超纯净18Ni马氏体时效钢的晶粒尺寸及其对拉伸性能的影响

研究了不同固溶处理温度下超纯净18Ni(2200 MPa级）马氏体时效钢晶粒尺寸及分布的变化，以及原奥氏体晶粒尺寸对马氏体时效钢在固溶和时效状态下拉伸性能的影响，初步探讨了其影响机理，结果表明，原奥氏体晶粒随固溶温度的升高而均匀持续地正常长大，晶粒尺寸对固溶态马氏体时效钢的强度和塑性影响微弱，有害元素含量的大幅度降低避免了Ti(C,N)等夹杂物在晶界偏聚而引起的高温固溶下的“热脆”现象，时效状态马氏时效钢的屈服强度与原奥氏体晶粒尺寸之间符合Hall-Petch关系，随着原奥氏体晶粒尺寸的增大，马氏体时效钢出现“时效脆性”是由于明效析出相在晶界偏聚所致。     

热处理对12Ni无钴马氏体时效钢微观组织和性能的影响

研究了高温固溶和时效热处理对12Ni无钴马氏体时效钢微观组织和性能的影响。结果表明:在原始固溶态试样中存在粒状和长粒状析出相,经能谱分析为Fe(Mo,Ti)或Fe2Ti型金属间化合物,消耗了大量的强化元素Mo,导致合金时效处理后强度不足(1100MPa);高温固溶处理后消除了粗大析出相,获得单一的板条马氏体组织;进一步改进时效热处理工艺,合金组织呈现弥散分布的纳米尺度的Ni3Mo、Ni3Ti强化相,使合金强度显著提高,达到1225MPa。     

多层次细化处理对18Ni马氏体时效钢断裂韧性的影响

利用逆变奥氏体再结晶原理对18Ni(1700 MPa)马氏体时效钢进行变温循环相变细化处理,分析了循环相变细化处理对晶粒度和亚结构的细化规律,研究了细化处理对马氏体时效钢常规力学性能及断裂韧性的影响。结果表明,细化处理可以同时实现晶粒和亚结构细化,显著提高强度、塑性和冲击性能。细化处理对18Ni马氏体时效钢断裂韧度的影响不明显,晶粒尺寸和马氏体板条的长宽比是影响断裂韧性的两个主要因素。     

18Ni马氏体时效钢原始奥氏体晶界显示方法

利用光学显微镜(蔡司)，在室温下，通过配制不同成分、浓度浸蚀剂和化学浸蚀方法，对经不同温度处理后的18Ni马氏体时效钢的原始奥氏体晶界显示方法进行了系统研究。结果表明：采用腐蚀性强、浓度高的浸蚀剂只能获得18Ni马氏体时效钢的金相显微组织，而采用体积比为4%的硝酸酒精溶液，对800~925 ℃固溶空冷后的18Ni马氏体时效钢试样进行化学浸蚀，能清晰地显示出18Ni马氏体时效钢试样原始奥氏体晶界，并可以进行准确的晶粒度级别数评定。     

18Ni马氏体时效钢原始奥氏体晶界显示方法

利用光学显微镜(蔡司)，在室温下，通过配制不同成分、浓度浸蚀剂和化学浸蚀方法，对经不同温度处理后的18Ni马氏体时效钢的原始奥氏体晶界显示方法进行了系统研究。结果表明：采用腐蚀性强、浓度高的浸蚀剂只能获得18Ni马氏体时效钢的金相显微组织，而采用体积比为4%的硝酸酒精溶液，对800~925 ℃固溶空冷后的18Ni马氏体时效钢试样进行化学浸蚀，能清晰地显示出18Ni马氏体时效钢试样原始奥氏体晶界，并可以进行准确的晶粒度级别数评定。     

循环相变对T250马氏体时效钢组织和性能的影响

通过DSC法测量T250马氏体时效钢的再结晶温度,随后采用多种α'→γ循环相变细化工艺进行试验,其加热温度高于再结晶温度50~150℃。结果表明,T250马氏体时效钢的再结晶温度为773℃;通过对比,确定先经过低温固溶的变温循环相变细化工艺为最佳细化工艺,其晶粒尺寸最终达到9.1μm;但循环相变对T250马氏体时效钢的硬度影响不大。利用T250马氏体时效钢进行循环热处理,成功地获得超细化晶粒,并且确定最佳细化工艺。经过循环热处理,晶粒得到明显细化,较好地达到晶粒超细化的目的。     

超高强度18Ni无钴马氏体时效钢的力学性能

研究了2000MPa级18Ni无钴马氏体时效钢的热处理对微观结构和力学性能的影响,并对无钴马氏体时效钢的强韧化机理进行了探讨.结果表明,固溶态18Ni无钴马氏体时效钢的硬度几乎不受固溶温度和固溶时间的影响;峰时效时屈服强度达到2000MPa以上,δ和KIc分别为9％,70Ma·m1/2,强度和韧性达到最佳配合.TEM观察表明,18Ni无钴马氏体时效钢通过在高密度位错基体中时效析出纳米尺度沉淀相Ni3（Mo,Ti）而实现强韧化,沉淀强化遵循Orowan位错绕过机制.     

热处理对SLM18Ni300马氏体时效钢组织及腐蚀性能的影响

目的探究热处理对激光选区熔化(SelectiveLaserMelting,SLM)成形18Ni300马氏体时效钢组织和耐腐蚀性能的影响。方法利用激光选区熔化技术成形18Ni300马氏体时效钢试样,分别对成形试样进行时效处理和固溶+时效处理。通过金相显微镜、扫描电镜、显微硬度计和电化学工作站,分别测试分析了不同热处理SLM 18Ni300马氏体时效钢的微观组织、显微硬度和耐蚀性。结果热处理后,试样微观组织发生显著变化,时效试样组织细化,得到板条马氏体组织;固溶+时效试样激光熔池消失,组织为均匀致密的板条马氏体,且均有细小析出物弥散分布于晶界和板条间。时效处理和固溶+时效处理显著提高了SLM18Ni300马氏体时效钢硬度,SLM试样硬度为376.6HV1,时效试样和固溶+时效试样硬度分别为651.5HV1和641.8HV1。0.5 mol/L H2SO4溶液中,SLM试样的Jcorr最小,为1.375×10?3 A/cm2,耐腐蚀性最好,各试样耐蚀性优劣有SLM试样固溶+时效试样时效试样。3.5%NaCl溶液中,SLM试样的极化曲线有明显的钝化平台,且Jcorr最小,为3.630×10?6A/cm2,耐腐蚀性最好,各试样耐蚀性优劣有SLM试样时效试样固溶+时效试样。结论时效处理和固溶+时效处理后,SLM 18Ni300马氏体时效钢得到板条马氏体组织,硬度显著提高,但在H2SO4溶液和Na Cl溶液中的耐腐蚀性能有所下降。     

室温等径转角挤压对18Ni(C-250)马氏体时效钢微观组织和拉伸性能的影响

采用等径转角挤压（ECAP）工艺在室温下对18Ni（C-250）马氏体时效钢进行单道次冷变形.对比固溶处理试样480℃时效曲线、固溶+ECAP处理试样的460和480℃时效曲线发现,一道次ECAP变形及随后的时效处理能够使马氏体时效钢的峰值时效时间明显缩短,峰值强度提高约100 MPa.结构分析表明,ECAP态实验钢的马氏体板条宽度为100—200 nm,随后的时效过程对马氏体板条宽度影响不大,而ECAP工艺对棒状δ-Ni3Mo相析出尺寸有显著影响.统计结果表明,经4 h时效处理后.固溶+480℃时效态、固溶+ECAP+480℃,460℃时效态的δ-Ni₃Mo宽度（直径）分别为4.92,12.33和3.54 nm.此外,ECAP工艺还促使18Ni马氏体钢中δ-Ni3Mo相在时效后期加速分解,使强度迅速衰减.     

7021马氏体时效钢(18Ni)焊接接头的应力腐蚀

本文研究了国产7021马氏体时效钢(18Ni)焊接接头在3.5%NaCl 水溶液中的应力腐蚀行为。结果表明,在峰值温度为1280℃左右的热影响区中焊接热循环并不影响断裂韧性,但严重降低对应力腐蚀的抗力,使该区成为焊接接头的薄弱环节。其原因可能与焊接,过程钛、钼等合金元素在晶界的偏聚和晶粒长大有关。焊后经820℃×1h 固溶处理,临界应力腐蚀强度因子K_(ISCC)得到一定提高,双重固溶处理可进一步改善,而三次900℃×20min 水冷处理效果最显著,晶粒明显细化,应力腐蚀裂纹由沿晶破坏转变为穿晶塑性破坏。但上述固溶处理对焊缝的作用与热影响区不同。一次或二次固溶有使焊缝K_(ISCC)降低的趋势,只有多次固溶可保持较好的水平并能与热影响区性能相匹配。     

超高强度马氏体时效不锈钢中逆转变奥氏体的析出与长大行为

研究了一种Cr-Ni-Co-Mo系超高强度马氏体时效不锈钢中逆转变奥氏体的析出与长大行为。结果表明,经540℃×4 h时效后钢的强度达到峰值1940 MPa,并有薄膜状逆转变奥氏体沿马氏体板条界上非连续析出,使钢具有良好的综合力学性能。时效初期逆转变奥氏体在马氏体板条、板条界或原奥氏体晶界处形核,随着保温时间的延长,薄膜状的逆转变奥氏体通过与扩散有关的形核长大方式生长,最终形成块状,并与板条马氏体间保持着K-S或N-W关系。     

Influence of Solution Treatment on Impact Toughness and Microstructure of Cobalt-free Maraging Steel

The influence of different solution temperature on microstructure and impact toughness of cobalt-free maraging steel 00Ni14Cr3Mo3Ti was investigated by SEM and X-Ray diffractometer.The experimental results showed that with the solution temperature variation, the martensite morphology has not changed, is still lath martensite.Undissolved Laves phase hindered the dislocation movement after 750 ℃ solution heat treatment, which result in a very low impact absorbed energy, the impact fracture has no obvious plastic deformation, with bad toughness.With the solution temperature increased, the undissolved phase gradually dissolved, the impact absorbed energy increased gradually.All the Laves phase dissolved when reach to 900 ℃, the impact absorbed energy reaches the maximum, is 61 J.Fracture morphology change from brittle fracture into toughness transgranular fracture with deep dimple. When solution temperature is above 900 ℃, with the solution temperature further increase, austenite grain size increases significantly.Average grain diameter of austenite is about 70 μm after 1050 ℃ solution treatment, the density of precipitates on the grain boundary of maraging steel is increase substantially, deformation compatibility deteriorate, which result in the impact absorbed energy decreased significantly.Fracture type becomes transgranular and quasi-cleavage mixed fracture with the characteristics of the river patterns from ductile transgranular fracture.     

Effect of Cr Contents and Heat Treating on Reverted Austenite in Maraging Steel Weldments

By conducting flux cored arc welding (FCAW) on maraging steels with Cr contents of 1.4 and 5.2 wt%, this study observed the effects of Cr content and heat treating on reverted austenite formation in welded maraging steel. Aging treatment was carried out at the temperatures of 450, 480 and 530 °C for 3 h in each condition. As the aging temperature increased, reverted austenite was formed along the interdendritic and intercellular grain boundaries, and the proportion of reverted austenite increased with increasing Cr addition. The aging process led to the segregation of Ti and Mo along the interdendritic and intercellular grain boundaries. Some of the welded specimens were subjected to solution heat treatment at 820 and 1250 °C for 1 h after welding, resulting in a decrease in reverted austenite fraction.     

Maragin behavior of an Fe-19.5Ni-5Mn alloy. III: Mechanical properties

A high maraging strength in Fe-Ni-Mn alloys can be achieved at the expense of a marked loss in ductility. Very fine precipitates are observed when peak strength is reached. At peak strength, the Fe-Ni-Mn alloys exhibit brittle failure, mainly along prior austenite grain boundaries, irrespective of the nickel content. The presence of a small amount of retained austenite prior to aging does not improve the ductility. Previous explanation of the embrittlement in Fe-Ni-Mn alloys was attributed to the segregation of Mn to prior austenite grain boundaries. However, this is not fully supported by the present studies. Auger electron spectroscopy reveals no decisive evidence of manganese segregation. Some degree of ductility in the aged martensite may be required in order to prevent brittle fracture. Dual aging recovers part of the ductility and improves the strength slightly. The effect of reversed austenite on ductility may vary, depending on its morphology. Matrix and recrystallized austenite are beneficial to both elongation and reduction of area, but lathlike austenite lowers the elongation, probably because of its lamellar morphology. The lamellar structure of the lath martensite is also detrimental to elongation.     

Relationship Between Microstructure and Corrosion Behavior of Cr12Ni3Co12Mo4W Ultra-High-Strength Martensitic Stainless Steel

The effect of tempering temperature on the microstructure and corrosion behavior of Cr12Ni3Co12Mo4W ultra-high-strength martensitic stainless steel was investigated using transmission electron microscopy, atomic force microscopy, X-ray diffraction, and electrochemical tests. The microstructures of the ultra-high-strength martensitic stainless steel consisted of some retained austenite and lath/plant martensite with the carbides distributed within the matrix and at the grain boundaries. Tempering of the steel for 4 h at various temperatures resulted in various carbide grain sizes and different amounts of the retained austenite. The results showed that larger carbide grains led to diminished corrosion resistance, whereas larger amounts of the retained austenite resulted in improved corrosion resistance. The steels exhibited good corrosion resistance in 0.017 mol/L NaCl solution and exhibited pitting corrosion in 0.17 mol/L Na Cl solution. The martensite and prior austenite crystal boundaries dissolved in solution with pH 1.     

新型高强高韧钢G99的超精细场研究

用Ｍｏｅｓｓｂａｕｅｒ谱学对新型高强度韧钢Ｇ９９在不同温度回火后的超精细场变化进行了研究。用透射电镜和电子衍射分析了合金碳化物的析出。结果表明,Ｇ９９钢中超精细场分布、碳化物和奥氏体量都随着回火温度和升高而变化,主要是由于在回火过程中回火马氏体内Ｆｅ－Ｃｏ,Ｆｅ－Ｎｉ近邻增多,Ｆｅ－Ｃｒ,Ｆｅ－Ｍｏ近邻减少,渗碳体的溶解与合金碳化物的析出以及残余奥氏体转变与逆转奥氏体的产生所致。合金碳化物的弥散     

Grain boundary embrittlement by Mn and eutectoid reaction in binary Fe–12Mn steel

The grain boundary embrittlement in a binary Fe–12Mn is due to the grain boundary segregation of Mn. During tempering at 400 °C (higher than the equilibrium eutectoid reaction temperature 247 °C), reverted austenite particles were formed at lath and grain boundaries through the equilibrium reaction of lath martensite to ferrite + austenite. Surprisingly, hydrostatic pressure, which is induced by the transformation of epsilon martensite to austenite during heating at the tempering temperature, resulted in the nonequilibrium eutectoid reaction producing α-Mn precipitates at the interface between lath martensite and the transformed austenite during the tempering. The segregation concentration kinetics of Mn formed a convex profile due to the active grain boundary precipitation of the reverted austenite particles and the α-Mn particles, which act as a sink for the segregated Mn. Finally, the convex segregation profile of Mn corresponded to the concave profile of intergranular fracture strength.     

晶粒细化对Fe-Ni-Mo-Cr系马氏体时效钢组织和性能的影响

采用显微组织观察和力学性能测试,研究了晶粒细化处理对Fe-Ni-Mo-Cr系马氏体时效钢组织和性能的影响.结果表明,等温循环相变可使晶粒平均尺寸达到8～10 μm;同时使合金的马氏体板条碎化,亚结构和析出相形核位置增多,逆转变奥氏体长大速度加快.循环细化后的时效合金中调幅组织更为明显,棒状的Ni3Mo、Ni3Ti及逆转变奥氏体的弥散度也比未经过循环细化处理的要大,合金的强度和塑性明显改善.     

淬火温度对高Ti低合金耐磨钢组织及力学性能的影响

研究了淬火温度对高Ti低合金耐磨钢组织转变、析出相和力学性能的影响,并分析了组织演变和力学性能变化的原因。结果表明:试验钢经不同温度淬火和200 ℃回火后的组织均为高位错密度板条马氏体;析出相尺寸主要为微米-亚微米-纳米三种尺度,微米级析出相呈杆棒状,亚微米以及纳米析出相呈球状,马氏体板条上分布着细小的(Ti, Mo)C析出相。随着淬火温度的升高,试验钢的屈服强度、抗拉强度和维氏硬度均先升高后降低,均在920 ℃时有最大值,分别为1248 MPa、1535 MPa和434 HV,此时伸长率为10.0%。随淬火温度升高,纳米级析出相逐渐回溶,数量减少且尺寸逐渐长大,沿轧制方向被压扁拉长的原奥氏体晶粒尺寸以及马氏体板条块尺寸略有增大,但马氏体板条宽度却无明显长大。大量的弥散分布的5～10 nm的(Ti, Mo)C粒子是促进耐磨钢硬度升高的主要因素。细小的(Ti, Mo)C析出相逐渐长大以及原奥氏体晶粒的增大都不利于耐磨钢硬度的提高。