Temperature Laser Scanning Confocal Microscopy Research Articles

In-situ observation of the incipient melting of borides and its effect on the hot-workability of Ni-based superalloys

The excellent creep properties of advanced wrought Ni-based superalloys are achieved by adding grain boundary strengthening elements such as B and C. Their low solubility in the γ matrix may promote precipitation of micrometre-sized borides and carbides which potentially deteriorate hot-workability, e.g. through incipient melting. However, their incipient melting has not yet been directly linked to a decrease in hot-workability in Ni-based superalloys. Here, we study the susceptibility of two Ni-based superalloy variants with main differences in B and C contents (high B & C variant with>triple B and C contents) to incipient melting and its effect on hot-workability. We show that incipient melting causes severe intergranular cracking at low strains during compression at 1200 °C in the high B & C variant only. Compression to higher strains separates grain boundaries fully, partially pulverising the macroscopic specimen. Metallographic specimens already show incipient melting at heating rates they experience when put into a pre-heated furnace. During subsequent cooling, the melt re-solidifies and forms lamellar structures consisting of various phases rich in Mo-Cr-B, Zr, and Ti, the constituents of M3B2 and MC. In-situ observations using a customised high temperature confocal laser scanning microscope set-up unambiguously confirmed the origin of these lamellar structures. We demonstrate for the first time directly the constituent liquation of M3B2. This liquation is assumed to be aided by the partial dissolution of adjacent MC carbides into the melt. These results will help to improve thermo-mechanical simulations and microstructural control during industrial processing of advanced wrought superalloy parts.

Study on microsegregation and homogenization process of a novel nickel-based wrought superalloy

In this paper, the as-cast microstructure, microsegregation, precipitates and suitable homogenization process of a novel Ni-based wrought superalloy prepared by vacuum induction melting (VIM) + vacuum arc remelting (VAR) were investigated by optical microscope (OM), scanning electron microscope (SEM), electron probe microanalysis (EPMA), differential scanning calorimetry (DSC), high temperature confocal laser scanning microscope (HT-CLSM) and thermal simulation compression. The results show that severe element segregation exists in the ingot. Nb, Ti and Al are mainly segregated in the interdendritic region, while W is mainly segregated in the dendrite arm. The precipitates in the alloy mainly include non-uniform γ′ strengthening phase, coarse (γ + γ′) eutectic phase and MC carbide, among which, the redissolution temperature range of γ′ phase is 1060–1220 °C; the (γ + γ′) eutectic phase can be redissolved obviously above 1180 °C but melted into liquid at 1250 °C; the redissolution temperature range of MC carbide is 1349–1358 °C, exceeding the solidus temperature of the alloy. After homogenization at 1220 °C/10 h, all the γ′ phase and most of the (γ + γ′) eutectic phase can be redissolved, and the element segregation can be significantly alleviated, moreover, the hot deformation resistance of the alloy is lower and the dynamic recrystallization (DRX) degree is higher, indicating that 1220 °C/10 h is an ideal single-stage homogenization process.

On the solid-state dendritic growth of [formula omitted] carbide at interfaces in an austenitic system

Solid-state growth of M7C3 carbide at different interfaces in an austenitic Ni–Cr–Fe alloy (Alloy 600) was studied in-situ by high temperature confocal laser scanning microscopy during continuous cooling from 1140 °C. The carbide develops a dendritic morphology and grows laterally across the free surface via a diffusion-assisted mechanism. Primary dendrite arms can extend beyond 100 μm, with some dendrites also developing secondary arms with spacing approximately 3.0 μm. By using focused ion beam tomography, some of the surface carbides are found to be directly connected to dendritic carbide at grain boundaries in the bulk confirming they originated from the same nucleus. Matrix deformation is induced in the vicinity of a carbide during growth. This work provides significant insight into the important topic of carbide development by a rare combination of both in-situ microscopy and a 3D tomographic technique; the new knowledge discovered is expected to apply to other austenitic systems.

Analysis on phase nucleation in Sn-Ni peritectic alloy combining confocal laser scanning in-situ observation and differential scanning calorimetry

The analysis of the phase nucleation requires not only the in-situ images but also the accurate nucleation information. Thus, the nucleation of both the primary Ni3Sn2 and peritectic Ni3Sn4 phases were studied during peritectic solidification of Sn-Ni alloy using the high temperature confocal laser scanning microscope (HT-CLSM) and differential scanning calorimetry (DSC). The results by both methods confirm that the nucleation undercooling ∆T of the solid phases decrease with increasing cooling rates, which is demonstrated to be caused by higher concentration difference at larger cooling rates. Besides, the freezing range of the alloy is also found to decrease with the increase in cooling rate. However, the nucleation undercooling of the peritectic Ni3Sn4 phase determined by HT-CLSM is larger than that by DSC at each cooling rate. This is attributed to the slower capture of peritectic reaction when using HT-CLSM. Furthermore, the nucleation of peritectic Ni3Sn4 phase is confirmed to be controlled by the heterogeneous nucleation on primary Ni3Sn2 phase by comparison between the HT-CLSM observation and DSC result. In addition, the wetting angles for heterogeneous nucleation of both phases which are important parameters in analyzing the nucleation of solid phases were determined through the entropy of solidification data from the DSC results. The smaller wetting angle of peritectic Ni3Sn4 phase as compared with that of the primary Ni3Sn2 phase further proving the smaller nucleation undercooling of Ni3Sn4 phase during solidification.

Influence of Cooling Parameters on the Microstructure and Primary Carbide Precipitation in GCr15 Steel

With the high temperature confocal laser scanning microscope applied, the effect of cooling rate, temperature interval, and cooling mechanism on the solidification microstructure and primary carbide participation in GCr15 steel are investigated. The solute distribution in interdendritic segregation and participation carbide are analyzed by electron probe microanalysis. The results show that solute concentrate is low in the dendrite zone but it increases clearly in the segregation zone. The carbon concentration in the precipitation can reach 6.49%, which means the primary carbide is M3C. In the heating process, the segregation zone and carbide participation melt first before it reaches the solidus temperature. During the solidification stage, the microstructure is refined and the size of primary carbide is reduced with a higher cooling rate, but the number density of primary carbide is increased. Moreover, it is found that the microstructure is formed in the earlier solidification, before the temperature declines to 1673 K. While the primary carbide participates in the later cooling stage and the transition temperature for the primary carbide is 1503 K. In addition, the primary carbide size can be reduced with the cooling rate larger than 300 K min−1 in the subsequent cooling stage.

In-situ observation of grain growth and phase transformation in weld zone of Ti-6Al-4V titanium alloy by laser welding with filler wire

Through in situ observation at high temperature confocal laser scanning microscope, the microstructures and phase transformation of Ti-6Al-4V titanium alloy welded joint by laser welding with filler wire during heating, heat preservation and cooling process in simulating welding thermal cycle were studied. When the weld microstructure was heated to 380 °C, obvious grain growth was observed. After heating to 1 050 °C, weld microstructures were mostly composed of coarse β-columnar grains. During the heat preservation process of the weld metal, it could be found that the β phase boundary moved slowly. In the cooling process of weld microstructures, with the increase of the cooling rate, the transition temperature for new phase precipitation decreased gradually, and that for ending the precipitation increased gradually. The microstructures after cooling to room temperature at a rate of 0.5 °C/s and 5 °C s−1 were composed of α phases. At 20 °C s−1, acicular α′ martensite appeared in the microstructures. At 80 °C s−1, precipitated phases were all composed of acicular α′ martensite.The Ti-6Al-4V titanium alloy weld microstructure by laser welding with filler wire is completely hexagonal close packed (HCP) crystal structure.The hardness of the weld microstructures was improved with the cooling rate getting faster.

Dendrite growth in nickel-based superalloy with in-situ observation by high temperature confocal laser scanning microscopy and numerical simulation

Dendrite growth of nickel-based superalloy was investigated by using high temperature confocal laser scanning microscopy (HT-CLSM) and numerical simulation method. The influence of cooling rate on the evolution of dendrite was discussed through in-situ observation experiments and simulation cases. The results indicate that secondaryand tertiary dendrites grow luxuriantly at the higher cooling rate and primary dendrite present well growth tendency at the lower cooling rate. The variation of secondary dendrite arm spacing (SDAS) with cooling rate was also analyzed, and the results show that SDAS decrease exponentially with the increasing of cooling rate, which is helpful for designing process parameters to obtain desirable dendrites.

Direct Observation of Austenite and Pearlite Formation in Thermally Simulated Coarse Grain Heat-Affected Zone of Pearlite Railway Steel

In the present study, coarse grain heat affected zone (CGHAZ) of the pearlite railway steel was thermally simulated at different cooling rates ranging from 1 to 4 °C/s to in–situ observe the austenite and pearlite formation by high temperature laser scanning confocal microscopy (HT–LSCM). During heating, austenite nucleation was started at 811 °C at fast heating rate of 9.1 °C/s. Pearlite was completely decomposed into austenite in 21 s at 1005 °C. At peak temperature of 1300 °C, austenite was composed of two microstructural compositions, i.e., high-carbon austenite and low-carbon austenite. Homogenization of austenite and formation of grain boundaries were continued even during cooling when the temperature was above the pearlite transformation. During cooling, Low-carbon austenite has increased the pearlite transformation by providing additional nucleation sites. By increasing the cooling rate from 1 to 4 °C/s, the pearlite transformation temperature was reducing, pearlite growth rate was increasing, and pearlite interlamellar spacing was becoming narrow, respectively. Mathematical interpretation of pearlite growth rate was developed that gives true changing behavior of pearlite growth rate with the varying cooling rate. Present study provides direct observation and unique quantitative information of austenite and pearlite formation in CGHAZ in pearlite railway steel.

In-situ real time observation of martensite transformation in duplex fcc+hcp cobalt based entropic alloys

Athermal martensite transformation in duplex fcc+hcp Co-based entropic alloys during continuous cooling was investigated in-situ. The real time observation was carried out using high temperature confocal laser scanning microscopy (HT-CLSM). This technique enables the detection of the athermal fcc to hcp transformation in entropic alloys, which is not sensitively detected by conventional thermomechanical methods e.g. dilatometer. The martensite fraction increases with increasing martensite starting temperature, and vice versa. Meanwhile, the martensite starting temperature decreases with the increasing grain size. In addition, the morphology and nucleation sites for martensite formation is discussed. This is the first time the that HT-CLSM technique is utilized in the field of entropic alloys. This in-situ observation technique coupled with thermodynamic calculations may help in the design of entropic alloys through the tailoring of the desired microstructure.

Study of the kinetics of austenite grain growth by dynamic Ti-rich and Nb-rich carbonitride dissolution in HSLA steel: In-situ observation and modeling

The effect of carbonitrides on the growth of austenite grains in high-strength low-alloy (HSLA) steel was investigated through microstructure analysis and high-resolution dilatometry. The austenite grain growth at various temperatures was measured in situ using high temperature laser scanning confocal microscopy. Two kinds of precipitates with different morphologies containing large amounts of Ti and Nb were observed in the austenitized samples at different temperatures. The smaller Nb-rich spherical carbonitrides dissolved at the higher temperature, while the lager Ti-rich rectangular carbonitrides have a higher thermal stability and can pin at the austenite grain boundary. This study reveals that the dissolution of Nb in austenite causes the rapid growth of austenite grains and slows down the ferrite phase transition, which is beneficial to the formation of bainite. A kinetic model of austenite growth considering the dynamic dissolution of different types of carbonitrides is proposed. The results of the model show the same overall trend as the experimental results, and the individual differences can be explained. The proposed model can be used to predict the austenite grain size during the austenitizing process of HSLA steel and can reflect the austenite grain change throughout the process more continuously.

Experimental Study of High Temperature Phase Equilibria in the Iron-Rich Part of the Fe-P and Fe-C-P Systems

During the solidification of steel, phosphorus strongly segregates in the interdendritic liquid phase. In the continuous casting process, even low levels of P may have a detrimental effect on the final product quality. However, phosphorus is partly added up to 0.10 wt pct to improve the mechanical properties of advanced steel grades nowadays, e.g., High-Strength Interstitial-Free (HSIF). To provide new experimental data for the development of thermodynamic databases and solidification models for P alloyed steel grades, phase equilibria in the Fe-P and Fe-C-P key systems were studied up to 1550 °C using differential scanning calorimetry (DSC) and high temperature laser scanning confocal microscopy (HT-LSCM). Special focus was placed on solid/liquid equilibrium temperatures in the Fe-rich part of the binary Fe-P system between 0.025 and 9 wt pct P. In the ternary system, three isoplethal sections with 0.10 mass pct. P, 0.20 mass pct. C and constant mass percent ratio P/C of 2 were investigated. In the latter section, HT-LSCM observations were linked with DSC signals to optically identify present phase stabilities. Particularly at [pct P] < 1, significant differences between performed measurements and calculated phase equilibrium temperatures using thermodynamic assessments from the literature were identified. In all ternary sections, the experiments indicate less influence of P on the hypo-peritectic range compared to the thermodynamic calculations.

Study on primary carbides precipitation in H13 tool steel regarding cooling rate during solidification

This study aims to investigate the primary carbides precipitation in H13 steel solidified at relatively high cooling rates, ranging from 300 to 6,000 °Cmin−1, based on in situ observations with a high temperature confocal laser scanning microscope. In the cooling rate range investigated, the solidification microstructure becomes more refined as cooling rate increases and the relationship between the secondary dendrite arm spacing (SDAS), λ2, and cooling rate, $${\dot T}$$ , can be expressed as $${\lambda _2} = 128.45{{\dot T}^{ - 0.124}}$$ . Regardless of cooling rates, two kinds of primary carbides, i.e., the Mo-Cr-rich and V-rich carbides, are precipitated along the interdendritic region and most of them are the Mo-Cr-rich carbides. The morphology of Mo-Cr-rich carbide is not obviously influenced by the cooling rate, but that of V-rich carbide is obviously affected. The increasing cooling rate markedly refines the primary carbides and reduces their volume fractions, but their precipitations cannot be inhibited even when the cooling rate is increased to 6,000 °C·min−1. Besides, the segregation ratios (SRs) of the carbides forming elements are not obviously affected by the cooling rate. However, compared with the conventionally cast ingot, the SDAS and primary carbides in the steel solidified at the investigated cooling rates are much finer, morphologies of the carbides have changed significantly, and SRs of the carbides forming elements are markedly greater. The variation of primary carbide characteristics with cooling rate is mainly due to the change in SDAS.

Dissolution kinetics of arbitrarily-shaped alumina in oxide melt: An integration of phase-field modelling and real-time observation study

Abstract A feasibility study of utilizing a phase-field model considering the convection effect is performed in this work to investigate the dissolution kinetics of arbitrarily-shaped alumina particle in the oxide melt. The established model has been benchmarked by high temperature confocal laser scanning microscope (HT-CLSM) to observe the polycrystalline sapphire dissolution in multicomponent oxide melt. The effects of alumina morphology and temperature on the dissolution kinetics were studied quantitatively. It is for the first time found that the dissolution of irregular alumina particle in oxide melt shows a double-fold smooth anisotropy behavior. The dissolution rate of alumina particle is governed by the interface interactions rather than the self-diffusion of dissolved component in oxide melt. Increasing the temperature, the interfacial mobility coefficient increases, and the effect of alumina particle shape on the dissolution rate decreases. The temperature variation has a minor influence on the shape evolution of alumina during dissolution process. The convection intensity affects both the dissolution rate and shape evolution of alumina particle. An increased convection intensity increases the dissolution rate. As the convection partially affects the contact area of alumina particle with oxide melt, a decreased alumina particle curvature increases the dissolution rate. When the convection affects the whole contact area of alumina particle with oxide melt, the contact area plays an important role on the dissolution rate. The obtained methodology can be applied to investigate a general dissolution phenomenon in the high temperature oxide melt in materials science.

Coupling Effect of Prior Austenite Grain Size and Inclusion Characteristics on Acicular Ferrite Formation in Ti-Zr Deoxidized Low Carbon Steel

The coupling effect of prior austenite grain size and inclusion characteristics on acicular ferrite (AF) formation was investigated in Ti-Zr deoxidized low carbon steel by utilizing the high temperature confocal laser scanning microscope (HT-CLSM), optical microscope (OM), and scanning electron microscope (SEM) equipped with energy-dispersive spectrometer (EDS). The results indicated that with the target heating temperature increased from 1100 °C to 1350 °C, the average size of prior austenite grain varied from 58.22 to 237.40 μm, and the average grain size increased rapidly when the temperature was above 1200 °C. For inclusion characteristics, different target heating temperatures had no obvious effect on inclusion types, but had a great influence on the average size and number density of each, especially for the intragranular effective inclusions. In addition, as the increase of target heating temperature, the types of microstructure were identical, but both AF volume fraction and AF relative nucleation ability increased first and then decreased. When the target heating temperature of sample was 1250 °C, the AF volume fraction reached the maximum of 49.48 pct. However, the AF relative nucleation ability reached the maximum of 474.5 at the target heating temperature 1200 °C, at this time, the AF volume fraction was 47.92 pct, only 1.56 pct smaller than that at 1250 °C. Therefore, considering the AF volume fraction and AF relative nucleation ability, the optimal target heating temperature for AF formation in this study was 1200 °C, and the corresponding prior austenite grain size was 69.58 μm.

In-situ analysis of incipient melting of Al2Cu in a novel high strength Al-Cu casting alloy using laser scanning confocal microscopy

Incipient melting in a novel Al-Cu alloy was investigated. Precipitation hardenable aluminum alloys are typically heat treated to further enhance their in-service properties. However, over heating during heat treatment leads to incipient melting thereby compromising mechanical properties. Advanced microscopy and real time imaging techniques such as a high temperature laser scanning confocal microscopy (LSCM) enable a novel direct in-situ observation of incipient melting and phase transformations. In this research, isothermal analysis was carried out using LSCM at elevated temperatures to analyze incipient melting with time. The predominant phase of this alloy was Al2Cu in both blocky and eutectic morphologies. The results showed that incipient melting was accompanied by a clustering of liquid micro-droplets followed by a complete melting of Al2Cu at approximately 548 °C. The in-situ analysis also revealed that eutectic Al-Al2Cu particles were found to melt prior to blocky Al2Cu particles. Further, localized melting was also observed to occur at a random sequence for eutectic Al-Al2Cu. As a result of incipient melting, the microstructure consisted of a proliferation of defects such as brittle ultra-fine eutectic clusters and porosity. The mechanisms of incipient melting were discussed using interfacial energies, diffusion of Cu, and particle coarsening.

In situ observation of high temperature microstructure and reverted austenite evolution in 13Cr supermartensitic stainless steel

In situ observation of high-temperature microstructure in 13Cr supermartensitic stainless steel was investigated by the high temperature laser scanning confocal microscopy (LSCM), and the effects of tempering temperature and tempering cooling rate on the morphology and contents of reverted austenite were characterized via transmission electron microscopy (TEM), x-ray diffraction (XRD) and electron backscattered diffraction (EBSD). The results indicate that only α phase appeared in the XRD diffraction pattern after quenching at 1050 °C, there was no retained austenite in the quenched microstructure. The martensite transformation starting temperature (Ms) was around 177.6 °C according to the results of LSCM. The amount of reverted austenite increased first and then decreased with the tempering temperature increasing, and it reached a maximum value when the sample tempered at 620 °C. With the cooling rate increasing, the amount of reverted austenite showed a sharp decrease after tempering at 620 °C. The reverted austenite precipitated on martensite laths, blocks and prior austenite grain boundaries, while the misorientation angles ranged from 0° to 60° in the tempered martensite structure.

In-situ observations and modeling of metadynamic recrystallization in 300M steel

The metadynamic recrystallization (MDRX) behaviors and microstructure evolution of 300 M steel are studied by hot compression experiments and high temperature laser scanning confocal microscopy (HTLSCM) experiments. The effects of insulation temperature, pre-strain rate and holding time on the MDRX behaviors are discussed in detail. Based on the statistical results of the microstructure evolution, the MDRX kinetics model and recrystallization (RX) grain size model of 300 M steel are established, respectively. It can be confirmed from the in-situ observations that strain-induced boundary migration mechanism and curvature-driven grain boundary migration mechanism are the main MDRX mechanisms of 300 M steel. The MDRX develops rapidly under the high temperature or low pre-strain rate. The insulation temperature has a more important effect on the MDRX rate. The RX grain size increases with the increased insulation temperature, pre-strain rate and holding time. Compared to the pre-strain rate, the effects of insulation temperature on the maximum MDRX fraction and RX grain size are negligible. Comparisons between the experimental and predicted results verify that the proposed MDRX kinetics models and RX grain size model can quantificationally reveal the MDRX behaviors of 300 M steel well.

In Situ Observation of Acicular Ferrite Nucleation and Growth at Different Cooling Rate in Ti-Zr Deoxidized Steel

The effects of cooling rate on acicular ferrite (AF) nucleation, growth, and inclusion characteristics in Ti-Zr deoxidation steel were studied by utilizing the high temperature confocal laser scanning microscope (HT-CLSM). The results indicated that with the increase of cooling rate, the ferrite start nucleation temperature decreased, and the difference of first nucleation temperature between AF and ferrite side plate (FSP) reduced. When the cooling rate increased to 10.0 °C/s, AF and FSP simultaneously nucleated at 564.5 °C. In addition, the AF actual growth rate rose with the increase of cooling rate and reached 30.13 µm/s at 10.0 °C/s cooling rate. The AF ratio in microstructure increased first and then decreased with the cooling rate increase and was up to the maximum 45.83 pct at 1.0 °C/s cooling rate. For inclusion characteristics, cooling rates had no obvious effect on inclusion types, but had a great influence on inclusions size distribution. With the cooling rate increase, the inclusion average diameter reduced, and diminished to 1.39 µm at 10.0 °C/s cooling rate. Finally, the AF nucleation on the Ti-Zr-Mn-O-S + TiN inclusion could be explained by the low lattice misfit between ferrite and TiN that precipitated on the Ti-Zr-Mn-O-S inclusion surface.

In-situ observations and modeling of static recrystallization in 300 M steel

The study of static recrystallization (SRX) has been widely concerned for its importance in regulating the microstructure and mechanical properties of deformed materials. In the paper, the effects of SRX on the flow behaviors of 300 M steel are investigated by thermal compression experiments. The SRX mechanism of 300 M steel is investigated by high temperature laser scanning confocal microscopy (HTLSCM) setup. The variations in the flow behaviors and microstructure under different experimental conditions are discussed in detail. Also, the relationships between microstructure evolution and mechanical properties are analyzed. The SRX mechanism is detected by the analysis of microstructure. According to the statistical results of microstructure, the SRX kinetics models and the average recrystallization (RX) grain size model are proposed. It can be found that the flow stress increases with the increased strain rate and reduced deformation temperature. The yield stress is affected by both the softening mechanisms of static recovery and SRX. The main SRX mechanism of 300 M steel is strain-induced boundary migration (SIBM). Compared to the pre-strain rate, the insulation temperature has a more significant effect on the SRX rate, maximum SRX volume fraction and average RX grain size. And the effects of pre-strain rate on the RX grain size are negligible at low pre-strain rate. The comparison between the calculated and experimental results is consistent, which implies that the established models can describe the SRX process accurately. Besides, compared to the softening volume fraction calculated based on the stress-strain curves, the SRX volume fraction calculated based on the statistic results of microstructure can reflect the SRX process more precisely, which indicates the effectiveness of the research method used in the paper.

In situ observation on microstructure evolution of 22MnB5 in hot stamping process

High temperature confocal laser scanning microscopy (CLSM) was used to investigate the microstructure evolution of high-strength boron steel 22MnB5 during hot stamping. The experimental results show that it is complete austenitized at temperatures about 810 °C during the heating process. Most of the initial austenite grain size is small and locally coarse. At 920 °C to 1000 °C, the phenomenon of B remelted and solidified was observed which played a very good pinning role at the austenite grain boundary, preventing coarsening of austenite grains. The segregation of B and the addition of Mn result in a significant reduction in both the minimum boron reverse melt content and the final solidification temperature. In the continuous cooling stage, martensitic transformation occurs at the cooling rate of 60 °C/s, and the martensite start point is 400 °C and martensite finish point is 280 °C. A large number of bursts are concentrated from 380 °C to 330 °C. There are two main forms of martensitic transformation: first, martensite begins to appear at the coarse austenite grain boundary, and grows transgranularly. Second, the new martensite laths starts from the previously formed laths and grows at a certain angle into the austenite grains. The main factor in the increase of martensite in continuous cooling is the formation of variable temperature martensite rather than the growth of martensite laths. At the cooling rate of 20 °C/s, the bainite and ferrite transformation appeared and the conversion temperature of bainite was about 600 °C. The cooling speed has a great influence on the performance of the 22MnB5 hot stamping component. The room temperature microhardness at cooling rates of 5 °C/s, 20 °C/s, and 60 °C/s was 194 HV, 243 HV, and 430 HV, respectively. Therefore, ensuring sufficient cooling rate is a key condition for obtaining ultra-high strength hot stamping components.