CN114752743A

CN114752743A - Preparation method of 55SiCrA wire rod for automobile suspension spring

Info

Publication number: CN114752743A
Application number: CN202210254054.5A
Authority: CN
Inventors: 李文武; 陶立志; 戴永刚
Original assignee: Jianlong Beiman Special Steel Co Ltd
Current assignee: Jianlong Beiman Special Steel Co Ltd
Priority date: 2022-03-15
Filing date: 2022-03-15
Publication date: 2022-07-15
Anticipated expiration: 2042-03-15
Also published as: CN114752743B

Abstract

A preparation method of a 55SiCrA wire rod for an automobile suspension spring belongs to the field of automobile suspension spring steel materials. The invention aims to solve the technical problems of reducing decarburization of a wire rod and solving the problem of extremely poor structure performance. The process route of the invention is as follows: converter smelting → LF refining → RH vacuum degassing → continuous casting of six-machine six-flow arc square billet continuous casting → steel billet polishing → heating of regenerative heating furnace → high-pressure water dephosphorization → wire rod rolling + coil cooling control → bundling → weighing → card hanging → storage. The tensile strength of the spring steel wire rod produced by the invention is 1005-1045MPa, the shrinkage rate is 51.0-54.7%, the depth of a decarburized layer is reduced to be below 0.6% D, the same-circle performance range is controlled to be within 40MPa, the uniformity of the sorbite proportion is better than 95%, the decarburization of the wire rod is reduced, the problem of great structural performance range is solved, and the fatigue life of the wire rod is prolonged.

Description

Preparation method of 55SiCrA wire rod for automobile suspension spring

Technical Field

The invention belongs to the field of automobile suspension spring steel materials; in particular to a preparation method of a 55SiCrA wire rod for an automobile suspension spring.

Background

The spring steel 55SiCrA is the most commonly used alloy spring steel at present, is mainly used for manufacturing vehicle suspension springs, and is an important part for buffering and damping in a damping system of an automobile chassis. Because of bearing high-frequency reciprocating compression motion for a long time, the material is required to have higher strength, better fatigue life, better damping performance and enough ductility and toughness. In order to ensure that 100 ten thousand fatigue life tests are qualified and have good processability, besides the surface quality, the component segregation and the purity of internal materials of the wire rod are required to be ensured, a proper cooling control process is required to be selected to ensure the tissue form and the performance of the wire rod.

The spring steel 55SiCrA has high Si content, and reasonable heating, controlled rolling and controlled cooling processes are required to reduce decarburization of a wire rod during production; the production characteristics of the wire rod enable the transverse accumulation thickness of the coil on the air cooling roller way to be inconsistent, so that the difference of metallographic structures is generated at different positions of each circle of the coil under the condition of the same fan air volume due to the inconsistent accumulation thickness, the uniformity of the whole structure and performance of the wire rod is further influenced, the local martensite structure of the wire rod is easy to generate when the cooling speed is too high, and the local Soxhlet body quantity of the wire rod is insufficient when the cooling speed is too low.

The invention patent CN102747210A, the stelmor controlled cooling method of 55SiCrA spring steel wire rod, the spinning temperature is controlled to 850 +/-10 ℃; setting the air quantity of the first fan to be 10-100%, and closing the rest fans; the first-stage roller speed is 0.3-0.5 m/s; meanwhile, the opening of the heat preservation cover is controlled, the front 25 m of the wire rod is rapidly cooled to 710 ℃ at the cooling speed of 0-2K/s within the range of 26-100 m, and the collection temperature of 550 ℃ is 630 ℃. The wire rod with high sorbite rate, stable strength and good plasticity can be obtained.

The invention patent CN106734261A, Stelmor air cooling line controlled cooling process for improving the structure and performance of spring steel wire rod, mentions that the spinning temperature is 805 + -15 ℃, the cooling speed of the front two fans is controlled to be 5-13 ℃/s, the temperature of the 4-5 fans is 10-50 ℃, the cooling speed of the 6 th fan and the rear fan is below 3 ℃/s, the wire rod is closed after the wire rod is in the air range of 670 plus 700 ℃, the cooling speed of the heat preservation cover is controlled to be 0.8-2 ℃/s, the temperature of the cover is 580 plus 630 ℃, the obtained structure is pearlite and a small amount of ferrite, the shrinkage can reach above 60%, and the strength, the hardness and the like can meet the performance requirements.

In the prior art, the cooling speed of each section of wire rod is changed by adjusting the air quantity of a stelmor air cooling line fan, so that the generation temperature range of a sorbite structure of the wire rod is controlled, most positions of the wire rod can obtain an ideal structure, but the uniformity problem of the structure and the performance of the wire rod cannot be solved by the above technology.

Disclosure of Invention

The invention aims to provide a preparation method of a 55SiCrA wire rod for an automobile suspension spring, which reduces decarburization of the wire rod and solves the problem of extremely poor structure performance.

The invention is realized by the following technical scheme:

a preparation method of a 55SiCrA wire rod for an automobile suspension spring comprises the following process routes: converter smelting → LF refining → RH vacuum degassing → continuous casting of six-machine six-flow arc square billet continuous casting → steel billet polishing → heating of regenerative heating furnace → high-pressure water dephosphorization → wire rod rolling + coil cooling control → bundling → weighing → card hanging → storage.

The invention relates to a preparation method of a 55SiCrA wire rod for an automobile suspension spring, which comprises the following steps of tapping temperature 1650-1700 ℃ in a converter smelting process, ladle argon bottom blowing strong stirring in the tapping process, and adding a deoxidizing agent and alloy slag: 800-810kg of lime, 10-10.5kg of low-aluminum silicon iron, 9.4-9.6kg of silicomanganese, 8-8.5kg of high-purity silicon iron and 7.5-8kg of low-titanium high-chromium alloy are added after 40 tons of steel are tapped, and 150-155kg of fluorite is added after 50 tons of steel are tapped.

The invention relates to a preparation method of a 55SiCrA wire rod for an automobile suspension spring, wherein carbon powder, ferrosilicon powder or silicon carbide is adopted as a deoxidizer in the LF refining process, the white slag refining time is more than 15 minutes, and the deoxidizer is added in the LF refining process in the sequence: 50-52kg of fluorite particles, 20-21kg of carbon powder and 65-68kg of silicon carbide are added in the first power transmission, and 255kg of silica, 205kg of acid slag, 45-47kg of silicon carbide and 25-26kg of carbon powder are added in batches 10 minutes before the refining is finished.

The invention relates to a preparation method of a 55SiCrA wire rod for an automobile suspension spring, which comprises the following steps of adjusting components in an LF refining process to 0.53-0.57 wt% of C, 1.43-1.50 wt% of Si, 0.63-0.68 wt% of Mn, 0.63-0.68 wt% of Cr, less than or equal to 0.015 wt% of P, less than or equal to 0.015 wt% of S, less than or equal to 0.005 wt% of Al, less than or equal to 0.005 wt% of Ti, less than or equal to 0.0008 wt% of Ca, and transferring the temperature of molten steel at 1602 and 1632 ℃.

The preparation method of the 55SiCrA wire rod for the automobile suspension spring comprises the steps of keeping vacuum for 15-20 minutes when the vacuum degree is less than or equal to 67Pa in the RH vacuum degassing process, carrying out soft blowing for more than 20 minutes after the vacuum is finished, adding 60-80kg of carbonized rice hulls for heat preservation, and transferring to the next working procedure when the temperature of molten steel is 1527-.

The invention relates to a preparation method of a 55SiCrA wire rod for an automobile suspension spring, wherein a six-machine six-flow arc-shaped square billet continuous casting machine is continuously cast into a six-machine six-flow arc-shaped 200mm by 200mm square billet continuous casting machine, and the liquid level insertion depth is 100 plus 120 mm. Filling argon gas in the continuous casting for blowing 3min before casting, and performing argon gas protection in the whole process, wherein the total reduction of the continuous casting billet is 15mm under static soft reduction, the reduction of a 1# withdrawal and straightening machine is 0mm, the reduction of a 2# withdrawal and straightening machine is 3mm, the reduction of a 3# withdrawal and straightening machine is 4mm, the reduction of a 4# withdrawal and straightening machine is 5mm, and the reduction of a 5-6# withdrawal and straightening machine is 0 mm.

The preparation method of the 55SiCrA wire rod for the automobile suspension spring comprises the steps of controlling the heating temperature of a regenerative heating furnace to 870-.

The preparation method of the 55SiCrA wire rod for the automobile suspension spring comprises the steps of controlling the cogging temperature of 900-980 ℃ in the wire rolling process, controlling the large reduction amount to be more than or equal to 53mm, controlling the temperature of 880-910 ℃ in a finishing mill group, and controlling the coiling and spinning temperature of 890-920 ℃.

The invention relates to a preparation method of a 55SiCrA wire rod for an automobile suspension spring, wherein cooling control adopts a stelmor air cooling line, a roller way of the air cooling line is divided into 13 sections, the length of the first section is 3.5 meters, the 2 nd to 12 th sections are respectively 8.8 meters, the 13 th section is 5 meters, the roller speed of the stelmor air cooling line is controlled to be 0.5m/s of the roller speed of the first section, the lead coefficient of the 2 nd to 12 th sections is 3 percent, and the lead coefficient of the 13 th section is 0.9 percent.

The 55SiCrA wire rod for the automobile suspension spring comprises the following components of 0.53-0.57 wt% of C, 1.43-1.50 wt% of Si, 0.64-0.70 wt% of Mn, 0.64-0.70 wt% of Cr, less than or equal to 0.015 wt% of P, less than or equal to 0.015 wt% of S, less than or equal to 0.10 wt% of Ni, less than or equal to 0.08 wt% of Cu, less than or equal to 0.010 wt% of Mo, less than or equal to 0.005 wt% of Al, less than or equal to 0.005 wt% of Ti, and the balance of Fe.

According to the preparation method of the 55SiCrA wire rod for the automobile suspension spring, the Si content in the 55SiCrA component of the spring steel is high, and reasonable heating, rolling and cooling control processes are required to be adopted during production so as to reduce decarburization of the wire rod; the inherent characteristics of the stelmor air cooling line lead the cooling rate of the wire rod to be inconsistent under the same condition, finally lead the uniformity of the structure and the performance of the wire rod to be reduced, the local part of the wire rod is easy to generate martensite structure when the cooling speed is too high, and the local part of the wire rod has insufficient sorbite quantity when the cooling speed is too low. Therefore, the controlled cooling process of the spring steel 55SiCrA can ensure the indexes of subsequent drawing performance, fatigue performance and the like by combining the decarburization of the wire rod and the comprehensive control of performance and structure uniformity.

According to the preparation method of the 55SiCrA wire rod for the automobile suspension spring, disclosed by the invention, the depth of the decarburized layer of the produced spring steel wire rod is reduced to be below 0.6% D, the same-circle performance range is controlled within 40MPa, the uniformity of the sorbite proportion of more than 95% is better, the decarburization of the wire rod is reduced, the problem of great structural performance range is solved, and the fatigue life of the wire rod is prolonged.

According to the preparation method of the 55SiCrA wire rod for the automobile suspension spring, the tensile strength of the produced spring steel wire rod is 1005-1045MPa, the shrinkage rate is 51.0-54.7%, the sorbite proportion is 95-96%, the grain size is 8.5 grade, the decarburization is less than or equal to 0.6% D, and the uniformity of the structure and the performance is greatly improved.

Drawings

FIG. 1 is a metallographic photograph showing the grain size of a 55SiCrA wire rod for automotive suspension springs prepared by the method according to one embodiment;

FIG. 2 is a metallographic photograph showing the sorbite ratio of a 55SiCrA wire rod for automotive suspension springs prepared by the method according to one embodiment;

fig. 3 is a metallographic photograph showing decarburization of a 55SiCrA wire rod for an automotive suspension spring manufactured by the method according to the embodiment.

Detailed Description

The first specific implementation way is as follows:

a preparation method of a 55SiCrA wire rod for an automobile suspension spring comprises the following process routes: converter smelting → LF refining → RH vacuum degassing → continuous casting of a six-machine six-flow arc square billet continuous casting → billet grinding → heating of a regenerative heating furnace → high-pressure water dephosphorization → wire rod rolling + coil cooling control → bundling → weighing → card hanging → storage.

According to the preparation method of the 55SiCrA wire rod for the automobile suspension spring, the tapping temperature is 1650-1700 ℃ in the converter smelting process, the ladle argon bottom blowing strong stirring is carried out in the tapping process, and the addition sequence of the deoxidizer and the alloy slag charge is as follows: after tapping 40 tons, adding 800kg of lime, 10kg of low-aluminum silicon iron, 9.4kg of silicomanganese, 8kg of high-purity silicon iron and 7.5kg of low-titanium high-chromium alloy, and after tapping 50 tons, adding 150kg of fluorite.

This embodiment a preparation method of 55SiCrA wire rod for automobile suspension spring, LF refining process adopt carbon powder, ferrosilicon powder or carborundum as the deoxidier, white sediment refining time should be more than 15 minutes, LF refining process in the deoxidier add order: 50kg of fluorite particles, 20kg of carbon powder and 65kg of silicon carbide are added by first power transmission, and 250kg of silica, 200kg of acid slag, 45kg of silicon carbide and 25kg of carbon powder are added in batches 10 minutes before refining is finished.

According to the preparation method of the 55SiCrA wire rod for the automobile suspension spring, the components in the LF refining process are adjusted to 0.53-0.57 wt% of C, 1.43-1.50 wt% of Si, 0.63-0.68 wt% of Mn, 0.63-0.68 wt% of Cr, less than or equal to 0.015 wt% of P, less than or equal to 0.015 wt% of S, less than or equal to 0.005 wt% of Al, less than or equal to 0.005 wt% of Ti, less than or equal to 0.0008 wt% of Ca, and the temperature of molten steel is transferred at 1602 and 1632 ℃ for the next process.

According to the preparation method of the 55SiCrA wire rod for the automobile suspension spring, RH vacuum degassing is performed in a vacuum maintaining time of 15-20 minutes when the vacuum degree is less than or equal to 67Pa, carbonized rice hulls of 60-80kg are added for heat preservation after soft blowing is performed for more than 20 minutes after the vacuum is finished, and the temperature of molten steel is 1527-.

The preparation method of the 55SiCrA wire rod for the automobile suspension spring comprises the steps of continuously casting a six-machine six-flow arc square billet continuous casting machine into a six-machine six-flow arc 200mm square billet continuous casting machine, inserting the liquid level into the continuous casting machine for 100 plus 120mm, filling argon gas into a tundish for blowing 3min before casting, and performing argon gas protection in the whole process, wherein the total pressure reduction of the continuous casting billet is 15mm under static soft reduction, the pressure reduction of a No. 1 withdrawal and straightening machine is 0mm, the pressure reduction of a No. 2 withdrawal and straightening machine is 3mm, the pressure reduction of a No. 3 withdrawal and straightening machine is 4mm, the pressure reduction of a No. 4 withdrawal and straightening machine is 5mm, and the pressure reduction of a No. 5 withdrawal and straightening machine is 0 mm.

According to the preparation method of the 55SiCrA wire rod for the automobile suspension spring, the temperature of a heating preheating section of a regenerative heating furnace is 885 ℃, the temperature of a heating section is 996 ℃, the temperature of a soaking section is 1017 ℃, the heating time is 114min, and the content of residual oxygen in the furnace is controlled to be below 1.5%.

According to the preparation method of the 55SiCrA wire rod for the automobile suspension spring, the cogging temperature is 900-980 ℃ in the wire rolling process, the large reduction is more than or equal to 53mm, the temperature of the feeding finishing mill group is controlled to be 885 ℃, and the coiling and spinning temperature is 902 ℃.

According to the preparation method of the 55SiCrA wire rod for the automobile suspension spring, the cooling control adopts a stelmor air cooling line, the roller path of the air cooling line is divided into 13 sections, the length of the first section is 3.5 meters, the lengths of the 2 nd section and the 12 th section are respectively 8.8 meters, the length of the 13 th section is 5 meters, the roller speed of the stelmor air cooling line is controlled to be 0.5m/s of the roller speed of the first section, the lead coefficients of the 2 nd section and the 12 th section are 3%, and the lead coefficient of the 13 th section is 0.9%.

The 55SiCrA wire rod for the automobile suspension spring comprises 0.53-0.57 wt% of C, 1.43-1.50 wt% of Si, 0.64-0.70 wt% of Mn, 0.64-0.70 wt% of Cr, less than or equal to 0.015 wt% of P, less than or equal to 0.015 wt% of S, less than or equal to 0.10 wt% of Ni, less than or equal to 0.08 wt% of Cu, less than or equal to 0.010 wt% of Mo, less than or equal to 0.005 wt% of Al, less than or equal to 0.005 wt% of Ti and the balance of Fe.

The preparation method of the 55SiCrA wire rod for the automotive suspension spring according to the embodiment comprises the following components: 0.56 wt%, Si: 1.47 wt%, Mn: 0.66 wt%, Cr: 0.67 wt%, P: 0.010 wt%, S: 0.006 wt%, Ni: 0.01 wt%, Cu: 0.02 wt%, Mo: 0.01 wt%, Al: 0.004 wt%, Ti: 0.002 wt% and the balance Fe.

According to the preparation method of the 55SiCrA wire rod for the automobile suspension spring, Ti, Mo and Ni waste steel is forbidden to be added in the converter smelting process so as to prevent high-temperature oxides from being generated and reduce the service life of a finished spring. The tapping components are adjusted according to the internal control lower limit to reduce the recarburization in the refining process and increase the nitrogen content by stirring, the C content is 0.47-0.50 wt%, the Si content is 1.38-1.43 wt%, the Mn content is 0.60-0.65 wt%, the Cr content is 0.60-0.65 wt%, and the P content is less than or equal to 0.010 wt%. In order to ensure the content of residual aluminum and titanium in the steel, the use level of final deoxidized aluminum and silicon-manganese alloy is required to be controlled, the ferrosilicon only has the function of Si increasing, the alloy adopts low-aluminum alloy, and the content of Al in the steel is required to be controlled below 0.005 wt%.

In the preparation method of the 55SiCrA wire rod for the automobile suspension spring, the refining slag system in the LF refining process is SiO₂25-30 wt%, CaO 48-55 wt%, Al₂O₃The content is 10 to 15 weight percent, the content of FeO and MnO is less than or equal to 0.8 weight percent, and the alkalinity R of the smelting slag system is controlled to be 2.5 to 3.0.

According to the preparation method of the 55SiCrA wire rod for the automobile suspension spring, the RH furnace mainly aims at circular degassing in the RH vacuum degassing process, the alloy components are not adjusted in principle, and corresponding alloy can be added only when the components deviate to perform fine adjustment.

According to the preparation method of the 55SiCrA wire rod for the automobile suspension spring, the crystallizer casting powder in the continuous casting process of the six-machine six-flow arc-shaped square billet continuous casting machine adopts the special peritectic steel casting powder, the start-up pulling speed is controlled to be 0.60m/min, the process pulling speed is 1.30m/min, and the water flow rate of the crystallizer is 125m³The stirring current at the head end of the electromagnetic stirring is 250A, the frequency is 3Hz, the stirring current at the tail end is 100A, the frequency is 18Hz, and the fluctuation of the liquid level in the crystallizer is less than or equal to +/-3 mm.

According to the preparation method of the 55SiCrA wire rod for the automobile suspension spring, the casting blank is ground, the grinding depth of the face part is 2mm, the depth of the inclined plane of the corner part is not less than 10mm, and the surface of the repaired steel blank is ground to be smooth and burr-free.

The preparation method of the 55SiCrA wire rod for the automobile suspension spring comprises the steps of controlling the total length of an air cooling line uncoiling and cooling line to be 105.3 meters in a cooling control process, and arranging 30 centrifugal fans in 10 groups, wherein 3 fans in each group are sequentially arranged from left to right, the air volume of each fan can be independently adjusted, the power of each fan is 160KW, and the maximum air volume is 120000m³H is the ratio of the total weight of the catalyst to the total weight of the catalyst. The air cooling line is provided with a heat-insulating cover to realize delayed cooling, and the cooling speed range is 0.5-20 ℃/s, so that the delayed cooling and the standard cooling can be realized. The air cooling line roller way is divided into 13 sections, the length of the first section is 3.5 meters, the lengths of the 2 nd section to the 12 th section are respectively 8.8 meters, the length of the 13 th section is 5 meters, and each section of roller way is provided with an independent motor to realize the sectional control of the speed of the roller way. Except the first section of roller way, each of the other sections is provided with 2 heat-insulating covers. The roller speed setting of each roller way of the stelmor air cooling line in the embodiment is shown in table 1:

TABLE 1 Stelmo air cooling line each section roller way roller speed setting

Roller way	1 paragraph	2 section	3 paragraph	4 stages	5 paragraph	6 paragraphs of	7 paragraph	8 paragraph	9 paragraph	10 paragraph	11 paragraph	12 sections	13 paragraph
														Lead coefficient%	——	3	3	3	3	3	3	3	3	3	3	3	0.9
Roll speed m/s	0.50	0.52	0.53	0.55	0.56	0.58	0.60	0.61	0.63	0.65	0.67	0.69	0.70
														Length m of roller bed	3.5	8.8	8.8	8.8	8.8	8.8	8.8	8.8	8.8	8.8	8.8	8.8	5.0

In the method for preparing the 55SiCrA wire rod for the automotive suspension spring according to the embodiment, the fan air volume is controlled as shown in table 2: the opening degrees of the front four groups of middle fans are 80 percent, and the opening degrees of the two side fans are 90 percent; the opening degree of the middle fan of the fifth group is 30 percent, and the opening degrees of the fans at the two sides are 40 percent; and the rest fans are turned off.

TABLE 2 Stelmo air-cooled line blower air volume setting

Fan blower

Group 1

2 groups of

3 groups of

4 groups of

5 groups of

6 groups of

7 groups of

8 groups of

9 groups of

10 groups of

Left side of the

90％

40％

Closing device

Intermediate (II)

80％

30％

Closing device

Right side of the

90％

40％

Closing device

In the method for manufacturing the 55SiCrA wire rod for the automotive suspension spring according to the embodiment, the opening/closing control of the heat-retaining cover is shown in table 3: and (3) opening the heat-insulating cover of the roller way from the 1 st section to the 6 th section, closing the heat-insulating cover of the roller way from the 7 th section to the 12 th section, and opening the heat-insulating cover of the roller way from the 13 th section.

TABLE 3 Stelmo air-cooling line each section roller way roller speed setting

Roller bed

1 paragraph

2 section

3 paragraph

4 stages

5 paragraph

6 paragraphs of

7 paragraph

8 paragraph

9 paragraph

10 paragraph

11 paragraph

12 sections

13 paragraph

On/off

Is opened

Close off

Is opened

In the method for manufacturing the 55SiCrA wire rod for the automotive suspension spring according to the embodiment, a high-precision pyrometer is used for monitoring the temperatures of the left, middle and right parts of the laying temperature, 1 group of fans, 2 groups of fans, 3 groups of fans, 4 groups of fans, 5 groups of fans, 6 groups of fans, 7 groups of fans, 8 groups of fans, 9 groups of fans, 10 groups of fans and the position coil.

TABLE 4 coiling temperature (deg.C) at each position of air-cooled roller way

Position of	Spinning	Group 1	2 groups of	Group 3	4 groups of	5 groups of	6 groups of	7 groups of	8 groups of	9 groups of	10 groups of
												Left side of	904	739	669	612	594	598	600	577	561	533	511
Intermediate of	899	732	667	601	589	587	592	573	553	531	506
												Right side of the	903	741	670	607	592	588	602	582	562	541	509
Extreme difference	5	9	3	11	5	11	10	9	9	10	5

According to the preparation method of the 55SiCrA wire rod for the automobile suspension spring, the temperature of the wire rod begins to tend to be stable at the 3 rd group of fans, the generation temperature range of a sorbite structure is reached, and austenite begins to be converted into the sorbite structure. The temperature range of the left, middle and right positions of the wire rod is 3-11 ℃, the transformed pearlite lamellar spacing tends to be consistent in the temperature range, and the sorbite rate, the grain size and the performance uniformity are high.

According to the preparation method of the 55SiCrA wire rod for the automobile suspension spring, each coil of the prepared wire rod is 3.1-3.3 m long, the coil produced by the process is cut into a circle, the circle is segmented according to 300mm, the marks are sequentially 01-10, the performance and the organization are tested, and the obtained coil has the tensile strength of 1005-1045MPa and the extreme difference of 37.0 MPa; the shrinkage is 51.0-54.7%, and the rate is extremely poor by 3.7%; the sorbite proportion is 95-96 percent, and the range is 1 percent; the grain size is 8.5 grade, and the depth of the decarburization layer is 66.36-71.01 μm (less than or equal to 0.6% D). The performance tests are shown in table 5:

TABLE 5 same circle Performance organization

Position of	01	02	03	04	05	06	07	08	09	10
											Ferrite proportion/%)	5％	5％	5％	5％	4％	5％	6％	5％	5％	4％
Sorbid proportion/%)	95％	95％	95％	95％	96％	95％	94％	95％	95％	96％
											Grain size/grade	8.5	8.5	8.5	8.5	8.5	8.5	8.5	8.5	8.5	8.5
Tensile strength/MPa	1041.5	1036.5	1042.2	1034.7	1040.9	1038.4	1007.2	1006.3	1005.2	1006.6
											Shrinkage percentage/%)	51.0	52.0	53.0	51.0	54.0	52.0	51.0	51.0	53.0	54.7
Decarburization/. mu.m	71.01	68.24	66.36	67.51	69.82	68.37	66.46	66.77	69.38	70.12

The metallographic photographs are shown in FIGS. 1 to 3, and it can be seen from FIG. 1 that the grain size is 8.5, from FIG. 2 that the sorbite ratio is 95%, and from FIG. 3 that the decarburized layer depth is 71 μm, 0.59% D.

The second embodiment is as follows:

According to the preparation method of the 55SiCrA wire rod for the automobile suspension spring, the Si content in the 55SiCrA component of the spring steel is high, and reasonable heating, controlled rolling and controlled cooling processes are required to be adopted during production to reduce decarburization of the wire rod; the inherent characteristics of the stelmor air cooling line lead the cooling rate of the wire rod to be inconsistent under the same condition, finally lead the uniformity of the structure and the performance of the wire rod to be reduced, the local part of the wire rod is easy to generate a martensite structure when the cooling speed is too high, and the local sorbite mass of the wire rod is insufficient when the cooling speed is too low. Therefore, the controlled cooling process of the spring steel 55SiCrA can ensure the indexes of subsequent drawing performance, fatigue performance and the like by combining the decarburization of the wire rod and the comprehensive control of the performance and the structure uniformity.

According to the preparation method of the 55SiCrA wire rod for the automobile suspension spring, the depth of the decarburization layer of the produced spring steel wire rod is reduced to be below 0.6% D, the same-circle performance range is controlled within 40MPa, the uniformity of the sorbite proportion is better than 95%, the decarburization of the wire rod is reduced, the problem of great structural performance range is solved, and the fatigue life of the wire rod is prolonged.

According to the preparation method of the 55SiCrA wire rod for the automobile suspension spring, the tensile strength of the produced spring steel wire rod is 1005-1045MPa, the shrinkage rate is 51.0-54.7%, the sorbite proportion is 95-96%, the grain size is 8.5 grade, the decarburization is less than or equal to 0.6% D, and the uniformity of the structure and the performance are greatly improved.

The third concrete implementation mode:

according to the second specific embodiment, the method for preparing the 55SiCrA wire rod for the automobile suspension spring comprises the following steps of tapping at 1650-1700 ℃ in the smelting process of a converter, bottom blowing and strong stirring of argon in a ladle in the tapping process, and adding a deoxidizer and alloy slag: after tapping 40 tons, adding 800kg of lime, 10kg of low-aluminum silicon iron, 9.4kg of silicomanganese, 8kg of high-purity silicon iron and 7.5kg of low-titanium high-chromium alloy, and after tapping 50 tons, adding 150kg of fluorite.

According to the preparation method of the 55SiCrA wire rod for the automobile suspension spring, the addition of Ti, Mo and Ni scrap steel is forbidden in the converter smelting process so as to prevent the generation of high-temperature oxides and reduce the service life of the finished spring. The tapping components are adjusted according to the internal control lower limit to reduce the recarburization in the refining process and increase the nitrogen content by stirring, the C content is 0.47-0.50 wt%, the Si content is 1.38-1.43 wt%, the Mn content is 0.60-0.65 wt%, the Cr content is 0.60-0.65 wt%, and the P content is less than or equal to 0.010 wt%. In order to ensure the content of residual aluminum and titanium in steel, the use level of final deoxidized aluminum and silicomanganese alloy is required to be controlled, ferrosilicon only has the function of increasing Si, the alloy adopts low-aluminum alloy, and the content of Al in steel is required to be controlled below 0.005 wt%.

The fourth concrete implementation mode is as follows:

according to embodiment two the preparation method of 55SiCrA wire rod for automobile suspension spring, LF refining process adopts carbon powder, ferrosilicon powder or carborundum as the deoxidier, white sediment refining time should be more than 15 minutes, the order is added to deoxidier in the LF refining process: 50kg of fluorite particles, 20kg of carbon powder and 65kg of silicon carbide are added by first power transmission, and 250kg of silica, 200kg of acid slag, 45kg of silicon carbide and 25kg of carbon powder are added in batches 10 minutes before refining is finished.

The fifth concrete implementation mode is as follows:

according to the preparation method of the 55SiCrA wire rod for the automobile suspension spring, according to the second specific embodiment, the components in the LF refining process are adjusted to 0.53-0.57 wt% of C, 1.43-1.50 wt% of Si, 0.63-0.68 wt% of Mn, 0.63-0.68 wt% of Cr, 0.015 wt% or less of P, 0.015 wt% or less of S, 0.005 wt% or less of Al, 0.005 wt% or less of Ti, 0.0008 wt% or less of Ca, and the temperature of molten steel is shifted to the next process at 1602-1632 ℃.

The sixth specific implementation mode is as follows:

according to the preparation method of the 55SiCrA wire rod for the automobile suspension spring, the RH vacuum degassing process comprises the steps of keeping the vacuum for 15-20 minutes when the vacuum degree is less than or equal to 67Pa, carrying out soft blowing for more than 20 minutes after the vacuum is finished, adding 60-80kg of carbonized rice hulls for heat preservation, and transferring to the next working procedure when the temperature of molten steel is 1527-.

The seventh concrete implementation mode:

according to the preparation method of the 55SiCrA wire rod for the automobile suspension spring, the continuous casting of a six-machine six-flow arc square billet continuous casting machine is a six-machine six-flow arc 200mm by 200mm square billet continuous casting machine, the liquid level insertion depth is 100 plus 120mm, argon is filled in a middle ladle for blowing and sweeping 3min before casting, and argon is used for protecting the whole process, wherein the total pressure reduction of the continuous casting billet is 15mm under static soft reduction, the pressure reduction of a 1# withdrawal and straightening unit is 0mm, the pressure reduction of a 2# withdrawal and straightening unit is 3mm, the pressure reduction of a 3# withdrawal and straightening unit is 4mm, the pressure reduction of a 4# withdrawal and straightening unit is 5mm, and the pressure reduction of a 5-6# withdrawal and straightening unit is 0 mm.

The specific implementation mode eight:

according to the second specific embodiment, the method for preparing the 55SiCrA wire rod for the automobile suspension spring comprises the steps of heating the preheating section of a regenerative heating furnace at 870-.

The specific implementation method nine:

according to the second specific embodiment, in the method for preparing the 55SiCrA wire rod for the automobile suspension spring, the cogging temperature is 900-.

The specific implementation mode is ten:

according to the second specific embodiment, the stelmor air cooling line is adopted for cooling control, the roller path of the air cooling line is divided into 13 sections, the length of the first section is 3.5 meters, the 2 nd to 12 th sections are respectively 8.8 meters, the 13 th section is 5 meters, the roller speed of the stelmor air cooling line is controlled to be 0.5m/s of the roller speed of the first section, the lead coefficient of the 2 nd to 12 th sections is 3%, and the lead coefficient of the 13 th section is 0.9%.

The preparation method of the 55SiCrA wire rod for the automobile suspension spring comprises the steps of controlling the total length of an air cooling line uncoiling and cooling line to be 105.3 meters in a cooling control process, and arranging 30 centrifugal fans in 10 groups, wherein 3 fans in each group are sequentially arranged from left to right, the air volume of each fan can be independently adjusted, the power of each fan is 160KW, and the maximum air volume is 120000m³H is the ratio of the total weight of the catalyst to the total weight of the catalyst. The air cooling line is provided with a heat-insulating cover to realize delayed cooling, and the cooling speed range is 0.5-20 ℃/s, so that the delayed cooling and the standard cooling can be realized. The air cooling line roller way is divided into 13 sections, the length of the first section is 3.5 meters, the lengths of the 2 nd section to the 12 th section are respectively 8.8 meters, the length of the 13 th section is 5 meters, and each section of roller way is provided with an independent motor to realize the sectional control of the speed of the roller way. Except the first section of roller way, each of the other sections is provided with 2 heat-insulating covers.

The concrete implementation mode eleven:

according to the second embodiment, the 55SiCrA wire rod for the automobile suspension spring comprises 0.53-0.57 wt% of C, 1.43-1.50 wt% of Si, 0.64-0.70 wt% of Mn, 0.64-0.70 wt% of Cr, less than or equal to 0.015 wt% of P, less than or equal to 0.015 wt% of S, less than or equal to 0.10 wt% of Ni, less than or equal to 0.08 wt% of Cu, less than or equal to 0.010 wt% of Mo, less than or equal to 0.005 wt% of Al, less than or equal to 0.005 wt% of Ti, and the balance of Fe.

Claims

1. A preparation method of a 55SiCrA wire rod for an automobile suspension spring is characterized by comprising the following steps: the preparation method of the 55SiCrA wire rod for the automobile suspension spring comprises the following process routes: converter smelting → LF refining → RH vacuum degassing → continuous casting of six-machine six-flow arc square billet continuous casting → steel billet polishing → heating of regenerative heating furnace → high-pressure water dephosphorization → wire rod rolling + coil cooling control → bundling → weighing → card hanging → storage.

2. The method for preparing a 55SiCrA wire rod for an automotive suspension spring according to claim 1, wherein the method comprises the steps of: the tapping temperature in the converter smelting process is 1650-1700 ℃, the ladle argon bottom blowing strong stirring is carried out in the tapping process, and the addition sequence of the deoxidizer and the alloy slag charge is as follows: after tapping 40 tons, adding 800-810kg of lime, 10-10.5kg of low-aluminum silicon iron, 9.4-9.6kg of silicomanganese, 8-8.5kg of high-purity silicon iron and 7.5-8kg of low-titanium high-chromium alloy, and after tapping 50 tons, adding 150-155kg of fluorite.

3. The method for manufacturing a 55SiCrA wire rod for an automotive suspension spring according to claim 2, characterized in that: carbon powder, ferrosilicon powder or silicon carbide is adopted as a deoxidizer in the LF refining process, the white slag refining time is more than 15 minutes, and the deoxidizer is added in the LF refining process in the order: 50-52kg of fluorite particles, 20-21kg of carbon powder and 65-68kg of silicon carbide are added in the first power transmission, and 255kg of silica, 205kg of acid slag, 45-47kg of silicon carbide and 25-26kg of carbon powder are added in batches 10 minutes before the refining is finished.

4. The method for preparing a 55SiCrA wire rod for an automobile suspension spring according to claim 3, which is characterized by comprising the following steps: the components in the LF refining process are adjusted to 0.53-0.57 wt% of C, 1.43-1.50 wt% of Si, 0.63-0.68 wt% of Mn, 0.63-0.68 wt% of Cr, less than or equal to 0.015 wt% of P, less than or equal to 0.015 wt% of S, less than or equal to 0.005 wt% of Al, less than or equal to 0.005 wt% of Ti, less than or equal to 0.0008 wt% of Ca, and the molten steel temperature is transferred at 1602 and 1632 ℃ for the next process.

5. The method for preparing a 55SiCrA wire rod for an automobile suspension spring according to claim 4, wherein the method comprises the following steps: the RH vacuum degassing process comprises the steps of keeping the vacuum for 15-20 minutes when the vacuum degree is less than or equal to 67Pa, carrying out soft blowing for more than 20 minutes after the vacuum is finished, adding 60-80kg of carbonized rice hulls for heat preservation, and transferring to the next working procedure at the temperature of 1527 and 1547 ℃.

6. The method for preparing a 55SiCrA wire rod for an automobile suspension spring according to claim 5, wherein the method comprises the following steps: the continuous casting of the six-machine six-flow arc-shaped square billet continuous casting machine is a six-machine six-flow arc-shaped 200 mm-200 mm square billet continuous casting machine, the liquid level insertion depth is 100 plus 120mm, argon is filled in a middle ladle for purging 3min before casting, the argon is protected in the whole process, the total pressure reduction of the continuous casting billet is 15mm under static soft reduction, the 1# withdrawal straightening machine reduction is 0mm, the 2# withdrawal straightening machine reduction is 3mm, the 3# withdrawal straightening machine reduction is 4mm, the 4# withdrawal straightening machine reduction is 5mm, and the 5-6# withdrawal straightening machine reduction is 0 mm.

7. The method for preparing a 55SiCrA wire rod for an automobile suspension spring according to claim 6, wherein the method comprises the following steps: the temperature of a heat storage type heating furnace in a heating preheating section is 870 plus 930 ℃, the temperature of the heating section is 980 plus 1020 ℃, the temperature of a soaking section is 1010 plus 1030 ℃, the heating time is 100 plus 130min, and the residual oxygen content in the furnace is controlled below 1.5 percent.

8. The method for preparing a 55SiCrA wire rod for an automotive suspension spring according to claim 7, wherein: the cogging temperature of the wire rolling process is 900-980 ℃, the large reduction is more than or equal to 53mm, the temperature of the wire entering a finishing mill group is controlled to be 880-910 ℃, and the coiling and spinning temperature is controlled to be 890-920 ℃.

9. The method for preparing a 55SiCrA wire rod for an automotive suspension spring according to claim 8, wherein: the controlled cooling adopts a stelmor air cooling line, a roller way of the air cooling line is divided into 13 sections, the length of the first section is 3.5 meters, the lengths of the 2 nd to 12 th sections are respectively 8.8 meters, the length of the 13 th section is 5 meters, the roller speed of the stelmor air cooling line is controlled to be 0.5m/s of the roller speed of the first section, the lead coefficient of the 2 nd to 12 th sections is 3 percent, and the lead coefficient of the 13 th section is 0.9 percent.

10. The method for preparing a 55SiCrA wire rod for an automotive suspension spring according to claim 9, wherein: the 55SiCrA wire rod for the automobile suspension spring comprises 0.53-0.57 wt% of C, 1.43-1.50 wt% of Si, 0.64-0.70 wt% of Mn, 0.64-0.70 wt% of Cr, less than or equal to 0.015 wt% of P, less than or equal to 0.015 wt% of S, less than or equal to 0.10 wt% of Ni, less than or equal to 0.08 wt% of Cu, less than or equal to 0.010 wt% of Mo, less than or equal to 0.005 wt% of Al, less than or equal to 0.005 wt% of Ti and the balance of Fe.