RU2482208C2 - Low-alloyed steel powder - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: water-sprayed previously alloyed steel powder contains the following components, in wt %: 0.4-2.0 Cr, 0.1-0.8 Mn, less than 0.1 V, less than 0.1 Mo, less than 0.1 Ni, less than 0.2 Cu, less than 0.1 C, less than 0.25 O, less than 0.5 unavoidable admixtures, balance - iron. The powder composition on the basis of the iron comprises a steel powder mixed with 0.35-1 wt % of graphite, 0.05-2 wt % of lubricant materials, and optionally, copper in the amount of up to 3%, and solid phase materials, and agents that improve treatability. A sintered item having perlite/ferrite microstructure is produced by means of pressing of a powder composition under the pressure of 400-2000 MPa, sintering in the reducing atmosphere at the temperature making 1000-1400°C and if required, forging of the heated item at the temperature making more than 500°C or thermal processing, or tempering of the produced item.

EFFECT: item has high ultimate strength, yield strength, extension and hardness.

13 cl, 2 tbl, 1 ex

Description

The present invention relates to a low alloy powder based on iron, a powder composition containing a powder and other additives, as well as an article obtained by pressing and sintering a powder composition based on iron containing a new low alloy steel powder. The mechanical properties of a product made from the powder according to the present invention are comparable to the mechanical properties of a product made from a more highly alloyed and more expensive diffusion bonded powder.

In various industries, the use of metal products made by pressing and sintering of metal and powder compositions is increasingly used. A number of different products of various shapes and thicknesses are produced while constantly increasing the requirements for their quality, because it is desirable to reduce their cost. Since the pressing and sintering of iron-based powder compositions in combination with a high degree of material utilization results in products having an almost final or close shape and requiring minimal machining to achieve a given shape, these methods have a great advantage over traditional methods of forming metal parts, such as molding or machining of bar stocks or forgings.

However, one of the problems associated with the method of pressing and sintering is that the sintered product has a certain number of pores that reduce its strength. Basically, there are two ways to overcome the negative impact on the mechanical properties caused by the porosity of the product. 1) The strength of the sintered product can be increased by the introduction of alloying elements such as carbon, copper, nickel, molybdenum and the like. 2) The porosity of the sintered product can be reduced by increasing the compressibility of the powder composition and / or increasing the pressing pressure to obtain a higher density of the untreated product or to increase the degree of shrinkage of the product during sintering. In practice, a combination of product hardening is used as a result of the addition of alloying elements and the minimization of porosity. Thus, various compositions of low alloy steel powders and methods for pressing such powders to obtain a PM product (powder metallurgy) having high strength and hardness are known. However, a characteristic feature of PM products is their relatively low viscosity compared to deformable steel materials. The so-called “diffusion-alloyed powders based on iron”, having a relatively high compressibility, despite the high degree of alloying, make it possible to obtain pressed and sintered products with high viscosity and strong elongation combined with high strength compared to pre-alloyed powders.

However, the drawback of currently used diffusion-alloyed powders is the relatively high content of expensive alloying elements, such as molybdenum and nickel. It was unexpectedly found that as a result of careful selection of a combination of alloying elements such as chromium and manganese, with their relatively low content, pre-alloyed powder can be obtained that gives the pressed and sintered product mechanical properties, such as elongation and strength, at the same or close the level that can be obtained by using a more alloyed, diffusion bonded powder.

US Pat. No. 4,266,974 describes examples of alloyed powders not included in the claimed volume, containing only manganese and chromium as intentionally added alloying elements. The powders described in the examples contain 2.92% chromium in combination with 0.24% manganese, 4.79% chromium in combination with 0.21 wt.% Manganese or 0.55% chromium in combination with 0.9 wt.% Manganese .

Japanese Patent Publication No. JP59173201, in one example illustrating a method for reducing annealing a low alloy steel powder containing chromium, manganese and molybdenum, describes a powder containing 1.14 wt.% Chromium and 1.44 wt.% Manganese as the only intentionally added alloying elements.

Pre-alloyed steel powder based on chromium, manganese and molybdenum is described in US 6348080. B WO03 / 106079 describes alloyed with chromium, manganese and molybdenum steel powder having a low content of alloying elements compared to steel powder described in US 6348080. Such a powder is capable of forming bainitic structures with a carbon content of more than about 0.4 wt.%.

OBJECTS OF THE INVENTION

The aim of the present invention is to develop an alloyed powder based on iron, which can be used to obtain extruded and sintered products, while such a powder is essentially free of expensive alloying elements such as molybdenum and nickel.

Another objective of the present invention is to provide a powder suitable for forming pressed and sintered products having good elongation, tensile strength and yield strength.

A further object of the present invention is to provide a sintered component having the above properties.

At least one of the listed goals is achieved by:

- Water-sprayed pre-alloyed steel powder based on iron, containing, in wt.%: 0.4-2.0 Cr, 0.1-0.8 Mn, less than 0.1 V, less than 0.1 Mo, less than 0 , 1 Ni, less than 0.2 Cu, less than 0.1 C, less than 0.25 O, less than 0.5 inevitable impurities, while the balance is iron.

- An iron-based powder composition based on steel powder mixed with 0.35-1 wt.% Graphite by weight of the composition, 0.05-2 wt.% Lubricants by weight of the composition and, optionally, copper in an amount of up to 3%, solid phase materials and machinability enhancing agents.

- A method of obtaining a sintered product, comprising the following stages:

a) obtaining a steel powder composition based on iron based on steel powder;

b) pressing the composition under pressure ranging from 400 to 2000 MPa;

c) sintering the resulting untreated product in a reducing atmosphere at a temperature of 1000-1400 ° C;

d) optional forging of the heated product at a temperature of more than 500 ° C, or heat treatment or hardening of the obtained sintered product.

The sintered product obtained by the above method has a pearlite / ferrite microstructure.

Steel powder has a low and defined chromium and manganese content and is substantially free of molybdenum, nickel and vanadium.

PRODUCTION OF ALLOYED STEEL POWDER ON THE BASIS OF IRON

Steel powder is obtained by water spraying a steel melt containing certain amounts of alloying elements. The atomized powder is then subjected to the reductive annealing process described in US Pat. No. 6,227,544 and incorporated herein by reference. The particle size of the steel powder can be any, provided that it can be used in the pressing and sintering or forging of powder products. An example of a suitable particle size is the particle size of the known ABC100.30 powder manufactured by Höganäs AB, Sweden, 10% by weight of particles of which are larger than 150 μm and about 20% by weight of particles of which are smaller than 45 μm.

STEEL POWDER COMPOSITION

Chrome serves to harden the matrix by quenching on a solid solution. Moreover, chromium increases hardenability, oxidation resistance and abrasion resistance of the sintered product. However, a chromium content of more than 2.0 wt.% Reduces the compressibility of the steel powder and makes it difficult to form a ferrite / pearlite microstructure. From the point of view of compressibility, the maximum chromium content is preferably about 1.8 wt.%, Even more preferably 1.5 wt.%. A Cr content of less than 0.4 wt.% Has a negligible effect on the desired properties. The chromium content is preferably at least 0.5 wt.%.

Like chromium, manganese increases the strength, hardness and hardenability of steel powder. A chromium content of more than 0.8 wt.% Enhances the formation of manganese-containing inclusions in the steel powder, and also has a negative effect on compressibility caused by solid solution quenching and increased ferrite hardness. The manganese content is preferably less than 0.7 wt.%, Even more preferably, the manganese content is less than 0.6 wt.%. In the event that the manganese content is less than 0.1%, the desired properties cannot be obtained, moreover, it becomes impossible to use recycled scrap without the implementation of specific recovery treatment in the course of steel production. For these reasons, the manganese content is preferably at least 0.2 wt.%, Even more preferably 0.3 wt.%. Thus, the manganese content should be 0.1-0.8 wt.%, Preferably 0.2-0.7 wt.%, Even more preferably 0.3-0.6 wt.%.

It was also found that to obtain a sufficiently high compressibility, the total content of chromium and manganese, which are interchangeable to some extent, should be not more than 2.5 wt.%, Preferably not more than 2.3 wt.%, Most preferably not more than 2.0 wt.%.

According to one embodiment of the present invention, comprising using a low chromium content of 0.4-0.6 wt.%, The low chromium content is offset by a relatively high manganese content of 0.6-0.8 wt.%, Preferably 0, 7-0.8 wt.%. This embodiment is preferred since manganese is cheaper than chromium.

According to another embodiment of the present invention, if the chromium content is at least 0.7 wt.%, The manganese content is at most 0.5 wt.%, And if the chromium content is at least , 1.0 wt.%, The manganese content is a maximum of 0.4 wt.%, Preferably a maximum of 0.3 wt.%. With a high chromium content, the manganese content can be low, thereby minimizing the formation of manganese-containing inclusions in the steel powder.

The maximum oxygen content is preferably 0.25 wt.% To prevent the formation of oxides with chromium and manganese, which impairs the strength and compressibility of the powder. For this reason, the maximum oxygen content is preferably not more than 0.18 wt.%.

The content of vanadium and nickel should be less than 0.1 wt.%, And copper - less than 0.2 wt.%. Too high a content of these elements has a negative effect on compressibility and can increase cost. The presence of nickel also inhibits the formation of ferrite, thus contributing to the formation of a brittle pearlite / bainitic structure. The molybdenum content should be less than 0.1 wt.% To prevent the formation of bainite, as well as to keep costs low, since molybdenum is a very expensive alloying element.

The maximum carbon content in the steel powder is 0.1 wt.%, And the maximum oxygen content is 0.25 wt.%. A higher content of these elements reduces the compressibility of the powder to an unacceptable level. For the same reason, the nitrogen content should be less than 0.1 wt.%.

The total amount of unavoidable impurities should be less than 0.5 wt.%, So as not to impair the compressibility of the steel powder and not cause the formation of harmful inclusions.

COMPOSITION OF POWDER ON THE BASIS OF IRON

Before pressing, iron-based steel powder is mixed with graphite and lubricants. Graphite is added in an amount of 0.35-1.0 wt.% By weight of the composition, and lubricants are added in an amount of 0.05-2.0 wt.% Of the composition. According to one of the embodiments of the present invention, copper in the form of copper powder can be added in an amount up to 3 wt.%. According to another embodiment, nickel powder may be added to the composition by mixing in an amount of up to 5% by weight, with or without the addition of copper powder.

GRAPHITE CONTENT

In order to increase the strength and hardness of the sintered product, carbon is introduced into the matrix. Carbon is added in the form of graphite in an amount of 0.35-1.0 wt.% By weight of the composition. The carbon content in an amount of less than 0.35 wt.%, Causes too low strength, and the carbon content in an amount of more than 1.0%, causes excessive formation of carbides, which leads to too high hardness, insufficient degree of elongation and degrades workability. In the event that after sintering or forging the product is subjected to heat treatment during a process involving carburization, the amount of added graphite may be less than 0.35%.

COPPER CONTENT

Copper is a commonly used alloying element in the field of powder metallurgy. Copper improves strength and hardness as a result of quenching on a solid solution. Copper also facilitates the formation of necks during sintering, since copper melts before reaching the sintering temperature, providing the so-called “liquid phase sintering”, which occurs much faster than solid sintering. According to one of the embodiments of the present invention, copper can be added in an amount up to 3 wt.%.

NICKEL CONTENT

Nickel is a commonly used alloying element in the field of powder metallurgy. Nickel improves strength and hardness as a result of quenching on a solid solution. Nickel also strengthens the neck during sintering. According to one embodiment of the present invention, nickel may be added in an amount of up to 5% by weight.

CONTENT OF LUBRICANTS

Lubricants are added to the composition to facilitate compression and extrusion of the pressed product. Adding less than 0.05 wt.% Lubricants by weight of the composition has insufficient effect, and adding more than 2% lubricants by weight of the composition leads to too low density of the pressed product. Lubricants can be selected from the group consisting of metal stearates, waxes, fatty acids and their derivatives, oligomers, polymers and other organic substances that have a lubricating effect.

OTHER SUBSTANCES

Other substances may be added, such as solid phase materials and processability enhancing agents, such as MnS, MoS ₂ , CaF ₂ , as well as various kinds of minerals and the like.

Sintering

The iron-based powder composition is placed in a mold and subjected to a pressure of about 400-2000 MPa to a wet density of more than about 6.75 g / cm ² . The resulting untreated product is then sintered in a reducing atmosphere or at a temperature of about 1000-1400 ° C, preferably about 1100-1300 ° C.

AFTER SINTERING

The sintered product can be subjected to a hardening process to obtain the desired microstructure as a result of heat treatment, including cooling at a controlled speed. The hardening process may include known processes such as carburizing, nitriding, induction hardening, and the like. In the event that the heat treatment includes carburization, the amount of added graphite may be less than 0.35%.

Alternatively, the sintered body may be forged to achieve full density. Forging can be carried out either immediately after the sintering operation, when the temperature of the product is about 500-1400 ° C, or after cooling the sintered product; in the latter case, the cooled product is reheated before forging to a temperature of about 500-1400 ° C.

Other post sintering treatments, such as surface rolling or shot peening, can also be used to provide compressive residual stress, which improves fatigue life.

PROPERTIES OF THE FINISHED PRODUCT

The present invention provides a new, pre-alloyed iron-based powder for the manufacture of sintered products having tensile and elongation properties comparable to the corresponding properties of products made from diffusion bonded powder having a higher total content of alloying elements and more expensive alloying elements, such as nickel and molybdenum. In particular, the present invention provides an iron-based powder prealloyed with chromium and manganese, as well as a pressed and sintered article made from such a powder composition. The elongation of such a pressed and sintered product is more than 2% in combination with a tensile strength of about 500 MPa. The microstructure is pearlitic or pearlitic / ferritic.

EXAMPLES

Various pre-alloyed iron-based powders 1-5 are prepared by spraying steel melts. Then the obtained crude powders are subjected to annealing in a hydrogen atmosphere at 1160 ° C and subsequent careful grinding to crush the caked cake from the powder. The particle size of the powders is less than 150 microns. Powder 6 is DISTALOY AB powder, a commercial, diffusion-alloyed powder from Höganäs, Sweden, based on high purity atomized powder ASC100.29 (pure iron).

Table 1 Powder Cr (%) Mn (%) V (%) Cu (%) Mo (%) Ni (%) C (%) O (%) one 0.80 0.35 - - - - 0.003 0,090 2 0.68 0.68 - - - - 0.003 0,093 3 1.78 0.10 - - - - 0.009 0,062 4 (Ref) 0.92 0,03 0.11 - - - 0.005 0,043 5 (Ref) 0.25 0.06 - - - - 0.003 0,039 6 - - - 1,50 0.50 1.75 0.002 0,092

Table 1 shows the chemical composition of the steel powder according to the present invention and reference materials.

The resulting steel powders 1-5 are mixed with 0.5% and 0.7% by weight of the composition, respectively, of graphite UF4 manufactured by Kropfmühle and 0.8% of amide wax PM manufactured by Höganäs AB, Sweden.

Powder 4 is outside the scope of the present invention, being doped with 0.11 wt.% Vanadium and having a manganese content of 0.03 wt.%. In powder 5, the content of both manganese and chromium is below the boundaries of the present invention.

A comparative mixture based on DISTALOY AB (powder 6) was also obtained. In this case, the resulting composition contains 0.5% graphite and 0.8% amide wax PM.

The resulting powder compositions are placed in a mold and pressed to obtain bars for tensile testing at a compression pressure of 600 MPa. Then, pressed test bars are sintered in a laboratory conveyor furnace at 1120 ° C for 30 minutes in an atmosphere of 90% nitrogen and 10% hydrogen.

Sintered samples are subjected to tensile and elongation tests according to ASTME9-89C, as well as hardness, HV10, according to EN ISO 6507-1. Samples are also analyzed for carbon and oxygen.

Impact energy is determined according to EN10045-1.

Table 2 below shows graphite content, chemical analysis results, and tensile and hardness test results.

table 2 Powder Based Composition Added graphite (%) FROM (%) O (%) Strength Limit (MPa) Tensile strength (MPa) Elongation (%) Hardness, HV10 Impact Energy (Du) one 0.5 0.50 0.05 345 512 4.6 139 25 one 0.7 0.69 0.05 417 627 3.0 178 23 2 0.5 0.55 0,07 371 540 3.3 168 24 2 0.7 0.72 0,07 398 611 3.0 181 21 3 0.5 0.56 0,03 427 625 3,1 172 28 3 0.7 0.72 0,03 496 697 2,3 195 23 4 (Comp.) 0.5 0.51 0,03 379 517 2,8 156 19 4 (Comp.) 0.7 0.70 0,03 462 610 1,6 192 fifteen 5 (Comp.) 0.5 0.48 0.02 287 391 4.2 113 23 5 (Comp.) 0.7 0.67 0.02 331 478 3.2 143 19 6-Dist AB 0.5 0.48 0.01 363 610 2,8 178 28

Table 2 shows the amount of graphite added to the compositions, the results of analyzes for the content of C and O in the obtained samples, as well as the results of tensile and hardness tests of the obtained samples.

When adding 0.7% graphite, samples based on powders 1, 2 show comparable or better test results for yield strength, tensile strength, elongation and hardness than DISTALOY AB mixed with 0.5% graphite powder. The value of the impact energy is somewhat lower, but still quite high, somewhat better for powder 1 than for powder 2.

When adding 0.5% graphite, samples based on powder 3 show comparable or better test results for yield strength, tensile strength, and elongation than DISTALOY AB mixed with 0.5% graphite powder. The values of impact energy and hardness correspond to DISTALOY AB.

For a powder-based sample 4, the elongation and impact energy are much lower than the same DISTALOY AB values with comparable tensile strength. As for the samples based on powder 5, it is seen that the impact energy and elongation decrease with increasing carbon content and will be much lower even with the addition of large amounts of graphite in order to increase the tensile strength to a level comparable to DISTALOY AB.

Claims (13)

1. Sprayed with water pre-alloyed steel powder containing, wt.%:
0.4-2.0 Cr,
0.1-0.8 Mn,
less than 0.1 V,
less than 0.1 mo
less than 0.1 Ni,
less than 0.2 Cu,
less than 0.1 C
less than 0.25 O,
less than 0.5 inevitable impurities,
the rest is iron. 2. The powder according to claim 1, in which the Cr content is a maximum of 1.8 wt.%, Preferably a maximum of 1.5 wt.%. 3. The powder according to claim 1, in which the Cr content is at least 0.5 wt.%. 4. The powder according to claim 2, in which the Cr content is at least 0.5 wt.%. 5. The powder according to any one of claims 1 to 4, in which the Mn content is at least 0.2 wt.%, Preferably at least 0.3 wt.%. 6. The powder according to any one of claims 1 to 4, in which the Mn content is a maximum of 0.7 wt.%, Preferably a maximum of 0.6 wt.%. 7. The powder according to any one of claims 1 to 4, in which the total content of chromium and manganese is less than 2.5 wt.%, Preferably less than 2.3 wt.% And most preferably less than 1.9 wt.%. 8. The powder according to claim 1, in which the Cr content is 0.4-0.6 wt.%, And the Mn content is 0.6-0.8 wt.%, Preferably the Mn content is 0.7-0.8 the weight.%. 9. The powder according to claim 1, in which the Cr content is at least 0.7 wt.%, And the Mn content is a maximum of 0.5 wt.%. 10. The powder according to claim 1, in which the Cr content is at least 1.0 wt.%, And the Mn content is a maximum of 0.4 wt.%, Preferably a maximum of 0.3 wt.%. 11. An iron-based powder composition comprising a steel powder according to any one of claims 1-10, mixed with 0.35-1 wt.% Graphite by weight of the composition, 0.05-2 wt.% Lubricants by weight of the composition and, optionally, copper in an amount of up to 3%, and, optionally, solid phase materials and machinability enhancing agents. 12. A method of obtaining a sintered product, comprising the following stages:
a) obtaining by mixing a powder composition based on iron having the composition according to claim 11;
b) pressing it under pressure ranging from 400 to 2000 MPa;
c) sintering the resulting untreated product in a reducing atmosphere at a temperature of 1000-1400 ° C;
d) if necessary, forging a heated product at a temperature of more than 500 ° C or heat treatment or hardening of the obtained sintered product. 13. The sintered product obtained from the powder composition according to claim 11, having a pearlite / ferrite microstructure.