KR20240004507A - Rolling method of high-toughness, low-alloy, high-strength steel - Google Patents

Abstract

In the rolling method of high toughness low-alloy high-strength steel, the rolling method includes the following steps in order: heating, phosphorus removal, rough rolling, continuous rolling, first direct water cooling, and precision rolling. , including secondary direct water cooling and cold bed air cooling; A billet continuously cast using a rotary furnace is used as a raw material, and the chemical composition and content of the continuously cast billet according to mass percentage are respectively C≤0.20; Si≤0.60; Mn: 1.00∼1.70; Cr≤0.30; P≤0.020; S≤0.020; V: 0.05∼0.10; Al≤0.03; N≤0.025; The remainder is iron and inevitable impurities; When using the above rolling method, the actual crystal grain size of low-alloy high-strength steel can be refined, the overall performance of low-alloy high-strength steel is excellent, and the metal structural structure consists of fine ferrite and pearlite ( pearlite), the crystal grain size reaches grade 9.0 or higher, the -20℃ Charpy V-type impact energy is greater than 100J, and the -40℃ Charpy V-type impact energy is greater than 80J.

Description

Rolling method of high-toughness, low-alloy, high-strength steel

The present invention relates to the field of rolling steel materials, and more specifically, to a method for rolling high toughness, low alloy, high strength steel.

As society's economy develops and science and technology advance, steel materials are already widely applied in various fields. Here, low-alloy high-strength steel has high strength and good plasticity and toughness, and has already been used in aerospace, ships, etc. It is widely applied in high-tech fields, especially in infrastructure such as oil pipelines, bridges, and large buildings, and in process fields such as vehicles, containers and machinery, chemical industry, medical care, and light industrial facilities. Low-alloy high-strength steel has high strength, excellent forming performance, and stable overall performance, so it is widely applied in fields such as mechanical equipment, vehicles, and pipe manufacturing.

Currently, the routes to improve the strength of steel materials include solid solution strengthening, dislocations strengthening, fine particle strengthening, and precipitation strengthening of second-phase particles; Here, the fine grain strengthening effect is most evident, and the steel material subjected to fine grain strengthening has relatively excellent strength and toughness. As crystal grains are refined and crack propagation resistance is improved, steel fatigue strength increases, toughness improves, and the brittleness turning point temperature decreases. Steel with fine crystal grains has good strength and matching toughness, and is widely applied in fields such as automobiles, ships, bridges, and process machinery.

Low-alloy high-strength steel according to the prior art cannot secure both strength and toughness, and the prior art only involves the rolling method of steel panels and strip-shaped panels, not the round steel rod rolling method, and the rolling process is offline. A normalizing step is required, the production cost is high, and it is disadvantageous for energy conservation, cost reduction, and eco-friendly manufacturing.

The present invention was created to solve the shortcomings of the prior art, and its purpose is to provide a rolling method of high toughness, low alloy, high strength steel. The rolling method of the high toughness low alloy high strength steel establishes reasonable production process control through microalloy elements and rolling control and cooling control process technology, The rolling method of high-strength steel was successfully researched, invented, and applied to production. By canceling the offline normalizing step in the product manufacturing process, the manufacturing process is reduced and manufacturing costs are saved; In the low-alloy high-strength steel manufactured using the above fixation method, the metal structural structure is fine ferrite with pearlite added, and the tensile strength is greater than 630 MPa and the yield strength is greater than 500 MPa, The rolled crystal grain size is fine and uniform, reaching a grain size of 9.0 or higher, and the overall mechanical performance far exceeds that of a typical rolling process.

The present invention provides the following technical solution to achieve the above object.

In the rolling method of high-toughness, low-alloy, high-strength steel, the rolling method includes the following steps in order: heating, phosphorus removal, rough rolling, continuous rolling, primary direct water cooling, precision rolling, and secondary rolling. Includes direct water cooling and cold bed cooling.

A billet continuously cast using a rotary furnace is used as a raw material, and the billet obtained by continuously casting the high-toughness, low-alloy, high-strength steel according to mass percentage has a chemical composition and content of C≤0.20; Si≤0.60; Mn: 1.00∼1.70; Cr≤0.30; P≤0.020; S≤0.020; V: 0.05∼0.10; Al≤0.03; N≤0.025; The rest is iron and inevitable impurities.

In a preferred implementation method for the rolling method of the high-toughness, low-alloy, high-strength steel, the heating step is divided into four steps, and the four steps are sequentially preheating, heating step 1, heating step 2, and heat uniformity. It's a step.

As a preferred implementation method for the rolling method of the high-toughness, low-alloy, high-strength steel, the temperature of the preheating step is ≦750°C.

As a preferred implementation method for the rolling method of the high-toughness, low-alloy, high-strength steel, the temperature in the first stage of heating is 900 to 1,050°C.

As a preferred implementation method for the rolling method of the high-toughness, low-alloy, high-strength steel, the temperature of the second heating step is 1050 to 1150°C.

As a preferred implementation method for the rolling method of the high-toughness, low-alloy, high-strength steel, the temperature of the heat uniformity step is 1150 to 1210°C.

In a preferred implementation method for the rolling method of the high-toughness, low-alloy, high-strength steel, the total heating time of the heating step is 3 to 5 h.

As a preferred implementation method for the rolling method of the high-toughness, low-alloy, high-strength steel, the heat uniformity time of the heat uniformity step is 30 to 80 min.

As a preferred implementation method for the rolling method of the high-toughness, low-alloy, high-strength steel, the heating step is performed in a four-stage step heating furnace.

As a preferred implementation method for the rolling method of the high-toughness, low-alloy, high-strength steel, in the rough rolling step, the entrance temperature of the rough rolling is 950 to 1050 ° C., and the rough rolling courses are 5 to 7 courses, preferably, The number of rough rolling mills installed in the above rough rolling stage is 6 units.

As a preferred implementation method for the rolling method of the high-toughness, low-alloy, high-strength steel, the continuous rolling step includes intermediate rolling and pre-precision rolling.

As a preferred implementation method for the rolling method of the high-toughness, low-alloy, high-strength steel, the entrance temperature of the intermediate rolling is 900 to 1000°C.

In a preferred implementation method for the rolling method of the high-toughness, low-alloy, high-strength steel, the number of intermediate rolling mills installed in the intermediate rolling is 6, the intermediate rolling courses are 5 to 7 courses, and preferably, the intermediate rolling mills are installed in the intermediate rolling mills. There are 6 rolling courses.

As a preferred implementation method for the rolling method of the high-toughness, low-alloy, high-strength steel, the exit temperature of the pre-precision rolling is 850 to 950°C.

As a preferred implementation method for the rolling method of the high-toughness, low-alloy, high-strength steel, the number of pre-precision rolling mills installed for the pre-precision rolling is 4, and the pre-precision rolling course is 3 to 5 courses, preferably. , the pre-precision rolling course is 4 courses.

As a preferred implementation method for the rolling method of the high-toughness, low-alloy, high-strength steel, the first direct water cooling is performed on the material provided after performing the continuous rolling step, wherein water cooling is performed. The water cooling speed is 25 to 50°C/s, and the water pressure is 0.2 to 0.6 MPa.

As a preferred implementation method for the rolling method of the high-toughness, low-alloy, high-strength steel, the entrance rolling start temperature of the precision rolling in the precision rolling step is 800 to 850°C.

As a preferred method for rolling the high-toughness, low-alloy, high-strength steel, precision rolling is performed using a reducing sizing unit.

As a preferred implementation method for the rolling method of the high-toughness, low-alloy, high-strength steel, the reducing sizing unit is a 3-roll reducing sizing unit.

As a preferred implementation method for the rolling method of the high-toughness, low-alloy, high-strength steel, the secondary direct water cooling is performed on the steel material after performing the precision rolling step, wherein water cooling is performed. The water cooling speed is 25 to 100°C/s, and the water pressure is 0.2 to 0.6 MPa.

In a preferred implementation method for the rolling method of the high-toughness, low-alloy, high-strength steel, the phosphorus removal step uses high-pressure water phosphorus removal for the purpose of removing oxide scale, and the water pressure of the high-pressure water is 15 to 20 MPa. .

More preferably, the water pressure of the high-pressure water is 17 to 20 MPa.

As a preferred implementation method for the rolling method of the high-toughness, low-alloy, high-strength steel, a high-toughness, low-alloy, high-strength steel rod material is obtained through the rolling method, and the steel rod material is The standard is Ø60∼120mm.

As a preferred implementation method for the rolling method of the high-toughness, low-alloy, high-strength steel, the cold bed cooling refers to air cooling in the cold bed for the steel material obtained by performing secondary direct water cooling. do.

Compared with the prior art, the present invention achieves the following beneficial effects.

(1) Regarding the chemical composition of the continuously cast billet, the addition of the microalloy element vanadium V improves the hardenability of the steel, reduces deformation of the steel material, avoids the occurrence of cracks, and further improves the hardenability of the steel material. , improves impact toughness; Since the microalloying element vanadium V only plays a role in delaying recrystallization below 900°C, the microalloying element vanadium V is almost completely dissolved after austenite conversion, and at the same time, the microalloying element N is affected by the impact of the microalloying element. To further strengthen the toughness, the impact toughness is improved by adding the microalloying element V to fully utilize the precipitation strengthening role of the microalloying element vanadium V and nitrogen N. At the same time, the microalloying element vanadium V is added to ferrite. ) to play a reinforcing role, forming stable carbides and refining crystal particles.

At the same time, the nitride precipitation process is controlled using the online TMCP process to form ferrite and pearlite structures, and the crystal grains are refined again using a relatively low final rolling temperature and cooling rate. The crystal grain refinement process is used to control the nitride precipitation process. In addition to improving strength, it can also improve its plasticity and impact toughness, realizing high-strength control of mechanical performance.

Using the above rolling method, the actual crystal grain size of the low-alloy high-strength steel can be refined, so the overall performance of the low-alloy high-strength steel obtained is excellent, and the metal structural structure is pearlite added to fine ferrite, The tensile strength is greater than 630MPa, the yield strength is greater than 500MPa, the crystal grain size is fine and uniform after rolling, the crystal grain size reaches grade 9.0 or higher, -20℃ impact energy is greater than 100J, and -40℃ impact energy is 80J. larger, and its overall mechanical performance far exceeds that of conventional rolling processes;

(2) Without performing offline normalizing processing during the rolling process, the mechanical performance can meet the usage demand. In this case, not only can processing time be saved, but also the cost can be reduced and the effectiveness can be increased. .

Figure 1 shows the metal structure obtained with a standard of Ø80mm in the rolling of Control Example 2;
Figure 2 shows the crystal grain size (grade 7.5) obtained in the rolling of Control Example 2 with a standard of Ø80mm;
Figure 3 shows the metal structure obtained in the standard of Ø80mm in the rolling of Example 2 according to the present invention;
Figure 4 shows the crystal grain size (grade 9.0) obtained in the rolling of Example 2 according to the present invention with a standard of Ø80mm.

Hereinafter, the technical solution of the embodiment according to the present invention will be clearly and comprehensively explained by combining the drawings of the embodiment according to the present invention. It is obvious that the described embodiments are only some embodiments of the present invention and are not all embodiments. All other embodiments obtained by those skilled in the art without making inventive efforts based on the embodiments of the present invention shall all fall within the protection scope of the present invention.

The rolling method disclosed by the present invention is designed based on the parameters of the continuous rolling process, combines the solid state phase change and plastic deformation of the rolling principle, and uses the plasticity of the heating process mechanism and the rolling reduction mechanism in a four-stage step heating furnace. Form the finished product, form the finished product through the deformation mechanism of rough rolling, intermediate rolling and precision rolling, and finally control the solid state phase change of the metal through the cooling control process to achieve the required product's excellent tissue form and excellent tissue mechanics. Obtain performance.

Hereinafter, the technical solution of the present invention will be described in more detail through examples combining the drawings.

In the rolling method of high toughness low-alloy high-strength steel, the rolling method includes the following steps in order: heating, phosphorus removal, rough rolling, continuous rolling, first direct water cooling, and precision rolling. , including secondary direct water cooling and cold bed air cooling; A billet continuously cast using a rotary furnace is used as a raw material, and the chemical composition and content of the continuously cast billet according to mass percentage are C≤0.20; Si≤0.60; Mn: 1.00∼1.70; Cr≤0.30; P≤0.020; S≤0.020; V: 0.05∼0.10; Al≤0.03; N≤0.025; The rest is Fe and inevitable impurities.

Regarding the chemical composition of the continuously cast billet, the addition of microalloy element vanadium V improves the hardenability of steel, reduces steel material deformation and crack occurrence, and further improves impact toughness; Since the microalloying element vanadium V only plays a role in delaying recrystallization below 900°C, the microalloying element vanadium V is almost completely dissolved after austenite conversion, and at the same time, the microalloying element N is a microalloying element vanadium V. Further enhance the impact toughness, and make full use of the precipitation strengthening role of microalloying elements vanadium V and nitrogen N.

The reason why crystal particle refinement can improve plasticity and toughness is because fine crystal particles provide better conditions for the occurrence and expansion of plastic deformation. All factors that lower the temperature Ar3, which causes austenite to transform into ferrite, are all related to the tendency for crystal grains to become finer. The impact toughness is improved by adding the microalloying element V, and at the same time, the microalloying element vanadium V is dissolved in ferrite to play a reinforcing role, forming stable carbides and refining the crystal grains.

The rolling method includes the following steps in order:

(1)Heating

The heating step is carried out in a four-stage step heating furnace; The heating stage is divided into four stages, and the four stages are, in order, preheating, heating stage 1, heating stage 2, and heat uniformity stage.

the temperature of the preheating step ≦750°C (e.g., a step section or step point between 600°C, 650°C, 665°C, 700°C, 750°C, and any two of these temperatures); In other words, if the furnace temperature exceeds 750℃, the heat conduction speed of the billet is too fast and the temperature difference between the billet and the heating furnace is too large, which may cause cracks to occur on the surface of the casting billet or the final rolled material. there is.

The temperature of the first stage of heating is 900 to 1050°C (e.g., 900°C, 950°C, 980°C, 1000°C, 1010°C, 1050°C, and a step section or step point between any two temperatures). The temperature of the second heating stage is 1050-1150°C (e.g., 1050°C, 1080°C, 1100°C, 1110°C, 1130°C, 1150°C, and a stage section or stage point between any two temperatures). Heating stage 1 and heating stage 2 mainly serve to reduce energy consumption and reduce oxidation burning loss of the billet.

The temperature of the thermal homogenization step is 1150 to 1210°C (e.g., 1150°C, 1160°C, 1165°C, 1170°C, 1185°C, 1190°C, 1205°C, 1210°C, and a step section between any two of these temperatures. or step point). The heat homogenization step mainly serves to reduce energy consumption and reduce oxidation loss of the billet, while also reducing decarbonization of the billet.

The total heating time of the heating step is 3 to 5 h (e.g., 3.5 h, 4 h, 4.5 h, 4.8 h, and any two time points in between); The heat uniformity time of the heat uniformity step is 30 to 80 min (e.g., 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, 60 min, 70 min, 75 min, 80 min, and any two time points between them).

The heating stage implements four goals: First, by omitting the offline normalizing step, energy consumption can be reduced and costs can be reduced; Second, the four-stage heating process reduces the oxidation loss of the billet; Third, reduce billet decarbonization; Fourth, the heating time is too long to reduce cracks that occur on the surface of the final rolled material.

(2) Phosphorus removal

The heated billet is removed using high-pressure water to remove phosphorus and oxidized scale, and the pressure of the high-pressure water is 15 to 20 MPa (e.g., 15 MPa, 16.5 MPa, 17 MPa, 18 MPa, 20 MPa, and any two of these pressure values). pressure value); Preferably, the pressure value of high-pressure water is 17 to 20 MPa. High-pressure water is used to remove the oxidized scale on the surface of the steel material. If the pressure is less than 15 MPa, the oxidized scale on the surface cannot be cleaned cleanly and completely, which affects the rolling effect of the steel material.

(3)Rough rolling

Preferably, in the rough rolling step, six rough rolling mills are installed; Here, the inlet temperature of rough rolling is 950 to 1050°C (e.g., 950°C, 980°C, 1000°C, 1020°C, 1035°C, 1050°C, and a step section or step point between any two temperatures) ), and the rough rolling course is 5 to 7 courses; Preferably, the rough rolling course is 6 courses. The rough rolling stage uses the rolling method of continuous rolling, mainly changes the surface size of the billet blank through plastic deformation, and the pass type design uses a box type pass design. The cross-sectional shape of the blank is changed and reduced through a strong pressing process.

(4)Continuous rolling

The continuous rolling step includes intermediate rolling and pre-precision rolling, and the entrance temperature of intermediate rolling is 900 to 1000°C (e.g., 905°C, 920°C, 940°C, 950°C, 970°C, 1000°C, and any of these. (step section or step point between two temperatures), preferably, the intermediate rolling stage is installed with 6 intermediate rolling mills, and the intermediate rolling course is 5 to 7 courses; Preferably, the middle rolling course is 6 courses. The pass type design mainly uses oval and circular pass type designs, and the cross-sectional shape of the blank is brought close to the shape of the finished product through the rolling process.

The exit temperature of precision rolling is 850 to 950°C (e.g., 855°C, 870°C, 890°C, 900°C, 910°C, 920°C, 930°C, 940°C, 950°C, and any two of these temperatures. step sections or step points between; Preferably, the pre-precision rolling stage is installed with four pre-precision rolling mills, the pre-precision rolling course is 3 to 5 courses, and preferably, the pre-precision rolling course is 4 courses, and the pass type design is mainly oval and circular pass types. Using design, the cross-sectional shape of the blank is made close to the shape of the finished product through the rolling process.

(5) Primary direct water cooling

After performing the continuous rolling step, first direct water cooling is performed on the provided material, and after first direct water cooling, the temperature is 750 to 800 ℃ (e.g., 750 ℃, 765 ℃, 780 ℃, 795 ℃, 798°C, 800°C, and a step section or step point between any two temperatures), where the primary direct water cooling is a water cooling rate of 25 to 50°C/s and a water pressure of 0.2 to 0.6. It is MPa. The target temperature required for precision rolling is obtained by controlling the temperature and water cooling speed of the first direct water cooling and controlling the temperature of the steel material before precision rolling.

(6)Precision rolling

Rolling is performed by entering the rolled material obtained in step (5) into a reducing sizing precision rolling unit. Preferably, the reducing sizing precision rolling unit is a 3 roll reducing sizing unit. That is, the KOCKS reducing sizing precision rolling unit has an entrance rolling start temperature of 800 to 850 ℃ (e.g., 800 ℃, 810 ℃, 820 ℃, 824 ℃, 832 ℃, 850 ℃ and any two of them) temperature between step sections or step points). When carrying out precision rolling using a three-roll reducing sizing unit, low-temperature rolling can be better carried out, improving the crystal grain size and overall mechanical performance of hot-rolled high-strength steel, so that the production of hot-rolled high-strength steel can achieve the excellent performance of hot-rolled high-strength steel. make it possible to achieve

(7)Secondary direct water cooling

The temperature at which the precision-rolled steel material is subjected to secondary direct water cooling, and the steel material after the precision rolling step is subjected to secondary direct water cooling is 600 to 700°C (e.g., 600°C, 625°C). , 640°C, 662°C, 683°C, 700°C, and a step section or step point between any two of these temperatures), where the water cooling rate is 25 to 100°C/s and the water pressure is 0.2 to 0.2°C. It is 0.6MPa. After performing precision rolling, secondary direct water cooling is performed, and by controlling the temperature of the secondary direct water cooling and the water cooling speed, the temperature of the steel material is controlled to achieve the final metal structural organization and mechanics required by the steel material. Obtain performance.

(8) Cold bed cooling, i.e. cold bed air cooling

The steel material obtained through the second direct water cooling is air-cooled in a cold room to finally obtain the finished steel material.

The rolling control and cooling control techniques described in steps (1) to (8) are the main steps in refining the grain size of high-carbon steel types, and control the heating temperature, degree of change and cooling rate. Combined, it achieves the goal of refining the actual crystal grain size and improving the rigidity and toughness of the steel material.

At the same time, the nitride precipitation process is controlled using an online TMCP process (i.e., thermomechanical control process) to form uniform ferrite and pearlite structures, and the crystal grains are refined again using a relatively low final rolling temperature and cooling rate. The process of refining crystal grains not only improves the strength of steel, but can also improve plasticity and impact toughness to achieve high-strength control over mechanical performance.

The rolling method of high-toughness, low-alloy, high-strength steel according to the present invention is unique in that it uses trace alloy elements and the rolling cooling control technology of the thermomechanical control process to work together to implement online control, and the process When using this method, the actual crystal grain size of the high-toughness, low-alloy, high-strength steel can be refined, the overall performance of the high-toughness, low-alloy, high-strength steel is excellent, and the metal structural structure is made up of fine ferrite and pearlite. The tensile strength is greater than 630MPa, the yield strength is greater than 500MPa, the crystal grain size is fine and uniform after rolling, the grain size reaches grade 9.0 or higher, and the -20℃ Charpy V-type impact energy is greater than 100J. Large, -40℃ Charpy V-type impact energy is greater than 80J, and its comprehensive mechanical performance far exceeds the ordinary rolling method.

High-toughness, low-alloy, high-strength steel does not undergo offline normalizing processing during the manufacturing process, and its mechanical performance can meet the requirements of use. In this case, not only can processing time be saved, but also cost reduction and effectiveness are achieved. can be increased.

Example 1

Example 1 provides a rolling method of high-toughness, low-alloy, high-strength steel. The required finished product size is Ø65mm, and a continuously cast billet with a cross-section of 300×400mm is selected; Here, each chemical component of the continuously cast billet is as listed in Table 2 according to mass percentage, and the sum of the mass fractions is 100%; It includes the steps below:

(1) Heating: After cutting the billet with continuously cast cross-section, heating is performed by placing it in a four-stage step-type heating furnace using a cooling transport method. The temperature of the preheating stage is 685℃, and the temperature of the first heating stage is 1005℃. ℃, the temperature of the second stage of heating is 1086 ℃, and the temperature of the heat uniformity stage is 1175 ℃; The total heating time of the heating step is 3.8h, and the heat uniformity time of the heat uniformity step is 43min.

(2) Phosphorus removal: Phosphorus removal is performed on the heated billet using high-pressure water to remove oxidized scale, and the pressure of the high-pressure water is 18.0 MPa.

(3) Rough rolling: The billet after phosphorus removal is sent to a high-strength rough rolling mill (6 units) and rough rolling is performed to obtain a rough rolled billet; The rough rolling entrance temperature is 1015°C, and the rough rolling course is 6 courses.

(4) Continuous rolling: The rough rolled billet obtained in step (3) is sent to the continuous rolling unit, the intermediate rolling entrance temperature is 925℃, the intermediate rolling course is 6 courses, and the exit temperature for precision rolling the billet in advance is 910℃, and there are 4 courses for precision rolling the billet in advance.

(5) First direct water cooling: First direct water cooling is performed on the rolled material that has undergone precision rolling in advance; The temperature is cooled to 790°C; The water cooling rate is 40℃/s and the water pressure is 0.5MPa.

(6) Precision rolling: Precision rolling is performed in advance to obtain a rolled material with a standard size of Ø80mm, and rolling is performed through a KOCKS reducing sizing unit. When the reducing sizing unit rolls, the entrance temperature of the rolled material is 845. ℃, and obtain a steel rod with a size of Ø65mm.

(7) Secondary direct water cooling: The precision rolled rolled material is subjected to secondary direct water cooling, and the temperature is cooled to 685°C; The water cooling rate is 75℃/s and the water pressure is 0.6MPa.

(8) Cold-bed cooling (cold-bed air cooling): Cold-bed air cooling is performed on the steel rod with the standard of Ø65mm obtained in step (7) to finally obtain a finished steel rod.

The hot-rolled structure of the high-toughness, low-alloy, high-strength steel obtained in Example 1 is uniform ferrite and pearlite, the actual crystal grain size is 9.0 grade, and the mechanical performance of the steel material product is as shown in Table 3. same. The hot-rolled structure of the high-toughness, low-alloy, high-strength steel obtained in Example 1 is uniform ferrite and pearlite, and the actual crystal grain size is 9.0 grade. As can be seen from Table 3, the steel material product is Mechanical performance is excellent.

Example 2

Example 2 provides a rolling method of high-toughness, low-alloy, high-strength steel. The required finished product size is Ø80mm, and a continuously cast billet with a cross-section of 300×400mm is selected; Here, each chemical component of the continuously cast billet is as listed in Table 2 according to mass percentage, and the sum of the mass fractions is 100%; The rolling method includes the following steps in order: (1) heating, (2) phosphorus removal, (3) rough rolling, (4) continuous rolling, (5) first direct water cooling, (6) precision rolling, (7) secondary direct water cooling and (8) cold-bed cooling (cold-bed air cooling), the processing steps of Example 2 are the same as Example 1, the processing parameters of the specific steps refer to Table 1, and the steel material The mechanical performance of the product is as listed in Table 3.

As shown in Figure 3, the hot-rolled structure of the high-toughness, low-alloy, high-strength steel obtained in Example 2 is uniform ferrite and pearlite; As shown in Figure 4, the actual crystal grain size is 9.0 grade. As can be seen from Table 3, the steel material product has excellent mechanical performance.

Example 3

Example 3 provides a rolling method of high-toughness, low-alloy, high-strength steel. The required finished product size is Ø100mm, and a continuously cast billet with a cross-section of 300×400mm is selected; Here, each chemical component of the continuously cast billet is as listed in Table 2 according to mass percentage, and the sum of the mass fractions is 100%; The rolling method includes the following steps in order: (1) heating, (2) phosphorus removal, (3) rough rolling, (4) continuous rolling, (5) first direct water cooling, (6) precision rolling, (7) secondary direct water cooling and (8) cold-bed cooling (cold-bed air cooling), the processing steps of Example 3 are the same as Example 1, the processing parameters of the specific steps refer to Table 1, and the steel material The mechanical performance of the product is as listed in Table 3.

The hot-rolled structure of the high-toughness, low-alloy, high-strength steel obtained in Example 3 is uniform ferrite and pearlite, and the actual crystal grain size is 9.0 grade. As can be seen from Table 3, the steel material product is Mechanical performance is excellent.

In Examples 1 to 3, specific processing step parameters are as listed in Table 1.

Table 1 Specific processing step parameters of steel materials obtained in Examples 1-3

The chemical components of the continuously cast billets selected in Examples 1 to 3 are as listed in Table 2.

Table 2 Chemical composition of continuously cast billets selected in Examples 1-3

Various performances of the high-toughness, low-alloy, high-strength steel obtained in Examples 1 to 3 are shown in Table 3.

Table 3 Mechanical performance parameters of steel materials obtained in Examples 1-3

Example 4-7

Examples 4 to 7 provide a rolling method of high-toughness, low-alloy, high-strength steel, which includes the following steps in order: (1) heating, (2) phosphorus removal, and (3) rough rolling. , (4) continuous rolling, (5) first direct water cooling, (6) precision rolling, (7) second direct water cooling, and (8) cold-bed cooling (cold-bed air cooling), and processing of Examples 4 to 7. The steps and machine parameters are the same as Example 1; The content of each chemical component of the continuously cast billets used in Examples 4 to 7 is as shown in Table 4 according to mass percentage, and the total mass fraction is 100%.

Table 4 Chemical composition of continuously cast billets selected in Examples 4-7

Various performances of the high-toughness, low-alloy, high-strength steel obtained in Examples 4 to 7 are shown in Table 5.

Table 5 Mechanical performance parameters of steel materials obtained in Runs 4-7

As can be seen from Table 5, the hot-rolled structure of the high-toughness, low-alloy, high-strength steel obtained in Examples 4 to 7 is uniform ferrite and pearlite, and the actual crystal grain size is 9.0 grade, and the steel material The product has excellent mechanical performance.

Control Example 1

The required finished product size is Ø65mm, and a continuously cast billet with a cross section of 300×400mm is selected; The content of each chemical component of the continuously cast billet is C: 0.45; Si: 0.28; Mn: 1.46; Cr: 0.16; V: 0.06; N: 0.010; Al: 0.020; P≤0.020; S≤0.020; The rest is Fe and inevitable impurities. The processing steps and parameters of alloy steel materials are as listed in Table 7.

As shown in Table 6, since the content of carbon C in the chemical composition of the continuously cast billet is 0.45%, that is, C>0.20, the elongation of the rolled steel material is 18%, as shown in Table 8, -20℃ Charpy V-type impact energy is 32J; -40℃ Charpy V-type impact energy is 17J.

Control Example 2

The required finished product size is Ø80mm, and a continuously cast billet with a cross section of 300×400mm is selected; The content of each chemical component of the continuously cast billet is C: 0.16; Si: 0.30; Mn: 0.8; Cr: 0.15; V: 0.07; N: 0.012; Al: 0.020; P≤0.020; S≤0.020, and the remainder is Fe and inevitable impurities. The processing steps and parameters of alloy steel materials are as listed in Table 7.

As shown in Table 6, since the content of manganese Mn in the chemical composition of the continuously cast billet is 0.8, that is, Mn < 1.0, the elongation of the rolled steel material is 26%, as shown in Table 8, - The 20℃ Charpy V-type impact energy is 54J; -40℃ Charpy V-type impact energy is 25J.

Control Example 3

The required finished product size is Ø100mm, and a continuously cast billet with a cross section of 300×400mm is selected; The content of each chemical component of the continuously cast billet is C: 0.16; Si: 0.30; Mn: 1.40; Cr: 0.15; N: 0.011; Al: 0.022; P≤0.020; S≤0.020; The rest is Fe and inevitable impurities. The processing steps and parameters of alloy steel materials are as listed in Table 7.

As shown in Table 6, since vanadium V was not added to the chemical composition of the continuously cast billet, the elongation of the rolled steel material was 25%, as shown in Table 8, and the -20°C Charpy V-type impact energy was 35J; -40℃ Charpy V-type impact energy is 19J.

Control Example 4

The required finished product size is Ø90mm, and a continuously cast billet with a cross section of 300×400mm is selected; The content of each chemical component of the continuously cast billet is C: 0.16; Si: 0.32; Mn: 1.47; Cr: 0.15; V: 0.06; N: 0.040; Al: 0.020; P≤0.020; S≤0.020; The rest is Fe and inevitable impurities. The processing steps and parameters of alloy steel materials are as listed in Table 7.

As shown in Table 6, since the content of nitrogen N in the chemical composition of the continuously cast billet is 0.040, that is, N>0.025, the elongation of the rolled steel material is 27%, as shown in Table 8, and -20 °C Charpy V-type impact energy is 62J; -40℃ Charpy V-type impact energy is 37J.

As can be seen from Table 8, compared to the rolling method disclosed in the present application, the rolling methods of Comparative Examples 1 to 4 have -20°C Charpy V-type impact energy of all less than 100J in terms of mechanical performance of the obtained steel material; -40℃ Charpy V-type impact energy was all less than 80J, and the crystal grain size of the rolled alloy steel material did not reach grade 9.0 or higher.

Table 6 Chemical composition of continuously cast billets selected from Control Examples 1-4

The processing steps and parameters of the alloy steel materials described in Comparative Examples 1 to 4 are as listed in Table 7.

Table 7 Specific processing step parameters of steel materials obtained in Control Examples 1-4

The various performances of the alloy steel materials obtained in Comparative Examples 1 to 4 are as shown in Table 8.

Table 8 Mechanical performance parameters of steel materials obtained in Comparative Examples 1-4

The foregoing has described preferred embodiments of the present invention, but those skilled in the art may make separate changes and modifications to these embodiments. Accordingly, the appended claims should be construed as including the preferred embodiments and all changes and modifications included within the scope of the present invention.

The above description is only a preferred embodiment of the present invention, and is not used to limit the present invention, and those skilled in the art may make various changes and modifications to the present invention. All modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims (16)

In the rolling method of high toughness low alloy high strength steel,
The rolling method has the following steps in order,
It includes heating, phosphorus removal, rough rolling, continuous rolling, primary direct water cooling, precision rolling, secondary direct water cooling and cold bed cooling;
A billet continuously cast using a rotary furnace is used as a raw material, and according to mass percentage, the billet continuously cast from the high-toughness low-alloy high-strength steel has a chemical composition and content of C≤0.20, respectively. ; Si≤0.60; Mn: 1.37∼1.70; Cr≤0.30; P≤0.020; S≤0.020; V: 0.07∼0.10; Al≤0.03; N: 0.008 to 0.025; The remainder is iron and inevitable impurities;
The temperature after performing the first direct water cooling is 765 to 800°C;
In the precision rolling step, the entrance rolling start temperature of precision rolling is 832 to 850°C;
The temperature at which the secondary direct water cooling is performed on the steel material after the precision rolling step is performed is 600°C to 700°C, and the water cooling rate is 25°C to 100°C/ s, and the water pressure is 0.2 to 0.6 MPa;
The cold-bed cooling is a rolling method of high-toughness, low-alloy, high-strength steel, characterized in that air cooling is performed on the cold bed for the steel material obtained after performing secondary direct water cooling. According to paragraph 1,
The heating step is divided into four steps, and the four steps are, in order, preheating, heating step 1, heating step 2, and heat uniformity step,
The temperature of the preheating step is ≤750°C;
The temperature of the first stage of heating is 900 to 1050°C;
The temperature of the second heating stage is 1050-1150°C;
A rolling method of high-toughness, low-alloy, high-strength steel, characterized in that the temperature of the heat uniformity step is 1150 to 1210 ° C. According to paragraph 2,
The total heating time of the heating step is 3 to 5 h; A rolling method of high-toughness, low-alloy, high-strength steel, characterized in that the heat uniformity time of the heat uniformity step is 30 to 80 min. According to paragraph 2,
A rolling method of high-toughness, low-alloy, high-strength steel, characterized in that the heating step is carried out in a four-stage step-type heating furnace. According to claim 1 or 2,
In the rough rolling step, the rough rolling entrance temperature is 950 to 1050°C, and the rough rolling course is 5 to 7 courses. According to clause 5,
A rolling method of high-toughness, low-alloy, high-strength steel, characterized in that the number of rough rolling mills installed in the rough rolling step is 6, and the rough rolling course is 6 courses. According to clause 6,
The continuous rolling step includes intermediate rolling and pre-precision rolling,
The entrance temperature of the intermediate rolling is 900 to 1000° C., and the intermediate rolling courses are 5 to 7 courses;
A rolling method of high-toughness, low-alloy, high-strength steel, characterized in that the exit temperature of the pre-precision rolling is 850 to 950 ° C. and the pre-precision rolling course is 3 to 5 courses. In clause 7,
The number of intermediate rolling mills installed in the intermediate rolling is 6; A rolling method of high-toughness, low-alloy, high-strength steel, characterized in that the intermediate rolling course is 6 courses. In clause 7,
The number of pre-precision rolling mills installed in the pre-precision rolling is 4; A rolling method of high-toughness, low-alloy, high-strength steel, characterized in that the pre-precision rolling course is 4 courses. According to clause 5,
The first direct water cooling is performed on the material provided after performing the continuous rolling step, where the water cooling rate is 25 to 50 ° C./s and the water pressure is 0.2 to 0.6 MPa. A rolling method of high-toughness, low-alloy, high-strength steel, characterized in that: According to clause 5,
A rolling method of high-toughness, low-alloy, high-strength steel characterized by precision rolling using a reducing sizing unit. According to clause 11,
A rolling method of high-toughness, low-alloy, high-strength steel, characterized in that the reducing sizing unit is a 3-roll reducing sizing unit. According to clause 5,
The phosphorus removal step is a rolling method of high-toughness, low-alloy, high-strength steel, characterized in that high-pressure water phosphorus removal is used for the purpose of removing oxide scale, and the water pressure of the high-pressure water is 15 to 20 MPa. According to clause 13,
A rolling method of high-toughness, low-alloy, high-strength steel, characterized in that the water pressure of the high-pressure water is 17 to 20 MPa. According to claim 1 or 2,
A rolling method of high-toughness, low-alloy, high-strength steel, characterized in that a high-toughness, low-alloy, high-strength steel rod material is obtained through the rolling method. According to clause 15,
A rolling method of high-toughness, low-alloy, high-strength steel, characterized in that the standard of the steel rod material is Ø60∼120mm.