AU2015281542B2 - Carburized alloy steel, method for preparing same, and use thereof - Google Patents
Carburized alloy steel, method for preparing same, and use thereof Download PDFInfo
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Abstract
A carburized alloy steel and a method for preparing same. The elements of the alloy are present in the following mass percentages: C: 0.15%-0.25%, Si: ≤0.30%, Mn: 0.30%-1.20%, P: ≤ 0.015%, S: ≤ 0.010%, Cr: 0.30%-1.50%, Ni: 2.80%-3.80%, Mo: 0.30%-1.00%, Al: 0.01%-0.08%, and at least one of V: 0.05%-0.15% and Nb: 0.025%-0.10%, the remainder being Fe and unavoidable impurities; and the mass percentage content of V, Nb and Al satisfies V+Nb+Al≤0.30%. The carburized alloy steel is obtained by means of smelting, blank casting, normalizing/tempering treatment, and quenching/tempering treatment. The quenching treatment involves increasing the temperature of a blank to 800°C-860°C, maintaining the temperature for 0.8h-1.5h, then placing into a rapid quench oil to cool to the temperature of the rapid quench oil.
Description
CARBURIZED ALLOY STEEL, METHOD OF PREPARING THE SAME AND
APPLICATION OF THE SAME
FIELD OF THE INVENTION [0001] The invention relates to alloy steel, and in particular to a carburized alloy steel 5 which is at least adapted to manufacture a heavy load gear, and pertains to the field of iron-based alloy.
BACKGROUND [0002] There are various types of carburized steels available in the world, but high grade carburized steels having high performances are not commonly seen. Carburized steels for 10 heavy load gear must have excellent hardenability, finer grain size, smaller internal oxidation, high fatigue property and good synthetically mechanical properties.
[0003] Currently in our country, locomotive gears which bear an axle load of 25 tons or above, high power wind power generation gears and high power mining machinery gears typically use high-grade high quality carburized steels which have material codes 15 20Cr2Ni4, 18Cr2Ni4W, 17Cr2Ni2Mo, etc. In these existing carburized steels for heavy load gears, the compositions thereof do not very reasonably match, and the synthetically mechanical properties are not very ideal, meaning that there are many shortcomings. For example, 17Cr2Ni2Mo, while having an excellent processing property, has a lower yield strength, and the hardenability thereof is deteriorated as compared to 20Cr2Ni4 and 20 18Cr2Ni4W; 18Cr2Ni4W, while having excellent hardenability and high strength, has a poor processing property, and due to a higher content of Ni element therein, has a higher production cost and a poor economical efficiency; and 20Cr2Ni4 has a better synthetically property and economical efficiency, but the hardenability thereof is not satisfactory, and the internal oxidation is large.
[0004] Chinese patent document CN1851024A (application No. 200510018605.4) discloses heavy load gear steel, and the weight percentages of the chemical compositions thereof are: C 0.14-0.20, Mn 1.2-1.60, Si<0.12, <0.03, S 0.015-0.04, Cr 1.30-1.80, W<0.05, Ti 0.04-0.10, 0<20ppm, and the residuals are Fe and other impurities.
2015281542 18 Feb 2019 [0005] Chinese patent document CN101397631A (application No. 200710153141.7) discloses a surface carburized steel which has a low deformation resistance and high limit compression ratio at low temperatures and thus has excellent cold forging property and smaller carburizing deformation; it is a surface carburized steel which has excellent cold 5 forging characteristic and low carburizing deformation characteristic, characterized by containing (by mass percentage): C: 0.07-0.3%, Si: 0.01-0.15%, Mn: 0.1-0.7%, P: below 0.03%, S: 0.002-0.10%, Al: 0.01-0.08%, Cr: 0.7~1.5%, Ti: 0.01-0.15%, B: 0.0005-0.005%, N: below 0.008%; residuals: Fe and unavoidable impurities; above 65% of the metallic components thereof are in ferritic phase, and bainitic phase is below 15%.
[0006] Alloys such as Mn, Cr, Ti or the like are added into the two carburized steels disclosed in the two above Chinese patents, but the alloy compositions such as Mn, Cr, Ti or the like, while increasing the strength of material, lead to significant reduction in plasticity and ductility of the material. In particular, for Ti element, although it can make grains finer and improve the strength, the addition of Ti element will make it extremely 15 easy to cause a reduction of fatigue life of gears.
[0007] Chinese patent document CN102080188A (application No. 201010603965.1) discloses a CrNiMo series free-cutting gear steel and a method of preparing the same, and the weight percentages of the chemical compositions thereof are: C 0.17-0.23, Si 0.15-0.37, Mn 0.60-0.95, Cr 0.35-0.65, Ni 0.35-0.75, Mo 0.15-0.25, P<0.030, S 20 0.010-0.040, Al 0.005-0.050, Ca/S 0.3-0.6, and the residual are Fe and micro impurities.
The preparation method comprises initial smelting furnace (electric furnace or converter furnace) smelting, LF+VD (or RH) secondary refining, continuous casting and rolling, characterized in that: the secondary refining and vacuum degassing are applied so that the oxygen content in the steel is no larger than 15 x IO'6; and the content of microelement S is 25 controlled so as to improving the cutting property of the CrNiMo series gear steel so that the alloy steel is suitable for high speed cutting machining and for important precision pieces. The contents of Ni element and Mo element in the gear steel are low and the synthetical property thereof is poor, thus making it not be able to meet requirements of heavy load gears.
[0008] Therefore, in order to meet performance requirements of heavy load gears such as locomotive gears which bear an axle load of 25 tons or above, high power wind power
2015281542 18 Feb 2019 generation gears and high power mining machinery gears, developing a high-performance carburized alloy steel seems to be very imminent.
[0008a] Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of common general knowledge in the field.
SUMMARY OF THE INVENTION [0008b] It is an object of the present invention to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative.
[0009] One object of a preferred embodiment of the invention is to optimize characteristics of carburized alloy steel in terms of hardenability, yield ratio, internal oxidation, and high temperature resistance of grain growth, etc.
[0010] Another object of a preferred embodiment of the invention is to improve anti-fatigue property and synthetical mechanical properties of carburized alloy steel.
[0011] In order to address one or more of the above or other objects, the invention 15 provides the following technical solutions.
[0011a] Unless the context clearly requires otherwise, throughout the description and the claims, the words “comprise”, “comprising”, and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of “including, but not limited to”.
[0012] According to an aspect of the invention, a carburized alloy steel is provided, of which the compositions and mass percentages thereof are: C: 0.15%~0.25%, Si: <0.30%, Mn: 0.30%~1.20%, Cr: 0.30%~1.50%, Ni: 3.05%~ 3.80%, Mo: 0.30%~1.00%, Al: 0.01%~0.08%, at least one of V and Nb, and residuals: Fe and unavoidable impurities; and when the alloy steel contains V, the mass percentage of V is 0.05%~0.15%, and when the alloy steel contains Nb, the mass percentage of Nb is 0.025%~0.10%, and the mass percentages ofV, Nb and Al satisfy that V+Nb+Al<0.30%.
[0013] Further, the mass percentage of Al in the above alloy steel can be 0.02%~0.05%, and the mass percentages of V, Nb and Al satisfy that V+Nb+Al<0.20%.
[0014] Further, the mass percentage of C in the above alloy steel is 0.15%~0.23%, and
2015281542 18 Feb 2019 the mass percentage of Si is < 0.25%.
[0015] Further, the mass percentage of Mn in the above alloy steel is 0.40%~1.00%, and the mass percentage of Cr is 0.40%~1.20%.
[0016] Further, the mass percentage of Ni in the above alloy steel is 3.00%~3.80%, and 5 the mass percentage of Mo is 0.40%~0.80%.
[0017] Further, the impurities in the alloy steel comprise P and S elements, wherein the mass percentage of P is <0.015%, and the mass percentage of S is <0.010%.
[0018] Further, the impurities in the alloy steel further comprise N, O and H elements, wherein the mass percentage of N is <0.02%, the mass percentage of O is <0.002%, and 10 the mass percentage of H is <0.0002% [0019] Preferably, the mass percentage of N is <0.01%.
[0020] According to another aspect of the invention, a method of preparing the above described carburized alloy steel is provided, comprising the following steps:
[0021] A. batching raw materials according to the compositions of the alloy steel and 15 their contents, and performing alloy smelting using existing smelting and refining processes;
[0022] B. casting a steel ingot and rolling the steel ingot into a workblank;
[0023] C. performing normalizing and tempering processing; and [0024] D. performing quenching and tempering processing, wherein the quenching and 20 tempering processing is to raise the temperature of the workblank to 800°C~860°C and keep that temperature for 0.8h~1.5h, after which the workblank is put into fast quenching oil so as to be cooled to an operational temperature of the fast quenching oil, and then the workblank is taken out for tempering processing again.
[0025] Further, the above normalizing and tempering processing is to raise the 25 temperature of the workblank to 900°C~960°C and keep that temperature for 0.8h~1.5h, after which the workblank is air-cooled to room temperature, and then the temperature of the workblank is raised to 630°C~750°C; and after that temperature is kept for 0.8h~1.5h, the workblank is air-cooled to room temperature.
[0026] Further, in the above quenching and tempering processing, the temperature of the
2015281542 18 Feb 2019 workblank is raised to 160°C~220°C during tempering, and after that temperature is kept for 2.5h~3.5h, the workblank is air-cooled to room temperature.
[0027] Further, in the smelting and refining processes of step A, an electric furnace is used to perform smelting, and a ladle refining furnace and a vacuum degassing furnace are 5 used to perform refining.
[0028] Further, in the above step D, the operational temperature of the fast quenching oil is 40°C~100°C.
[0029] According to still another aspect of the invention, the application of the above carburized alloy steel is to manufacture heavy load gears.
[0030] A detailed description is given below as to the functions of the elements contained in the carburized alloy steels of the embodiments of the invention as well as preferred contents thereof (the range of mass percentages):
[0031] C: which is a main solid solution strengthening element; in order to ensure a sufficient strength, the content of C has to be above 0.15%; however, when the content of 15 C exceeds 0.25%, the strength will become extremely high and the ductility will degrade significantly; therefore, the content of C in the alloy steel of the invention is controlled to be in the range of 0.15%~0.25%, and preferably 0.15%~0.23%;
[0032] Si: which is a deoxidizer; in order to improve internal oxidation resistance, the content of Si in the alloy steel of the invention is controlled to be below 0.30%, and in 20 order to ensure the deoxidizing effect and certain yield strength, the content is further preferably below 0.25%.
[0033] Mn: which is good deoxidizer and desulfurizer, and simultaneously can improve the hardenability and heat processing property of steel; however, an excessive content of Mn will reduce the ductility of carburized layer; therefore, the content of Mn in the alloy 25 steel of the invention is controlled to be 0.30%~1.20%, and further preferably
0.40%~1.00%;
[0034] P: which is prone to form micro-segregation during the molten steel solidification process and is then aggregated to grain boundaries during the austenization process so that the brittleness of steel is significantly increased; therefore, the content of P in the alloy 30 steel of the invention is controlled to be below 0.015%;
2015281542 18 Feb 2019 [0035] S : which is an unavoidable impurity element, and forms MnS inclusion with Mn, which inclusion will decrease the ductility of steel when the grain boundary has a micro-segregation; therefore, the content of S in the alloy steel of the invention is controlled to be below 0.010%;
[0036] Cr: which is a main hardenability element and can improve the strength, hardness and wearability of steel; however, an excessive content of Cr will degrade the cold processing performance of steel; therefore, the content of Cr in the alloy steel of the invention is controlled to be 0.30%~1.50%, and further preferably 0.40%~1.20%;
[0037] Ni: which is a main solid solution strengthening element; with the increase of Ni content, a normal temperature strength of steel is also increased, and the addition of Ni does not have much influence on the plasticity and ductility of the alloy; however, an excessive content of Ni will degrade the heat processing performance of steel and lead to an overly high cost; therefore, the content of Ni in the alloy steel of the invention is controlled to be 2.80%~3.80%, and further preferably 3.00%~3.80%;
[0038] Mo: which is a main hardenability element and can improve the hardenability of matrix and carburized layer simultaneously; however, an excessive content of Mo will lead to a degradation of forging property and to an overly high cost; therefore, the content of Mo in the alloy steel of the invention is controlled to be 0.30%~1.00%, and further preferably 0.40%~0.80%;
[0039] Al, Nb, V: Al is deoxidizer and grain refining element; when the content of Al is below 0.01%, the effect of grain refining is not obvious, but when the content of Al is above 0.08%, the improvement in deoxidizing effect is also not obvious, and larger inclusions are easily formed, thus affecting fatigue characteristic; therefore, the content of Al in the alloy steel of the invention is controlled to be 0.01%~0.08%, and further preferably 0.02%~0.05%; Nb is grain refining element; when the content of Nb is below 0.025%, the effect of grain refining is not obvious, and when the content of Nb is above 0.10%, the effect of refining grains is saturated, and the amplitude of increase is also not obvious; therefore, the content of Nb in the alloy steel of the invention is controlled to be 0.025%~0.10%; V is grain refining element; when the content of V is below 0.05%, the effect of grain refining is not obvious, and when the content of V is above 0.15%, the effect of refining grains is saturated, and the amplitude of increase is also not obvious; therefore,
2015281542 18 Feb 2019 the content of V in the alloy steel of the invention is controlled to be 0.05%~0.15%. Meanwhile, when Al, V and Nb are added in combination, V+Nb+Al<0.30% must be satisfied, which can be further optimized as V+Nb+Al<0.20%. This is because a reasonable control over an addition amount of combined Al, V and Nb can indirectly affect 5 the ductility of alloy by refining grain size; when V+Nb+Al>0.30%, the effect of refining grain size is not obvious, and a larger grain size will have an adverse influence on the ductility of alloy; and when V+Nb+Al<0.20%, the effect of refining grain size is better, and the ductility of alloy reaches the best;
[0040] N: which is an unavoidable gas element during smelting, and can form a 10 compound with Al, Nb and V, thus refining grains; however, an overly high content of N will cause aggregation to grain boundaries and reduce grain boundary strength; therefore, the content of N in the alloy steel of the invention is controlled to be <0.02%, and further preferably <0.01%;
[0041] O: which is a harmful gas element, and will degrade the fatigue performance 15 when the content is overly high; therefore, the content of O in the alloy steel of the invention is controlled to be <20ppm;
[0042] H: which is a harmful gas element, and will degrade the ductility when the content is overly high; therefore, the content of H in the alloy steel of the invention is controlled to be <2.0ppm.
[0043] The invention has the following advantageous effects:
[0044] (1): through a reasonable ratio of Mn, Cr, Ni, Mo and C in the carburized alloy steel of the invention, when ensuring an increase of steel strength of the material, it can be also ensured that the plasticity and ductility of the material considerably unaffected, thus avoiding a phenomenon that the plasticity and ductility of the material are significantly 25 reduced during to an increase of strength. The resulting carburized alloy steel material has excellent synthetical mechanical performances, and obviously overcomes the contradiction that the strength, plasticity and ductility cannot be taken care of simultaneously due to unreasonable proportions of various compositions in the carburized alloy steel in the prior art. In addition, the hardenability of carburized alloy steel is also effectively improved, thus 30 enabling the steel to be suitable for large module gears;
2015281542 18 Feb 2019 [0045] (2) through addition of Al, V, Nb or a combined addition of these elements, the carburized alloy steel of the invention enables the alloy to have excellent anti-grain growth characteristic during formation, which is especially suitable for high temperature carburized pieces;
[0046] (3) through an optimized match of Si, Ni and Mo, the carburized alloy steel of the invention can reduce internal oxidation at grain boundaries during carburizing, and the internal oxidation characteristics have lower internal oxidation depth values than conventional steels during a long time period of carburizing, thus making the carburized alloy steel of the invention especially suitable for mechanical elements which have high requirements on internal oxidation;
[0047] (4) through a reasonable choosing and proportion of Cr, Ni and Mo, the carburized alloy steel of the invention enables the steel material to be easily produced and the processing characteristic to be excellent, and the production cost is relatively low, which is advantageous for improving economic effects;
[0048] (5) the carburized alloy steel of the invention has very little internal oxidation, high hardenability, high yield ratio and anti-high temperature grain growth characteristic, etc., thus making it especially suitable for manufacturing mechanical elements which have very high requirements on anti-fatigue performance and synthetical mechanical performances, such as heavy load gears, etc.
BRIEF DESCRIPTION OF THE DRAWINGS [0049] Fig. 1 is a comparison diagram of hardenability between the carburized alloy steel of the first embodiment of the invention and the carburized alloy steel of 20Cr2Ni4, 18Cr2Ni4 and 17Cr2Ni2Mo;
[0050] Fig. 2 is a comparison diagram of hardenability of the carburized alloy steel among the first to seventh embodiments of the invention;
[0051] Fig. 3 is a diagram showing the relationship between internal oxidation depth and carburized layer depth of the carburized alloy of 17Cr2Ni2Mo in the first comparison example, wherein three samples are given;
[0052] Fig. 4 is a diagram showing the relationship between internal oxidation depth and
2015281542 18 Feb 2019 carburized layer depth of the carburized alloy of the first embodiment of the invention, wherein three samples are given; at a carburized layer depth of about 0.5mm, the value of oxidation depth of sample No.2 substantially overlaps with the value of oxidation depth of sample No.3, both of which are about 0.002mm; at a carburized layer depth of about 5 1.25mm, the value of oxidation depth of sample No.l substantially overlaps with the value of oxidation depth of sample No.2, both of which are about 0.002mm; at a carburized layer depth of about 1.8mm, the value of oxidation depth of sample No.l substantially overlaps with the value of oxidation depth of sample No.3, both of which are about 0.002mm; at a carburized layer depth of about 2.5mm, the value of oxidation depth of sample No.2 10 substantially overlaps with the value of oxidation depth of sample No.3, both of which are about 0.002mm; and at a carburized layer depth of about 3.25mm, the value of oxidation depth of sample No.2 substantially overlaps with the value of oxidation depth of sample No. 3, both of which are about 0.002mm.
[0053] Fig. 5 is a diagram and a data table showing the relationship of internal oxidation 15 depth and carburized layer depth of the carburized alloy steel among the first to seventh embodiments of the invention;
[0054] Fig. 6 is a diagram showing the relationship of grain size and heating temperature of the carburized alloy steel of the first embodiment.
DETAIFED DESCRIPTION OF THE INVENTION [0055] The embodiments of the above described carburized alloy steels and methods of preparing them will be described in detail below, and these embodiments are essentially used for illustrating the invention rather than limiting the scope of the invention.
[0056] The first embodiment:
[0057] The compositions of the carburized alloy steel of this embodiment and mass 25 percentages thereof are: C: 0.18%, Si: 0.16%, Mn: 0.69%, P: 0.009%, S: 0.005%, Cr:
1.00%, Ni: 3.55%, Mo: 0.62%, Al: 0.04%, V: 0.05%, Nb: 0.03%, N: 0.0092%, O: 0.0019%, H: 0.00015%; and residuals: Fe and unavoidable impurities.
[0058] The method of preparing carburized alloy steel of the first embodiment comprises the following specific steps:
2015281542 18 Feb 2019 [0059] A. batching raw materials according to the compositions of the alloy steel and their contents, and performing alloy smelting in a refining process using conventional electric furnace, ladle refining furnace (LF) and vacuum degassing furnace;
[0060] B. casting a steel ingot and rolling the steel ingot into a round steel, and taking a sample workblank from the round steel in accordance with national standard GB/T2975-1998 “Steel and steel products-location and preparation of test pieces for mechanical testing”;
[0061] C. performing normalizing and tempering processing on the sample workblank: firstly, the workblank is heated to 950°C and that temperature is kept for lh, after which 10 the workblank is air-cooled to room temperature by a blower; and then the workblank is heated to 750°C and that temperature is kept for lh, after which the workblank is air-cooled to room temperature by the blower;
[0062] D. performing quenching and tempering processing on the sample workblank: firstly, the workblank is heated to 860°C and that temperature is kept for lh, after which 15 the workblank is put into a fast quenching oil so as to be cooled to an operational temperature of the fast quenching oil, which is controlled at 60±5°C; and then the workblank is taken out and heated to 220°C, and after that temperature is kept for 3h, the workblank is air-cooled to room temperature by the blower.
[0063] The second embodiment:
[0064] The compositions of the carburized alloy steel of this embodiment and mass percentages thereof are: C: 0.15%, Si: 0.20%, Mn: 0.95%, P: 0.008%, S: 0.006%, Cr: 1.20%, Ni: 3.75%, Mo: 0.41%, Al: 0.08%, V: 0.12%, N: 0.0080%, O: 0.0016%, H: 0.00016%; and residuals: Fe and unavoidable impurities.
[0065] The method of preparing carburized alloy steel of the second embodiment comprises the following specific steps:
[0066] A. batching raw materials according to the compositions of the alloy steel and their contents, and performing alloy smelting in a refining process using conventional electric furnace, ladle refining furnace (LF) and vacuum degassing furnace;
[0067] B. casting a steel ingot and rolling the steel ingot into a round steel, and taking a 30 sample workblank from the round steel in accordance with national standard io
2015281542 18 Feb 2019
GB/T2975-1998;
[0068] C. performing normalizing and tempering processing on the sample workblank: firstly, the workblank is heated to 900 °C and that temperature is kept for lh, after which the workblank is air-cooled to room temperature by a blower; and then the workblank is 5 heated to 630°C and that temperature is kept for lh, after which the workblank is air-cooled to room temperature by the blower;
[0069] D. performing quenching and tempering processing on the sample workblank: firstly, the workblank is heated to 800°C and that temperature is kept for lh, after which the workblank is put into a fast quenching oil so as to be cooled to an operational 10 temperature of the fast quenching oil, which is controlled at 60±5°C; and then the workblank is taken out and heated to 160°C, and after that temperature is kept for 3h, the workblank is air-cooled to room temperature by the blower.
[0070] The third embodiment:
[0071] The compositions of the carburized alloy steel of this embodiment and mass 15 percentages thereof are: C: 0.23%, Si: 0.14%, Mn: 0.45%, P: 0.008%, S: 0.004%, Cr:
0.45%, Ni: 3.05%, Mo: 0.79%, Al: 0.02%, Nb: 0.09%, N: 0.0078%, O: 0.0012%, H: 0.00013%; and residuals: Fe and unavoidable impurities.
[0072] The method of preparing carburized alloy steel of the third embodiment comprises the following specific steps:
[0073] A. batching raw materials according to the compositions of the alloy steel and their contents, and performing alloy smelting in a refining process using conventional electric furnace, ladle refining furnace (LF) and vacuum degassing furnace;
[0074] B. casting a steel ingot and rolling the steel ingot into a round steel, and taking a sample workblank from the round steel in accordance with national standard 25 GB/T2975-1998;
[0075] C. performing normalizing and tempering processing on the sample workblank: firstly, the workblank is heated to 920°C and that temperature is kept for lh, after which the workblank is air-cooled to room temperature by a blower; and then the workblank is heated to 700°C and that temperature is kept for lh, after which the workblank is 30 air-cooled to room temperature by the blower;
2015281542 18 Feb 2019 [0076] D. performing quenching and tempering processing on the sample workblank: firstly, the workblank is heated to 840 °C and that temperature is kept for lh, after which the workblank is put into a fast quenching oil so as to be cooled to an operational temperature of the fast quenching oil, which is controlled at 60±5 °C; and then the 5 workblank is taken out and heated to 200°C, and after that temperature is kept for 3h, the workblank is air-cooled to room temperature by the blower.
[0077] The fourth embodiment:
[0078] The compositions of the carburized alloy steel of this embodiment and mass percentages thereof are: C: 0.20%, Si: 0.05%, Mn: 0.50%, P: 0.007%, S: 0.005%, Cr:
0.85%, Ni: 3.30%, Mo: 0.50%, Al: 0.02%, V: 0.10%, Nb: 0.07%, N: 0.0089%, O: 0.0018%,
H: 0.00015%; and residuals: Fe and unavoidable impurities.
[0079] The method of preparing carburized alloy steel of the fourth embodiment comprises the following specific steps:
[0080] A. batching raw materials according to the compositions of the alloy steel and their contents, and performing alloy smelting in a refining process using conventional electric furnace, ladle refining furnace (LF) and vacuum degassing furnace;
[0081] B. casting a steel ingot and rolling the steel ingot into a round steel, and taking a sample workblank from the round steel in accordance with national standard GB/T2975-1998;
[0082] C. performing normalizing and tempering processing on the sample workblank:
firstly, the workblank is heated to 930°C and that temperature is kept for lh, after which the workblank is air-cooled to room temperature by a blower; and then the workblank is heated to 680°C and that temperature is kept for lh, after which the workblank is air-cooled to room temperature by the blower;
[0083] D. performing quenching and tempering processing on the sample workblank:
firstly, the workblank is heated to 820°C and that temperature is kept for lh, after which the workblank is put into a fast quenching oil so as to be cooled to an operational temperature of the fast quenching oil, which is controlled at 60±5 °C; and then the workblank is taken out and heated to 180°C, and after that temperature is kept for 3h, the workblank is air-cooled to room temperature by the blower.
2015281542 18 Feb 2019 [0084] The fifth embodiment:
[0085] The compositions of the carburized alloy steel of this embodiment and mass percentages thereof are: C: 0.17%, Si: 0.06%, Mn: 0.73%, P: 0.006%, S: 0.005%, Cr: 1.15%, Ni: 3.52%, Mo: 0.65%, Al: 0.02%, V: 0.11%, N: 0.0065%, O: 0.0015%, H:
0.00012%; and residuals: Fe and unavoidable impurities.
[0086] The method of preparing carburized alloy steel of the fifth embodiment comprises the following specific steps:
[0087] A. batching raw materials according to the compositions of the alloy steel and their contents, and performing alloy smelting in a refining process using conventional 10 electric furnace, ladle refining furnace (LF) and vacuum degassing furnace;
[0088] B. casting a steel ingot and rolling the steel ingot into a round steel, and taking a sample workblank from the round steel in accordance with national standard GB/T2975-1998;
[0089] C. performing normalizing and tempering processing on the sample workblank:
firstly, the workblank is heated to 930 °C and that temperature is kept for lh, after which the workblank is air-cooled to room temperature by a blower; and then the workblank is heated to 680°C and that temperature is kept for lh, after which the workblank is air-cooled to room temperature by the blower;
[0090] D. performing quenching and tempering processing on the sample workblank:
firstly, the workblank is heated to 820°C and that temperature is kept for lh, after which the workblank is put into a fast quenching oil so as to be cooled to an operational temperature of the fast quenching oil, which is controlled at 60±5 °C; and then the workblank is taken out and heated to 180°C, and after that temperature is kept for 3h, the workblank is air-cooled to room temperature by the blower.
[0091] The sixth embodiment:
[0092] The compositions of the carburized alloy steel of this embodiment and mass percentages thereof are: C: 0.22%, Si: 0.08%, Mn: 0.50%, P: 0.007%, S: 0.004%, Cr: 0.76%, Ni: 3.19%, Mo: 0.74%, Al: 0.03%, Nb: 0.08%, N: 0.0072%, O: 0.0016%, H: 0.00015%; and residuals: Fe and unavoidable impurities.
[0093] The method of preparing carburized alloy steel of the sixth embodiment
2015281542 18 Feb 2019 comprises the following specific steps:
[0094] A. batching raw materials according to the compositions of the alloy steel and their contents, and performing alloy smelting in a refining process using conventional electric furnace, ladle refining furnace (LF) and vacuum degassing furnace;
[0095] B. casting a steel ingot and rolling the steel ingot into a round steel, and taking a sample workblank from the round steel in accordance with national standard GB/T2975-1998;
[0096] C. performing normalizing and tempering processing on the sample workblank: firstly, the workblank is heated to 930 °C and that temperature is kept for lh, after which 10 the workblank is air-cooled to room temperature by a blower; and then the workblank is heated to 680°C and that temperature is kept for lh, after which the workblank is air-cooled to room temperature by the blower;
[0097] D. performing quenching and tempering processing on the sample workblank: firstly, the workblank is heated to 820°C and that temperature is kept for lh, after which 15 the workblank is put into a fast quenching oil so as to be cooled to an operational temperature of the fast quenching oil, which is controlled at 60±5 °C; and then the workblank is taken out and heated to 180°C, and after that temperature is kept for 3h, the workblank is air-cooled to room temperature by the blower.
[0098] The seventh embodiment:
[0099] The compositions of the carburized alloy steel of this embodiment and mass percentages thereof are: C: 0.21%, Si: 0.25%, Mn: 0.49%, P: 0.008%, S: 0.004%, Cr: 0.53%, Ni: 3.25%, Mo: 0.66%, Al: 0.05%, V: 0.09%, Nb: 0.05%, N: 0.0069%, O: 0.0014%, H: 0.00014%; and residuals: Fe and unavoidable impurities.
[00100] The method of preparing carburized alloy steel of the seventh embodiment comprises the following specific steps:
[00101] A. batching raw materials according to the compositions of the alloy steel and their contents, and performing alloy smelting in a refining process using conventional electric furnace, ladle refining furnace (FF) and vacuum degassing furnace;
[00102] B. casting a steel ingot and rolling the steel ingot into a round steel, and taking a 30 sample workblank from the round steel in accordance with national standard
2015281542 18 Feb 2019
GB/T2975-1998;
[00103] C. performing normalizing and tempering processing on the sample workblank: firstly, the workblank is heated to 930 °C and that temperature is kept for lh, after which the workblank is air-cooled to room temperature by a blower; and then the workblank is 5 heated to 680°C and that temperature is kept for lh, after which the workblank is air-cooled to room temperature by the blower;
[00104] D. performing quenching and tempering processing on the sample workblank: firstly, the workblank is heated to 820°C and that temperature is kept for lh, after which the workblank is put into a fast quenching oil so as to be cooled to an operational 10 temperature of the fast quenching oil, which is controlled at 60±5°C; and then the workblank is taken out and heated to 180°C, and after that temperature is kept for 3h, the workblank is air-cooled to room temperature by the blower.
[00105] The first comparison example:
[00106] This comparison example uses carburized alloy steel with material code 15 17Cr2Ni2Mo, and the chemical compositions of this alloy are shown in table 1.
[00107] The method of preparing carburized alloy steel of the first comparison example comprises the following specific steps:
[00108] A. batching raw materials according to the compositions of the alloy steel and their contents, and performing alloy smelting in a conventional refining process using ladle 20 refining furnace, vacuum-oxygen decarbonizing furnace and vacuum degassing furnace;
[00109] B. casting a steel ingot and rolling the steel ingot into a round steel, and taking a sample workblank from the round steel in accordance with national standard GB/T2975 “Steel and steel products-location and preparation of test pieces for mechanical testing”;
[00110] C. performing normalizing and tempering processing on the sample workblank: 25 firstly, the workblank is heated to 920°C and that temperature is kept for lh, after which the workblank is air-cooled to normal temperature by a blower; and then the workblank is heated to 700°C and that temperature is kept for lh, after which the workblank is air-cooled to normal temperature by the blower;
[00111] D. performing quenching and tempering processing on the sample workblank: 30 firstly, the workblank is heated to 840°C and that temperature is kept for lh, after which
2015281542 18 Feb 2019 the workblank is cooled to an oil temperature of a fast quenching oil by the fast quenching oil; and then the workblank is heated to 200°C, and after that temperature is kept for 3h, the workblank is air-cooled to normal temperature by the blower.
[00112] The second comparison example:
[00113] This comparison example uses carburized alloy steel with material code
2oCr2Ni4, and the chemical compositions of this alloy are shown in table 1.
[00114] The method of preparing carburized alloy steel of the second comparison example comprises the following specific steps:
[00115] A. batching raw materials according to the compositions of the alloy steel and their contents, and performing alloy smelting in a conventional refining process using ladle refining furnace, vacuum-oxygen decarbonizing furnace and vacuum degassing furnace;
[00116] B. casting a steel ingot and rolling the steel ingot into a round steel, and taking a sample workblank from the round steel in accordance with national standard GB/T2975 “Steel and steel products-location and preparation of test pieces for mechanical testing”;
[00117] C. performing normalizing and tempering processing on the sample workblank:
firstly, the workblank is heated to 930°C and that temperature is kept for lh, after which the workblank is air-cooled to normal temperature by a blower; and then the workblank is heated to 680°C and that temperature is kept for lh, after which the workblank is air-cooled to normal temperature by the blower;
[00118] D. performing quenching and tempering processing on the sample workblank:
firstly, the workblank is heated to 820°C and that temperature is kept for lh, after which the workblank is cooled to an oil temperature of a fast quenching oil by the fast quenching oil; and then the workblank is heated to 180°C, and after that temperature is kept for 3h, the workblank is air-cooled to normal temperature by the blower.
[00119] The third comparison example:
[00120] This comparison example uses carburized alloy steel with material code 18Cr2Ni4W, and the chemical compositions of this alloy are shown in table 1.
[00121] The method of preparing carburized alloy steel of the third comparison example comprises the following specific steps:
2015281542 18 Feb 2019 [00122] A. batching raw materials according to the compositions of the alloy steel and their contents, and performing alloy smelting in a conventional refining process using ladle refining furnace, vacuum-oxygen decarbonizing furnace and vacuum degassing furnace;
[00123] B. casting a steel ingot and rolling the steel ingot into a round steel, and taking a sample workblank from the round steel in accordance with national standard GB/T2975 “Steel and steel products-location and preparation of test pieces for mechanical testing”;
[00124] C. performing normalizing and tempering processing on the sample workblank: firstly, the workblank is heated to 930 °C and that temperature is kept for lh, after which the workblank is air-cooled to normal temperature by a blower; and then the workblank is 10 heated to 680°C and that temperature is kept for lh, after which the workblank is air-cooled to normal temperature by the blower;
[00125] D. performing quenching and tempering processing on the sample workblank: firstly, the workblank is heated to 820°C and that temperature is kept for lh, after which the workblank is cooled to an oil temperature of a fast quenching oil by the fast quenching 15 oil; and then the workblank is heated to 180°C, and after that temperature is kept for 3h, the workblank is air-cooled to normal temperature by the blower.
[00126] I . Chemical compositions:
[00127] The chemical compositions of carburized alloy steels of the first to seventh embodiments of the invention and the first to third comparison examples are shown in 20 table 1.
Table 1: chemical composition table
| chemical compositions (wt%) | the first embodiment | the second embodiment | the third embodiment | the fourth embodiment | the fifth embodiment |
| C | 0.18 | 0.15 | 0.23 | 0.20 | 0.17 |
| Si | 0.16 | 0.20 | 0.14 | 0.05 | 0.06 |
| Mn | 0.69 | 0.95 | 0.45 | 0.50 | 0.73 |
| P | 0.009 | 0.008 | 0.008 | 0.007 | 0.006 |
2015281542 18 Feb 2019
| s | 0.005 | 0.006 | 0.004 | 0.005 | 0.005 |
| Cr | 1.00 | 1.20 | 0.45 | 0.85 | 1.15 |
| Ni | 3.55 | 3.75 | 3.05 | 3.30 | 3.52 |
| Mo | 0.62 | 0.41 | 0.79 | 0.5 | 0.65 |
| Al | 0.04 | 0.08 | 0.02 | 0.02 | 0.02 |
| V | 0.05 | 0.12 | - | 0.10 | 0.11 |
| Nb | 0.03 | - | 0.09 | 0.07 | - |
| W | - | - | - | - | - |
| 0 | 0.0019 | 0.0016 | 0.0012 | 0.0018 | 0.0015 |
| N | 0.0092 | 0.008 | 0.0078 | 0.0089 | 0.0065 |
| H | 0.00015 | 0.00016 | 0.00013 | 0.00015 | 0.00012 |
| chemical | the sixth | the seventh | the first | the second | the third |
| compositions | embodiment | embodiment | comparison | comparison | comparison |
| (wt%) | example | example | example | ||
| C | 0.22 | 0.21 | 0.20 | 0.21 | 0.18 |
| Si | 0.08 | 0.25 | 0.25 | 0.26 | 0.27 |
| Mn | 0.50 | 0.49 | 0.86 | 0.43 | 0.48 |
| P | 0.007 | 0.008 | 0.009 | 0.01 | 0.006 |
| S | 0.004 | 0.004 | 0.006 | 0.05 | 0.006 |
| Cr | 0.76 | 0.53 | 1.78 | 1.35 | 1.51 |
| Ni | 3.19 | 3.25 | 1.68 | 3.42 | 4.23 |
| Mo | 0.74 | 0.66 | 0.33 | - | - |
| Al | 0.03 | 0.05 | 0.05 | 0.035 | 0.03 |
| V | - | 0.09 | - | - | - |
| Nb | 0.08 | 0.05 | - | - | - |
2015281542 18 Feb 2019
| w | - | - | - | - | 0.96 |
| 0 | 0.0016 | 0.0014 | 0.0015 | 0.0018 | 0.0019 |
| N | 0.0072 | 0.0069 | 0.0079 | 0.0081 | 0.0089 |
| H | 0.00015 | 0.00014 | 0.00019 | 0.00016 | 0.00014 |
[00128] II. Mechanical properties:
[00129] The carburized alloy steels of the first to seventh embodiments of the invention and the first to third comparison examples are tested for mechanical properties in accordance with GB/T228-2010 “Tensile Testing Method for Metallic Materials at Room
Temperature”, and the results are shown in table 2, wherein Rm represents a tensile strength; Rp0.2 specifies a tensile strength at a non-proportional elongation percentage of 0.2%, i.e., reflecting a yield strength of the invention; A represents an elongation percentage after fracture; Z represents a contraction percentage of cross sectional area; KV2 represents an absorbed impact energy of V-shaped gap at a gap depth of 2mm.
[00130] As can be seen from table 2, due to a more reasonable proportion of compositions of the carburized alloy steel of the invention, the Rpo.2 (MPa) of the first to seventh embodiments are significantly increased as compared to the first to third comparison examples; at the same time of having a higher yield strength, the absorbed impact energy KV2 (J) is not decreased, and is even increased; therefore, it reflects that the alloy steels of the embodiments of the invention have higher yield ratio; moreover, other mechanical properties are not degraded; for example, the tensile strengths Rm of the first to seventh embodiments are substantially identical to or improved over those of the first to third comparison examples, and only the alloy steel of the second embodiment is slightly lower due to a higher carbon content; therefore, a better ductility is kept.
Table 2: mechanical property table
| properties | the first embodiment | the second embodiment | the third embodiment | the fourth embodiment | the fifth embodiment |
| Rm (MPa) | 1436 | 1429 | 1529 | 1450 | 1431 |
| Rp0.2 (MPa) | 1187 | 1165 | 1238 | 1198 | 1179 |
| A (%) | 13.5 | 14 | 12.5 | 13.5 | 13.5 |
2015281542 18 Feb 2019
| Z (%) | 61 | 65 | 54 | 62 | 61 |
| KV2 (J) | 80.0 | 81.0 | 73.0 | 83.0 | 81.0 |
| 79.0 | 82.0 | 72.0 | 80.0 | 81.5 | |
| 80 | 79 | 76 | 83 | 81.0 | |
| properties | the sixth embodiment | the seventh embodiment | the first comparison example | the second comparison example | the third comparison example |
| Rm (MPa) | 1501 | 1489 | 1450 | 1470 | 1420 |
| Rp0.2 (MPa) | 1219 | 1208 | 1086 | 1100 | 1093 |
| A (%) | 12.5 | 12.5 | 13 | 13.5 | 13.5 |
| Z (%) | 60 | 62 | 60 | 55 | 59 |
| KV2 (J) | 76.0 | 79.0 | 60.0 | 69.0 | 86.0 |
| 75.5 | 78.5 | 62.0 | 76.0 | 84.0 | |
| 76.0 | 78.5 | 60 | 74 | 86 |
[00131] III. Hardenability:
[00132] The hardenabilities of the carburized alloy steels of the first to seventh embodiments of the invention and the first to third comparison examples are determined in accordance with GB/T225-2006 “Steel Hardenability Test by End-quenching”.
[00133] As shown in Fig. 1, the hardenabilities of the carburized alloy steels of the invention are superior to those of the comparison examples, and AHRC (JI .5-J50) <3.
[00134] As shown in Figs. 1 and 2, in a range of 0-50mm from the end quenching, the hardness of all the first to seventh embodiments are larger than 41, and with an increase of the distance from the end quenching, the decrease of hardness becomes slower. Therefore, 10 it reflects that the carburized alloy steels of the embodiments of the invention have good hardenabilities.
[00135] IV. Internal oxidation property:
2015281542 18 Feb 2019 [00136] The internal oxidation depth and carburized layer depth of the carburized alloy steels of the first to seventh embodiments of the invention and the first comparison example are determined in accordance with GB/T25744-2010 “Metallographic Examination for Carburizing Quenching and Tempering of Steel Parts”. For each of the 5 first embodiment the first comparison example, three samples are taken at each identical carburizing condition so as to measure internal oxidation depth.
[00137] As shown in Figs. 3 and 4, at the same carburized layer depth, the internal oxidation depth in the first embodiment of the invention is much smaller than that of 17Cr2Ni2Mo, and a fluctuation of the internal oxidation depth is also small.
[00138] As shown in Fig. 5, in which corresponding oxidation depths of the carburized alloy steels of the first to seventh embodiments at carburized layer depths of 0.5mm, 1.2mm, 1.8mm, 2.5mm and 3.2mm are given, all the first to seventh embodiments have small internal oxidation depths.
[00139] Therefore, it can be seen that the carburized alloy steels of the invention is greatly 15 improved in terms of internal oxidation as compared to the carburized alloy steel of the first comparison example.
[00140] V. Grain size:
[00141] The grain size level and average grain diameter of the carburized alloy steels of the first to seventh embodiments of the invention are determined in accordance with 20 GB/T6394-2002 “Metal-methods for Estimating the Average Grain Size”.
[00142] As shown in Fig. 6, after being kept at the temperature 930 °C for 8h, the carburized alloy steel of the first embodiment of the invention has a grain size level of 9 (larger than level 5), meaning that it is essentially fine grain steel, and the grain size thereof is above level 6 within a temperature interval of 1020°C~1050°C, which means that the 25 carburized alloy steel of the invention can be carburized at a high temperature without deteriorating the properties of material. For example, at a quenching condition of 860 °C (austenite temperature) in the first embodiment, the average grain diameter is smaller than 14pm, thus exhibiting a good anti-high temperature grain growth characteristic.
[00143] Table 3 below further shows the grain sizes of the carburized alloy steels of the 30 first to seventh embodiments.
2015281542 18 Feb 2019
Table 3: Grain Sizes
| the first embodiment | the second embodiment | the third embodiment | the fourth embodiment | the fifth embodiment | the sixth embodiment | the seventh embodiment | |
| Temperature | average | average | average | average | average | average | average |
| CC) | grain | grain | grain | grain | grain | grain | grain |
| diameter | diameter | diameter | diameter | diameter | diameter | diameter | |
| (pm) | (pm) | (pm) | (pm) | (pm) | (pm) | (pm) | |
| 930 | 14 | 15 | 19 | 20 | 17 | 16 | 19 |
| 950 | 19 | 18 | 20 | 20 | 19 | 18 | 21 |
| 980 | 20 | 19 | 20 | 21 | 20 | 18 | 22 |
| 1020 | 22 | 23 | 22 | 23 | 22 | 18 | 22 |
| 1050 | 41 | 48 | 45 | 49 | 49 | 39 | 47 |
| 1070 | 51 | 61 | 56 | 66 | 62 | 48 | 57 |
[00144] It can be seen that the carburized alloy steels of all the first to seventh embodiments have excellent anti-grain growth characteristic.
[00145] The carburized alloy steel of the invention and the preparation method thereof are not limited to the above described various embodiments. Obviously, the above embodiments are merely examples for clearly illustrating the invention, and are not provided for limiting the embodiments of the invention. For those with ordinary skills in the art, other different variations or modifications can be also made on the basis of the above description. For example, the smelting refining process of carburized alloy steel of 10 the invention can also use the method disclosed in Chinese patent document
CN102080188A (application No.: 201010603965.1). There is no need to enumerate all the embodiments herein, and such an enumeration is also not possible. Obvious variations or modifications that originate from the spirit of the invention will also fall within the scope of protection of the invention.
2015281542 18 Feb 2019
Claims (14)
1. A carburized alloy steel, wherein the compositions of the alloy steel and mass percentages thereof are: C: 0.15%~0.25%, Si:<0.30%, Mn: 0.30%~1.20%, Cr: 0.30%~1.50%, Ni: 3.05%~ 3.80%, Mo: 0.30%~1.00%, Al: 0.01%~0.08%, at least one of V
5 and Nb, and residuals: Fe and unavoidable impurities; and when the alloy steel contains V, the mass percentage of V is 0.05%~0.15%, and when the alloy steel contains Nb, the mass percentage of Nb is 0.025%~0.10%, and the mass percentages of V, Nb and Al satisfy that V+Nb+Al<0.30%.
10
2. The carburized alloy steel according to claim 1, wherein the mass percentage of Al in the above alloy steel is 0.02%~0.05%, and the mass percentages of V, Nb and Al satisfy that V+Nb+Al<0.20%.
3. The carburized alloy steel according to claim 1 or claim 2, wherein the mass percentage 15 of C in the above alloy steel is 0.15%~0.23%, and the mass percentage of Si is < 0.25%.
4. The carburized alloy steel according to any one of claims 1-3, wherein the mass percentage of Mn in the above alloy steel is 0.40%~1.00%, and the mass percentage of Cr is 0.40%~1.20%.
5. The carburized alloy steel according to any one of claims 1-4, wherein the mass percentage of Mo is 0.40%~0.80%.
6. The carburized alloy steel according to any one of claims 1-5, wherein the impurities in 25 the alloy steel comprise P and S elements, wherein the mass percentage of P is <0.015%, and the mass percentage of S is <0.010%.
7. The carburized alloy steel according to claim 6, wherein the impurities in the alloy steel further comprise N, O and H elements, wherein the mass percentage of N is <0.02%, the
30 mass percentage of O is <0.002%, and the mass percentage of H is <0.0002%.
8. The carburized alloy steel according to claim 7, wherein the mass percentage of N is
2015281542 18 Feb 2019 <0.01%.
9. A method of preparing the carburized alloy steel according to any one of claims 1-8, comprising the following steps:
5 A. batching raw materials according to the compositions of the alloy steel and their contents, and performing alloy melting using smelting and refining processes;
B. casting a steel ingot and rolling the steel ingot into a workblank;
C. performing normalizing and tempering processing; and
D. performing quenching and tempering processing, wherein the quenching and tempering
10 processing is to raise the temperature of the workblank to 800°C~860°C and keep that temperature for 0.8h~1.5h, after which the workblank is put into fast quenching oil so as to be cooled to an operational temperature of the fast quenching oil, and then the workblank is taken out for tempering processing again.
15 10. The method of preparing the carburized alloy steel according to claim 9, wherein the normalizing and tempering processing is to raise the temperature of the workblank to 900°C~960°C and keep that temperature for 0.8h~1.5h, after which the workblank is air-cooled to room temperature, and then the temperature of the workblank is raised to 630°C~750°C; and after that temperature is kept for 0.8h~1.5h, the workblank is air-cooled 20 to room temperature.
11. The method of preparing the carburized alloy steel according to claim 10, wherein in the quenching and tempering processing, the temperature of the workblank is raised to 160°C~220°C during tempering, and after that temperature is kept for 2.5h~3.5h, the
25 workblank is air-cooled to room temperature.
12. The method of preparing the carburized alloy steel according to claim 9, wherein the operational temperature of the fast quenching oil is 40 °C ~ 100 °C.
30
13. The method of preparing the carburized alloy steel according to any one of claims 9-12, wherein in the smelting and refining processes of step A, an electric furnace is used to perform smelting, and a ladle refining furnace and a vacuum degassing furnace are used to
2015281542 18 Feb 2019 perform refining.
14. An application of the carburized alloy steel according to any one of claims 1 to 8, wherein the carburized alloy steel is used to manufacture heavy load gears.
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| PCT/CN2015/082298 WO2015197007A1 (en) | 2014-06-26 | 2015-06-25 | Carburized alloy steel, method for preparing same, and use thereof |
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| CN115074631B (en) * | 2022-06-30 | 2023-07-25 | 马鞍山钢铁股份有限公司 | Nb-B microalloyed high surface hardness high torque output gear steel and manufacturing method thereof, carburization method for producing gear and application thereof |
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| CN102162069A (en) * | 2010-02-23 | 2011-08-24 | 宝山钢铁股份有限公司 | Flying-shear main-transmission gearwheel steel and preparation method thereof |
Also Published As
| Publication number | Publication date |
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| CN106661705B (en) | 2019-12-10 |
| CN104109816B (en) | 2017-05-17 |
| WO2015197007A1 (en) | 2015-12-30 |
| AU2015281542A1 (en) | 2017-01-12 |
| CN106661705A (en) | 2017-05-10 |
| CN104109816A (en) | 2014-10-22 |
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