Structural superplasticity at higher strain rates of hypereutectoid Fe-5.5Al-1Sn-1Cr-1.3C steel

A fine-grained ultra-high-carbon steel—UHC steel—containing 1.35 wt pct carbon, 5.5 wt pct aluminum, 1 wt pct tin, and 1 wt pct chromium exhibits fine-structure superplasticity in the temperature regime between 775 °C and 900 °C at higher strain rates up to 10⁻² s⁻¹. Thermomechanical processing was performed in order to achieve a fine-grained equiaxed microstructure consisting of κ-carbides of about 0.7 to 2.5 μm in size finely distributed within the ferritic Fe(Al, Sn, Cr) solid solution matrix with a linear intercept grain size of 3 to 5 μm. Superplasticity occurred in the strain rate regime of 10⁻⁴<- ≤10⁻² s⁻¹ with m values of 0.5 to 0.6 (stress exponent n=1.6 to 2). Tensile elongations of more than 900 pct were recorded. From thermal activation analysis, activation energies of Q=230 to 243 kJ/mole were determined, which clearly reveal a contribution of the alloying elements Al and Sn to the lattice diffusion of iron. The governing deformation mechanism is grain boundary sliding accommodated by dislocation climb controlled by lattice diffusion sustained by chemical diffusion. At very high strain rates of ≳2 · 10⁻² s⁻¹, the strain-rate-sensitivity exponent decreases to about 0.2≤m≤0.27, which indicates class II solid solution behavior of this material.     

High strain rate superplasticity in the fine-grained duplex stainless steel Fe-22Cr-5Ni-3Mo-0.3N

The fine-grained duplex stainless steel Fe-22Cr-5Ni-3Mo-0.3N consisting of α- and γ-Fe(Cr,Ni,Mo) solid solutions exhibits structural superplasticity at deformation temperatures of 900 to 1050°C. The equiaxed microstructure with an average grain size of d_α,γ ≈ 3 μm was produced by thermomechanical processing. This steel shows also superior superplastic properties at high strain rates up to ε ≈ 5 · 10^?2 s^?1. Maximum strain rate exponents of m ≈ 0.5 and elongations to failure of more than 800% were achieved. The superplastic deformability (m > 0.3) of this steel in a wide strain rate range enables near net shape deep drawing or blow forming of parts with complex shape applying low flow stresses. A deformation model is presented to describe the superplastic behaviour at high strain rates. Grain and interphase boundary sliding is accommodated by sequential steps of dislocation glide and climb. The maximum m -value of about 0.5 and an activation energy of 260 kJ/mol, which is comparable to that of self diffusion of Iron in γ-Fe (270 kJ/mol), and high dislocation densities indicate that dislocation climb in the slightly solid solution hardened γ-Fe phase (solid solution class II type of material) is the rate controlling step for superplastic flow.     

Fe-17Mn-13Cr-0.3N奥氏体不锈钢的晶间腐蚀研究

用电化学动电位再活化(即EPR)法研究了Fe-17Mn-13Cr-0.3N奥氏体不锈钢的耐晶间腐蚀的程度.通过改变敏化时间和敏化温度,研究了不同的时间和温度对不锈钢的耐晶间腐蚀性能的影响,并结合Thermo-calc相图进行分析.结果表明在一定温度下,Ra值随时间变化的基本趋势都是先逐渐增大,达到1个峰值然后开始下降,Fe-17Mn-13Cr-0.3N奥氏体不锈钢种在750 ℃左右敏化时晶间腐蚀倾向最严重,不同于一般的Cr-Ni奥氏体钢种.w(Cr)太低,即使w(C)低于0.02 %,而且在没有碳化物析出的情况下,也会有严重的晶间腐蚀倾向;在w(Cr)为13 %以上,w(C)为0.065 %左右时,晶间腐蚀倾向不明显;氮有利于防止晶间腐蚀的发生,却对抗选择性腐蚀不利.     

Improving High-Temperature Strength of Ti-6Al-2.5Mo-1.5Cr-0.5Fe-0.3Si Titanium Alloy by Cryogenic Pre-treatment and Laser Peening

Metallurgical and Materials Transactions A - The plastic deformation behavior and microscopic strengthening mechanism of Ti-6Al-2.5Mo-1.5Cr-0.5Fe-0.3Si (TC6) titanium alloy treated by the...     

Thermal processing of ferritic 5Mn steel for toughness at cryogenic temperatures

It is shown that a thermal treatment which combines grain refinement with an intercritical temper (the 2BT treatment) may be used to achieve a promising combination of strength and toughness in a nickel-free ferritic steel of nominal composition Fe-5Mn-0.2Mo-0.04C at temperatures as low as -196 °C. The properties achieved are attributed to a symbiotic influence between the grain refinement treatment and the introduction of thermally stable retained austenite during intercritical tempering, a conclusion supported by a comparison of the results to those obtained with simpler heat treatments. The influence of carbon, manganese, and nickel additions to the base compositions are studied. An increase in carbon content above 0.04 wt pct causes a deterioration in toughness, as does an increase in manganese to 8 wt pct. An addition of 1 to 3 wt pct nickel is beneficial giving an increase in alloy strength at -196 °C without loss of toughness. Formerly Visiting Scientist, Lawrence Berkeley Laboratory.     

Fe-13Cr-5Ni马氏体不锈钢在连续加热过程中两相区的奥氏体生长行为

通过光学显微镜、透射电子显微镜、X射线衍射仪以及显微硬度仪研究Fe-13Cr-5Ni马氏体不锈钢在加热过程中的组织转变行为.结果表明,Fe-13Cr-5Ni钢在10℃·s^-1的加热速率下,加热至奥氏体单相区,冷却至室温后具有明显的“组织遗传冶现象.奥氏体以“针状冶形式在马氏体板条界处形核并沿着马氏体板条界长大,与母相间保持Kurdjumov-Sachs （K-S）位向关系.加热至两相区不同温度然后淬火至室温,奥氏体的量随两相区保温温度的升高先增加再减少,650℃时对应室温下残余奥氏体的极大值,并且这一变化趋势与试样显微硬度测试结果所得结论一致.     

The improvement of cryogenic mechanical properties of Fe-12 Mn and Fe-8 Mn alloy steels through thermal/mechanical treatments

An investigation has been made to improve the low temperature mechanical properties of Fe-8Mn and Fe-12Mn-0.2 Ti alloy steels. A reversion annealing heat treatment in the two-phase (α+ γ) region following cold working has been identified as an effective treatment. In an Fe-12Mn-0.2Ti alloy a promising combination of low temperature (-196°C) fracture toughness and yield strength was obtained by this method. The improvement of properties was attributed to the refinement of grain size and to the introduction of a uniform distribution of retained austenite (γ). It was also shown that an Fe-8Mn steel could be grain-refined by a purely thermal treatment because of its dislocated α martensitic structure and absence of ε martensite. As a result, a significant reduction of ductile to brittle transition temperature was obtained. formerly with the Lawrence Berkeley Laboratory, University of California.     

Ti-44Al-5V-1Cr-0.3Ni-0.1Hf-0.15Gd合金的微观组织和拉伸性能

针对变形量达86%的锻造Ti-44Al-5V-1Cr-0.3Ni-0.1Hf-0.15Gd(原子分数,%)合金,对其进行热处理获得近层片组织,研究变形合金及其近层片组织的微观组织特征,并进行了室温、700℃和800℃拉伸实验.组织观察发现,近层片组织由层片团、分布于层片团界的β相以及弥散分布于基体的椭圆状Gd析出物组成.层片团的平均尺寸为40μm,层片组织、β相和Gd析出物的体积分数分别为93.73%、5.25%和1.02%.拉伸结果显示,室温下合金试样的平均抗拉强度为865MPa,平均延伸率可达4.17%,700℃时其平均抗拉强度和延伸率分别为643MPa和22%.Ti-44Al-5V-1Cr-0.3Ni-0.1Hf-0.15Gd合金不仅具有与高β相TiAl合金相当的塑性变形能力,且室温塑性也得到显著提高,这主要归因于β相体积分数的下降和Gd化合物对微观组织室温塑性的贡献.     

Electrochemical polarization and passive film of a cryogenic and non-magnetic steel in aqueous solution

The corrosion behaviour of the austenitic steel Fe-23Mn-4Al-5Cr-0.3C in different aqueous solutions of pH-0.8 to 15.3 and the corrosion protection mechanism induced by adding Al or Al and Cr have been investigated by electrochemical measurements and AES/XPS analysis. The corrosion behaviour of Fe-Mn base steel have been compared with those of mild steel, cryogenic 9 % Ni steel, stainless steels 1Cr13 and 1Cr18Ni9Ti. The addition of manganese to mild steel is very detrimental to the corrosion resistance. Fe-25Mn steel passivates with difficulty even in such neutral aqueous electrolytes as 1 M Na₂SO₄ solution. The addition of 5 % aluminum to Fe-25Mn steel confers passivity to the steel in neutral or oxidizing, chloride-free solution. The addition of 5 % Cr to Fe-Mn-Al steel further improves resistance to corrosion. The passivity of Fe-23.5Mn-4Al-5Cr-0.3C steel in aqueous electrolytes tested is superior to that of 9 % Ni steel and approximate to that of 1Cr13 stainless steel. The corrosion resistance is probably imparted by a thin barrier film of oxides. The outer part of the passive film formed on the surface of Fe-23.5Mn-4Al-5Cr-0.3C steel in 1 M Na₂SO₄ solution is enriched in Al³⁺, Cr³⁺ and Fe³⁺, and this means that the film is probably made up of a mixture of Al₂O₃, Cr₂C₃ and Fe₂O₃.     

Influence of Ti and C on the Solidification Microstructure of Fe-10Al-5Cr Alloys

The influence of Ti and C on the solidification microstructure of Fe-10Al-5Cr (all composition values in weight percent) alloys was examined with solidification modeling and a variety of experimental techniques. Several Fe-10Al-5Cr-Ti-C alloys were fabricated using the arc button melting process and characterized using quantitative image analysis and electron microscopy techniques. The experimental alloys exhibited primary ferrite dendrites with an interdendritic ferrite/TiC eutectic constituent, and the amount of eutectic was affected by the Ti and C concentrations. A liquidus projection and primary solidification paths were calculated for the Fe-10Al-5Cr-Ti-C system in order to estimate the amount of TiC that is expected to form during solidification. The range in the calculated amount of TiC-containing eutectic matched the experimentally measured values reasonably well. The ability to control the amount of TiC that forms during solidification of an Fe-10Al-5Cr-Ti-C-based alloy shows promise for developing corrosion-resistant weld overlay claddings with resistance to hydrogen cracking.     

Fe-5Mn-2Al-0.15C中锰钢连铸凝固偏析及粒子析出行为

为研究Fe-Mn-Al-C系中锰钢连铸凝固偏析及粒子析出特性,采用光学显微镜观察Fe-5Mn-2Al-0.15C中锰钢的显微组织,并通过Thermo-Calc热力学软件研究了其凝固模式、溶质元素偏析及粒子析出行为。结果表明,该中锰钢铸锭的显微组织主要为板条状马氏体,且含有少量铁素体;其凝固模式为L→L+δ→L+δ+γ→δ+γ→γ;Al元素的平衡分配系数大于1,发生负偏析,偏聚到δ-铁素体枝晶内部;而Mn、Nb、V、S等溶质元素发生正偏析,均偏聚到枝晶间。AlN主要在枝晶内析出,其析出温度为1 448 ℃;MnS、Nb和V的富集物主要在枝晶间析出,且MnS和Nb的富集物均在1 400 ℃以上开始析出,而V的富集物的析出温度为760 ℃。     

Electron microscopy study on the grain-boundary precipitation during aging of Fe-10Ni-5Mn steel

In order to determine the mechanism of grain-boundary embrittlement and de-embrittlement in age-hardened Fe-Mn-Ni alloys, a detailed analysis on the grain-boundary precipitation behavior was conducted using electron diffraction and electron energy loss spectroscopy (EELS) techniques. The precipitation of θ-MnNi intermetallic particles as well as the precipitation of the austenite phase at prior austenite grain boundaries in association with the grain-boundary embrittlement was confirmed. Interlath fracture was also observed with the precipitation of θ-MnNi particles at the interlath boundaries. The de-embrittlement of these boundaries appears to be a result of the conversion of the θ-MnNi phase to a more ductile austenite phase after extended aging.     

Fe-23Cr-15Co-2Mo-0.5Ti永磁合金的SpinodaⅠ分解与磁硬化

用磁性测量、透射电镜、穆斯堡尔效应和磁畴观察（静态与准静态）等方法研究了Fe—23Cr—15Co—2Mo—0.5Ti合金在磁场处理和等级时效过程中的Spinodas分解和磁硬化。实验结果表明,合金的调幅分解是连续地进行的,没有明显的阶段性。分解后显微组织也是不均匀的,从而限制了含金矫顽力的提高。等级时效前,α₁相和α₂相都是铁磁性的,合金是多畴体,合金的矫顽力是畴壁位移决定的,而等级时效后,α₂相区已变成非铁磁性。合金内部存在相互作用畴。但合金的矫顽方是由单畴粒子的磁矩转动来决定。     

Ti-5Al-2Zr-2Sn-4Cr-4Mo合金时效强化特性

研究了Ｔｉ１７合金在相变点以下，经不同固溶温度处理、不同温度时效后亚稳β相的分解特性和硬化效应。结果表明，该合金在α＋β相区固溶处理，６３０℃附近温度时效，亚稳β相直接析出α相，具有较高的时效硬化速率。在时效初期，α相的含量随时间的增加而增加，而α相的形态经较长时间的时效方发生变化。最后，对α相的析出机制作了简要讨论。     

Fe-19Cr-0.2Ni-5Mn-0.2Si在循环加载下的马氏体相变规律及其影响

 相变诱导塑性(TRIP)双相不锈钢具有优良的强度和塑性,且兼顾经济性,因此工业应用潜力很大。而厘清TRIP型双相不锈钢在循环加载下产生的马氏体相变对其循环力学性能的影响规律,是促进其进一步开发及工业化应用的基础。以TRIP型双相不锈钢Fe-19Cr-0.2 Ni-5Mn-0.2Si为研究对象,开展循环性能及相变特征研究。应用INSTRON试验机,分别进行拉伸试验和应变幅为0.6%的对称循环加载试验,测定试验钢的拉伸力学性能及循环软硬化性能。在循环加载过程中,应用铁素体测量仪测量不同循环周次下的马氏体转变量,分析马氏体相变特征。利用透射电镜,观测典型循环周次下的微观结构,分析马氏体相变和位错结构演化规律。进而,研究马氏体相变和位错结构演化对循环软硬化性能的作用机制。结果表明,试验钢在拉伸条件下,表现出明显的TRIP效应;循环初期马氏体转变速率较快,之后转变速率逐渐降低并且逐渐趋于零;循环软硬化特征可分为3个阶段,初始循环硬化、循环软化和二次循环硬化阶段;初始循环硬化由两相中位错的增殖引起的硬化效应起主导作用;随后的循环软化,由铁素体中低能位错结构所引起的软化效应起主导作用;在二次循环硬化阶段,相变马氏体对材料的硬化起主导作用。总的来说,马氏体相变对试验钢循环加载初期的循环软硬化性能影响较小,但对循环后期的性能影响较大。     

Abrasive Wear Behaviors of Light-weight Austenitic Fe-24Mn-7Al-1C Steel and Mn13Cr2 Steel

The impact abrasive wear behaviors of light-weight austenitic Fe-24Mn-7Al-1C steel with increasing impact wear conditions were studied by comparing with the modified Hadfield (Mn13Cr2)steel.Wear tests were performed with the MLD-10 abrasive wear testing machine.Main parameters such as impact energy,impacting frequency and wear time were evaluated.To explore the abrasive wear behaviors under different impact energies,the parameters in-cluding mass loss,wear resistance and hardness were evaluated in detail.The microstructures of the steels were fur-ther analyzed using optical microscopy (OM),scanning electron microscopy (SEM),transmission electron micros-copy (TEM)and X-ray diffraction (XRD).Results showed that the light-weight austenitic Fe-24Mn-7Al-1C steel had a better wear resistance than Mn13Cr2 steel under the impact energy tested.The wear resistance of light-weight austenitic Fe-24Mn-7Al-1C steel was about 1.09-1.17 times as high as that of Mn13Cr2 steel under low and medi-um impact energy (0.5-2.0 J)conditions,and 1.41 times under high impact energy (4.0 J)condition.In Mn13Cr2 steel,the evolution of dislocation substructure with increasing impact energy showed typical stacking fault,interac-tion of twins and dislocations,as well as mechanical twins.The high work-hardening rate in Fe-24Mn-7Al-1C steel was caused by Taylor lattice and high density of dislocation tangles.     

退火处理对热轧Fe-12Mn-8Al-0.8C轻质钢组织性能的影响

利用OM, SEM, TEM及XRD等,对不同退火温度下热轧Fe-12Mn-8Al-0.8C轻质钢的组织演变及力学性能进行了研究.研究结果表明,较低温度下退火时,实验钢组织为奥氏体+铁素体+κ-碳化物.随着退火温度的升高,实验钢中κ-碳化物发生溶解,奥氏体晶粒尺寸逐渐增加,实验钢的屈服强度和抗拉强度逐渐降低,伸长率则先增大后降低.不同退火温度下实验钢应变硬化行为的差异与其组织组成有关.750℃退火0.5 h的实验钢具有铁素体+κ-碳化物体积分数较高的复相组织,其加工硬化能力较高.随着退火温度的升高,铁素体与κ-碳化物的体积分数逐渐降低,应变硬化率有所降低,但应变硬化行为表现得更为持续.950℃退火0.5 h的实验钢与其他退火温度下的实验钢相比,获得了良好的综合性能,抗拉强度为930 MPa,伸长率为35.48%,韧脆转变温度约为-40℃.     

Research on Stress-Induced Nucleation of ε-Martensite in Fe-17Mn-10Cr-5Si-4Ni Polycrystalline Alloy

ForFeMnSifamilyalloy ,thestress inducedγ→εmartensitictransformationisthebasisofSMEproduction[1 3 ] ,thusthestudyonmechanismofγ→εmartensitictransformation ,especiallyonnucle ationofε martensite ,hasgreatsignificanceforun derstandingthenatureofshapememorycharacterandapplicationofthistypealloy .Anequationde ducedbyHsuTYforstackingfaultprobabilityPsfandMsinlowstackingfaultenergyalloyfromther modynamicsis :Ms=C -D /Psf,whereCandDareplusconstants[4 ] .InagakiHetalhavealsore portedthatu…