JPS63145713A - Production of high-strength steel wire having excellent hydrogen induced cracking resistance characteristic - Google Patents

Abstract

PURPOSE:To obtain a high-strength steel wire having an excellent hydrogen induced cracking resistance characteristic in a wet hydrogen sulfide environment, by subjecting steel specified in the contents of C, Si and Mn to patenting, then to cold working under specific conditions. CONSTITUTION:The steel wire rod contg. 0.3-0.6% C, 0.01-0.5% Si, and 0.1-1% Mn and consisting of the balance Fe and inevitable impurities is subjected to lead patenting or air patenting. The wire rod is then subjected to the cold working at <=20% reduction in area, by which the steel wire is formed. The steel wire having >=60kgf/mm<2> tensile strength is obtd. by this method. Since this steel wire has the excellent hydrogen induced cracking resistance, the wire does not break even when used in the severe wet hydrogen sulfide environment.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method for manufacturing high-strength steel wire with a tensile strength of 60 kgr/+n'' or more, and more specifically, to a method for manufacturing a high-strength steel wire that has a tensile strength of 60 kgr/+n'' or more, and more specifically relates to a method for manufacturing a high-strength steel wire that has a tensile strength of 60 kgr/+n'' or more. High strength M with excellent induced cracking properties
The present invention relates to a method for producing vA.

(Prior art) High-strength ￥A cotton used in ljJ-hydrated hydrogen sulfide environments, such as the sheathing and glands of flexible pipes for high-pressure fluid transport, is usually made of deformed steel wire (with a tensile strength of 60 kg r/sn2 or more) ( flat pressure wire or groove wire). The most important characteristic required of these steel wires is that they are sufficiently stable against hydrogen penetrating into the steel wires from the usage environment, and are resistant to hydrogen-induced cracking.
ckir+B (hereinafter referred to as Hf C) does not occur.

Conventionally, steel wire used in a humid hydrogen sulfide environment is produced by drawing a low carbon steel wire with a C content of 0.2% or less, then drawing it into a different shape,
Steel wires are formed into a predetermined cross-sectional shape by irregular processing such as roller die processing or rolling, and then used as is or after being annealed at a low temperature of 500° C. or less.

The problem with this conventional manufacturing method is that the degree of cold working is high, and even if annealing is performed, low temperature annealing is required to ensure strength, so the resistance to hydrogen penetrating from the environment is low. is small. For this reason, HIC is likely to occur in the area where strain is relatively concentrated inside the chemical line.
If the damage is severe, the steel wire may break during use, ie, it may break.

These HICs are the chemical components of steel and impurities such as P and S.
Although it is affected by the amount of carbon dioxide, it also strongly depends on the strength of the steel wire, and tends to occur in steel wires with a tensile strength of 60 kgf/am'' or more.

On the other hand, the influence of the environment is also large, and HIC increases as the hydrogen ion concentration of the environment increases.

Therefore, the recent trend toward higher strength steel wires and harsher usage environments requires steel wires to have better hydrogen-induced cracking resistance than ever before.

(Problems to be Solved by the Invention) An object of the present invention is to provide a method for manufacturing a high-strength steel wire that is used in a humid hydrogen sulfide environment and has low hydrogen-induced cracking resistance.

(Means and effects for solving the problems) That is, the present invention provides C: 0.3-0.6%, Si: 0.01-0.
5%, Mn: 0.1 to 1%, with the remainder consisting of iron and unavoidable impurities after patenting, cold working with a reduction in area of 20% or less. Tensile strength of 60 kgf. This is a method for producing a high-strength steel wire with excellent hydrogen-induced cracking resistance of 1/am" or higher.

First, the reasons for limiting the chemical components related to the present invention will be explained. C is a reinforcing element for steel, and at the same time, it is used in order to obtain a uniform pearlite MI weave through patenting.
．． 3% or more. However, if it exceeds 0.6%, the elongation value decreases, so the upper limit is set at 0.6%.

Since Si is a deoxidizing element for steel, it is added in an amount of 0.01% or more.

In addition, Si is effective as a strengthening element for steel, but 0.5
%, the elongation value decreases, so the upper limit is set at 0.5%.

Like Si, Mn is essential for deoxidizing steel, and
Add 0.1% or more for the purpose of preventing hot embrittlement caused by S. Furthermore, since Mn improves the hardenability of steel, it is desirable to have a high Mn content in order to obtain a uniform pearlite m weave through patenting, but if it exceeds 1%, H I C due to center segregation will increase. The upper limit is set at 1% as the frequency of occurrence is high.

In addition to the above-mentioned elements, it is effective to add 0.6% or less of Cr when the hardenability is insufficient due to the large thickness of the deformed steel wire. Furthermore, 0.3% or less of Cu and 0.02% or less of W have the effect of suppressing hydrogen intrusion into the steel, so if these are added as necessary, the hydrogen-induced cracking resistance can be further improved. can be improved.

P and S are impurities that are inevitably mixed in, but since these elements promote HIC, it is better to have as little as possible. Particularly regarding S, it is effective to lower the ductility of sulfides by adding Ca in the steelmaking process.

Note that Al is usually 0.0 as a deoxidizing element for molten steel.
35% or less is added.

Next, the heat treatment and subsequent processing method according to the present invention will be explained.

The greatest feature of the present invention is that while the conventional method relied only on wire drawing and subsequent work hardening during deformation as a strengthening means, strength is ensured by patenting and plastic working is performed using E-wire. The point is that the degree of processing is kept to the minimum necessary to adjust the shape (linearity and cross-sectional profile). That is,
The wire rod having the above-mentioned composition is preliminarily roughly formed by wire drawing and profile processing, then patented to adjust the strength, and then finished formed to obtain the final product. The present inventors believe that the pearlite & 11-weave high-strength steel wire manufactured by such a method has localized areas that serve as the origin of HIC and the propagation path of fracture, which were observed in the W4 wire manufactured by the conventional method. We have newly discovered that the hydrogen-induced cracking resistance is significantly improved due to the absence of high dislocation density regions.

Patenting is air patenting, in which the steel wire is heated to an austenite temperature range and then air cooled, or
This is done by lead patenting, which is immersed in a lead bath kept at 00°C for 30 seconds to 2 wins. After patenting, finish forming of the opening line is performed by plastic working such as straightening, drawing, and rolling. In this case, if the area reduction rate exceeds 20%, the above-mentioned localized high dislocation density region is formed, thereby generating IIIc. Therefore, the area reduction rate of cold working after patenting is set to 20% or less.

(Example) A high carbon steel wire rod with a diameter of 12 mm is drawn to a diameter of 10 mm.
It was made into a 5 mm copper wire, and then flat-rolled to a thickness of 4 mm.
It was a flat line with a width of 12 layers. Next, the temperature was raised to the austenite temperature range by electrical heating, and immediately immersed in a lead bath (lead patenting) or blast-cooled (air patenting). After patenting, flat rolling was performed again to produce a high-strength wire (flat wire) with a thickness of 3.51 m and a width of 12 mm. Note that for some materials, only straightening processing was performed after patenting. The straightening method is repeated bending with rolls, and the area reduction rate in this case is approximately 0.

HIC characteristics were evaluated by the following method. Cut the above-mentioned flat wire into 100cm long pieces, add 5% NaCl 1-0, 5% Cl
lffC00I+ -9 in 1123 saturated solution at 25 °C
After 6 hours of immersion, the cross section was examined at three locations and the presence or absence of microcracks was observed using an optical microscope.

The chemical composition of the materials used, heat treatment conditions, mechanical properties of the product, and It I C properties are shown in Table 1.

1Vkll -Ni15 is C content, and floors 6 to 9 are Si
Content, k10~m13 is Mn content, m16~11h
No. 19 shows that the degree of cold working after patenting does not affect the product properties. Kan 14 and ll&l1
5 is a manufacturing method shown for comparison, in which quenching and tempering is performed instead of patenting. Moreover, M2O and Ni21 are conventional manufacturing methods and are shown for comparison with the present invention. Here, when Kan 20 is manufactured using only wire drawing and flat pressure processing, also! 1kL21 is 4 to 20 patients
This is the case where an annealing process of 5 C''cx2 hours was added.

Floor 1 has a low C content, so the target strength is 60 kg f/
It has not reached Ryu 2, and on the other hand! '! In No. 15, the elongation value was low because the C content was too high, and HIC also occurred.

Corner 2 to Kan 4 had no H[C.

Yin 6 is an aluminum killed steel with a low Si content.

Since the elongation value decreases as the Si content increases, it is necessary to suppress Si to 0.5% or less in order to secure the target elongation value (8% or more).

In 11h13, 25% If I C was generated because martensite was generated in the center segregation area. HIC occurred in patients with Mn below 1% [L12] (did not occur).

Regarding the influence of the degree of cold working after heat treatment, HIC occurred at 40% in I'1h19 where the area reduction rate exceeded 20%, but the area reduction rate was kept below 20%! 1h16
~ No HIC was observed at all in No. 18.

In all of the above, the structure after heat treatment is pearlite structure, but 11kL14 and 15 are quenched and tempered m weave for comparison. In both cases, the mechanical properties have reached the target values, but the HIG properties are clearly inferior to the pearlite structure.

(Effects of the Invention) As described above, the steel wire manufactured according to the method of the present invention has extremely excellent hydrogen-induced cracking resistance and does not break even when used in a harsh humid hydrogen sulfide environment.

In addition, although we have described flat tension wires, it is possible to manufacture steel materials with excellent hydrogen-induced cracking resistance by manufacturing other general steel materials such as deformed wires, bolts, and steel bars using the same method. be.

Claims (1)

[Claims] A steel containing C: 0.3 to 0.6%, Si: 0.01 to 0.5%, and Mn: 0.1 to 1%, with the remainder consisting of iron and unavoidable impurities. A method for producing a high-strength steel wire with a tensile strength of 60 kgf/mm^2 or more and excellent hydrogen-induced cracking resistance, which is characterized by cold working with a reduction in area of 20% or less after heating.