CN110373607B

CN110373607B - High-temperature carburized steel, high-temperature carburized steel component and preparation method thereof

Info

Publication number: CN110373607B
Application number: CN201910677640.9A
Authority: CN
Inventors: 刘年富; 包锋; 张强; 刘锦标
Original assignee: SGIS Songshan Co Ltd
Current assignee: SGIS Songshan Co Ltd
Priority date: 2019-07-25
Filing date: 2019-07-25
Publication date: 2021-04-02
Anticipated expiration: 2039-07-25
Also published as: CN110373607A

Abstract

The invention designs a low-cost high-temperature carburized steel aiming at a high-temperature carburization environment of more than 1000 ℃, which comprises the following chemical components in percentage by weight: c: 0.16-0.20%, Si: less than or equal to 0.04 percent, Mn: 0.75-0.90%, Cr: 1.15-1.25%, Mo: 0.20-0.30%, Al: 0.040-0.050%, N: 0.0120-0.0180%, P: less than or equal to 0.025 percent, S: 0.015 to 0.025%, O: less than or equal to 0.0010 percent, and the balance of Fe and inevitable impurities. The Al/N ratio is controlled to be 2.0-4.0, the Si content is controlled to be lower, and the deoxidation process in steel making and the stopper curve control process in continuous casting are combined, so that large-scale continuous casting can be realized, additional process treatment before high-temperature carburization is not needed, the steel structure before carburization is not strictly controlled, and the process flow is greatly simplified. The grade of B-type coarse inclusion, B-type fine inclusion and Ds inclusion of the high-temperature carburized steel is below 0.5, simulated carburization is carried out for 2-6h at the temperature of 1000-1030 ℃, mixed crystal does not appear, and after the carburized steel is applied to parts such as gears and the like, the fatigue life of the parts can be effectively ensured.

Description

High-temperature carburized steel, high-temperature carburized steel component and preparation method thereof

Technical Field

The invention relates to the field of steel alloys, in particular to high-temperature carburized steel, a high-temperature carburized steel component and a preparation method thereof.

Background

The domestic high-temperature carburization technology is already applied to gear part companies. A large number of researches show that when the carburizing temperature is increased from conventional 920-930 ℃ to 950 ℃, the carburizing period can be reduced by about 30 percent, and when the carburizing temperature is increased to 1000 ℃, the carburizing period can be reduced by about 55 percent. However, when the carburizing temperature of the common gear steel reaches 950 ℃, a small amount of coarse austenite grains appear, which easily causes the gear deformation and greatly reduces the use performance of the gear; and when the carburizing temperature is 1000 ℃, a large amount of coarse austenite grains appear, so that the gear parts are scrapped.

In order to prevent the austenite grains from being abnormally coarse after the high-temperature carburization of the gear, a small amount of Nb, Ti, or V alloy is mainly added to form grain boundaries of particles such as Nb (C, N) and Ti (C, N), thereby suppressing the austenite grains from growing large. In order to reduce the cost of steel, patent techniques have proposed that austenite grain growth is suppressed by forming a large amount of an AlN precipitate phase by adding a large amount of Al or N alloy without adding alloying elements such as Nb, V, and Ti, and controlling the Al/N ratio within a suitable range.

Patent JP patent No. 2000-160288A discloses a carburized steel whose steel components are, in weight percent, C0.15-0.25%, Si 0.8% or less, Mn 1.5% or less, P0.03% or less, S0.005-0.03%, Ni 1.8% or less, Cr 1.5% or less, Mo 0.7% or less, Al 0.03-0.07%, Nb 0.03-0.06%, N0.013% or more, and the balance of Fe and inevitable impurities. Although the carburizing temperature can reach more than 1000 ℃, the carburizing steel of the patent contains more Ni, thereby causing higher cost, and the microalloy Nb is adopted to inhibit the coarsening of the steel structure, thereby easily causing cracks of the casting blank.

The patent JP patent open 2007-291497A and JP patent open 2008-189989A both disclose a steel that can be carburized at high temperature over 1000 ℃, the composition of the steel is: 0.1 to 0.3 percent of C, 0.03 to 0.06 percent of Nb, 0.001 to 0.003 percent of Ti, 0.005 to 0.015 percent of V, less than 0.06 percent of Al and 0.0185 to 0.03 percent of N. The steel material adopts Nb, V and Ti microalloying to inhibit coarsening of steel material structure, and has the problem that the casting blank is easy to crack. Further, the steel requires strict control of hot forging and rolling conditions such as a temperature rise rate and a cooling rate at the time of hot forging before carburization so that the amount of precipitation of carbonitride and AlN is 0.01% by mass or more and the total number of complex carbonitrides having a diameter of 20 to 80nm is 300 per a steel structure of 1000 μm or more, thereby increasing production costs.

Patent JP patent laid open 2016-199784A discloses a high-temperature carburized component and a method of manufacturing the same. The steel comprises the following components: c: 0.10-0.30%, Si: 0.05 to 1.00%, Mn: 0.30-2.00%, P: 0.030% or less, S: 0.030% or less, Cr: 0.30-1.50%, Mo: 0.50% or less, Al: 0.016 to 0.060%, N: 0.0085-0.030%, contains Fe and inevitable impurity. Although Nb, V and Ti are not added, the cracking risk is reduced. However, the steel needs to be strictly controlled to proceed to a predetermined cooling temperature of 600 to 700 ℃ at a predetermined cooling rate of 0.5 ℃/sec or less after the hot forging process before carburization, and to be heated and held at the cooling temperature for 30 minutes or more to control the pearlite volume area and the AlN deposition amount, thereby increasing the production cost.

It is seen that in the prior art, in order to obtain high temperature carburized steel of 1000 ℃ or higher, a complicated process is required to produce a specific steel structure before carburization. Furthermore, the addition of a large amount of Al to the case hardening steel causes a significant problem in that a high Al content tends to form a large amount of Al₂O₃The problem that the continuous production of the carburizing steel with high Al content cannot be solved is not given in the patent documents.

Therefore, aiming at the problems in the prior art, a low-cost high-temperature carburized steel, a high-temperature carburized steel component and a preparation method of the high-temperature carburized steel are provided.

Disclosure of Invention

As described above, when the carburizing temperature of the high-temperature carburized steel is increased to 1000 ℃, although the carburizing period can be greatly reduced, a large number of coarse austenite grains are likely to occur at a high carburizing temperature, which results in rejection of the carburized steel member. In order to prevent austenite grains from being abnormally coarse after high-temperature carburization of steel, the prior art proposes that Al and N components are added, the Al/N ratio is controlled within a proper range, and the growth of austenite grains is inhibited by forming a large amount of AlN precipitated phases. However, in the prior art, the process parameters are strictly controlled in the heat treatment process before carburization to obtain a specific steel structure, so that the production cost is increased. In addition, the prior art does not solve the problem that the continuous casting tundish nozzle is blocked due to high Al content, so that the batch production cannot be realized.

Aiming at the technical problems, the invention provides the high-temperature carburized steel prepared by low cost and short process, the carburized steel can be prepared by matching component control and a reasonable steelmaking continuous casting process, a large amount of alloy elements are not required to be added, and complicated treatment and structure control on the steel before carburization are not required.

One of the objects of the present invention is to provide a high temperature carburized steel. The steel comprises the following components in percentage by weight: c: 0.16-0.20%, Si: less than or equal to 0.04 percent, Mn: 0.75-0.90%, Cr: 1.15-1.25%, Mo: 0.20-0.30%, Al: 0.040-0.050%, N: 0.0120-0.0180%, P: less than or equal to 0.025 percent, S: 0.015 to 0.025%, O: less than or equal to 0.0010 percent, and the balance of Fe and inevitable impurities. Wherein, the mass percentage of Al/N is controlled to be 2.0-4.0.

Through the selection of the content of the components and the reasonable matching of the Al/N ratio, fine AlN can be formed in the steel, so that a pinning effect is achieved in the carburizing process, and the growth (coarsening) of crystal grains is inhibited. In addition, by controlling the Si content to be less than or equal to 0.04 percent, the oxidation in the grain boundary of the steel in the subsequent heat treatment process can be well inhibited while the strength of the steel is met.

Preferably, the component content is further: mo: 0.22-0.26%, N: 0.0130-0.0170% and Al/N ratio is controlled to be 2.5-3.5.

Preferably, the carburizing temperature of the high-temperature carburized steel is 1000 ℃ or higher.

Preferably, the Al-containing brittle B-type inclusions in the high-temperature carburized steel are rated at 0.5 or less, and the Ds-type inclusions are rated at 0.5 or less.

Preferably, the austenite grain size of the high-temperature carburized steel after simulation of high-temperature carburization is more than 7.5, and mixed grains do not exist.

Another object of the present invention is to provide a member prepared by using the above high temperature carburized steel.

Preferably, the member is a gear.

Gears are important mechanical parts that require high surface hardness and wear resistance while maintaining a certain core toughness. Generally, a surface treatment process such as carburizing is performed on the gear steel to improve the fatigue life of the gear steel. And important factors influencing the fatigue life of the gear steel are the grain size and the inclusion grade of the gear steel.

The high-temperature carburized steel product can inhibit the coarsening of crystal grains of the steel product in the carburization process, and the Al-containing brittle B-type inclusion and Ds-type inclusion are controlled below 0.5 grade by combining the steel-making and continuous casting processes, so that the fatigue property of the steel product can be greatly improved, and the high-temperature carburized steel product is suitable for mechanical components needing good fatigue property. Is especially suitable for gear steel.

The invention also aims to provide a preparation process of the high-temperature carburized steel, which comprises the following specific steps:

the first step is as follows: smelting in a converter;

the second step is that: refining in an LF ladle furnace;

the third step: RH vacuum degassing;

the fourth step: continuous casting;

wherein the second step comprises a deoxidation process: aluminum particles are taken as a deoxidizing agent and are subjected to diffusion deoxidation and comprehensive deoxidation by silicon carbide, the addition amount of the aluminum particles is 80kg +/-20 kg, sufficient aluminum wires are fed in 10 minutes in the early stage of refining, the Al content is ensured to be 0.050-0.060% for deep deoxidation, and the feeding of the Al wires is not allowed in the middle and later stages of refining;

the aluminum particles and the silicon carbide have the advantages of comprehensive deoxidation, and compared with the single deoxidation of the aluminum particles, the method can ensure more sufficient deoxidation reaction and better deoxidation effect. Feeding Al wire in the middle and later periods to cause Al to react with oxygen in steel to generate alumina inclusions, and the alumina inclusions are remained in the steel and cannot be removed, so that B-type inclusions in the molten steel are more. Therefore, feeding of Al wire in the middle and late stages of refining must be strictly avoided.

The fourth step involves strictly controlling the stopper curve of the continuous casting process: and the casting blank with the stopper rod curve suddenly rising to exceed 5mm is subjected to waste judgment treatment, so that the enriched inclusions on the stopper rod are prevented from falling into molten steel to pollute the molten steel.

For the control of the stopper rod curve, after a large number of tests and adjustments, the fact that the stopper rod curve suddenly rises to a casting blank with the thickness exceeding 5mm, inclusions on the stopper rod enter molten steel and cannot be removed, large-size inclusions are generated, and the gear is easy to lose efficacy is found. Therefore, the casting blank exceeding 5mm is cut and judged to be waste, so that the quality risk is reduced, and the fatigue life of the gear is prolonged.

Preferably, the first step further comprises: end point tapping control target: more than or equal to 0.10 percent of C, less than or equal to 0.015 percent of P, and beginning to alloy after about 90 seconds after tapping, wherein the adding amount of the aluminum-iron alloy is controlled to be 100 plus or minus 10 kg; the tapping temperature is ensured to be more than or equal to 1610 ℃.

Preferably, the second step further comprises: the alkalinity of the slag is controlled to be 2.0-3.0, and the flow of Ar gas is well controlled, so that slag entrapment caused by severe rolling of molten steel is prevented.

Preferably, the third step further comprises: and after the molten steel is subjected to vacuum treatment for 5min, adding a small amount of ferrotitanium for nitrogen fixation, keeping the vacuum degree below 0.266kPa for more than or equal to 15min, and being beneficial to reducing large-particle inclusions, in order to ensure that the nitrogen is stable and controllable, nitrogen increasing is carried out in the whole vacuum treatment process by blowing nitrogen gas, nitrogen increasing is carried out by feeding a nitrogen-chromium line after the vacuum treatment is finished, calcium treatment is forbidden after the vacuum treatment is finished, the water gap is prevented from being blocked by formed Ca and Al composite inclusions, and argon blowing is carried out for more.

Preferably, the fourth step further comprises: in the continuous casting process, the whole-process protective pouring is carried out on the molten steel by using the measures of argon sealing of a large ladle long nozzle, immersion of a middle ladle nozzle, covering agent of a middle ladle and mold powder, and the superheat degree of the molten steel pouring is controlled according to the production at 15-30 ℃, so that the steady-state casting production of the molten steel at constant temperature and constant pulling speed is ensured.

Effects of the invention

(1) The invention can realize large-scale production continuous casting mainly by controlling the contents of Al and N and the Al/N ratio in steel and combining a deoxidation process in steel making and a stopper curve control process in continuous casting, does not need to carry out an additional treatment process before high-temperature carburization, does not need to strictly control the steel structure before carburization, and greatly simplifies the process flow.

(2) The steel components can ensure that enough Al (C, N) and AlN pinning crystal boundaries are formed, the austenite crystal boundaries are refined, the growth of the austenite crystal boundaries is inhibited, and the contradiction that the continuous casting cannot be carried out due to high Al content and easy nodulation at a molten steel outlet is solved; the carburizing steel does not contain Nb, V, Ti, Ni, Cu, B and other alloy elements, so that the production cost is greatly reduced.

(3) In the steel, the grades of B-type coarse inclusion, B-type fine inclusion and Ds inclusion containing Al are below 0.5, simulated carburization is carried out for 2-6h at the temperature of 1000-1030 ℃, no mixed crystal appears, and the fatigue life of the carburized steel can be effectively ensured after the carburized steel is applied to parts such as gears and the like; in addition, the steel contains low Si content, and can effectively reduce the oxidation in the grain boundary in the subsequent heat treatment process.

Drawings

FIG. 1a is a structural metallographic picture of the high-temperature carburized steel of example 2 after carburization at 1020 ℃ for 3 hours.

FIG. 1b is a structural metallographic picture of the high-temperature carburized steel of example 3 after carburization at 1010 ℃ for 6 hours.

FIG. 2 is a structural metallographic picture of a carburized steel of comparative example 2 after carburization at 1030 ℃ for 6 hours.

Detailed Description

The present inventors have recognized that the conventional carburized steel has problems in that the cost of steel is increased if alloying elements such as Nb, V, and Ti are added to the steel, and that excessive Nb easily causes cracks in the cast slab, and that large-scale production has not been achieved at present. When steel with high Al and N contents is adopted, the problem of nozzle blockage of the continuous casting tundish is easily caused. Therefore, it is necessary to design the components of the steel and the smelting and casting process reasonably, so as to reduce the cost of the steel, ensure that the steel has enough precipitation phase to inhibit the growth of crystal grains, and avoid new problems such as the blockage of a molten steel outlet caused by component adjustment.

Chemical composition design (mass percent) of steel for high-temperature carburizing

C：0.16-0.20％

C is an essential component for ensuring the service strength of the gear steel. The steel for gears requires sufficient core impact toughness in addition to surface strength, and C is one of the most important elements affecting hardenability of the steel. The C content is too low, the strength of the gear steel is not enough, the requirement of good hardenability cannot be guaranteed, and the requirement of the toughness of the gear core cannot be met too high. Therefore, the present invention determines the C content to be 0.16 to 0.20%, and more preferably, the C content is 0.16 to 0.19%.

Si：≤0.04％

Si is soluble in ferrite and austenite to increase the hardness and strength of the steel, but too high a Si content tends to worsen the tendency of the steel to oxidize at grain boundaries in subsequent heat treatments. Therefore, the silicon content in the steel of the present invention is strictly controlled to 0.04% or less, and more preferably, the Si content is 0.03 to 0.04%.

Mn：0.75-0.90％

Mn is an effective element for deoxidation and desulfurization, and is also one of the elements that affect the hardenability of steel. The addition of the catalyst during smelting can play roles in deoxidation and desulfurization. When the Mn content is less than 0.75%, the deoxidation and desulfurization effects are small, and when the Mn content is more than 0.9%, the hardenability is not well controlled, and meanwhile, the thermoplasticity is poor, so that the production is influenced. Meanwhile, Mn can be dissolved in ferrite to play a role in solid solution strengthening, and can partially replace alloy elements such as Cr, Ni and the like. Accordingly, the present invention determines the Mn content to be 0.75 to 0.90%, and more preferably, the Mn content is 0.80 to 0.90%.

Cr：1.15-1.25％

Cr can increase hardenability in steel, improve the wear resistance of a carburized layer and improve the mechanical property of the steel. In addition, Cr can stabilize the heat treatment process of the steel and obtain good carburization performance. Too low Cr content can not ensure the hardenability of the carburizing steel, too high Cr content and increased steel cost. Therefore, the present invention determines the content of Cr to be 1.15 to 1.25%, and more preferably, the content of Cr to be 1.18 to 1.22%.

Mo：0.20-0.30％

The performance of Mo in steel is similar to that of Cr, so that the hardenability can be increased, the wear resistance of a carburized layer can be improved, and the mechanical property, particularly the toughness effect, of the steel can be improved. In addition, Mo can improve the wear resistance and the carburizing performance, the content of Mo is too low, the hardenability of carburizing steel cannot be ensured, the content of Mo is too high, and the cost of steel is increased. Therefore, the present invention determines the content of Mo to be 0.2 to 0.3%, more preferably, the content of Mo is 0.22 to 0.26%.

Al：0.040-0.050％

Besides reducing the oxygen content in the steel, the aluminum can form dispersed and fine aluminum nitride with nitrogen, so that the aluminum has the effect of refining grains, has a strong solid solution strengthening effect, and can improve the tempering resistance and the high-temperature strength of the steel. In the present invention, the Al content has an important influence on the structural properties of the steel material, and in order to form sufficiently dispersed and fine aluminum nitride with nitrogen and to perform the function of refining crystal grains, the Al content must be 0.040% or more. Meanwhile, in order to avoid the problem that the Al content is too high to cause the clogging of a molten steel outlet, the Al content needs to be controlled below 0.050%. More preferably, the Al content is controlled to 0.040-0.048%.

N：0.0120-0.0180％

N mainly reacts with Al in the steel to generate AlN fine pinning particles, and in order to enable AlN to play the best pinning effect and avoid nodulation and the influence of the overlarge AlN particle size on the quality of steel, the contents of Al and N need to be strictly controlled. In order to generate sufficient AlN particles, the nitrogen content is controlled to be 0.0120% or more, and at the same time, the nitrogen content is too high, so that the steel quality is affected by the formation of subcutaneous bubbles, and therefore, the nitrogen content is controlled to be 0.0180% or less. More preferably, the N content is controlled to 0.0130-0.0170%.

Al/N：2.0-4.0

Based on the Al and N contents, the Al/N content is optimized, and is different from the prior patent technology only focusing on the Al/N ratio, the Al/N ratio of the invention needs to be matched with a reasonable steelmaking and continuous casting process, the Al/N content is reasonably adjusted, sufficient Al (C, N) and AlN pinning crystal boundaries are ensured to be formed, the austenite crystal boundaries are refined, and the austenite crystal grain growth is inhibited. After a large number of process parameter adjustments, the Al/N range in the steel of the invention is determined to be 2.0-4.0. More preferably, the Al/N ratio ranges from 2.5 to 3.5.

P：≤0.025％

The segregation and enrichment of phosphorus in the steel with low inclusion content are more obvious in the grain boundary. P not only promotes the formation of liquated carbides, but also promotes the precipitation of secondary carbides during austenitization. Efforts are made to reduce P in steel. The phosphorus content in the steel is controlled below 0.025%. More preferably, the P content is 0.018% or less.

S：0.015-0.025％

S is generally an impurity element in steel, and increases the brittleness of steel. Therefore, the S content is controlled to be less than 0.025%, but a certain S content can improve the workability of the steel, which is advantageous for the working of some steel parts such as gears, and the like, and thus the S content is controlled to be more than 0.015%. More preferably, the S content is 0.015-0.022%.

O：≤0.0010％

O is an impurity gas element in steel, and the higher the content of O, the more the oxide inclusions are, the larger the size of the oxide inclusions is, the serious segregation is, the higher the inclusion level is, and the damage to the comprehensive performance of steel is aggravated. Therefore, efforts are made to reduce O in steel. The O content in the steel is controlled to be below 0.0010 percent.

The invention relates to a method for preparing high-temperature carburizing steel

A preparation method of high-temperature carburized gear steel and a manufacturing method for ensuring that the content of brittle Al-containing B-type impurities is small and improving the service fatigue life of a gear are provided, wherein the manufacturing method comprises the following steps:

the first step is as follows: smelting in a converter, and tapping at the end point to control the target: more than or equal to 0.10 percent of C, less than or equal to 0.015 percent of P, and beginning to alloy after about 90 seconds after tapping, wherein the adding amount of the aluminum-iron alloy is controlled to be 100 plus or minus 10 kg; ensuring the tapping temperature to be more than or equal to 1610 ℃;

the second step is that: and refining the LF ladle furnace, controlling the alkalinity of the furnace slag to be 2.0-3.0, and simultaneously controlling the flow of Ar gas to prevent slag entrapment caused by severe rolling of molten steel. Aluminum particles are taken as a deoxidizer and are subjected to diffusion deoxidation and comprehensive deoxidation by silicon carbide, the addition amount of the aluminum particles is 80kg +/-20 kg, sufficient aluminum wires are fed in 10 minutes in the early stage of refining, the Al content is ensured to be 0.050-0.060% for deep deoxidation, and the feeding of the Al wires is not allowed in the middle and later stages of refining.

The aluminum particles and the silicon carbide have the advantages of comprehensive deoxidation, and compared with the single deoxidation of the aluminum particles, the method can ensure more sufficient deoxidation reaction and better deoxidation effect. Feeding Al wire in the middle and later periods to cause Al to react with oxygen in steel to generate alumina inclusions, and the alumina inclusions are remained in the steel and cannot be removed, so that B-type inclusions in the molten steel are more. Therefore, feeding of Al wire in the middle and late stages of refining must be avoided.

The third step: RH vacuum degassing, adding a small amount of ferrotitanium for nitrogen fixation after vacuum treatment of molten steel for 5min, and keeping the vacuum degree below 0.266kPa for more than or equal to 15min, which is favorable for reducing large-particle inclusions. In order to ensure that the nitrogen is stable and controllable, nitrogen is increased by blowing nitrogen in the whole process in vacuum treatment, and nitrogen is increased by feeding a nitrogen chromium line after the vacuum treatment is finished. After the vacuum treatment is finished, the calcium treatment is forbidden to prevent the water gap from being blocked by Ca and Al composite impurities, and argon is blown for more than 20 min;

the fourth step: and in the continuous casting process, measures such as argon sealing of a large ladle long nozzle, immersion of a middle ladle nozzle, covering agent of a middle ladle, mold protecting slag and the like are used for carrying out whole-process protective pouring on the molten steel. The superheat degree of the molten steel casting is controlled according to the production at 15-30 ℃, and the steady-state casting production of the molten steel at constant temperature and constant drawing speed is ensured. In the continuous casting process, a stopper rod curve in the continuous casting process is strictly controlled, and the casting blank with the stopper rod curve suddenly rising to exceed 5mm is subjected to waste judgment treatment, so that enriched inclusions on the stopper rod are prevented from falling into molten steel and polluting the molten steel.

Examples

For the purpose of facilitating an understanding of the present invention, the present invention will now be described by way of examples. It should be understood by those skilled in the art that the examples are only for the understanding of the present invention and should not be construed as the specific limitations of the present invention.

The melting chemistries (wt%) of examples 1, 2, 3 and comparative examples 1, 2 were produced using the chemical composition ranges described in the present invention as shown in table 1, wherein comparative example 1 has an Al content of 0.035% relative to the examples, which is lower than the minimum Al content of 0.04% of the present invention; comparative example 2 relative to the examples, the contents of the respective components thereof, although satisfying the present invention, had an Al/N ratio of 4.2, which was higher than the highest Al/N ratio of 4 of the present invention.

According to the steelmaking continuous casting process shown in the table 2, converter smelting, LF refining, RH refining and square billet continuous casting are respectively adopted, a plurality of smelted furnace billets are heated and rolled into round steel with the specification of 30 mm-70 mm, the round steel is cooled to room temperature in a natural cooling mode after rolling, compared with the embodiment of the comparative example 1, 80m of aluminum wire is fed in the later stage of LF smelting for deoxidation, the RH vacuum deoxidation time is 16min, the requirement of the invention on the minimum 18min is not met, and the maximum rising of a stopper rod curve is 8 mm; comparative example 2 an aluminum wire of 80m was also fed to the late stage of the smelting for deoxidation, and the maximum rise of the stopper rod curve was 11 mm.

The obtained round steel was subjected to off-line chamfering and straightening, and sampled to test the round steel and evaluate non-metallic inclusions, and the results are shown in table 3.

A round steel sample simulation carburizing and quenching process comprises the following steps: carburizing at 1000, 1020 deg.c and 1030 deg.c for 2-6 hr, quenching at 860 deg.c and tempering at 200 deg.c. The austenitic grain size was evaluated according to the standard GB/T6394, the results of which are shown in Table 4.

TABLE 1 chemical composition of high temperature carburized steel (wt%)

Smelting composition	C	Si	Mn	Cr	P	S	Mo	Al	O/ppm	N/ppm	Al/N
												Example 1	0.17	0.04	0.80	1.24	0.012	0.020	0.28	0.042	7	133	3.1
Example 2	0.20	0.03	0.85	1.15	0.010	0.018	0.22	0.041	8	164	2.5
												Example 3	0.18	0.04	0.89	1.18	0.011	0.017	0.25	0.046	9	130	3.5
Comparative example 1	0.18	0.04	0.86	1.20	0.013	0.020	0.023	0.035	8	160	2.1
												Comparative example 2	0.17	0.03	0.82	1.16	0.012	0.017	0.025	0.050	7	120	4.2

TABLE 2 Steel-making continuous casting Process parameters

TABLE 3 inclusion condition of high-temperature carburized steel

From the above table, it can be seen that the steel of the embodiment of the invention has the advantages that through reasonable component content control, especially control of Al and N content and Al/N ratio, and accurate control of the process in the steel making and continuous casting processes, especially the comprehensive deoxidation of aluminum particles and silicon carbide (Al wire is not fed in the middle and later period of refining) is combined with the scrap judgment standard of the rising amplitude of a stopper curve, so that the level of brittle Al-containing B-type inclusions and large particle Ds-type inclusions in the cast steel is very low, the fatigue resistance of the steel can be improved, and the steel is especially suitable for components such as gear steel.

In the comparative example, the composition contents and the steel-making continuous casting process were not strictly controlled, and the grade of the brittle Al-containing inclusions, B-type (coarse-type and fine-type) large-particle inclusions Ds, was lower than that of the examples, although the grades of the A-type inclusions, C-type inclusions and D-type inclusions were similar to those of the examples in the steel structure after casting. It can be seen that Al and N in the steel material of the comparative example were not sufficiently formed into fine particles to cause formation of coarse inclusions, which deteriorated the mechanical properties of the steel material, and the formed type B inclusions were likely to form nodules at the tap hole to block the outflow of molten steel, thereby failing to allow continuous casting.

TABLE 4 grain size of simulated high-temperature carburized steel

Further, a part of the steel sample after high temperature carburization is selected, and the gold phase diagram of the structure is observed, and the result is shown in fig. 1-2, wherein, fig. 1(a) is the gold phase diagram of the structure of the high temperature carburized steel of the example 2 after carburization for 3 hours at 1020 ℃; FIG. 1b is a structural metallographic picture of the high temperature carburized steel of example 3 after carburization at 1010 ℃ for 6 hours; FIG. 2 is a structural gold phase diagram of the carburized steel of comparative example 2 after carburization at 1030 ℃ for 6 hours.

As can be seen from Table 4 and FIGS. 1-2, the steels of examples 1-3 were carburized at 1000, 1020 and 1030 ℃ for 2-6 hours, quenched at 860 ℃ and tempered at 200 ℃ to obtain fine and uniform grains with a grain size of 7.5 or more, and no coarse grains, i.e., no mischcrystallization; in contrast, in the steel material of the comparative example, after carburization, quenching and tempering, the crystal grain size becomes large as a whole, and coarse crystal grains (as shown in fig. 2, part of the crystal grains have a size close to 200 μm) appear, that is, the mixed crystal phenomenon appears. This shows that the steel material of the present invention can effectively prevent austenite grains from coarsening and growing abnormally by combining with simple steel-making and continuous casting processes even if carburized at a high temperature of 1000 ℃ or higher and at a high Al content, thereby producing a high-temperature carburized steel at a low cost.

The applicant states that the present invention is illustrated by the above examples to show the detailed components, organization and process flow of the invention, but the present invention is not limited to the above detailed components, organization and process flow, i.e. it is not meant to imply that the present invention must rely on the above detailed components, organization and process flow to be practiced. It should be understood by those skilled in the art that any modifications of the present invention, equivalent substitutions of the raw materials and steps of the product of the present invention, and the selection of specific modes, etc., are within the scope and disclosure of the present invention.

Claims

1. The high-temperature carburized steel is characterized by comprising the following components in percentage by weight: c: 0.16-0.20%, Si: less than or equal to 0.04 percent, Mn: 0.80-0.90%, Cr: 1.15-1.25%, Mo: 0.20-0.26%, Al: 0.040-0.050%, N: 0.0120-0.0180%, P: less than or equal to 0.025 percent, S: 0.015 to 0.025%, O: not more than 0.0010 percent, and the balance of Fe and inevitable impurities, wherein the Al/N ratio is controlled to be 2.0-4.0, and the carburizing temperature of the high-temperature carburizing steel is more than 1000 ℃.

2. The high temperature carburized steel of claim 1 further characterized by the following composition in weight percent: mo: 0.22-0.26%, N: 0.0130-0.0170% and Al/N ratio is controlled to be 2.5-3.5.

3. A high temperature carburized steel according to claim 1, characterized in that the Al-containing brittle B-type inclusions in said high temperature carburized steel are rated at 0.5 or less and the Ds-type inclusions are rated at 0.5 or less.

4. The high temperature carburized steel according to claim 1, characterized in that it has an austenite grain size of 7.5 or more after simulated high temperature carburization and no mixed grains.

5. A component produced by using the high temperature carburized steel according to any one of claims 1 to 4.

6. The member of claim 5, wherein the member is a gear.

7. A method for producing a high temperature carburized steel according to any one of claims 1 to 4, characterized by comprising the steps of: the first step is as follows: smelting in a converter; the second step is that: refining in an LF ladle furnace; the third step: RH vacuum degassing; the fourth step: continuous casting; wherein the second step comprises a deoxidation process: aluminum particles are taken as a deoxidizing agent and are subjected to diffusion deoxidation and comprehensive deoxidation by silicon carbide, the addition amount of the aluminum particles is 80kg +/-20 kg, sufficient aluminum wires are fed in 10 minutes in the early stage of refining, the Al content is ensured to be 0.050-0.060% for deep deoxidation, and the feeding of the Al wires is not allowed in the middle and later stages of refining; the fourth step involves strictly controlling the stopper curve of the continuous casting process: and the casting blank with the stopper rod curve suddenly rising to exceed 5mm is subjected to waste judgment treatment, so that the enriched inclusions on the stopper rod are prevented from falling into molten steel to pollute the molten steel.

8. The method of claim 7, wherein the first step further comprises: end point tapping control target: more than or equal to 0.10 percent of C, less than or equal to 0.015 percent of P, and beginning to alloy 90 seconds after tapping, wherein the adding amount of the aluminum-iron alloy is controlled to be 100 plus or minus 10 kg; the tapping temperature is ensured to be more than or equal to 1610 ℃.

9. The method of claim 7, wherein the second step further comprises: the alkalinity of the slag is controlled to be 2.0-3.0, and the flow of Ar gas is well controlled, so that slag entrapment caused by severe rolling of molten steel is prevented.

10. The method of claim 7, wherein the third step further comprises: and after the molten steel is subjected to vacuum treatment for 5min, adding a small amount of ferrotitanium for nitrogen fixation, keeping the vacuum degree below 0.266kPa for more than or equal to 15min, and being beneficial to reducing large-particle inclusions, in order to ensure that the nitrogen is stable and controllable, nitrogen increasing is carried out in the whole vacuum treatment process by blowing nitrogen gas, nitrogen increasing is carried out by feeding a nitrogen-chromium line after the vacuum treatment is finished, calcium treatment is forbidden after the vacuum treatment is finished, the water gap is prevented from being blocked by formed Ca and Al composite inclusions, and argon blowing is carried out for more.

11. The method of claim 7, wherein the fourth step further comprises: in the continuous casting process, the whole-process protective pouring is carried out on the molten steel by using the measures of argon sealing of a large ladle long nozzle, immersion of a middle ladle nozzle, covering agent of a middle ladle and mold powder, and the superheat degree of the molten steel pouring is controlled according to the production at 15-30 ℃, so that the steady-state casting production of the molten steel at constant temperature and constant pulling speed is ensured.