碳素双相钢强度规律的研究

本文在六种不同含碳量的普通碳钢上用亚温淬火获得铁素体加马氏体双相组织,研究了各相的性能和分布对双相钢拉伸强度的影响。试验结果表明:①碳素双相钢的强度与马氏体含量间并不呈简单线性关系;②存在着马氏体对铁素体的相硬化和铁素体对马氏体的相软化,使得两相的显微硬度都随马氏体的含量和马氏体的含碳量的增加而线性上升。文中提出,作为强化相的马氏体对强度的贡献可分为本身承载的直接作用和对铁素体加工硬化的间接作用。双相钢中两相的性能变化和组织形态都促成了混合律不能适用于双相钢。     

低碳双相钢冲击韧性及断裂特征

本文研究了低碳双相钢中不同体积百分比及不同强度比的铁素体、马氏体双相组织对钢的冲击韧性及断裂过程的影响。结果表明:马氏体数量增加使钢的韧性降低,回火温度升高使钢的韧性提高。冲击断口形貌由室温的韧窝型转变为-78℃时以准解理为主及-196℃时全部解理型。     

高强度高塑性双相15Mn2Nb钢的组织和性能

本文以Mn为主加元素强化铁素体与提高淬透性,以Nb为辅加元素细化组织,发展了一种双相15Mn_2Nb钢。研究了在亚温淬火和亚温形变淬火条件下组织和性能的变化规律,并与15碳素双相钢进行了对比。结果表明,15Mn2Nb钢经予先淬火和随后亚温(α γ)区重新加热淬火,可使马氏体和铁体素晶粒呈细小条状,相间分布,形成一种特殊的“类珠光体型”双相组织。亚温形变淬火时,铁素体和马氏体呈细长纤维定向分布,其中铁素体纤维由大量极细小(相似文献   

450~780 MPa系列双相钢扩孔性能实验

目的避免双相钢在成形过程中经常出现的翻边或扩孔开裂的问题,提高生产效率。方法以几种强度级别为450~780 MPa的双相钢为实验对象,测试材料的单向拉伸和扩孔性能,并从微观组织上分析影响双相钢强度和扩孔性能的因素。结果 450~780 MPa强度级别双相钢的屈服强度随铁素体晶粒尺寸的减小而增加,抗拉强度随马氏体体积分数的增加呈近似线性增加。双相钢的扩孔性能随着材料强度的提高呈下降的趋势。DP500与DP450和DP600相比,抗拉强度(579 MPa)居中,伸长率最高,但由于其马氏体形态和分布的差异,其扩孔性能反而最低。结论双相钢的扩孔性能会受到马氏体的含量、尺寸、形态和分布的影响,与材料强度和伸长率没有必然的关系,当马氏体呈颗粒状均匀分布时,具有更好的扩孔性能。     

冷却模式对热轧双相钢组织及断裂机制的影响

为研究冷却模式对热轧双相钢显微组织及断裂机制的影响,采用两段式(空冷+水冷)、连续式两种冷却方式,得到不同相比例和力学性能的热轧双相钢,轧后取样并在扫描电镜上进行原位拉伸实验.结果表明,两段式冷却模式得到的马氏体呈小岛状,而连续式冷却模式得到的马氏体呈块状,马氏体含量和形貌的不同导致两种冷却方式得到的双相钢力学性能存在差异.原位拉伸过程中,裂纹首先萌生于铁素体与夹杂物界面处,随着变形继续进行,在铁素体与马氏体界面处开始出现裂纹,当变形量进一步增大时,细小岛状马氏体始终不发生断裂,而块状马氏体在颈缩阶段发生断裂.     

低碳予冷轧型铁素体加马氏体双相钢的组织和性能

本文研究了予先冷轧对低碳铁素体加马氏体双相钢显微组织和拉伸性能的影响,并用了Jaoult-Crussard法对有关的应变硬化行为进行了分析。结果表明,予先冷轧易于使低碳铁素体加马氏体双相钢呈现较弥散的马氏体分布和较细的铁素体晶粒,从而有较低的屈强比,较高的应变硬化率以及良好的强塑性组合。相应的应变硬化曲线由三段斜率不同的直线部分所组成。随着第二段的斜率的降低,塑性提高。通过调整第二相中马氏体与未溶碳化物的相对数量,可以达到不同的强塑性组合。     

超高强铁素体-马氏体双相钢在动态拉伸变形条件下组织和性能研究

通过分段淬火连续退火实验,获得两组铁素体晶粒尺寸大致相同、马氏体体积分数不同的双相钢。选取应变速率为10-4s-1进行准静态拉伸实验;选取应变速率为500s-1和2250s-1在分离式霍普金森拉杆技术进行动态拉伸实验。利用动态因子、Feret比率等定量分析方法研究超高强铁素体-马氏体双相钢在动态拉伸变形条件下的组织和性能。结果表明:应变速率效应在双相钢的动态变形行为中主要起强化作用;马氏体体积分数越低的双相钢应变速率敏感性越大;相比抗拉强度而言,超高强冷轧双相钢屈服强度的应变速率敏感性更大。计算在应变速率为2250s-1动态拉伸变形下产生绝热温升分别为98K和89K,并抵消部分应变速率强化作用。     

C-Si—Mn冷轧双相钢的应变硬化特性

试制了C-Si-Mn冷轧双相钢.采用力学测试、显微组织观察与修正的C-J分析方法研究了双相钢的应变硬化特性.研究结果表明,双相钢的应变硬化具有两阶段.第一阶段应变硬化能力较强,第二阶段硬化能力减弱.两阶段硬化之间存在一个转折应变.当马氏体体积分数小于16%,随马氏体体积分数的增加,两阶段硬化能力均增强.当马氏体体积分数大于16%,随马氏体体积分数的增加,两阶段硬化能力均减弱.硬化转折应变则随马氏体体积分数增加单调递减.铁素体与马氏体的弹塑性行为差异是导致双相钢两阶段硬化的主要原因.马氏体体积分数增加,其强化效果增加,但是由于马氏体中的碳含量降低,其塑性抗力降低.只有当马氏体量增加带来的强化效应大于碳含量减少的弱化效应时,双相钢的应变硬化能力才随之增加.     

热轧双相钢的发展现状及高强热轧双相钢的开发

介绍了热轧双相钢的发展现状及存在问题,指出低成本热轧双相钢、高延伸凸缘型铁素体+贝氏体热轧双相钢(F-B热轧双相钢)及高强度热轧双相钢的开发及应用,将促进我国热轧双相钢的发展,推动汽车工业的"以热代冷"进程。同时,探讨了纳米析出强化型热轧双相钢的强化机理及工艺控制原理,并在实验室进行了中试,开发出铁素体基体析出强化型的热轧双相钢,其抗拉强度达770~830 MPa,屈强比0.75,组织为铁素体+马氏体,且铁素体基体中存在大量细小的纳米级尺寸的TiC过饱和析出和相间析出。     

双相钢冲击拉伸变形行为本构方程的建立

利用旋转盘式冲击拉伸试验装置，对马氏体含量为３０％，４２％，４８％，５０％和６０％的２０Ｃｒ双相钢进行３个应变率的冲击拉伸试验，得到了这些材料在不同高应变率下 绝热应力应变曲线；发现２０Ｃｒ双相钢的屈服应力随马氏体的含量和应变率的增加而增加，且马氏体的含量对应变率的强化系数影响不大。     

Effect of martensite strength on the tensile strength of dual phase steels

Fe-2% Si-1.5% Mn steels with three levels of carbon content (0.10, 0.14 and 0.19 wt%) were intercritically annealed followed by water quenching to obtain dual phase (martensite plus ferrite) structure. It is found that the ultimate tensile strength of dual phase steels increased with increasing the volume fraction as well as the tensile strength of martensite. The tensile strength of dual phase steel can be predicted using the law of mixtures although the predicted tensile strength is slightly higher than the experimental one. It is suggested that martensite never reaches its ultimate tensile strength when the necking of dual phase steels occurs.     

The effect of dynamic strain aging on fatigue properties of dual phase steels with different martensite morphology

Dual phase (DP) steels with network and fibrous martensite were produced by intercritical annealing heat treatment cycles. Some of these steels were deformed at dynamic strain aging temperatures. Room temperature tensile tests of specimens deformed at 300 °C showed that both yield and ultimate tensile strengths for both morphologies increased, while total elongation decreased. Fatigue test results before and after high temperature deformation showed that dynamic strain aging has a stronger effect on fatigue properties of dual phase steels with fibrous martensite. Cracks in DP steels with fibrous martensite propagate in a tortuous path in soft ferrite phase, while they pass of both hard and soft phases in DP steels with network martensite.     

Enhancement of work‐hardening behavior of dual phase steel by heat treatment

The work‐hardening response and mechanical properties of dual phase steels originated from different initial microstructures under low and high martensite volume fractions were investigated using a typical carbon‐manganese steel. The modified Crussard‐Jaoul analysis was used for studying the work‐hardening stages and the deformation behavior of ferrite and martensite. It was revealed that the initial martensitic microstructure before intercritical annealing is much better than the full annealed banded ferritic‐pearlitic and spheroidized microstructures in terms of work‐hardening capacity and strength‐ductility trade off. By increasing the amount of martensite, via intercritical annealing at higher temperatures, the ductility decreased but the tensile toughness of dual phase steels increased toward reaching the domain of extra‐advanced high‐strength steels due to the enhancement of work‐hardening rate.     

Microscopic deformation behaviour of martensitic–ferritic dual-phase steels

Abstract

The deformation behaviour of the two phases of three plain carbon dual–phase steels after various treatments has been studied using a scanning electron microscope equipped with a tensile straining stage. The distribution of strains between the ferrite and martensite phases, as well as among the different grains of each phase, was observed to be inhomogeneous. The martensite/ferrite strain ratio, which defines the degree of uniformity of straining between the phases, depends on the microstructural parameters of the steels: it increases with increasing volume fraction of martensite, but decreases as the carbon content of the martensite increases. Tempering at various temperatures causes a decrease in the martensite/ferrite microhardness ratio and hence causes an increase in the strain ratio. The macroscopic strain of the specimen at which the martensite begins to deform was also found to be dependent on the microstructural parameters. Regions of applicability of the existing theories of the strength of dual–phase steels can be estimated according to the deformation condition of the martensite.

MST/235     

Acoustic emissions during tensile test of DC06 and HCT600X

In this paper the acoustic emission behaviour during tensile tests of the materials DC06 and HCT600X is studied. Two steels with different characteristics (mild deep‐drawing steel DC06 and high‐strength steel HCT600X) are consciously chosen to show the influence of the material properties on the generated acoustic emissions. The acoustic emission behaviour and the corresponding signals differ clearly from each other. In addition, the effect of the strain rate as well as the rolling direction (0°, 90°) on the acoustic emission behaviour is investigated. Both parameters have a significant influence on the resulting acoustic emissions during tensile deformation. Furthermore, a new criterion based on the acoustic emission parameter FCOG (centroid frequency) for detection of damage beginning in dual‐phase steels is developed. The criterion supports the assumption that during tensile deformation of dual‐phase steels two failure mechanisms, ferrite/martensite interface decohesion and martensite phase fracture, exist.     

Characterization of Dual-Phase Steels Using Magnetic Barkhausen Noise Technique

The aim of this work is to nondestructively characterize the dual phase steels using the Magnetic Barkhausen Noise (MBN) method. By quenching of AISI 8620 steel specimens having two different starting microstructures, from various intercritical annealing temperatures (ICAT) in the ferrite-austenite region, the microstructures consisting of different volume fractions of martensite with morphological variations have been obtained. The microstructures were first conventionally characterized by metallographical investigations and hardness tests. Then, the MBN measurements were performed using a μSCAN commercial system. Good correlations between the martensite volume fraction, hardness and MBN emission have been obtained. MBN signal height clearly decreased as the ICAT, therefore the volume fraction of martensite increased. The effect of the initial microstructure prior to intercritical annealing has also been differentiated by the MBN measurements. It has been concluded that MBN method can be used as a useful tool for nondestructive characterization of dual phase steels.     

Correlating microstructural features with wear resistance of dual phase steel

In order to explore the tribological potential of the dual phase (DP) steel as a wear resistant material, the wear characteristics of the dual phase (DP) steel have been investigated with varying amounts of martensite from 43 to 81 vol pct, developed by varying holding time at the intercritical annealing temperature of 780 °C. Dry sliding wear tests have been conducted on DP steels using a pin-on-disk machine under different normal loads of 61.3, 68.5, 75.7 and 82.6 N and at a constant sliding speed of 1.20 m/s. At these loads, the mechanism of wear is mainly delamination, which has been confirmed by SEM micrographs of the subsurface and wear debris of the samples. Wear and friction properties have been found to be improved with increasing martensite volume fraction in dual phase steels.     

复相材料中微观组织开裂的力学分析

本文从力学角度对复相材料中微观组织的开裂进行了分析,论述了微观组织的等强度设计思想和方程,计算了 F(铁素体)-M(马氏体)双相钢中 M 体的临界长度 l_c,利用临界长度的概念,对 F-M 双相钢中微观组织的开裂位置进行了分析计算。     

A Study on the Wear Behaviour of Dual Phase Steels

Dual phase （DP） steels containing four different amounts of martensite ranging from 43 vol. pct to 81 vol. pct have been developed from 0.2 wt pct carbon steel by intercritical heat treatment at a fixed temperature of 780℃ with varying holding times followed by water quenching. Dry sliding wear tests have been conducted on DP steels using a pin- on-disk machine under different normal loads of 61.3, 68.5, 75.7 and 82.6 N and at a constant sliding speed of 1.20 m/s. At these loads, the mechanism of wear is primarily delamination, which has been confirmed by SEM micrographs of subsurface and wear debris of samples. Wear properties have been found to improve with the increase in martensite volume fraction in dual phase steels.