°C or higher is hot rolled at a reduction rate of 35% or less per pass.

By subsequently cooling the material to 300°C, it is possible to produce sendust plate material with excellent magnetic properties at low cost on an industrial scale.

Next, the reason why the composition of the steel and the hot rolling/cooling conditions are numerically limited as described above in the method for producing a sendust plate material of the present invention will be explained.

A. Component composition (a) C C is an impurity element that is more preferable if its content is as small as possible, but especially when the C content exceeds 0.015%, the hot ductility of sendust is reduced in a solid solution state. In addition, the C content 't-0,015% also causes NbC or VCt-shaped bottoms to precipitate during slow cooling after hot rolling and deteriorates the toughness of the sendust plate.
It was determined as follows.

Φ) 5t Sl is an effective element for increasing the magnetic permeability and specific resistance of sendust, and in order to obtain the desired excellent magnetic properties, it is necessary to have a total content of 4.5 or more, but 12.0
Since hot working becomes almost impossible if the St content exceeds 4.5% to 2.0%.

(c) P P is contained in an amount not exceeding o, o s o.
In fact, P is an element that has the effect of slightly increasing magnetic permeability, but if it is contained in excess of o, o so, it deteriorates toughness and makes subsequent cold working completely impossible. Content t: Set at 0.050% or less.

(d) S S is an impurity element that deteriorates the hot ductility of sendust, so the lower its content is, the more preferable it is. However, in consideration of economic efficiency, the S content was set at 0.010- or less.

(a) sot, ht Sot and At, like St, are important components that increase the magnetic permeability and specific resistance of sendust, but if their content is less than 2.5-, it is difficult to achieve the desired magnetic properties. If the content exceeds -7.5%, hot processing of sendust becomes impossible, so the tsoL and AL content was set at t-2.5 to 7.5%.

(f) N N is an impurity element that forms various nitrides in steel and precipitates at grain boundaries and causes embrittlement, so the smaller the amount, the better. The N content was determined to be below '1o, ooas.

00 is also an impurity element that should be reduced as much as possible because it forms various oxides in steel, deteriorating magnetic properties and reducing hot ductility. In consideration of performance, the O content was determined to be less than o, o s%.

(G)) As mentioned above, ■■ is an important element that significantly improves the hot ductility of sendust by eliminating the harmful effects of C and N mixed in as impurities, and its addition is an important element that significantly improves the hot ductility of sendust. The main point is that ■ If the content is less than 0.05%, the desired effect on improving hot workability cannot be obtained;
If the content exceeds V, the adverse effect of V will occur and the hot ductility will be lowered by 1.
．． 05 to O, SO, it is particularly preferable to add V in an amount of about 0.2% or more.

(i) Nb Nb is an element effective in refining the microstructure of steel,
By containing o, o o s% or more together with special KV, it has the effect of refining the ferrite grains of sendust and improving cold workability, but if it is contained in excess of 0.40%, sendust will harden. K may cause a significant deterioration of hot ductility.

The island content was determined to be 0.005 to 0.40 inches.

(j)　Mn Corridor is fixed as SkMnS in Sendust.

It is a preferable element that improves hot ductility, and even if its content is small, a remarkable effect can be obtained.
If the content exceeds 0.0, s o s , the magnetic permeability of sendust will decrease and its significance as a high magnetic permeability steel will be diminished, so the seed content was set at 0.50 or less.

Normally, about 0.1 to 0.2 inches of iron is mixed into steel as an impurity, but even if the applied content is at this level or lower than this value, a good effect of improving hot ductility is exerted. Therefore, in practice, active addition of corridors is not necessarily necessary.

B. Hot rolling/cooling conditions (JL) Hot rolling conditions The steel (sendust) with the composition targeted by the method of this invention C is rolled in a temperature range of 900°C or higher, and at a rolling reduction rate of 9 per pass. If it is not 35% or less, cracks will occur during rolling. In order to finish the plate to a specified thickness by rolling at such finishing temperature and rolling reduction rate per pass, K is practically required when the holding temperature of the slab or steel slab immediately before rolling is 1150°C or higher. Otherwise, f'L will not be true.

That is, the temperature of the slab or steel slab just before rolling is 1150'Ck.
If the rolling reduction ratio per slot or slot exceeds 35%, cracks will occur during rolling, making it impossible to manufacture sendust plate material.

Of course, if it is not possible to finish the plate to the specified thickness by hot rolling under these conditions, rolling may be repeated as many times as necessary until the specified thickness is achieved.
The process of reheating to 150°C or higher and finishing hot rolling at 900°C or higher is repeated, but even in such a case, it is natural that the rolling reduction per one blank must be 35- or less. be.

By the way, the steel targeted by the method of this invention (Sendust) is extremely brittle in the as-cast state. If the entire rolling process is used, there is a risk that brittle fracture will occur due to the thermal stress generated during the rolling process, making it impossible to produce stable sendust plates.
Thermal stress that occurs in the low-temperature range from 00°C to temperature is likely to cause cracks, so slow cooling is necessary to lower the temperature to 200°C or less, and when reheating, it is extremely difficult to cool down to a temperature exceeding 200°C. A certain heating rate is required.

However, in actual operation, slow cooling or slow heating in the above low temperature range will disadvantage production efficiency and significantly reduce productivity, so after casting the slab, the temperature above 1150℃ (Especially the center temperature) or directly hot rolling while keeping the slab temperature above 200℃.
A method of reheating to 150° C. or higher and hot rolling is recommended.

(b) Cooling conditions after hot rolling Controlled cooling at a cooling rate range of 300 to 30°C/hr after the end of hot rolling is to: ■ Alleviate thermal stress and prevent the risk of 5 cracks; The V added to improve ductility and the teeth added to make grains finer combine with C and N mixed as impurity elements to form V (C,N) and Nb(C,N)t.
- Aiming for an annealing effect to suppress the negative effects of hardening and embrittlement (precipitation, sendas). ■ However, if the cooling rate is slow, recrystallization of grains will occur, and coarse grains will cause toughness. This is because it causes deterioration.

If the cooling rate after hot rolling exceeds 300°C/hr, there is an extremely high risk of cracking in the sendust plate, and if the cooling rate is slower than 30°C/hr, it will also lead to deterioration of toughness. Therefore, it is difficult to stably produce Sendust plate material with desired performance with high efficiency.

Next, the present invention will be explained using examples and comparing with comparative examples.

<Example> First, steel (Sendust) A to A having the composition shown in Table 1 was melted by full melting, and then a slab with a thickness of 25 mm was cast by continuous casting.

These slabs were then subjected to hot rolling and cooling conditions as shown in Table 2 to produce sendust plates having the thicknesses also shown in Table 2.

The resulting sendust plate material was investigated for crack occurrence and magnetic properties, and the results are also shown in Table 2.

From the results shown in Table 2, it is clear that the method of the present invention can stably produce Sendust hot-rolled sheet metal with excellent magnetic properties. - In comparative examples where the cooling conditions were outside the scope of the present invention, cracks occurred during rolling or cooling,
It can be seen that Sendust hot-rolled sheets cannot be stably manufactured.

Overall effect> As mentioned above, according to the present invention, it is possible to mass produce sendust plates with excellent magnetic properties etc. on an industrial scale by hot rolling which does not require any complicated means in actual operation. As a result, we can provide various magnetic head materials and magnetic shielding materials at low cost, and we can also manufacture large components, so we are expanding the use of Sendust to, for example, components of buildings that require shielding from the geomagnetic field. This brings about extremely useful effects industrially.

Applicant: Sumitomo Metal Industries, Ltd. Agent Tomi 1) Kazuo TL or one person

Claims (1)

[Claims] In terms of weight percentage: C: 0.015% or less j+ 81' 4-5 to 1
2.0% TP: 0.050% or less, S: 0.0
Less than 10%. aoL, At: 2.5-7.5%, N: 0.0
08% or less. 0: 0.008 inches or less, V: 0.05 to 0.
80 chi. Nb: 0.005-0.40'A, Mn: 0.
A slab or steel slab containing 50% or less, the remainder being substantially Fe, and having a temperature of 1150°C or higher is hot rolled at a reduction rate of 35% or less per pass, and then 300-b A method for producing a sendust plate material with excellent magnetic properties, characterized by cooling.