冷轧中锰钢退火过程中硬度及组织的演化

 利用EBSD技术研究了冷轧中锰钢在退火过程中的组织演化规律,从而揭示了其硬度变化的原因。研究结果表明:冷轧中锰钢在650℃退火,获得了0.3~0.6μm等轴状奥氏体和铁素体的超细晶组织,且随着退火时间的延长组织结构没有发生明显粗化;在550~650℃退火,随着温度的升高,奥氏体含量不断增加;在700℃退火时,奥氏体稳定性降低,出炉空冷过程中发生了马氏体转变,硬度升高;逆转变奥氏体相的稳定性主要受其碳含量控制,碳含量越高越容易获得大量稳定的逆转变奥氏体。     

冷轧中锰钢的成形性能

 研究了两相区退火时间对中锰钢(0.1C-5Mn)的微观组织结构、力学性能及扩孔性能的影响。利用扫描电镜(SEM)和背散射电子成像技术(EBSD)对退火过程中微观组织结构的演化进行了表征;通过拉伸和扩孔试验测定了不同退火状态下中锰钢的强度、塑性和扩孔率。研究表明,中锰钢在650℃下逆转变退火获得了含有大量奥氏体相的基体为超细晶组织的奥氏体、铁素体双相钢组织,强塑积（Rm·A）达到30GPa·%以上;奥氏体体积分数随退火时间的延长而逐步增加,但过多亚稳奥氏体对钢的综合成形性能不利。     

Microstructure characterization and creep deformation of an Al-10 Wt Pct Ti-2 Wt Pct Cu nanocomposite

The creep behavior of a cryomilled Al-10Ti-2Cu nanocomposite has been studied at temperatures of 533, 588, and 644 K at initial applied stresses ranging from 55 to 117 MPa. Although the strain rates fall within the 10⁻¹⁰ to 10⁻⁹ S⁻¹ regime, we observe no evidence of threshold-type creep behavior in this material. We attribute this to the unique microstructure of the present material combined with the mechanism of dislocation slip in ultrafine grain size materials. In particular, the very fine AIN precipitates present within the microstructure are ineffective as obstacles to dislocations during high-temperature deformation. The coherent nature of these fine particles along with their extremely small size prevents a strong dislocation-particle attraction. The inability of the activation energy for self-diffusion in Al to successfully collapse the present creep data onto a single slope combined with the fact that the true activation energy for creep exceeds the value for lattice self-diffusion are both features found in materials containing second-phase particles, which deform simultaneously with the matrix during high-temperature deformation. In the present case, these particles are likely to be Al₃Ti.     

High strain rate superplasticity of a 25 Wt Pct Cr-7 Wt Pct Ni-3 Wt Pct Mo-0.14 Wt Pct N duplex stainless steel

Effects of prior thermomechanical treatments on the superplasticity of a 25 wt pct Cr-7 wt pct Ni-3 wt pct Mo-0.14 wt pct N δ/γ duplex stainless steel have been studied by means of hot tensile testing with constant crosshead speeds. The objective is to increase the strain rate suitable for superplasticity. The strain rate is found to be markedly increased by a special prior treatment,i.e., solution treatment at temperatures in the δ single-phase region with subsequent heavy cold-rolling. In hot tensile tests at 1273 K, elongations greater than 1000 and 300 pct were observed at initial strain rates (έ) of 10⁻³ to 10⁻¹ s⁻¹ and 1 x 10⁰ s⁻¹, respectively. The results for strain rates 〈10⁻¹ s⁻¹ can be explained in terms of a structural superplastic effect due to grain refinement. In the case of έ 〉 10⁻¹ s⁻¹, transformation superplastic effects due to γ-phase precipitation from the σ-ferrite matrix are also important, especially in the early stages of deformation. In the equiaxedδ/γ microduplex structures during stable superplastic deformation, there exists a mixture of two different structures,i.e., dislocated and recovered/ recrystallized δ grains with a homogeneous dispersion of dislocation-free γ particles. This result shows that dynamic recrystallization ofδ grains occurs locally and intermittently due to the dispersion of relatively hardγ particles. The apparent average grain growth rate during deformation is small compared to static grain growth, because grain refinement due to dynamic recrystallization reduces the superplasticity-enhanced grain growth.     

Retained Austenite Transformation during Heat Treatment of a 5 Wt Pct Cr Cold Work Tool Steel

Retained austenite transformation was studied for a 5 wt pct Cr cold work tool steel tempered at 798 K and 873 K (525 °C and 600 °C) followed by cooling to room temperature. Tempering cycles with variations in holding times were conducted to observe the mechanisms involved. Phase transformations were studied with dilatometry, and the resulting microstructures were characterized with X-ray diffraction and scanning electron microscopy. Tempering treatments at 798 K (525 °C) resulted in retained austenite transformation to martensite on cooling. The martensite start (M _s ) and martensite finish (M _f ) temperatures increased with longer holding times at tempering temperature. At the same time, the lattice parameter of retained austenite decreased. Calculations from the M _s temperatures and lattice parameters suggested that there was a decrease in carbon content of retained austenite as a result of precipitation of carbides prior to transformation. This was in agreement with the resulting microstructure and the contraction of the specimen during tempering, as observed by dilatometry. Tempering at 873 K (600 °C) resulted in precipitation of carbides in retained austenite followed by transformation to ferrite and carbides. This was further supported by the initial contraction and later expansion of the dilatometry specimen, the resulting microstructure, and the absence of any phase transformation on cooling from the tempering treatment. It was concluded that there are two mechanisms of retained austenite transformation occurring depending on tempering temperature and time. This was found useful in understanding the standard tempering treatment, and suggestions regarding alternative tempering treatments are discussed.     

冷轧薄钢板退火过程组织演变的Monte Carlo模拟

利用 Monte Carlo方法及模型进行了冷轧薄钢板静态再结晶退火组织的模拟 ,实现了退火组织的连续动态变化过程 ,可以观察晶界的迁移及晶粒在退火过程中相互吞并的机理和过程。还模拟了冷轧钢板退火过程中晶粒尺寸及再结晶分数的变化规律及冷轧压下率对再结晶的影响。将模拟结果与实验结果进行对比发现 ,两者基本吻合。     

Effect of Heating Rate on Microstructure Evolution and Magnetic Properties of Cold Rolled Non-Oriented Electrical Steel

The effects of heating rate (ranging from 50 to 300 ℃/s) during the final annealing process on microstructure evolution and magnetic properties of cold rolled non-oriented electrical steel were investigated. It was found that increasing heating rate increased the nucleation temperature and complete recrystallization temperature. At the same time, heating rate increasing could cause the substantially refined structures for the recrystallization grains and this grain refinement would decline when the heating rate was beyond 50 ℃/s. The recrystallization texture exhibited pronounced improvement with heating rate, such as the intensity decrease of 111ND (normal direction) fiber and the intensity increase of {110}001 Goss texture component. The texture improvement and grain size refinement caused by heating rate increasing resulted in complicated variation of the magnetic properties. The magnetic induction (B50) keeps increasing while heating rate increases from 15 to 300 ℃/s which is due to the recrystallized texture optimization caused by rapid heating. The core losses (P1.5/50) decrease while heating rate increases from 15 to 100 ℃/s; however, the core losses would increase when heating rate is higher than 100 ℃/s, which is caused by the mean grain size refinement after rapid heating annealing. The results indicate that recrystallization texture and the magnetic properties of the non-oriented electrical steel can be improved definitely by rapid heating during the final annealing treatment.     

CSP工艺冷轧薄板组织演变和第二相分析

采用金相显微镜和QUANTA-400型环境扫描电子显微镜研究了包钢CSP工艺冷轧薄板生产过程中的组织演变,用化学相分析及X射线小角散射法研究了不同状态钢板中第二相的成分、数量及粒度分布。结果表明:包钢CSP薄板坯中复合夹杂物的数量极少。在CSP工艺冷轧薄板生产过程中,热轧板、冷硬板和退火薄板沿宽向边部的组织均较中部的组织细小,且热轧状态下最为明显。作为冷轧基料的CSP工艺热轧板中稳定氧化物夹杂的总量(质量分数)仅约14.3×10-6。冷硬板和退火薄板中的析出相主要为纳米级的M3C型和MC型析出物。冷硬板退火后M3C型析出物的总量比MC型析出物的总量多26～27倍。     

冷轧过程中IF钢的织构演变

以铁素体区热轧低温卷取的Ti-IF钢为研究对象,选择13%~75%的冷轧压下率,观察在冷轧过程中织构的演变。研究表明,压下率为46%是一个转折点,冷轧压下率较小(13%~35%)时,表面上取向变化为{110}001→{554}225→{111}112→{111}110→{223}110,{114}110转向{001}110;压下率达到46%时,{111}织构消失;继续增加压下率,{111}织构再次出现,并随压下率增加而增强。随着冷轧压下率的增加,中心面上的{111}织构强度先增加,压下率达到46%后又降低,最强组分先由{001}110向{223}110转动;压下率达46%时,又向反方向转动。     

Tensile Mechanical Behavior of Cold Rolled Si-Mn Steel Under Different Strain Rates

Tensile mechanical behavior of cold rolled Si-Mn steel after TRIP (TRansformation Induced Plasticity) and DP (Dual Phase) treatment were investigated under different strain rates.The dynamic tensile test was carried out using the rotation disk bar-bar tensile impact apparatus.At static tension test condition,the values of total elongation for TRIP steel was approximately 2-3 times higher than DP steel because of TRIP effect;the DP steel showed a higher tensile strength because of 39.6vol% martensite in the matrix.The results of tension test at high strain rate condition were different.For the studied steel,the elongation increased with increasing strain rate due to softening of matrix caused by adiabatic heating;in addition,TRIP steel at low strain rate was always higher than that at high strain rate because progressive strain induced retained austenite was suppressed at high strain rate.     

Effects of Electromagnetic Vibration Frequencies on Microstructure and Tensile Properties of Al-15 Wt Pct Sn Alloy in Semi-continuous Casting Process

Metallurgical and Materials Transactions A - The electromagnetic vibration (EMV) generated by the action of the AC current and the magnetic field was applied in the crystallizer during the...     

一种高Nb-IF冷轧薄板钢的组织性能及织构

 采用拉伸试验、金相、ODF织构分析及电子背散射衍射(EBSD)技术研究了一种冷轧高Nb-IF钢和传统Nb+Ti-IF钢在不同退火温度下的组织性能、织构及晶界特征。结果表明：与传统Nb+Ti-IF钢相比,该新型高Nb-IF钢由于添加了质量分数为60×10-6的碳和010%的铌,其再结晶温度和再结晶完成温度均大幅度提高;新型高Nb-IF钢具有晶粒细小、组织均匀性良好的组织和γ取向织构发展充分且强点密度高的织构,能够获得强度高、伸长率高和r值高的优异的综合性能。EBSD分析结果表明,该新型高Nb-IF钢中小角度晶界和低指数重位点阵(ΣCSL)晶界含量较多,这也是试验钢获得优良成形性能的原因之一。     

Microstructure and mechanical properties of Ti-40 Wt Pct Ta (Ti-15 At. Pct Ta)

Of the β-isomorphous Ti-X alloy systems, Ti-Ta is one of the least studied. In the current work, the microstructure and mechanical properties of Ti-40 wt pct Ta (Ti-15 at. pct Ta) are investigated. Annealing at 810 °C produces a two-phase microstructure consisting of Ti-richa idiomorphs in a continuous Ta-rich β matrix; this suggests the β-transus temperature is higher than indicated by the most recently published phase diagram. Water quenching from 810 °C causes the β phase to partially transform to orthorhombic martensite (α), while furnace cooling yields secondarya The primary α formed isothermally remains unchanged in both cases. Subsequent aging causes transformation of the martensite to type 1a plus residual β, with a corresponding increase in strength and decrease in ductility. The maximum ductility (20 pct elongation) occurs in the water-quenched condition in which metastable β is retained. Analysis of the true stresstrue strain data suggests that transformation-induced plasticity may contribute to the enhanced ductility of the water-quenched material.     

Properties and Microstructure of One-Step Cold Rolled Steel Strip for Shadow Mask

The effect of recrystallization annealing temperature on the properties and microstructure of one-step cold rolled steel strip for shadow mask was studied.The results showed that there was no yield point elongation when the tensile tests were performed on the samples for annealing temperatures ranging from 750℃ to 810 ℃.Moreover,increasing annealing temperature resulted in large grains,which was beneficial to the formability and magnetic property of steel strips.On the other hand,when the sample was annealed at 840 ℃,its microstructure showed ununifortuity with 0.04% yield point elongation,which was not good for the function of the shadow mask.Therefore,the proper recrystallization annealing temperature was about 810 ℃ for the present steel strip for shadow mask.     

Microstructure of rapidly solidified laser molten AI-4.5 Wt Pct cu surfaces

The microstructure of rapidly solidified laser molten or electron beam molten Al-4.5 wt pct Cu alloyed surfaces has been investigated. A variety of electron microscopy techniques was employed. The epitaxially resolidifying melt undergoes three different solidification modes: about 3 μm to 5 μm of material near the fusion line resolidify in a plane front mode. The next bulk resolidifies in a cellular dendritic mode, which then turns dendritic. The major impact of resolidification is refinement of the surface microstructure, which by itself shows various characteristics for the different resolidification modes. Particularly, the validity of the relationship of secondary interdendritic arm spacing, as inversely dependent on the one-third power of the average local cooling rate, was verified for cooling rates up to 10⁶ K per second.     

Reverse Martensitic Transformation and Resulting Microstructure in a Cold Rolled Metastable Austenitic Stainless Steel

The reverse martensitic transformation in cold‐rolled metastable austenitic stainless steel has been investigated via heat treatments performed for various temperatures and times. The microstructural evolution was evaluated by differential scanning calorimetry, X‐ray diffraction and microscopy. Upon heat treatment, both diffusionless and diffusion‐controlled mechanisms determine the final microstructure. The diffusion reversion from α′‐martensite to austenite was found to be activated at about 450°C and the shear reversion is activated at higher temperatures with A_f′ ~600°C. The resulting microstructure for isothermal heat treatment at 650°C was austenitic, which inherits the α′‐martensite lath morphology and is highly faulted. For isothermal heat treatments at temperatures above 700°C the faulted austenite was able to recrystallize and new austenite grains with a low defect density were formed. In addition, carbo‐nitride precipitation was observed for samples heat treated at these temperatures, which leads to an increasing M_s‐temperature and new α′‐martensite formation upon cooling.     

Texture Evolution in Ferritic Rolled Ti-IF Steel during Cold Rolling

 Texture evolution of ferritic hot rolled Ti-IF steel was investigated during cold rolling in the reduction from 15% to 85%. It was found that, α fibre intensified monotonously with the increase of the cold reduction, but γ fibre changed in a different way. As the cold reduction was in the range of 15%-35% or 45%-75%, γ fibre intensified. While the reduction was between 35%-45% or 75%-85%, the intensity of γ fibre reduced. γ fibre displayed the maximum intensity at 75% and the highest average plastic strain ratio due to the favorable recrystallization texture was obtained at this point.     

40Mn_2链条用冷轧钢带的试生产

介绍了40Mn2钢带材料的选择和使用性能要求,针对该材料的要求制定了合理的工艺路线及工艺,成功开发了链条用40Mn2冷轧钢带。