A method for removing surface deformation streak defects of a cold-rolled steel sheet

Abstract

The application discloses a method for removing surface deformation stripe defects of a cold-rolled steel plate, adopts a degreasing agent and a degreasing additive compatible with the degreasing agent to perform degreasing treatment on the steel plate after rolling, and then performs annealing treatment on the steel plate after the degreasing treatment; the degreasing additive comprises sodium dodecyl benzene sulfonate, sodium sulfate and sodium benzoate. Through improvement of the degreasing process and the annealing process, the cold-rolled steel plate does not generate stripe defects after deformation in the use process, the normal use and smooth production of the cold-rolled steel plate are ensured, and customer satisfaction is improved.

Description

Technical Field

[0001] This invention belongs to the field of surface treatment technology for cold-rolled steel sheets, and relates to a method for removing deformation stripe defects on the surface of cold-rolled steel sheets. Background Technology

[0002] Cold rolling is a rolling process that uses hot-rolled coils as raw materials and rolls them below the recrystallization temperature at room temperature. Cold-rolled steel sheets are steel sheets produced through this process. Because cold-rolled steel sheets are rolled at room temperature, they do not produce iron oxide scale, resulting in good surface quality and high dimensional accuracy. Furthermore, annealing treatment significantly improves their mechanical and technological properties. Cold-rolled steel sheets offer advantages such as good paintability, high strength, excellent stamping performance, and relatively low price. Therefore, cold-rolled steel sheets have a wide range of applications, including in the automotive, electrical product, locomotive, aerospace, precision instrument, and food canning industries. As the application areas of cold-rolled steel sheets continue to expand and market competition intensifies, the requirements for the surface quality of cold-rolled products are becoming increasingly stringent.

[0003] The cold rolling production process generally includes multiple steps such as raw material preparation, pickling, rolling, degreasing, annealing (heat treatment), and finishing. Cold rolling uses hot-rolled products as raw materials. Before cold rolling, the raw materials must be dephosphorized to ensure the surface cleanliness of the cold-rolled products. Rolling is the main process that deforms the material. The purpose of degreasing is to remove the lubricating grease adhering to the rolled material during rolling to prevent contamination of the steel surface during annealing. Annealing includes intermediate annealing and finished product heat treatment. Intermediate annealing eliminates work hardening through recrystallization, restores the material's plasticity, and reduces the metal's resistance to deformation, thereby obtaining the desired microstructure and product properties. The complex production process involves contact with various chemical media necessary for production, such as emulsions, degreasing agents, leveling solutions, and rinsing water. It also requires high-temperature heat treatment. The complexity of the cold-rolled steel sheet production process determines that cold-rolled steel sheets are heterogeneous materials, resulting in significant differences in surface characteristics. Various quality defects frequently appear on the surface of cold-rolled steel sheets. One particularly serious surface defect is highly concealed but poses a significant potential hazard. While the defect may not be visible on the surface before leaving the factory, it can manifest as large-area striped defects after the user performs stamping and deformation treatment. These defects severely reduce the surface appearance quality of the steel sheet, affect its surface performance, cause significant problems for subsequent coating processes, greatly impact production flow, lead to customer complaints and objections, and seriously affect the reputation and market expansion of the steel manufacturer. Summary of the Invention

[0004] To address the aforementioned deficiencies in existing technologies, the purpose of this invention is to provide a method for removing deformation stripe defects from the surface of cold-rolled steel sheets. By improving the degreasing and annealing processes, the method ensures that stripe defects no longer occur after deformation of the cold-rolled steel sheets during use, guaranteeing normal use and smooth production, and improving customer satisfaction. The method of this invention has advantages such as accuracy, good repeatability, and strong operability, providing important theoretical basis for adjusting material composition and optimizing production processes in mass production, and solving the problem of stripe-like defects appearing on the surface of cold-rolled steel sheets after subsequent deformation processing.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] This invention provides a method for removing deformation stripe defects on the surface of cold-rolled steel sheets. The method involves degreasing the rolled steel sheet using a degreasing agent and a degreasing additive compatible with the degreasing agent, followed by annealing the degreased steel sheet. The degreasing additive includes sodium dodecylbenzenesulfonate, sodium sulfate, and sodium benzoate.

[0007] Preferably, the degreasing additive comprises the following components by mass percentage: 1-10% sodium dodecylbenzenesulfonate, 2-7% sodium sulfate, 0.2-2% sodium benzoate, and the balance being water.

[0008] Preferably, in the degreasing treatment, the degreasing additive is added to the degreasing agent, and the concentration of the degreasing additive in the mixed solvent of the degreasing agent and the degreasing additive is 1-8 wt%.

[0009] Preferably, the degreasing treatment employs chemical degreasing and electrolytic degreasing;

[0010] In the chemical degreasing process, the degreasing temperature is 60–85°C, and the alkaline soaking time is 2–10 seconds.

[0011] In the electrolytic degreasing process, the electrolysis time is 0.2–0.9 s and the current density is 10–25 A / dm³. 2 .

[0012] Preferably, the annealing process includes a heating stage and a slow cooling stage;

[0013] During the heating stage, the heating temperature is 600–900℃, and the holding time is 40–150 seconds.

[0014] During the slow cooling stage, the heated steel plate is reduced to a slow cooling temperature and held at that temperature. The slow cooling temperature is 620–780°C, and the holding time is 8–40 seconds.

[0015] Preferably, during the heating stage, the heating rate is 4–8 °C / s.

[0016] Preferably, during the slow cooling stage, the cooling rate is 2–6 °C / s.

[0017] Preferably, during the annealing process, the cold-rolled steel sheet travels at a speed of 120–400 m / s.

[0018] The method for removing deformation stripe defects on the surface of cold-rolled steel sheets provided by this invention has the following beneficial effects:

[0019] The method for removing deformation stripe defects on the surface of cold-rolled steel sheets according to the present invention improves the degreasing and annealing processes, so that no stripe defects are generated after the cold-rolled steel sheets are deformed during use, thereby improving the surface quality of the cold-rolled steel sheets, ensuring normal use and smooth production, and increasing customer satisfaction. The method of the present invention has the advantages of accuracy, good repeatability, and strong operability. It can be used to study the formation mechanism of deformation stripe defects on the surface of cold-rolled steel sheets, and can also be used for laboratory production process simulation studies. It provides important theoretical basis for adjusting material composition and optimizing production processes in large-scale production, and solves the problem of stripe-like defects appearing on the surface of cold-rolled steel sheets after subsequent deformation processing. Detailed Implementation

[0020] To better understand the above-mentioned technical solutions of the present invention, the technical solutions of the present invention will be further described below in conjunction with embodiments.

[0021] The method for removing deformation stripe defects on the surface of cold-rolled steel sheets provided by the present invention includes multiple production processes such as raw material preparation, pickling, rolling, degreasing, annealing (heat treatment), and finishing. In the degreasing process, a degreasing agent and a degreasing additive compatible with the degreasing agent are used to degrease the rolled steel sheet. After the degreasing treatment, the steel sheet is annealed. The resulting cold-rolled steel sheet will not have deformation stripe defects on its surface after stamping and other processing.

[0022] The method for removing deformation stripe defects on the surface of cold-rolled steel sheets according to the present invention specifically includes the following steps:

[0023] (1) Prepare a degreasing additive using sodium dodecylbenzenesulfonate, sodium sulfate, and sodium benzoate. The specific degreasing additive includes the following components by mass percentage: sodium dodecylbenzenesulfonate 1-10%, sodium sulfate 2-7%, sodium benzoate 0.2-2%, and the remainder is water.

[0024] (2) Degreasing treatment: The prepared degreasing additive is added to the degreasing agent, and the rolled steel plate is degreased. The degreasing agent can be commercially available Kao alkaline degreasing agent, Henkel alkaline degreasing agent, or Yinuo alkaline degreasing agent, etc. The concentration of the degreasing additive in the mixed solvent formed by the degreasing additive and the degreasing agent is 1-8 wt%. The degreasing treatment includes chemical degreasing and electrolytic degreasing. In chemical degreasing, the degreasing temperature is 60-85℃ and the alkaline immersion time is 2-10s. In electrolytic degreasing, the electrolysis time is 0.2-0.9s and the current density is 10-25A / dm³. 2 .

[0025] (3) Annealing treatment: The degreased steel plate is annealed. The annealing treatment includes a heating stage and a slow cooling stage. In the heating stage, the degreased steel plate is first heated to 600-900℃ (heating temperature) and held for 40-150s (holding time). The heating rate during this process is 4-8℃ / s. Then, the slow cooling stage begins, where the heated steel plate is slowly cooled to 620-780℃ (slow cooling temperature) and held for 8-40s (holding time). The cooling rate during this process is 2-6℃ / s. During the annealing process, the cold-rolled steel plate travels at a speed of 120-400m / s.

[0026] After the cold-rolled steel sheet obtained by the above treatment arrives at the user, no deformation stripe defects occur on its surface after deformation treatment such as stamping, which does not affect subsequent coating and other processes.

[0027] The method for removing deformation stripe defects on the surface of cold-rolled steel sheets according to the present invention will be further described below with specific examples.

[0028] Example 1

[0029] In this embodiment, the cold-rolled steel sheet is obtained through multiple production processes, including raw material preparation, pickling, rolling, degreasing, annealing (heat treatment), and finishing. The method for removing deformation stripe defects on the surface of the cold-rolled steel sheet according to this invention is employed during the preparation process, including the following steps:

[0030] (1) Preparation of degreasing additive: The main components of the degreasing additive and the mass percentage of each component are: sodium dodecylbenzenesulfonate 2-5%, sodium sulfate 3-4%, sodium benzoate 0.5-0.8%, and the remainder is water.

[0031] (2) Degreasing treatment: Degreasing additives are added to the degreasing agent used in the degreasing process, with the concentration of the degreasing additives being 2-5%. Then, the rolled steel plate is degreased using the aforementioned mixed solvent. The degreasing process includes chemical degreasing and electrolytic degreasing. In chemical degreasing, the degreasing temperature is 65-75℃, and the alkaline immersion time is 5-8s; in electrolytic degreasing, the electrolysis time is 0.3-0.6s, and the current density is 12-18 A / dm³. 2.

[0032] (3) Annealing treatment: The steel plate after degreasing is then annealed. The main process parameters for annealing are: heating temperature and holding time in the heating stage are 660-700℃ and 80-120s, respectively; slow cooling temperature and holding time in the slow cooling stage are 630-650℃ and 20-30s, respectively; and the running speed of the cold-rolled steel plate during the annealing process is 150-200m / s.

[0033] After the above-mentioned process, the cold-rolled steel sheet obtained does not develop deformation stripe defects on its surface after subsequent hot stamping and other deformation treatments.

[0034] Example 2

[0035] In this embodiment, the cold-rolled steel sheet is obtained through multiple production processes, including raw material preparation, pickling, rolling, degreasing, annealing (heat treatment), and finishing. The method for removing deformation stripe defects on the surface of the cold-rolled steel sheet according to this invention is employed during the preparation process, including the following steps:

[0036] (1) Preparation of degreasing additive: The main components of the degreasing additive and the mass percentage of each component are: sodium dodecylbenzenesulfonate 3-6%, sodium sulfate 5-7%, sodium benzoate 1.5-1.8%, and the remainder is water.

[0037] (2) Degreasing treatment: Degreasing additives are added to the degreasing agent used in the degreasing process, with the concentration of the degreasing additives being 5-7%. Then, the rolled steel plate is degreased using the aforementioned mixed solvent. The degreasing process includes chemical degreasing and electrolytic degreasing. In chemical degreasing, the degreasing temperature is 75-85℃, and the alkaline immersion time is 5-9s; in electrolytic degreasing, the electrolysis time is 0.5-0.8s, and the current density is 15-20 A / dm³. 2 .

[0038] (3) Annealing treatment: The steel plate after degreasing is then annealed. The main process parameters for annealing are: heating temperature and holding time in the heating stage are 750-800℃ and 50-90s, respectively; slow cooling temperature and holding time in the slow cooling stage are 680-720℃ and 20-30s, respectively; and the running speed of the cold-rolled steel plate during the annealing process is 300-400m / s.

[0039] After the above-mentioned process, the cold-rolled steel sheet obtained does not develop deformation stripe defects on its surface after subsequent hot stamping and other deformation treatments.

[0040] Example 3

[0041] In this embodiment, the cold-rolled steel sheet is obtained through multiple production processes, including raw material preparation, pickling, rolling, degreasing, annealing (heat treatment), and finishing. The method for removing deformation stripe defects on the surface of the cold-rolled steel sheet according to this invention is employed during the preparation process, including the following steps:

[0042] (1) Preparation of degreasing additive: The main components of the degreasing additive and the mass percentage of each component are: sodium dodecylbenzenesulfonate 6-9%, sodium sulfate 3-5%, sodium benzoate 0.8-1.5%, and the remainder is water.

[0043] (2) Degreasing treatment: Degreasing additives are added to the degreasing agent used in the degreasing process, with the concentration of the degreasing additives being 4-7%. Then, the rolled steel plate is degreased using the aforementioned mixed solvent. The degreasing process includes chemical degreasing and electrolytic degreasing. In chemical degreasing, the degreasing temperature is 65-75℃, and the alkaline immersion time is 3-7s. In electrolytic degreasing, the electrolysis time is 0.4-0.8s, and the current density is 12-18 A / dm³. 2 .

[0044] (3) Annealing treatment: The steel plate after degreasing is then annealed. The main process parameters for annealing are: heating temperature and holding time in the heating stage are 760~820℃ and 110~150s, respectively; slow cooling temperature and holding time in the slow cooling stage are 690~750℃ and 20~30s, respectively; and the running speed of the cold-rolled steel plate during the annealing process is 180~260m / s.

[0045] After the above-mentioned process, the cold-rolled steel sheet obtained does not develop deformation stripe defects on its surface after subsequent hot stamping and other deformations.

[0046] Those skilled in the art should recognize that the above embodiments are merely illustrative of the present invention and are not intended to limit the present invention. Any variations or modifications to the above embodiments that are within the spirit and essence of the present invention will fall within the scope of the claims of the present invention.

Claims

1. A method for removing deformation stripe defects from the surface of cold-rolled steel sheets, characterized in that, The rolled steel plate is degreased using a degreasing agent and a degreasing additive compatible with the degreasing agent, and then the degreased steel plate is annealed. The defatting additives include sodium dodecylbenzenesulfonate, sodium sulfate, and sodium benzoate. The defatting additive comprises the following components by mass percentage: sodium dodecylbenzenesulfonate 1-10%, sodium sulfate 2-7%, sodium benzoate 0.2-2%, with the balance being water. In the degreasing process, the degreasing additive is added to the degreasing agent, and the concentration of the degreasing additive in the mixed solvent of the degreasing agent and the degreasing additive is 1-8 wt%. The degreasing process employs both chemical and electrolytic degreasing. In the chemical degreasing process, the degreasing temperature is 60–85°C, and the alkaline soaking time is 2–10 seconds. In the electrolytic degreasing process, the electrolysis time is 0.2–0.9 s and the current density is 10–25 A / dm³. 2 , The annealing process includes a heating stage and a slow cooling stage; During the heating stage, the heating temperature is 600–900℃, and the holding time is 40–150 seconds. During the slow cooling stage, the heated steel plate is lowered to a slow cooling temperature and held at that temperature. The slow cooling temperature is 620–780°C, and the holding time is 8–40 seconds. The cold-rolled steel sheet obtained by the method did not develop deformation stripe defects on its surface after subsequent hot stamping deformation treatment.

2. The method for removing deformation stripe defects on the surface of cold-rolled steel sheets according to claim 1, characterized in that, During the heating stage, the heating rate is 4–8 °C / s.

3. The method for removing deformation stripe defects on the surface of cold-rolled steel sheets according to claim 1, characterized in that, During the slow cooling phase, the cooling rate is 2–6 °C / s.

4. The method for removing deformation stripe defects on the surface of cold-rolled steel sheets according to claim 1, characterized in that, During the annealing process, the cold-rolled steel sheet travels at a speed of 120–400 m / s.