稀土管线钢轧制工艺的模型研究

为了研究稀土对变形奥氏体晶粒的影响,建立了稀土管线钢的轧制模型,实验验证表明,模型可以精确预测稀土管线钢轧制过程中奥氏体晶粒的长大行为.研究发现,稀土改变了X80管线钢的奥氏体变形行为,原有的TMCP工艺不适合稀土管线钢.对于稀土管线钢而言,通过适当的调整轧制工艺,稀土的微合金作用可以得到充分发挥,相变之前的奥氏体组织明显细化.     

Effect of Austenite Recrystallization on Microstructure and Properties of Q345 Steel

The Q345 plate steel austenite recrystallization behavior and strain accumulation during rolling were investigated through thermal simulation and rolling. The effect of the recrystallization behavior on the microstructure and properties of the steel was discussed and analyzed. The control principles of the pass reduction in the austenite recrystallization region and partial recrystallization region were established. It is found that to increase the thickness of intermediate billet in the finish temperature interval of 880-820℃ is favorable to grain refinement. The result has been applied to the industrial production of the 3 500 mm plate mill of Shougang Group. The average grain size of the steel plate conforms to ASTM No. 10-12, and the grade of band structure has been reduced to below 1.5.     

Dynamic and Static Recrystallization Behaviour of Coarse-grained Austenite in a Nb-V-Ti Microalloyed Steel简

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.     

Analysis of DWTT property of thick X70 pipeline steel

The microstructures of X70 pipeline steels with different thickness specifications and different rolling reduction ratios were analyzed by metallographic microscope, scanning electron microscope, and electron backscatter diffraction techniques, and the original austenite microstructures were compared. The effect of compression ratio on the original austenite structure was studied. The results show that the large compression ratio in the rolling process is more conducive to refine austenite grains and improve the low- temperature toughness of thick X70 pipeline steel. However, due to the fact that the temperature during the finish rolling process is too low to permeate the center of the deformation, it is necessary to further use the low- temperature stage of the rough rolling process to perform deformation infiltration. Ultra- rapid cold cooling after rolling can improve the DWTT performance of the steel, but it is not sufficient to compensate for the fluctuation of DWTT performance caused by insufficient early austenite grain refinement.     

温度参数对铌微合金高强度结构钢组织性能的影响

通过控轧控冷试验,力学性能检验和组织的光学显微观察,研究了温度参数对铌微合金钢组织性能的影响。结果表明:两阶段控轧及控冷所获晶粒尺寸明显小于常规轧制+快速冷却的晶粒尺寸;随冷却速率的增大或终冷温度的降低或精轧开轧温度的降低,试验钢晶粒细化,混晶程度加重,强度增大,塑性降低;精轧低温开轧利于韧性提高;铁素体混晶可能源于因铸坯中Nb(C,N)的不均匀分布造成的原始奥氏体混晶,粗轧大压缩比轧制可以消除这种混晶现象。     

低成本90mm Q345E特厚板的生产

为了降低强韧性特厚板的生产成本,在某公司通过试验,以碳、锰成分为基本成分,采用300mm断面钢坯,通过执行较为严格的TMCP工艺,使奥氏体再结晶区的轧制温度控制在1100～1050℃,未再结晶区轧制温度在770～800℃,并严格控制轧制速度和道次压下量,同时利用ACC层流冷却避? 糠衷俳峋⑼ü?.6℃/s的冷却速度将轧后钢板冷却在620℃温度范围,最终生产出厚度为90mm、性能符合Q345E级别要求的特厚板,并满足符合Z25的厚度方向性能要求。     

Effect of Thermomechanical Controlled Processing on Mechanical Properties of 490 MPa Grade Low Carbon Cold Heading Steel

Thermomechanical controlled processing (TMCP) of low carbon cold heading steel in different austenite conditions were conducted by a laboratory hot rolling mill.Effect of various processing parameters on the mechanical properties of the steel was investigated.The results showed that the mechanical properties of the low carbon cold heading steel could be significantly improved by TMCP without heat treatment.The improvement of mechanical properties can be attributed mainly to the ferrite grain refinement due to low temperature rolling.In the experiments the better ultimate tensile strength and ductility are obtained by lowering finishing cooling temperature within the temperature range from 650 ℃ to 550 ℃ since the interlamellar space in pearlite colonies become smaller.Good mechanical properties can be obtained in a proper austenite condition and thermomechanical processing parameter.The ferrite morphology has a more pronounced effect on the mechanical behavior than refinement of the microstructure.It is possible to realize the replacement of medium-carbon by low-carbon for 490 Mpa grade cold heading steel with TMCP.     

沙钢宽厚板工艺技术装备

沙钢集团于2006年建成现代化宽厚板生产线,采用当今世界上诸多先进的工艺装备和工艺技术,亚稳态奥氏体区热机轧制实现晶粒细化,靠中间坯待温时间及未再结晶区γ／α相变较低终轧温度抑制新晶粒成长。MULPIC装置加速冷却或直接淬火钢板。终轧通过MULPIC装置加速冷却使固溶体内保持大量Nb、V、Ti、Mo微合金元素粒子,有利于γ／α相变及在铁素体与贝氏体内沉淀而改善组织性能,终轧温度低及增加冷却速率增加沉淀强化和位错强化效果。能满足各种高难度品种钢板的生产要求。     

Effects of TMCP Schedule on Precipitation,Microstructure and Properties of Ti-microalloyed High Strength Steel

Using the similar compositions of the Ti-microalloyed high-strength steels produced by the thin-slab casting process of compact strip production(CSP),four thermo-mechanical control processes(TMCP)after the simulated thickslab casting,i.e.the two hot rolling routes and the two cooling processes,were designed,aiming at achieving the same mechanical properties as the thin strip products.The final microstructures after the four TMCP processes were examined by optical microscope(OM),scanning electron microscope(SEM)and transmission electron microscope(TEM).The tensile properties and Charpy impact energy were measured correspondingly.Strain-induced TiC precipitation was found in the two-stage rolling route with the finish rolling temperature at low levels,leading to grain refinement due to the pinning effect during austenite recrystallization.Precipitation hardening in ferrite was observed when a period of isothermal holding was applied after hot rolling.It could be concluded that both finish rolling temperature and the subsequent isothermal holding temperature were crucial for the achieved strength level due to the combined effect of grain refinement and precipitation hardening.At the same time,it was found that the isothermal holding led to poor impact toughness because of remarkable precipitation hardening.Therefore,it was suggested that the precipitation kinetics of titanium carbides in both austenite and ferrite should be investigated in future.     

Prediction of Rolling Load, Recrystallization Kinetics, and Microstructure During Hot Strip Rolling

 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.     

Effect of Controlled Cooling After Hot Rolling on Mechanical Properties of Hot Rolled TRIP Steel

A three-step cooling pattern on the runout table（ROT）was conducted for the hot rolled TRIP steel.Microstructural evolution during thermomechanical controlled processing（TMCP）was investigated.Processing condition of controlled cooling on a ROT in the laboratory rolling mill was discussed.The results indicated that the microstructure containing polygonal ferrite,granular bainite and a significant amount of the stable retained austenite can be obtained through three-step cooling on the ROT after hot rolling.TMCP led to ferrite grain refinement.Controlled cooling after hot rolling resulted in the stability of the remaining austenite and a satisfactory TRIP effect.Excellent mechanical properties were obtained through TMCP for the hot rolled TRIP steel.     

贝氏体非调质紧固件用钢静态再结晶行为分析

为分析贝氏体非调质紧固件用钢的静态再结晶行为,在Gleeble 3500热模拟试验机上进行了双道次压缩试验,并计算了静态再结晶软化率。研究表明,所研究钢种的奥氏体在1 050℃以上易于发生静态再结晶,在850℃以下静态再结晶发生困难;所确定的再结晶模型1可用于预测所研究钢种的静态再结晶的发生情况;利用道次间的静态再结晶细化奥氏体,适宜的轧制温度应控制在950~1 050℃,热机轧制温度应控制在850℃左右。     

控轧控冷条件下Q345中厚板的生产工艺研究

通过试验模拟和实机轧制试验,对传统Q345钢的静态再结晶行为、应变累积效应和晶粒细化机制等进行研究,分析了影响中厚钢板显微组织和力学性能的主要因素。结合首钢中板厂3500mm机组的特点,确定出Q345中厚钢板的TMCP生产工艺。实践表明该工艺可使钢板的平均组织晶粒度达到10～12级,带状组织降至1．5级以下。     

X70管线钢热连轧过程奥氏体再结晶、晶粒尺寸和平均流变应力的预测

在考虑动态、亚动态再结晶及静态再结晶的基础上,建立了X70管线钢的物理冶金模型,并应用于板带钢热连轧过程奥氏体再结晶、晶粒尺寸和流变应力的预测.结果表明,在合理的温度和压下条件下,应变累积可导致在精轧过程出现动态 亚动态再结晶行为,促进奥氏体晶粒的进一步细化.终轧温度的降低可引起奥氏体晶粒的粗化和残余应变的显著提高.建立了考虑晶粒尺寸和残余应变影响的平均流变应力(MFS)的人工神经网络预测模型,大大提高了热连轧过程MFS预测精度.     

热轧高锰TRIP/TWIP钢组织性能研究

利用控轧控冷工艺开发了锰质量分数为18.8%的热轧高锰TRIP/TWIP钢板,分析了轧制工艺参数对热轧高锰钢组织和性能的影响,讨论了实验钢的断裂机理。结果表明：通过控轧控冷方法可以热轧出抗拉强度达到940 MPa左右,断裂伸长率在40%以上的高锰钢板。冷却速度和卷取温度等工艺参数对实验钢组织性能影响不是非常明显。高锰钢优异的力学性能是TRIP和TWIP效应共同作用的结果。高锰钢拉伸呈韧性断裂,裂纹多沿奥氏体/马氏体晶界萌生、扩展。     

特厚板温度梯度轧制有限元模拟与实验研究

针对特厚板再结晶型轧制,板坯中心难以变形导致心部晶粒粗大的问题,使用Q345B钢,采用有限元方法建立了特厚板轧制的仿真模型,以研究在特厚板轧制过程中引入厚度方向上的温度梯度对钢板心部应变的影响,并与传统均温轧制进行对比,预测了两种温度场条件下奥氏体再结晶的晶粒尺寸.采用大试样平面应变实验对模拟结果进行验证.研究结果表明,温度梯度轧制有利于增加坯料心部应变量,最大增加了61.35%.计算和实验结果显示温度梯度轧制可以减小特厚板心部晶粒尺寸,晶粒度级别提高了一个等级,说明该工艺对提高特厚板中心区域性能有利.      

采用TMCP技术的低碳低合金高强钢生产的研究现状及进展

TMCP(Thermal Mechanical Control Process)是20世纪钢铁业最伟大的成就之一.TMCP技术是通过控制轧制温度和轧后冷却速度、冷却的开始温度和终止温度,来控制钢材高温奥氏体组织形态以及相变过程,最终控制钢材的组织类型、形态和分布,提高钢材的组织和力学性能.介绍了低碳低合金高强钢基于TMCP的发展历程、研究进展、组织分析,并展望了TMCP技术下低碳低合金高强钢未来的发展方向.     

Artificial Neural Network Modeling of Microstructure During CMn and HSLA Plate Rolling

An artificial neural network (ANN) model for predicting transformed microstructure in conventional rolling process and thermomechanical controlled process (TMCP) is proposed. The model uses austenite grain size and retained strain, which can be calculated by using microstructure evolution models, together with a measured cooling rate and chemical compositions as inputs and the ferrite grain size and ferrite fraction as outputs. The predicted results show that the model can predict the transformed microstructure which is in good agreement with the measured one, and it is better than the empirical equations. Also, the effect of the alloying elements on transformed products has been analyzed by using the model. The tendency is the same as that in the reported articles. The model can be used further for the optimization of processing parameters, microstructure and properties in TMCP.     

Development of High Deformation X70 Pipeline Steel Plates in NISCO

A series of trial tests for high deformation (HD) X70 pipeline steel plates were performed in NISCO,and the technical routes as thermal mechanical controlled rolling process (TMCP),TMCP + Quenching (Q) and TMCP +Q & tempering (T) were studied systematically through the plate shape quality,properties and microstructure characters.The results show that problems as plate shape and inhomogeneous microstructures are for finish rolling at low temperature and high cooling rate after the rolling by the route of TMCP.By the route of TMCP+Q,the yield strength (YS) of the trial steels is not sufficient.By the route of TMCP+QT,the YS is enhanced,as well as good toughness and plasticity due to the martensite decomposition at low temperature tempering process,and 4 sheets of HD X70 pipeline steel plates by the route TMCP+QT with superior plate shape quality,microstructure and comprehensive properties were successfully developed in NISCO.     

TMCP型Q500qENH特厚耐候桥梁钢板的工业试制

 提出一种低碳微合金MnCuNiCrMo钢,测试了其过冷奥氏体连续冷却相变（CCT）曲线,分别研究未再结晶区变形量、冷却速率对其相变行为的影响。使用厚板坯连铸(CC)—钢板控轧控冷(TMCP)工艺流程,在5m宽厚板工业生产线上成功开发出60mm特厚Q500qENH桥梁钢板。开发钢板的显微组织为细密粒状贝氏体(GB)+针状铁素体(AF)+多边形铁素体(PF);横向室温屈服强度大于560MPa,抗拉强度大于660MPa, 伸长率大于20%;Z向面缩率大于76%;-40℃下纵向Charpy冲击吸收能量(KV2)大于170J;零塑性温度为-85℃。