CN112853040B

CN112853040B - 440C stainless bearing steel grain refiner and preparation method thereof

Info

Publication number: CN112853040B
Application number: CN202011631096.3A
Authority: CN
Inventors: 李阳; 杨皓; 李花兵; 孙深; 孙萌; 姜周华; 陈常勇; 李立业; 王琪; 王�琦
Original assignee: Northeastern University China
Current assignee: Northeastern University China
Priority date: 2020-12-31
Filing date: 2020-12-31
Publication date: 2022-05-27
Anticipated expiration: 2040-12-31
Also published as: CN112853040A

Abstract

The invention relates to a 440C stainless bearing steel grain refiner and a preparation method thereof, wherein the 440C stainless bearing steel grain refiner comprises Mg powder, Fe powder and nano C powder, and the mass ratio of the Fe powder to the Mg powder to the nano C powder is 93.9-94.1: 4.9-5.1: 0.9-1.1. According to the 440C stainless bearing steel grain refiner provided by the invention, the adhesion of Mg in the pressed refiner is effectively avoided through the nano C powder, and meanwhile, Mg particles can be quickly separated from the blocky refiner by fine CO bubbles generated by the reaction of the nano C powder and oxygen in molten steel in the steelmaking process, so that magnesium is uniformly distributed in the molten steel. Magnesium can be partially gathered at a crystal boundary in the solidification process of molten steel, and the defect of the surface of the crystal boundary is filled, so that the surface tension on a two-phase interface is reduced, the nucleation speed is increased, the crystal boundary energy is reduced, the driving force for growing the crystal grains is reduced, the growth of the crystal grains is limited, and the performances of the 440C stainless bearing steel, such as strength, toughness and the like, are improved.

Description

440C stainless bearing steel grain refiner and preparation method thereof

Technical Field

The invention belongs to the technical field of metal material grain refinement, and relates to a grain refiner of 440C stainless bearing steel.

Background

440C is used as stainless bearing steel, the carbon content is 1.0 percent, and the chromium content is 16 to 18 percent. The method is mainly used for manufacturing bearing parts working in a corrosive environment and a non-lubricating strong oxidizing atmosphere. 440C has better high-temperature dimensional stability, so the steel can also be used as corrosion-resistant high-temperature bearing steel. In addition, the method can be used for manufacturing high-quality cutters such as medical scalpels, scissors and the like. The bearings are subjected to extreme pressures and friction during operation, so that 440C bearing steel is required to have high and uniform hardness and wear resistance, and a high elastic limit. The requirements on the uniformity of chemical components of bearing steel, the content and distribution of non-metallic inclusions, the distribution of carbides and the like are all very strict, and the steel is one of the most strict steel types in all steel production.

The too coarse grains in the bearing steel can reduce the number of grain boundaries in the material, facilitate the propagation of cracks, and obviously influence the performance of the steel, so that the strength, the plasticity and the toughness of the steel are reduced. The reduction of the mechanical property can lead to the great reduction of the fatigue life of the bearing, and the quality of the bearing does not reach the standard. The Fe-X-C grain refiner and the preparation method thereof disclosed in the Chinese patent CN 101649411B and the ferritic stainless steel grain refiner, the preparation method and the application thereof disclosed in the Chinese patent CN 108642241A both need extremely high temperature when preparing the refiner. Under such high temperature conditions, not only a large amount of energy is consumed for temperature rise, but also the raw materials are inevitably oxidized to generate certain loss. In addition, at the steel-making temperature, magnesium is easy to gasify and quickly floats to the surface of molten steel, and the effect of refining crystal grains is difficult to exert.

Disclosure of Invention

The invention aims to overcome the defects that the existing technology has no grain refiner used for 440C stainless bearing steel prepared at normal temperature and magnesium is easy to gasify at the steelmaking temperature, and aims to provide the grain refiner prepared at normal temperature for 440C stainless bearing steel, which is used for the production process of 440C stainless bearing steel.

In order to achieve the above object, the present invention provides a grain refiner applicable to 440C stainless bearing steel. The method comprises the steps of taking Fe powder, Mg powder and nano C powder as raw materials, and mixing the raw materials according to the mass ratio of the Fe powder to the nano C powder of 93.9-94.1: 4.9-5.1: 0.9-1.1, wherein the purity of the Fe powder and the Mg powder is more than 99.99%, and the particle diameter of the grinded Fe powder and the grinded Mg powder is less than 1 mu m.

The invention also provides a preparation method of the grain refiner for 440C stainless bearing steel, which comprises the following steps:

a. taking Fe powder and Mg powder as raw materials, and mixing according to the weight ratio of the Fe powder to the Mg powder of 94.8-95.1: 4.9-5.2;

b. and C, placing the raw materials prepared in the step a into a ball mill for primary grinding and mixing, drying after grinding, mixing the dried Fe powder and Mg powder with the nano C powder according to the mass ratio of 98.9-99.1: 0.9-1.1, then grinding for the second time, pressing into blocks in a die, keeping the blocks under pressure for 20-30 min, and taking out to obtain the 440C stainless bearing steel grain refiner.

Further, in the step b, in the first grinding of the step b, the ball milling mode is wet grinding; the second grinding is dry grinding.

Further, in the step b, the pressure of the briquetting is 28-30 MPa.

Further, in the step b, the time for the first mixing and grinding is 4-5 h, and the particle diameters of the Fe powder and the Mg powder after ball milling are less than 1 μm.

The invention is also characterized in that the addition amount of the grain refiner is 2-6 kg per ton of steel.

Compared with the prior art, the invention has the following beneficial effects:

the invention provides a grain refiner for 440C stainless bearing steel at normal temperature and a preparation method thereof, aiming at the defect that the grain refiner for 440C stainless bearing steel is not prepared at normal temperature in the prior art. In the using process, the nano C powder in the grain refiner plays two roles: (1) in the pressing process, the particles are fine in size and can be effectively wrapped around Fe powder and Mg powder particles, so that the phenomenon that the particle size is increased due to adhesion of the Mg powder in the pressing process is avoided, and large-size Mg bubbles are easily generated in the large-size Mg particles at the steelmaking temperature and quickly float to the surface of molten steel, so that the Mg treatment effect is influenced; (2) the nano C powder preferentially reacts with oxygen in the molten steel in the steel-making process to generate a large amount of fine CO bubbles, so that the deoxidation effect is achieved, the oxidation of Mg is reduced, and the Mg particles are easily separated from the blocky grain refiner rapidly due to the CO bubbles generated around the Mg particles and are uniformly distributed in the molten steel, so that the utilization rate of magnesium is improved. Magnesium is partially gathered at the crystal boundary in the process of molten steel solidification, and the defect of the surface of the crystal boundary is filled, so that the surface tension on the interface of two phases is reduced, the nucleation speed is increased, the crystal boundary energy is reduced, the driving force for growing the crystal grains is reduced, the growth of the crystal grains is limited, and the purpose of refining the crystal grains is achieved.

Drawings

FIG. 1 is a gold phase diagram of the grains of 440C stainless bearing steel obtained in example 1.

FIG. 2 is a gold phase diagram of the 440C stainless bearing steel grains obtained in example 2.

FIG. 3 is a gold phase diagram of the 440C stainless bearing steel grains obtained in example 3.

FIG. 4 is a gold phase diagram of the grains of 440C stainless bearing steel obtained in comparative example 1.

Detailed Description

Magnesium is an active element with a very low melting point and boiling point, and is normally added into molten steel, so that a large amount of magnesium is volatilized, and the yield is extremely low. The prepared Fe-Mg-nano C block is used as the grain refiner, because the grain diameters of Fe powder and Mg powder are extremely small, the nano C powder is wrapped around the grains, and the mixed powder is very tightly combined under the high pressure of 28-30 MPa, the nano C powder is smaller in size in the pressing process, so that the nano C powder can be effectively wrapped around the Fe powder and the Mg powder grains, and the phenomenon that the size of the grains is increased due to adhesion of the Mg powder in the pressing process is prevented, and the phenomenon that large-size Mg bubbles are easily generated by the large-size Mg grains at the steelmaking temperature and quickly float to the surface of molten steel to influence the Mg treatment effect is avoided. The nano C powder preferentially reacts with oxygen in the molten steel in the steel-making process to generate a large amount of fine CO bubbles, so that the deoxidation effect is achieved, the oxidation of Mg is reduced, and the Mg particles are easily separated from the blocky grain refiner rapidly due to the CO bubbles generated around the Mg particles and are uniformly distributed in the molten steel, so that the utilization rate of magnesium is improved. Magnesium added into the molten steel fills up the surface defects of the crystal grain boundary in the solidification process of the molten steel, thereby reducing the surface tension on a two-phase interface, increasing the nucleation speed, simultaneously reducing the crystal grain boundary energy, reducing the driving force for the growth of the crystal grains, limiting the growth of the crystal grains and refining the crystal grains. Thereby improving the hardness and the obdurability of the 440C stainless bearing steel.

In order to make the technical solution of the present invention better understood by those skilled in the art, the present invention will be further described with reference to specific examples 1, 2, 3 and comparative example 1, but the examples are not intended to limit the present invention.

Example 1

Taking tempered 440C stainless bearing steel added with a grain refiner, wherein the grain refiner accounts for 0.2 percent of the total mass of the 440C stainless bearing steel, and the grain refiner comprises the following chemical components (in mass percent): c: 1.02, Si: 0.45, Mn: 0.4, Cr: 18.03, Ni: 0.57, Mo: 0.53, Mg: 0.0029 and the balance Fe. The grain size is shown in table one.

Example 2

Taking tempered 440C stainless bearing steel added with a grain refiner, wherein the grain refiner is 0.4 percent of the total mass of the 440C stainless bearing steel, and the grain refiner comprises the following chemical components (in mass percent): c: 1.04, Si: 0.46, Mn: 0.4, Cr: 18.49, Ni: 0.61, Mo: 0.54, Mg: 0.0081, and the balance Fe. The grain size is shown in table one.

Example 3

Taking tempered 440C stainless bearing steel added with a grain refiner, wherein the grain refiner accounts for 0.6 percent of the total mass of the 440C stainless bearing steel, and the grain refiner comprises the following chemical components (in mass percent): c: 1.00, Si: 0.45, Mn: 0.4, Cr: 17.84, Ni: 0.59, Mo: 0.53, Mg: 0.0160 and the balance of Fe. The grain size is shown in table one.

Comparative example 1

Taking 440C stainless bearing steel in a tempered state, adding no grain refiner, and comprising the following chemical components in percentage by weight: c: 1.04, Si: 0.46, Mn: 0.4, Cr: 17.67, Ni: 0.59, Mo: 0.54 and the balance Fe. The grain size is shown in table one.

TABLE 1 average grain size in examples 1 to 3 and comparative example 1

As can be seen from Table 1, the crystal grains of the 440C stainless bearing steels obtained in examples 1-3 are significantly smaller than those of comparative example 1. The technical proposal of the invention shows that the 440C stainless bearing steel obtained has smaller crystal grains.

In conclusion, the 440C stainless bearing steel grain refiner prepared by the method can effectively refine grains, and the preparation method is simple and easy to implement, and the loss of the grain refiner in the preparation process is very small.

The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention in other forms, and any person skilled in the art can change or modify the technical content disclosed above into an equivalent embodiment with equivalent changes. However, any simple modification, equivalent change and modification of the above embodiments according to the technical essence of the present invention are within the protection scope of the technical solution of the present invention.

Claims

1. The 440C stainless bearing steel grain refiner is characterized by comprising Fe powder, Mg powder and nano C powder, wherein the mass ratio of the Fe powder to the Mg powder to the nano C powder is 93.9-94.1: 4.9-5.1: 0.9-1.1.

2. The grain refiner of 440C stainless bearing steel according to claim 1, wherein the purity of Fe powder and Mg powder is 99.99% or more.

3. The method for preparing the grain refiner of 440C stainless bearing steel according to claim 1, which comprises the following steps:

4. The preparation method of claim 3, wherein in the step b, the time for the first grinding and mixing is 4-5 h, and the particle diameters of the Fe powder and the Mg powder after ball milling are both less than 1 μm.

5. The method of claim 3, wherein in the first milling of step b, the ball milling means is wet milling; the second grinding is dry grinding.

6. The method according to claim 3, wherein in the step b, the pressure of the briquette is 28 to 30 MPa.