JP2658101B2 - Manufacturing method of wire rod for non-heat treated steel bolt - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention

[Industrial applications]

The present invention relates to a method of manufacturing a wire rod for a non-heat-treated steel bolt, and more particularly to a method of manufacturing a wire rod capable of giving an 8T-class bolt.

[Prior art]

In general, steel bolts are manufactured by rolling steel for machine structural use represented by S45C into wires, softening it by annealing, drawing it (performing spheroidizing annealing if necessary), and performing header processing and rolling in the cold. After the quenching, quenching and tempering are performed in accordance with the process. In order to simplify the above steps as much as possible and supply a large amount of bolts at low cost, various attempts have been made to manufacture non-heat treated steel bolts without heat treatment. The applicant has previously determined that a steel having a specific composition determined by examining the balance of alloy components is subjected to wire rod rolling under the selected conditions, whereby a 7T class (70 to 80 kgf / mm ² ) to an 8T class (80 ~ 100
Kgf / mm ² ) Established the technology to manufacture bolts without tempering,
It has already been disclosed (JP-A-59-107063). Bolts made from this wire have the advantage of not breaking under the neck in a wedge tension test, which is a practical test for bolts. The strength of the bolt is, of course, determined by the tensile strength of the material after drawing. When higher strength is required from the 7T class to the 8T class, the strength of the drawn wire may be increased. However, if the strength of the drawn material is too high, the workability of cold working the bottle is reduced, the life of the header tool is shortened, and the demand for lowering the cost of the bolt is contradicted. The strength of the material after wire drawing is obtained by adding the hardness after wire rolling to the strength after wire rod rolling. Therefore, in the production of the non-heat treated steel bolt, the strength after the wire rod rolling and the strength after the wire drawing must be set to appropriate levels. As a result of research, the tensile strength after wire rod rolling was 65 to 75 kgf / mm ²
Header when the range of, when performing ordinary wire drawing, the tensile strength after wire drawing, thus the tensile strength of the bolt is determined by it but reaches a level greater than 80 kgf / mm ^2, which are commonly used It was found that the life of the tool was in the practical range and the strength could be balanced.

[Problems to be solved by the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a non-heat-treated steel having an appropriate tensile strength after wire rolling from the above-described viewpoints, and having a bolt-processed bolt that does not break under the neck in a wedge tensile test. An object of the present invention is to provide a bolt wire. Structure of the invention

[Means for solving the problems]

The method for producing a wire rod for a non-heat treated steel bolt of the present invention is as follows: C: 0.12
~ 0.17%, Si: 0.15 ~ 0.35%, Mn: 1.3 ~ 1.6%, Cr: 0.25
% And V: 0.08 to 0.13%, P: 0.020% or less, S: 0.010% or less, the balance being substantially Fe, and the carbon equivalent represented by the following formula: Ceq = C + Si / 7 + Mn / A steel with 5 + Cr / 9 + V / 2 in the range of 0.53-0.55 is heated to a heating temperature of 1000-1050.
℃, temperature 750-850 ° C in rolling stage, area reduction rate 50%
By rolling the wire under the above conditions and cooling at a cooling rate of 4.5 to 6.5 ° C./sec, the tensile strength of the wire after rolling is 65 to 75.
characterized in that the range of kgf / mm ^2. The cooling rate is preferably in the range of 5.0 to 6.0 ° C / sec. Thereby, the tensile strength after wire rod rolling is in the optimal range of 65 to 75 kgf /
It is easier to obtain a wire that fits in mm ² .

[Operation]

The alloy composition of the steel described above is based on the alloy composition of the non-heat treated bolt wire disclosed above, and a narrow range that can achieve the above object is selected. The reasons for limiting the composition of each alloy component are described below. C: 0.12 to 0.17% The above lower and upper limits are provided to provide the required strength to the bolt and to maintain the workability and toughness at a high level. Si: 0.15-0.35% In addition to the necessity as a deoxidizing agent, it is useful for solid solution strengthening of the matrix. However, considering the workability and cold formability, this range was selected. Mn: 1.3 to 1.6% Contributes to deoxidation and desulfurization, enhances hardenability and gives appropriate strength. It is useful for toughness, but if it is too large, it is harmful. Cr: 0.25% or less Increases hardenability and gives strength to steel. In order to bring the effect to an appropriate level, it is necessary to adjust the hardenability provided by other alloy components within the above limits. V: 0.08 to 0.13% Sintered structure is refined to maintain high toughness, while strengthening by precipitation hardening of carbonitride. The lower limit is the limit at which the effect is recognized, and the upper limit is determined from the viewpoint of keeping the strength at an appropriate level. P: 0.02% or less, S: 0.010% or less Since these impurities are harmful to workability and toughness, the smaller the content, the better, and the above-mentioned values are respectively set as allowable limits. Carbon equivalent Ceq = C + Si / 7 + Mn / 5 + Cr / 9 + V / 2 = 0.53 to 0.55
In order to give an appropriate range of tensile strength to the rolled wire,
It is necessary to satisfy the carbon equivalent conditions together with the processing conditions. Wire rod rolling conditions: heating temperature 1000 to 1050 ° C, temperature 750 to 850 ° C in the rolling finishing stage, area reduction rate 50% or more The heating temperature prior to rolling is that V is dissolved once to precipitate its carbonitride. Although higher from the viewpoint, it is better to lower it for the purpose of making the crystal grains fine, and the harmony point between the two is set in the above range. If the temperature in the finishing stage is too low, the workability and the dimensional accuracy of rolling are reduced or winding becomes difficult. Therefore, a lower limit of 750 ° C. is set as a guideline. The upper limit of 850 ° C. is provided to avoid coarsening of crystal grains. In normal rolling, a finishing temperature below the lower limit is not conceivable, but rather it is necessary to cool so as not to exceed the upper limit. In any case, one feature is that generally lower temperatures are employed, compared to the processing conditions conventionally used in the manufacture of this type of material. The area reduction rate of 50% or more is a condition necessary for realizing the refinement of crystal grains to a desired degree. Cooling rate: 4.5 to 6.5 ° C./sec, preferably 5.0 to 6.0 ° C./sec The purpose is to provide a predetermined strength by appropriately selecting the time of passing through the ferrite + pearlite region in the cooling process. In order to prevent the formation of bainite, cooling should be performed at a rate not exceeding the upper limit, while cooling at a rate not less than the lower limit is required to obtain a certain quenching effect. Such cooling can be realized by controlling the finishing temperature of rolling, that is, the winding temperature, and adjusting the air volume of the blast cooling.

【Example】

A steel having an alloy composition shown in Table 1 was melted, rolled and cooled under the conditions shown in Table 2 to obtain a wire rod having a diameter of 6.5 mm. The pre-finishing temperature in Table 2 is the temperature at the stage of 17 mm in diameter during rolling. The reduction in area of rolling from 17 mm to 6.5 mm in diameter is 85%. The tensile strength of each wire was measured, and the results are shown in Table 2. From these wires, bolts were manufactured by header processing and rolling. The numerical values obtained by performing the bolt tensile test are also listed in Table 2. In the wedge-shaped tensile test, there was no break under the bolt neck. The manufacturing method of the present invention is useful as a bolt material due to the combination of the requirements of heating and wire rolling a carefully selected alloy composition at a different low temperature range and cooling at a controlled rate. It is possible to obtain a wire for a non-heat treated steel bolt. This wire has the optimal level of tensile strength to be processed into a bolt by header processing and rolling, and the resulting bolt secures 8T-class strength by work hardening and breaks under the neck. An excellent product that does not occur. Thus, the present invention can provide high quality bolts at low cost.

Claims (2)

(57) [Claims] (1) C: 0.12-0.17%, Si: 0.15-0.35%, Mn: 1.
It contains 3 to 1.6%, Cr: 0.25% or less and V: 0.08 to 0.13%, P: 0.020% or less, S: 0.010% or less, and the balance substantially consists of Fe, and is represented by the following formula A steel having a carbon equivalent Ceq = C + Si / 7 + Mn / 5 + Cr / 9 + V / 2 in the range of 0.53 to 0.55 is heated to a heating temperature of 1000 to 1050.
℃, temperature 750-850 ° C in rolling stage, area reduction rate 50%
By rolling the wire under the above conditions and cooling at a cooling rate of 4.5 to 6.5 ° C./sec, the tensile strength of the wire after rolling is 65 to 75.
A method for producing a wire rod for a non-heat-treated steel bolt, characterized by being in the range of kgf / mm ² . 2. The method according to claim 1, wherein the cooling rate is set to 5.0 to 6.0 ° C./sec.