JPH01108315A - Manufacture of hot rolled steel plate for magnetic shielding having superior machinability - Google Patents

Abstract

PURPOSE:To manufacture a hot rolled steel plate for magnetic shielding having superior machinability by hot rolling and annealing a dead soft Al killed steel slab contg. specified percentages of C, Si, Mn, P, S and Al under specified conditions. CONSTITUTION:A dead soft Al killed steel slab having a compsn. consisting of, by weight, <=0.004% C, <=0.10% Si, <=0.30% Mn, <=0.030% P, 0.010-0.030% S, 0.005-0.080% Al and the balance essentially Fe is prepd. The slab is hot rolled at the Ar3 transformation point or above and the resulting hot rolled plate of 1.2-10.0mm thickness is annealed at 750 deg.C- the Ac3 transformation point for >=20min. A hot rolled steel plate for magnetic shielding having superior workability, especially suitability to drilling and shearing work is easily obtd.

Description

[Detailed Description of the Invention] (Industrial Application Field) This invention is used to protect devices that generate strong magnetic fields, such as nuclear magnetic resonance tomography devices, from external magnetic fields, or to prevent the generated magnetism from being transmitted to the outside. The present invention relates to an advantageous method of manufacturing a hot-rolled steel sheet for magnetic shielding that effectively prevents leakage.

(Prior art) In recent years, medical equipment for image diagnosis has been developed by placing predetermined measurement points on the human body in a strong magnetic field using superconducting magnets or normal conducting magnets, and by utilizing the nuclear magnetic resonance of H atoms in the human body. Nuclear magnetic resonance tomography systems, which perform image diagnosis on patients by converting tomographic images of various parts of the human body into images, are attracting attention.

When such a device is used, a strong magnetic field is generated around the device, and when the magnetism acts on a watch, magnetic tape, pacemaker, etc., the problem arises that various functions of the device are impaired.

In addition, there is also the problem that obtaining good images is hindered by external geomagnetism and radio waves, so it is necessary to shield the device itself or the location where the device is installed from the effects of these factors.
There is a need for magnetic shielding materials with so-called high magnetic permeability.

Such magnetic shielding materials include, for example, Japanese Unexamined Patent Application Publication No. 1988-60
-Thick steel plates with a thickness of 25 m or more used in medical cyclotrons, etc. proposed in Publications No. 208417 and No. 60-208418, or JP-A No. 60-255924
Thickness 0.0 for color cathode ray tubes proposed in the publication.
15mm cold-rolled steel plate, and also Special Publication No. 58-44146
A Ni-Fe based alloy steel plate called Permalloy proposed in the above publication is known.

(Problems to be solved by the invention) However, JP-A-60-208417 and JP-A-60-208417
Although the products disclosed in each publication of No. 208418 are produced by hot rolling, they require alloying elements such as Nb, V, and Ti in order to satisfy both high magnetic permeability and mechanical properties. This increases the cost, and since it is a thick steel plate mainly used for structural members, its thickness and weight make it difficult to install and handle for magnetic shielding of medical equipment, and it also has poor mechanical properties as well as magnetic permeability. However, because the material is so well coated, its machinability is poor, which also causes the problem of difficulty in construction.

Furthermore, since the one disclosed in JP-A-60-255924 is a cold-rolled steel plate used for color cathode ray tubes,
Even if thin steel sheets with high magnetic permeability and good press formability can be obtained, their machinability is poor, and if they are to be used in medical equipment that requires relatively thick materials, many sheets must be laminated. The problem was that it had to be used.

Furthermore, what is disclosed in Japanese Patent Publication No. 58-44146 is
Since it is an alloy steel, it increases the cost and, like the above-mentioned conventional steel, it still has the problem of poor machinability and workability.

This invention advantageously solves the above problems and proposes an advantageous manufacturing method for hot-rolled steel sheets for magnetic shielding, which not only have excellent magnetic shielding ability but also excellent machinability and workability. The purpose is to

(Means for solving the problem) As a result of intensive research to improve machinability, the inventors have found that it is preferable to reduce the amount as much as possible since it usually impairs mechanical properties and weldability. It has been found that containing a relatively large amount of S is extremely effective in achieving the intended purpose.

This invention is based on the above knowledge.

That is, the present invention provides C: 0.004wtχ (hereinafter simply expressed as %) or less, Si: 0.10% or less, Mn
: 0.30% or less, P: 0.030% or less, S
: 0.010-0.030% and Al: 0.0
An ultra-low carbon aluminum killed steel piece containing 0.05 to 0.080% and the remainder being substantially Fe is hot rolled at a temperature above the Ars transformation point to a thickness of 1.2 to 10.0 mm. This is a method for producing a hot-rolled steel sheet for magnetic shielding with excellent machinability, which comprises forming a hot-rolled sheet and then annealing the sheet at a temperature range of 750° C. or higher and lower than the AC5 transformation point for 20 minutes or more.

Further, in this invention, C: 0.004% or less, Si:
0.10% or less, Mn: 0.30% or less, p:
0.030% or less, S: 0.010-0.030%
and At: Q, O05~o, os.

%, along with B: 0.0003 to 0.0040%, and the remainder is substantially Fe, is hot rolled at a temperature higher than the Ar3 transformation point to a thickness of 1. After making it into a hot-rolled sheet of .2 to 20.0 m, 750
This is a method for producing a hot-rolled steel sheet for magnetic shielding having excellent machinability, which comprises performing an annealing treatment for 20 minutes or more in a temperature range of .degree. C. or above and below the Acs transformation point.

This invention will be specifically explained below.

Now, the magnetic shielding property depends on the magnetic permeability, and the higher the magnetic permeability, the better the magnetic shielding property.

Since the magnetic permeability μ can be expressed as μ·B/H, the higher the magnetic flux density (B) is at a low magnetizing force (H), the higher the magnetic permeability can be obtained. In other words, under the same magnetizing force, the higher the magnetic flux density, the higher the magnetic permeability.

By the way, in ordinary inexpensive carbon steel, it is extremely difficult to obtain a high magnetic flux density B of 1.3 Tesla (T) or more when the magnetizing force H is 200 A/m.

Therefore, in this invention, as a guideline for high magnetic permeability, we set the target characteristic to be a magnetic flux density of 1.3 T or more at a low magnetizing force of 20 OA/m, and based on this index, we limited the component composition and manufacturing conditions as follows. be.

S: 0.010-0.030% According to the inventors' experiments, most of S exists as MnS, but if the S amount is less than o or oio%, the frequency of seizure during drilling increases. Since machinability deteriorates, the lower limit of S was set at 0.010%. On the other hand, the DC magnetization characteristics tend to deteriorate as the amount of S increases, and when Si1 exceeds 0.030%, the magnetic flux density at a magnetizing force of 200 A/n+ decreases to 1.3 T.
Therefore, the upper limit was set at 0.030%.

In Figure 1, C: 0.0025%, Si: 0.0
5%, Mn: 0.020%, P: 0.015
% and AI: Contains 0.025% and S is 0.
880
After hot rolling at ℃ to 4mm thickness, 850℃1
The results of investigating the relationship between the machinability and magnetic flux density of steel sheets obtained by annealing for 50 minutes are summarized in relation to the amount of S in the steel.

As is clear from the figure, the S content in the steel is 0.010
Good values for both properties were obtained in the range of ~0.030%.

C: 0.004% or less Although C is as low as possible, it is easier to coarsen the ferrite grains and is advantageous in obtaining high magnetic permeability, but a range of 40 ppm or less is acceptable.

Si: 0.10% or less Si effectively contributes to improving machinability, but if it exceeds 0.10% as a substituted solid solution atom, the surface quality deteriorates significantly, so the upper limit was set at 0.10%. .

Mn: 0.30% or less Mn is an essential element for suppressing hot embrittlement due to FeS, but on the other hand, excessive Mn addition to the extent that it exceeds the stoichiometric equivalent as MnS is a substitutional solid solution element. The upper limit was set at 0.30% because this would lead to deterioration of the magnetization characteristics.

P: 0.030% or less P is a substitutional solid solution element that effectively contributes to improving machinability, and if it exceeds 0.030%, the magnetization characteristics deteriorate significantly, so the upper limit is set to 0.030%. did.

Al: 0.005 to 0.080% Al requires addition of at least 0.005% as a deoxidizing agent, but if it exceeds 0.080%, the magnetization properties will deteriorate, so it should be added to 0.005 to 0.080%. It was assumed that the content was added within a range of 0.080%.

B: 0.0003 to 0.0040% B binds with C and N to fix solid solution C and N, suppressing the occurrence of yield elongation,
It effectively contributes to preventing the occurrence of surface defects called buckling, but if it is less than 3 ppn+, the addition effect is poor, while if it exceeds 40 ppm, the deterioration of the magnetic properties is significant, so it should be added in the range of 3 to 40 ppm. And so.

Hot rolling conditions: Ar, if hot rolling is completed below the transformation point, the crystal grains will not become coarse even if annealing is performed afterwards, and the expected magnetization characteristics will not be obtained; The hot rolling was then terminated.

Hot-rolled plate thickness: If the plate thickness is less than 1.2 tm, the pickling efficiency after hot rolling will be poor (and the cost will be high, making it uneconomical), so the lower limit plate thickness is set to 1.2 mm. did.

On the other hand, if the plate thickness exceeds 10 nn, there is a high possibility that a surface defect called buckling will occur when the coil is unwound to form a flat plate. However, as mentioned above, when 3 to 40 ppm of B is contained, the occurrence of yield elongation is suppressed by fixing the steel inner surface IC and N, so when B is contained, buckling defects on the plate surface occur up to a plate thickness of 20fflI11. It is possible to correct and flatten the plate without causing any damage. Therefore, when 3 to 40 ppm of B is present, the upper limit plate thickness is 20non, while when B is not present, it is 10mm.

Annealing conditions: According to experiments, when the annealing temperature is less than 700°C, good magnetization characteristics cannot be obtained because strain (dislocation) recovery is insufficient.
If the value exceeds the point e, the α-10T→α transformation is repeated, so that sufficiently coarse grains cannot be obtained and the magnetization properties deteriorate as well. Further, even if the annealing time is less than 20 minutes, the annealing is insufficient.

For this reason, the annealing temperature was set at 750° C. or higher and below the Ac point, and the annealing time was set at 20 minutes or longer.

In Figure 2, C: 0.028%, SR: 0.05%
, Mn: 0°25%, P: 0.015%,
Ultra-low carbon A1 killed steel billet containing S: 0.025% and Al: 0.028% (Ar3: approx. 9
00℃) was hot-rolled at 885℃ to a thickness of 2cm, and then annealed under various conditions. It is shown by the relationship.

As is clear from the figure, when the annealing temperature is in the range of 750 to Ac= point and the annealing time is 20 minutes or more, a high magnetic flux density of 1.3 T or more, which is the target of the present invention, is obtained.

(Example) Steel slabs having various compositions shown in Table 1 were hot rolled and then annealed under the same conditions shown in Table 1.

Table 1 also shows the results of an investigation of the magnetic properties of the thus obtained hot-rolled steel sheet for magnetic shielding, as well as seizure resistance and buckling resistance during drilling.

The seizure index as an evaluation of drill perforability was defined as follows.

51 on a 0°5 HP tabletop drilling machine! ! Attach a lφ drill and measure the change in torque when drilling into a 4m thick steel plate with a load of 5kg without oil. If the value is less than 1.1 times the steady torque value: Rating 1.1.1~1
．． Less than 2 times: Score 2. Less than 1.2 to 1.3 times: Score 3
．． 1° 3 to less than 1.5 times: Rating 4. 1.5 to less than 3.0 times: Rating 4.5. 3.0 times or more: Rating 5.

As is clear from the same table, all of the hot rolled steel sheets obtained according to the present invention exhibited excellent magnetization properties, drillability, and surface texture.

(Effects of the Invention) Thus, according to the present invention, it is possible to easily obtain a hot-rolled steel sheet for magnetic shielding that not only has excellent magnetic shielding properties but also has excellent workability, particularly drilling performance and shearing workability.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between S'I in steel, magnetic flux density and workability, and FIG. 2 is a graph showing the relationship between annealing temperature and magnetic flux density using annealing time as a parameter. Figure 1 S (%)

Claims (1)

[Claims] 1. C: 0.004 wt% or less, Si: 0.10 wt% or less, Mn: 0.30 wt% or less, P: 0.030 wt% or less, S: 0.010 to 0.030 wt% and Al: 0.005 to 0.080 wt%, and the balance is essentially Fe, and is hot rolled at a temperature above the Ar_3 transformation point to a thickness of 1.2 Production of a hot-rolled steel sheet for magnetic shielding with excellent machinability, which is characterized by subjecting the hot-rolled sheet to a thickness of ~10.0 mm and then annealing it for 20 minutes or more in a temperature range of 750°C or higher and lower than the Ac_3 transformation point. Method. 2, C: 0.004 wt% or less, Si: 0.10 wt% or less, Mn: 0.30 wt% or less, P: 0.030 wt% or less, S: 0.010 to 0.030 wt% and Al: 0.005 ~0.080 wt% together with B: 0.0003~0.0040 wt%, and the remainder is essentially Fe, and hot rolled at a temperature higher than the Ar_3 transformation point. After applying it to a hot-rolled sheet with a thickness of 1.2 to 20.0 mm, it was heated at a temperature range of 750°C or higher and Ac_3 transformation point or lower.
A method for producing a hot-rolled steel sheet for magnetic shielding having excellent machinability, characterized by subjecting it to annealing treatment for 0 minutes or more.