JP4038541B2 - Heat treatment method for steel wire - Google Patents

Description

The present invention relates to a method for producing a quenched and tempered steel wire.

Quenched and tempered steel wire is widely used for springs, concrete reinforcement, machine parts, etc. A general manufacturing method uses a hot-rolled wire as a material and first draws it to the product diameter to obtain a coiled intermediate material. Next, the coil is supplied to a continuous heat treatment apparatus, is linearly run, heated, quenched, and tempered under the same conditions, and then wound into a coil again to obtain a product coil. Two schemes are competing when performing this process.

The first method is called a low-speed multi-strand system, and processes a plurality of intermediate materials in parallel. Usually, a flame-type heating furnace, an oil quenching tank, and a tempering furnace are passed through each in the order of individual winders. It is wound up. The second method is a high-speed single-strand method, in which one intermediate material is processed at a high speed. As a heating method, high-frequency induction heating or direct current heating is used. This is an effective method for large-diameter products around 10 mm in diameter. This method is advantageous for product refinement such as crystal grain refinement and smooth and beautiful surface by rapid heating, but operation cost and equipment cost such as electric power and labor cost are expensive. In particular, when applied to the manufacture of steel wires for springs and machine parts having a wide variety of steel types, varieties, and dimensions, process switching is frequent. In addition, today's short delivery times and small lot production to cope with inventory reductions have many problems such as halving production efficiency and equipment capacity, lowering yield, and increasing work man-hours.

Regardless of which heat treatment method is employed, a major burden on the manufacturing cost of the quenched and tempered steel wire is that the wire drawing step is indispensable prior to the heat treatment. The first reason is that the dimensions of hot-rolled wire rods are aggregated and standardized in stages, but the steel wire dimensions are arbitrarily set, and the second reason is that the allowable range of the steel wire dimensions is This is because it is small and the accuracy cannot be reached by hot rolling. The same is true for the difference in eccentric diameter (= difference between major axis and minor axis of the cross section).
The third reason is that some surface scratches remain in the hot-rolled wire. For this reason, in the wire drawing process, care and treatment are usually performed by flaw detection inspection. If the wire drawing is omitted, the operation is brought into the heat treatment process and the productivity is hindered. As described above, it is extremely difficult to use a hot-rolled wire as it is for a quenched and tempered steel wire.

In addition to productivity problems, “delayed fracture” is an inherent chronic material problem in hardened and tempered steel. This is a phenomenon in which the material defect portion gradually expands immediately after production due to the unique behavior of the contained H under stress, leading to destruction. As countermeasures, the application of vacuum degassing in molten steel refining, and the addition of low-temperature aging heat treatment after product heat treatment, etc. are serious problems such as cost increase.

References 1 and 2 detail research that can be applied to the partial solution of the above problem. The proposed new process of dieless drawing is to perform drawing without using any tools such as dies. As shown in FIG. 3, the steel wire is run while applying a constant tension, and is rapidly heated by induction heating and then immediately cooled immediately to be stretched at a high temperature portion. The features and key points of this process are shown below.

1) The cross-sectional area ratio of the steel wire before and after processing is exactly inversely proportional to the wire speed ratio before and after processing, and the cross-sectional shape of the steel wire before and after processing is exactly similar.
2) Processing with a reduction in area of 40% or more is possible, and heat treatment such as hardening and softening can be added by appropriately controlling the thermal conditions.
3) The first stabilization condition of the mechanism is that the deformation resistance ratio (after processing / before processing, low temperature side / high temperature side) immediately before and after stretching must exceed the cross-sectional area ratio (before processing / after processing). . That is, it is in the strength of cooling. If the conditions are not met, it breaks on the low temperature side.
4) As for the 2nd stabilization conditions, a heating part and a quenching part must be brought close. If the conditions are not met, the drawing out occurs on the high temperature side. The reason is that the high temperature portion is stretched corresponding to the speed difference. When the cooling timing is delayed, a simple hot tensile process is performed. While the stress of the first stretched portion increases in inverse proportion to the stretching, work hardening is caught up in the middle, and hardening by cooling is also delayed. As a result, strain concentrates only on the stretched portion.

It would be advantageous to apply the dieless drawing to a high-speed single strand quenching and tempering line so that the product wire diameter can be freely changed, but many problems are expected.
A) The process must be stabilized at an order of magnitude greater than the experimental conditions in the study. As a result of the speed increase, the heating part, the extending part, and the cooling part are each expanded in the traveling direction. In particular, the expansion of the heating unit adversely affects the second condition. Dealing with the enhancement of induction heating capacity leads to overheating of the epidermis. The fact that it is difficult and unknown to cope with high speed is a major reason that the process has not yet been put into production.

B) Appropriate thermal conditions for dieless processing must match the original heat treatment conditions. As Example 1 of the problem, usually, in the heating process, after austenitization, moderate holding for carbide solution is performed. This does not meet the second condition. As Example 2, direct energization heating with high energy efficiency and excellent thermal uniformity cannot be applied to the second condition because of the structure of the electrode space and the like.

C) For the management of product cross-sectional dimensions, there is a new axial variation that did not exist in the past due to variations in thermal and mechanical factors.
D) Even if the diameter reduction by stretching can be controlled appropriately, the difference in diameter of the material is not eliminated. That is, it is impossible to use the hot-rolled wire directly.
E) Since it is a kind of thermomechanical processing, the metal structure and surface properties are different from the conventional products. There is a problem that the material problem is not understood.

On the other hand, for the unresolved delayed fracture problem, in recent years, it has been elucidated in literature 3 that an improved ausfoam treatment (a method of quenching and tempering immediately after hot working) is effective in solving the problem. A problem in the application of the technology is that ausfoam processing (processing of supercooled austenite + quenching and tempering) is an old technology, but because it is complicated, it is not practical except for specific steel materials. The above-described research also requires prior processing of multiple passes of hot rolling, and it is extremely complicated to insert into an existing quenching and tempering line.

Kosuge et al .; "Dieless drawing study 1" Plasticity and processing, vol20, no.224 (1979-9), p814 Kosuge et al .; "Dieless drawing study 2" Plasticity and processing, vol21, no.228 (1980-1), p52 Matsuoka et al., “AMF analysis of tempered martensite with improved aus foam and excellent resistance to hydrogen cracking”, Journal of the Japan Institute of Metals 66-7 (2002), p745

The present invention addresses the problems in the conventional heat treatment method for quenched and tempered steel wires, that is, the following items.
1) In the heat treatment line, hardened and tempered steel wires of various diameters are efficiently formed from non-fixed intermediate materials in a non-stop operation to improve productivity.
2) Omit the wire drawing process to make the intermediate material and use the hot-rolled wire directly as the material for heat treatment to reduce the cost.
3) Improve delayed fracture resistance.

In order to solve the above three major problems, the following solutions are provided.
a) Practical use of dieless drawing.
b) Therefore, the current heat treatment conditions are matched with the thermal and mechanical conditions of dieless drawing.
c) Devise a stabilization method for high-speed dieless drawing.
d) Ausfoam treatment for improving delayed fracture resistance is easy to implement.
e) Improve the material supply system so that welding between materials can be performed without stopping the line.
f) Eliminating inconsistencies in the deviation in diameter that are unavoidable with hot-rolled wires.
g) Reasonably improve product cross-sectional dimension standards to improve availability.
h) Efficiently eliminate the part outside the cross-sectional dimension control.
i) Efficiently treats inevitable surface flaws on hot-rolled wire.

In order to solve the above problems, the following guidelines were obtained by comprehensively examining materials, wire drawing, heat treatment, and spring processing. First, for the matching of heat treatment and processing, a two-step heating method of primary heating mainly for heat treatment and secondary heating mainly for dieless drawing was conceived and applied. Secondly, it was found that dieless drawing includes aus forms and modified aus forms depending on the conditions. Expecting a new measure to eliminate the bias from the appropriate metal structure due to the two-stage heating by integrating both technologies with the Ausfoam effect, the effect is achieved by a simple preliminary test using a tensile tester. confirmed. As a result, we decided to proceed with dieless drawing and ausfoam processing with certainty. Thirdly, it has been clarified that the two-stage heating method is appropriate for the speed-up conditions of dieless drawing. Fourthly, in order to eliminate the wire drawing step, a die drawing was skillfully added to the upstream side of the dieless drawing mechanism in order to eliminate the inevitable deviation in the diameter of the hot-rolled wire. Fifth, with regard to dimensional control of high-speed dieless drawing, we have clarified, applied and operated the new dimensions and cross-sectional area specifications that are necessary and sufficient while respecting the specifications and intentions of conventional product dimensional specifications. It helped to improve the rate. Sixth, since the mechanism becomes more complicated than before and the hot-rolled wire is used directly, the number of defects may increase. As a countermeasure, we devised a system for eliminating defective parts, including the downstream spring machining process, and improved the reliability of the entire process.

The first of the present invention is a line-type continuous heat treatment method in which a steel wire travels linearly and is heated, quenched, and tempered under the same conditions. 1) A high temperature part of the wire is made to act on the wire. 2) A method of applying the tension to reduce the cross-sectional area by 20% or more is performed by the difference in speed between the two wire feeding devices arranged on the upstream side of heating and the downstream side of quenching, 3) The method of heating is 50 ° C. or more and 250 ° C. higher than the primary heating temperature by high-frequency induction heating in the immediate vicinity of the upstream side of the cooling / quenching part after primary heating to 50 ° C. or more and 150 ° C. or less on the AC3 point. It consists of rapid secondary heating to the following high temperatures: 4) The quenching cooling rate and cooling time are set to be larger than the larger one required for dieless drawing and quenching, respectively. 5) Product cross-sectional dimensions are adjusted. How to It is a continuous heat treatment method for steel wire, characterized in that the cross-sectional area ratio before and after reduction is made inversely proportional to the speed ratio of the both wire feeders.

According to a second aspect of the present invention, there is provided a method for changing a product diameter by continuously changing a speed ratio of both wire feeding devices and resetting the speed to a new predetermined value. The continuous heat treatment method according to the first aspect of the present invention is characterized in that steel wires having a diameter of 5 mm are formed without stopping.

According to a third aspect of the present invention, the steel wire to be supplied is a hot-rolled wire, and with the wire coil stationary, one end is pulled out in the axial direction of the coil and supplied to the line. It consists of a single drawing die (including overlapping dies) and a capstan, and is characterized in that the wire is die-drawn by the wire feeding device and shaped into a perfect circle, ellipse or egg shape. It is the continuous heat processing method as described in 1st or 2nd invention.

In the fourth aspect of the present invention, when the cross-sectional area detected and calculated between quenching and tempering is out of the standard range, or when a surface defect is detected in the same section, the tempering temperature is set to a predetermined value for the corresponding part. more 50 ° C. or higher, a first or second or third continuous heat treatment method according to the invention is characterized in 100 ° C. to cause excessive softening is changed to a high temperature of below.

According to the present invention, a hardened and tempered steel wire having various diameters thinner than that of a drawn intermediate material having a constant diameter can be produced without interruption, continuously and efficiently. Conventional product dimensional specifications are rationally relaxed, and costs can be reduced through improvements in yield, operating rate, work efficiency, and facility capacity.

Secondly, the complicated ausfoam treatment is easily incorporated into a conventional quenching and tempering line. As a result, the delayed fracture resistance, which has been a chronic material problem in quenched and tempered steel, is expected to be sufficiently improved.

Thirdly, it becomes possible to directly use a hot-rolled wire instead of an intermediate material, and the delivery time is shortened through manufacturing and omission of wire drawing in addition to significant cost reduction.

For the induction of new quality defects due to the direct use of hot-rolled wire, only the defective part is reliably removed by the removal system integrated with the molding process such as downstream spring processing, so the overall yield is improved and new Improves process reliability.

FIG. 1 is a schematic side view illustrating an apparatus for carrying out the quenching and tempering methods of the first to fourth aspects of the invention. FIG. 2 shows an example of an alternative method to the method shown in FIG. The fourth invention covering all elements will be described below with reference to the drawings.
A hot-rolled wire 2 having a circular cross section is used as a material, and one end of the coil of the wire 2 placed on the coil mount 1 is drawn in the coil axial direction and supplied to the quenching and tempering line 3. This payout method is generally called a dead supply. The line sequentially moves downstream, film removal device 4, drawing die 5, capstan 6, primary heating device 7, secondary heating device 8, cooling device 9, steel wire profile meter 10, pinch roll 11, flaw detector. 12, a tempering device 13, a tempering / cooling device 14, and a winder 15.

The wire 2 to be processed first passes through a film removal apparatus 4 such as shot blasting, and the oxide film on the surface is removed to perform a preliminary drawing process. Next, one-pass drawing is performed by the drawing die 5 and the capstan 6, and the cross section of the wire 2 becomes a perfect circle or a predetermined deformed shape. The capstan 6 also has the function of an upstream wire feeder. The wire 2 travels while being pulled at a speed higher than the peripheral speed of the capstan 6 by a pinch roll 11 which is a downstream wire feeding device. When an intermediate material is used, the above-described die drawing mechanism is not necessary, and only an upstream wire feeding device is required.

Next to該線material 2 typically solenoid type high frequency heating primary heating device 6 made of a coil through upper _C3 point A, 50 ° C. or more, it is heated to 0.99 ° C. or less and held briefly. The temperature is near the lower limit of the normal temperature range suitable for quenching. The metal structure of the material is austenite. Next, the wire 2 passes through a secondary heating device 8 composed of a normal solenoid type high frequency heating coil, is heated to 50 ° C. or more and 250 ° C. or less on the primary heating temperature, and is further softened. Stretching occurs due to tension.

Next, the wire 2 passes through a cooling device 9 including a powerful water-cooling nozzle disposed close to the secondary heating device 8 and is cooled. Deformation resistance increases and stretching stops and then quenching proceeds. The cooling rate and cooling time are set as necessary and sufficient for complete quenching and dieless machining. The wire 2 is stretched only at a narrow portion between the secondary heating device 8 and the cooling device 9. As a result, an ausfoam process different from normal quenching is applied. The cross-sectional shape is similar before and after stretching.

Since both the capstan 6 and the pinch roll 11 are designed and maintained so as not to slip, the cross-sectional area ratio before and after stretching is exactly inversely proportional to the speed ratio before and after stretching. Therefore, the wire 2 can be processed into a desired steel wire diameter by setting only the speed ratio.
When the product diameter is changed, the speed ratio is continuously changed and reset to a predetermined speed ratio that matches the changed diameter. In this way, steel wires of various diameters thinner than that can be continuously formed from a material having a constant diameter, excluding the transition period.

A steel wire profile meter 10 is disposed upstream of the pinch roll 11 to monitor the processing status. Corresponding to the measured / calculated cross-sectional area, the speed of the pinch roll 11 is finely adjusted via the speed controller 18, and the cross-sectional area is normally controlled within ± 2.0% of the reference value. Here, the reference value is a cross-sectional area when the wire diameter is the standard center value. The allowable width value corresponds to the allowable wire diameter (usually ± 1.0%). The same applies to the irregular cross section.

The wire rod having a dimension within a predetermined range then becomes a quenched and tempered steel wire 16 through a flaw detector 12 for detecting surface flaws, a tempering device 13 by induction heating, and a tempering and cooling device 14 constituted by water-cooled nozzles. The product coil. In the cross-sectional shape measurement by the steel wire profilometer 10, the tempering temperature is changed to a predetermined temperature (depending on the steel type and size, usually 430 ° C. or more, 530 ° C.) via the tempering controller 19 for the part whose dimension exceeds the control range. To 50 ° C. to 100 ° C. to cause excessive softening. That is, the defective dimension portion is included in the defective strength portion, and is excluded in a later process as described later.

When the hot-rolled wire is used directly, the remaining surface scratches are a problem as described above. The portion where the surface flaw is detected by the flaw detector 12 is also excessively softened and treated in the same manner as described above. The degree of softening is not particularly critical.

Various alternatives are conceivable in the implementation method described above. According to FIG. 2, for example, an endless belt type driving device 21 can be used as a wire feeding device instead of the capstan 6. For primary heating, if the direct current heating device 22 is used instead of induction heating, the thermal efficiency is improved. In this case, the oxide film is previously removed by the film removal apparatus 20 for stabilization of energization. There is also a method in which a light rolling mill 23 is applied instead of die drawing. As a cross-sectional profile meter, there is a method in which a length measuring sensor is fixedly arranged and measured as in the fixed type profile meter 24 of FIG. 2 instead of a commercially available laser length measuring device having a turning mechanism. Assuming that the cross section is a perfect circle, it can be done with a one-point measuring sensor.

The reason for limiting the dead supply method to supplying the wire 2 to the line is as follows. The first reason is that, even when the line is in operation, since the wire is stationary on the coil mount 1, welding for each coil is easy and non-stop operation is possible. The second reason is that the strength of the drawn intermediate material increases to about 1500 MPa, and when the wire diameter is large, dead supply is difficult due to twisting resistance. This is because it becomes possible easily.

Next, the reason why the heating is performed in two stages is as follows. First, in order to stabilize the dieless drawing, it is necessary to soften at high temperature only just before cooling. On the other hand, normal quenching heating has an upper limit temperature and must be properly maintained. As described above, the minimum temperature and time required for quenching are secured as the primary heating for matching both conditions, and the appropriate temperature range for dieless drawing is set as the secondary heating at a temperature higher than the primary and for quenching. On the other hand, even if it became somewhat inappropriate, the temperature was set so that it could be eliminated by the ausfoam effect.
The second reason is that, when speeding up the dieless drawing, it is indispensable to shorten the heating / cooling zone that extends in the line direction as much as possible in order to strictly observe the above-mentioned stabilization 2 condition. It must be two-stage heating that can limit the length.

The reason why the primary heating temperature is set to 50 ° C. or higher and 150 ° C. or lower on the AC3 point of the target steel type is to combine the minimum temperature necessary for the quenching and the secondary heating to obtain an appropriate solution condition. . The secondary heating is overheated to 50 ° C. or higher and 250 ° C. above the primary heating temperature, and the degree mainly depends on the degree of processing. If the degree of processing is low, low overheating is sufficient. If the degree of processing is high and the degree of superheat is low, there is a risk that the stretching may be upstream due to insufficient deformation resistance. If it exceeds 250 ° C., the austenite crystal grains are not uniform and are likely to grow improperly, although there is no holding time after secondary heating. The reason why the degree of superheat can be increased in this way is that the higher the degree of work, the more the above problem can be solved by the Ausfoam effect through crystal grain refinement. The reason for specifying the area reduction rate as 20% or more is that the area reduction rate needs to be at least 20 to 25% in order to obtain the Ausfoam effect.

The first reason for limiting the cooling rate and cooling time to the larger one required for dieless drawing and quenching is that the appropriate cooling rate and time for both processes are the steel type, wire diameter, and drawing. This is because it is indispensable in terms of quality even if there are some difficulties, although it varies depending on the ratio and abnormal quality prevention such as burn cracking.
The second reason is that the stretch zone is reduced as much as possible by the interaction between the secondary heating described above and the strong cooling in the cooling section, the processing time is shortened, the recrystallization of the processed structure is suppressed, and the ausforming effect is not lost. Because.

The reason for specifying the upstream wire feeding device as a capstan is that it is simple and optimal for die drawing, and a frictional force that generates sufficient tension for dieless drawing can be easily obtained and shared.

Next, there is a basis for replacing the conventional hardened and tempered steel wire that has undergone the wire drawing process with the steel wire of the present invention, which is manufactured by combining the hot-rolled wire material with die drawing, dieless drawing, and ausforming. The spring will be described.
The spring constant k (= load / strain) is emphasized as the basic performance of the spring. In the coil spring, the constant is proportional to the fourth power of the wire diameter as shown by the equation (1), so that only the wire diameter is strictly regulated, and the allowable width is ± 0.5% in the special standard. This value corresponds to ± 1.0%, which is twice the cross-sectional area. The spring constant is limited to within ± 2.0%.
k = d4G / 8D3N -------------- (1)
(D: wire diameter, G: transverse elastic modulus, D: coil diameter, N: number of turns)

Examine the effect of roundness on the spring constant. The major axis and minor axis are elliptical sections (α = 1.02, 0.98) with median value + 1.0% and median value -1.0%, respectively, twice the special standard, and the major axis direction is parallel to the coil axis. In each case of right angle, the spring constant k ′ was estimated according to equation (2) derived from Document 4.
k′≈2GS2 / (π2ND3) × (2.1α−1.1) / α2 −−− (2)
(Α: sectional aspect ratio (= width / thickness), S: sectional area)
It was clarified that the calculation result of the spring constant k ′ with respect to the variation of the aspect ratio of ± 2.0% was + 0.15% and −0.25%, respectively, compared with the perfect circle, and can be neglected.

In the JIS standard regarding the allowable value of the wire diameter, the majority is within ± 1.0%, and in a specific specification, it is within ± 0.5%. If the latter is used for precision springs, this allowable width corresponds to ± 1.0% in cross-sectional area. In the implementation of the first invention, the cross-sectional area may be controlled within the reference value ± 2 × wire diameter allowable value (%). Thereafter, there is no problem with respect to the spring constant even if the permissible value of the major axis and the minor axis is increased to twice the above, that is, ± 1.0%. Conventionally, the cross-sectional dimensions are managed extremely finely in the wire drawing process. In the present invention, the cross-sectional area is strictly managed in the dieless drawing control. Long and short diameters can be managed simply. The purpose of expanding the allowable range is to prevent a reduction in operating rate due to die replacement. The above discussion is applicable not only to springs but also to many other applications.
Japan Spring Industry Association Spring Technology Research Group "Spring Technology" p106

As another point of view, the spring often uses torsional stress. That is, it is desirable that the shear yield stress is large and constant. However, the tensile strength is generally substituted as a standard. It is known that the former variation among lots is considerably larger than that of the latter and that of the fourth power of the wire diameter. Therefore, it is more reasonable as a material for precision springs to improve the stabilization of torsional performance than dimensional accuracy.
The present invention is advantageous in stabilizing the twisting performance. This is because the drawn intermediate material has a strong bending wrinkle, which is not sufficiently eliminated even by line-type heat treatment, and causes a variation in twisting performance. In the present invention, hot straightening and heat treatment are performed under tension, so that a highly straight steel wire can be obtained.

By the way, in the spring forming process, there is a system that is processed almost automatically nowadays, and in some cases all the dimensions are measured and the strength is measured, and non-standard products are eliminated. In the present invention, this system is utilized. In other words, as described above, when the defective dimension portion of the steel wire is excessively softened and the strength becomes insufficient, the spring has an abnormal size and abnormal strength and is surely excluded as a defective product. The new defective product elimination method may lower the yield at the time of forming the spring, but since it is partial and local, it is clearly advantageous in terms of the overall yield from the wire and the overall cost.

The following experiment was conducted to verify the mechanism and effect of the present invention. Using the conventional line-type quenching and tempering apparatus, which is the prototype of FIG. 1, a drawn Si-Cr steel, a 4.0 mm diameter steel wire having a strength of 1700 MPa is applied at 80 m / min from a coil on a turntable. It was supplied to the line at a speed, and the surface was heated to 930 ° C. by induction heating, held for 3 seconds, water-cooled for 4 seconds at a heat transfer rate of about 5000 to 10,000 W / m 2 K, and tempered at 490 ° C. for 7 seconds. In normal production, the speed difference between the upper and lower pinch rolls is 2%, but in the experiment it was increased to 15%. When it was less than 10%, the film was stretched smoothly, but thereafter, breakage due to partial drawing occurred. When a secondary heating coil was attached and heated rapidly to 1030 ° C., no problem occurred with stretching up to 30%.

The diameters of the obtained steel wires varied somewhat in the length direction, but there was no partial drawing. On the surface of the wire, four indentations were generated by the upstream pinch roll. The straightness of the steel wire was greatly improved. The tensile strength of the steel wire was about 30 MPa higher than usual. It is thought that the ausform effect worked. Therefore, when re-tempering at 510 ° C. off-line, the strength was adjusted and the elongation was slightly improved, but the aperture value was slightly improved.

From the above experimental results, 1) the effectiveness of the two-stage heating was confirmed, 2) the necessity and rationality of the introduction of precision speed control were supported, and the validity of the present invention was proved.

It is a schematic side view of the apparatus which enforces the quenching and tempering method of 4th invention. The example of the alternative method of each part method shown in FIG. 1 is shown. It is a principle diagram of the dieless drawing method to which the present invention is basically applied.

Explanation of symbols

1: Coil mount 2: Hot rolled wire 3: Quenching and tempering line 4: Film removal device 5: Drawing die 6: Capstan 7: Primary heating device 8: Secondary heating device 9: Cooling device 10: Steel wire profile Meter 11: Pinch roll 12: Flaw detector 13: Tempering device 14: Tempering cooling device 15: Winding machine 16: Quenching and tempering steel wire 18: Speed controller 19: Tempering controller 20: Delaminating device for energization 21: Belt Type drive device 22: Direct current heating device 23: Light rolling mill 24: Fixed profile meter

Claims (4)

In each of the line-type continuous heat treatment methods in which the steel wire is run in a straight line and heated, quenched and tempered under the same conditions, 1) the tension is applied to the wire and the cross-sectional area is 20% or more at the high temperature part of the wire. 2) The difference between the drawing speed of the wire feeding device arranged on the upstream side of the heating and the drawing speed of the wire feeding device arranged on the downstream side of the quenching is a method of performing dieless drawing for reduction and applying the tension. made by, 3) a method of heating, after primary heating ranges are the a _C3 point + 50 ℃ or a of _C3 point + 150 ℃ below, the primary by high-frequency induction heating at the upstream side nearest the cooling-the hardened position consists in rapidly secondary heating to the primary heating temperature + 150 ℃ temperature range below be the primary heating temperature + 50 ℃ or higher than the heating temperature, 4) quenching cooling rate and the cooling time to die-less pull-out and hardening And each required size larger or more, 5) a method of adjusting the product cross-sectional dimension, made by inverse proportion to the cross-sectional area ratio of the front and rear reduced to the both the speed ratio of the both wire feeder, it A method for continuous heat treatment of steel wires characterized by the following. Transient part by changing the product diameter by continuously changing the ratio of the feeding speed of the upstream wire feeding device and the drawing speed of the downstream wire feeding device to a new predetermined value The continuous heat treatment method according to claim 1, wherein steel wires having various diameters are formed without interruption from a wire having a constant diameter except for. The supplied steel wire is a hot-rolled wire, one end is pulled out in the axial direction of the coil in a state where the wire coil is stationary, and the wire is supplied to the line. The upstream wire feeding device includes one drawing die. The continuous heat treatment according to claim 1 or 2, comprising a capstan, wherein the wire is die-drawn by the wire feeder and formed into a perfect circle, an ellipse, or an oval shape. Method. When the cross-sectional area detected and calculated between quenching and tempering is out of the standard range, or when a surface defect is detected in the same section, the tempering temperature for each part is 50 ℃ to 100 ℃ continuous heat treatment method according to claim 1 or claim 2 or claim 3, characterized in that to over the softening is raised.

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