EP0497714A1 - Process for preparing a sintered article based on steel powder and article obtained thereby - Google Patents

Abstract

Process in which steel powders are prepared, are compressed into a blank, this blank is infiltrated with copper, thus obtaining an article (1), characterised in that the powders are chosen and the sintered blank is infiltrated so as to obtain either of the following two compositions (in mass %) in the case of the said article: either C 0.6 to 1.2, Ni 0 to 5, Mo 0.3 to 2, Cr 0 to 4, V 0 to 0.6, Ni + Mo + Cr + V + metallic impurities 0.1 to 5, infiltrated Cu 4 to 15, remainder essentially Fe, or C 0.6 to 1.5, Mo 0 to 10, Cr 2 to 5, W 0 to 15, V 0.2 to 6, Co 0 to 10, Mo + Cr + W + V + Co + metallic impurities 5 to 50, infiltrated Cu 7 to 20, remainder essentially Fe, the said article thus having a steel skeleton not broken by the infiltration of copper and having a good resistance to fatigue-wear and producing little or no wear on an antagonist article in repeated impacts or friction. Another subject of the invention is the use of the process for the manufacture of a distribution article (1) of a heat engine, and the articles obtained. <IMAGE>

Description

The invention relates to a method for manufacturing a sintered part based on steel having both good resistance to wear and fatigue and little wear of an opposing part in repeated impacts or friction. It also relates to the use of this method for the manufacture of parts for distributing a heat engine, for example an automobile engine, and the parts obtained. These parts typically work under high stress, more than 500 MPa, in the oil which heats up in regime at more than 100 ° C.

By patent US-A-4606708, it is known that a sintered part based on iron or steel infiltrated by copper has a higher impact strength when its porosity not infiltrated with copper is reduced overall size and volume.

Copper infiltration is therefore carried out under vacuum

This process alone does not make it possible to obtain sintered steel parts with very good wear resistance and which do not wear or very little one or more antagonists, for example in the distribution system of a heat engine. Fatigue resistance is also essential for such dispensing parts, and attempts have been made to develop a method for manufacturing parts having a satisfactory combination of these properties.

STATEMENT OF THE INVENTION

• a) on prépare des poudres d'acier :
• b) on les comprime en une ébauche,
• c) on traite cette ébauche par frittage,
• d) on infiltre l'ébauche frittée obtenue de cuivre, obtenant ainsi ladite pièce,

caractérisé en ce que selon (a) on choisit les poudres et selon (d) on infiltre l'ébauche frittée de façon à obtenir pour ladite pièce l'une des deux compositions suivantes (en % en masse):
soit C 0,6 à 1,2 - Ni 0 à 5 - Mo 0 à 2 - Cr 0 à 4 - V 0 à 0,6 - Ni + Mo + Cr + V + impuretés métalliques 0,1 à 5 - Cu infiltré 4 à 15 - solde essentiellement Fe - cette composition étant dite d'un acier faiblement allié;
soit C 0,6 à 1,5 - Mo 0 à 10 - Cr 2 à 5 - W 0 à 15 - V 0,2 à 6 - Co 0 à 10 et de préférence 1 à 10 - Mo + Cr + W + V + Co + impuretés métalliques 5 à 50 - Cu infiltré 10 à 30 - solde essentiellement Fe - cette composition étant dite d'un acier fortement allié;
ladite pièce ayant ainsi une bonne résistance à l'usure et à la fatigue et usant peu ou pas une pièce antagoniste dans des chocs ou frottement répétés.The subject of the invention is a method for manufacturing a sintered part based on steel, in which:

• a) steel powders are prepared:
• b) they are compressed into a blank,
• c) this blank is treated by sintering,
• d) the sintered blank obtained from copper is infiltrated, thereby obtaining said part,

characterized in that according to (a) the powders are chosen and according to (d) the sintered blank is infiltrated so as to obtain for said part one of the following two compositions (in% by mass):
or C 0.6 to 1.2 - Ni 0 to 5 - Mo 0 to 2 - Cr 0 to 4 - V 0 to 0.6 - Ni + Mo + Cr + V + metallic impurities 0.1 to 5 - Cu infiltrated 4 to 15 - essentially Fe balance - this composition being called a low alloy steel;
or C 0.6 to 1.5 - Mo 0 to 10 - Cr 2 to 5 - W 0 to 15 - V 0.2 to 6 - Co 0 to 10 and preferably 1 to 10 - Mo + Cr + W + V + Co + metallic impurities 5 to 50 - Cu infiltrated 10 to 30 - essentially Fe balance - this composition being said of a highly alloyed steel;
said part thus having good resistance to wear and to fatigue and using little or no antagonistic part in repeated shocks or friction.

This process provides in particular surprising resistance to wear (of the part itself and of the opposing part), by the combination of several technical factors: copper infiltration and the interaction of infiltrated copper with the grains of steel powder, the hardness of these grains, and the structure obtained - The infiltration can be done by a conventional process, for example by sintering treatment and infiltration in two stages under hydrogenated atmosphere, or under vacuum as taught by the cited document.

In the two cases of composition of the invention, the C content of 0.6 to 1.2% and preferably 0.8 to 1% makes it possible to preserve, during the infiltration of copper, the contacts between grains coming from the sintering. This surprising effect is interpreted as follows from the observations made: when the C content is increased to 0.6 to 0.8% in such a low alloy steel, the wetting angle of the infiltrated liquid copper relative to to the steel changes and there is no more erosion of the bridges between grains by copper. It can then be seen in the above-mentioned C content range that the dimensional variation of a part due to copper infiltration becomes zero. This gives an unbroken steel skeleton and clogging with copper which leads to an increase in macroscopic static and dynamic mechanical properties, an increase in microscopic properties, the infiltration retaining grains or pieces of steel grains or hard particles, and an increase in thermal conductivity improving the evacuation of the heat generated by friction. These effects lead to a surprising reduction in the wear or wear of the part in its repeated shock or friction zone (s), as well as by reaction a reduction in the wear of the opposing part (s). . Tests have shown that the content of C, therefore the skeleton of unbroken steel, here leads not only to a significant increase in the non-wear properties, but also to an increase in the resistance to bending fatigue.

In the case of the high-alloy steels according to the invention, the grains of steel and carbides after sintering are harder than in the case of the low-alloy steels, which further strengthens the mechanical properties of the steel skeleton infiltrated with copper, even if this skeleton is slightly eroded by copper.

In the case of low alloy steels, the Ni + Mo + Cr + V content is preferably adjusted between 0.5 and 4%.

In the case of highly alloyed steels, preferably annealed starting steel powders are used to improve their compression, and the blank is hardened to sintering by the formation of carbides, with a sintering temperature above 1100 ° C. Preferably for this hardening and for the wear resistance properties, C is chosen between 1 and 1.5% and (Mo + Cr + W + V + Co) between 10 and 40.

In either case, it is advantageous to incorporate 0.1 to 50% by volume of ceramic powders and / or solid lubricant (s) into the steel powders. Preferably, there is incorporated into said steel powders 3 to 10% by volume of ceramic powders belonging to the group formed by: ZrO₂, Cr₂O₃, TiN, BN, TiC, VC, WC, MoS₂, Cr₂₃C₆, Al₂O3, TiO₂, Si₃N₄.

Preferably also, simultaneously or alternatively, one or more solid lubricant (s) stable to sintering is used, preferably belonging to the group formed by: MoS₂, BN, MnS, CeF₃.

Such additions, increasing the hardness or decreasing the friction effects, further improve wear resistance properties.

• on dispose les poudres en acier faiblement allié dans un outillage de compression puis on dispose sur elles une couche de poudres en acier fortement allié, puis on comprime ensemble lesdites poudres. La suite du procédé de fabrication s'applique, en particulier l'ébauche de pièce est co-frittée et co-infiltrée de cuivre;
• on ajoute à la fabrication une trempe locale d'au moins une portion de la pièce devant être soumise à des chocs ou frottements répétés. On utilise typiquement un chauffage local par induction HF suivi d'un refroidissement rapide.

To locally increase the resistance to wear without reducing the resistance to fatigue in bending of the part, two types of solution are used:

• the low-alloy steel powders are placed in a compression tool and then a layer of high-alloy steel powders is placed on them, then said powders are compressed together. The rest of the manufacturing process applies, in particular the part blank is co-sintered and co-infiltrated with copper;
• a local quenching of at least a portion of the part to be subjected to repeated impacts or rubbing is added to the manufacturing. HF induction local heating is typically used followed by rapid cooling.

• une pièce frittée à base d'acier contenant (% en masse) :
  C 0,6 à 1,2% - Ni + Mo + Cr + V + impuretés métalliques 0,1 à 5% avec Ni ≦5, Mo 0,3 à 2, Cr ≦4, et V ≦ 6 - Cu infiltré 4 à 15% - solde Fe, l'essentiel de la pièce étant de structure perlitique, et de dureté 250 à 350 H_V5 ; cette pièce comportant au moins une zone de surface ou d'extrémité de structure martensitique et de dureté au moins égale à 600 H_V5. Dans cette pièce homogène, la zone plus dure martensitique a été traitée par chauffage local et trempe.
• une pièce frittée à base d'acier comprenant un corps et une couche rapportée sur ce corps, cette couche ayant été co-comprimé, co-frittée puis co-infiltrée de cuivre avec ledit corps; ce corps ayant comme composition (% en masse):
  C 0,6 à 1,2 - Ni ≦5 - Mo 0,3 à 2 - Cr ≦4 - V 0,2 à 6 - Ni + Mo + Cr + V + impuretés métalliques 0,1 à 5 - Cu infiltré 7 à 20% - solde essentiellement Fe et ladite couche ayant comme composition (% en masse) : C 0,2 à 2 - Mo ≦10 - Cr 2 à 5 - W ≦15 - V 0,5 à 6 - Co ≦10 - Mo + Cr + W + V + Co + impuretés métalliques 5 à 50 - Cu infiltré 7 à 20 - solde essentiellement Fe. Dans cette pièce, l'augmentation de la résistance locale à l'usure est obtenue par la première solution décrite, la co-compression d'une couche de poudre plus fortement alliée.
• une pièce frittée à base d'acier contenant (% en masse): C 0,6 à 1,2 -Mo ≦10 - Cr 2 à 5 - W ≦15 - V 0,2 à 6 - Co ≦10 - Mo + Cr + W + V + Co + impuretés métalliques 5 à 50 - Cu infiltré 10 à 30%, l'essentiel de la pièce ayant une dureté de 350 à 450 H_V5 , et cette pièce comportant au moins une zone de surface ou d'extrémité de structure martensitique et de dureté au moins égale à 700H_V ; Il s'agit d'une pièce homogène, en acier fortement allié, traitée localement comme la première pièce.

The invention also relates to some of the parts obtained by the process described, namely:

• a steel-based sintered part containing (% by mass):
  C 0.6 to 1.2% - Ni + Mo + Cr + V + metallic impurities 0.1 to 5% with Ni ≦ 5, Mo 0.3 to 2, Cr ≦ 4, and V ≦ 6 - Cu infiltrated 4 at 15% - Fe balance, most of the part being of pearlitic structure, and hardness 250 to 350 H _V5 ; this part comprising at least one surface or end zone of martensitic structure and of hardness at least equal to 600 H _V5 . In this homogeneous part, the harder martensitic zone was treated by local heating and quenching.
• a steel-based sintered part comprising a body and a layer attached to this body, this layer having been co-compressed, co-sintered and then co-infiltrated with copper with said body; this body having as composition (% by mass):
  C 0.6 to 1.2 - Ni ≦ 5 - Mo 0.3 to 2 - Cr ≦ 4 - V 0.2 to 6 - Ni + Mo + Cr + V + metallic impurities 0.1 to 5 - Cu infiltrated 7 at 20% - balance essentially Fe and said layer having as composition (% by mass): C 0.2 to 2 - Mo ≦ 10 - Cr 2 to 5 - W ≦ 15 - V 0.5 to 6 - Co ≦ 10 - Mo + Cr + W + V + Co + metallic impurities 5 to 50 - Cu infiltrated 7 to 20 - essentially Fe balance. In this piece, the increase in local resistance to wear is obtained by the first described solution, the co-compression of a layer of more highly alloyed powder.
• a sintered steel-based part containing (% by mass): C 0.6 to 1.2 -Mo ≦ 10 - Cr 2 to 5 - W ≦ 15 - V 0.2 to 6 - Co ≦ 10 - Mo + Cr + W + V + Co + metallic impurities 5 to 50 - Cu infiltrated 10 to 30%, most of the part having a hardness of 350 to 450 H _V5 , and this part comprising at least one surface area or end of martensitic structure and hardness at least equal to 700H _V ; It is a homogeneous part, made of high-alloy steel, treated locally as the first part.

Another subject of the invention is the use of its process for the manufacture of a distribution part for a heat engine, part such as: rocker shoe, adjusting grain, pawl, mechanical plunger, pawl guide.

BENEFITS

• Obtaining distribution parts having both good resistance to fatigue and very good resistance to wear by repeated shocks or friction, both for the opposing part and for the part itself.
• the wear resistance is improved locally, by variation in composition or by local quenching treatment.

EXAMPLES

FIG. 1 represents a drive part of a valve by a "latch", in the form of a lever, and its actuation and testing device, this latch and its guide being cut longitudinally according to A-A.

Figure 2 shows this latch in top view.

Figure 3 shows a setting grain of a second valve and its drive device, in partial section passing through the axis of the valve.

1) In FIGS. 1 and 2 showing a latch 1 made of sintered steel and infiltrated with copper, of composition (% by mass): C 0.8 - Ni 1.5 - Mo 0.5 - Cu 7- Fe and impurities balance, with the exception of a layer 2 of maximum thickness 2.5 mm co-compressed, co-sintered and at the same time infiltrated with copper of composition: C 1.4 - W 6 - Mo 5 - Cr 4 - V 3 - Cu 15 intended to increase the wear resistance of the latch 1 at the location of the stresses on the cam 3 of the camshaft 4. The sintered layer 2 is more porous than the rest of the latch, its powders being less compressible, it absorbs more copper during joint infiltration.

The pawl works in the following manner: its hemispherical lower cavity 5 bears on the steel ball joint 6 of the hydraulic plunger 7 and when the pawl 1 is lowered by the cam 3, this cavity 5 rubs under moderate pressure on this ball joint 6, while its beak 8 descends by rubbing through the latch guide 9 and strikes the very hard thrust end 10 of the stem 11 of the valve 12. In order to better resist wear, this beak 8 has been treated by local heating by high frequency induction followed by water quenching: it has a martensitic structure.
It is added to the stresses of the ends 5 and 8 of the latch 1 the attack or the support of its back 13 coated with the more strongly alloyed layer 2 and the friction of the cam, causing a bending force between the supports that are the ball joint 6 and the end 10 of the stem 11 of the valve.

• portion majoritaire 14 du linguet en acier faiblement allié et de structure perlitique fine, résistant au frottement sous pression modérée en 5 et à la fatigue en flexion.
• couche 2 d'attaque de la came, en acier plus fortement allié selon l'invention du type "acier rapide", avec résistance accrue à l'usure;
• bec d'extrémité 8 rendu martensitique, résistant vis-à-vis des frappes de l'extrémité 10.

L'arbre à came est en fonte de dureté 52 HR_c. Les niveaux de dureté du linguet 1 sont, en H_V5 : portion 14 perlitique : 300; couche 2 co-comprimée : 400; bec 8 martensitique: 750.Thus, the compositions, structures and hardnesses are adapted to the four types of stress:

• majority portion 14 of the low alloy steel latch and of fine pearlitic structure, resistant to friction under moderate pressure in 5 and to bending fatigue.
• cam layer 2, made of higher alloy steel according to the invention of the "high speed steel" type, with increased resistance to wear;
• end nozzle 8 rendered martensitic, resistant to strikes from the end 10.

The camshaft is made of cast iron with a hardness of 52 HR _c . The hardness levels of latch 1 are, in H _V5 : pearlitic portion 14: 300; layer 2 co-compressed: 400; martensitic beak 8: 750.

The latch 1 was tested in the arrangement shown, at 3000 rpm of the cam 3 and for 200 h, on a bench reproducing particularly severe conditions of use, with used oil and at 130 ° C.

• A - comme le linguet 1, mais sans couche 2 co-comprimée;
• B - linguet non infiltré de cuivre mais cémenté et avec un bec trempé et une couche d'attaque de la came brasée et cémentée.

There were 2 comparison latches:

• A - like latch 1, but without layer 2 co-compressed;
• B - latch not infiltrated with copper but cemented and with a hardened spout and a layer of attack of the brazed and cemented cam.

Majority portion containing: C 0.8 (initial 0.2) - Ni 0.5 - Mo 0.2 - Fe and impurities: the balance, and hardness H _V5 750 for the hardened spout and 300 for the rest. Brazed and case-hardened added layer containing C 0.8 and Mo 25 for attacking the cam.

The wear results (thickness removed in mm) are as follows after 200 h:

We also tested a solid high speed steel pawl (not sintered): the wear of the cam was 0.100 mm, that of the attack surface of the pawl zero.

It can be seen that the catches according to the invention 1 and A, that is to say respectively: with a highly alloyed attack layer 2, and homogeneous in low alloy steel according to the invention, give less wear to the cam and also in the case of A much less wear of the spout on the striking of the valve.

2) EXAMPLE 2 (Figure 3)

Cylinder head with direct attack of an adjusting grain 15 of the valve 12 by the cam 3 of a camshaft.

The system comprises means 16 and 17 for guiding the valve 12 and a return spring 18.

The grain according to the invention 15 is 4 mm thick and has the same composition as the latch 1 of the first example. It is homogeneous without tempering.

It was tested under the same conditions as before: camshaft in cast iron with hardness 52 H _RC , 3000 rpm and for 200 h, with used oil at 130 ° C. There were 3 witnesses of the same geometry, in hardened solid tempered steel. The wear results are as follows (mm):

Reducing wear on the cam is very important. Grain wear is limited vis-à-vis these tool steel indicators.

3) Low alloy steels of the invention, influence of the C content

We prepared 7 latches with C contents staggered from 0 to 1.2% and a composition also equal to (% by mass):
Ni 1.7 - Mo 0.5 - Cu infiltrated 7 - Fe and impurities the balance.

• pendant la fabrication de chaque linguet, la variation dimensionnelle linéaire (VD%) résultant de l'infiltration de cuivre,
• après les tests de 200 h, l'usure de la surface de frappe de l'extrémité 10 de la soupape (voir Figure 1).

We tested them in the same way as latch 1 (1st example) and we measured:

• during the manufacturing of each latch, the linear dimensional variation (VD%) resulting from the infiltration of copper,
• after the 200 h tests, the wear of the striking surface of the end 10 of the valve (see Figure 1).

The results obtained are:

Excessive dimensional variations mean that machining has to be redone. C contents higher than 1.2% lead to a hypereutectoid structure which is not very favorable in fatigue. The minimum of V _D between 1.0 and 1.2 gives a particularly low wear. Given the structural problems, the optimal ranges are slightly shifted downwards: 0.6 to 1.2 and preferably 0.8 to 1.0. The corresponding effects have been commented on in the description.

Claims (12)

Method for manufacturing a sintered part (1; 15) based on steel, in which: a) steel powders are prepared, b) they are compressed into a blank, c) this blank is treated by sintering, d) the sintered blank obtained from copper is infiltrated, thereby obtaining said part (1; 15), characterized in that according to (a) the powders are chosen and according to (d) the sintered blank is infiltrated so as to obtain for said part one of the following two compositions (in% by mass):
or C 0.6 to 1.2 - Ni 0.5 to 5 - Mo 0.3 to 2 - Cr 0 to 4 - V 0 to 0.6 - Ni + Mo + Cr + V + metallic impurities 0.1 to 5 - Cu infiltrated 4 to 15 - essentially Fe balance - this composition being said of a low alloy steel;
or C 0.6 to 1.5 - Mo 0 to 10 - Cr 2 to 5 - W 0 to 15 - V 0.2 to 6 - Co 0 to 10 - Mo + Cr + W + V + Co + metallic impurities 5 to 50 - Cu infiltrated 7 to 20 - essentially Fe balance - this composition being said of a highly alloyed steel;
said part (1; 15) having a steel skeleton not ruptured by copper infiltration and consequently having good resistance to wear-fatigue and using little or no antagonistic part (3; 10) in shocks or repeated rubbing. Method according to claim 1, in the case where said part (1) is made of low-alloy steel and where the C content of the steel powders is adjusted between 0.8 and 1% and their content of Ni + Mo + Cr + V between 0.5 and 4%. Method according to Claim 2, in the case where said part (2) is made of high-alloy steel, and where a annealed powders are prepared in a) and where the blank is hardened in c) by sintering above 1100 ° C, this sintering producing carbide formations. Process according to any one of Claims 1 to 3, in which 0.1 to 50% by volume of ceramic powder (s) and / or solid lubricant (s) is incorporated into the steel powders. Process according to Claim 4, in which said steel powders are incorporated with 3 to 10% by volume of ceramic powders belonging to the group formed by: ZrO₂, Cr₂O₃, TiN, BN, TiC, VC, WC, Cr₃ C₆, Al₂O₃, TiO₂, Si₃N₄. Method according to one of claims 4 or 5, wherein one or more solid lubricant (s) stable to sintering, preferably belonging to the group formed by: MoS₂, BN, MnS, CeF₃. Method according to one of claims 1 to 6, in which (b) the low-alloy steel powders are placed in a compression tool and then a layer of high-alloy steel powders is placed on them, then said powders are compressed together . Method according to one of claims 1 to 7, in which a local quenching is then carried out of at least a portion (8) of said part (1) to be subjected to repeated shocks or friction. Sintered part (1) based on steel containing (% by mass):
C 0.6 to 1.2% - Ni + Mo + Cr + V + metallic impurities 0.1 to 5% with Ni ≦ 5, Mo 0.3 to 2, Cr ≦ 4, and V ≦ 6 - Cu infiltrated 4 at 15% - Fe balance, most of the part being of pearlitic structure, and hardness 250 to 350 H _V5 , this part comprising at least one surface or end zone (8) of martensitic structure and hardness at less than 600 H _V5 . Sintered part (1) based on steel comprising a body and a layer (2) attached to this body, this layer (2) having been co-compressed, co-sintered then co-infiltrated with copper with said body, this body having as composition (% by mass): C 0.6 to 1.2 - Ni ≦ 5 - Mo 0.3 to 2 - Cr ≦ 4 - V 0.2 to 6 - Ni + Mo + Cr + V + metallic impurities 0.1 to 5 - Cu infiltrated 8 to 15% - essentially Fe balance and said layer (2) having as composition (% by mass): C 0.2 to 2 - Mo ≦ 10 - Cr 2 to 5 - W ≦ 15 - V 0.5 to 6 - Co ≦ 10 - Mo + Cr + W + V + Co + metallic impurities 5 to 50 - Cu infiltrated 7 to 20% - essentially Fe balance. Sintered steel-based part containing (% by mass): C 0.2 to 2 - Mo ≦ 10 - Cr 2 to 5 - W ≦ 15 - V 0.5 to 6 - Co ≦ 10 - Mo + Cr + W + V + Co + metallic impurities 5 to 50 - Cu infiltrated 10 to 30%, most of the part having a hardness of 350 to 450 H _V5 , and this part comprising at least one surface or structural end zone martensitic and hardness at least equal to 700 H _V5 . Use of the method of any one of claims 1 to 8 for the manufacture of a distribution part (1; 15) of a heat engine, part such: rocker shoe, adjusting grain, latch, mechanical pusher, guide of latch.

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