Magnetic Small-angle Neutron Scattering Study on Nano-precipitate of 17-4PH Stainless Steel

By taking advantage of neutron scattering technique, such as magnetic sensitivity and deep penetration, the magnetic smallangle neutron scattering (SANS) technique was applied to investigate the 174PH stainless steel sample from the valve rod which has been served for around 14 years in nuclear power plants. The results show that, compared with no magnetic field, the twodimensional scattering pattern is obviously anisotropic when the magnetic field is loaded, and the scattering intensity is significantly enhanced when the scattering vector is perpendicular to the direction of the magnetic field. The scattering intensity where the scattering vector is perpendicular to the direction of the magnetic field is significantly higher. By analyzing the SANS data along two different directions using polydisperse sphere model, it is concluded that the increase of the contrast is helpful for accurately analyzing the size of the Cu nanoprecipitate. This is because that the relative contribution of the scattering from the fluctuations of the composition in the vicinity of Cu nanoprecipitate, which has been shown by previous atom probe tomography experiment, can be largely reduced by the magnetic scattering.