JP2007211321A - Method for producing steel sheet for cpu socket frame or cpu fixing cover - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a cold rolled steel sheet suitable for a CPU (central processing unit) socket frame and a CPU fixing cover used when a CPU chip is fitted to a wiring board. <P>SOLUTION: Regarding this production method, the continuously cast slab of a steel comprising, by mass, 0.01 to 0.20% C, ≤0.5% Si, ≤1.5% Mn, ≤0.05% P, ≤0.01% S, 0.005 to 0.10% acid soluble Al and ≤0.007% N, and, if required, further comprising 0.01 to 0.15% Ti and/or 0.01 to 0.15mass% Nb is subjected to hot rolling, is pickled, and is thereafter subjected to cold rolling at a cold rolling ratio of 20 to 50%. Since the steel sheet has been subjected to working strengthening by the cold rolling, excellent characteristics of a 0.2% proof stress satisfying ≥600 N/mm<SP>2</SP>, bending workability satisfying the tip radius of ≤0.7 mm and sheet thickness precision satisfying ≤20 μm are imparted thereto. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method of manufacturing a steel plate for a CPU socket frame and a CPU fixing cover for attaching a CPU (Central Processing Unit) such as a computer to a wiring board.

CPUs of computers and the like have been increased in the number of pins of electronic equipment components with the increase in processing speed. In order to increase the number of pins, it is necessary to securely connect the pins and the board, and the CPU chip is connected and fixed to the wiring board using the CPU socket frame and CPU fixing cover.
As the material for the CPU socket frame and CPU fixing cover, metal, which is highly reliable and has high fastening performance, is beginning to be used instead of conventional resin.
A metal CPU socket frame 1 is attached to a CPU socket 4 with a CPU fixing cover 2 and a CPU hook 3 attached thereto. The CPU fixing cover 2 has a claw 5 for hooking the CPU hook 3, and is integrated with the CPU socket frame 1 through the connecting portion 6. When CPU chip 7 is mounted on CPU socket 4 on the wiring board (Fig. 1) and CPU fixing cover 2 is fastened to CPU socket frame 1 by engaging CPU hook 3 and claw 5, CPU chip 7 is attached to CPU fixing cover 2. (Fig. 2).

In order to obtain a pressing force necessary for fixing the CPU chip 7, the CPU fixing cover 2 between the claw 5 and the connecting portion 6 is warped. When the claw 5 of the CPU fixing cover 2 with the upper warp is pressed with the CPU hook 3, the restoring force of the upper warp acts as a pressing force to securely connect and fix the CPU chip 7.
The CPU socket frame and the CPU fixing cover are manufactured by punching a cold-rolled material of austenitic stainless steel such as SUS301 and SUS304 or ferritic stainless steel such as SUS409 and press-working them (Patent Documents 1 and 2). Stainless steel is excellent in corrosion resistance because it contains a large amount of alloy components such as Cr and Ni, but is expensive and often has problems with workability.
JP 2004-68033 A Japanese Patent Application No. 2005-27269

If ordinary steel can be used instead of stainless steel, material costs and manufacturing costs can be reduced. In recent years, with the reduction in size and weight of electronic device parts, the demand for thinning has become severe, and steel plates with high thickness accuracy are strongly demanded as materials.
In a high-strength material such as a cathode ray tube frame (Patent Documents 3 and 4), since Mo is added to improve high-temperature strength, the material cost is relatively high. The cathode ray tube band material (Patent Document 5) with an increased Si content deteriorates the bending workability and the plate thickness accuracy due to the deterioration of the surface properties, and does not satisfy the required level of the CPU socket frame and CPU fixing cover.
JP 2001-59129 A JP-A-8-67945 Japanese Patent Laid-Open No. 11-158548

The material characteristics required for materials such as metal CPU socket frames and CPU fixing covers are 0.2% proof stress: 600N / mm ² or more so that the required strength can be obtained even if it is thin and lightweight. Required. Regarding workability, since it is commercialized by bending, it is required to be able to bend with a radius of 0.7 mm or less at the bending tip. In addition, in order to accurately and stably collect parts having a predetermined size by cutting or punching, a material having a thickness of 20 μm or less is required.

The present inventors investigated and examined the manufacturing conditions that promoted work strengthening in order to satisfy the required characteristics of the CPU socket frame and CPU fixing cover with ordinary steel cheaper than stainless steel. As a result, when cold rolling with a cold rolling ratio of 20 to 50% is applied to a hot rolled steel strip of low carbon aluminum killed steel whose component system has been specified, it has a strength comparable to that of a stainless steel plate, and the CPU socket frame and CPU It has been found that the steel sheet can be used sufficiently for the fixed cover.
The present invention is based on such knowledge, and by specifying the combination of the component system, hot rolling conditions, and cold rolling conditions, the required performance of the CPU socket frame and CPU fixing cover is fully satisfied, and the bending workability, plate thickness It aims at providing the steel plate excellent in the precision.

The production method of the present invention is characterized by steel composition, hot rolling conditions, and cold rolling conditions.
Steel composition: C: 0.01 to 0.20 mass%, Si: 0.5 mass% or less, Mn: 1.5 mass% or less, P: 0.05 mass% or less, S: 0.01 mass% Hereinafter, acid-soluble Al: 0.005 to 0.10% by mass, N: 0.007% by mass or less, Ti: 0.01 to 0.15% by mass and / or Nb: 0.01 to 0 if necessary It contains 0.15% by mass, and the balance is substantially Fe.
After continuously casting the steel material having the composition, it is hot-rolled at a finishing temperature of Ar ₃ transformation point or more and a winding temperature of 450 to 600 ° C. Next, pickling and cold rolling at a cold rolling rate of 20 to 50%.

Effects and embodiments of the invention

  For strengthening steel, work strengthening method, solid solution strengthening method, transformation strengthening method, etc. are known. However, in solid solution strengthening and transformation strengthening, bending workability deteriorates because alloy elements such as Si and Mn are added in large quantities. Cheap. In addition, it is difficult to manufacture a CPU socket frame and a CPU fixing cover material with a plate thickness accuracy of 20 μm or less if the cold-rolled sheet is annealed, and leveling, skin pass and other correction processing are required after annealing.

On the other hand, in the process strengthening method, high strength can be achieved at low cost, and a steel plate with high thickness accuracy can be obtained. Therefore, in the present invention, a work strengthening method is employed, and a low carbon aluminum killed steel having a specified steel composition is hot-rolled at a finishing temperature: Ar ₃ transformation point or higher, a winding temperature: 450-600 ° C., and then pickled. By cold rolling at a cold rolling rate of 20 to 50%, 0.2% proof stress: 600 N / mm ² or more tensile property, tip radius: 0.7 mm or less bending workability, plate thickness accuracy: 20 μm The following properties are added to the CPU socket frame and CPU fixing cover.

  That is, by cold rolling a hot rolled sheet of low carbon aluminum killed steel having a specific steel component at a cold rolling rate of 20 to 50%, high strength is achieved, and excellent bending workability is secured. The plate thickness accuracy of the material steel plate is also improved. On the other hand, high strength hot rolling such as 0.12% C-0.3% Si-2.0% Mn containing relatively large amounts of Si and Mn, such as C—Mn and C—Si—Mn. When the steel strip is rolled at a relatively low cold rolling rate, the thickness variation due to slight differences in processing conditions cannot be avoided, and the thickness accuracy: 20 μm or less cannot be satisfied. Conversely, when a relatively low-strength steel sheet is processed and strengthened at a high rolling rate, although the sheet thickness accuracy of 20 μm or less is satisfied, the bending workability is significantly degraded.

Hereinafter, the alloy components and production conditions defined in the present invention will be described individually.
[Alloy components]
C: 0.01 to 0.20% by mass
It is an effective component for increasing the strength of the steel strip, and the lower limit is set to 0.01% by mass as a value that can achieve the required level of strength at a cold rolling rate of 50%. The strength increases with an increase in the C content, but an excessive amount deteriorates the local ductility that affects bending workability, so 0.20% was made the upper limit. Preferably, the C content is selected in the range of 0.05 to 0.15% by mass.

-Si: 0.5 mass% or less It is an alloy component added as needed, and contributes to strength improvement. The effect of adding Si becomes noticeable at 0.05% by mass or more, and the strength increases as the amount increases. However, excessive addition causes cracking of the ears during cold rolling and deterioration of surface properties, so the upper limit was made 0.5 mass%. Preferably, the Si content is selected in the range of 0.05 to 0.30 mass%.

Mn: 1.5% by mass or less An alloy component that contributes to strength improvement. An effect of addition of Mn is observed at 0.20% by mass or more, and a greater strength improvement effect is obtained as the content increases. However, if an excessive amount of Mn is contained, the band-like structure of pearlite grows significantly on the hot-rolled sheet due to Mn segregation, and the bending workability is extremely deteriorated, so the upper limit was set to 1.5% by mass. Preferably, the Mn content is selected in the range of 0.30 to 1.20% by mass.

-P: 0.05% by mass or less Although it is an effective component for increasing the strength, when an excessive amount of P exceeding 0.05% by mass is contained, a pearlite band-like structure grows remarkably in the same manner as Mn, Bending workability deteriorates. Therefore, the P content is preferably as low as possible.
-S: 0.01 mass% or less Since it will cause high temperature embrittlement when it is contained in a large amount, it is preferably as low as possible. It is also an adverse effect due to S that string-like inclusions MnS are generated with an increase in the amount and the bending workability is remarkably deteriorated. However, if the level is 0.01% by mass or less, which is usually inevitably contained, the adverse effects due to S can be ignored.

Acid-soluble Al: 0.005 to 0.10% by mass
It is an alloy component added as a deoxidizer, and 0.005% by mass or more is required as acid-soluble Al in order to obtain a sufficient deoxidation effect. The effect of Al deoxidation is saturated at 0.10% by mass, and adding more than that will only cause an increase in steel material cost. Preferably, the Al content is selected in the range of 0.01 to 0.05 mass%.
N: 0.007% by mass or less N is an element that easily forms a precipitate harmful to bending workability, and is preferably as low as possible. If it is a level of 0.007% by mass or less which is usually inevitably contained, an adverse effect on bending workability can be ignored.

Ti: 0.01 to 0.15% by mass
It is an alloy component added as necessary, reacts with C, S, N in the steel to become precipitates, and exhibits the effect of increasing the strength of the steel strip by precipitation strengthening. Further, since the generation of MnS harmful to the bending workability is suppressed, the bending workability can be improved. The effect of addition of Ti is observed at 0.01% by mass or more, but is saturated at 0.15% by mass, and adding more than that causes an increase in steel material cost. Preferably, the Ti content is selected in the range of 0.02 to 0.10% by mass.

・ Nb: 0.01 to 0.15 mass%
Like Ti, it reacts with C to form precipitates and exhibits the effect of increasing the strength of the steel strip by precipitation strengthening. Nb is an effective alloy component also in increasing the strength by refining the metal structure of the steel sheet. Such an effect is seen at 0.01% by mass or more, but is saturated at 0.15% by mass, and even if added more, the cost of the steel material is increased. Preferably, the Nb content is selected in the range of 0.02 to 0.10% by mass.

(Hot rolling)
A continuous cast piece of steel material having a predetermined composition is hot-rolled at a finishing temperature: Ar ₃ transformation point or higher and a coiling temperature: 450-600 ° C.
The finishing temperature is set to be higher than the Ar ₃ transformation point in order to suppress variation in hot strength and improve the thickness accuracy. At the finishing temperature that does not reach the Ar ₃ transformation point, the variation in hot strength accompanying the transformation is large and the thickness accuracy is not stable. Preferably, the finishing temperature is set to a temperature 10 to 30 ° C. higher than the Ar ₃ transformation point.

  Increasing the coiling temperature can be expected to improve the ductility, but at high temperature coiling exceeding 600 ° C, the iron carbide becomes coarse and the cold rolling rate needs to be set high to compensate for the strength reduction of the steel sheet. Causes workability degradation. On the other hand, at low temperature winding at 450 ° C. or lower, the strength increases due to transformation strengthening, but the strength fluctuation in the coil longitudinal direction increases. In addition, the cold rolling rate during the subsequent cold rolling is 20% or less, and the required level of sheet thickness accuracy cannot be obtained. Preferably, the winding temperature is selected in the range of 500 to 580 ° C.

(Cold rolling)
Cold rolling is performed at a cold rolling rate of 20% or more in order to increase the strength by processing strengthening. A cold rolling rate of 20% or more is effective in improving the plate thickness accuracy. As the cold rolling rate increases, both strength and sheet thickness accuracy are improved. However, when the cold rolling rate exceeds 50%, the bending workability is remarkably deteriorated and the manufacturing cost is increased. In order to balance the strength, plate thickness accuracy and bending workability at a high level, it is preferable to set the cold rolling rate within a range of 25 to 40%.

The steels in Table 1 were melted and continuously cast into slabs. The slab was heated to 1200 ° C., and a hot-rolled steel strip having a thickness of 2.0 mm was manufactured through rough rolling and finish rolling. In the finish rolling, the finishing temperature was set to the range of Ar ₃ transformation point or higher and the winding temperature: 500 to 550 ° C.

After pickling the hot-rolled steel strip, it was subsequently cold-rolled at a cold rolling rate of 10 to 70% to produce a cold-rolled steel strip having a plate thickness of 1.0 mm.
A No. 5 test piece of JIS Z2201 was cut out along the C direction (direction orthogonal to the rolling direction) of the obtained cold-rolled steel strip and subjected to a tensile test at room temperature.
Also, the plate thickness is measured with a micrometer at a plurality of locations along the width direction of the cold-rolled steel strip, and the maximum and minimum values of the measurement values obtained by the plate thickness measurement over the width of the steel strip: 980 mm The difference was calculated as the plate thickness accuracy.
Table 2 shows the results of investigations on tensile properties and plate thickness accuracy.

Furthermore, bending workability was investigated by the following V block method (90 degree V bending test based on JIS Z2248).
Using punches with different tip radii R, the test piece was bent 90 degrees V in two directions: a bending axis parallel to the rolling direction (C direction bending) and a bending axis perpendicular to the rolling direction (L direction bending). The crack generation was evaluated by observing the occurrence of cracks in relation to the radius R, with ○ indicating a test piece without cracks and × indicating a test piece with cracks.
The evaluation results are shown in Table 3.

As can be seen in Tables 2 and 3, with No. 1-8 cold rolled at a cold rolling rate of 20-50%, the 0.2% proof stress exceeds 600 N / mm ² at the minimum, and the bending workability is also in the C direction. Bending was as good as 0.5 mmR and plate thickness accuracy was 18 μm or less.
On the other hand, in No. 9 using a steel type with excessive Mn, the bending workability was inferior to 1.0 mmR in the C direction bending, and an adverse effect of the pearlite band-like structure generated on the hot-rolled sheet was observed. . In No. 10 cold-rolled with an excessive cold rolling rate (70%), both 0.2% proof stress and bending workability were inferior. On the contrary, No. cold-rolled with a low cold rolling rate (10%). In No. 11, although 0.2% proof stress and bending workability were good, the plate thickness accuracy was as large as 45 μm, and did not reach the required level.

  From the above test results, any of the tensile properties, bending workability, and plate thickness accuracy can be achieved by cold rolling a hot-rolled steel strip of low carbon aluminum killed steel with specified alloy components at a cold rolling rate of 20-50%. It is also a material that satisfies the required characteristics of the CPU socket frame and CPU fixing cover.

  Therefore, cold-rolled steel strips other than test Nos. 9 and 10 that were inferior in bending workability were sized into strips of a predetermined width, and the strips were pressed with the direction of the claw 5-connecting portion 6 aligned with the C direction By processing, a CPU socket frame and a CPU fixing cover (FIGS. 1 and 2) having an effective area of 47 mm × 57 mm in a predetermined shape were produced.

  A CPU socket frame made of the same cold-rolled steel strip and a CPU fixing cover were combined to provide a CPU mounting portion on the wiring board, and the test was conducted to mount a CPU chip of size 45 mm × 47 mm. In the mounting test, a pressure measurement film is sandwiched between the CPU chip 7 and the CPU socket 4, the claw 5 is put on the CPU hook 3, the CPU fixing cover 2 is closed, and the pressure when the CPU chip 7 is fixed (hereinafter referred to as "fixing pressure"). Was measured). If the fixed pressure is 1.0 MPa or more, it can be used satisfactorily, but the more severe condition of 1.2 MPa or more was used as a criterion for the pass / fail judgment.

Further, in order to examine changes in the fixed pressure when the CPU fixed cover 2 was repeatedly opened and closed, the fixed pressure was measured after a predetermined number of opening and closing operations. In the opening / closing operation, with the CPU chip 7 placed on the CPU socket 4, the opening / closing operation of the CPU fixing cover 2 was repeated 1000 times by engaging and disengaging the claw 5 and the CPU hook 3.
After the opening / closing operation was repeated 1000 times, the amount of warpage of the CPU fixing cover 2 was also measured. The warpage amount was obtained as the height from the surface plate surface by turning the CPU fixing cover 2 that is warped upside down and placing it on the surface plate. The warpage amount before and after the test was compared, and the difference in the warpage amount was determined as the fixed cover deformation amount. If the amount of deformation of the fixed cover is 300 μm or less, it can be said that the CPU fixed cover is durable and maintains a sufficient fixed pressure even after repeated opening and closing operations.

As can be seen from the test results in Table 4, the CPU fixed cover 2 made from a cold rolled steel strip with a finish rolling ratio of 20 to 40% exhibits good characteristics exceeding the fixed pressure pass / fail criterion of 1.2 MPa, and is deformed. The amount was also a small value of 300 μm or less.
On the other hand, Comparative Example No. 11 having a plate thickness variation of 45 μm or more was a small value at which the fixed pressure did not reach the pass / fail criterion 1.2 MPa. Therefore, the CPU fixing cover 2 is inferior in performance as compared with the example of the present invention.

  As explained above, cold rolled steel strip with a thickness accuracy of 20 μm or less and a bending tip radius of 0.7 mm or less by increasing the strength of low-carbon aluminum killed steel with specified alloy components by the work strengthening method. It becomes. This cold-rolled steel strip is used as a material suitable for the CPU socket frame and CPU fixing cover when attaching a CPU such as a computer to the wiring board, and the CPU chip is pressed against the wiring board with the necessary fixing pressure even after long-term use. Fixing leads to improved reliability of electronic equipment.

Perspective view with CPU chip mounted on CPU socket on wiring board A perspective view of the CPU fixing frame with the CPU fixing cover fastened to the CPU socket frame.

Explanation of symbols

1: CPU socket frame 2: CPU fixing cover 3: CPU hook 4: CPU socket 5: Claw 6: Connecting part 7: CPU chip

Claims (2)

C: 0.01-0.20 mass%, Si: 0.5 mass% or less, Mn: 1.5 mass% or less, P: 0.05 mass% or less, S: 0.01 mass% or less, acid acceptable Molten Al: 0.005 to 0.10% by mass, N: 0.007% by mass or less, and the balance is continuously cast with a steel having an Fe composition excluding inevitable impurities. Finishing temperature: Ar ₃ transformation point or higher, winding A method for producing a steel plate for a CPU socket frame or a CPU fixing cover, which is hot-rolled at a temperature of 450 to 600 ° C. and cold-rolled after pickling and at a cold rolling rate of 20 to 50%. C: 0.01-0.20 mass%, Si: 0.5 mass% or less, Mn: 1.5 mass% or less, P: 0.05 mass% or less, S: 0.01 mass% or less, acid acceptable Melted Al: 0.005 to 0.10% by mass, N: 0.007% by mass or less, Ti: 0.01 to 0.15% by mass and / or Nb: 0.01 to 0.15% by mass, the balance being Continuously cast steel with Fe composition excluding inevitable impurities, finishing temperature: Ar ₃ transformation point or higher, coiling temperature: 450-600 ° C, hot rolling after pickling, 20-50% A method of manufacturing a CPU socket frame or a CPU fixing cover steel plate, which is cold-rolled at a temperature.

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