JPH03287743A - Low carbon nonaging wire rod excellent in machinability and workability - Google Patents

Abstract

PURPOSE:To manufacture a low carbon nonaging wire rod excellent in machinability and workability by preparing a steel having a specified compsn. in which the content of S and Nb is regulated. CONSTITUTION:A low carbon nonaging wire rod constituted of <=0.01% C, <=0.03% Si, 0.1 to 0.3% Mn, 0.010 to 0.025% S, <=0.03% Al and 0.04 to 0.1% Nb, in which the balance amt. of N is regulated to Nb/(C+N)>=7 and the balance inevitable impurities and steel components is prepd. In this way, the steel wire in which age hardening at the time of cold forging can be suppressed and provided with good machinability and workability can stably be obtd.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention is applicable to steel wire drawn with a high area reduction ratio, cold working by flat rolling, and cold working of bolts, nuts, spark plugs, etc. of complicated shapes. The present invention relates to wire rods used in the field of intermediate forging.

[Prior Art] A conventional technique for improving workability by suppressing age hardening that occurs during cold working is proposed in Japanese Patent Publication No. 62-52015. In this invention, B and Nb are added as additive elements mainly to suppress C and N aging.

This method is characterized by using steel added with Ti and controlling the cooling rate after rolling the wire rod. With this invention,
Although the tool life has been dramatically improved compared to conventional materials, the amount of age hardening has not been completely suppressed. For this reason, it cannot be said that it still has sufficient characteristics for the multi-pass processing that will occur in the future as high-speed processing and shapes become more complex. Furthermore, since the ductility is too high, problems such as poor machinability remain.

The present invention is based on the study of the optimum components for improving machinability by reducing the amount of age hardening to zero in contrast to the above-mentioned patents.

[Problems to be Solved by the Invention] Various production machines in the field of cold working and forming are oriented towards higher speeds in order to improve productivity.

Furthermore, as the shapes of products to be cold forged are becoming more complex, multi-stage forming processes with multiple punches are becoming mainstream in production machine structures. When performing multi-stage machining at high speed,
The issues are tool life and cutting stability.

The object of the present invention is to completely suppress age hardening during high-speed processing, which could not be achieved with conventional techniques, and to provide a wire rod with excellent cold workability that has good machinability and workability.

[Means for solving the problem] In the process leading to the present invention, the present inventors
We investigated the mechanism of suppressing age hardening by the i element and found knowledge that can overcome the above-mentioned problems.

In other words, Ti fixes C and N and suppresses aging, but at the same time, Ti also reacts with S in the steel, causing Ti
The fact that S becomes S or Ti2S and S is fixed was revealed by observation using a transmission electron microscope.

This suggests something technically important.

That is, S is an effective element for machinability, but when Ti is added, S reacts with Ti, so the effect of S is not fully exhibited. The present inventors focused on Nb, which has a smaller tendency to form sulfides than Ti, as a means to suppress age hardening, and conducted various studies with the aim of inventing a wire rod that completely suppresses age hardening and has excellent machinability. layered. As a result, we have experimentally discovered a new fact that age hardening can be completely suppressed by controlling the Nb content (C+N) ratio to 7 or more as shown in FIG. Furthermore, with regard to machinability, which is another problem with the prior art, consideration has been given to ensuring that the effect of S is sufficiently exhibited.

That is, in the present invention, C: 0.01% or less, Si:o
, 03% or less, M n : 0, 1-0, 3%, S
: 0.010-0.025%, AQ: 0.0.3
% or less, Nb: 0.04 to 0.1%, N is the amount of Nb (C+
N) A steel with excellent workability and machinability, which is adjusted to a balance amount of ≧7, and has a steel composition with the remainder consisting of unavoidable impurities, and is characterized by completely suppressing aging during cold working. It is a carbon non-aging wire.

[Effect] Next, the reason for limiting the ingredients of the present invention will be described.

C is a basic element that controls the strength and ductility of steel, and the strength increases as C increases.The present invention sets the upper limit to 0.01% from the viewpoint of suppressing C aging.

Si is selectively oxidized and enriched on the steel surface, significantly impairing plating properties and mechanical descaling properties.

For this reason, the upper limit was set at 0.03%.

Mn is used as a deoxidizing element, and the lower limit was set at 0.1% because below this level, bubble defects occur, making it impossible to obtain a good steel wire surface, and inhibiting flash butt welding performed during the manufacturing process. In addition, the amount of MnS that is effective during cutting decreases, making it impossible to obtain good machinability. Set the upper limit to 0.
The reason why it is set at 3% is that if it exceeds this value, the strength will increase and this will be disadvantageous to the tool life.

S is one of the elements that plays an important role in the present invention. In order to improve machinability, it is necessary to increase the amount of S, but excessive addition induces cracking during cold forging. Therefore, its use is naturally subject to restrictions. The reason why the lower limit is set to 0.01% is because machinability cannot be ensured below this, and the reason why the upper limit is set to 0.025% is because workability deteriorates.

Al is used only as a deoxidizing element, and is determined based on the balance with the amount of Mn. The upper limit was set at 0.03% mainly for economic reasons.

Nb is an element that plays an important role in the present invention.

Since Nb fixes N as NbC and NbN, it is an element that suppresses age hardening during high-speed processing.

In order to understand the effect, after giving 8 and 10% prestrain, artificial aging was performed at 100° C. for 1 hour, and the aging index (age hardening amount) was measured by the method described later.

The results are shown in FIG. As is clear from these results, as the amount of Nb added increases, the aging index decreases rapidly, making it difficult for age hardening to occur. What is noteworthy is that the aging index becomes zero and no age hardening occurs at all. Lower limit of Nb to 0.04%
The reason for this is that, as shown in FIG. 1, if the amount of Nb is less than this, age hardening cannot be sufficiently suppressed.

The reason why the upper limit is set to 0.1% is that the effect is saturated if the amount of Nb is higher than this.

N is an element that accelerates aging, and in the present invention, the smaller the amount, the more preferable. In the present invention, the amount of N is
The reason why N)≧7 was determined from the Nb amount (c+N) and the twenty-gin gain index shown in Figure 2. If the N amount does not satisfy this relationship, age hardening cannot be completely suppressed and the tool life will be shortened. This is because it deteriorates. Describing a specific implementation method that satisfies the Nb amount (C+N)≧7, the N amount can be reduced to 0.0028% by taking into account the operational variations in Nb and C.
It will be easier to control N if it is managed as follows.

(Example) Examples will be described below.

Table 1 shows examples of the invention. Both the inventive steel and the comparative steel were melted in a 250 ton converter, continuous casted into an ingot, bloomed into a billet, and then wire rod rolled into a 5.5 m wire rod. Table 1 shows the chemical composition and mechanical properties of the invention steel and comparative steel. Steel types A to E indicate the steels of the present invention. F ~ indicates comparative steel. Table 2 shows the amount of strain age hardening (Zinge index). The aging index was measured by the method shown in Figure 3. After applying pre-strain, artificial aging treatment was performed at 100°C for 1 hour and re-stretching was performed, and A and I in Figure 3 were measured. This is what I did. The smaller this value is, the less age hardening the material becomes. As is clear from Table 2, the aging index of the steel of the present invention is superior to that of the comparative steel. In particular, steel type A of the steel of the present invention.

It can be seen that in B, C, D, and E, the Nb amount (c+N) ratio is 7 or more, and the aging suppressing effect is significantly impaired.

Comparative steels F and H indicate those without Nb addition.

Comparative steel G is a comparative steel prototyped in the process of the present invention.
This is the level where a small amount of is added. The aging index of comparative steel G shows a value of 4.6 to 5.2, and the aging index of comparative steel G shows a value of 4.6 to 5.2.
The amount of aging is smaller than G. This is due to the effect of Nb, but the amount of Nb is 0.02%, which is lower than that of the steel of the present invention. Therefore, it can be seen that the effect is insufficient.

As described above, the present invention provides a material having an excellent age hardening inhibiting effect.

Next, machinability and workability will be explained.

The present inventors evaluated the machinability and workability in the case of cold forging from the following viewpoints. When steel wire is continuously cold forged (rei is bolt processing).

Nail forming processing), the cut surface cut by the cutter comes into contact with the processing punch surface and the next product is formed.

In this case, if there is a free surface during cold forging, the product shape will be affected by the shape of the cut surface. In other words, if the cut surface is parallel to the processing punch surface, the product shape will be stabilized. Therefore, the nail was formed using a nail making machine, and the deviation of the major axis and minor axis of the nail head was determined. The results are shown in Table 3, where the deviation is 1/100 mm or less, expressed as 0, and the deviation greater than 1/100 mm is expressed as x.For workability evaluation, microcracks in the nail head were observed.

From the results in Table 3, all of the steels A to E of the present invention have a machinability of 0. This indicates that the shape of the cut surface cut by the cutter is stable.

On the other hand, comparative steels F and G have a small amount of S and are highly ductile, so the cut surface of the cutter cannot be cut smoothly and the cut surface cannot be fed parallel to the processing punch surface. Comparative steel H has good machinability and workability, but as shown in Table 1, the amount of aging is large. Comparative steel weight is S
Micro-cracking occurs on the side surface of the nail head due to the large amount.1 As explained above, it can be seen that only the steel of the present invention satisfies the low 21 Jinge index, machinability, and workability. .

[Effects of the Invention] As described above, according to the present invention, it is possible to stably supply a steel wire that can suppress age hardening during cold forging and has good machinability and workability. In particular, even if the material temperature rises due to high-speed machining and multi-stage baths that will become increasingly popular in the future, the amount of age hardening can be completely suppressed, resulting in a longer tool life. In addition, since it has good machinability and workability, the product dimensions are stable when it has a free surface during forging. These characteristics not only have the direct effect of reducing forging tool material costs, but also eliminate the hassle of tool replacement, improving productivity and contributing to cost reduction.

[Brief explanation of drawings]

Figure 1 shows the relationship between aging index and Nb amount, and Figure 2 shows the relationship between aging index and Nb amount (C+N).
FIG. 3 is a diagram showing the aging index measurement method.

Claims (1)

[Claims] C: 0.01% or less, Si: 0.03% or less, Mn: 0
．． 1-0.3%, S: 0.010-0.025%, Al
: 0.03% or less, Nb: 0.04 to 0.1%, N is N
A low carbon non-aging wire rod with excellent machinability and workability, characterized by having a steel component adjusted to a balance such that b/(C+N)≧7 and the remainder consisting of unavoidable impurities.