CN110724875A

CN110724875A - Steel plate for railway and manufacturing method for improving yield strength of steel plate

Info

Publication number: CN110724875A
Application number: CN201910897621.7A
Authority: CN
Inventors: 奚艳红; 夏政海; 吴俊平; 方磊; 张仪杰; 姜在伟; 于生; 刘心阳; 王思聪; 李庆春
Original assignee: Nanjing Iron and Steel Co Ltd
Current assignee: Nanjing Iron and Steel Co Ltd
Priority date: 2019-09-20
Filing date: 2019-09-20
Publication date: 2020-01-24
Anticipated expiration: 2039-09-20
Also published as: CN110724875B

Abstract

The invention discloses a steel plate for a railway and a manufacturing method for improving yield strength of the steel plate, and belongs to the technical field of steel. The steel plate for the railway has the advantages that through reasonable component design, the steel plate obtains excellent welding performance and has lower cost. The manufacturing method obtains uniform and fine ferrite, pearlite structures and a small amount of carbide precipitates through a controlled rolling and controlled cooling rolling process and a medium-low temperature rapid tempering technology, so that the yield strength of the steel plate is greatly improved, and the problem that the yield strength of the existing steel plate is surplus and insufficient or cannot meet the technical requirements is solved. Meanwhile, the internal stress of the steel plate is eliminated, so that the steel plate has high strength and toughness, corrosion resistance and good processing and forming performance.

Description

Steel plate for railway and manufacturing method for improving yield strength of steel plate

Technical Field

The invention belongs to the technical field of steel, and particularly relates to a steel plate for a railway and a manufacturing method for improving yield strength of the steel plate.

Background

With the recent development of railway vehicles at high speed, heavy load and low cost. The steel plate as the raw material for railway also starts to be updated, and the improvement of the strength of the steel plate is one of the most direct means for realizing the light weight, heavy load and low cost of railway vehicles. At present, the methods for improving the strength of rolled delivery steel plates for railways are mostly the following two methods: 1. by adding a large amount of alloy elements such as Nb, V, Cr, Ni, Mo, Cu and the like, the carbon equivalent is higher, the welding crack sensitivity is further increased, and the welding performance of the material is reduced. 2. The final cooling temperature in the rolling process is reduced through water cooling or air cooling equipment, the internal stress of the steel plate is increased in the mode, the processing and forming performance of the material is affected, and the conditions of uneven cooling and uneven performance of the steel plate are easily caused.

For example, the chinese patent application No. 201510652360.4 discloses a quenching machine accelerated cooling method for improving the strength of normalized steel plate with thickness of more than or equal to 50mm, the normalized steel plate enters the quenching machine along with the roller way of the quenching machine after leaving the quenching furnace to start water cooling, four or six low-pressure sections are determined to be opened according to the steel type and specification, and the opening degree, the ratio of the upper opening degree and the lower opening degree and the roller way speed of each zone of the low-pressure sections are adjusted to make the steel plate 'red-returning' temperature reach 580 plus 630 ℃ and then naturally cooled, and the water cooling can greatly improve the strength of the normalized steel plate. The application number 201510323163.8 discloses a heat treatment production method of air cooling after normalizing, which uses air cooling to replace water cooling to achieve the purpose of improving the strength of the steel plate and realize the effect of producing low-cost low-alloy series steel plates by the air cooling after normalizing method. Both methods can cause the internal stress of the steel plate to be increased, and the processing and forming performance of the material is influenced. The problem of improving the yield strength of the rolled delivery steel plate for the railway at present cannot be solved.

Disclosure of Invention

The purpose of the invention is as follows: in order to overcome the defects of the prior art, the invention provides a steel plate for railways, which has higher yield strength.

Another object of the present invention is to provide a method for manufacturing the above steel sheet with improved yield strength.

The technical scheme is as follows: the invention relates to a steel plate for a railway, which comprises the following components in percentage by mass: c: 0.08-0.10%, Mn: 0.90-1.60%, Si: 0.25-0.35%, P: less than or equal to 0.020 wt.%, S: less than or equal to 0.010 wt.%, Cr: 0.10 to 0.30%, Cu: 0.10 to 0.40%, Nb: 0.010-0.040%, Ti: 0.010-0.020% of Al: 0.010-0.050%; the balance of Fe and impurities; the carbon equivalent CE of the steel is less than 0.45, and the metallographic structure is uniform and fine ferrite, pearlite and carbide precipitates.

The design principle of the alloy components of the steel plate for the railway is as follows:

c is an indispensable element for improving the strength and the hardness of steel in steel, and has obvious influence on steel structure. C is dissolved in the matrix to form a gap solid solution, so that the solid solution strengthening effect is achieved, and the strength of the matrix is obviously improved. However, the carbon element has the greatest influence on the carbon equivalent value, and when the content of the C element is increased, the welding performance of the steel plate material is reduced.

Mn can improve the strength of the steel sheet material, but Mn is an element that has a secondary influence on carbon equivalent in addition to carbon, and excessively high Mn content deteriorates weldability and weld heat-affected zone toughness of the steel.

Cu effectively improves the corrosion resistance of steel, but too high content of Cu easily causes hot brittleness, which causes cracks in the steel sheet.

Cr can form a compact oxide film on the surface of steel, can effectively improve the corrosion resistance of the steel and can also improve the strength of materials, and when the Cr and Cu are added into the steel at the same time, the effect is particularly obvious; but too high a content deteriorates the weldability of the steel.

Nb can refine grains, improve the strength of the steel plate, improve the corrosion resistance, and does not participate in the calculation of carbon equivalent, so that when the requirement on welding performance is higher, the addition of Nb instead of V can be considered.

The carbon equivalent calculation formula is Ceq (%) ═ C + Mn/6+ (Cr + Mo + V)/5+ (Ni + Cu)/15, and when the carbon equivalent is more than 0.45, the carbon equivalent has a large influence on the welding performance of the steel plate. Therefore, the carbon equivalent of the steel plate to be welded is controlled to be less than 0.45.

According to the control principle, the composition design is carried out firstly and secondly according to the size of each chemical element playing a role in performance indexes, the upper limit and the lower limit of C, Mn elements are preferably considered, and the contents of other alloy elements are determined according to the principle that the carbon equivalent is less than 0.45.

Further, the steel plate for the railway comprises the following components in percentage by mass: c: 0.090-0.095%, Mn: 1.30-1.40%, Si: 0.28-0.30%, P: less than or equal to 0.020 wt.%, S: less than or equal to 0.010 wt.%, Cr: 0.15 to 0.26%, Cu: 0.25 to 0.35%, Nb: 0.030-0.035%, Ti: 0.014 to 0.018%, Al: 0.030-0.040%; the balance being Fe and impurities.

The thickness specification range of the steel plate is 6-30 mm.

The manufacturing method for improving the yield strength adopts the technical scheme that the manufacturing method corresponds to the steel plate for the railway, and comprises the following steps: the process comprises the following steps: molten iron pretreatment → converter smelting → LF refining → RH refining → continuous casting → blank heating → rolling → controlled cooling → medium and low temperature tempering; wherein in the blank heating procedure, the blank is heated for 1.5 to 3.5 hours under the environment of 1050 ℃ and 1220 ℃; the rolling procedure adopts two-stage rolling, the reduction rate is more than 60%, the initial rolling temperature of rough rolling is 980-1180 ℃, the initial rolling temperature of finish rolling is 830-950 ℃, and the final rolling temperature is 780-900 ℃; the controlled cooling process controls the temperature of the returned red to be 590-690 ℃; in the medium-low temperature tempering process, the tempering temperature is 600-680 ℃, and then the temperature is kept for 30-50 min.

The molten iron pretreatment process comprises the step of carrying out composite injection desulfurization on lime powder and magnesium powder injected into a ladle, wherein the mass percentage content of S after molten iron pretreatment is less than or equal to 0.010%.

The converter smelting process adopts top-bottom combined blowing and auxiliary lance to carry out smelting; the top blowing oxygen and the bottom blowing inert gas are combined with the sublance for smelting, so that the advantages of the top blowing technology are maintained, and the advantages of certain bottom blowing methods are absorbed to make up the defects of the top blowing, so that the blowing is stable, and the production of low-sulfur and low-phosphorus steel is facilitated; the LF refining process and the RH refining process adopt a double-ladle car type LF-double-station RH refining technology. The LF/RH device is adopted for refining, so that the temperature of the molten steel can be raised, the components of the molten steel are uniform, the alloy is micro-adjusted, and the molten steel is desulfurized, degassed and the like; provides guarantee for the production of molten steel with strict requirements on production components and high cleanliness.

Furthermore, in the LF refining process, measures including slagging, deep desulfurization, narrow component control, inclusion spheroidization and static stirring are adopted, so that the components and the temperature of the molten steel are uniform, and the inclusions are fully floated and meet the morphological requirements.

Furthermore, in the RH refining process, the contents of steel type gas and inclusions are reduced by controlling the vacuum degree and the vacuum treatment time.

The continuous casting process adopts the whole-course non-oxidation protection pouring and adopts the continuous bending, continuous straightening, whole-course multi-fulcrum close-row rollers and the solidification tail end soft pressing mode to continuously cast into a blank. The casting blank is ensured to be smooth and the internal metal is compact.

Has the advantages that: the steel plate for the railway has the advantages that through reasonable component design, the steel plate obtains excellent welding performance and has lower cost. The manufacturing method obtains uniform and fine ferrite, pearlite structures and a small amount of carbide precipitates through a controlled rolling and controlled cooling rolling process and a medium-low temperature rapid tempering technology, so that the yield strength of the steel plate is greatly improved, and the problem that the yield strength of the existing steel plate is rich in margin or cannot meet the technical requirements is solved. Meanwhile, the internal stress of the steel plate is eliminated, so that the steel plate has high strength and toughness, corrosion resistance and good processing and forming performance.

Drawings

FIG. 1 is a metallographic structure diagram of example 1;

FIG. 2 is a metallographic structure diagram of example 2;

FIG. 3 is a schematic diagram of the detection of internal stress in a steel sheet in a rolled state;

FIG. 4 is a schematic diagram of the detection of the internal stress of the steel plate after medium and low temperature tempering.

Detailed Description

The following provides 6 examples and 6 comparative examples to explain the properties of the steel for railways of the present invention in detail. The chemical composition of each case of steel is shown in table 1:

TABLE 1 chemical composition of the steels (balance Fe and impurities)

Numbering	C	Mn	Si	P	S	Cr	Nb	Cu	V	Ti	Al	CE
													1	0.08	1	0.27	0.02	0.009	0.26	0.03	0.25		0.018	0.02	0.32
2	0.09	0.9	0.34	0.018	0.007	0.29	0.04	0.38		0.02	0.01	0.32
													3	0.085	1.6	0.25	0.015	0.06	0.1	0.01	0.38		0.01	0.05	0.40
4	0.095	1.4	0.3	0.012	0.009	0.15	0.02	0.1		0.014	0.04	0.37
													5	0.09	1.3	0.35	0.014	0.01	0.3	0.035	0.4		0.018	0.01	0.39
6	0.1	1.5	0.28	0.017	0.006	0.26	0.038	0.35		0.015	0.03	0.43
													Comparative example 1	0.094	1.4	0.31	0.015	0.008	0.27	0.02	0.25		0.016	0.02	0.40
Comparative example 2	0.089	1.3	0.3	0.016	0.007	0.19	0.03	0.2		0.012	0.04	0.36
													Comparison 3	0.096	1.2	0.33	0.018	0.006	0.25	0.036	0.33		0.017	0.03	0.37
Comparative example 4	0.088	0.95	0.27	0.015	0.005	0.25	0.018	0.28		0.011	0.02	0.32
													Comparative example 5	0.1	1.55	0.33	0.011	0.007	0.3		0.4	0.06	0.02	0.03	0.46
Comparative example 6	0.17	1.35	0.3	0.01	0.09	0.28	0.36	0.35		0.016	0.02	0.47

Wherein, the comparative examples 1 to 4 are designed according to the component requirements of the invention, and the comparative examples 5 to 6 are not designed by the components of the invention. In the case of comparative example 5 in which no Nb element is added and V is added, comparative example 6 exceeds the upper limit requirement of the C content of the present invention, resulting in the carbon equivalent exceeding the required amount.

The preparation method of the invention is adopted in each embodiment, and the process route comprises the following steps: molten iron pretreatment → converter smelting → LF refining → RH refining → continuous casting → blank heating → rolling → controlled cooling → medium and low temperature tempering → finished product marking → inspection → warehousing → delivery.

The manufacturing process parameters for each case are shown in table 2:

table 2 process parameters of the steels of the examples

In which comparative examples 1 to 4 were not subjected to the tempering heat treatment, and comparative examples 5 to 6 were subjected to the tempering heat treatment.

The various properties of the above case are shown in tables 3 to 5:

TABLE 3 mechanical Properties of the steels

TABLE 4 mechanical Properties of 40 ℃ steels

From the data of tables 3 and 4, it can be obtained: after the steel plates are tempered at the medium and low temperatures in the examples 1-6, the yield strength and the tensile strength of the steel plates are greatly improved compared with the performance in a rolling state, and the improvement effect of the yield strength is better than the tensile performance. Meanwhile, the low-temperature impact toughness also tends to be improved.

In connection with comparative example 5, addition of element V without addition of Nb only affects the value of carbon equivalent and the weldability. Does not affect the relevant mechanical properties of the steel plate. The C content of comparative example 6 is too high, except that the carbon equivalent value and the weldability are affected. The steel plate has high strength and poor impact toughness due to the influence on the relevant mechanical properties of the steel plate, and cannot be improved after medium and low temperature tempering.

TABLE 5 weather resistance of the steels

As can be seen from Table 5, the steel plates have good corrosion resistance in both the rolled state and the medium-low temperature tempering state, and after a 72-hour periodic infiltration corrosion test, the relative corrosion rate is less than or equal to 50% compared with Q345B, and the weather resistance is obviously superior to that of ordinary carbon steel. Comparative example 6 has a high content of C element, resulting in deterioration of the surface of the steel sheet and deterioration of corrosion resistance.

The metallographic structures of the steel obtained in the embodiments 1 and 2 are further detected, and as shown in fig. 1 and 2, the steel obtains uniform and fine ferrite, pearlite structures and a small amount of carbide precipitates through a controlled rolling and controlled cooling rolling process and a medium-low temperature rapid tempering technology, so that the yield strength of a rolled steel plate is further improved, and the steel also has excellent low-temperature impact performance, corrosion resistance and good welding performance. As shown in fig. 3 and 4, the steel plate in a rolled state has high and uneven internal stress, and the internal stress of the steel plate is released after medium and low temperature tempering, so that the steel plate has excellent processing and forming properties.

Claims

1. The steel plate for the railway is characterized by comprising the following components in percentage by mass: c: 0.08-0.10%, Mn: 0.90-1.60%, Si: 0.25-0.35%, P: less than or equal to 0.020 wt.%, S: less than or equal to 0.010 wt.%, Cr: 0.10 to 0.30%, Cu: 0.10 to 0.40%, Nb: 0.010-0.040%, Ti: 0.010-0.020% of Al: 0.010-0.050%; the balance of Fe and impurities;

the carbon equivalent CE of the steel is less than 0.45, and the metallographic structure is uniform and fine ferrite, pearlite and carbide precipitates.

2. The steel sheet for a railway according to claim 1, which is composed of the following components in percentage by mass: c: 0.090-0.095%, Mn: 1.30-1.40%, Si: 0.28-0.30%, P: less than or equal to 0.020 wt.%, S: less than or equal to 0.010 wt.%, Cr: 0.15 to 0.26%, Cu: 0.25 to 0.35%, Nb: 0.030-0.035%, Ti: 0.014 to 0.018%, Al: 0.030-0.040%; the balance being Fe and impurities.

3. The steel sheet for railways according to claim 1, wherein the thickness of the steel sheet is in a range of 6 to 30 mm.

4. A method for manufacturing a steel sheet for a railway having an improved yield strength according to claim 1, comprising the steps of: molten iron pretreatment → converter smelting → LF refining → RH refining → continuous casting → blank heating → rolling → controlled cooling → medium and low temperature tempering; wherein the content of the first and second substances,

in the blank heating procedure, the blank is heated for 1.5 to 3.5 hours under the environment of 1050 ℃ and 1220 ℃;

the rolling procedure adopts two-stage rolling, the reduction rate is more than 60%, the initial rolling temperature of rough rolling is 980-1180 ℃, the initial rolling temperature of finish rolling is 830-950 ℃, and the final rolling temperature is 780-900 ℃;

the controlled cooling process controls the temperature of the returned red to be 590-690 ℃;

in the medium-low temperature tempering process, the tempering temperature is 600-680 ℃, and then the temperature is kept for 30-50 min.

5. The manufacturing method for improving the yield strength according to claim 4, wherein the hot metal pretreatment process comprises the step of carrying out composite injection desulfurization on lime powder and magnesium powder injected into a hot metal ladle, and the S content is less than or equal to 0.010 percent by mass after the hot metal pretreatment.

6. The manufacturing method for improving the yield strength according to claim 4, wherein the converter smelting process adopts top-bottom combined blowing and sublance smelting; the LF refining process and the RH refining process adopt a double-ladle car type LF-double-station RH refining technology.

7. The manufacturing method for improving the yield strength according to claim 6, wherein the LF refining process adopts the means of slagging, deep desulfurization, narrow component control, inclusion spheroidization and static stirring to make the molten steel uniform in component and temperature, so that the inclusions are sufficiently floated and meet the morphological requirement.

8. The method according to claim 6, wherein the RH refining process reduces the content of steel grade gas and inclusions by controlling the degree of vacuum and the vacuum treatment time.

9. The method according to claim 4, wherein the continuous casting step comprises a full-process non-oxidation protection casting, and continuous casting of the billet by continuous bending, continuous straightening, full-process multi-fulcrum close-packed rolls and solidification end soft reduction.