CN117802399A - Yield strength 1050MPa grade yield ratio controllable steel, round steel and manufacturing method thereof - Google Patents
Yield strength 1050MPa grade yield ratio controllable steel, round steel and manufacturing method thereof Download PDFInfo
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Abstract
The invention discloses steel with 1050 MPa-grade yield strength and controllable yield ratio, which contains Fe and unavoidable impurities and also contains the following chemical elements in percentage by mass: c:0.25 to 0.35 percent of Si:0.10 to 0.40 percent of Mn:0.30 to 0.80 percent of Cr:0.60 to 1.00 percent of Mo:0.30 to 1.0 percent of Ni:2.50 to 3.50 percent of Al:0.01 to 0.05 percent, V:0.04 to 0.12 percent, less than or equal to 0.20 percent of Cu, less than or equal to 0.10 percent of Nb, less than or equal to 0.003 percent of Ti and less than or equal to 0.005 percent of Ca. Correspondingly, the invention also discloses round steel prepared from the steel and a manufacturing method of the round steel. The invention develops the ultra-high strength high toughness steel with yield strength up to 1050MPa level through reasonably designing chemical components and combining with an optimized rolling process, and the ultra-high strength steel also has good low temperature toughness and plasticity.
Description
Technical Field
The present invention relates to steel, round steel and a method for manufacturing the same, and more particularly, to high-strength steel, round steel and a method for manufacturing the same.
Background
Yield is well known as a basis for judging failure of materials and is also a strength design criterion for work piece service. In design, the higher yield strength is beneficial to reducing the weight of a workpiece and realizing light weight, but the excessively high yield strength can improve the yield ratio of the material, and the brittleness is increased, so that the stress release in certain stress concentration areas is not beneficial, and brittle fracture is easy to cause.
Therefore, in the current part processing process, the control material has lower yield ratio, is very beneficial to part processing, can enable the material to be easier to mold and is not easy to generate brittle fracture. However, during service, too low a yield ratio can easily cause failure of the work piece yield. Therefore, in many engineering applications, enterprises want to control the yield ratio of steel to a specific range as required, so that the steel has excellent impact toughness while obtaining higher strength.
In the field of steel materials, common steel strengthening mechanisms may include: solid solution strengthening, dislocation strengthening, dispersion strengthening, fine grain strengthening, precipitation strengthening, and the like. However, during the actual processing, the material undergoes multiple passes of cold deformation, thermal deformation, heat treatment and other processes, so that the process diversity can affect the yield ratio to different degrees, and the effects produced by the different strengthening means are difficult to effectively control, which also results in a sharp increase in the difficulty of controlling the yield ratio.
For example: chinese patent document with publication number CN103667953a, entitled "a low environmental crack sensitivity superhigh strength and toughness mooring chain steel and method for manufacturing same", discloses: 0.12 to 0.24 percent of C, 0.10 to 0.55 percent of Mn, 0.15 to 0.35 percent of Si, 0.60 to 3.50 percent of Cr, 0.35 to 0.75 percent of Mo, less than or equal to 0.006 percent of N, 0.40 to 4.50 percent of Ni, less than or equal to 0.50 percent of Cu, less than or equal to 0.005 percent of S, 0.005 to 0.025 percent of P, less than or equal to 0.0015 percent of O, less than or equal to 0.00015 percent of H, and the balance of Fe and unavoidable impurities. The high-performance marine mooring chain steel has the tensile strength (Rm) of not less than 1110MPa, the Yield Ratio (YR) of 0.88-0.92, the elongation (A) of not less than 12%, the reduction of area (Z) of not less than 50% and the impact energy (Akv) of not less than 50J at minus 20 ℃. The patent C has low content, and the aim of the invention is achieved based on the design of alloy element components and the cooperation of two quenching processes.
For another example, chinese patent document publication No. CN112011727a, entitled "ultra-high strength low temperature ductile steel, ultra-high strength low temperature ductile bar, and method for manufacturing the same", discloses: c:0.150 to 0.240 percent of Si:0.10 to 0.50 percent of Mn:0.60 to 1.50 percent of Cr:0.30 to 1.20 percent of Mo:0.20 to 0.80 percent of Ni: 2.00-4.00%, nb:0 to 0.10 percent, B:0.0010 to 0.0050 percent, V:0 to 0.12 percent of Ti:0.003 to 0.06 percent of Al:0.01 to 0.08 percent, and the balance of Fe and unavoidable impurities; the yield strength is more than or equal to 950MPa, the tensile strength is more than or equal to 1150MPa, the Charpy impact energy Akv below-20 ℃ is more than or equal to 75J, the elongation is more than or equal to 15%, and the reduction of area is more than or equal to 55%. The steel grade is added with B and Ti elements to achieve the aim of the invention, and the yield strength of the steel grade still cannot meet the requirements of the invention.
Based on the above, the invention aims to obtain the steel with the yield strength of 1050MPa, and the steel has good low-temperature toughness and elongation.
Disclosure of Invention
The invention aims to provide steel with yield strength of 1050MPa and controllable yield ratio, which develops ultra-high strength and high toughness steel with yield strength of 1050MPa through reasonably designing chemical components and combining an optimized rolling process, and the ultra-high strength steel has good strength, low temperature toughness and plasticity and can be used for producing ocean platform mooring chains of R6 grade and above.
In order to achieve the above purpose, the invention provides steel with 1050MPa grade yield strength and controllable yield ratio, which contains Fe and unavoidable impurities and also contains the following chemical elements in percentage by mass:
C：0.25～0.35％、Si：0.10～0.40％、Mn：0.30～0.80％、Cr：0.60～1.00％、Mo：0.30～1.0％、Ni：2.50～3.50％、Al：0.01～0.05％、V：0.04～0.12％、Cu≤0.20％、Nb≤0.10％、Ti≤0.003％、Ca≤0.005％。
further, the invention also provides steel with 1050 MPa-grade yield strength and controllable yield ratio, which comprises the following chemical elements in percentage by mass:
c:0.25 to 0.35 percent of Si:0.10 to 0.40 percent of Mn:0.30 to 0.80 percent of Cr:0.60 to 1.00 percent of Mo:0.30 to 1.0 percent of Ni:2.50 to 3.50 percent of Al:0.01 to 0.05 percent, V:0.04 to 0.12 percent, less than or equal to 0.20 percent of Cu, less than or equal to 0.10 percent of Nb, less than or equal to 0.003 percent of Ti and less than or equal to 0.005 percent of Ca; the balance being Fe and other unavoidable impurities.
Further, among the unavoidable impurities of the steel with 1050 MPa-grade yield strength and controllable yield ratio, P is less than or equal to 0.015%, S is less than or equal to 0.003%, O is less than or equal to 0.003% and N is less than or equal to 0.012%.
In the yield strength 1050 MPa-grade yield ratio controllable steel, the design principle of each chemical element is as follows:
c: c is added into the steel, so that the hardenability of the steel is improved, a low-temperature phase transformation structure with higher hardness is formed in the quenching and cooling process of the steel, and the strength of the steel is improved. The increase in the C content increases the ratio of the hard phase such as the martensite phase to the lower bainite phase, and increases the number of carbide precipitated phases in the matrix to form a dispersion strengthening effect, thereby increasing the hardness of the steel, but causing a decrease in toughness. Too low a C content may result in low contents of low temperature transformation structures such as martensite and lower bainite, and higher tensile strength may not be obtained. Based on this, the present invention controls the C content to be 0.25 to 0.35%.
Si: si replaces Fe atoms in steel in a replacement mode, a solid solution strengthening effect is formed, dislocation movement is blocked, and the strength of the steel can be effectively improved. Si is a ferrite formation suppressing element, and can reduce the ability of C to diffuse in ferrite, so that an appropriate amount of Si can prevent coarse carbide from being formed and precipitated at defects during tempering. Higher Si content reduces the low temperature impact toughness of the steel. Based on this, the present invention controls the Si content as follows: 0.10 to 0.40 percent.
Mn: in the quenching process of the steel, mn can inhibit diffusion phase transformation, improves the hardenability of the steel, forms a low-temperature phase transformation structure, has higher strength, and has a certain deoxidization effect. The excessive Mn content can lead to the formation of more residual austenite, reduces the yield strength of steel, meanwhile, the overheating sensitivity of the manganese-containing steel is higher, austenite grains are easy to grow up when the quenching and heating of the excessive Mn content is carried out, and Mn can promote the segregation of harmful elements in grain boundaries and increase the tempering brittleness tendency of the steel. The Mn of 0.30-0.80% is added in the invention, which is beneficial to improving the strength and hardenability of steel and avoiding forming excessive residual austenite.
P: p in the steel is biased at the grain boundary, so that the bonding energy of the grain boundary is reduced, the low-temperature impact property of the steel is deteriorated, and the cold brittleness of the steel is increased. P which is concentrated at the grain boundary can lead the steel to be broken along the grain when being impacted and form a larger cleavage surface, thereby reducing the energy absorbed by the steel when being impacted. The content of the impurity element P is controlled to be not more than 0.015 percent, so that the low-temperature impact toughness of the ultra-high strength steel is ensured.
S: s has small solubility in delta ferrite and austenite, and in the molten steel solidification process, S can undergo segregation to form more sulfide inclusions, so that the ultrasonic flaw detection performance and low-temperature impact performance of the steel are jeopardized. S forms a low melting point FeS with Fe, creating hot shortness. The main factor considered in the control of S content of the steel grade disclosed by the invention is to avoid the damage of coarse sulfides to impact performance. The invention controls the content of the impurity element S not to exceed 0.003 percent, thereby ensuring that the steel has good low-temperature impact performance.
Cr: cr is added into steel to reduce gamma-alpha transformation driving force, inhibit diffusion type transformation of steel, raise hardenability of steel, form hardened martensitic structure and obtain steel with high strength. Meanwhile, in the heating process, if Cr carbide is not completely dissolved, the effect of inhibiting the growth of austenite grains is achieved. The Cr content is too high, coarse carbide is formed, and the low-temperature impact performance is deteriorated, so that the Cr content is 0.60-1.00% in the invention, and the strength and the low-temperature impact performance of the steel are ensured.
Mo: mo delays the transformation of proeutectoid ferrite, promotes the formation of acicular ferrite and bainite, and improves the toughness of low alloy steel; mo improves the solid solubility of microalloy elements (Nb, V, ti) in austenite, delays the precipitation of microalloy carbonitride, and leads more microalloy elements to be retained and precipitated in the tempering process, thereby generating larger precipitation strengthening effect. Mo can be dissolved into a lattice of microalloy carbonitride precipitated in ferrite to form (M, mo) (C, N) (M is microalloy element), so that the volume fraction of a precipitated phase is increased, the size of microalloy precipitate is obviously thinned, the precipitation strengthening effect is enhanced, the thermal stability of the Mo-containing microalloy carbonitride is good, and coarsening is not easy at high temperature. Therefore, 0.30 to 1.0 percent of Mo is added in the invention to obtain the matching of high strength and toughness.
Ni: ni exists in steel in a solid solution form, and in the component system of the invention, ni exists in an FCC phase of Fe-Ni-Mn, thereby reducing the stacking fault energy, reducing the dislocation movement resistance, reducing the distribution of Ni on a theta/alpha interface, reducing the carbon flux, preventing the growth of cementite, effectively preventing the abnormal growth of carbide, improving the toughness of a steel matrix and improving the low-temperature impact performance of the steel. Ni is an austenitizing forming element, and too high Ni content can cause too high residual austenite content in steel, so that the strength of the steel is reduced, and 2.50-3.50% of Ni is added in the invention to ensure the low-temperature impact toughness and strength of the steel.
V: v and C form VC, fine VC can play a certain role in blocking dislocation, meanwhile, the VC dissolving temperature is high, grain boundary movement can be effectively organized, grains are refined, and the strength of steel is improved. Under the condition of higher temperature tempering, if the contents of C and V are higher, coarse VC particles can be formed, and the impact property of the steel is reduced.
Al: al forms fine AlN precipitation during steelmaking, suppresses austenite grain growth in a subsequent cooling process, achieves the purposes of refining austenite grains and improving the toughness of steel at low temperature, is a good deoxidizer, and can effectively reduce oxygen in the steel. Too high an Al content results in the formation of larger Al oxides, which makes the steel unsuitable for ultrasonic flaw detection. Coarse alumina inclusions deteriorate the fatigue properties of the steel. Therefore, 0.01 to 0.05% of Al is added to improve the toughness of the steel.
N: n forms AlN or TiN in the steel grade to refine austenite grains, but the increase of the N content can lead to the increase of enrichment of the austenite grains at defects, and coarse nitride precipitation particles are formed to influence the low-temperature impact energy of the steel, so that the N content is controlled to be less than or equal to 0.0120 percent.
O: o forms Al with Al of steel grade 2 O 3 TiO, and the like, and the content of the impurity element O is controlled to be not more than 0.0030 percent in order to ensure the uniformity of the steel structure and the low-temperature impact energy.
In order to further improve the performance of the steel material of the present invention, the present invention may optionally further include the following elements:
nb: nb is added into steel to inhibit recrystallization of the steel, the Nb exists in the steel as substitutional solute atoms, the Nb atoms are larger than Fe atoms in size, and are easy to be aggregated at dislocation lines, so that the Nb has a strong dragging effect on dislocation movement. Meanwhile, nb can form interstitial mesophases such as NbC and NbN in steel, and plays a role in blocking the pinning of dislocation and the migration of subgrain boundaries in the recrystallization process, so that grains can be effectively refined, coarsening of the grains of a welded junction in the welding process is prevented, and the impact performance is reduced. The Nb content is high, coarse NbC particles can be formed under the high-temperature tempering condition, and the low-temperature impact energy of the steel is deteriorated. By matching with other alloy elements, nb with the content of less than 0.10% is added in the invention, so that the mechanical property of the steel is further improved.
Cu: cu is added into steel, fine nano-grade epsilon-Cu precipitation is formed in the tempering process, the strength of the steel is improved, and meanwhile, a certain amount of Cu is added to be beneficial to improving the corrosion resistance of the steel, but because the melting point of Cu is low, if the Cu content is too high, the Cu is concentrated in a crystal boundary in the heating austenitizing process, and the crystal boundary is weakened to cause cracking, so that the Cu content in the invention is not more than 0.20%.
Ti: when the Ti content is too high, coarse TiN precipitates are formed, resulting in deterioration of impact properties and fatigue properties of the steel. If the Ti content is too high during tempering, the fluctuation amplitude of the low-temperature impact energy is increased. Therefore, the Ti content in the invention is controlled to be 0-0.003%.
Ca: the Ca element is added into steel to form CaS, improve the size and morphology of the inclusion and the low temperature impact toughness of the steel, so that the Ca content is controlled to be less than or equal to 0.005%.
Further, in the yield strength 1050MPa grade yield ratio controllable steel, each element also satisfies at least one of the following formulas:
Ni/C≥7.5；
Mn/C≤3；
4≤(Cr+Mo)/C≤7；
13％≤5Mn+2.7Ni+3.3Cr+2.4Mo≤17％；
wherein each chemical element is substituted into the numerical value in front of the percentage of the mass percentage of the chemical element.
The chemical component system adopted by the steel with the yield strength of 1050MPa grade and the yield ratio is characterized in that multiple coupling of different toughness mechanisms is achieved by controlling the proportion of different alloy elements within the range of 13% -5 Mn+2.7Ni+3.3Cr+2.4Mo% -17%, and finally, the coupling of the strength, the low-temperature impact toughness and the elongation of the steel is realized, so that the high-strength steel with the yield strength of 1050MPa grade and the ultrahigh toughness and the strong plasticity can be obtained.
In addition, the yield strength 1050MPa grade yield ratio controllable steel of the invention, mn and Ni atoms are all substitution solid solutions before and after heat treatment, and part of Cr and Mo are converted into carbide precipitation after heat treatment, so the invention can lead carbon atoms to form carbide precipitation from interstitial solid solutions through tempering according to the corresponding heat treatment process combined with the three ratios by controlling the ratio of Ni/C, mn/C and (Cr+Mo)/C, and the multiple coupling of a plurality of strengthening mechanisms such as Mn atom solid solution strengthening, C atom solid solution strengthening, carbide precipitation strengthening and the like is realized, thereby achieving the accurate control of the yield ratio of the steel
Further, the microstructure matrix of the steel with the yield strength of 1050MPa grade and the yield ratio controllable is tempered martensite and tempered bainite.
The optimized chemical components designed by the invention fully utilize the influence of various alloy elements on phase transformation and microstructure, form a complex-phase microstructure mainly comprising tempered martensite and tempered bainite, and simultaneously control the content of P, S, N, O, thereby ensuring the strength, low-temperature impact toughness and elongation of the steel.
Further, the microstructure of the steel with the yield strength of 1050MPa grade and the yield ratio of controllable has precipitated carbide particles, the size of the carbide particles is not more than 120nm, the length-width ratio of the carbide particles is less than or equal to 4, and the density of the carbide particles is 8 x 10 7 -15*10 7 Individual/mm 2 。
After quenching and tempering heat treatment, the size and the distribution of carbide greatly influence the low-temperature impact toughness of the material, mainly because the size and the density of the carbide can influence dislocation movement, the invention utilizes different alloy elements to generate multiple lattice distortion, increases the diffusion activation energy of carbon atoms, leads the carbon atoms to generate short-range diffusion, reduces the formation of coarse strip-shaped carbide of the carbon atoms due to long-range diffusion and strong carbide alloy elements, leads the carbide to be granular, the size of the grain is not more than 120nm, the length-width ratio of the carbide grain is less than or equal to 4, and the density of the carbide grain is 8 x 10 7 -15*10 7 Individual/mm 2 Thereby obtaining the mechanical properties which the invention is intended to achieve.
Further, the yield strength Rp0.2 is equal to or greater than 1050MPa, the tensile strength Rm is equal to or greater than 1149MPa, the Charpy impact energy Akv below-20 ℃ is equal to or greater than 75J, the elongation A is equal to or greater than 12%, the reduction of area Z is equal to or greater than 60%, and the yield ratio Rp0.2/Rm is 0.85-0.95.
It is another object of the present invention to provide a round steel, which is manufactured using the above steel with a yield strength of 1050MPa grade and a controllable yield ratio.
Further, the diameter of the round steel is phi 20-180 mm.
Still another object of the present invention is to provide a method for manufacturing round steel, comprising the steps of:
(1) Smelting;
(2) Casting;
(3) Heating;
(4) Rolling: controlling the finishing temperature T not lower than 900 ℃, controlling the rolling deformation to be 20% -40% and meeting the requirement of 3.4-ln (T-800) to be less than or equal to 4;
(5) Quenching;
(6) And (5) tempering.
According to the invention, the composition proportion of round steel is controlled, the optimized rolling process is combined, the final rolling temperature T is controlled to be not lower than 900 ℃, the rolling deformation is controlled to be 20% -40%, and 3.4-ln (T-800) is satisfied, so that the dynamic recrystallization process is adjusted, the steel substrate is kept to be fine and uniform, the interface energy is increased, the nucleation number of carbide is increased, the carbide is dispersed and distributed more uniformly, and a good reinforcing and toughening effect is further generated.
Further, in the step (3) of the production method of the present invention, the heating temperature is 1050 to 1250 ℃.
Further, in the step (5) of the production method of the present invention, the austenitizing temperature in the quenching step is controlled to 840 to 1000 ℃, and water quenching is adopted after austenitizing.
Further, in the step (6) of the production method of the present invention, the tempering temperature is controlled to 580 to 640 ℃, and air cooling or water cooling is performed after tempering.
The yield strength 1050MPa grade steel with controllable yield ratio and the round steel prepared by the steel have the advantages that the yield strength reaches 1050MPa grade through reasonably designing chemical components and combining an optimization process, and meanwhile, the steel has good low-temperature toughness and plasticity.
After quenching, the round steel adopts a tempering process to form a tempered martensite and tempered bainite matrix structure, and refined granular carbide is precipitated on the matrix, so that the internal stress of the steel is eliminated, and the round steel has good structure uniformity.
The steel has yield strength of more than or equal to 1050MPa, tensile strength Rm of more than or equal to 1200MPa, charpy impact energy Akv (-20 ℃) of more than or equal to 75J, elongation of more than or equal to 12%, reduction of area of more than or equal to 60%, yield ratio Rp0.2/Rm of 0.85-0.95, so that the steel has good strength, low-temperature toughness and plasticity, and can be used for producing ocean platform mooring chains of R6 grade and above.
Drawings
FIG. 1 shows the microstructure morphology of round steel of example 3 of the present invention under a 500-times optical microscope.
FIG. 2 shows the microstructure morphology of the round bar of example 3 of the present invention under a 2000-fold optical microscope.
FIG. 3 shows the morphology of carbides in round steel of example 4 of the present invention.
Fig. 4 shows the morphology of carbides in the round steel of comparative example 1.
Detailed Description
The steel with 1050MPa yield strength and the round steel with controllable yield ratio and the manufacturing method thereof are further explained and illustrated by the following specific examples and the attached drawings, but the explanation and the illustration do not limit the technical scheme of the invention inappropriately.
Examples 1 to 6 and comparative examples 1 to 4
Round steels of examples 1-6 were each prepared using the following steps:
(1) Smelting was performed according to the chemical compositions shown in the following tables 1-1 and 1-2.
(2) Casting: casting is performed by die casting or continuous casting to obtain an ingot.
(3) Heating: the ingot is placed in a heating furnace to be heated, and the heating temperature can be preferably controlled to be 1050-1250 ℃.
(4) Rolling: firstly rolling to the size of an intermediate billet, then carrying out intermediate heating, wherein the intermediate heating temperature can be controlled between 1050 and 1250 ℃, then rolling to the size of a final finished product, controlling the final rolling temperature T to be not lower than 900 ℃, controlling the rolling deformation to be 20-40%, and meeting the requirement that ln (T-800) is not more than 3.4 and not more than 4.
(5) Quenching: controlling the austenitizing temperature of the quenching step to 840-1000 ℃, preserving the heat for 60-240 min, and adopting water quenching after austenitizing.
(6) Tempering: the tempering temperature is controlled to be 580-640 ℃, the temperature is kept for 90-270 min, and air cooling or water cooling is carried out after tempering.
It should be noted that the preparation of comparative examples 1-4 also basically uses the above-described procedure, except that the design of the chemical components and the related processes have parameters that do not meet the design specifications of the present invention.
Table 1-1 shows the mass percentages of the chemical elements of the round steels of examples 1-6 and the comparative steels of comparative examples 1-4.
Table 1-1 (wt.%), balance Fe and unavoidable impurities other than P, S, O, N
Tables 1-2 show the elemental synergy from the round steels of examples 1-6 and the comparative steels of comparative examples 1-4.
Tables 1-2.
| Examples | Ni/C | Mn/C | (Cr+Mo)/C | 5Mn+2.7Ni+3.3Cr+2.4Mo |
| Example 1 | 10.00 | 2.64 | 5.20 | 14.07 |
| Example 2 | 10.04 | 1.14 | 6.73 | 14.06 |
| Example 3 | 10.24 | 2.31 | 4.73 | 15.45 |
| Example 4 | 9.11 | 1.69 | 4.12 | 14.22 |
| Example 5 | 9.79 | 2.42 | 4.58 | 16.89 |
| Example 6 | 10.00 | 1.34 | 4.14 | 16.09 |
| Comparative example 1 | 6.05 | 2.14 | 5.16 | 12.84 |
| Comparative example 2 | 10.21 | 4.64 | 4.75 | 18.09 |
| Comparative example 3 | 8.87 | 2.12 | 8.98 | 18.23 |
| Comparative example 4 | 11.19 | 2.48 | 4.93 | 15.33 |
Each chemical element in the formulas of tables 1-2 is substituted into the numerical value preceding the percentage by mass of the chemical element.
Table 2 shows the specific process parameters for the round steels of examples 1-6 and the steels of comparative examples 1-4.
Table 2.
The round steels of the final examples 1 to 6 obtained were sampled respectively, and a metallographic specimen was prepared according to GB/T13298-2015, and the microstructure was analyzed. The results of the correlation analysis are shown in Table 3 below.
Table 3 shows the results of metallographic structure analysis of the round steels of examples 1 to 6.
Table 3.
As can be seen from Table 3, in the present invention, the microstructure substrates in the round steels of examples 1 to 6 were tempered martensite+tempered bainite, the substrates had precipitated granular carbide particles, the size of the carbide particles did not exceed 120nm, the aspect ratio of the carbide particles was 4 or less, and the density of the carbide particles was 8X 10 7 -15*10 7 Individual/mm 2 。
In addition, FIG. 1 also shows the microstructure morphology of the round bar of example 3 of the present invention under an optical microscope. FIG. 2 also shows the microstructure morphology of round steel of example 3 of the present invention.
As can be seen from fig. 1 and 2, the microstructure matrix of the round steel of example 3 of the present invention is tempered martensite+tempered bainite.
FIG. 3 shows the morphology of carbides in round steel of example 4 of the present invention. Fig. 4 shows the morphology of carbides in the round steel of comparative example 1.
As can be seen from FIG. 3, the carbide in example 4 of the present invention is in the form of particles having a diameter of not more than 120nm and an aspect ratio of not more than 4. As can be seen from fig. 4, the carbide in comparative example 1 exhibits a stripe-like distribution.
Accordingly, after the observation and analysis of the metallographic structure are completed, the round steel prepared by the method has very excellent mechanical properties for further explanation. Based on the obtained round steels of examples 1 to 6 and comparative examples 1 to 4, the inventors sampled the steels of these examples and comparative examples, respectively, and further examined the mechanical properties of the steels according to GB/T228-2009, and the examination results are shown in Table 4 below.
Table 4.
Note that: three sets of data, one column of longitudinal impact energy at-20 ℃, represent the results of three measurements.
As can be seen from Table 4 above, the round steels of examples 1-6 have a yield strength of 1066-1132MPa, a tensile strength of 1149-1248MPa, an elongation of 14.5-15%, a reduction of area of 60-65%, and a Charpy impact energy of 82-135J at-20deg.C or lower, and not only have high strength but also have good low-temperature impact toughness and good plasticity.
With continued reference to tables 1-1, 1-2, 3 and 4, it can be seen that the composition ratios of comparative examples 1-3 do not meet the composition ratio requirements of the present invention, and comparative example 4 does not meet the rolling process requirements of the present invention, and thus the performance thereof is inferior to that of the examples of the present invention.
It should be noted that the combination of the technical features in the present invention is not limited to the combination described in the claims or the combination described in the specific embodiments, and all the technical features described in the present invention may be freely combined or combined in any manner unless contradiction occurs between them.
It should also be noted that the above-recited embodiments are merely specific examples of the present invention. It is apparent that the present invention is not limited to the above embodiments, and similar changes or modifications will be apparent to those skilled in the art from the present disclosure, and it is intended to be within the scope of the present invention.
Claims (13)
1. The yield strength 1050MPa grade yield ratio controllable steel contains Fe and unavoidable impurities, and is characterized by further comprising the following chemical elements in percentage by mass:
C：0.25～0.35％、Si：0.10～0.40％、Mn：0.30～0.80％、Cr：0.60～1.00％、Mo：0.30～1.0％、Ni：2.50～3.50％、Al：0.01～0.05％、V：0.04～0.12％、Cu≤0.20％、Nb≤0.10％、Ti≤0.003％、Ca≤0.005％。
2. the steel with 1050 MPa-grade yield strength and controllable yield ratio according to claim 1, wherein the steel comprises the following chemical elements in percentage by mass:
c:0.25 to 0.35 percent of Si:0.10 to 0.40 percent of Mn:0.30 to 0.80 percent of Cr:0.60 to 1.00 percent of Mo:0.30 to 1.0 percent of Ni:2.50 to 3.50 percent of Al:0.01 to 0.05 percent, V:0.04 to 0.12 percent, less than or equal to 0.20 percent of Cu, less than or equal to 0.10 percent of Nb, less than or equal to 0.003 percent of Ti and less than or equal to 0.005 percent of Ca; the balance being Fe and other unavoidable impurities.
3. The yield strength 1050 MPa-grade yield ratio controllable steel according to claim 1 or 2, wherein each element further satisfies at least one of the following formulas:
Ni/C≥7.5；
Mn/C≤3；
4≤(Cr+Mo)/C≤7；
13％≤5Mn+2.7Ni+3.3Cr+2.4Mo≤17％；
wherein each chemical element is substituted into the numerical value in front of the percentage of the mass percentage of the chemical element.
4. The steel with a yield strength of 1050 MPa-level yield ratio control as claimed in claim 1 or 2, wherein among the unavoidable impurities, P is 0.015% or less, S is 0.003% or less, O is 0.003% or less, and N is 0.012% or less.
5. Yield strength 1050 MPa-grade yield ratio controllable steel according to claim 1 or 2, characterized in that the matrix of its microstructure is tempered martensite+tempered bainite.
6. The steel of claim 1 or 2, wherein the microstructure comprises precipitated carbide particles having a size of not more than 120nm and an aspect ratio of 4 or less, and the carbide particles have a density of 8 x 10 7 -15*10 7 Individual/mm 2 。
7. The steel with controllable yield strength at 1050MPa level according to claim 1 or 2, wherein the yield strength rp0.2 is equal to or higher than 1050MPa, the tensile strength Rm is equal to or higher than 1149MPa, the charpy impact energy Akv below-20 ℃ is equal to or higher than 75J, the elongation a is equal to or higher than 12%, the reduction of area Z is equal to or higher than 60%, and the yield ratio rp0.2/Rm is 0.85-0.95.
8. Round steel, characterized in that it is produced with a yield strength of 1050MPa grade of controllable steel according to any one of claims 1-7.
9. Round steel according to claim 8, characterized in that it has a diameter Φ20-180 mm.
10. Method for manufacturing round steel according to claim 8 or 9, characterized in that it comprises the steps of:
(1) Smelting;
(2) Casting;
(3) Heating;
(4) Rolling: controlling the finishing temperature T not lower than 900 ℃, controlling the rolling deformation to be 20% -40% and meeting the requirement of 3.4-ln (T-800) to be less than or equal to 4;
(5) Quenching;
(6) And (5) tempering.
11. The method according to claim 10, wherein in the step (3), the heating temperature is 1050 to 1250 ℃.
12. The method according to claim 10, wherein in the step (5), the austenitizing temperature in the quenching step is controlled to be 840 to 1000 ℃, and water quenching is used after austenitizing.
13. The method according to claim 10 or 12, wherein in the step (6), the tempering temperature is controlled to be 580 to 640 ℃, and air cooling or water cooling is performed after tempering.
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