Transformation-Induced Ductility of Reverse Austenite Evolved by Low-Temperature Tempering of Martensite

A novel steel combining the “quenching and tempering (Q&T)” process was exploited that can achieve the enhancement of austenite by interface migration during tempering the martensitic matrix mixed with films of austenite. A high uniform elongation (12%) combined with high yield tensile strength (1500 MPa) was obtained, which showed distinct advantages over all the other advanced high strength steels under development for a lightweight car body. Furthermore, the effect of austenite on enhancement of ductility in “Q&T” steels with a martensite matrix was elucidated, which suggested that the ductility was promoted by enhancing boundary sliding and delaying work hardening of the martensitic matrix.

Technological increase of adhesive wear-resistance of parts added with chromium powder wire alloyed with complex of boron and nitrogen compounds

It is shown that the structure of metal padded with powder wire having the following mixture: 15% Cr – 0,5% B4C – 0,5% BN – 2,5% TiB2 – 1,0% ZrB2, is a martensitic matrix with (Fe, Cr)2B boride eutectic, carbon boride of (Fe, Cr)7(C, B)3 type and ε –(Fe, Cr)2-3N nitrides. Such a wire can be used for strengthening weld deposition of parts operated under conditions of heavy friction loading.

Investigating the Difference in Mechanical Stability of Retained Austenite in Bainitic and Martensitic High-Carbon Bearing Steels using in situ Neutron Diffraction and Crystal Plasticity Modeling

In situ neutron diffraction of the uniaxial tension test was used to study the effect of the surrounding matrix microstructure on the mechanical stability of retained austenite in high-carbon bearing steels. Comparing the samples with bainitic microstructures to those with martensitic ones, it was found that the retained austenite in a bainitic matrix starts transforming into martensite at a lower strain compared to that within a martensitic matrix. On the other hand, the rate of transformation of the austenite was found to be higher within a martensitic microstructure. Crystal plasticity modeling was used to analyze the transformation phenomenon in these two microstructures and determine the effect of the surrounding microstructure on elastic, plastic, and transformation components of the strain. The results showed that the predominant difference in the deformation accumulated was from the transformation strain and the critical transformation driving force within the two microstructures. The retained austenite was more stable for identical loading conditions in case of martensitic matrix compared to the bainitic one. It was also observed that the initial volume fraction of retained austenite within the bainitic matrix would alter the onset of transformation to martensite, but not the rate of transformation.

Effect of Ageing Treatment on the Microstructure and Hardness of the Ti6Al4V Alloy

The effects of ageing temperature, time and cooling medium on the microstructure and hardness of a solution treated Ti6Al4V alloy were investigated. The furnace cooling after ageing for 0.5 hours gave a homogenous structure with higher hardness values than the solution treated and water quenched Ti6Al4V alloy. Increasing the ageing time to 2 hours reduced the alloy hardness. Ageing at temperatures between 500 and 700°C, followed by furnace cooling, led to homogenously distributed α- and β-phases within a fully martensitic matrix leading to improved hardness. A heterogeneous structure with a high variation in microhardness was revealed when ageing at 800 and 900°C.

Effect of Austenizing Temperature on Microstructures and Mechanical Properties of Cr-W-Ni-Alloy Steel

An investigation was made to determine the effect of austenizing temperature on microstructure and tensile properties of Cr-W-Ni-alloy steel. Correlations of microstructure tensile properties and austenizing temperature parameters were established. Analysis of optical and scanning electron microscope show that there were a lot of coarse spherical undissolved carbides dispersed on the lath martensitic matrix in as-quenched specimens when austenized at 900°C while there were only very little nanometer carbides when austenized at 1000°C and 1100°C. The tensile properties show that austenizing temperature had large effect on the mechanical property of the Cr-W-Ni-alloy steel. Oil quenching after austenized at 1100°C for 26 minutes followed with tempering at 260°C for 3h, Cr-W-Ni-alloy steel obtained best strength and ductility match.