Process Modeling and Control Simulation for a 500W@4.5K Helium Refrigerator

In order to investigate dynamic behaviors of a 500W@ 4.5K helium refrigerator,the process simulator has been completed. The cryogenic process model is described and main components are customized. The realtime communication between the process model and the control system has been achieved. Compared with the preliminary experimental data,the errors of temperatures during the process of 300 K-80 K are less than 10%.The process model is validated to predict the cool-down process very well. The controller parameters are tuned in simulation and applied to the actual refrigerator suitably. Based on the dynamic simulation,the operation of Joule-Thomson( JT) by pass valve has been optimized. And the cool- down process from 300 K to 4. 5 K has been simulated under the control programs. Simulation results indicate that this dynamic simulator based on actual control architecture is available to process control and operation optimization for the helium refrigerators.     

Composition Optimization of Nb-Ti Microalloyed High Strength Steel

Four Nb-Ti microalloyed steels were refined and rolled to study the composition optimization of Nb-Ti microalloyed steels. The effects of Nb and Ti on the microstructures, precipitates and properties of Nb-Ti microalloyed steel were investigated. The results showed that an increase in Ti content resulted in the appearance of many fine precipitates leading to a strong precipitation strengthening effect. Hence, the yield strength increased. Besides, the increased strength by the combined increase of Nb and Ti was similar to that observed for the increase in Ti content alone. This increase in strength was attributed widely to the increase in the Ti content alone rather than Nb. Moreover, the increase in Nb content beyond 0.036 wt% exerted no significant effect on the strength of Ti-Nb microalloyed steels, in which more Ti could be added to further improve the strength of steels.     

High performance low cost steels with ultrafine grained and multi-phased microstructure

Ultrafine grained ferrite was obtained through tempering cold rolled martensite with an average grain size of 200―400 nm in a low carbon and a microalloyed steel. Thermal and mechanical stability of the two steels was studied. Due to the pinning effect of microalloyed precipitates on the movement of dislocations and grain boundaries, the recrystallization and grain growth rate were retarded, and the thermal stability of ultrafine grained microstructure was improved. The ultrafine grained ferritic steel was ...     

Dissolving of Nb and Ti carbonitride precipitates in microalloyed steels

The dissolving behaviour of Nb and Ti carbonitride precipitates in microalloyed steels during isothermal holding at 1300℃ was investigated by Transmission electron microscopy (TEM) and energy dispersion x-ray spectrum (EDX). It was found that all precipitates in Nb-Ti microalloyed steel are (Nb, Ti)(C, N). With holding time increasing, the atomic ratio of Nb/Ti in precipitates decrease gradually. These precipitates still existe even after holding for 48 h at 1300℃while Nb(C, N) precipitates dissolve away in Nb microalloyed steel only after 4 h at the same temperature. These results show that formation and thermostability of precipitates are considerably influenced by interaction between Nb and Ti.     

Nb微合金化冷轧双相钢DP980的试制研究

采用C-Si-Mn-Cr-Nb合金系,采取两种热轧、退火工艺,在实验室试制Nb微合金化冷轧双相钢DP980。结果表明,两种试制钢的抗拉强度分别为1034 MPa和1048 MPa,屈服强度分别为534 MPa和499 MPa,伸长率分别为11.2%和11.3%,n值分别为0.28和0.27,屈强比分别为0.52和0.48;试制钢的热轧组织为F＋P,连续退火后的组织为F＋M,退火后的应力应变曲线表现出连续屈服的特点。     

Experimental study on Ti+Nb bearing ultra-low carbon bake hardening sheet steel hot-rolled in the ferrite region

A Ti+Nb bearing ultra-low carbon bake hardening sheet steel hot-rolled in the conventional austenite region and in the ferrite region with lubrication was experimentally studied.Subsequent cold rolling and continuous annealing processes were also conducted.The results show that microstructures of ultra-low carbon bake hardening hot strips at room temperature are basically irregular polygonal ferrites.The yield strength,ultimate tensile strength,n value,and r value of the No.2 specimen hot-rolled in the ferr...     

Ultra-fine ferrite grains obtained in the TSDR process

By careful design of rolling schedule,ultra-fine （～2μm） ferrite grains in a low carbon high niobium （0.09wt%Nb） microalloying steel with average austenite grain sizes above 800 μm can be achieved in the simulated thin slab direct rolling process. The 5-pass deformation was divided into two stages： the refinement of austenite through complete recrystallization and the refinement of ferrite through dynamic strain-induced transformation. The effects of Nb in solution and strain-induced NbCN precipitates on the ferrite transformation were also extensively discussed.     

Effect of cooling parameters on the microstructure and properties of Mobearing and Cr-bearing steels

To develop low-cost low carbon bainitic steel,Mo-bearing and Cr-bearing steels were melted in a vacuum induction furnace and were researched by thermal simulation and hot rolling at the laboratory.As the cooling rate increases from 0.2 to 50℃/s,the transformation temperatures of two steels lie between 650 and 400℃,and the final microstructures of them change from quasi-polygonal ferrite and granular bainite to lath bainite.Compared with cooling in air or by interrupted cooling,Mo-bearing and Cr-bearing steel plates cooled by sprayed water boast higher strength and superior toughness,for large-size islands are responsible for the poor mechanical properties.Compared to Mo,Cr is effective to isolate the bainitic reaction in low carbon steel,and the bainitic microstructure can also be obtained in Cr-bearing steel cooled at a wide range of cooling rate.     

Effects of Mn on Microstructures and Properties of Hot Rolled Low Carbon Bainitic Steels

Two kinds of Mn-Si-Mo low carbon steels were designed to study the effects of Mn on the microstructures and properties of hot rolled low carbon bainitic steels.To reduce the production cost,a very low Mo content of 0.13%was added in both steels.After hot rolling,the mechanical properties of samples were tested.Microstructure was observed and analyzed by optical microscope and transmission electron microscope.The results show that the strength of tested steels increases with the increase in Mn content,while the elongation decreases.When Mn content increases,the bainite microstructure increases.The results can provide a theoretical basis for composition design and industrial production of low cost low carbon bainitic steels.     

合金元素Mo对冷轧双相钢组织的影响

分析Mo微合金冷轧双相钢和普通C-Mn冷轧双相钢在不同双相热处理工艺下微观结构,讨论Mo对冷轧双相钢组织变化规律的影响。实验结果表明：当两种双相钢以1700℃／s冷却时,均获得了铁素体、马氏体双相组织,马氏体均匀分布在铁素体基体上,随着加热温度的升高,普通C-Mn双相钢得到的马氏体体积分数多。当以5．4℃／s冷却时,Mo微合金双相钢得到的马氏体体积分数多;当加热到820℃保温结束后以5．4℃／s的速率冷却时,普通C-Mn钢的组织组成相为铁素体、珠光体、马氏体;Mo微合金钢的组织组成相为铁素体、贝氏体、马氏体;Mo对铁素体晶粒的细化作用不明显。     

钒和钼对微合金化贝氏体钢第二相析出的影响

利用热模拟试验机Gleeble-3800,热模拟试验研究了V、Mo、V＋Mo等元素、加热温度、保温时间对微合金化贝氏体钢中第二相析出的影响.结果表明,Nb、V、Ti、Mo的复合加入有利于第二相的析出,加热温度和保温时间对析出量的影响较小.     

Behavior of precipitation in bainitic steel during relaxation processing of RPC technique

Thermal simulation test, TEM (Transmission Electron Microscope) and nanobeam EDS (Energy Dispersed x-ray Spectrum) techniques were used to investigate the precipitation behavior of Nb, Ti, Mo etc. in HSLA (High Strength Low Alloy) steel. The strain induced precipitation occurred during the isothermal relaxation stage after deformed in the non-recrystallization temperature region. After 30% predeformation at 850 and 900~C, there are two kinds of particles, (Ti,Nb)(C,N) and a few Nb(C,N), to precipitate during holding. The content of Nb in particles rises with the relaxation time increasing. During the final holding stage, some Nb and Ti atoms in the lattice sites of the precipitates would be replaced by Mo atoms, and the Mo content in the precipitates increases with the relaxation time. The results were compared with the refinement effect of microstructures caused by relaxationprecipitation controlling transformation (RPC) processing.     

Effect of Titanium Content on Microstructure and Wear Resistance of Hardfacing Alloy

The hardfacing alloys with different concentrations of titanium were deposited on carbon steel substrates by shielded metal arc welding, and the effect of titanium content on the microstructure characteristics of the hardfacing alloys was investigated. The wear resistance test of the hardfacing alloys was carried out by using a slurry rubber wheel abrasion test machine, and the wear behaviour was also studied. The results indicate that the addition of titanium can effectively promote the precipitation of the complex carbides of Nb and Ti due to the prior precipitation of titanium carbide which acts as nucleation sites for complex carbides. With the increase of titanium content, the wear resistance of the hardfacing alloys is increased gradually resulting from the refinement of microstructure and dispersive distribution of fine carbide precipitates. And the wear mechanism is mainly minimum plastic deformation with interrupted grooves due to the strengthening and protecting effects of carbide precipitates.     

Relaxation of Deformed Austenite and Refinement of Bainite in a Nb-Containing Microalloyed Steel

By means of stress relaxation and strain-induced precipitation in deformed austenite, bainite with micron sheaves size was ob-tained in Nb-containing steel. Microstructures of deformed samples isothermally relaxed for various time followed by cooling in water were examined. Stress relaxation test and transmission electron microscopy (TEM) were employed to detect precipitation of microalloy elements, such as Nb, Ti, during isothermal holding after deformation. All the samples were constituted by lath-like bainite along with acicular ferrite, but the size of bainitic sheaves and the amount of acicular ferrite were changed with relaxation time. To achieve optimum refinement, relaxation should be confined in the stage when the precipitates have sufficiently grown and started to coarsen. The sample having not undergone relaxation does not exhibit obvious refinement despite of its higher dislocation density. These results indicate that relaxation promotes bainite to refine, which is because deformed austenitic grains are divided by dislocation walls formed during rela-xation and acicular ferrite formed before bainitic transformation.     

Theoretical calculation of the impact work in the alloying non-quenched and tempered steel

Liu et al.[1―5]1) have calculated the finishing rolling tensile strength σb, yield strength σs, elongation δ of the alloying non-quenched and tempered steel with the covalent elec-1) Liu Z L, Lin C, Guo Y C. Theoretical calculation of the finishing rolling elongation in alloying non-quenched and tempered steel. Progress in Natural Science, in presstron number nA of the strongest bond in alloying phases and the smallest electron density difference ?ρ of phase interfaces. It is calculat…     

Effect of zirconium addition on the austenite grain coarsening behavior and mechanical properties of 900 MPa low carbon bainite steel

The ultra-free bainitic microstructure of a 900 MPa low carbon bainitic Cu-Ni-Mo-B steel was obtained by a newly developed relaxation precipitation control (RPC) phase transformation processing.In a pan-cake like prior-anstenite grain,the microstructure consisted of lath bainite,a little of abnormal granular bainite,and acicular ferrite.The effect of zirconium carbonitrides on the austenite grain coarsening behavior was studied by transmission electron microscopy (TEM).The results show that,the lath is narrower with increasing cooling rate.The ratio of all kinds of bainitic microstructure is proper with the intermediate cooling rate;and Zr-containing precipitates distribute uniformly,which restrains austenite grain growing in heat-affected welding zone.     

Precipitation characteristic of high strength steels microalloyed with titanium produced by compact strip production

Transmission electron microscopy (TEM) and physics-chemical phase analysis were employed to investigate the precipitates in high strength steels microalloyed with Ti produced by compact strip production (CSP). It was seen that precipitates in Ti microalloyed steels mainly included TiN, Ti4C2S2, and TiC. The size of TiN particles varied from 50 to 500 nm, and they could precipitate during or before soaking. The Ti4C2S2 with the size of 40-100 nm might precipitate before rolling, and the TiC particles with the size of 5-50 nm precipitated heterogeneously. High Ti content would lead to the presence of bigger TiC particles that precipitated in austenite, and by contrast, TiC particles that precipitated in ferrite and the transformation of austenite to ferrite was smaller. They were less than 30 nm and mainly responsible for precipitate strengthening. It should be noted that the TiC particles in higher Ti content were generally smaller than those in the steel with a lower Ti content.     

冷轧压下率对 ELC-BH 钢板织构的影响

通过极图分析方法研究了冷轧压下率（８０％～９０％）对Ｎｂ＋Ｔｉ处理的ＥＬＣ－ＢＨ钢板冷轧和退火织构的影响．结果表明,冷轧和退火织构的基本特性与冷轧压下率无关,冷轧压下率增大对于退火织构的有利组分与不利组分的强度比影响不大．     

800 MPa级CSiMnNb与CSiMnCr系冷轧双相钢组织与性能

在实验室采用CCT-AY-Ⅱ连续退火模拟器研究不同退火温度条件下800 MPa级CSiMnCr与CSiMnNb系冷轧双相钢的力学性能,并对其显微组织进行分析.结果表明：在同一成分试验钢中,770℃退火较790℃退火时所获得的强度高;钢中添加少量的Nb细化了铁素体与岛状马氏体组织,并且岛状马氏体更纯净,屈强比低,加工硬化指数n值更高.     

14SiMnVNbRE钢沉淀强化的高温应力法研究

应用高温应力法测定了Ｖ－Ｎｂ微合金化钢在不同冷却速率下的沉淀强化效应，结果表明，应用高温应力法可以定性地微合金化的沉淀强化效应。根据高温应力状态，可以确定微合金化钢铁得最佳沉淀强化效应效应的冷却速度。