Influence of Strain Rate and Temperature on Tensile Deformation and Fracture Behavior of Type 316L(N) Austenitic Stainless Steel

Tensile tests were performed at strain rates ranging from 3.16 × 10^?5 to 3.16 × 10^?3 s^?1 over the temperatures ranging from 300 K to 1123 K (27 °C to 850 °C) to examine the effects of temperature and strain rate on tensile deformation and fracture behavior of nitrogen-alloyed low carbon grade type 316L(N) austenitic stainless steel. The variations of flow stress/strength values, work hardening rate, and tensile ductility with respect to temperature exhibited distinct three temperature regimes. The steel exhibited distinct low- and high-temperature serrated flow regimes and anomalous variations in terms of plateaus/peaks in flow stress/strength values and work hardening rate, negative strain rate sensitivity, and ductility minima at intermediate temperatures. The fracture mode remained transgranular. At high temperatures, the dominance of dynamic recovery is reflected in the rapid decrease in flow stress/strength values, work hardening rate, and increase in ductility with the increasing temperature and the decreasing strain rate.     

Role of Microstructure and Temperature on the Tensile Fracture Behavior of Oxide Dispersion Strengthened 18Cr Ferritic Steel

The tensile fracture behavior of oxide dispersion strengthened 18Cr (ODS-18Cr) ferritic steels milled for varying times was studied along with the oxide-free 18Cr steel (NODS) at 25, 200, 400, 600, and 800 °C. At all the test temperatures, the strengths of ODS–18Cr steels increased and total elongation decreased with the duration of milling time. Oxide dispersed 18Cr steel with optimum milling exhibited enhanced yield strength of 156 pct at room temperature and 300 pct at 800 °C when compared to oxide-free 18Cr steel. The ductility values of ODS-18Cr steels are in the range 20 to 35 pct for a temperature range 25 to 800 °C, whereas NODS alloy exhibited higher ductility of 37 to 82 pct. The enhanced strength of ODS steels when compared to oxide-free steel is due to the development of ultrafine grained structure along with nanosized dispersion of complex oxide particles. While the pre-necking elongation decreased with increasing temperature and milling time, post-necking elongation showed no change with the test temperature. Fractographic examination of both ODS and NODS 18Cr steel fractured tensile samples, revealed that the failure was in ductile fracture mode with distinct neck and shear lip formation for all milling times and at all test temperatures. The fracture mechanism is in general followed the sequence; microvoid nucleation at second phase particles, void growth and coalescence. The quantified dimple sizes and numbers per unit area were found to be in linear relation with the size and number density of dispersoids. It is clearly evident that even nanosized dispersoids acted as sites for microvoid nucleation at larger strains and assisted in dimple rupture.

     

应变速率对Q&P钢拉伸变形行为的影响

以汽车用先进高强度Q&P钢为研究对象,分析了应变速率对Q&P钢拉伸性能及变形行为的影响。结果表明,随应变速率增加,Q&P钢的强度增加,断裂延伸率则呈先下降(10-4s-1～10s-1),后上升至峰值(8×10s-1),之后再下降(102s-1～103s-1)的趋势。变形过程中强度的增加可能同形变回复受限,位错运动受阻有关。而断裂延伸率的变化主要与不同应变速率下Q&P钢中残余奥氏体向马氏体转变(即TRIP效应)有关。     

Effect of Tempering Time on Microstructure, Tensile Properties, and Deformation Behavior of a Ferritic Light-Weight Steel

In the present study, a ferritic light-weight steel was tempered at 973 K (700 °C) for various tempering times, and tensile properties and deformation mechanisms were investigated and correlated to microstructure. ??-carbides precipitated in the tempered band-shaped martensite and ferrite matrix, and the tempered martensite became more decomposed with increasing tempering time. Tempering times for 3 days or longer led to the formation of austenite as irregular thick-film shapes mostly along boundaries between the tempered martensite and the ferrite matrix. Tensile tests of the 1-day-tempered specimen showed that deformation bands were homogeneously spread throughout the specimen, and that the fine carbides were sufficiently deformed inside these deformation bands resulting in high strength and ductility. The 3-day-tempered specimen showed a small amount of boundary austenite, which readily developed voids or cracks and became sites for fracture. This cracking at boundary austenites became more prominent in the 7- and 15-day-tempered specimens, as the volume fraction of boundary austenites increased with increasing tempering time. These findings suggested that, when the steel was tempered at 973 K (700 °C) for an appropriate time, i.e., 1 day, to sufficiently precipitate ??-carbides and to prevent the formation of boundary austenites, that the deformation occurred homogeneously, leading to overall higher mechanical properties.     

1000MPa级DP钢的准静态拉伸行为与应变速率的关系

研究1000MPa的双相钢（DP钢）在室温下的准静态拉伸行为与应变速率（10^-2、10^-1、10^-1s^-1）的关系。结果表明,在准静态拉伸条件下,DP钢的拉伸性能是与应变速率相关的。随着应变速率提高,材料的屈服强度、抗拉强度、屈强比和加工硬化指数明显升高,而均匀伸长率、断裂伸长率略有下降;另外,应变速率对材料的...     

Hot Deformation Behavior of P92 Steel Used for Ultra-Super-Critical Power Plants

 Hot compression tests of P92 steel at temperatures in the range of 1173 to 1523 K and at strain rates in the range of 0.1 to 10 s-1 were carried out on a Gleeble-3500 thermal-mechanical simulator, and the corresponding flow curves were measured. The results showed that the flow stress and the peak strain increase with decreasing deformation temperature and increasing strain rate. The critical Z value, below which the complete dynamic recrystallization may occur, was determined to have 4.61×1018. The hot deformation activation energy of the steel was about 437 kJ/mol. The hot deformation equation and the microstructure diagram of P92 steel were obtained. For the convenience of the practical application, the empirical equation for the peak stress can be described as σP=17.17ln+902499T-524.1.     

Effect of Microstructure in TRIP Steel on Its Tensile Behavior at High Strain Rate

Ｔｈｅｓｔｕｄｉｅｓ[1,2 ] ｈａｖｅｓｔａｔｅｄｔｈａｔｒｅｔａｉｎｅｄａｕｓｔｅｎｉｔｅｉｎａｄｕａｌ ｐｈａｓｅｓｔｅｅｌｉｓｔｒａｎｓｆｏｒｍｅｄｔｏｍａｒｔｅｎｓｉｔｅｕｎｄｅｒｔｅｎｓｉｌｅｓｔｒａｉｎ .Ｓｕｃｈｓｔｒａｉｎ ｉｎｄｕｃｅｄｔｒａｎｓｆｏｒｍａｔｉｏｎｏｆｒｅｔａｉｎｅｄａｕｓｔｅｎｉｔｅｃａｎｅｎｈａｎｃｅｄｕｃｔｉｌｉｔｙｏｆｓｔｅｅｌｗｈｅｎｔｈｅｒｅｔａｉｎｅｄａｕｓｔｅｎｉｔｅｉｓｒａｔｈｅｒｓｔａｂｌｅａｇａｉｎｓｔｓｔｒａｉｎｉｎｇ[3 ] .Ｂａｓｅｄｏｎｔｈｉ…     

Influence of Strain Rate on Compressive Deformation Behavior of a Zr-Cu-Ni-Al Bulk Metallic Glass at Room Temperature

The compressive-deformation behavior of the Zr_50.7Cu₂₈Ni₉Al_12.3 bulk metallic glass (BMG) was investigated over a wide strain-rate range at room temperature. The yield strength of the BMG studied is independent of the strain rates applied upon quasi-static loading; however, it decreases remarkably upon dynamic loading. Serrated flows and shear bands appear at low quasi-static strain rates; nevertheless, they vanish as the strain rate increases to 1.0 × 10⁻¹ s⁻¹. Cracks appearing on the side surface of the fractured sample after dynamic compression yield a strain-accommodation deformation mechanism upon dynamic loading. Scanning electron microscopy observations reveal that molten liquids increase on the fractured surfaces with increasing strain rate, indicating that adiabatic heating in the shear bands is enhanced as the strain rate increases.     

The Effects of Strain Rate and Temperature on the Deformation Behavior of Cold‐Rolled TRIP800 Steel

In the present study, the influences of temperature and strain rate on the deformation behavior of cold‐rolled TRIP800 steel were investigated. Microstructural observation and tensile tests were performed and volume fractions of retained austenite were measured at various temperatures and strain rates. The results reveal that both temperature and strain rate affect the volume fractions of retained austenite that transforms into martensite. The strain‐induced transformation of retained austenite is retarded with increasing temperature and the retained austenite becomes more stable against straining. The amount of retained austenite that transforms into martensite is not influenced significantly by strain rate. The variation in mechanical properties with temperature and strain rate was related to the effects of dynamic strain aging, tempering of banite, high temperature softening, and the volume fractions of retained austenite.     

Effects of Temperature and Strain Rate on Flow Behavior and Microstructural Evolution of Super Duplex Stainless Steel under Hot Deformation

Hot compression tests were carried out in the temperature range of 1 223-1 473 Kand strain rate range of0.01-30s-1 to investigate the flow behavior and microstructural evolution of super duplex stainless steel 2507(SDSS2507).It is found that most of the flow curves exhibit a characteristic of dynamic recrystallization(DRX)and the flow stress increases with the decrease of temperature and the increase of strain rate.The apparent activation energy Qof SDSS2507 with varying true strain and strain rate is determined.As the strain increases,the value of Qdeclines in different ways with varying strain rate.The microstructural evolution characteristics and the strain partition between the two constituent phases are significantly affected by the Zener-Hollomon parameter(Z).At a lower lnZ,dynamic recovery(DRV)and continuous dynamic recrystallization(CDRX)of the ferrite dominate the softening mechanism during the compression.At this time,steady state deformation takes place at the last stage of deformation.In contrast,a higher lnZ will facilitate the plastic deformation of the austenite and then activate the discontinuous dynamic recrystallization(DDRX)of the austenite,which leads to a continuous decline of the flow stress even at the last deformation stage together with CDRX of the ferrite.     

IF钢铁素体区热变形后的静态软化行为

在Ｇｌｅｅｂｌｅ热模拟实验机上,采用双道次压缩法研究了ＩＦ钢铁素体区变形后的静态软化行为。结合静态软化过程中的组织变化和软化率曲线,总结了变形量与变形温度对静态软化率的影响。结合实验数据,求出ＩＦ钢的铁素体静态再结晶激活能Ｑｒｅｘ＝１７３ｋＪ／ｍｏｌ,并采用Ａｖｒａｍｉ方程得到ＩＦ钢的静态再结晶动力学方程     

Nb和Ti对444超纯铁素体不锈钢高温氧化行为的影响

研究了444Nb和444NbTi不锈钢在1100℃下短时(4h)高温氧化行为,利用X射线衍射、扫描电子显微镜和能谱仪分析氧化膜物相、微观形貌及化学成分分布.结果表明,444NbTi钢每cm2氧化增重为444Nb钢两倍,这与Ti改变Cr2O3氧化膜缺陷结构相关.444Nb钢存在氧化膜剥落现象,原因可能为Mn的快速扩散促进...     

409L铁素体不锈钢热轧变形行为研究

本文通过轧制理论以及对黑卷显微组织的观察,对比分析了409L和410S热轧过程的变形抗力和动态回复再结晶能力。结果表明,409L热轧态组织基本为等轴状,其动态软化能力较410S好。     

Tensile Properties of TWIP Steel at High Strain Rate

 Tensile tests of TWIP steels of two compositions are performed in the strain rate range of 10-5-103 s-1. Results indicate that steel 1# does not exhibit TWIP effect but deformation induced martensitic transformation appears only. There exists TWIP effect in steel 3#. Tensile properties at room temperature are sensitive to strain rate in the studied strain rate ranges. Analysis on the relationship between strain hardening exponent and strain rates shows that strain induced martensitic transformation and formation of twins during deformation have significant influence on their strain hardening behavior.     

P92钢的蠕变行为研究

在不同温度和压力条件下完成P92钢的蠕变及持久试验,采用SEM、TEM研究P92钢的强化机制及退化机制。持久试验外推强度同欧洲蠕变委员会公布的数据基本相同。Norton应力指数数值表明,高应力阶段的蠕变机制为位错蠕变。组织观察结果表明:P92钢的主要强化机制为位错强化及弥散强化,淬火得到的马氏体内部有高密度的位错,板条间的碳化物M23C6及弥散分布碳氮化物MX是P92钢热强性高的原因。随着位错密度的降低及析出相的粗化,P92钢的高温耐热性也降低。     

Analysis of Tensile Stress-Strain and Work-Hardening Behavior in 9Cr-1Mo Ferritic Steel

Detailed analysis on tensile true stress (??)-true plastic strain (??) and work-hardening behavior of 9Cr-1Mo steel have been performed in the framework of the Voce relationship and Kocks-Mecking approach for wide range of temperatures, 300 K to 873 K (27 °C to 600 °C) and strain rates (6.33 × 10^?5 to 6.33 × 10^?3 s^?1). At all test conditions, ??-?? data were adequately described by the Voce equation. 9Cr-1Mo steel exhibited two-stage work-hardening behavior characterized by a rapid decrease in instantaneous work-hardening rate (?? = d??/d??) with stress at low stresses (transient stage) followed by a gradual decrease in ?? at high stresses (stage III). The variations of work-hardening parameters and ??-?? as a function of temperature and strain rate exhibited three distinct temperature regimes. Both work-hardening parameters and ??-?? displayed signatures of dynamic strain aging at intermediate temperatures and dominance of dynamic recovery at high temperatures. Excellent correlations have been obtained between work-hardening parameters evaluated using the Voce relationship and the respective tensile properties. A comparison of work-hardening parameters obtained using the Voce equation and Kocks-Mecking approach suggested an analogy between the two for the steel.