Papers by Keyword: Strengthening Mechanisms

Paper TitlePage

Authors: Michael Korchynsky
Abstract: The recent worldwide surge of steel consumption, mainly of low-strength carbon grades, has created raw-materials shortages and price increases. These supply-demand strains could be relaxed by satisfying engineering needs with less steel. However, materials used for such a substitution must combine high weight reducing potential with low cost. Microalloyed (MA) steels are cost- effective substitutes, since their high strength is the result of grain refinement and precipitation hardening. The optimum alloy design of MA steels combines superior properties with lowest processing cost. The growing use of EAF and thin slab casting technology improve the economics of MA steels, especially when alloyed with vanadium. The monetary value of weight reduction is sufficient to increase the profitability of steel makers and to lower the material cost to steel users. This “win-win” situation is financed by the elimination of efforts spent in producing inefficient steel, yielding an increase in wealth formation. To gain acceptance of substitution by the consumer, a long-term strategic plan is needed to be implemented by the beneficiaries – steel producers and steel users. The successful substitution is of importance to the national economy, resources and energy conservation, and the environment. Since microalloyed steels, used as a replacement for carbon steels, offer low-cost weight savings, they deserve to be classified as advanced structural materials.
471
Authors: Xiang Peng Xiao, Bai Qing Xiong, Qiang Song Wang, Guo Liang Xie, Li Jun Peng
Abstract: The microstructural features and heat treatment response of Cu-2.1Ni-0.5Si-0.2Zr-0.05Cr (wt.%) alloy have been investigated. The alloy was aged at 400°C、450°C and 500°C after a cold deformation of 70% reduction. The variation in hardness and electrical conductivity of the alloy was measured as a function of aging time. The results indicated the highest peak hardness value of approximately 205HV for the alloy aged at 400°C for 4h after the solution treatment and cold deformation. The alloy has two main phases, one is Ni2Si phase, and the other is Cr2Zr phase. The strengthening mechanisms of the alloy include spinodal decomposition strengthening, ordering strengthening and precipitation strengthening.
294
Authors: S.W. Jung, Jae Hyup Lee, Jae Bok Nam, H.W. Nam, Kyung Seop Han
1297
Authors: Hideo Awaji, Seong Min Choi
Abstract: Intra-type nanocomposites, in which nanosized second-phase particles are embedded within matrix grains, generate dislocations around the dispersed nanoparticles. The intra-type nanostructure induces a thermal expansion mismatch between the matrix and the dispersed particles, which will yield nanoscale stress distribution around the particles and generate lattice defects, such as dislocations. The dislocations of ceramics can be generated at elevated temperatures, become sessile dislocations at room temperature, and serve as nanocrack nuclei in highly stresses fields, e.g. at a main crack tip. The frontal process zone size ahead of a crack tip is expanded due to creation of nanocracks and hence the fracture toughness is improved. Annealing after sintered nanocomposites is important in controlling the dislocation activities. Appropriate annealing will disperse dislocations into the matrix grains. However, dislocations are sensitive to temperature, and higher temperature or longer annealing time result in dislocation disappearance and cause the reduction of the strength and fracture toughness of nanocomposites. In this study, commercially available γ-alumina agglomerated powder with high porosity was used to create the intra-type nanostructure. Nickel nitrate solution was infiltrated into nanopores of the γ-alumina agglomerates in vacuum. The alumina/nickel composite powder following reduction in hydrogen atmosphere was sintered using a pulse electric current sintering method. The volume fraction of nickel was about 3 vol %. After appropriate annealing, the highest fracture toughness was obtained to be 7.6 MPam1/2, which is two times higher than that of monolithic alumina.
1632
Authors: Jae Il Jang, Sang Hoon Shim, Shinichi Komazaki, Takayuki Sugimoto
Abstract: As advanced ferritic/martensitic heat-resistant steels generally have a complex structure consisting of several microstructural units (lath, block, packet, and prior austenite grain), it is very hard to separate the contribution of each microstructural unit (or its each boundary) to the strengthening mechanism in such steels. Here we explore the role of each microstructural unit in strengthening of advanced high Cr steel through nanoindentation experiments performed at different load levels. Nanoindentation results are analyzed by comparing with microstructural observations and discussed in terms of prevailing descriptions of strengthening mechanism.
277
Authors: C. Mitterer, P.H. Myrhofer
453
Authors: Xian Hua Tian, Jun Zhao, Shuai Liu, Zhao Chao Gong
Abstract: Close attention has been paid to Functional graded materials (FGMs) worldwide for their novel design ideas and outstanding properties. To verify the advantage of FGMS in the design of ceramic tool materials, Si3N4/(W, Ti)C nanocomposite ceramic tool materials with homogenous and graded structure were fabricated by hot pressing and sintering technology. The flexural strength, fracture toughness and hardness of the sintered composites were tested and compared. The experimental results showed that the graded structure improved mechanical properties of the ceramic tool materials, especially the flexural strength and fracture toughness. The introduction of residual compressive stress in the surface layer contributes to the improvement of the properties .
511
Authors: G. Wu, Yongbing Zhao, N. Kono, H. Watanabe, T. Takahashi
467
Authors: Wojciech Borek, Małgorzata Czaja, Krzysztof Labisz, Tomasz Tański, Mariusz Krupiński, Stanislav Rusz
Abstract: The aim of this paper is to determine the high-manganese austenite propensity to twinning induced by the cold working and its effect on structure and mechanical properties, and especially the strain energy per unit volume of new-developed high-manganese Fe – Mn – (Al, Si) investigated steel with various structures after their thermo-mechanical treatments. The new-developed high-manganese steel provides an extensive potential for automotive industries through exhibiting the twinning induced plasticity (TWIP) and transformation induced plasticity (TRIP) mechanisms. TWIP steels not only show excellent strength, but also have excellent formability due to twinning, thereby leading to excellent combination of strength, ductility, and formability over conventional dual phase steels or transformation induced plasticity TRIP steels. The microstructure evolution in successive stages of deformation was determined in metallographic investigations using light, scanning and transmission electron microscopies as well as X-ray diffraction methods.
18
Authors: Leszek Adam Dobrzański, Wojciech Borek, Janusz Mazurkiewicz
Abstract: The aim of this paper is to determine the high-manganese austenite propensity to twinning induced by the cold working and its effect on structure and mechanical properties, and especially the strain energy per unit volume of new-developed high-manganese Fe – Mn – (Al, Si) investigated steel, containing about 24,5 % of manganese, 1% of silicon, 3 % of aluminium and microadditions Nb and Ti with various structures after their heat- and thermo-mechanical treatments. The new-developed high-manganese Fe – Mn – (Al, Si) steel provide an extensive potential for automotive industries through exhibiting the twinning induced plasticity (TWIP) mechanisms. TWIP steel not only show excellent strength, but also have excellent formability due to twinning, thereby leading to excellent combination of strength, ductility, and formability over conventional dual phase steels or transformation induced plasticity (TRIP) steels. Results obtained for high-manganese austenitic steel with the properly formed structure and properties in the thermo-mechanical processes indicate the possibility and purposefulness of their employment for constructional elements of vehicles, especially of the passenger cars to take advantage of the significant growth of their strain energy per unit volume which guarantee reserve of plasticity in the zones of controlled energy absorption during possible collision resulting from activation of twinning induced by the cold working as the fracture counteraction factor, which may result in significant growth of the passive safety of these vehicles' passengers.
113
Showing 1 to 10 of 27 Paper Titles