TWI290073B - Sintered metal parts and method for the manufacturing thereof - Google Patents

Abstract

The invention relates to a method consisting of the steps of providing a pre-alloyed iron-based metal powder comprising at least 1.3-3.5% chromium, 0.15-0.7% molybdenum, manganese and unavoidable impurities, mixing said powder with 0.1-1.0% graphite, compacting the obtained mixture at a pressure of at least 600 MPa, sintering the compacted part in a single step at a temperature above 1100 degree C, shot-peening the part and after sintering optionally hardening the component. The invention also relates to a powder metallurgical part and use of a low chromium prealloyed powder for preparing notched sintered parts having a bending fatigue limit of at least 340 MPa at a sintered density of 7.15 g/cm<3>, preferably at least 400 MPa at a sintered density of 7.3 g/cm<3>.

Description

1290073 IX. DESCRIPTION OF THE INVENTION: TECHNICAL FIELD OF THE INVENTION The present invention relates to powder metallurgy techniques, and more specifically to pre-alloyed chromium powder metal parts having improved fatigue properties. [Prior Art] Generally, a sintered product produced by powder metallurgy technology is cost-effective than an ingot obtained by a forging and rolling step, and is widely used as a part in, for example, a motor vehicle. However, the sintered product has pores that are inevitably formed during the manufacturing process. These retained pores of the sintered powder metallurgical material impair the mechanical properties of the material as compared to a fully dense material. This is the result of stress concentration as well as the reduction of the effective volume of the pores under stress. Therefore, the strength, ductility, fatigue strength, macroscopic hardness, etc. of iron-based powder metallurgy materials decrease with increasing porosity. Despite its low fatigue strength, iron-based powder metallurgy materials are still used in a range of parts requiring high fatigue strength. Distal〇y® Hp (available from Sweden, H5ganas ΑΒβ) is a steel powder that can be used for high performance applications. At the end of this Distaloy®*, the base powder is alloyed with the expensive alloying element nickel. This highly active material is relatively expensive and, therefore, requires inexpensive materials having at least excellent fatigue strength. One way to improve the fatigue properties of powder metallurgy steel is the second operation. All hardening, case hardening or beading treatments (or combinations) are possible ways to obtain the highest fatigue resistance of the part. In order to utilize the compressive residual stress in the surface, a beading treatment is performed. The pores that open to the surface are weak points in the powder metallurgical material. These pores are at least partially inhibited by the introduction of surface compression residues 102671 - 960206.doc !29〇〇73 9 (3⁄4 positive replacement F| residual stress. The beading treatment of j-pressed parts is disclosed in, for example, US Patent No. 6 J 7 J S46. According to this patent 'the final sintering step is carried out after the bead blasting process. The main powder containing, for example, nickel is used as a raw material. As shown above, since nickel 17 shells are required for the nickel-free powder Increasing. Other disadvantages of using recorded powders are dusting problems. 'S dust can occur during powder processing and can cause a small amount of allergic reactions. Therefore, I US Patent Application No. 2_/〇177719 should also be avoided. Regarding a method including the bead blasting method, the § hai application discloses a method in which the squeezing: the surface of the bovine-P knives is subjected to a bead blasting process after sintering. The performance of the pressed parts requires a compact method including powder forging or sizing. The purpose of each month is to provide a cost-effective method for preparing powder metallurgy with high fatigue strength without any step of achieving core densification. A purpose is to provide a nickel-free U-containing product. [Summary of the Invention] It has been found in the field that a sintered part prepared from a bismuth powder having a low content of nickel and molybdenum can be obtained by a bead blasting method to obtain a high fatigue strength.

Parts of the degree. W The powder used in the present invention is 4 J θ 士 i ^ for the pre-alloying of low chromium and molybdenum with iron as 1 °, preferably in an amount of U·3·5 wt% of chromium and 0.15-〇.7 The % by weight of the powder is contained in a small amount, and the amount of the powder is a small amount. * The powder is known by the US Patent No. 6 348 _ and WO 03/106079. 102671 -960206.doc 1290073 ^ Μ '日绿几) is replacing the page... The base powder is further mixed with graphite to obtain the required material strength. The amount of graphite mixed with iron-based powder is g1m.g%, preferably 〇15 to 0.85% ^ Pressing the powder mixture in a mold to produce a body. The force is at least 600 megapascals, preferably at least 7 megapascals, more preferably _ megapascals. The compaction can be by cold Pressing or hot pressing. After pressing, the obtained green part is sintered at a temperature higher than 110 (the sintering temperature of rc is preferably higher than 1220 ° C. The sintering atmosphere is preferably a mixture of nitrogen and hydrogen. In the sintering process The normal cooling rate is 〇.rc/sec, preferably in the range of 〇5 sec and between. The sintered density is preferably higher than 7.15 g/cm 3 , more preferably higher than 7.3. g/cm 3. With the lower chromium and molybdenum content, the resulting microstructure in the sintered material is mainly peaditic, and for slightly higher and higher content, it is mamnsitie or lower. Bayesian type c) It has been unexpectedly found that (iv) a significant increase in the fatigue limit can be obtained by the bead blasting process of the sintered low (tetra) end material. A particularly significant increase is obtained for the incision parts, which can be seen from the following examples. Up to more than 5% and even more than 70% increase is obtained. The bead stroke degree defined by the intensity of the Alman (α1_) α is preferably between 0 · 2 0 and 〇 · 3 7 mm. Improved, the second operation can be performed before the bead blasting process, for example, all hardening and surface hardening. Therefore, after all hardening and subsequent tempering, the material is mainly the granulated iron type, and the fatigue limit is treated by the bead blasting method. The increase in the surface formed during the surface hardening of the granulated iron type forms a compressive stress which is favorable for the fatigue limit. Sintering hardening is an optional method applied in the sintering process. Burning the hardening at the end of the part sintering process With forced cooling, this produces hardening. 102671 -960206.doc 1290073 r—————————^ 0 丨 E丨修魏) is replacing the page 丨 fatigue test on the stress concentration factor uncut sample. Test shows In the case of the bead blasting treatment of the incision sample, the greater bending fatigue limit is increased than when the non-incision sample is subjected to the bead blasting treatment. In this context, the "cutting" refers to a sample or a part having a stress concentration factor higher than 丨·3. [Embodiment] The present invention is illustrated by the following non-limiting examples. Example 1 Two prealloyed base powders Astai〇y® crL and

Astaloy® CrM and a diffusion alloyed base powder, Distai〇y® HP.

Distaloy® HP is alloyed with Ni and Cu diffusion and pre-alloyed with Mo. The three materials included in this study are shown in Table 1. Table 1 Materials Ni [%] Cu [%] Mo [%] Cr [%] One Astaloy CrL 0.2 1.5 Astaloy CrM 0.5 3.0 Distaloy HP 4.0 2.0 1.5 Details on process parameters, density and carbon content are given below. The plane bending fatigue properties of the uncut samples were shown in Table 2 for different alloys sintered in 90/10 N2/H2 at a cooling rate of about 〇8 ° C / sec for 30 minutes. Fatigue testing of uncut samples was performed using a 5 mm is〇3928 sample with chamfered edges. The test was carried out in a four-point plane bent at a load ratio of R = -1. In the ladder, the ladder method was used with 13-18 samples, and 2 million cycles were used as the breakthrough limit. Staircase evaluation (50% probability fatigue limit and standard deviation) was performed according to the MPIF 56 standard. The test frequency is 27_3 Hz. 102671-960206.doc 1290073 • Vt;| 4&gt;;:; Table 2 ι —1 — ....:-...— Powder Density [g/Amy 3] Sintered Carbon [%] σ A, 50% [Million Pascals] Standard deviation [million pascals] ^ A, 90% [million pascals] Astaloy CrL 7.17 0.60 244 7 234 7.16 0.80 267 5 260 Astaloy CrM 7.06 0.35 284 7.0 274 7.04 0.56 316 8.4 300 Distaloy HP 7.13 0.65 295 22.5 261 7.13 0.85 330 &lt;5 &gt; 322 The microstructure of Astaloy CrL having less than 0.6% sintered carbon and a cooling rate of about 0.8 °c/sec is a higher Babbitt type. Above 0.74°/. The addition of carbon changes the microstructure to fine pearlite. The Astaloy CrM material sintered at 1120 ° C and a cooling rate of 0.8 ° C / sec and a microstructure analysis using a sintered carbon content between 0.32% and 0.49% showed a dense higher Bayesian microstructure. The densely higher Bayesian type has the same characteristics as the conventional higher Bayesian type, i.e., an irregular mixture of ferrite and cementite. The difference is the smaller distance between the carbides and the size of the carbide. The increased sintered carbon transfers the microstructure to a mixture of the granulated iron type and the lower Bayesian type. Table 3 shows the effects of the compression pressure and carbon content of cold pressed Astaloy CrL. All materials were sintered at 1120 ° C for 30 minutes in 90/10 N2/H2. In Table 3, a summary of the plane bending fatigue properties (standard deviation &lt; 5) of Astaloy CrL at two compacting pressures and two additions of graphite shows that the scattering is small and the MPIF 56 cannot be used to assess the standard deviation. The samples in Table 3 were not cut. 102671-960206.doc -9- T290073 —«m» 妒· __(10)·_ — .... w repair (edge) replacement page Table 3 Material Graphite C-UF4 [%] Pressing pressure [Million Pascals] Sintering Density [g / cm3] Sintered carbon [%] σ A, 50% [million pascals] Standard deviation [million pascals] σ A, 90% [million pascals] Astaloy CrL 1120°C 30 minutes 90/10 N2 /H2 0.8〇C/sec 0.6 600 6.94 0.56 224 11.6 205 0.8 600 6.93 0.75 233 9.5 218 0.6 800 7.13 0.55 236 8.5 222 0.8 800 7.09 0.74 252 &lt;5 &gt;244 Table 4 shows the sintering temperature versus the use of uncut samples The effect of fatigue performance. The microstructure of the materials in Table 4 is characterized by predominantly higher Babbitt type (1120 ° C 0.58% C) and fine pearlite (1120 ° C, 〇 · 77% C and 1250 ° C, 0.74% C). Table 4 Powder sintering temperature Sintering density [g/cm3] Sintered carbon [%] σ A, 50% [million pascals] Standard deviation [million pascals] σ A, 90% [million pascals] Astaloy CrL 1120°C 7.10 0.58 220 11 203 1120°C 7.08 0.77 236 9.7 222 1250〇C 7.02 0.74 290 18 264 Example 2 The effect of the combination of bead blasting and heat treatment with bead blasting was investigated for Astaloy CrL 3 mm edge incision samples. The slit is included in the press and is not machined. The stress concentration factor in bending is obtained by FEM up to kt = 1.38. The test frequency is 27-30 Hz. The material was sintered in 1280 ° CKH2 for 30 minutes. The cooling rate was 0.8 ° C / sec. A bead blasting treatment was performed to obtain an Alman A intensity of 0.32 mm. The evaluation plane bending fatigue properties of the sintered and sintered + bead blasted samples are shown in Table 5. 102671-960206.doc -10· •Ί 1290073 Table 5 Powder Sintered Carbon [%] Sintering Density [g/Amy 3] Second Operation Bending Fatigue Limit [Million Pascals] Bead Strike Treatment Increases Bead Strike Treatment Astaloy CrL 0.70 7.30 No 235 is 420 +79% Uncut Astaloy CrL 0.85 7.30 No 340 is 450 +32% Table 6 shows the evaluation of plane bending fatigue properties of all hardened temper and bead blasted samples. Complete hardening was carried out at an arstenitization temperature of 880 °C. After the austenite reaction, cooling was carried out at 8 ° C / sec. Finally, the sample was tempered at 250 ° C for 1 hour. Table 6 Powder Sintered Carbon [%] Sintering Density [g/Amy 3] Second Operation Bending Fatigue Limit [Million Pascals] After Ball Beading Treatment Increases All Hardening 250〇C Retempering 1 hour Bead Strike Treatment of Insaloy CrL 0.50 7.30 is 285 0.50 7.30 Yes Yes 490 +73% Uncut Notched Astaloy CrL 0.50 7.30 Yes 370 0.50 7.30 Yes Yes 520 +41% Can be found from Tables 5 and 6, the bending fatigue limit is increased by the bead method Handling of materials containing chromium and noodles. 102671-960206.doc -11 -

Claims (1)

90090073 r X. 申申 patent range: Package: i 2: method for improving the fatigue strength of powder metallurgy parts, pre-:: containing at least H3.5% by weight of chromium, 〇ΐ5_〇·7 wt% of the key Ό Menghua iron-based metal powder, - the powder is mixed with 0.1-1.0% by weight of graphite, - at least _ million Pascals force the resulting mixture, the piece, at a temperature above 11 〇 (rc The part is treated by a single step of sintering by a squeezed bead shot method. [Method of = item! wherein the increase in fatigue strength is at least 5 %.. Method of hitting the moon or 2] wherein the pressing and The sintered part is hardened and tempered prior to the bead blasting process. 4. A powder metallurgy part manufactured by the method of any one of claims 1 to 3, having a main pearlite microstructure, preferably mainly fine A pearlite microstructure. The powder metallurgy part manufactured by the method of any one of claims 1 to 3, having a 麻田散铁 type and a lower Bayesian type microstructure. 1290073 f Pascal, preferably 7.3 g/ Cm 3 of sintered Af Feng * with a degree of at least 400 million Pascal test The limit is characterized in that the (7) is not subjected to compaction, sintering and selective tempering and annealing, and is subjected to a bead blasting process. &amp; 9. The use of the powder metallurgy part of claim 8 has a high Stress concentration factor at 1.3. 102671-960206.doc