JPS6056211B2 - Continuous heat treatment method for carbon steel rods and wires - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for heat treatment of carbon copper rods and wires, and in particular, after heating the copper rods and wires to a temperature higher than the Ac state temperature, during the cooling process, pressure is applied to the wires with a die. In addition, by rapidly cooling to just above the transformation point and then transforming, a uniform and fine transformed structure is provided.

In the production of carbon copper rods and wires, a patenting method is generally used as a heat treatment method to improve material properties such as toughness and strength.

In this process, a wire heated to a temperature higher than the Ac transformation point is sent to a bath controlled at a constant temperature (usually about 500 to 550 degrees Celsius) to rapidly cool it, and is maintained at the same temperature to undergo isothermal transformation. This is intended to obtain a transformed structure consisting of fine pearlite and the like. Lead baths are widely used for this treatment. A lead bath has a very large cooling capacity and a large heat capacity, so it is extremely suitable as a refrigerant, and a uniform and fine transformed structure can be obtained. However, even when processing using a lead bath, as the diameter of the wire to be treated increases, the temperature drop in the center of the wire during the cooling process is slower than that in the surface layer, so the temperature difference increases. A uniform metamorphosed tissue cannot be obtained.

This tendency is particularly strong in steel types with a short transformation start time, making it extremely difficult to obtain a desired patenting effect. As a countermeasure to this, steels have been proposed in which the start of transformation is delayed by adding appropriate alloying elements, and the composition is devised so that transformation begins when both the center and surface parts of the wire are cooled to a predetermined temperature. However, since this also involves a delay in the completion time of transformation, it is necessary to lengthen the residence time of the wire in the lead bath, which has the disadvantage of significantly deteriorating processing efficiency.

Further, addition of a large amount of alloying elements often has an unfavorable effect on the material properties of the wire rod. In order to solve this problem, the inventors of the present invention filed an earlier application (Japanese Unexamined Patent Publication No.
In JP-A No. 1291-1291-1, Japanese Patent Laid-Open No. 54-6950), we proposed a heat treatment method that takes advantage of the fact that phase transformation of a metal material can be delayed by cooling the metal material under pressure.

The present invention relates to improvements in these heat treatment methods, and in particular uses a continuously moving die as a pressurizing means, and uses the pressurizing and quenching effect of the die to impart a uniform transformed structure to the carbon-copper rod and wire. This is what I did. That is,
The present invention uses Ac. After being heated to a temperature above the transformation point to austenite, the wire is cooled to just above the transformation start temperature while pressurized by a mold dozen that moves in synchronization with the feeding speed of the wire, and then the pressure is removed. To provide a continuous heat treatment method for causing transformation. According to the present invention, pressure is applied by a die to the steel rod and wire heated to the austenitizing temperature during the cooling process.

This operation is performed, for example, as shown in FIG. 1, by pressing mold dies 1, 1'' against the steel rod wire M with an appropriate pressure force.Adjusting the pressure force by this die,
By applying a pressure sufficient to supercool the wire to a temperature that causes a predetermined transformation, uniform transformation can occur at the time when both the surface layer portion and the inside of the wire reach the predetermined temperature. Furthermore, if the pressure is removed just before the start of transformation, the end of transformation will not be delayed. Note that the heat treatment according to the present invention may be applied to the carbon steel rod and wire rod after hot rolling. The die functions not only as a pressurizing means but also as a refrigerant for rapidly cooling the steel rod and wire.

Therefore, if the die temperature is adjusted to a predetermined transformation temperature in advance and the wire is pressurized, it is possible to supercool the wire to that temperature without causing transformation, and the die can be removed once the same temperature is reached. Therefore, isothermal transformation can occur at that temperature. For example, set the die temperature to about 50
Adjust the temperature to 0 to 550℃, and apply a pressure of about 100kg.
/Tni. A uniform fine pearlite structure can be obtained by compressing the steel rod and wire rod, supercooling it to this temperature, and then removing the die. FIG. 2 shows a specific example of a pressurizing device for steel rods and wires.

The device consists of a plurality of mold dies 1, 1'' arranged opposite to each other with a steel rod wire M in between, and pressure rolls 2 arranged so as to come into contact with the back surface of the dies on each side. , 2″. The dies on each side are connected in a chain, each forming a loop surrounding the rollers 2, 2''.
, 2" is moved in the direction of the arrow. The moving speed of the die is adjusted by the rotational speed of the rolls 2 and 2" so as to be synchronized with the feeding speed of the steel rod and wire to be processed. Ru. The steel rod wire M heated in the heating furnace to a predetermined temperature higher than the AC3 transformation point is continuously passed through dies '1,
It is fed during 1″.

The dies 1 and 1'' move together with the steel rod and wire rod M due to the rotational drive of the rolls 2 and 2'', and as they pass between the rolls 2 and 2'', they receive a pressure force L from the rolls, which applies pressure to the steel rod and wire M. The pressure on the steel rod and wire rod is adjusted to an appropriate value by the pressing force of the rolls 2, 2'' on the back of the die. The mold die has a large cooling capacity due to its thermal conductivity and heat capacity, and can provide a cooling effect on steel rods and wires comparable to that of a lead bath.

Figure 2 ■ shows the temperature change (solid line) of the steel rod and wire rod caused by the above device.
and the applied pressure status (dashed line). When the steel rod and wire rod are sandwiched between dies and pressed with rolls, AC3
Pressure P is applied at the same time as rapid cooling from a predetermined temperature T1 above the transformation point to T2. In this case, the degree of cooling of the steel rod wire varies depending on the die size, moving speed, etc. For example, for a steel rod wire with a wire diameter of about 9 to 14 mm, a length of about 30 mm
~Uses 15011r1R dice, movement speed approximately 30
Loading at ~200c1/min, pressure approximately 50~150k9
/ml, the temperature ranges from about 900 to 110 (s) above the AC3 transformation point to about 500 to 550C.
The microparticles are supercooled to a temperature of 100%, and fine pearlite, which is a transformed structure at the same temperature, is obtained. Note that the pressure on the steel rod and wire rod during passage through the rolls in the above device is maintained by the frictional force between the steel rod and wire rod and the die.

Continuous isostatic extrusion equipment is known as a pressurizing method that uses such frictional force, but since this equipment uses frictional force as a pulling force for the material, there is no need for sudden temperature rises during pressurization. accompanied by a rise. On the other hand, in the above device, the pulling force of the material (steel rod and wire rod) is given by the rotational drive of the rolls 2, 2'', and the frictional force is mainly involved in maintaining the pressure, so even when the rolls are compressed. There is almost no temperature rise and it is possible to cool to a predetermined temperature.
As shown in the figure or FIG. 4, one or both of the pressure rolls can be constructed of a plurality of small rolls 3, 3'' arranged in parallel.

By supporting and pressing the die with a plurality of small rolls in this manner, the pressure distribution on the steel rod and wire rod is made uniform, and a stable pressing effect can be obtained. In particular, if small rolls are used on both sides and pressure force is applied to multiple dies as shown in Figure 4, depending on the number of dies,
The pressurizing and cooling effects of steel rods and wires can be adjusted as desired. In addition, in order to increase the processing efficiency of steel rods and wire rods, when processing multiple steel rods and wires at the same time, it is possible to arrange multiple dies as shown in Fig. 5 or to use multiple dies as shown in Fig. 6. A die with book grooves can also be used.

When processing steel rods and wires using the above equipment, the die in contact with the steel rods receives conduction heat from the steel rods and wires, but if the shape of the die is designed appropriately, the heat can be balanced with the heat dissipated from the die surface, and the die can be constantly Steel rods and wires can be pressurized at a constant die temperature.

When the die temperature rises, the die after passing through the pressure roll may be cooled by an appropriate cooling means such as air cooling or water cooling, and the die may be maintained at a predetermined temperature at all times. In addition,
The steel rods and wires that have undergone the above treatment may have fins in the portions corresponding to the gaps between the dies, so in that case, they can be removed by machining.

Next, the present invention will be specifically explained with reference to Examples.

EXAMPLE Heat treatment of high carbon steel rods and wires was carried out using a pressurizing apparatus as shown in FIG. 2 above.

The processing conditions are as follows. (4) Steel rod wire composition: C
O. 82%, SiO. 2%, MnO. 5% Wire diameter: 12 order φ Heating temperature: Approximately 950°C (B) Pressure device die size Length 10'', Groove diameter 12T! The n1 die pressurizing force was 2120 tons (pressure 100 kg/Td), the die temperature was maintained at approximately 550°C, and under the above conditions, the steel rod and wire were fed at a linear speed of 50 C1f1/min (dice pressurizing time when passing through the rolls). (approximately 12 seconds), from approximately 900°C to 550°C under pressure.
The mixture was cooled to ℃, then released from die pressure, and transformed from the same temperature.

Note that no fins were generated in the wire due to pressurization of the die. The hardness distribution of the obtained steel rod and wire rod is shown by curve i in FIG.

In the figure, curve 11 is a value obtained by patenting a steel rod and wire rod of the same steel type and wire diameter as above (using a lead bath). The steel rod and wire rod obtained by the present invention have higher hardness over the entire cross section of the wire than lead patented material,
It is also seen that the distribution is flat and has a uniform and fine transformed structure.

[Brief explanation of the drawing]

Fig. 1 is a side view illustrating the shape of the die, Fig. 2 I is a schematic diagram showing a specific example of the pressurizing device, Fig. 3 and 4 are schematic diagrams showing other specific examples of the pressurizing device, FIG. 5 is a diagram showing an example of the die arrangement mode, FIG. 6 is a side view showing another specific example of the die shape, and FIG. FIG. 7 is a graph showing the hardness distribution in the cross section of the steel rod and wire rod. The main symbols in the drawings are as follows. 1,1゛: die, 2,2'': pressurized roll, 3,3'': pressurized small roll, M: steel rod and wire rod.

Claims (1)

[Claims] 1 After heating a carbon steel bar wire rod to a temperature equal to or higher than the Ac_3 transformation point, the wire rod is held under pressure with a mold die that moves continuously in synchronization with the feeding speed of the wire rod, and the wire rod is placed under pressure. 1. A continuous heat treatment method for carbon steel rods and wires, which comprises cooling the wire to a transformation start temperature, and then removing the pressure to transform the wire.