The temperature dependence of the martensite formation and the mechanical properties of three high alloyed Cr‐Mn‐Ni as‐cast steels with varying Ni contents were studied. The results showed that the Ms and Md temperatures of the steels decrease with increasing nickel contents. Therefore the strain‐induced martensite formation, the TRIP effect and the temperature anomaly of the elongations occurs at lower temperatures. The steel alloyed with 3% nickel shows a stress induced formation of martensite and a dynamic strain aging. Depending on the nickel content and the temperature a TWIP effect occurs additionally to the TRIP effect in the investigated steels. The study was performed by using static tensile tests, dilatometer tests, optical microscopy and the magnetic scale for the detection of ferromagnetic phase fractions.

Abstract. High alloyed metastable austenitic or austenitic-martensitic steels show a strain induced formation of martensite during mechanical loading. These kinds of steels are well known as material for rolled products. Based on the System Fe-Cr-Mn-Ni a new generation of cast steels with TRIP effect will be discussed. The investigations show how the mechanical properties and the fraction of the formed martensite are influenced by varying Ni contents. The mechanical properties in the cast state of the material are quite similar to those in the rolled state. This is valid for tensile as well as compression loading. Under certain conditions, an isothermal formation of martensite was observed in some of the steels. The experimental results are based on tensile and compression tests. The specimens were analysed by optical microscopy, electron backscatter diffraction (EBSD), dilatometer tests and a special method for the detection of the ferromagnetic phase contents, the magnetic balance.

Stress‐Temperature‐Transformation (STT) and Deformation‐Temperature‐Transformation (DTT) diagrams are well‐suited to characterize the TRIP (transformation‐induced plasticity) and TWIP (twinning‐induced plasticity) effect in steels. The triggering stresses for the deformation‐induced microstructure transformation processes, the characteristic temperatures, the yield stress and the strength of the steel are plotted in the STT diagram as functions of temperature. The elongation values of the austenite, the strain‐induced twins and martensite formations are shown in the DTT diagram. The microstructure evolution of a novel austenitic Cr‐Mn‐Ni (16%Cr, 6% Mn, 6% Ni) as‐cast steel during deformation was investigated at various temperatures using static tensile tests, optical microscopy and the magnetic scale for the detection of ferromagnetic phase fraction. At the temperatures above 250 °C the steel only deforms by glide deformation of the austenite. Strain‐induced twinning replaces the glide deformation at temperatures below 250 °C with increasing strain. Below 100 °C, the strain‐induced martensite formation becomes more pronounced. The kinetics of the α'‐martensite formation is described according to stress and deformation temperatures. The STT and DTT diagrams, enhanced with the kinetics of the martensite formation, are presented in this paper.

Within the Collaborative Research Center 799 novel composite materials which consist of a highly alloyed TRansformation-Induced Plasticity/Twinning-Induced Plasticity (TRIP/TWIP) CrMnNi cast steel matrix and a partially stabilized zirconium dioxide (Mg-PSZ) ceramic, referred to as TRIP-Matrix-Composites, are developed. [1] By applying an external load larger than the yield strength, the TRIP steel matrix shows a strain-induced phase transformation from metastable austenite to a 0 -martensite which leads to a concurrent increase of strength and ductility. By contrast, stress-induced formation of a 0 -martensite occurs at stresses below the yield strength, i.e., during elastic deformation. [2] The stress-induced transformation of the partially stabilized ZrO 2 from tetragonal phase to monoclinic modification can result in a further increase of the strength. Currently the interstitial-free austenitic CrMnNi cast stainless steels with TRIP/TWIP effect are in use. Representative alloys are 16Cr-7Mn-3Ni, 16Cr-7Mn-6Ni, and 16Cr-7Mn-9Ni. [3,4] These austenitic steel grades typically show low yield strengths of the order of 180-200 MPa. As a result of the low stress levels, only small fractions of the ceramic phase can transform to the monoclinic structure. In order to assist the phase transformation of the ceramic phase from tetragonal to monoclinic, the current steel research in the CRC 799 is focused on the increase of strength, especially the yield strength of the austenitic TRIP/TWIP CrMnNi cast steels by solid solution strengthening by nitrogen. Furthermore, the reduction of delta ferrite volume fractions, the adjustment of a pronounced TRIP/TWIP effect at operating temperatures and improved resistance against the intercrystalline corrosion by the addition of nitrogen is desired. In recent years, highly alloyed TRIP and TWIP steels have received much attention in both academia and industry because of their superior mechanical properties. [5][6][7]12] The high-manganese TWIP steels can be divided in the alloying systems FeMnC and CrMnC with additions of the main alloying elements such as N, Al, Si. In these steels g ! e transformation and deformation-induced twinning can appear in dependence of the SFE of the austenite. It is commonly believed that stacking fault energies below 18-20 mJ m À2 favor the g ! e phase transformation and higher values favor the twinning of austenite. [8][9][10] The longest known FeMnC steels are characterized by manganese contents between 15 and 30% and an austeniticThe effect of the manganese content (0-11%) on the transformation temperatures, the mechanical properties and microstructure development of five highly alloyed 14Cr-XMn-6Ni cast stainless steels with 0.1% nitrogen was studied. The examinations reveal that the M s , A s , and A f temperatures decrease with increasing manganese contents. As a result of low austenite stability, room temperature austenitic-martensitic as-cast microstructure was formed at manganese contents between 0 and 3%. At manganese levels of 6% and higher a fu...

The martensite start temperature (Ms), the martensite austenite re‐transformation start temperature (As) and the re‐transformation finish temperature (Af) of six high alloyed Cr‐Mn‐Ni steels with varying Ni and Mn contents in the wrought and as‐cast state were studied. The aim of this investigation is the development of the relationships between the Ms, As, Af, T0 temperatures and the chemical composition of a new type of Cr‐Mn‐Ni steels. The investigations show that the Ms, As and Af temperatures decrease with increasing nickel and manganese contents. The Af temperature depends on the amount of martensite. Regression equations for the transformation temperatures are given. The experimental results are based on dilatometer tests and microstructure investigations.