CN114540705A

CN114540705A - Smelting method of steel for high-fatigue-performance spring

Info

Publication number: CN114540705A
Application number: CN202210117250.8A
Authority: CN
Inventors: 晁月林; 吕迺冰; 孙齐松; 王翔; 徐士新; 熊家泽; 郭青
Original assignee: Shougang Group Co Ltd
Current assignee: Shougang Group Co Ltd
Priority date: 2022-02-08
Filing date: 2022-02-08
Publication date: 2022-05-27
Anticipated expiration: 2042-02-08
Also published as: CN114540705B

Abstract

The application relates to the technical field of spring steel smelting, in particular to a method for smelting high-fatigue-performance spring steel. The steel for the spring comprises the following chemical components in percentage by mass: c: 0.50% -0.70%, Si: 1.4% -2.0%, Mn: 0.7% -0.9%, Als: 0.015% -0.025%, Cr: 0-1%, Ca: 0.0015 to 0.0025 percent, and the balance of Fe and inevitable impurities. The content of Si, Al, Mn and Ca is controlled through the design of key chemical components, so that the density and the size of inclusions in steel are controlled, and the fatigue property of the spring steel is improved.

Description

Smelting method of steel for high-fatigue-performance spring

Technical Field

The application relates to the technical field of spring steel smelting, in particular to a smelting method of high-fatigue-performance spring steel.

Background

Spring steel is mainly adopted for manufacturing railway spring bars in China, and with the development of high speed and light weight of railways, new requirements are provided for used spring bar fasteners, and the requirements for the steel are that the elasticity limit is large, the stability is good, the fatigue life is long, and the anti-bullet-reducing performance is good.

Railway rails are components that support locomotives and the direction of the locomotives, and are fixed to sleepers of a track bed by elastic fasteners. The elastic fastener is mainly bent and twisted through the elastic strip, and the deformed elastic strip generates fastening pressure to act on the rail, so that the long-term reliable connection between the steel rails is effectively ensured, and the integrity of the rail is kept; meanwhile, the elastic fasteners are used for preventing the longitudinal and transverse movement of the steel rail relative to the sleeper, so that the normal gauge is ensured, and the running safety of the rail vehicle is ensured. In addition, the contact between the train wheels and the steel rails is rigid contact, so that vibration cannot be avoided, and the special elastic structure of the elastic strip can absorb impact energy generated when the train runs, so that the shock absorption effect is achieved. The elastic strip works under repeated alternating stress, bears various effects of bending, torsion, fatigue, corrosion and the like, and also bears extremely high instantaneous impact load when a vehicle passes through, so that the requirement on the performance of the elastic strip is very strict.

Fatigue fracture is the most important failure mode of springs subjected to cyclic stress action of load such as tension, bending, compression, torsion, and impact, and how to improve fatigue resistance of steel for springs is a major research focus.

Disclosure of Invention

The application provides a smelting method of steel for a high-fatigue-performance spring, which aims to solve the technical problem that the steel for the spring is easy to generate fatigue fracture.

In a first aspect, the present application provides a steel for a high fatigue spring, which comprises the following chemical components by mass: c: 0.50% -0.70%, Si: 1.4% -2.0%, Mn: 0.7% -0.9%, Als: 0.015% -0.025%, Cr: 0-1%, Ca: 0.0015 to 0.0025 percent, and the balance of Fe and inevitable impurities.

Optionally, the density of inclusions in the steel for the spring is 27-50/mm²The average size of the inclusions is 1.8 to 2.2 μm.

Optionally, the proportion of the inclusions with the size less than or equal to 5 mu m in the inclusions is more than or equal to 95%.

Optionally, the fatigue life of the steel for the spring is more than or equal to 500 ten thousand times.

In a second aspect, the present application provides a method for smelting steel for a spring according to the first aspect, the method comprising the steps of:

carrying out electric furnace treatment on the scrap steel to obtain molten steel;

carrying out LF refining treatment on the molten steel to obtain LF refined molten steel;

carrying out VD refining treatment on the LF refined molten steel to obtain VD refined molten steel;

continuously casting the VD refined molten steel to obtain high-fatigue-performance spring steel;

and the VD refining treatment comprises the steps of controlling the calcium content in the LF refined molten steel, bottom blowing argon and controlling the pressure of the argon to be less than or equal to 0.15 Mpa.

Optionally, the LF refining process includes controlling Al, Si, and Mn content and controlling slag binary basicity.

Optionally, the range of the binary alkalinity is 3-4.

Optionally, the electric furnace treatment comprises controlling the mass fraction of C to be more than 0.08%, controlling the temperature of the molten steel to be 1620-1650 ℃, and adding tapping slag, refining slag and deoxidizer.

Optionally, the refining slag comprises the following components in percentage by mass: CaO: 25 to 40 percent of Al₂O₃：25％～35％、SiO₂Less than or equal to 10 percent, Al: 10-15%, the balance being unavoidable impurities.

Optionally, the section of the steel for the high fatigue performance spring is 150mm²-250mm²In the continuous casting, the secondary cooling specific water amount is 08-1.0L/kg, and the electromagnetic stirring intensity is 320A/6 Hz-340A/6 Hz.

Compared with the prior art, the technical scheme provided by the embodiment of the application has the following advantages:

the steel for the spring provided by the embodiment of the application comprises the following chemical components by controlling: c: 0.50% -0.70%, Si: 1.4% -2.0%, Mn: 0.7% -0.9%, Als: 0.015% -0.025%, Cr: 0-1%, Ca: 0.0015 to 0.0025 percent, and the balance of Fe and inevitable impurities, and the content of Si, Al, Mn and Ca is controlled through the design of key chemical components, so that the density and the size of inclusions in the steel are controlled, and the fatigue performance of the spring steel is improved.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and together with the description, serve to explain the principles of the invention.

In order to more clearly illustrate the embodiments or technical solutions in the prior art of the present invention, the drawings used in the description of the embodiments or prior art will be briefly described below, and it is obvious for those skilled in the art to obtain other drawings without inventive exercise.

FIG. 1 is a schematic flow chart of a smelting method of steel for a spring provided in an embodiment of the present application;

fig. 2 is a schematic diagram of the size distribution of inclusions provided in example 2 of the present application.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are some embodiments of the present application, but not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.

Specifically, the total oxygen content in the high fatigue performance spring steel is controlled within 6-12 ppm, and the average content is 9.3 ppm.

As an optional embodiment, the density of inclusions in the steel for the spring is 27-50 inclusions/mm²The average size of the inclusions is 1.8 to 2.2 μm.

Specifically, the inclusions are oxides, MnS, oxides coated with sulfides, and the like; the oxide is controlled in a low melting point region, and the plasticizing control can be realized.

As an alternative embodiment, the proportion of the inclusions with a size of 5 μm or less in the inclusions is 95% or more.

As an optional implementation mode, the fatigue life of the steel for the spring is more than or equal to 500 ten thousand times.

In a second aspect, the present application provides a method for smelting steel for a spring according to the first aspect, as shown in fig. 1, the method comprising the steps of:

s1, carrying out electric furnace treatment on scrap steel to obtain molten steel;

as an optional embodiment, the electric furnace treatment comprises the steps of controlling the mass fraction of C to be more than 0.08%, controlling the temperature of the molten steel to be 1620-1650 ℃, and adding tapping slag charge, refining slag and deoxidizer.

Specifically, the addition amount of the tapping slag charge and the deoxidizer is as follows: lime: 50-200 kg/ton steel, fluorite: 20-40 kg/ton steel, silicon carbide: 50-100kg and aluminum ingot: 0.5-1 kg/ton steel.

As an alternative embodiment, the refining slag comprises the following components in percentage by mass: CaO: 25 to 40 percent of Al₂O₃：25％～35％、SiO₂Less than or equal to 10 percent, Al: 10-15%, the balance being unavoidable impurities.

Specifically, the addition amount of the refining slag is 10-20 kg/ton steel.

S2, carrying out LF refining treatment on the molten steel to obtain LF refined molten steel;

as an alternative embodiment, the LF refining process includes controlling the Al, Si and Mn content and controlling the slag binary basicity.

Specifically, lime and fluorite are added according to the slag condition and the sulfur content during tapping, and the binary alkali of the slag is controlled.

In an optional embodiment, the binary alkalinity is in a range of 3 to 4.

Specifically, the binary alkalinity of the refining slag is controlled to be CaO/SiO₂Is 3 to 4, is matched with Al₂O₃Is 15 to 25 percent

S3, carrying out VD (vacuum degassing) refining treatment on the LF refined molten steel to obtain VD refined molten steel;

s4, continuously casting the VD refined molten steel to obtain high-fatigue-performance spring steel;

Specifically, after VD is finished, feeding Si-Ca wire, controlling the mass fraction of Ca in the molten steel to be 0.0015-0.0025%, and after wire feeding, blowing argon at the bottom for weak stirring for more than or equal to 8 min. After VD soft blowing is finished, standing the molten steel for 10min, and then hanging the ladle to enter a continuous casting process; in the continuous casting step, protective casting is performed first.

As an alternative embodiment, the section of the steel for the high fatigue performance spring is 150mm²-250mm²In the continuous casting, the secondary cooling specific water amount is 0.8-1.0L/kg, and the electromagnetic stirring intensity is 320A/6 Hz-340A/6 Hz.

In the embodiment of the application, the quality of the steel scrap is controlled, and the content of Ti in the finished product is reduced from 0.013% to 0.007%; the control level of the oxide density which has the greatest influence on the fatigue performance can reach 14.32/mm²The average size can be up to 2.14 μm.

The process of the present invention will be described in detail below with reference to examples, comparative examples and experimental data.

Example 1

The application provides a steel for a high-fatigue-performance spring, which comprises the following chemical components in percentage by mass: c: 0.56%, Si: 1.8%, Mn: 0.7%, Als: 0.015% -0.025%, Cr: 0. ca: 0.0015 to 0.0025 percent, and the balance of Fe and inevitable impurities.

In a second aspect, the application provides a method for smelting steel for springs, which comprises the following steps when the steel is produced by adopting a full scrap steel electric furnace-LF-VD-CC process:

s1, carrying out electric furnace treatment on scrap steel to obtain molten steel; and controlling the mass fraction of C in the molten steel to be 0.083% at the end point of the electric furnace, and controlling the temperature of the molten steel to be 1620 ℃. Adding the steel tapping slag charge and the deoxidizer: 50kg of lime per ton of steel, 40kg of fluorite per ton of steel, 50kg of silicon carbide and 0.5kg of aluminum ingot per ton of steel; and 20kg of refining slag per ton of steel is added.

S2, carrying out LF refining treatment on the molten steel to obtain LF refined molten steel; adjusting the Al content in the molten steel by feeding an Al wire after the LF seat ladle, adding ferrosilicon and ferromanganese alloy to adjust the components of Si and Mn in the molten steel, controlling the Si content to be 1.6%, the Als content to be 0.015% and the Mn content to be 0.7%, and enabling other alloy component components to meet the standard requirements of steel grades; the mass fraction of the refining slag components is as follows: CaO: 25% of Al₂O₃：25％、SiO₂: 8%, metal Al: 10%, the balance being unavoidable impurities; in the LF stage, lime and fluorite are added according to the slag condition and the sulfur content during tapping, and the binary alkalinity R of the slag is controlled: CaO/SiO₂Is 4, match Al in slag₂O₃15% by mass;

s3, performing VD refining treatment on the LF refined molten steel to obtain VD refined molten steel; feeding Si-Ca line after VD is finished, controlling the mass fraction of Ca in the molten steel to be 0.0015%, and after the line is fed, blowing argon from the bottom for weak stirring for 10min, wherein the Ar pressure is 0.15 Mpa; after VD soft blowing is finished, standing the molten steel for 10min, and then hanging the ladle to enter a continuous casting process;

s4, continuously casting the VD refined molten steel to obtain high-fatigue-performance spring steel; in continuous casting, the secondary cooling specific water amount is 1.0L/kg, the electromagnetic stirring intensity of the matched tail end is 340A/6Hz, and the production section is 150mm²The billet of (2).

The steel for springs of the present example had a total oxygen (T.O) content of 8ppm and a fatigue life of 500 ten thousand or more.

Example 2

The steel for the high-fatigue-performance spring comprises the following chemical components in percentage by mass: c: 0.70%, Si: 1.4%, Mn: 0.9%, Als: 0.015% -0.025%, Cr: 1%, Ca: 0.0015 to 0.0025 percent, and the balance of Fe and inevitable impurities.

The application provides a smelting method of the steel for the spring, which comprises the following steps of:

s1, carrying out electric furnace treatment on scrap steel to obtain molten steel; the mass fraction of C in the molten steel is controlled to be 0.1% at the end of the electric furnace, and the temperature of the molten steel is 1650 ℃. Adding the steel tapping slag charge and the deoxidizer: 200kg of lime per ton of steel, 40kg of fluorite per ton of steel, 100kg of silicon carbide and 1kg of aluminum ingot per ton of steel; and 20kg of refining slag per ton of steel is added. The mass fraction of the refining slag components is as follows: CaO: 40% of Al₂O₃：35％、SiO₂: 9%, metal Al: 10%, the balance being unavoidable impurities;

s2, carrying out LF refining treatment on the molten steel to obtain LF refined molten steel; adjusting the Al content in the molten steel by feeding an Al wire after the LF seat ladle, adding ferrosilicon and ferromanganese alloy to adjust the components of Si and Mn in the molten steel, controlling the Si content to be 1.4 percent, the Als content to be 0.025 percent and the Mn content to be 0.9 percent, and enabling other alloy component components to meet the standard requirements of steel grades; in the LF stage, lime and fluorite are added according to the slag condition and the sulfur content during tapping, and the binary basicity R of the slag is controlled to be CaO/SiO₂3, matching Al in the slag₂O₃25% by mass;

s3, performing VD refining treatment on the LF refined molten steel to obtain VD refined molten steel; after VD, feeding Si-Ca wire, controlling the mass fraction of Ca in the molten steel to be 0.0025%, after wire feeding, blowing argon at the bottom and stirring for 8min, wherein the Ar pressure is 0.15 Mpa; after VD soft blowing is finished, standing the molten steel for 10min, and then hanging the ladle to enter a continuous casting process;

s4, continuously casting the VD refined molten steel,obtaining the spring steel with high fatigue performance; the secondary cooling specific water amount of the continuous casting is 1.0L/kg, the electromagnetic stirring intensity of the matched tail end is 340A/6Hz, and the method is suitable for the continuous casting with the section of 250mm²The billet of (2).

The steel for a spring of the present example had a T.O content of 6ppm, and the distribution of the sizes of inclusions in the wire rod of the present example was shown in FIG. 2, where the abscissa represents the size of inclusions and the abscissa represents the percentage, and the size distribution of inclusions was described, and the proportion of inclusions was 95.1% or less than 5 μm. The fatigue life reaches more than 500 ten thousand times.

Performance detection

The main types of inclusions in the wire rod of the steel for the spring are detected as follows: MnS, CaS and other sulfides, TiN, deoxidation products, and partial oxides wrap the sulfides or accompany with the TiN. The results are given in the table below.

Table 1 table of inclusion detection results.

Table 2 inclusion size and number results table.

Item	1＜ECD≤2μm	2＜ECD≤3μm	3＜ECD≤5μm	5＜ECD≤10μm	10μm＜ECD
						Example 1	57.58	31.45	9.33	1.46	0.18
Example 2	67.050	19.281	8.777	4.173	0.719

Wherein, ECD means size, and further statistics on two types of inclusions which influence the fatigue performance of the product are found:

table 3 oxide and TiN detection results.

As is clear from tables 1 to 3, the steel for springs has an inclusion density of 27 to 50 pieces/mm²The average size of the inclusions is 1.8-2.2 mu m, the average size of the oxides is 2.05-2.14 mu m, and the average size of the TiN is 2.13-2.25 mu m; the number of the inclusions in unit area is small, the control is consistent with the total oxygen content, the average size of the inclusions is also less than or equal to 2.5 mu m, and the proportion of the inclusions of 95.1 percent is less than 5 mu m. Through the control of the inclusions in tables 1 to 3, the fatigue performance of the steel for the spring is finally subjected to a bench test after the steel for the spring is manufactured into a finished spring product, and the test is performed for more than 500 ten thousand times.

One or more technical solutions in the embodiments of the present invention at least have the following technical effects or advantages:

the influence of non-metallic inclusions in steel on fatigue properties depends on the one hand on the type, number, size, shape and distribution of the inclusions; on the other hand, the damage of brittle inclusion and spherical non-deformable inclusion which have weak bonding force with the matrix and large size is the largest due to the restriction of the structure and the properties of the matrix of the steel. The higher the strength level of the steel, the more harmful the inclusions are to the fatigue limit. At present, the Si-Mn deoxidation process is mainly adopted in the production aspect of the railway elastic buckle, the total oxygen content of a final finished product is 20ppm, and the main inclusion in steel is SiO-containing₂Higher larger-sized plastic inclusions; on the basis of a total scrap short-flow long steel making process, according to the characteristic of high total oxygen at the end point of an electric furnace, the production process for producing the anti-fatigue high-strength spring steel by Al deoxidation is developed, so that the total oxygen in the steel is within 6-12 ppm and averagely 9.3ppm, the inclusion control method comprises the step of controlling the electric furnace-LF-VD-CC process to control the density and average size of inclusions, and finally the anti-fatigue performance of the spring steel reaches the level of 500 ten thousand times.

It is noted that, in this document, relational terms such as "first" and "second," and the like, may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.

The foregoing are merely exemplary embodiments of the present invention, which enable those skilled in the art to understand or practice the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. The steel for the spring with high fatigue performance is characterized by comprising the following chemical components in percentage by mass: c: 0.50% -0.70%, Si: 1.4% -2.0%, Mn: 0.7% -0.9%, Als: 0.015% -0.025%, Cr: 0-1%, Ca: 0.0015 to 0.0025 percent, and the balance of Fe and inevitable impurities.

2. The steel for springs as set forth in claim 1, wherein the density of inclusions in the steel for springs is 27 to 50 inclusions/mm²The average size of the inclusions is 1.8 to 2.2 μm.

3. The steel for springs as set forth in claim 2, characterized in that the inclusions having a size of 5 μm or less account for 95% or more of the inclusions.

4. The steel for springs as set forth in claim 1, characterized in that the steel for springs has a fatigue life of 500 ten thousand or more.

5. A method for smelting steel for springs according to any one of claims 1 to 4, characterized by comprising the steps of:

6. The method of claim 5, wherein the LF refining process includes controlling Al, Si, and Mn content and controlling slag binary basicity.

7. The method of claim 6, wherein the binary basicity is in the range of 3 to 4.

8. The method of claim 5, wherein the electric furnace treatment comprises controlling the mass fraction of C to be more than 0.08%, controlling the temperature of the molten steel to be 1620-1650 ℃, and adding a tapping slag charge, a refining slag and a deoxidizer.

9. The method of claim 8, wherein the refining slag comprises the following components in percentage by mass: CaO: 25 to 40 percent of Al₂O₃：25％～35％、SiO₂Less than or equal to 10 percent, Al: 10-15%, the balance being unavoidable impurities.

10. The method as claimed in claim 5, wherein the steel for high fatigue performance springs has a cross-section of 150mm²-250mm²In the continuous casting, the secondary cooling specific water amount is 0.8-1.0L/kg, and the electromagnetic stirring intensity is 320A/6 Hz-340A/6 Hz.