共查询到20条相似文献,搜索用时 46 毫秒
1.
By means of interrupted torsion tests, the kinetics of metadynamic recrystallization (MDRX) were studied in a Mo, a Nb, and
a Ti microalloyed steel at temperatures ranging from 850 °C to 1000 °C and strain rates from 0.02 to 2 s1. Quenches were also performed after full MDRX. In contrast to the case of static recrystallization (SRX), the kinetics of
MDRX are shown to be highly sensitive to a change of an order of magnitude in strain rate and are relatively insensitive to
temperature changes within the range of values applicable to industrial hot-rolling practice. A similar algebraic dependence
of the MDRX grain size on strain rate and temperature was found in the three steels. The kinetics of MDRX were slower in the
Nb than in the Mo steel, and those of the Ti steel were slower than in the Nb and Mo steels. Above 900 °C and 950 °C, the
retardation of MDRX in the Nb and Ti steels, respectively, is due to solute drag. Models predicting the start time for Nb
and Ti carbonitride precipitation showed that MDRX is delayed below these temperatures by this mechanism. Comparison of the
MDRX and precipitation start times in the Nb steel indicated that a temperature of “no-MDRX” could not be defined, in contrast
to the well-definedT
nr (no recrystallization temperature) of SRX. By means of torsion simulations composed of multiple interruptions, it is shown
that MDRX is retarded decreasingly as the accumulated strain is increased. This appears to be due to the promotion of precipitate
coarsening by the continuing deformation. 相似文献
2.
The microstructural evolution during the hot rolling of coarse grain sized austenite has been modeled considering all the microstructural mechanisms (dynamic, static and metadynamic recrystallization, strain induced precipitation) that can take place during an industrial TSDR production of three Nb microalloyed steels. Based on the results obtained from the model, processing maps have been drawn for 0.02%, 0.035% and 0.05% Nb microalloyed steels. Optimum processing conditions to exploit all the benefits of the Nb microalloying have been defined considering a final gauge thickness range between 1.5 and 12.65 mm. In addition, and facing the difficulties present in the production of thick hot strip, several alternative thermomechanical schedules are proposed, which would originate microstructures with a suitable combination of homogeneity and retained strain prior to transformation. 相似文献
3.
Prediction of Rolling Load, Recrystallization Kinetics, and Microstructure During Hot Strip Rolling 总被引:1,自引:0,他引:1
The recrystallization kinetics and grain size models were developed for the C Mn and niobium containing steels to describe the metallurgical phenomenon such as softening, grain growth, and strain accumulation. Based on the recrystallization kinetics equations, the mean flow stress and the rolling load of each pass were predicted and the optimum rolling schedule was proposed for hot strip rolling. The austenite grain refinement is associated with the addition of niobium, the decrease of starting temperature of finish rolling, and the reduction of finished thickness. The mean flow stress curve with a continuous rising characteristic can be usually observed in the finish rolling of niobium containing steel, which is formed as a result of the heavy incomplete softening and strain accumulation. The predicted rolling loads are in good agreement with the measured ones. 相似文献
4.
Militzer M. Hawbolt E. B. Meadowcroft T. R. 《Metallurgical and Materials Transactions A》2000,31(4):1247-1259
The microstructural evolution during hot-strip rolling has been investigated in four commercial high-strength low-alloy (HSLA)
steels and compared to that of a plain, low-carbon steel. The recrystallization rates decrease as the Nb microalloying content
increases, leading to an increased potential to accumulate retained strain during the final rolling passes. The final microstructure
and properties of the hot band primarily depend on the austenite decomposition and precipitation during run-out table cooling
and coiling. A combined transformation-ferrite-grain-size model, which was developed for plain, low-carbon steels, can be
applied to HSLA steels with some minor modifications. The effect of rolling under no-recrystallization conditions (controlled
rolling) on the transformation kinetics and ferrite grain refinement has been evaluated for the Nb-containing steels. Precipitation
of carbides, nitrides, and/or carbonitrides takes place primarily during coiling, and particle coarsening controls the associated
strengthening effect. The microstructural model has been verified by comparison to structures produced in industrial coil
samples. 相似文献
5.
Medium carbon V-N treated steel grade applied for long products and small drop forged parts investigated in a state of incomplete solution of V(C,N) precipitates. Activation energy changes investigated in the 850–1200°C temperature range and 0.6–30 s?1 strain rate range is revealed to be temperature dependent. Calculated for σp flow stress value this energy in some cases expresses a combination of various processes. It is found that DRX starts well below ?p. Softening during a short interpass time is caused by dynamic recrystallization DRX during forming and is followed by metadynamic recrystallization MDRX and static recrystallization SRX. At longer interpass times softening progress is hindered by precipitation. 相似文献
6.
Twinning induced plasticity (TWIP) steels, which rely on high Mn contents to promote twinning as the deformation mechanism, exhibit high ultimate strengths together with outstanding combinations of ultimate strength and ductility. In terms of mechanical properties, one of the most important microstructural features is grain size. The knowledge of the kinetics of recrystallization mechanisms, i.e., dynamic recrystallization (DRX) and static recrystallization (SRX), can be used in order to control the grain size of the final product by a proper rolling schedule design. The focus of this work is the characterization of the DRX kinetics of two TWIP steels. The basic composition of the steels is Fe–21Mn–0.4C–1.5Al–1.5Si, and one of them is further alloyed with 0.12% V. With this objective, compression tests were carried out at 900, 1000, and 1100°C and strain rates ranging from 1 × 10?1 s?1 to 1 × 10?4 s?1. Furthermore, metallographic observation by optical microscopy (OM) was done to assess the evolution of grain size for the different deformation conditions. According to the results, the existence of V in the composition does not affect the hot flow behavior of the steel, although recrystallization fraction and recrystallized grain size decrease for the V‐containing steel. 相似文献
7.
The dynamic recrystallization (DRX) and static recrystallization (SRX) behaviour of coarse-grained aus- tenite in a Nb-V-Ti microalloyed steel were studied by using a Gleeble thermomechanical simulator. Continuous and interrupted compression tests of coarse-grained austenite were performed in the temperature range of 1000-1 150 ℃ at a strain rate of 0. 1- 5 s 1. The peak and critical strains for the onset of DRX were identified with strain hardening rate analysis, and the ratio of critical strain to peak strain was found to be consistent with the one reported for fine- grained austenite. An equation of the time for 50% softening was proposed by considering the activation energy of steel without microalloying elements and the solute drag effect of microalloying elements. Strain-induced precipitation may not take place at the deformation temperature above 1000 ℃, which indicates that SRX of coarse-grained aus- tenite is mainly retarded by coarse grain size and Nb in solution during rough rolling. 相似文献
8.
Effect of prestrain and deformation temperature on the recrystallization behavior of steels microalloyed with niobium 总被引:1,自引:0,他引:1
The evolution of microstructure during the hot working of steels microalloyed with Nb is governed by the recrystallization
kinetics of austenite and the recrystallization-precipitation interaction. The present study focuses on the effects of prestrain
and deformation temperature on the rectrystallization behavior in these steels. The extent of recrystallization is characterized
by a softening parameter calculated from a series of interrupted plane strain compression tests carried out at different deformation
temperatures and strain levels. The results indicate that at low temperatures, softening is caused by static recovery, while
at higher temperatures, static recrystallization is the predominant mechanism. The recrystallization-stop temperature (T
5pct) and the recrystallization-limit temperature (T
95pct), marking the beginning and end of recrystallization, respectively, are determined as a function of strain. In order to achieve
a homogeneous microstructure, finish rolling should be carried out outside the window of partial recrystallization (T
5pct<T<T
95pct), as determined in this study. The Nb(CN) precipitation kinetics have been calculated using a model proposed in an earlier
work, and these results are used to estimate the precipitate pinning force under the given processing conditions. Based on
these estimations, a criterion has been proposed to predict the onset of recrystallization. The predicted results are found
to be in reasonably good agreement with the experimental measurements. 相似文献
9.
Detailed knowledge of the material behaviour during austenite decomposition is of great importance for the development of new strategies in hot strip rolling, like direct and hot charging or ferritic rolling, as well as for the development of new steel grades. Especially the influence on flow curves, precipitation behaviour and microstructure in the hot strip is relevant. Two steels were investigated with regard to their softening behaviour in ferrite, ferriteaustenite and austenite region. An Avrami type modelling approach, based on the experimental softening results and the microstructural investigation was applied to model the softening in the two‐phase‐region. Thus the quantitative prediction of the softening can be found as a function of temperature, strain rate and interpass time. 相似文献
10.
Nb对C-Si-Mn-Cr双相钢相变规律、组织和性能的影响 总被引:4,自引:0,他引:4
根据C Si Mn Cr和C Si Mn Cr Nb实验钢的相变规律,在实验室进行了控轧控冷实验研究,分析了微合金元素Nb对高强度热轧双相钢相变规律、组织和性能的影响。实验结果表明,Nb可显著推迟铁素体和珠光体转变,并显著降低铁素体开始转变温度,但对铁素体终止转变温度和贝氏体转变温度区间基本没有影响。经Nb微合金化后,实验钢的屈服强度和抗拉强度增幅均在100 MPa以上,屈服强度的增幅高于抗拉强度,且在强度大幅度升高的同时,伸长率下降并不明显,表明Nb的细晶强化作用对提高中温卷取热轧双相钢强度级别的效果明显。 相似文献
11.
Effect of molybdenum,niobium, and vanadium on static recovery and recrystallization and on solute strengthening in microalloyed steels 总被引:4,自引:0,他引:4
H. L. Andrade M. G. Akben J. J. Jonas 《Metallurgical and Materials Transactions A》1983,14(10):1967-1977
The effect of molybdenum, niobium, and vanadium on the occurrence of static recovery and recrystallization after high temperature
deformation was investigated in a series of microalloyed steels. The steels had a base composition of 0.05 pct C and 1.40
pct Mn. To this, single additions of 0.30 pct Mo, 0.035 pct Nb, and 0.115 pct V were made. Interrupted hot compression tests
were performed at 900 and 1000 °C, and at a constant true strain rate of 2 s-1. The load-free time was decreased from 5000 s to 50 ms, and the degree of static softening during this period was determined.
Both graphite and glass were used as lubricants. Percent softeningvs delay time curves are presented and the retarding effect of molybdenum, niobium, and vanadium addition on the rate of static
recovery and recrystallization is discussed. The greatest solute retardation of static recovery and recrystallization is produced
by niobium addition, followed by that of molybdenum, vanadium leading to the smallest delay. Although the rank order of this
effect is the same as found under dynamic softening conditions, the relative contribution of niobium is more profound for
the static condition. The solute strengthening attributable to each element was also assessed, and found to follow the same
order as for the recovery and recrystallization results. At 900 °C, the onset of the static precipitation of Nb (CN) was detected
at approximately 10 seconds, somewhat earlier than previously reported.
Formerly Graduate Student at McGill University, Montreal, Quebec. 相似文献
12.
C. L. Miao C. J. Shang H. S. Zurob G. D. Zhang S. V. Subramanian 《Metallurgical and Materials Transactions A》2012,43(2):665-676
Through a series of experiments conducted on three kinds of high Mn steels with different Nb content, including stress relaxation
tests, physical metallurgical modeling, and observation of prior austenite grains and precipitates, the effect of Nb on recrystallization
and precipitation behaviors were investigated. The results indicate the existence of a novel deformation temperature range
for grain refinement resulting from complete static recrystallization (SRX) in high Mn, high Nb steel, whereas slow SRX kinetics
can be accelerated by a finer initial grain size. In this deformation temperature range, the effect of precipitation is too
weak to prohibit SRX nucleation efficiently, but solute drag is still large enough to slow down growth rate. As a consequence,
shorter incubation and homogeneous recrystallized nucleation can be realized at relative low temperature, and the coarsening
rate of grains is much slower because of the high solute drag effect in the rolling of low C high Mn, high Nb line pipe steel. 相似文献
13.
Gholam Reza Ebrahimi Amir Momeni Mohammad Jahazi Philippe Bocher 《Metallurgical and Materials Transactions A》2014,45(4):2219-2231
The influence of precipitation on the kinetics of static and dynamic recrystallization (DRX) was investigated in AISI 403 and 403Nb martensitic stainless steels. Hot compression tests were performed in the temperature range of 1073 K to 1473 K (800 °C to 1200 °C) and strain rates of 0.001 and 0.1 s?1 to study DRX and precipitation behaviors. In parallel, stress relaxation tests were conducted with pre-strains of 0.1, 0.15, 0.2, and 0.25, a strain rate of 0.1 s?1, and in the 1073 K to 1473 K (800 °C to 1200 °C) temperature range to study the kinetics of precipitation and recrystallization. Samples of hot compression and stress relaxation tests were quenched and the evolution of the microstructure was examined using optical and scanning electron microscopy. The results indicated that DRX interacts with dynamic precipitation (DP) over the temperature range of 1173 K to 1273 K (900 °C to 1000 °C). Hot compression testing results, confirmed by EBSD analysis, indicated that partial DRX occurs before precipitation in 403Nb, at 1073 K (800 °C). By contrast, no DRX was observed in 403 steel. At higher temperatures, i.e., over 1273 K (1000 °C), DRX preceded DP in both steels. Increasing the strain rate raised the temperature range of interaction between DRX and DP up to 1373 K (1100 °C). Strain-induced precipitation (SIP) was observed over the entire range of investigated test temperatures. Static recrystallization (SRX) took place predominantly in the temperature range of 1173 K to 1373 K (900 °C to 1100 °C), at which SIP significantly delayed the SRX finishing time. The results are analyzed in the framework of the classical nucleation theory and the underlying mechanisms are identified. 相似文献
14.
采用Gleeble-3800D热模拟试验机在应变量0.6、变形温度750~1050℃、应变速率0.01~1 s-1工艺条件范围内, 研究了Fe-(5.5%、6.0%、6.5%) Si高硅电工钢的热变形与动态再结晶行为.采用线性回归方法, 建立了三种成分实验钢的流变应力本构方程.计算得到Fe-5.5% Si、Fe-6.0% Si和Fe-6.5% Si高硅电工钢的热变形激活能分别为310.425、363.831和422.162 kJ·mol-1, 说明Fe-(5.5%、6.0%、6.5%) Si高硅电工钢的热变形激活能随Si质量分数的增加而增大, 这使得Fe-(5.5%、6.0%、6.5%) Si高硅电工钢相同条件下的变形抗力随Si含量的升高而增大.采用金相截线法对不同成分和变形条件下实验钢的动态再结晶百分数进行了统计, 结果表明: 同一热变形条件下, Fe-(5.5%、6.0%、6.5%) Si高硅电工钢的动态再结晶百分数随Si质量分数的升高而减小.本文实验条件下, 当变形温度为750~850℃时, Fe-(5.5%、6.0%、6.5%) Si高硅电工钢软化机制主要为动态回复; 而变形温度为950~1050℃时, Fe-(5.5%、6.0%、6.5%) Si高硅电工钢软化机制主要为动态再结晶. 相似文献
15.
16.
High temperature deformation characteristics of a semiaustenitic grade of precipitation hardening stainless steels were investigated by conducting hot compression tests at temperatures of 900-1 100 ℃ and strain rates of 0001-1 s-1. Flow behavior of this alloy was investigated and it was realized that dynamic recrystallization (DRX) was responsible for flow softening. The correlation between critical strain for initiation of DRX and deformation parameters including temperature and strain rate, and therefore, Zener Hollomon parameter (Z) was studied. Metallographic observation was performed to determine the as deformed microstructure. Microstructural observation shows that recrystallized grain size increases with increasing the temperature and decreasing the strain rate. The activation energy required for DRX of the investigated steel was determined using correlations of flow stress versus temperature and strain rate. The calculated value of activation energy, 460 kJ/mol, is in accordance with other studies on stainless steels. The relationship between peak strain and Z parameter is proposed. 相似文献
17.
Jun-ichi Kokado Natsuo Hatta Hirohiko Takuda Shiomi Kikuchi Tetsu Hirabayashi 《国际钢铁研究》1985,56(12):619-624
It has been ascertained whether or not the model capable of predicting the stress-strain relation of plain carbon steels, previously proposed, is applicable to the estimation of mill loads in the finishing process (consisting of six mill stands) of a hot strip mill. An appreciably good agreement with the predicted and measured mill load values has been obtained in the earlier passes where the strip microstructure is regarded to have completed static recrystallization, and the predicted mill loads in the later passes have been far less than the measured load owing to the effect of the strain accumulated in the previous rolling process. Then, a simple model to predict the accumulated strain has been constructed and introduced into the calculation of mill loads. As a result, the predicted mill loads have been fairly improved over the whole passes in the finishing process. 相似文献
18.
通过Gleeble 1500热模拟试验机试验研究了Nb-Ti微合金化低碳钢(/%:0.06C,0.22Si,1.80Mn,0.03Nb,0.15Ti,≤0.007N,≤0.002S)10mm带钢在850~1100℃,以应变速率0.1~20.0 s-1,总变形量75%单道次压缩变形时动态再结晶,由真应力-真应变曲线,结合加工硬化率曲线,得出动态再结晶临界应变0.4~0.7和完全再结晶应变量1.1~1.4。该钢的热变形激活能为618.225 kJ/mol。根据试验结果得到Zener-Hollomon方程和动态再结晶状态图,利用Johnson-Mehl-Avrami(JMA)方程法得到再结晶体积分数实际值,采用Epsilon-P模型对实验数据进行回归,得到试验钢的再结晶动力学模型。 相似文献
19.