237 EFFECT OF SINTERING ATMOSPHERE ON

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Acta Metallurgica Slovaca - Conference, Vol. 3, 2013, p. 237-246 Acta Metall. Slovaca Conf.

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EFFECT OF SINTERING ATMOSPHERE ON MICROSTRUCTURE, PROPERTIES AND FRACTURE OF Cr-Mn SINTERED STEELS Maciej Sulowski1)*, Margita Kabátová2), Eva Dudrová2) 1) AGH University of Science and Technology, Krakow, Poland 2) Institute of Materials Research of SAS, Kosice, Slovakia Received: 21.10.2012 Accepted: 05.03.2013 *

Corresponding author: e-mail: [email protected], Tel.: +48 12 617 2627, AGH University of Science and Technology, Faculty of Metals Engineering&Industrial Computer Science, Deparment of Physical Metallurgy and Powder Metallurgy, Mickiewicz Ave. 30, 30-059 Krakow, Poland

Abstract The effect of sintering at 1120°C and 1250°C in 5%H2+95%N2 and pure N2 atmosphere on microstructure, mechanical properties and fracture mechanisms of the Fe-(Cr)-(Mn)-(Mo)-C sintered steels was studied. Also sintering in air, as well using an idea of a „self-cleaning” effect of manganese was investigated. The results of investigations of mechanical properties show that the investigated alloys belong to medium strength steels with tensile and yield strengths of up to 957 and 562 MPa, respectively. The advantage of investigated steels is they have a higher hardness, up to 473 HV30. Following microstructural research, the change of fracture mechanisms from predominantly interparticle ductile mode with shallow dimples to mixture of cleavage/intergranular modes was identified for low carbon (~0.15%C) and high carbon (~0.7%C) for both levels of Cr content. The effect of the “self-cleaning” of air atmosphere with optimal addition of ferromanganese lumps reflected in strength properties comparable with N2 and H2+N2 atmosphere has been identified as a relatively positive. Keywords: fracture, prealloyed powders, sintered steels 1 Introduction Manganese is a very effective and cheap alloying element and is so employed in wrought alloys. The powder metallurgy industry is interested in using this element because of its cost to preformance ratio. Traditionally, the high strength sintered steels are alloyed with Ni, Cu and Mo. This expensive and price instable alloying elements led to the attempt to use Cr and Mn in alloying sintered steels for more than fifty years [1-13]. The easiest way was to use admixed different powder carriers of Cr and Mn, such as ferroalloys, carbides, and master alloys, such as MCM, MVM, respectively. It resulted in different variants of pre-mixed systems, but there was not theirs real industrial production. Several previous attempts to develop Mn steels [14-17], were unsuccessful due to the high affinity of Mn for oxygen, leading to the formation of continuous oxide networks during conventional sintering in atmospheres with dew points no better than -25°C [18]. Mn, as Cr, thus has been traditionally avoided in ferrous powder metallurgy [19] but the recent industrial developments, however, include the introduction of

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3% Cr [20] and up to 1.5% Mn [21, 22]. It means that the most important for sintering of CrMn alloyed powders is the ensuring reduction conditions during the sintering cycle [23-26]. Following the thermodynamics, simple iron oxide can be reduced by H 2 at temperature lower than 500°C. More stable Cr and Mn oxides, and their spinells, require higher temperature and another reducing agent – carbon, which is creating during carbothermal reduction [11, 26]. As Hryha et al. reported [24, 25], the simple iron oxide transforms during sintering to more stable Cr-Mn-Si complex oxides. As was reported in [27], the final strength properties of Mn alloyed steels strongly depend on cooling rate which controls the austenite transformation and hence the final microstructure composition. This phenomenon, which occurs also in Cr-Mn low alloyed steels, provides the formation of microstructures in a wide spectrum of microstructural constituents [28]. The second, crucial factor is the oxidic purity of interfaces in sintered microstructure. The presence of residual oxide phases leads to the degradation of mechanical properties, even in the case of high strength bainitic-martensitic microstructure of metallic matrix. This paper focuses on the possibility of achieving a combination of acceptable performance the F(1.5/3.0)%Cr-3.0%Mn-(0.2/0.5)%Mo-(0.3/0.8)%C sintered steels applying real technological processing conditions. For this purpose the effect of sintering in low-H2 or N2 atmospheres as well as in air, using an idea of the „self-cleaning effect” of manganese first presented by Salak [14], have been investigated. Finally, the effect of composition and processing conditions on mechanical properties, microstructure and fracture behaviour was correlated. 2 Experimental procedure Commercial Höganäs AB pre-alloyed Astaloy CrL and Astaloy CrM powders have been used in the investigation. The Mn in the amount of 3 wt.% was added in the form of the mediumcarbon ferromanganese (FeMn: 77% Mn, 1.3% C) powder with particle size under 20 µm. Carbon was added in the form of ultra fine graphite in the amount of 0.3% and 0.8 wt.%. The basis powders were mixed in the Turbula mixer for 30 minutes with any lubricant. Two types of specimen (green density of 6.81-7.08 g/cm3) were prepared - “dog-bone” tensile (ISO 2740) and rectangular bend and unnotched impact energy (ISO 3325), 55x10x6mm3, samples. The sintering process was carried out in a horizontal laboratory furnace at 1120°C and 1250°C in 5%H2-95%N2, and pure N2 atmospheres with the purity of both at the level 99,999% and with inlet dew point -60°C. The heat resistant steel tube was equipped with water rapid convective cooling zone with cooling rate 65°C/min. The temperature inside the boat containing samples was measured using CKY 506R thermometer equipped with NiCr-NiAl thermocouple [29] with accuracy ±0.1°C. Convective cooling specimens were subsequently tempered at 200°C for 60 minutes in air. One group of the specimens with the addition of 0.3% C was also sintered in air in semi-closed boat in which together with the specimens were the pieces of FeMn (ferromanganese lumps) in the amount of 52 grams (9.4 g per 100 g of specimens). In the Table 1 formulation of the tested alloys and sintering conditions was presented. After sintering specimens were subsequently tested in static tension, simple bending, both tests on the machines at a crosshead speed of 5 mm/min, and in an impact energy tester (W=15J). Light and scanning electron microscopy were employed for microstructural and failure evaluations. LECO instruments were employed to check the C and O2 contents in sintered materials. The alloys formulation and processing conditions are in Table 1.

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Table 1 Formulation of the tested alloys and sintering conditions; throughout the experiment the cooling rate of 65°C/min and tempering at 200°C for 60 min in air were used Sintering and Tempering Conditions Alloy Composition and T [°C]; time Atmospher No. Formulation Tempering [min] e 1 95N2+5H2 1120; 60 Fe-1.5CrAstaloy CrL 2 N2 0.2Mo ferromanganese 3 95N2+5H2 -3Mn-0.8C graphite 1250; 60 4 N2 5 95N2+5H2 1120; 60 Fe-3.0CrAstaloy CrM 6 N2 0.5Mo ferromanganese 7 95N2+5H2 -3Mn-0.8C graphite 1250; 60 8 N2 9 95N2+5H2 Fe-1.5CrAstaloy CrL 200°C for 0.2Mo ferromanganese 1120; 60 10 N2 60 minutes -3Mn-0.3C graphite 11 Air + FeMn in air 12 95N2+5H2 Fe-1.5CrAstaloy CrL 0.2Mo ferromanganese 1250; 60 13 N2 -3Mn-0.3C graphite 14 Air + FeMn 15 95N Fe-3CrAstaloy CrM 2+5H2 0.5Mo ferromanganese 1120; 60 16 N2 -3Mn-0.3C graphite 17 Air + FeMn 18 95N2+5H2 Fe-3CrAstaloy CrM 0.5Mo ferromanganese 1250; 60 19 N2 -3Mn-0.3C graphite 20 Air +FeMn 3 Results and discussion 3.1 Mechanical properties Table 2 presents the results of mechanical investigations of Fe-(1.5/3%)Cr- (0.2/0.5%)Mo3%Mn-0.3 and 0.8%C PM steels. In Table 3 , the C and O 2 contents in sintered specimens are summarized. It can be noticed from Table 2 that generally mechanical properties of steels based on Astaloy CrL powder with addition of 3%Mn and 0.8%C sintered in the H 2-containing atmosphere are comparable or lower with those steels sintered in N2. For all sintering combinations, PM steels containing Fe+CrM+3%Mn+0.8%C reached higher mechanical properties than Astaloy CrL-based steels (up to 671 MPa in tensile and 1274 MPa in bend strengths after sintering at 1250°C in N2 atmosphere). The mechanical properties of Astaloybased steels with lower carbon content were comparable or higher than those recorded for high-carbon steels. The highest UTS and TRS were recorded for Fe-CrM+3%Mn+0.3%C system sintered at 1250°C in N2. Following the data presented in Table 2, there is no evident difference in properties of steels sintered both in the H 2 and N2-containing atmosphere. Mechanical properties of investigated Astaloy CrM- based steels (Fe+CrM+3%Mn+0.3%C), sintered at 1120°C and at 1250°C, were higher than those achieved for Astaloy CrL-based steels with 0.3% carbon addition. It can be also pointed out the properties of Astaloy-based steels sintered in air with addition of FeMn are satisfactory, both for Astaloy CrL and Astaloy CrM-based powders. The differences in values of mechanical properties were not big, what

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means that air sintering of Mn-Cr-Mo steels seems to be very promising. The toughness and elongation of investigated steels also depend on sintering temperature and carbon content. Higher plastic properties were achieved after high temperature sintering for Astaloy CrL and Astaloy CrM-based steels with lower carbon content (up to 15.25 J/cm2 in toughness and 2.75% in elongation). Table 2 Mechanical properties of investigated steels processed by sintering with cooling rate of 65°C/min and tempering at 200°C; mean values of 5 measurements, standard deviation Alloy

CrL +3Mn +0.8C CrM +3Mn +0.8C

CrL +3Mn +0.3C

CrM +3Mn +0.3C

Sintering temperature [°C] and atmosphere 1120 1250 1120 1250 1120

1250

1120

1250

95N2+5H2 N2 95N2+5H2 N2 95N2+5H2 N2 95N2+5H2 N2 95N2+5H2 N2 Air + FeMn 95N2+5H2 N2 Air + FeMn 95N2+5H2 N2 Air + FeMn 95N2+5H2 N2 Air + FeMn

R0,2 UTS TRS offset [MPa] [MPa] [MPa] 417±41 474±36 487±39 432±52 N/D 360±10 560±39 517±23 481±66 481±55 468±34 535±6 554±20 482±58 537±38 535±29 554±26 562±26 562±26 561±51

429±7 431±7 680±4 684±6 413±4 389±2 654±8 671±3 556±3 556±7 603±4 792±4 832±4 570±5 665±7 716±1 541±7 957±2 957±2 642±3

314±1 343±6 6 367±2 5 403±2 7 459±2 9 413±2 0 469±2 3 473±2 5 284±8 274±1 6 202±3 5 268±1 5 262±1 3 224±2 1 323±1 1 320±1 1 300±2 0 315±6 315±6 300±3 5

HV 30 3.50±0.25 3.34±0.73 5.14±1.03 5.24±1.64 4.33±0.36 4.51±0.63 8.61±0.38 8.63±1.61 3.04±0.47 3.40±0.52 5.26±0.86 6.31±1.41 15.25±1.3 2 7.10±1.12 3.34±0.25 4.05±0.37 3.62±0.43 10.71±0.4 8 7.98±0.24 5.35±1.23

KC [J/cm2]

A [%]

1.22±0.3 1.18±0.3 8 2.59±0.0 6 2.58±0.1 6 1.27±0.1 6 1.31±0.2 1 2.31±0.5 5 2.58±0.3 8 0.78±0.1 0 0.82±0.1 5 2.57±0.3 8 1.69±0.1 1 1.98±0.1 1 2.57±0.2 6 1.68±1.0 9 2.53±0.2 1 1.59±0.3 5 2.75±0.1 7 2.73±0.1 7 2.08±0.2 6

955±108 924±53 967±104 1178±32 877±50 910±28 1352±19 1274±70 1020±22 1191±22 1138±20 1169±34 1702±27 1158±11 982±98 855±143 1294±11 1610±25 1658±40 1203±12

Following the data presented in Table 3, with increasing the sintering temperature the carbon content in sintered steels is decreased. The differences are in the range from 0.062% (for FeCrM+3%Mn+0.3%C system sintered in N2) to 0.128% (Fe-CrL+3%Mn+0.8%C system sintered in 5%H2-95%N2 atmosphere). This phenomena was observed in all studied here steels except air sintering variant; in this case the carbon content was on constant level (the change was by 0.005% and 0.008% for Astaloy CrL and Astaloy CrM-based material, respectively). The decreasing of carbon content in both steels with 0.3% and 0.8%C, can be explain by oxides reduction – higher decarburization implicit higher oxygen loose. As was shown in Table 3, for Astaloy CrM-based steels sintered in air, the oxide content was lower than for those sintered in 95%N2-5%H2 atmosphere; the effect was observed in steels based on Astaloy-CrL pre-alloyed powder. This phenomenon could be explain that the oxide reduction is multiply by the use of FeMn lumps. For all investigated steels (both 0.3% and 0.8%C) the initial level of

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manganese was 3 wt.%. When FeMn lumps were used during sintering, the “self-cleaning” effect was increased. Probably in steels sintered in N2-H2 mixture, the carbon content wasn’t sufficient for oxide reduction. It should be noted that there was no significant difference in microstructural composition after sintering in N2 and 5%H2-95%N2 atmospheres. It is obvious that microstructure is controlled by sintering temperature and the carbon content. A relatively significant decrease of carbon, by ~45% (see Table 3), during the sintering in air results in a higher amount of ferrite in final microstructure. This is also reflected in a slight decrease in hardness when compared with values after sintering in an atmosphere of 5%H2-95%N2 (see Table 2). Table 3 The carbon and oxide contents in investigated steels processed by sintering with cooling rate of 65°C/min and tempering at 200°C (mean values of 3 measurements) Sintering temperature [°C] and Alloy C [wt.%] O2 [wt.%] atmosphere CrL +3Mn +0.8C CrM +3Mn +0.8C

CrL +3Mn +0.3C

CrM +3Mn +0.3C

1120 1250 1120 1250 1120

1250

1120

1250

95N2+5H2 N2 95N2+5H2 N2 95N2+5H2 N2 95N2+5H2 N2 95N2+5H2 N2 Air+52g FeMn 95N2+5H2 N2 Air+52g FeMn 95N2+5H2 N2 Air+52g FeMn 95N2+5H2 N2 Air+52g FeMn

0.665 0.724 0.537 0.599 0.717 0.770 0.618 0.628 0.289 0.274 0.187 0.190 0.191 0.182 0.304 0.276 0.172 0.228 0.214 0.164

0.343 0.569 0.488 0.398 0.559 0.587 0.410 0.385 0.460 0.338 0.300 0.157 0.165 0.321 0.390 0.333 0.348 0.290 0.280 0.275

3.2 Structural observation The microstructure of the tested alloys, sintered both at 1120°C and 1250°C, are presented in Figs. 1a,b-6a,b. The “dissolution” of the FeMn particles during sintering results in typical “sponge” morphology of residual FeMn particles. Their presence is practically eliminated by sintering at 1250°C, but the resultant pores left in place FeMn particles are observed. The pore sizes are controlled by the original size of the FeMn particles. All the microstructures examined are complex and heterogeneous. The sinter-hardened microstructure of the 3% Mn alloys with 0.3% C consists of bainitic and ferritic areas. In the case of higher carbon content (0.8%), the microstructure contains mixed bainitic-martensitic areas with some retained austenite. The Mn distribution coincides with “dissolution” of FeMn particles; the degree depending on the sintering temperature.

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Fig. 1 a Microstructure of CrL-3Mn-0.8C PM steel, 1120°C, 5H295N2

Fig. 1b Microstructure of CrL-3Mn-0.8C PM steel, 1250°C, 5H295N2

Fig. 2b Microstructure of CrM-3Mn-0.8C PM steel, 1250°C, 5H295N2

Fig.3a Microstructure of CrL- Fig. 3b Microstructure of 3Mn-0.3C PM steel, CrM-3Mn-0.3C PM 1120°C, 5H2-95N2 steel, 1120°C, 5H295N

Fig. 4a Microstructure of CrL-3Mn-0.3C PM steel, 1120°C, air + FeMn lumps

Fig. 4b Microstructure of CrM-3Mn-0.3C PM steel, 1120°C, air + FeMn lumps

Fig. 5a Microstructure of CrL-3Mn-0.3C PM steel, 1250°C, 5H295N2

Fig. 5b Microstructure of CrM-3Mn-0.3C PM steel, 1250°C, 5H295N2

Fig. 6a Microstructure of CrL-3Mn-0.3C PM steel, 1250°C, air + FeMn lumps

Fig. 6b Microstructure of CrM-3Mn-0.3C PM steel, 1250°C, air + FeMn lumps

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Fig. 2a Microstructure of CrM-3Mn-0.8C PM steel, 1120°C, 5H295N2

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The fracture surface morphology (Figs. 7 and 8) after tensile tests is strongly dependent on the type of microstructure, which is controlled by sintering temperature and carbon content. For alloys based on both pre-alloyed powders with lower carbon content dominates interparticle failure with shallow dimples together with some small cleavage facets and facets corresponding to failure in intergranular decohesion mode (Figs. 7, 8). In some areas of ductile dimples, particularly for specimens sintered at 1250°C, a localised plastic flow occurs which is in good agreement with macroscopic strain recorded as the elongation higher than 2 %. The local developed plastic flow is associated with a higher amount of ferrite and a better developed particle connections. The deleterious effect of residual FeMn particles resulting in large pores is more pronounced for lower sintering temperature and lower carbon content (Fig. 7a). The fracture surface areas around the prior FeMn particles consists of a large amount of small intergranular facets which is associated with the presence of oxide phase distributed along the grain boundaries. In some of these sites it can be also seen some groups of small Mn oxide particles. Even for material with low carbon content sintered at 1250°C the interparticle failure occurs (Fig. 7b, 8b). However, shallow dimples initiated by oxide particles are predominant. In addition to dimples there has been identified failure in intergranular decohesion mode. Unlike after sintering at 1120°C, there have not been observed groups of the Mn oxide particles. The presence of intergranular failure in specimens sintered both at low and high temperature indicates that some grain boundaries were degraded by oxides, which correlates with relatively low impact toughness (Table 2). The microstructure of alloys with high carbon content contains a higher amount of high-strength martensitic and bainitic areas and the fracture surface composition is determined by quality of interface areas, particularly of bainite packets surface and cleavage fracture of martensite, as well. This results in a mixed character of the fracture surface consisting of fine shallow dimples and cleavage facets (Figs. 7a, b and Figs. 8a, b). Both lower sintering temperature and lower carbon content lead to higher amount of intergranular decohesion (Fig. 7a). It may be also associated with the formation of carbide phase at grain boundaries (the eutectoid carbon content for Astaloy CrM-C system~ 0.36%).

Fig.7

a) b) The fracture surface of Fe-CrL-3Mn-0.3C PM steels sintered in 5H2-95N2 atmosphere and tempered at 200°C; a) 1120°C and b) 1250°C

4 Discussion The properties obtained for the investigated alloys correspond to medium strength steels which are used for structural parts in ferrous powder metallurgy and with success can substitute

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traditional, expensive PM steels. The recorded UTS and R0.2 of investigated steels were up to 957 and 562 MPa, respectively. The higher hardness (due to oxides), up to 473 HV30, could be advantageous, for example with regard of wear. In flowing N2 atmosphere, reduction of MnO oxides by solid carbon below 1425°C is impossible. Only control of the local microclimate in semi-closed container, ensures optimum conditions for thermal oxide reduction and efficient sintering [10]. Specimens sintered at 1250°C possessed higher mechanical properties, irrespective of the H2/N2 ratio in the furnace atmosphere. Cr enhances the detrimental effects of N2 on the strength of the Mn steels [11]. The recorded values of mechanical properties are higher than presented in [30]. Because of the price of Ni and its cancerogenic effect, the Ni-containing steels are substituted by PM Mn or Mn-Cr-Mo steels reaching the comparable or higher mechanical properties. On the other hand, the properties of the investigated steels are lower than those given in Ref. [31] for Astaloy CrL and Astaloy CrM-based steels. The presence of Mn oxides giving the investigated steels high hardness, but the low values of impact energy. It should be noted that during air sintering, the increase of O2 content is lower than during the sintering in N2 as well as in 5%H2– 95%N2, particularly at 1120°C.

a) b) Fig.8 The intergranular ductile fracture of Fe-CrM-3Mn-0.3C PM steels sintered in 5H2-95H2 atmosphere and tempered at 200°C; a) 1120°C and b) 1250°C The differences in properties of investigated steels sintered in various atmospheres are small (see Table 2). Better properties were recorded for steels with 0.3% carbon content. The presence of 0.8%C increased hardenability of investigated steels; hardness was higher and toughness was lower than those in low-carbon steels. The higher carbon content in investigated steels does not improve the tensile and bend strengths. Even if the high strength microstructure of the matrix was obtained, the problem was in interfaces contaminated with oxide phases which results in low impact properties, but this is problem of admixed Mn. The results presented in Table 2 correspond well with the microstructure (Figs. 1a-6b) and the fracture of investigated steels (Figs. 7-8). The mechanical properties of investigated PM steels appear comparable to other studies [10-13]. A comparison of the UTS, A and impact values found quite good agreement. The effect of using a higher sintering temperature than 1120°C on mechanical properties is evident from the results obtained. The UTS and TRS data shoved a measurable effect of the sintering temperature. Increasing Cr content from 1.5% to 3% offers improvement in properties under conditions employed. The application of semi-closed container offers a means to increase the mechanical properties of single compacted steels to those typical of double pressed and sintered steels.

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Relatively promising seems to be sintering Mn-Cr-Mo steels in air using semi-closed boat with presence of ferromanganese lumps. But to get better mechanical properties, which requires the elimination of oxide contamination, has to be investigated in further experiments. 5 Conclusions The investigations allowed the following conclusions to be drawn: 1. The investigated alloys belong to medium strength steels with UTS and R0.2 of up to 957 and 562 MPa, respectively. The advantage of investigated steels is they have a higher hardness (due to oxides), up to 473 HV30. 2. The addition of Mn in the form of FeMn is not suitable way to improve the mechanical properties of Astaloy CrL and Astaloy CrM-based steels. The only way to achieve very high properties of this steels are Cr and Mn pre-alloyed powders. 3. Sintering in air with lumps of FeMn seems to be interesting. After further research and promising results to be achieved, air sintering could be not expensive alternative for “gas sintering”. References [1] EU Cancerogenic Directives 90/394/EEC and 91/322/EEC [2] S. C. Mitchell, A. S. Wronski, A. Cias, M. Stoytchev: Microstructure and Mechanical Properties of Fe-Mn-Cr-Mo-C Steels Sintered at >1140C, In: Proc. of PM2TEC 1999, Vancouver, MPIF/Princeton, Vol. 3, 1999, part 7, p. 129-143 [3] S. C. Mitchell, A. S. Wronski, A. Cias: Inżynieria Materiałowa, Vol. 5, 2001, p. 633-646 [4] A. S. Wronski et al.: Tough, fatigue and wear resistance sintered gear wheels. Final Report on EU Copernicus Contract no ERB CIPA-CT94-0108, European Commission, 1998 [5] M. Sulowski, A. Cias: Inżynieria Materiałowa, Vol. 4, 1998, p. 1179-1182 [6] A. Cias, M. Sulowski, M. Stoytchev: Tin Alloying Additions to PM Fe-3%Mn-0,6%C Sinter-hardened Steels, In: Proc. of 7th European Conf. on Advanced Materials and Processes - EUROMAT 2001, Rimini, Italy, June 2001 [7] R. Keresti, M. Selecká, A. Šalak: Effect of Molybdenum Form Additionon Properties of 3MnSintered Steel, In: Proc. of Int. Conf. DFPM’99, Piešťany, Vol. 2, 1999, p. 108-111 [8] S. C. Mitchell, B. S. Becker, A. S. Wronski: Further Alloying Additions to PM Fe-Mn-C Steels, In: Proc. of. 2000 PM World Congress, Kyoto, EPMA/Shrewsbury, Vol. 2, 2001, p. 923 -926 [9] A. Cias, M. Stoytchev, A. S. Wronski: Processing, Strength, Ductility and Toughness of Sintered Mn-(Mo)-C Steels, In: Proc. of 2001 Int. Conf. on Powder Metallurgy and Particulate Materials, New Orleans, MPIF/Princeton, part 10, 2001, p. 131-137 [10] A. Cias: Development and Properties of Fe-Mn-(Mo)-(Cr)-C Sintered Structural Steels, AGH-UST, Uczelniane Wydawnictwo Naukowo-Dydaktyczne, Cracow 2004 [11] A. Cias, S. C. Mitchell, K. Pilch, H. Cias, M. Sulowski, A. S. Wronski: Powder Metallurgy, Vol. 46, 2003, No. 2, p. 165-170 [12] M. Sulowski: The structure and mechanical properties of iron-manganese-carbon PM structural parts, Ph.D. Thesis, AGH-UST, Cracow, 2003 (in Polish) [13] A. Cias, M. Sulowski, S. C. Mitchell, A. S. Wronski: Sinter-hardening of Fe-Mn-C steels, In: Proc. PM2001 Powder Metallurgy Congress and Exhibitions, Nice, EPMA/Shrewsbury, Vol. 4, 2001, p. 246-251

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DOI 10.12776/amsc.v3.134

ISSN 1338-1660