CN113755761B - A kind of production method of high-strength and toughness automobile suspension spring steel - Google Patents

Abstract

The invention relates to the technical field of automobile suspension spring steel, in particular to high-strength and high-toughness automobile suspension spring steel and a production method thereof. The chemical components of the material by weight percentage are as follows: c: 0.5% -0.6%, Si: 1.2% -1.6%, Mn: 0.60-0.9%, Cr: 0.6% -0.9%, V: 0.01-0.3%, P is less than or equal to 0.015%, S is less than or equal to 0.015%, Ti is less than or equal to 0.0015%, and the weight ratio of all aluminum: 0.0005% -0.0050%, total oxygen: less than or equal to 0.0025 percent, less than or equal to 0.0050 percent of N, less than 0.1 percent of inevitable impurities, and the balance of iron. The invention solves the technical problems of surplus strength and insufficient ductility and toughness of 2000MPa automotive suspension spring steel wires by brand-new chemical component design with low alloy content and low cost and matching with proper converter smelting, refining, continuous casting, continuous rolling, wire rod rolling, drawing, heat treatment and other processes. The tensile strength of the invention can reach 2000MPa and 2100MPa respectively, and the surface shrinkage rate is more than or equal to 45 percent. The spring steel has the excellent high-strength and high-toughness mechanical properties, and also has the advantages of low cost, low decarburization, high surface quality, high purity and excellent fatigue property.

Description

A kind of production method of high-strength and toughness automobile suspension spring steel

technical field

The invention relates to the technical field of automobile suspension spring steel, in particular to a high-strength and toughness automobile suspension spring steel and a production method thereof.

Background technique

55SiCr spring steel is Si-Cr series spring steel, mainly used for making automobile suspension springs. It is the most widely used steel for making automobile suspension springs. This steel has excellent fatigue properties and anti-elasticity reduction properties. .

At present, in the industrial production process, the tensile strength of the oil-quenched and tempered steel wire made of the steel wire rod after drawing and heat treatment can reach 1800MPa (1750MPa~1850MPa) and 1900MPa (1850MPa) according to different production processes. ~1950MPa) and 2000MPa class (1950MPa ~ 2050MPa).

However, in the actual production process of 2000MPa oil quenched and tempered suspension spring steel wire, if there is a certain degree of center segregation in the core of the wire rod material used to make the steel wire, there will be a tempering defect in the core of the steel wire after drawing and heat treatment. With sufficient organization, the strength of the steel wire can finally meet the requirements, but the area shrinkage cannot meet the technical requirements (≥40%), that is, the quality problem of excess strength and insufficient toughness.

In order to solve this quality problem, technicians in the industry usually adopt the method of reducing the wire speed and/or increasing the tempering temperature to eliminate the insufficient structure of the center tempering, thereby increasing the area shrinkage. However, the above method will sacrifice the strength, which will eventually lead to the reduction of the strength of the steel wire, which will not meet the technical standard requirements of the 2000MPa grade steel wire.

SUMMARY OF THE INVENTION

In order to overcome the deficiencies of the prior art, the present invention provides a high-strength and toughness automobile suspension spring steel and a production method thereof, which not only have excellent high-strength and toughness mechanical properties, but also have low cost and low decarburization, high surface quality, and high purity. and excellent fatigue properties.

In order to achieve the above object, the present invention adopts the following technical solutions to realize:

A high-strength and toughness automobile suspension spring steel, its chemical composition is:

C: 0.5%～0.6%, Si: 1.2%～1.6%, Mn: 0.60%～0.9%, Cr: 0.6%～0.9%, V: 0.01%～0.3%, P≤0.015%, S≤0.015%, Ti≤0.0015%, full aluminum: 0.0005%～0.0050%, full oxygen: ≤0.0025%, N≤0.0050%, inevitable impurities less than 0.1%, the rest is iron.

A production method of high-strength and toughness automobile suspension spring steel, which specifically comprises the following steps:

1) The blast furnace molten iron is pretreated and desulfurized. After desulfurization, the S content in the molten steel is ≤ 0.002%, the Ti content is ≤ 0.030%, and the molten iron temperature is ≥ 1320 °C;

2) The converter adopts high carbon tapping, the carbon content of the converter smelting end point is greater than 0.3%, and the converter end point temperature is controlled above 1600 ℃;

3) The converter adopts the double-slag method for smelting, and the P content at the end point of the converter is ≤0.007%;

4) After the converter is tapped, use the aluminum-free deoxidized steel rinse tank or use the cord steel special tank to prevent the increase of Al in the molten steel;

5) Slag removal is carried out after the converter is tapped, the thickness of the slag layer after the slag removal is less than 80mm, and 200-400kg/tank (or 2-4kg/t) of pre-melted wollastonite is added after the slag removal;

6) Use special ferrosilicon L, medium carbon ferromanganese and low carbon ferrochromium for deoxidation and alloying during converter tapping;

7) During the LF refining process, only pre-melted wollastonite is added to make slag, and the addition amount is not less than 800kg/tank (or 8kg/t); after the slag is made, the refining time is 30-70 minutes, and the temperature during the refining process is controlled at 1520-1620 ℃; The oxygen content of molten steel at the end of refining is controlled at 0.0010% to 0.0040%, and the content of acid-soluble Al in molten steel is controlled at 0.0005 to 0.0020%;

8) VD vacuum degassing and pressure holding time is more than 15min, and after breaking the air, weakly blowing argon and stirring for more than 20 minutes;

9) Using bloom continuous casting, the whole process of protection pouring, the superheat degree of molten steel is less than 25 ℃, and the pulling speed is 0.5 ~ 0.7m/min;

10) The heating temperature of the continuous casting billet in the heating furnace is controlled above 1200 ℃ before the 280mm×380mm continuous casting bloom is continuously rolled into a 160mm×160mm continuous rolling billet; the surface of the continuous rolling billet is subjected to secondary full grinding and surface defects Flaw detection and internal ultrasonic flaw detection;

11) The temperature of the continuous rolling billet in the soaking section of the heating furnace is 1030 ~ 1120 ℃, and the heating and holding time is 90min ~ 120min; after the continuous rolling billet is released from the furnace, high-pressure water dephosphorization is carried out, and the phosphorus removal pressure is greater than 22MPa, and the surface iron oxide scale is removed;

12) The diameter of the wire rod is 12～18mm, the temperature of entering the double module is 900～910℃, the spinning temperature is 890～900℃, the cooling rate before the phase change after spinning is 3～7℃/s, and the pearlite phase change temperature is 650～710 ℃, the initial roller speed is 0.4～0.6m/s;

13) Drawing process: the diameter of the steel wire is 11mm~16mm, the drawing speed is 30~50m/min, the number of times of drawing is 1~2 times, and the reduction rate of each pass is 15%~30%; Conduct on-line eddy current flaw detection and on-line grinding of surface defects with a sensitivity below 50 microns;

14) Heat treatment process: electromagnetic induction heating is adopted, the wire speed is 10~25m/min, the quenching temperature is 880~1000℃, the quenching medium is water, the tempering temperature is 350~500℃, and the water is cooled;

15) The finished steel wire is subjected to online surface defect detection and painting marking.

Compared with the existing methods, the beneficial effects of the present invention are:

The invention solves the problem of 2000MPa-class automobile suspension through a new low alloy content, low-cost chemical composition design, and at the same time with appropriate processes such as converter smelting, refining, continuous casting, continuous rolling, wire rod rolling, drawing and heat treatment. The spring steel wire has a technical problem of excess strength and insufficient plasticity and toughness due to the central segregation (insufficient tempering) in the core of the wire rod raw material.

The tensile strength of the invention can reach 2000 MPa grade (1950 MPa-2050 MPa) and 2100 MPa grade (2050 MPa-2150 MPa) respectively, and the area shrinkage rate is all ≥45%. In addition to the above-mentioned excellent mechanical properties of high strength and toughness, spring steel also has low cost and low decarburization, high surface quality, high purity and excellent fatigue properties.

Detailed ways

The invention discloses a high-strength toughness automobile suspension spring steel and a production method thereof. Those skilled in the art can learn from the content of this document and appropriately improve the process parameters to achieve. It should be particularly pointed out that all similar substitutions and modifications are obvious to those skilled in the art, and they are deemed to be included in the present invention. The method and application of the present invention have been described through the preferred embodiments, and it is obvious that relevant persons can make changes or appropriate changes and combinations of the methods and applications described herein without departing from the content, spirit and scope of the present invention to achieve and Apply the technology of the present invention.

A production method of high-strength and toughness automobile suspension spring steel, which specifically comprises the following steps:

1) Hot metal production process: blast furnace ironmaking, hot metal pretreatment desulfurization, S content in molten steel after desulfurization ≤ 0.002%, Ti content ≤ 0.030%, molten iron temperature ≥ 1320 ℃.

2) Converter smelting: The converter adopts high-carbon tapping, the carbon content at the end of the converter smelting is greater than 0.3%, and the end temperature of the converter is 1600 ° C ~ 1650 ° C; Use aluminum-free deoxidized steel shabu-shabu tanks or use cord steel special tanks to prevent molten steel from increasing Al; slag removal is carried out after tapping in the converter. Wollastonite; special ferrosilicon L, medium carbon ferromanganese and low carbon ferrochromium are used for deoxidation and alloying in converter tapping.

3) LF refining: in the LF refining process, only pre-melted wollastonite is added to make slag, and the added amount is not less than 800kg/tank. After the slag is made, the refining time is 30 to 70 minutes, and the temperature during the refining process is controlled at 1520 to 1620 ° C; the oxygen content of the molten steel at the end of refining is 0.0010% to 0.0040%, and the content of acid-soluble Al in the molten steel is 0.0005 to 0.0020%.

4) VD treatment process: VD vacuum degassing and pressure holding time is more than 15min, and argon is weakly blown and stirred for more than 20 minutes after the air is broken.

5) Continuous casting: using bloom continuous casting, the whole process is protected and poured, the superheat degree of molten steel is less than 25 ℃, and the pulling speed is 0.5 ~ 0.7m/min.

6) Continuous rolling: 280mm×380mm continuous casting blooms are continuously rolled into 160mm×160mm continuous rolling billets, and the heating temperature of the continuous casting billets in the heating furnace is controlled above 1200°C; and surface flaw detection and internal ultrasonic flaw detection.

7) Wire rolling: the temperature of the continuous rolling billet in the soaking section of the heating furnace is 1030 ~ 1120 ℃, and the heating and holding time is 90 min ~ 120 min; Wire rod diameter: 12～18mm, temperature of entering double module is 900～910℃, spinning temperature is 890～910℃, cooling rate before phase change after spinning is 3～7℃/s, pearlite phase change temperature is 650～710℃, The initial roller speed is 0.4～0.6m/s.

8) Steel wire production process:

a) Drawing process: steel wire diameter: 11mm~16mm, drawing speed: 30~50m/min, drawing passes 1~2 times, and the surface reduction rate of each pass is 15%~30%; On-line eddy current inspection of surface defects (sensitivity below 50 microns) and on-line grinding.

b) Heat treatment process: electromagnetic induction heating is adopted, the wire speed is 10~25m/min, the quenching temperature is 880~1000℃, the quenching medium is water, the tempering temperature is 350~500℃, and the water is cooled; the finished steel wire is subjected to online surface defects Flaw detection and paint marking.

【Example】

The following are the chemical components and corresponding production processes of the examples and comparative examples in the present invention. Wherein, table 1 is the concrete composition design of comparative example and the high-strength toughness automobile suspension spring steel embodiment of the present invention, table 2 is comparative example and the production process of high-strength toughness automobile suspension spring steel of the present invention, table 3 is comparative example and the present invention Mechanical properties test results of examples of high-strength and toughness automotive suspension spring steels.

Table 1 Specific chemical composition (% by weight)

Example C, % Si, % Mn, % Cr, % V, % P, % S, % Ti, % 1 0.54 1.42 0.68 0.71 0.032 0.012 0.008 0.0008 2 0.56 1.45 0.65 0.68 0.028 0.013 0.006 0.0010 Comparative ratio 0.53 1.47 0.66 0.72 - 0.013 0.005 0.0011

Table 2 Production process situation

Table 3 Mechanical properties test results

Example Tensile strength of steel wire, MPa Shrinkage of steel wire, % Suspension spring fatigue life, ten thousand times 1 1998 49 50 2 2067 50 50 Comparative ratio 1996 32 50

The invention solves the problem of 2000MPa-class automobile suspension through a new low alloy content, low-cost chemical composition design, and at the same time with appropriate processes such as converter smelting, refining, continuous casting, continuous rolling, wire rod rolling, drawing and heat treatment. The spring steel wire has a technical problem of excess strength and insufficient plasticity and toughness due to the central segregation (insufficient tempering) in the core of the wire rod raw material.

The tensile strength of the invention can reach 2000 MPa grade (1950 MPa-2050 MPa) and 2100 MPa grade (2050 MPa-2150 MPa) respectively, and the area shrinkage rate is all ≥45%. In addition to the above-mentioned excellent mechanical properties of high strength and toughness, spring steel also has low cost and low decarburization, high surface quality, high purity and excellent fatigue properties.

The above description is only a preferred embodiment of the present invention, but the protection scope of the present invention is not limited to this. The equivalent replacement or change of the inventive concept thereof shall be included within the protection scope of the present invention.

Claims (5)

1. The production method of the high-strength and high-toughness automobile suspension spring steel is characterized by comprising the following chemical components in percentage by weight:

c: 0.5% -0.6%, Si: 1.2% -1.6%, Mn: 0.60-0.9%, Cr: 0.6% -0.9%, V: 0.01-0.3%, P is less than or equal to 0.015%, S is less than or equal to 0.015%, Ti is less than or equal to 0.0015%, and the weight ratio of all aluminum: 0.0005% -0.0050%, total oxygen: less than or equal to 0.0025 percent, less than or equal to 0.0050 percent of N, less than 0.1 percent of inevitable impurities, and the balance of iron;

the tensile strength of the high-strength and high-toughness automobile suspension spring steel reaches 2000MPa, the tensile strength of 2000MPa is 1950 MPa-2050 MPa, and the surface shrinkage is more than or equal to 45%;

the method specifically comprises the following steps:

1) the blast furnace molten iron is pretreated for desulfurization, and the S content and the Ti content in the desulfurized molten steel are respectively less than or equal to 0.002% and less than or equal to 0.030%;

2) the converter adopts high-carbon steel tapping, the carbon content at the smelting end point of the converter is more than 0.3 percent, and the temperature at the end point of the converter is controlled to be more than 1600 ℃;

3) the converter adopts a double-slag method for smelting, and the content of P at the end point of the converter is less than or equal to 0.007 percent;

4) after tapping of the converter, rinsing the tank by using aluminum-free deoxidized steel or using a special tank for cord steel;

5) slagging off after tapping of the converter;

6) when tapping from the converter, carrying out deoxidation alloying by adopting special ferrosilicon L, medium-carbon ferromanganese and low-carbon ferrochrome;

7) only adding premelted wollastonite for slagging in the LF refining process, wherein the adding amount is not less than 800 kg/tank; refining 30-70 minutes after the slag is manufactured, and controlling the temperature in the refining process to be 1520-1620 ℃; controlling the oxygen content of the molten steel at the refining end point to be 0.0010-0.0040 percent, and controlling the acid-soluble Al content of the molten steel to be 0.0005-0.0020 percent;

8) VD vacuum degassing and pressure maintaining time is more than 15min, and weak argon blowing and stirring are carried out for more than 20min after the air is broken;

9) continuous casting by adopting a bloom, protecting and pouring in the whole process, wherein the superheat degree of molten steel is less than 25 ℃, and the drawing speed is 0.5-0.7 m/min;

10) before a 280mm multiplied by 380mm continuous casting bloom is continuously rolled and cogging into a 160mm multiplied by 160mm continuous rolling billet, the heating temperature of the continuous casting billet in a heating furnace is controlled to be more than 1200 ℃; carrying out secondary full grinding, surface defect flaw detection and internal ultrasonic flaw detection on the surface of the continuously rolled blank;

11) the temperature of the continuous rolling blank in a soaking section of a heating furnace is 1030-1120 ℃, and high-pressure water dephosphorization is carried out after the continuous rolling blank is taken out of the furnace to remove surface iron oxide scales;

12) the diameter of the wire rod is 12-18 mm, the temperature of the wire rod entering the double modules is 900-910 ℃, and the spinning temperature is 890-900 ℃; cooling speed after spinning before phase change is 3-7 ℃/s, pearlite phase change temperature is 650-710 ℃, and initial roller speed is 0.4-0.6 m/s;

13) drawing process: the diameter of the steel wire is 11-16 mm, the drawing speed is 30-50 m/min, the drawing passes are 1-2 passes, and the surface reduction rate of each pass is 15-30%;

14) the heat treatment process comprises the following steps: electromagnetic induction heating is adopted, the steel wire speed is 10-25 m/min, the quenching temperature is 880-1000 ℃, the quenching medium is water, the tempering temperature is 350-500 ℃, and the water is cooled;

15) and carrying out online surface defect flaw detection and paint spraying marking on the finished steel wire.

2. The production method of the high-strength high-toughness automobile suspension spring steel according to claim 1, wherein the temperature of blast furnace molten iron in the step 1) is more than or equal to 1320 ℃.

3. The production method of the high-strength high-toughness automobile suspension spring steel according to claim 1, wherein the thickness of the slag layer after slag skimming in the step 5) is less than 80mm, and 200-400 kg/tank of pre-melted wollastonite is added after slag skimming.

4. The production method of the high-strength high-toughness automobile suspension spring steel according to claim 1, wherein the heating and heat preservation time in the step 11) is 90-120 min, and the dephosphorization pressure is greater than 22 MPa.

5. The production method of the high-strength high-toughness automobile suspension spring steel according to claim 1, wherein in the step 13), surface defects are subjected to online eddy current testing and online coping before the steel wire is drawn, and the sensitivity of the online eddy current testing of the surface defects is less than 50 microns.