Martensitic transformations, structure, and strengthness of processed high-nitrogen and high-carbon ferrous alloys

Structures and properties of metastable austenitic alloys Fe-18Cr-16Ni-I2Mn-(0.17 to 0. 50)N, Fe-18Cr-12Mn-(0.48 to 1.12)N, Fe-18Cr-(0.1 to 1.18)N, and Fe-(12 to 20)Ni-(0.6 to 1.3)C, Fe-(6 to 8)Mn-(0.6 to 1.0)C, Fe-(5 to 6)Cr-(4 to 5)Mn-(0.6 to 0.8)C, Fe-6Cr-(1.0 to 1.3)C resulting from martensitic transformations under cooling and cold deformation (CD), as well as following tempering processes, were studied by magnetometry, X-ray and electron microscopy analyses, hardness measurements and mechanical properties tests. Martensite with a b.c.t. lattice was formed in all alloys with ${\rm M_s}{>}-196^\circ$C during cooling. Under CD transformations of $\gamma{\to}\alpha$, $\gamma{\to}\varepsilon{\to}\alpha$, or $\gamma{\to}\varepsilon$ types were realized depending on the alloy composition. Carbon increased but nitrogen decreased stacking fault energy. Thus carbon assists $\alpha$-martensite formation but nitrogen promotese. As CD level and/or concentration of carbon and nitrogen increase residual stresses resulting from the CD also increase. The martensitic transformation during CD can decrease the residual stresses. Kinetic of tempering of b.c.t. thermal martensite differs from those of CD-induced martensite. In the second case, deformation aging, texture, and residual stresses are more visible. The maximal strengthening under CD takes place in (Mn+N)-steels. (Cr+N) and (Cr+Mn+N)-steels are high-strength, non-magnetic and corrosion resistant and are easily hardened by a low level of plastic deformation

Transformation of retained austenite during tempering of high carbon steel

Dilatometric, electron microscopic, and X-ray diffraction techniques have been employed to analyze transformations of the retained austenite in a 1.85 wt % C steel during tempering. The quenched steel contained 82% of retained austenite. Depending on the tempering temperature, transformations of the retained austenite in the highcarbon steel manifest themselves as the formation of bainite “fringes" around the martensite crystals, new lenticular and thin-plate crystals of isothermal martensite also surrounded with the bainite “fringes" as well as the thin-plate pearlite

Texture Transformations in Thermomechanically Treated Steels Having Increased Nitrogen Content and Alloys

In this study the results of mathematical simulation and experimental research of texture transition in stress assisted shear phase transformations are discussed. The orientation distribution function (ODF) calculation model to the any type crystalline lattice symmetry materials has been suggested. By crystalline lattice symmetry analysis this computer program determines necessary amount of the initial experimental data. The experimental verification supports this model well. The ODF calculation model after shear phase transformation with equal use of all possible variants of orientation relationship or with various degrees of variant selection worked out. In this study the experimental and calculating data of the direct and reversal shear transformations α←→γin Fe-alloys and B2←→B119' in Ti-Ni alloys are discussed. The stress assisted shear phase transformation model and computer program to calculate ODF after transformation have been worked out

Peculiarities of structure and thermomechanical strengthening of martensitic structural steels microalloyed by nitrogen

The effect of thermomechanical treatments on structure and properties of structural C(0.35-0.50)CrNiMoV steels microalloyed by nitrogen were studied using optical microscopy, X-ray diffraction analysis and mechanical testing. The hardness of martensite change as a function of austenitization temperature is presented for the steels with the same main composition but various summary C and N contents. Microalloying of structural steels by nitrogen results in complication of phase transformations and raising austenitization temperature for quenching and HTMT. A small quantity of undissolved carbonitrides promotes fine-grained structure preservation and heredity of the initial ascast structure. The heat and thermomechanical treatment regimes were determined which allowed the use of nitrogenmicroalloyed structural steels as high-strength ones. A complete dissolution of special carbonitrides during HTMT and following low-temperature tempering provide high strength level (by 300-500 MPa higher than for nitrogen-free analogs) combined with sufficient ductility and fracture toughness

Martensitic Transformations and Shape Memory Effect in Thermomechanically Treated Ti-Ni Alloys

The possibilities to regulate the martensitic transformation temperature range, mechanical and special properties of Ti-Ni-based shape memory alloys by high-temperature and low-temperature thermomechanical treatments were studied

Formation of austenite structure during hot hydrodynamic extrusion in a high-temperature thermomechanical treatment cycle

22.00; Translated from Russian (Izv. Vyssh. Uchebn. Zaved., Chern. Metall. 1987 (7) p. 118-121)Available from British Library Document Supply Centre- DSC:9022.06(BISI-Trans--26273)T / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo