Research on obtaining wear-resistant sintered parts from metal powders recovered.

Radu, Stefan ; Demian, Mihai ; Didu, Anca 等

1. INTRODUCTION

Global trends can be grouped as: recycling, development of new technologies to reduce consumption of powder metallurgy and metal (Sinha et. al., 1992).

Obtaining metal powders from wastes of production has many implications for both the higher capitalization of waste and the finished product.

Processing chips from classic pieces of iron or steel is in a mechanical workshop, a small value for remelting scrap or reuse them and can be turned into dust by grinding, forming and sintering (for parts with medium quality).

The performed researches have proposed to obtain some basic material with similar qualities as the classical ones, but for a lower price (Cesar et. al., 2003), (Hong al., 2000).

2. EXPERIMENTAL RESEARCH

We present the results of experimental research regarding wear behaviour of sintered samples obtained from HSS (high speed steel) collected during the process of recovery and grinding of high speed steel chips during the rectification operation.

The chips were grinded inside a Fritsch planetary mill type Pulverisette 4 with grinding balls in conditions of variable rotation of the drum and of the grinding bowl, making possible in this way to determine the optimal grinding times for the obtaining micrometric powders with different granulation of HSS.

It was analyzed the time influence of MA on the morphology of the particles of micrometer powders by electron microscopy SEM. To determine the grain shape it has been used the SEM at JEOL 5600 LV microscope, fig.1.

The chemical composition of the high speed steel (HSS) powder was studied using the EDAX analysis, fig.2.

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The recovered samples were obtained through unilateral compacting techniques at pressures of 600 and 800 MPa The green densities evolution function the milling time and the pressing forces are presented in the figure 3.

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The samples were sintered in an electrical owen using Argon atmosphere at 1150[degrees]C, 1200[degrees]C 1250[degrees]C, 1 hour and 2 hour. After sintering, the box was cooled in furnace into the protective argon atmosphere. Figure 4 present the densities of the samples sintered at 1250[degrees]C with dwell time at the sintering temperature of 1 and 2 hours. The hardness of the samples was studied and is it was presented in figure 5.

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The samples were submitted to wear forces on a tribometer type TRB-01-02541 and a profilometer type TRB-0-WM-0000. As a result of the experimental research conducted we obtained important correlations between wear resistance and the morphology of the high speed steel recovered powder, compacting pressure and sintering temperatures.

In Fig.6 and Fig. 7., can be see the evolution of the friction coefficient versus sintering temperature and pressing force.

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3. CONCLUSION

The experimental work lead to the following conclusions: Recycled steel powder can be produced using steel scrap in the planetary milling process;

During the milling, the scrap is laminated, micro-forged, cracked continuously, and then finally formed into a spherical shape powder; The size and shape of the spherical powder produced depend on the milling time.

Increasing the milling time will reduce the size of the powder and produce spherical-like powder.

The best values at the coefficient of friction have the HSS produced from recovered chips obtained by milling for 20 hours, pressing for 800 MPa and sintered of 1250[degrees]C and dwell time 2 hours.

4. REFERENCES

Cesar Edil da Costa, Walter Contreras Parucker & Moises Luiz Parucker, (2003). Characterization of casting iron powder from recycled swarf, Journal of Materials Processing Technology 143-144, pp. 138-143.

Hong, S.H. D.W.Lee & B.K. Kim, (2000). Manufacturing of aluminum flake powder from foil scrap by dry ball milling process, Journal of Materials Processing Technology. 100, pp. 105-109.

Randall M. German, (1994). Powder Metallurgy Science.2nd, Metal Powder Industries Federation USA.

Sinha, A.K. (1992). Recent Developments in Iron and Steel Powder Production for High Performance P/M Components, In: Production of Iron, Steel and HIgh Quality Product Mix. Ch. 2, ASM International, USA

Trudel, Y.(1998). Metal Powder Production and Characterizaion, In: Powder Metal Technologies and Application. Ch. 2, ASM International, USA