Production process for improving toughness of cable steel

Abstract

The invention discloses a production process for improving the toughness of cable steel, which comprises the steps of molten iron desulfurization, smelting, RH treatment, continuous casting and high-speed wire rolling, and the key control points of the high-speed wire rolling step are as follows: the heating time of a heating furnace is greater than or equal to 150 minutes, the rolling starting temperature is 1150-1250 DEG C, the finish rolling temperature is 960-970 DEG C, the reducing sizing temperature is 950-960 DEG C, and the spinning temperature is 940-950 DEG C; a Stelmor wire is adopted in the controlled cooling step of high-wire rolling, a heat preservation cover on the Stelmor wire is fully opened, the roller way speed is 0.25-0.30 m / s, the temperature of the part out of the heat preservation cover is larger than or equal to 780 DEG C, and the temperature of the part in a coil is larger than or equal to 600 DEG C. By optimizing steel components and combining rolling temperature control and Stelmor air cooling process technology, online softening of the wire rod is realized, and the toughness of the cable can be remarkably improved; and the tempering temperature and the tempering time of the cold-drawn steel wire are reduced, so that the heat treatment cost of a user is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of steel material preparation, and particularly relates to a production process for improving the toughness of cable steel. Background Art

[0002] Cable steel has composition characteristics such as ultra-low carbon, low silicon, low manganese, and low sulfur. Its finest drawing diameter can reach 0.06 mm, and the drawing performance is one of the most important performance indicators of cable steel. Production practice shows that "the softer the hot-rolled wire rod, the easier it is to draw", so it is necessary to control the strength of the cable steel wire rod and improve the strength and plasticity of the material. As an ultra-low carbon steel, the composition of cable steel is close to that of industrial pure iron, and its mechanical properties usually mainly depend on the control of grain size, but at the same time, the requirements for electrical conductivity need to be met. On the premise of ensuring the conductivity (conductivity > 16.5%), more easily drawable cable steel will help reduce the tempering temperature and time of the wire after cold drawing, thereby reducing the heat treatment cost of users.

[0003] Patent application CN107435123A discloses an extremely low linear expansion cable steel, and its chemical composition is by mass percentage: C 0.03 - 0.10%, Si ≤ 0.02%, Mn 0.05 - 0.2%, P ≤ 0.020%, S ≤ 0.01%, Als 0.010 - 0.030%, Ti 0.10 - 0.20%, Ni 30 - 33%, Cu + Cr + Mo ≤ 0.030%, and the balance is iron and inevitable impurities; it has good cold drawing performance, high conductivity, relatively high strength and low thermal expansion, and is suitable for the production of extremely low linear expansion cable steel wires; however, the improvement effects on conductivity and drawing performance involved are limited. Patent application CN107675068A discloses a production method for steel wire rods for extremely fine copper-clad steel wires. The steel wire rods produced by this method have extremely good cold drawing performance and relatively high conductivity, meeting the requirements for steel wire rods for 0.05 - 0.10 mm extremely fine copper-clad steel wires for mobile phones and other electronic products; however, the rolling temperature of this scheme is relatively low, rolling is carried out in the two-phase region, and inevitably mixed crystal structures will be generated, and the cooling rate reaches up to 1.5 °C / s at most. Therefore, the strength of the steel wire is relatively high and brittle, and the heat treatment temperature and time of the steel wire are high during the production and processing process, which will lead to an increase in the manufacturing cost of the user side.

[0004] In view of the new development requirements of the cable steel industry, on the premise of ensuring high conductivity performance (conductivity > 16.5%), it is urgent to develop a production process for cable steel with excellent drawing performance. Summary of the Invention

[0005] The main object of the present invention is to provide a production process technology for improving the toughness of cable steel in view of the problems and deficiencies existing in the prior art. By utilizing the waste heat of hot-rolled wire rods on the Stelmor air-cooling line, the strength of the hot-rolled wire rods is controlled at ≤280 MPa, the elongation is ≥40%, and the electrical conductivity of the cable steel can be stably guaranteed to be ≥16.5%.

[0006] To achieve the above solution, the technical solution adopted by the present invention is as follows:

[0007] A production process for improving the toughness of cable steel, including steps of hot metal desulfurization, smelting, RH treatment, continuous casting and high-speed wire rolling. The key control points in the high-speed wire rolling step include: the heating time in the heating furnace is ≥150 min, the starting rolling temperature is 1150 - 1250 °C, the temperature entering the finishing mill is 960 - 970 °C, the temperature entering the sizing mill is 950 - 960 °C, and the laying head temperature is 940 - 950 °C;

[0008] The controlled cooling step of high-speed wire rolling uses the Stelmor line. All the heat preservation covers on the Stelmor line are fully opened, the roller table speed is 0.25 - 0.30 m / s, the temperature leaving the heat preservation cover is ≥780 °C, and the temperature entering the coiling reel is ≥600 °C.

[0009] In the above solution, the chemical composition of the continuously cast slab obtained is as follows by weight percentage: C ≤ 0.001%, Si ≤ 0.02%, Mn ≤ 0.015%, P ≤ 0.010%, S ≤ 0.003%, N ≤ 0.005%, Alt ≤ 0.003%, [O] ≤ 200 ppm, Cu + Ni + Cr + Mo 0.009 - 0.015%; the rest is Fe and inevitable impurities.

[0010] Further, 3 ≤ (Cu + Ni + Cr + Mo) / Alt ≤ 9.

[0011] Further, in the wire rod, C is 0.0001 - 0.0005%, Si is 0.002 - 0.005%, Mn is 0.005 - 0.010%, P ≤ 0.004%, S ≤ 0.003%, N ≤ 0.004%, Alt is 0.001 - 0.003%, [O] is 130 - 150 ppm, and the rest is Fe and inevitable impurities.

[0012] Preferably, in the wire rod for high-conductivity cables, the Cu content is 0.004 - 0.006%, the Ni content is 0.001 - 0.002%, the Cr content is 0.001 - 0.002%, and the Mo content is 0.003 - 0.004%.

[0013] Furthermore, in the controlled rolling and controlled cooling process, the heating time in the heating furnace is ≥180 min, the starting rolling temperature is 1200 - 1250 °C, the temperature entering the finishing mill is 960 - 965 °C, the temperature entering the sizing mill is 955 - 960 °C, and the wire laying temperature is 945 - 950 °C.

[0014] In the above solution, the cooling rate on the Stelmor line is ≤0.5 °C / s. For the wire rod of cable steel prepared according to the above solution, its strength is ≤280 MPa, the elongation is ≥40%, and the conductivity is ≥16.5%.

[0015] In the above solution, the wire rod of cable steel meets the wire drawing requirement for wires with a diameter of 0.02 - 0.04 mm.

[0016] The functions of each element in the steel are as follows:

[0017] C: It is the most important constituent element in the steel, and the carbon content directly determines its strength and plasticity. In the cold-drawn state, the tensile strength of the steel continuously increases with the increase of the carbon content, while the plasticity decreases with the increase of the carbon content. Generally, ultra-low carbon steel is selected as the raw material for making copper-clad steel because ultra-low carbon steel has good deformability, meeting the deformation requirements of copper-clad steel. In this application, C is limited to ≤0.002%, and further preferably 0.0001 - 0.0005%.

[0018] Si: It is used as a control element. This element destroys the cold formability of the steel, improves the elastic limit of the wire, and is also an important source of inclusions. The presence of silicon will affect the conductivity of the steel. The higher the silicon content, the lower the conductivity of the steel. Therefore, Si ≤0.02%, and further preferably 0.002 - 0.005%.

[0019] Mn: It can improve the strength of the wire rod and is also a good deoxidizer in steelmaking. Manganese combines with sulfur to form MnS, which can reduce the harmful effect of sulfur, but has a strong correlation with the electrical conductivity of the steel. Its presence affects the conductivity of the steel. At the same time, a low manganese content can shift the carbon content range of the peritectic reaction point to the left. Therefore, Mn ≤0.015%, and further preferably 0.005% - 0.010%.

[0020] P: It is a harmful impurity element, which reduces the plasticity and toughness of the steel, and sharply increases the brittle transition temperature of the steel, that is, it increases the cold brittleness (becomes brittle at low temperatures) of the steel. The presence of phosphorus will affect the conductivity of the steel. The higher the phosphorus content, the lower the conductivity of the steel. Therefore, P ≤0.010%, and further preferably ≤0.004%.

[0021] S: It is one of the important indicators for measuring the cleanliness of molten steel, which greatly restricts the improvement of the performance of steel. Its greatest harm is cracking during hot processing, resulting in hot brittleness. A high sulfur content in the steel increases the content of sulfide inclusions, leading to a decrease in the plasticity and toughness of the steel. Therefore, S ≤0.004%, and further preferably ≤0.003%.

[0022] N: Nitrogen increases the brittleness of steel and often forms second-phase particles with Al, V, Ti, etc. to refine the grain size, thus deteriorating the conductivity of cable steel. Therefore, N ≤ 0.005%, and further preferably ≤ 0.004%.

[0023] [O]: Oxygen in steel can lead to an increase in inclusions, deteriorate the purity of steel quality and thus affect the conductivity. And too high oxygen content can cause defects such as surface bubbles of the continuous casting billet. Therefore, [O] ≤ 200 ppm, and further preferably 130 - 150 ppm.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] 1) By optimizing the chemical composition of the wire rod for high-conductivity cables, under the conditions of using a lower amount of Cu + Ni + Cr + Mo and controlling a lower (Cu + Ni + Cr + Mo) / Alt ratio, the conductivity and toughness of the obtained steel are effectively taken into account;

[0026] 2) For the composition of the cable steel described in the present invention, the heating temperature, rolling start temperature, entry temperature into the finishing mill and entry temperature into the sizing mill are significantly increased to increase the austenite grain size and promote the improvement of the conductivity of the steel; combined with control means such as heat preservation and cooling on the Stelmor line, the toughness of the wire rod is further improved.

[0027] 3) By optimizing the chemical composition of the cable steel and improving the rolling temperature control conditions, using the waste heat of the hot-rolled wire rod on the Stelmor air-cooling line, the strength of the hot-rolled wire rod is controlled at ≤ 280 MPa and the elongation is ≥ 40%, and the conductivity of the cable steel can be stably guaranteed to be ≥ 16.5%; it helps to reduce the tempering temperature and tempering time of the wire after cold drawing, thus reducing the heat treatment cost of users. Specific embodiments

[0028] In order to make the purpose, technical solutions and advantages of the present invention clearer, the following further details the present invention in combination with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0029] The key process control steps of each embodiment of the present invention are as follows:

[0030] 1. Requirements for the chemical composition of the continuous casting billet and the wire rod:

[0031] The chemical composition of the continuous casting billet is by weight percentage: C ≤ 0.001%, Si ≤ 0.02%, Mn ≤ 0.015%, P ≤ 0.010%, S ≤ 0.002%, N ≤ 0.005%, Alt ≤ 0.02%, [O] ≤ 200 ppm, Cu + Ni + Cr + Mo 0009 - 0.015%; the balance is Fe and unavoidable impurities.

[0032] Furthermore, 5 ≤ (Cu + Ni + Cr + Mo) / Alt ≤ 9, the Cu content is 0.004 - 0.006%, the Ni content is 0.001 - 0.002%, the Cr content is 0.001 - 0.002%, and the Mo content is 0.003 - 0.004%.

[0033] The chemical composition of the wire rod is by weight percentage: C 0.0001 - 0.0005%, Si 0.002 - 0.005%, Mn 0.005 - 0.010%, P ≤ 0.004%, S ≤ 0.003%, N ≤ 0.004%, Alt 0.001 - 0.003%, [O] 130 - 150 ppm, and the balance is Fe and unavoidable impurities.

[0034] 2. The continuous casting billet enters the high - speed wire rolling: the heating time in the heating furnace is ≥ 150 min, the heating temperature is 1250 - 1350 °C, the starting rolling temperature is 1150 - 1250 °C, the entry temperature into the finishing mill is 960 - 970 °C, the entry temperature into the sizing mill is 950 - 960 °C, and the spinning temperature is 940 - 950 °C;

[0035] Furthermore, in the controlled rolling and controlled cooling process, the heating time in the heating furnace is ≥ 180 min, the starting rolling temperature is 1200 - 1250 °C, the entry temperature into the finishing mill is 960 - 965 °C, the entry temperature into the sizing mill is 955 - 960 °C, the spinning temperature is 945 - 950 °C, all the heat - retaining covers on the Stelmor line are fully open (40 heat - retaining covers), the roller table speed is 0.25 - 0.30 m / s, and the entry temperature into the coiling unit is ≥ 600 °C.

[0036] For the wire rod for cable steel prepared according to the above - mentioned scheme, its strength ≤ 280 MPa, elongation ≥ 40%, and conductivity ≥ 16.5%.

[0037] Table 1 Chemical compositions of examples and comparative examples, wt%

[0038]

[0039]

[0040] Note: The value of (Cu + Ni + Cr + Mo) / Alt in Table 1 is rounded to an integer.

[0041] Table 2 Process parameters of the steel rolling process for examples and comparative examples

[0042]

[0043] Table 3 Comparison of Quality Indexes of Wire Rods in Examples and Comparative Examples

[0044]

[0045]

[0046] The cable steel produced according to the above process can achieve on-line softening of wire rods by optimizing the steel composition and combining rolling temperature control and Stelmor air cooling process technology on the premise of ensuring high conductivity (conductivity > 16.5%), significantly improving the toughness of the cable; when drawing steel wires of the same diameter, the cable steel that is more easily drawn and "softened" in this invention patent will help reduce the tempering temperature and tempering time of the steel wires after cold drawing, thus reducing the heat treatment cost of users.

[0047] It is easy for those skilled in the art to understand that the above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A production process for improving the toughness of cable steel, characterized in that, It includes the steps of hot metal desulfurization, smelting, RH treatment, continuous casting and high-speed wire rolling. The key control points of the high-speed wire rolling step include: the heating time in the heating furnace is ≥150 min, the starting rolling temperature is 1150 - 1250 °C, the entry temperature into the finishing mill is 960 - 970 °C, the entry temperature into the sizing mill is 950 - 960 °C, and the laying head temperature is 940 - 950 °C. The controlled cooling step of the high-speed wire rolling adopts the Stelmor line. All the heat preservation covers on the Stelmor line are fully open, the roller table speed is 0.25 - 0.30 m / s, the temperature out of the heat preservation cover is ≥780 °C, and the entry temperature into the coiler is ≥600 °C.

2. The production process according to claim 1, characterized in that, The chemical composition of the continuously cast billet is by weight percentage: C ≤ 0.001%, Si ≤ 0.02%, Mn ≤ 0.015%, P ≤ 0.010%, S ≤ 0.003%, N ≤ 0.005%, Alt ≤ 0.003%, [O] ≤ 200 ppm, Cu + Ni + Cr + Mo 0.009 - 0.015%; the rest is Fe and inevitable impurities.

3. The production process according to claim 2, characterized in that, In the chemical composition of the continuously cast billet, 3 ≤ (Cu + Ni + Cr + Mo) / Alt ≤ 9.

4. The production process according to claim 2, characterized in that, In the wire rod, it is characterized in that C is 0.0001 - 0.0005%, Si is 0.002 - 0.005%, Mn is 0.005 - 0.010%, P ≤ 0.004%, S ≤ 0.003%, N ≤ 0.004%, Alt is 0.001 - 0.003%, [O] is 130 - 150 ppm, and the rest is Fe and inevitable impurities.

5. The production process according to claim 2, characterized in that, In the wire rod, it is characterized in that in the wire rod for high conductivity cables, the Cu content is 0.004 - 0.006%.

6. The production process according to claim 2, characterized in that, In the wire rod for high conductivity cables, the Mo content is 0.003 - 0.004%.

7. The production process according to claim 1, characterized in that, In the controlled rolling and controlled cooling process, the heating time in the heating furnace is ≥180 min, the starting rolling temperature is 1200 - 1250 °C, the entry temperature into the finishing mill is 960 - 965 °C, the entry temperature into the sizing mill is 955 - 960 °C, and the laying head temperature is 945 - 950 °C.

8. The production process according to claim 1, characterized in that, In the controlled rolling and controlled cooling process, the cooling rate on the Stelmor line is ≤ 0.5 °C / s.

9. The wire rod of cable steel prepared by the production process for improving the toughness of cable steel according to any one of claims 1 to 8, characterized in that, Its strength is ≤ 280 MPa, the elongation is ≥ 40%, and the conductivity is ≥ 16.5%.

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