CN111945070A - Narrow-hardenability gear steel and preparation method thereof - Google Patents
Narrow-hardenability gear steel and preparation method thereof Download PDFInfo
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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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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
- B22D11/10—Supplying or treating molten metal
- B22D11/11—Treating the molten metal
- B22D11/114—Treating the molten metal by using agitating or vibrating means
- B22D11/115—Treating the molten metal by using agitating or vibrating means by using magnetic fields
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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
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/06—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
- C21D8/065—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires of ferrous alloys
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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
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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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
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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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
- C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
Abstract
The application provides narrow-hardenability gear steel and a preparation method thereof, and relates to the field of steel. The narrow hardenability gear steel comprises the following components in percentage by mass: c: 0.19% -0.21%, Si: 0.22% -0.28%, Mn: 0.82% -0.87%, Cr: 0.52% -0.58%, Ni: 0.50-0.55%, Mo 0.19-0.21%, Al 0.025-0.035%, N: 0.0080% -0.0120% and the balance of Fe and inevitable impurities, wherein Al/N is 3-3.6, the obtained narrow hardenability pinion steel not only meets the hardenability requirement of steel grades, but also reduces the influence tendency on the surface quality brought by steel grade components, and effectively improves the surface quality of the narrow hardenability pinion steel.
Description
Technical Field
The application relates to the field of steel, in particular to narrow-hardenability gear steel and a preparation method thereof.
Background
In the actual production process, the narrow hardenability pinion steel is easy to crack, and because the narrow hardenability pinion steel series steel is Ni-containing steel, when the narrow hardenability pinion steel is heated by a heating furnace, an oxidizing atmosphere exists in the furnace, so that a deep oxidation layer is formed on the surface of a continuous casting billet, and the Ni-containing steel has high viscosity and is compact and attached to the surface of the steel billet, high-pressure water descaling cannot be removed, and the descaling effect is influenced, as shown in fig. 1, the gray part in fig. 1 is the oxidation layer remained after high-pressure water descaling. The residual iron oxide scale on the surface of the blank is pressed into the surface of the round steel in the rolling process to cause surface pits, as shown in figure 2, the round steel needs to be peeled, and when the surface pits are serious, the round steel needs to be scrapped if the diameter tolerance after peeling can not meet the requirement, so that the production cost is increased.
Disclosure of Invention
An object of embodiments of the present application is to provide a narrow hardenability gear steel and a method for manufacturing the same, which can improve at least one of the above-described technical problems.
In a first aspect, embodiments of the present application provide a narrow hardenability gear steel, which includes, by mass percent: c: 0.19% -0.21%, Si: 0.22% -0.28%, Mn: 0.82% -0.87%, Cr: 0.52% -0.58%, Ni: 0.50-0.55%, Mo 0.19-0.21%, Al 0.025-0.035%, N: 0.0080% -0.0120% and the balance of Fe and inevitable impurities, wherein Al/N is 3-3.6.
In the implementation process, the obtained narrow-hardenability pinion steel not only meets the hardenability requirement of steel grades, but also reduces the surface crack sensitivity of the steel, reduces the influence tendency on the surface quality brought by steel grade components, and effectively improves the surface quality of the narrow-hardenability pinion steel.
In a second aspect, embodiments of the present application provide a method for preparing the narrow hardenability gear steel, including the following steps performed in sequence: converter smelting, external refining, square billet continuous casting, casting blank slow cooling and heating rolling.
Wherein, in the step of heating and rolling, the temperature of the high-temperature section is 1140-1180 ℃, the time of the casting blank in the high-temperature section is 120-180min, the air-fuel ratio is 1.6-1.8, and the residual oxygen content of the whole furnace is controlled to be 1.7-2.0%.
In the implementation process, the temperature, the time and the atmosphere of the casting blank in the high-temperature section of the heating furnace are controlled, so that the descaling effect of the surface of the casting blank is effectively improved, the phenomenon that the surface of round steel is pressed into subsequent residual iron oxide scales in the rolling process to cause pits is avoided, the surface thermal stress of the casting blank in the heating process and the round steel in the rolling process can be reduced, and the surface quality of the finally obtained narrow-hardenability gear steel is improved.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings that are required to be used in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present application and therefore should not be considered as limiting the scope, and for those skilled in the art, other related drawings can be obtained from the drawings without inventive effort.
FIG. 1 is a photograph of a cast slab of a conventional narrow hardenability gear steel after phosphorus removal;
fig. 2 is a photograph of a conventional narrow hardenability gear round steel having dimples on the surface.
Detailed Description
Embodiments of the present application will be described in detail below with reference to examples, but those skilled in the art will appreciate that the following examples are only illustrative of the present application and should not be construed as limiting the scope of the present application. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.
The noun explains: ac 1: refers to the onset temperature of ferrite to austenite transformation in steel upon heating; ar 1: the onset temperature of transformation of austenite to pearlite and ferrite in the steel upon cooling.
The following is a detailed description of a narrow hardenability gear steel and a method for manufacturing the same according to an embodiment of the present application:
al and N are added into the narrow hardenability gear steel, and second phase ions are precipitated from the grain boundary during heating to pin the grain boundary, so that the grain growth is prevented, the purpose of refining the grain is achieved, and the hardenability of the steel is reduced, thereby meeting the requirements of the narrow hardenability and high strength of the steel. However, the applicant found that the existence of more second phase ions in the grain boundary weakens the strength of the grain boundary, and the crack sensitivity of the steel surface is enhanced. When Ni-containing steel is heated, oxides formed on the surface of the Ni-containing steel have high viscosity and are attached to the surface of a billet, high-pressure water descaling cannot be removed, iron scales remaining on the surface of a blank are pressed into the surface of round steel in the rolling process, surface pits are caused, the surface of the round steel is cooled unevenly in the rolling process, strong thermal stress exists, and the surface crack sensitivity of the round steel is aggravated.
Therefore, the applicant optimized the steel type composition in order to reduce the generation of the second phase and the influence of the Cr, Ni, Mo alloy elements on the surface crack sensitivity of the round steel, compared to Cr, Ni, Mo-based gear steel.
Specifically, the present application provides a narrow hardenability pinion steel, which includes, by mass percent: c: 0.19% -0.21%, Si: 0.22% -0.28%, Mn: 0.82% -0.87%, Cr: 0.52% -0.58%, Ni: 0.50-0.55%, Mo 0.19-0.21%, Al 0.025-0.035%, N: 0.0080% -0.0120% and the balance of Fe and inevitable impurities, wherein Al/N is 3-3.6. That is, the contents of Cr, Ni, Mo, Al, and N are particularly optimized, and Al/N is 3 to 3.6.
Specifically, the mass percentage of Cr is 0.52% to 0.58%, specifically for example, the mass percentage of Cr is any one value or between any two values of 0.52%, 0.53%, 0.54%, 0.55%, 0.56%, 0.57%, or 0.58%; the mass percent of Ni is 0.50% to 0.55%, specifically for example, the mass percent of Ni is any one value or between any two values of 0.50%, 0.52%, 0.53%, 0.54%, or 0.55%; the mass percent of Mo is 0.19% to 0.21%, specifically for example, the mass percent of Mo is any one value or between any two values of 0.19%, 0.20%, or 0.21%; the mass percentage of Al is 0.025% to 0.035%, specifically, for example, the mass percentage of Al is any one value or between any two values of 0.25%, 0.27%, 0.28%, 0.29%, 0.30%, 0.32%, or 0.25%; the mass percentage of N is 0.0080% to 0.0120%, specifically, for example, the mass percentage of N is any one value or between any two values of 0.0080%, 0.0090%, 0.0095%, 0.0100%, 0.0110%, 0.0115%, or 0.0120%.
The mass percent of C is 0.19% to 0.21%, specifically for example, the mass percent of C is any one value or between any two values of 0.19%, 0.20% or 0.21%; the mass percentage of Si is 0.22% to 0.28%, specifically, for example, the mass percentage of Si is 0.22%, 0.23%, 0.35%, 0.26%, 0.27%, or 0.28%, or between any two values; the mass percentage of Mn is 0.82% to 0.87%, and specifically, for example, the mass percentage of Mn is 0.82%, 0.83%, 0.85%, 0.86%, or 0.87%, or between any two values.
That is, through reasonable selection, the Ni content adopts a more optimal range with a lower limit on the basis that the original Ni content is larger than 0.4 percent to reduce the influence of the nickel-containing steel on the surface quality, meanwhile, the Cr and Mo steels select a more optimal range with a middle limit on the national standard steel grade to make up for the influence of reducing Ni on the comprehensive performance of the steel grade, in addition, the Al/N ratio is properly improved by optimizing the Al/N ratio and cannot be higher than 3.6, the hardenability requirement of the steel grade can be met, crystal grains are refined, the surface crack sensitivity of the steel is reduced, and the influence tendency on the surface quality caused by the components of the steel grade is reduced.
Further, by mass percent, N > 0.0092%, Al > 0.032%, and Al/N ═ 3.1 to 3.5. According to the proportion, the requirement of the hardenability of the steel grade can be met, crystal grains are refined, the surface crack sensitivity of the steel is effectively reduced, the influence tendency on the surface quality caused by the components of the steel grade is reduced, and the gear round steel with narrow band width of the hardenability at the tail end and good surface quality can be obtained.
Specifically, the tip hardenability of the pinion steel satisfies: j4.7 mm: 36-41HRC, J7.9mm: 28-32HRC, j12.7 mm: 21-26 HRC; the yield strength satisfies: rp0.2 is more than or equal to 785MPa, the tensile strength is more than or equal to 985MPa, the elongation after fracture is more than or equal to 9 percent, and the reduction of area is more than or equal to 40 percent. That is, the end hardenability satisfies the standard requirements, and the yield strength also satisfies the standard requirements.
The applicant finds that the narrow hardenability pinion steel series steel has strong crack sensitivity, volume expansion generates structural stress in the solidification process of a continuous casting billet, and thermal stress is generated when the billet is cooled; when the temperature is raised by heating, the structure is transformed to generate structure stress, the surface of a casting blank is heated too fast, the temperature difference between the inside and the outside is large to cause thermal stress, the combined action forms larger comprehensive stress, and when the comprehensive stress is larger than the intercrystalline strength, the material is cracked.
In view of the above, the present application also provides a method for preparing the narrow hardenability gear steel, which includes the following steps:
s1, smelting in a converter.
S2, refining outside the furnace.
The step S2 includes a degassing and soft blowing process, and specifically, the degassing and soft blowing process includes:
carrying out vacuum degassing treatment on the molten steel, using nitrogen as circulation lifting gas in the whole process, wherein the N content range before RH treatment is required to be 40-60ppm, the treatment time is more than or equal to 10min below the vacuum degree of less than 0.266kPa, using nitrogen with 0.8MPa for circulation for more than 15min after pump withdrawal, controlling the N content to be 80-120ppm, and carrying out bottom-blown argon soft blowing after RH treatment is finished to promote floating of inclusions.
And S3, square billet continuous casting.
In order to improve component segregation, the continuous casting process adopts square billet with the cross section size of 280mm x 280mm for processing.
In the continuous casting process of the square billet, the superheat degree of the molten steel is controlled at 15-30 ℃, a crystallizer is adopted for electromagnetic stirring, and the electromagnetic stirring is combined with the superheat degree control of the molten steel to ensure the component uniformity of the casting blank from the surface to the inside. According to the characteristics of the section and the steel type of a casting blank (the narrower component requirements of Cr, Ni and Mo and the lower hardenability in the Al/N range), the electromagnetic stirring of the crystallizer adopts weak stirring, specifically, the parameters are controlled to be 100A +/-5A/2.5 Hz, the stirring intensity is too high, so that the more serious negative segregation (elements such as C, Cr, Ni and Mo) is generated at the edge of the casting blank, the positive segregation is generated from the edge to the center 1/2, the intensity is too low, the stirring effect cannot be achieved, the columnar crystals of the casting blank are developed, and the sensitivity of surface and subcutaneous cracks is increased. The electromagnetic stirring parameters at the tail end are controlled to be 250A +/-10A/3.5 Hz, and the segregation of central components (C, Cr, Ni, Mo, Al, N and other elements) of the round steel is improved.
In summary, the above parameters are combined to ensure the uniformity of the components of the cast slab obtained by the processing in step S3 and to reduce the crack sensitivity.
And S4, slowly cooling the casting blank.
Alternatively, the pit entry temperature is raised 10-35 ℃ based on the Ar1 temperature of the narrow hardenability pinion steel.
Specifically, when the continuous casting billet is cooled, and when the casting billet is cooled to the phase transition temperature, the structure is transformed to pearlite, volume expansion occurs in the transformation process to generate structure stress, thermal stress is generated due to uneven temperature distribution in the cooling process, the temperature drop is quicker, the structure stress and the thermal stress are larger, at the moment, the temperature of the slow cooling pit is controlled to rise by 10-35 ℃ on the basis of the phase transition temperature of the gear steel, the internal stress of the gear steel under the component can be reduced, and the surface stress defect caused by overlarge cooling temperature gradient and overlarge internal stress of the continuous casting billet can be avoided.
Alternatively, the transformation temperature of the gear steel is measured by using a Gleeble 3800 thermal simulation tester, wherein the Ar1 temperature is 605 ℃, so that the temperature of the annealing pit is 615-640 ℃, specifically, for example, any one of 615 ℃, 618 ℃, 620 ℃, 625 ℃, 630 ℃, 635 ℃ or 640 ℃ or between any two values.
Furthermore, in order to effectively reduce the surface stress of the casting blank, the surface quality of the narrow-hardenability gear steel round steel is improved. On the premise of the temperature of entering the slow cooling pit, the heat preservation time is 48-72h, the pit outlet temperature is less than 400 ℃, and specifically, the heat preservation time is any one value or any two values of 48h, 50h, 55h, 60h, 66h, 70h or 72 h.
Because the steel has multiple specifications and small order amount of single specification, hot charging can not be carried out, the steel can only be cold charged into a heating furnace, the pit outlet temperature is higher than 400 ℃, and the slow cooling effect can not be achieved, so the pit outlet temperature is lower than 400 ℃, the temperature gradient of the inner surface and the outer surface of a casting blank can be reduced, and the surface stress defect caused by overlarge internal stress can be avoided.
And S5, heating and rolling.
Specifically, the step of heating rolling includes:
and (4) placing the casting blank obtained in the step (S4) into a heating furnace.
Wherein optionally the upper temperature limit of the preheating section is reduced by 50-15 ℃ on the basis of Ac1 of the narrow hardenability pinion steel.
Under the above setting conditions, when the temperature of the cast slab is increased from the charging temperature to Ac1, the ferrite thereof is transformed into austenite, and this process is a process of volume contraction, and the structural stress at this time is tensile stress. The heating process is a process of heating the surface and conducting heat inside the continuous casting billet, the surface layer and the subsurface layer generate thermal stress due to temperature difference, the temperature rise is faster, the internal and external temperature difference is larger, the structure stress and the thermal stress are also larger, at the moment, the preheating section upper limit temperature is reduced by 50-15 ℃ on the basis of Ac1 of the narrow hardenability gear steel, the internal stress under the steel component can be effectively reduced, the stress rise problem caused by temperature rise rolling after slow cooling under the steel component is reduced by reducing the preheating section upper limit temperature, the temperature difference is reduced, the stress is reduced, and the surface quality is improved.
Further, the transformation temperature of the gear steel is measured by using a Gleeble 3800 thermal simulation testing machine, wherein the Ac1 temperature of the gear steel is 743 ℃, so that optionally, the preheating section upper limit temperature is 693-728 ℃, specifically, for example, the preheating section upper limit temperature is any one value or between any two values of 693 ℃, 695 ℃, 698 ℃, 700 ℃, 706 ℃, 710 ℃, 715 ℃, 720 ℃, 726 ℃ or 728 ℃.
Under the condition of the upper limit temperature of the preheating section, in order to further reduce stress and improve surface quality, optionally, the residence time of the casting blank in the preheating section is more than or equal to 90min, and the casting blank is uniformly stepped in the preheating section, wherein the stepping speed is more than or equal to 3 steps/min, and the heating rate of the casting blank is less than or equal to 8 ℃/min, so that the problem that the surface thermal stress of the casting blank is increased and the surface crack sensitivity of the casting blank is improved due to the fact that the heating rate is too high and the internal and external temperature difference is large.
In the step of heating and rolling, the temperature of the high-temperature section is 1140-1180 ℃. That is, the temperature in the high temperature section is any value or between any two values of 1140 ℃, 1150 ℃, 1165 ℃, 1170 ℃, 1175 ℃ or 1180 ℃. When the temperature is higher than 1180 ℃, the surface of the casting blank is seriously oxidized, the high-pressure water descaling effect is poor, the temperature is lower than 1140 ℃, the core part of the casting blank is burnt incompletely, and the defects of the core part of the casting blank cannot be improved during rolling.
In the present application, the high-temperature stage refers to a heating second stage and a soaking stage.
Wherein the in-furnace time of the casting blank in the high temperature section is 120-180min, at this time, the air-fuel ratio is 1.6-1.8, specifically, for example, the air-fuel ratio is any one value or between any two values of 1.6, 1.7 or 1.8, the total residual oxygen content is controlled to be 1.7-2.0%, specifically, for example, the total residual oxygen content is controlled to be any one value or between any two values of 1.7%, 1.8%, 1.9% or 2.0%.
Through the mode, the air-fuel ratio is effectively controlled to be lower, the residual oxygen content is controlled, the high-temperature time is shortened, the possibility that surface oxides are pressed into the surface of the narrow-hardenability gear steel to form pits is reduced, the surface cooling is more uniform during rolling, the temperature gradient is small, the surface thermal stress of the narrow-hardenability gear steel is reduced, and the surface quality of the narrow-hardenability gear steel is improved, wherein the narrow-hardenability gear steel obtained by the method is round steel.
Optionally, the method for producing the narrow hardenability pinion steel provided by the present application further includes steps S6 and S7 performed in this order after step S5. S6, magnetic flux leakage flaw detection was performed on the surface of the obtained cylindrical narrow hardenability pinion steel. And S7, detecting the tissue and the performance of the sample.
The narrow hardenability gear steel and the method for producing the same according to the present application will be described in further detail with reference to examples.
Example 1
A preparation method of narrow hardenability gear steel comprises the following steps:
s1, smelting in a converter.
S2, refining outside the furnace: carrying out vacuum degassing treatment on the molten steel, using nitrogen as circulation lifting gas in the whole process, wherein the N content range before RH treatment is required to be 40-60ppm, the treatment time is more than or equal to 10min below the vacuum degree of less than 0.266kPa, using nitrogen with 0.8MPa for circulation for more than 15min after pump withdrawal, controlling the N content to be 80-120ppm, and carrying out bottom-blown argon soft blowing after RH treatment is finished to promote floating of inclusions.
S3, square billet continuous casting: the size of the cross section of the square billet is 280mm x 280mm, a crystallizer is adopted for electromagnetic stirring and weak stirring, the electromagnetic stirring parameter of the crystallizer is 100A +/-5A/2.5 Hz, and the electromagnetic stirring parameter of the tail end is 250A +/-10A/3.5 Hz.
S4, slowly cooling a casting blank: the temperature of entering a slow cooling pit is 615 ℃, the heat preservation time is 64h, and the pit outlet temperature is 282 ℃.
S5, heating and rolling: the upper limit temperature of the preheating section is 693-720 ℃, the residence time of the casting blank in the preheating section is 92-135min, the casting blank is stepped at a constant speed in the preheating section, wherein the stepping speed is more than or equal to 3 steps/min, and the heating rate of the casting blank is less than or equal to 8 ℃/min. The temperature of the high-temperature section is 1135-1168 ℃, the time of the casting blank in the high-temperature section is 123-167min, the air-fuel ratio is 1.6, and the residual oxygen content of the whole furnace is controlled to be 1.82%.
S6, magnetic flux leakage flaw detection is performed on the surface of the cylindrical narrow hardenability pinion steel thus obtained.
S7, detecting sample structure and performance: sampling at the D/4 position of the round steel, and carrying out heat treatment on a sample: normalizing at 925 +/-10 ℃ and quenching at 925 +/-5 ℃, and detecting the hardenability of the tail end of the round steel; preparing a sample by using a blank with the diameter of 15mm, carrying out heat preservation at 860 +/-10 ℃ for more than or equal to 30min, and carrying out oil cooling; tempering at 200 +/-10 ℃, keeping the temperature for more than or equal to 90min, air cooling, and measuring the longitudinal mechanical property.
The chemical compositions of the narrow hardenability gear steel provided in example 1 are shown in table 1.
Examples 2 to 4 and comparative examples 1 to 6
Examples 2 to 4 and comparative examples 1 to 6 were set, wherein the chemical compositions of the narrow hardenability gear steels of examples 2 to 4 and comparative examples 1 to 6 are shown in table 1, and wherein the narrow hardenability gear steels of examples 2 to 4 and comparative examples 1 to 6 were prepared in a similar manner to example 1 except for some parameters in step S4 and step S5 shown in table 2.
The properties, surface quality, and pass rate of leakage flux flaw detection of the round steels obtained in examples 1 to 4 and comparative examples 1 to 6 are shown in table 3.
TABLE 1 chemical composition of Gear Steel (wt%)
| Smelting composition | C | Si | Mn | Cr | Mo | Ni | Al | N | Al/N |
| Example 1 | 0.20 | 0.24 | 0.85 | 0.56 | 0.20 | 0.53 | 0.032 | 0.0092 | 3.48 |
| Example 2 | 0.20 | 0.25 | 0.85 | 0.54 | 0.20 | 0.51 | 0.033 | 0.00956 | 3.45 |
| Example 3 | 0.19 | 0.25 | 0.86 | 0.52 | 0.19 | 0.50 | 0.033 | 0.0101 | 3.27 |
| Example 4 | 0.21 | 0.25 | 0.82 | 0.52 | 0.19 | 0.54 | 0.035 | 0.0112 | 3.13 |
| Comparative example 1 | 0.20 | 0.26 | 0.85 | 0.56 | 0.20 | 0.52 | 0.027 | 0.0045 | 6.00 |
| Comparative example 2 | 0.19 | 0.24 | 0.82 | 0.45 | 0.19 | 0.45 | 0.031 | 0.0076 | 4.08 |
| Comparative example 3 | 0.19 | 0.25 | 0.80 | 0.45 | 0.18 | 0.45 | 0.029 | 0.0042 | 6.90 |
| Comparative example 4 | 0.21 | 0.25 | 0.86 | 0.56 | 0.22 | 0.51 | 0.032 | 0.0142 | 2.25 |
| Comparative example 5 | 0.20 | 0.24 | 0.87 | 0.53 | 0.20 | 0.53 | 0.032 | 0.0095 | 3.37 |
| Comparative example 6 | 0.20 | 0.25 | 0.85 | 0.54 | 0.20 | 0.51 | 0.031 | 0.00856 | 3.62 |
TABLE 2 main production process parameters of gear steel
TABLE 3 round steel Performance, surface quality, and magnetic flux leakage inspection qualification rate
From table 3, it can be seen that the gear steel provided by the present application has a tip hardenability satisfying: j4.7 mm: 36-41HRC, J7.9mm: 28-32HRC, j12.7 mm: 21-26 HRC; the yield strength satisfies: rp0.2 is more than or equal to 785MPa, the tensile strength is more than or equal to 985MPa, the elongation after fracture is more than or equal to 9 percent, and the reduction of area is more than or equal to 40 percent. And the descaling effect is good, no pockmark is formed on the surface of the round steel, the generation of cracks is effectively reduced, and the pass rate of magnetic flux leakage flaw detection is higher than 95%. Meanwhile, according to tables 1 and 2, it can be seen that the change of the element content (especially, Cr, Ni, Mo, Al, N) and the change of the parameters in the preparation method have great influence on the performance, surface quality, and magnetic flux leakage flaw detection yield of the finally prepared gear steel.
In conclusion, the preparation method provided by the application not only effectively improves the descaling effect of the surface of the casting blank, avoids pits caused by pressing the subsequent residual iron oxide scale into the surface of the round steel in the rolling process, but also can improve the surface quality of the finally obtained narrow-hardenability gear steel, reduce the generation of cracks and improve the qualification rate. The narrow-hardenability gear steel provided by the application not only meets the hardenability requirement of steel grades, but also reduces the surface crack sensitivity of steel, reduces the influence tendency on the surface quality caused by steel grade components, and effectively improves the surface quality of the narrow-hardenability gear steel.
The above description is only a preferred embodiment of the present application and is not intended to limit the present application, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present application shall be included in the protection scope of the present application.
Claims (10)
1. A narrow hardenability gear steel characterized by comprising, in mass percent: c: 0.19% -0.21%, Si: 0.22% -0.28%, Mn: 0.82% -0.87%, Cr: 0.52% -0.58%, Ni: 0.50-0.55%, Mo 0.19-0.21%, Al 0.025-0.035%, N: 0.0080% -0.0120% and the balance of Fe and inevitable impurities, wherein Al/N is 3-3.6.
2. The narrow hardenability gear steel according to claim 1, characterized in that said N > 0.0092%, said Al > 0.032%, and said Al/N ═ 3.1-3.5, in mass%.
3. The narrow hardenability pinion steel according to claim 1, wherein the tip hardenability of the pinion steel satisfies: j4.7 mm: 36-41HRC, J7.9mm: 28-32HRC, j12.7 mm: 21-26 HRC; the yield strength satisfies: rp0.2 is more than or equal to 785MPa, the tensile strength is more than or equal to 985MPa, the elongation after fracture is more than or equal to 9 percent, and the reduction of area is more than or equal to 40 percent.
4. A method of producing a narrow hardenability gear steel according to any one of claims 1 to 3, characterized by comprising the following steps performed in sequence: converter smelting, external refining, square billet continuous casting, casting blank slow cooling and heating rolling;
wherein, in the step of heating and rolling, the temperature of the high-temperature section is 1140-1180 ℃, the time of the casting blank in the high-temperature section is 120-180min, the air-fuel ratio is 1.6-1.8, and the residual oxygen content in the whole furnace is controlled to be 1.7-2.0%.
5. The production method according to claim 4, wherein in the step of heating and rolling, the upper limit temperature of the preheating section is lowered by 50 to 15 ℃ based on Ac1 of the narrow hardenability gear steel, and the residence time of the cast slab in the preheating section is not less than 90 min.
6. The process as claimed in claim 5, wherein the upper temperature limit of the preheating zone is 693-728 ℃.
7. The preparation method according to claim 5 or 6, wherein the casting blank is stepped at a constant speed in the preheating section, wherein the stepping speed is more than or equal to 3 steps/min, and the heating rate of the casting blank is less than or equal to 8 ℃/min.
8. The preparation method according to claim 4, wherein in the step of slowly cooling the casting blank, the temperature of a pit entering part rises by 10-35 ℃ based on the Ar1 temperature of the narrow hardenability gear steel, the holding time is 48-72h, and the pit leaving temperature is less than 400 ℃.
9. The method as claimed in claim 8, wherein the temperature of the buffer cooling pit is 615-640 ℃.
10. The preparation method according to claim 4, wherein the step of continuous billet casting adopts a crystallizer for electromagnetic stirring and weak stirring, the electromagnetic stirring parameter of the crystallizer is 100A +/-5A/2.5 Hz, and the electromagnetic stirring parameter at the tail end is 250A +/-10A/3.5 Hz;
optionally, the step of continuous billet casting uses billet sections with dimensions of 280mm by 280 mm.
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