Disclosure of Invention
The invention aims to provide a production method of a low yield ratio steel plate suitable for large heat input welding and the low yield ratio steel plate prepared by the production method and suitable for large heat input welding, so as to solve the problems that the steel plate for a bridge is difficult to control, low in welding efficiency, poor in steel plate shape and the like.
In order to achieve the above object, an embodiment of the present invention provides a method for producing a low yield ratio steel sheet suitable for large heat input welding, comprising the steps of molten steel smelting, continuous casting, heating, controlled rolling, controlled cooling and controlled temperature straightening sequentially performed;
in the rolling control process, the final rolling temperature is 800-840 ℃;
in the cooling control procedure, the cooling speed before the phase transformation of the polygonal ferrite is 15-25 ℃/s, the cooling speed during the phase transformation of the polygonal ferrite is 3-8 ℃/s, and the cooling speed during the phase transformation of the acicular ferrite is 10-20 ℃/s;
in the temperature control straightening process, the steel plate subjected to the cooling control process is straightened in a first stage, and the straightening temperature of the first stage straightening is 500-600 ℃; then the mixture is sent to a cooling bed for cooling, and the second stage straightening is carried out after cooling, wherein the straightening temperature of the second stage straightening is 250-450 ℃; and then air-cooling until the temperature of the steel plate is less than or equal to 100 ℃.
Preferably, in the controlled cooling process, the steel plate obtained in the controlled rolling process is sent to an accelerated cooling device for cooling, the steel plate sequentially passes through a first cooling zone, a second cooling zone and a third cooling zone, the ratio of cooling water amounts of the first cooling zone, the second cooling zone and the third cooling zone is 3:1:2, and the roller way speed is 0.9-1.5 m/s.
Preferably, in the controlled cooling step, the final cooling temperature of the steel sheet is 520 to 580 ℃.
Preferably, in the molten steel smelting process, the flow of molten iron pre-desulfurization, converter smelting, LF refining and RH vacuum refining is adopted for steelmaking; wherein, in the molten iron pre-desulfurization process, S is less than or equal to 0.002 percent when molten iron comes out of the station.
Preferably, in the converter smelting process, alloy and slag are added into molten steel according to the sequence of ferrosilicon, manganese metal and lime, and P in the molten steel is less than or equal to 0.01% during tapping.
Preferably, in the LF refining process, O in molten steel is less than or equal to 0.005% during tapping.
Preferably, in the RH vacuum refining process, RH circulation degassing equipment is adopted to carry out vacuum degassing and inclusion removal treatment, then Ti-Fe cored wires are fed into molten steel to carry out alloying treatment, then net circulation treatment is carried out, the net circulation treatment time is more than or equal to 8min, and N in the molten steel is less than or equal to 0.0045 percent during tapping
In order to achieve the above object, an embodiment of the present invention further provides a low yield ratio steel plate suitable for high heat input welding, the steel plate is manufactured by the manufacturing method as described above, and the steel plate comprises the following chemical components in percentage by mass: 0.07 to 0.10 percent of C, 0.21 to 0.29 percent of Si, 1.4 to 1.5 percent of Mn, 0.1 to 0.2 percent of Cr, 0.2 to 0.3 percent of Ni, 0.02 to 0.04 percent of Nb, 0.02 to 0.05 percent of Ti, 0.0005 to 0.0020 percent of B, 0.0015 to 0.0035 percent of O, 0.003 to 0.006 percent of N, less than or equal to 0.012 percent of P, less than or equal to 0.005 percent of S, less than or equal to 0.004 percent of Al, and the balance of Fe and unavoidable impurities, and the following conditions are satisfied: the Ti is greater than or equal to 3.5 N+1.5O.
As a further improvement of an embodiment of the invention, in the low yield ratio steel plate suitable for large heat input welding, the density of the inclusions with the equivalent diameter of 0.5-2 mu m is more than or equal to 2 multiplied by 10 5 Individual/mm 3 The method comprises the steps of carrying out a first treatment on the surface of the Under the condition that the welding heat input amount is 50-500 kJ/cm, the impact energy of a welding heat affected zone at minus 60 ℃ is more than or equal to 100J.
As a further improvement of an embodiment of the invention, the structure of the low yield ratio steel plate suitable for large heat input welding is a two-phase structure of acicular ferrite and polygonal ferrite, wherein the content of the acicular ferrite is more than or equal to 60 percent, and the sum of the content of the grain boundary M/A and the content of the grain boundary ferrite is less than or equal to 3 percent.
As a further improvement of one embodiment of the invention, the yield ratio of the low-yield-ratio steel plate suitable for large heat input welding is less than or equal to 0.85, and the unevenness is less than or equal to 1mm/m.
Compared with the prior art, the invention has the beneficial effects that:
(1) The phase transformation structure of the steel plate can be controlled by controlling the production process of the steel plate, particularly the cooling and temperature control straightening processes, so that the two-phase structure of polygonal ferrite and acicular ferrite is obtained, the steel plate has low yield ratio, and has excellent deformation energy storage capacity for geological disasters when the steel plate is applied to bridge steel, so that the bridge quality, the manufacturing efficiency and the use safety are improved, the problem of plate shape in the rolling and cooling processes can be solved, the steel plate keeps good plate shape, and the unevenness is less than or equal to 1mm/m. The finally prepared steel plate can be welded by adopting large heat input during welding, has good welding quality and higher welding efficiency, and can meet the application requirements of the steel plate for the bridge.
(2) Through the optimized design of the chemical composition design scheme and the combination of the strict control of the production process, the production method is suitable for large heat input weldingSteel plate with low yield ratio and equivalent diameter of 0.5-2 mu m, and the density of inclusions is more than or equal to 2 multiplied by 10 5 Individual/mm 3 The welding method is suitable for large heat input welding, and under the condition that the welding heat input amount is 50-500 kJ/cm, the impact energy of a welding heat affected zone at minus 60 ℃ is more than or equal to 100J, so that the welding method has good welding quality and higher welding efficiency, and can meet the application requirements of the steel plate for the bridge.
(3) The prepared low yield ratio steel plate suitable for large heat input welding has a two-phase structure of acicular ferrite and polygonal ferrite, wherein the content of the acicular ferrite is more than or equal to 60%, the sum of the content of crystal boundary M/A and the content of the crystal boundary ferrite is less than or equal to 3%, the yield ratio is less than or equal to 0.85, the unevenness is less than or equal to 1mm/M, and the steel plate has excellent deformation energy storage capacity for geological disasters when applied to bridge steel, so that the quality, the manufacturing efficiency and the use safety of the bridge are improved, and the steel plate has good shape.
Detailed Description
The technical scheme of the present invention will be further described with reference to the specific embodiments, but the scope of the claims is not limited to the description.
The embodiment of the invention provides a production method of a low yield ratio steel plate suitable for large heat input welding and the low yield ratio steel plate prepared by the production method and suitable for large heat input welding. The low yield ratio steel plate suitable for large heat input welding, namely the steel plate can be welded by large heat input when being welded, so that the steel plate has good welding quality and high welding efficiency, has low yield ratio, has excellent deformation energy storage capacity facing geological disasters when being applied to bridge steel, and is beneficial to improving bridge quality, manufacturing efficiency and use safety.
In terms of process flow, as previously described, the production method comprises the following steps performed in sequence:
(1) Smelting molten steel: smelting molten iron into molten steel.
Specifically, the process of molten iron pre-desulfurization, converter smelting, LF refining and RH vacuum refining is adopted for steelmaking.
Preferably, in the molten iron pre-desulfurization process, the molten iron is pre-desulfurized, and S is less than or equal to 0.002% when the molten iron is discharged. By optimizing the components of the blast furnace molten iron, the S content in the molten iron is reduced to a lower level, slag rolling or strong slag-metal reaction caused by a large amount of desulfurization in the subsequent refining process can be avoided, thereby reducing the generation of large-size inclusions in molten steel, effectively controlling the types of the inclusions and reducing the sizes of the inclusions.
Preferably, in the converter smelting process, the molten iron after pre-desulfurization is sent into a converter to be mixed with scrap steel to form molten steel, and alloy and slag materials are added into the molten steel according to the sequence of ferrosilicon, manganese metal and lime, wherein P in the molten steel is less than or equal to 0.01% during tapping, so that good dephosphorization effect is ensured, and the low-temperature toughness of the finally prepared steel plate is improved.
Preferably, in the LF refining process, chemical component adjustment, temperature regulation and inclusion regulation are carried out on molten steel smelted by a converter, and O in the molten steel is less than or equal to 0.005% during tapping, so that the problem that the size of inclusions in a finally prepared steel plate is larger due to the fact that the O content is too high can be avoided, and further the subsequent welding performance is influenced.
Preferably, in the RH vacuum refining process, RH circulation degassing equipment is adopted to carry out vacuum degassing and inclusion removal treatment, then Ti-Fe cored wires are fed into molten steel to carry out alloying treatment, and then net circulation treatment is carried out, wherein the net circulation treatment time is more than or equal to 8min, and the N in the molten steel is less than or equal to 0.0045% during tapping. By feeding the Ti-Fe cored wire in the process, the stable control of the nitride and the oxide of Ti is facilitated, and the inclusion with sufficient quantity, moderate size and uniform distribution can be obtained by combining with sufficient net circulation, so that the finally prepared steel plate is suitable for large heat input welding.
(2) Continuous casting: casting molten steel obtained by smelting into a continuous casting blank.
(3) Heating: and heating the obtained continuous casting blank.
(4) And (3) rolling control: feeding the heated continuous casting blank into a roughing mill for rough rolling, wherein the rough rolling temperature is 980-1050 ℃; and then the steel plate is sent into a finishing mill for finish rolling, so that the steel plate is manufactured, the initial rolling temperature of the finish rolling is 840-920 ℃, and the final rolling temperature of the finish rolling is 800-840 ℃.
(5) And (3) controlling cooling: and (3) conveying the rolled steel plate into an accelerated cooling device for cooling in three stages.
Wherein, the first stage is from the end of rolling to the beginning of polygonal ferrite transformation, namely, the stage before polygonal ferrite transformation, and the cooling rate of the stage is 15-25 ℃/s. Specifically, the steel sheet is water-cooled at this stage through a cooling-zone of the accelerated cooling equipment, and is cooled by using a large amount of water to avoid the occurrence of grain boundary ferrite at the austenite grain boundaries.
The second stage is a polygonal ferrite transformation stage, and the cooling speed during polygonal ferrite transformation is controlled to be 3-8 ℃/s. Specifically, the steel sheet is water-cooled at this stage through a cooling second zone of the accelerated cooling equipment, and is cooled by using a small amount of water so that a part of austenite undergoes polygonal ferrite transformation.
The third stage is acicular ferrite transformation stage, and the cooling rate during acicular ferrite transformation is controlled to be 10-20 ℃/s. Specifically, the steel sheet is water-cooled at this stage through a cooling three zone of the accelerated cooling device, and the steel sheet is cooled by using a large amount of water so that acicular ferrite transformation of the remaining austenite occurs.
In order to realize the sectional control cooling of the three stages, when the steel plate is sent into an accelerated cooling device for cooling, the steel plate sequentially passes through a first cooling zone, a second cooling zone and a third cooling zone, the ratio of the cooling water quantity of the first cooling zone to the cooling water quantity of the second cooling zone to the cooling water quantity of the third cooling zone is 3:1:2, and the roller way speed is 0.9-1.5 m/s.
Preferably, the final cooling temperature of the steel plate is 520-580 ℃.
By matching the roller way speed with the cooling water quantity, the cooling speed can be effectively controlled, and further the control of the final cooling temperature is combined, so that the control of the phase transformation structure of the steel plate can be realized, the two-phase structure of polygonal ferrite and acicular ferrite can be obtained, and the steel plate has low yield ratio. If the roller speed is too high and the final cooling temperature is too low, the polygonal ferrite phase transformation of the second stage can be restrained, and the third stage can be converted into lath bainite phase transformation, so that the low yield ratio of the steel plate is not facilitated; if the roller way speed is too slow and the final cooling temperature is too high, grain boundary ferrite can appear in the cooling process of the first stage, and the third stage can be converted into polygonal ferrite phase transformation, so that the low yield ratio of the steel plate is not facilitated.
(6) And (3) temperature control straightening: and carrying out phased temperature control straightening on the steel plate subjected to the cooling control procedure.
Specifically, straightening the steel plate after the cooling control procedure in a first stage, wherein the straightening temperature of the first stage is 500-600 ℃ so as to straighten buckling generated in the cooling control process of the steel plate; then the steel plate is sent to a cooling bed for cooling, and is subjected to second-stage straightening after cooling, wherein the straightening temperature of the second-stage straightening is 250-450 ℃ so as to straighten buckling which is generated again due to the release of internal stress of the steel plate in the cooling process of the steel plate on the cooling bed; and then air-cooling until the temperature of the steel plate is less than or equal to 100 ℃. Thus, the problem of plate shape in the rolling and cooling processes can be eliminated by controlling the temperature and straightening in stages, and the steel plate still has a certain temperature after being straightened in two stages, so that the steel plate has smaller internal stress than the steel plate straightened at room temperature, thereby keeping good plate shape and the unevenness is less than or equal to 1mm/m.
In the production method, the phase transformation structure of the steel plate can be controlled by controlling the production process of the steel plate, particularly the cooling and temperature control straightening processes, so that the two-phase structure of polygonal ferrite and acicular ferrite is obtained, the steel plate has low yield ratio, and has excellent deformation energy storage capacity facing geological disasters when the steel plate is applied to bridge steel, so that the bridge quality, the manufacturing efficiency and the use safety are improved, the plate shape problem generated in the rolling and cooling processes can be eliminated, the steel plate keeps good plate shape, and the unevenness is less than or equal to 1mm/m. The finally prepared steel plate can be welded by adopting large heat input during welding, has good welding quality and higher welding efficiency, and can meet the application requirements of the steel plate for the bridge.
The invention also provides a low yield ratio steel plate suitable for large heat input welding, which is prepared by adopting the production method of the low yield ratio steel plate suitable for large heat input welding, wherein the steel plate comprises the following chemical components in percentage by mass: 0.07 to 0.10 percent of C, 0.21 to 0.29 percent of Si, and Mn
1.4 to 1.5 percent, 0.1 to 0.2 percent of Cr, 0.2 to 0.3 percent of Ni, 0.02 to 0.04 percent of Nb, 0.02 to 0.05 percent of Ti, 0.0005 to 0.0020 percent of B, 0.0015 to 0.0035 percent of O, 0.003 to 0.006 percent of N, less than or equal to 0.012 percent of P, less than or equal to 0.005 percent of S, less than or equal to 0.004 percent of Al, and the balance of Fe and unavoidable impurities, and satisfies the following conditions: the Ti is greater than or equal to 3.5 N+1.5O.
Wherein [ Ti ] represents a mass percentage of Ti, [ N ] represents a mass percentage of N, and [ O ] represents a mass percentage of O.
The effect of each chemical component has the following characteristics:
c: as a main strengthening element in the steel, the hardenability and strength of the steel can be improved, but too high C can generate more martensite/austenite (M/A) components during phase transformation, so that the low-temperature toughness and welding performance of the steel plate are deteriorated, and the content of C is controlled to be 0.07-0.10%;
si: is a common deoxidizing element in steel, has the functions of solid solution strengthening and pearlite transformation inhibition, but excessively high Si is not beneficial to primary oxide scale removal in the rolling process of the steel plate, and is easy to cause the increase of M/A content, and is unfavorable for the low-temperature toughness and the toughness of a welded HAZ zone of the steel plate, and the Si content range is controlled to be 0.21-0.29%;
mn: the alloy is an important strengthening element in steel, has solid solution strengthening effect, can increase the hardenability of the steel and promote acicular ferrite to form, but too high Mn can deteriorate the welding performance of the steel and aggravate center segregation, and the Mn content range is controlled to be 1.4-1.5%;
cr: is a strengthening element in steel, has solid solution strengthening effect, but when the Cr content is too high, the stability of supercooled austenite is affected, the formation of acicular ferrite structure is not facilitated, and the Cr content range is controlled to be 0.1-0.2%;
ni: the strength, hardenability, low-temperature toughness and crack-arrest toughness of the steel can be obviously improved, and the Ni content range is controlled to be 0.2-0.3%;
nb: the alloy is an important refined grain element in steel, can promote the formation of acicular ferrite, improve the strength of the steel and improve the low-temperature toughness, but when the Nb content is too high, a large amount of large-size M/A is easily formed in a welding heat affected zone, and the welding performance of the steel plate is deteriorated, and the Nb content range is controlled to be 0.02-0.04%;
ti: the Ti-containing alloy is a microalloy strengthening element and has the functions of precipitation strengthening and fine grain strengthening, the nitride and the oxide of Ti are mainly utilized in the invention, the growth of austenite grains and the nucleation induction in the grains can be inhibited, and the content range of Ti is controlled to be 0.02-0.05%, so that the steel is provided with enough Ti nitride and Ti oxide inclusion;
b: the invention mainly utilizes the grain boundary segregation effect of B to inhibit the formation of grain boundary ferrite, thereby improving the impact toughness of a welding heat affected zone, but when the B content is too high, excessive B atoms are segregated at the grain boundary to easily cause the decrease of the grain boundary strength, thereby being unfavorable for improving the toughness, and the B content range is controlled to be 0.0005-0.002%;
o, N: the method is characterized in that the method is used for smelting residual impurity elements in steel, but the residual impurity elements are beneficial elements, and nitride and oxide inclusions are formed by the beneficial elements and Ti, so that austenite grains can be restrained from excessively growing in the heating process of a welding heat affected zone, and meanwhile, phase transformation nucleation in the grains is induced in the cooling process of the welding heat affected zone to refine the structure of the heat affected zone, so that the welding performance is improved. The number of the inclusions is insufficient when the O, N content is too low, and the size of the inclusions is larger when the O, N content is too high, so that the O content range is controlled to be 0.0015-0.0035% and the N content range is controlled to be 0.003-0.006%;
p, S, al: is an impurity element in steel, and is unfavorable for the low-temperature toughness of the steel, so that the content of P is less than or equal to 0.012 percent, the content of S is less than or equal to 0.005 percent and the content of Al is less than or equal to 0.004 percent.
The design scheme of the chemical components of the low yield ratio steel plate suitable for large heat input weldingThe optimized design of the steel plate, the strict control of the production process is combined, and the density of inclusions with equivalent diameter of 0.5-2 mu m in the finally obtained steel plate is more than or equal to 2 multiplied by 10 5 Individual/mm 3 Therefore, the steel plate is suitable for large heat input welding, and under the condition that the welding heat input amount is 50-500 kJ/cm, the impact energy of a welding heat affected zone at minus 60 ℃ is more than or equal to 100J, so that the steel plate has good welding quality and higher welding efficiency, and can meet the application requirements of the steel plate for the bridge.
Further, the structure of the low yield ratio steel plate suitable for large heat input welding is a two-phase structure of acicular ferrite and polygonal ferrite, wherein the content of the acicular ferrite is more than or equal to 60 percent, and the sum of the content of the grain boundary M/A and the content of the grain boundary ferrite is less than or equal to 3 percent, so that the steel plate has low yield ratio.
Through tests, the low yield ratio steel plate suitable for large heat input welding has the yield ratio less than or equal to 0.85 and the unevenness less than or equal to 1mm/m, has excellent deformation energy storage capacity for geological disasters when applied to bridge steel, is beneficial to improving the bridge quality, the manufacturing efficiency and the use safety, and has good plate shape.
For the purpose of making the objects, technical solutions and advantages of one embodiment of the present invention more clear, the present embodiment will be further described with reference to examples 1 to 2 according to one embodiment of the present invention. It is apparent that embodiments 1-2 described are some, but not all, embodiments of the invention.
The production methods of the respective embodiments are described in detail below.
Example 1
(1) Smelting molten steel: and steel making is carried out by adopting the flow of molten iron pre-desulfurization, converter smelting, LF refining and RH vacuum refining.
Wherein, in the molten iron pre-desulfurization procedure, the S content of molten iron when the molten iron comes out of the station is 0.001%; in the converter smelting process, the pre-desulfurized molten iron is sent into a converter to be mixed with scrap steel into molten steel, and alloy and slag materials are added into the molten steel according to the sequence of ferrosilicon, manganese metal and lime, wherein P in the molten steel is less than or equal to 0.01% during tapping; in the LF refining process, chemical component adjustment, temperature regulation and inclusion regulation are carried out on molten steel smelted by a converter, and the O content in the molten steel during tapping is 0.0035%; in the RH vacuum refining process, RH circulation degassing equipment is adopted to carry out vacuum degassing and inclusion removal treatment, then Ti-Fe cored wires are fed into molten steel to carry out alloying treatment, then net circulation treatment is carried out, the net circulation treatment time is 12min, and the N content in the molten steel during tapping is 0.003%.
(2) Continuous casting: casting molten steel obtained by smelting into a continuous casting blank.
(3) Heating: and heating the obtained continuous casting blank.
(4) And (3) rolling control: firstly, feeding the heated continuous casting blank into a roughing mill for rough rolling, wherein the rough rolling temperature is 994-1032 ℃; and then feeding the steel plate into a finishing mill to finish the steel plate into a steel plate with the thickness of 16mm, wherein the finish rolling temperature is 912 ℃, the finish rolling temperature is 802 ℃, and the chemical components of the obtained steel plate comprise, in mass percent: 0.07% of C, 0.21% of Si, 1.41% of Mn, 0.12% of Cr, 0.2% of Ni, 0.025% of Nb, 0.023% of Ti, 0.0008% of B, 0.0018% of O, 0.0035% of N, 0.011% of P, 0.004% of S, 0.003% of Al, and the balance of Fe and unavoidable impurities.
(5) And (3) controlling cooling: and (3) conveying the rolled steel plate into an accelerated cooling device for cooling in three stages, wherein the length of a cooling section is 24m.
Wherein, the first stage is from the end of rolling to the beginning of polygonal ferrite transformation, namely, the stage before polygonal ferrite transformation, and the cooling rate of the stage is 23.5 ℃/s. Specifically, the steel sheet was water-cooled at this stage through a cooling zone of an accelerated cooling device with a cooling water amount of 690L/s.
The second stage is polygonal ferrite transformation stage, and the cooling speed during polygonal ferrite transformation is controlled to be 4.8 ℃/s. Specifically, at this stage, the steel sheet was water-cooled by passing it through a cooling two-stage zone of an accelerated cooling device with a cooling water amount of 230L/s.
The third stage is acicular ferrite transformation stage, and the cooling rate during acicular ferrite transformation is controlled to be 14 ℃/s. Specifically, the steel plate was water-cooled in this stage through the cooling three zones of the accelerated cooling equipment with a cooling water amount of 460L/s.
In the cooling process, the roller way speed of the accelerated cooling device is 1.4m/s, and the final cooling temperature of the steel plate is 560 ℃.
(6) And (3) temperature control straightening: straightening the steel plate subjected to the cooling control procedure in a first stage, wherein the straightening temperature of the first stage straightening is 530 ℃; then the mixture is sent to a cooling bed for cooling, and the second stage straightening is carried out after cooling, wherein the straightening temperature of the second stage straightening is 380 ℃; and then air-cooling until the temperature of the steel plate is less than or equal to 100 ℃.
As a result of microscopic examination of the temperature-controlled straightened steel sheet, as shown in fig. 1, it can be seen from fig. 1 that the structure of the low yield ratio steel sheet suitable for high heat input welding is a two-phase structure of acicular ferrite + polygonal ferrite, and the sum of the acicular ferrite content, grain boundary M/a and grain boundary ferrite content is shown in table 1.
The inclusion density of the steel plate after temperature control and straightening was counted by using a scanning electron microscope to obtain an inclusion density of 0.5 to 2 μm as shown in Table 1.
Mechanical property detection, welding performance detection and flatness detection are carried out on the steel plate subjected to temperature control straightening, and the yield ratio, welding heat input quantity and-60 ℃ impact power KV of a corresponding welding heat affected zone of the steel plate in example 1 are measured 2 And the unevenness are shown in table 1.
Example 2
(1) Smelting molten steel: and steel making is carried out by adopting the flow of molten iron pre-desulfurization, converter smelting, LF refining and RH vacuum refining.
Wherein, in the molten iron pre-desulfurization procedure, the S content of molten iron when the molten iron comes out of the station is 0.001%; in the converter smelting process, the pre-desulfurized molten iron is sent into a converter to be mixed with scrap steel into molten steel, and alloy and slag materials are added into the molten steel according to the sequence of ferrosilicon, manganese metal and lime, wherein P in the molten steel is less than or equal to 0.01% during tapping; in the LF refining process, chemical component adjustment, temperature regulation and inclusion regulation are carried out on molten steel smelted by a converter, and the O content in the molten steel during tapping is 0.0038%; in the RH vacuum refining process, RH circulation degassing equipment is adopted to carry out vacuum degassing and inclusion removal treatment, then Ti-Fe cored wires are fed into molten steel to carry out alloying treatment, then net circulation treatment is carried out, the time of the net circulation treatment is 10min, and the N content in the molten steel during tapping is 0.0037%.
(2) Continuous casting: casting molten steel obtained by smelting into a continuous casting blank.
(3) Heating: and heating the obtained continuous casting blank.
(4) And (3) rolling control: firstly, feeding the heated continuous casting blank into a roughing mill for rough rolling, wherein the rough rolling temperature is 1006-1042 ℃; and then feeding the steel plate into a finishing mill to finish the steel plate into a steel plate with the thickness of 40mm, wherein the initial rolling temperature of the finish rolling is 853 ℃, the final rolling temperature of the finish rolling is 832 ℃, and the obtained steel plate comprises the following chemical components in percentage by mass: 0.09% of C, 0.28% of Si, 1.48% of Mn, 0.18% of Cr, 0.28% of Ni, 0.035% of Nb, 0.033% of Ti, 0.0016% of B, 0.0023% of O, 0.0030% of N, 0.011% of P, 0.002% of S, 0.003% of Al, and the balance of Fe and unavoidable impurities.
(5) And (3) controlling cooling: and (3) conveying the rolled steel plate into an accelerated cooling device for cooling in three stages, wherein the length of a cooling section is 24m.
Wherein, the first stage is from the end of rolling to the beginning of polygonal ferrite transformation, namely, the stage before polygonal ferrite transformation, and the cooling rate of the stage is 21 ℃/s. Specifically, the steel sheet was water-cooled at this stage through a cooling zone of an accelerated cooling device with a cooling water amount of 1320L/s.
The second stage is polygonal ferrite transformation stage, and the cooling speed during polygonal ferrite transformation is controlled to be 4.2 ℃/s. Specifically, the steel plate was water-cooled at this stage by passing it through the cooling two zones of the accelerated cooling equipment with the cooling water amount of 440L/s.
The third stage is acicular ferrite transformation stage, and the cooling rate during acicular ferrite transformation is controlled to be 13.2 ℃/s. Specifically, the steel sheet was water-cooled at this stage by passing it through the cooling three zones of the accelerated cooling equipment with a cooling water amount of 880L/s.
In the cooling process, the roller way speed of the accelerated cooling device is 1.0m/s, and the final cooling temperature of the steel plate is 530 ℃.
(6) And (3) temperature control straightening: straightening the steel plate subjected to the cooling control procedure in a first stage, wherein the straightening temperature of the first stage straightening is 500 ℃; then the mixture is sent to a cooling bed for cooling, and the second stage straightening is carried out after cooling, wherein the straightening temperature of the second stage straightening is 350 ℃; and then air-cooling until the temperature of the steel plate is less than or equal to 100 ℃.
As a result of microscopic examination of the temperature-controlled straightened steel sheet, as shown in fig. 2, it can be seen from fig. 2 that the structure of the low yield ratio steel sheet suitable for high heat input welding is a two-phase structure of acicular ferrite + polygonal ferrite, and the sum of the acicular ferrite content, grain boundary M/a and grain boundary ferrite content is shown in table 1.
The inclusion density of the steel plate after temperature control and straightening was counted by using a scanning electron microscope to obtain an inclusion density of 0.5 to 2 μm as shown in Table 1.
Mechanical property detection, welding performance detection and flatness detection are carried out on the steel plate subjected to temperature control straightening, and the yield ratio, welding heat input quantity and-60 ℃ impact power KV of a corresponding welding heat affected zone of the steel plate in the example 2 are measured 2 And the unevenness are shown in table 1.
TABLE 1
In general, compared with the prior art, the invention has the following beneficial effects:
(1) The phase transformation structure of the steel plate can be controlled by controlling the production process of the steel plate, particularly the cooling and temperature control straightening processes, so that the two-phase structure of polygonal ferrite and acicular ferrite is obtained, the steel plate has low yield ratio, and has excellent deformation energy storage capacity for geological disasters when the steel plate is applied to bridge steel, so that the bridge quality, the manufacturing efficiency and the use safety are improved, the problem of plate shape in the rolling and cooling processes can be solved, the steel plate keeps good plate shape, and the unevenness is less than or equal to 1mm/m. The finally prepared steel plate can be welded by adopting large heat input during welding, has good welding quality and higher welding efficiency, and can meet the application requirements of the steel plate for the bridge.
(2) Through the optimized design of the chemical composition design scheme and the combination of the production processThe low yield ratio steel plate suitable for large heat input welding, which is prepared by the production method of the invention, has the inclusion density of more than or equal to 2 multiplied by 10, and the equivalent diameter of 0.5-2 mu m 5 Individual/mm 3 The welding method is suitable for large heat input welding, and under the condition that the welding heat input amount is 50-500 kJ/cm, the impact energy of a welding heat affected zone at minus 60 ℃ is more than or equal to 100J, so that the welding method has good welding quality and higher welding efficiency, and can meet the application requirements of the steel plate for the bridge.
(3) The prepared low yield ratio steel plate suitable for large heat input welding has a two-phase structure of acicular ferrite and polygonal ferrite, wherein the content of the acicular ferrite is more than or equal to 60%, the sum of the content of crystal boundary M/A and the content of the crystal boundary ferrite is less than or equal to 3%, the yield ratio is less than or equal to 0.85, the unevenness is less than or equal to 1mm/M, and the steel plate has excellent deformation energy storage capacity for geological disasters when applied to bridge steel, so that the quality, the manufacturing efficiency and the use safety of the bridge are improved, and the steel plate has good shape.
It should be understood that although the present disclosure describes embodiments, not every embodiment is provided with a separate embodiment, and that this description is for clarity only, and that the skilled artisan should recognize that the embodiments may be combined as appropriate to form other embodiments that will be understood by those skilled in the art.
The above detailed description is merely illustrative of possible embodiments of the present invention, which should not be construed as limiting the scope of the invention, and all equivalent embodiments or modifications that do not depart from the spirit of the invention are intended to be included in the scope of the invention.