Enhancing Strain Capacity by the Introduction of Pearlite in Bainite and Polygonal Ferrite Dual-Phase Pipeline Steel

In this study the strain capacity and work-hardening behavior of bainite (B), bainite + polygonal ferrite (B + PF), and bainite + polygonal ferrite + pearlite (B + PF + P) microstructures are compared. The work hardening exponent (n), instantaneous work hardening value (ni), and differential Crussard-Jaoul (DC-J) analysis were used to analyze the deformation behavior. The best comprehensive mechanical properties were obtained by the introduction of the pearlite phase in B + PF dualphase with the tensile strength of 586 MPa and total elongation of 31.0%. The additional pearlite phase adjusted the strain distribution, which increased the initial work hardening exponent and then maintained the entire plastic deformation at a high level, thus delayed necking. The introduction of pearlite reduced the risk of micro-void initiation combined with the high frequency of high angle grain boundaries (HAGBs) in triple-phase steel, which led to a low crack propagation rate.

Prediction of the Work-Hardening Exponent for 3104 Aluminum Sheets with Different Grain Sizes

A practical approach to predict the yield strength and work-hardening exponent (n value) to evaluate the deep-drawing performance of annealed 3104 aluminum sheets is presented in the present work by only measuring and analyzing the grain size of the sheet. The various grain sizes were obtained through the different annealing treatment and then the evolution of the n value under different strains and the yield strength of annealed 3104 aluminum sheet were evaluated. Results showed that the n value and yield strength vary greatly with the grain size. A mathematical model relating grain size d, work-hardening exponent n, target strain ε, and yield strength Rp0.2 was developed in the present work. Within the studied grain size range d (12–29 μm), the n value generally increased with d in a strain-dependent manner, such that n = 0.1875 − 85.03 × exp [ − d / 1.94 ] when the ε was less than 0.5%, but n = 0.3 − 0.15 d − 1 / 2 when the ε was greater than 2%. On the other hand, the n value was found to depend on the target strain ε as n = 0.276 − A 1 × exp [ − e / 1.0435 ] , where A1 varies with d and its value is in the range of 0.132–0.364. In addition, the relationship between Rp0.2 and d followed the Hall-Petch equation ( R p 0.2 = 36.273 + 139.8 × d − 1 / 2 ).

The Study on the Effects of Physical Factors on the Machinability of GDL-4 Tool Steel

GDL-4 is a new kind of tool steel, but the machinability was the key factor for the application of it. In order to improve the machinability of GDL-4 tool steel, the factors influencing the machinability, such as the thermal property, work hardening exponent, carbides were studied comparing with M2 in this paper. The results show that under the same cutting condition, the thermal property is the key factor which makes the machinability of GDL-4 worse, and Si is the key element affecting the thermal property.

Catalogue of maximum crack opening stress for CC(T) specimen assuming large strain condition

In this paper, values for the maximum opening crack stress and its distance from crack tip are determined for various elastic-plastic materials for centre cracked plate in tension (CC(T) specimen) are presented. Influences of yield strength, the work-hardening exponent and the crack length on the maximum opening stress were tested. The author has provided some comments and suggestions about modelling FEM assuming large strain formulation.

Influence of Volume Fraction of Bainite on Mechanical Properties of X80 Pipeline Steel with Excellent Deformability

The pipeline steel with excellent deformability with ferrite and bainite dual-phase microstructure are obtained by inter-critically accelerating cooling method, aiming to get good deformation capability of avoiding failure from the geological disasters such as landslides and earthquake. The influence of volume fraction of bainite on the mechanical properties of dual-phase pipeline steels was investigated by means of microscopic analysis method and mechanical properties testing. The results indicated that both yield strength and ultimate tensile strength of the steels increase almost linearly with the increasing volume fraction of bainite, while ductility, work hardening exponent and impact absorption energy decrease. When the volume fraction of bainite is about 50%, the yield strength, the yield strength/tensile strength ratio (Y/T), work hardening exponent, uniform elongation and impact absorption energy of X80 pipeline steels with excellent deformability is 665MPa, 0.8, 0.12, 8% and 245J respectively.

Catalogue of the J-Q trajectories for CC(T) and SEN(T) specimens in tension

In this paper a short theoretical background about elastic-plastic fracture mechanics is presented and the O’Dowd-Shih theory is discussed. Using FEM, the values of the Q-stress determined for various elastic-plastic materials for two specimens in tension — SEN(T) specimen and CC(T) specimen are presented. The influence of geometry of the specimen, crack length and material properties (work-hardening exponent and yield stress) on the Q-parameter are tested. The numerical results were approximated by closed form formulas. The results are summarized in a catalogue of the Q-stress value, which may be used in engineering analysis for calculation of the real fracture toughness and the stress distribution near crack tip.

Time-dependent deformation behavior of interfacial intermetallic compound layers in electronic solder joints

Using nanoindentation, this study develops the criteria to evaluate the creep performance of the intermetallic compounds (IMCs) formed at the interface of microelectronic solder joints. Regardless of crystal structure and melting point, the creep stress exponent (X), one of the parameters determining creep resistance, is in good agreement with tendencies of the work-hardening exponent (n) and also the ratio of yield stress (Y) to Young's modulus (E), which reveals the ability against plastic deformation.