CN114635086B - High-strength and high-toughness cast steel - Google Patents
High-strength and high-toughness cast steel Download PDFInfo
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- CN114635086B CN114635086B CN202210261469.5A CN202210261469A CN114635086B CN 114635086 B CN114635086 B CN 114635086B CN 202210261469 A CN202210261469 A CN 202210261469A CN 114635086 B CN114635086 B CN 114635086B
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/18—Hardening; Quenching with or without subsequent tempering
- C21D1/185—Hardening; Quenching with or without subsequent tempering from an intercritical temperature
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/26—Methods of annealing
- C21D1/28—Normalising
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
Abstract
The high-strength and high-toughness cast steel comprises the following chemical components in percentage by weight: c:0.23-0.32%, si:0.37-0.65%, mn:0.95-1.35%, cr:0.75 to 1.08%, ni:0.46-0.87%, mo:0.25-0.45%, RE:0.035 to 0.075%, ti:0.005-0.016%, B:0.004-0.008%, N:0.005-0.01 percent, the balance of Fe and inevitable impurities, and the percentage content of each element satisfies: available nitrogen N eff = N-Ti/3.42, boron available B eff ＝B‑0.77N eff Effective boron B eff 0.002-0.006; coefficient of hardenability Q eff ＝C×(1+0.53Si)×(1+2.87Mn)×(1+2.34Cr)×(1+0.77Ni)×(1+2.61Mo)×(1.2+5.45RE)×(4753B eff 2 + 5.25); coefficient of hardenability Q eff Ratio to maximum thickness T (in mm) of cast steel, Q eff /T≥0.55。
Description
Technical Field
The invention relates to a high-strength and high-toughness cast steel, which has low austenite critical cooling speed and high hardenability, has excellent strength and toughness when non-liquid quenching is adopted, and is particularly suitable for casting large castings.
Background
Cast steel is a commonly used engineering structural material, and has strength and toughness superior to cast iron, particularly has obvious advantages over cast iron materials at low temperature, but cast steel has slightly poor casting fluidity, so the cast steel is often used for casting large-wall-thickness castings in engineering.
In the prior art, in order to obtain cast steel with excellent strength and toughness, the cast steel needs to be subjected to heat treatment. The heat treatment of cast steel basically adopts the working procedures of normalizing, quenching and tempering. And since rapid cooling (e.g., up to 3 ℃/s or more) is required after quenching, such cooling rates are typically achieved with the aid of liquid quench media (e.g., oil, water, oil-based, water-based quenches, etc.). This therefore faces two major challenges for large wall thickness cast steel castings: on one hand, due to the wall thickness of the casting, the casting is cracked and scrapped because of the generation of great thermal stress caused by the excessively high cooling speed; on the other hand, the quenching of large castings requires large quenching equipment, the requirements on the quenching equipment are higher, the control difficulty of the quenching process is increased, the quenching of the liquid medium needs to be completed in a short time, the temperature of the quenching medium is rapidly increased due to the large heat exchange in the short time, the quenching medium is easy to boil and splash, and the safe operation of the quenching process is not facilitated.
In view of the above problems, a cast steel that can be quenched using a non-liquid medium (e.g., air) and is excellent in strength and toughness has been proposed.
Disclosure of Invention
The present invention provides a cast steel excellent in strength and toughness, which can be quenched by a non-liquid medium (e.g., air) without quenching with a liquid medium in a heat treatment step after casting to obtain a cast steel material satisfying performance requirements.
The technical object of the present invention is achieved by the following means.
The invention provides a high-strength and high-toughness cast steel material, which comprises the following chemical components in percentage by weight: c:0.23-0.32%, si:0.37-0.65%, mn:0.95-1.35%, cr:0.75 to 1.08%, ni:0.46-0.87%, mo:0.25-0.45%, RE:0.035 to 0.075%, ti:0.005-0.016%, B:0.004-0.008%, N:0.005-0.01%, and the balance of Fe and inevitable impurities; and the percentage content of each element satisfies: available nitrogen N eff = N-Ti/3.42, boron available B eff ＝B-0.77N eff Available boron B eff 0.002-0.006; coefficient of hardenability Q eff ＝C×(1+0.53Si)×(1+2.87Mn)×(1+2.34Cr)×(1+0.77Ni)×(1+2.61Mo)×(1.2+5.45RE)×(4753B eff 2 + 5.25); coefficient of hardenability Q eff Ratio to maximum thickness T (in mm) of cast steel, Q eff /T≥0.55。
The basic principle of the invention is based on the following:
the addition of a trace amount of B, and the addition of C, si, mn, cr, ni, mo and RE elements improve the hardenability of the cast steel and reduce the critical cooling speed of austenite, thereby ensuring that the cast steel can be fully quenched even if the cast steel is quenched by a non-liquid medium (such as air), and ensuring that the strength and the toughness of the cast steel reach corresponding levels.
Since N is not completely removed in cast steel and its presence is easily combined with B, thus hindering the B action, seriously affecting the improvement of B in hardenability, and N significantly deteriorates the strength and toughness of cast steel, while limiting N to trace levels is not friendly to the cost of the smelting process, and cast steel pieces are generally heavy, and strict control of N at lower levels in steel leads to significant cost increase.
Based on the above knowledge, the inventor of the present invention, from a technical point of view different from "removing N as much as possible", fully utilizes N to exert a positive effect on the premise of maintaining a certain N content, thereby reducing the production cost and ensuring the properties of cast steel. Specifically, a certain amount of Ti is added to the cast steel, and Ti combines with N before B to form TiN, and as a result, a trace amount of TiN proves effective for improving both toughness and strength of the cast steel.
The strength and toughness improvement effect of TiN is also particularly manifested in that, when non-liquid medium (e.g. air) is used for quenching, the cast steel is more or less deteriorated in strength and toughness as compared with liquid medium quenching, and a slight amount of TiN compensates for the deterioration in toughness and strength, with the result that, even if non-liquid medium (e.g. air) quenched cast steel is used, it has excellent strength and toughness as the cast steel obtained by liquid medium quenching, on the basis of containing a slight amount of N, a slight amount of Ti, and a slight amount of B.
Therefore, in addition to Ti being added to steel, the relation between Ti and N is controlled to define N eff Is the available nitrogen remaining after Ti combines with N, and also defines B eff Is the available boron remaining after B combines with available nitrogen, B eff Boron content for actually improving hardenability.
Further, in combination with B eff Together with other elements defining the hardenability coefficient Q of the cast steel eff As a result, it was found that when Q is turned on eff When the maximum thickness T of the cast steel satisfies a certain relationship, the steel casting can always have excellent hardenability in non-liquid medium (such as air) quenching, and finally has satisfactory strength and toughness.
By way of non-limiting illustration, the maximum thickness T of the high-strength and high-toughness cast steel is 30-400mm; the inventors found that when Q is eff When the/T satisfies the above relationship, the hardenability effect is particularly sufficient for a steel casting having a thickness of 30 to 400 mm.
In one embodiment, the high-toughness cast steel has a room-temperature tensile strength of 850MPa or more, preferably 900MPa or more, a room-temperature yield strength of 760MPa or more, preferably 800MPa or more, a room-temperature impact toughness of 120J or more, preferably 130J or more, and an impact toughness at-40 ℃ of 90J or more, preferably 100J or more.
As a non-limiting description, the high-strength high-toughness cast steel of the present invention is excellent in hardenability, and has an austenite critical cooling rate of not higher than 0.3 ℃/s, preferably not higher than 0.2 ℃/s, more preferably not higher than 0.1 ℃/s, which is much lower than the cooling rate of a liquid quenching, typically 3 ℃/s, so that the cast steel of the present invention has excellent hardenability when quenched in a non-liquid medium (such as air) and finally has satisfactory strength and toughness. Based on the characteristics of the cast steel of the present invention, although liquid quenching is still feasible (because of the higher cooling rate of liquid quenching), the use of quenching in a non-liquid medium (such as air) is the best solution from the standpoint of cost and operation.
As a preferred embodiment, the non-liquid medium quenching is air quenching, including but not limited to a blower, a fan, etc., to increase the flow rate of the air medium and thus to improve the heat exchange efficiency, and is economical when the cooling rate is in the range of 0.05 ℃/s to 0.3 ℃/s and the strength and toughness of the cast steel are satisfactory.
The roles of the individual elements and the significance of the control of the individual parameters are described in more detail below.
C: carbon is an element for improving the strength and hardenability of cast steel, but too high C content causes a decrease in toughness, and therefore, C is controlled to 0.23 to 0.32% in order to obtain the strength and toughness of the present invention.
Si: silicon is an element for improving the strength and hardenability of cast steel, but since an excessively high Si content increases inclusions and drastically lowers toughness, si is controlled to 0.37 to 0.65% in order to obtain the strength and toughness of the present invention.
Mn: manganese is an element that improves the strength and hardenability of cast steel, but too high Mn content results in a decrease in toughness, and therefore, mn is controlled to 0.95 to 1.35% in order to obtain the strength and toughness of the present invention.
Cr: chromium is an element that improves the strength and hardenability of cast steel, but too high a Cr content easily forms Cr with carbon 23 C 7 And carbides, which serve as the starting points for ductile fracture. Therefore, cr is controlled to 0.75 to 1.08% in order to obtain the strength and toughness of the present invention.
Ni: nickel can improve the low temperature toughness, strength and hardenability of cast steel, but once the Ni content is too high, the toughness and strength improvement is no longer significant and the cost is increased, so in order to obtain the strength and toughness of the present invention, ni is controlled to be 0.46-0.87%.
Mo: molybdenum is an element that improves the strength and hardenability of cast steel, but if the content of Mo is too high, it easily forms carbides such as MoC with carbon, and becomes a starting point of ductile fracture. Therefore, in order to obtain the strength and toughness of the present invention, mo is controlled to be 0.25 to 0.45%.
RE: the rare earth can improve the strength and the toughness of the cast steel and remarkably improve the hardenability, has the function of improving the form of inclusions and can effectively improve the low-temperature toughness of the cast steel, but the RE content is too high, so the cost is not economical, and the function is basically not remarkably improved any more, therefore, in order to obtain the strength and the toughness of the invention, the RE is controlled to be 0.035-0.075%.
Ti: in the present invention, ti is added mainly for the purpose of forming TiN in combination with N, and a trace amount of TiN improves the strength and toughness of the cast steel, but the toughness of the cast steel is drastically reduced when the TiN is excessive, so that the present invention controls the Ti content to 0.005-0.016%.
N: compared with the traditional technical idea of removing N, the invention does not need to limit N to trace level intentionally, but adds a certain amount of Ti to combine with N on the premise of keeping a certain N content, the trace amount of TiN improves the strength and toughness of cast steel, makes full use of N to play a positive role, reduces the production cost, but leads to the sharp reduction of the toughness of the cast steel when the amount of TiN is too high, and controls the N content to be 0.005-0.01%.
N eff ：N eff I.e. available nitrogen, which characterizes the amount of N remaining after immobilization by Ti bonds, as can be seen readily by the contents of Ti and N in the aforementioned invention, N eff N-Ti/3.42 can always be guaranteed at a level greater than 0, i.e. N is surplus and Ti is absent, since excess N can be further bonded by B, while excess Ti easily forms TiC as a starting point of ductile failure resulting in toughness reduction, but N is eff Too high indicates too much N bonded to B, and too much BN will drastically reduce the strength and toughness of the cast steel, with N being preferred eff ＝0.001-0.006。
B: boron is an element which strongly improves the strength and hardenability of cast steel, but it is easily bonded to N, so the present invention first bonds N to Ti to ensure that a certain amount of B remains after bonding with the remaining N, thereby exerting the effect of improving the strength and hardenability of cast steel, and the B content of the present invention is limited to 0.004-0.008% in order to obtain the above technical effects.
B eff ：B eff Namely available boron, B eff ＝B-0.77N eff Which characterizes B and available nitrogen N eff The amount of available boron remaining after bonding, i.e. the amount of boron actually contributing to the strength and to the hardenability, B eff Too high, on the contrary, results in a decrease in strength and toughness, and is not preferable in terms of cost. B of the present invention for obtaining the technical effect of boron eff Is 0.002-0.006%.
Q eff : coefficient of hardenability by synthesis of B eff And the content of other elements are obtained to represent the hardenability of the cast steel, and the higher the hardenability coefficient is, the lower the critical cooling speed is, so that the cast steel is more beneficial to obtaining excellent strength and toughness at the lower cooling speed in the quenching process.
Q eff T: the quenching effect of the casting is obtained, and Q needs to be controlled eff T (mm) in relation to the maximum thickness of the cast steel, since as the thickness of the cast becomes thicker and thicker, the critical cooling rate required must be as low as possibleThis means that thicker cast steels require a higher hardenability factor. The inventors have found that by defining Q eff has/T of 0.55 or more, and can achieve good hardenability even in a quenching step using a non-liquid as a quenching medium (such as air) for a thick cast steel, thereby ensuring excellent strength and toughness of the cast steel, and when Q is greater than Q eff When the/T is less than 0.55, the effect of slowing down the quenching cooling speed is brought by the temperature returning effect of the steel plate core part, so that the actual cooling speed brought by non-liquid medium quenching cannot be lower than the critical cooling speed, and the quenching cannot be carried out completely.
Another aspect of the present invention is to provide a method for producing the aforementioned high-toughness cast steel, which employs smelting, casting, and heat treatment, the heat treatment including normalizing, quenching, and tempering, which are sequentially performed. The quenching can be selected from non-liquid quenching due to the process design for reducing the cost and simplifying the working procedure, the non-liquid quenching is preferably air quenching, the quenching cooling speed can be 0.1 ℃/s-0.3 ℃/s, and the mechanical property of the cast steel obtained by using the cast steel composition provided by the invention after quenching and cooling reaches more than 850MPa, the room-temperature yield strength is more than 760MPa, the room-temperature impact toughness is more than 120J, and the-40 ℃ impact toughness can reach more than 90J.
The invention has the beneficial effects that: by adjusting the contents of basic elements C, si, mn, cr, ni and Mo, a trace amount of B, N, ti is added at the same time, and B is controlled eff And Q eff the/T can ensure that the finally obtained cast steel obtains excellent strength and toughness under the condition of non-liquid medium quenching (such as air) within a certain range, the room-temperature tensile strength is more than 850MPa, the room-temperature yield strength is more than 760MPa, the room-temperature impact toughness is more than 120J, and the-40 ℃ impact toughness can reach more than 90J.
The cast steel adopting the components of the invention avoids the defect that liquid medium is needed for quenching in the production process, does not need large quenching furnace equipment, does not need to worry about boiling and splashing of liquid quenching liquid in the quenching process, and does not need to worry about the problem of stress cracking caused by overhigh quenching cooling speed, thereby reducing the production cost, simplifying the production process and improving the operation conditions.
Detailed Description
In order to make those skilled in the art fully understand the technical scheme and the beneficial effects of the present invention, the following further description is made in combination with specific test examples.
Molten steel is melted according to the design components and cast into ingots, and the specific components are shown in a table 1,N eff 、B eff 、Q eff 、T(mm)、Q eff the/T is shown in Table 2, all steel ingots are subjected to heat treatment of normalizing, quenching and tempering, the normalizing process is 920 ℃ plus air natural cooling, the quenching process is 910 ℃ plus air quenching to room temperature, the tempering process is 610 ℃ plus air natural cooling, the heat preservation time in the heat treatment process is calculated according to 1.3 (min/mm) multiplied by T (mm), air quenching adopts an air blower for blowing heat exchange, and the blowing flow is per m 2 Wind-receiving surface of steel plate 400m 3 And calculating the/h normal temperature air.
The ingots after heat treatment were tested for tensile strength and room temperature toughness as well as-40 ℃ low temperature toughness, and the results are shown in table 3. The tensile strength is tested according to GB/T228.1-2010, and the room temperature toughness and the low temperature toughness at minus 40 ℃ are tested according to GB/T229-2020.
Table 1: the components of each cast steel are in percentage by mass, and the balance is Fe
| Serial number | C | Si | Mn | Cr | Ni | Mo | RE | Ti | B | N |
| 1 | 0.25 | 0.39 | 1.32 | 0.78 | 0.52 | 0.33 | 0.048 | 0.013 | 0.005 | 0.007 |
| 2 | 0.28 | 0.62 | 1.02 | 0.94 | 0.67 | 0.41 | 0.062 | 0.008 | 0.007 | 0.008 |
| 3 | 0.23 | 0.42 | 1.28 | 1.02 | 0.77 | 0.28 | 0.072 | 0.009 | 0.004 | 0.005 |
| 4 | 0.31 | 0.64 | 1.31 | 0.88 | 0.74 | 0.45 | 0.058 | 0.014 | 0.008 | 0.009 |
| 5 | 0.30 | 0.58 | 1.28 | 1.05 | 0.85 | 0.47 | 0.074 | 0.015 | 0.007 | 0.006 |
| 6 | 0.27 | 0.54 | 1.16 | 0.98 | 0.48 | 0.31 | 0.039 | 0.007 | 0.008 | 0.006 |
| 7 | 0.29 | 0.48 | 1.08 | 0.82 | 0.58 | 0.39 | 0.068 | 0.011 | 0.006 | 0.008 |
| 8 | 0.24 | 0.45 | 0.97 | 0.79 | 0.49 | 0.26 | 0.036 | 0.006 | 0.006 | 0.005 |
| 9 | 0.25 | 0.39 | 1.32 | 0.78 | 0.52 | 0.33 | 0.048 | 0.013 | 0.004 | 0.007 |
| 10 | 0.30 | 0.58 | 1.28 | 1.05 | 0.85 | 0.47 | 0.074 | 0.015 | 0.008 | 0.006 |
| 11 | 0.31 | 0.64 | 1.31 | 0.88 | 0.74 | 0.45 | 0.058 | 0.018 | 0.008 | 0.009 |
| 12 | 0.31 | 0.64 | 1.31 | 0.88 | 0.74 | 0.45 | 0.058 | 0.004 | 0.008 | 0.009 |
| 13 | 0.28 | 0.62 | 1.02 | 0.94 | 0.67 | 0.41 | 0.062 | 0.008 | 0.011 | 0.008 |
| 14 | 0.23 | 0.42 | 1.28 | 1.02 | 0.77 | 0.28 | 0.072 | 0.009 | 0.003 | 0.005 |
| 15 | 0.31 | 0.64 | 1.31 | 0.88 | 0.74 | 0.45 | 0.058 | 0.014 | 0.008 | 0.011 |
4 samples with different thicknesses are respectively cast for test numbers 5 and 6 and are respectively named as 5-1, 5-2, 5-3, 5-4,6-1, 6-2, 6-3 and 6-4, and specific N is eff 、B eff 、Q eff 、T(mm)、Q eff The ingot was cast into rectangular parallelepiped specimens of 5T length, 3T width and T thickness, respectively, as shown in Table 2.
Table 2: n of each cast steel eff 、B eff 、Q eff T (mm) and Q eff /T
Table 3 shows the test results of the strength and toughness of the cast steels described above.
TABLE 3 mechanical Properties of the cast steels
The inventive and comparative examples are further illustrated by the following analyses in conjunction with tables 1-3.
Number 11 in Table 1Ti content of 12 out of the range of the present invention, B content of No. 13 and 14 out of the range of the present invention, N content of No. 15 out of the range of the present invention, Q of No. 5-4 and No. 6-4 in Table 2 eff B of numbers 9, 10, 13, 14,/T not being within the scope of the invention eff Not within the scope of the invention, N numbered 12, 15 eff Numbers 5-4, 6-4, 9-15 are all comparative examples of the present invention, and are not within the scope of the present invention.
Comparative example 5-4 used the same composition as in inventive examples 5-1 to 5-3, and comparative example 6-4 used the same composition as in inventive examples 6-1 to 6-3, and the heat treatment process was the same, differing only in the thickness of the castings. Q of the cast steels of comparative examples 5-4 and 6-4 was too thick eff The steel plate has a cooling rate lower than a critical cooling rate due to the fact that the cooling rate actually generated by air-cooled quenching is lower than the critical cooling rate because the temperature return phenomenon in the steel plate has a neutralization effect on the quenching cooling rate during air-cooled quenching, and the cast steel cannot be fully quenched, so that the tensile strength and yield strength of the cast steel at room temperature, the room-temperature toughness and the-40 ℃ toughness of the cast steel cannot meet the requirements of the invention.
On the other hand, as can be seen from the comparison of the examples 5-1 to 5-3 and 6-1 to 6-3 in the transverse direction, the lower the thickness of the steel castings, the Q of the same material, the lower the air-cooled quenching conditions, is eff The larger the/T is, the better the hardenability effect is, and finally the mechanical property is better.
Comparative example 9 is a comparative example of inventive example 1, and the content of B was adjusted under the same content of other elements, and although the adjusted content of B was still within the inventive range, the adjustment of B resulted in B being present eff If the content of boron is too low, the effective boron is reduced, the hardenability is greatly reduced, and finally the tensile strength and yield strength at room temperature, room temperature toughness and toughness at-40 ℃ of the cast steel cannot meet the requirements of the invention.
Comparative example 10 is a comparative example of inventive example 5-1, and the content of B was adjusted under the same content of other elements, and although the adjusted content of B was still within the scope of the invention, the adjustment of B resulted in B eff Too high outside the scope of the invention, leads to an increase in the available boron, resulting in a cast steelThe strength and the toughness of the cast steel are reduced on the contrary, and the tensile strength and the yield strength at room temperature, the room temperature toughness and the toughness at minus 40 ℃ of the finally obtained cast steel can not meet the requirements of the invention.
Comparative example 11 is a comparative example of invention example 4, and the Ti content was adjusted under the same conditions as the other element contents, although B was adjusted eff 、Q eff The Ti content is still within the scope of the invention, but the Ti content is too high, which results in too high TiN content, although TiN slightly contributes to the strength, and the strength is improved compared with the invention example 4, the too high TiN becomes the starting point of toughness fracture, which results in toughness reduction, and the room temperature toughness and the-40 ℃ toughness of the finally obtained cast steel can not meet the requirements of the invention.
Comparative example 12 is a comparative example of invention example 4, and the Ti content was adjusted under the same conditions as the other element contents, although B was adjusted eff 、Q eff The value of/T is still within the scope of the invention, but N eff The Ti content is too low, the TiN content is insufficient, the strengthening and toughening effects are not obvious enough, and the N content is too high eff And the BN is generated too much, so that the strength and the toughness are reduced, and the finally obtained cast steel cannot meet the requirements of the invention on tensile strength and yield strength at room temperature, room temperature toughness and toughness at-40 ℃.
Comparative example 13 is a comparative example of invention example 2, in which the content of B was adjusted under the condition that the contents of other elements were the same, and B were adjusted eff Too high is not in the invention range, which leads to increase of effective boron and reduction of strength and toughness of the cast steel, and finally the obtained cast steel has tensile strength and yield strength at room temperature, room temperature toughness and-40 ℃ toughness which can not meet the requirements of the invention.
Comparative example 14 is a comparative example of invention example 3, in which the content of B was adjusted under the condition that the contents of other elements were the same, and B were adjusted eff If the content of boron is too low and not in the invention range, the effective boron is reduced, the hardenability is greatly reduced, and finally the tensile strength and yield strength of the cast steel at room temperature, the room temperature toughness and the-40 ℃ toughness can not meet the requirements of the invention.
Comparative example 15 is an invention exampleComparative example No. 4 in which the N content was adjusted under the same conditions as the other element contents, though B was adjusted eff 、Q eff The value of/T is still within the scope of the invention, but N is so high that N eff Too high leads to too much BN generation and the reduction of the strength and toughness of the cast steel, and the finally obtained cast steel can not meet the requirements of the invention on tensile strength and yield strength at room temperature, room temperature toughness and toughness at-40 ℃.
In conclusion, the invention simultaneously adds a trace amount of B, N, ti and controls B by adjusting the contents of basic elements C, si, mn, cr, ni and Mo eff And Q eff the/T is within a certain range, the finally obtained cast steel can be ensured to obtain excellent obdurability under the condition of non-liquid medium quenching, the room temperature tensile strength is more than 850MPa, more even more than 900MPa, the room temperature yield strength is more than 760MPa, more even more than 800MPa, the room temperature impact toughness is more than 120J, more even more than 130J, and the-40 ℃ impact toughness can be more than 90J, more even more than 100J.
The above description of the embodiments is only intended to facilitate the understanding of the method of the invention and its core idea. It should be noted that, for those skilled in the art, it is possible to make various improvements and modifications to the present invention without departing from the principle of the present invention, and those improvements and modifications also fall within the scope of the claims of the present invention.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (6)
1. The high-strength and high-toughness cast steel is characterized by comprising the following chemical components in percentage by weight: c:0.23-0.29%, si:0.37-0.65%, mn:0.95-1.35%, cr:0.75-1.08%, ni:0.46-0.87%, mo:0.25-0.45%, RE:0.035 to 0.075%, ti:0.005-0.016%, B:0.004-0.008%, N:0.005-0.01%, and the balance of Fe and inevitable impurities, and the percentage content of each element satisfies:
available nitrogen N eff = N-Ti/3.42, boron available B eff =B-0.77N eff Available nitrogen N eff 0.001-0.006% of boron effective B eff 0.002-0.006;
coefficient of hardenability Q eff =C×(1+0.53Si)×(1+2.87Mn)×(1+2.34Cr)×(1+0.77Ni)×(1+2.61Mo)×(1.2+5.45RE)×(4753B eff 2 +5.25)；
Coefficient of hardenability Q eff Ratio to maximum thickness T of cast steel, Q eff the/T is more than or equal to 0.55, and the unit of the maximum thickness T is mm; the maximum thickness T of the high-strength and high-toughness cast steel is 30-400mm; the austenite critical cooling speed of the high-strength and high-toughness cast steel is not higher than 0.3 ℃/s.
2. The high-toughness cast steel according to claim 1, wherein said high-toughness cast steel has a room-temperature tensile strength of 850MPa or more, a room-temperature yield strength of 760MPa or more, and a room-temperature impact toughness of 120J or more.
3. The high-toughness cast steel according to claim 1, wherein the high-toughness cast steel has an impact toughness of 90J or more at-40 ℃.
4. A method of producing the high-toughness cast steel according to any one of claims 1 to 3, characterized by comprising: smelting, casting and heat treatment are adopted, wherein the heat treatment comprises normalizing, quenching and tempering which are sequentially carried out.
5. The method of claim 4, wherein the quenching is a non-liquid quenching.
6. The method of claim 5, wherein the non-liquid quench is an air quench.
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