Microstructure and mechanical properties of a cast TRIP-assisted multiphase stainless steel

Stainless steels are used in a wide range of complex environments due to their excellent corrosion resistance.Multiphase stainless steels can offer an excellent combination of strength,toughness and corrosion resistance due to the coexistence of different microstructures.The microstructure and mechanical properties of a novel cast multiphase stainless steel,composed of martensite,ferrite,and austenite,were investigated following appropriate heat treatment processes:solution treatment at 1,050℃ for 0.5 h followed by water quenching to room temperature,and aging treatment at 500℃ for 4 h followed by water quenching to room temperature.Results show reversed austenite is formed by diffusion of Ni element during aging process,and the enrichment of Ni atoms directly determines the mechanical stability of austenite.The austenite with a lower Ni content undergoes a martensitic transformation during plastic deformation.The tensile strength of the specimen exceeds 1,100 MPa and the elongation exceeds 24%after solid solution,and further increases to 1,247 MPa and 25%after aging treatment.This enhancement is due to the TRIP effect of austenite and the precipitation of the nanoscale G-phase pinning dislocations in ferrite and martensite.

Effects of Warm Deformation on Mechanical Properties of TRIP Aided Fe-C-Mn-Si Multiphase Steel

Warm deformation tests were performed using a kind of tubby heater. The microstructures and mechanical properties of an Fe-C-Mn-Si multiphase steel resulting from different warm deformation temperatures were investiga- ted by using LOM （light optical microscopy）, SEM and XRD. The results indicated that the microstructure contai- ning polygonal ferrite, granular bainite and a significant amount of the stable retained austenite can be obtained through hot deformation and subsequent austempering. Warm deformation temperature affects the mechanical prop- erties of the hot rolled TRIP steels. Ultimate tensile strength balance reached maximum （881 MPa） when the speci- men was deformed at 250 ~C, and the total elongation and strength-ductility reached maximum （38% and 28 614 MPa ~ ~, respectively） at deforming temperature of 100 ~C. Martensite could nucleate when austenite was deformed above M~, because mechanical driving force compensates the decrease of chemical driving force. The TRIP effect occurs in the Fe-C-Mn-Si multiphase steel at deforming temperature ranging from 15 to 350 ~C. The results of the effects of warm deformation on the mechanical properties of the Fe-C-Mn-Si multiphase steel can provide theoretical basis for the ap- plications and the warm working of the hot rolled TRIP sheet steels in industrial manufacturing.

Influence of Hot Deformation and Subsequent Austempering on the Mechanical Properties of Hot Rolled Multiphase Steel

Influence of hot deformation and subsequent austempering on the mechanical properties of hot rolled multiphase steel was investigated. Thermo-mechanical control processing （TMCP） was conducted by using a laboratory hot rolling mill, where three different kinds of finishing rolling reduction, and austemperings with various isothermal holding duration were applied. The results have shown that a multiphase microstructure consisting of polygonal ferrite, granular bainite and larger amount of stabilized retained austenite can be obtained by controlled rolling processes. Mechanical properties increase with increasing the amount of deformation because of the stabilization of retained austenite. Ultimate tensile strength （σb）, total elongation （σ） and the product of ultimate tensile strength and total elongation （σb-σ） reach the maximum values （791 MPa, 36% and 28476 MPa%, respectively） at optimal processes.

Simulation of macrosegregation in a 36-t steel ingot using a multiphase model

Macrosegregation is the major defect in large steel ingots caused by solute partitioning and melt convection during casting.In this study,a three-phase(liquid,columnar dendrites,and equiaxed grains)model is proposed to simulate macrosegregation in a 36-t steel ingot.A supplementary set of conservation equations are employed in the model such that two types of equiaxed grains,either settling or adhering to the solid shell,are well simulated.The predicted concentration agrees quantitatively with the experimental value.A negative segregation cone was located at the bottom owing to the grain settlement and solute-enriched melt leaving from the mushy zone.The interdendritic liquid flow was carefully analyzed,and the formation of A-type segregations in the mid-height of the ingot is discussed.Negative segregation was observed near the riser neck due to the specific relationship between flow direction and temperature gradient.Additionally,the as-cast macrostructure of the ingot is presented,including the grain size distribution and columnar–equiaxed transition.

EFFECT OF AUSTEMPERING ON TRANSFORMATION INDUCED PLASTICITY OF HOT ROLLED MULTIPHASE STEELS

Effect of austempering on the transformation induced plasticity （TRIP） of hot rolled multiphase steel was investigated. Polygonal ferrite, granular bainite, and a large amount of stabilized retained austenite could be obtained in the hot rolled multiphase steel. Strain induced martensite transformation （SIMT） of retained austenite and TRIP effectively occur under straining owing to austempering after hot rolling, and mechanical properties of the present steel remain at a relatively high constant value for austempering at 400℃. The mechanical properties of the steel exhibited a good combination of tensile strength （791MPa） and total elongation （36%） because the stability of retained austenite is optimal when the steel is held for 20min.

Effects of finishing rolling temperatures and reduction on the mechanical properties of hot rolled multiphase steel

Effects of finishing rolling temperatures and reduction on the mechanical properties of hot rolled multiphase steel were investigated. Thermo-mechanical control processing (TMCP) was conducted by using a laboratory hot rolling mill, in which three different kinds of finishing rolling temperatures and reduction and various austempering times were applied. The results showed that polygonal ferrite, granular bainite and larger amount of stabilized retained austenite can be obtained by controlled rolling processes, and that the strain-induced transformation to martensite from the retained austenite can occur gradually when the steel is deformed during tensile test. Mechanical properties increase with decreasing finishing rolling temperature and increasing amount of deformation. The most TRIP (transformation induced plasticity) effect, and ultimate tensile strength (UTS), total elongation (TEL) and the product of ultimate tensile strength and total elongation (UTS×TEL) are obtained at 20 min.

Evaluation of factors affecting the edge formability of two hot rolled multiphase steels

In this study, the effect of various factors on the hole expansion ratio and hence on the edge formability of two hot rolled multiphase steels, one with a ferrite–martensite microstructure and the other with a ferrite-bainite microstructure, was investigated through systematic microstructural and mechanical characterization. The study revealed that the microstructure of the steels, which determines their strain hardening capacity and fracture resistance, is the principal factor controlling edge formability. The influence of other factors such as tensile strength, ductility, anisotropy, and thickness, though present, are secondary. A critical evaluation of the available empirical models for hole expansion ratio prediction is also presented.

Thermomechanical controlled processing of hot-rolled multiphase steel containing Nb

Influence of thermo-mechanical controlled processing(TMCP),including two-stage rolling with laminar cooling,air cooling and ultra-fast cooling,on the microstructure and mechanical properties of three kinds of Nb-microalloeyed steels was investigated by hot-rolling experiment.Effect of chemistry compositions and microstructure on mechanical properties and the relationship between the multiphase microstructure' s formation with TMCP were analyzed.The results showed that the mixed microstructure containing ferrite,bainite,martensite and a small amount of retained austenite can be obtained by thermo-mechanical controlled processing.Size, quantity and distribution of the constituents(ferrite grain,bainite packet and M-A islands) significantly affect the mechanical properties of three kinds of Nb-microalloyed steels.Under the condition of similar TMCP parameters, there is a gradually decreasing tendency in tensile strength from high silicon Nb steel,high silicon Nb-Ti steel to low silicon Nb-Ti steel,and an opposite tendency in total elongation and product of tensile strength and ductility. Total elongation and product of tensile strength and ductility reach the maximum values(41%and 25256 MPa% respectively) for low silicon Nb-Ti steel.

Phase transformation of TRIP-aided multiphase steel during continuous cooling

The phase transformation characteristics of a high-strength TRIP-aided multiphase cold-rolled steel during continuous heating at different cooling rates were studied by means of dilatometry,and the critical temperatures were also determined.The samples were fully austenitized at 1 050 ℃ and then cooled at different cooling rates ranging from 0.5 ℃/s to 100 ℃/s.The continuous cooling transformation （CCT） curves were obtained for the experimental steel.The experimental results showed that a high cooling rate depressed the formation of ferrite and pearlite and promoted the formation of balnite and martensite,leading to a higher hardness.A large amount of martensite in high-strength TRIP-aided multiphase cold-rolled steel can be obtained at cooling rates in excess of 50 ℃/s.The experimental results provide guidelines for cooling control and heat treatment in real steel production.

Role of Dilatometrical Measurements in the Development of Multiphase Steels

Possibilities of means of dilatometry in connection with production of multiphase (DP- and TRIP-) steels were examined in detail. These steels are characterized by an excellent combination of high strength and good press formability, which are essentially important in the automotive industry. Transformation processes, cooling rates, holding temperatures, composition and technological parameters play a very important role in formation of applicable microstructure of multiphase steels. Dilatometrical experiments were carried out to study the processes of intercritical annealing and hot rolling of several DP- and TRIP-steels.

Improving flangeability of multiphase steel by increasing microstructural homogeneity

Multiphase microstructure significantly increases the strength,usually at the expense of flangeability because of lacking microstructure homogeneity.To further improve the strength-flangeability of multiphase steel,the microstructural homogeneity was advanced by adjusting the hard martensite/austenite(M/A)islands.The strength-flangeability was measured via uniaxial tensile tests and hole expansion tests.Their microstructures were characterized using a scanning electron microscope equipped with an electron backscatter diffraction detector and a transmission electron microscope.Nanoindentation tests were supplementally used to quantitatively reveal the microstructural homogeneity of the steels.Results show that the adjusted multiphase steel achieves an excellent ultimate tensile strength(~800 MPa)and flangeability(~135%hole expansion ratio).A promising homogeneous multiphase microstructure was obtained by controlling undercooled austenite transformed at about 600℃.This microstructure consists of soft polygonal ferrite,blocky bainitic ferrite,and hard M/A islands.The volume fraction of M/A islands is around 5%,and the average size is less than l pm.Detailed nanoindentation analysis indicated that the participation of M/A islands impressively influenced the microstructural homogeneity.Weakened strain partition and better mechanical compatibility were present in the adjusted multiphase steel since the plasticity initiation started late,which resulted in a positive flangeability.Moreover,avoiding M/A islands distributed in the chain along the rolling direction on the matrix hindered the possibility of voids coalescing into cracks and stabilized the flanging performance.

吹氩模式对钢包内多相流流动行为影响的数值模拟研究

以某钢厂150 t钢包为对象,通过数值模拟手段研究了吹氩模式和吹氩流量对钢包流场、钢渣界面行为和壁面剪应力分布的影响。结果表明:单孔吹氩模式下,钢包内环流远端流速低,钢渣界面流动不活跃,易导致此处渣层冷凝结壳;双孔等流量吹氩模式下,随着吹氩流量增大,钢渣界面流速增加,但其流动活跃性降低;双孔差流量吹氩下,大吹氩流量时钢渣界面能维持一定范围的活跃流动。当吹氩流量在120~240 L/min范围,单孔吹氩所形成的渣眼面积大于两种双孔吹氩模式;当吹氩流量超过240 L/min,双孔等流量吹氩下渣眼面积最大,双孔差流量吹氩对应的渣眼面积最小。另外,单孔吹氩下壁面剪应力最大,应力面积较小,双孔等流量吹氩下剪应力虽然显著降低,但分布区域面积增大。综上所述,双孔差流量吹氩模式可以在提高钢液精炼效率的同时,降低对钢包内衬耐火材料的流动侵蚀。

Design of microstructure for damage tolerance in high strength steels

With the extensively wide application of advanced high strength steels(AHSS) in various fields for the excellent mechanical properties,the industrial interest on the damage of AHSS is increasing in the recent years.For these modern steels,due to the complex microstructure and the relevant deformation mechanisms,the damage concept needs to be reexamined.In this paper,the definition,length scale and different mechanisms of damage are introduced.Both experimental evaluation of damage and the numerical damage models are briefly viewed and compared.The approaches to improve the damage tolerance are given in the framework of damage tolerance design principle.

船舶多相感应电机外部磁场分析

针对多相感应电机某一相存在不平衡的情况,基于磁场计算和屏蔽理论建立不平衡电机的简化等效模型,分析其外部磁场特征,进而针对铁质船壳对电机外部磁场的屏蔽效果进行理论分析和计算。研究结果表明,运行状态下的不平衡感应电机在指定评估线上存在100 n T级的外泄磁场,铁质船壳能将这部分磁场削减至原来的50%~80%,对其有一定的屏蔽效果。

Effect of Cooling Patterns on Microstructure and Mechanical Properties of Hot-Rolled Nb Microalloyed Multiphase Steel Plates

The effect of the run-out table cooling patterns on the microstructure and mechanical properties of Nb microalloyed steel plates was investigated by hot rolling experiment. The results showed that the mixed microstrueture containing ferrite, bainite and significant amounts of retained austenite can be obtained through three kinds of cooling patterns on the run-out table under the same hot rolling condition. Three kinds of cooling patterns possess different austenite transformation kinetics, which leads to variations in microconstituent characteristics. The yield strength increases, the tensile strength decreases and the total elongation tends to increase as the cooling patterns Ⅰ , Ⅱ and Ⅲ were applied respectively. The yield strength, the total elongation and the product of tensile strength and ductility reach the maximum values （547 MPa, 37. 2% and 28 384 MPa% respectively） for the steel plate processed by cooling pattern Ⅲ.

Effect of Thermomechanical Processing on Mechanical Properties of Hot Rolled Multiphase Steel

The effect of thermomechanical processing（TMP）on the mechanical properties of hot rolled multiphase steel was investigated.TMP was conducted using a laboratory hot rolling mill,in which three different kinds of finish rolling deformation degrees and temperatures were applied.The results indicate that polygonal ferrite,granular bainite,and a considerable amount of stabilized retained austenite can be obtained by TMP.The stability of the retained austenite increases with decreasing finish rolling temperature and increasing finish rolling deformation degrees.Ultimate tensile strength（σb）,total elongation（δ）,and the product of ultimate tensile strength by total elongation（σb·δ）for 50% reduction at finish rolling temperature of 700 ℃ reach maximum values [791 MPa,36% and 28 476（MPa·%）,respectively].

多相炭黑G10填充半钢轮胎胎面胶性能研究

研究偶联剂Si69用量对多相炭黑G10填充半钢轮胎胎面胶性能的影响,并与炭黑及炭黑/白炭黑并用填充胎面胶性能进行对比。结果表明:与炭黑填充胶料相比,炭黑/白炭黑并用填充胶料的门尼粘度较大,t_(90)延长,t_(10)缩短;与炭黑/白炭黑并用填充胶料相比,多相炭黑G10填充胶料的门尼粘度明显减小,t_(90)缩短,混炼胶的Payne效应明显减弱,硫化胶的拉伸强度增大,阿克隆磨耗量和DIN磨耗量减小,压缩生热明显降低,混炼胶中炭黑分散性明显改善;随着多相炭黑G10填充胶料中偶联剂Si69用量的增大,胶料硫化特性和物理性能变化不大,损耗因子减小,其中偶联剂Si69用量为白炭黑用量8%的胶料生热较低,多相炭黑G10分散效果较好。

CT80连续油管液固两相流冲蚀磨损试验研究

针对国产CT80连续油管在服役过程中发生的冲蚀磨损问题,采用自制的室内喷射式冲蚀试验装置,与油套管用N80钢进行对比试验,研究了冲击角度、流速以及砂含量3种影响因素对冲蚀速率的影响。结果表明:CT80钢在冲击角度为30°时,冲蚀速率最大可达9.06×10^(-7)kg/kg,而N80钢在冲击角度为15°时冲蚀速率最大值为6.03×10^(-7)kg/kg。N80钢在流速从1 m/s增大到5 m/s时,最大冲蚀速率从4.56×10^(-8)kg/kg增加到6.03×10^(-7)kg/kg,增幅约为13.2倍,是增长速率最快的阶段。CT80钢在相同流速阶段增幅比N80钢小,约为10倍。N80钢在砂含量从0.5%增加到1%时,冲蚀速率增长最快,由5.28×10^(-7)kg/kg增长到6.1×10^(-7)kg/kg,而CT80钢在砂含量从0.5%增加到3%时,冲蚀速率呈现先增大再减小的波动趋势。该试验为油田复杂环境下完井管柱的选材提供了参考。

20SiMn低合金钢和0Cr13Ni5Mo不锈钢的多相流损伤行为

对水轮机用金属材料20SiMn低合金钢和0Cr13Ni5Mo不锈钢进行了旋转圆盘仪空蚀和冲刷磨损单元和组合多相流损伤实验.结果表明, 20SiMn低合金钢和0Cr13Ni5Mo不锈钢的冲刷磨损及空蚀和冲刷磨损联合作用损伤累积质量损失-时间曲线均呈线性关系,空蚀和冲刷磨损联合作用对材料所造成的损伤显著高于空蚀和冲刷磨损单独作用,空蚀和冲刷磨损的交互作用在空蚀和冲刷磨损联合作用中起重要的作用;在空蚀和冲刷磨损联合作用中,液体空化及随后的空泡溃灭改变了流体中固相颗粒的运动方向,引起固相颗粒的流速增加和攻角改变,从而加剧了固相颗粒对材料表面的损伤.

X52钢的CO_2腐蚀行为

通过扫描电镜观察及X射线衍射分析 ,研究X5 2钢在模拟输送管腐蚀环境条件下的腐蚀行为 .结果表明 ,X5 2钢的平均腐蚀速率为 0 6 2 89mm/a ,其表面形成三层形貌及成分各异的腐蚀产物 ,三层膜中主要的腐蚀产物均是FeCO3 和Fe2 O3,宏观腐蚀形态基本为均匀腐蚀 。