Production method for reducing occurrence rate of pit defects of pickled plate

Abstract

The invention discloses a production method for reducing the occurrence rate of pit defects of a pickled plate. The production method comprises the following steps: (1) classifying hot rolling raw materials; (2) production scheduling: the continuous scheduling of C-type hot-rolling raw materials in each group is less than or equal to 10 pieces, no more than 2 groups are arranged every day, the A-type hot-rolling raw materials are adopted for transition between the two groups, and the number of transition materials is more than or equal to 20; the continuous production scheduling of the B-type hot-rolling raw materials in each group is less than or equal to 20 pieces, no more than 4 groups are arranged every day, the A-type hot-rolling raw materials are adopted for transition between the two groups, and the number of transition materials is more than or equal to 10; and B-class and C-class transition is conducted, A-class hot rolling raw materials are adopted for transition, and the number of transition materials is larger than or equal to 15. According to the method, the hot rolling raw materials are classified from the thickness, the composition, the hot rolling process and the tensile strength according to the occurrence probability of pit defects, risk grades are distinguished, then production scheduling is distinguished, the probability of scale falling and pit occurrence is reduced in a reasonable transition mode, new equipment investment is not needed, the surface quality of a product is improved, and the production cost is reduced. And the working intensity of manual quality inspection is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of hot-rolled pickling plate production, in particular to a production method for reducing the occurrence rate of pit defects of pickling plates. BACKGROUND

[0002] The pickling plate is a product delivered to the user after removing the oxide layer, trimming, finishing and other processes by the pickling unit with high-quality hot-rolled plates as raw materials. Compared with the hot-rolled plate, the pickling plate has good surface quality, and the surface oxide scale of the hot-rolled pickling plate is removed to improve the surface quality of the steel, which is convenient for welding, oiling and painting. With the continuous progress of rolling technology, the performance of hot-rolled sheet is approaching to that of cold-rolled sheet, so that the "hot instead of cold" can be realized in technology.

[0003] However, sometimes pit defects occur on the surface of the pickling plate in production, and the color of the pit defect is not different from the plate surface, so it is difficult to be found under the stroboscope, and manual inspection with a flashlight is required. The pit defects occur on the upper and lower surfaces of the strip, and are mostly at the head and tail of the strip, with no fixed width and irregular distribution. The size of the pit defect varies from a needle point to a soybean size, and the depth is generally not more than 0.2 mm, and the shape is circular, oval or irregular small pits, which is generally considered to be caused by the adhesion of oxide scale or oxide scale powder on the roller system in the pickling production process.

[0004] At present, there are two methods to solve this defect: one is to invest or reform the equipment, increase the brush roller device or scale blowing device, which increases the production cost; the other is to strengthen the manual quality inspection, find and deal with such defects in time, which improves the working strength of the quality inspection. In view of this, a production method for reducing the occurrence rate of pit defects of pickling plates is needed to improve the surface quality of the product and reduce the working strength of the manual quality inspection. SUMMARY

[0005] The technical problem to be solved by the present application is to provide a production method for reducing the occurrence rate of pit defects of pickling plates.

[0006] To solve the above technical problems, the technical scheme adopted by the present application includes the following steps: (1) hot-rolled raw material classification: hot-rolled raw materials with a thickness of ≤4.0 mm, hot-rolled raw materials with a thickness of >4.0 mm, Si≥0.05%, and hot-rolled with a non-quenching mode and a laminar cooling rate of ≤100℃ / s, hot-rolled raw materials with Si≥0.5%, and hot-rolled raw materials with a tensile strength of ≥500 MPa, which are classified as A class; 4.0mm < thickness < 8.0mm, Si < 0.05% and tensile strength < 500, and hot-rolled raw materials with a thickness of 4.0mm < thickness < 8.0mm, hot-rolled with a concentrated cooling mode and 100 < laminar cooling rate ≤300℃ / s, and tensile strength < 500, which are classified as B class; Hot-rolled raw materials with a thickness ≥ 8.0 mm, Si < 0.5% and tensile strength < 500, hot-rolled raw materials with a thickness ≥ 8.0 mm, hot-rolled using centralized cooling mode with 100 < laminar cooling rate ≤ 300℃ / s and tensile strength < 500, and hot-rolled raw materials with a thickness > 4.0 mm, hot-rolled using quenching mode with laminar cooling rate ≥ 300℃ / s and tensile strength < 500 are classified as Category C. (2) Production scheduling: For Class C hot-rolled raw materials, each group should have ≤10 pieces of continuous production, and no more than 2 groups should be arranged per day. Class A hot-rolled raw materials should be used for transition between the two groups, with ≥20 pieces of transition material. For Class B hot-rolled raw materials, each group should continuously produce ≤20 pieces, with no more than 4 groups per day. Class A hot-rolled raw materials should be used for transition between two groups, with ≥10 pieces of transition material. The transition between Class B and Class C uses Class A hot-rolled raw materials, with a transition material quantity of ≥15 pieces.

[0007] Furthermore, in step (2), the winding tension during the production process is ≤250KN.

[0008] The beneficial effects of adopting the above technical solution are as follows: This invention classifies hot-rolled raw materials according to the probability of pit defects by thickness, composition, hot rolling process and tensile strength, distinguishes risk levels, and then reduces the probability of iron oxide scale falling off and pits by differentiating production scheduling and reasonable transition. No new equipment investment is required, the surface quality of the product is improved and the workload of manual quality inspection is reduced. Detailed Implementation

[0009] The present invention will now be described in further detail with reference to specific embodiments.

[0010] This production method for reducing the incidence of pit defects in pickled steel plates includes the following steps: (1) Classification of hot-rolled raw materials: The hot-rolled raw materials refer to raw materials that have not been pickled after hot rolling, and each hot-rolled raw material is ≤25 tons. The hot-rolled raw materials are classified according to thickness, composition, hot rolling process and tensile strength, as shown in Table 1 below; Table 1: Classification of Hot-Rolled Raw Materials

[0011] (2) Production scheduling: The production scheduling for the pickling process is as follows.

[0012] For Class C hot-rolled raw materials, each group should continuously produce ≤10 pieces, with no more than 2 groups per day. Class A hot-rolled raw materials should be used as transition materials between the two groups, with ≥20 pieces of transition materials.

[0013] For Class B hot-rolled raw materials, each group should continuously produce ≤20 pieces, with no more than 4 groups per day. Class A hot-rolled raw materials should be used as transition materials between two groups, with ≥10 pieces of transition material.

[0014] The transition between Class B and Class C hot-rolled raw materials includes transition from Class B to Class C and transition from Class C to Class B. Class A hot-rolled raw materials are used as transition materials, and the number of transition materials is ≥15 pieces.

[0015] No transition is required when producing Class A hot-rolled raw materials.

[0016] The winding tension in the above pickling process is ≤250KN.

[0017] (3) According to statistics, the incidence of pit defects in pickled plates was 2% to 5% before the method was adopted. After the method was adopted, the incidence of pit defects in pickled plates was reduced to ≤0.5%.

[0018] Example: The specific production method for reducing the incidence of pit defects in pickled plates is as follows.

[0019] (1) A batch of hot-rolled raw materials is classified according to thickness, composition, hot rolling process and tensile strength as shown in Table 2 below; Table 2: Classification of Hot-Rolled Raw Materials in Examples

[0020] (2) The specific production schedule for the pickling process is as follows: ≤25 tons per raw material: Production schedule for day 1: 10 SS400 units → 20 4.0mm thick SPHC units → 10 SS400 units → 15 4.0mm thick SPHC units → 10 S420MC units → 5 4.2mm thick HC550 / 980QP units → 5 7.0mm thick 700L units → 14 S420MC units → 12 HC420 / 780DP units → 20 5.0mm thick SPHC units.

[0021] Production schedule for the second day: 10 SS400 strips → 20 4.0mm thick SPHC strips → 5 SS400 strips + 5 SAE1008 strips → 15 4.0mm thick SPHC strips → 17 5.0mm thick SPHC strips → 50 4.0mm thick SPHC strips.

[0022] Production schedule for day three: 10 SAE1008 strips → 20 4.0mm thick SPHC strips → 9 QStE420TM strips → 41 4.0mm thick SPHC strips.

[0023] During production, the winding tension is ≤250KN.

[0024] (3) After 3 days of production, a total of 323 pickling plates were produced, of which 1 pickling plate had a pit defect, with a probability of 0.3%.

Claims

1. A production method for reducing the incidence of pit defects in pickled steel plates, characterized in that, The following steps are included: (1) Classification of hot-rolled raw materials: hot-rolled raw materials with a thickness ≤ 4.0 mm, hot-rolled raw materials with a thickness > 4.0 mm, Si ≥ 0.05%, and hot-rolled using a non-quenching mode with a laminar flow cooling rate ≤ 100℃ / s, hot-rolled raw materials with Si ≥ 0.5%, and hot-rolled raw materials with a tensile strength ≥ 500 MPa are classified as Class A; Hot-rolled raw materials with a thickness of 4.0 mm < 8.0 mm, Si < 0.05% and tensile strength < 500, and hot-rolled raw materials with a thickness of 4.0 mm < 8.0 mm, hot-rolled using centralized cooling mode and with a laminar flow cooling rate of 100 < 300℃ / s and tensile strength < 500, are classified as Category B. Hot-rolled raw materials with a thickness ≥ 8.0 mm, Si < 0.5% and tensile strength < 500, hot-rolled raw materials with a thickness ≥ 8.0 mm, hot-rolled using centralized cooling mode with 100 < laminar cooling rate ≤ 300℃ / s and tensile strength < 500, and hot-rolled raw materials with a thickness > 4.0 mm, hot-rolled using quenching mode with laminar cooling rate ≥ 300℃ / s and tensile strength < 500 are classified as Category C. (2) Production scheduling: For Class C hot-rolled raw materials, each group should have ≤10 pieces of continuous production, and no more than 2 groups should be arranged per day. Class A hot-rolled raw materials should be used for transition between the two groups, with ≥20 pieces of transition material. For Class B hot-rolled raw materials, each group should continuously produce ≤20 pieces, with no more than 4 groups per day. Class A hot-rolled raw materials should be used for transition between two groups, with ≥10 pieces of transition material. The transition between Class B and Class C uses Class A hot-rolled raw materials, with a transition material quantity of ≥15 pieces.

2. The production method for reducing the incidence of pit defects in pickled steel plates according to claim 1, characterized in that: In step (2), the winding tension during the production process is ≤250KN.

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