JPS6157891B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Fields] Steel bars and wires for cold forging used for bolts, automobile machine parts, etc. are often treated to make the carbides in the steel spheroidized in order to improve cold forgeability.
Specifically, JISG4051~G4052, G4102~4108,
Medium- and low-alloy steel rods and wire rods with a carbon content of 1.5% or less as specified by G4202, G4805, G4403, G4805, G4301, etc. are subject to spheroidization treatment. The present invention aims at reducing the amount of carbon to be subjected to such spheroidization treatment.
This paper relates to improvements in the spheroidization treatment of carbides in steel for steel bars and wires made of medium- to low-alloy steel with a content of 1.5% or less. [Prior Art] Conventionally, this spheroidizing treatment has been carried out by the following method. FIG. 1 is an explanatory diagram showing an example of a conventional spheroidization treatment method, in which 1 is a raw material coil, 2 is a pickling device, 3 is a lubrication treatment device, 4 is a die wire drawing device, and 5
is a spheroidizing annealing furnace. The raw material coil 1 is descaled and decarburized in a pickling device, then transported to a lubrication device, where it is lubricated, unwound in an uncoiler 6, and cut into a desired size (diameter) by a die 7. The wire is drawn to improve its spheroidizing properties, and after being wound around a coiler 8, it is transported to a spheroidizing annealing furnace 5, where it is subjected to a spheroidizing annealing process. This conventional method is a so-called batch method in which each coil is processed in each step, and has the following drawbacks. [Problems to be solved by the invention] Since there are multiple steps, productivity is low and costs are therefore high. There are many work-in-progress items in the process, which requires time and effort to manage, and problems such as defects during transportation are likely to occur. Spheroidizing annealing takes an extremely long time, ranging from several hours to over 20 hours, and is costly. Pollution countermeasures by pickling are required. On the other hand, in addition to the above-mentioned conventional method, for applications that do not require a high level of cold forgeability, there is also a simple method in which the pickled material cost is immediately annealed, omitting the lubrication and die wire drawing steps. However, this method not only has the disadvantage that the product diameter is limited by the diameter of the rolled material, but also does not solve the above-mentioned disadvantages in any way. In addition, a method has been developed in which a mechanical descaler is used instead of pickling and the steps of mechanical descaler → lubrication → die wire drawing are performed continuously in-line, but the above-mentioned drawbacks due to spheroidizing annealing still remain. The present invention was made to eliminate all of the above-mentioned four drawbacks of the conventional method, and it eliminates both the pickling and lubrication steps in the conventional method, and replaces the expansion and contraction using a die with a roll bending device.
The purpose is to simplify the entire spheroidization process including the pretreatment process, and to significantly shorten processing time and reduce costs by performing continuous spheroidization processing in-line. [Means for Solving the Problem] As a result of various experimental studies regarding spheroidization treatment, the present inventors found that when plastic deformation is applied to steel in a temperature range below the _A3 transformation point, 30 to 50% of the carbides in the steel are % of the carbide becomes spheroidized, and by holding it at that temperature for a short time, almost all of the carbide becomes spheroidized. Based on this knowledge, we aim to shorten the spheroidization treatment time and improve the overall processing process. This has led to the completion of the in-line continuous method of the present invention. That is, the present invention provides the following features: (1) The material for steel bars and wires is heated to a temperature of 350°C or higher and 850°C or lower, elongated to an elongation rate of 5% or more using a roll bending device in that temperature range, and then wound on a coiler. Before or after winding
A method for continuous spheroidization of steel bars and wires, in which a process is continuously carried out at a temperature of 450°C or higher and 750°C or lower for 2 minutes or more. (2) The material for steel rods and wires is given an appropriate elongation in advance by cold roll bending equipment, and further
Heat to a temperature of ℃ to 850℃, elongate the elongation rate to 5% or more using a roll bending device in that temperature range, and then apply it to a coiler at a temperature of 450℃ to 750℃ before or after winding. A method for continuous spheroidization of steel bars and wires, in which a process is continuously carried out to hold the steel wire for more than 1 minute. The main points are as follows. The present invention will be explained in detail below based on the drawings. FIG. 2 is an explanatory diagram of a steel wire spheroidization treatment line in which the method of the present invention is applied. In the method of the present invention, the steel wire material 10 is continuously fed out from the uncoiler 11.
The wire is directly sent from the uncoiler 11 with or without passing through the cold wire drawing step 12, passed through a heating step 13, a warm wire drawing step 14, and a heat retention treatment step 15 in order to undergo a spheroidization treatment, and then transferred to a coiler 16. It is wound up. First, the cold wire drawing step 12 will be explained. Generally, cold wire drawing of the material before annealing is considered effective for further enhancing the spheroidizing annealing process, and conventionally die wire drawing was performed, but die wire drawing is used as a pretreatment. It required pickling and lubrication of the material, which increased costs and made it difficult to implement in-line. Therefore, in the cold wire drawing step 12 of the present invention, wire drawing using a roll bending device in which a plurality of rolls 17 are arranged on a line is used. Wire drawing using roll bending equipment does not require the above-mentioned lubrication treatment of the material, and descaling can be performed at the same time as wire drawing, so hot-rolled material can be drawn as is without the need for pretreatment such as pickling. This has the advantage of being able to significantly reduce costs. Furthermore, since the wire drawing diameter can be changed by the amount of reduction of the rolls, the wire diameter can be changed in-line or between runs, making it most suitable for in-line continuous wire drawing processing. The elongation rate in this cold wire drawing step 12 is suitably 5% or more from the viewpoint of improving the spheroidizing annealing effect, and within this range, the larger the elongation, the more spheroidizing effect. Naturally, this is limited by the deformability and work hardening ability of the wire material. In other words, in general, in the cold wire drawing process, the maximum elongation rate per unit consisting of a combination of a roll bending device and a drawing drive device is limited by the deformability and work hardening ability of the material. In the case of medium and low alloy steel with a content of 1.5% or less, the elongation is 75%, and even if multiple units consisting of this one set are installed in a line in tandem, the limit is 95% elongation, and in reality, this 95% % is the upper limit of the growth rate. Note that this cold wire drawing step 12 may be omitted especially when attempting to obtain a practically usable steel wire for applications that do not require a high degree of spheroidization. In heating step 13, the material is heated to 350°C or higher at 850°C.
It is heated to a temperature of 500°C or higher and 750°C or lower, preferably 500°C or higher and 750°C or lower. The reason why the heating temperature is limited as above is that in the next warm wire drawing process where wire drawing is performed in the above temperature range, 850 If the temperature exceeds 350°C, the _A3 transformation point will be exceeded, and the carbides in the steel will form a solid solution, so no spheroidizing effect can be expected.If the temperature is below 350°C, the diffusion rate of carbon in the steel will slow down, resulting in short-term spheroidization. Because it becomes impossible. As for the heating method, when the line speed is low, atmospheric heating using a tunnel furnace can be used, but when the line speed is high, high frequency induction heating or direct current heating is suitable. In the case of direct current heating, it is necessary to remove surface scale in advance, so it must be combined with a descaling process. The wire drawing of the raw material in the warm wire drawing step 14 is performed by a roll bending device as in the cold wire drawing described above. The raw material 10 heated to the above temperature in the heating process is immediately passed through a roll bending device and drawn at a high temperature in the above temperature range. Through this warm wire drawing, high to medium carbide
50% spheroidized. The elongation rate in this warm wire drawing was limited to 5% or more because if it is less than 5%, the descaling of the material is insufficient and the effect of promoting spheroidization by wire drawing is insufficient. . Further, as described in the cold wire drawing process, the larger the maximum value is, the better within the range limited by the deformability and work hardening ability of the material, but in reality, the upper limit is 95% elongation. In addition, a roll bending device was used in the warm wire drawing process 14 because it is difficult to lubricate at high temperatures, so die wire drawing cannot be used, but in the case of a roll bending device, wire drawing can be performed without lubrication. This is because it is possible. In the heat retention treatment step 15, carbide in steel, which is a material partially spheroidized in the warm wire drawing step 14, is
The purpose is to further promote spheroidization by keeping warm. Heat retention treatment equipment uses a regular heat retention furnace surrounded by insulating material to prevent internal heat dissipation, and uses the self-retained heat of the high-temperature material charged in the furnace to maintain the temperature at the required temperature. However, in the case of in-line heat retention, if there is a risk that the end temperature of the heat retention may decrease, it is desirable to use an auxiliary heating source (not shown). The heat retention treatment of the material is carried out by holding the material at a temperature of 450° C. or higher and 750° C. or lower, preferably 600° C. or higher and 720° C. or lower, for 2 minutes or more, preferably 7 minutes or more. The actual heat retention start temperature of the material is the exit temperature of the warm wire drawing step 14, but even if the temperature is low, the heat retention end temperature may be set to 450° C. or higher. The reason why the heat retention temperature is limited as above is that when the material is heated at a high temperature, if the temperature exceeds 750℃, the carbides in the steel will melt and spheroidization will not occur, and if the temperature is lower than 450℃, the carbon in the steel will melt. This is because the diffusion rate of the particles decreases, making short-term spheroidization impossible. Further, the reason why the holding time in the above temperature range was limited to 2 minutes or more is because if it is less than 2 minutes, the progress of spheroidization is insufficient. Furthermore, if the cold wire drawing step 12 is not performed, the speed of spheroidization will be slightly slower, so a holding time of 7 minutes or more is desirable. Regarding the upper limit of the holding time, in normal annealing, heating and holding is performed for 10 hours to 100 hours, but in the present invention, effective annealing is performed in a short time as described above, and heating and holding for more than 10 hours is not possible. Thermoeconomically unfavorable. There are two types of heat retention methods; one is to pass through an in-line heat retention furnace 15 for a required period of time before being wound around a coiler 16, as shown in the example shown, and the other is to wind the winding around a coiler. This method involves placing the subsequent raw material coil in a heat retention furnace and holding it for the required time.
In either case, the effect of promoting spheroidization by heat retention is the same. [Example] Next, the effects of the method of the present invention will be explained with reference to Examples. Test Example 1 A hot-rolled wire material made of S45C and a wire diameter of 11.0 mmφ was heated through a high-frequency heating device, then immediately subjected to bending drawing through a roll bending device, and then wound around a coiler in a heat retention furnace. A spheroidization process was performed to retain heat. The conditions for heating, wire drawing, and heat retention in this treatment are as follows. 1 High frequency heating Heating temperature: 300℃ - 900℃ 2 Warm bending wire drawing Roll diameter: 90mmφ, pitch: 130mm Number of rolls: 5 horizontally, 5 vertically Inlet wire temperature: 700℃, outlet wire temperature: 680℃ Applied elongation rate: 5% to 55% 3 Heat retention furnace Furnace temperature: 700℃, coiler diameter: 800mmφ Heat retention time: 2 minutes to 120 minutes after coiler winding Atmosphere gas: _N2 gas test example 2 Material is S45C, After heating a hot-rolled wire material with a wire diameter of 11.0 mmφ through a high-frequency heating device, it is immediately subjected to bending drawing through a roll bending device, then passed through a tunnel furnace for heat retention, and then wound onto a coiler outside the furnace. A spheroidization process was performed. The conditions for heating, wire drawing, and heat retention in this treatment are as follows. 1 High frequency heating Heating temperature: 700℃ 2 Warm bending wire drawing Roll diameter: 90mmφ, pitch: 130mm Number of rolls: 5 horizontally, 5 vertically Inlet wire temperature: 700℃, outlet wire temperature: 680℃ Applied elongation rate :55% 3 Heat retention furnace Furnace temperature: 700℃ Passage time: 7 minutes Atmosphere gas: _N2 gas Test example 3 A hot-rolled wire material made of SCM435, SCr435 and wire diameter 12.7mmφ was cold rolled and bent. After descaling through a descaling device, the wire was heated with an electric heating device, immediately subjected to warm bending wire drawing through a roll bending device, and then spheroidized by being wound around a coiler in a heat retention furnace to retain heat. . The conditions for heating and wire drawing heat retention in this treatment are as follows. 1 Cold bending wire drawing Applied elongation rate: 25% 2 Electrical heating Heating temperature: 700℃ 3 Warm bending wire drawing Roll diameter: 90mmφ, pitch: 130mm Number of rolls: 5 horizontally, 5 vertically Inlet wire temperature: 700℃, outlet wire temperature: 680℃ Applied elongation rate: 55% 4 Heat retention furnace Furnace temperature: 690℃, coiler diameter: 800mmφ Heat retention time: 15 minutes after coiler winding Atmosphere gas: _N2 gas test example 4 Material A hot-rolled wire material of S45C with a wire diameter of 12.7 mmφ is cold descaled through a roll bending device, heated with an electric heating device, immediately subjected to warm bending wire drawing through a roll bending device, and then continued. The material was passed through a tunnel furnace for heat retention, and then wound into a spheroid by winding it around a coiler outside the furnace. The conditions for heating, wire drawing, and heat retention in this treatment are as follows. 1 Cold bending wire drawing, applied elongation rate: 25% 2 Electrical heating Heating temperature: 700℃ 3 Warm bending wire drawing Roll diameter: 90mmφ, pitch: 130mm Number of rolls: 5 horizontally, 5 vertically Inlet wire temperature : 700℃, outlet linear temperature: 680℃ Applied elongation rate: 55% 4 Heat retention furnace Furnace temperature: 690℃ Heat retention time: 7 minutes Atmosphere gas: _N2 gas Under each condition according to Test Examples 1 to 4 above , 27 test materials were manufactured by continuously in-line spheroidizing various hot-rolled wire materials. For comparison, a hot-rolled wire material made of S45C with a wire diameter of 90 mmφ was processed through both pickling and lubrication processes to a diameter of 7.37 mm with a die, and then heated to 750℃ for 3.75 hours.
Hold at 750℃ for 3 hours, then 550℃ at 10℃/H.
A conventional example was obtained by performing spheroidizing treatment using the usual method of spheroidizing annealing for 26.65 hours by lowering the temperature to ℃ and then allowing it to cool.

〔Effect of the invention〕

As explained above, the continuous spheroidization treatment method for steel bars and steel wires of the present invention simplifies the process by omitting the conventional pretreatment steps such as pickling and lubrication, and also simplifies the process, and also simplifies the annealing process, which requires a long time. Since this process does not require continuous in-line processing in an extremely short period of time, it is highly effective in improving productivity and reducing costs in the spheroidizing process of steel bars and wires for cold forging.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing an example of a conventional spheroidizing method for steel wire. FIG. 2 is an explanatory diagram showing an example of a steel wire spheroidization treatment line that implements the method of the present invention. 1: Material coil, 2: Pickling device, 3: Lubrication treatment device, 4: Die wire drawing device, 5: Spheroidizing annealing furnace,
6,11: Ungoiler, 7: Dice, 8,1
6: Coiler, 10: Steel wire material, 12: Cold wire drawing process, 13: Heating process, 14: Warm wire drawing process, 1
5: Heat retention treatment step, 17: Roll.

Claims (1)

[Scope of Claims] 1. A steel bar steel wire material made of medium/low alloy steel with a carbon content of 1.5% or less is heated to a temperature of 350°C or more and 850°C or less, and the elongation rate is determined by a roll bending device in that temperature range. Give an elongation of 5% to 95% and continue to coil the coiler at 450℃ before or after winding.
1. A continuous spheroidizing method for steel bars and wires, characterized by continuously carrying out treatment at a temperature of 750° C. or lower for 2 minutes or more and 10 hours or less. 2. A steel bar and wire material made of medium- and low-alloy steel with a carbon content of 1.5% or less is subjected to cold elongation using a roll bending device at an elongation rate of 5% to 95%,
Furthermore, it is heated to a temperature of 350℃ to 850℃, and in that temperature range, the elongation rate is 5 by roll bending equipment.
% or more and 95% or less, and is continuously subjected to a treatment in which the coiler is held at a temperature of 450°C or more and 650°C or less for 2 minutes or more and 10 hours or less before or after winding. Continuous spheroidization treatment method for steel wire bars.