On the Tensile Behavior of High-Manganese Twinning-Induced Plasticity Steel

High-manganese FeMnC and FeMnAlC austenitic twinning-induced plasticity (TWIP) steel exhibits excellent strain-hardening properties due to the gradual reduction of the mean free path for dislocations glide resulting from deformation twinning. Serrated stress-strain curves are often obtained when this type of steel is tested in a uniaxial tensile test. This phenomenon is due to dynamic strain aging (DSA). It is related to the occurrence of localized Portevin–LeChatelier (PLC) deformation bands. The properties of the PLC bands were accurately determined for a FeMnAlC TWIP steel using a combination of high-sensitivity infrared (IR) thermographic imaging and optical strain analysis carried out in situ during tensile deformation. Strain rate jump tests were conducted at room temperature to measure the instantaneous and steady-state strain rate sensitivity as a function of true stress and true strain. Negative values of the steady-state strain rate sensitivity were measured in both upward and downward jump tests. These measurements explain why FeMnC and FeMnAlC TWIP steels have a limited postuniform elongation. A model for the room-temperature DSA of high-Mn austenitic TWIP steel containing C in solid solution is proposed.     

Influence of Al on Microstructure and Mechanical Behavior of Cr-Containing Transformation-Induced Plasticity Steel

Chromium in transformation-induced plasticity (TRIP) steel is known to have a detrimental effect on the mechanical properties by increasing the hardenability of austenite introduced during intercritical heat treatment. In this study, it is suggested that an Al addition can counterbalance the effect of Cr by encouraging ferrite formation during fast cooling and austempering. This contributes to securing the thermal stability of austenite and to retrieving the excellent mechanical properties of TRIP steel even with the addition of Cr.     

冷却工艺对Si-Mn系热轧双相钢组织和性能的影响

通过热轧试验研究了3种冷却工艺对传统成分Si-Mn系热轧双相钢组织及性能的影响。试验结果表明：在3种冷却工艺条件下,试验钢的最终组织为铁素体和马氏体双相组织。当终轧后采用空冷＋超快冷的冷却工艺时,钢板的屈强比最低,伸长率和n值最大,晶粒尺寸较大,但强度相对最小;当终轧后采用层流冷却＋空冷＋超快冷的冷却工艺时,钢板的晶粒...     

Mechanical Behavior of CrMo4 Steel With Dual-Phase Microstructure

Multi-phase microstructures having good ductility may replace the conventional microstructures in different technological applications such as pressure vessels.Mechanical properties including the fracture behavior and the service life of pressure vessels are strongly affected by the microstructure.The objective of this study was to investigate the correlation between different dual-phase microstructures and mechanical properties of 42CrMo4 (AISI 4140) steel.To produce the martensite-bainite (M-B),the martensite-ferrite (M-F),and the ferrite-bainite (F-B) microstructures,the step quenching heat treatment was used.Mechanical properties of heat treated samples including the strength,ductility,and impact energy were measured.Tensile experiments revealed a discontinuous yielding in the F-B specimen with ferritic matrix.Fracto\graphic results showed high concentration bright facets (BFs) on broken specimen surfaces indicating the brittle cleavage fracture was the predominant mechanism in the dual-phase microstructures.     

Austenite Stability Effects on Tensile Behavior of Manganese-Enriched-Austenite Transformation-Induced Plasticity Steel

Manganese enrichment of austenite during prolonged intercritical annealing was used to produce a family of transformation-induced plasticity (TRIP) steels with varying retained austenite contents. Cold-rolled 0.1C-7.1Mn steel was annealed at incremental temperatures between 848 K and 948 K (575 °C and 675 °C) for 1 week to enrich austenite in manganese. The resulting microstructures are comprised of varying fractions of intercritical ferrite, martensite, and retained austenite. Tensile behavior is dependent on annealing temperature and ranged from a low strain-hardening “flat” curve to high strength and ductility conditions that display positive strain hardening over a range of strain levels. The mechanical stability of austenite was measured using in-situ neutron diffraction and was shown to depend significantly on annealing temperature. Variations in austenite stability between annealing conditions help explain the observed strain hardening behaviors.     

Correlation of Microstructure and Texture in a Two-Phase High-Mn Twinning-Induced Plasticity Steel During Cold Rolling

Metallurgical and Materials Transactions A - The evolution of microstructure and texture of a two-phase austenite-ferrite twinning-induced plasticity steel during cold rolling was investigated and...     

Evolution of Crystallographic Texture and Microstructure During Cold Rolling of Twinning-Induced Plasticity (TWIP) Steel: Experiments and Simulations

A systematic investigation of the evolution of deformation microstructure and texture of twinning-induced plasticity (TWIP) steel during cold rolling has been carried out using electron backscatter diffraction and X-ray diffraction, as well as viscoplastic self-consistent simulations. It is found that extensive twinning leads to the formation of the strong Brass {110}??112?? and Goss {110}??001?? components in TWIP steel even at low strains. At higher reduction, heterogeneous deformation contributes to further strengthening of Brass (Bs) component. The origin and stability of Bs component as well as the impact of the evolution of texture and microstructure on mechanical anisotropy is further explored using viscoplastic self-consistent simulations.     

Tetragonality of bcc Phases in a Transformation-Induced Plasticity Steel

In a low-alloyed multi-phase transformation-induced plasticity steel, solute carbon content in polygonal ferrite, bainitic ferrite, and martensite was characterized using site-specific atom probe tomography. Selected area diffraction patterns were obtained using transmission electron microscopy, and the geometric distortion thereof was determined. The results showed that the lattice distortion increased in a sequence of polygonal ferrite, lath-like bainitic ferrite, and martensite. This increasing distortion corresponded to an increase in carbon content of the phase.     

Study of Microstructure and Mechanical Properties of Boron-Containing Hot-Rolled Steel Reinforcement

Metallurgist - Stiffened specifications for quality of reinforcement product are dictated by the contemporary market that is expressed in the introduction of new TU and GOST for manufactured...     

Serration Phenomena Occurring During Tensile Tests of Three High-Manganese Twinning-Induced Plasticity (TWIP) Steels

In this study, the serration phenomena of two high-Mn TWIP steels and an Al-added TWIP steel were examined by tensile tests, and were explained by the microstructural evolution including formation of localized Portevin–Le Chatelier deformation bands and twins. In stress–strain curves of the high-Mn steels, serrations started in a fine and short shape, and their height and periodic interval increased with increasing strain, whereas the Al-added steel did not show any serrations. According to digital images of strain rate and strain obtained from a vision strain gage system, deformation bands were initially formed at the upper region of the gage section, and moved downward along the tensile loading direction. The time when the band formation started was matched with the time when one serration occurred in the stress–time curve. This serration behavior was generally explained by dynamic strain aging, which was closely related with the formation of deformation bands.     

Tailoring the Mechanical Properties of a Twinning-Induced Plasticity Steel by Retention of Deformation Twins During Heat Treatment

The relation between microstructure and mechanical properties of a 30 pct cold-rolled, recovery-annealed, and recrystallization-annealed Fe-23Mn-1.5Al-0.3C twinning-induced plasticity (TWIP) steel was studied. The thermal stability of deformation-induced twin boundaries along with a reduced dislocation density due to annihilation during recovery annealing at 903 K (630 °C) was found to be a simple, promising processing route to overcome the shortcoming of low yield strength usually associated with TWIP steels.     

Microstructure and Mechanical Behavior of a Mini-Thixoformed Tool Steel

We report on mini-thixoforming of a hard and wear-resistant crucible particle metallurgy tool steel. Significant microstructural modifications associated with the special semisolid forming process are characterized in detail by scanning electron microscopy and X-ray diffraction. The mechanical performance of the material is assessed both pre-thixoforming and post-thixoforming by nanoindentation of the constituent phases. The novel microstructural changes that result from mini-thixoforming, which are discussed in this article for the first time, are beneficial in further improving the hardness of the steel.     

Processing of Ultrafine-Grained Twinning-Induced Plasticity Steel Using Martensite Treatment

For the first time, martensite treatment was used to fabricate an ultrafine-grained (UFG) twinning-induced plasticity (TWIP) steel. The effects of cold rolling with 70 pct reduction at the liquid nitrogen temperature and subsequently annealing at 973 K (700 °C) for 5 to 20 minutes on the microstructure and mechanical properties of Fe-22Mn-0.4C-1.5Al-1Si TWIP steel were investigated. The results showed that a fully recrystallized UFG TWIP steel with a mean grain size of about 400 to 600 nm can be produced by the designed martensite treatment. The UFG TWIP steel exhibited high yield and tensile strengths and relatively high ductility.     

TRIP-相变诱发塑性钢的研究进展

相变诱发塑性钢是一种汽车用钢，通过相变诱发塑性(TRIP)效应使钢板中残余奥氏体在塑性变形作用下诱发马氏体生核和形成，并产生局部硬化，继而变形不再集中在局部，使相变均匀扩散到整个材料以提高钢板的强度和塑性。典型TRIP钢c含量为0．2％，Mn 1％～2％，Si 1％～2％，通过热轧变形热处理或冷轧 热处理，TRIP钢的组织由50％～60％铁素体，25％～40％贝氏体或少量马氏体和5％-15％残余奥氏体组成。TRIP钢的强度和韧性高于双相钢和微合金钢。介绍了TRIP钢的生产工艺和性能，残余奥氏体、合金元素、热处理对TRIP效应的影响和TRIP钢研究趋势。     

Characterization of a Continuously Cooled Dual-Phase Steel Microstructure

Continuous-cooling transformation behavior of a DP steel was analyzed from dilation curves with cooling rates that range between 10 °C/s and 98 °C/s and data taken in 10 °C/s increments. For a precise understanding of the problem, several metallographic techniques were used in order to determine which phases and types of transformation are present, the grain structure and crystal defects generated for each cooling rate, among other characteristics. The local distribution of the main alloying elements was analyzed by wave dispersive spectroscopy. From the dilation curves, the relative amount of transformed phase was estimated, as well as the first derivatives as a function of both temperature and time to analyze the characteristics of the transformation and correlate these with a characteristic microstructure. To further understand these results, the mobility of suitable alloying elements such as Cr, Mn, Al, and P was evaluated. The analysis showed that at lower cooling rates, 10 °C/s to 20 °C/s, the transformation occurs at temperatures above 700 °C (at which the majority of alloying atoms have good mobility) in a relatively slow process producing polygonal ferrite. At cooling rates greater than 40 °C/s, the transformation occurs below 700 °C in a relatively short time, where massive transformation takes place. Finally, a cooling rate of 30 °C/s gives a mixed transformation, producing an appreciably smaller grain structure with a high density of crystal defects.