Corrosion resistance of wires of cr-ni-mo steel used in endourology cd.

2. Materials and research methods

The investigations have been carried out for the samples of Cr-Ni-Mo steel of 1.4404 grade in a wire form. Chemical composition is given in a table 1.

Initial material was solutioned wire rod with diameter of 5,5mm. Wire rod was drawn up to diameter of 1,35mm. After each drawing process samples were cut off to be put to corrosion tests. Deformation step was different for samples of wire. Corrosion resistance tests were carried out in artificial urine at the temperature 37±10C and pH 7,0±0,2. Table 2 presents chemical composition of artificial urine. An artificial urine made of both solution A and B mixed in proportion 1:1. Suggested solution featured molar concentration of chloride ions in the amount of 0,460.

The electrochemical tests of the investigated wire were performed with the use of a potentiodynamic method by recording of anodic polarization curves. The VoltaLab® PGP 201 potentiostat with the software for electrochemical tests was applied [1].

The saturated calomel electrode (SCE) was applied as the reference electrode and the auxiliary electrode was a platinium foil. The recording of anodic polarization curves was carried out from potential value E=Ecorr - 100mV with polarization in direction of positive values and with the potential changes rate equal to 1mV/s. When the current density has achieved the value equal to 1mA/cm2 the direction of polarization was changed and the returned curve has recorded. On the basis of the obtained curves: the breakdown potentials Eb, repassivation potential Erp, polarization resistance Rp, corrosion current density icorr and corrosion rate have been determined [4,5].