CN110468328B - Steel for steel structure bolt - Google Patents
Steel for steel structure bolt Download PDFInfo
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- CN110468328B CN110468328B CN201910716503.1A CN201910716503A CN110468328B CN 110468328 B CN110468328 B CN 110468328B CN 201910716503 A CN201910716503 A CN 201910716503A CN 110468328 B CN110468328 B CN 110468328B
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/18—Hardening; Quenching with or without subsequent tempering
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
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Abstract
The steel for the steel structure bolt comprises the following components in percentage by mass: 0.1 to 0.3, Si: 0.10 to 0.35, Mn: not more than 1.5, not more than 0.01 of S, not more than 0.015 of P, Cr: 0.5 to 1.4, Mo: 0.6-1.2, and the balance of Fe and inevitable impurities, wherein the tempering temperature is more than or equal to 600 ℃ during the final heat treatment of the steel material. According to the invention, based on the practical steel structure application environment and the existing application delayed fracture morphology analysis fracture morphology, the precipitation quantity and precipitation form of grain boundary carbide are improved by optimizing alloy components, and the delayed fracture resistance of the material is improved. The steel for the steel structure bolt can reach tensile strength of more than 1040MPa and upper limit of 1240MPa after heat treatment. The performance grade of the fastener meets GB/T1231-2006 standard 10.9S grade, and the fastener has excellent delayed fracture resistance.
Description
Technical Field
The invention belongs to the field of fastener materials, and particularly relates to high-strength steel structure bolt steel with good delayed fracture resistance and formability, which is suitable for manufacturing and application of large hexagon head bolts and flange face bolts for steel structures.
Background
The large hexagon head bolt of the steel structure has large size and specification, the hexagon opposite side has large size, the deformation of the upset forging head is large, and the requirement on the plasticity of the bolt material is high. For example, the common size of the large hexagon head bolt of the railway steel structure bridge is M22-M30. For example, the 10.9S-grade bolt material in the GB/T1231-2006 standard is as follows: 20MnTiB, ML20MnTiB, 35VB, etc. The medium-low carbon B steel has low content of alloy elements, good plastic forming performance and low cost and is widely applied to the field of fasteners. However, with the rapid development of economy, the rapid development of industries such as transportation and ocean engineering and the like puts higher requirements on large-scale steel structures, and the requirements on bridge span and application safety are continuously improved. Higher requirements are also provided for the strength and the delayed fracture resistance of the high-strength fastener for steel structure connection.
High-strength bolts on facilities such as steel structures in the industries of transportation, ocean engineering and the like are usually positioned on water surfaces of rivers, lakes, seas and the like due to long-term exposure environment, particularly steel structure bridges and ocean engineering, have high humidity and severe environment, and are easy to generate electrochemical corrosion on the surface of the conventional high-strength fastener to absorb hydrogen, so that delayed cracking is caused, and the application safety of the structure is influenced.
Studies have shown that delayed fracture sensitivity increases significantly with increasing material strength for high strength fasteners. The tensile strength is usually more than 1000MPa, and the high-strength steel plate bears extremely high pre-tightening stress in the use process, and has higher possibility of delayed fracture when exposed and used in a field environment. Therefore, for high strength fasteners, it is desirable to have good delayed fracture resistance. In order to avoid delayed fracture in a large amount in the application process of the existing high-strength fastener for the steel structure in China, the upper limit of the strength grade is limited to 10.9 grade, and the tensile strength range is 1040-1240 MPa. But delayed bolt breakage still occurs in practical applications.
The existing technologies for improving the hydrogen-induced delayed fracture resistance of high-strength materials are numerous and mainly divided into: 1) reducing the formation and adsorption of external active hydrogen, such as improving environmental conditions, and adjusting the pH value and surface adsorption state of an environmental medium by using a corrosion inhibitor; the corrosion resistant material is adopted to avoid the generation of corrosive hydrogen. 2) The hydrogen barrier isolation layer is adopted to avoid the entering of environmental hydrogen, if the hydrogen barrier isolation layer is coated by a high polymer material, the surface is coated with a metal-infiltrated isolation layer or a ceramic isolation layer to realize the shielding of the hydrogen. 3) Reducing the content of internal hydrogen and avoiding the aggregation of the internal hydrogen, for example, adopting alloy elements such as V, Ti, Nb and the like to precipitate and form a hydrogen trap, fixing the internal hydrogen and avoiding the aggregation of the hydrogen; the stress concentration of the material is reduced through the structural design, and the diffusion and the aggregation of hydrogen under the stress induction are avoided; by reducing the hydrogen diffusion coefficient of the material, the hydrogen accumulation speed of the material is slowed down.
Such as: in the patent CN 108070796A, by adding alloy elements of Cr, Ni and Cu, the corrosion resistance of the material is improved, and the delayed fracture performance of the material is further improved; the CN 109161794A is added with Cr, Ni, Cu and Nb of 0.02-0.06 and V of 0.25-0.45 to improve the weather resistance of the material, refine crystal grains and form hydrogen traps to improve the delayed fracture resistance of the material; CN 108220809A improves the delayed fracture resistance of the material by adding 0.80-1.60 of Cr, 3.50-5.50 of Ni, 0.80-1.20 of Mo and 0.10-0.25 of V through adopting measures of forming hydrogen traps and residual austenite; CN 107429352A improves the delayed fracture resistance of the material by adding Si in a ratio of 1.0-3.0 and increasing the amount of Si added to stabilize transition carbides such as epsilon carbide. The core of the above patent is to improve the resistance to delayed fracture by means of improving the weather resistance, reducing the corrosion rate, increasing the hydrogen trap, and the like.
For the high-strength bolt for the steel structure, because long-term exposure is in the outdoor environment, the application part is dispersed, and the delayed fracture is difficult to avoid through environmental improvement, and the high-strength bolt for the steel structure belongs to long-term exposure application, and the delayed fracture is mainly caused by the continuous entering of external corrosive hydrogen, and the delayed fracture problem of the harsh environment is difficult to effectively solve through the hydrogen trap. The surface coating/plating/seeping layer isolation has certain feasibility, but the existing steel structure high-strength fasteners are all friction pre-tightening type fasteners, the requirement on axial force control is strict, and the coating/plating/seeping layer can cause the torque coefficient of the bolt to be dispersed, so that the construction is difficult. Meanwhile, creep deformation, embedding and the like of the coating/plating/seeping layer can cause the violent attenuation of the pre-tightening axial force, and the application safety of the steel structure connecting pair is influenced. Therefore, at the present stage, no suitable hydrogen barrier coating/plating/cementation layer has been developed for the steel structural bolts.
In the process of improving the delayed fracture resistance of a material matrix, aiming at the problem that crack source regions of delayed fracture bolts in practical application all present the crystal fracture appearance, the existing patent has targeted solution measures.
Disclosure of Invention
In order to solve the technical problems, the invention provides steel for steel structure bolts, which improves the delayed fracture resistance of the conventional high-strength fastener and has lower production cost. According to the invention, based on the practical steel structure application environment and the existing application delayed fracture morphology analysis fracture morphology, the precipitation quantity and precipitation form of grain boundary carbide are improved by optimizing alloy components, and the delayed fracture resistance of the material is improved. The steel for the steel structure bolt can reach tensile strength of more than 1040MPa and upper limit of 1240MPa after heat treatment. The performance grade of the fastener meets GB/T1231-2006 standard 10.9S grade, and the fastener has excellent delayed fracture resistance.
In order to realize the technical purpose, the adopted technical scheme is as follows: the steel for the steel structure bolt comprises the following components in percentage by mass: 0.1 to 0.3, Si: 0.10 to 0.35, Mn: not more than 1.5, not more than 0.01 of S, not more than 0.015 of P, Cr: 0.5 to 1.4, Mo: 0.6-1.2, and the balance of Fe and inevitable impurities, wherein the tempering temperature is more than or equal to 600 ℃ during the final heat treatment of the steel material; and the steel material needs to meet the following conditions:
(1) index 1: [ Mo ]/8+ [ Cr ]/4.4- [ C ] not less than 0.01
(2) Index 2: 3.5[ C ] +0.18[ Si ] +0.45[ Mn ] +0.4[ Cr ] +1.17[ Mo ] +1.5[ C ]. Mo ] -0.32[ Cr ]. Mo ≧ 1.9
(3) Index 3: 30[ C ] + [ Si ] +1.5[ Mn ] +1.5[ Cr ] +1.6[ Mo ] less than or equal to 13.
Preferably, the steel material contains C: 0.15 to 0.25, Si: 0.15 to 0.25, Mn: 0.4-1.0, S is less than or equal to 0.01, P is less than or equal to 0.015, Cr: 0.6 to 0.9, Mo: 0.7 to 1.1, and the balance of Fe and inevitable impurities.
The tempering temperature is 600-700 ℃ when the steel material is finally heat treated.
Preferably, the tempering temperature during the final heat treatment of the steel material is 640-680 ℃.
The invention has the beneficial effects that:
1. 0.1 to 0.3C, preferably 0.15 to 0.25C is selected. The hardenability of the material with the C lower than 0.1 is too low to meet the manufacturing requirement of large-size bolts, and the too low C can cause the reduction of the material strength, inevitably influences the tempering temperature of the material, the types and forms of precipitated phases and deteriorates the delayed fracture resistance of the material. C of more than 0.3 can cause the plasticity of the material to be deteriorated, the deformation resistance is increased, and the forming process performance of the steel structure bolt is seriously influenced. Meanwhile, the increase of the content of C can cause the variety and volume fraction of precipitated phases to change, and the delayed fracture resistance of the material is deteriorated.
The reasonable selection of C realizes the balance matching of carbide precipitation quantity, precipitation form and material strength. Is beneficial to the formation of continuous low-energy grain boundaries. Effectively avoids the grain boundary carbide and impurity element segregation in continuous distribution to deteriorate the delayed fracture resistance of the material.
2. Si belongs to an element which can strongly deteriorate the cold heading performance of the material, so that the Si content of the material is controlled at a lower level, but Si belongs to an element which can improve hardenability, and the excessively low Si content puts a very high requirement on smelting furnace materials, so that the material cost is greatly increased, and the Si content is selected to be 0.10-0.35. Preferably 0.15 to 0.25,
3. mn can improve the hardenability of the material, and the Mn alloying can effectively reduce the material cost, but Mn has a negative effect on inhibiting grain boundary precipitation, so that Mn is not excessively high, and is preferably 0.4-1.0.
4. Cr can effectively increase the tempering temperature and improve the carbide distribution of the material, but too high Cr content has adverse effects on the cold forming performance and the cost of the material, and too high Cr content can cause the precipitation of a large amount of M23C6 phase, thus deteriorating the delayed fracture resistance of the material. Cr is preferably 0.6 to 0.9.
5. Mo can effectively improve the segregation of elements in a crystal boundary and the precipitation form of carbide, and by adding more than 0.6 percent of Mo, the full precipitation and solidification of C can be realized, the tempering temperature can be greatly increased, the continuous film precipitation and the segregation of harmful elements in the crystal boundary can be avoided, and the crystal-following cracking can be avoided. Mo is preferably 0.7 to 1.1. Too high Mo content deteriorates the formability of the material and increases the material cost considerably.
6. As a necessary control requirement for avoiding grain boundary segregation of impurity elements, the content of S, P is limited, S is less than or equal to 0.01, and P is less than or equal to 0.015, so that on the basis of the existing material, the purity of the material is further improved, and the influence of grain boundary segregation on delayed fracture is reduced.
7. In order to ensure the full precipitation and spheroidization of carbide, the tempering temperature of the material of the invention is more than or equal to 600 ℃ during the final heat treatment.
8. The core of the invention is that the C content is controlled, and the sufficient hardenability and mechanical property of the material are ensured. By adding proper carbide forming elements and tempering stabilizing elements, the full and uniform precipitation of the carbide is realized, the precipitation state of the carbide is controlled, and the continuous precipitation and film-shaped segregation of grain boundaries are prevented. The material is ensured to obtain a higher strength performance grade, and simultaneously, a low-energy pure crystal boundary with good continuity is formed at the position of the crystal boundary, so that the occurrence of crystal boundary cracking is prevented, and the delayed fracture resistance of the material is improved.
The invention is also suitable for the occasions of bolts with the specification of M20 and below with lower requirements on molding and heat treatment. And adding hardenability alloy elements on the basis of the invention to aim at the application of larger-size bolts and adding refined crystal grain elements and hydrogen trap forming elements to expand the application occasions. However, the adverse effects of the addition of alloy elements on the type of precipitated phase, the morphology of precipitated phase, the formability of the material, and the cracking during heat treatment must be considered.
Drawings
FIG. 1 is a schematic view of a high C content, low temperature tempered grain boundary structure;
FIG. 2 is a schematic view of a low C content, high temperature tempered grain boundary structure.
Detailed Description
The steel for the steel structure bolt comprises the following components in percentage by mass: 0.1 to 0.3, Si: 0.10 to 0.35, Mn: not more than 1.5, not more than 0.01 of S, not more than 0.015 of P, Cr: 0.5 to 1.4, Mo: 0.6-1.2, and the balance of Fe and inevitable impurities, wherein the tempering temperature is more than or equal to 600 ℃ during the final heat treatment of the steel material.
The steel material can obtain more excellent steel material if the following conditions are met:
(1) index 1: [ Mo ]/8+ [ Cr ]/4.4- [ C ] not less than 0.01
(2) Index 2: 3.5[ C ] +0.18[ Si ] +0.45[ Mn ] +0.4[ Cr ] +1.17[ Mo ] +1.5[ C ]. Mo ] -0.32[ Cr ]. Mo ≧ 1.9
(3) Index 3: 30[ C ] + [ Si ] +1.5[ Mn ] +1.5[ Cr ] +1.6[ Mo ] less than or equal to 13.
Index 1, in general low alloy structural steel material, when the Cr and Mo contents of the material are low, the precipitated phase of the material after quenching and tempering is a coarse carburized phase (Fe)3C) The volume fraction of carbide is large, the strengthening effect is limited, but the addition of Mo and Cr in the invented material reduces C and makes the carbide have coarse carburized body phase (Fe)3C) When tempered at the temperature of the invention, the alloy dissolves and precipitates a strengthening phase as micro spheroidized M2(C, N) and M7C3Mainly, note (M refers to Fe, Cr, Mo metal elements). And the precipitated phase is uniformly precipitated, so that the strengthening effect is ensured, the volume fraction of carbide is reduced, and the continuous precipitation of crystal boundary is avoided. To ensure a coarse cementite phase (Fe)3C) Fully dissolved and fine carbide M2(C, N) and M7C3The relationship among Cr, Mo and C must be controlled, the range of the components of the material of the invention can ensure that the coarse cementite phase (Fe) is formed by high-temperature tempering3C) The spheroidization dissolution has good precipitated form, and the combination index 1 can realize the control of the precipitated phase type and form of the material within the operation time of the common tempering process. The index 1 is obtained by calculation based on the precipitated phase species, volume fraction and precipitated phase atomic ratio of the material.
Index 2, for the steel structure bolt, the bolt of the invention must meet the strength requirement of national standard grade and the hardenability requirement suitable for the steel structure large-specification bolt, and for the high Mo content material, the influence of the tempering precipitated phase type is influenced, and the influence of the alloy element on the performance needs to be fully considered. The index 2 is obtained by calculating based on test data according to the performance grade requirement of the bolt based on the theoretical research of the hardenability of the material and comprehensively considering the influence of the interaction of C and alloy elements.
Index 3, because the steel structure bolt consumption is large (the single bridge can reach more than 100 ten thousand), the specification is large (generally more than or equal to M22), the quenching stress is large, the quenching is easy to crack, because of mass production, the quenching defect is difficult to sort, if the bolt with the crack defect is installed and applied, great potential safety hazard can be brought, and the quenching defect of the material needs to be strictly avoided.
Meanwhile, the steel structure bolt material produced in large scale can obtain stable quality and good economic benefit only by adopting cold heading manufacturing, the requirement on the cold heading performance of the material is higher, and the difficulty of improving the cold heading performance of the material by annealing is increased sharply due to the change of precipitated phase types of the material. On the basis of research and control of the equivalent of the quenching carbon of the material, the content of C and alloy elements of the material is effectively controlled through the design of an index 3. The material has good quenching stability and excellent cold heading performance.
Preferably, the steel material contains C: 0.15 to 0.25, Si: 0.15 to 0.25, Mn: 0.4-1.0, S is less than or equal to 0.01, P is less than or equal to 0.015, Cr: 0.6 to 0.9, Mo: 0.7 to 1.1, and the balance of Fe and inevitable impurities.
The tempering temperature is 600-700 ℃ when the steel material is finally heat treated.
Preferably, the tempering temperature during the final heat treatment of the steel material is 640-680 ℃.
Beneficial elements such as V, Ti, Nb, W, B, Ni, Cu, rare earth and the like can be added according to requirements, such as grain refinement, grain boundary purification, hardenability improvement and the like.
Example (b):
a vacuum furnace is adopted to smelt 50Kg steel ingots, and the chemical analysis components of the smelted materials are shown in Table 1: cogging and forging to a round bar with the diameter of 38mm, and turning and processing the sawn material to a smooth bar with the diameter of 33 x 200 mm.
TABLE 1 chemical composition and performance index of the examples
Examples 1 to 7 were quenched with a 7% PVP (polyvinylpyrrolidone) quench using a 900 ℃ heat. Examples 8 and 9 were quenched with 7% PVP (polyvinylpyrrolidone) quench liquid by heating at 860 ℃. The detailed tempering temperature and mechanical property detection results are shown in Table 2, and the stress ring is 20% NH4The SCN solution stress corrosion results are shown in Table 3.
TABLE 2 tempering temperature and mechanical properties of the examples
TABLE 3 20% NH4SCN solution stress corrosion test results
According to the embodiment, it can be seen that: the indexes of the examples 1 and 2 meet the requirement of the invention, and the strength of the example 1 is close to the lower limit of the optimization because the content of C is close to the lower limit of the optimization, and the strength is close to the lower limit of the 10.9S grade. The material C of the example 2 has the content close to the upper limit of the preferable components and has higher strength. The material is treated with 20% NH4The stress corrosion test of the SCN aqueous solution can meet the continuous requirement of 2000h, and the material resists delayThe fracture performance is good. In example 3, the tempering temperature is not higher than 600 ℃ as the lower tempering temperature is selected. The grain boundary precipitated phase cannot be sufficiently spheroidized and aggregated. The material has high strength, and the delayed fracture resistance can not meet the continuous requirement of 2000 h.
In examples 4, 5, 6 and 7, since the C content of example 7 does not meet the invention requirements, the index 2 does not meet the invention requirements ≧ 1.9. The material has lower strength and tensile strength R after heat treatmentmThe mechanical property of the material can not be fully exerted only by 838MPa, and the requirement of 10.9S-level performance of GB/T1231-2006 standard can not be met. Examples 4, 5, 6, 7 materials were treated with 20% NH4The stress corrosion test of the SCN aqueous solution can meet the continuous requirement of 2000 h.
In examples 8 and 9, since the C content does not meet the invention requirements, the C content is high, both index 1 and index 3 exceed the invention requirements, the index 1 is lower, the carbon content is high, the number of carbide precipitates in grain boundaries is not reduced, large-area continuous low-energy grain boundaries are difficult to form in the grain boundaries, and the delayed fracture resistance of the grain boundaries is deteriorated. The index 3 is higher, so that the plasticity and toughness of the material are lower, and the quenching cracking tendency is high. For steel structure bolts, the specification is large, the quenching stress is large, cracking easily occurs during quenching, so that the cracking occurs during heat treatment quenching of the material, and the forming performance of the material is deteriorated when the index is 3.
Claims (3)
1. The steel for the steel structure bolt is characterized in that: the steel material comprises the following components in percentage by mass: 0.1 to 0.25, Si: 0.15 to 0.25, Mn: 0.4-1.0, S is less than or equal to 0.01, P is less than or equal to 0.015, Cr: 0.6 to 0.9, Mo: 0.7-1.1, and the balance of Fe and inevitable impurities, wherein the tempering temperature is more than or equal to 600 ℃ during the final heat treatment of the steel material;
the steel material needs to meet the following conditions:
(1) index 1: [ Mo ]/8+ [ Cr ]/4.4- [ C ] not less than 0.01
(2) Index 2: 3.5[ C ] +0.18[ Si ] +0.45[ Mn ] +0.4[ Cr ] +1.17[ Mo ] +1.5[ C ]. Mo ] -0.32[ Cr ]. Mo ≧ 1.9
(3) Index 3: 30[ C ] + [ Si ] +1.5[ Mn ] +1.5[ Cr ] +1.6[ Mo ] less than or equal to 13.
2. The steel for steel structural bolts according to claim 1, wherein: the tempering temperature is 600-700 ℃ when the steel material is finally heat treated.
3. The steel for steel structural bolts according to claim 1, wherein: the tempering temperature is 640-680 ℃ when the steel material is finally thermally treated.
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| CN111155031A (en) * | 2020-01-15 | 2020-05-15 | 南京福贝尔五金制品有限公司 | Atmospheric corrosion resistant high-strength bolt and manufacturing method thereof |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH05105957A (en) * | 1991-10-18 | 1993-04-27 | Kawasaki Steel Corp | Production of heat resistant high strength bolt |
| WO2004007785A1 (en) * | 2002-07-11 | 2004-01-22 | Samhwa Steel Co., Ltd. | Quenched and tempered steel wire with superior cold forging characteristics |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| JP3319303B2 (en) * | 1996-09-27 | 2002-08-26 | 日本鋼管株式会社 | Steel for high-strength bolts without annealing and excellent in fire resistance and method of manufacturing the same |
| JP3751707B2 (en) * | 1997-04-04 | 2006-03-01 | 株式会社神戸製鋼所 | High-strength bolt wire excellent in strength and ductility and its manufacturing method |
| JP4142853B2 (en) * | 2001-03-22 | 2008-09-03 | 新日本製鐵株式会社 | High strength bolt with excellent delayed fracture resistance |
| JP4415219B2 (en) * | 2004-07-28 | 2010-02-17 | 大同特殊鋼株式会社 | Age hardened steel |
| CN101539163B (en) * | 2008-03-19 | 2011-01-26 | 洛阳双瑞特钢科技有限公司 | Manufacturing method of anti-delayed fracture 16.9 grade bolt |
| JP4712882B2 (en) * | 2008-07-11 | 2011-06-29 | 株式会社神戸製鋼所 | High strength cold-rolled steel sheet with excellent hydrogen embrittlement resistance and workability |
| CN105088078A (en) * | 2014-05-22 | 2015-11-25 | 宁波瑞亚紧固件制造有限公司 | Anchor bolt material and preparation method thereof |
| JP6267618B2 (en) * | 2014-09-30 | 2018-01-24 | 株式会社神戸製鋼所 | Bolt steel and bolts |
| CN109750221A (en) * | 2017-11-06 | 2019-05-14 | 慈溪市得鑫五金配件有限公司 | A kind of bolt production technology |
| CN109868409A (en) * | 2017-12-01 | 2019-06-11 | 宁波群力紧固件制造有限公司 | A kind of improved bolt production technology |
| CN108754303A (en) * | 2018-04-20 | 2018-11-06 | 北京交通大学 | A kind of high strength bolting steel of atmospheric corrosion resistance and excellent in resistance to delayed fracture |
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Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH05105957A (en) * | 1991-10-18 | 1993-04-27 | Kawasaki Steel Corp | Production of heat resistant high strength bolt |
| WO2004007785A1 (en) * | 2002-07-11 | 2004-01-22 | Samhwa Steel Co., Ltd. | Quenched and tempered steel wire with superior cold forging characteristics |
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