CN115125445A

CN115125445A - High-strength steel with good strength and toughness and manufacturing method thereof

Info

Publication number: CN115125445A
Application number: CN202210749197.3A
Authority: CN
Inventors: 赵四新; 高加强
Original assignee: Baoshan Iron and Steel Co Ltd
Current assignee: Baoshan Iron and Steel Co Ltd
Priority date: 2022-06-28
Filing date: 2022-06-28
Publication date: 2022-09-30
Anticipated expiration: 2042-06-28
Also published as: CN115125445B

Abstract

The invention discloses high-strength steel with good obdurability, which contains Fe and inevitable impurities, and also contains the following chemical elements in percentage by mass: c: 0.20 to 0.35%, Si: 0.05-0.80%, Mn: 0.20 to 1.30%, Al: 0.005-0.06 percent of V, less than or equal to 0.15 percent of V, more than 0 and less than or equal to 0.028 percent of N, less than or equal to 0.30 percent of Cu, less than or equal to 0.09 percent of Nb and less than or equal to 0.02 percent of Ti; and Cr: 0.50 to 1.80%, Ni: 2.00-4.50%, Mo: 0.05 to 0.90% of at least one of them. Correspondingly, the invention also discloses a manufacturing method of the high-strength steel, which comprises the following steps: (1) smelting; (2) casting; (3) heating: controlling the heating temperature to 1050-1250 ℃ and the heat preservation time to 3-24 h; (4) forging or rolling: controlling the finish rolling temperature or the finish forging temperature to be more than or equal to 800 ℃, and cooling after rolling or forging; (5) quenching and tempering heat treatment: wherein the quenching temperature is 850-1000 ℃, the heat preservation time is 60-240 min, and water quenching treatment is adopted after austenitizing; the tempering temperature is 350-550 ℃, the heat preservation time is 60-240 min, and air cooling or water cooling is carried out after tempering.

Description

High-strength steel with good strength and toughness and manufacturing method thereof

Technical Field

The present invention relates to a steel material and a method for manufacturing the same, and particularly to a high-strength steel and a method for manufacturing the same.

Background

As is well known, high-strength and high-toughness steel has wide application in industrial production, and is often used for manufacturing high-safety mechanical parts and structural parts, such as mooring chains in the energy field or mining round-link chains.

Mooring chains are often used to secure large floating bodies such as ocean platforms, which are very critical security elements; the mining round-link chain is a commonly used part in the field of coal mining and is also a key wearing part of coal mining machinery, so that the market requires that steel used by the mining round-link chain has high strength, high toughness, wear resistance, corrosion resistance and high fatigue performance so as to ensure that the prepared mechanical part has sufficient safety and reliability.

In the prior art, a lot of researches have been made on high-strength and high-toughness steel at home and abroad, and the general design concept is as follows: proper chemical components are selected and the controlled rolling cooling or quenching and tempering process is adopted to produce high-strength and high-toughness steel. When the controlled rolling and cooling mode is adopted to produce the high-strength steel, the overall uniformity of the mechanical property of the steel can be influenced to a certain extent due to the greater control difficulty of the process scheme in the rolling and cooling processes.

When the quenching and tempering process is adopted to produce the high-strength steel, an operator can improve the hardenability of the steel by specifically optimizing the contents of alloy elements and carbon elements so that the steel forms a martensite structure in the cooling process. However, it should be noted that the high strength steel material mainly composed of martensite has a high dislocation density, which causes deterioration of impact toughness of the steel material, and such high strength steel is liable to have minute defects such as microcracks during drawing, in which case the high strength steel is rapidly broken to fail and has low fracture toughness.

In the ultra-high strength and toughness steels designed at present, a microstructure of bainite, bainite + martensite or martensite is generally adopted. In such a microstructure, the bainite or martensite structure contains supersaturated carbon atoms, and the lattice constant is changed to suppress the movement of dislocations, thereby improving the tensile strength of the steel. In addition, the refined structure can ensure that the steel absorbs more energy under the stressed condition, and further higher tensile strength and impact toughness are realized.

At present, although some researchers have developed high-strength and high-toughness steels, the mechanical properties of these steels are still greatly limited.

For example: publication No. CN102747303AThe Chinese patent document entitled "a high-strength steel plate with yield strength of 1100MPa level and a manufacturing method thereof" is 24/10/2012, and discloses a high-strength steel plate with yield strength of 1100MPa level and low-temperature impact energy of-40 ℃ and a manufacturing method thereof, wherein the steel plate comprises the following components in percentage by weight: 0.15 to 0.25%, Si: 0.10 to 0.50%, Mn: 0.60-1.20%, P: less than or equal to 0.013%, S: less than or equal to 0.003 percent, Cr: 0.20 to 0.55%, Mo: 0.20-0.70%, Ni: 0.60 to 2.00%, Nb: 0-0.07%, V: 0 to 0.07%, B: 0.0006-0.0025%, Al: 0.01 to 0.08%, Ti: 0.003-0.06%, H: less than or equal to 0.00018 percent, less than or equal to 0.0040 percent of N, less than or equal to 0.0030 percent of O, and the balance of Fe and inevitable impurities, and the carbon equivalent satisfies that CEQ is less than or equal to 0.60 percent. Yield strength is more than or equal to 1100MPa, tensile strength is more than or equal to 1250MPa, and Charpy impact energy A _kv (-40 ℃) is greater than or equal to 50J. The steel plate obtained by the technical scheme has ultrahigh strength, but the aging impact performance is not specified.

Another example is: chinese patent publication No. CN103667953A, published as 3/26/2014, entitled "marine mooring chain steel with low environmental crack sensitivity and ultrahigh toughness and manufacturing method thereof", discloses a mooring chain steel in which C: 0.12 to 0.24%, Mn: 0.10 to 0.55%, Si: 0.15-0.35%, Cr: 0.60 to 3.50%, Mo: 0.35-0.75%, N is less than or equal to 0.006%, Ni: 0.40-4.50%, Cu is less than or equal to 0.50%, S is less than or equal to 0.005%, P: 0.005-0.025 percent, less than or equal to 0.0015 percent of O, less than or equal to 0.00015 percent of H, the tensile strength of the high-strength and high-toughness mooring chain steel produced by adopting the components and the twice quenching process is more than or equal to 1110MPa, the yield ratio is 0.88-0.92, the elongation is more than or equal to 12 percent, the reduction of area is more than or equal to 50 percent, and the impact energy (A) at the temperature of minus 20 ℃ is _kv ) The thickness is more than or equal to 50J. As can be seen from the examples of this patent, the elongation is 15.5%, 13.5% and 15.0%, respectively, and the low temperature impact energy is-20 ℃ A _kv 67J, 63J, 57J and 62J, respectively. In the technical scheme, the low-temperature impact energy of the obtained steel cannot stably meet the requirement that the Charpy impact energy of DNV classification society is more than or equal to 60J; in addition, the steel material is aged after 5% strain, dislocation density in the steel increases, and interstitial atoms are enriched in dislocations, so that aged impact energy is lower than conventional impact energy. According to the technical schemeThe calculated data shows that the designed mooring chain steel has the aging impact energy A at the temperature of-20 DEG C _kv The value also fails to meet the 60J requirement.

Therefore, the ultrahigh-strength steel designed by the prior art cannot give consideration to high strength and toughness, high yield strength, high aging impact energy and hydrogen induced cracking resistance, and cannot meet the comprehensive performance requirements of steel for ocean engineering or engineering machinery. For this reason, in order to meet the demands of the current market, the present invention is expected to obtain a new high-strength steel having good toughness.

Disclosure of Invention

One of the purposes of the invention is to provide high-strength steel with good obdurability, which has excellent mechanical properties, the yield strength of the high-strength steel after quenching and tempering heat treatment can reach 1050MPa, and the high-strength steel also has good impact toughness, elongation and section shrinkage, higher impact toughness after strain aging, good hydrogen embrittlement resistance, good corrosion resistance, wear resistance, weldability and fatigue resistance.

In order to achieve the above object, the present invention provides a high-strength steel having excellent toughness, which contains Fe and unavoidable impurities, and further contains the following chemical elements in mass percent:

c: 0.20 to 0.35%, Si: 0.05-0.80%, Mn: 0.20 to 1.30%, Al: 0.005-0.06%, V is less than or equal to 0.15%, N is more than 0 and less than or equal to 0.028%, Cu is less than or equal to 0.30%, Nb is less than or equal to 0.09%, and Ti is less than or equal to 0.02%; and Cr: 0.50 to 1.80%, Ni: 2.00 to 4.50%, Mo: 0.05 to 0.90% of at least one of them.

Further, in the high-strength steel with good obdurability, the mass percentages of the chemical elements are as follows:

c: 0.20 to 0.35%, Si: 0.05-0.80%, Mn: 0.20 to 1.30%, Al: 0.005-0.06 percent of V, less than or equal to 0.15 percent of V, more than 0 and less than or equal to 0.028 percent of N, less than or equal to 0.30 percent of Cu, less than or equal to 0.09 percent of Nb and less than or equal to 0.02 percent of Ti; and Cr: 0.50 to 1.80%, Ni: 2.00 to 4.50%, Mo: 0.05 to 0.90% of at least one of them; the balance being Fe and other unavoidable impurities.

In the high-strength steel with good obdurability, the design principle of each chemical element is as follows:

c: in the high-strength steel with good obdurability, the element C can improve the hardenability of the steel, and the steel can form a phase transformation structure with higher hardness in the quenching and cooling process. When the content of C element in the steel is too low, the content of transformation structures such as martensite and bainite of the steel is too low, and the steel cannot obtain sufficient tensile strength. Meanwhile, the content of the element C in the steel is not too high, and when the content of the element C in the steel is increased, the proportion of a hard phase is increased, the hardness of the steel is increased, and the toughness of the steel is reduced. Therefore, in consideration of the influence of the content of the C element on the performance of the steel, the mass percentage content of the C element in the high-strength steel with good strength and toughness is controlled to be 0.20-0.35%.

Si: in the high-strength steel with good obdurability, Si element is beneficial to improving the strength of the steel, and the addition of a proper amount of Si can avoid the formation of coarse carbides during tempering. However, when the content of Si element in steel is too high, the performance of steel is affected and the impact toughness of steel is lowered. Therefore, in the high-strength steel with good obdurability, the mass percentage content of the Si element is controlled to be 0.05-0.80%.

Mn: in the high-strength steel with good obdurability, Mn element mainly exists in the steel in a solid solution form, which can effectively improve the hardenability of the steel and form a high-strength low-temperature phase transformation structure during quenching so as to ensure that the steel obtains good wear resistance. However, it should be noted that the content of Mn element in the steel should not be too high, and when the content of Mn element in the steel is too high, it may cause formation of more retained austenite, decrease yield strength of the steel, and easily cause center segregation. Therefore, in the high-strength steel with good obdurability, the mass percentage of the Mn element is controlled to be 0.20-1.30%.

Al: in the high-strength steel with good toughness, Al element can be matched with N in the steel to form fine AlN precipitates, so that the growth of austenite grains is effectively inhibited. However, it should be noted that the content of Al element in the steel should not be too high, and too high content of Al may cause formation of larger Al oxide, while coarse AlN hard inclusions may reduce the impact toughness and fatigue property of the steel. Therefore, in consideration of the influence of the Al element content on the performance of the steel, the mass percentage of the Al element in the high-strength steel with good toughness is controlled to be 0.005-0.06%.

V: in the high-strength steel having excellent toughness of the present invention, the V element may form precipitates with the C element or the N element in the steel, thereby improving the strength of the steel. In order to exert the beneficial effect of the V element, the content of the V element in the steel is also not too high, and if the content of the C element and the V element in the steel is too high, coarse VC particles can be formed, so that the impact toughness of the steel is reduced. Therefore, in the high-strength steel with good obdurability, the mass percentage content of the V element is controlled to be less than or equal to 0.15 percent.

N: in the high-strength steel having excellent toughness of the present invention, N is a interstitial atom and is also an MX type precipitate-forming element. However, it should be noted that the content of N element in steel should not be too high, and when the content of N element in steel is too high, the plasticity and toughness of steel material are reduced. Therefore, in order to avoid the enrichment of N element in the steel, in the high-strength steel with good obdurability, the mass percentage content of the N element is more than 0 and less than or equal to 0.028 percent.

Cu: in the high-strength steel with good obdurability, a proper amount of Cu element is added, so that the strength of the steel can be improved, and the corrosion resistance of the steel can be improved. However, it should be noted that the content of Cu element in the steel should not be too high, and if the content of Cu element in the steel is too high, it will concentrate at grain boundaries during heating and cause weakening of grain boundaries to cause cracking. Therefore, in the high-strength steel with good obdurability, the mass percentage content of the Cu element is controlled to be less than or equal to 0.30 percent.

Nb: in the high-strength steel with good obdurability, the Nb element is added into the steel, so that a fine precipitated phase can be formed, the recrystallization of the steel can be inhibited, and the crystal grains can be effectively refined. The grain refinement plays an important role in improving the mechanical properties of the steel, particularly the strength and the toughness, and meanwhile, the grain refinement is also beneficial to reducing the hydrogen embrittlement sensitivity of the steel. However, the content of Nb element in steel should not be too high, and when the content of Nb element in steel is too high, coarse NbC particles are formed in the smelting process, which may reduce the impact toughness of the steel. Therefore, in order to exert the beneficial effect of the Nb element, in the high-strength steel with good obdurability, the mass percentage content of the Nb element is controlled to be Nb less than or equal to 0.09%.

Ti: in the high-strength steel with good obdurability, a proper amount of Ti element is added to effectively form a fine precipitated phase. However, the Ti content in the steel should not be too high, and when the Ti content in the steel is too high, coarse angular TiN particles are formed in the smelting process, which reduces the impact toughness of the steel. Therefore, in order to exert the beneficial effect of Ti, in the high-strength steel with good obdurability, the mass percentage content of Ti element is controlled to be less than or equal to 0.02 percent.

Note that, in the high-strength steel designed according to the present invention, in order to ensure the performance of the steel material, at least one of three elements, that is, Cr, Ni, and Mo, is further selectively added in the design of the chemical elements.

Cr: in the high-strength steel with good toughness, Cr element can remarkably improve the hardenability of the steel, and can form a hardened bainite structure, thereby improving the strength of the steel. Accordingly, the Cr content in the steel should not be too high, and when the Cr content in the steel is too high, coarse carbides are formed and the impact properties of the steel are lowered. Therefore, in consideration of the influence of the content of the Cr element on the performance of the steel, the content of the Cr element in percentage by mass is controlled to be between 0.50 and 1.80 percent in the high-strength steel with good toughness.

Ni: in the high-strength steel with good obdurability, Ni element exists in the steel in a solid solution form, and the low-temperature impact property of the steel can be improved by adding a proper amount of Ni element into the steel. However, the content of Ni element in steel should not be too high, and too high content of Ni not only increases the cost, but also causes too high content of residual austenite in steel and reduces the strength of steel. Therefore, in the high-strength steel with good obdurability, the mass percentage of the Ni element is controlled to be 2.00-4.50%.

Mo: in the high-strength steel with good obdurability, Mo element can be dissolved in the steel in a solid manner, and the hardenability of the steel can be improved, so that the strength of the steel can be improved. In addition, when the steel is tempered at a relatively high temperature, Mo element forms fine carbides to further increase the strength of the steel. However, considering that Mo is a noble metal element, the content of Mo in steel should not be too high in order to effectively control the cost of the alloy. Therefore, in the high-strength steel with good obdurability, the mass percentage of the Mo element is controlled to be 0.05-0.90%.

Furthermore, in the high-strength steel with good obdurability, the content of P is less than or equal to 0.015 percent, the content of S is less than or equal to 0.005 percent, the content of B is less than or equal to 0.0010 percent, the content of Ca is less than or equal to 0.004 percent, the content of O is less than or equal to 0.0020 percent, the content of H is less than or equal to 0.0002 percent, the content of As is less than or equal to 0.03 percent, the content of Pb is less than or equal to 0.02 percent, the content of Sn is less than or equal to 0.01 percent, and the content of Bi is less than or equal to 0.01 percent in inevitable impurities.

In the above technical solution, the P element, S element, B element, Ca element, O element, H element, As element, Pb element, Sn element, Sb element, and Bi element are all impurity elements in steel, and the content of the impurity elements in the material should be reduced As much As possible in order to obtain a steel material with better performance and better quality when the technical conditions allow.

P: in the present invention, the P element is easily segregated at grain boundaries in the steel, which lowers grain boundary bonding energy and deteriorates impact toughness of the steel. Therefore, in the high-strength steel with good obdurability, the content of the P element by mass percent is controlled as follows: p is less than or equal to 0.015 percent.

S: in the present invention, S element is segregated in steel and forms more sulfide inclusions, which lower the impact resistance of steel. Therefore, in the high-strength steel with good obdurability, the mass percentage of the S element is controlled as follows: s is less than or equal to 0.005 percent.

B: in the invention, the B element is easy to be segregated at the grain boundary of the steel, so that in the high-strength steel with good obdurability, the mass percentage of the B element is controlled as follows: b is less than or equal to 0.0010 percent.

Ca: in the invention, in order to accurately control the non-metallic inclusions in the steel, the Ca element with active chemical property is not adopted for treatment. Therefore, in the high-strength steel with good obdurability, the mass percentage of Ca element is controlled as follows: ca is less than or equal to 0.004 percent.

O: in the present invention, the O element forms oxides and complex oxides with the Al element in the steel, which affect the properties of the steel. Therefore, in order to ensure the uniformity of the steel structure, the low-temperature impact energy and the fatigue performance, in the high-strength steel with good obdurability, the mass percentage of the O element is controlled as follows: o is less than or equal to 0.0020 percent.

H: in the present invention, the H element is accumulated at the defect site in the steel, and it is subjected to hydrogen-induced delayed fracture in the steel having a tensile strength level exceeding 1000 MPa. Therefore, in the high-strength steel with good obdurability, the mass content of the H element is controlled as follows: h is less than or equal to 0.0002 percent.

Correspondingly, in the high-strength steel designed by the invention, trace elements such As arsenic (As), lead (Pb), tin (Sn), antimony (Sb), bismuth (Bi) and the like can be segregated to grain boundaries at the tempering temperature during the tempering process, so that the intercrystalline bonding force is weakened, and the performance of the material is influenced. Further, elements such As As, Pb, Sn, Sb, and Bi adversely affect the environment. Therefore, in the present invention, As is 0.03% or less, Pb 0.02% or less, Sn 0.02% or less, Sb 0.01% or less, and Bi 0.01% or less are set.

Further, in the high-strength steel having good toughness of the present invention, it also satisfies: j. the design is a square _H Less than or equal to 0.050, wherein J _H ＝([P]+[Sn]+[As]+[Pb]+[Sb]+[Bi])*([Si]+[Mn]) And substituting each chemical element into the numerical value before the mass percentage of the chemical element.

In the above technical solution of the present invention, the influence of the P element is also considered when the impurity elements arsenic (As), lead (Pb), tin (Sn), antimony (Sb), and bismuth (Bi) are set in the high-strength steel with excellent toughness of the present invention. Therefore, in order to obtain a more preferable effect, in the present invention, J can be further controlled _H ≤0.050。

Furthermore, in the high-strength steel with good obdurability, the critical ideal diameter Di value of the hardenability is more than or equal to 0.05 m; wherein:

Di＝0.0137[C]×(3.33[Mn]+1)×(0.700[Si]+1)×(0.363[Ni]+1)

×(2.16[Cr]+1)×(3.00[Mo]+1)×(0.365[Cu]+1)×(1.73[V]+1)

and substituting each chemical element into the numerical value in front of the percentage of the mass percentage of the chemical element.

In the technical scheme of the invention, the high-strength steel with good toughness further optimizes and controls the critical ideal diameter Di value of hardenability while controlling the mass percentage content of a single chemical element, and controls the critical ideal diameter Di value to be more than or equal to 0.05 m.

Of course, in some preferred embodiments, it may be preferable to control the Di value to be between 0.05 and 0.40 m. This is because: when the Di value is less than 0.05m, the hardenability of the steel material is insufficient; when the designed Di value is higher than 0.40m, the manufacturing is difficult and the cost is high.

Furthermore, in the high-strength steel with good obdurability, the microalloy element coefficient r is _M/N The range of (a) is 1.0 to 5.9; wherein:

r _M/N ＝([Al]/2+[Nb]/7)/[N]

In the technical scheme of the invention, the inventor conducts the calculation on the coefficient r of the microalloy element _M/N The range of (2) is optimally designed. It is understood that the microalloy coefficient r _M/N Higher microalloy coefficient r associated with nanosized precipitates _M/N The steel has coarse precipitates, the precipitation strengthening effect cannot be achieved, and the adverse effect similar to inclusions is caused, so that the fatigue strength of the steel is reduced; and a lower microalloying coefficient r _M/N The number of precipitates is small and the dispersion strengthening effect cannot be obtained.

Therefore, in the invention, the inventor further controls the proportional relation between the contents of the micro-alloy elements Al and Nb and the content of N while controlling the mass percentage content of a single chemical element, and particularly adjusts the coefficient r of the micro-alloy element _M/N The range of (a) is controlled to be 1.0-5.9.

Further, in the high-strength steel having excellent toughness according to the present invention, the carbon equivalent Ceq is 1.00 or less, wherein Ceq ═ C ] + [ Mn ]/6+ ([ Cr ] + [ Mo ] + [ V ])/5+ ([ Ni ] + [ Cu ])/15, and each chemical element is substituted for a value before the percentage of the mass percentage of the chemical element.

In the technical scheme, the inventor further carries out optimization design on the value of the carbon equivalent Ceq, and controls the value to be less than or equal to 1.00, so that the prepared high-strength steel can effectively meet the requirements of welding occasions.

Furthermore, in the high-strength steel with good obdurability, the atmospheric corrosion resistance index I is more than or equal to 6.0, wherein:

I＝26.0[Cu]+3.9[Ni]+1.2[Cr]+1.5[Si]+17.3[P]-7.3[Cu][Ni]-9.1[Ni][P]-33.4[Cu] ² ；

and substituting each chemical element in the formula into a numerical value in front of the percentage number of the mass percentage of the chemical element.

Further, in the high-strength steel with good toughness of the present invention, the microstructure thereof is tempered bainite + tempered martensite + residual austenite.

In the art, it is generally accepted that the order of the susceptibility of the different structures to hydrogen embrittlement ranges from large to small, as original martensite > low-temperature tempered martensite > tempered troostite with original martensite orientation > bainite > tempered martensite (high-temperature tempering).

The inventors have found that the microstructure of the high-strength chain steel conventionally used in the prior art is generally a tempered martensite structure. The chemical components designed by the invention fully utilize the influence of various alloy elements and micro-alloy elements on phase change and microstructure, and after quenching and tempering heat treatment, the alloy can form: a complex phase structure of tempered bainite, tempered martensite and a small amount of residual austenite.

In the technical scheme designed by the invention, the strength, impact toughness, elongation, plasticity and the like of the steel are ensured by controlling the chemical component proportion of the steel grade, so that the high-strength, high-toughness and high-strength steel with ultrahigh toughness and strong plasticity matching is produced, and the prepared steel has good weather resistance, wear resistance, hydrogen induced cracking resistance and fatigue resistance.

Further, in the high-strength steel with good strength and toughness of the present invention, the properties thereof satisfy: yield strength R _p0.2 Not less than 1050MPa, tensile strength R _m 1150MPa or more, elongation A or more than 14 percent, reduction of area Z or more than 55 percent, Charpy impact energy A at-20 DEG C _kv More than or equal to 75J, charpy impact energy A at-20 ℃ after strain aging _kv Not less than 65J, and the hydrogen embrittlement resistance coefficient eta (Z) not less than 0.85.

In the technical scheme of the invention, the charpy impact energy A at minus 20 ℃ is measured when the performance of the high-strength steel is detected _kv In addition, it is necessary to further measure the Charpy impact energy A at-20 ℃ after strain aging (accelerated aging at 100 ℃ for 60min after 5% deformation) _kv 。

As is well known, high strength steel inevitably deforms (strains) during use, and needs to have good low temperature impact toughness after deformation, so strain aging impact energy is an important technical index for steel used in ocean engineering or engineering machinery. Therefore, the high-strength steel is reasonably designed, and the Charpy impact energy A at the temperature of 20 ℃ below zero is obtained after the strain aging (5 percent of deformation and 100 ℃ accelerated aging for 60min) of the prepared steel _kv Not less than 65J, so as to be suitable for severe service conditions of high-strength steel products in ocean engineering or engineering machinery.

In addition, the change of the surface shrinkage rate of a tensile test under the environmental condition is usually adopted in the engineering field to reflect the stress corrosion tendency, and the invention prepares a circular section sample according to GB/T2975-2018 sample preparation in the mechanical property test sampling position and sample preparation of steel and steel products by referring to the requirement of Norwegian classification society on hydrogen embrittlement sensitivity, wherein the sample diameter is 10 mm. And performing a tensile test according to the national standard GB/T228.1, obtaining the reduction of area Z with the strain rate less than or equal to 0.0003/s, and defining the hydrogen embrittlement sensitivity index eta (Z) to evaluate the hydrogen induced cracking resistance of the steel:

η(Z)＝Z ₂ /Z ₁

wherein Z is ₁ The reduction of area obtained after the round steel which is baked at 250 ℃ for 2h for dehydrogenation is subjected to a tensile test is shown; z ₂ The reduction of area obtained after the round steel was subjected to a tensile test is shown.

The greater the hydrogen embrittlement resistance coefficient η (Z) is, the smaller the stress corrosion tendency of the steel material is, based on the hydrogen embrittlement resistance coefficient η (Z) designed in the present invention. In the invention, the hydrogen embrittlement resistance coefficient eta (Z) of the high-strength steel prepared by the technical scheme is more than or equal to 0.85, and the high-strength steel has good hydrogen embrittlement resistance and stress corrosion resistance.

Accordingly, another object of the present invention is to provide a method for manufacturing the above-mentioned high-strength steel with good toughness, which is simple in production and reasonable in process design, and the obtained high-strength steel not only has very high strength, but also has good impact toughness, elongation and surface shrinkage, and is excellent in hydrogen embrittlement resistance and stress corrosion resistance, and has good corrosion resistance, wear resistance, weldability and fatigue resistance.

In order to achieve the above object, the present invention provides a method for manufacturing the above high strength steel having good toughness, comprising the steps of:

(1) smelting;

(2) casting;

(3) heating: controlling the heating temperature to 1050-1250 ℃ and the heat preservation time to 3-24 h;

(4) forging or rolling: controlling the finish rolling temperature or the finish forging temperature to be more than or equal to 800 ℃, and cooling after rolling or forging;

(5) quenching and tempering heat treatment: wherein the quenching temperature is 850-1000 ℃, the heat preservation time is 60-240 min, and water quenching treatment is adopted after austenitization; the tempering temperature is 350-550 ℃, the heat preservation time is 60-240 min, and air cooling or water cooling is carried out after tempering.

In the technical scheme of the invention, in the smelting process in the step (1), the smelting can be performed by electric furnace smelting or converter smelting, and refining and vacuum treatment are performed. Of course, in some other embodiments, the operator may also use a vacuum induction furnace for smelting.

Accordingly, in the present invention, casting is required after the smelting is completed, and in the casting process of the above step (2), the casting process may specifically be die casting or continuous casting.

In the step (3), the heating temperature is controlled to be 1050-1250 ℃, and the heat preservation time is 3-24 h. The high-strength steel is heated between 1050 ℃ and 1250 ℃ and can be completely austenitized. Carbides and nitrides of Al, Nb, V and carbonitrides, carbides of Cr and Mo are partially or entirely dissolved in austenite during heating, Al, Nb, V can form fine precipitates during subsequent rolling/forging and cooling, and Mn, Cr and Mo dissolved in austenite in solid solution can improve the hardenability of steel and improve the hardness and strength of martensite.

Therefore, in the step (4), the finishing rolling temperature or the finishing forging temperature is controlled to be more than or equal to 800 ℃, a complex phase matrix structure with refined martensite and a small amount of bainite and retained austenite can be formed, and fine and dispersed precipitates are formed. It should be noted that in the forging or rolling process of step (4) of the present invention, in some embodiments, the billet may be subjected to descaling with high pressure water after exiting the heating furnace, and then the billet may be subjected to forging or rolling, and then cooled by air cooling or slow cooling after rolling or forging.

Correspondingly, after the step (4) is completed, quenching and tempering heat treatment are carried out on the steel, and the steel is heated to 850-1000 ℃ under control and then is quenched after heat preservation, so that full austenitizing is realized in the heat preservation process. During the heating, precipitates of carbide-forming elements Al, Nb, V, Cr and Mo are partially dissolved, and undissolved precipitates pin the grain boundary and suppress the coarsening of austenite grains (austenite grain size. gtoreq.6 grade). During the quenching and cooling process, the alloy elements dissolved in austenite make the steel have high strength and good toughness. The quenched steel is subjected to tempering heat treatment at 350-550 ℃, Al, Nb, V, Cr and Mo can form fine precipitates with C, N, and the matching of the strength and the ductility and toughness of the steel is improved.

In conclusion, the technological parameters of quenching and tempering heat treatment designed by the invention can ensure that the steel has good strong plasticity and toughness, and are beneficial to processing and using bars, such as: the bar is forged or welded to produce high-performance mineral chain.

Further, in the manufacturing method of the present invention, in step (4), rolling or forging is directly performed to a finished size.

Further, in the manufacturing method of the present invention, in the step (4), the blank is rolled to the size of the intermediate blank, and then the intermediate heating is performed, and then the blank is rolled to the size of the final product; wherein the intermediate heating temperature is 1050-1250 ℃, and the heat preservation time is 3-24 h.

In the above technical solution of the present invention, in the forging or rolling process of step (4), when a forging process is adopted, the forging process can be directly forged to the size of the final product; when the rolling process is adopted, the billet can be directly rolled to the size of a final finished product, or the billet can be firstly rolled to the size of a specified intermediate billet, and then intermediate heating and rolling are carried out to the size of the final finished product.

Compared with the prior art, the high-strength steel with good strength and toughness and the manufacturing method thereof have the advantages and beneficial effects as follows:

the invention develops the high-strength steel with good obdurability by reasonably designing chemical components and combining an optimization process, and the designed rolled or forged bar corresponding to the high-strength steel can form a microstructure of tempered martensite, a small amount of tempered bainite and residual austenite by adopting a tempering heat treatment process after quenching, and has fine and dispersed precipitates.

The high-strength steel prepared by the invention has excellent mechanical properties, and the yield strength of the high-strength steel after quenching and tempering heat treatmentThe degree can reach 1050MPa level, and the performance of the alloy meets the following requirements: yield strength R _p0.2 Not less than 1050MPa, tensile strength R _m 1150MPa or more, elongation A or more than 14 percent, reduction of area Z or more than 55 percent, Charpy impact energy A at-20 DEG C _kv More than or equal to 75J, charpy impact energy A at-20 ℃ after strain aging _kv Not less than 65J, and the hydrogen embrittlement resistance coefficient eta (Z) not less than 0.85.

Therefore, the high-strength steel has high impact toughness, elongation and reduction of area while having ultrahigh strength, has high impact toughness after strain aging, good hydrogen embrittlement resistance, good corrosion resistance, wear resistance, weldability and fatigue resistance, can be effectively applied to occasions requiring high-strength and high-toughness steel products such as ocean engineering, engineering machinery and the like, and has good popularization and application prospects.

Correspondingly, the manufacturing process of the high-strength steel is optimized, the manufacturing process is reasonable in design, the process window is loose, batch commercial production can be realized on bar or high-speed wire production lines, the applicability is wide, and the production and the preparation are simple.

Detailed Description

The high-strength steel with excellent toughness and the method for manufacturing the same according to the present invention will be further explained and illustrated with reference to specific examples, which, however, should not be construed as unduly limiting the technical scope of the present invention.

Examples 1 to 15 and comparative examples 1 to 4

The high strength steels of examples 1-15 were all made using the following steps:

(1) smelting is carried out according to the chemical components shown in the following tables 1-1, tables 1-2 and tables 1-3: in practical operation, the smelting can be carried out by adopting a 50kg vacuum induction furnace, a 150kg vacuum induction furnace or a 500kg vacuum induction furnace, or by adopting a mode of electric furnace smelting, external refining and vacuum degassing, or by adopting a mode of converter, external refining and vacuum treatment.

(2) Casting: casting is performed by die casting or continuous casting to obtain an ingot.

(3) Heating: and heating the cast ingot in a heating furnace, controlling the heating temperature to 1050-1250 ℃, and keeping the temperature for 3-24 hours.

(4) Forging or rolling: forging or rolling: controlling the finish rolling temperature or the finish forging temperature to be more than or equal to 800 ℃, and cooling after rolling or forging. Wherein, when forging, the forging can be directly carried out to the size of a final finished product; when rolling, the billet can be directly rolled to the size of the final finished product, or the billet can be rolled to the specified size of an intermediate billet, then intermediate heating is carried out, and then the billet is rolled to the size of the final finished product. Wherein, the intermediate heating temperature can be controlled between 1050 ℃ and 1250 ℃, and the heat preservation time can be controlled between 3h and 24 h.

In the present invention, the chemical composition design and related processes of the high strength steels with good toughness of examples 1-15 meet the design specification requirements of the present invention. Accordingly, in the comparative examples, the chemical composition designs of comparative examples 1-4 and related processes all have parameters that do not meet the design specification requirements of the present invention.

Tables 1 to 1 and tables 1 to 2 show the mass percentage ratios of the respective chemical elements of the high-strength steels with good toughness of examples 1 to 15 and the comparative steels of comparative examples 1 to 4.

Table 1-1. (wt.%, balance Fe and other unavoidable impurities other than P, S, B, Ca, O, H, As, Pb, Sn, Sb and Bi)

Tables 1-2.

Tables 1 to 3 show the harmful element coefficients J calculated from the mass percentages of the respective chemical elements of the high-strength steels with good toughness of examples 1 to 15 and the comparative steels of comparative examples 1 to 4 _H Value, critical ideal diameter Di value of hardenability and microalloy element coefficient r _M/N Carbon equivalent Ceq and atmospheric corrosion resistance index I.

Tables 1 to 3.

Note: in the above table, J _H ＝([P]+[Sn]+[As]+[Pb]+[Sb]+[Bi])*([Si]+[Mn])

Di＝0.0137[C]×(3.33[Mn]+1)×(0.700[Si]+1)×(0.363[Ni]+1)×(2.16[Cr]+1)×(3.00[Mo]+1)×(0.365[Cu]+1)×(1.73[V]+1)

r _M/N ＝([Al]/2+[Nb]/7)/[N]；

Ceq＝[C]+[Mn]/6+([Cr]+[Mo]+[V])/5+([Ni]+[Cu])/15；

In the present invention, the specific production process operations of the high-strength steels with good toughness of examples 1 to 15 and the comparative steels of comparative examples 1 to 4 were as follows:

example 1

The chemical compositions shown in tables 1-1 and 1-2 were smelted in a 50kg vacuum induction furnace, and the molten steel obtained by the smelting was cast into a steel ingot, heated and forged to cogging. Wherein the heating temperature of the steel ingot is controlled to be 1180 ℃, the steel ingot is subjected to subsequent forging after heat preservation is carried out for 9 hours, the finish forging temperature is controlled to be 910 ℃, the steel ingot is finally forged into a bar stock with the diameter of phi 50mm, and the bar stock is air-cooled after forging. And then carrying out quenching and tempering heat treatment on the bar, wherein the quenching is carried out after heat preservation is carried out for 90min at 890 ℃, and then the water cooling is carried out after heat preservation is carried out for 60min at the tempering temperature of 430 ℃.

Examples 2 to 6

In the present invention, the process parameters and means used in the embodiments of examples 2 to 6 were exactly the same as those of example 1, except that the chemical element compositions used in tables 1 to 1 and tables 1 to 2 were different from those of example 1.

Example 7

The chemical compositions shown in tables 1-1 and 1-2 were smelted in a 150kg vacuum induction furnace, and the molten steel was cast into ingots, heated and blanked by forging. Wherein the heating temperature of the steel ingot is controlled to be 1200 ℃, the subsequent forging is carried out after the heat preservation is carried out for 10h, the final forging temperature is controlled to be 960 ℃, the steel ingot is finally forged into a bar with the diameter of phi 90mm, and the bar is stacked and slowly cooled after the forging. Correspondingly, the bar is subjected to quenching and tempering heat treatment, wherein the bar is quenched after being subjected to heat preservation at 910 ℃ for 150min, and then is subjected to heat preservation at the tempering temperature of 460 ℃ for 100min and then is subjected to water cooling.

Examples 8 to 9

In the present invention, the embodiment of example 8 was carried out in the same manner as in example 7 except that the chemical element components used in tables 1-1 and 1-2 were different from those used in example 7 except for the quenching temperature. It should be noted that in the embodiment of example 9, the process parameters and means used are exactly the same as those in example 7, except for the quenching temperature, which is 970 ℃ in example 9.

Example 10

The chemical compositions shown in tables 1-1 and 1-2 were subjected to electric furnace smelting, refining and vacuum treatment, and then continuously cast into a 280mm × 280mm continuous slab. And in the heating process, the continuous casting blank is controlled to be slowly heated to 1200 ℃, and the temperature is kept for 4 hours for subsequent rolling. The billet is taken out of the heating furnace and is descaled by high pressure water, then the billet is rolled directly into a finished product, the final rolling temperature is controlled at 970 ℃, the billet is finally rolled into a bar with the diameter of phi 90mm, the billet is air-cooled after being rolled, and is peeled by a grinding wheel and subjected to ultrasonic inspection, magnetic powder inspection and other inspections. Correspondingly, the bar is subjected to quenching and tempering heat treatment, wherein the bar is firstly quenched after being kept at 850 ℃ for 180min, and then is kept at the tempering temperature of 390 ℃ for 120min and then is cooled in air.

Example 11

The chemical compositions shown in tables 1-1 and 1-2 were subjected to electric furnace smelting, refining and vacuum treatment, and then continuously cast into a 320mm × 425mm continuous cast slab. In the heating process, the continuous casting slab is controlled to be slowly heated to 1210 ℃, and the subsequent rolling is carried out after the heat preservation is carried out for 5 hours. The billet is taken out of the heating furnace and starts to be rolled after being descaled by high-pressure water, an intermediate billet is rolled, and the finishing temperature is controlled to be 820 ℃ so as to obtain the intermediate billet with the size of 140mm multiplied by 140 mm. And then heating the intermediate billet to 1180 ℃, preserving heat for 12 hours, discharging the intermediate billet out of the furnace, descaling by high-pressure water, then starting rolling, controlling the final rolling temperature of the intermediate billet to 870 ℃, so as to obtain a finished bar with the specification of phi 25mm, and cooling in air after rolling. Correspondingly, the bar is subjected to quenching and tempering heat treatment, wherein quenching is carried out after heat preservation for 60min at 870 ℃, and then water cooling is carried out after heat preservation for 60min at the tempering temperature of 530 ℃.

Example 12

According to the chemical compositions shown in tables 1-1 and 1-2, the steel is subjected to electric furnace smelting, refining and vacuum treatment, and then is continuously cast into a 320mm × 425mm continuous casting slab. In the heating process, the continuous casting billet is controlled to be heated to 1230 ℃, and the subsequent rolling is carried out after the heat preservation is carried out for 3.5 hours. The billet is taken out of the heating furnace and is descaled by high pressure water, then the billet is rolled into an intermediate billet, and the finishing temperature is controlled to be 1080 ℃ so as to obtain the intermediate billet with the size of 260mm multiplied by 260 mm. And then heating the intermediate billet to 1160 ℃, preserving heat for 3.5h, discharging from the furnace, descaling by high-pressure water, then starting rolling, controlling the final rolling temperature of the intermediate billet to be 880 ℃, so as to obtain a finished bar material with the specification of phi 50mm, and carrying out air cooling after rolling. Correspondingly, the bar is subjected to quenching and tempering heat treatment, wherein the bar is firstly quenched after being kept at 890 ℃ for 70min, and then is kept at the tempering temperature of 430 ℃ for 60min and then is cooled by water.

Example 13

Converter smelting is carried out according to chemical components shown in tables 1-1 and 1-2, refining and vacuum treatment are carried out, die casting is carried out to obtain a die casting blank, the die casting blank is heated to 1180 ℃, and heat preservation is carried out for 12 hours for subsequent rolling. The billet is taken out of the heating furnace and is descaled by high pressure water, then the billet is rolled into an intermediate billet, the finishing temperature is controlled to be 1050 ℃, and the intermediate billet with the size of 220mm multiplied by 220mm is obtained. And then heating the intermediate billet to 1150 ℃, preserving heat for 3 hours, discharging from the furnace, descaling by high-pressure water, then starting rolling, controlling the final rolling temperature of the intermediate billet to be 850 ℃ to obtain a finished bar with the specification of phi 75mm, and carrying out air cooling after rolling. Correspondingly, the bar is subjected to quenching and tempering heat treatment, wherein the bar is firstly quenched after being subjected to heat preservation at 900 ℃ for 80min, and then is subjected to heat preservation at the tempering temperature of 450 ℃ for 60min and then is subjected to water cooling.

Example 14

Performing converter smelting according to chemical components shown in tables 1-1 and 1-2, refining and vacuum treatment, then die casting into a casting blank, controlling the casting blank to be slowly heated to 1220 ℃, and performing subsequent rolling after heat preservation for 10 hours. And (3) taking the billet out of the heating furnace, descaling by high-pressure water, then starting rolling, controlling the final rolling temperature to be 940 ℃, and finally rolling into a phi 160mm bar. And (4) slowly cooling in air after rolling, and then peeling by using a grinding wheel. Correspondingly, the bar is subjected to quenching and tempering heat treatment, wherein the bar is firstly quenched after being subjected to heat preservation at 900 ℃ for 200min, and then is subjected to heat preservation at the tempering temperature of 460 ℃ for 180min and then is subjected to water cooling.

Example 15

The chemical compositions shown in tables 1-1 and 1-2 were smelted in a 500kg vacuum induction furnace, and the molten steel was cast to obtain a steel ingot, heated and forged to produce a slab. Wherein the heating temperature of the steel ingot is controlled to be 1060 ℃, the steel ingot is subjected to subsequent forging after being kept for 20 hours, the finish forging temperature is controlled to be 920 ℃, the steel ingot is finally forged into a bar with the diameter of phi 90mm, and the bar is stacked and slowly cooled after being forged. And then carrying out quenching and tempering heat treatment on the bar, wherein the bar is quenched after being subjected to heat preservation at 900 ℃ for 160min, and then is subjected to heat preservation at the tempering temperature of 420 ℃ for 90min and then is cooled by water.

Comparative example 1

In comparative example 1, smelting was carried out in a 50kg vacuum induction furnace according to the chemical compositions shown in tables 1-1 and 1-2, as in example 1. And casting the molten steel into a steel ingot, heating and forging and cogging, controlling the steel ingot to be heated to 1180 ℃, keeping the temperature for 9 hours, then performing subsequent forging, controlling the finish forging temperature to be 910 ℃, finally forging into a bar with the diameter of phi 50mm, and performing air cooling after forging. And then carrying out quenching and tempering heat treatment on the bar, wherein the bar is quenched after heat preservation at 890 ℃ for 120min, and then is cooled by water after heat preservation at the tempering temperature of 430 ℃ for 60 min.

Comparative example 2: the steel is selected from commercial steel products, the preparation process is not repeated here, the specific specification is a bar with the diameter of phi 50mm, the bar also needs quenching and tempering heat treatment, the bar is firstly quenched after being kept at 910 ℃ for 150min, and then is kept at 460 ℃ for 100min and then is cooled by water.

Comparative example 3

In comparative example 3, smelting was carried out in a 150kg vacuum induction furnace according to the chemical compositions shown in tables 1-1 and 1-2, as in example 7. Casting the molten steel into a steel ingot, heating and forging and cogging, controlling the steel ingot to be heated to 1200 ℃, keeping the temperature for 10 hours, then performing subsequent forging, controlling the finish forging temperature to be 960 ℃, finally forging the steel ingot into a bar with the diameter of phi 50mm, and stacking and slowly cooling the bar after forging. And then carrying out quenching and tempering heat treatment on the bar, wherein the bar is quenched after heat preservation at 890 ℃ for 150min, and then is cooled by water after heat preservation at the tempering temperature of 430 ℃ for 100 min.

Comparative example 4

In comparative example 4, smelting was performed in a 500kg vacuum induction furnace according to the chemical compositions shown in tables 1-1 and 1-2, and molten steel was cast to obtain a steel ingot, which was heated and forged to be cogging. In the heating process, the steel ingot heating temperature is controlled to be 1060 ℃, the subsequent forging is carried out after the temperature is kept for 20 hours, the final forging temperature is controlled to be 920 ℃, the steel ingot with the diameter of 90mm is finally forged, and the steel ingot is air-cooled after the forging. And then carrying out quenching and tempering heat treatment on the bar, wherein the bar is quenched after being subjected to heat preservation at 900 ℃ for 180min, and then is subjected to heat preservation at the tempering temperature of 420 ℃ for 90min and then is cooled by water.

Tables 2-1 and 2-2 show specific process parameters in the above-described process steps (1) to (4) for the high-strength steels having good toughness of examples 1 to 15 and the comparative steels of comparative examples 1 to 4.

Table 2-1.

Table 2-2.

In the present invention, in three embodiments of example 11, example 12 and example 13, in the rolling process, the billets were first rolled to the respective designated intermediate billet size, and then heated and rolled again to the final finished product size.

The high-strength steels having good toughness of the finished examples 1 to 15 and the comparative steels of comparative examples 1 to 4 were sampled, respectively, and the microstructures of the steels were observed and analyzed. It was observed that in the present invention, the microstructures in the high-strength steels having good toughness of examples 1 to 15 were tempered bainite + tempered martensite + residual austenite.

After the observation and analysis of the metallographic structure are completed, the properties of the high-strength steel prepared by the method are further explained. The inventors further sampled the prepared high-strength steels with good toughness of finished examples 1-15 and the comparative steels of comparative examples 1-4, respectively, prepared samples according to GB/T2975-2018 sampling position and sample preparation for mechanical property test of steel and steel products, and according to GB/T228.1-2010 part 1 of tensile test of metallic materials: the tensile test is carried out according to the room temperature test method, and the Charpy impact energy A at the temperature of-20 ℃ of each example and each comparative example is tested by adopting GB/T229- _kv And Charpy impact energy A at-20 ℃ after strain aging (accelerated aging at 100 ℃ for 60min after 5% deformation) _kv 。

In the present invention, three test pieces were specifically designed for each of the examples and comparative examples to perform the impact test, and the three data in the columns of the impact power in table 3 correspond to the test results of the three test pieces, respectively. The results of the mechanical property measurements are shown in Table 3 below.

In addition, in the present invention, the sample steels of each example and comparative example were further subjected to water quenching after heat-holding at 930 ℃ for 4 hours, and the austenite grain sizes thereof were evaluated according to the ASTM E112 standard after the samples were prepared.

It should be noted that the engineering field usually adopts the change of the surface shrinkage rate of the tensile test under the environmental condition to reflect the stress corrosion tendency, and the invention refers to the requirement of the Norwegian classification society on the hydrogen embrittlement sensitivity to prepare a round section sample according to GB/T2975 plus 2018 sample position and sample preparation of the mechanical property test of steel and steel products, wherein the diameter of the sample is 10 mm. And performing a tensile test according to the national standard GB/T228.1, wherein the strain rate is less than or equal to 0.0003/s to obtain the reduction of area Z, and defining the hydrogen embrittlement sensitivity index eta (Z) to evaluate the hydrogen induced cracking resistance of the steel:

η(Z)＝Z ₂ /Z ₁

wherein Z is ₁ The reduction of area obtained after the round steel which is baked at 250 ℃ for 2 hours for dehydrogenation is subjected to a tensile test is shown; z is a linear or branched member ₂ The reduction of area obtained after the round steel was subjected to a tensile test is shown.

Based on the hydrogen embrittlement resistance coefficient eta (Z) designed in the present invention, the larger the hydrogen embrittlement resistance coefficient eta (Z), the smaller the stress corrosion tendency of the steel material, and the more excellent the hydrogen embrittlement resistance and the stress corrosion resistance.

Table 3 shows the results of the tests of the mechanical properties and austenite grain sizes of the high-strength steels having good toughness of examples 1 to 15 and the comparative steels of comparative examples 1 to 4.

Table 3.

As can be seen from the above Table 4, the high-strength steels of examples 1 to 15 according to the present invention have a combination of properties significantly superior to those of comparative examples 1 to 4.

In the present invention, comparative example 1 has yield strength exceeding 1050MPa, good plasticity, but slightly low toughness, and not all of the impact energy after strain agingMore than 65J, the hydrogen embrittlement resistance coefficient was low, and the austenite grain size was not preferable, wherein 6.5(3) means that the average grain size was 6.5, but a double grain size occurred, and coarse grains of grade 3 were present. As can be seen from the combination of tables 1-1 and tables 1-2, the steel of comparative example 1 has a lower aluminum content; the microalloying coefficient r of comparative example 1 can be found by referring to Table 2 _M/N And is low.

Accordingly, in the present invention, the steel designed in comparative example 2 has a low strength, which is associated with a low carbon content. In the chemical components designed in the comparative example 3, the Nb content is high, and the precipitation strengthening effect is not formed, so that the finally obtained steel is low in strength; comparative example 4 has a high Cr content, a high carbon equivalent, a high sulfur content, a high oxygen content, a low impact toughness and a low hydrogen embrittlement resistance of the finally obtained steel, a slightly coarse austenite grain (rating 6), and early fatigue fracture of the produced chain during the test.

The steels obtained in the examples 1 to 15 of the invention have very excellent performance and the yield strengths R _p0.2 Between 1055-1175MPa, tensile strength R _m The elongation A is between 14 and 17 percent and the reduction of area Z is between 56 and 67 percent between 1154 and 1247MPa, and the Charpy impact energy A is at-20 DEG C _kv 76-150J, hydrogen embrittlement coefficient eta (Z) 0.85-0.98, Charpy impact energy A at-20 deg.C after strain aging (5% deformation and 100 deg.C accelerated aging for 60min) _kv Between 69 and 123J.

Accordingly, the austenite grain size of the high strength steels obtained in examples 1 to 15 was between 7 and 8 grades. The microstructures of the high strength steels of examples 1 to 15 were bainite, tempered martensite, and a small amount of retained austenite, while the microstructures after heat treatment of the chains prepared using the high strength steels of examples 1 to 15 were refined tempered bainite and tempered martensite.

It should be noted that the combination of the features in the present application is not limited to the combination described in the claims of the present application or the combination described in the specific examples, and all the features described in the present application may be freely combined or combined in any manner unless contradicted by each other.

It should also be noted that the above-mentioned embodiments are only specific embodiments of the present invention. It is apparent that the present invention is not limited to the above embodiments and similar changes or modifications can be easily made by those skilled in the art from the disclosure of the present invention and shall fall within the scope of the present invention.

Claims

1. The high-strength steel with good obdurability contains Fe and inevitable impurities, and is characterized by also containing the following chemical elements in percentage by mass:

c: 0.20 to 0.35%, Si: 0.05-0.80%, Mn: 0.20 to 1.30%, Al: 0.005-0.06 percent of V, less than or equal to 0.15 percent of V, more than 0 and less than or equal to 0.028 percent of N, less than or equal to 0.30 percent of Cu, less than or equal to 0.09 percent of Nb and less than or equal to 0.02 percent of Ti; and Cr: 0.50 to 1.80%, Ni: 2.00-4.50%, Mo: 0.05 to 0.90% of at least one of them.

2. The high-strength steel with good strength and toughness as claimed in claim 1, wherein the chemical elements comprise, in mass percent:

c: 0.20 to 0.35%, Si: 0.05-0.80%, Mn: 0.20 to 1.30%, Al: 0.005-0.06 percent of V, less than or equal to 0.15 percent of V, more than 0 and less than or equal to 0.028 percent of N, less than or equal to 0.30 percent of Cu, less than or equal to 0.09 percent of Nb and less than or equal to 0.02 percent of Ti; and Cr: 0.50 to 1.80%, Ni: 2.00-4.50%, Mo: 0.05 to 0.90% of at least one of them; the balance being Fe and other unavoidable impurities.

3. A high-strength steel having good toughness As claimed in claim 1 or 2, wherein among the inevitable impurities, P is 0.015% or less, S is 0.005% or less, B is 0.0010% or less, Ca is 0.004% or less, O is 0.0020% or less, H is 0.0002% or less, As is 0.03% or less, Pb is 0.02% or less, Sn is 0.02% or less, Sb is 0.01% or less, and Bi is 0.01% or less.

4. A high-strength steel having good toughness according to claim 3, further satisfying: j. the design is a square _H Less than or equal to 0.050, wherein J _H ＝([P]+[Sn]+[As]+[Pb]+[Sb]+[Bi])*([Si]+[Mn]) Wherein each chemical element is substituted before the mass percentage of the elementThe numerical value of (c).

5. The high-strength steel with good toughness as claimed in claim 1 or 2, wherein the critical ideal diameter Di of hardenability is not less than 0.05 m; wherein:

6. High-strength steel with good toughness according to claim 1 or 2, characterized in that it has a microalloy element coefficient r _M/N The range of (a) is 1.0 to 5.9; wherein:

r _M/N ＝([Al]/2+[Nb]/7)/[N]；

7. The high-strength steel having excellent toughness according to claim 1 or 2, wherein the carbon equivalent Ceq is 1.00 or less, and Ceq ═ C ] + [ Mn ]/6+ ([ Cr ] + [ Mo ] + [ V ])/5+ ([ Ni ] + [ Cu ])/15, in which each chemical element is substituted for a value preceding a percentage of the mass percentage of the chemical element.

8. A high-strength steel with good toughness according to claim 1 or 2, characterized in that its atmospheric corrosion resistance index I is not less than 6.0, wherein:

9. The high-strength steel having good toughness according to claim 1 or 2, wherein the microstructure thereof is tempered bainite + tempered martensite + residual austenite.

10. High-strength steel with good toughness according to claim 1 or 2, characterized in that its properties satisfy: yield strength R _p0.2 Not less than 1050MPa, tensile strength R _m 1150MPa or more, elongation A or more than 14 percent, reduction of area Z or more than 55 percent, Charpy impact energy A at-20 DEG C _kv Not less than 75J, charpy impact energy A at-20 ℃ after strain aging _kv Not less than 65J, and the hydrogen embrittlement resistance coefficient eta (Z) not less than 0.85.

11. A method of manufacturing a high strength steel according to any one of claims 1 to 10, characterized in that it comprises the steps of:

(1) smelting;

(2) casting;

12. The method of manufacture of claim 11, wherein in step (4), rolling or forging is performed directly to finished dimensions.

13. The manufacturing method according to claim 11, wherein in the step (4), the blank is rolled to an intermediate size, then the intermediate heating is performed, and then the blank is rolled to a final finished size; wherein the intermediate heating temperature is 1050-1250 ℃, and the heat preservation time is 3-24 h.