Effect of silicon content and annealing temperature on formation of retained austenite and mechanical properties in multi-phase steels

Cold-rolled and annealed ultra-high strength sheet steels with good ductility accompanied by TRIP of retained austenite have received considerable attention in recent years. This paper discusses the effect of silicon content and annealing temperature on the formation of retained austenite and the mechanical properties in Fe-0.34%C-1.7% Mn steels whose structure consists of ferrite, bainite and retained austenite. Silicon inhibited the cementite formation in bainite during isothermal holding and partitioned carbon from bainite to austenite, resulting in an increase in retained austenite content. When the silicon content was increased to 1.0 wt.% or higher, the amount of retained austenite markedly increased leading to good mechanical properties. 0.34%C-1.03%Si-1.7%Mn steel showed a high tensile strength of 1,030 MPa and a total elongation of 34.5% when annealed at 780°C for 5 min followed by isothermal holding at 400°C for 5 min. In this case, the amount of retained austenite was about 25%. The variation in tensile strength-elongation combination had good correlation with that in the amount of retained austenite with both annealing temperature and silicon content. The most retained austenite was obtained in the steel annealed at just above A_C1 temperature. The annealing temperature which gives the most retained austenite was decreased with decreasing the silicon content.     

Effects of Intercritical Annealing Temperature on the Tensile Behavior of Cold Rolled 7Mn Steel and the Constitutive ModelingEI北大核心CSCD

Medium Mn steel is composed of sub-micron grained ferrite and austenite, the unstable austenite may transform to martensite during plastic straining. Although the mechanical properties of medium Mn steel could be easily tested by tensile test, it is quite difficult to directly measure the influences of different constituent phases on the tensile and work hardening behavior. Thus, at the present work, EBSD, TEM, XRD and a constitutive model based on dislocation density have been used to study the effects of intercritical annealing (IA) temperature on the tensile properties and work hardening behavior of a newly designed medium Mn steel, Fe-7% Mn-0.3% C-2% Al (mass fraction). Experimental results showed that with the increase of IA temperature, the mechanic stability of reverted austenite decreased gradually and the kinetics of strain induced martensite rose rapidly. The stability of the reverted austenite was moderate when intercritically annealed at 700 degrees C this led to the best plasticity and the optimal mechanical properties. Simulated results exhibited that the mechanic stability of austenite has a decisive influence on the tensile behavior of the material. The austenite stability will be too high if the IA temperature is lower, and this will lead to the lower work hardening rate and uniform elongation; when the IA temperature is moderate, the stability of austenite will be optimum, consequently strain-induced martensite would be progressively produced during straining and result in the higher work hardening rate and prolonged uniform elongation; the stability of austenite will be too lower if the IA temperature is higher, thus larger volume fraction of strain- induced martensite would be formed in a short period, and this would result in the higher tensile strength but the inferior uniform elongation.     

铸态锰钢的抗磨性能

通过化学成分的优化,N、Cr等元素的加入和变质处理等措施,得到在稳定产低的奥氏体基体上弥散分布有粒状碳化物的铸态组织。这种铸态锰钢具有初始硬度高、韧性好、加工硬化能力强和抗磨性高等特点。并重点分析了铸态锰钢的抗磨机理。     

Effect of heat treatment on formability in 0.15C−1.5Si−1.5Mn multiphase cold-rolled steel sheet

The effects of volume fraction and the stability of retained austenite on the formability of a 0.15C−1.5Si−1.5Mn (hereafter all in wt.%) TRIP-aided multiphase cold-rolled steel sheet were investigated after various heat treatments. The steel sheets were intercritically annealed at 800°C, and isothermally treated at 400°C and 430°C. Microstructural observation, tensile tests and limiting dome height (LDH) tests were conducted on the heat-treated sheet specimens, and the changes in retained austenite volume fraction as a function of tensile strain were measured using an X-ray diffractometer. The results showed a plausible relationship between formability and retained austenite stability. Although the same amount of retained austenite was obtained after isothermal holding at different temperatures, better formability was obtained in the specimens with the higher stability of retained austenite. If the stability of the retained austenite is high, the strain-induced transformation of retained austenite to martensite can be stably progressed, resulting in a delay of necking to the high strain region and improvement in formability.     

A STEEL MATRIX WEAR RESISTANT COMPOSITE REINFORCED BY IN-SITU GRANULAR EUTECTICS

1. 'IntroductionA pajrticle reinforced metal matrix composite has higher strength and wear resistancethan that of its matrix material because the particle phases can strongly resist abrasivewearll--']. However, this material has significallt disadvatages of complex manufactureprocess and high cost, so it is very limited in applications. In this research, a new in sitegranular eutectic reinforced phase can be obtained for the first time by modifying witha St-Ce-Ti compound in the steel melt to…     

Q&P工艺对Fe-0.45C-1.6B高硼钢组织和性能的影响

借助Thermo-Calc、光学显微镜、扫描电镜、X射线衍射仪、洛氏硬度计及冲击磨损试验机对Fe-0.45C-1.6B高硼钢铸态和经Q&P工艺处理后的组织和性能进行分析。结果表明:高硼钢铸态组织由铁素体、马氏体及残留奥氏体构成的基体和共晶硼化物组成。经Q&P工艺处理发现,高硼钢在Ms点以下为马氏体等温转变,随着淬火时间的增加,基体中残留奥氏体越来越多,在淬火时间为120 s时达到极限。随着配分时间的增加,高硼钢中残留奥氏体增加,配分时间为80 s时残留奥氏体量最多,但是由于较多的残留奥氏体不能支撑硼化物,因此高硼钢的耐磨性降低。     

退火温度对冷轧8Mn钢低温热成形后组织和性能的影响

采用冷轧8Mn钢为试验材料,利用光学显微镜、扫描电镜、电子拉力万能试验机等,结合EBSD和XRD分析技术研究了不同退火温度对低温热成形前后试验钢组织和性能的影响。结果表明,热成形前,试验钢中的奥氏体含量随着退火温度的升高而降低。低温热成形后试验钢的显微组织为马氏体、铁素体和残留奥氏体。不同温度退火并热成形后试验钢的抗拉强度均为1400 MPa左右,屈服强度为900 MPa左右,伸长率为10%左右。退火温度对8Mn钢低温热成形后力学性能影响较小。     

两相区回火温度对含7%锰Q690钢组织和性能的影响

采用SEM、XRD、TEM和Thermo-Calc软件计算等手段研究了两相区回火温度对0.02C-7Mn钢的组织和性能变化的影响。结果表明,淬火后试验钢组织以淬火马氏体为主,伴有极少量的残留奥氏体;两相区回火后,基体组织以回火马氏体为主,出现逆转变奥氏体,空冷后转变为残留奥氏体。随着回火温度的升高,残留奥氏体的含量逐渐增加,在650 ℃回火后到达峰值为18.78%;与此同时出现了6.57%的ε-马氏体。两相区回火后,试验钢的抗拉强度均有下降,但是屈服强度有不同程度的升高,这归因于回火过程中位错密度的下降以及弥散第二相的析出。另外,ε-马氏体的存在不仅迅速降低了屈服强度,而且还损害了韧性。在600 ℃回火后,试验钢具有优异的综合力学性能(横向:抗拉强度为984 MPa、屈服强度为973 MPa,-40 ℃冲击吸收能量为163 J,纵向:抗拉强度为947 MPa、屈服强度为919 MPa,-40 ℃冲击吸收能量为186 J),满足Q690用钢的力学性能需求。     

Fe-C-Cr-Mn系亚稳奥氏体基耐磨铸造合金的开发

亚稳奥氏体基加Ｍ７Ｃ３型共昌碳化物双相结构白口铁基铸造合金具有良好的耐磨性和较高的冲击韧性。利用该理论开发了Ｆｅ－Ｃ－Ｃｒ－Ｍｎ系新型亚稳奥氏体基耐磨合金。通过滑动磨损试验发现，它们的耐磨性优于传统耐磨材料Ｃｒ２５这种新材料的使用对节省能源有重要意义。     

Influence of carbon content on microstructure and mechanical properties of Mn13Cr2 and Mn18Cr2 cast steels

In this paper, a comparison study was carried out to investigate the influence of carbon content on the microstructure, hardness, and impact toughness of water-quenched Mn13Cr2 and Mn18Cr2 cast steels. The study results indicate that both steels＇ water-quenched microstructures are composed of austenite and a small amount of carbide. The study also found that, when the carbon contents are the same, there is less carbide in Mn18Cr2 steel than in Mn13Cr2 steel. Therefore, the hardness of Mn18Cr2 steel is lower than that of Mn13Cr2 steel but the impact toughness of Mn18Cr2 steel is higher than that of Mn13Cr2 steel. With increasing the carbon content, the hardness increases and the impact toughness decreases in these two kinds of steels, and the impact toughness of Mn18Cr2 steel substantially exceeds that of Mn13Cr2 steel. Therefore, the water-quenched Mn18Cr2 steel with high carbon content could be applied to relatively high impact abrasive working conditions, while the as-cast Mn18Cr2 steel could be only used under working conditions of relatively low impact abrasive load due to lower impact toughness.     

Si、Mn元素对奥氏体不锈钢微观组织和拉伸性能的影响

为提高奥氏体不锈钢耐蚀性,合金中可同时加入Si、Mn元素,提高合金氧化膜形成能力,同时增加奥氏体基体稳定性,但Si、Mn的添加还能够对合金的冷变形组织和力学性能产生影响。本研究设计了不同硅、锰含量的奥氏体不锈钢,采用SEM、EPMA以及TEM等方法表征合金显微组织形貌,采用室温拉伸分析合金的力学性能。结果表明,Si质量分数由1.0%提高至2.0%,20%冷变形合金组织中变形孪晶体积分数由4.98%增加至8.33%,合金屈服强度由620 MPa提高至682 MPa,延伸率基本保持不变;Mn质量分数由1.5%提高至2.0%,变形孪晶体积分数由8.33%减少至7.22%,屈服强度由682 MPa降低至627 MPa,延伸率由16.0%增加至21.3%;添加Si元素,合金中孪晶数量增加,合金强度提高并保持塑性;添加Mn元素,合金中孪晶数量减少,强度降低塑性增强。     

碳含量对铸态Mn6系钢奥氏体稳定性的影响

分析了碳含量的变化对铸态Mn6系钢显微组织的影响,探讨了Mn6系钢在铸态下碳含量与奥氏体稳定性的关系。结果表明,当碳含量在0.93%以下时,凝固组织中发生部分珠光体转变和马氏体转变;当碳含量在1.19%时,凝固组织为全奥氏体。而当碳含量达到1.28%时,凝固组织中开始析出第二相碳化物。含碳量1.19%为奥氏体稳定性的一个重要分界点。     

Influence of carbon content on wear resistance and wear mechanism of Mn13Cr2 and Mn18Cr2 cast steels

By means of impact abrasion tests, micro-hardness tests, and worn surface morphology observation via SEM, a comparison research based upon different impact abrasive wear conditions was conducted in this research to study the influence of different carbon contents(1.25 wt.%, 1.35 wt.%, and 1.45 wt.%) on the wear resistance and wear mechanism of water-quenched Mn13Cr2 and Mn18Cr2 cast steels. The research results show that the wear resistance of the Mn18Cr2 cast steel is superior to that of the Mn13Cr2 cast steel under the condition of the same carbon content and different impact abrasive wear conditions because the Mn18Cr2 cast steel possesses higher worn work hardening capacity as well as a more desirable combination of high hardness and impact toughness than that of the Mn13Cr2 cast steel. When a 4.5 J impact abrasive load is applied, the wear mechanism of both steels is that plastic deformation fatigue spalling and micro-cutting coexist, and the former dominates. When the carbon content is increased, the worn work hardening effect becomes increasingly dramatic, while the wear resistance of both steels decreases, which implies that an increase in impact toughness is beneficial to improving the wear resistance under severe impact abrasive wear conditions. Under the condition of a 1.0 J impact abrasive load, the wear mechanism of both steels is that plastic deformation fatigue spalling and micro-cutting coexist, and the latter plays a leading role. The worn work hardening effect and wear resistance intensify when the carbon content is increased, which implies that a higher hardness can be conducive to better wear resistance under low impact abrasive condition.     

Effect of annealing temperature on microstructural modification and tensile properties in 0.35 C–3.5 Mn–5.8 Al lightweight steel

The microstructural modifications occurring during annealing treatment of an Fe–0.35 C–3.5 Mn–5.8 Al ferrite-based lightweight steel and its effects on the tensile properties were investigated with respect to (α + γ) duplex microstructures. Steels annealed above the dissolution finishing temperature of κ-carbides (795 °C) were basically composed of ferrite band and austenite band in a layered structure. As the annealing temperature was increased the tensile strength increased, while the yield strength and elongation decreased. This could be explained by a decrease in the mechanical as well as thermal stability of austenite with increasing size and austenite volume fraction. In the 980 °C annealed steel in particular, whose mechanical stability due to austenite was lowest, cracks were readily formed at ferrite/austenite (or martensite) interfaces with little deformation, thereby leading to the least tensile elongation. In order to obtain the best combination of strength and ductility the formation of austenite having an appropriate mechanical stability was essentially needed, and could be achieved when 22–24 vol.% fine austenite was homogeneously distributed in the ferrite matrix, as in the 830 °C or 880 °C annealed steels.     

中锰奥氏体基耐磨钢中马氏体的应用

合理设计了中锰奥氏体基耐磨钢的成分,并选择合适的水韧处理工艺来获得一种介稳的单相奥氏体,在此组织基础上进行不同的等温热重申２工艺岖得一定量的马氏体,以提高基体的初始硬度,又不恶化其冲击韧度。再通过与高锰钢（Ｍｎ１３）在同等工况条件下进行耐磨性模拟对比试验,来选择适合中锰钢中、低冲击磨料磨损条件下使用的热处理工艺和组织,同时对试样进行金相组织观察及力学性能测试。     

Mn和Ce对Fe-Ni-Mn-C-Si-Ce系合金组织和性能的影响

采用熔炼法制备出新型高耐磨的Fe-20Ni-xMn-3.5C-2.5Si系固体自润滑材料,研究稀土元素Ce对Fe-20Ni-xMn-3.5C-2.5Si系合金中石墨的球化作用及Mn含量对力学性能及摩擦磨损性能的影响。结果表明：随着Mn含量的增加,合金凝固组织中奥氏体的硬度逐渐增大,特别是Fe-20Ni-xMn-3.5C-2.5Si-0.75Ce系合金在摩擦过程中的表面硬度大幅度提高,呈现出高锰钢特有的表面加工硬化性质,通过TEM可以观察到磨损表面生成孪晶型马氏体;添加0.75%（质量分数）的稀土Ce可以使结晶的石墨球化,使抗拉强度和抗弯强度大幅度提高,大约比未经球化处理的提高3～5.8倍;稀土Ce的加入可以促进Fe1.1Mn3.9C2型碳化物的生成,使材料的耐磨性进一步提高,其中Fe-20Ni-16Mn-3.5C-2.5Si-0.75Ce合金的磨损率最低,大约是QT500球墨铸铁的1/13。     

Influence of titanium content on wear resistance of electrolytic low-titanium eutectic Al-Si piston alloys

The wear resistance of six kinds of the electrolytic low-titanium eutectic Al-Si piston alloys with various Ti content ranging from 0.00wt.% to 0.21wt.% has been studied. A new method of adding Ti is adopted in the electrolytic low-titanium aluminum alloy ingots. The electrolytic low-titanium eutectic AI-Si piston alloys are produced by remelting the electrolytic low-titanium aluminum alloy, crystal silicon, pure magnesium, Al-50%Cu and Al-10%Mn master alloy. The wear experiments are conducted using MM200 wear testing machine under lubricating condition. The results indicate that the better wear resistance and the less weight loss are achieved in the study for the eutectic AI-Si piston alloys with 0.08wt.%-0.12wt.% Ti content. The highest ultimate tensile strength of 135.94 MPa at 300℃ and HV141.70 hardness of the alloys are obtained at 0.12wt.% and 0.08wt.% Ti content, respectively. The wear mechanism of the eutectic Al-Si piston alloys under lubricating condition is abrasive wear.     

Influence of titanium content on wear resistance of electrolytic low-titanium eutectic AI-Si piston alloys

The wear resistance of six kinds of the electrolytic low-titanium eutectic AI-Si piston alloys with various Ti content ranging from 0.00wt.% to 0.21wt.% has been studied. A new method of adding Ti is adopted in the electrolytic low-titanium aluminum alloy ingots. The electrolytic low-titanium eutectic AI-Si piston alloys are produced by remelting the electrolytic low-titanium aluminum alloy, crystal silicon, pure magnesium, AI-50%Cu and AI-10%Mn master alloy. The wear experiments are conducted using MM200 wear testing machine under lubricating condition. The results indicate that the better wear resistance and the less weight loss are achieved in the study for the eutectic AI-Si piston alloys with 0.08wt.%-0.12wt.% Ti content. The highest ultimate tensile strength of 135.94 MPa at 300℃ and HV141.70 hardness of the alloys are obtained at 0.12wt.% and 0.08wt.% Ti content, respectively. The wear mechanism of the eutectic AI-Si piston alloys under lubricating condition is abrasive wear.     

Achieving Excellent Strength–Ductility and Impact Toughness Combination by Cyclic Quenching in Medium Mn TRIP-Aided Steel

A novel heat treatment process combined cyclic quenching (CQ) with austenite reversion treatment (ART) is proposed to obtain high strength–ductility and high-impact toughness combination in Fe-0.18C-8.92Mn-3.43Al (in mass%) steel. The process referred as CQ-ART was designed for accomplishing the following objectives: (i) refine the prior austenite grains during cyclic quenching process, (ii) further obtain the refined austenite–ferrite block and (iii) improve the stabilities of retained austenite with Mn/C enrichment during ART process. The outstanding product of tensile strength and total elongation of CQ-ART-treated steels was 41.53 and 37.39 GPa%, respectively, and higher than the ART steel of 27.45 GPa%. The highest Charpy impact toughness of CQ-ART steel can reach to 221 J, which is mainly attributed to the refined grains and discontinuous transformation-induced plasticity (TRIP) effect.     

钛对铁锰基减振合金阻尼性能和耐蚀性能的影响

采用内耗检测技术研究了Ti对Fe-14Mn、Fe-17Mn和Fe-23Mn合金阻尼性能的影响,研究了Ti对Fe-Mn系合金相组成和耐蚀性能的影响.结果表明,Fe-17Mn比Fe-14Mn和Fe-23Mn具有更高的阻尼性能;在Fe-Mn合金中加入质量分数为1.0％的钛,合金的阻尼性能均受到影响,合金在固溶处理时,发生了γ...