CN114686762B - Production method of high-strength high-toughness hot continuous rolling thin steel plate with Brinell hardness of 500HBW - Google Patents

Abstract

The invention relates to a production method of a Brinell hardness 500HBW steel plate, in particular to a production method of a Brinell hardness 500HBW high-strength high-toughness hot continuous rolling thin steel plate. The thickness is less than or equal to 10mm, and the coating consists of the following chemical elements in percentage by weight: c:0.21 to 0.26 percent, si:0.60 to 0.80 percent, mn:0.90 to 1.30 percent, P is less than or equal to 0.015 percent, S is less than or equal to 0.003 percent, al:0.10 to 0.13 percent, cr:0.70-0.90%, B:0.0010 to 0.0025 percent, N is less than or equal to 0.0040 percent, H is less than or equal to 0.00020 percent, and Nb:0.020 to 0.040 percent, ti:0.020 to 0.050 percent, mo:0.20 to 0.50 percent, and satisfies Ti/N more than or equal to 5, ceq less than or equal to 0.68, wherein Ceq=C+Mn/6+ (Cr+Mo+V)/5+ (Cu+Ni)/15, and the balance of Fe and unavoidable impurities. The invention adopts an economic C-Mn component design, is assisted with a small amount of Nb, ti and MO microalloy elements, does not need to add noble alloying elements such as Ni, adopts intermediate frequency rapid heating in the quenching heating temperature rising process, further reduces the addition of the microalloy elements, realizes high strength and high hardness of steel, good low-temperature impact toughness and cold bending processability, and has excellent plate shape.

Description

Production method of high-strength and high-toughness hot-rolled thin steel plate with Brinell hardness 500HBW

technical field

The invention relates to a production method of a steel plate with a Brinell hardness of 500HBW, in particular to a production method of a high-strength and high-toughness hot-rolled thin steel plate with a Brinell hardness of 500HBW.

Background technique

Under the background of green manufacturing, low-carbon and environmental protection, domestic construction machinery, commercial vehicles and other industries are paying more and more attention to product structure upgrading in the direction of high strength, weight reduction and green longevity. More corrosion resistance and other high requirements.

In recent years, my country has made significant progress in the R&D and production of high-strength steel. Construction machinery users have begun to use ultra-high-strength structural steel with a yield of more than 960MPa to manufacture crane booms and pump truck booms. Dump truck users began to use steel plates with a yield strength of 700Mpa or even 1000Mpa to replace 345MPa grade products. However, in metallurgy, mining, building materials, transportation and other fields, many workpieces and equipment quickly fail due to wear, resulting in a huge waste of materials and energy. It is necessary for the steel plate to have high hardness and high wear resistance to reduce the wear of the steel plate and prolong the service life of the steel plate life.

CN102943212A discloses "A NM500 high-strength wear-resistant steel plate and its heat treatment process", its chemical composition is C0.25-0.28%, Mn0.80-1.20%, Si0.20-0.40%, S≤0.010%, P ≤0.020%, Cr0.45～0.70%, Mo0.10～0.30%, Ti0.010～0.030%, B0.0010～0.0030%, Als0.015～0.045%, Nb0.015～0.050%, the rest are Fe and unavoidable impurities. A low quenching temperature will affect the hardenability of the steel plate and the hardness of the product.

CN105385951A discloses "NM500 wear-resistant steel plate with high hardness and high toughness and its production method", its chemical composition is C0.25-0.30%, Si0.10-0.30%, Mn0.10-0.60%, P≤0.015 %, S≤0.005%, Als0.020-0.035%, Ti0.010-0.020%, Cr0.5-1.0%, Mo0.2-0.5%, Ni0.3-0.5%, the rest are Fe and unavoidable impurities ;Heat treatment includes quenching and tempering, the quenching temperature is 880-910°C, the quenching holding time is 15-25 minutes, the tempering temperature is 220-290°C, and the tempering holding time is 25-40 minutes; this technology adds Ni, etc. Noble alloy elements, higher cost.

CN102943212A discloses "A NM500 high-strength wear-resistant steel plate and its heat treatment process", its chemical composition is C0.25-0.28%, Mn0.80-1.20%, Si0.20-0.40%, S≤0.010%, P ≤0.020%, Cr0.45～0.70%, Mo0.10～0.30%, Ti0.010～0.030%, B0.0010～0.0030%, Als0.015～0.045%, Nb0.015～0.050%, the rest are Fe and unavoidable impurities. A low quenching temperature will affect the hardenability of the steel plate and the hardness of the product.

Contents of the invention

In order to overcome the deficiencies in the prior art, a kind of production method of Brinell hardness 500HBW high-intensity, high-toughness hot continuous rolling thin steel plate is provided, and the product produced according to the chemical composition of the steel of the present invention and production process requirements has high strength, high toughness, Low cost, Brinell hardness 500HBW, and good wear resistance.

In order to achieve the above object, the present invention adopts the following technical solutions to realize:

A high-strength, high-toughness hot-rolled thin steel plate with a Brinell hardness of 500HBW, with a thickness of ≤10mm, composed of the following chemical elements in weight percentage:

C: 0.21%～0.26%, Si: 0.60%～0.80%, Mn: 0.90%～1.30%, P≤0.015%, S≤0.003%, Al: 0.10%～0.13%, Cr: 0.70%～0.90%, B: 0.0010%～0.0025%, N≤0.0040%, H≤0.00020%, Nb: 0.020%～0.040%, Ti: 0.020%～0.050%, Mo: 0.20%～0.50%, and satisfy Ti/N≥5, Ceq≤0.68, where Ceq=C+Mn/6+(Cr+Mo+V)/5+(Cu+Ni)/15, and the rest are Fe and unavoidable impurities.

A method for producing a high-strength, high-toughness hot-rolled thin steel plate with a Brinell hardness of 500HBW, specifically comprising:

1) Smelting and casting

Smelting and casting into billets according to the above composition;

2) Slab reheating

The slab is hot-loaded into the furnace, the furnace temperature is ≥500°C, the heating temperature is 1220-1270°C, and the holding time is 2.5-4 hours, of which the soaking time is not less than 45 minutes;

3) Controlled rolling

Rolling is divided into two stages: rough rolling and finish rolling. In the rough rolling stage, large-reduction rolling is adopted, and the pass reduction rate is controlled above 20% or the pass reduction is above 45mm. At the same time, the intermediate billet and the finished product are required Thickness ratio ≥ 5, and control the reduction ratio of the last pass of finishing rolling not less than 12%; the finishing rolling temperature is controlled at 900-950°C;

4) coiling

The coiling temperature is controlled between 700 and 750°C;

5) The heat treatment adopts the continuous heat treatment method of the whole coil, quenching→tempering→straightening→cutting;

Quenching: The heating temperature is controlled at 55-100°C above the Ac3 point of the steel grade, and the heating temperature is 900-930°C; the steel strip is first heated to 650-700°C at a frequency of 5-20Hz by intermediate frequency induction, and then heated to quenching by a resistance furnace temperature and heat preservation; quenching and heat preservation time is T1, T1=steel plate thickness × (3.0～3.5) min, steel plate thickness unit is mm, T1 unit is min; after the strip is taken out of the furnace, it is directly water-quenched to room temperature to form a martensitic structure, which requires cooling Speed ≥ 40℃/s;

Tempering: After the steel strip is quenched, it enters the tempering furnace immediately, and is tempered at 190-230°C and kept warm; the tempering holding time is T2, T2=steel plate thickness×(5.0-5.5)min, the unit of steel plate thickness is mm, T2 The unit is min;

Straightening: After tempering, use a strong straightening machine to straighten the steel plate to ensure the shape and unevenness of the steel plate, and the unevenness of the steel plate is controlled at ≤4mm/m;

Cutting board: The diagonal cutting of the steel plate shall not exceed 10mm.

Compared with prior art, the beneficial effect of the present invention is:

The method of the present invention can realize the production of steel plates with a thickness of ≤10mm, high hardness and high wear resistance, with yield strength above 1250MPa, tensile strength above 1450MPa, elongation ≥8%, hardness 500±20HBW, and impact energy value at -40°C exceeding 20J .

The invention adopts economical C-Mn composition design, supplemented by a small amount of Nb, Ti, MO microalloy elements, and does not need to add precious alloy elements such as Ni. The quenching and heating process adopts intermediate frequency rapid heating to further reduce the addition of microalloy elements and realize It guarantees the high strength, high hardness, good low temperature impact toughness and cold bending processing performance of the steel grade, and the steel plate has excellent plate shape.

Detailed ways

The invention discloses a production method of a high-strength and high-toughness hot-rolled thin steel plate with a Brinell hardness of 500HBW. Those skilled in the art can refer to the content of this article to appropriately improve the process parameters to achieve. In particular, it should be pointed out that all similar replacements and modifications are obvious to those skilled in the art, and they are all considered to be included in the present invention. The method and application of the present invention have been described through preferred embodiments, and the relevant personnel can obviously make changes or appropriate changes and combinations to the method and application described herein without departing from the content, spirit and scope of the present invention to realize and Apply the technology of the present invention.

A high-strength, high-toughness hot-rolled thin steel plate with a Brinell hardness of 500HBW, with a thickness of ≤10mm, composed of the following chemical elements in weight percentage:

C: 0.21%～0.26%, Si: 0.60%～0.80%, Mn: 0.90%～1.30%, P≤0.015%, S≤0.003%, Al: 0.10%～0.13%, Cr: 0.70%～0.90%, B: 0.0010%～0.0025%, N≤0.0040%, H≤0.00020%, Nb: 0.020%～0.040%, Ti: 0.020%～0.050%, Mo: 0.20%～0.50%, and satisfy Ti/N≥5, Ceq≤0.68, where Ceq=C+Mn/6+(Cr+Mo+V)/5+(Cu+Ni)/15, and the rest are Fe and unavoidable impurities.

In the composition design of steel of the present invention:

C: 0.21-0.26%. Carbon can improve the hardenability of the steel plate, has a strong solid solution strengthening effect, and significantly improves the strength and hardness of the high wear-resistant martensitic wear-resistant steel plate; an appropriate amount of carbon and titanium combine to form TiC particles, which can significantly improve the wear resistance. Abrasive. If the weight percentage of C is too high, the volume fraction of TiC particles formed is too high, the elongation and impact energy performance of the high wear resistance martensitic wear-resistant steel plate will be reduced, and the welding performance will be deteriorated.

Si: 0.60-0.80%. Si plays the role of solid solution strengthening in steel grades. Adding Si element to metal materials can significantly improve the strength and hardness of materials. Si can also improve the tempering resistance of the material, so the material can be used at a higher temperature.

Mn: 0.90-1.30%. Adding Mn element in the metal material can play the role of expanding the austenite zone. In addition, this element can also significantly improve the hardenability of the steel. Therefore, more horses can be obtained at the same cooling rate. Body organization. The increase of Mn content will aggravate the high temperature temper brittleness and heat sensitivity of steel.

P:≤0.015%, S≤0.003%. Sulfur combines with manganese in steel to form plastic inclusions such as manganese sulfide, which is especially detrimental to the transverse plasticity and toughness of steel, so the sulfur content should be as low as possible. Phosphorus is also a harmful element in steel, which seriously damages the plasticity and toughness of the steel plate. For the present invention, both sulfur and phosphorus are unavoidable impurity elements, and the lower the better.

Cr: 0.70-0.90%. The austenite phase zone can be reduced. Due to the outstanding binding ability between chromium atoms and carbon atoms, it can form different carbides with carbon in steel. At the same time, chromium can sometimes replace some iron atoms in cementite to form cementite containing chromium atoms. Cr can also improve the hardenability of steel, because the amount of this element in cementite is greater than that in solid solution, so Cr will inevitably diffuse from cementite to solid solution when phase transformation occurs However, due to the small gap between austenite grains, diffusion is more difficult, and during the diffusion process, Cr needs to be combined with C atoms, which will slow down the diffusion rate of C element, and finally lead to a delay in the decomposition time of austenite.

Al: 0.10-0.13%. It is usually added in steel as a deoxidizer in the process of steelmaking. A small amount of Al is also beneficial to refine grains and improve the strength and toughness of steel. However, too high Al will increase the brittleness of ferrite in steel and lead to a decrease in steel toughness.

B: 0.0010-0.0025%. The segregation of solid solution B in the steel to the austenite grain boundary reduces the interface energy and hinders the formation of ferrite nuclei, thereby prolonging the incubation period of proeutectoid ferrite and upper bainite transformation, while for The transformation of lower bainite and martensite basically has no effect, so the main function of B in low alloy wear-resistant steel is to greatly improve the hardenability of steel. At the same time, substituting a small amount of B for some precious alloying elements such as Ni, Cr and Mo is beneficial to save the cost of the alloy. When the B content is too high, the excessive solid solution B and C on the austenite grain boundary combine to reduce the hardenability and impact toughness of the steel, and the fracture mode of the steel gradually changes from cleavage fracture to intergranular fracture.

Ti: 0.020-0.050%, Ti/N≥5. It is a very active metal element and has a strong affinity with elements such as O, N and C. During the smelting process, Ti can be preferentially combined with N to form TiN, which can inhibit the formation of BN and ensure the solid solution of B elements in the matrix. In addition, during the solidification process, the precipitated TiN can serve as the heterogeneous nucleation core of the primary phase &-ferrite, and can reduce the peritectic reaction rate of ferrite and liquid phase transformation to austenite, hindering the subsequent austenite. Dendrite grows up, thus obviously refining the solidified structure.

Nb: 0.020-0.040%. It is a strong carbonitride forming element, and its role in steel is similar to that of Ti, mainly through the formation of fine and stable MX-type precipitates, which play a microalloying role in inhibiting grain growth at high temperatures and precipitation strengthening at low temperatures. Especially when combined with thermal deformation technologies such as controlled rolling and controlled cooling, the effect of Nb microalloying is more obvious. In addition, during the low temperature tempering process, Nb can delay the precipitation of carbides and the decomposition of retained austenite, and improve the stability of the tempered structure.

Mo: 0.20-0.50%. Mo promotes the separation of the transformation lines of pearlite and bainite, and significantly shifts to the right the beginning transformation lines of proeutectoid ferrite and pearlite, which has little effect on the beginning transformation line of bainite, which is beneficial to the acquisition of bainite structure. Improve the hardenability of bainite. Adding Mo can refine the structure, improve toughness, and promote the matching of strength and toughness of steel. In order to greatly improve the hardenability of the steel plate.

A production method of a Brinell hardness of 500HBW high-strength and high-toughness continuous rolling thin steel plate, which comprises the steps:

1) Smelting and casting

Smelting and casting into billets according to the above composition;

2) Slab reheating

The slab needs to be hot-loaded into the furnace, the furnace charging temperature is ≥500°C, the heating temperature is 1220-1270°C, and the holding time is 2.5h-4h, of which the soaking holding time is not less than 45min;

3) Controlled rolling

Rolling is divided into two stages: rough rolling and finish rolling. In the rough rolling stage, large-reduction rolling is adopted, and the pass reduction rate is controlled above 20% or the pass reduction is above 45mm. At the same time, the intermediate billet and the finished product are required Thickness ratio ≥ 5, and control the reduction ratio of the last pass of finishing rolling not less than 12%; the finishing rolling temperature is controlled at 900-950°C;

4) coiling

The coiling temperature is controlled between 700-750°C;

5) The heat treatment adopts the continuous heat treatment method of the whole coil, quenching→tempering→straightening→cutting.

Quenching, the heating temperature is controlled at 55°C-100°C above the Ac3 point of the steel grade, and the heating temperature is 900°C-930°C; the steel strip is first heated to 650-700°C quickly at a frequency of 10Hz by medium frequency induction, and then heated to 650-700°C by a resistance furnace. Quenching temperature and keep warm. Holding time T1,min=thickness of the steel plate×(3.0-3.5)min, the steel strip is water-quenched to room temperature directly after it comes out of the furnace to form a martensitic structure, and the cooling rate is required to be ≥40°C/s;

Tempering, the steel strip enters the tempering furnace immediately after quenching, and is tempered in the range of 190-230°C. The tempering holding time and holding time T1,min=steel plate thickness×(5.0-5.5)min. After tempering, the matrix of the steel plate is a tempered martensite structure, which has suitable hardness and good low-temperature impact toughness, and improves cold bending performance at the same time.

After tempering, the steel plate is straightened by a strong straightening machine to ensure the shape and unevenness of the steel plate. The unevenness of the steel plate is controlled at 4mm/m. Finally, the steel plate is cut, and the diagonal cut of the steel plate is required not to exceed 10mm. .

In the production method of steel plate of the present invention:

Control the maximum amount of carbon equivalent elements such as C and Mn, so that the maximum carbon equivalent is limited within 0.68, so that the steel plate has certain weldability.

The slab needs to be hot loaded into the furnace, and the furnace charging temperature is ≥500°C. First, after the casting slab is cooled to room temperature, the tendency of cracking will increase significantly, threatening production safety, and twenty can reduce energy consumption. The heating temperature is 1220-1270°C, and the holding time is 2h-4h, of which the soaking time is not less than 45min, which is to ensure that the slab is evenly burned through, and to provide strong conditions for rolling, but it will not cause over-burning and detachment. The carbon phenomenon occurs. Rolling is divided into two stages of rough rolling and finish rolling. In order to obtain fine grain size of original austenite, the cast slab is rolled with a large reduction in the rough rolling stage, and the pass reduction rate is controlled at 20% or more. The pass reduction is more than 45mm. In order to obtain fine grain size and good plate shape, the thickness ratio of the intermediate billet to the finished product is required to be ≥ 5, and the reduction rate of the final pass of the finish rolling should not be lower than 12%, so as to ensure that the deformation exceeds the critical deformation, so that Obtain good plate shape and uniform matrix structure.

Since the present invention relates to off-line heat treatment of steel grades after rolling, there is no special requirement on the rolling temperature of the slab. However, in order to reduce the rolling load, the final rolling temperature is as high as possible, and the higher coiling temperature is also to reduce the load of the coiler and ensure a good coil shape.

The heat treatment adopts the continuous heat treatment method of the whole coil, which has the advantages of high treatment efficiency, and during the heat treatment process, the steel strip has been running with tension in the unit, which can effectively ensure that the steel plate has a good original shape during and after heat treatment . The steel plate adopts intermediate frequency rapid heating, one is that it can increase the heating speed of the steel plate, and the other is that it can effectively avoid the grain growth, so as to obtain a fine original austenite grain size, effectively improve the quenched thickness, strength and hardness of the steel plate, and play a role The effect of saving alloys.

The quenching heating temperature directly affects the grain size of the subsequent martensite structure, which in turn affects the toughness of the steel plate. If the heating temperature is too high, the austenite grains will be coarsened, the martensite structure will be coarse after quenching, and the toughness will deteriorate; while the heating temperature will be too low to cause insufficient austenitization, and a complete martensite structure cannot be obtained after quenching, and Avoid that due to the fast cooling speed of the thin steel plate, the fast temperature drop before entering the quenching machine after leaving the holding furnace cannot guarantee the quenching temperature. Holding time also has a similar rule on quenching performance. If the time is too long, the crystal grains will be coarse, and at the same time, energy consumption will be increased, and the cost will be increased. If the time is too short, the austenitization will be insufficient, and the hardness and strength after quenching will not meet the requirements. Quenching, the heating temperature is controlled at 55°C-100°C above the Ac3 point of the steel grade, and the heating temperature is 880°C-930°C; the steel strip is firstly heated to 650-700°C by medium frequency induction at a frequency of 10Hz, and then heated to 650-700°C by a resistance furnace. Quenching temperature and keep warm. Holding time T1,min=steel plate thickness mm×(3.0-3.5)min, after the steel strip is taken out of the furnace, it is directly water-quenched to room temperature to form a martensitic structure, and the cooling rate is required to be ≥40°C/s;

Tempering is mainly to slow down and eliminate quenching stress, improve toughness and toughness. A higher tempering temperature will easily reduce the strength and hardness of the steel plate too much, which cannot meet the design requirements, and at the same time increase the cost. Therefore, the tempering process parameters of the steel plate should be limited. In the present invention, the steel plate is tempered in the range of 190-230°C, and the tempering holding time T1,min=thickness of the steel plate mm min. The quenched and tempered steel plate is cold straightened to ensure the shape and unevenness of the steel plate. The unevenness of the steel plate is controlled at 4mm/m. Finally, the steel plate is cut, and the diagonal cut of the steel plate is required to be no more than 10mm.

The method of the present invention can realize the production of steel plates with a thickness of ≤10mm, high hardness and high wear resistance, with yield strength above 1250MPa, tensile strength above 1450MPa, elongation ≥8%, hardness 500±20HBW, and impact energy value at -40°C exceeding 20J .

Example:

The chemical composition of the embodiment of the present invention is shown in Table 1; the rolling process of the corresponding embodiment is shown in Table 2; the heat treatment process of the corresponding embodiment is shown in Table 3; the mechanical properties and steel plate roughness of the corresponding embodiment are shown in Table 4.

The chemical composition wt% of the embodiment of the present invention in table 1

The rolling process of the embodiment of the invention of table 2

The heat treatment process of the embodiment of the present invention of table 3

The mechanical property of table 4 embodiment of the present invention and the roughness of steel plate

The invention adopts economical C-Mn composition design, supplemented by a small amount of Nb, Ti, MO microalloy elements, and does not need to add precious alloy elements such as Ni. The quenching and heating process adopts intermediate frequency rapid heating to further reduce the addition of microalloy elements and realize It guarantees the high strength, high hardness, good low temperature impact toughness and cold bending processing performance of the steel grade, and the steel plate has excellent plate shape.

The method of the present invention can realize the production of steel plates with a thickness of ≤10mm, high hardness and high wear resistance, with yield strength above 1250MPa, tensile strength above 1450MPa, elongation ≥8%, hardness 500±20HBW, and impact energy value at -40°C exceeding 20J .

The above is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto, any person familiar with the technical field within the technical scope disclosed in the present invention, according to the technical solution of the present invention Any equivalent replacement or change of the inventive concepts thereof shall fall within the protection scope of the present invention.

Claims (1)

1. A production method of a Brinell hardness 500HBW high-strength, high-toughness hot-rolled thin steel plate, characterized in that, 2mm≤steel plate thickness≤10mm, composed of the following chemical elements in percentage by weight: C: 0.24%～0.26%, Si: 0.74%～0.80%, Mn: 0.90%～1.30%, P≤0.015%, S≤0.003%, Al: 0.10%～0.13%, Cr: 0.73%～0.90%, B: 0.0010%～0.0025%, N≤0.0040%, H≤0.00020%, Nb: 0.020%～0.040%, Ti: 0.020%～0.050%, Mo: 0.22%～0.50%, and satisfy Ti/N≥5, Ceq≤0.68, where Ceq=C+Mn/6+(Cr+Mo+V)/5+(Cu+Ni)/15, the rest are Fe and unavoidable impurities; Specifically include: 1) Smelting and casting Smelting and casting into billets according to the above composition; 2) Slab reheating The slab is hot-loaded into the furnace, the furnace temperature is ≥500°C, the heating temperature is 1220-1270°C, and the holding time is 2.5-4 hours, of which the soaking time is not less than 45 minutes; 3) Controlled rolling Rolling is divided into two stages: rough rolling and finish rolling. In the rough rolling stage, large-reduction rolling is adopted, and the pass reduction rate is controlled above 20% or the pass reduction is above 45mm. At the same time, the intermediate billet and the finished product are required Thickness ratio ≥ 5, and control the reduction ratio of the last pass of finishing rolling not less than 12%; the finishing rolling temperature is controlled at 900-950°C; 4) coiling The coiling temperature is controlled between 700-750°C; 5) The heat treatment adopts the continuous heat treatment method of the whole coil, quenching→tempering→straightening→cutting; Quenching: The heating temperature is controlled at 55-100°C above the Ac3 point of the steel grade, and the heating temperature is 900-930°C; the steel strip is first heated to 650-700°C at a frequency of 5-20Hz by intermediate frequency induction, and then heated to the quenching temperature by a resistance furnace And heat preservation; after the steel strip is out of the furnace, it is directly water-quenched to room temperature to form a martensitic structure, and the cooling rate is ≥40°C/s; Tempering: After the steel strip is quenched, it enters the tempering furnace immediately, and is tempered at 190-230°C and kept warm; Straightening: the unevenness of the steel plate is controlled at ≤4mm/m; Cutting board: the diagonal cutting of the steel plate shall not exceed 10mm; The quenching and holding time is T1, T1=steel plate thickness×(3.0～3.5)min, the unit of steel plate thickness is mm, and the unit of T1 is min; Tempering holding time is T2, T2 = steel plate thickness × (5.0 ~ 5.5) min, the unit of steel plate thickness is mm, and the unit of T2 is min.