JPS62133020A - Production of 6t bolt made of low carbon aluminum killed steel - Google Patents

Abstract

PURPOSE:To easily produce a 6T bolt having prescribed strength at a low cost by subjecting a low carbon aluminum killed steel wire of a specific carbon equiv. to Stelmor cooling, adjusting the tensile strength thereof and working the wire to a bolt shape then subjecting the bolt to a bluing treatment. CONSTITUTION:The low carbon aluminum killed steel wire of which the carbon equiv. defined as C%+1/6Mn% is 0.32+ or -0.03% is subjected to still more cooling in a steel making stage by which stable pearlite structure is obtd. The tensile strength of the above-mentioned wire is adjusted to 50+ or -3kg/mm<2> the tensile strength and to about 0.7kg/mm<2>/% rising tensile strength in the stage of rolling. The material is then worked to the shape of the bolt by drawing, cold-pressing and thread rolling. The bolt shape body is thereafter subjected to the bluing treatment in a blue brittleness range temp. of about 250-400 deg.C to recover the yield point and elastic limit. The 6T bolt made of the low carbon aluminum killed steel wire having the prescribed strength is obtd. while the working crack of the head part and the decrease of the lifetime of working tools are prevented by the above-mentioned simple stage which eliminates the need for an annealing stage for spheroidization.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention has a tensile strength of 60 according to the JIS bolt/nut standard.
6T pole made of low carbon aluminum killed steel that can manufacture 6T bolts with a specified weight of kg/w2 or more and a yield point of 36 kl'/ms or more at a low cost]・
The present invention relates to a manufacturing method.

(Prior art) Conventionally, 6T bolts are made of carbon steel wire rods for cold heading, such as 5WRCH45, and are subjected to spheroidizing annealing treatment to improve cold forging properties in order to prevent processing cracks in the bolt heads during processing. After that, wire drawing, heading, and thread rolling are performed, and stress relief annealing is performed at 400 to 600°C to reduce the hardening of the bolt neck caused by this process to a level that does not cause head popping. . However, in this conventional method, the material cost is 20 to 40 yen per spheroidizing annealing.
Since the weight also increases, there is a drawback that the cost of the bolt becomes high.

(Problems to be Solved by the Invention) The present invention solves the problems of the conventional 6T bolt manufacturing method as described above, and eliminates machining cracks in the bolt head through a simple process that omits the spheroidizing annealing process. This was completed with the aim of creating a method for manufacturing 6T bolts made of low carbon aluminum killed steel that can sufficiently satisfy the strength specified by JTS while preventing a decrease in processing die life.

(Means for Solving the Problems) The present invention utilizes a low carbon aluminum killed steel wire rod having a carbon equivalent defined as 0% + 1/6 Mn% of 0.32±0.03% to stabilize pearlite by Stillmore cooling. After adjusting the tensile strength to 50±3 kg/dragon2 and the increasing tensile strength to approximately 0.7 kg/w''/%, the material was shaped into a bolt through the processes of wire drawing, heading, and thread rolling. It is characterized by being processed to a temperature of blue brittleness and then subjected to a pluing treatment at a temperature in the blue brittle region.

In the present invention, even if the spheroidizing annealing process, which is a cause of cost increase as described above, is omitted, the ductility is comparable to that of a material obtained by subjecting a carbon steel wire rod for cold heading to spheroidizing annealing, such as 5WRCH45. A low carbon aluminum killed steel wire such as 5WRCH15A to 2OA is used as a material that can have the following properties. In order to maintain stable workability of this material without causing processing cracks or reduction in processing die life during bolt processing, in the present invention, the chemical components that have the greatest effect on the properties of the material are reduced to 0% + 1 /
The carbon equivalent, defined as 6M n%, is calculated and strictly controlled to be within the range of 0.32±0.03%. If the carbon equivalent exceeds 0.35%, the tensile strength will increase, leading to processing cracks and reduced mold life. Conversely, if the carbon equivalent is less than 0.29%, the tensile strength required for 6T bolts will not be obtained. There will be no. In addition, in the present invention, the above-mentioned material is subjected to Stillmore cooling, which is forced air cooling of the material during the steel manufacturing stage, to make the low carbon aluminum killed steel into a stable pearlite structure, and by these means, the tensile strength of the wire material before being processed into a bolt shape is reduced. 50±3kir/Ryu2, increasing tensile strength about 0.7kg1
/%. At this stage, the tensile strength of the wire is 53
If the tensile strength exceeds 47 kg/fl, the tensile strength during the subsequent wire drawing process will become too high, leading to problems such as cracking of the head during processing and a reduction in the lifespan of the processing die.On the other hand, the tensile strength of the wire at this stage is 47 kg. /*m”, it becomes difficult to achieve the tensile strength required for 6T bolts. In addition, as shown in the drawing, elevated tensile strength is a physical property value defined as the amount of increase in tensile strength per 1% area reduction (reduction rate of cross-sectional area) due to wire drawing, and is a value that is approximately determined by the material. However, in the low carbon aluminum killed steel wire rod used in the present invention as described above, it is generally 0.6 to 0.
Since it is 9 kg/n+2/%, it is adjusted to about 0.7 kg/mm2/% by adjusting the normalizing method. Next, this wire is drawn.
As can be seen from the drawing, wire rods with a tensile strength of 50 ± 3 kg/Ryu 2 and an elevated tensile strength of approximately 0.7 kg/Ryu 2/% are drawn and processed to obtain the required 6T bolt.
To obtain a tensile strength of 0 kIr/w'', the area reduction must be 19
It is necessary to manage the rolling so that it is ~23%. Conversely, in a process where the area reduction rate is set to a constant value of about 20%, the tensile strength of the wire material is reduced to about 0.
．． If it is not adjusted to 7 kg/am"/%, problems will occur, such as the tensile strength required for 6T bolts not being achieved, or the tensile strength becoming too large, resulting in poor workability. After wire drawing, the bolt head is pressed and rolled according to conventional methods, and processed into a bolt shape.

As a result of the above-mentioned processing, the strength of the bolt head increases due to work hardening, but the yield point and elastic limit of the bolt shaft section are significantly lowered due to compressive stress, and the strength required for a 6T bolt cannot be guaranteed if this continues. Therefore, in the present invention, the yield point and elastic limit are restored by subjecting the obtained bolt to a pluing treatment at a temperature in the late blue zone of 250 to 400'C. Generally, in killed steel, AI or Si sufficiently fixes N in the steel through deoxidation, so that strain age hardening is said to be small. When subjected to the pluing treatment, carbon generated by decomposition of cementite in the steel during wire drawing and heading is fixed, and a phenomenon is observed in which the yield point, elastic limit, etc. are significantly recovered by precipitation hardening of carbides. Furthermore, this pluing process also fixes machining distortion in the bolt head, which is effective in preventing the head from flying off. The bolt thus obtained weighs 60 kg, as shown in later examples.
/ It has a tensile strength that far exceeds that of Ryu 2, and fully satisfies the standards for a 6T bolt.

(Example) Next, examples of the present invention will be shown.

0.18% specified in JIS as 5WRCH18A
C, 0.03%S i , 0.74%M n , 0
．． 02%p, o, oi%S, 0.05%AI,
A low carbon aluminum guild steel wire rod (carbon equivalent: 0.30) with a composition of balance Fe was made into a pearlite composition by stillmore cooling, and the tensile strength was reduced to 50 kg1, and the elevated tensile strength was reduced to 0.
．． 7 kg / *recommended” The wire rod was adjusted to 7%.This wire was drawn while precisely controlling the area reduction rate to be 19%, and then subjected to heading and thread rolling according to conventional methods, and the tensile strength was 6.
1.1 kg/tm”, 0.2% proof stress 49.Ok
A bolt with a diameter of 1.3 g, a breaking elongation of 8.0%, and a yield ratio (0.2% proof stress/tensile strength) of 79.5% was obtained. Next, add this to 20
When heat-treated at 0°C, 300°C, 400°C, and 550°C, as shown in the following table, those subjected to pluing in the blue brittle region of 300 to 400°C showed strength that fully exceeded the standard for 6T bolts. In addition, no machining cracks occurred on the bolt head during heading and thread rolling, and the machining die life was the same as that of the conventional 5WRC845K, which was subjected to spheroidizing annealing.
It was no different from when using O.

(Effects of the Invention) As is clear from the above description, the present invention applies stillmore cooling to a special material whose carbon equivalent is strictly controlled, adjusts the tensile strength and elevated tensile strength within a predetermined range, and then wire-draws, It is possible to manufacture a 6T bolt that satisfies JIS standards by processing it into a bolt shape by forging and thread rolling and then subjecting it to special heat treatment, thereby omitting the spheroidizing annealing process. Therefore, according to the present invention, there is no need for the spheroidizing annealing process that causes cost increases, and the manufacturing cost of 6T bolts can be significantly reduced. As a manufacturing method for 6T bolts made of aluminum killed steel,
It makes a huge contribution to the industry.

[Brief explanation of drawings]

The drawing is a graph showing the relationship between area reduction rate and tensile strength during wire drawing.

Claims (1)

[Claims] Carbon equivalent defined as C%+1/6Mn% is 0.3
2±0.03% low carbon aluminum killed steel wire is made into a stable pearlite structure by stillmore cooling, and its tensile strength is 50±3kg/mm^2, and the elevated tensile strength is approximately 0.7kg/mm^2/%. A method for manufacturing a 6T bolt made of low carbon aluminum killed steel, which comprises adjusting the material, processing the material into a bolt shape through the processes of wire drawing, heading, and thread rolling, and then subjecting it to a pluing treatment at a temperature in the blue brittle region. .