共查询到19条相似文献,搜索用时 140 毫秒
1.
2.
800MPa 级超细晶粒钢是通过多向变形热处理,大角度交叉轧制,大变形应变诱导动态相变和 铁素体动态相变,大变形诱导铁素体相变,弛豫析出控制相变,促进针状铁素体形成等轧制技术,将钢中的晶 粒尺寸由10 μm 降到1 μm 以下,从而达到高强韧性的一种低碳(0.05%C)微合金化钢。介绍了国内外800MPa级超细晶粒钢的理论研究、生产工艺和焊接技术的新进展和今后发展趋势。 相似文献
3.
超细晶粒钢及其力学性能特征 总被引:6,自引:0,他引:6
探索了在新一代钢中获得超细晶粒的方法。通过低温轧制和应变诱导铁素体相变,可以在碳素结构钢中获得晶粒尺寸小于5μm的超细晶粒,屈服强度大于400MPa。采用应变诱导铁素体相变可以在微合金钢中得到晶粒尺寸为1μm的超细晶粒。低碳微合金钢的屈服强度达到了600MPa,超低碳微合金钢的屈服强度超过了800MPa。采用微合金化和循环热处理可以在合金结构钢中获得2μm的奥氏体晶粒,1500MPa级抗拉强度下改善了耐延迟断裂性能。 相似文献
4.
为了实现Cu-P-Cr-Ni-Mo耐候钢的铁素体晶粒细化从而充分提高其强塑性,通过热模拟压缩试验,利用金相、SEM、EBSD等微观组织分析方法研究了其在双相区的多道次压缩变形过程中的组织演变。结果表明,试验钢在变形过程中,第二相(马氏体、贝氏体)呈条带状分布于铁素体基体上,随着道次增加,铁素体晶粒逐步细化,第5道次变形后得到1.8 μm左右的超细晶铁素体。前期铁素体晶粒细化的主要机制是形变强化铁素体相变,即多道次的累积大变形使组织内畸变能增大,铁素体形核点增多,促进铁素体快速析出,形成细小铁素体晶粒;后面几道次变形中,随着应变量继续增大,在铁素体晶粒内形成大量亚晶界,且亚晶界逐步累积扭转成大角度晶界,分割原来的粗大晶粒,发生铁素体连续动态再结晶细化。 相似文献
5.
6.
通过对3种不同铌、钒含量的低碳钢进行多道次热压缩变形以模拟中厚板的超细晶轧制工艺,考察了显微组织演变过程、微合金元素和变形条件对组织演变的影响。结果表明:变形过程中有部分奥氏体通过形变诱导相变转变为铁素体;变形并快速冷却后得到平均晶粒尺寸为3~6μm的超细晶组织.铌促进、钒抑制形变诱导铁素体相变,铌、钒微合金化均有较好的细化作用,铌的作用优于钒.再结晶温度以上进行的粗轧有利于精轧时形变诱导铁素体的形成;在精轧温度范围内,增加变形道次、降低道次应变率有利于获得细化的显微组织;降低终轧变形温度对组织细化是最有效的. 相似文献
7.
8.
9.
通过热处理试验和单道次压缩热模拟试验,研究了微合金钢加热到两相区变形时的组织演变规律,并分析了变形量的影响,使用OM、SEM和EBSD技术分析了试验钢的微观组织和取向分布。结果表明,试验钢加热到两相区保温后,奥氏体相变在原铁素体晶界上发生,变形时晶界上的奥氏体发生应变诱导相变,形成细小的仿晶界铁素体,变形铁素体发生动态回复或动态再结晶。随变形量和变形温度的提高,硬度下降,800℃下增加变形量,动态回复向动态再结晶发展,动态再结晶形核机制是亚晶转动生长,名义变形量为70%时得到均匀的超细晶组织,有效晶粒平均等效直径为2.7μm,大角度晶界的体积分数达到92.8%。 相似文献
10.
11.
Qi Chao Peter D. Hodgson Hossein Beladi 《Metallurgical and Materials Transactions A》2014,45(5):2659-2671
In the current study, ultrafine equiaxed grains with a size of 150 to 800 nm were successfully produced in a Ti-6Al-4V alloy through thermomechanical processing of a martensitic starting microstructure. This was achieved through a novel mechanism of grain refinement consisting of several concurrent processes. This involves the development of substructure in the lath interiors at an early stage of deformation, which progressed into small high-angle segments with increasing strain. Consequently, the microstructure was gradually transformed to an equiaxed ultrafine grained structure, mostly surrounded by high-angle grain boundaries, through continuous dynamic recrystallization. Simultaneously, the supersaturated martensite was decomposed during deformation, leading to the progressive formation of beta phase, mainly nucleated on the intervariant lath boundaries. 相似文献
12.
Samples with ultrafine grained austenite were prepared by repetitive rapid heating and quenching for three times and were used to investigate the dynamic microstructural evolving behaviors at different temperatures. A simultaneous development of dynamic strain induced transformation (DSIT) and austenite grain growth was detected at the deformation temperatures above Ar3, while only DSIT happened as the deformation proceeded at lower temperatures close to and below Ar3. In addition, a reverse ferrite to austenite transformation was also observed. Most of the strain induced ferrite nucleated on the boundaries of ultrafine prior austenite grains, especially at the corners and no evidence about intragranular nucleus was obviously obtained. 相似文献
13.
In order to improve the low ductility of nanostructured materials,a layered and nanostructured (LN) 304 SS (stainless steel)is prepared from warm co-rolled 304 SS pre-treated by surface mechanical attrition treatment.The microstructure and mechanical properties,as well as strain hardening,are analyzed in details.The LN steels exhibit both high strength and large ductility resulting from good strain hardening behaviors.The strain hardening can be subdivided into two stages,which involves a multiple cracking along interlaminar at the first stage and a strain-induced martensite(SIM)transformation at the second stage.The SIM transformation of nanocrystallines and ultrafine grains induces a larger work hardening exponent by the formation of nanoscaled martensite phase.The effect of grain size on the transformation dynamics is discussed. 相似文献
14.
C. X. Huang G. Yang C. Wang Z. F. Zhang S. D. Wu 《Metallurgical and Materials Transactions A》2011,42(7):2061-2071
The technique of equal-channel angular pressing (ECAP) was used to refine the microstructure of an AISI 301 austenitic stainless
steel (SS). An ultrafine-grained (UFG) microstructure consisting mainly of austenite and a few martensite was achieved in
301 steel after ECAP processing for four passes at 523 K (250 °C). By submitting the as-ECAP rods to annealing treatment in
the temperature range from 853 K to 893 K (580 °C to 620 °C) for 60 minutes, fully austenitic microstructures with grain sizes
of 210 to 310 nm were obtained. The uniaxial tensile tests indicated that UFG 301 austenitic SS had an excellent combination
of high yield strength (>1.0 GPa) and high elongation-to-fracture (>30 pct). The tensile stress–strain curves exhibited distinct
yielding peak followed by obvious Lüders deformation. Measurements showed that Lüders elongation increased with an increase
in strength as well as a decrease in grain size. The microstructural changes in ultrafine austenite grains during tensile
deformation were tracked by X-ray diffraction and transmission electron microscope. It was found that the strain-induced phase
transformation from austenite to martensite took place soon after plastic deformation. The transformation rate with strain
and the maximum strain-induced martensite were promoted significantly by ultrafine austenite grains. The enhanced martensitic
transformation provided extra strain-hardening ability to sustain the propagation of Lüders bands and large uniform plastic
deformation. During tensile deformation, the Lüders bands and martensitic transformation interacted with each other and made
great contribution to the excellent mechanical properties in UFG austenitic SS. 相似文献
15.
16.
In the current study,a 0.3C-2Si-2Mn-0.28Mo (in wt%) steel with high hardenability was deformed at a relatively low temperature followed by isothermal static phase transformation.This novel thermomechanical processing made it possible to successfully produce an ultrafine ferrite grained structure (~2 μm) in the absence of both dynamic phase transformation and controlled cooling.The use of a model Ni-30Fe austenitic alloy showed that the low temperature deformation induced very fine intragranular defects throughout the microstructure,which would then act as fine spaced ferrite nucleation sites at an early stage of phase transformation.As a result,the coarsening of ferrite was extremely limited during isothermal phase transformation,resulting a very fine ferrite grained structure;even nanoscale in the region of the prior austenite grain boundary. 相似文献
17.
Hot torsion testing was performed on a low carbon Nb-Ti microalloyed steel to study the effects of hot torsion parameters, strain and strain rate, on ultrafine ferrite grains production through dynamic strain-induced transformation, at a deformation temperature just above Ar3. The initiation and evolution of ultrafine ferrite grains were studied. The results show that the amount of strain and strain rate has conversely effect on the volume fraction and grain size of ultrafine ferrite grains. With increasing strain, the interior of austenite grains become activated as nucleation sites for fine ferrite grains. As a result, ferrite grains continuously nucleate not only at the former austenite grain boundaries but also inside the austenite grains which leads to a rapid increase in volume fraction of ultrafine grains. Increasing of strain rate reduces the tendency of ferrite grains coarsening so that ultrafine ferrite grains are achieved, while the volume fraction of ultrafine grains decreases at the same strain level. 相似文献
18.
On the Effect of Manganese on Grain Size Stability and Hardenability in Ultrafine-Grained Ferrite/Martensite Dual-Phase Steels 总被引:1,自引:0,他引:1
Marion Calcagnotto Dirk Ponge Dierk Raabe 《Metallurgical and Materials Transactions A》2012,43(1):37-46
Two plain carbon steels with varying manganese content (0.87 wt pct and 1.63 wt pct) were refined to approximately 1 μm by large strain warm deformation and subsequently subjected to intercritical annealing to produce an ultrafine grained ferrite/martensite
dual-phase steel. The influence of the Mn content on microstructure evolution is studied by scanning electron microscopy (SEM).
The Mn distribution in ferrite and martensite is analyzed by high-resolution electron backscatter diffraction (EBSD) combined
with energy dispersive X-ray spectroscopy (EDX). The experimental findings are supported by the calculated phase diagrams,
equilibrium phase compositions, and the estimated diffusion distances using Thermo-Calc (Thermo-Calc Software, McMurray, PA)
and Dictra (Thermo-Calc Software). Mn substantially enhances the grain size stability during intercritical annealing and the
ability of austenite to undergo martensitic phase transformation. The first observation is explained in terms of the alteration
of the phase transformation temperatures and the grain boundary mobility, while the second is a result of the Mn enrichment
in cementite during large strain warm deformation, which is inherited by the newly formed austenite and increases its hardenability.
The latter is the main reason why the ultrafine-grained material exhibits a hardenability that is comparable with the hardenability
of the coarse-grained reference material. 相似文献
19.
Oscar A. Ruano Jeffrey Wadsworth Oleg D. Sherby 《Metallurgical and Materials Transactions A》1982,13(3):355-361
It is shown that densification of white cast iron powders under stress can be enhanced by multiple phase transformations through
thermal cycling. This enhancement occurs by accelerated creep flow during phase changes (transformation superplasticity).
The approximate stress range where transformation-assisted densification can occur is shown to be between 1.7 MPa (250 psi)
and 34.5 MPa (5000 psi). Below 1.7 MPa insufficient strain occurs during phase transformation to cause significant densification
even after many transformation cycles. Above 34.5 MPa, densification occurs principally by normal slip creep. Transformation
warm pressing of white cast iron powders leads to dense compacts at low pressures and short times. In addition, because the
transformation temperature is low, the ultrafine structures existing in the original powders are retained in the densified
compacts.
formerly with the Department of Materials Science and Engineering, Stanford University, 相似文献