* Correspondence address: Universite Joseph Fourier, Lab- oratoire de Cristallographie, CNRS BP 166, 38042 Grenoble Cedex 9, France. Fax: #33-476887411. E-mail address: tavares@polycnrs-gre.fr (S.S.M. Tavares). Journal of Magnetism and Magnetic Materials 226}230 (2001) 1103}1105 The use of thermomagnetic analysis for detection and quanti"cation of 4753C embrittlement of duplex stainless steels M.R. da Silva, S.S.M. Tavares*, D. Fruchart, S. Miraglia, J.M. Neto Escola Federal de Engenharia de Itajuba & , C.P. 50, CEP 37500-000, Itajuba-MG, Brazil Depto. de Engenharia Meca L nica - UFF, Rua Passo da Pa H tria, 156, 24210-240, Niteroi-RJ, Brazil Laboratoire de Cristallographie, CNRS BP 166, 38042 Grenoble Cedex 9, France Instituto de Fn & sica - UFRJ, C.P. 68528, CEP 21945-970, Rio de Janeiro-RJ, Brazil Abstract A duplex stainless steel was aged at 4753C for di!erent times up to 500 h. The thermal embrittlement was investigated by thermomagnetic analysis using a vibrating sample magnetometer and a thermomagnetic balance. The results obtained with the two equipment were similar and show that the Curie temperature increases with the ageing time. Relationships between T  and mechanical properties (hardness and toughness) were proposed.  2001 Elsevier Science B.V. All rights reserved. Keywords: Thermomagnetic analysis; Phase transitions 1. Introduction The duplex stainless steels (DSS) have been success- fully used in the chemical, petrochemical, nuclear and fertilisers industries. Their "ne microstructure consisting of ferrite (ferromagnetic) and austenite (paramagnetic) provides excellent mechanical properties and, by opti- mising the concentration of the elements Cr, Mo, Ni and N, excellent corrosion resistance was achieved. Neverthe- less, compounds of this family of stainless steels are likely to undergo embrittlement phenomena when temper- atures in the 300}5503C range are imposed during opera- tion. This embrittlement e!ect, also known as 4753C- embrittlement, is attributed to the precipitation of Cr-rich particles (). In the DSS the precipitation occurs by a mechanism of spinodal decomposition of the ferrite phase [1}3]. The thermal ageing embrittlement of DSS may be investigated by magnetic methods. Tsuchiya et al. [4] and Evanson [5] found that the hysteresis loss, residual induction and coercive force increased with the ageing time in cast DSS. Kim et al. [6] found an increase of the Curie temperature in ferritic stainless steels during ageing. In the present work, the thermal embrittlement at 4753C of a DSS UNS S31803 was evaluated by means of Curie temperature measurements. The results obtained were correlated to the mechanical properties changes. 2. Material and methods The initial material was a 3mm sheet of solution treated DSS UNS S31803 (22.5%Cr, 5.3%Ni, 0.030%C, 0.112%N, in weight). Sub-size V-notched Charpy sam- ples (2.5 mm) [7] were machined and aged at 4753C in vacuum by di!erent periods up to 500 h. The Brinnel hardness was measured at each condition. The thermom- agnetic analysis (TMA) was carried out in two equip- ments: a thermomagnetic balance (TB) of the Laboratory 0304-8853/01/$-see front matter  2001 Elsevier Science B.V. All rights reserved. PII:S0304-8853(00)00685-5