CN109252110B - A kind of low-carbon hot-rolled pickling plate for automobile and preparation method thereof - Google Patents

Abstract

The invention provides a low-carbon hot-rolled pickling plate for automobiles and a preparation method thereof. The composition of the steel plate is as follows by weight percentage: C: 0.03% to 0.08%, Si: ≤0.05%, Mn: 0.1% to 0.25% %, P: <0.012%, S: <0.005%, Als: 0.050%-0.080%, N<0.003%, and Als/N≥20, and the rest are Fe and unavoidable impurities. The preparation method includes molten iron pretreatment→converter smelting→LF refining→calcium treatment→continuous casting→slab heating→rough rolling→finish rolling→coiling→uncoiling→welding→pickling. The occurrence of defects does not require a leveling process to eliminate product cross-folding defects, the equipment is simple and the cost is low.

Description

A kind of low-carbon hot-rolled pickling plate for automobile and preparation method thereof

technical field

The invention belongs to the field of metal materials, in particular to a low-carbon hot-rolled pickling plate with high surface quality suitable for automobiles and a preparation method thereof.

Background technique

The hot-rolled pickled plate is a steel plate product with good surface quality after the oxide layer on the surface of the steel plate is removed by the pickling unit, and its surface quality and use requirements are between the hot-rolled plate and the cold-rolled plate. Compared with cold-rolled sheets, it has lower cost and higher cost performance, and is an ideal substitute product for some cold-rolled sheets. Pickling sheet has a wide range of applications and can be used in automobiles, compressors, machinery manufacturing, spare parts processing and other industries. Among them, the automotive industry has high requirements for the surface quality of hot-rolled pickling sheets. Therefore, iron and steel enterprises at home and abroad have improved the production process and technical equipment of key processes. For example, through the application of fast AGC control technology and process lubrication technology, the quality of hot-rolled pickled plates has been significantly improved, but hot-rolled pits still appear , Horizontal folding and other defects. Especially for low-carbon hot-rolled pickled plates, due to their low yield and tensile strength, pitting and cross-folding defects occur at a very high rate when producing thin-gauge products, which seriously affects the yield of pickled plates and increases product quality. cost.

Cross fold marks are straight line marks that penetrate the plate surface and are perpendicular to the rolling direction in the local area of the strip during the uncoiling process of hot-rolled low-carbon steel. The occurrence of transverse fold defects is related to the yield phenomenon of low carbon steel. When the steel coil is uncoiled and straightened by the uncoiler, when the uncoiling tension is too large or the deformation is too large in the process of bending and straightening, the surface stress of the strip reaches or exceeds the yield strength of the material, which will cause plastic deformation of the strip , due to the existence of the yield platform, it is concentrated in a certain area, thus forming uneven transverse fold defects.

The existence of the yield plateau is caused by the Coriolis air mass in the steel. A kind of atomic cloud formed by interstitial solid-solution atoms C and N dissolved in steel around dislocations is the Coriolis air mass. When the steel strip undergoes plastic deformation under force, the Coriolis air mass pins the slip of the movable dislocation, making the upper yield point appear in the strip steel during the strain process. After the dislocation moves a certain distance with the increase of the stress, it can Get rid of the resistance of the air mass and move under the normal stress, this stress is the lower yield point, and this process forms the yield platform.

Generally, the method of flattening before pickling is used in production to solve the defects of cross-folding. Although temper rolling can avoid the occurrence of cross-fold defects in the subsequent production process, cross-fold defects will also occur during the uncoiling process of the tempering process. This defect area can only be cut off on the recoiling unit, resulting in steel The coil yield is low, which increases the cost.

"A Low-Carbon Aluminum Killed Steel Hot-Dip Galvanized Sheet and Its Production Method" (publication number CN104451377A) discloses that the low-carbon aluminum killed steel adopts the chemical composition of C: 0.015% ~ 0.08%, Si: ≤ 0.03%, Mn: 0.1 %～0.15%, P: <0.020%, S: <0.010%, Als: 0.035%～0.060%, N≤0.002%, the balance is Fe and unavoidable impurities. The design of the chemical composition adopts higher Al content and lower N content to ensure that N is fully separated in the form of AlN, reduce the solid solution N content in low-carbon aluminum-killed steel hot-dip galvanized sheets, and avoid low-carbon aluminum in terms of chemical composition. Killed steel hot-dip galvanized sheet is bent and ribbed after color coating. At the same time, according to the carbon content of different products, the invention adopts a coiling temperature higher than that of the middle part for different lengths of the head and tail of the hot-rolled coil, so as to avoid the hot-rolled galvanized sheet from the production method, especially the folding of the head and tail after color coating. Bend the edges. However, because the invention requires strict setting of the coiling temperature at the beginning and end according to the length, the requirements for equipment are relatively high.

"A Hot-Rolled Pickled Plate and Its Production Method" (publication number CN104480391A) discloses that the hot-rolled pickled plate is based on the composition system of ordinary low-carbon steel, by adding microalloying elements B and Ti, and combining Heat preservation in the hot coil box, relaxation and cooling after finishing rolling, finally achieve the control of structure and precipitated phase, reduce the effect of Coriolis air mass in low carbon steel, reduce the stress difference between the upper and lower yield points of the hot-rolled strip to below 5MPa, and eliminate the heat loss. The surface cross-folding defect of the rolled plate during the pickling, decoiling and straightening process. However, since the invention adds microalloying elements such as B and Ti, the steelmaking cost is relatively high. And the addition of B and Ti elements is easy to form coarse precipitates, which damages the final product performance.

Contents of the invention

The purpose of the present invention is to overcome the above problems and deficiencies and provide a method of controlling the content of carbon and nitrogen elements in the low-carbon hot-rolled pickling plate to reduce the elongation at the yield point, and at the same time cooperate with the optimized hot-rolling and pickling process, A low-carbon hot-rolled pickled sheet for automobiles with stable coil performance and high surface quality and a preparation method thereof.

The main method of the present invention is to reduce the content of solid-dissolved nitrogen atoms in the ferrite matrix by controlling the relative content of nitrogen and acid-soluble aluminum in the chemical composition. The influence of the Coriolis air mass makes the hot-rolled pickled product have a lower elongation at the yield point and is less likely to produce cross-folding defects. At the same time, with the optimized hot rolling and pickling decoiling process, the yield strength of the product can be improved, so as to effectively eliminate the cross-folding defect on the surface of the low carbonic acid washed plate without increasing the cost.

A low-carbon hot-rolled pickled sheet for automobiles. The composition of the steel sheet is as follows by weight percentage: C: 0.03% to 0.08%, Si: ≤0.05%, Mn: 0.1% to 0.25%, P: <0.012%, S: <0.005%, Als: 0.050%~0.080%, N<0.003%, the rest is Fe and unavoidable impurities; at the same time, Als/N≥20 is required to ensure that N elements can completely form AlN.

The composition design reason of the present invention is as follows:

Carbon: A low-cost, effective solid-solution strengthening element. In low-carbon hot-rolled pickling plates, the strength of ferrite structure can be guaranteed through solid-solution strengthening. With the increase of carbon content, a small amount of Fe3C carbide and A very small amount of pearlite structure. When there are more carbon atoms in the solid solution in the steel, it is easy to form a Coriolis air mass, forming a yield platform, which makes the strip steel have a higher yield point elongation, and forms a transverse fold defect during the pickling and uncoiling process. However, when the carbon content is too low, the yield and tensile strength of the strip cannot be guaranteed, and the use requirements cannot be met, and when the carbon content is less than 0.02%, it is necessary to increase the process for decarburization treatment, which increases the production cost. Therefore, the present invention controls the carbon content between 0.03% and 0.10%.

Silicon: It is a cheap alloying element, which can effectively deoxidize and play a role of solid solution strengthening. Considering that the yield and tensile strength of low-carbon hot-rolled pickling plates are not high, and high silicon content will affect rolling Descaling effect and pickling surface quality, so the silicon content of the hot-rolled pickling plate of the present invention is controlled between ≤0.05.

Manganese: In the present invention, Mn is mainly used to improve the strength and toughness of the strip steel. When the Mn content is low, the yield of the strip steel is too low, and it is easy to form a cross fold in the pickling and uncoiling process. When the Mn content is high, the product will be reduced. The elongation rate is not conducive to the stamping performance of the product, so the present invention controls the Mn content at 0.1-0.25%.

Aluminum: It is a strong deoxidizing element. By adding a certain amount of aluminum element, the oxygen content in the steel can be kept as low as possible. The excess aluminum after deoxidation can form AlN precipitates with nitrogen in the steel, reducing the solid solution of N atoms in the steel. Therefore, in the present invention, the content of Als is controlled at 0.050-0.080wt%.

Nitrogen: The Coriolis air mass formed by nitrogen in the steel will hinder dislocation slippage during stretching and form a yield platform. Therefore, in the present invention, the N content is controlled to be less than or equal to 0.0030%. By reducing the solid solution nitrogen content in the low-carbon hot-rolled pickling plate, at the same time, Als/N is required to be greater than or equal to 20 so as to ensure that the N element can completely form AlN, and further reduce the solid solution N content. , from the chemical composition to reduce the occurrence of cross-folding defects.

Phosphorus and sulfur are impurity elements. In principle, the lower the better, considering the cost, the present invention controls the content of phosphorus and sulfur to P≤0.012%, S≤0.005%.

The second technical solution of the present invention is to provide a method for preparing low-carbon hot-rolled pickled plates for automobiles, including molten iron pretreatment→converter smelting→LF refining→calcium treatment→continuous casting→slab heating→rough rolling→finish rolling→ coiling→uncoiling→welding→pickling,

The heating temperature of the continuous casting slab is 1140～1200℃. The continuous casting slab is rolled on the rolling mill for multiple passes. The thickness of the intermediate slab is 35～45mm. 1070°C, the final rolling temperature is 840-880°C, and the coiling temperature is controlled between 580-680°C. Afterwards, the stacking is slow cooling, and the stacking slow cooling time is ≥ 8h; the strip steel stacking slow cooling after hot rolling ensures that carbides and AlN have sufficient time for analysis. When the steel coil is cooled to below 45°C, it is uncoiled and straightened again. After pickling with hydrochloric acid, the strip steel is rinsed and dried, and finally the edge is trimmed and oiled to the final product.

Further, the temperature control during the coiling process after hot rolling is as follows:

The strength of the steel plate of the present invention is mainly achieved by solid solution strengthening of C and Mn, so the parameter λ=C+Mn/20 is selected as the measure standard of material strength, and λ is divided into 0.035～0.055, 0.056～0.75, 0.076～0.0925 Three intervals, and the thickness is divided into three intervals: 1.4mm～2.5mm, 2.51mm～4.0mm and 4.01mm～6.0mm

In order to ensure the yield strength ≥ 240MPa further, the temperature control during the coiling process after hot rolling is as follows:

Further, the temperature control during the coiling process after hot rolling is as follows:

When 0.035≤λ≤0.055, the thickness of the finished hot-rolled pickling plate within the range of 1.4mm～2.5mm, the coiling temperature is controlled at 650±20℃;

When 0.035≤λ≤0.055, the finished hot-rolled pickling plate with a thickness in the range of 2.51mm～4.0mm, the coiling temperature is controlled at 630±20℃;

When 0.035≤λ≤0.055, the thickness of the finished hot-rolled pickling plate within the range of 4.01mm～6.0mm, the coiling temperature is controlled at 610±20℃;

When 0.056≤λ≤0.075, the thickness of the finished hot-rolled pickling plate within the range of 1.4mm～2.5mm, the coiling temperature is controlled at 660±20℃;

When 0.056≤λ≤0.075, the finished hot-rolled pickling plate with a thickness in the range of 2.51mm～4.0mm, the coiling temperature is controlled at 640±20℃;

When 0.056≤λ≤0.075, the thickness of the finished hot-rolled pickling plate within the range of 4.01mm～6.0mm, the coiling temperature is controlled at 620±20℃

When 0.076≤λ≤0.0925, the finished hot-rolled pickling plate with a thickness within the range of 1.4mm to 2.5mm, the coiling temperature is controlled at 670±20°C;

When 0.076≤λ≤0.0925, the finished hot-rolled pickling plate with a thickness in the range of 2.51mm～4.0mm, the coiling temperature is controlled at 650±20℃;

When 0.076≤λ≤0.0925, the finished hot-rolled pickling plate with a thickness in the range of 4.01mm～6.0mm, the coiling temperature is controlled at 630±20℃;

When the ambient temperature is ≥28°C, the above-mentioned coiling temperatures are all reduced by 20°C.

The method ensures that the yield strength of the produced low-carbon hot-rolled pickling plate is ≥240MPa.

In the present invention, in order to produce low-carbon hot-rolled pickled plates with high surface quality, Als is increased and N content is reduced to ensure that N is fully separated in the form of AlN, thereby reducing the content of solid solution nitrogen in low-carbon hot-rolled pickled plates. At the same time, through stacking and cooling of hot-rolled coils, it is ensured that the C element is precipitated in the form of carbides as much as possible, the concentration of interstitial solid-solution atoms carbon and nitrogen in the ferrite structure is reduced, the elongation at the yield point is reduced, and the cross-folding during uncoiling is reduced. The probability of a defect occurring.

Also in the hot rolling process, because the low-carbon hot-rolled pickling plate does not contain difficult-to-dissolve microalloying elements, a low heating temperature is used to prevent grain coarsening on the one hand, and on the other hand, it can be easily controlled to obtain a lower The final rolling temperature and coiling temperature can produce hot-rolled pickled sheets with fine grains, taking into account the strength and toughness, so that the yield strength of hot-rolled pickled sheets is ≥240MPa, and the elongation is ≥40%. It is not easy to form horizontal fold defects in the process of washing and unwinding.

The beneficial effects of the present invention are:

In the composition system of ordinary low-carbon steel, the present invention increases the content of Als appropriately, reduces the content of N atoms, and makes it exist in the form of AlN, combined with stacking and slow cooling after rolling, the yield point elongation of the product itself is reduced; at the same time, it optimizes The final hot rolling process ensures the yield strength ≥ 240MPa, eliminating the occurrence of transverse fold defects in the uncoiling process. The present invention does not need to adopt a leveling process to eliminate product transverse folding defects, and the equipment is simple and the cost is low.

Description of drawings

Fig. 1 is the tensile stress-strain curve of Example 2 of the present invention.

Detailed ways

Below by embodiment the present invention will be further described.

In the embodiment of the present invention, according to the composition ratio of the technical solution, molten iron pretreatment → converter smelting → LF refining → calcium treatment → continuous casting → slab heating → rough rolling → finish rolling → coiling → uncoiling → welding → pickling.

The heating temperature of the slab is 1140-1200°C, and then the slab is rolled. The thickness of the intermediate slab is 35-45mm, the total reduction ratio of the finish rolling is ≥85%, the entrance temperature of the finish rolling is controlled at 1030-1070°C, and the finish rolling temperature The temperature is 840-880°C, the coiling temperature is controlled between 580-680°C, and then stacked and slowly cooled, and the stacking and slow cooling time is ≥8h; when the steel coil is cooled to below 45°C, it will be uncoiled and straightened again.

The further coiling temperature is:

Select the parameter λ=C+Mn/20 as the measure of material strength, divide λ into three intervals of 0.035~0.055, 0.056~0.75, and 0.076~0.0925, and divide the thickness into 1.4mm~2.5mm, 2.51mm~4.0mm And three intervals from 4.01mm to 6.0mm;

When 0.035≤λ≤0.055, the thickness of the finished hot-rolled pickling plate within the range of 1.4mm～2.5mm, the coiling temperature is controlled at 650±20℃;

When 0.035≤λ≤0.055, the finished hot-rolled pickling plate with a thickness in the range of 2.51mm～4.0mm, the coiling temperature is controlled at 630±20℃;

When 0.035≤λ≤0.055, the thickness of the finished hot-rolled pickling plate within the range of 4.01mm～6.0mm, the coiling temperature is controlled at 610±20℃;

When 0.056≤λ≤0.075, the thickness of the finished hot-rolled pickling plate within the range of 1.4mm～2.5mm, the coiling temperature is controlled at 660±20℃;

When 0.056≤λ≤0.075, the finished hot-rolled pickling plate with a thickness in the range of 2.51mm～4.0mm, the coiling temperature is controlled at 640±20℃;

When 0.056≤λ≤0.075, the thickness of the finished hot-rolled pickling plate within the range of 4.01mm～6.0mm, the coiling temperature is controlled at 620±20℃

When 0.076≤λ≤0.0925, the finished hot-rolled pickling plate with a thickness within the range of 1.4mm to 2.5mm, the coiling temperature is controlled at 670±20°C;

When 0.076≤λ≤0.0925, the finished hot-rolled pickling plate with a thickness in the range of 2.51mm～4.0mm, the coiling temperature is controlled at 650±20℃;

When 0.076≤λ≤0.0925, the finished hot-rolled pickling plate with a thickness in the range of 4.01mm～6.0mm, the coiling temperature is controlled at 630±20℃;

When the ambient temperature is ≥28°C, the above-mentioned coiling temperatures are all reduced by 20°C.

The composition of the steel of the embodiment of the present invention is shown in Table 1. The main process parameters of the steel of the embodiment of the present invention are shown in Table 2. The performance of the steel of the embodiment of the present invention is shown in Table 3.

Table 1 Composition (wt %) of the embodiment steel of the present invention

Example C Si mn P S als N Als/N 1 0.030 0.01 0.18 0.011 0.005 0.060 0.0019 31.6 2 0.050 0.02 0.16 0.012 0.004 0.035 0.0017 20.6 3 0.065 0.04 0.25 0.011 0.005 0.040 0.0012 33.3 4 0.070 0.03 0.12 0.009 0.005 0.045 0.0014 32.1 5 0.08 0.05 0.1 0.008 0.003 0.055 0.0015 36.7

Table 2 The main process parameters of steel in the embodiment of the present invention

The performance of table 3 embodiment steel of the present invention

In order to describe the present invention, the present invention has been properly and fully described through the examples above. The above embodiments are only used to illustrate the present invention, rather than to limit the present invention. In the case of the spirit and scope of the invention, various changes and modifications can also be made, and any modifications, equivalent replacements, improvements, etc., should be included in the protection scope of the present invention, and the patent protection scope of the present invention should be determined by Claims limited.

Claims (1)

1. a kind of automobile low-carbon hot-rolling acid-cleaning plate, which is characterized in that the ingredient of the steel plate is as follows by weight percentage: C: 0.03%~0.08%, Si :≤0.05%, Mn:0.1%~0.25%, P: < 0.012%, S: < 0.005%, Als:0.050% ~0.080%, N < 0.003%, and Als/N >=20, remaining is Fe and inevitable impurity；The automobile low-carbon hot-rolling acid The preparation method of board-washing, including molten iron pretreatment → converter smelting → LF refining → Calcium treatment → continuous casting → heating of plate blank → roughing → finish rolling → batches → uncoiling → welding → pickling,

Slab heating temperature is 1140~1200 DEG C, is rolled later to slab, and workpiece thickness is 35~45mm, and finish rolling is total Reduction ratio >=85%, entry temperature at finishing control is at 1030~1070 DEG C, and finishing temperature is 840~880 DEG C, oiler temperature control Between 580~680 DEG C, stacking slow cooling later, the stacking slow cooling time >=8h；It is opened again after when coilcooling is to 45 DEG C or less Volume aligning；

Coiling temperature are as follows:

λ point as the measurement standard of the strength of materials is 0.035~0.055 by selected parameter λ=C+Mn/20,0.056~0.75, 0.076~0.0925 3 sections, at the same by thickness be divided into 1.4mm~2.5mm, 2.51mm~4.0mm and 4.01mm~ Tri- sections 6.0mm；

When 0.035≤λ≤0.055, hot rolled plate of the thickness within the scope of 1.4mm~2.5mm, oiler temperature control is 650 ± 20 ℃；

When 0.035≤λ≤0.055, finished product hot rolling acid-cleaning plate of the thickness within the scope of 2.51mm~4.0mm, oiler temperature control It is 630 ± 20 DEG C；

When 0.035≤λ≤0.055, finished product hot rolling acid-cleaning plate of the thickness within the scope of 4.01mm~6.0mm, oiler temperature control It is 610 ± 20 DEG C；

When 0.056≤λ≤0.075, finished product hot rolling acid-cleaning plate of the thickness within the scope of 1.4mm~2.5mm, oiler temperature control is 660±20℃；

When 0.056≤λ≤0.075, finished product hot rolling acid-cleaning plate of the thickness within the scope of 2.51mm~4.0mm, oiler temperature control It is 640 ± 20 DEG C；

When 0.056≤λ≤0.075, finished product hot rolling acid-cleaning plate of the thickness within the scope of 4.01mm~6.0mm, oiler temperature control It is 620 ± 20 DEG C

When 0.076≤λ≤0.0925, finished product hot rolling acid-cleaning plate of the thickness within the scope of 1.4mm~2.5mm, oiler temperature control It is 670 ± 20 DEG C；

When 0.076≤λ≤0.0925, finished product hot rolling acid-cleaning plate of the thickness within the scope of 2.51mm~4.0mm, oiler temperature control It is 650 ± 20 DEG C；

When 0.076≤λ≤0.0925, finished product hot rolling acid-cleaning plate of the thickness within the scope of 4.01mm~6.0mm, oiler temperature control It is 630 ± 20 DEG C；

When environment temperature >=28 DEG C, above-mentioned coiling temperature reduces by 20 DEG C.