KR20010064990A - Weathering steel wire and strand, and its production method - Google Patents

Abstract

PURPOSE: A process for preparing weathering steel wire and strand remarkably increased in toughness by controlling the chemical composition of steel, adding a deposition hardening element and applying a suitable processing method is provided. Whereby, the steel can be used as steel requested for high strength and high atmospheric corrosion resistance. CONSTITUTION: This weathering steel wire is characterized in that it comprises 0.30 to 0.60% by weight of C, 0.15 to 0.65% by weight of Si, below 0.85% by weight of Mn, 0.20 to 0.50% by weight of Cu, 0.45 to 0.75% by weight of Cr, 0.05 to 0.30% by weight of Ni, 0.05 to 0.30% by weight of Ni, 0.02 to 0.2% by weight of W and 0.05 to 0.30% by weight of Nb or Ti and the balance of Fe and inevitable impurities. This steel wire has a toughness of 160 to 215kgf/mm¬2.

Description

Weathering steel wire and strand and its manufacturing method {Weathering steel wire and strand, and its production method}

The present invention relates to weathering steel wire and strand wire having a resistance to atmospheric corrosion, and more particularly, to a tungsten, vanadium, titanium in a carbon alloy steel containing weathering elements copper, nickel, chromium, silicon, etc. And steel wires and strands having a high tensile strength and a method of producing the same, by adding a precipitated curable element such as niobium, and by appropriately combining secondary drawing after primary drawing (drawing) and annealing heat treatment. .

The weathering steel generally used is mainly steel plate steel, which is widely used in bridges, transmission towers, building structures, ships, railway cars, etc., with a low carbon content of less than 0.18% and a tensile strength of 50-60 Kgf / mm ² . .

The corrosion resistance of the weathering steel to the atmosphere is obtained by the addition of weathering elements such as phosphorus, copper, nickel, chromium and silicon. In other words, the weatherability of the weather resistant steel is almost dependent on the chemical composition and does not depend on the structure or manufacturing process of the steel.

In addition, the evaluation of the weather resistance is based on the following Equation 1 prescribed in ASTM G101, and when this index is 6.0 or more, it is known to have an atmospheric corrosion resistance of 4 to 8 times that of ordinary carbon steel.

Atmospheric Corrosion Resistance Index = 26.01 × (wt% Cu) + 3.88 × (wt% Ni) + 1.20 × (wt% Cr) + 17.28 × (wt% P)-7.29 × (wt% Cu × wt% Ni) 9.10 × (wt% N × wt% P)

According to Equation 1 it can be seen that the most effective element in the weather resistance of the steel is the order of copper, phosphorus, nickel, chromium, silicon.

As shown in FIG. 1, when the steel 1 is exposed to the atmosphere and a scale 3 occurs on the surface, the cracks on the scale surface are formed by forming the amorphous concentrated layer 2 within the scale 3. 4) It hinders the progress, and the supply of oxygen through the gap is reduced and the progress of corrosion of the steel is suppressed.

Conventional weathering steels include 0.18 wt% or less C, 0.15 to 0.65 wt% Si, 1.40 wt% or less Mn, 0.035 wt% or less P, 0.035 wt% or less S, 0.30 to 0.50 wt% Cu, 0.45 to 0.75 wt% Cr , SWA50BW steel with 0.05 ~ 0.30wt% Ni, residual Fe chemical composition and 50Kgf / mm ² tensile strength has been widely used.

However, these steels have good weather resistance, but they cannot be used for reinforcing steel wires or color ropes that require strengths of 160 Kgf / mm ² or more, and have improved toughness and rapid protective coating. A weather resistant steel of 0.18 wt% or less is disclosed in US Pat. No. 4,094,670, but this steel also has a tensile strength of only about 60 Kgf / mm ² .

Therefore, although carbon steel having a high tensile strength is used as a rust preventive treatment for large cables or hanger ropes using weather resistant steels, it is difficult to prevent aging due to rusting because it is used in an air-exposed state.

As described above, conventional weather resistant steel wire and strand wire mainly used for large structures exposed to the air have low tensile strength, and thus their use is limited.

In order to solve the problems of the conventional weathering steel as described above, the weather resistance by improving the weather resistance by newly adjusting the chemical composition of the steel, and the addition of precipitation-reinforced elements and the appropriate processing method, the weathering steel wire and strand and dramatically increased the tensile strength and its It is an object to provide a manufacturing method.

1 is a schematic diagram of a corrosion preventing mechanism of weathering steel,

(A) is a cross-sectional view of the initial scale generation process,

(B) is sectional drawing in which an amorphous layer and a scale layer were isolate | separated.

2 is a cross-sectional view of the present invention weather resistant strand.

((Explanation of symbols for main part of drawing))

1. Weather resistant steel 2. Amorphous layer

3. Scale 4. Crack

The weather resistant steel wire and the stranded wire of the present invention are the same as the conventional one in that steel materials having C-Si-Mn-Cu-Cr-Ni as the basic composition are used, but the carbon content is 0.30 to 0.60 wt%, and the precipitation hardening and The difference is that the microstructured elements V, W, Ti, Nb and the like are added.

In addition, the steel material of the composition through the cold drawing and heat treatment for two times through the precipitation hardening effect and the dislocation (dislocation) by strengthening the structure of the structure by the tensile strength is significantly higher than the conventional to produce weathering steel wire and strand wire There is a characteristic.

The technical features of the method of the present invention can be seen in terms of the addition of specific chemical components and the processing of steels of selected chemical components. First, in terms of chemical components, the chemical components of the inventive steels and their respective additive elements The characteristics are as follows.

division C Si Mn Cu Cr Ni V W Nb Fe wt% 0.30 to 0.60 0.15 to 0.65 0.85 or less 0.20 to 0.50 0.45 to 0.75 0.05 to 0.30 0.05 to 0.30 0.02 to 0.2 0.05 to 0.30 Remaining amount

Nb can be replaced with Ti.

In Table 1, the effects of the weather-resisting elements Si, Mn, Cu, and Cr are as described above, and the Ni and the increase of the newly added reinforcing element and the basic element of steel to increase the tensile strength of the steel, and the weather resistance of Ni The roles are as follows.

C is a basic element of steel that directly affects the strength of steel. As its content increases, the strength of steel increases, but when it exceeds 0.60wt%, C is generated by the influence of Cu during the continuous casting and rolling process of wire rod manufacturing. There is a limit to the suppression of surface defects, and the target strength cannot be obtained at less than 0.30 wt%.

V is a precipitation hardening element that finely precipitates in the form of V ₄ C _{3 in a} ferrite structure, which is a matrix of steel wire, to strengthen a weak ferrite structure. In order to cause such precipitation hardening, 0.05 wt% However, when excessively added, the carbide precipitates in a film form at the austenite grain boundary, causing grain boundary corrosion or lowering the bonding strength of the steel, thereby lowering the rigidity of the steel. Therefore, the content is preferably 0.30 wt% or less.

W promotes the precipitation of other precipitation hardening elements, and because it itself precipitates with W ₂ C, the addition effect is large. It is effective when it is more than 0.02wt%, and when it exceeds 0.2wt%, it precipitates as a mass at grain boundary and embrittles the grain boundary.

Nb and Ti are not only contributing to strengthening the ferrite precipitation of the mother phase but are also effective elements for particle refinement, and the effect is insignificant at less than 0.05 wt%. To lower the toughness of the steel.

And the characteristic of the processing method which raises the intensity | strength of this invention weather resistant steel wire and a stranded wire together with the effect of the strength increase of the said additional element is performed between two cold drawing processes and two drawing processes performed with an appropriate processing rate. It is in annealing treatment.

According to the method of the present invention, the pickling and coating of weathering wire having a diameter of 5.5 to 22 mm based on the final diameter of the weathering steel wire and the stranded wire, and the primary cold drawing process with a reduction ratio of 30 to 75% And performing annealing heat treatment of the primary drawn wire at 650 to 930 ° C. for 10 hours or less, performing secondary pickling and coating, and performing secondary cold drawing on the annealed wire with a reduction rate of 95% or less. It is made of.

In the above processing method, the reduction rate of the primary cold drawing is limited to 30 to 75%. The larger the processing amount before the heat treatment, the higher the residual stress accumulated in the metal structure, and the residual stress is a recrystallization process occurring in the tissue during heat treatment. This is because it helps to refine the newly formed recrystallized grains and precipitate carbide, which is a compound with precipitation strengthening element, by increasing the strength and toughness of the wire rod.

However, if the reduction rate is less than 30%, the residual stress accumulated in the metal structure is small, so that the effect of recrystallization and carbide precipitation is insignificant, so that the target strength cannot be obtained. There is a problem that re-crystallization does not occur or wire rods may be twisted or distorted due to abnormal coarsening of the initial grains.

When the reduction rate is about 75%, the effect of the residual stress on the recrystallization and carbide precipitation becomes saturated, and further processing increases the processing cost and risks of causing internal cracking due to excessive processing. It is desirable that the reduction rate should not exceed 75% because it becomes large.

Annealing heat treatment after the primary drawing process is a process of recrystallization of the hardened metal structure to form a new structure.At less than 650 ° C, the recrystallization process and the progress of carbide precipitation are slow and the precipitates segregating at the grain boundaries are increased. If the temperature exceeds 930 ° C, the growth rate of recrystallized grains is increased, which makes it difficult to control the target tensile strength affected by grain size.

In addition, the annealing time of 10 hours is for the case of annealing at a temperature near 650 ° C. At this temperature, the recrystallization and carbide precipitation process is slow, so it is 10 hours to obtain an effective precipitate required for precipitation hardening. It needs time.

The secondary cold drawing process after annealing is the process of hardening the surface to refinish the recrystallized wire surface to obtain final target strength. The limit of the processing is limited to 95% or less reduction rate when the wire rod exceeds 95%. This is because the toughness of the saline decreases rapidly, resulting in lower salt characteristics.

The purpose and technical configuration of the present invention and the effects thereof according to the present invention will be clearly understood by the following detailed description through preferred embodiments of the present invention with reference to the drawings.

Weathering wires of the present invention containing weatherable elements and precipitation hardening elements having a carbon content of 0.33 to 0.55 wt% and a wire diameter of 13 mm were prepared. The chemical composition and mechanical properties of each wire were shown in the following table. 2 and Table 3.

(Unit; wt%, where N is ppm) division C Si Mn P S Cu Cr Ni V W Ti Nb N Al Invention One 0.33 0.41 0.78 0.015 0.003 0.35 0.58 0.25 0.10 0.09 0.10 55 0.021 2 0.44 0.44 0.79 0.014 0.003 0.34 0.61 0.24 0.11 0.08 0.11 61 0.023 3 0.56 0.43 0.77 0.014 0.002 0.33 0.57 0.26 0.12 0.10 0.09 48 0.019 4 0.35 0.42 0.76 0.016 0.003 0.35 0.60 0.23 0.13 0.09 0.06 42 0.025 5 0.47 0.41 0.78 0.015 0.004 0.36 0.62 0.29 0.12 0.08 0.05 58 0.026 6 0.55 0.45 0.77 0.014 0.005 0.34 0.59 0.27 0.11 0.11 0.07 56 0.020 Comparative material 7 0.08 0.28 1.20 0.016 0.003 0.41 0.78 0.02 48 0.022 8 0.34 0.43 0.77 0.015 0.004 0.35 0.61 0.24 54 0.021

The comparative material 7 was prepared by hot rolling an ingot made through melting with an electric furnace at 1200 ° C., cooling it to 650 ° C. at a cooling rate of 40 ° C./sec, and then air-cooling to room temperature. It has the same chemical composition as steel of 4,094,670.

In addition, the comparative material 8 is a wire rod in which the precipitation hardening element is not added in the chemical component of this invention in order to investigate the effect of a precipitation hardening element.

division Tensile Strength (Kgf / mm ² ) Sectional shrinkage (%) Elongation (%) Atmospheric Corrosion Resistance Index Invention One 84 60 20 6.91 2 93 58 18 6.95 3 105 57 17 6.90 4 82 61 20 6.94 5 91 59 19 7.01 6 103 58 18 6.98 Comparative material 7 61 63 22 6.68 8 76 54 16 6.69

Table 2 and Table 3 show that as the carbon content increases, the tensile strength of the wire rod increases, and the tensile strength of the present invention material is 21 to 44 Kg / mm ² higher than the comparative material according to the US patent (Comparative Material 7). Can be.

In addition, when comparing the inventive materials 1 and 4 with comparatively similar carbon contents and the comparative material 8, the tensile strength of the inventive material appears to be about 6 to 8 Kg / mm ² , which is due to the addition of the precipitation hardening element.

In addition, it can be seen that the wire rod of the present invention is equal or more than the comparative material 7 of the same chemical composition as the conventional patent material in the atmospheric corrosion resistance index.

The weatherproof wire of Table 2 is subjected to the first scale removal and coating treatment → 62% first cold drawing process → 760 ° C × 3 hours annealing → second scale removal and coating treatment → 89.4% second cold drawing process A weather resistant steel wire with a diameter of 2.6 mm was manufactured, and the results of the mechanical properties of the annealing heat treatment line and the secondary cold drawing line were shown in Table 4.

division Annealed Heat Treatment Wire Secondary cold drawing line Tensile Strength (Kgf / mm) Sectional shrinkage (%) Tensile Strength (Kgf / mm) Torsion value (times / 100d) Elongation (%) Invention One 97 58 177 31 2.3 2 105 56 193 27 2.1 3 117 53 212 23 1.9 4 92 59 174 33 2.4 5 102 57 191 29 2.2 6 112 56 209 25 2.0 Comparative material 7 67 58 115 35 2.5 8 80 53 142 30 2.2

As can be seen from Table 4, in the case of annealing heat treatment wire, the steel wire of the present invention has a tensile strength of about 25 to 50 Kg / mm ² higher than that of the comparative material 7 having the chemical composition of the conventional patent, and in the case of a similar carbon content, compared to the comparative material 8 12-17 Kg / mm ² higher.

In the second case of the cold drawing overhead lines, the present invention tensile strength of the comparative material 7 than the high 59~97Kg / mm ² material, showing a comparative material 8 32~35Kg / mm ² degree of a higher value than in the case of similar carbon content .

The increase in tensile strength is because the dislocation reinforcing effect by the annealing heat treatment and the secondary cold drawing process cause the newly created dislocation in the metal structure to adhere to the precipitate, making it difficult to move.

The secondary cold drawn material 21 of the Inventive Material 5 was twisted as shown in the cross-sectional structure of FIG. 2 with a pitch of 140 mm, and a stranded wire was manufactured. As a result of the tensile test of the stranded wire, the cutting load was 7254 Kgf. The quality efficiency, 92%, is similar to that of stranded steel, which is usually made of carbon steel.

And the annual efficiency is calculated | required by the following formula.

As described above, the method of the present invention increases the carbon content and adds precipitation hardening elements as compared to the conventional weather resistant steels, thereby maintaining the corrosion resistance to the atmosphere at an equivalent level or higher and significantly increasing the tensile strength without reducing the annual efficiency. Therefore, it can be used for applications requiring high strength and high atmospheric corrosion resistance such as reinforcing steel wire, color rope and hanger rope.

Claims (6)

Chemical composition 0.30 to 0.60 wt% C, 0.15 to 0.65 wt% Si, 0.85 wt% or less Mn, 0.20 to 0.50 wt% Cu, 0.45 to 0.75 wt% Cr, 0.05 to 0.30 wt% Ni, 0.05 to 0.30 wt% V , 0.02 to 0.2 wt% W, and 0.05 to 0.30 wt% Nb or Ti and weathering steel wire, characterized in that it is composed of the remaining amount of iron and inevitable impurities. The weather resistant steel wire according to claim 1, wherein the steel wire has a tensile strength of 160 to 215 Kgf / mm ² . Chemical composition 0.30 to 0.60 wt% C, 0.15 to 0.65 wt% Si, 0.85 wt% or less Mn, 0.20 to 0.50 wt% Cu, 0.45 to 0.75 wt% Cr, 0.05 to 0.30 wt% Ni, 0.05 to 0.30 wt% V And 0.02-0.2 wt% W, and 0.05-0.30 wt% Nb or Ti, and the weathering strand is characterized by being composed of a residual amount of iron and inevitable impurities. The weathering strand according to claim 3, wherein the strand comprises a weather resistant steel wire having a tensile strength of 160 to 215 Kgf / mm ² . Chemical composition 0.30 to 0.60 wt% C, 0.15 to 0.65 wt% Si, 0.85 wt% or less Mn, 0.20 to 0.50 wt% Cu, 0.45 to 0.75 wt% Cr, 0.05 to 0.30 wt% Ni, 0.05 to 0.30 wt% V Primary pickling and coating of weather-resistant wire having a diameter of 5.5 to 22 mm comprising one of 0.02 to 0.2 wt% W, and 0.05 to 0.30 wt% Nb or Ti and composed of residual iron and unavoidable impurities; A first cold drawing process with a reduction rate of ˜75%, a heat treatment step of 10 hours or less at 650 to 930 ° C., a second pickling and coating process, and a second cold drawing process of 95% or less. Method for producing a weathering steel wire, characterized in that the production. Chemical composition 0.30 to 0.60 wt% C, 0.15 to 0.65 wt% Si, 0.85 wt% or less Mn, 0.20 to 0.50 wt% Cu, 0.45 to 0.75 wt% Cr, 0.05 to 0.30 wt% Ni, 0.05 to 0.30 wt% V Primary pickling and coating of weather-resistant wire having a diameter of 5.5 to 22 mm comprising one of 0.02 to 0.2 wt% W, and 0.05 to 0.30 wt% Nb or Ti and composed of residual iron and unavoidable impurities; A first cold drawing process with a reduction rate of ˜75%, a heat treatment step of 10 hours or less at 650 to 930 ° C., a second pickling and coating process, and a second cold drawing process of 95% or less. A method for producing weathering stranded steel, characterized in that it is produced by stranding the weathering steel wire produced.