CN106498293A - A kind of preparation method of hot forming with high-carbon hot continuous rolling pickling steel band - Google Patents

Abstract

The invention relates to a method for preparing a high-carbon hot continuous rolling pickled steel strip for thermoforming, and belongs to the technical field of pickled steel strip preparation. The technical problem solved by the invention is to provide a low-cost method for preparing a high-carbon hot continuous rolling pickled steel strip for hot forming. This method mainly uses C and Mn elements, increases the C content, and controls the smelting process without adding Nb, Ti, V, B, Mo, La, Cr and other alloying elements to ensure the purity and chemical composition of the billet steel. Under the premise of uniformity, combined with reasonable controlled rolling and controlled cooling technology, a hot-rolled steel plate with moderate strength and high elongation can be obtained. After cutting, blanking and heating, it is hot-formed and heat-treated to finally obtain medium strength. Parts with high plasticity and toughness are widely used in automotive structural parts, and can replace some hot-rolled and cold-rolled continuous annealed steel plates and steel strips for high-strength automotive structures with high alloy content and high production costs.

Description

A kind of preparation method of high-carbon hot continuous rolling pickled steel strip for hot forming

technical field

The invention relates to a method for preparing a high-carbon hot continuous rolling pickled steel strip for thermoforming, and belongs to the technical field of pickled steel strip preparation.

Background technique

The hot-rolled pickled plate is made of high-quality hot-rolled thin plate as raw material. The oxide layer is removed, trimmed and finished by the pickling unit. The main processes include uncoiling of hot-rolled raw materials → laser welding → scale breaking by the stretching and leveling unit → pickling → rinsing → On-line leveling→edge trimming→on-line oiling→baling→packing and storage, the surface quality and use requirements (mainly cold-rolled forming or stamping performance) are intermediate products between hot-rolled sheets and cold-rolled sheets, which are partly hot-rolled An ideal substitute for rolled and cold-rolled plates. Hot-rolled pickled plate is an emerging product in the plate market. Its market development direction is mainly to replace cold-rolled plate and replace hot-rolled plate. Become the development trend of the international market.

Compared with hot-rolled sheets, the advantages of hot-rolled pickled sheets are mainly: good surface quality, high dimensional accuracy, high surface finish, and can reduce environmental pollution caused by scattered pickling by users; compared with cold-rolled sheets, pickled sheets The advantage lies in the effective cost reduction under the premise of ensuring the surface quality requirements.

Hot forming technology is a new technology developed and promoted in recent years for the production of advanced high-strength steel stamping parts. The steel plate is heated above the austenite temperature, and then quickly transferred to the module for stamping and quenching to obtain a martensitic structure or multiple structures. The strength of the stamped part is up to 1700MPa. Due to its high strength, it can be applied to Car body safety components such as front and rear bumpers, door anti-collision beams, A-pillars, B-pillars, C-pillars, and middle tunnels. Due to the advantages of weight reduction, improved safety and strong formability, this technology is developing rapidly in Europe, the United States and other regions, and high-strength and ultra-high-strength components are increasingly used in car bodies. In 2015, the global hot stamping components The demand exceeds 600 million pieces, and as the world's largest automobile production and consumption country, the demand is also rising sharply.

Existing steels for hot forming are generally added with alloying elements such as Ti, Nb, B, etc. to obtain ultra-high-strength alloy steels. For example, the patent CN104195443A "High-strength bending-resistant thermoforming steel for automobiles and its manufacturing method" discloses a high-bending-resistant thermoforming steel and its manufacturing method. The mass percentage of the main chemical components of the steel is: 0.18%≤Cwt .≤0.30%, Siwt.≤0.50%, 1.00%≤Mnwt.≤1.60%, Pwt.≤0.015%, Swt.≤0.002%, 0.1%≤Crwt.≤0.3%, 0.02%≤Tiwt.≤0.06%, 0.02%≤Als wt≤0.06%, 0.0005%≤Bwt.≤0.004%, [N]≤0.004%, [O]≤0.003%, the rest is Fe and unavoidable impurities. Its manufacturing method includes low-temperature heating of billets, two-stage controlled rolling, rapid cooling, low-temperature coiling, cold rolling and critical annealing to prepare steel coils, shearing to prepare parts blanks, and hot-pressing forming. The manufacturing method can refine the crystal grains, improve the plasticity and toughness of the material, make it absorb more energy during the deformation process, and improve the safety of the car. However, this manufacturing method needs to add Ti and B alloy elements to achieve the purpose of improving the material strength. The final yield strength reaches more than 1000MPa, the tensile strength exceeds 1300MPa, and the elongation reaches more than 5%. It is an ultra-high-strength hot-formed steel, although The strength is high, but the elongation is low, usually below 10%. The purpose of expanding the rolling process window can be realized after adding Cr alloy elements, but this will increase the cost of material design.

There are relatively few studies on low-cost, medium-to-high-strength hot-formed steel. At present, the commonly used medium-strength steel for automotive structural parts is QSTE420 or QSTE500. These grades of steel are mostly hot-rolled steel for cold deformation, and their tensile strength is 400. ~600MPa, but alloy elements such as Ti and Nb are still added to the composition, and the cost is relatively high.

Contents of the invention

The technical problem solved by the invention is to provide a low-cost method for preparing a high-carbon hot continuous rolling pickled steel strip for hot forming.

The preparation method of the high-carbon hot-rolled pickled steel strip for hot forming of the present invention comprises successively hot-rolled, hot-rolled raw material decoiling, scale breaking and pickling to obtain the high-carbon hot-rolled pickled steel strip, wherein the hot-rolled pickled steel strip is The chemical composition of the billet before rolling is composed of the following components in weight percentage: 0.20≤C≤0.45%, Si≤1.00%, 1.00≤Mn≤1.80%, P≤0.015%, S≤0.005%, 0.010≤Als≤0.060% , N≤0.0050%, O≤0.0040%, the rest is Fe and unavoidable impurities;

During the hot continuous rolling, the billet heating temperature is 1180-1240°C, the finish rolling temperature is 820-900°C, and the coiling temperature is 580-680°C;

The scale is broken by a tension leveling unit to break phosphorus, and the elongation of the tension leveling unit is 1.0-2.0%.

Preferably, the high-carbon hot-rolled pickled steel strip for hot forming has a yield strength R _eH ≥ 355 MPa, a tensile strength R _m 490-680 MPa, and an elongation A ₈₀ ≥ 20%. After heat treatment in the range of 880-950 °C, the thickness of the decarburized layer on the surface is less than 20 μm, and the mechanical properties meet the requirements.

Further, the specific steps of the method of the present invention are: vanadium extraction from molten iron → desulfurization → converter smelting → LF refining → RH refining → continuous casting → heating in a heating furnace → rough rolling → finish rolling → laminar cooling → coiling → air cooling to room temperature → Uncoiling of hot-rolled raw materials→laser welding→scale breaking by tension leveling unit→pickling→rinsing→edge trimming→on-line oiling→bundling→packing and storage.

Preferably, when the heating furnace is heated, the temperature of casting slab entering the furnace is ≤300°C.

Preferably, argon blowing treatment is performed during the converter smelting, and calcium treatment is performed at the end of the RH refining.

Further, preferably, the non-metallic inclusions of type A, type B, type C, type D and type DS of the high-carbon hot continuous rolling pickled steel strip for hot forming are all less than 1.0 level.

Compared with the prior art, the present invention has the following beneficial effects:

The invention mainly uses C and Mn elements, increases the C content, and under the condition of not adding alloy elements such as Nb, Ti, V, B, Mo, La, Cr, etc., the smelting process ensures the purity of the billet steel and uniform chemical composition Under the premise of reasonable controlled rolling and controlled cooling technology, a hot-rolled steel plate with moderate strength and high elongation can be obtained. After cutting, blanking and heating, hot-forming is carried out. Parts with high toughness are widely used in automotive structural parts, and can replace some hot-rolled and cold-rolled continuous annealed steel sheets and strips for high-strength automotive structures with high alloy content and high production costs.

detailed description

The preparation method of the high-carbon hot-rolled pickled steel strip for hot forming of the present invention comprises successively hot-rolled, hot-rolled raw material decoiling, scale breaking and pickling to obtain the high-carbon hot-rolled pickled steel strip, wherein the hot-rolled pickled steel strip is The chemical composition of the billet before rolling is composed of the following components in weight percentage: 0.20≤C≤0.45%, Si≤1.00%, 1.00≤Mn≤1.80%, P≤0.015%, S≤0.005%, 0.010≤Als≤0.060% , N≤0.0050%, O≤0.0040%, the rest is Fe and unavoidable impurities;

During the hot continuous rolling, the billet heating temperature is 1180-1240°C, the finish rolling temperature is 820-900°C, and the coiling temperature is 580-680°C;

The scale is broken by a tension leveling unit to break phosphorus, and the elongation of the tension leveling unit is 1.0-2.0%.

Preferably, the high-carbon hot-rolled pickled steel strip for hot forming has a yield strength R _eH ≥ 355 MPa, a tensile strength R _m 490-680 MPa, and an elongation A ₈₀ ≥ 20%. After heat treatment in the range of 880-950 °C, the thickness of the decarburized layer on the surface is less than 20 μm, and the mechanical properties meet the requirements.

Further, the specific steps of the method of the present invention are: vanadium extraction from molten iron → desulfurization → converter smelting → LF refining → RH refining → continuous casting → heating in a heating furnace → rough rolling → finish rolling → laminar cooling → coiling → air cooling to room temperature → Uncoiling of hot-rolled raw materials→laser welding→scale breaking by tension leveling unit→pickling→rinsing→edge trimming→on-line oiling→bundling→packing and storage.

Preferably, when the heating furnace is heated, the temperature of casting slab entering the furnace is ≤300°C.

Preferably, argon blowing treatment is performed during the converter smelting, and calcium treatment is performed at the end of the RH refining.

Further, the non-metallic inclusions in the high-carbon hot-rolled pickled steel strip for hot forming meet the requirements in Table 1.

Table 1 Requirements with non-metallic inclusions

Preferably, the non-metallic inclusions of type A, type B, type C, type D and type DS of the high-carbon hot continuous rolling pickled steel strip for hot forming are all less than 1.0 grade.

Specifically, the method of the present invention is that the molten iron is sequentially subjected to vanadium extraction, desulfurization, converter (argon blowing treatment is required), LF refining, RH refining (calcium treatment is performed at the end of the process), and continuous casting into slabs; the temperature of the casting slab is reduced to 300°C The furnace can be installed below, heated to 1180-1240°C, rolled into an intermediate billet through 5 passes of a single-stand reversible roughing mill, and then entered into a 7-stand hot continuous rolling finish rolling unit after being kept warm by a hot coil box. 980～1050℃, the final rolling temperature is 820～900℃, and then enter the coiler coil to obtain the strip steel after laminar flow cooling, the coiling temperature is 580～680℃; the steel coil can be uncoiled after air cooling to room temperature. Anti-wrinkle rolls are required for uncoiling, and the scales are broken by the tension leveling unit (the elongation rate of the tension leveling unit is 1.0-2.0%), and then pickled by the pickling unit, and then oiled and packaged into finished products.

The specific implementation of the present invention will be further described below in conjunction with the examples, and the present invention is not limited to the scope of the examples.

Example 1

The 2050 hot rolling unit (7-stand continuous rolling and finishing unit) is used to produce high-carbon hot-rolled pickled steel strip for low-cost hot forming. The weight percent of the chemical composition of the starting billet is: Cwt.: 0.41%, Siwt.: 0.25%, Mnwt.: 1.18%, Pwt.: 0.007%, Swt.: 0.002%, Alswt.: 0.036%, [N] : 0.0040%, [O]: 0.0029%, the rest is Fe and unavoidable impurities. The production process is: vanadium extraction from molten iron→desulfurization→converter (argon blowing treatment required)→LF refining→RH refining (calcium treatment at the end of the process)→continuous casting→heating furnace heating (slab entering furnace temperature≤300℃)→ Rough rolling→finish rolling→laminar cooling→coiling→air cooling to room temperature→raw material uncoiling→laser welding→stretching and leveling unit breaking scale→pickling→rinsing→edge trimming→online oiling→baling→packing and storage. The steel billet is 230mm×1450mm×Cmm, heated at 1210°C, descaled after being released from the furnace, and rolled into a 42mm×1450mm×C ₁ mm intermediate billet by 5 passes in a single-stand reversible roughing mill, and then heat-preserved by a hot coil box. Then it enters the 7th continuous rolling and finishing mill, and rolls into a steel coil of 5.0mm×1450mm×C ₂ mm. The starting rolling temperature is 1020°C, and the finishing rolling temperature is 835°C. After laminar flow cooling, enter the coiler to obtain strip steel, and the coiling temperature is 586°C. The steel coil is cooled to room temperature (≤40°C), uncoiled (with an anti-wrinkle roll), welded to the tail of the previous coil, and then scaled by the stretching and leveling unit, then enters the acid tank for pickling, and the pickling speed is 80m /min, and then oiled and divided into coils to obtain a high-carbon hot-rolled pickled steel strip for thermoforming with a specification of 5.0mm×1450mm×C ₂ mm.

It has been determined that the properties of the high-carbon hot-rolled pickled steel strip for hot forming are as follows: yield strength, tensile strength, and elongation are 475MPa, 670MPa, and 21.5% respectively; non-metallic inclusions are A, B, and C Classes D, D, and DS are all less than 1.0 grades. After heat treatment in the range of 880-950 °C, the thickness of the decarburized layer on the surface is less than 20 μm, and the mechanical properties meet the requirements.

The yield strength, tensile strength, elongation, and non-metallic inclusion levels in the examples of the present invention are all measured according to national standards.

Example 2

The 2050 hot rolling unit (7-stand continuous rolling and finishing unit) is used to produce high-carbon hot-rolled pickled steel strip for low-cost hot forming. The weight percent of the chemical composition of the starting billet is: Cwt.: 0.22%, Siwt.: 0.22%, Mnwt.: 1.76%, Pwt.: 0.009%, Swt.: 0.003%, Alswt.: 0.043%, [N] : 0.0049%, [O]: 0.0033%, the rest is Fe and unavoidable impurities. The production process is: vanadium extraction from molten iron→desulfurization→converter (argon blowing treatment is required)→LF refining→RH refining (calcium treatment at the end of the process)→continuous casting→heating furnace heating (slab entering furnace temperature≤300℃)→ Rough rolling→finish rolling→laminar cooling→coiling→air cooling to room temperature→raw material uncoiling→laser welding→stretching and leveling unit scale breaking→pickling→rinsing→edge trimming→online oiling→bundling→packing and storage. The steel billet is 230mm×1450mm×Cmm, heated at 1210°C, descaled after being released from the furnace, and rolled into a 42mm×1400mm×C ₁ mm intermediate billet by a single-stand reversible roughing mill for 5 passes, and then heat-preserved by a hot coil box. Then enter the 7th continuous rolling and finishing mill, and roll into a steel coil of 6.0mm×1400mm×C ₂ mm. The starting rolling temperature is 1000°C, and the finishing rolling temperature is 881°C. After laminar cooling, enter the coiler to obtain the strip steel, and the coiling temperature is 620°C. The steel coil is cooled to room temperature (≤40°C), uncoiled (with an anti-wrinkle roll), welded to the tail of the previous coil, and then scaled by the stretching and leveling unit, then enters the acid tank for pickling, and the pickling speed is 70m /min, and then oiled and divided into coils to obtain a high-carbon hot-rolled pickled steel strip for thermoforming with a specification of 6.0mm×1400mm×C ₂ mm.

It has been determined that the properties of the high-carbon hot-rolled pickled steel strip for hot forming are as follows: yield strength, tensile strength, and elongation are 462MPa, 654MPa, and 25.0% respectively; non-metallic inclusions are A, B, and C Classes D, D, and DS are all less than 1.0 grades. After heat treatment in the range of 880-950 °C, the thickness of the decarburized layer on the surface is less than 20 μm, and the mechanical properties meet the requirements.

The yield strength, tensile strength, elongation, and non-metallic inclusion levels in the examples of the present invention are all measured according to national standards.

Example 3

The 2050 hot rolling unit (7-stand continuous rolling and finishing unit) is used to produce high-carbon hot-rolled pickled steel strip for low-cost hot forming. The weight percent of the chemical composition of the starting billet is: Cwt.: 0.30%, Siwt.: 0.38%, Mnwt.: 1.45%, Pwt.: 0.005%, Swt.: 0.004%, Alswt.: 0.031%, [N] : 0.0038%, [O]: 0.0026%, the rest is Fe and unavoidable impurities. The production process is: vanadium extraction from molten iron→desulfurization→converter (argon blowing treatment is required)→LF refining→RH refining (calcium treatment at the end of the process)→continuous casting→heating furnace heating (slab entering furnace temperature≤300℃)→ Rough rolling→finish rolling→laminar cooling→coiling→air cooling to room temperature→raw material uncoiling→laser welding→stretching and leveling unit scale breaking→pickling→rinsing→edge trimming→online oiling→bundling→packing and storage. The steel billet is 230mm×1250mm×Cmm, heated at 1210°C, descaled after being released from the furnace, and rolled into a 42mm×1250mm×C ₁ mm intermediate billet by a single-stand reversible rough rolling mill for 5 passes, and then heat-preserved by a hot coil box. Then it enters the 7th continuous rolling and finishing rolling unit, and rolls into a steel coil of 3.0mm×1250mm×C ₂ mm. The starting rolling temperature is 1000°C, and the finishing rolling temperature is 842°C. After laminar cooling, enter the coiler to obtain the strip steel, and the coiling temperature is 656°C. The steel coil is cooled to room temperature (≤40°C), uncoiled (with an anti-wrinkle roll), welded to the tail of the previous coil, and then scaled by the stretching and leveling unit, then enters the acid tank for pickling, and the pickling speed is 90m /min, and then oiled and coiled to obtain a high-carbon hot-rolled pickled steel strip for thermoforming with a specification of 3.0mm×1250mm×C ₂ mm.

It has been determined that the properties of the high-carbon hot-rolled pickled steel strip for hot forming are as follows: yield strength, tensile strength, and elongation are 408MPa, 590MPa, and 23.5% respectively; non-metallic inclusions are A, B, and C Class, D class and DS class are all less than 0.5 grade. After heat treatment in the range of 880-950 °C, the thickness of the decarburized layer on the surface is less than 20 μm, and the mechanical properties meet the requirements.

The yield strength, tensile strength, elongation, and non-metallic inclusion levels in the examples of the present invention are all measured according to national standards.

Example 4

The 2050 hot rolling unit (7-stand continuous rolling and finishing unit) is used to produce high-carbon hot-rolled pickled steel strip for low-cost hot forming. The weight percent of the chemical composition of the starting billet is: Cwt.: 0.26%, Siwt.: 0.38%, Mnwt.: 1.35%, Pwt.: 0.005%, Swt.: 0.002%, Alswt.: 0.031%, [N] : 0.0038%, [O]: 0.0026%, the rest is Fe and unavoidable impurities. The production process is: vanadium extraction from molten iron→desulfurization→converter (argon blowing treatment is required)→LF refining→RH refining (calcium treatment at the end of the process)→continuous casting→heating furnace heating (slab entering furnace temperature≤300℃)→ Rough rolling→finish rolling→laminar cooling→coiling→air cooling to room temperature→raw material uncoiling→laser welding→stretching and leveling unit scale breaking→pickling→rinsing→edge trimming→online oiling→bundling→packing and storage. The steel billet is 230mm×1250mm×Cmm, heated at 1210°C, descaled after being released from the furnace, and rolled into a 42mm×1250mm×C ₁ mm intermediate billet by a single-stand reversible rough rolling mill for 5 passes, and then heat-preserved by a hot coil box. Then it enters the 7th continuous rolling and finishing rolling unit, and rolls into a steel coil of 3.0mm×1250mm×C ₂ mm. The starting rolling temperature is 1000°C, and the finishing rolling temperature is 834°C. After laminar flow cooling, enter the coiler to obtain strip steel, and the coiling temperature is 588°C. The steel coil is cooled to room temperature (≤40°C), uncoiled (with an anti-wrinkle roll), welded to the tail of the previous coil, and then scaled by the stretching and leveling unit, then enters the acid tank for pickling, and the pickling speed is 90m /min, and then oiled and coiled to obtain a high-carbon hot-rolled pickled steel strip for thermoforming with a specification of 3.0mm×1250mm×C ₂ mm.

It has been determined that the properties of the high-carbon hot-rolled pickled steel strip for hot forming are as follows: yield strength, tensile strength, and elongation are 428MPa, 612MPa, and 27.5% respectively; non-metallic inclusions are A, B, and C Class, D class and DS class are all less than 0.5 grade. After heat treatment in the range of 880-950 °C, the thickness of the decarburized layer on the surface is less than 20 μm, and the mechanical properties meet the requirements.

The yield strength, tensile strength, elongation, and non-metallic inclusion levels in the examples of the present invention are all measured according to national standards.

Comparative example 1

Adopt the method for embodiment 2, only change the chemical composition of initial billet, its chemical composition weight percent is: Cwt.: 0.16%, Siwt.: 0.32%, Mnwt.: 1.78%, Pwt.: 0.010%, Swt. : 0.004%, Alswt.: 0.029%, [N]: 0.0033%, [O]: 0.0021%, and the rest is Fe and unavoidable impurities.

It has been determined that the properties of the high-carbon hot-rolled pickling steel strip produced for hot forming are as follows: yield strength, tensile strength, and elongation are 409MPa, 588MPa, and 30.2% respectively; non-metallic inclusions are A, B, and C Class, D class and DS class are all less than 0.5 grade. However, after heat treatment in the range of 880-950 °C, the thickness of the decarburized layer on the surface is more than 30 μm, and the yield strength after heat treatment is all lower than 355 MPa, which does not meet the requirements.

Claims (6)

1. a kind of preparation method of hot forming with high-carbon hot continuous rolling pickling steel band, includes hot continuous rolling, hot rolling raw material uncoiling successively, breaks Squama and pickling, obtain high-carbon hot continuous rolling pickling steel band, it is characterised in that：Before hot continuous rolling, the chemical composition of steel billet is by following weight hundred The group of ratio is divided to be grouped into：0.20≤C≤0.45%, Si≤1.00%, 1.00≤Mn≤1.80%, P≤0.015%, S≤ 0.005%, 0.010≤Als≤0.060%, N≤0.0050%, O≤0.0040%, remaining are Fe and inevitable impurity；

During the hot continuous rolling, billet heating temperature is 1180～1240 DEG C, and finishing temperature is 820～900 DEG C, and coiling temperature is 580～680 DEG C；

The scale breading is 1.0～2.0% using the broken phosphorus of withdrawal straightening stands, withdrawal straightening stands elongation percentage.

2. preparation method of the hot forming according to claim 1 with high-carbon hot continuous rolling pickling steel band, it is characterised in that：Described Hot forming high-carbon hot continuous rolling pickling steel band yield strength R_eH>=355MPa, tensile strength R_m490～680MPa, elongation percentage A₈₀≥ 20%.

3. preparation method of the hot forming according to claim 1 with high-carbon hot continuous rolling pickling steel band, it is characterised in that：Production Method is concretely comprised the following steps：Vanadium extraction from hot metal → desulfurization → converter smelting → LF refining → RH refines → continuous casting → heating stove heat → Roughing → finish rolling → section cooling → batch → be air cooled to room temperature → hot rolling raw material uncoiling → laser welding → withdrawal straightening stands scale breading → pickling → rinsing → trimming → online oiling → bundling → packaging and storage.

4. preparation method of the hot forming according to claim 3 with high-carbon hot continuous rolling pickling steel band, it is characterised in that：Described During heating stove heat, strand charging temperature≤300 DEG C.

5. preparation method of the hot forming according to claim 3 with high-carbon hot continuous rolling pickling steel band, it is characterised in that：Described Argon process is carried out during converter smelting, and the RH refines latter stage carries out Calcium treatment.

6. preparation method of the hot forming according to claim 3 with high-carbon hot continuous rolling pickling steel band, it is characterised in that：Described The hot forming non-metallic inclusion A classes of high-carbon hot continuous rolling pickling steel band, B classes, C classes, D classes and DS classes are respectively less than 1.0 grades.