Effects of cooling rate and isothermal holding on the characteristics of MnS particles in high-carbon heavy rail steels

2020 ◽  
Vol 117 (1) ◽  
pp. 110 ◽  
Author(s):  
Xuewei Zhang ◽  
Caifu Yang ◽  
Lifeng Zhang
Keyword(s):  
Cooling Rate ◽  
Isothermal Holding ◽  
Average Diameter ◽  
Holding Time ◽  
Area Fraction ◽  
Air Cooling ◽  
Steel Matrix ◽  
Number Density ◽  
3D Morphology ◽  
Holding Temperature

The characteristics of MnS particles were intensively investigated at three different cooling rate of 80.4 K · s−1 (water cooling), 3.8 K · s−1 (air cooling) and 1.8 K · s−1 (furnace cooling) as well as the different isothermal holding temperature and time in laboratory experiments. The three-dimensional (3D) morphology of MnS particles was extracted from steel samples using non-aqueous solution electrolysis. The results showed that the 3D morphology of MnS changed from a nearly spherical into rod-like and the area fraction and average diameter of MnS increased with decreasing cooling rate. During isothermal holding process, the morphology of MnS changed little at 1473 K (1200 °C), but their shape profiles varied from a nearly spherical and spindle-like to irregular at higher holding temperature 1673 K (1400 °C) when the holding time exceeded 60 min. Moreover, the number density and area fraction of MnS decreased with increasing holding time at 1573 K (1300 °C) and 1673 K (1400 °C), respectively. Especially at 1573 K (1300 °C), the 1 ∼ 3 µm MnS inclusions were dissolved and lead to decreasing of number density, but that > 3 µm one occurs growth and resulted in increasing of average diameter. The calculation results show that the starting temperature of precipitation of MnS was about 1627 K (1354 °C) and effect of cooling rate on the segregation of Mn and S is insignificant. Considering the segregation of solutes, MnS formation and growth takes place in the solid/liquid interface of steel when the solid fraction is close to 0.9567 during solidification. It has been found that the increase of cooling rate gives rise to the decreased of MnS diameter because the growth time of MnS is short. Furthermore, thermodynamic calculations of MnS solid solubility product were carried out to reveal the high holding temperature and long holding time favors the dissolution of MnS particles. It is necessary to decrease the sulfur content by less than 16 ppm in order to assure that the larger MnS which formed during solidification redissolves in the steel matrix, rather than relying on increasing the heating temperature which is above 1649 K (1376 °C). Subsequent, the MnS will precipitate again in a finely dispersive state during rolling process, and it can hinder annealing grain growth and finally make for the improvement of the toughness property of the steel.

Numerical Simulation of Intermediate Cooling Temperature Field in Controlled Rolling

2010 ◽  
Vol 148-149 ◽  
pp. 359-362
Author(s):  
Wen Feng Huo ◽  
Xian Lei Hu ◽  
Bing Xing Wang ◽  
Xiang Hua Liu
Keyword(s):  
Cooling Rate ◽  
Controlled Rolling ◽  
Holding Time ◽  
Air Cooling ◽  
Thickness Direction ◽  
Cooling Mode ◽  
Cooling Strategy ◽  
Profile Characteristics ◽  
Intermediate Cooling ◽  
Rolling Efficiency

Air cooling may decrease rolling efficiency in controlled rolling for needing long holding time to obtain the correct rolling temperature because of small cooling rate. The intermediate cooling can increate the cooling rate, and improve rolling efficiency. Experiment was carried out to research the effect of intermediate cooling on rolling efficiency. The influence of different cooling mode on the temperature distribution and the temperature profile characteristics of different cooling strategy are analyzed with FEM. It shows that intermediate cooling can decrease the holding time effectively, and improve rolling efficiency; the temperature homogeneity in thickness direction can be improved by opening the header one after another and cooling the plate by oscillating cooling.

Microstructural Evolution of AZ31 Mg Wrought Alloy during Partial Remelting for Thixoextrusion

2006 ◽  
Vol 116-117 ◽  
pp. 251-254
Author(s):  
Young Ok Yoon ◽  
Shae K. Kim
Keyword(s):  
Grain Size ◽  
Microstructural Evolution ◽  
Liquid Fraction ◽  
Isothermal Holding ◽  
Holding Time ◽  
Interesting Point ◽  
Grain Sizes ◽  
Partial Remelting ◽  
Average Grain Size ◽  
Holding Temperature

An attempt has been made to investigate feasibility of thixoextrusion for AZ31 Mg wrought alloy through simple partial remelting. Microstructural evolution of AZ31 Mg wrought alloy for thixoextrusion was investigated as functions of isothermal holding temperature and time in the partially remelted semisolid state. The interesting point of this study was that the thixotropic structures of AZ31 Mg wrought alloy without additional pretreatment could be obtained through simple partial remelting. The uniform average grain size and liquid fraction according to the isothermal holding time were very important for the thixoextrusion. Because, it is must be considered on actual extrusion time. The liquid fraction was increased with increasing isothermal holding temperature and time. But, the liquid fraction was almost uniform after 10 min. The average grain size was decreased with increasing isothermal holding temperature. On the other hand, as the holding time increased, the average grain sizes were uniform at 615 and 622. This phenomenon is very useful for thixoextrusion in terms of process control such as actual extrusion time.

scholarly journals OPTIMIZATION OF SYNTHESIS PROCESS OF NANOSTRUCTURED CARBIDE-CORUNDUM SILUMIN MODIFIER

2021 ◽  
Vol 1 (54) ◽  
pp. 71-79
Author(s):  
Dmitry V. ORDA ◽  
Keyword(s):  
Mathematical Model ◽  
Titanium Carbide ◽  
Response Function ◽  
Isothermal Holding ◽  
Holding Time ◽  
Synthesis Process ◽  
Synthesis Parameters ◽  
Response Equation ◽  
Main Factors ◽  
Holding Temperature

A mathematical model is developed for the process of synthesis of nanostructured modifier TiC-Al2O3 by gasphase deposition based on the system of starting materials TiO2-Al-C. To construct the response equation in the form of a polynomial of the second degree, the experiments were carried out in accordance with the model of a rotatable composite plan of the second order with three factors, including 20 experiments. The main factors considered were the isothermal holding temperature T (°C), the isothermal holding time t (s), and the proportion of the chlorinating component Q (wt.%), and as a response function — the proportion of titanium carbide q(TiC) (wt.%) in the composition of the synthesized modifier. The paper describes the results of computational and experimental modeling, from which it can be concluded that to obtain a modifier with the highest content of titanium carbide, the synthesis parameters should be as follows: T = 900–930 °C; t = 2–2.5 h; Q = 4–4.5 wt.%. The resulting TiC-Al2O3 modifier contains 34 wt.% TiC and has a nanostructured structure, with spherical and filamentous particles which diameter does not exceed 100 nm.

Effect of Isothermal Holding in Solid-Liquid Phase Region on Mg2Si Morphology in Hypereutectic Al-Si In Situ Composite

2012 ◽  
Vol 430-432 ◽  
pp. 711-714
Author(s):  
Zheng Liu ◽  
Hong Biao Xu ◽  
Kai Cao ◽  
Mei Yan Huang
Keyword(s):  
Liquid Phase ◽  
Shape Factor ◽  
Isothermal Holding ◽  
Phase Region ◽  
Holding Time ◽  
In Situ Composite ◽  
Size And Morphology ◽  
Solid Liquid ◽  
Holding Temperature

Mg2Si reinforced hypereutectic Al-Si in-situ composite was prepared and the effects of the isothermal holding temperature and time on Mg2Si in the composite were researched. The results showed that there were the important effects of holding temperature and time in the solid-liquid phase region of the Al-Si alloy on the size and morphology of Mg2Si. The size and morphology of Mg2Si became smaller and round with the rising of the holding temperature and prolonging of the holding time. The suitable technology in the test was obtained, in which when being held at 615°C for 300s, the size of Mg2Si decreased to 20.54μm and the shape factor of Mg2Si reached about 0.67.

Preparation and Crystal Analysis of V-Type Amylase-n-Octanol Complex

2013 ◽  
Vol 448-453 ◽  
pp. 1109-1114 ◽  
Author(s):  
Yan Qi Liu ◽  
Qi Ling Liu ◽  
Shuang Li
Keyword(s):  
Crystal Structure ◽  
Cooling Rate ◽  
Ethanol Concentration ◽  
Holding Time ◽  
Single Factor ◽  
X Ray Diffraction ◽  
X Ray ◽  
Holding Temperature

In the EtOH/H2O system, by means of heating reflux, V-type amylose-n-octanol complex which B-type microcrystalline starch made a combination with n-octanol was prepared. Through single factor experiments, the effects of the starch/n-octanol ratio, the ethanol concentration, cooling rate, holding temperature and holding time on the crystallinity of the V-type amylose-n-octanol complex have been investigated. The X-ray diffraction was used to analysis the crystal structure of complex. The synthetic conditions were as follows: the starch / n-octanol ratio 10:1, the ethanol concentration 35%, holding temperature 80°C, holding time 60min and cooling rate 5°C/h.V-type amylose-n-octanol complex was prepared under the condition, the crystal structure of complex was V type and the crystallinity reached 61.29%.

Micro-Structural Evolution of AlCu5MnCdVA Cast Aluminum Alloy by Semi-Solid Isothermal Annealing Process

2007 ◽  
Vol 26-28 ◽  
pp. 489-493
Author(s):  
Guang Yu Yang ◽  
Wan Qi Jie ◽  
Qi Tang Hao ◽  
Run Qiang Zhang
Keyword(s):  
Aluminum Alloy ◽  
Cast Alloy ◽  
Isothermal Holding ◽  
Structural Evolution ◽  
Average Diameter ◽  
Rate Variation ◽  
Cast Aluminum Alloy ◽  
Cast Aluminum ◽  
Semi Solid ◽  
Holding Temperature

Isothermal grain coarsening of AlCu5MnCdVA aluminum alloy prepared by permanent mould casting during semi-solid treatment process was studied. It was found that the relationship between the average diameter of α (Al) grains and the isothermal holding time fitted the formula r − r = K ⋅ t − − ' 3 0 3 , where the coarsening rate K’ varied with the holding temperature, which equaled to 4.288×10-10m3/s and 5.962×10-10m3/s at the holding temperature. A modified model of liquid film migration has been proposed for explaining of 622°C and 631°C respectively the coarsening rate variation with annealing temperature. The diffusion of the solutes as well as vacancies, and the grain boundary tension are responsible for the microstructure evolution of AlCu5MnCdVA cast alloy.

Influence of Melt Holding Time on Microstructure and Mechanical Properties of Ductile Iron

2011 ◽  
Vol 279 ◽  
pp. 16-21
Author(s):  
Zhe Liu ◽  
Wei Ping Chen ◽  
Yu Deng
Keyword(s):  
Cooling Rate ◽  
Ductile Iron ◽  
Average Diameter ◽  
Holding Time ◽  
The Other ◽  
Spheroidal Graphite ◽  
Cooling Rates ◽  
Globular Graphite ◽  
Graphite Morphology ◽  
Nodular Graphite

Six groups of castings which solidified at different cooling rates with or without addition of 0.03%Sb were fabricated. The effects of the melt holding time, cooling rate, and Sb on the microstructure of ductile iron were studied. Results show that as for the other three blocks with addition of 0.03%Sb, reducing the length of eutectic plateau could improve the graphite morphology, and sufficient residual contents of spheroidizing elements REE and Magnesium could also lead to small and diffuse globular graphite particles no matter what the cooling rate is. As for the other three blocks with addition of 0.03%Sb, no matter what the cooling rate is, the nodularity index values are all about 90%. The main difference among the three blocks is just the size of nodular graphite. And even if two of the blocks solidified at different cooling rates, they own nearly identical NI value and globular graphite average diameter value, which is because they both possess the tolerated rare-earth elements/antimony ratio for spheroidal graphite formation.

Effect of Partial Remelting Procedure on the Microstructural Evolution of 7075 Al Wrought Alloy for Thixoextrusion

2006 ◽  
Vol 116-117 ◽  
pp. 336-339 ◽  
Author(s):  
Hyung Ho Jo ◽  
Young Ok Yoon ◽  
Jin Kyu Lee ◽  
Shae K. Kim
Keyword(s):  
Grain Size ◽  
Feasibility Study ◽  
Microstructural Evolution ◽  
Liquid Fraction ◽  
Isothermal Holding ◽  
Holding Time ◽  
Interesting Point ◽  
Partial Remelting ◽  
Average Grain Size ◽  
Holding Temperature

The feasibility study for thixoextrusion of 7075 Al wrought alloys was carried out with respect to reheating profile, isothermal holding temperature and time during the partial remelting through simple partial remelting. The reheating rates were 40/min and 60/min. The isothermal holding temperatures were controlled at 609, 622, 628 and 632 for 0, 2, 5, 10 and 30 min. The interesting point of this study was that the thixotropic structures of 7075 Al wrought alloy without additional pretreatment could be obtained through simple partial remelting. The average grain size was significantly smaller in the quickly heated specimen. The liquid fraction was increased with increasing isothermal holding temperature and time while the average grain size was inversely proportional to isothermal holding temperature and time. However, there was no big change of liquid fraction and average grain size with respect to isothermal holding time. The important fact that the liquid fraction and average grain size were almost uniform after 5 min is considered very useful for thixoextrusion in terms of actual extrusion time.

scholarly journals Crystallization and Mechanical Properties of Polypropylene under Processing-Relevant Cooling Conditions with respect to Isothermal Holding Time

2016 ◽  
Vol 2016 ◽  
pp. 1-11 ◽  
Author(s):  
Christopher Fischer ◽  
Dietmar Drummer
Keyword(s):  
Mechanical Properties ◽  
Isothermal Holding ◽  
Holding Time ◽  
Crystal Modification ◽  
Time Behavior ◽  
Scanning Calorimetry ◽  
Ordered Structures ◽  
Roll Temperature ◽  
Temperature Time ◽  
Holding Temperature

For semicrystalline thermoplastics, aside from pressure and shear, the temperature-time behavior while cooling the melt significantly affects the geometry and degree of ordered structures (e.g., spherulite size, degree of crystallization, and crystal modification) and, as a consequence, the resulting global component properties. Previous research has shown that a higher isothermal holding temperature (e.g., mold temperature and chill-roll temperature) leads to the formation of more distinct ordered structures and, therefore, can lead to greater stiffness and strength. Nevertheless, isothermal holding time during manufacturing is typically not taken into account. In this paper, fast scanning calorimetry (FSC) measurements were taken using polypropylene to analyze the crystallization during idealized temperature-time profiles based on the dynamic temperature process and to investigate the crystallization behavior at different temperatures and isothermal holding times analytically. Furthermore, iPP foils were extruded and tested mechanically to investigate the knowledge gained experimentally. Analytical and mechanical results show that foils produced at the same isothermal holding temperature can obtain significantly different ordered structures and mechanical properties depending primarily on the isothermal holding time.

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