JPS61520A - Manufacture of high-strength and high-ductility steel wire - Google Patents

Abstract

PURPOSE:To obtain a low-carbon steel wire having high strength and ductility and excellent weldability by wire-drawing a steel wire rod of a low-alloy steel whose Al/N ratio is specified, and subjecting the wire to two-stage annealing at appropriate temps. CONSTITUTION:A steel wire rod, consisting of <=0.1wt% C, <=0.3% Si, 0.1-0.6% Mn, 0.005-0.1% Al, N specified by an Al/N ratio of 2.5-7.5, and the balance Fe and inevitable impurities, is wire-drawn at >=50% total reduction of area. Then the wire is primarily annealed by keeping the temp. at 500-600 deg.C, and then secondarily annealed by keeping the temp. at 600-750 deg.C. The precipitation of AlN can be controlled with said steel composition, amt of wire to be drawn, and annealing conditions, and a low-carbon steel wire having high strength and ductility can be manufactured.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a method for manufacturing high-strength and high-ductility steel wire that is widely used for screws and screws, wire mesh, glass-enclosed wire, plated steel wire, etc. .

(Prior art and problems) Conventional methods for providing high strength and high ductility include:
For example, regarding rivets and screws, JP-A-50-51920
No., JP-A-50-51921, JP-A-55-4192
Seed-tooth-V system and Mn-T represented by each publication No. 7 cage
Non-tempered steel that is controlled and rolled using i-series, and tempered steel that is quenched and tempered alloy steel to which Cr and Mo are added are used. However, it is difficult to obtain homogeneous mechanical properties in non-temperature control rolled materials.

Tempered steel has a high C content, so it has a limited ductility and is expensive to manufacture. Further, in the case of a glass-encapsulated wire, if the strength is increased by increasing C, a problem arises in that bubbles are likely to occur. On the other hand, increasing the strength of wire mesh and plated steel wire with carbon is limited due to the deterioration of cold workability and bending properties of spot welds, and problems remain, such as difficulty in achieving the desired strength and ductility. .

(Object of the Invention) In order to solve the above-mentioned problems, the present invention stabilizes ultra-fine grain steel by utilizing the precipitation of aluminum nitride (hereinafter referred to as AtN) in order to obtain a high-strength, high-ductility steel wire. This paper proposes a manufacturing method for steel wire that can be obtained by

With the establishment of the present invention, the problems of the prior art have been solved, and it has become possible to produce high strength and high ductility steel wire at low C.

(Means for Solving the Problems) The present invention includes CO, 1wt% or less, Si 0.3wt% or less, seeds 0.1-0.6wt%, At0OO5-0.1
wt% and AA wt%/N wt% ratio of 2.5 to 7
．． Using a steel wire rod containing N in a range of 5°C and the balance consisting of iron and unavoidable impurities, the wire rod is drawn at a total area reduction of 50% or more, and then heated to a temperature range of 500 to 600°C. One frame held for 30 minutes or more: Next annealed, followed by secondary annealing held at a temperature range of 600 to 750°C for 30 minutes or more, or after the first annealing, wire drawn with a total area reduction of 20% or more. This is a method for producing a high-strength, high-ductility steel wire, characterized in that the wire is then subjected to the secondary annealing to obtain properties such as a tensile strength of 5QKg/ran2 or more and a reduction of area of 80% or more.

The reasons for determining the component range, processing conditions, and annealing conditions in the present invention will be described below.

C is a basic element that controls the strength and ductility of steel, and as C increases, the strength increases and the ductility deteriorates.

In the present invention, the upper limit is set at 0.1 wt% as a range that ensures high ductility and does not deteriorate the cold workability and bending properties of the welded part.

Si is useful as a deoxidizing element 7, but on the other hand, as the amount of Si increases, ductility deteriorates. The upper limit is 0.3wt%
The reason for limiting this is that as the amount of Si increases, ductility deteriorates, and plating removability and mechanical descaling properties are significantly impaired.

Earth is a deoxidizing element and an element that suppresses hot embrittlement caused by S. The reason why the lower limit is set at 0.1 wt% is that if the content is lower than this, hot embrittlement caused by S cannot be suppressed. Furthermore, the reason why the upper limit is set at 0.6 wt% is due to economic reasons.

At is a strong deoxidizing element and is an essential element for cleaning steel, as well as an element that combines with N in steel to form AtN. The reason why the lower limit of At is set at 0.005 wt% is that if it is less than this, the deoxidation of the steel will be insufficient, and the amount of fine AtN precipitation of 0.1 μm or less, which will be described later, will be insufficient. The upper limit was set at 0.1 wt% because of deoxidation and A
This is because the tN precipitate generation effect becomes saturated above this point.

Next, the reason for limiting the component ratio of A2 and N will be described. The present inventors conducted a detailed study on the relationship between the size and quantity of A7N precipitated during annealing and the size of ferrite crystal grains after annealing, and as a result, the following became clear. That is, as the number of fine AtN0 of 01μ or less increases, the ferrite crystal grain size after annealing becomes smaller. In addition, the number of fine AtN precipitations of 0.1μ or less is determined by the At wt%/Nwt% ratio of 2.
It has been experimentally discovered that it increases significantly in the range of 5 to 7.5. Based on the above results, the Atwt%/Nwt% component ratio was set to 2.
．． It was limited to 5 to 7.5.

The reason why the wire drawing area reduction ratio is set to 50% or more is to increase the precipitation sites of AtN such as slip deformation zones and uniformly disperse fine AtN, and a sufficient effect is not obtained when the wire drawing area reduction ratio is 50% or less. I can't do it.

- The reason why the secondary annealing temperature is 500 to 600°C is to promote the precipitation of fine AtN during the recovery stage of the processed structure. The lower limit was set at 500°C because below 500°C, the amount of AtH precipitated is small and recrystallized grains are not sufficiently refined.The upper limit was set at 600°C because the size of AtN that precipitates above 600°C. becomes larger, and the target fine A
This is because tN cannot be obtained and, as a result, recrystallized grains cannot be refined. - The reason why the subsequent annealing time is set to 30 minutes or longer is that if it is shorter than 30 minutes, precipitation of M prisoners will be insufficient and the desired effect will not be obtained.

The reason why the secondary annealing temperature is limited to 600 to 750°C is to complete recrystallization.

The reason why the upper limit is set to 750°C is that if the temperature is higher than 750°C, crystal grains will become coarse due to secondary recrystallization phenomenon, making it impossible to obtain high strength.

The reason why the lower limit is set to 600°C is that recrystallization becomes insufficient below 600°C, leaving a processed structure and making it impossible to obtain high ductility. The reason why the secondary annealing time is set to 30 minutes or more is because if it is 30 minutes or less, recrystallization is insufficient and high ductility cannot be obtained.

- If wire drawing is performed with a total area reduction of 20% or more between the secondary annealing, - dislocations due to the wire drawing will multiply around the fine AtN precipitated in the - next annealing, and - next crystal grains will be generated. We have experimentally determined that this has the effect of making the particles even finer. 20%
High strength and high ductility steel wire can be easily obtained by the above wire drawing process. However, the effect is insufficient when wire drawing is less than 20%.

(Example) Table 1 shows the steel compositions of the present invention steels (A, B, C) and conventional steels (D, E).

For each of these steels, 250 steel was melted in a converter, continuously cast, then bloomed into a 117wn96 billet, then hot rolled into a 5.5 m+nl wire rod, and cooled in a Stelmore cooling facility. Table 2 shows the properties of the steel wire obtained after drawing and annealing the wire.

As is clear from the results in Table 2, the steel wire manufactured by the method of the present invention (level 3.4.7.8.10.11) has a ferrite grain size number of 11 or more, and has high strength and high ductility. A steel wire was obtained. In addition, level 1.2.5.6.9 is the steel of the present invention, but the annealing conditions are not the method of the present invention at °C, and the amount of AtN precipitation of 0.1μ or less is reduced.
High strength cannot be obtained through grain refinement. Levels 10 and 11 vary the amount of wire drawing after primary annealing.

As is clear from the comparison between the two, when the wire drawing area reduction rate is 30% between secondary annealing and secondary annealing, higher strength is achieved, but when it is 15%, there is no effect. It is enough. In addition, conventional steel (level 12.13) was annealed using the method of the present invention, but recrystallization was 1.5 yen due to insufficient number of fine AtN precipitates during annealing. It progresses smoothly, and the ferrite grain size number is 7.2 to 8.0, and although it has ductility, high strength cannot be achieved. Level 14 is a conventional steel annealed using the method of the present invention. Due to the high C content, it is easy to achieve high strength, but the ductility is degraded.

(Effect of the invention) With the steel composition, wire drawing amount, and annealing conditions described in the present invention, At
As a result of controlling the precipitation state of N and refining the recrystallized grains, it is possible to produce a low carbon steel wire with high strength, high ductility, and excellent weldability. By applying the present invention, cold forgeability, spot weldability, bending properties, etc. of studs and screws, wire mesh, glass-enclosed wire, plated steel wire, etc. can be improved.

Claims (1)

[Claims] 1 C0.1wt% or less, Si0.3wt% or less, Mn
0.1-0.6wt%, Al0.005-0.1wt%
Using a steel wire rod having an Alwt%/Nwt% ratio of N in the range of 2.5 to 7.5, with the balance consisting of iron and unavoidable impurities, the wire is drawn with a total area reduction of 50% or more. After this, primary annealing is performed by holding in a temperature range of 500 to 600°C for 30 minutes or more, followed by annealing at a temperature of 600 to 750°C.
A method for producing a high-strength, high-ductility steel wire, which is characterized by performing secondary annealing at a temperature range of 30 minutes or more to obtain properties of a tensile strength of 50 Kg/mm^2 or more and a reduction of area of 80% or more. 2. The method for producing a high-strength, high-ductility steel wire according to claim 1, characterized in that, after the primary annealing, the wire is drawn at a total area reduction of 20% or more, and then the secondary annealing is performed.