WO2015197007A1

WO2015197007A1 - Carburized alloy steel, method for preparing same, and use thereof

Info

Publication number: WO2015197007A1
Application number: PCT/CN2015/082298
Authority: WO
Inventors: 文超; 董雯; 刘忠伟; 陈亮; 梁会雷; 徐宁
Original assignee: 南车戚墅堰机车车辆工艺研究所有限公司
Priority date: 2014-06-26
Filing date: 2015-06-25
Publication date: 2015-12-30
Also published as: CN104109816A; CN106661705B; CN106661705A; CN104109816B; AU2015281542A1; AU2015281542B2

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

Carburizing alloy steel and preparation method and application thereof

Technical field

The invention relates to an alloy steel, in particular to a carburized alloy steel suitable for at least manufacturing heavy-duty gears, and belongs to the field of iron-based alloys.

Background technique

There are many types of carburized steel that can be used in the world, but high-performance high-quality carburized steel is relatively rare. Carburized steel for heavy duty gears must have superior hardenability, finer grain size, less internal oxidation, high fatigue properties and good overall mechanical properties.

At present, China's 25-ton and above axle load locomotive gears, high-power wind power gears and high-power mining machinery gears are usually graded 20Cr2Ni4, 18Cr2Ni4W, 17Cr2Ni2Mo and other high-quality carburized steel. These existing heavy-duty gears use carburized steel, the composition of which is not reasonable, and the comprehensive mechanical properties are not ideal, and there are many deficiencies. For example, although 17Cr2Ni2Mo has excellent process performance, the yield strength is low, and the hardenability is poor compared with 20Cr2Ni4 and 18Cr2Ni4W. Although 18Cr2Ni4W has excellent hardenability and high strength, the process performance is poor, and due to the Ni element The content is high, the production cost is high, and the economy is poor; 20Cr2Ni4 has good comprehensive performance and economy, but the hardenability is still not satisfactory, and the internal oxidation is large.

Chinese patent document CN1851024A (Application No.: 200510018605.4) discloses a heavy-duty gear steel whose chemical composition weight percentage is: C 0.14 to 0.20, Mn 1.2 to 1.60, Si ≤ 0.12, P ≤ 0.03, S 0.015 to 0.04, Cr 1.30 to 1.80, W ≤ 0.05, Ti 0.04 to 0.10, O ≤ 20 ppm, and the balance is Fe and other impurities.

Chinese Patent Document CN101397631A (Application No.: 200710153141.7) discloses a surface carburized steel having low deformation resistance and high ultimate compression ratio at low temperature, thereby excellent cold forgeability and small carburization deformation; A surface-carburized steel excellent in properties and low-permeability carbon deformation characteristics, comprising: C: 0.07 to 0.3%, Si: 0.01 to 0.15%, Mn: 0.1 to 0.7%, P: 0.03% by mass% Hereinafter, S: 0.002 to 0.10%, Al: 0.01 to 0.08%, Cr: 0.7 to 1.5%, Ti: 0.01 to 0.15%, B: 0.0005 to 0.005%, and N: 0.008% or less, the balance being Fe and inevitable The impurity is composed; more than 65% of the metal structure is a ferrite phase, and a bainite phase is 15% or less.

The two kinds of carburized steels disclosed in the above Chinese patents are alloyed with Mn, Cr, Ti, etc., however, Alloy compositions such as Mn, Cr, and Ti increase the strength of the material while causing a significant decrease in material ductility and toughness. In particular, the Ti element, although it can refine the grains and increase the strength, the addition of the Ti element is liable to cause a decrease in the fatigue life of the gear.

Chinese Patent Document CN102080188A (Application No.: 201010603965.1) discloses a CrNiMo-based free-cutting gear steel and a preparation method thereof, wherein the chemical composition percentage of steel is: C 0.17 to 0.23, Si 0.15 to 0.37, Mn 0.60 to 0.95, Cr 0.35 to 0.65, Ni 0.35 to 0.75, Mo 0.15 to 0.25, P ≤ 0.030, S 0.010 to 0.040, Al 0.005 to 0.050, Ca/S 0.3 to 0.6; the balance is Fe and trace impurities. The preparation method comprises the smelting of the preliminary furnace (electric furnace or converter), the LF+VD (or RH) furnace refining, continuous casting and rolling, and is characterized in that the oxygen content in the steel is not determined by the external refining and the vacuum degassing treatment. It is larger than 15×10 ^-6 ; it controls the content of trace element S and improves the cutting performance of CrNiMo gear steel, making it suitable for high-speed machining and important precision parts. The content of Ni element and Mo element in the gear steel is low, and its comprehensive mechanical properties are poor, which cannot meet the requirements of heavy-duty gears.

Therefore, in order to meet the performance requirements of heavy-duty gears such as locomotive gears, high-power wind power gears and high-power mining machinery gears with axle loads of 25 tons and above, it is particularly urgent to develop a high-performance carburized alloy steel.

Summary of the invention

One of the objects of the present invention is to optimize the properties of carburized alloy steel in terms of hardenability, yield ratio, internal oxidation, and high temperature grain growth resistance.

Still another object of the present invention is to improve the fatigue resistance and overall mechanical properties of carburized alloy steel.

To achieve the above or other objects, the present invention provides the following technical solutions:

According to an aspect of the invention, there is provided a carburized alloy steel having a composition and a mass percentage of C: 0.15% to 0.25%, Si: ≤ 0.30%, Mn: 0.30% to 1.20%, Cr: 0.30% to 1.50%, Ni: 2.80% to 3.80%, Mo: 0.30% to 1.00%, Al: 0.01% to 0.08%, and at least one of V and Nb, the balance being iron and unavoidable impurities; And when the alloy steel contains V, the mass percentage of V is 0.05% to 0.15%, and when the above alloy steel contains Nb, the mass percentage of Nb is 0.025% to 0.10%, and the mass of the V, Nb and Al The percentage content is in accordance with V+Nb+Al≤0.30%.

Further, the mass percentage of Al in the alloy steel described above may be 0.02% to 0.05%; the mass percentage content of the V, Nb and Al is in accordance with V+Nb+Al≤0.20%.

Further, the mass percentage of C in the above alloy steel is 0.15% to 0.23%, and the mass percentage content of Si is ≤0.25%.

Further, the mass percentage of Mn in the above alloy steel is 0.40% to 1.00%, and the mass percentage of Cr is 0.40% to 1.20%.

Further, the mass percentage of Ni in the above alloy steel is 3.00% to 3.80%, and the mass percentage of Mo is 0.40% to 0.80%.

Further, the impurities in the above alloy steel include P and S elements, wherein the mass percentage content of P is ≤0.015%, and the mass percentage content of S is ≤0.010%.

Further, the impurities in the alloy steel further include N, O and H elements, wherein the mass percentage of N is ≤ 0.02%, the mass percentage of O is ≤ 0.002%, and the mass percentage of H is ≤ 0.0002%.

The mass percentage content of the above N is preferably ≤0.01%.

According to still another aspect of the present invention, a method for preparing the above carburized alloy steel is provided, comprising the steps of:

A. According to the composition and content of the alloy steel, the alloy is smelted by the existing smelting and refining process;

B. pouring a steel ingot to roll the steel ingot into a blank;

C. normalizing tempering; and

D. quenching and tempering treatment, wherein the quenching and tempering treatment is to raise the temperature of the blank to 800 ° C ~ 860 ° C, after the temperature of 0.8 h ~ 1.5 h, put into the rapid quenching oil to cool to the use temperature of the rapid quenching oil, and then The blank is taken out and tempered.

Further, the normalizing and tempering treatment is to raise the temperature of the blank to 900 ° C to 960 ° C, heat the temperature for 0.8 h to 1.5 h, and then air-cool to room temperature, and then raise the blank to 630 ° C to 750 ° C, and keep warm for 0.8 h to 1.5. After h, air cool to room temperature.

Further, in the above quenching and tempering treatment, the billet is heated to 160 ° C to 220 ° C during tempering, and after being kept for 2.5 h to 3.5 h, it is air-cooled to room temperature.

Further, in the above step A, the smelting and refining process uses an electric furnace for smelting and a refining process using a ladle refining furnace + a vacuum degassing furnace.

Further, in the above step D, the quick quenching oil is used at a temperature of 40 ° C to 100 ° C.

According to still another aspect of the present invention, the above carburized alloy steel is used for manufacturing heavy loads gear.

The role of the elements contained in the carburized alloy steel of the embodiment of the present invention in the alloy, and its preferred content (range of mass percentage) are described in detail below:

C: the main solid solution strengthening element; in order to ensure sufficient strength, C must be above 0.15%, but when the C content exceeds 0.25%, the strength is extremely high, and the toughness is seriously degraded, therefore, in the alloy steel of the present invention The C content is controlled to be 0.15% to 0.25%, and more preferably 0.15% to 0.23%.

Si: a deoxidizer; in order to improve the resistance to internal oxidation, the Si content in the alloy steel of the present invention is controlled to 0.30% or less, and more preferably 0.25% or less in order to secure the deoxidation effect and a certain yield strength.

Mn: good deoxidizer and desulfurizer, but also improve the hardenability of steel and improve the hot workability of steel; however, too high Mn content will reduce the toughness of the layer, therefore, the control of Mn content in the alloy steel of the invention It is 0.30% to 1.20%; more preferably 0.40% to 1.00%.

P: Microsegregation is easily formed during solidification of the molten steel, and then segregated to the grain boundary during austenitizing, so that the brittleness of the steel is remarkably increased; therefore, the P content in the alloy steel of the present invention is controlled to be less than 0.015%.

S: an unavoidable impurity element which reduces the toughness of the steel when the MnS inclusions are segregated at the grain boundary with the Mn; therefore, the S content in the alloy steel of the present invention is controlled to be 0.010% or less.

Cr: Main hardenability element, which improves the strength, hardness and wear resistance of steel; however, too high Cr content will reduce the cold workability of steel. Therefore, the Cr content in the alloy steel of the present invention is controlled at 0.30% to 1.50%. More preferably, it is 0.40% - 1.20%.

Ni: The main solid solution strengthening element, with the increase of Ni content, the room temperature strength of steel will also increase, and the addition of Ni has little effect on the plasticity and toughness of the alloy; but too high Ni will reduce the hot workability of steel. Further, the cost is too high. Therefore, the Ni content in the alloy steel of the present invention is controlled to 2.80% to 3.80%, and more preferably 3.00% to 3.80%.

Mo: The main hardenability element can simultaneously improve the hardenability of the matrix and the layer; however, excessive Mo causes the forging property to decrease and the cost is too high. Therefore, the Mo content in the alloy steel of the present invention is controlled at 0.30%. ～1.00%; more preferably 0.40% to 0.80%.

Al, Nb, V: Al is a deoxidizer and refined grain elements; when the Al content is below 0.01%, the effect of refining grains is not obvious, but when the Al content is above 0.08%, the deoxidation is not obvious. Moreover, it is easy to form large inclusions and affect fatigue performance. Therefore, the Al content in the alloy steel of the present invention is controlled to be 0.01% to 0.08%; further preferably 0.02% to ～ 0.05%. Nb is refined grain element. When the Nb content is below 0.025%, the grain refining effect is not obvious. When the Nb content is above 0.10%, the grain refining effect is saturated and the increase is not obvious. Therefore, the alloy of the present invention is not obvious. The Nb content in the steel is controlled to be 0.025% to 0.10%. V is refined grain element, the V content is below 0.05%, the grain refining effect is not obvious, and when the V content is above 0.15%, the grain refining effect is saturated, and the increase is not obvious. Therefore, the alloy steel of the invention The V content in the control is controlled to be 0.05% to 0.15%. At the same time, when Al, V and Nb are added in the alloy steel of the invention, it must conform to V+Nb+Al≤0.30%, and further optimized to V+Nb+Al≤0.20%, which is due to reasonable control of Al, V, Nb. The composite addition amount can indirectly affect the toughness of the alloy by refining the grain size. When V+Nb+Al>0.30%, the effect of refining the grain size is not obvious, and the coarse grain size brings about the toughness of the alloy. Unfavorable influence, when V+Nb+Al≤0.20%, the effect of refining the grain size is better, and the toughness of the alloy is the best.

N: An inevitable gas element in smelting, which can combine with Al, Nb, V, etc. to form a compound to refine grains; but too high, it will segregate grain boundaries and reduce grain boundary strength. Therefore, N in the alloy steel of the present invention The content is controlled to be ≤0.02%, and more preferably ≤0.01%.

O: Harmful gas element, when it is too high, the fatigue property is lowered; therefore, the content of O in the alloy steel of the present invention is controlled to be ≤ 20 ppm.

H: Harmful gas element, when it is too high, the toughness is lowered; therefore, the content of H in the alloy steel of the present invention is controlled to be ≤ 2.0 ppm.

The invention has positive effects:

(1) The carburized alloy steel of the present invention passes through the Mn, Cr, Ni, Mo elements and its reasonable ratio with C, and ensures the strength of the material steel while ensuring that the plasticity and toughness of the material are not greatly affected. This avoids the phenomenon that the plasticity and toughness of the material decrease significantly due to the increase in strength. The obtained carburized alloy steel material has excellent comprehensive mechanical properties; obviously overcomes the contradiction between the strength, the plasticity and the toughness of the carburized alloy steel in the prior art due to the unreasonable matching of the components. In addition, the hardenability of the carburized alloy steel is effectively improved, so that the steel can be applied to a large modulus gear.

(2) The carburized alloy steel of the present invention is added or compositely added by Al, V, Nb elements, so that the alloy has excellent resistance to grain growth during the molding process, and is particularly suitable for high temperature carburized parts.

(3) The carburized alloy steel of the present invention can reduce the internal oxidation of the grain boundary during the carburizing process by the optimized combination of Si, Ni and Mo elements, and the internal oxidation characteristics of the grain boundary during the long carburizing time. Lower internal oxidation depth than conventional steel, especially suitable for internal oxygen Mechanical parts with very high requirements.

(4) The carburized alloy steel of the invention has a reasonable selection of Cr, Ni and Mo elements and a ratio thereof, so that the steel is easy to manufacture, the processing performance is excellent, and the production cost is relatively low, which is beneficial to improving economic benefits.

(5) The carburized alloy steel of the invention has extremely small internal oxidation, high hardenability, high yield ratio and high temperature grain growth resistance, and is particularly suitable for manufacturing fatigue resistance and comprehensive mechanical properties. Mechanical parts, such as heavy-duty gears.

DRAWINGS

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a graph showing the comparison of the hardenability of a carburized alloy steel of Example 1 of the present invention with carburized alloy steels of 20Cr2Ni4, 18Cr2Ni4W and 17Cr2Ni2Mo.

Fig. 2 is a graph showing the comparison of hardenability of carburized alloy steels of Examples 1 to 7 of the present invention.

Fig. 3 is a graph showing the relationship between the internal oxidation depth of the carburized alloy steel of 17Cr2Ni2Mo of Comparative Example 1 and the depth of the carburized layer, and the case of three samples is shown.

Fig. 4 is a graph showing the relationship between the internal oxidation depth of the carburized alloy steel and the depth of the carburized layer in Example 1 of the present invention, and shows the case of the three samples of Example 1. Wherein, at a carburization depth of about 0.5 mm, the value of the oxidation depth of sample No. 2 substantially overlaps with the value of the oxidation depth of sample No. 3, both being about 0.002 mm; at a carburization depth of about 1.25 mm, the sample The value of the oxidation depth of No. 1 substantially overlaps with the value of the oxidation depth of sample No. 2, both being about 0.002 mm; at the carburization depth of about 1.8 mm, the value of the oxidation depth of sample No. 1 and the sample No. 3 The values of the oxidation depths are substantially overlapped, both being about 0.002 mm; at a carburization depth of about 2.5 mm, the value of the oxidation depth of sample No. 2 substantially overlaps with the value of the oxidation depth of sample No. 3, both being about 0.002 mm; At a carburization depth of about 3.25 mm, the value of the oxidation depth of sample No. 2 substantially overlaps with the value of the oxidation depth of sample No. 3, both being about 0.002 mm.

Fig. 5 is a graph showing the relationship between the internal oxidation depth of the carburized alloy steels of Examples 1 to 7 of the present invention and the depth of the carburized layer, and a data table.

Fig. 6 is a graph showing the relationship between the grain size of the carburized alloy steel and the heating temperature in Example 1 of the present invention.

detailed description

The above-described examples of the carburized alloy steel and the preparation method thereof are specifically described below, and the examples are intended to be illustrative of the invention and are not intended to limit the scope of the invention.

Example 1

The components of the carburized alloy steel of the present embodiment and the mass percentage 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%, the balance being iron and unavoidable impurities.

The preparation method of the carburized alloy steel of the first embodiment includes the following specific steps:

A. According to the composition and content of the alloy steel, the alloy is smelted by a steelmaking refining process of a conventional electric furnace + ladle refining furnace (LF) + vacuum degassing furnace;

B. Casting steel ingots, rolling steel ingots into round steel, taking sample blanks on round steel according to national standard GB/T2975-1998 "Sampling position and sample preparation of mechanical properties of steel and steel products";

C. Normalizing and tempering the sample blank: firstly raise the blank to 950 ° C, heat it for 1 h, then air-cool to room temperature by blower blowing; then warm the blank to 750 ° C, keep warm for 1 h, blow by blower Way of air cooling to room temperature;

D. Quenching and tempering the sample blank: firstly raise the blank to 860 ° C, heat it for 1 h, then put it into the rapid quenching oil to cool to the use temperature of the quenching oil. The use temperature of the quenching oil is controlled at 60±5. °C; Then take out the blank, then raise the blank to 220 ° C, keep warm for 3h, and then air-cool to room temperature by blower.

Example 2

The components of the carburized alloy steel of the present embodiment and the mass percentage 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%, the balance being iron and unavoidable impurities.

The preparation method of the carburized alloy steel of the second embodiment includes the following specific steps:

B. pouring steel ingot, rolling the steel ingot into round steel, taking the sample blank on the round steel according to the national standard GB/T2975-1998;

C. Normalizing and tempering the sample blank: firstly raise the blank to 900 ° C, heat it for 1 h, then air-cool to room temperature by blowing air through a blower; then raise the blank to 630 ° C, After 1 h of heat preservation, air-cooled to room temperature by blowing air through a blower;

D. Quenching and tempering the sample blank: firstly raise the blank to 800 ° C, heat it for 1 h, then put it into the rapid quenching oil to cool to the use temperature of the quenching oil. The use temperature of the quenching oil is controlled at 60±5. °C; Then take out the blank, then raise the blank to 160 ° C, keep warm for 3h, then air-cooled to room temperature by air blower.

Example 3

The components of the carburized alloy steel of the present embodiment and the mass percentage 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%, the balance being iron and unavoidable impurities.

The preparation method of the carburized alloy steel of the third embodiment includes the following specific steps:

C. Normalizing and tempering the sample blank: firstly raise the blank to 920 ° C, heat it for 1 h, then air-cool to room temperature by blowing air with a blower; then warm the blank to 700 ° C, keep warm for 1 h, blow by blower Way of air cooling to room temperature;

D. Quenching and tempering the sample blank: firstly raise the blank to 840 ° C, heat it for 1 h, and then put it into the rapid quenching oil to cool to the use temperature of the quenching oil. The use temperature of the quenching oil is controlled at 60±5. °C; Then take out the blank, then raise the blank to 200 ° C, keep warm for 3h, then air-cooled to room temperature by air blower.

Example 4

The components of the carburized alloy steel of the present embodiment and the mass percentage 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%, the balance being iron and unavoidable impurities.

The preparation method of the carburized alloy steel of the fourth embodiment includes the following specific steps:

A. According to the composition and content of the alloy steel, the alloy is smelted by a steelmaking refining process of a conventional electric furnace + ladle refining furnace (LF) + vacuum degassing furnace.

C. Normalizing and tempering the sample blank: firstly raise the blank to 930 ° C, heat it for 1 h, then air-cool to room temperature by air blower; then warm the blank to 680 ° C, keep warm for 1 h, blow by blower Way of air cooling to room temperature;

D. Quenching and tempering the sample blank: firstly raise the blank to 820 ° C, heat it for 1 h, then put it into the rapid quenching oil to cool to the use temperature of the quenching oil. The use temperature of the quenching oil is controlled at 60±5. °C; then the blank was taken out, and the blank was heated to 180 ° C, and after 3 hours of heat preservation, it was air-cooled to room temperature by a blower.

Example 5

The components of the carburized alloy steel of the present embodiment and the mass percentage 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%, the balance being iron and unavoidable impurities.

The preparation method of the carburized alloy steel of the embodiment includes the following specific steps:

Example 6

The components of the carburized alloy steel of the present embodiment and the mass percentage 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%, the balance being iron and unavoidable impurities.

Example 7

The components of the carburized alloy steel of the present embodiment and the mass percentage 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%, the balance being iron and unavoidable impurities.

Comparative example 1

The comparative example was selected from carburized alloy steel of the grade 17Cr2Ni2Mo. The chemical composition of the alloy is shown in Table 1.

The preparation method of the carburized alloy of Comparative Example 1 comprises the following specific steps:

A. According to the composition and content of the alloy, the alloy is smelted by a conventional steel ladle refining furnace + vacuum oxygen decarburization furnace + vacuum degassing furnace steelmaking refining process;

B. pouring steel ingot, rolling the ingot into round steel, taking the sample blank on the round steel according to the national standard GB/T2975 "Sampling position and sample preparation of mechanical properties test of steel and steel products";

C. Normalizing and tempering the sample blank: firstly raise the blank to 920 ° C, heat it for 1 h, then air-cool to normal temperature by blowing air through the blower; then warm the blank to 700 ° C, keep warm for 1 h, blow through the blower Way of air cooling to normal temperature;

D. Quenching and tempering of the sample blank: firstly raise the blank to 840 ° C, after 1 h of heat preservation, quench the oil to cool to oil temperature; then warm the blank to 200 ° C, keep warm for 3 h, then blow by the blower Cold to normal temperature.

Comparative example 2

For the comparison, the carburized alloy steel with the grade of 20Cr2Ni4 is used. The chemical composition of the alloy is shown in Table 1.

The preparation method of the carburized alloy steel of Comparative Example 2 comprises the following specific steps:

C. Normalizing and tempering the sample blank: firstly raise the blank to 930 ° C, heat it for 1 h, then air-cool to normal temperature by blowing air by blower; then warm the blank to 680 ° C, keep warm for 1 h, blow by blower Way of air cooling to normal temperature;

D. Quenching and tempering the sample blank: firstly raise the blank to 820 ° C, after 1 h of heat preservation, quickly quench the oil to oil temperature; then heat the blank to 180 ° C, keep warm for 3 h, then blow by the blower Cold to normal temperature.

Comparative example 3

The comparative example was selected from carburized alloy steel of 18Cr2Ni4W. The chemical composition of the alloy is shown in Table 1.

The preparation method of the carburized alloy steel of the proportion 3 comprises the following specific steps:

First, the chemical composition:

The chemical compositions of the carburized alloy steels of Examples 1 to 7 and Comparative Examples 1 to 3 of the present invention are shown in Table 1.

Table 1 chemical composition table

Second, the mechanical properties:

The mechanical properties of the carburized alloy steels of Examples 1 to 7 and Comparative Examples 1 to 3 of the present invention were tested in accordance with GB/T 228-2010 "Metal Material Tensile Test Method", and the results are shown in Table 2. Wherein R _m : tensile strength; R _p0.2 : tensile strength of 0.2% of non-proportional elongation, ie, yield strength of the present invention; A: elongation after fracture; Z: reduction of area; KV ₂ : Shock absorption energy, V-shaped notch, notch depth 2mm.

It can be seen from Table 2 that the carburized alloy steel of the present invention is more reasonable in the distribution ratio, and R _p0.2 (MPa) of Examples 1-7 has a significant improvement relative to Comparative Examples 1-3, and has a high yield strength. At the same time, the impact absorption energy KV ₂ (J) does not decrease or even increases, and therefore, the alloy steel reflecting the embodiment of the present invention has a high yield ratio; and, there is no decrease in other mechanical properties, for example, tensile strength R _m All of Example 1 and Examples 2-7 were substantially the same or improved relative to Comparative Examples 1-3, and only the alloy steel of Example 2 had a relatively high carbon content and was slightly lower, and therefore, maintained good toughness.

Table 2 mechanical properties table

Third, hardenability:

The hardenability of the carburized alloy steels of Examples 1 to 7 and Comparative Examples 1 to 3 of the present invention was measured in accordance with GB/T 225-2006 "Testing Method for Hardenability End Quenching of Steel".

As shown in Fig. 1, the carburized alloy steel of the present invention is superior in hardenability to the carburized alloy steels of Comparative Examples 1 to 3, and ΔHRC (J1.5-J50) ≤ 3.

1 and 2, all of the carburized alloy steels of Examples 1-7 have a hardness of more than 41 in the range of 0-50 mm from the end, and the hardness decreases as the quenching distance increases. Slower. Therefore, the carburized alloy steel reflecting the embodiment of the present invention has good hardenability.

Fourth, internal oxidation:

The internal oxidation depth and the depth of the carburized layer of the carburized alloy steels of Examples 1 to 7 and Comparative Example 1 of the present invention were measured in accordance with GB/T 25744-2010 "Carbon carburizing quenching and tempering metallographic test". Example 1 and Comparative Example 1 Three samples were taken to measure the internal oxidation depth under each of the same carburizing conditions.

As shown in FIG. 3 and FIG. 4, in the same carburized layer depth, in the first embodiment of the present invention The internal oxidation depth is much smaller than the internal oxide layer depth of 17Cr2Ni2Mo, and the fluctuation of the inner oxide layer depth is also small.

As shown in Fig. 5, the respective oxygen depths of the carburized alloy steels of Examples 1 to 7 at carburized depths of 0.5 mm, 1.2 mm, 1.8 mm, 2.5 mm, and 3.2 mm are shown. All of Examples 1 through 7 have a small inner oxide depth.

From this, it can be seen that the carburized alloy steel of the present invention has made great progress in internal oxidation as compared with the carburized alloy steel of Comparative Example 1.

5. Grain size:

The grain size grade and the average grain diameter of Examples 1 to 7 of the present invention were measured in accordance with GB/T6394-2002 "Metal Average Grain Size Measurement Method".

As shown in FIG. 6, the carburized alloy steel of Example 1 of the present invention has a grain size of 9 grades (greater than 5 grades) after being kept at 930 ° C for 8 hours, indicating that it is an intrinsic fine grain steel, and it is at 1020 ° C to 1050. The grain size in the temperature range of °C is above 6 grades, which indicates that the carburized alloy steel of the present invention can perform high temperature carburization without deteriorating the properties of the material, for example, the quenching condition of 860 ° C in the first embodiment (Austen At body temperature, the average grain diameter is less than 14 microns. Therefore, it has good resistance to high temperature grain growth.

The grain sizes of the carburized alloy steels of Examples 1 to 7 are further given in Table 3 below.

Table 3 grain size

It was found that the carburized alloy steels of Examples 1 to 7 all have excellent resistance to grain growth.

The carburized alloy steel of the present invention and a method for producing the same are not limited to the above embodiments. It is apparent that the above-described embodiments are merely illustrative of the invention and are not intended to limit the embodiments of the invention. Other variations or variations of the various forms, such as carburizing of the present invention, may also be made by those skilled in the art based on the above description. The smelting and refining process of the alloy steel can also be carried out by the method disclosed in Chinese Patent Publication No. CN102080188A (Application No.: 201010603965.1). There is no need and no way to exhaust all of the implementations. Obvious changes or variations that come within the spirit of the invention are still within the scope of the invention.

Claims

A carburized alloy steel, characterized in that the composition of the alloy steel and its mass percentage are C: 0.15% to 0.25%, Si: ≤ 0.30%, Mn: 0.30% to 1.20%, Cr: 0.30% to 1.50 %, Ni: 2.80% to 3.80%, Mo: 0.30% to 1.00%, Al: 0.01% to 0.08%, and at least one of V and Nb, the balance being iron and unavoidable impurities; When the alloy steel contains V, the mass percentage of V is 0.05% to 0.15%, and when the above alloy steel contains Nb, the mass percentage of Nb is 0.025% to 0.10%, and the mass percentage of the V, Nb and Al is in accordance with V. +Nb+Al≤0.30%.
The carburized alloy steel according to claim 1, wherein a mass percentage of Al in the alloy steel is 0.02% to 0.05%; and a mass percentage of the V, Nb, and Al is in accordance with V+Nb+ Al ≤ 0.20%.
The carburized alloy steel according to claim 1, wherein a content percentage of C in the alloy steel is 0.15% to 0.23%, and a mass percentage of Si is ≤0.25%.
The carburized alloy steel according to claim 1, wherein the alloy steel has a mass percentage of Mn of 0.40% to 1.00% and a mass percentage of Cr of 0.40% to 1.20%.
The carburized alloy steel according to claim 1, wherein a mass percentage of Ni in the alloy steel is 3.00% to 3.80%, and a mass percentage of Mo is 0.40% to 0.80%.
The carburized alloy steel according to claim 1, wherein the impurities in the alloy steel include P and S elements, wherein a mass percentage of P is ≤0.015%, and a mass percentage of S is ≤0.010%.
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%, and the mass percentage of O is ≤ 0.002%, the mass percentage content of H is ≤0.0002%.
The carburized alloy steel according to claim 7, wherein the mass percentage of N is ≤0.01%.
A method of preparing a carburized alloy steel according to any one of claims 1 to 8, comprising the steps of:

A. According to the composition and content of the alloy steel, the alloy is smelted by the smelting and refining process;

B. pouring a steel ingot to roll the steel ingot into a blank;

C. normalizing tempering; and

D. quenching and tempering treatment, wherein the quenching and tempering treatment is to first raise the billet to 800 ° C ~ 860 ° C, after the temperature of 0.8 h ~ 1.5 h, put into the rapid quenching oil to cool to the use temperature of the rapid quenching oil, The blank is then removed and tempered.
The method for preparing a carburized alloy steel according to claim 9, wherein the normalizing and tempering treatment is to raise the temperature of the blank to 900 ° C to 960 ° C, heat the temperature for 0.8 h to 1.5 h, and then air-cool to room temperature. The billet is further heated to 630 ° C to 750 ° C, held for 0.8 h to 1.5 h, and then air cooled to room temperature.
The method for preparing a carburized alloy steel according to claim 10, wherein in the quenching and tempering treatment, the billet is heated to 160 ° C to 220 ° C during tempering, and the wind is kept for 2.5 h to 3.5 h. Cool to room temperature.
The method for producing a carburized alloy steel according to claim 9, wherein the rapid quenching oil is used at a temperature of from 40 ° C to 100 ° C.
The method for preparing a carburized alloy steel according to claim 9, wherein in the step A, the smelting and refining process is performed by an electric furnace for smelting and a refining process using a ladle refining furnace + a vacuum degassing furnace.
Use of the carburized alloy steel according to any one of claims 1 to 8, characterized in that it is used for the manufacture of heavy duty gears.