JPS61266522A - Powder extruded steel - Google Patents

Abstract

PURPOSE:To obtain a steel having an extremely long fatigue life by forming once a molten steel into powder then working the powder by hot extrusion to form a steel product thereby dispersing extremely finely and uniformly, carbide and non-metallic inclusions. CONSTITUTION:The powder contg. >=60% particles of a carbon steel and low- and high alloy steels contg. 0.1-3.0% carbon and having <=44mu diameter to provide high wear resistance and to decrease compressive deformation is molded to a billet. The billet is put into a container and is worked by one time of hot extrusion to a building material or steel pipe unlike rolling. The non-metallic inclusions are thereby elongated in the longitudinal direction and are made finer than in the case of rolling. The powder extruded steel product of this invention provides the improvement of the service life by about 200-300% in any kinds of steel or applications when compared with the steel products produced by the conventional melting rolling.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for manufacturing a steel material that exhibits excellent performance when used in various tools and rolling bearings that are exposed to severe usage conditions.

(Prior art) In high-carbon cold forging tools, high-speed steel, high-temperature bearings, and steel for corrosion-resistant bearings, the refinement of so-called primary carbides produced during casting is essential for improving performance. Improving the shape of the mold, increasing the forging ratio, and learning about forging methods.

Attempts have been made to adopt the ESR redissolution method.

In order to improve its performance, it is necessary not only to make carbides finer but also to reduce or make them finer nonmetallic inclusions (mainly oxide inclusions and sulfide inclusions).

The amount of sulfide inclusions can be reduced by adjusting the amount of sulfur in the steel.
Furthermore, the amount of oxide inclusions can be reduced by degassing molten steel, but it is difficult to do so beyond a certain point, and conventional techniques are not sufficient to finely disperse large inclusions that have a negative impact on performance. Ta.

(Problems to be Solved by the Present Invention) As mentioned above, it has been desired that steel having finer carbides and nonmetallic inclusions be used as a material for tools and bearings.

The inventors of the present invention have studied the M-adjustment method for steel, which has significantly superior performance in tools and bearings used in high-hardness conditions.

We discovered that by converting the powder into molten steel powder and then hot extruding it into a steel material, carbides and nonmetallic inclusions are dispersed extremely finely and uniformly, making it possible to manufacture steel with an extremely long fatigue life. It is something. Note that in low carbon steels such as carburizing steels, the effect of refining carbides is not direct and small, but instead the effect of refining nonmetallic inclusions becomes more pronounced.

(Means for Solving the Problems) The present invention has been made in view of the above, and its gist is [diameter of carbon steel containing α1 to 3.0% carbon and low/high alloy steel of 44μ or less]. A powder containing 60% or more of particles is formed into a billet.

A method for producing steel characterized by obtaining a steel material by hot extrusion.

Next, we will discuss each component of the present invention. Tools, bearings, and other items that require high wear resistance and low compressive deformation require at least a hardness of Rcso or higher.Usually, 0.5% or higher hardness is required. If carbon is present, HRc of 50 or more can be obtained by converting it into austenite as it is and then quenching it.

On the other hand, when trying to improve toughness by creating an internal part with lower hardness than the surface, such as carburized steel, the internal hardness is HR03.
If it is not more than 0, there is a possibility that dents will be formed due to high surface pressure.

For this purpose, it is necessary to set the lower limit of carbon to 0.1%.

Note that the upper limit of 3.0% is set as the upper limit because even if the content is increased further, both the hardness and the wear resistance are saturated.

It has been found that if the powder does not contain 60% or more of powder with a diameter of 44 μm or less and 60% or more of powder with a diameter of 44 μm or less, nonmetallic inclusions become large as described later, and sufficient performance cannot be obtained.

Here, the ratio of the powder particle size with a diameter of 44μ was specified because 1) the sieve used for particle size control at the powder manufacturing site was 325μ;
The particle size passing through the mesh is 44μ.

2) A sieve finer than this will clog and is not suitable for on-site work. (by.

Why Hot Extrusion is Necessary> Hot extrusion is a process in which a billet is put into a container and extruded several times to quickly turn it into a bar or steel tube, unlike rolling. It can be made finer than by stretching or rolling. By doing so, excellent performance can be obtained as described below.

Next, the reason for the improvement in life due to the miniaturization of carbides and nonmetallic inclusions in the present invention will be described.

Since the present invention is applied to tools and bearings, high hardness (for example, even 1% C) is required to improve wear resistance and compression resistance.
(IRC65 is the maximum), so it is preferable that the range in which stress concentration acts is narrow. The effect of the refinement of carbides and nonmetallic inclusions in the present invention lies in the reduction of this stress concentration effect.

Example) First, a base material whose components have been adjusted in advance is induction melted in a vacuum, and then the molten metal is water atomized in a chamber with an Ar atmosphere at a pressure of 190 kol/14. The obtained powder was dried and reduced at 900° C. in a hydrogen stream. This powder was poured into a rubber mold and formed into a billet at a pressure of 50,001 g/d, then degassed and sealed in a mild steel capsule with a wall thickness of 2H, and the entire capsule was then cold-casted again at 5,000 #//d. After compaction and densification, the billet was hot extruded.

After cooling, remove the mild steel part and use it as a steel material.

Table 1 shows a comparison example of the life of cold forging dies and the life of bearings of steel manufactured by this method compared to melt rolled steel. As described above, the steel material according to the present invention has excellent performance due to the fineness of inclusions in case hardened steel and the fineness of inclusions and carbides in high carbon steel.

Table 1 Comparison of lifespan in cold forging molds Rolled material: Steel ingot → Rolled material Extruded material: Powder → Extruded material = Invention Next, we compared the performance when extruding and forging billets made from powder. Ta. Table 2 shows the lifespan of 5KH51 powder forged and extruded products.

It's a comparison.

Table 2: Comparison of lifespan between powder extruded products (invention) and powder forged products using extrusion punches The reason why extruded products are superior is because of the miniaturization of inclusions through extrusion. This may be true for other steel types as well.

Furthermore, we investigated the relationship between powder particle size and performance. Table 3
investigated the relationship between the proportion of powder with a particle size of 44μ or less and rolling fatigue life.

It can be seen that an excellent lifespan can be obtained when the ratio of particles with a diameter of 44μ or less is 6096 or more. This is probably due to the miniaturization of inclusions.

(Effect) By implementing the present invention, conventional mlI! →It was found that the service life of any steel type or application can be improved by approximately 200-300% compared to rolled steel materials.

Claims (1)

[Claims] It is characterized by forming a powder containing 60% or more of particles with a diameter of 44μ or less of carbon steel containing 0.1 to 3.0% carbon and low/high alloy steel into a billet, and obtaining a steel material by hot extrusion. A method of manufacturing steel.