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Li Lin - One of the best experts on this subject based on the ideXlab platform.

  • Recrystallization behavior of ultra-high strength low carbon micro-alloyed Complex Phase Steel
    Materials Science and Technology, 2011
    Co-Authors: Li Lin
    Abstract:

    The dynamic and static recrystallization behavior of a 0.11%(in mass) Ti-microalloyed Complex Phase Steel(CP Steel) were studied by single-hit hot compression and double-hit isothermal hot compression tests.The influences of different deforming temperature,strain rate,strain and different holding times on microstructure transformation were investigated.It was found that the high contain of micro-alloyed element Ti improved the deformation activation energy of dynamic and static recrystallization.The precipitations was fine Ti(CN) located at the grain boundary and the austenitic matrix,and the size of precipitations is about 50nm-200nm.The calculated kinetic results and microstructures show that the no-recrystallization temperature(Tnr) is about 950℃.Based on the stress-strain curves,a kinetic equation was estabilished to predict the static recrystallization fraction of Ti-microalloyed Steel.

  • Flow Behavior and Dynamic Recrystallization Model for Ultra-high-strength Low Carbon Micro-alloyed Complex Phase Steel During Hot Deformation
    Hot Working Technology, 2010
    Co-Authors: Li Lin
    Abstract:

    The deformation behavior and evolution process of dynamic recrystallization for ultra-high-strength low carbon micro-alloyed Complex Phase Steel(CP Steel) were studied by isothermal compression test in the temperature range of 900～1150 ℃ and the strain rate range of 0.1～10 s-1.The effects of thermodynamic parameters on flow stress and grain size were analyzed.A constitutive relationship was proposed based on the Jonas equation.It is found that the high micro-alloyed elements of Ti restain the recrystallization behavior and improve apparent activity energy(439.09 kJ/mol).The calculation results of the proposed model well agree with the experimental data.Therefore,the proposed model and results can lay the foundation of the quality control and process design of the rolling process for CP Steel.

Dirk Mohr - One of the best experts on this subject based on the ideXlab platform.

  • stress state and strain rate dependent ductile fracture of dual and Complex Phase Steel
    Mechanics of Materials, 2018
    Co-Authors: Borja Erice, Christian C Roth, Dirk Mohr
    Abstract:

    Abstract A comprehensive combined hybrid numerical-experimental program is executed on three advanced high strength Steels (DP980, CP980 and CP1180) with the objective of validating (1) the hypothesis of a positive strain rate effect on the ductility under biaxial tension, as well as (2) the Hosford–Coulomb model assumptions with regards to the Lode parameter and stress triaxiality dependency of fracture initiation. The basic low strain rate testing program included punch, notched tension, central hole tension and smiley shear experiments. In addition, intermediate and high strain rate SHPB experiments are carried out to characterize the effect of strain rate. A non-associated quadratic plasticity model with Swift-Voce hardening and Johnson–Cook type of strain rate and temperature dependency is employed to model the large deformation response. The fracture model parameters are identified based on the loading paths to fracture extracted from numerical simulations with fine solid element meshes up to the point of fracture initiation in the experiments. It is found that the simple three-parameter Hosford–Coulomb model can describe the pronounced stress state effect on the strain to fracture for all materials. The results for notched tension also confirm that the ductility increases as function of the loading velocity for biaxial loading.

Mei Zhang - One of the best experts on this subject based on the ideXlab platform.

  • Forming Performance of 800MPa Grade Advanced High Strength Steels
    Applied Mechanics and Materials, 2013
    Co-Authors: Mei Zhang, Yu Xiang Ning, Jun Zhang, Tao Wang
    Abstract:

    800MPa grade Advanced High Strength Steels (AHSS), including Complex Phase Steel CP800 and Ferrite-Bainite Steel FB800, were chosen to test the forming performance in different test conditions and compared with the reference traditional high strength low alloy (HSLA) Steels HR700LA. Tensile test, hole expansion (HE) test, and HAT shape stamping test were taken to investigate the forming performance of the materials. Test results indicated that the studied 800MPa grade AHSS showed a better strength ductility balance compared with the reference Steel. Among all the Steels researched, FB800 showed the best hole expansion ratio (HER), and CP800 the worst. Springback angles of AHSS after HAT shape stamping tests were markedly smaller than those of HR700LA Steels, though the springback angles of HR700LA decreased continuously with blank holding force (BHF) increasing. Steel FB800, CP800S and CP800B had much better shape stability compared with Steels HR700LA. AHSS showed much smaller springback behavior under the same stamping condition, especially for Steels CP800-B, FB800-2 and FB800-1. When increasing the BHF to 100KN, AHSS showed the largest springback deformation. Among the three kinds of CP800 Steels researched, Steel CP800-B indicated outstanding springback restrain trend in BHF further increasing attempt. So, springback behavior could be restricted obviously by using a larger BHF in AHSS CP800B forming operations.

  • recrystallization behavior of 0 11 ti added Complex Phase Steel during hot compression
    Materials Science Forum, 2013
    Co-Authors: Mei Zhang, Chao Bin Huang, Wei Ming Zeng
    Abstract:

    Double-hit isothermal deformation and multi-pass continuous cooling hot compression tests were carried out to study the recrystallization behavior of a 0.11 (in mass %) Ti-microalloyed Complex Phase (CP) Steel. The influence of different deforming temperatures and holding times on microstructure evolution was investigated. The results showed that a pronounced austenite grain refinement after appropriate recrystallization process has been detected. The grain size decreases continuously from 176μm to 20μm after four-pass compression. It has been verified that non-crystallization temperature (Tnr) of the experimental Steel is about 975°C under the deformation conditions. Based on the stress-strain curves, a kinetic method was established to predict the non-recrystallization temperature of the studied Steel during nonisothermal continuous hot deformation.

  • Thermodynamic Calculation and Experimental Study on Complex Phase Steel
    Advanced Materials Research, 2013
    Co-Authors: Jun Jie Zhao, Na Qiong Zhu, Mei Zhang
    Abstract:

    Using Thermo-calc software, transformation points as well as bainite starting temperature of the CP Steel studied in the present work were calculated. Based on the measured CCT curve, the Steels were treated at different conditions using Gleeble-3500 thermal simulation tester. To study the effects of cooling conditions on mechanical properties and microstructure of the Steels after austenization, a combination of tensile tests at room temperature, SEM and TEM techniques was applied. Results showed that effective design of chemical composition and heat treatments can be achieved using Thermo-Calc software. The CP Steel with carbon equivalent of 0.43% achieved B/M Complex microstructure when austenized at 975 °C and followed by isothermal holding at bainitic transformation temperature of 450 °C. The tensile strength is 843.29 MPa and the elongation is 14.28%.

  • Recrystallization Behavior of 0.11% Ti-Added Complex Phase Steel during Hot Compression
    Materials Science Forum, 2013
    Co-Authors: Mei Zhang, Chao Bin Huang, Wei Ming Zeng
    Abstract:

    Double-hit isothermal deformation and multi-pass continuous cooling hot compression tests were carried out to study the recrystallization behavior of a 0.11 (in mass %) Ti-microalloyed Complex Phase (CP) Steel. The influence of different deforming temperatures and holding times on microstructure evolution was investigated. The results showed that a pronounced austenite grain refinement after appropriate recrystallization process has been detected. The grain size decreases continuously from 176μm to 20μm after four-pass compression. It has been verified that non-crystallization temperature (Tnr) of the experimental Steel is about 975°C under the deformation conditions. Based on the stress-strain curves, a kinetic method was established to predict the non-recrystallization temperature of the studied Steel during nonisothermal continuous hot deformation.

  • Weldability of Ti-Microalloyed Advanced High Strength Steel CP 800
    Advanced Materials Research, 2013
    Co-Authors: Mei Zhang, Chao Bin Huang, Ping Fang
    Abstract:

    Complex Phase Steel CP 800, a kind of advanced high strength Steel (AHSS), exhibited quite high carbon equivalent (CE) which was a detrimental factor for weldability of Steels. Thus the weldability of CP 800 Steels containing (in wt%) 0.06C-0.45Si-1.71Mn-0.11Ti was extensively studied. Mechanical properties and impact toughness of butt joint, the welding crack susceptibility of weld and heat-affected-zone (HAZ) for tee joint, Control Thermal Severity (CTS) welded joint, and 60°Y-groove butt joint were inspected after gas shielded arc welding tests. The impact toughness was larger than 27J either at room temperature (RT) or at -20°C, indicating good impact toughness of the weld of the Steel. In addition, welding crack susceptibility tests revealed that the weldments were free of surface crack and other imperfection, showed fairly good weldability. In application, the longitudinal control arm of automobile made of this Steel exhibited excellent fatigue and durability performance.

Zhi Xiao - One of the best experts on this subject based on the ideXlab platform.

  • Effects of pre-strain and annealing on the fatigue properties of Complex Phase Steel CP800
    International Journal of Fatigue, 2020
    Co-Authors: Haofei Sun, Wei Kai, Xujing Yang, Zhi Xiao
    Abstract:

    Abstract This work was to experimentally explore the fatigue properties under the conditions of pre-strain and annealing for CP800. Meanwhile, the elongation of grains caused by pre-strain and the increase content of bainite and martensite caused by annealing were observed by using optical microscopy (OM) and scanning electron microscopy (SEM), respectively. An effective pre-strain range was found to increase the yield and tensile strengths by dislocation strengthening. Besides, the pre-strain presents a negative effect on fatigue life, while the fatigue life can be increased by annealing treatment. It is confirmed that the combined effect of the large pre-strain and annealing treatment leads to cyclic hardening fracture. Furthermore, two kinds of failure modes caused by surface defects and inclusions were revealed by using SEM. Eventually, the fatigue life can be well predicted with a model based on strain energy method.

Matthias Militzer - One of the best experts on this subject based on the ideXlab platform.

  • Microstructure evolution model for hot strip rolling of Nb–Mo microalloyed Complex Phase Steel
    Materials Science and Technology, 2009
    Co-Authors: S. Sarkar, Matthias Militzer
    Abstract:

    AbstractA microstructure model for hot strip rolling of an Nb–Mo microalloyed Complex Phase Steel has been proposed. The constitutive behaviour of austenite is described by the Kocks–Mecking model. The static softening kinetics is simulated by a combined recovery recrystallisation model using the law of mixtures. Ferrite transformation start is modelled with an approach that considers the early growth of corner nucleated ferrite. Bainite start is related to a critical driving pressure. Both ferrite and bainite reactions are described using the Johnson–Mehl–Avrami–Kolmogorov (JMAK) approach in combination with the additivity rule. The martensite fraction is empirically related to the carbon enrichment in austenite and is, thus, a function of the ferrite fraction formed in the final microstructure. Precipitation strengthening during coiling is simulated with a modified Shercliff–Ashby model. The microstructure models for these metallurgical phenomena have been validated with experimental studies of laborato...