CN107475608A - Manufacturing method for improving surface quality of low-carbon boron-added steel wire rod - Google Patents

Abstract

This application discloses a manufacturing method for improving the surface quality of low-carbon boron-added steel wire rods, including continuous casting and hot rolling, and the control conditions in the continuous casting process: the degree of superheat is controlled at 25°C to 40°C, and the casting speed of continuous casting is 2.6 m/min～2.85m/min, the cooling water volume of the crystallizer is 1680L/min～1720L/min, the vibration frequency of the crystallizer is 160Hz～200Hz, and the amplitude is 6.5mm～8.0mm. The present invention realizes preliminary stepped cooling of the surface temperature of the continuous casting slab by optimizing and adjusting the process parameters of the continuous casting crystallizer and the secondary cooling process parameters, reduces the thermal stress in the continuous casting process, and avoids boron elements in low-carbon boron-added steel The high-temperature brittle area caused by the addition can effectively prevent the formation of crack defects on the surface of the low-carbon boron-added steel continuous casting slab, which is beneficial to the subsequent control of the surface quality of the finished low-carbon boron-added steel wire rod; by heating the low-carbon boron-added steel billet And the influence of BN on the high-temperature plasticity during the rolling process reduces or eliminates the influence of low-carbon boron-added steel on the surface quality of the finished wire rod due to improper rolling temperature control.

Description

A manufacturing method for improving the surface quality of low-carbon boron-added steel wire rod

technical field

The application relates to the technical field of iron and steel metallurgy, in particular to a manufacturing method for improving the surface quality of low-carbon boron-added steel wire rods.

Background technique

Boron-containing steel refers to steel with boron as the main alloying element. A very small amount (5-30ppm) of boron can significantly improve the hardenability of steel, and can improve the overall performance of steel while reducing production costs. However, the addition of B also greatly increases the crack sensitivity of the steel. Therefore, by adding Al or Ti to the steel, the influence of B on the surface quality of the low-carbon boron-containing steel can be reduced. Both methods are based on different thermodynamic conditions, by adding elements that are easier to combine with [N] elements to reduce or avoid the formation of BN, thereby reducing the accumulation of BN at grain boundaries. However, the AlN formed after the addition of Al is also easy to gather and precipitate along the grain boundary, which will also have a greater impact on the high-temperature shaping of the steel, but its precipitation temperature range is different from that of BN, so the surface temperature control range in the continuous casting process is different. ; and after adding Ti element, TiN will precipitate at the grain boundary and within the grain during the solidification process, gather less at the grain boundary, and have less influence on high-temperature plasticity, but the chemical activity of Ti element is relatively large, and it is easy to combine with O, N The combination of elements to form TiO _x and TiN causes nozzle nodulation, which affects the pourability of the continuous casting process, and also causes large fluctuations in the liquid level of the mold, thereby affecting the surface quality of the continuous casting slab. Therefore, the method of adding Al or Ti elements to the steel cannot improve and solve the surface quality problem of the low-carbon boron-added steel, and also increases the production cost.

Contents of the invention

The purpose of the present invention is to provide a manufacturing method for improving the surface quality of low-carbon boron-added steel wire rods, through the control and optimization of the process parameters of the continuous casting process and the heating furnace and rolling temperature of the rolling process, so as to reduce or eliminate the boron element The purpose of affecting the surface quality of low-carbon boron-added steel is to improve the qualified rate of finished products of wire rod.

To achieve the above object, the present invention provides the following technical solutions:

The embodiment of this application discloses a manufacturing method for improving the surface quality of low-carbon boron-added steel wire rod. The chemical composition of low-carbon boron-added steel wire rod includes: 0.05%≤C≤0.30%, 8ppm≤B≤30ppm , 0.08%≤Si≤0.20%, Mn≤0.80%, 0≤Al≤0.005%, the rest are Fe and unavoidable impurity elements; its manufacturing methods include continuous casting and hot rolling, and the control conditions in the continuous casting process: superheat The temperature is controlled at 25°C-40°C, the continuous casting casting speed is 2.6m/min-2.85m/min, the cooling water volume of the crystallizer is 1680L/min-1720L/min, the crystallizer vibration frequency is 160Hz-200Hz, and the amplitude is 6.5mm- 8.0mm.

Preferably, in the above-mentioned manufacturing method for improving the surface quality of low-carbon boron-added steel wire rod, in the continuous casting process, control conditions: the specific water volume of the secondary cooling is 0.75L/kg-1.00L/kg.

Preferably, in the above-mentioned manufacturing method for improving the surface quality of low-carbon boron-added steel wire rods, the secondary cooling is divided into four zones, wherein the secondary cooling zone 1 and zone 2 adopt the full water cooling mode, and the secondary cooling zone 3 and 4 zones with mist cooling mode.

Further, according to the different cooling lengths of each zone, the step control principle of gradually reducing the cooling intensity is adopted to distribute the water volume in the secondary cooling zone.

Preferably, in the above-mentioned manufacturing method for improving the surface quality of low-carbon boron-added steel wire rods, in the secondary cooling, the ratio R of the sub-regional cooling water to the total water volume and the length L of the secondary cooling sub-region satisfy the following relationship:

Zone 1, 105≤R ₁ /L ₁ ≤128;

Zone 2, 16≤R ₂ /L ₂ ≤25;

Zone 3, 4.5≤R ₃ /L ₃ ≤8.0;

Zone 4, 2.5≤R ₄ /L ₄ ≤5.0.

Preferably, in the above-mentioned manufacturing method for improving the surface quality of low-carbon boron-added steel wire rod, in the hot rolling process, the control conditions: the temperature of the soaking section of the heating furnace is controlled at 1050°C to 1150°C, and the starting temperature of the billet is controlled at It is 950℃～1050℃.

Compared with the prior art, the present invention has the advantages of:

1. The present invention realizes preliminary stepwise cooling of the surface temperature of the continuous casting billet by optimizing and adjusting the process parameters of the continuous casting crystallizer and the secondary cooling process parameters, reduces the thermal stress in the continuous casting process, and avoids the low-carbon boron-added steel at the same time. The high-temperature brittle area caused by the addition of boron can effectively prevent the formation of crack defects on the surface of low-carbon boron-added steel continuous casting slabs, which is beneficial to the control of the surface quality of subsequent low-carbon boron-added steel wire rod products;

2. In the present invention, through the influence of BN on the high-temperature plasticity of the low-carbon boron-added steel billet in the heating and rolling process, the influence of low-carbon boron-added steel on the surface quality of the finished wire rod due to improper rolling temperature control is reduced or eliminated .

3. The present invention avoids the comprehensive influence of BN on the surface quality of low-carbon boron-added steel wire rods through technological innovation. Compared with the method of fixing N by adding elements such as Al and Ti, it has the characteristics of simplicity and economy, and will not Bring other quality problems such as nozzle nodulation.

detailed description

The present invention is further illustrated by the following examples: According to the following examples, the present invention can be better understood. However, those skilled in the art can easily understand that the specific material ratios, process conditions and results described in the examples are only used to illustrate the present invention, and should not and will not limit the present invention described in the claims.

The steel grades in each embodiment of the present invention do not add Ti element, and the Al content is trace or not contained. The surface quality of steel wire rod mainly includes defects such as cracks, scars, pits, and folds on the surface of the wire rod. The lower the occurrence rate of these defects, the better the surface quality of the wire rod.

Example 1

The steel type in this example is SAE1006B. Through molten steel smelting, the mass percentage of the chemical composition of the finished product is controlled as follows: 0.05%≤C≤0.10%, 12ppm≤B≤20ppm, 0.08%≤Si≤0.20%, Mn≤0.80%, Al≤0.005 %, the rest is Fe and unavoidable impurity elements.

This type of steel is produced on a billet continuous casting machine. The section of the continuous casting slab is 140mm*140mm. During the continuous casting process, the superheat is controlled within the range of 25-35°C, and the casting speed is stable at 2.7±0.05m/min. The cooling water volume of the crystallizer is 1700±20L/min, the vibration frequency of the crystallizer is controlled at 180Hz, and the amplitude is controlled at 7.0mm.

The specific water volume of the secondary cooling in continuous casting is controlled at 0.90L/kg, of which the secondary cooling zone 1 and 2 adopts the full water cooling mode, the secondary cooling zone 3 and 4 adopts the air mist cooling mode, and the cooling water volume of the secondary cooling zone accounts for the total water volume R (unit: %) and the length L (unit: m) of the secondary cooling section satisfy the following relationship: secondary cooling zone 1, R ₁ /L ₁ =115; secondary cooling zone 2, R ₂ /L ₂ =24; secondary cooling zone 3 zone, R ₃ /L ₃ =4.5; secondary cooling zone 4, R ₄ /L ₄ =2.5.

In the steel rolling process control, the temperature of the soaking section of the heating furnace is controlled to be 1060°C ± 10°C, and the rolling start temperature of the billet is controlled to be 970°C ± 10°C.

The surface quality of the low-carbon boron-added steel continuous casting slab produced in this embodiment is good, the average depth of the vibration marks is 0.28mm, no defects such as cracks are found in the pickling of the surface of the slab, and the average return rate of the finished wire rod after rolling is only 0.35 %.

Example 2

The type of steel in this example is SAE1015B. Through molten steel smelting, the mass percentage of the chemical composition of the finished product is controlled to be: 0.12%≤C≤0.18%, 12ppm≤B≤18ppm, 0.10%≤Si≤0.16%, Mn≤0.80%, Al≤0.005 %, the rest is Fe and unavoidable impurity elements.

This type of steel is produced on a billet continuous casting machine. The section of the continuous casting slab is 140mm*140mm. During the continuous casting process, the superheat is controlled within the range of 25-40°C, and the casting speed is stable at 2.75±0.05m/min. The cooling water volume of the crystallizer is 1700±20L/min, the vibration frequency of the crystallizer is controlled at 200Hz, and the amplitude is controlled at 6.5mm.

The specific water volume of the secondary cooling in continuous casting is controlled at 0.98L/kg, of which the secondary cooling zone 1 and zone 2 adopt the full water cooling mode, the secondary cooling zone 3 and 4 adopt the air mist cooling mode, and the cooling water volume of the secondary cooling zone accounts for the total water volume R (in %) and the length L of the secondary cooling zone (in m) satisfy the following relationship: secondary cooling zone 1, R1/L1=108; secondary cooling zone 2, R2/L2=23; secondary cooling zone 3, R3/ L3=5.2; Secondary cooling zone 4, R4/L4=3.0.

In the steel rolling process control, the temperature of the soaking section of the heating furnace is controlled to be 1100°C ± 10°C, and the rolling start temperature of the billet is controlled to be 990°C ± 10°C.

The surface quality of the low-carbon boron-added steel continuous casting slab produced in this example is better, the average depth of the vibration marks is 0.25mm, no defects such as cracks are found in the pickling of the surface of the slab, and the average scrap rate of the finished wire rod after rolling is only 0.27 %.

Comparative Example 1

The steel grade of this comparative example is SAE1015B, and through molten steel smelting, the mass percent of chemical composition of the finished product is controlled as follows: 0.12%≤C≤0.18%, 12ppm≤B≤18ppm, 0.10%≤Si≤0.16%, Mn≤0.80%, Al ≤0.005%, the rest is Fe and unavoidable impurity elements;

This type of steel is produced on a billet continuous casting machine. The section of the continuous casting slab is 140mm*140mm. The continuous casting process parameters are as follows: the superheat is controlled within the range of 25-35°C, and the continuous casting casting speed is stable at 2.65±0.05m/min , the cooling water volume of the mold is 1800±20L/min, the vibration frequency of the mold is controlled at 180Hz, and the amplitude is controlled at 7.8mm.

The specific water volume of the secondary cooling in continuous casting is controlled at 1.22L/kg, among which, the 1st and 2nd zones of the secondary cooling adopt the full water cooling mode, the 3rd and 4th zones of the secondary cooling adopt the air mist cooling mode, and the cooling water volume of the secondary cooling zone accounts for the total water volume R (in %) and the length L of the secondary cooling zone (in m) satisfy the following relationship: secondary cooling zone 1, R1/L1=98; secondary cooling zone 2, R2/L2=27; secondary cooling zone 3, R3/ L3=6.6; Secondary cooling zone 4, R4/L4=4.2.

In the steel rolling process control, the temperature of the soaking section of the heating furnace is controlled to be 1100°C ± 10°C, and the rolling start temperature of the billet is controlled to be 900°C ± 30°C.

The surface quality of the low-carbon boron-added steel continuous casting slab produced in this embodiment is poor, the average depth of vibration marks is 0.38mm, there are many claw-like crack defects near the corner of the billet, and the crack occurrence rate on the surface of the billet sample is as high as 20.5%. The average scrap rate of the finished wire rod is 3.99%.

Finally, it should also be noted that the term "comprises", "comprises" or any other variation thereof is intended to cover a non-exclusive inclusion such that a process, method, article or apparatus comprising a set of elements includes not only those elements, but also Other elements not expressly listed, or inherent to the process, method, article, or apparatus are also included.

Claims (5)

1. a kind of manufacture method for improving low-carbon and adding boron steel wire rod surface quality, it is characterised in that low-carbon adds the change of boron steel wire rod Study point includes by percentage to the quality：0.05%≤C≤0.30%, 8ppm≤B≤30ppm, 0.08%≤Si≤0.20%, Mn≤0.80%, 0≤Al≤0.005%, remaining is Fe and inevitable impurity element；Its manufacture method includes continuous casting and heat Roll, control condition in casting process：Degree of superheat control is 25 DEG C~40 DEG C, and pulling speed of continuous casting is 2.6m/min~2.85m/min, knot Brilliant device cooling water inflow is 1680L/min~1720L/min, and mold oscillation frequency is 160Hz~200Hz, amplitude be 6.5mm~ 8.0mm。

2. the manufacture method according to claim 1 for improving low-carbon and adding boron steel wire rod surface quality, it is characterised in that：Continuous casting During, control condition：The specific water of secondary cooling is 0.75L/kg~1.00L/kg.

3. the manufacture method according to claim 2 for improving low-carbon and adding boron steel wire rod surface quality, it is characterised in that：It is secondary Cooling is divided into 4th area, and wherein but pattern, the area of secondary cooling 3 and 4th area are cold using aerosol using full water cooling for the area of secondary cooling 1 and 2nd area But pattern.

4. the manufacture method according to claim 3 for improving low-carbon and adding boron steel wire rod surface quality, it is characterised in that：It is described Secondary cooling in, subregion cooling water inflow accounts for the cold partition length L of total Water ratio R and two and meets following relation：

1st area, 105≤R₁/L₁≤128；

2nd area, 16≤R₂/L₂≤25；

3rd area, 4.5≤R₃/L₃≤8.0；

4th area, 2.5≤R₄/L₄≤5.0。

5. the manufacture method according to claim 1 for improving low-carbon and adding boron steel wire rod surface quality, it is characterised in that：It is described In hot rolling technology, control condition：Heating furnace soaking zone temperature control is 1050 DEG C~1150 DEG C, and the control of blank start rolling temperature is 950 DEG C~1050 DEG C.