Impact toughness of tungsten films deposited on martensite stainless steel

Tungsten films were deposited on stainless steel Charpy specimens by magnetron sputtering followed by electron beam heat treatment. Charpy impact tests and scanning electron microscopy were used to investigate the ductile-brittle transition behavior of the specimens. With decreasing test temperature the fracture mode was transformed from ductile to brittle for both kinds of specimens with and without W films. The data of the crack initiation energy, crack propagation energy, impact absorbing energy, fracture time and deflection as well as the fracture morphologies at test temperature of-70 ℃ show that W films can improve the impact toughness of stainless steel.     

Influence of nickel and molybdenum on the phase stability and mechanical properties of maraging steels

The effect of nickel and molybdenum concentrations on the phase transformation and mechanical properties of conventional 18Ni(350) maraging steel has been investigated. Both of these elements act as strong austenite stabilizers. When the concentration of molybdenum or nickel is greater than 7.5 or 24 wt %, respectively, the austenite phase remains stable up to room temperature. In both molybdenum- and nickel-alloyed steels, the austenite phase could be transformed to martensite by either dipping the material in liquid nitrogen or subjecting it to cold working. When 7.5 wt% Mo and 24 wt% Ni were added in combination, however, the austenite phase obtained at room temperature did not transform to martensite when liquid-nitrogen quenched or even when cold rolled to greater than 95% reduction. The aging response of these materials has also been investigated using optical, scanning electron, and scanning transmission electron microscopy.     

贝体/马氏体复相组织对低碳合金钢强韧性的影响

对低碳Mn-Cr系和低碳Mn-Si-Cr系低合金钢采用空冷和油淬方式分别处理成贝氏体/马氏体复相组织和马氏体组织,探讨了显微组织和回火温度对钢的强韧性的影响.电镜分析表明,空冷处理的低碳Mn-Cr系和低碳Mn-Si-Cr系低合金钢中的贝氏体分别为典型贝氏体和无碳化物贝氏体.Formaster-F相变仪测定表明经空冷处理后,两种钢复相组织中的贝氏体含量均约为20%.力学性能实验表明,空冷低碳Mn-Cr系合金钢在未回火状态下就具有较高的冲击韧度.低碳Mn-Si-Cr系低合金钢油淬后的低温回火脆性开始温度约为220℃,而空冷后其低温回火脆性开始温度提高至360℃以上.示波冲击实验表明,未回火状态的空冷低碳Mn-Cr系低合金钢和360℃回火后的空冷低碳Mn-Si-Cr系低合金钢具有较高的冲击韧度是由于在该状态下实验钢具有较高的裂纹扩展功所致,因此,空冷低碳Mn-Cr系合金钢可在未回火状态下使用,空冷低碳Mn-Si-Cr系低合金钢必须在回火后使用,经340-360℃回火后,空冷低碳Mn-Si-Cr系低合金钢具有较高的强韧性.     

冲击能力验证中可疑数据的分析

阐述了冲击能力验证产生可疑数据的原因，并通过试验作了验证。试验表明，由于使用的JB30B摆锤式冲击试验机在摆锤铅垂时，冲击刀刃到垂直支撑面的距离公差过小，且砧座之间跨距公差过大，造成了金属夏比能力验证在高能量级组数据出现了可疑数据的现象。就冲击试验现行的有关国家标准对这两项指标的规定作了比较与分析，提出了建议。     

Simulation Charpy impact energy of functionally graded steels by modified stress-strain curve through mechanism-based strain gradient plasticity theory

In the present work, Charpy impact energy of functionally graded steels produced by electroslag remelting composed of graded ferritic or austenitic layers in both crack divider and crack arrester configurations has been modeled by finite element method. The yield stress of each layer was related to the density of the statistically stored dislocations of that layer and assuming by Holloman relation for the corresponding stress-strain curves, tensile strengths of the constituent layers were determined via numerical method. By using load-displacement curves acquired from instrumented Charpy impact tests on primary specimens, the obtained stress-strain curves from uniaxial tensile tests were modified. The data used for each layer in finite element modeling were predicted modified stress-strain curves obtained from strain gradient plasticity theory. A relatively good agreement between experimental results and those obtained from simulation was observed.     

Investigation of the behaviour of a chopped strand mat/woven roving/foam-Klegecell composite lamination structure during Charpy testing

This paper presents the investigation of the characteristic behaviour of polymer matrix composites under Charpy impact conditions with different design configurations of the laminate structure. The aim of this study was to evaluate the capability of different lamination designs for composite materials, in term of contact load, energy absorption, deflection and damage behaviour. In this study, laminated panels were fabricated using chopped strand mat (CSM), woven roving fabric (WR) and foam-PVC Klegecell as reinforcement with a combination of epoxy or polyester resin, respectively. Structural panels of composite laminates were produced using a hand lay-up technique. Each configuration design was impact tested to failure. Finite element analyses (FEA) were employed in this study to correlate the experimental value of energy absorption with simulation results. The characteristics of different reinforcement types, matrix type, hybrid type, architecture and orientation type were studied. These characteristics need to be considered, due to their affecting the characteristic behaviour of the composite lamination structures. Based on the results, it was found that differences in configuration design of the lamination structure of the polymer matrix composites do influence the strength and weakness of the materials.     

管线钢管夏比冲击试验注意事项

结合管线钢管标准规范,分别从取样、试样加工、试验设备及试验过程等方面分析了管线钢管夏比冲击试验中可能出现的问题,并针对试验温度控制和操作过程提出了几点建议.     

Deformation and fracture of high-temperature steels at different temperatures and loading rates

Charpy impact tests were conducted at different temperatures and loading rates. Temperature dependences of the crack initiation and propagation energies were determined for carbon steel 45, steels St. 3 and 15Kh2NMFA from the load-time curves obtained with due account of the impact test results. The effect of the loading rate on the temperature dependence of the impact toughness was analyzed within the range from 1 to 4.4 m/s. __________ Translated from Problemy Prochnosti, No. 1, pp. 29–34, January–February, 2009.     

An Effect of Temperature and Notch Geometry on Correlated Toughness of a Stainless Steel

To determine the toughness of materials, Charpy V notch test has been widely used over the world. Originally, the Charpy-V or U tests were used mainly as a quality control tests. In this paper, effects of temperature and notch geometry on variation of toughness/yield stress ratio were investigated. The experimental work has been performed on austenitic stainless steel 316L using Charpy tests and carried out at temperature range from 20 ℃ to 250 ℃ on different dimension of V- and U-notch specimens. Energy of fracture was determined directly from machine tests. Furthermore, Barsoum correlation has been applied to determine toughness/yield stress ratio as function of temperature. In addition, several parameters were investigated namely specimen thickness and notch cut angles. U-notch specimen offers a high resistance comparatively to the V-notch and that toughness depends on temper situation and orientation of notch relative to the rolling direction.     

Impact fracture of a ferritic steel in the lower shelf regime

This paper reports the results of a systematic investigation on the fracture of Charpy-V notch A508 steel specimens, tested in the lower shelf regime. The fracture energy has been determined for quasi-static, standard Charpy and one-point-bend impact. The results show a general trend for the fracture energy to increase with the loading rate, at the lower temperature (–160 °C). At this temperature, the roughness of the fracture surface increases markedly with the loading rate. The fractographic analysis shows the presence of 3–4 cleavage initiation sites situated at 100–800 m from the crack front, irrespective of the loading rate. Numerous cleavage microcracks are observed underneath the main fracture plane. The statistical analysis shows that the length distribution of the microcracks is adequately described by Weibull statistics. It is also found that the number of microcracks increases with the loading rate. It is suggested that the larger number of microcracks is responsible for the observed increased roughness and energy dissipation.