STEEL AND COUPLER MADE FROM THE SAME

Abstract

The present invention provides a type of steel and a coupler made from same, comprising the following compositions in percentages by weight: carbon: 0.24-0.32%, silicon: 0.20-0.50%, manganese: 1.30-1.70%, phosphorus: less than or equal to 0.02%, sulphur: less than or equal to 0.02%, copper: less than or equal to 0.30%, chromium: 0.50-0.80%, nickel: 0.40-0.70%, molybdenum: 0.25-0.45%, aluminium: 0.02-0.08%, and the remainders are iron and other inevitable elements. The steel of the present invention is advantaged in high strength and excellent toughness and therefore the mechanical property thereof is better than the standard of conventional grade E steel.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of international application No. PCT/CN2010/074332 filed on Jun. 23, 2010, which claims the priority benefit of China Patent Application No. 201010202732.0, filed on Jun. 13, 2010. The contents of the above identified applications are incorporated herein by reference in their entirety.

FIELD OF THE TECHNOLOGY

The present invention relates to metallurgical technology, in particular to a type of steel with higher mechanical property and to a coupler made from the same.

BACKGROUND

Along with the development of industry, the requirement to the mechanical property of steel material becomes higher and higher. For example, during the development of “speed-rising and heavy-haul” of railway wagon, total traction weight of railway wagon has been increased greatly and therefore the requirement to the quality of components on wagon also becomes higher and higher; as a connection part between wagons, the coupler bears large tensile stress and impact force in a running railway wagon; the coupler knuckle of the coupler is a weak link of a railway wagon and easy to be fractured in a running railway wagon. The fracture of the coupler knuckle in a running railway wagon is generally fatigue fracture, for which the reasons include poor toughness, insufficient strength etc. of the materials for coupler knuckle.

Therefore, the strength and toughness of steel should be improved to meet the constantly increasing industry requirements, such as prolonging the fatigue life of a wagon coupler.

SUMMARY

The present invention aims at providing a type of steel and a coupler made from the same, so as to improve mechanical property of steel, in particular the strength and toughness thereof, and to therefore provide a coupler with excellent mechanical property.

In order to achieve the above purposes, the present invention provides a steel, comprising the following compositions in percentages by weight: carbon: 0.24-0.32%, silicon: 0.20-0.50%, manganese: 1.30-1.70%, phosphorus: less than or equal to 0.02%, sulphur: less than or equal to 0.02%, copper: less than or equal to 0.30%, chromium: 0.50-0.80%, nickel: 0.40-0.70%, molybdenum: 0.25-0.45%, aluminium: 0.02-0.08%, and the remainders are iron and other inevitable elements.

Wherein, the percentage of carbon by weight is preferably 0.25-0.29%, and more preferably 0.25-0.28%.

The percentage of manganese by weight is preferably 1.35-1.60%, and more preferably 1.35-1.55%.

The percentage of phosphorus by weight is preferably: less than or equal to 0.015%.

The percentage of sulphur by weight is preferably: less than or equal to 0.015%. And

The percentage of aluminium by weight is preferably 0.02-0.06%, and more preferably 0.02-0.05%.

In order to achieve the above purpose, the present invention further provides a coupler made of the steel provided by the present invention.

The steel and the coupler made from the same are advantaged in high strength and excellent toughness and therefore the mechanical property thereof is better than the standard of conventional grade E steel.

DETAILED DESCRIPTION

The technical solution of the present invention is further described in detail in connection with embodiments.

The present invention provides a steel, comprising the following compositions in percentages by weight: carbon: 0.24-0.32%, silicon: 0.20-0.50%, manganese: 1.30-1.70%, phosphorus: less than or equal to 0.02%, sulphur: less than or equal to 0.02%, copper: less than or equal to 0.30%, chromium: 0.50-0.80%, nickel: 0.40-0.70%, molybdenum: 0.25-0.45%, aluminium: 0.02-0.08%, and the remainders are iron and other inevitable elements.

Wherein, the percentage of carbon by weight is preferably 0.25-0.29%, and more preferably 0.25-0.28%; the percentage of manganese by weight is preferably 1.35-1.60%, and more preferably 1.35-1.55%; the percentage of phosphorus by weight is preferably: less than or equal to 0.015%; the percentage of sulphur by weight is preferably: less than or equal to 0.015%; and the percentage of aluminium by weight is preferably 0.02-0.06%, and more preferably 0.02-0.05%.

The percentage of silicon by weight is preferably 0.20-0.40%, and more preferably 0.21-0.39%; the percentage of chromium by weight is preferably 0.50-0.65%, and more preferably 0.50-0.60%; the percentage of nickel by weight is preferably 0.40-0.60%, and more preferably 0.40-0.55%; and the percentage of molybdenum by weight is preferably 0.25-0.35%, and more preferably 0.25-0.30%.

The chemical compositions of steel substantially decide the mechanical property thereof; by improving the purity of molten steel and reducing the content of gas and harmful elements therein, the metallurgical process can create a good condition for the subsequent processing of the steel material; the heat treatment process after smelting process can achieve best potential of the mechanical property of the steel material. Therefore, chemical compositions play an important role in improving the mechanical property of steel. Among all compositions, carbon and manganese are major elements to improve the strength of material; the toughness of material can be improved by reducing the content of harmful elements P and S and properly increasing the content of nickel; the hardenability of material can be improved by properly increasing the content of manganese, chromium and molybdenum; meanwhile, the increasing of the content of molybdenum can effectively restrict the temper brittleness of material; the content of aluminium can be controlled to refine grains in subsequent heat treatment.

The present invention further provides a coupler made of the steel provided by the present invention. The couple has excellent mechanical property such as high strength and good toughness and can bear larger tensile stress and impact force. The wagon coupler can be applied to multiple applications, for example, to the railway wagon or railway carriage.

EMBODIMENTS

The chemical compositions of the steel of the embodiments 1-1 to 1-10 provided by the present invention are shown in Table 1; the mechanical properties of the steel of embodiments 1-1 to 1-10 are shown in Table 2. Wherein the heat treatment process of embodiments 1-1 to 1-10 is the conventional heat treatment process, namely thermal refining (including quenching and tempering processes), in which the quenching temperature is 910 DEG C, the temperature holding time is 2 hours, and the cooling method is water quenching; and the tempering temperature is 560 DEG C, the temperature holding time is 3.5 hours, and the cooling method is wind cooling.

TABLE 1
Embodiments	C %	Si %	Mn %	P %	S %	Cr %	Ni %	Mo %	Cu %	Al %
1-1	0.27	0.39	1.48	0.014	0.012	0.59	0.48	0.29	0.08	0.04
1-2	0.28	0.38	1.50	0.011	0.013	0.60	0.52	0.30	0.09	0.05
1-3	0.26	0.40	1.52	0.010	0.011	0.62	0.53	0.33	0.10	0.04
1-4	0.29	0.35	1.49	0.012	0.013	0.58	0.51	0.31	0.07	0.05
1-5	0.28	0.41	1.54	0.013	0.011	0.61	0.54	0.32	0.08	0.03
1-6	0.27	0.38	1.53	0.010	0.011	0.63	0.49	0.34	0.09	0.04
1-7	0.26	0.36	1.55	0.012	0.010	0.60	0.50	0.32	0.010	0.06
1-8	0.28	0.37	1.46	0.011	0.012	0.57	0.55	0.28	0.08	0.05
1-9	0.27	0.39	1.47	0.010	0.012	0.58	0.53	0.30	0.09	0.04
1-10	0.29	0.40	1.50	0.014	0.012	0.61	0.49	0.32	0.08	0.05

TABLE 2
	Yield strength	Tensile strength		Reduction of	Impact energy
Embodiment	MPa	MPa	Elongation %	cross section %	J(−40 DEG C.)
1-1	835	930	17.0	53.5	55.3
1-2	855	945	16.5	46.0	47.0
1-3	845	930	18.0	53.5	57.0
1-4	840	930	17.5	53.5	51.0
1-5	850	940	17.5	55.0	52.3
1-6	855	965	17.0	50.5	39.7
1-7	860	960	17.0	49.5	47.7
1-8	840	940	17.5	51.5	53.0
1-9	850	955	18.0	53.5	48.7
1-10	845	945	17.5	50.5	49.3
Grade E	More than or	More than or	More than or	More than or	More than or
steel	equal to 690	equal to 830	equal to 14	equal to 30	equal to 27

Table 1 and Table 2 show that the mechanical property of the steel provided by the present invention is significantly better than that of grade E steel; for example, the yield strength is 20% higher than that of grade E steel; the tensile strength is 13% higher than that of grade E steel; the impact energy is 90% higher than that of grade E steel; in addition, the elongation and reduction of cross section are also much higher than those of grade E steel; hereinto, higher impact energy means higher toughness of steel.

According to standard M201 of American AAR (Association of American Railroads), steel is classified into the following grades on the basis of strength thereof: grade A steel, grade B steel, grade B+ steel, grade C steel, and grade E steel, in which the grade E is the highest grade.

Due to the above chemical compositions, the steel provided by the present invention has excellent mechanical property, including high strength and good toughness, and the mechanical property is better than that of grade E steel.

In order to further improve the mechanical property of material, the steel material of the present invention can be obtained through the following heat treatment process, which includes pre-heat treatment and thermal refining; the pre-heat treatment comprises normalizing treatment; the thermal refining comprises quenching and tempering procedures. Specifically, the process comprises the following steps:

Step 1: performing pre-heat treatment to steel, wherein the normalizing temperature is 900-960 DEG C, the temperature holding time is 3-5 hours, and the cooling method is air cooling or wind cooling; the normalizing temperature is preferably 920-950 DEG C, and more preferably 930-950 DEG C; the temperature holding time is preferably 3.5-4.5 hours, and more preferably 4 hours.

Step 2: quenching the steel after the pre-heat treatment of step 1, wherein the quenching temperature is 900-920 DEG C, the temperature holding time is 2-3 hours, and the cooling method is water quenching.

Step 3: tempering the steel after quenching of step 2, wherein the tempering temperature is 520-580 DEG C, the temperature holding time is 3-5 hours, and the cooling method is water cooling; the tempering temperature may also be 550-570 DEG C or 530-550 DEG C.

After the pre-heat treatment procedure to the steel provided by the present invention, the as-cast structure of steel can be eliminated and the crystalline grain can be refined, so as to prepare for the thermal refining; furthermore, water cooling is adopted in the tempering procedure to eliminate the temper brittleness, and therefore the mechanical property of steel can be greatly improved.

Before the heat treatment to steel, metallurgy procedure should also be executed. The metallurgy procedure can be ex ecuted using the conventional metallurgy process, for example, including the following steps:

Step a1: preparing raw material: according to the requirements of compositions of steel to be melted, weighing the iron alloy necessary in smelting process, conveying it beside arc furnace, and also conveying various slagging materials, carburetant, oxidizing material and reduction materials beside the furnace.

Step a2: feeding material: feeding the cut and selected waste steel, of which the size and weight meet the requirements of furnace, into the hopper of furnace, according to the arrangement of “large, medium, small and light”; adding carburetant and a part of iron alloy to the steel; conveying all materials to charging bay via battery truck; weighing these materials; and feeding the materials in batches into the arc furnace.

Step a3: electrifying the furnace to melt the materials: electrifying the arc furnace after the waste steel is fed thereinto, where different currents and voltages can be adopted to covert electric energy into heat energy and therefore to melt the waste steel into molten steel. In order to speed up the smelting, oxygen can be blown to accelerate the melting when the arc furnace is electrified.

Step a4: oxidizing: adding the slagging materials to make a layer of slag cover on the surface of molten steel after the waste steel is melted into molten steel; and adding oxidizing material when the molten steel is at a proper temperature, to boil the molten steel under the reaction of carbon and oxygen, so as to eliminate gas from the molten steel. Since the molten steel is boiled, the molten steel can contact with slag fully, and therefore the harmful element phosphorus can be transferred from the molten steel to the slag. The compositions of the molten steel can be checked for 2-3 times during the oxidizing process. At the end of the oxidizing process, steel ladle can be dried.

Step a5: removing slag: at the end of oxidizing, under the condition that all compositions and temperature comply with the technical requirements, shutting off the power and removing all slag generated in the oxidizing process, so as to prevent the harmful element, phosphorus, from entering molten steel again.

Step a6: reduction: after all slag generated in oxidizing process is removed, electrifying the arc furnace and adding slagging materials rapidly; removing oxygen element from the molten steel by diffusible desoxydation method and precipitation desoxydation method; and adding iron alloy into the molten steel in sequence according to oxidability of iron alloy. In reduction process, inert gas can be adopted for mixing so as to make the molten steel flow and contact with the slag fully and therefore transfer the harmful element sulphur from the molten steel into the slag. The temperature of molten steel is continuously improved to prepare for tapping during deoxygenation, desulfuration and adjustment of molten steel compositions.

Step a7: tapping: on the basis that compositions of molten steel are qualified, the temperature of molten steel and drying of steel ladle are in accordance with requirements and desoxydation experiment of molten steel is under good condition, the power can be shut off and the tapping can be executed.

And step a8: refining molten steel: during the tapping process, blowing inert gas into the steel ladle and keeping it for a certain time; and after the end of tapping, feeding deoxidant into steel ladle.

In order to ensure the reliability and safety of vehicles running at a high load, more requirement to the mechanical property of material for making coupler has been proposed by mine manufacturer; the requirement is even higher than grade E; the steel hereafter meets the requirement is classified as grade E+ steel; the requirement to the mechanical property of grade E+ steel is shown in Table 3.

TABLE 3
Mechanical	Yield strength	Tensile strength		Reduction of	Impact energy
property	MPa	MPa	Elongation %	cross section %	J(−40 DEG C.)
Grade E	More than or	More than or	More than or	More than or	More than or
steel	equal to 690	equal to 830	equal to 14	equal to 30	equal to 27
Grade E+	More than or	More than or	More than or	More than or	More than or
steel	equal to 760	equal to 910	equal to 14	equal to 30	equal to 33

As shown in Table 3, the mechanical property of grade E+ steel is higher than that of grade E steel; the yield strength and tensile strength of grade E+ steel are 10% higher than those of grade E steel; and the impact energy is 20% higher than that of grade E steel.

The mechanical property of grade E steel part can be obtained as shown in Table 4 from the grade E steel (embodiments 2-1 to 2-10) through the conventional heat treatment process. Wherein, the raw material of embodiments 2-1 to 2-10 can be either commercial grade E steel or the grade E steel made by manufacturer according to the requirements thereof.

TABLE 4
	Yield strength	Tensile strength		Reduction of cross	Impact energy
Embodiments	MPa	MPa	Elongation %	section %	J(−40 DEG C.)
2-1	855	945	16.5	46.0	25.6
2-2	855	945	18.0	52.5	31.3
2-3	865	945	17.0	52.5	39.7
2-4	845	935	19.0	52.5	32.7
2-5	865	955	16.5	51.5	30.7
2-6	865	945	18.0	50.5	36.5
2-7	845	935	17.0	51.5	40.5
2-8	870	955	17.5	55.0	41.3
2-9	870	960	17.5	52.5	24.0
2-10	855	955	18.0	53.5	38.7
Grade E+	760	910	14	30	33
steel standard
values

Wherein, the heat treatment process of the conventional grade E steel part comprises: quenching temperature is 910 DEG C, the temperature holding time is 2 hours and the quenching method is water quenching; the tempering temperature is 560 DEG C, the temperature holding time is 3.5 hours and the cooling method is wind cooling.

As shown in Table 4, with the increasing of strength (yield strength and tensile strength), the parameter of impact energy (toughness) of grade E steel part reduces and cannot be stabilized. Compared with the requirement of grade E+ steel, the mechanical property can only meet 50% of the requirement thereof.

The mechanical property of the steel (embodiments 3-1 to 3-10) with new compositions provided by the present invention, after smelting process and through the heat treatment process provided by the present invention is shown in Table 5:

TABLE 5
	Yield strength	Tensile strength		Reduction of cross	Impact energy
Embodiments	MPa	MPa	Elongation %	section %	J(−40 DEG C.)
3-1	840	945	19.0	55.0	81.3
3-2	880	955	18.5	48.5	65.7
3-3	850	940	18.5	51.5	78.3
3-4	875	960	20.0	52.0	66.3
3-5	875	955	19.0	58.0	65.0
3-6	865	945	18.5	52.0	71.7
3-7	855	945	19.5	52.5	70.0
3-8	880	970	18.5	54.0	71.3
3-9	865	955	19.0	57.0	72.3
3-10	875	975	16.0	42.5	60.3
Grade E+	760	910	14	30	33
steel standard
values

Wherein, the specific compositions of the steel in embodiments 3-1 to 3-10 are shown in Table 6.

TABLE 6
Embodiments	C %	Si %	Mn %	P %	S %	Cr %	Ni %	Mo %	Cu %	Al %
3-1	0.27	0.39	1.48	0.014	0.012	0.59	0.48	0.29	0.08	0.04
3-2	0.28	0.38	1.50	0.011	0.013	0.60	0.52	0.30	0.09	0.05
3-3	0.26	0.40	1.52	0.010	0.011	0.62	0.53	0.33	0.10	0.04
3-4	0.29	0.35	1.49	0.012	0.013	0.58	0.51	0.31	0.07	0.05
3-5	0.28	0.41	1.54	0.013	0.011	0.61	0.54	0.32	0.08	0.03
3-6	0.27	0.38	1.53	0.010	0.011	0.63	0.49	0.34	0.09	0.04
3-7	0.26	0.36	1.55	0.012	0.010	0.60	0.50	0.32	0.010	0.06
3-8	0.28	0.37	1.46	0.011	0.012	0.57	0.55	0.28	0.08	0.05
3-9	0.27	0.39	1.47	0.010	0.012	0.58	0.53	0.30	0.09	0.04
3-10	0.29	0.40	1.50	0.014	0.012	0.61	0.49	0.32	0.08	0.05

As shown in Table 5, the mechanical property of the steel, with new compositions, provided by the present invention after the heat treatment process provided by the present invention is noticeably higher than that of grade E+ steel (in particular the impact energy) and completely meets the requirement thereof. Compared with the conventional grade E steel shown in Table 4, the mechanical property provided by the present invention is greatly higher than that of grade E steel.

As shown in Table 5 and Table 2, the mechanical property of the steel with new compositions provided by the present invention after special heat treatment process (Table 5) is noticeably higher than that of the steel only executed with the conventional heat treatment process; especially, based on keeping the strength, the impact energy is greatly improved; namely, the toughness of the steel with new compositions provided by the present invention is also improved on the basis of keeping or even improving the strength thereof.

The present invention provides a steel material with high strength and excellent toughness, the steel can be applied to multiple fields, such as coupler of railway wagon, in order to meet the requirement of “speed-rising and heavy-haul” of railway wagon.

Finally, it should be understood that the above embodiments are only used to explain, but not to limit the technical solution of the present invention. In despite of the detailed description of the present invention with referring to above preferred embodiments, it should be understood that various modifications, changes or equivalent replacements can be made by those skilled in the art without departing from the scope of the present invention and covered in the claims of the present invention.

Claims

1. A steel, characterized by comprising the following compositions in percentages by weight: carbon: 0.24-0.32%, silicon: 0.20-0.50%, manganese: 1.30-1.70%, phosphorus: less than or equal to 0.02%, sulphur: less than or equal to 0.02%, copper: less than or equal to 0.30%, chromium: 0.50-0.80%, nickel: 0.40-0.70%, molybdenum: 0.25-0.45%, aluminium: 0.02-0.08%, and the remainders are iron and other inevitable elements.

2. The steel in claim 1, characterized in that: the percentage of the carbon by weight is 0.25-0.29%.

3. The steel in claim 2, characterized in that: the percentage of the carbon by weight is 0.25-0.28%.

4. The steel in claim 1, characterized in that: the percentage of the manganese by weight is 1.35-1.60%.

5. The steel in claim 4, characterized in that: the percentage of the manganese by weight is 1.35-1.55%.

6. The steel in claim 1, characterized in that: the percentage of the phosphorus by weight is less than or equal to 0.015%.

7. The steel in claim 1, characterized in that: the percentage of the sulphur by weight is less than or equal to 0.015%.

8. The steel in claim 1, characterized in that: the percentage of the aluminium by weight is 0.02-0.06%.

9. The steel in claim 8, characterized in that: the percentage of the aluminium by weight is 0.02-0.05%.

10. A coupler made of the steel in the claim 1.

11. A coupler made of the steel in the claim 2.

12. A coupler made of the steel in the claim 3.

13. A coupler made of the steel in the claim 4.

14. A coupler made of the steel in the claim 5.

15. A coupler made of the steel in the claim 6.

16. A coupler made of the steel in the claim 7.

17. A coupler made of the steel in the claim 8.

18. A coupler made of the steel in the claim 9.