CN112853040B - A kind of 440C stainless bearing steel grain refiner and preparation method thereof - Google Patents

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

A kind of 440C stainless bearing steel grain refiner and preparation method thereof

technical field

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

Background technique

As a stainless bearing steel, 440C has a carbon content of 1.0% and a chromium content of 16% to 18%. Mainly used to manufacture bearing parts working in corrosive environment and non-lubricated strong oxidizing atmosphere. 440C has good high temperature dimensional stability, so it can also be used as corrosion resistant high temperature bearing steel. In addition, it can also be used to manufacture high-quality knives, such as medical scalpels, scissors, etc. Bearings are subjected to great pressure and friction during operation, so 440C bearing steel is required to have high and uniform hardness and wear resistance, as well as high elastic limit. The requirements for the uniformity of the chemical composition of the bearing steel, the content and distribution of non-metallic inclusions, and the distribution of carbides are very strict, and it is one of the most stringent steel grades in all steel production.

The grains in bearing steel are too coarse, which will reduce the number of grain boundaries inside the material, make the expansion of cracks easier, significantly affect the properties of the steel, and reduce the strength, plasticity and toughness of the steel. The reduction of the above mechanical properties will lead to a significant decrease in the fatigue life of the bearing, and the bearing quality will not meet the standard. "Fe-X-C grain refiner and its preparation method" published by Chinese patent CN 101649411B and "a ferritic stainless steel grain refiner, its preparation method and application" published by Chinese patent CN 108642241 A in the preparation of fine When chemicals are used, extremely high temperatures are required. Under such high temperature conditions, not only will a lot of energy be consumed for heating, but also the raw materials will inevitably be oxidized, resulting in a certain loss. In addition, at the steelmaking temperature, magnesium is easily vaporized and quickly floats to the surface of the molten steel, making it difficult to play its role in refining grains.

SUMMARY OF THE INVENTION

The present invention is aimed at the deficiencies that the existing technology does not have the normal temperature preparation of the grain refiner used for 440C stainless bearing steel and that magnesium is easily gasified at the steelmaking temperature, and aims to provide a 440C stainless steel prepared at normal temperature Grain refiner for bearing steel for 440C stainless bearing steel production process.

In order to achieve the above purpose, the present invention provides a grain refiner suitable for 440C stainless bearing steel. It uses Fe powder, Mg powder and nano-C powder as raw materials, and is batched according to the mass ratio of Fe powder, Mg powder and nano-C powder as 93.9-94.1:4.9-5.1:0.9-1.1, wherein Fe powder, Mg powder The purity of the powder is above 99.99%, and the particle diameter of Fe powder and Mg powder after grinding must be less than 1 μm.

The present invention also provides the above-mentioned preparation method of the grain refiner for 440C stainless bearing steel, and the preparation method of the grain refiner comprises the following steps:

a. Using Fe powder and Mg powder as raw materials, according to the mass ratio of Fe powder and Mg powder, which is 94.8～95.1:4.9～5.2, the ingredients are proportioned;

B, the raw material prepared in step a is placed in a ball mill for the first time grinding and mixing, and drying is carried out after grinding, and the powder of the dried Fe powder+Mg powder and the nano-C powder are 98.9～99.1 by mass ratio: After mixing the components 0.9-1.1, they are ground for a second time, and then pressed into a block in a mold, kept under pressure for 20-30 minutes, and taken out to obtain a 440C stainless bearing steel grain refiner.

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

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

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

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

With respect to the prior art, the beneficial effects of the present invention are as follows:

The invention provides a grain refiner for 440C stainless bearing steel at normal temperature and preparation thereof, aiming at the deficiency of the existing technology that there is no normal temperature preparation of the grain refiner used for 440C stainless bearing steel. In the process of use, the nano-C powder in the grain refiner has two functions: (1) During the pressing process, due to its small size, it can be effectively wrapped around Fe powder and Mg powder particles, preventing The Mg powder sticks during the pressing process, which causes the particle size to become larger, and the large-sized Mg particles are prone to generate large-sized magnesium bubbles at the steelmaking temperature, which quickly float to the surface of the molten steel, thereby affecting the Mg treatment effect; (2) Nano C powder preferentially reacts with the oxygen in molten steel during the steelmaking process to generate a large number of fine CO bubbles. On the one hand, it plays a role in deoxidation and reduces the oxidation of Mg. The Mg particles are quickly separated from the block-like grain refiner and evenly distributed in the molten steel, which improves the utilization rate of magnesium. Magnesium segregates at the grain boundary during the solidification of molten steel, filling the surface defects of the grain boundary, thereby reducing the surface tension on the two-phase interface, increasing the nucleation speed, reducing the grain boundary energy and reducing the grain length. The large driving force limits the growth of the grains, so as to achieve the purpose of refining the grains.

Description of drawings

FIG. 1 is a metallographic diagram of the crystal grains of the 440C stainless bearing steel obtained in Example 1. FIG.

FIG. 2 is a metallographic diagram of the crystal grains of the 440C stainless bearing steel obtained in Example 2. FIG.

3 is a metallographic diagram of the crystal grains of the 440C stainless bearing steel obtained in Example 3. FIG.

4 is a metallographic diagram of the grains of 440C stainless bearing steel obtained in Comparative Example 1.

Detailed ways

Magnesium is a very active element with low melting point and boiling point. Under normal circumstances, magnesium will volatilize in molten steel, and the yield is extremely low. In the present invention, the prepared Fe-Mg-nano-C block is used as the grain refiner, because the particle diameters of Fe powder and Mg powder are extremely small, and the nano-C powder will be wrapped around the particles, and under high pressure of 28-30MPa In the process of pressing, due to the smaller size of the nano-C powder, it can be effectively wrapped around the Fe powder and Mg powder particles, preventing the Mg powder from sticking during the pressing process and causing the particle size to become larger, so as to avoid Therefore, the large-sized Mg particles are prone to generate large-sized magnesium bubbles at the steelmaking temperature, which quickly float to the surface of the molten steel, which affects the effect of Mg treatment. The nano-C powder reacts preferentially with the oxygen in the molten steel during the steelmaking process to generate a large number of small CO bubbles. On the one hand, it plays the role of deoxidation and reduces the oxidation of Mg. It is easy to make the Mg particles quickly break away from the massive grain refiner, and evenly distribute in the molten steel, which improves the utilization rate of magnesium. The magnesium added to the molten steel fills the surface defects of the grain boundary during the solidification of the molten steel, thereby reducing the surface tension on the two-phase interface, increasing the nucleation speed, reducing the grain boundary energy and reducing the grain growth. The driving force limits the growth of grains and refines the grains. Thus, the hardness and toughness of the 440C stainless bearing steel are improved.

In order to enable those skilled in the art to better understand that the technical solutions of the present invention can be implemented, the present invention is further described below in conjunction with specific embodiments 1, 2, 3 and comparative example 1, but the examples are not intended to limit the present invention.

Example 1

Take the tempered 440C stainless bearing steel with grain refiner added, wherein the grain refiner is 0.2% of the total mass of the 440C stainless bearing steel, and its chemical composition (mass fraction wt%) is: C: 1.02, Si: 0.45, Mn: 0.4, Cr: 18.03, Ni: 0.57, Mo: 0.53, Mg: 0.0029, and the rest are Fe. Its grain size is shown in Table 1.

Example 2

Take the tempered 440C stainless bearing steel with grain refiner added, wherein the grain refiner is 0.4% of the total mass of the 440C stainless bearing steel, and its chemical composition (mass fraction wt%) is: C: 1.04, Si: 0.46, Mn: 0.4, Cr: 18.49, Ni: 0.61, Mo: 0.54, Mg: 0.0081, and the rest are Fe. Its grain size is shown in Table 1.

Example 3

Take the tempered 440C stainless bearing steel with grain refiner added, wherein the grain refiner is 0.6% of the total mass of the 440C stainless bearing steel, and its chemical composition (mass fraction wt%) is: C: 1.00, Si: 0.45, Mn: 0.4, Cr: 17.84, Ni: 0.59, Mo: 0.53, Mg: 0.0160, and the rest are Fe. Its grain size is shown in Table 1.

Comparative Example 1

Take tempered 440C stainless bearing steel without grain refiner, its chemical composition (mass fraction wt%) is: C: 1.04, Si: 0.46, Mn: 0.4, Cr: 17.67, Ni: 0.59, Mo: 0.54, and the rest is Fe. Its grain size is shown in Table 1.

Table 1 Average grain size in Examples 1 to 3 and Comparative Example 1

It can be seen from Table 1 that the crystal grains of the 440C stainless bearing steel obtained in Examples 1 to 3 are significantly smaller than those in Comparative Example 1. It is explained that the crystal grains in the 440C stainless bearing steel obtained by the technical solution of the present invention are relatively small.

To sum up, the 440C stainless bearing steel grain refiner prepared by the method of the present invention can effectively refine the grains, and the preparation method is simple and feasible, and the loss of the grain refiner in the preparation process is extremely small.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention in other forms. Any person skilled in the art can use the above-disclosed technical content to change or remodel into equivalent embodiments with equivalent changes. . However, any simple modifications, equivalent changes and modifications made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solutions of the present invention still belong to the protection scope of the technical solutions of the present invention.

Claims (6)

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:

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.

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.

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