Investigations of ferritic/martensitic super heat resistant 11‐12 %Cr steels for 650 °C power plants

The investigations of advanced ferritic/martensitic 11–12 %Cr steels for 650 °C power plant components focus on the improvement of high‐temperature creep properties with respect to chemical composition. The claim of the DFG research work was the development of new heat‐resistant 12 %Cr ferritic‐martensitic steels with sufficient creep and oxidation resistance for a 650 °C application by using basic principles and concepts of physical metallurgy on the basis of the state of art and to overcome the usual trial and error industrial alloy development. Efforts are focussed on a 100,000h creep strength of 100MPa at 650 °C in combination with a sufficient corrosion resistance by a Cr content of 12 % with contents 4‐5 %W, 3.4‐5,5 %Co, V, B and 1 %Cu as well as the choice of Ta or Ti instead of Nb. The results demonstrate that the aim is not to realize with the used alloying concept. In the long term range all 12 %Cr melts have a lower creep rupture strength than the advanced 9 %Cr piping steel P92. A high creep strength could be reached with a 0.06 % Ta alloyed 11 %Cr melt, which is in addition alloyed with a higher C and B content and as well as with lower W and Co portions. The results indicate in accordance with the finding of other steel researcher that a lower Cr content allows more effectiveness for the alloying partners respectively for the generation of more stable precipitates.     

Advanced cold rolled steels for automotive applications

Advanced multiphase steels offer a great potential for bodies‐in‐white through their combination of formability and achievable component strength levels. They are first choice for strength and crash‐relevant parts of challenging geometry. The intensive development of high‐strength multiphase steels by ThyssenKrupp has led to hot dip galvanizing concepts with an outstanding forming potential. Hot rolled, hot dip galvanized complex phase steels are currently produced in addition to cold rolled DP and RA steels. New continuously annealed grades with tensile strength levels of up to 1000 MPa in combination with sufficient ductility for applications mainly in the field of structural automobile elements make use of the classic advantages of microalloying as well as the principles of DP and TRIP steels. Further improvement of properties will be reached by the new class of high manganese alloyed steels.     

Verschleißbeständige Fe‐Basislegierungen mit Niobkarbid

Wear Resistant Fe‐Base Alloys with Niobium Carbide Martensitic Fe‐base alloys from the system Fe‐Cr‐C are widely used as chilled cast irons and tool steels. Because of the low hardness of their FeCr‐carbides this paper reports about new alloys with primarily solidified harder niobium carbides. It focuses on a secondary hardenable welding alloy, a coating material for composite castings, a chilled casting and a corrosion resistant cold work tool steel, which are investigated with respect to their process related microstructure and abrasive wear behaviour.     

Fatigue assessment of cut edges in high strength steel – Influence of surface quality

The influence of surface roughness on the fatigue strength in high strength steels and different cutting processes are studied. Fatigue testing is conducted on S700 and S960 material for different plate thicknesses cut in dog bone specimens using oxygen, plasma, laser and waterjet cutting. The surface roughness is measured for all specimens and residual stress measurements are carried out. Estimations of the fatigue strength are made based on the measured surface roughness and the ISO 9013:2002 standard for thermal cutting quality tolerances. The testing shows a 15–70 % increase in the fatigue strength compared to the estimation, proving a weak connection between the surface quality levels in ISO 9013:2002 and the fatigue test results. Different codes and design recommendations (IIW, EC3 and EN 13001) for fatigue strength of cut surfaces are compared with the fatigue test results which clearly shows an increased fatigue strength with enhanced quality and steel grades. However, the codes and design recommendations do not allow for any fatigue strength improvement with improved quality and increased yield strength.