JP4386271B2 - Door material - Google Patents

Description

  The present invention relates to a door member such as a residence, and more particularly to a door member that is used around a keyhole and is difficult to drill even with a tool such as a drill.

Steel doors are often used in houses and offices. The conventional door material is a plain steel coated steel plate having a thickness of about 0.6 to 1.0 mm. Since plain steel coated steel sheet is excellent in workability, it can be formed into a door shape that meets the needs, and various patterns can be imparted by painting. In addition, the use of high Cr austenitic stainless steel with excellent corrosion resistance has been studied as a door member that maintains a beautiful appearance for a long period of time.
In addition to processability, designability, and durability, doors are required to have a function to prevent entry from the outside. Conventionally, the door has been devised to improve locks that cannot be easily unlocked with tools. .
However, in recent years, in response to the advancement of anti-unlocking measures, a small hole is made in the door member around the keyhole with an electric drill, and a special tool is inserted from the hole to the inside of the door. Increasing the number of cases of illegal intrusion into the house by means of unlocking with a hand turned from the hole to the inside of the door after the hole is widened to the extent that the arm can be inserted using a gold clip.

As countermeasures against intrusion by unlocking the door member from the inside of the door, a method of using a material that is difficult to drill in the door outer plate, a structure that incorporates a member that is difficult to drill in the door wall around the keyhole, etc. Therefore, there is a strong demand for a steel sheet having excellent drillability.
Here, in addition to using a drill, it is also assumed that a tool such as a hole saw or a hammer is used as a method for drilling a hole, but in general, drilling with a drill can be performed in the shortest time. This means that it is difficult to drill in the sense that it considers drilling.
As for the security of steel doors, we are developing doors on the condition that it takes more than 5 minutes to unlock. Against this backdrop, as a material that makes up steel plates or door parts with excellent drillability, it is necessary at the current stage to "take more than three times the time required for drilling holes". Has been.

There is a safe material as a material expected to be diverted to a door member steel plate. The material for safes is a material with improved hard drillability and fusing resistance, a material in which ceramics are clad between alloy steels (Patent Document 1), and a low alloy tool steel with hard drillability is austenitic heat resistant steel. There are known a material clad in (Patent Document 2), a material (Patent Document 3) in which a hard-cutting stainless steel is built up on the surface side of a Mn steel plate having hard drillability.
JP-A-6-166136 Japanese Patent Laid-Open No. 5-92280 Japanese Patent Laid-Open No. 9-21276

However, all of them are expensive materials because they are made into products by cladding or build-up, and there is a problem in recycling waste materials with materials clad with ceramics.
Therefore, the present invention has been found as a result of investigating and examining materials with excellent drilling workability in order to protect against illegal intrusion by opening a door member and unlocking from the inside, and reducing the product cost. By specifying the metal structure and hardness without depending on the clad or build-up to be raised, from a difficult-to-drill workable steel sheet satisfying that "it takes more than 3 times longer than conventional materials to drill holes" It aims at providing the door member which becomes.

The door member of the present invention has C: 0.36 to 1.0 mass%, Si: 2.0 mass% or less, Mn: 0.1 to 2.0 mass%, P: 0.05 mass% or less, S : see contains 0.05 mass% or less, the balance has composed of Fe and inevitable impurities, it exhibits a martensitic structure, and characterized by comprising the steel sheet having the above base material hardness 400HV .
Furthermore, Cr: 1.2 wt% or less, Mo: 0.5 wt% or less, V: 0.5 mass% or less, N b: 0.1 wt% or less, Ti: 0.1 wt% or less, B: You may consist of a steel plate which has a component composition containing 0.01 type% or less 1 type or 2 types or more.

  According to the present invention, a steel plate that requires more than three times the time required for drilling a hole is used for the front plate or back plate of the door member, or between the front and back plates around the keyhole. Therefore, it is difficult to drill the door member near the keyhole with a drill. Moreover, this invention door member is obtained only by adjusting a component composition, a metal structure, and base material hardness. Therefore, according to the present invention, a door having an excellent crime prevention effect can be provided at a relatively low cost.

As a result of intensive studies on the drillability of a steel sheet using a drill, the present inventors have found that hardening a work material is difficult to drill, that is, one technique for improving difficult drilling workability. . The reason is considered as follows.
In the process of drilling with the drill, the loaded drill tip bites into the work material, and the drill rotates to cut the depth of the bite. By the way, the biting depth of the drill corresponds to the biting depth of the indenter when the hardness is measured with a Vickers hardness tester. The greater the load, the softer the work material, the deeper the bite depth of the drill and the hardness measurement indenter. Therefore, the harder the work material, the shallower the biting depth, and the more difficult it is to drill with a drill.

  The inventors of the present invention experimentally produced steel sheets with varying hardness by varying the component composition and production conditions. And the indentation depth of the drill when pushing a drill into each steel plate was measured. As a result, as shown in FIG. 1, the indentation depth of the drill decreased as the hardness of the steel plate increased. The indentation depth of the drill was measured by observing and measuring with a microscope a section of a steel sheet into which the drill was pushed, embedded in a resin, polished. The hardness was measured at a load of 9.8 N using a Vickers hardness meter equipped with a diamond square pyramid indenter with a face angle of 136 degrees.

Next, a hole was drilled in each steel plate having a thickness of 1.0 mm, and the time until the hole penetrated was investigated.
As a result, as shown in FIG. 2, it was found that a material having a hardness exceeding 400 HV requires a penetration time three times (60 s) or more that of the conventional material (17 s).
The conditions of the drilling test are as shown in Table 1, and the drill used is a general HSS straight drill specified in JIS B4301.

Further, when the relationship between the indentation depth of the drill and the steel plate penetration time is graphed, the relationship is almost linear as shown in FIG. This relationship indicates that drill penetration time is related to material hardness.
In order to harden the steel material, the metal structure needs to be a martensite structure. The martensite structure is a metal structure obtained by a quenching process, and has a higher hardness than bainite and pearlite structures. Further, when tempering is performed, cementite is precipitated, but this cementite is also precipitated almost uniformly and finely, so that there is almost no influence on the drill when drilling.
Therefore, a relationship that can be explained by the relationship between the hardness and the drill indentation depth is established between the hardness of the steel sheet having the martensitic structure and the drill penetration time.

Next, the components and composition of the steel plate constituting the door member of the present invention will be described.
C: 0.2-1.0 mass%
In order to obtain a hardness of 400 HV or higher by an industrial quenching process, it is necessary to contain 0.2 mass% or more of C. However, if the C content exceeds 1.0% by mass, it may become too hard and cause burning cracks. Therefore, the C content is in the range of 0.2 to 1.0 mass%.

Si: 2.0% by mass or less Si is a component necessary for deoxidation of steel. Moreover, it has the effect | action which suppresses the softening at the time of tempering. However, when it exceeds 2.0 mass% and it adds excessively, graphite will produce | generate abundantly and will improve free-cutting property and will deteriorate the difficult drill workability which is a subject of this invention. Therefore, the upper limit was set to 2.0% by mass.

Mn: 0.1 to 2.0% by mass
Mn is an element that improves hardenability, and it is necessary to add 0.1% by mass or more in order to obtain the effect. However, when it exceeds 2.0 mass% and it adds excessively, ductility and toughness will fall remarkably. Therefore, the Mn content is in the range of 0.1 to 2.0% by mass.
P: 0.05% by mass or less, S: 0.05% by mass or less Steels usually contain P and S as impurities. However, these elements adversely affect toughness, so it is preferable to reduce them. In order to make the material not harmful, the P and S contents are regulated to 0.05% by mass or less.

If necessary, Cr, Mo, V, Ni, Nb, Ti, B or the like may be added to the steel plate constituting the door member of the present invention.
Cr: 1.2% by mass or less Cr is a component that increases the hardenability of the steel material and increases the hardness, but excessive addition causes generation of bainite. Therefore, when added, the upper limit is 1.2% by mass. To do.
Mo: 0.5 mass% or less Mo is a component that increases the hardenability of the steel material and increases the hardness. However, it is an expensive element, and excessive addition is economically disadvantageous. Therefore, when adding, it is 0.5 mass% or less.

V: 0.5% by mass or less V is a carbide forming element. Since vanadium carbide is not sufficiently dissolved at the normal austenitizing temperature, it has an effect of refining the prior austenite crystal grain size and is effective in improving toughness. By using a material having excellent toughness as the door member, it becomes easy to weld to the cutting edge of the machining drill, resulting in difficult drillability. However, it is an expensive element, and excessive addition is economically disadvantageous. Therefore, when adding, it is 0.5 mass% or less.

Ni: 0.1 to 1.0% by mass
Ni is an effective component for improving the hardenability of steel and improving toughness. In order to obtain these effects, the content of 0.1% by mass is necessary. However, even if added excessively, the effect is saturated and uneconomical, so when added, the content is made 0.1 to 1.0% by mass.
Nb: 0.1% by mass or less Nb has an action of forming carbonitrides and suppressing coarsening of prior austenite grains during high-temperature heating, and is effective in improving toughness. However, the addition effect is saturated at 0.1% by mass, and excessive addition is economically disadvantageous. Therefore, even when added, the content is 0.1% by mass or less.

Ti: 0.1% by mass or less Ti has an action of combining with N to form nitrides and suppressing coarsening of prior austenite grains during high-temperature heating, and is effective in improving toughness. However, the addition effect is saturated at 0.1% by mass, and excessive addition is economically disadvantageous. Therefore, when adding, it is made 0.1 mass% or less.
B: 0.01% by mass or less B is an effective component for improving hardenability and improving toughness. However, since the addition effect is saturated at 0.01% by mass, even when added, the content is made 0.01% by mass or less.

A method for manufacturing a door member having a base metal hardness of 400 HV or more, in which the metal structure becomes a martensite structure using the steel sheet having the component composition defined above, will be briefly described.
As one method, a steel plate having a predetermined composition, which has been subjected to heat treatment, has a martensitic structure, and has a base metal hardness of 400 HV or more, is used as a material for cutting, drilling, bending, etc. There is a method of manufacturing a door member by processing.
As another method, annealing is performed to obtain a soft steel plate, and the steel plate is used as a raw material to perform cutting, drilling, bending, etc., to form a door member of a predetermined shape, and then heat treatment is performed to obtain a predetermined steel plate. And a method of imparting the martensite structure and the base material hardness.
The heat treatment for providing a predetermined base material hardness with a martensite structure may be performed at any stage, but if the metal structure is hardened as a martensite structure, it becomes difficult to process, so in the manufacture of an actual door member In this case, it is preferable to adopt the latter. Note that since heat distortion is likely to occur during heat treatment, it is preferable to perform heat treatment with countermeasures against heat distortion.

In order to change the metal structure to a martensite structure and the base material hardness to 400 HV or higher, it is necessary to heat the steel to form an austenite structure at a high temperature and then quench the steel.
In the steel having the component composition in the range specified in the present invention, the proper quenching temperature range is 780 to 900 ° C. Moreover, you may give a tempering process and in that case, it is preferable to carry out on the conditions for 500 degrees C or less and 120 minutes or less.
When the heat treatment is performed within the above range, the metal structure exhibits a martensite structure and a base material hardness of 400 HV or higher is obtained.

Steel melts having the component compositions shown in Table 2 were prepared. Hot rolling was performed under the conditions of these finishing temperatures of 800 to 900 ° C. and the winding temperature of 500 to 600 to finish the plate thickness to 2.0 mm. Thereafter, the surface was removed by dipping in a 10% hydrochloric acid solution.
Next, steels D, E, F, and G were annealed at 730 ° C. for 18 hours, and then steels A, B, and C were cold-rolled without annealing and finished to a thickness of 1 mm. It was.
Furthermore, Steel A was annealed at 710 ° C. for 18 hours. Except for Steel A, the Vickers hardness was set to 300 to 600 Hv by performing quenching or quenching and tempering. Quenching was performed at 850 to 950 ° C. for 2 to 17 minutes and then rapidly cooling to about 60 ° C., and tempering was performed at 200 to 600 ° C. for 2 to 180 minutes and then air cooling.

A test piece was cut out from each sample material, measured for hardness, and subjected to a drilling test.
The hardness was measured at a load of 4.9 N using a Vickers hardness meter equipped with a diamond square pyramid indenter with a face angle of 136 degrees. In the drilling test, a new general-purpose straight drill (JIS B4301) having a blade diameter of 10 mm, a tip angle of 118 degrees, and a groove length of 95 mm was used, and under the same conditions as those shown in Table 1 above, The time required for a hole of the same size (drill penetration time) was measured.
In addition, the case where the through-hole was not formed even when 120 seconds passed from the start of drilling was evaluated as “no penetration”. Further, since the drill penetration time of steel A corresponding to the current material was 17 seconds, those requiring a drill penetration time of 60 seconds or more, which is three times as much as that, were evaluated as “difficult to drill easily”.
The survey results are shown in Table 3 and FIG.

As can be seen from the results shown in Table 3 and FIG. 4, the sample composition having a component composition and hardness of 400 HV or more in the range specified in the description of the claim both exhibit good hard drillability. Recognize.
On the other hand, B1, C1, and G1 were tempered at a high temperature or for a long time, so that a hardness of 400 HV or higher was not obtained, and the drillability was insufficient.

Graph showing the relationship between steel sheet hardness and drill indentation depth Graph showing the relationship between steel sheet hardness and drill penetration time Graph showing the relationship between drill depth and drill penetration time The graph which shows the investigation result of the relationship between the hardness of the steel plate in the example and the drill penetration time

Claims (2)

C: 0.36 to 1.0 mass%, Si: 2.0 mass% or less, Mn: 0.1 to 2.0 mass%, P: 0.05 mass% or less, S: 0.05 mass% or less only contains, has a component composition and the balance being Fe and inevitable impurities, it exhibits a martensitic structure, and the door member, characterized in that it consists of steel plate having the above base material hardness 400 HV. Furthermore, Cr: 1.2 wt% or less, Mo: 0.5 wt% or less, V: 0.5 mass% or less, N b: 0.1 wt% or less, Ti: 0.1 wt% or less, B: The door member according to claim 1, wherein the door member is made of a steel sheet having a component composition containing one or more of 0.01 mass% or less.

Images