CN113430467B - Thin 1400 MPa-grade bainite steel and manufacturing method thereof - Google Patents

Abstract

The invention belongs to the technical field of steel production, and discloses thin 1400 MPa-grade bainite steel and a manufacturing method thereof. The molten steel comprises the following chemical components in percentage by mass: c: 0.20-0.25%; si: 0.80-1.50%; mn: 1.20-1.70%; cr: 0.10-0.20%; nb: 0.02-0.04%; al: less than or equal to 0.003 percent; p: less than or equal to 0.020%; s: less than or equal to 0.004 percent. The invention adopts medium and low temperature coiling to obtain the microstructure of the steel strip, which comprises bainite and 4 to 7 percent of residual austenite. The thickness of the steel coil of the 1400 MPa-level bainite steel is 0.8-1.8 mm. The steel belt has excellent mechanical property, wherein the tensile strength grade is more than or equal to 1400MPa, and the elongation after fracture is more than or equal to 13%. The method solves the problem that the traditional hot rolling process is difficult to produce thin ultrahigh-strength products.

Description

A kind of thin gauge 1400MPa grade bainitic steel and its manufacturing method

technical field

The invention belongs to the technical field of iron and steel production, and in particular relates to a bainitic steel with a thin specification of 1400 MPa and a manufacturing method thereof.

Background technique

As the world's energy and environmental protection issues and requirements become increasingly prominent, industries such as automobiles, agricultural machinery, and equipment manufacturing attach great importance to lightweighting. Reducing the thickness of the steel plate by increasing the strength of the steel plate is an important means to achieve weight reduction. The proportion of ultra-high-strength steel sheets with a tensile strength of 1400 MPa is increasing, but thin-gauge ultra-high-strength steels need to rely more on hot rolling followed by cold rolling to ensure their thinner thickness, and cold rolling followed by annealing to ensure that its performance. It is difficult to directly use the hot rolling production line to produce ultra-high-strength steel plates.

Patent document 201310241442.0 discloses "a hot-rolled martensitic steel and its production method", which adds a lot of Mn, Ti, and Cr elements, resulting in high alloy costs. In this method, the coiling temperature is controlled at 150-200°C. Such high strength and low coiling temperature put forward higher requirements on the coiler. The method does not specify the limit thickness specification, and the thickness in the implementation case is 4.0 to 6.0 mm.

Patent document 201110154249.4 discloses "a carbon-silicon-manganese-based Q&P steel and its preparation method", which adds a lot of C, which is not conducive to the subsequent welding process.

Patent document 201310121568.4 discloses "a 700MPa grade high-strength hot-rolled Q&P steel and its manufacturing method". In this method, adding more Si is not conducive to the surface quality control of the steel strip, adding more Al is not conducive to casting, adding more Mn, Ti, the alloy cost is higher. This method requires two-stage cooling after hot rolling, and the two-stage cooling needs to be air-cooled at a high temperature for 5-10 seconds. It is difficult to use this method to produce thin steel strips. The thickness of the steel coil is in the range of 3.0 to 12.0 mm, and the thickness of the steel coil is greater than 2 mm.

It can be seen that the method of the above-mentioned prior art has at least the following deficiencies:

(a) The Si content in molten steel is too high, which is not conducive to the surface quality control of the steel strip;

(b) The Al content in molten steel is too high, which is not conducive to casting;

(c) Too many other alloys are added in the molten steel, and the cost of the alloy is high;

(d) The cooling after hot rolling is multi-stage cooling, and high temperature air cooling is required for several seconds between cooling sections, which is not conducive to the production of thin-gauge steel strips;

(e) The coiling temperature is too low, and the requirements for the coiler are relatively high;

(f) After hot rolling, heat treatment is required to achieve ultra-high strength.

Therefore, the purpose of the present invention is to provide a method for manufacturing thin gauge 1400MPa grade bainitic steel, so as to overcome the above-mentioned technical defects in the prior art.

SUMMARY OF THE INVENTION

In order to achieve the purpose of the present invention, the present invention adopts the following technical solutions.

According to a first aspect of the present invention, there is provided a method for manufacturing a thin gauge 1400MPa grade bainitic steel, the method comprising the steps of:

(1) Smelting to obtain molten steel, the molten steel is batched according to the following chemical composition and mass fraction:

C: 0.20～0.25%;

Si: 0.80～1.50%;

Mn: 1.20～1.70%;

Cr: 0.10～0.20%;

Nb: 0.02～0.04%;

P:≤0.020%;

Al:≤0.003%;

S:≤0.004%;

The balance is Fe and inevitable impurities;

(2) Under the protection of inert gas, the molten steel obtained in step (1) is subjected to thin strip continuous casting using a twin-roll casting process to obtain a cast strip. The casting speed of the thin strip continuous casting is 20-60 m/min, and the obtained The thickness of the cast strip is 1.5 ~ 2.0mm,;

(3) hot rolling the cast strip obtained in step (2) into a thin strip through one pass, the hot rolling reduction ratio is 10-40%, and the hot-rolling outlet temperature is 820-900 °C;

(4) The steel strip obtained in step (3) is cooled to 450-500°C through an aerosol cooling system, and air-cooled to room temperature after coiling, and the coiling temperature is 350-400°C.

According to the method for manufacturing thin gauge 1400MPa grade bainitic steel of the present invention, preferably, in the step (1), Si is deoxidized without adding Al.

According to the method for manufacturing thin gauge 1400MPa grade bainitic steel of the present invention, preferably, in the step (2), the pouring temperature of molten steel is 1500-1600°C.

According to the method for manufacturing thin-gauge 1400MPa grade bainitic steel of the present invention, preferably, in the step (2), the rolling speed of the thin-strip continuous casting is 42-60 m/min

According to the method for manufacturing thin gauge 1400MPa grade bainitic steel of the present invention, preferably, in the step (3), the outlet temperature of the hot rolling of the steel strip is 838-900°C.

According to the method for manufacturing thin gauge 1400MPa grade bainitic steel of the present invention, preferably, the steel strip is further 2 to 3 seconds after the hot rolling in step (3) and before the aerosol cooling in step (4). air cooling to refine the bainitic ferrite lath bundles in the microstructure.

According to a second aspect of the present invention, there is provided a thin gauge 1400 MPa class bainitic steel manufactured using the aforementioned method.

According to the thin gauge 1400MPa grade bainitic steel of the present invention, preferably, the thickness of the finished steel coil is 0.8-1.8 mm.

According to the thin gauge 1400MPa grade bainite steel of the present invention, preferably, the thin gauge 1400MPa grade bainitic steel has a tensile strength of ≥1400MPa and an elongation after fracture ≥13%.

According to the thin gauge 1400MPa grade bainitic steel of the present invention, preferably, the microstructure of the thin gauge 1400MPa grade bainite steel contains bainite+4-7% retained austenite.

beneficial technical effect

Compared with the prior art, the technical advantages and beneficial technical effects of the present invention are at least as follows:

(1) The Si content in the present invention is only 0.8% to 1.5%, which is significantly lower than that of the prior art. With the technical route of the present invention, 4 to 7% of retained austenite can be stably obtained, ensuring that the bainitic steel of the present invention has At the same time of high strength, it has higher elongation after fracture; at the same time, due to the low Si content of the present invention, the pickling surface quality of the steel strip is also good, and the subsequent welding process is easier.

(2) The present invention is Si deoxidation without adding Al, thereby eliminating the shortcoming that Al is easy to block the water outlet, and ensuring that 5 furnaces can be continuously poured during normal production.

(3) The Mn and Cr added in the present invention are relatively low, and the Nb content is only 0.02-0.04%, and the alloy cost is low. With the technical route of the present invention, bainitic ferrite laths can be stably obtained, so that the Tensitic steel has a strength of ≥1400MPa.

(4) The hollow air cooling section of the present invention is only 2 to 3 seconds, and the air cooling section is arranged after the hot rolling and before the cooling section. With the overall process route of the present invention, the number of sub-grains in the austenite grains can be increased, and the number of sub-grains in the austenite grains can be further refined. The bainitic ferritic lath bundle is easy to produce thin gauge steel strip - the bainitic steel strip of the present invention has high strength and high elongation of ≥1400MPa, and at the same time, the thickness is controlled at 0.8-1.8mm.

(5) The present invention only performs one-time hot rolling with a reduction of 10% to 40%, and the hot rolling temperature is 820° C. to 900° C., so that the present invention can easily obtain a 0.8-1.8 mm sheet that meets the requirements of thin gauge and high strength. Bainitic high-strength steel strip.

(6) The coiling temperature of the present invention is 350° C. to 400° C., which is significantly higher than that of the prior art, so that the method of the present invention has lower requirements on the coiler, and is less likely to have defects such as poor coil shape during coiling. .

Description of drawings

In order to illustrate the technical solutions of the embodiments of the present invention more clearly, the accompanying drawings of the embodiments will be briefly introduced below. Apparently, the accompanying drawings in the following description only relate to some embodiments of the present invention, rather than limit the present invention.

1 is a flow chart of a production process for manufacturing thin gauge 1400 MPa grade bainitic steel according to an embodiment of the present invention.

2 is a metallographic structure diagram of the ultra-high strength steel produced according to Example 1 of the present invention.

3 is a metallographic structure diagram of the ultra-high strength steel produced according to Example 2 of the present invention.

4 is a metallographic structure diagram of the ultra-high strength steel produced according to Example 3 of the present invention.

Detailed ways

In order to make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be described clearly and completely below. Obviously, the described embodiments are some, but not all, embodiments of the present invention. Based on the described embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present invention.

Unless otherwise defined, technical or scientific terms used in the present invention should have the ordinary meaning as understood by one of ordinary skill in the art to which this invention belongs.

Example 1

(1) Smelting of molten steel: steelmaking in electric furnace, degassing in VD vacuum furnace, refining in LF furnace, to obtain molten steel with qualified composition, by weight percentage: C: 0.233%; Si: 1.2%; Mn: 1.48%; Cr: 0.18 %, Nb: 0.034%; Al: 0.0020%; P: 0.010%; S: 0.0020%; the balance is iron and inevitable impurity elements.

(2) Thin-strip continuous casting: The qualified molten steel is continuously cast by the twin-roll casting process. The opening temperature of the molten steel is 1560 °C, the casting speed is 42 m/min, and the molten steel is thin-strip continuous casting under the protection of inert gas. , the thickness of the cast strip is 1.85mm.

(3) Hot rolling: The cast strip is hot rolled into a hot rolled strip with a thickness of 1.50mm at a reduction of 18.9% in one pass. The hot rolling outlet temperature is 866 °C, and the temperature of the strip steel after aerosol cooling is 465 °C. , the coiling temperature is 387℃.

The mechanical properties of the high-strength steel produced according to the above composition and process are: yield strength 1134MPa, tensile strength 1487MPa, elongation 15%, and retained austenite content 6%.

According to the above embodiment, the metallographic structure of the obtained thin gauge 1400MPa grade bainitic steel is shown in FIG. 2 .

Example 2

(1) Smelting of molten steel: steelmaking in electric furnace, degassing in VD vacuum furnace, refining in LF furnace, to obtain molten steel with qualified composition, by weight percentage: C: 0.217%; Si: 0.95%; Mn: 1.62%; Cr: 0.20 %, Nb: 0.032%; Al: 0.0025%; P: 0.012%; S: 0.0017%; the balance is iron and inevitable impurity elements.

(2) Thin-strip continuous casting: The qualified molten steel is continuously cast by the twin-roll casting process. The pouring temperature of the molten steel is 1530 ° C, the casting speed is 57 m/min, and the molten steel is thin-strip continuous casting under the protection of inert gas. , the thickness of the cast strip is 1.6mm.

(3) Hot rolling: The cast strip is hot rolled into a hot rolled strip with a thickness of 1.20mm with a reduction of 25% in one pass. The hot rolling outlet temperature is 838°C, and the temperature of the strip after the aerosol cooling is 465°C. , the coiling temperature is 395℃.

The mechanical properties of the high-strength steel produced according to the above composition and process are: yield strength of 1075MPa, tensile strength of 1436MPa, elongation of 14%, and retained austenite content of 4%.

According to the above embodiment, the metallographic structure of the obtained thin gauge 1400MPa grade bainitic steel is shown in FIG. 3 .

Example 3

(1) Smelting of molten steel: steelmaking in electric furnace, degassing in VD vacuum furnace, refining in LF furnace, to obtain molten steel with qualified composition, by weight percentage: C: 0.225%; Si: 1.3%; Mn: 1.66%; Cr: 0.14 %, Nb: 0.037%; Al: 0.0021%; P: 0.0130%; S: 0.0021%; the balance is iron and inevitable impurity elements.

(2) Thin-strip continuous casting: The qualified molten steel is continuously cast by the twin-roll casting process. The opening temperature of the molten steel is 1570°C, the casting speed is 55m/min, and the molten steel is thin-strip continuous casting under the protection of inert gas. , the thickness of the cast strip is 1.5mm.

(3) Hot rolling: The cast strip is hot-rolled into a hot-rolled strip with a thickness of 0.90mm by one pass at a reduction of 40%. The hot-rolled outlet temperature is 841 °C, and the temperature of the strip after the aerosol cooling is 482 °C. , the coiling temperature is 410 ℃.

The mechanical properties of the high-strength steel produced according to the above-mentioned composition and process are: yield strength of 1044MPa, tensile strength of 1438MPa, elongation of 13%, and retained austenite content of 4%.

According to the above embodiment, the metallographic structure of the obtained thin gauge 1400MPa grade bainitic steel is shown in FIG. 4 .

The above are only specific embodiments of the present invention. It should be pointed out that for those skilled in the art, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be It is regarded as the scope of protection of the present invention.

Claims (10)

1. A method of manufacturing thin gauge 1400MPa grade bainitic steel, comprising the steps of:

(1) smelting to obtain molten steel, wherein the molten steel is prepared from the following chemical components in percentage by mass:

C：0.20～0.25％；

Si：0.80～1.30％；

Mn：1.20～1.70％；

Cr：0.10～0.20％；

Nb：0.02～0.04％；

P：≤0.020％；

Al：≤0.003％；

S：≤0.004％；

the balance of Fe and inevitable impurities;

(2) carrying out strip continuous casting on the molten steel obtained in the step (1) by using a double-roll casting process under the protection of inert gas to obtain a cast strip, wherein the casting speed of the strip continuous casting is 20-60 m/min, and the thickness of the obtained cast strip is 1.5-2.0 mm;

(3) hot rolling the cast strip obtained in the step (2) into a thin strip for one time, wherein the hot rolling reduction rate is 10-40%, and the hot rolling outlet temperature is 820-900 ℃;

(4) cooling the steel strip obtained in the step (3) to 450-500 ℃ by an aerial fog cooling system, air-cooling to room temperature after coiling, wherein the coiling temperature is 350-400 ℃,

and (3) after the hot rolling in the step (3) and before the gas spray cooling in the step (4), air cooling for 2-3 seconds is further carried out on the steel strip so as to refine the bainite ferrite lath bundle in the microstructure.

2. The method of claim 1, wherein: in the step (1), Si is deoxidized, and Al is not added.

3. The method of claim 1, wherein: in the step (2), the casting temperature of the molten steel is 1500-1600 ℃.

4. The method of claim 1, wherein: in the step (2), the casting and rolling speed of the strip continuous casting is 42-60 m/min.

5. The method of claim 1, wherein: in the step (3), the hot rolling outlet temperature of the steel strip is 838-900 ℃.

6. The method of claim 5, wherein: in the step (3), the hot rolling outlet temperature of the steel strip is 838-866 ℃.

7. A thin 1400MPa grade bainite steel is characterized in that: the thin gauge 1400MPa grade bainitic steel is manufactured using the method according to any one of claims 1-6.

8. A thin gauge 1400MPa grade bainite steel according to claim 7, characterised in that: the thickness of the finished steel coil of the thin 1400MPa grade bainite steel is 0.8-1.8 mm.

9. A thin gauge 1400MPa grade bainite steel according to claim 7, characterised in that: the tensile strength of the thin 1400MPa grade bainite steel is more than or equal to 1400MPa, and the elongation after fracture is more than or equal to 13%.

10. A thin gauge 1400MPa grade bainitic steel according to any one of claims 7-9, characterized in that: the microstructure of the thin 1400MPa grade bainite steel comprises bainite and 4-7% of residual austenite.

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