Crack Paths 2006

microstructural investigation was carried out on the samples sintered both at 1120°C

and 1250°C.

M A T E R I A CL HS A R A C T E R I Z A T I O N

Three steels, obtained from AstaloyCrM powders sintered at different temperatures in

hydrogen (90%) and nitrogen (10%) atmosphere, were investigated. The nominal

density was 7.0 g/cm3. In table 1 the sintering conditions are reported, while table 2

shows the chemical composition. For Cr2 and Cr3 materials a tempering at 200°C for 1

hour was carried out after sintering.

Table 1. Sintering conditions.

Material code Sintering Temperature [°C] Cooling rate after sintering [°C/s]

Cr1

1120

0.8

1120

Cr2

2.5

Cr3

1250

2.5

Table 2. Chemical composition of the steels.

Material code % C r % M o % added graphite

% Cafter sintering

Cr1

3

0.5

0.50

0.47

0.5

0.68

Cr2

3

0.57

0.5

0.68

Cr3

3

0.62

Firstly, the dimensions and characteristics of the pores were analysed, by the calculation

of porosity through an image analysis software. The materials were classified

considering the area and the roundness of the pores. The total porosity was estimated

equal to 10.1%. Figures 1a and 1b show the pores area distribution and the pores

roundness, varying the sintering temperature. The data related to 1120°C sintering

temperature refer to both Cr1 and Cr2 series, because it’s knownin the literature that the

pores area distribution and roundness depend only on sintering temperature [6-10].

100

100

90

80

1120°C

80

1120°C

60

70

1250°C

1250°C

[% 560 ]

40

20

40

30

0

20

5

0

5 .25 .6

0

2

5

5

- 2

- 4

- 5

.1

.5

.1

.2

.2

.2

10

0

5

4

3

2

1

-1

6

1.6

.1

- 1

- 6

=

3

0

2

1

.12 -

5

0

>

.5

2

1 1

Poresroundness

10-100 Area [ m 2 ] P

1-10

100-1000

Figure 1 a): pores area distribution varying the sintering temperature; b): pores

roundness varying the sintering temperature