JPH0356647A - Sintered chromium-molybdenum alloy - Google Patents

Abstract

PURPOSE:To obtain the powder metallurgical sintered chromium-molybdenum alloy by which machine elements and structural parts which are inexpensive and having precision can be manufactured by specifying the compsn. constituted of Cr, Mo, VC and Fe and incorporating a specified amt. of foams thereto. CONSTITUTION:Chromium steel powder and metallic powder such as Mo and V are mixed in a prescribed ratio, to which an aggregate is furthermore added to obtain raw material powder. The raw material powder is subjected to compacting, and the green compact is subjected to properly controlled sintering. Next, the sintered body is subjected to gas carburizing to form VC. Thus, the sintered chromium-molybdenum alloy constituted of, by weight, 1 to 3% Cr, 0.1 to 0.5% Mo, 0.1 to 0.5% VC and the balance Fe and having 6 to 13% content of foams can be obtd. In this way, the above alloy in which the characteristics of carburized steel is obtd. by a powder metallurgy method and by which machine elements or the like which are inexpensive and having precision are manufacturable can be obtd.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is a sintered chromium-molybdenum alloy, more specifically, the characteristics of carburized steel are obtained by means of powder metallurgy, and an inexpensive and precise machine element is produced. and sintered chromium-molybdenum alloys capable of producing structural parts.

[Prior art] The characteristics of carburized steel are physical properties that correspond to steel type SCM415, which is standardized for mechanical structures.
415 has 0.13 to 0.18% carbon and 0.1% silicon.
5-0.35%, manganese 0.60-0.85%, chromium 0.90-1.20%, molybdenum 0.15-0.
It has a composition of 0.30%. This material is manufactured by forging, cutting, and heat treatment, and is used as a metal material that requires strength and wear resistance, such as clutches and pinions. There are almost no sintered W4 types obtained by current powder metallurgy methods that have such characteristics.

[Problem to be solved by the invention] If the characteristics of carburized steel are attempted to be obtained using current powder metallurgy techniques, only similar characteristics can be obtained, and even if they could be obtained, the manufacturing process would be complicated. The cost is too high, resulting in an expensive alloy with almost no marketability. Therefore, the present invention has been made in view of these points, and is a sintered chromium-molybdenum material that can obtain the characteristics of carburized steel by means of powder metallurgy, and can be manufactured into inexpensive and precise mechanical elements and structural parts. The purpose is to provide alloys. [Means for Solving the Problems] In order to solve such problems, in the present invention, chromium is 1 to 3% and molybdenum is 0.1 to 0.5% by weight.
, the composition was 0.1 to 0.5% vanadium carbide, the remainder was iron, and the air bubble content was 6 to 13%. [Function] With this configuration, it is possible to obtain a sintered body having stable physical properties with a bubble content of about 6 to 13% as a low-density sintered body, and moreover, it is possible to obtain a sintered body having stable physical properties with a bubble content of about 6 to 13%. The subsequent physical property values are obtained. In this way, the properties of carburized steel can be obtained by means of powder metallurgy, resulting in a sintered chromium-molybdenum alloy from which mechanical elements and structural parts can be manufactured at low cost and with precision.

[Examples] The present invention will be described in detail below based on preferred examples.

First, in this example, metal powders such as molybdenum and vanadium are added using chromium steel powder as a matrix. In this case, the metal added to improve the properties of the sintered body is made into a fine powder of its compound or intermetallic compound, and a raw material powder for compaction is prepared by mixing a lubricant with chromium steel powder as the main component.

Next, this mixed powder is pressure-molded to form a compact (green). In this case, the dimensions and weight should be ±0.015 per unit.
This is done with an accuracy of g. Subsequently, this green compact is placed in a vacuum heating furnace and vacuum sintered.

The sintering process includes dewaxing, preheating (first sintering), and sintering (second sintering).
The process consists of sintering) and cooling, and each process is performed in the same room. The conditions in this case are that the dewaxing process is from room temperature to 220℃ for 10~220℃.
It was carried out at an evacuation rate of 600 liters/min under a reduced pressure of 20 mmJIg, and then heated at a temperature increase of 5°C/min at aoo°C to a Kieb vacuum of 10-'Torr of about 20~
Sintering is carried out for 30 minutes and further heated at a temperature of 1,220 to 1,240°C. During heating, Ar gas is introduced from 900° C. and the degree of vacuum is lowered from 10-'Torr to 2-JTorr to suppress sublimation of volatile matter from the green compact and generation of carbon atmosphere in the furnace.

The time during this period varies depending on the amount of compacted powder inserted into the furnace, but the degree of vacuum becomes stable and sintering is completed in about 30 minutes.

Next, gas carburizing is performed. In this process, the sintered body is heated to a temperature of 90 to 90% in a mixed atmosphere of carbon monoxide and carbon dioxide.
Carburizing is performed by heating to a temperature of 830 to 880°C, followed by quenching by rapid cooling at a temperature of 830 to 880°C.

In the above process, carrying out the initial dewaxing step at 220°C allows complete dewaxing to be performed in a reduced pressure with low oxygen content to avoid the rise in boiling point due to halthration and salutulation of the wax component, which is the main component of the lubricant. be. Furthermore, a major feature of the present invention lies in the temperature range in which vanadium mixed as an additive metal is not precipitated and grain boundary diffusion occurs.

In this example, the composition of the alloy is 1 to 3% by weight of chromium, 0.1 to 0.5% of molybdenum, 0.1 to 0.5% of vanadium carbide, and the remainder is iron. has. In this case, the bubble content is between 6 and 13%. If the content of chromium is less than the above-mentioned components, the tensile strength of carburization cannot be obtained, and if it is too large, it becomes too expensive. Furthermore, if molybdenum and vanadium carbide are too less than the above-mentioned components, hardness cannot be obtained, and if they are too large, the product will be too expensive. The bubble content is
If it is too small, the dimensional accuracy will deteriorate, and if it is too large, the strength will be reduced, so it is limited to the above range. In this example, since the bubble content was set within the above range, a sintered body with low density and stable physical properties was obtained.

Furthermore, in order to minimize dimensional changes after sintering, proper selection of the type and amount of lubricant (wax), sintering temperature, and degree of vacuum (Ar) also have a large effect on material properties. There is.

FIG. 1 shows a micrograph of the structure before carburizing and quenching, and FIG. 2 shows a comparison result of the strength and wear resistance of the sintered body of the present invention and SCM415.

In addition, the green compact produced in the above example (sintering condition 1240
The density, tensile strength, elongation, and hardness of the sintered body according to this example (solid line) and the sintered standard product SMF2025 (dotted line) were measured using a hydraulic lOO ton press (℃/60IIlin).
The results obtained by comparing the results are shown in FIGS. 3 to 5.

The sintered body of the present invention is a conventional sintered body (SMF2025),
Compared to materials such as SCM415, it has a lower specific gravity and is porous, so its tensile strength is weaker, but the carburized layer can be more than doubled by carburizing and quenching. In addition, the quenching hardness is HRC45~
60, which is extremely high, and the wear resistance is much improved. Since the structure before quenching is composed of ferrite and low carbon, it is characterized by a soft, elongated porous structure with extremely little dimensional change. Furthermore, since carburizing is carried out as desired by gas, it penetrates into the capillary pores and can perform deep hardening.

In addition, SCM415 has poor hardenability, and when making parts that can withstand repeated wear such as molds, the surface is nitrided to manufacture parts such as molds, clutches, pinions, etc. , is shallow at about 0.1 mm and cannot withstand long-term use.However, the present invention compensates for such drawbacks and improves the SC.
This material satisfies the quality improvement of M415 equivalent products and cost reduction through sintering. [Effects of the Invention] As explained above, the present invention provides sintered chromium-molybdenum that can obtain the characteristics of carburized steel by means of powder metallurgy, and can produce inexpensive and precise mechanical elements and structural parts. It becomes possible to donate alloys.

[Brief explanation of drawings]

FIG. 1 is a micrograph (magnification: 100 times) of the sintered alloy of the present invention before carburizing and quenching, and shows a structure diagram showing the metal structure;
Figure 2 is a table comparing the performance of the sintered alloy of the present invention and SCM415, and Figures 3 to 5 are characteristic diagrams comparing the performance of the sintered alloy of the present invention and the standard sintered product SMF2025. It is.斂叡g /cc ) Figure 3 Z-ku (9/CC) Figure 5 Tsuba ((]/CC) Figure 4

Claims (1)

[Claims] 1) Chromium is 1-3% and molybdenum is 0.1-3% by weight
A sintered chromium-molybdenum alloy having a composition of 0.5% vanadium carbide, 0.1 to 0.5% vanadium carbide, and the remainder iron, with a bubble content of 6 to 13%.