16MnR 钢弹塑性断裂韧性Ji的韧脆转变温度特性

研完了16MnR钢弹塑性断裂韧性Ji的韧脆转变温度特性。结果表明,断裂韧性Ji的韧脆转变非常明显,其韧脆转变温度大大低于夏比冲击韧性的韧脆转变温度。根据试验结果,建议采用以弹塑性断裂韧性Ji的韧脆转变温度曲线为基础来确定受静载荷低温设备的最低使用温度。     

A simplified method for charpy impact testing near liquid helium temperature

A simplified method of examining the impact properties of materials below 5 K is proposed.     

锰、铜含量对锌铝合金组织与性能的影响

研究了不同含量的锰和铜对锌铝合金的组织与力学性能的影响。结果表明：锰和铜含量较低时,对合金的力学性能无显著影响;随着锰和铜含量的升高,合金的硬度大幅提高,冲击韧度基本不变。     

THE LOCAL FRACTURE STRESS AS A FRACTURE TOUGHNESS PARAMETER TO CHARACTERIZE AN HETEROGENEOUS WELD ZONE

Abstract— The toughnesses of specimens of heterogeneous multipass weldments with various ratios of weld metal to base metal can be characterized by a single value of the local fracture stress within a narrow scatter band. Relationships were found between the normalized value of this parameter and the lower bound values of fracture toughness parameters such as the fracture load, the energy absorbed, and the crack opening displacement. These facts indicate that using such a toughness parameter, it is possible to assess a heterogeneous multipass weldment by a single value; within a narrow scatter band. Further experiments indicate that this parameter could be measured on specimens simulating the microstructure of the weakest zone where cleavage cracking is initiated.     

Mechanical properties and fracture behavior of high-strength steels

Typical thicknesses of high-strength steels (HSS) sheets used in the car industry are inapplicable for standardized testing procedures. The aim of this study is to propose an appropriate methodology for testing and comparing of thin HSS sheets. Microstructures were observed by means of light and scanning electron microscopy. The modified Charpy impact tests and fracture toughness tests were used in order to compare the fracture properties of three different HSS sheets (Docol 1200 M, Multiphase 1200 and BTR 165). Ductile-to-brittle transition curves and tearing resistance (J − Δa) curves were measured. From the fracture toughness linked to the specimen thicknesses the value of fracture toughness K_Ic was estimated. Fractographic analysis of broken specimens has revealed that due to the fine microstructure of mixed ferrite-martensite fracture mechanism remains ductile even at low temperatures (down to −100°C). __________ Translated from Problemy Prochnosti, No. 1, pp. 155–158, January–February, 2008.     

Evaluation of dynamic fracture toughness KId by Hopkinson pressure bar loaded instrumented Charpy impact test

A novel method for measuring the dynamic fracture toughness, K_Id, using a Hopkinson pressure bar loaded instrumented Charpy impact test is presented in this paper. The stress intensity factor dynamic response curve (K_I(t)−t) for a fatigue-precracked Charpy specimen is evaluated by means of an approximate formula. The onset time of crack initiation is experimentally detected using the strain gauge method. The value of K_Id is determined from the critical dynamic stress intensity factor at crack initiation. A K_Id value for a high-strength steel is obtained using this method at a stress-intensity-factor rate () greater than 10⁶ MPa .     

拉伸、冲击和硬度试验方法国际标准的修订和问题

介绍了ISO/TC 164技术委员会对于拉伸和冲击试验方法标准的修订及执行中涉及的问题;另外还介绍了硬度试验方法标准主要的修订内容和原因以及仪器化压痕试验方法测试拉伸性能的研究工作。     

激光熔覆与等离子熔覆的镍基合金熔覆层组织和性能对比

在低碳钢等廉价金属表面熔覆一层高强高韧或高耐蚀性的熔覆层可极大提高材料的使用性能及利用率,但是不同熔覆方法对熔覆层组织和性能可能会造成不同影响。利用激光熔覆和等离子熔覆技术分别在Q345基材表面熔覆镍基合金粉末,获得具有一定厚度的熔覆层。通过对2种熔覆方法获得的熔覆层进行微观组织、冲击韧性以及耐磨损性能对比分析可知,激光熔覆镍基合金的熔覆层组织细密,冲击吸收功略低于等离子熔覆试样,但稳定性优于等离子熔覆层,耐磨损性能及表面硬度明显优于等离子熔覆层。     

舰船结构钢的夏比冲击韧性与断口形貌

论述了从夏比冲击韧性分解出来的断裂扩展功与断口形貌的关系，指出冶金因素对夏比冲击韧性α＿ｋ值和扩展功的影响不完全是一致的，提出采用α＿ｋ，值和断口纤维率作为韧性指标的互补性，建议在我国的舰船结构钢韧性指标中增加断口纤维率的要求。     

Influence of Long-Term Operation on the Toughness of 17GS Pipeline Steel

We study the influence of long-term (30 yr) operation on the levels of toughness and brittle-fracture resistance of 17GS pipeline steel in the presence of notches and cracklike defects. We present the results of low-temperature testing (13–293 K) of specially prepared cylindrical specimens for uniaxial tension. The specimens were cut out from the base metal of an archival (reference) pipe and a pipe taken after operation for 30 yr. It was discovered that long-term operation does not affect the microscopic cleavage resistance R_mc (minimum brittle-fracture stress) of steel and has practically no influence on the strain-hardening exponent. The application of the local approach to the analysis of fracture demonstrates that the toughness of steel after operation decreases mainly as a result of the increase in the yield limit. It is shown that a small (15%) increment of the yield limit increases the critical temperature of the lower Charpy shelf by 40 K and may be responsible for a twofold drop of the crack resistance of steel.     

An efficient method for estimating from sparse data the parameters of the impact energy variation in the ductile-brittle transition region

An efficient method is proposed for estimating from sparse data the parameters of the systematic variation of the Charpy impact energy in the ductile-brittle transition region of low-carbon weld steels. The parameter estimates are practically unbiased and with a very good precision even in the case of very large scatter of the absorbed impact energy. Furthermore, the parameter estimates determining the shape of the transition curve are not affected by its location along the temperature axis. The method is robust regarding the temperature corresponding to a specified impact energy level. Thus, for different type of scatter of the impact toughness and different lengths of the scatter intervals, the estimates of the temperature corresponding to a specified impact energy vary in narrow limits. The transition temperature corresponding to a specified impact energy level is estimated with a very good precision, which is important for quantifying the deterioration of properties due to embrittlement.     

Long-term service effect on the toughness of pipeline steel 17GS

A transit oil pipeline, 720 mm in diameter, 334 km in length, and made of steel 17GS, after 30 years of service was twice non-destructively tested with intelligent Pipeline Inspection Gauges (PIGs). Two segments of this pipeline were cut in order to investigate the steel structure, composition, and mechanical properties and to compare these properties with those of `archive' material. Metallographic and microprobe analyses revealed no significant difference between the `archive' and `aged' materials. Specimens for testing tensile mechanical properties, for fatigue-crack growth rate measurements, and for a Charpy test were used. All those specimens were fabricated from both the base and weld metal in longitudinal and circumferential directions. At room temperature, the ultimate strength of the aged steel was found to be 5% higher than that of the `archive' material, whereas the yield point was 18% higher for the aged material. Charpy energy changed more significantly; decreasing by approximately 40% at room temperature. In addition to conventional mechanical properties, new characteristics such as `microcleavage stress' R _MC (minimum brittle fracture stress) and the toughness index K _T were determined. It has been found that a long period of operation does not affect the values of the steel microcleavage stress R _MC and does not influence the hardening exponent significantly. The use of the local approach to fracture has shown that an increase in yield stress is the main cause of the decrease in its toughness after long-term service. It is shown that a minor (15%) increase in the yield stress results in a rise (by 40°) in the Charpy transition temperature and may cause a twofold reduction in the fracture toughness K _IC.     

Galvanising and galvannealing behaviour of B added TiNb IF high strength steel

Abstract

Solid solution strengthened steels stabilised with Ti and Nb are known to have poor galvanising and galvannealing properties. When these steels are alloyed with boron to prevent cold work embrittlement, the selective oxidation processes are influenced by the presence of B. The continuous galvannealing process has therefore been simulated in a laboratory in order to study the effect of B on the fundamental surface and interface processes that control the wetting of the surface by liquid Zn, the inhibition layer formation, and the Fe-Zn reaction.     

FRACTURE TOUGHNESS TESTING OF WELD METAL: RESULTS OF A EUROPEAN ROUND ROBIN

Abstract— This paper presents the results of a collaborative project on fracture mechanics toughness testing of weldments, carried out by twelve European laboratories. Each collaborator was asked to measure the fracture toughness of a steel weldment, notched in the weld metal. Tests were carried out at two temperatures, using three test geometries, in accordance with a standard procedure. Results are reported in terms of the effect of temperature and specimen geometry on fracture toughness (mean value and standard deviation), the extent of inter-laboratory reproducibility of results and the effect of "invalid" results on the measured value of fracture toughness. As a result of the study, it is recommended that a number of the current validity criteria in BS7448:Part 1 should be relaxed in Part 2 when applied to tests on weld metal.     

Influence of carbides morphology on fracture toughness of cast steel G200CrMoNi4-3-3

We analyze the influence of small modification of chemical composition of G200CrMoNi4-3-3 cast steel on the morphology of carbides and on material crack resistance. Using the Termo-Calc software the volume fraction of carbide phase was determined and the results correlated with microstructure observations. Crack resistance of cast steel was determined using SENB specimens and finding critical values of stress intensity factor K_Q. Metallographic and fractographic observations of fracture surfaces allowed identifying the mechanism of cracking. __________ Translated from Problemy Prochnosti, No. 1, pp. 137–140, January–February, 2008.     

燃烧合成TiC-Ni材料的室温及高温力学性能

研究了燃烧合成新工艺制备的TiC-Ni金属陶瓷材料的力学性能。结果表明:TiC-Ni金属陶瓷硬度值和抗弯强度在Ni含量为20 wt%时达到最高值,断裂韧性在Ni含量为30 wt%时达到最大值,TiC-Ni材料在室温下具有无宏观塑性变形的脆性断裂特征。随着温度的升高,TiC-Ni材料弯曲强度下降,温度超过1000℃开始发生塑性变形。其强度与传统方法生产的相近成分材料相比比较接近。