铈对S32750超级双相不锈钢低温冲击性能的影响

通过夏比冲击和示波冲击方法分析了两种Ce含量S32750超级双相不锈钢在20~－100 ℃范围内的冲击吸收能量及能量构成差异,利用Aspex自动扫描电镜分析仪、SEM、EDS研究了Ce对钢中夹杂物的改性行为及冲击断裂行为的影响。结果表明:高Ce试验钢的抗低温冲击断裂性能明显优于低Ce试验钢,前者韧脆转变温度相较后者下降16 ℃;Ce的添加使得试验钢－80 ℃冲击吸收能量提高45 J,其主要源于裂纹扩展能W_p的提升(76%)。冲击断口形貌观察和夹杂物分析结果显示,低Ce试验钢在－80 ℃冲击断口表现为完全解理断裂;相较于低Ce试验钢,高Ce试验钢中Al₂O₃夹杂显著减少,多为改性后的铈铝氧复合夹杂;硬脆Al₂O₃夹杂数量的减少有效改善了钢的冲击性能。     

390 MPa级复合钢板极地低温环境适应性分析

目的 验证复合钢板的极地低温环境适应性。方法 采用爆炸复合的方法制备低温复合钢板。通过全浸腐蚀试验、间浸腐蚀试验、腐蚀磨损试验、系列温度冲击试验、系列温度动态撕裂试验和全厚度止裂试验,分别评价复合钢板的耐蚀性、耐磨性能、低温断裂性能及止裂性能,并对复合钢板的低温断裂性能及极地低温环境适应性进行分析。结果 全浸腐蚀条件下,复合钢板基层材料的腐蚀速率是复层材料的105倍;间浸腐蚀条件下,复合钢板基层材料的腐蚀速率是复层材料的350倍;全浸和间浸状态下,复层钢板的腐蚀速率均远小于基层钢板,复层材料的耐蚀性远远好于基层材料。模拟海水条件下,复合钢板复层317L不锈钢的磨损量为0.003,基层FH40钢的磨损量为0.75,基层材料的磨损量是复层的250倍,复层材料的耐磨性远远好于基层材料。分析了20组大厚度规格低温钢的韧脆转变特征温度与止裂温度的相关性关系,指出了现有规范与标准以冲击功作为低温钢断裂性能技术指标的局限性,建立了止裂温度与动态撕裂韧脆转变特征温度相关性方程,给出了低温钢极地环境低温服役下的韧脆转变特征温度建议值,确定了复合钢板极地低温环境服役的最低温度。结论 模拟海水环境下,复合钢...     

Room-Temperature Charpy Impact Property of 3D-Printed 15-5 Stainless Steel

In this study, the room-temperature Charpy impact property of 3D-printed 15-5 stainless steel was investigated by a combined experimental and finite element modeling approach. The experimentally measured impact energy is 10.85 ± 1.20 J/cm², which is comparable to the conventionally wrought and non-heat treated 15-5 stainless steel. In parallel to the impact test experiment, a finite element model using the Johnson–Cook material model with damage parameters was developed to simulate the impact test. The simulated impact energy is 10.46 J/cm², which is in good agreement with the experimental data. The fracture surface from the experimentally tested specimen suggests that the 3D-printed specimens undergo predominately brittle fracture.     

Influence of Martensite Volume Fraction on Impact Properties of Triple Phase (TP) Steels

Ferrite-bainite-martensite triple phase (TP) microstructures with different volume fractions of martensite were obtained by changing heat treatment time during austempering at 300 °C. Room temperature impact properties of TP steels with different martensite volume fractions (V _M) were determined by means of Charpy impact testing. The effects of test temperature on impact properties were also investigated for two selected microstructures containing 0 (the DP steel) and 8.5 vol.% martensite. Test results showed reduction in toughness with increasing V _M in TP steels. Fracture toughness values for the DP and TP steels with 8.5 vol.% martensite were obtained from correlation between fracture toughness and the Charpy impact energy. Fractography of Charpy specimens confirmed decrease in TP steels’ toughness with increasing V _M by considering and comparing radial marks and crack initiation regions at the fracture surfaces of the studied steels.     

Technological special features of methods of supersonic thermal spraying

The effect of accelerated ageing on the toughness and fracture of the longitudinal weld metal of an API5L-X52 linepipe steel was evaluated by a Charpy V-notch impact test, fracture analysis and transmission electron microscopy. Ageing was performed at 250°C for 100–1000 h. The impact results indicated a significant reduction in the fracture energy and impact toughness as a function of ageing time, which were achieved by the scanning electron microscope fractographs that showed a decrease in the volume fraction of microvoids by Charpy ductile failure with the ageing time, which promoted brittle fracture due to transgranular cleavage. The minimum volume fraction of microvoids was reached at 500 h due to the peak age. The microstructural analysis indicated the precipitation of transgranular iron nanocarbides in the aged specimens, which was related to the deterioration of toughness and change in the ductile to brittle behaviour.     

回火温度对工程机械用超高强钢组织及回火脆性的影响

通过SEM、TEM、-20 ℃夏比V型冲击试验等分析手段研究了回火温度对工程机械用超高强钢微观组织及回火脆性的影响,并结合断口特征及微观组织分析裂纹扩展路径。结果表明,试验钢在200~500 ℃回火时,随着回火温度的升高,马氏体分解后形成的碳化物的析出位置从马氏体板条内逐步过渡到原始奥氏体晶界和马氏体板条界,其形状由针状变为粒状,并不断粗化。回火温度为200 ℃和500 ℃时,冲击试样断口的不稳定断裂区为韧性断裂。300 ℃回火时,出现了回火脆性,其冲击试样断口的不稳定断裂区为准解理断裂,裂纹扩展路径相对平直。微观组织分析发现,在原始奥氏体晶界及马氏体板条界析出大量的针状碳化物,这些碳化物提供了裂纹形核位置,促进了裂纹扩展,导致了回火脆性的产生。     

TCS不锈钢焊接接头CTOD断裂韧度试验研究

在TCS不锈钢前期焊接试验中发现其焊接接头热影响区的冲击吸收功值在熔合线附近较低,原因是接头热影响区晶粒粗大所致.为了解TCS不锈钢焊接接头发生脆性裂纹的温度,进行了TCS不锈钢焊接接头CTOD断裂韧度试验研究,试验结果得出了发生脆性裂纹的温度.从试验结果和使用情况得出相应的结论,为今后的进一步研究奠定了基础.     

Impact property analysis of weld metal and heat-affected zone for low-alloy carbon steel multi-pass welded joint

Welded joint impact performances of low-alloy carbon steel plates welded by full-automatic gas metal arc welding (GMAW) were evaluated. To clarity the effect of impact temperature on impact properties of weld metal (WM) and heat-affected zone (HAZ), Charpy V impact tests at different temperatures and fracture surface analysis were carried out. The Charpy V impact energy decreases with the decreasing test temperature both for the WM and HAZ, while the proportion of crystal zone on WM and HAZ impact fracture surface increases with the decreasing test temperature. Research results indicate that the welding defects (void and slag) make the impact energy of WM more scattered and lower than that of HAZ.     

热老化对Z3CN20-09M不锈钢微区力学性能和冲击断裂行为的影响

通过纳米力学探针对铁素体相在热老化过程中的力学性能变化进行了研究.采用仪器化冲击试验机研究了材料的冲击行为,使用SEM观察冲击断口形貌.结果表明:长期热老化导致铁素体相的塑性变形能力不断下降,材料的冲击韧性也显著下降.热老化过程中冲击功的损失主要是由于裂纹扩展能量的降低引起,在400℃热老化1×10~4h后裂纹稳定扩展能几乎降为0.热老化材料的冲击断裂过程为:在冲击载荷下裂纹首先在铁素体内萌生并快速扩展,铁素体相发生解理断裂,裂纹扩展到奥氏体相,最后裂纹连接贯穿整个试样.     

低合金高强钢激光电弧复合焊热模拟热影响区组织与冲击韧性

采用焊接热模拟技术制备了低合金高强钢激光电弧复合焊热影响区的均匀化组织试样,并结合示波冲击试验和组织精细化表征技术分析了热模拟试样组织与韧性之间的关系.?结果表明,热模拟粗晶区、细晶区组织为板条马氏体,临界区组织为马氏体和晶界碳化物,亚临界区组织为回火马氏体;峰值温度对热模拟试样裂纹形成功影响不大,对裂纹扩展功具有较大...     

固溶温度与冷变形量对S32750双相不锈钢管低温冲击性能的影响

通过金相显微镜、扫描电镜及冲击试验对S32750双相不锈钢管的显微组织和冲击吸收能量进行研究,分析了固溶温度和冷变形量对S32750不锈钢管低温冲击吸收能量和显微组织的影响。结果表明:随着冷变形量从30%逐渐增加到60%,γ相的圆度系数从7.10增加到27.25,低温冲击吸收能量逐渐增加,特别是-46 ℃冲击吸收能量增加约2倍,冲击断口形貌发生变化。随着热处理温度从1060 ℃升高到1120 ℃,γ相比例减少,低温冲击吸收能量降低,特别是-40 ℃冲击吸收能量值降低53.4%。     

不同热处理态的304和321奥氏体不锈钢在氯化铵环境中的应力腐蚀行为对比研究

目的 对比研究原始、固溶和敏化态的304和321奥氏体不锈钢在模拟加氢催化氯化铵环境中的应力腐蚀（SCC）行为及机理。方法 将304和321奥氏体不锈钢经过热处理制备成固溶和敏化态试样,采用U形弯试样在模拟加氢催化氯化铵环境中浸泡的应力腐蚀试验方法对其进行研究,通过观察U形弯弧顶的腐蚀形貌和开裂时间,并结合腐蚀及裂纹的SEM照片和电化学测试结果进行分析。结果 原始和固溶状态304不锈钢U形弯试样在氯化铵溶液环境中开裂时间为25 d左右,断口形貌分别为穿晶断口和沿晶断口;敏化态试样18 d后发生开裂,断口形貌为穿晶和沿晶的混合断口。原始和固溶态321不锈钢U形弯试样在该环境中经过39 d均无应力腐蚀裂纹;敏化试样经30 d后产生宏观开裂。电化学测试结果显示,不同热处理态的304不锈钢在氯化铵溶液中均具有明显的点蚀敏感性,321不锈钢在该环境中耐点蚀和应力腐蚀的能力优于304不锈钢。结论 不同状态的304不锈钢在高温氯化铵环境中具有较强的应力腐蚀倾向,特别是敏化态试样;321不锈钢在该环境中的应力腐蚀敏感性相对较小,但敏化处理显著增加了其沿晶应力腐蚀倾向,而固溶态试样具有明显的沿晶腐蚀特征。     

Effect of Short-Time Aging on the Pitting Corrosion Behavior of a Novel Lean Duplex Stainless Steel 2002

The effect of short-time aging in the temperature range between 400 and 1000 °C on the pitting corrosion behavior and mechanical property of a novel lean duplex stainless steel(LDSS) 2002 was investigated through the potentiostatic critical pitting temperature(CPT) tests and the Charpy impact tests. Both the pitting corrosion resistance and the toughness of aged specimens degraded due to the precipitation of detrimental secondary phases and the most significant reduction of CPT and impact energy emerged at 650 °C concurrently. The CPT of LDSS 2002 specimen aged at 650 °C decreased by 28 °C, and the impact energy dropped from 69 to 29 J/cm~2 compared with the solution-annealed sample. Transmission electron microscopy characterization showed that the main precipitates in LDSS 2002 were Cr_2N and M_(23)C_6 along the ferrite–austenite grain boundaries.     

SLM成形17-4PH不锈钢微观组织与动态断裂性能

通过激光选区熔化(selective laser melting, SLM)技术制备了17-4PH不锈钢,采用电子背散射衍射(electron backscattered diffraction, EBSD)和透射电子显微镜(transmission electron microscope, TEM)等方法对沉积态和固溶态试样微观组织结构进行了分析.通过示波冲击试验确定了裂纹萌生扩展的特征阶段和动态裂纹扩展阻力曲线(J-R曲线),研究了微观组织与动态断裂性能之间的关系.结果表明,沉积态试样主要由<100>择优且沿增材方向拉长的δ铁素体柱状晶、取向随机的细小马氏体,以及少量奥氏体组成,不同截面具有显著的组织各向异性;大尺寸δ铁素体柱状晶与细小晶粒的结合面作为薄弱环节,使其脆性增加,J-R曲线的撕裂模量较低,以准解理方式断裂.固溶热处理明显弱化组织各向异性,微观组织由尺寸细小、均匀的马氏体组成,其冲击吸收能量提升1倍,动态断裂韧性优良,属于韧性断裂.大尺寸δ铁素体柱状晶与周围细小马氏体晶粒界面结合较弱是沉积态17-4PH不锈钢动态断裂性能较差的主要原因.     

Fatigue crack growth and fracture toughness properties of 304 stainless steel pipe for LNG transmission

The fatigue crack growth rate and fracture toughness tests of type 304 stainless steel were studied over a temperature range of −162°C to room temperature. Girth weld metal specimens were fabricated using a combination of gas-tungsten-arc-welding and shielded-metal-arc-welding. The seam weld metal was made with submerged arc welding. Fatigue crack growth rate tests were conducted using compact tension specimens in accordance with ASTM E647. Fracture toughness was evaluated through CTOD tests with three point bend specimens. The CTOD values were affected by crack orientation with respect to the rolling direction, but orientation had no influence on fatigue crack growth rates. The fatigue crack growth rates and the CTOD values decreased with decreasing test temperature.     

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 夏比（Charpy）冲击试验是评价冲击载荷下材料塑性变形和断裂过程中吸收能量的能力的试验方法。虽然试验中测定的冲击吸收功Ak值不能作为表征金属制件实际抵抗冲击载荷能力的韧性判据,但是因为其试样加工简便,试验时间短,实验数据对材料组织结构、冶金缺陷等敏感,因而成为评价金属材料冲击韧性的一种传统力学性能试验方法,被世界各国广泛采用。不同国家的冲击试验标准对试验机、试样、试验程序和试验结果的处理与修约的规定不尽相同,对日本的JIS 标准、美国的ASTM标准和中国的GB标准中关于钢产品的冲击试验规定进行比较,列举了它们之间的差异并对这些差异对试验结果的影响进行讨论。由于均源自ISO148,中国和日本的冲击试验标准对冲击试验机及其附件、冲击试样、冲击试验程序和冲击试验结果处理与修约的规定基本一致,只是日本标准对试样部分尺寸的允许偏差要求较中国严格。与日本和中国的标准相比,ASTM标准在试验机及其附件、试验程序、试样和试验结果处理与修约方面的规定存在较大差异。ASTM使用刀刃曲率半径8 mm的摆锤,同一组试样得到的冲击吸收功可能与中国标准存在差异。对试验温度的控制要求更严格,分别为规定温度的±2 ℃和±1 ℃。冲击试样取样位置和对冲击试样方向的定义也不完全相同。ASTM标准对试样尺寸的允许偏差更严格,缺口角度分别为45±2°和45±1°、缺口深度分别为2±0.15 mm和2±0.025 mm以及相邻面角度分别为90±2°和90±0167°;由此引起的冲击吸收功变化也较小。ASTM标准的试验结果处理与修约方面与中国标准也有较大区别。     

16MnR钢板低温冲击过程的声信号特性

在20℃至-55℃下对16MnR材料进行Charpy冲击试验,用声发射技术监测各温度下冲击开裂的过程。采用小波分析结合傅里叶变换的方法,得到了16MnR试样开裂过程的波形频谱特性及电压幅值,并且采用金相和SEM对冲击断口进行了组织、形貌分析。结果表明:随着温度的下降,声发射计数率、声发射能量及声发射持续时间均呈降低趋势,声信号幅值变化不大。小波分解后的d2层能量包含冲击断裂的主要能量,与冲击功的变化趋势相似,具有较强的相关性。试验结果为声发射技术监测冲击载荷作用下的材料内部结构演化提供了一个思路。     

Ductile—brittle transition of steel electron beam weld metal in small punch test

Abstract

Toughness evaluation of narrow high energy beam welds via the conventional Charpy V notch (CVN) impact test is not always successful because cracks often deviate from the fusion zone into the heat affected or unaffected base metal zones. The small punch (SP) test was applied to electron beam welds of a 490 MPa strength steel to evaluate the toughness by measuring the ductile-brittle transition temperature (DBTT). The steel was electron beam welded using various heat inputs and the welds were examined via CVN and SP tests at 40-298 K. The SP DBTTs obtained from the SP energy showed a linear correlation with the CVN DBTTs. The load-deflection curves during the SP tests and the fractography of SP tested specimens indicated the existence of ductile-brittle transitions. The results suggest that the SP test can be used to predict the DBTTs of electron beam welds, which cannot be accomplished via the conventional CVN impact test.     

Role of tandem submerged arc welding thermal cycles on properties of the heat affected zone in X80 microalloyed pipe line steel

The influence of thermal cycles on the properties of the coarse grained heat affected zone in X80 microalloyed steel has been investigated. The thermal simulated involved heating the X80 steel specimens to the peak temperature of 1400 °C, with different cooling rates. The four-wire tandem submerged arc welding process, with different heat input values, was used to generate a welded microstructure. The martensite/austenite constituent appeared in the microstructure of the heat affected zone region for all the specimens along the prior-austenite grain boundaries and between the bainitic ferrite laths. The blocky-like and stringer martensite/austenite morphology were observed in the heat affected zone region. The fractional area of M/A particles due to different cooling rate was the main factor in increasing of the hardness values in the coarse grained heat affected zone. The Charpy absorbed energy of specimens was assessed using Charpy impact testing at −50 °C. The martensite/austenite constituent's size such as mean diameter and length are important factors influencing Charpy impact properties of coarse grained heat affected zone. The micro crack nucleation may occur from M/A particles at the intersection of prior-austenite grain boundaries. Similar crack initiation sites and growth mechanism were investigated for specimens welded with different heat input values.     

An Experimental Evaluation of Material Properties and Fracture Simulation of Cryorolled 7075 Al Alloy

This work presents an experimental evaluation of yield strength, tensile strength, and impact toughness of 7075 Al alloy. The extended finite element method (XFEM) has been chosen for quasi-static crack growth simulations using Charpy impact energy as the crack growth criterion for both Bulk and ultrafine-grained (UFG) 7075 Al alloy. The 7075 Al alloy is rolled for different thickness reductions (40 and 70%) at cryogenic (liquid nitrogen) temperature, and its mechanical properties are studied by performing the tensile and Charpy impact testing. The microstructural characterization of the alloy was carried out using field emission scanning electron microscopy (FE-SEM). The rolling of the Al alloy at cryogenic temperature suppresses dynamic recovery, and dislocation cells formed during processing, transformed into fully formed ultrafine-grains (600?nm) at 70% thickness reduction. The impact energy used as the crack growth criterion under quasi-static loading condition based on the Griffith energy concept. The elastic-plastic ductile fracture simulations are performed by XFEM using ABAQUS Software (Version 6.9). For crack modeling, two different types of functions are used to model a crack based on partition of unity concept. A discontinuous function is used to model the portion behind the crack tip, whereas crack tip is modeled by near-tip asymptotic functions. This permits the crack is to be represented explicitly without meshing the crack surfaces, thus crack propagation simulations can be carried out without a need of re-meshing. Strain energy release and stress distribution ahead of the crack tip is found for some practical crack problems. The numerical examples indicate a significant improvement in crack growth properties of UFG 7075 Al alloy as compared to its bulk form due to an effective grain refinement.