JP2003041350A - Martensitic stainless steel sheet for flapper valve and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a martensitic stainless steel sheet for a flapper valve, which has corrosion resistance and high fatigue characteristics, and generates little burr after stamped due to high hardness. SOLUTION: The martensitic stainless steel sheet for the flapper valve includes, by mass%, 0.15% or less C, 2.0% or less Si, 2.0% or less Mn, 0.060% or less P, 0.020% or less S, 2.0-6.0% Ni, 12.0-20.0% Cr, 2.0% or less Mo, 0.10% or less N, and 0.02% or less O, has Md(N) of 125 or more, which is defined in the expression (1): Md(N)=580-520C-2Si-16Mn-16Cr-23Ni-26Cu-300 N-10Mo...(1), includes the balance substantially Fe, consists of martensitic single-phase, and has Vickers hardness of 400 or more. The method for manufacturing the steel sheet is characterized by solution treating the steel material of the above composition, cold rolling it at a rolling rate of 5%, and further aging it at 550 deg.C or lower, as needed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a martensitic stainless steel sheet for flapper valves having both corrosion resistance and high fatigue properties.

[0002]

2. Description of the Related Art Conventionally, as a flapper valve, a steel sheet obtained by quenching and tempering a special steel containing about 1% carbon has been used. However, when special steel is used for the flapper, the special steel itself has poor oxidation resistance,
It is necessary to remove the surface oxide formed during the heat treatment and the internal oxide layer in the vicinity of the surface. For this reason, pickling or surface polishing must be performed by wet polishing or the like.
The surface irregularities generated by this polishing are the main cause of deterioration in fatigue characteristics. Therefore, post-treatment such as barrel polishing is further required in order to eliminate and smooth the surface irregularities, and the productivity is reduced.

[0003]

On the other hand, from the viewpoint of protecting the global environment, a new carbon dioxide gas or the like has emerged as a substitute gas due to the abolition of Freon gas which is a refrigerant for air conditioners and the like. As a result, the operating environment becomes higher pressure and lower temperature, and naturally the flapper valve material is required to have improved corrosion resistance and fatigue properties.However, the problem arises that current special steel cannot meet this requirement. There is. In addition, such a use environment becomes severe, and further, the compressor is required to have a large size and a sealing property, which requires a small burr after punching on the flapper valve.

[0004]

SUMMARY OF THE INVENTION The present invention has been devised to solve such a problem and has corrosion resistance and high fatigue characteristics without using special steel and has a Vickers hardness of 400. It is an object of the present invention to provide a martensitic stainless steel sheet for flapper valves, which has a small amount of burr after punching.

[0005]

In order to achieve the object, the martensitic stainless steel sheet for flapper valves of the present invention has C: 0.15 mass% or less and Si: 2.0.
Mass% or less, Mn: 2.0 mass% or less, P: 0.060
Mass% or less, S: 0.020 mass% or less, Ni: 2.0
-6.0 mass%, Cr: 12.0-20.0 mass%, M
o: 2.0 mass% or less, N: 0.10 mass% or less, O:
Contains 0.02 mass% or less, has a value of Md (N) defined by the following formula (1) of 125 or more, and has a composition in which the balance is substantially Fe, and is composed of a martensite single phase. It is characterized by having a structure, a Vickers hardness of 400 or more, and a small amount of burr after punching. Md (N) = 580-520C-2Si-16Mn-16Cr-23Ni-26Cu-300N-10Mo ... (1) Further, 3.0% by mass or less of Cu, 0.50% by mass or less of Nb, 0. 50 mass% or less Ti, 0.20 mass% or less Al, 0.015 mass% or less B, 0.2 mass% or less REM, 0.2 mass% or less Y, 0.10 mass% or less One or two or more of Ca and 0.10 mass% or less of Mg may be contained. The steel having the above composition can be manufactured by subjecting the steel to solution treatment, followed by cold rolling at a rolling ratio of 5% or more, or by further performing aging treatment at 550 ° C. or less.

[0006]

[Function] The present inventors have excellent corrosion resistance as an alternative to special steel,
When we examined materials with excellent fatigue properties, and flapper valves with a small flash height after punching, we found that the Vickers hardness was 400 or more and the martensite generated during cooling after solution heat treatment and induced by cold rolling. It was found that this can be achieved by making a martensite single phase including the above-mentioned work-induced martensite, and positively utilizing an aging treatment as necessary. Not just using martensitic stainless steel, but punching by Vickers hardness of 400 or more by performing cold rolling of 5% or more after solution heat treatment and aging treatment if necessary. It is possible to reduce the occurrence of burr after processing. When austenite remains, it has ductility and thus easily causes burrs. However, when the martensite single phase is used, ductility is lost and burrs are less likely to occur.
Also, the destruction like the cup cone type is eliminated. Furthermore, by performing this aging treatment, the transformation strain generated by the martensitic transformation during cooling to room temperature after the solution treatment and the non-uniform strain in the plate thickness direction during cold rolling are made uniform,
By reducing the residual stress variation before punching, the change in shape after punching can be reduced.

Next, matters specifying the present invention will be described. In addition, "%" showing the content of each element below means "mass%". C: 0.15% or less C is an austenite forming element and is formed at high temperature δ
It is extremely effective in suppressing ferrite and strengthening the martensite phase. However, as the carbon content increases, Cr carbide precipitates at grain boundaries during cooling after solution treatment and during aging treatment,
Considering that it can cause intergranular corrosion resistance and deterioration of fatigue characteristics and can be industrially avoided under heat treatment conditions and cooling rates, the upper limit of allowable C is 0.15%.

Si: 2.0% or less Si is a ferrite-forming element, which forms a solid solution in the martensite phase and hardens it to increase the strength after cold working. Furthermore, in the aging treatment, strain hardening promotes the age hardening ability. As described above, Si has various effects, but excessive addition easily causes hot cracking, which causes manufacturing problems. Therefore, the upper limit of Si is 2.0%.

Mn: 2.0% or less Mn suppresses the formation of a δ ferrite phase in a high temperature range. However, the inclusion of a large amount of Mn increases the amount of retained austenite after annealing, which causes a decrease in strength. Therefore, the Mn content is set to 2.0% or less. P: 0.060% or less P is an element having a large solid solution strengthening ability, but it may adversely affect the toughness, and therefore, it is a generally accepted 0.
060% or less.

S: 0.020% or less S is an unfavorable element from the viewpoint of occurrence of edge cutting in hot rolling, and the lower the value, the more preferable. However, the allowable S amount is increased by adding B, so that the upper limit of the S amount is 0.020%. Ni: 2.0 to 6.0% Similarly to Mn, Ni also suppresses the formation of the δ ferrite layer in the high temperature region. Further, although it is an element that effectively contributes to the precipitation effect capability, a large amount of Ni content increases the amount of retained austenite after annealing, which causes a decrease in strength. Therefore Ni
The content range is 2.0 to 6.0%.

Cr: 12.0 to 20.0% Cr is an essential component for imparting corrosion resistance. At least 12.0% Cr is required to provide the intended corrosion resistance. However, since Cr is also a ferrite-forming element, if it is made too high, a large amount of δ-ferrite phase will be produced at high temperatures. Therefore, in order to suppress the δ ferrite phase, austenite forming elements (C, N, Ni, Mn, Cu
Etc.), but excessive addition of these elements leads to stabilization of austenite at room temperature, making it impossible to obtain high strength after aging treatment. Therefore C
The upper limit of the r content was 20.0%.

Mo: 2.0% or less Mo has the effects of improving corrosion resistance and finely dispersing carbonitrides during the aging treatment. Since Mo forms a precipitate that contributes to the strength improvement upon aging treatment, addition of Mo makes it possible to prevent the strength from decreasing even if the aging treatment is carried out in a considerably high temperature range. However, if a large amount of Mo is added, δ ferrite is formed at high temperature, so the content of Mo is set to 2.0% or less.

N: 0.10% or less N is also an austenite forming element similarly to C, suppresses the formation of δ ferrite, and contributes to the strengthening of martensite. However, because it is easy to form Ti and intermetallic compounds,
It was set to 0.10% or less. O: 0.02% or less O forms an oxide-based non-metallic inclusion to reduce the cleanliness of steel and adversely affects the fatigue characteristics, so the content is made 0.02% or less.

Cu: 3.0% or less Cu brings about age hardening. However, excessive addition deteriorates the hot workability and causes cracking. Therefore, when Cu is contained, the upper limit is 3.0%. Nb: 0.50% Nb is effective in increasing the strength during aging treatment, but it causes a decrease in hot workability due to an increase in high-temperature strength. Therefore, when Nb is contained, its upper limit is 0.50%.

Ti: 0.50% or less Ti is an element effective in precipitation hardening and is effective in increasing strength during aging treatment. However, if contained too much,
Surface flaws in the steelmaking slab are easily generated, which causes a problem in the steelmaking aspect. Therefore, when Ti is contained, the upper limit is 0.50%. Al: 0.20% or less Al is an element effective for deoxidation at the time of steel making, and works effectively for precipitation hardening like Ti and Nb. However, if it is contained excessively, not only the effect is saturated, but also the weldability is deteriorated and the surface defects are increased. Therefore, when Al is contained, the upper limit is 0.20%.

B: 0.015% or less B is an element effective in preventing the generation of edge cracks in the hot-rolled steel strip caused by the difference in deformation resistance between the δ ferrite phase and the austenite phase in the hot rolling temperature range. However, excessive addition tends to form a low-melting-point boride, and conversely deteriorates hot workability. Therefore, when B is contained, the upper limit is 0.015%.

REM: 0.20% or less Y: 0.20% or less Ca: 0.10% or less Mg: 0.10% or less All of these elements are effective elements for improving hot workability, It is also effective in improving the oxidation resistance. However, the effect is saturated in both cases due to an increase in the added amount, so when these elements are contained, REM and Y are 0.
The upper limit is 20%, and 0.10% for Ca and Mg.

Md (N): 125 or more In the present invention, as described above, after solution treatment, cold rolling is performed to completely transform the retained austenite into martensite, thereby enhancing the strength and reducing the occurrence of burr after punching the product. is doing. In order to facilitate the formation of a martensite phase after the solution treatment, it is necessary to adjust the component amounts so that the value of Md (N), which is the stability for austenite processing, becomes 125 or more. If the value of Md (N) is less than 125, residual austenite remains even after cold rolling, and the intended purpose cannot be achieved.

Residual austenite: None When punching a martensitic stainless steel sheet for a flapper valve, if a part of ductile austenite phase remains, the burr height after punching becomes high and the product deforms, The original function of the flapper valve will be lost. Vickers hardness: 400 or more A flapper valve is required to have a sealing property because of its function. That is, the spring property and the fatigue property capable of withstanding high-speed motion are required. To satisfy these two points, the hardness is HV
400 or more is required.

Cold rolling ratio: 5% or more In the steel of the present invention, martensite is formed during the cooling after the solution treatment, but there may be some thermally stable residual austenite. When part of ductile austenite remains in the martensite base, the burr height after punching becomes high. In order to eliminate this effect, it is necessary to perform cold rolling to completely transform the retained austenite into martensite. In order to completely transform into martensite, it is necessary to perform cold rolling with a rolling ratio of 5% or more.

Aging treatment: 550 ° C. or less The aging treatment removes the strain uniformly when transformation strain at the time of transformation from austenite to martensite in solution treatment and rolling strain at the time of next cold rolling are nonuniform. It is an effective way to do it. However, if this treatment is performed at a temperature higher than 550 ° C., the hardness decreases due to the softening of the martensite phase and the generation of reverse transformation austenite, making it difficult to stably maintain the Vickers hardness at 400 or more. In that case, there arises a problem that the sealability cannot be maintained. Therefore, when performing the aging treatment, 5
It needs to be performed at 50 ° C or lower.

[0022]

[Examples] Table 1 shows the chemical composition and Md (N) of the test material.
(= 580-520C-2Si-16Mn-16Cr-23Ni-26Cu-300N-10Mo). In the table, steel No. Steel No. 1 of the present invention having chemical composition values of 1 to 8 within the range of the present invention. Comparative steels having other chemical composition values of 9 to 14 are comparative steels.

[0023]

Each of the steels was melted in a vacuum melting furnace at 250 kg and forged, hot rolled, annealed and cold rolled to a plate thickness of 1.0 to
It was 1.5 mm and was subjected to cold rolling annealing with uniform heating at 1050 ° C. for 1 minute. Further, cold working was performed at a rolling rate as shown in Table 2 to obtain a plate having a plate thickness of 0.3 mm. Some of the test materials were further aged. The test materials of the respective steels manufactured in this manner were punched into the amount of austenite, surface Vickers hardness (load 1 kg), fatigue limit in the double swing bending fatigue test, and elliptical shape (major axis 50 mm, minor axis 15 mm). The burr height of the punched part was measured. The results are also shown in Table 2. The amount of austenite was measured by a magnetic method using a vibrating sample magnetometer. The amount of austenite is the total amount of austenite remaining after cold rolling and austenite formed by reverse transformation after aging.
In the double swing fatigue test, the stress ratio was -1, and the frequency was 1
It was performed at 000 rpm. The burr height is 1000 punched under the condition of a clearance of 0.03 mm (10% of the plate thickness), and 10 punched materials are taken every 100 pieces.
It was calculated from the average value of 100 measurement points.

[0025]

As can be seen from the results in Table 2, the invention sample N
o. In Nos. 1 to 12, there was no retained austenite, the average Vickers hardness was 400 or more, and the burr height of the punched material was 8.0 μm or less. On the other hand, even if the composition and composition were within the ranges specified in the claims, the aging temperature after cold rolling was too high and reverse-transformed austenite was generated. In Test No. 13, the hardness was low, and the retained austenite remained because the cold rolling was not performed or the rolling ratio was small even after the cold rolling.
o. In Nos. 14 to 16, the burr height of the punching material is large, and it is not suitable as a flapper valve material.

Further, steel type No. 1 having a low Ni content was used. Test No. 9 using No. 9 No. 17 has low hardness and poor fatigue characteristics.
Steel type with a high C content No. Test No. 12 using No. 12 Two
The fatigue limit of 0 is too low, probably because the precipitation amount of carbide is large. Furthermore, steel grades with Md (N) below the specified value 10,1
Steel type No. 1 using No. 1, 13, 14 18, 19, 2
Nos. 1 and 22 have a low austenite content even after cold rolling at a predetermined rolling rate or higher, have low hardness, and have a low fatigue limit. 17 to 22 are also unsuitable as flapper valve materials.

[0028]

As described above, according to the present invention, the composition of the martensitic stainless steel having high corrosion resistance and high strength and the cold rolling rate are optimized so that the structure is composed of the martensitic single phase. Moreover, with the Vickers hardness of 400 or more, it was possible to reduce the occurrence of burr after punching. As a result, it was possible to provide a martensitic stainless steel sheet useful for flapper valves. The material for the flapper valve of the present invention, which requires high strength and flatness together with corrosion resistance, is naturally a shock absorber valve, a press plate, a face plate, a precision plate, as an application range.
Dicing saw tape frame, stainless steel frame,
Applications can be expected to expand in various spring fields such as leaf springs, friction rings, metal gaskets, wrapping carrier materials, carrier plate materials, stainless steel mirrors, damper springs, disc brakes, brake master keys, steel belt materials and metal masks.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Seiichi Isozaki             4976 Nomura-Minami-cho, Shinnanyo-shi, Yamaguchi Nissin             Steel Business Division, Stainless Steel Company F-term (reference) 4K037 EA01 EA02 EA04 EA05 EA09                       EA12 EA13 EA14 EA15 EA17                       EA18 EA19 EA20 EA21 EA22                       EA23 EA25 EA27 EA28 EA31                       EA36 EB02 EB06 EB07 EB08                       FG01 FL01 FL02

Claims (4)

[Claims] 1. C: 0.15 mass% or less, Si: 2.0
Mass% or less, Mn: 2.0 mass% or less, P: 0.060
Mass% or less, S: 0.020 mass% or less, Ni: 2.0
-6.0 mass%, Cr: 12.0-20.0 mass%, M
o: 2.0 mass% or less, N: 0.10 mass% or less, O:
Contains 0.02 mass% or less, has a value of Md (N) defined by the following formula (1) of 125 or more, and has a composition in which the balance is substantially Fe, and is composed of a martensite single phase. A martensitic stainless steel sheet for flapper valves, which has a structure, has a Vickers hardness of 400 or more, and has little burr after punching. Md (N) ＝ 580-520C-2Si-16Mn-16Cr-23Ni-26Cu-300N-10Mo ・ ・ ・ ・ (1) 2. C: 0.15 mass% or less, Si: 2.0
Mass% or less, Mn: 2.0 mass% or less, P: 0.060
Mass% or less, S: 0.020 mass% or less, Ni: 2.0
-6.0 mass%, Cr: 12.0-20.0 mass%, M
o: 2.0 mass% or less, N: 0.10 mass% or less, O:
Including 0.02 mass% or less, further 3.0 mass% or less Cu, 0.50 mass% or less Nb, 0.50 mass% or less Ti, 0.20 mass% or less Al, 0.015 mass% %
The following B, 0.2% by mass or less of REM, 0.2% by mass or less of Y, 0.10% by mass or less of Ca, 0.10% by mass or less of Mg, and one or more kinds thereof are contained, Following (1)
Md (N) defined by the formula has a value of 125 or more, the balance has a composition consisting essentially of Fe, and has a structure of martensite single phase, Vickers hardness of 400 or more, and after punching Martensitic stainless steel sheet for flapper valves, characterized by less burr. Md (N) ＝ 580-520C-2Si-16Mn-16Cr-23Ni-26Cu-300N-10Mo ・ ・ ・ ・ (1) 3. The flapper valve according to claim 1 or 2, wherein the steel having the composition according to claim 1 or 2 is subjected to solution treatment and then cold-rolled at a rolling ratio of 5% or more. For producing martensitic stainless steel sheet for automobiles. 4. The method for producing a martensitic stainless steel sheet for flapper valves according to claim 3, further comprising aging treatment at 550 ° C. or lower after cold rolling.