TW200535258A - Steel wire for high strength bolts and method for fabricating high strength bolts - Google Patents

Abstract

This invention provides a steel wire for high strength bolts, which has excellent delayed fracture property and cold rolling plastic forming property, and a method for fabricating high strength bolts. Because this invention can exhibit good delayed fracture property and good cold rolling plastic forming property, the steel wire for high strength bolts has a lubrication coating layer coated on the steel wire for performing cold rolling plastic forming. The so-called novel lubrication coating layer is a multilayer coating comprising an inorganic salt lubrication coating coated onto the contact steel wire surface and a non-phosphorus special lubrication coating staked onto the inorganic salt lubrication coating, in which the best selection for the above-mentioned inorganic salt lubrication coating is potassium silicate and the best selection for the above-mentioned non-phosphorus special lubrication coating is calcium stearate. A good cold rolling plastic forming is carried out onto the steel wire for high strength bolts coated with the novel lubrication coating layer, which is followed by performing a heat treatment onto the steel surface layer for decarburization control until a specified depth so that high strength bolts with excellent delayed fracture property can be obtained.

Description

200535258 V. Description of the invention α) [Technical field to which the invention belongs], the present invention relates to a manufacturer of steel wires (steel wires) for bolts and bolts, and particularly has a property of delayed fracture resistance and excellent cold rolling plastic workability Steel wire (steel wire) for high-strength bolts and a method for manufacturing high-strength bolts. [Previous technology] In the high-strength bolts with a strength exceeding 1000N / mm2, after a long period of time, the phenomenon of the bolt top falling off or the bolt shaft portion breaking occasionally occurs. This phenomenon is called delayed failure. Among the causes of the delayed failure, a known cause is that the surface of the steel wire is coated with a disk gman salt lubricant film in order to ensure excellent ductility during cold rolling. The composition of the π-phosphate phosphate film is that a dish component containing a metal soap and the like is mixed in the salt film during heat treatment, and the layer becomes the main factor of delayed failure. After the cold-rolling plastic processing is completed, the phosphate film can improve the structure. The acid salt coating is a lime soap coating that is extremely difficult to improve the resistance to delayed destructive phosphorus. Instead of the phosphorus film, the delayed destructive resistance and the ductility during cold-rolling plastic processing are poor or the tool life is significantly reduced. Phosphate or phosphate It is composed of an acid-filled lubricant such as calcium. However, an embrittlement layer is formed on the surface of the steel, and the embrittlement may cause delayed damage. Before heat treatment, if the delayed failure of the bolt can be removed, it is completely difficult. Among the countermeasures, there is a known method for forming a film containing no acid salt. However, the lime soap 'is very poor in the wire drawing process before the heat treatment, and there is a problem that the molding tool is broken.

$ 8 页 200535258 V. Description of the invention (2) In addition, among other countermeasures to improve the resistance to delayed destructiveness, a method for controlling the amount of decarburization during heat treatment is known, but the method of decarburization will make high-strength bolts The non-uniformity of the delayed damage performance, and the occurrence of bad bolts at several percentage points, is not in line with economic benefits. SUMMARY OF THE INVENTION In view of the shortcomings and problems that cannot be solved in the prior art, the present invention proposes a method for manufacturing a high-strength bolt steel wire and a high-strength bolt, which can ensure delayed fracture resistance while maintaining cold-rolling plastic workability. Therefore, in order to achieve the above object, a wire for high-strength bolts according to the present invention is characterized in that a lubricating film layer coated on a steel wire is made of a contact surface ^ an inorganic salt lubricating film and laminated with an inorganic salt lubricating film. A multi-layer coating composed of a special non-phosphorus lubricant coating on the surface. 'go with? tΓ, a manufacturing method of high-strength bolt steel wire mentioned in the Ming = 疋 processing to form a sliding wire film, forming a semi-finished screw two pairs of high-strength bolt manufacturing method, characterized in Rolling and plastic working, as well as performing dippers, reduce the amount of decarburization of the steel surface layer to the central part of I ~. Effect of the invention The coating of the lubricating film on the wire is completely free of structure and is used: Good: Multiplying the lubricating performance and the amount of decarburization during heat treatment to delay the breaking: :: Excellent cold rolling plastic working, τ to greatly improve the resistance to delayed destruction. (2) Especially while eliminating the delay to destroy the unevenness, the delay

Page 9 200535258 V. Description of the invention (3)

The occurrence rate of damage is almost zero, so the failure rate can be significantly reduced. Therefore, a high-quality high-strength bolt can be economically manufactured. X (3) Since the lubricity of the lubricating film layer is good, it is possible to stably deepen the conventional lime soap film by about twice the reduction in cross section. Operation C 4) Due to the good sintering resistance of the lubricating film layer, the advantages of the tool due to the breakage of the molding tool and the bite, as well as the plugging of the checker. Therefore, in order to avoid upsetting molds, there is no forming. (5) The special high strength suitable for JIS classification is related to the present invention as follows: [Embodiment] and Iso specifications are strongly restricted in phosphorus immersion. Manufacturing. The feasible implementation methods are described in conjunction with the drawings

Hereinafter, the best implementation of the present invention will be described with reference to the drawings. (1) Coating of lubricating film + > &# ″ As shown in the figure below, when using a steel wire for high-strength bolts to build a bolt with a strength, the force point 丨 ″ 0c 丞] ~ 丞 The system is, for example, SC 4 3 5, 4 4 0 H 和 烂 钢 # After coating the lubricating film, the bismuth 4 τ _ Peng Gang's steel wire was processed to a specified diameter. Furthermore, the embarrassing process of plastic rolling makes it possible to obtain high-strength bolts with a cold shape and low heat treatment of semi-finished products. temple.丨 I thread "^ Figure 2" "is a measure of the surface layer of the lubricating steel wire covered by the lubricating steel wire before the heat treatment, such as t]. The surface of the steel wire 1 is covered with a lubricating film layer 2 having a multilayer structure having a conventional and powerful structure.来 / 又 Φ 的 Inorganic lubricating coating layer 2 directly covered by the surface of the contact wire 1 ， Η 山 # Α

Page 10 200535258

~ The following is the detailed description of lubrication. 5. Description of the invention (4) The salt-based lubricant coating 3 and the inorganic salt-based special lubricant coating 4 are laminated and covered in two times. Coating layer 2. In addition, in the present invention, the case of forming into two layers will be described, but inorganic salts may also be used to lubricate the peritoneum 2: the special lubricating film 4 of the film layer 2 system, which may be mixed and covered on one layer. , And non-phosphorus [inorganic salt-based lubricating film], inorganic salt-based lubricating film 3 is an aqueous solution coating film composed of components with excellent adhesion properties that do not contain phosphorus at all, and for example, a coating film composed of β (K2Si〇3) may be used. Laminated. ^ Unload

The inorganic salt lubricating film 3 composed of Γϊΐi (K2si03) is a 3m or spraying method, and a humidified aqueous solution is physically attached to the steel wire i with an appropriate layer thickness. The inorganic salt lake slip coating film 3 is formed to supplement the lack of adhesion of the special lubricating film 4, and the special lubricating film 4 is attached to the steel wire 1. In addition, the inorganic salt-based lubricating film 3 has a property of disappearing by heating. [Special lubrication coating]

The special lubricating film 4 is a film composed of a component that does not contain phosphorus at the same time as the inorganic salt-based lubricating film 3. For example, the special lubricating film 4 may be a weakly susceptible aqueous solution or a powdery film composed of calcium stearate as a lubricating component 0 Other compounding elements of the special lubricant film 4 can be appropriately selected and added with various compounding components of a known non-phosphorus lubricant film.

Page 11 200535258 5. Description of the invention (5) The special lubricating film 4 containing calcium stearate can exhibit excellent extension # (cold-dry plastic workability) during cold-rolled plastic processing of the steel wire 1 described later! !! _ ′ Has excellent rust resistance, even if it is stored indoors for 3 months, it will not cause deterioration of the recording and tissue. · Ί 3 ^ ν? Λ4-^ ^ ^ ^ 1 ^ ^ ^ ^ ^ In the upper state of the sliding film 3, it is coated with steel wire on the wire in a clever manner. It is solidified by frictional heat during pulling and catching. Since the inorganic salt-based lubrication film 3 and the non-phosphorus-based special lubrication film 4 that lubricate the coating film 2 do not contain phosphorus, they must be removed during heat treatment. (2) Cold-rolled plastic processing Then, the wire i that forms the lubricating coating film 2 is subjected to wire drawing processing, and is added with :) and cold-rolled plastic processing to have a predetermined bolt shape. Cold-rolled plastic processing after forming a lime soap lubricating film on steel, 糸 1

Ittf Λ, between the external and Λ ′, the steel surface causes undercutting (that is, 妯 = not %%) to perform axial deep drawing processing with a cross-section reduction rate of more than 20%. This: Inversely, the present invention is a steel wire "The surface of the spoon is covered with a new lubricating film layer 2. Even if the screw inspection of the semi-finished product that is scheduled to be formed is complicated and the special lubricating film 4 constituting the lubricating film layer 2 can exert its excellent sintering resistance, It can be stably advanced = 2 ::; In the case of the conventional lime-based coating, the axial drawing processing with a double reduction of the cross-section can be performed. ^

I Page 12 200535258 V. Description of the invention (6) (3) Heat treatment In the present invention, since the lubricating film layer 2 does not contain a phosphorus component, it is not necessary to forcibly remove the lubricating film before heat treatment as in the past, so it is not necessary There are special equipment and operations to remove the lubricating film. A semi-finished bolt in a state where the coating layer 2 is attached is used as the object, and heat treatment is performed in the following manner. The heat treatment is performed in a continuous furnace for bolts with a carbon control function. However, the present invention is not only a heat treatment for quenching purposes, but also a heat treatment for controlling the depth of decarburization. The depth of decarburization is achieved by managing the atmosphere in the furnace. Conditions (temperature and time) are adjusted to form a modified layer of a predetermined depth in the steel surface layer portion. [Atmosphere conditions in the furnace] In the state of managing the temperature and time in the heat treatment furnace, the atmosphere in the furnace is managed individually or in combination with the following decarburization methods, and the semi-finished bolts are heat treated for a certain period of time under the management of the atmosphere . Among them, one of the methods for decarburization is to arrange a carbon sensor in the furnace to adjust the amount of carbon in the atmosphere, and it is best to adjust the amount of oxygen forcibly supplied to the furnace to adjust the amount of carbon in the atmosphere. Another method is to adjust the amount of carbon in the furnace atmosphere by changing the gas (methane gas or LP gas) into the furnace. By managing the atmosphere time and atmosphere in the furnace, the specific decarburization depth of the semi-finished bolts that can be adjusted can be achieved through heat treatment to lower the hardness of the steel surface layer than the central part, and its hardness difference is 40Hv ~ 8 OHv. range. The π surface layer here refers to a range of 0.5 mm from the surface, "in

Page 13 200535258 V. Description of the invention (7) The central part π refers to a depth of more than 0.5 mm from the surface. Please refer to "Fig. 4", which shows the results of the delayed fracture resistance test for bolts of a plurality of test pieces for the purpose of manufacturing a plurality of test bolts in which the decarburization amount of the steel surface layer was changed (the hardness difference between the steel surface layer and the central portion was changed) . From "Figure 4", it can be clearly seen that the decarburization amount of the steel surface layer is not practical for a high bolt breakage rate when the central part of the steel is less than 40 Hv. In addition, its upper limit 'is 80 η v from the viewpoint of its inherent hardness relationship with steel. Therefore, when the hardness difference is in the range of 40Ην to 808ν described above, it can be confirmed that the breakage rate is zero.

-In the present invention, since the lubricating coating layer 2 on the surface of the steel does not contain any phosphorus component at all, during the heat treatment, there is no phenomenon of immersion in phosphorus that causes the cause of delayed damage, so there is no obstacle to delayed financial damage. Reasons for performance. The special lubrication film 4 of π ... Ί / 入 啡 / 百 6 τ can be heated by heating without the need for a separate removal process, ... and there is no need to worry about the bad influence on the brother. As shown in "Fig. 3", it is a model diagram of your part of 埶 void. The steel surface with bolts on the steel surface layer i

Rigid stone layer 5, ... Rigid stone layer 5 centering: two or three, interlayer film 3 shape improvement and tensile strength uniformity both play a role of C delayed failure [evaluation of high-strength bolts] 彳. Next, the present invention applies a plurality of bolts made of steel with lubricating bolts and conventional steel coatings with lubricating coatings, and a plurality of bolts, respectively. 200535258 V. Description of the invention (8) The test of resistance to delayed damage. In the above test of resistance to delayed damage, the test fixture clamps the bolts, and the clamp in the fixture == salt ;: when 2 ”is used as a cycle: the survival (existence) rate after taking two ^” (to 10 As a result of the test, the results of the conventional high-strength screw inspection have uneven performance and breaking strength. The survival rate of the bolt-right, compared with this, it can be confirmed that the high-strength bolt of the present invention ^ — Non-uniformity of the breaking strength and the survival rate of the bolt; From the above results, it can be confirmed that using the steel wire 1 coated with a lubricating film, the delay resistance can be obtained by controlling the amount of decarburization during heat treatment. The bolts shown above are only the preferred embodiments of the present invention and are not used to limit the scope of the present invention; #Every equivalent change and modification made according to the scope of the present invention are patents of the present invention Covered targets

Page 15 200535258 The diagram briefly illustrates the first flowchart of the method for manufacturing the high-strength bolts of the present invention. The second diagram is the breaking of the surface layer portion of the steel wire covered with the lubricating film before the heat treatment of the present invention. Surface model diagram; FIG. 3 is a cross-sectional model diagram of a steel surface layer portion after heat treatment according to the present invention: and FIG. 4 is a relationship between the hardness difference between the surface layer and the central portion of the steel and the survival rate according to the present invention An explanatory diagram of the test results. [Illustration of Symbols] 1 Steel wire 2 Lubricating coating 3 Inorganic salt lubrication coating 4 Special lubrication coating 5 Hard silicon layer

Page 16

Claims (1)

200535258 1 · A steel wire for high-strength bolts, characterized in that the lubricating film layer is composed of an inorganic salt lubricating film which is coated on the steel wire and laminated on the inorganic salt lubricating film in contact with the surface of the steel wire: Its multilayer coating. * Special lubricating coatings of the sixth category of patent application ______ 2. High-strength snails as described in item 丨 of the patent application scope. The inorganic salt lubricant coating is made of potassium silicate and steel wire, among which the coating is . 'Composition' has cohesiveness. 3 · High strength as described in item 2 of the patent application. This special lubricating film is an aqueous solution or powder coating of calcium stearate acting steel wire '. ,,, θ Cheng Dao's weak testability 4. As mentioned in item 1 of the scope of patent application, the surname surname, name, Cheng, Shang X Xie Cai Wang used steel wire 'which. The special lubricant coating film is made of calcium stearate as Λ 7 (C ,, KOH, JIE +, 丄 7 1 is a weak alkaline water / fungus or powder coating with a slippery composition. ^ A The manufacturing method of high-strength steel wire for bolts is a cold-rolled plastic working shape, a lubricating coated wire material, and a method for manufacturing the W-shaped bolt with a heat treatment after forming-semi-finished bolts, which is characterized by: The steel wire for high-strength bolts described in any one of the fourth to fourth items is subjected to cold-rolled plastic working and a heat treatment to reduce the decarburization amount of the steel surface layer to the range of 40 HV to 80 Ην for the central portion.