•In this paper, the corrosion of hot stamping water channel was studied systematically. The experiment was carried out by immersing in deionized water. The corrosion behavior and mechanism were ...studied by using different stress, hardness and different heat treatment process. Obtained 3 kinds of hardness, applied stress from 50MPa to 700MPa, got different corrosion morphologies. Used corrosion area and pitting aspect ratio to measure corrosion degree. Analyzed corrosion mechanism from microstructure and carbide type distribution. The pitting formation model of Cr-Mo-V alloys was discussed.
Adopted immersion method to systematically study the corrosion behavior of SDCM steel for hot stamping. For specimens with the same hardness of 54 HRC, the corrosion resistance of 1030 °C quenched samples were better than that of 1060 °C quenched samples. After 1030 °C quenched, the hardness was adjusted to 50 HRC, 52 HRC and 54 HRC by tempering process, and then applied 50 MPa tensile stress to these three kinds of hardness samples. With the increase of hardness, the corrosion area decreased from 21.82% to 13.47%, and the number of large pits decreased from 27 to 7 on the area of 40 mm2. Stress has an important effect on corrosion. When the loading stress was less than 100 MPa, the corrosion area/pitting numbers increased with the increase of stress, but the aspect ratio decreased, and the decreasing range was large. When the loading stress was more than 100 MPa, the corrosion area/pitting number decreased with the increase of stress, the aspect ratio also decreased, but the decreasing range was smooth, which was mainly related to the concentration of adsorbed dissolved oxygen; finally, we discussed the initiation and growth behavior of pitting pits and then schematically described its model.
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•The steel 4Cr2Mo2V studied in this paper is a new steel developed by our research group, it has been widely used in hot stamping plants.•Now the service life of materials is studied ...through isothermal fatigue, and the best life model is obtained for better die design.
In this paper, the isothermal fatigue behavior and life of 4Cr2Mo2V steel for new hot stamping die were studied. Axial tension compression symmetric fatigue tests with different strains were carried out at 300 ℃. When the half strain amplitude was from 0.3% to 0.9%, the response stress continued to soften, and the decline rate of response stress gradually increased, but when the half strain amplitude was 0.9%, the material would fail early. Used Coffin-Manson (C-M), Basquin-Coffin-Manson (BCM) and original Ostergren models to predict the life, the prediction effect was not good. Box-Cox variable transformation was carried out on the cycle life, and then the modified Ostergren model could accurately predict the life. The life prediction model was also established by fitting the response stress curve, but the appropriate d value needs to be set to accurately simulate the life.
Abstract
For 4Cr2Mo2V hot stamping die steel, the isothermal fatigue test was suspended at different cycles, and the stress-relief annealing was carried out
in situ
. After annealing, the fatigue ...tests were continued. The stress-relief annealing was carried out at 30%, 50% and 70% of the cycle life when the total strain amplitude was 0.5%, and the fatigue life was increased by 30.27%, 23.84% and 10.24% respectively. On the basis of Basquin-Coffin-Manson life prediction model, by adding the influence of stress-relief annealing on life, obtained the stress-relief annealing life prediction model. The dislocation density, microstructure and pole figure were analyzed by TEM and XRD to explore the mechanism of stress-relief annealing on prolonging fatigue life. After stress-relief annealing, the full width at half maximum (FWHM) decreased, and the dislocations originally piled up at the grain boundary moved into the grain, delayed the time of dislocation cell or wall formation. At the same time, it could also eliminate the trend of consistent orientation of most grains in the fatigue process. This is the main reason why stress-relief annealing prolongs fatigue life.
The service life of hot work die steel is significantly influenced by its microstructure and thermal fatigue properties. This paper explores the impact of deep cryogenic treatment (DCT) on H13 hot ...work die steel's microstructural evolution and mechanical as well as thermal fatigue properties. The results demonstrate that a portion of unstable retained austenite transforms into martensite during deep cryogenic treatment and numerous finely dispersed carbides precipitate from the matrix, thereby enhancing hardness. Analysis of the average crack length and distribution of thermal fatigue test samples reveals that the average crack length and crack density of DCT-treated samples are lower than those of non-DCT-treated samples. Thermal fatigue cracks in the specimens primarily originated from trigeminal grain boundaries and the carbides are found at the crack tips. DCT facilitates the precipitation of fine and dispersed carbides, imparting a robust pinning effect on boundary migration and thereby impeding the initiation and propagation of thermal fatigue cracks. Furthermore, deep cryogenic treatment results in a reduction in the number of M23C6 type carbides with large particles and an increase in smaller M6C type carbides during the thermal fatigue test. This indicates a positive influence on the carbide distribution and further contributes to the improved thermal fatigue resistance of the hot work die steel.
In this paper, the alternate immersion corrosion test of Cr-Mo-V series SDCM steel for hot stamping was carried out, and different stresses were loaded with self-made fixture. The results shown that ...regardless of hardness and stress, the corrosion mode of the material is uniform corrosion. Stress could significantly increase the corrosion rate, with lower hardness and higher corrosion rate. Because of the existence of Corrosion Removal Layer (CRL), the maximum corrosion pit depth would be reduced. The maximum corrosion pit depth and Corrosion Pit density (CPD, ρv) were used to describe the degree of corrosion damage. From low to high hardness, the CPD ρv and corrosion resistance increased gradually. With the increased of tempering temperature, the hardness decreased, and the percentage of carbide area in the field of view increased from 16.36% to 24.32%. The irregular spherical carbide M23(C, N)6 rich in Cr coarsens and consumes Cr element in the material, which lead to the decrease of corrosion resistance. Through the polarization curve of the dynamic potential, we known that the current density was increased with the hardness decreased, from 28.53 μA/mm2 to 40.93 μA/mm2.
To obtain excellent mechanical properties from large cross-sections of plastic mould steel (SDP1), we conducted multi-directional forging (MDF) to control the microstructure of ingots. To investigate ...the microstructural evolution of SDP1 steel during MDF, we performed hot forging at 1150 °C using a THP01–500A hydraulic press. The dimensions of the specimens were Φ38 mm × 80 mm. The microstructure of the specimens after forging was observed under a metallographic microscope. Furthermore, the results of the finite element method (FEM) simulations were employed to improve the quality of the forgings. The predicted results agreed well with the experimental ones, indicating that FEM is effective for analysing microstructural evolution during MDF. Thus, MDF for large cross-sections of SDP1 steel (Φ1000 mm × 2200 mm) was simulated. The results showed that the average grain size of SDP1 steel at the core of an ingot after MDF ranged from 40.6 to 43.3 μm. Although this was slightly higher than the grain size of the sample after traditional upsetting and stretching forging (TUSF) (35.7–46.0 μm), the microstructure of the SDP1 steel sample after MDF was more uniform than that after TUSF. Compared with TUSF, MDF not only refines the grain size but also improves the microstructure uniformity of the sample.
Background
Nowadays, liver cancer is the second leading cause of cancer death in the world. Therefore, it is very important to understand tumor progression and evaluate tumor microcirculation for ...treatment strategy.
Objective
To explore the application of MRI quantitative hemodynamic parameter histogram analysis in the development of a rabbit VX2 liver cancer.
Methods
Five New Zealand white rabbits were randomly selected each time for liver Dynamic contrast- enhanced MR perfusion (DCE-MRI) imaging at the 1st, 2nd, 3rd, 4th and 5th weeks after liver tumor implantation. The dynamic changes and the significant differences between the tumor volume and related derived parameters during tumor progression were compared and analyzed.
Results
In the development of the VX2 liver cancer model, the tumor volume between the end of 1 ~ 5w group (
F
= 44.11;
P =
0.000) was statistically significant (
P
< 0.01), and the significant differences were found between the 5th week and the 1st, 2nd, 3rd, 4th week, the 4th week and the 1st, 2nd week, the 3rd week and the 5th week (
P
< 0.01), respectively. The skewness and kurtosis of the volume transport constant (Ktrans) value, the maximum, 90th percentile and skewness of the reverse reflux rate constant (Kep) value, and the skewness, kurtosis, 75th and 90th percentiles of the plasma fraction (Vp) value were statistically significant (
P
< 0.05) at the end of each week. The 10th, 25th, 50th percentiles of the Kep value, the 10th, 25th percentiles of the extracellular space (EES) fraction (Ve) value, the 10th percentile of the Vp value was positively correlated with tumor volume (
r
> 0,
P
< 0.05). The expression of α-smooth muscle actin (α-SMA) was negatively correlated with the mean, 75th percentile of the Ktrans value, the 50th, 75th percentiles of the Kep value, the mean, minimum of the Vp value (
r <
0,
P
<0.05). It was positively correlated with the skewness, kurtosis of the Ktrans value, the skewness of the Vp value (
r
> 0,
P
<0.05).
Conclusions
MRI quantitative hemodynamic parameter histogram analysis can reflect the progress of the rabbit VX2 liver cancer. In particular, the skewness, kurtosis and percentiles of Ktrans, Kep and Vp can reflect the microvascular information and can be used as biomarkers to assess the development of Hepatocellular Carcinoma(HCC).
The hysteresis loops, stress and strain behavior, lifetime behavior and fracture characteristic of 4Cr5MoSiV1 hot work die steel at a wide range of mechanical strain amplitudes (from 0.5% to 1.3%) ...during the in‐phase (IP) and out‐of‐phase (OP) thermomechanical fatigue (TMF) tests cycling from 400 °C to 700 °C under full reverse strain‐controlled condition were investigated. Stress‐mechanical strain hysteresis loops of 4Cr5MoSiV1 steel are asymmetric, and stress reduction appears at high‐temperature half cycles owing to a decrease in strength with increasing temperature. 4Cr5MoSiV1 steel always exhibits continuous cyclic softening for both types of TMF tests, and the cyclic softening rate is larger in OP loading condition. OP TMF life of 4Cr5MoSiV1 steel is approximately 60% of IP TMF life at the same mechanical strain amplitude and maximum temperature. Lifetime determined and predicted in both types of TMF tests is adequately described by the Ostergren model. Fracture surfaces under IP TMF loading display the striation and tear ridge, showing quasi‐cleavage characteristics, and the cracks are less but longer. However, fracture surfaces under OP TMF loading mainly display the striation and dimple characteristics, and the cracks are more and shorter.
The hysteresis loops, stress and strain behavior, lifetime behavior and fracture characteristic of 4Cr5MoSiV1 hot work die steel at a wide range of mechanical strain amplitudes (from 0.5% to 1.3%) ...during the in-phase (IP) and out-of-phase (OP) thermomechanical fatigue (TMF) tests cycling from 400 °C to 700 °C under full reverse strain-controlled condition were investigated. Stress-mechanical strain hysteresis loops of 4Cr5MoSiV1 steel are asymmetric, and stress reduction appears at high-temperature half cycles owing to a decrease in strength with increasing temperature. 4Cr5MoSiV1 steel always exhibits continuous cyclic softening for both types of TMF tests, and the cyclic softening rate is larger in OP loading condition. OP TMF life of 4Cr5MoSiV1 steel is approximately 60% of IP TMF life at the same mechanical strain amplitude and maximum temperature. Lifetime determined and predicted in both types of TMF tests is adequately described by the Ostergren model. Fracture surfaces under IP TMF loading display the striation and tear ridge, showing quasi-cleavage characteristics, and the cracks are less but longer. However, fracture surfaces under OP TMF loading mainly display the striation and dimple characteristics, and the cracks are more and shorter.
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