马氏体时效不锈钢热处理工艺优化

利用热力学计算软件Thermo-Calc,研究了马氏体时效不锈钢Fe-13Cr-7Ni-4Mo-4Co-2W在不同温度下的基体组织和析出相的变化.通过TEM、SADP法分析研究了马氏体时效不锈钢在固溶处理与时效处理过程中显微组织与析出行为.热力学计算与实验研究结果一致表明,马氏体时效不锈钢高温析出Laves-Fe2Mo相,固溶温度超过1050℃,Laves-Fe2Mo相全部溶解;时效析出R相,其含量在8%左右.根据计算结果优化了相应的热处理工艺,力学性能研究结果表明,用所确定的时效工艺进行热处理后,马氏体时效不锈钢的强韧性最好.     

热处理温度对新型马氏体时效不锈钢微观组织和性能的影响

针对一种以Al作为主要强化元素的新型马氏体时效不锈钢,通过力学性能测试、光学显微镜观察和透射电子显微分析方法,研究不同的热处理温度对实验钢力学性能和微观组织的影响。结果表明:该实验钢的抗拉强度最高可达1876MPa,屈服强度可达1762MPa,具有良好的强韧性配合。固溶处理后形成了具有高密度位错的细小板条马氏体组织,在时效过程中,马氏体基体上弥散析出的NiAl相使其强度得到大幅度的提升。随着时效温度的提高,NiAl析出相颗粒逐渐长大粗化,从而使强度在到达峰值后迅速下降,出现了过时效现象。实验钢经过820℃固溶+(-70℃)冷处理+540℃时效处理后可获得良好的综合力学性能。     

超高强度马氏体时效钢的力学行为与微观组织演化的关系

用高分辨透射电镜(HRTEM)和原子探针层析技术(APT)等手段研究了2.4 GPa级超高强度马氏体时效钢在时效过程中析出相的演化规律及其与材料力学性能的关系。对组织观察的结果表明,马氏体时效钢在时效过程中析出相的演化规律分为三个阶段：时效初期富Ni和富Ti团簇的形成、峰时效期金属间化合物Ni₃Ti及其界面处富Mo相的形成、过时效阶段Ni₃Ti的粗化和富Mo相过渡为Ni₃Mo。力学性能的实验结果表明,随着时效时间的延长抗拉强度呈现先提高后降低的趋势,时效时间为4 h时抗拉强度达到最大值2560 MPa。断裂韧性呈现与抗拉强度相反的变化趋势,时效时间为4 h时的断裂韧性值最低,仅为20 MPa·m^1/2。根据不同时效阶段材料中析出相的演化规律,探讨了马氏体时效钢的力学行为与析出相的关系。     

18Ni马氏体时效钢低周疲劳性能的影响因素分析

本文主要对具有优异综合性能和加工特性的18Ni马氏体时效超高强度钢的低周疲劳性能影响因素进行了分析研究,系统分析了18Ni马氏体时效钢合金元素对其力学性能的影响机理,并从晶粒度、材料微观组织、低周疲劳试验条件、疲劳试样加工状态以及非金属夹杂物等方面综述了18Ni马氏体时效钢低周疲劳性能的影响机制。     

超高强β钛合金等温相转变特性及力学性能

近β钛合金的等温相转变具有多样性和复杂性的特点,对温度敏感性强,直接影响其时效后的力学性能.本工作所用合金为自主研发的Ti-Al-V-Mo-Cr-Zr-Fe-Nb超高强β钛合金,采用扫描电子显微镜(SEM)、透射电子显微镜(TEM)、硬度计等分析表征手段对等温处理后合金的微观组织演变及力学性能进行系统研究.结果表明,合金300℃时效时只析出等温ω相,等温ω相随时效时间的延长发生长大.合金400℃时效时先析出等温ω相,随着时效时间的延长,α相依附于ω/β界面处形核.合金500℃时效时无ω相析出,针状α相直接从β基体中析出,呈"V"字形均匀分布在β基体中.400℃时效12 h时抗拉强度为1716.1 MPa,伸长率为2％.500℃时效12 h时抗拉强度为1439.8 MPa,伸长率为9.84％,具有良好的强塑性匹配.     

时效温度对00Cr12Ni10MoTi马氏体时效不锈钢组织与性能的影响

使用X射线衍射(XRD)、扫描电镜(SEM)、电子背散射衍射(EBSD)、透射电镜(TEM)和拉伸和冲击实验等手段,研究了时效温度对00Cr12Ni10MoTi马氏体时效不锈钢的组织和力学性能的影响。结果表明：随着时效温度的升高,实验钢的强度逐渐提高,析出强化效应明显增强。在500℃时效后基体中析出大量棒状Ni₃Ti,实验钢的强度达到峰值。随着时效温度的升高,实验钢的室温和低温冲击韧性衰减,在400℃时效后低温(-196℃)冲击功出现最低值51 J。时效温度升高到500℃后,实验钢的冲击韧性回升,因为马氏体基体中生成的逆转变奥氏体抑制了裂纹萌生并缓解其扩展。在500℃时效产生了Ni₃Ti析出强化效应和逆变奥氏体韧化效应,使实验钢具有良好的强韧性匹配。     

T250马氏体时效钢旋压薄壁圆筒变形

通过金相、透射电镜、XRD分析及应力测试,对T250马氏体时效钢旋压薄壁圆筒时效后的变形进行研究。结果表明时效后板条马氏体的基体中弥散析出强化相,位错密度下降,残余应力有所消除,同时有少量逆变奥氏体生成。时效引起的应力消除是薄壁圆筒径缩的主要原因,位错密度的下降,逆变奥氏体及析出相也对变形有明显影响。     

变质高锰钢析出相的演变及力学性能的研究

为了有效改善高锰钢的组织和性能,通过变质处理和弥散处理相结合的方法,采用X射线衍射(XRD)、光学显微镜、扫描电镜(SEM)及透射电镜(TEM),对稀土-低熔点合金变质高锰钢时效析出相进行研究.结果表明:实验用钢在460℃时效1 h时,基体上开始有球状析出相析出,随着时效时间的延长,析出相由球状向针状转变;520℃时效1 h,晶界上有少量的球状析出相,基体上析出相为细针状;580℃时效1 h,析出相为粗大的针状,且基体发生了奥氏体向珠光体转变.随着时效温度的升高,变质高锰钢时效析出相由球状转变为针状,针状析出相与球状析出相晶体结构不同,针状析出相更加趋于稳定.变质高锰钢的硬度随着析出相增多而升高,(Mn,Fe)7C3细针状析出相在冲击韧性和耐磨性起主导因素,变质高锰钢最佳时效工艺应使耐磨析出相析出,且未引起微观应变增大.本次实验用钢最佳时效工艺参数为520℃下时效1 h.     

三维原子探针表征10Ni3MnCuAl钢时效过程中析出相NiAl和Cu的变化规律

本研究使用三维原子探针表征了10Ni3Mn Cu Al钢在540℃时效过程中析出相随时间的变化规律,使用透射电镜分析了Ni Al析出相的晶体结构及其在基体上的分布状态。结果表明:10Ni3Mn Cu Al钢在540℃时效过程中,Ni Al析出相由时效2 h后的近球状转变为时效100 h后的长条状,平均粒子半径由1. 13 nm长大到2. 13 nm,数量密度由1. 70×10~(22)m~(-3)降低到3. 40×10~(21)m~(-3); Cu析出相由时效2 h后的球状转变为时效100 h后的长条状,平均粒子半径由1. 04 nm长大到2. 08 nm,数量密度由6. 04×10~(21)m~(-3)降低到2. 00×10~(21)m~(-3)。两种析出相由相邻位置转变为以Cu为核心,Ni Al为外壳的壳状结构。B2结构的Ni Al相对基体的强化作用大于Cu相对基体的强化作用,Ni Al相弥散分布在马氏体板条上,并在基体的[200]方向存在超结构反射斑点。     

马氏体时效钢的物理冶金学

本文综合论述国内外有关马氏体时效钢物理冶金学的研究结果。在简单介绍与马氏体时效钢相关的二、三元合金系统的相组成之后,主要描述了常规Fe-Ni-Mo-Ti(-Co)马氏体时效钢的时效初期反应和析出强化过程,并着重论述了一些强化元素的作用。然后简要介绍了一些新型马氏休时效钢的研究开发工作。在最后的结语中,展示了马氏体时效钢的发展应用前景。     

Development of an ultrahigh strength low alloy steel for armour applications

Abstract

The present paper describes a steel with yield strength exceeding 1900 MPa and fracture toughness in the range of 40–50 MPa?m^1/2, in its optimum heat treated condition. Its strength is similar to that of 18 Ni (300) grade of maraging steel with good fracture toughness. When tempered at 300°C, it shows tempered martensite along with a small amount of retained austenite phase. The steel shows nearly 25% reduction in weight over typical rolled homogeneous armour (RHA) steel against high velocity hard steel core projectiles. The processing, microstructure, mechanical and ballistic properties of the steel are demonstrated.     

Effect of Aging on Microstructure and Mechanical Property of 1900 MPa Grade Maraging Stainless Steel

The 18%Ni alloy steels provide high strength and toughness, while age-hardenable or PH stainless steels also have good corrosion resistance. This paper focuses on an investigation of the heat treatment, mechanical properties and microstructural development of a new maraging stainless steel. It is reported that the heat treatment process should consist of solution treatment and cryogenic cooling to attain a fully martensitic structure, followed by aging at 813 K. This heat treatment resulted in an ultimate tensile strength of over 1900 MPa combined with good impact toughness. Transmission electron microscopy is used to show that, for the peak-aged condition （813 K/4 h）, nano-sized precipitates, e.g. Ni3Mo and/or R-phase, and a high density of dislocations were uniformly dispersed in the lath martensite matrix. The calculated yield strength, based on a revised Orowan mechanism, is in good agreement with the test data. The steel studied has an ultimate tensile strength over 1900 MPa, excellent fracture toughness, and good resistance against over-aging and relatively good corrosion resistance as well.     

Evaluation of Mechanical Properties According to Nb Content of High Strength Steel Manufactured in VIM

As the aircraft and aerospace industry and the automobile industry are developed, the demand of reliable materials with high strength and high toughness is steadily increased. The grain miniature method which improves the ductility and the toughness simultaneously under high strength is the miniature of the casting microstructure. In this paper, the Nb which affects the austenite grain miniature is added by 0.00%, 0.03% and 0.06% in this steel and the ingot is manufactured in a vacuum induction melting furnace （VIM）. The casting microstructure and the mechanical property of the maraging steel according to Nb contents are analyzed by conducting the solution annealing and the age hardening after hot rolling. In this result, a specimen containing 0.03% Nb is most miniature. When it does the long time age hardening, the precipitation estimated as the carbide is appeared. The mechanical properties are excellent if a specimen containing 0.06% Nb does the age hardening during 8 h in 482℃.     

Development of an ultra-high-strength low-alloy NiSiCrCoMo steel

An ultra-high-strength low-alloy NiSiCrCoMo steel has been developed. The development work is part of a major programme at the Defence Metallurgical Research Laboratory in the field of ultra-high-strength, high-fracture-toughness steels. In this context we undertook investigations to understand the effect of solute additions on the fracture behaviour of Armco iron and Fe-C alloys. We investigated Fe-Ni, Fe-Co, Fe-Si, Fe-Mo, Fe-C-Ni and Fe-C-Co alloys for mechanical behaviour. The report by Garrison (1986) on a Fe-C-Ni-Si-Cr alloy was an important pointer to a low-alloy, ultra-high-strength steel with high fracture toughness. The material we have now arrived at is a Fe-C-Ni-Si-Cr-Co-Mo steel with tensile, impact and fracture toughness properties matching those of maraging steel 250 grade in tonnage scale melts.     

Role of pulsed current on metallurgical and mechanical properties of dissimilar metal gas tungsten arc welding of maraging steel to low alloy steel

This research work encompasses the investigations carried out on the mechanical and metallurgical properties of maraging steel and AISI 4340 aeronautical steel weldments. The materials were joined by continuous current gas tungsten arc welding (CCGTA) and pulse current (PCGTA) gas tungsten arc welding processes using ErNiCrMo-3 filler wire. Cross sectional macrostructures confirmed proper deposition of the fillers and lack of discontinuities. Optical microscopy studies revealed that at the maraging steel–weld interface, martensite in distorted and block forms prevailed in CCGTA and PCGTA weldments whereas tempered martensite was predominant at the low alloy–weld interfaces of both the welds. Scanning electron microscopy (SEM) with energy dispersive analysis of X-rays (EDAX) analysis apparently showed less elemental migration in PCGTA weldments as compared to the other. Results of X-ray diffraction analysis recorded possible phase formations in various zones of the weldments. Microhardness profiles in either weld zones followed a constant trend whereas it showed a downtrend in the heat affected zones (HAZ) of the maraging steel and very high hardness profiles were observed in the low alloy steel side. Tensile studies on various factors and impact testing showed that PCGTA weldments outperformed the continuous ones in terms of strength, ductility and toughness. Fractograph analysis depicted the nature of failures of tensile and impact tested specimens. Comparison analyses involving influence and nature of pulsed current welds over continuous ones were done to determine the possibility of implementing these joining processes in aerospace applications. Weldments fabricated using PCGTA technique proved to be superior to the other, resulting in exceptional mechanical properties.     

稀土对18Ni（350）马氏体时效钢韧塑性的影响

通过对钢的光滑轴对称拉伸性能、冲击韧性及平面应变断裂韧性的测定和对钢中夹杂物的定性、定量分析，表明在１８Ｎｉ（３５０）马氏体时效钢中加入适量的稀土可以改善其韧塑性，但由于受该钢本身成分特点等因素的影响，这种改善作用不如在其它类型超高强度钢（如ＡＦ１４１０）中显著。     

The effect of microstructure on the fracture toughness of 300 and 350 grade maraging steels

The fracture toughness of 300 and 350 grade maraging steel that has been given simple heat treatments has been studied. By heating into the austenite region at well-controlled rates and holding for short times, the toughness can be increased significantly above that which is obtained for the standard treatment. It is shown that the toughness increase is due to plastic deformation of the austenite for single-cycled material. When multiple cycles are used, the 300 grade steel undergoes a strain-induced transformation at the crack tip that contributes significantly to the toughness. When singly cycled, 300 grade material is tested at −196°C, its properties approach those obtained for conventionally treated material at room temperature. Models for the toughness improvements are developed that take crack tip phenomena into account, and they are in good agreement with experiment.