氢致304L不锈钢晶体结构变化与相变

利用X射线衍射方法,研究了304L不锈钢中电解充氢过程和随后时效过程中的氢致奥氏体结构变化和氢致马氏体相变。结果表明,电解充氢可导致奥氏体晶格膨胀和马氏体相变,α’相和ε相同时出现,并且在室温时效过程中并不能消失。     

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.     

The Investigation of Strain-Induced Martensite Reverse Transformation in AISI 304 Austenitic Stainless Steel

This paper presents a comprehensive study on the strain-induced martensitic transformation and reversion transformation of the strain-induced martensite in AISI 304 stainless steel using a number of complementary techniques such as dilatometry, calorimetry, magnetometry, and in-situ X-ray diffraction, coupled with high-resolution microstructural transmission Kikuchi diffraction analysis. Tensile deformation was applied at temperatures between room temperature and 213 K (−60 °C) in order to obtain a different volume fraction of strain-induced martensite (up to ~70 pct). The volume fraction of the strain-induced martensite, measured by the magnetometric method, was correlated with the total elongation, hardness, and linear thermal expansion coefficient. The thermal expansion coefficient, as well as the hardness of the strain-induced martensitic phase was evaluated. The in-situ thermal treatment experiments showed unusual changes in the kinetics of the reverse transformation (α′ → γ). The X-ray diffraction analysis revealed that the reverse transformation may be stress assisted—strains inherited from the martensitic transformation may increase its kinetics at the lower annealing temperature range. More importantly, the transmission Kikuchi diffraction measurements showed that the reverse transformation of the strain-induced martensite proceeds through a displacive, diffusionless mechanism, maintaining the Kurdjumov–Sachs crystallographic relationship between the martensite and the reverted austenite. This finding is in contradiction to the results reported by other researchers for a similar alloy composition.

     

Effect of Texture and Temperature on Strain-Induced Martensitic Transformation in 304 Austenitic Stainless Steel

The austenitic stainless steel's remarkable mechanical properties are caused by twinning-induced plasticity and transformation-induced plasticity mechanisms. Numerous studies focus on stacking fault energy's effect, which is affected by various factors, to interpret and control these mechanisms. However, crystallographic orientation is also an important parameter for mechanical properties in metals. This study compares the mechanical properties and microstructural features of 304 austenitic stainless steel, focusing on the effect of initial texture and deformation temperature. Microstructural characterization is identified by an interrupted tensile test based on strain, tensile direction, and temperature conditions, and X-ray diffraction and electron back-scattered diffraction analysis are performed. The results show that the mechanical features and strain-induced martensitic transformation rate depend on the tensile directions. In addition, this trend is maintained irrespective of the temperature conditions. The attribute reason is that the difference in the Taylor factor and the formation rate of the deformed band structure is induced by the initial crystallographic orientations. Moreover, a decrease in temperature significantly increases the dislocation densities and abundant twins and transformed martensites formation. Furthermore, the yield and tensile strengths are enhanced while the elongation decreased with the tensile strains.     

Effect of High-Pressure Torsion Processing and Annealing on Hydrogen Embrittlement of Type 304 Metastable Austenitic Stainless Steel

The effect of high-pressure torsion (HPT) and annealing on hydrogen embrittlement (HE) of a type 304 stainless steel was studied by metallographic characterization and tensile test after hydrogen gas charging. A volume fraction of ~78 pct of the austenite transformed to α′ martensite by the HPT processing at an equivalent strain of ~30. Annealing the HPT-processed specimen at a temperature of 873 K (600 °C) for 0.5 hours decreased the α′ martensite to ~31 pct with the average grain size reduced to ~0.43 μm through the reverse austenitic transformation. Hydrogen charge into the HPT-processed and the HPT+annealed specimens in the hydrogen content of ~10 to 20 ppm led to no severe HE but appeared in the solution-treated specimen. Especially the 873 K (600 °C) annealed specimen had the ~1.4 GPa tensile strength and the ~50 pct reduction of area (RA) despite the hydrogenation.     

Ti-5Mo-5V-2Cr-3Al合金中的冲击相变研究

利用Hopkinson压杆装置,对Ti-5Mo-5V-2Cr-3Al(TB10)合金进行高速冲击试验,采用光学显微镜和透射电镜分析其冲击相变与动态承载能力之间的关系.结果表明,显微组织状态对绝热剪切敏感性影响很大,在相同的应变率条件下,两相区固溶+时效、两相区固溶+双重时效的TB10合金试样中均可观察到明显的绝热剪切带...     

Strain-Induced Phase Transformation and Nanocrystallization of 301 Metastable Stainless Steel Upon Ultrasonic Shot Peening

The following study investigated the strain-induced phase transformation in metastable austenitic 301 stainless steels via an ultrasonic shot peening treatment (USP) for 5 to 30 minutes. Following the USP, the microhardness increased to a depth of 400 μm and from 200 to 400 HV. The deformed grains and the phase transformation were monitored via X-ray diffraction and electron backscattered diffraction analysis. The grain evolution was studied via transmission electron microscopy. Approximately 500 nm α′-martensite grains formed in the top-most region after 5 minutes of the USP treatment. The grains were then further refined to ~?100 nm when the peening time increased to 10 and 15 minutes. The grains refined down to tens of nanometers after the specimen was treated for 30 minutes, where the phases were composed of α′-martensite (~?50 nm). There was a mixture of austenite with α′-martensite (~?25 nm). The grain refinement and the phase transformation of austenite to α′-martensite during ultrasonic shot peening were systematically investigated.     

Effects of Strain Rate and Plastic Work on Martensitic Transformation Kinetics of Austenitic Stainless Steel 304

The martensitic transformation behavior and mechanical properties of austenitic stainless steel 304 were studied by both experiments and numerical simulation.Room temperature tensile tests were carried out at various strain rates to investigate the effect on volume fraction of martensite,temperature increase and flow stress.The results show that with increasing strain rate,the local temperature increases,which suppresses the transformation of martensite.To take into account the dependence on strain level,strain rate sensitivity and thermal effects,a kinetic model of martensitic transformation was proposed and constitutive modeling on stress-strain response was conducted.The validity of the proposed model has been proved by comparisons between simulation results and experimental ones.     

Effect of Cyclic Thermal Process on Ultrafine Grain Formation in AISI 304L Austenitic Stainless Steel

As-received hot-rolled commercial grade AISI 304L austenitic stainless steel plates were solution treated at 1060 °C to achieve chemical homogeneity. Microstructural characterization of the solution-treated material revealed polygonal grains of about 85-μm size along with annealing twins. The solution-treated plates were heavily cold rolled to about 90 pct of reduction in thickness. Cold-rolled specimens were then subjected to thermal cycles at various temperatures between 750 °C and 925 °C. X-ray diffraction showed about 24.2 pct of strain-induced martensite formation due to cold rolling of austenitic stainless steel. Strain-induced martensite formed during cold rolling reverted to austenite by the cyclic thermal process. The microstructural study by transmission electron microscope of the material after the cyclic thermal process showed formation of nanostructure or ultrafine grain austenite. The tensile testing of the ultrafine-grained austenitic stainless steel showed a yield strength 4 to 6 times higher in comparison to its coarse-grained counterpart. However, it demonstrated very poor ductility due to inadequate strain hardenability. The poor strain hardenability was correlated with the formation of strain-induced martensite in this steel grade.     

Ultrasonic Fatigue Damage Behavior of 304L Austenitic Stainless Steel Based on Micro-plasticity and Heat Dissipation

Very high cycle fatigue behavior(107-109 cycles)of 304 Laustenitic stainless steel was studied with ultrasonic fatigue testing system(20kHz).The characteristics of fatigue crack initiation and propagation were discussed based on the observation of surface plastic deformation and heat dissipation.It was found that micro-plasticity(slip markings)could be observed on the specimen surface even at very low stress amplitudes.The persistent slip markings increased clearly along with a remarkable process of heat dissipation just before the fatigue failure.By detailed investigation using a scanning electron microscope and an infrared camera,slip markings appeared at the large grains where the fatigue crack initiation site was located.The surface temperature around the fatigue crack tip and the slip markings close to the fracture surface increased prominently with the propagation of fatigue crack.Finally,the coupling relationship among the fatigue crack propagation,appearance of surface slip markings and heat dissipation was analyzed for a better understanding of ultrasonic fatigue damage behavior.     

C、Cr、Ni和Mn含量对304不锈钢变形诱发马氏体相变的影响

用X射线衍射技术研究了304奥氏体不锈钢变形诱发马氏体相变倾向对成分的敏感性.在液氮内的拉伸结果表明: C、Mn、Cr和Ni的含量从标准范围的上限降到下限,显著增大形变诱发马氏体相变倾向和形变强化能力,尤其是C、Mn、Cr和Ni的含量接近下限的钢在室温下拉伸形成ε马氏体和α'马氏体,其中α'马氏体快速形成使流变应力迅速上升;此外发现,在液氮温度下,变形早期ε马氏体与α'马氏体同时存在,α'马氏体的体积分数累积到约70%后,ε马氏体消失.     

Interfacial Phase in Ti-5Al-2Mo-3Zr Alloy

Under appropriate cooling condition, intcrfacial phase appeared between α and β phases in Ti-5Al-2M0-3Zr alloy. Its thickness could reach 100 nm. The interfacial phase was either single layer structure or double layer structure. The monolithic layer adjacent to 3 phase was indentified as fee structure with relationship （110）_β// （001）_m, [11$\\mathop 1\\limits^{{\\rm{ - - }}} $]_β /[110]_m. The striated layer adjacent to a phase was indentified as hep with twin relationship {10$\\bar 1$1}<1$\\bar 0$12> to α. Thus, the study provided a new experimental fact for the controversial topic on structure of striated layer. Chemical composition of interfacial phase varied slightly with heat treatments, but always between that of α and β phases.     

In-Situ Measurements of Load Partitioning in a Metastable Austenitic Stainless Steel: Neutron and Magnetomechanical Measurements

In order to construct physically based models of the mechanical response of metastable austenitic steels, one must know the load partitioning between the austenite and the strain-induced martensitic phases. While diffraction-based techniques have become common for such measurements, they often require access to large facilities. In this work, we have explored a simple magnetic technique capable of providing a measure of the stresses in an embedded ferromagnetic phase. This technique makes use of the coupling between the elastic strain and the magnetic response of the $\alpha^{\prime}$ -martensite in an austenitic stainless steel undergoing straining. The magnetic technique proposed here is compared to neutron diffraction measurements made on the same material and is shown to give nearly identical results. The resulting predictions of the load partitioning to the $\alpha^{\prime}$ -martensite phase suggest that $\alpha^{\prime}$ deforms in a complex fashion, reflecting the fact that the microstructure is progressively transformed from austenite to martensite with straining. In particular, it is shown that the apparent hardening of the $\alpha^{\prime}$ -martensite suggests elastic deformation as an important source of high macroscopic work-hardening rate in this material.     

Phase Stability and Deformation Modes in Functionally Graded Metastable Austenitic Stainless Steel; A Novel Approach to Evaluate the Role of Nitrogen

Metallurgical and Materials Transactions A - An austenitic stainless steel AISI 304 plate was functionally graded by interstitial alloying with nitrogen by high-temperature solution nitriding,...     

钛合金-不锈钢相变超塑性扩散连接接头分析

探讨了TA17钛合金和OCr18Ni9Ti不锈钢相变超塑性扩散连接工艺；分析了接头微观组织结构，元素的扩散及断口形貌。结果表明，钛合金和不锈钢两侧的元素有不同程度的扩散，在界面处形成β-Ti、TiFe和TiFe2。控制金属间化合物厚度在5μm以内可以提高接头强度。接头受力的主要物相是以β-Ti为基的固溶体，该物相的面积对接头的强度影响很大，面积越大，接头强度越高；反之越低。     

445J2超纯铁素体不锈钢和316L超低碳奥氏体不锈钢在溴化锂溶液的点蚀分析

445J2铁素体不锈钢由于高的导热率、低的热膨胀系数以及良好的耐蚀性能使得其作为溴冷机中一些部件的良好候选材料,本文采用电化学测试方法对比研究了445J2超纯铁素体不锈钢(/%:0.01C,22.5Cr, 1.9Mo, 0.27Nb, 0.20Ti, 0.09Al, 0.36Cu, 0.015P,0.001S,0.015N)和316L奥氏体不锈钢(/%:0.002C,16.8Cr, 10.19Ni, 2.02Mo, 0.025P,0.0008S)在20～60℃0.1～1M的溴化锂溶液中的点蚀行为,并采用扫描电镜(SEM)和能谱分析仪(EDS)对电化学结果进行表征。结果表明,随着LiBr温度和浓度的升高,两种钢腐蚀电流密度增大,点蚀电位降低,耐点蚀性变差;氧化物和硫化物夹杂会引起两种钢的点蚀;高含量的Cr以及Mo、Ti、Nb、Al等合金元素使445J2钢具有优异的耐点蚀性能。     

Martensite Formation in Conventional and Isothermal Tension of 304 Austenitic Stainless Steel Measured by X-ray Diffraction

The temperature above which neither stress nor plastic strain can cause austenite to transform to martensite is determined for 304 austenitic stainless steel by X-ray diffraction measurements on specimens that were previously subjected to isothermal tension tests. The specimens were tested at 273 K, 298 K, 308 K, 333 K, and 373 K (0 °C, 25 °C, 35 °C, 60 °C, and 100 °C). A new isothermal testing technique was used not only for controlling the testing temperature but also for averting deformation-induced heating. Hence, the effect of temperature on the strain-induced martensite is decoupled from that of strain. The diffraction measurements reveal that the martensite volume fraction decreases linearly with the testing temperature up to a critical temperature, which is found by linearly extrapolating to zero martensite volume fraction.     

不同熔炼条件下B、C元素对Ti-47Al-2Cr-2Nb合金铸态组织的影响

研究了不同熔炼条件下B、C元素对Ti-47Al-2Cr-2Nb合金的铸态组织的影响。研究结果表明：B、C元素的添加显著地细化了Tim基合金的组织片层,C元素的细化效果优于B元素。在所研究的精炼时间内,无论添加微量元素B还是C元素,精炼时间为30min时获得的铸锭组织中片层最细。     

Microstructural studies on lattice imperfections in irradiated titanium and Ti-5 Pct Ta-2 Pct Nb by X-ray diffraction line-profile analysis

Microstructural parameters such as the average domain size, effective domain size at a particular crystallographic direction, and microstrain within the domains of titanium and Ti-5 pct Ta-2 pct Nb, irradiated with 116 MeV O⁵⁺ ion, have been characterized as a function of dose by X-ray diffraction line-profile analysis (XRDLPA) using different model-based approaches. The dislocation density and stacking-fault probabilities have also been estimated from the analysis. The analysis revealed that there was a significant decrease of the average domain size with dose as compared to the unirradiated sample. The estimated values of dislocation density increased significantly for the irradiated samples and were found to be an order of magnitude more as compared to the unirradiated one. However, the dislocation density became saturated with an increase in dose. The deformation (stacking-fault) probabilities were found to be negligible even with the increase in dose of irradiation.