Magnetic measurement of retained austenite in sintered steels – benefits and limitations

Figures & data

Table 1. ‘Attenuation coefficients’ for the alloying elements according to the different models (Maurer and Schroeter, Exner and Hoselitz) [6].

Alloying element	Ai–Maurer and Schroeter	Ai–Exner	Ai–Hoselitz
C	–3E–06*xc+8E–06	2E–05*xc+1E–05	15.08E–06
Cr	3.02E–06	3.70E–06	3.77E–06
Ni	2.41E–06	0.25E–06	0.94E–06
Mo	2.09E–06	1.26E–06	1.51E–06
Co	2.41E–06	2.12E–06	–
Mn	2.90E–06	2.90E–06	2.39E–06
W	1.11E–06	1.26E–06	–
Si	9.25E–06	6.04E–06	3.02E–06
Al	7.98E–06	6.92E–06	3.27E–06
V	3.53E–06	1.52E–06	–
P	–	–	3.77E–06
S	–	–	8.80E–06
Cu	–	–	2.89E–06
N	–	–	7.54E–06

Table 2. Powders used for producing the sintered steel bars.

Steel	Steel powder	Carbon carrier	Lubricant
Fe–Mo–C	Astaloy85Mo	Graphite UF4	HWC
Fe–Cr–C	AstaloyCrA	Graphite UF4	HWC
Fe–Ni–C	MSP4	Graphite UF4	HWC

Astaloy85Mo: water atomised prealloyed steel powder with 0.85% Mo, Höganäs, Sweden.

AstaloyCrA: water atomised prealloyed steel powder with 1.80% Cr, Höganäs, Sweden.

MSP4: water atomised prealloyed steel powder with 4.00% Ni and 0.50% Mo, QMP (former Mannesmann, now Rio Tinto) Germany.

Graphite: UF4, Kropfmühl, Germany.

HWC: Ethylenbisstereamide, Höganäs, Sweden.

Table 3. Carbon content of the sintered steels (C-combined).

Fe–Mo–C-steels		Fe–Cr–C-steels		Fe–Ni–C-steels
C-admixed (mass%)	C-combined (mass%)	C-admixed (mass%)	C-combined (mass%)	C-admixed (mass%)	C-combined (mass%)
0.3	0.292	0.3	0.237	0.3	0.265
0.5	0.478	0.5	0.415	0.5	0.471
0.7	0.670	0.7	0.591	0.7	0.654
1.0	0.946	1.0	0.900	1.0	0.970

Figure 1. Microstructures of the hardened Fe–0.85Mo–1.0C-steels, magnification: ×500. (a) austenitised at 800°C and quenched in water. (b) austenitised at 800°, quenched in water and cooled in liquid N₂.

Figure 2. Microstructures of the hardened Fe–1.8Cr–1.0C-steels, magnification: ×500. (a) austenitised at 800°C and quenched in water. (b) austenitised at 800°, quenched in water and cooled in liquid N₂.

Figure 3. Microstructures of the hardened Fe–4.0Ni–0.5Mo–1.0C-steels, magnification: ×500. (a) austenitised at 800°C and quenched in water. (b) austenitised at 800°, quenched in water and cooled in liquid N₂.

Figure 4. Retained austenite content in the hardened steel Fe–0.85Mo–C as a function of the carbon content (C-combined), calculated from the magnetic saturation using different models. (a) Fe–Mo–C-steels, austenitised at 800°C and quenched in water. (b) Fe–Mo–C-steels, austenitised at 800°C, quenched in water and cooled in liquid N_2.

Figure 5. Retained austenite content in the hardened steel Fe–1.8Cr–C as a function of the carbon content (C-combined), calculated from the magnetic saturation using different models. (a) Fe–Cr–C-steels, austenitised at 800°C and quenched in water. (b) Fe–Cr–C-steels, austenitised at 800°C, quenched in water and cooled in liquid N_2.

Figure 6. Retained austenite content in the hardened steel Fe–4Ni–0.5Mo–C as a function of the carbon content (C-combined), calculated from the magnetic saturation using different models. (a) Fe–Ni–C-steels, austenitised at 800°C and quenched in water. (b) Fe–Ni–C-steels, austenitised at 800°C, quenched in water and cooled in liquid N_2.

Figure 7. Retained austenite content in the hardened steel Fe–0.85Mo–C as a function of the carbon content (C-combined), calculated from the magnetic saturation using different models. (a) Fe–Mo–C-steels, austenitised at 900°C and quenched in water. (b) Fe–Mo–C-steels, austenitised at 900°C, quenched in water and cooled in liquid N_2.

Figure 8. Retained austenite content in the hardened steel Fe–1.8Cr–C as a function of the carbon content (C-combined), calculated from the magnetic saturation using different models. (a) Fe–Cr–C-steels, austenitised at 900°C and quenched in water. (b) Fe–Cr–C-steels, austenitised at 900°C, quenched in water and cooled in liquid N_2.

Figure 9. Retained austenite content in the hardened steel Fe–4.0Ni–0.5Mo–C-steels as a function of the carbon content (C-combined), calculated from the magnetic saturation using different models. (a) Fe–Ni–C-steels, austenitised at 900°C and quenched in water. (b) Fe–Ni–C-steels, austenitised at 900°C, quenched in water and cooled in liquid N_2.

Table 4. Retained austenite content measured by XRD/Rietveld.

Samples austenitised at 800°C
Samples quenched in water		Samples quenched in water and cooled in liquid N2
Steel	RA^Rietveld [mass%]	Steel	RA^Rietveld[mass%]
Fe–Mo–1.0C	17	Fe–Mo–1.0C	9
Fe–Cr–1.0C	9	Fe–Cr–1.0C	7
Fe–Ni–1.0C	29	Fe–Ni–1.0C	12

Table

Sample-nomination	[mass%]	RA^Plain Iron [mass%]	RA^Mauer&Schroeter [mass%]	RA^Exner [mass%]	RA^Hoselitz [mass%]
Samples austenitised at 800°C and quenched in water
Fe–Mo–0.3C	n.m.	7	6	5	5
Fe–Mo–0.5C	n.m.	8	6	4	5
Fe–Mo–0.7C	n.m.	11	8	4	6
Fe–Mo–1.0C	17	20	17	10	14
Fe–Cr–0.3C	n.m.	8	6	4	4
Fe–Cr–0.5C	n.m.	9	6	3	4
Fe–Cr–0.7C	n.m.	11	8	4	5
Fe–Cr–1.0C	9	17	14	9	11
Fe–Ni–0.3C	n.m.	5	1	3	2
Fe–Ni–0.5C	n.m.	9	4	5	5
Fe–Ni–0.7C	n.m.	16	12	11	12
Fe–Ni–1.0C	29	33	28	24	27
Samples austenitised at 800°C. quenched in water and cooled in liquid N2
Fe–Mo–0.3C	n.m.	6	5	4	4
Fe–Mo–0.5C	n.m.	7	5	3	4
Fe–Mo–0.7C	n.m.	9	6	2	4
Fe–Mo–1.0C	9	10	7	0	4
Fe–Cr–0.3C	n.m.	8	5	4	4
Fe–Cr–0.5C	n.m.	8	6	3	4
Fe–Cr–0.7C	n.m.	10	6	3	4
Fe–Cr–1.0C	7	13	9	4	7
Fe–Ni–0.3C	n.m.	6	1	3	2
Fe–Ni–0.5C	n.m.	6	1	2	2
Fe–Ni–0.7C	n.m.	9	4	3	4
Fe–Ni–1.0C	12	15	9	4	8
Samples austenitised at 900°C and quenched in water
Fe–Mo–0.3C	n.m.	7	6	5	5
Fe–Mo–0.5C	n.m.	8	6	4	5
Fe–Mo–0.7C	n.m.	11	9	5	7
Fe–Mo–1.0C	n.m.	19	17	9	14
Fe–Cr–0.3C	n.m.	8	5	4	4
Fe–Cr–0.5C	n.m.	9	6	4	4
Fe–Cr–0.7C	n.m.	11	8	4	6
Fe–Cr–1.0C	n.m.	23	20	13	17
Fe–Ni–0.3C	n.m.	6	1	3	3
Fe–Ni–0.5C	n.m.	8	4	4	4
Fe–Ni–0.7C	n.m.	15	10	9	10
Fe–Ni–1.0C	n.m.	32	28	23	27
Samples austenitised at 900°C. quenched in water and cooled in liquid N2
Fe–Mo–0.3C	n.m.	6	5	4	4
Fe–Mo–0.5C	n.m.	7	5	3	4
Fe–Mo–0.7C	n.m.	9	7	3	5
Fe–Mo–1.0C	n.m.	10	8	0	5
Fe–Cr–0.3C	n.m.	7	5	3	3
Fe–Cr–0.5C	n.m.	8	5	2	3
Fe–Cr–0.7C	n.m.	9	6	2	3
Fe–Cr–1.0C	n.m.	12	9	0	5
Fe–Ni–0.3C	n.m.	5	1	3	2
Fe–Ni–0.5C	n.m.	7	2	3	3
Fe–Ni–0.7C	n.m.	9	4	3	4
Fe–Ni–1.0C	n.m.	14	9	3	7

Ouda K. Magnetische Bestimmung von Restaustenit in unterschiedlich legierten Stählen [master thesis]. Technische Universität Wien; 2017.

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