JP3968406B1 - Patenting method for steel wire rod - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lead-free patenting method / apparatus capable of ensuring the same quality as lead patenting applied to a wire material in the production of a high quality piano wire and capable of parallel processing of various types and sizes, and lead consumption Solve the problem of danger of heavy metal contamination by
[Solution]
This equipment consists of wire supply, heating furnace, cooling furnace, air cooling zone, heat insulation furnace, and wire winding, and consolidates a number of wires with different wire diameters into several stages of wire diameters and travels straight in parallel. Pass through and patent continuously. A fluidized bed with parallel bulkheads is applied to each cooling furnace, and appropriate furnace length, furnace temperature, air cooling length, and heat insulation length are set for each group. The transformation is completed in the air-cooled zone next to the fluidized bed of the relatively low-temperature refrigerant in order to improve the constant temperature. The reference line speed of each group is made inversely proportional to the reference wire diameter, and the individual wire rods in each group are finely adjusted according to the difference from the reference wire diameter.
[Selection] Figure 1

Description

The present invention relates to patenting of high carbon steel or high carbon low alloy steel wire used as a material for high-strength steel wire (the operation of inducing isothermal transformation by quenching in a lead bath usually at about 1000 ° C. to about 550 ° C. ).

A type of isothermal transformation called patenting is applied to the high carbon steel wire before drawing. Precision steel wire such as piano wire is modified by patenting into a fine lamella homogeneous pearlite. As a result, the material is strengthened and the toughness and cold workability are improved. The material is remarkably strengthened by work hardening by wire drawing to become a high-strength steel wire. It is well known that the quality and performance level of this process depends on the transformation temperature and its constant temperature (small transformation temperature range), and the lead bath quenching is currently the best quality and work aspect as a cooling method. Yes.

The basis for this is that the value of the heat transfer coefficient in lead bath quenching is extremely large, so that 1) almost the required cooling rate can be obtained in the preliminary cooling (rapid cooling to the transformation temperature) of the wire (usually 5 to 15 mm diameter), 2) The difference between the desired transformation temperature and the lead bath temperature is relatively small, and therefore isothermal transformation is likely to be induced. 3) The same metallurgical effect can be obtained even if the wire diameter is different at the same bath temperature. .

Since the lead bath is a single bath with a constant temperature, any wire diameter can be dealt with by designing the lead bath length to the longest required. Usually, the wire speed is smaller and the dipping time is longer as the diameter of the larger diameter wire is not inconvenienced. On the contrary, there is a hidden effect that the wire rod having segregation defects inside was safely digested, although not generally noticed. The reason is that the segregation part has high hardenability and a long transformation time, so that the theoretical immersion time is insufficient.
Based on the above characteristics, the lead bath quenching type patenting furnace can achieve heat treatment close to isothermal transformation, and also compare parallel operations when different wire diameters are used and the maximum / minimum ratio of wire diameters is tripled. Easy.

A major problem in lead bath quenching is the risk of heavy metal contamination.
1) Agglomerated foreign bodies such as lead-lead oxide-iron oxide are generated in the quenching tank and discarded.
2) Lead remains on the surface of the lead bath-hardened wire, and a part of it is scattered in the factory.
3) Adhered lead becomes a residue in the next pickling and water washing, and is finally discarded.
The use of toxic heavy metals is expected to be abolished not only due to cost issues but also from environmental regulations. Lead-free patenting has been sought, but unsolved or inadequate. The related prior examples of the present invention will be described below.

A: Cooling by fluidized bed (for example, Patent Document 1)
In this method, sand having a particle size of about 1 mm is suspended on an air stream ejected from the floor surface to form a heat transfer medium. The heat transfer coefficient is about 50 (kcal / m ² h ° C.) with a simple air flow, but is amplified to about 1000 and stable. It is applied to the patenting of thin steel wires with a diameter of 2 mm or less.
The problem is that the heat transfer coefficient is less than half that of 2000-2500 of the lead bath. As a result, a wire with a diameter of 4 mm or more is insufficiently cooled, and the strength obtained is inferior to lead bath quenching. If the fluidized bed temperature is set low to achieve the same cooling capacity as the lead bath (= heat transfer coefficient x temperature difference between the material and refrigerant), the first half of the high heat generation will be adequate, but the second half of the low heat generation will be overcooled. Become. In this case, quality defects such as increase in bainite and martensite are generated.

B: Cooling with a multi-chamber fluidized bed 1 (Patent Document 2)
This method solves the above problem by connecting several fluidized bed chambers in the running direction in patenting small diameter steel wires and appropriately setting the temperature of each chamber. It is disclosed that the first chamber is set to a minimum temperature (250 ° C. or higher) to ensure a necessary and sufficient cooling rate. In the transformation part, it is set around 550 ° C. The problem is extremely difficult to follow changes in wire diameter and steel type, and becomes more difficult when mixed. That is, when steel wires having different wire diameters are processed in parallel, one of the conditions is appropriate but the other is inappropriate. It is monofunctional and suitable for simple mass production, but unsuitable for large variety and small volume production. Moreover, no mention is made of the applicability to a thick wire having a diameter of 5 mm or more. In order to simultaneously process wires with a maximum / minimum ratio of the wire diameter of 3 times, it is impossible to adjust the space, furnace length, control system, conditions, and management.

C: Molten salt quenching (for example, Non-Patent Document 1)
A heat transfer coefficient of 1500 to 2000 is obtained, which is similar to a lead bath. In other words, in order to obtain the same cooling capacity as the lead bath, the same effect as the lead bath quenching can be obtained by installing a pre-stage tank in which the salt bath temperature is set slightly lower than that of the lead bath and a post-stage tank that maintains the desired transformation temperature. Yes. Although it is directly connected to and followed by the wire rod rolling process and is monofunctional, it can be applied to any wire diameter.
The first problem with this method is that the quality is the same as that of lead bath quenching, and heavy metal contamination is also eliminated, but newly contaminated ambient fume by molten salt fume and the occurrence of dross (compound / mixture of salt and iron oxide). Environmental problems such as disposal and disposal due to deterioration of molten salt remain.
The second problem is a typical mass production system, so that it is suitable for a general steel maker wire factory, but unsuitable for a small quantity and a wide variety of wire secondary processing factories.

D: Cooling 2 with multi-chamber fluidized bed (Patent Document 3)
In the above-mentioned document, a ring-row processed material is run in one fluidized bed furnace, a partition is provided in a direction perpendicular to the running to form a multi-chamber, and each chamber is individually set to a furnace temperature to perform various heating and cooling. A method of performing is disclosed. Compared with the above-described method B, the equipment is simplified, but it is not suitable for parallel processing of wire rods having different wire diameters.

E: Parallel processing of various types of wire (Patent Document 4)
The above document discloses a method in which a plurality of wires are grouped into several groups and passed through a heating furnace, and partition walls are provided in parallel in the heating furnace to set the processing temperature for each group. In addition, a plurality of heating furnaces are arranged in series, and various heating conditions can be easily set simultaneously by combining paths, so that a wide variety of production can be efficiently performed. A method of providing a partition wall in parallel with the traveling direction and individually setting the heating temperature is often employed in the secondary processing of the wire. There are no examples where this method is applied to cooling or fluidized beds. It is not suggested at all whether or not the present invention can be applied to patenting in which the emphasis is on cooling, the processing temperature is narrow, and the processing time is short, and those skilled in the art can deduce that special measures are required.

JP2001-073113 Iron and Steel Vol. 69 (1983) S570 JP-A-3-146623 JP 2006-144032 A JP-A-4-276028

As mentioned above, in lead bath quenching of high carbon steel wire, lead used in operation is consumed in various places such as processing tanks, processing plants, pickling and water washing in subsequent processes, and many of them are recovered.・ Although it is considered to be waste, there is an environmental problem of danger of heavy metal contamination.
Although conventional methods that can replace lead baths, such as fluidized bed cooling, can solve the environmental problems described above, if the wire diameter is large due to insufficient cooling capacity, the quality of the lead bath is inferior, and a furnace is used in the previous stage to compensate for cooling capacity. By adopting a series of multi-chamber fluidized bed furnaces where the temperature is set to a relatively low temperature and the furnace temperature is increased in the middle and subsequent stages, parallel processing of wires with different wire diameters and hardenability is possible even if the specific wire diameter can be met. If you do, there is a problem that you can not cope.
In the heat treatment, a method of providing a heat insulating partition in the heating furnace parallel to the running direction and individually setting the temperature to carry out multiple types of parallel operation is advantageous for productivity, but cooling of patenting that requires precise control Has no application examples.
An object of the present invention is to ensure a constant temperature transformation equivalent to lead bath quenching in a fluidized bed cooling patenting that does not use a lead bath, and to rationally treat a wide variety of wires.

In order to solve the above problem, the following element means are effectively combined.
1) A fluidized bed furnace is used as the cooling furnace without using a lead bath, and the lack of cooling capacity is dealt with by setting the refrigerant at a low temperature.
2) Combine multiple wire rods of various wire diameters into several wire diameter groups and process them together.
3) Set the appropriate wire speed, furnace length, and furnace temperature for each group of wire diameters.
4) Compensate for constant temperature by a combination of forced cooling, air cooling and heat insulation.
5) Fine-tune the wire speed of each wire in accordance with the wire diameter difference within each county.

The gist of the present invention is that a high-carbon steel and a high-carbon low-alloy steel are heated to a predetermined temperature by passing through a plurality of wires having different wire diameters while traveling straight in parallel with the wire axis direction, and then flowing to a predetermined temperature. In the method of continuously patenting by passing through the floor cooling furnace, 1) collect the wire rods with similar wire diameters and run as a group of wire diameters in several stages, and 2) set the reference linear velocity of each group. Set in inverse proportion to the reference wire diameter of each group. 3) In the fluidized bed cooling furnace, partition walls are provided in parallel to separate each wire diameter group, and the furnace temperature is set individually for each group to correspond to the wire diameter. 4) The effective length of the fluidized bed cooling furnace is set in accordance with the reference wire diameter of each group, and 5) The cooling rate is obtained by directly connecting and following the air cooling zone downstream of the fluidized bed cooling furnace. 6) Further, in each group, the wire speed of each wire is changed to the wire diameter of the wire. A patenting process of steel wire rod, characterized in that fine adjustment in response to the ratio of the reference wire diameter.

In the above gist, the patenting of the steel wire material is characterized in that the air cooling zone is passed next to the heat insulation furnace, and the length of the air cooling zone and the heat insulation furnace is set in inverse proportion to the reference wire diameter of each group, respectively. The method is more desirable.

Furthermore, in the invention of the preceding paragraph, the fluidized bed effective length of each group is set to the reference linear velocity × [cooling time to pearlite transformation + transformation time × (0.5 to 1.0)], and the length of the air cooling zone is set to the reference line. Steel wire rod patenting method, characterized in that speed x transformation time x (0.3 to 1.0) and the length of the heat-retaining furnace is set to reference linear speed x transformation time x (1 to 4), respectively. Is more desirable.

In the invention of the above three methods, a preliminary cooling zone in which a partition through which a wire can penetrate perpendicularly to the traveling direction is provided in each group of passes in the fluidized bed cooling furnace, and the upstream side has a furnace temperature with a constant furnace length at each path. A steel wire patenting method is also desirable in which the downstream side is a transformation maintaining zone having a furnace length inversely proportional to the reference wire diameter for each pass and having an individual furnace temperature.

As a first effect of the above invention, lead is not used at all for patenting, which helps to improve the environment.
As a second effect, a cooling condition equivalent to that of the conventional lead bath quenching can be obtained, so that quality deterioration due to fluidized bed cooling can be avoided.
As a third effect, it is possible to perform parallel processing of multi-size wires similar to lead bath quenching that cannot be obtained by conventional fluidized bed quenching.

Hereinafter, embodiments will be described with reference to the drawings.
FIG. 1 is a schematic plan view showing the overall configuration of an example of a patenting apparatus according to the method of the present invention, and FIG. 2 is a schematic longitudinal sectional view of the main part. A large number of wire coils 1 of high carbon steel or high carbon low alloy steel of various wire diameters are supplied to the apparatus. Each wire 2 travels in a straight line in the direction of the line axis in parallel with a distance from each other and is supplied to the heating furnace 3. The heating furnace 3 has a width that allows several to tens of parallel processing. Each wire 2 is heated to about 1000 ° C. while being passed through the heating furnace 3 in a group of wire diameter groups 4 such as 13 to 15 mm diameter, 10 to 12 mm diameter,. It is sent to the cooling furnace 5.

There are various ways of determining the wire speed when the wire diameters are different, and there are advantages and disadvantages. In the present invention, the wire speed is inversely proportional to the wire diameter. To be precise, the reference linear velocity for each group is inversely proportional to the reference wire diameter. As a result, the passage time is inversely proportional to the wire diameter for the same heating length. Since the heating / cooling rate is inversely proportional to the wire diameter, the temperature of the wire rod at the outlet of the heating furnace is the same regardless of the wire diameter. Since the heating furnace 3 has a soaking zone, the wire is sent to the cooling furnace 5 at the same temperature even if the linear velocity is somewhat increased or decreased.

The cooling furnace 5 is provided with a large number of blowing nozzles 7 on the hearth 6 and floats and flows the fluidized sand 8 deposited on the hearth by blowing at a predetermined pressure to make a refrigerant, and the wire rod is passed through the floating layer for cooling. It has a structure to do. The cooling capacity depends on the set temperature, and naturally, the lower the temperature, the stronger the cooling. The inside of the cooling furnace 5 is partitioned for each wire diameter group 4 by a partition wall 9 in parallel with the traveling direction to form a wire diameter group path 10. Each path length is set corresponding to the reference wire diameter of the wire diameter group, and increases as the wire diameter decreases.
The partition wall 9 is similar to the method of arranging a plurality of furnaces disclosed in Patent Document 2 in parallel arrangement, and there is an example in a heating furnace, but it is not found in a fluidized bed cooling furnace. Moreover, it can be carried out very simply.

The heat transfer coefficient of the fluidized bed is about 1/2 to 1/3 that of the lead bath, but by setting the furnace temperature low, the same cooling capacity as that of the lead bath can be obtained and the first condition for induction of isothermal transformation is solved. Is done.
The temperature of the cooling furnace 5 is set for each pass. The larger the wire diameter, the lower the temperature is set to approximate the cooling rate of the lead bath quenching. The furnace temperature is adjusted by a burner 17, a water cooling pipe 18, and the like. When cooled to about 600 ° C., pearlite transformation begins. In one embodiment of the present invention, one furnace temperature is set for each pass as described above.

In the other method, a partition wall 11 through which the wire can penetrate perpendicularly to the traveling direction of the wire is provided in the middle of each path of the fluidized bed, and the upstream side is divided into a cooling zone 12 and the downstream side is divided into a transformation maintaining zone 13. If the furnace length and furnace temperature of the cooling zone are set to be the same for each path, the cooling rate is inversely proportional to the wire diameter, and the wire speed is inversely proportional to the wire diameter. Becomes the same temperature.

Fever begins with the start of transformation. The exothermic efficiency (kcal / h / kg) is not constant, and increases rapidly from zero over time according to the rate of progression of metamorphosis (so-called logistic curve). The peak is about 30% from before the transformation time. The second condition for inducing the constant temperature transformation is to perform cooling corresponding to the heat generation. The appropriate furnace temperature for the wire diameter is empirically known, for example, about 530 ° C. for a 2 mm diameter.

The isothermal transformation is faster in the pre-transformation cooling, and is required to be balanced against heat during the transformation. The proper furnace temperature for cooling and the proper furnace temperature for maintaining the transformation temperature are different. In the present invention, the furnace temperature is set individually by the partition walls 11 in principle and optimized in principle. In order to simplify the equipment, the temperature can be set to the same furnace temperature without providing the partition wall 11, and the temperature can be set somewhat lower than that of a conventional general fluidized bed. New necessary means in that case will be described later.

The transformation time depends on the steel type and transformation temperature, but is almost independent of the wire diameter and constant. Therefore, if the required length of the transformation maintenance zone is equivalent to the transformation time, it becomes linear velocity × transformation time and is inversely proportional to the wire diameter. The length of the fluidized bed cooling furnace is the sum of the pre-transformation cooling zone and the transformation maintenance zone, and the former is basically constant, but differs for each pass when the partition wall 11 is not provided. The determination of the length of the cooling section is related to the cooling capacity to be applied, that is, the heat transfer rate of the refrigerant and the set temperature of the refrigerant, and no special difficulty is required by those skilled in the art.

Here, if the fluidized bed temperature is set with priority given to transformation maintenance, the cooling capacity until transformation is insufficient. Conversely, if cooling is prioritized, the cooling capacity during transformation becomes excessive. Strictly speaking, even in the early stage of transformation with large exotherm, even if it is close to the proper level, the latter stage is obviously overcooled, and bainite is mixed instead of pearlite, and martensite is mixed, which deteriorates workability and normal patenting. It will not be.

In the present invention, as described above, the furnace temperature is set lower than the normal fluidized bed, the cooling before and during the transformation is moderately strengthened, and the cooling time is shortened as a measure for preventing the excessive cooling in the latter half of the transformation. deal with. This is a new necessary measure. As the time, an appropriate value between 0.5 and 1.0 of the transformation time is selected. Therefore, the furnace length is set slightly shorter than the sum of the time required for cooling and transformation in each wire diameter group. Passing through fluidized bed cooling usually means air cooling automatically and has no special intention unless special measures are taken. In the present invention, air cooling has a positive meaning. Since the cooling capacity of air cooling is relatively small, on the other hand, it functions to prevent overcooling and maintain constant temperature, and on the other hand, it eliminates heat generation after transformation and maintains constant temperature, which is an essential element of the present invention. It becomes. This is the third condition for induction of isothermal transformation.

Each wire passed through the fluidized bed cooling furnace is intentionally air-cooled in the air-cooling zone 14 and then guided to the heat-retaining furnace 15. The transformation of the untransformed part is almost completed during air cooling. The length of the air cooling zone 14 is linear velocity × transformation time × (0.3 to 1.0). That is, it is made inversely proportional to the wire diameter.

If the material is homogeneous, the above processing is completed, but usually segregation defects within the material are unavoidable. If there is segregation, the transformation time of the part may be several times. In that case, martensitic transformation occurs during air cooling. As a countermeasure, pass the heat-retaining furnace to maintain the transformation temperature. The successor to the incubation furnace is known. In the present invention, a heating furnace having a temperature common to each wire diameter group is followed. The appropriate length of the incubation furnace depends on the degree of segregation and the allowable level, and is empirically determined as transformation time × linear velocity × (1 to 4). This is not a necessary condition for induction of isothermal transformation, but a practical condition. The transformation time is around 4 seconds in the case of high carbon steel. Since the set temperature of the heat-retaining furnace is close to mere time earning, no strictness is required. Since the heat input and output is small, a simple heating device, a heat insulating wall, and a control device are sufficient. The transformation is reliably completed after passing through the heat-retaining furnace, and each wire is wound up to become the product coil 16.

The cooling behavior of the wire will be analyzed for the cooling method described above.
FIG. 3A shows cooling from the heating temperature to the transformation temperature. The heat transfer coefficient of the fluidized bed was 700 (kcal / m ² h ° C.). 400, 250, and 150 ° C. were set as appropriate furnace temperatures for 5, 10, and 15 mm diameter wires, respectively. Cooling rate than lead baths quenching of 10mm diameter in each diameter inferior homeothermic is feared, but becomes similar to the lead bath quenching Looking below A ₃ temperature related to transformation, as shown in FIG. 3 (B) There is no problem.

FIG. 4 shows a cooling diagram during and after the transformation. The transformation time is corrected (apparently increased) with respect to the wire diameter in consideration of the cooling delay at the center of the wire. For each diameter, the same thermostability as lead bath quenching is obtained by appropriate furnace temperature setting. However, the cooling after completion of transformation is fast, and if the untransformed part remains and falls below the nose temperature (540 to 570 ° C.), abnormal tissue is induced as described above. The application of air cooling and heat insulation from the middle of transformation maintains the constant temperature as indicated by the dotted line in the figure to solve the problem.

Naturally thick and thin wires are mixed in each wire diameter group. Due to the difference from the reference diameter, the heat treatment conditions are not optimal. In the present invention, the deviation is corrected by finely adjusting the linear velocity for each individual wire. If it is narrow, increase the line speed slightly. The temperature at the beginning of transformation is slightly lowered, but it is the same at the end of transformation. The heating temperature is not affected by a slight change in the linear velocity.

Depending on the type of steel, the transformation time varies and the overall length of the cooling furnace may become excessive or insufficient. In many cases, this can be dealt with by correcting the linear velocity.

An appropriate value of the cooling time rate during the transformation in the fluidized bed (cooling time of the transformation maintaining part / transformation time) is preferably 0.6 to 0.8, but the reason why the lower limit is set to 0.5 is not below this value. Since the transformation part generates heat, the subsequent temperature increase is inconvenient. The reason why the upper limit value is set to 1.0 is that the furnace temperature is relatively low, so that overcooling is apparent at the end of the transformation.

The air cooling part has another function. Since each wire is exposed, it is very convenient for installation of the temperature measuring device 19 and visual check. All the progress of transformation can be read immediately by dark field.

A low alloy steel wire with high hardenability can be treated in the same manner as carbon steel because the furnace length has a sufficient margin as a segregation countermeasure. If there is still a shortage, use the small diameter group path with a long furnace length. One wire diameter group path can be temporarily set for the steel type. Specifically, the speed may be lower than the standard, and the fluidized bed temperature may be equivalent to that of a lead bath. Since the temperature of the cooling furnace can be adjusted for each group of wire diameters, it can be widely applied to parallel processing of a wide variety of wires.

Patenting is indispensable for the production of high-carbon steel high-grade steel wires, and lead bath quenching is still performed in the conventional secondary processing plant for wire rods. The lead bath quenching method has a feature that it is easy to perform parallel processing of wires having different wire diameters. By replacing the equipment with the present invention, the use of lead can be abolished. Eliminates the problem of lead bath installation regulations and makes it easier to enter new markets.

It is a schematic plan view of the example of the patenting line which implements this invention. It is a schematic longitudinal cross-sectional view of the principal point same as the above. The cooling diagram before transformation of the wire according to the present invention is shown. It is a cooling diagram after transformation during transformation of a wire rod by the present invention.

Explanation of symbols

1: Wire Coil 2: Wire Material 3: Heating Furnace 4: Wire Diameter Group 5: Fluidized Bed Cooling Furnace 6: Furnace Bed 7: Blowing Nozzle 8: Fluidized Sand 9: Bulkhead 10: Wire Diameter Group Pass 11: Bulkhead 12: Cooling Zone 13: Transformation maintenance zone 14: Air cooling zone 15: Incubator 16: Product coil 17: Burner 18: Water-cooled tube 19: Temperature measuring device

Claims (2)

A number of wire rods of high carbon steel and high carbon low alloy steel with different wire diameters are linearly run parallel to the wire axis direction and passed through the same heating furnace and heated to a predetermined temperature, and then passed through a fluidized bed cooling furnace. In the method of applying patenting continuously, 1) wire rods having similar wire diameters are aggregated and run together as a group of wire diameters of several stages, and 2) the reference linear velocity of each group is set to the reference wire diameter of each group. 3) In the fluidized bed cooling furnace, partition walls are provided in parallel so as to separate each group of wire diameters, the furnace temperature is set individually for each group, and cooling corresponding to the wire diameter is performed. ) Set the effective length of each group of the fluidized bed cooling furnace to the standard linear velocity x [cooling time to pearlite transformation + transformation time x (0.5 to 1.0)], and proceed the majority of transformation. 5) An air cooling zone in which the length of each group is a reference linear velocity × transformation time × (0.3 to 1.0) downstream of the fluidized bed cooling furnace. Then, the cooling rate is lowered from the previous time to finish the transformation. 6) Next to the air-cooling zone, the length of each group is passed through a heat-retaining furnace whose basic linear velocity × transformation time × (1 to 4), 7) Furthermore, in each group, the wire speed of the individual wire rod is finely adjusted in accordance with the ratio of the wire diameter of the wire rod to the reference wire diameter. In each group of passes in the fluidized bed cooling furnace, a partition that allows the wire to penetrate perpendicularly to the traveling direction is provided, the upstream side is a precooling zone with a constant furnace length and a constant furnace temperature, and the downstream side is a pass. The steel wire rod patenting method according to claim 1, wherein a transformation maintenance zone having an individual furnace temperature is used for each.

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