List of Abstracts 2016: SESSION F - ADVANCED STEELS
Date: November 11, 2016
Twinning Induced Plasticity steel, or TWIP steel, has had increased interest in recent years from various industry sectors. This is due to it being light weight, strong, and ductile; which are all properties that are useful in the automotive and aerospace industries. These steels potentially can offer lighter weight vehicles and parts with increased strength and other mechanical properties. This combination could offer greater fuel efficiency and performance while at the same time improving the safety features of the vehicle. This steel is characterized by being a high alloy steel, specifically having a high manganese content. It also has a fully austenitic microstructure at room temperature, which is a unique characteristic. But, for TWIP steel to be useful in various industrial sectors, it must have good weldability. This paper deals with the description of the strengthening due to the cold rolling on experimental heats of manganese steel with TRIP/TWIP effect. Impacts on microstructure, yield strength and tensile strength are described. Also the weldability of experimental TWIP steel by studying fusion zones, heat affected zones and the residual base metal after laser and TIG welding is described.
The paper describes the development of prototype equipment for laser beam welding in combination with induction heating. Samples create from a tool steel H13 are tested structurally and mechanically, while the influence of the individual parameters are evaluated to optimize additive technology process. Residual stresses are measured and correlated with the numerical model of temperature fields. To verify the industrial potential, technological durability test of forging dies was carried out, which confirmed a higher durability after additive manufacturing compared to conventional tools.
Multilayered metal composites consisting of alternating metals or alloys have been well developed to obtain the superior mechanical properties different from those in any of the constituent materials. In the present work, hot rolling bonded multi-layered composites consisting of austenitic stainless steel and martensitic tool steel with high nitrogen content are focused. The effects of hot rolling on microstructure of composites with different variety of layers are discussed. Influence of the tempered microstructure on the tensile behaviour of a 3-layer to 64-layer laminated composite steels will be also described and discussed. Also will be investigated possible the enhanced plasticity of the brittle layer in the composite.
Today's requirements for the design of functional parts and components demand low weight and, at the same time, high strength. There are several heat treatment methods which can satisfy such requirements. These include TRIP heat treatment, long-time low-temperature austempering, and Q&P processing. It is the Q&P processing which delivers excellent results in terms of mechanical properties and light weight. It relies on stabilising retained austenite through partitioning of carbon between martensite and austenite. The carbon-enriched austenite then becomes a ductile constituent in the otherwise brittle martensitic matrix. A precondition for successful Q&P processing consists in sufficient silicon content in the steel, which precludes precipitation of undesirable cementite. Cementite would otherwise form as a result of enrichment of retained austenite with carbon. To ascertain the usefulness of higher silicon level in steel for Q&P processing, one can compare Q&P processes in steels with various levels of this element.
We report recent research in our laboratory on the thermal stabilization and phase transformation of nanocrystalline stainless steels. Fe-Cr-Ni alloys with the addition of Zr and Y are studied. The thermal stability and phase transformation of these nanocrystalline alloys, prepared by mechanical alloying of powders both at room temperature and at cryogenic temperature, is studied by XRD, STEM, FIB and hardness as a function of annealing temperature and alloy composition. The relative importance of composition and solute additions in various temperature ranges are discussed with respect to grain growth and phase stability for the different alloys. Depending on the alloy compositions, partially or fully martensitic transformation is observed as a result of mechanical alloying whereas the annealing induces reverse transformation of martensite-to-austenite. It is found that Y solute additions are more effective in stabilizing the nanocrystalline grain size in the Fe-Cr-Ni than Zr additions. The research reported in this work was supported by TUBITAK under Grant number 114M214. The authors wish to thank TUBITAK for the support.