Special manufacturing method for fastener with ultrahigh strength higher than 14.9 grade

Abstract

The invention discloses a manufacturing method of a fastener with ultrahigh strength higher than 14.9 grade. The manufacturing method comprises the following steps: creatively adopting domestic extremely common existing steel 20MN2 and 30MN2; the alloy comprises 20 CrMnTi and 35 CrMo; after heat treatment, the steel of which the metallographic structure is strong and tough low-carbon martensite and high-strength alloy steel structural steel is used for manufacturing the ultrahigh-strength fastener. In the manufacturing process, special heat treatment is adopted, lower bainite isothermal quenching or martensite transformation temperature interval hot bath quenching and tempering are adopted, the ultra-high-strength fastener made of extremely-high-quality steel is manufactured, and the domestic blank is filled. The ultrahigh-strength nut is matched with a bolt for use, and has similar mechanical and physical properties and the same manufacturing method.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing ultra-high strength fasteners with a strength higher than grade 14.9. The method uses a special heat treatment process and very common domestic 20Mn2, 30Mn2; 20CrMnTi, 35CrMo; 42CrMo, 50CrVA, etc., which have a strong and tough metallographic structure of low-carbon martensite and high-strength alloy steel structure after heat treatment, to manufacture ultra-high strength fasteners that foreign companies need to use extremely high-quality alloy steel to manufacture, thus filling the domestic gap in this technical field. Background Art

[0002] Fasteners are used in electromechanical equipment, tooling and tools used in electronic products, metallurgy, chemical industry, construction, rail transit, aerospace, aviation and other industries, and the technical performance requirements for high-strength bolts, screws, studs, rivets and nuts are very high. At present, large-scale enterprises producing fasteners in my country generally produce fasteners of grade 10.9 and below, which are usually made of high-strength materials. The screws, nuts and washers of high-strength bolts are usually made of 45 steel, 40 boron steel, 20 manganese titanium boron steel, 35CrMoA, etc. There is a national standard for grade 12.9, but there are few companies that can produce and manufacture them, and most of them rely on imports. For example, UNBRAKO brand high-strength fasteners produced by UNBRAKO in the United States are widely used in my country's steel, non-ferrous metals, electricity, automobiles, mechanical equipment, electrical instruments, environmental equipment and other manufacturing enterprises. The raw materials are limited and the price is too high. Taking the fasteners used on the bogies of rail transit vehicles as an example, due to the high frequency of steering use, the connection screws that often need to be overhauled are worn, loose or stripped. It has strict requirements on specifications, tensile strength, high toughness, yield strength, etc. How to mass-produce ultra-high strength fasteners, especially those above grade 14.9, with domestic steel has become a difficult problem. Summary of the invention

[0003] The purpose of the present invention is to solve the above-mentioned technical problems existing in the prior art, creatively adopt extremely common domestically produced steel materials, and use unique processes to manufacture ultra-high strength fasteners that can only be made by foreign companies using extremely high-quality steel materials.

[0004] In order to solve the above technical problems, the solution adopted by the present invention is as follows:

[0005] A method for manufacturing ultra-high strength fasteners with a strength higher than grade 14.9, wherein the steel grades are 20Mn2 or 30Mn2; 20CrMnTi, 35CrMo; 42CrMo, 50CrVA within the hypoeutectoid steel range.

[0006] Process plan: quenching → cooling → spheroidizing annealing → cold heading and thread rolling → heat treatment (heating, rapid cooling, tempering) → cleaning → surface treatment (blackening, galvanizing or nickel plating) → anti-corrosion treatment.

[0007] In the above technical solution, three groups of specifications are further described.

[0008] The first group of M6-M12 fasteners are made of 20Mn2 or 30Mn2.

[0009] When the workpiece is heated in a salt bath furnace, the workpiece is quenched and heated, and the temperature is controlled at 880°C to 900°C;

[0010] Furthermore, the workpiece is spheroidized annealed at 720° C. for 4 hours, cooled in the furnace to below 500° C., and then air-cooled after being taken out of the furnace.

[0011] The workpiece is taken out of the furnace and quenched in water, which is about 200-300° C., and then air-cooled.

[0012] Cold heading and thread rolling;

[0013] Tempering treatment: The workpiece that has been cooled in the air should be tempered in time. The tempering temperature is determined by the upper or lower limit of the manganese content and carbon content in the steel composition, and is generally controlled at 360±20℃. The hardness of the workpiece after tempering is 45~47HRC, and it is cleaned.

[0014] Surface treatment: blackening or electroplating zinc or nickel, and finally cleaning with hydrochloric acid.

[0015] Anti-corrosion treatment.

[0016] The second group of M14-M30 fasteners are made of 20CrMnTi or 35CrMo.

[0017] In the above technical solution, the workpiece is quenched and heated in a salt bath furnace, and the temperature is controlled at 880°C to 900°C;

[0018] Furthermore, the workpiece is spheroidized annealed at 760°C isothermally, cooled in the furnace to below 500°C after 4 hours, and then air-cooled after being taken out of the furnace.

[0019] The workpiece is taken out of the furnace and quenched in water, which is about 200-300° C., and then air-cooled.

[0020] Cold heading and thread rolling;

[0021] Heat treatment, use lower bainite isothermal quenching: the workpiece cooled in the air should be tempered in time, and the tempering temperature is generally controlled at 360±20℃. The hardness of the workpiece after tempering is 45~47HRC, and it is cleaned.

[0022] Surface treatment (nickel plating, hot dip tin)

[0023] Anti-corrosion treatment.

[0024] The third group of M36-M56 specification fasteners are made of 42CrMo or 50CrVA steel.

[0025] When the workpiece is heated in a salt bath furnace, the workpiece is quenched and heated, and the temperature is controlled at 880°C to 900°C;

[0026] Furthermore, the workpiece is subjected to isothermal spheroidizing annealing (isothermal 780° C., 4 hours / isothermal 650° C., 4 hours), and then furnace cooled to below 500° C. and air cooled after being taken out of the furnace.

[0027] The workpiece is taken out of the furnace and quenched in water, which is about 200-300° C., and then air-cooled.

[0028] The workpiece is subjected to mechanical metalworking processing.

[0029] Special heat treatment, hot bath quenching in martensitic transformation temperature range, tempering at 420℃. Cleaning.

[0030] Surface treatment (nickel plating).

[0031] Anti-corrosion treatment. The beneficial effects of the present invention are:

[0032] As various industries develop towards high, precise, advanced, lightweight and intelligent development, especially military industry, aerospace, aviation, navigation, high-speed rail, subway, etc., they can all use domestically produced ultra-high strength fasteners with extremely high cost performance, saving a lot of foreign exchange.

[0033] The present invention creatively adopts very common domestically produced steel to manufacture high-strength fasteners with performance equal to or even exceeding that of other high-quality steels, thus filling the domestic gap and having high cost performance. DETAILED DESCRIPTION

[0034] Example 1 For fasteners of M6-M12 specifications, use 20Mn2 or 30Mn2. When heating in a salt bath furnace, quenching heating is performed and the temperature is controlled at 880°C to 900°C. Spheroidizing annealing, isothermal 720℃, after 4 hours, cooling with the furnace to below 500℃ and air cooling after being taken out of the furnace. After taking out of the furnace, quench in water. After taking out of the furnace, the workpiece can be scattered on the wire grid, and the wire grid is quenched in water together. When the hissing sound is about to stop, take out the grid (the workpiece is about 200-300℃ at this time) and air cool. Cold heading and thread rolling; Tempering treatment: The workpiece that has been cooled in the air should be tempered in time. The tempering temperature is determined by the upper or lower limit of the manganese content and carbon content in the steel composition, and is generally controlled at 360±20℃. The hardness of the workpiece after tempering is 45~47HRC, and it is cleaned. Surface treatment: blackening or electroplating zinc or nickel, and finally cleaning with hydrochloric acid. Anti-corrosion treatment.

[0035] Example 2 For fasteners of specifications M14-M30, 20CrMnTi or 35CrMo should be used. When heating in a salt bath furnace, quenching heating, the temperature is controlled at 880℃~900℃; Spheroidizing annealing, isothermal 760℃, after 4 hours, cooling with the furnace to below 500℃ and air cooling after being taken out of the furnace. After taking out of the furnace, quench in water. After taking out of the furnace, the workpiece can be scattered on the wire grid, and the wire grid is quenched in water together. When the hissing sound is about to stop, take out the grid (the workpiece is about 200-300℃ at this time) and air cool. Cold heading and thread rolling; Heat treatment, use lower bainite isothermal quenching: the workpiece cooled in the air should be tempered in time, and the tempering temperature is generally controlled at 360±20℃. The hardness of the workpiece after tempering is 45~47HRC, and it is cleaned. Surface treatment (nickel plating, hot dip tin) Anti-corrosion treatment.

[0036] Example 3 For fasteners of specifications M36-M56, 42CrMo or 50CrVA steel is used. When heating in a salt bath furnace, quenching heating, the temperature is controlled at 880℃~900℃; Isothermal spheroidizing annealing (isothermal 780℃, 4 hours / isothermal 650℃, 4 hours), then furnace cooling to below 500℃ and air cooling after leaving the furnace. After taking out of the furnace, quench in water. After taking out of the furnace, the workpiece can be scattered on the wire grid, and the wire grid is quenched in water together. When the hissing sound is about to stop, take out the grid (the workpiece is about 200-300℃ at this time) and air cool. Mechanical metalworking. Special heat treatment, hot bath quenching in martensitic transformation temperature range, tempering at 420℃. Cleaning. Surface treatment (nickel plating). Anti-corrosion treatment.

[0037] The design and technical requirements of the manufacturing process of the ultra-high strength fastener of the present invention comply with the design standards and specifications in the national standards GB / T 3098.2, GB / T3098.4, and the national standard (ISO898.J-1999), and have passed the inspection of the National Standard Parts Product Quality Supervision and Inspection Center in accordance with ISO898.J-1999 "Mechanical properties of fasteners made of carbon steel and alloy steel Part 1. Bolts, screws and studs". The test data are as follows: Test items Standard regulations Test results Hardness test HRC 39～44 47.0 Tensile strength MPa ≥1220 1450 Elongation after break / % ≥8 12.5 Compared with the tensile strength of 14.9 grade, which is 1420 MPa, and the elongation after fracture, which is 7-10%, the test results of the present invention are higher than those of grade 14.9, so the present invention is a fastener with ultra-high strength higher than that of grade 14.9.

[0038] The description of the present invention is considered to be illustrative rather than restrictive. On the basis of the present invention, those skilled in the art can make some substitutions and modifications to some of the technical features according to the disclosed technical content without creative labor, all of which are within the protection scope of the present invention.

Claims

1. A method for manufacturing ultra-high strength fasteners higher than grade 14.9, characterized in that: In the range of hypoeutectoid steel, domestically produced 20Mn2, 30Mn2; 20CrMnTi, 35CrMo; 42CrMo, 50CrVA, which have a strong and tough metallographic structure of low-carbon martensite and high-strength alloy steel structure after heat treatment, are selected to make ultra-high strength fasteners.

2. A method for manufacturing the ultra-high strength fastener according to claim 1, characterized in that: Divide into three groups and choose different corresponding steel materials using specifications: The steel grades used for the fasteners of M6-M12 are: 20Mn2, 30Mn2; The steel grades used for the fasteners of M14 to M30 are: 20CrMnTi, 35CrMo; The steel grades used for the fasteners of M36~M56 are: 42CrMo, 50CrVA.

3. The method for manufacturing an ultra-high strength fastener according to claim 2, characterized in that: The method comprises the following steps: selecting the steel material, and subjecting the steel material to quenching, cooling, spheroidizing annealing, cold heading and thread rolling, heat treatment, cleaning, surface treatment and anti-corrosion treatment.

4. The method for manufacturing an ultra-high strength fastener according to claims 2 and 3, characterized in that: The three groups of specifications include the following steps: The first group of M6-M12 ultra-high strength fasteners uses 20Mn2 or 30Mn2 steel. After heat treatment, the metallographic structure of this type of steel is a strong and tough low-carbon martensite and high-strength alloy steel. Quenching → cooling → spheroidizing annealing (720℃, 4 hours) → cold heading and thread rolling → heat treatment (heating, annealing, tempering) → cleaning → surface treatment (blackening, galvanizing or nickel plating) → anti-corrosion treatment. The second group of M14-M30 ultra-high strength fasteners uses 20CrMnTi or 35CrMo steel, which is also a low-carbon martensitic, high-strength, high-toughness alloy structural steel. Quenching → cooling → spheroidizing annealing (760℃, 4 hours) → cold heading and thread rolling → heat treatment (lower bainite isothermal quenching) → cleaning → surface treatment (nickel plating, hot dip tin) → anti-corrosion treatment. The third group of M636-M56 ultra-high strength fasteners uses 42CrMo or 50CrVA steel with better hardenability. 42CrMo steel is a high-strength alloy structural steel, and 50CrVA steel is a high-strength spring steel. Quenching → cooling → isothermal spheroidizing annealing (780℃, 4 hours / 670℃, 4 hours) → mechanical metalworking → special heat treatment (hot bath quenching in the martensitic transformation temperature range and tempering at 420℃) → surface treatment (nickel plating) → anti-corrosion treatment.