Level V, expert opinion/agreement conference.

The precipitation of titanium nitride in undeformed solid carbon-manganese steel has been investigated by means of metallography and electron microscopy at in-situ melted samples the cooling of which was interrupted at different temperatures for a defined time. The deformation-induced precipitation of titanium nitride was studied on samples which were in-situ melted in a torsion plastometer, deformed after solidification, re-deformed after a holding time, and quenched. Additionally, 50 mm slabs were investigated after direct rolling in a pilot plant, partially with a preceding soaking. In the range of delta ferrite fast homogenization of segregated titanium takes place. No TiN nuclei were formed. In undeformed austenite some large precipitates were formed indicating the solidification structure. In the 1200 to 1100 "C range particle sizes between 20 and 70 nm were reached. A high density of deformation-induced particles smaller than 10 nm could be obtained at or below 1050 "C. The density of the particles increased with decreasing deformation temperature. After fast cooling, below 1000 "C also in undeformed material finely dispersed precipitates were formed.Ausscheidung von Titannitrid in niedriglegiertem Stahl wiihrend des AbkOhlens und Umformens. Die Bildung von Titannitrid in unverformtem festem Kohlenstoff-Mangan-Stahl wurde metallographisch und elektronenoptisch an Proben, deren AbkOhlung nach dem Erstarren bei unterschiedlichen Temperaturen fOr vorgegebene Zeiten unterbrochen wurde, untersucht. Eine verformungsinduzierte Ausscheidung von Titannitrid erfolgte an Proben, die in einem Torsionsplastometer in-situ geschmolzen, nach dem Erstarren umgeformt, nach einer Haltezeit nochmals verformt und abgeschreckt wurden. Zusatzllch wurden 50-mm-Platinen nach Direktwalzen in einer Versuchsanlage untersucht, teilweise mit AusgleichsglOhung vor dem Walzen.

The solubility of titanium nitride in liquid iron is described by the solubility product log([%Ti][%N])1 = −17040/T + 6.40 reported by Turkdogan. The solubility in δ ferrite measured by Kunze is log<[%Ti][%N])δ = −17205/T + 5.56. Combining the solubilities in both phases and the solubilities of nitrogen the distribution equilibrium of titanium can be derived. It is characterized by the thermodynamic distribution coefficient kδ/Io,Ti = [%Ti]δ/[%Ti] = 0.40. By zone melting and secondary ion mass spectrometry of the titanium distribution kδ/ITi = 0.53 was measured. An analysis of all known data led to kδ/Io,Ti = 0.40…0.50. Measurements of the TiN solubility in austenite by heat treatment were not significant. They led to distribution coefficients between 0.07 and > 1. By zone melting in a carburizing atmosphere a distribution coefficient kγ/ITi = 0.12 was measured. From a thermodynamic analysis performed by Ohtani et al., from the TiN solubility in the melt, and from the solubilities of nitrogen kγ/Io,Ti = 0.13 was deduced. Basing on the distribution equilibria of titanium and nitrogen and on the measured temperature dependence the solubility product log([%Ti][%N])γ = −15000/T + 4.06 was obtained.

The microsegregation of titanium and manganese and the precipitation of titanium nitride during dendritic solidification were investigated on an Fe‐0.051%Ti‐0.77%Mn alloy. Carbon and nitrogen were introduced into the liquid sample via the gas phase. The material solidifies as delta ferrite at a carbon mass content of about 0.08% but predominantly as austenite at ≥ 0.3%. At ferritic solidification, an about 3fold enrichment of the titanium in the residual melt between secondary dendrite arms is attained by segregration, whereas in the corners between some dendrites or grains in maximum a 10fold enrichment was detected. TiN particles of 0.5 to 1.0 μm size are formed only in the regions of maximum segregation where the supersaturation is higher than 15fold. An equal supersaturation has been calculated for homogeneous nucleation in the melt. The number of particles is moderate at 0.016% nitrogen but low at 0.008%. At austenitic solidification, the titanium content in the residual melt increases to more than the 30fold of the starting value. Particles formed in the melt grow to diameters in the 2 μm range.

The following recommendations are based on expert opinions of an international multidisciplinary panel endorsed by the “European Federation of National Associations of Orthopaedics and Traumatology” (EFORT), the “European Hip Society” (EHS), the German “Arbeitsgemeinschaft Endoprothetik” (AE) and the “Deutsche Arthrosehilfe” (DAH)