JPS5848017B2 - Intermediate annealing method for steel wire for welding - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for intermediate annealing of steel wire for welding.

Steel wire for welding is usually hot rolled. The wire is cold drawn to a specified wire diameter. When the area reduction rate (processing rate) increases to a certain extent, the degree of hardening due to processing also increases (usually 14% in tensile strength).
0 kg/mA is considered to be the economical limit of processing.

) If you perform one more cold wire drawing. Wire drawability will deteriorate dramatically, such as the die becoming rough or the wire breaking. Intermediate annealing is performed during wire drawing.

This is particularly noticeable in steel wires for carbon dioxide gas arc welding (JIS Z3312) type 1 or 3 wire rods. If the wire is hot rolled, the tensile strength of the wire itself will vary. This variation is inherited even after cold wire drawing. % Kaisho 5
As disclosed by Publication No. 1-101746. This has a negative effect not only on wire drawability but also on welding workability. Also from this point of view, intermediate annealing is performed during cold wire drawing.

Conventionally, as intermediate annealing conditions for stress relief, heating for a long time of about 1 hour or more in a temperature range of about 450 to 700° C. below AC1 point has been adopted.

The reason is as follows.

Ordinary C-S i -M n steel wire for welding is. AC1
When heated above this point, the γ phase begins to precipitate. Heating temperature. It depends on the time. Gradually increase the particle size. If it is air cooled as it is, it will work fine for mild steel wire rods. Ferrite. Pearlite particles become finer. Moreover, it becomes an intermediate stage organization such as Pay Knight. In addition, martensite is generated in HT wire rods. The hardness is almost the same as or even higher than that of the wire before intermediate annealing, so there is no point in intermediate annealing. On the other hand, an annealing temperature of 450°C or lower requires extremely long heating times, for example 1000 hours, to sufficiently soften the material. The annealing conditions described above are used.

However, even the conventional intermediate annealing conditions described above have the following drawbacks.

(1) Annealing requires a long time (about 1 hour or more). Unable to perform continuous processes. It's inefficient.

In other words. Even if a high-speed continuous wire drawing process is adopted. Once the wire is wound onto a bobbin, etc. We have no choice but to use a batch method in which this is placed in an annealing furnace and annealed for several hours. It is impossible to continuously perform the wire drawing process and the annealing process.

(2) Since annealing takes a long time, fuel costs are high. Significant economic loss.

(3) Since annealing takes a long time, atmospheric annealing is virtually impossible. There is an equipment problem in that the process must be carried out under an inert atmosphere to prevent the oxidation of the raw material.

The present invention was developed in view of the above-mentioned circumstances. In addition to reducing the time and continuity of the intermediate annealing process during cold drawing of hot rolled steel wire for welding. This was completed as a result of intensive research to fully demonstrate the effects of intermediate annealing, especially in reducing variations in tensile strength.

The basic idea of the present invention is to soften the α phase hardened by cold working by recrystallization in an extremely short period of time.
At this time, the purpose of intermediate annealing is achieved by suppressing the precipitation of harmful γ phase to about 30φ or less.

The gist of the present invention is as follows. For cold drawing of hot rolled steel for welding. Cold drawn wire rod. Before starting the next cold wire drawing process. In the temperature range of AC1 or higher and AC1 + 70°C or lower. The α phase hardened by cold working recrystallizes. After holding for a time such that the precipitation ratio of the γ phase is approximately 30φ or less in terms of area ratio. A method for intermediate annealing of a steel wire for welding, characterized by cooling at a cooling rate lower than air cooling.

The structure and requirements of the present invention will be explained.

The reason why the heating temperature is limited to AC1 or more and AC1+70°C or less in the present invention will be described.

At a heating temperature of AC1 or lower, it takes a long time to recrystallize and soften the α phase hardened by cold working.

On the other hand, if the heating temperature exceeds AC1+70℃. γ phase**
The precipitation rate is approximately 30 fO or more in terms of area ratio. C-Si-
In Nn-based steel wires, depending on the cooling rate, a hardened structure may be formed or the purpose of annealing may not be achieved.

In the present invention, the heating and holding time is set within a range in which sufficient recrystallization of the α phase occurs but does not result in precipitation of the γ phase in an area ratio of about 30% or more.

This holding time is necessary and sufficient to relieve stress and reduce variations in tensile strength.

Specifically, when using a heating means by resistance heating or induction heating, the lower limit is 8 seconds.

Also, when using heating means using hot air. It is necessary to consider the time required for heat to be transferred from the surface of the wire to the center and uniformly heated. Experimentally, the time that satisfies the following equations (1) and (2) at the same time is the lower limit.

T (eog 1o +16.4)≧1.4000
+40 8・-<1) T: Heating holding temperature (0K) t: Heating holding time (seconds) S: Tensile strength of wire before annealing (kg/mA) t>4
D2 ・・・・・・・・・ (2) t: Heating holding time (seconds) D= Diameter of wire (Z) Next, the reason why the cooling condition in the present invention is set at a cooling rate lower than air cooling is that At the cooling rate, when the γ phase transforms into the α phase, a hardened structure such as martensite or lower venant occurs. This is because intermediate annealing becomes meaningless.

The present invention will be explained based on Example 1.

Examples Table 1 shows the specifications of the hot rolled steel wire rods tested in Examples.

Figure 2 shows the relationship between the heating holding temperature with hot air and the tensile strength when the heating holding time is constant, and the holding time and tensile strength when the heating holding temperature is constant for these test wires. ~ Shown in Figure 5.

Figure 2 shows three types of wire rods each having approximately the same tensile strength as sample wire rod 1 before annealing. FIG. 3 is a diagram showing the influence of heating temperature on tensile strength after annealing at a holding time of 60 seconds.

As is clear from this figure, the tensile strength before annealing is approximately 10
0 kg/my? The tensile strength, which was t, significantly decreased to approximately 60 kg/mm after the 1 point hAc. This tensile strength remains almost unchanged up to Ac1+70℃. It can be seen that at temperatures higher than that, the tensile strength increases rapidly.

That is, the annealing temperature is Acl~A. c 1 +7 0
It shows that you should choose a temperature range of ℃.

Figure 3 shows that the variation in tensile strength before annealing is approximately 99~l l
Three types of wire rods with a weight of 2 kg/mi ■1. Figure 4 shows that the tensile strength before annealing varies from approximately 105 to 115.
kg/m4 of 3 types of wires and heating retention time 6
This is a diagram showing the effect of heating temperature on tensile strength at 0 seconds. As in the case of Fig. 2, the tensile strength suddenly decreases at the holding temperature AcI point. It can be seen that the variation in tensile strength also decreases, and this tendency is maintained up to the holding temperature of =Ac 1 +70°C, and that the tensile strength increases when the temperature exceeds Ac 1 +70°C.

From these figures, it can be seen that the heating holding temperature is set to Ac 1 according to the present invention.
It turns out that the temperature should be selected within the range of = Ac 1 +7 0°C.

FIG. 5 is a diagram showing the influence of the holding time (seconds) on the tensile strength of the wire I at a constant heating temperature of 750°C.

From this figure, the holding time (seconds) is at least t=4D2 (16 seconds since the wire diameter is 2 mm) or T0ogto
+ 16.4 = 1 8 0 0.0 must be selected. In other words, it is shown that when using a heating means using hot air, the purpose of intermediate annealing can be sufficiently achieved by holding it for at least 16 seconds.

According to the research I of the present inventors. It has been confirmed that Equations 1 and 2 are applicable to wire diameters in the range of about 0.8 to 32 mm.

As is clear from the above examples, 1. According to the present invention, intermediate annealing of steel wire for welding can be carried out in an extremely short time. Continuity of the cold wire drawing process and the intermediate annealing process is essential, especially when continuous processes such as the loop mouth method or helicofil method are adopted. The effects of the present invention can be significantly exhibited.

Furthermore, according to the present invention, variations in tensile strength can be significantly reduced. It is also possible to reduce the variation in tensile strength of the wire rod after wire drawing, which adversely affects welding workability.

Furthermore, according to the present invention, the amount of scale generated on the wire surface is reduced by shortening the intermediate annealing process. It can be annealed in the atmosphere.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the annealing conditions (shaded range) for test wire 1 using hot air within the scope of the present invention. Figures 2 to 4 are diagrams showing the influence of heating humidity on the tensile strength after annealing (air cooling) for each test wire (I~dish) at a heating holding time of 60 seconds with hot air. Figure 5 shows sample wire I after annealing (
FIG. 3 is a diagram showing the influence of heating holding time on the tensile strength (air cooling).

Claims (1)

[Claims] 1. When cold drawing hot rolled steel wire for welding. Cold drawn wire rod. Before starting the next cold wire drawing process 1,
In a temperature range of 1 or more Ac 1 + 70°C or less, the α phase hardened by cold working recrystallizes, but after being held for a time such that the precipitation ratio of the γ phase is about 30φ or less in terms of area ratio. A method for intermediate annealing of steel wire for welding, characterized by cooling at a cooling rate lower than air cooling.