马氏体时效不锈钢时效析出相及位向关系的研究

系统研究了Custom 465钢510℃时效析出相及相关的位向关系,结果表明:Ni3Ti是钢的主要时效析出相,析出相为杆状,杆的长度方向与马氏体基体的[111]M方向一致;(011)M///(0001)Ni3Ti、[111]M//[1120]Ni3Ti是马氏体和Ni3Ti金属间化合物确切的位向关系,这种位向关系使Ni3Ti在马氏体基体内出现12种可能的亚型.     

预先冷轧变形对马氏体时效钢强化的影响

系统研究了预先冷轧变形对马氏体时效钢强化的影响,研究结果表明:510℃×3 h时效引起的强度净增加值恒定,与冷轧变形量无关,最终的强度为:σ=σ0 △σCR △σAge,即初始强度、冷加工强化和时效强化的叠加,其中只有冷加工强化△σCR随变形量变化.电子衍射花样及衍射斑强度分布证实:510℃×3 h时效后马氏体基体内析出六方结构的Ni3(Ti,Mo)和正交结构的Ni3 Mo,冷轧变形量对时效析出行为没有明显的影响.     

马氏体时效不锈钢00Cr10Ni10Mo2Ti的形变热处理强化机制的研究

本文通过光学显微镜、电子显微镜、X射线衍射仪等手段研究了马氏体时效不锈钢00Cr10Ni10Mo2Ti经形变热处理后的组织与力学性能,主要结果是: ①通过电子衍射观察与计算,确定了该钢的时效相有Ni_3Ti,Ni_3Mo及逆转变奥氏体。 ②该钢经过亚稳奥氏体形变以后,马氏体产生明显细化,同时奥氏体中大量缺陷遗传给马氏体,为时效相的析出提供了更多的场所。 ③形变热处理对马氏体时效不锈钢00Cr10Ni10Mo_2Ti的强化是行之有效的。其产生强化的原因主要为马氏体细化,位错的增加,以及由此而导致金属间化合物更多、更弥散地析出,从而有效地钉扎了位错的运动。     

马氏体时效钢时效强化相稳定性分析及时效工艺改进的研究

本文利用透射电子显微镜研究了18Ni(350)马氏体时效钢中析出相,利用三个低指数晶带的电子衍射一致地鉴别出材料经510℃×3 h时效后析出相为Nj_3Mo_1Ni_3Ti及弥教的逆转变奥氏体。试样在受1900 MPa应力,室温连续恒载2万小时及120℃连续恒载l万小时后,原有析出相未发生转变,但析出相及逆转变奥氏体数量略有增加,尺寸略微变大,且发现在120℃温度环境中析出相变化速率比室温时     

用X射线评价马氏体时效钢冷轧材的回复效应

用X射线衍射技术研究了马氏体时效钢冷轧变形和衍射峰宽化效应的关系，结果表明冷轧变形使X射线衍射峰型发生明显的变化，其中衍射峰的宽化间接证明材料塑性变形的不均匀性；510℃×3h时效使冷轧变形引起的衍射峰宽化效应大幅下降，从而证明时效析出前或析出过程中马氏体基体发生了较大程度的回复。更高温度时效后（540℃×3h），X射线衍射峰宽化已不受冷轧变形的影响，证明马氏体基体已回复到与未冷轧材料相当的程度。     

马氏体时效钢时效强化相稳定性分析及时效工艺改进的研究

本文利用透射电子显微镜研究了18Ni(350)马氏体时效钢中的析出相,利用三个低指数晶带的电子衍射一致地鉴别出材料经510℃×3h时效后析出相为Ni_3Mo,Ni_3Ti及弥散的逆转变奥氏体。试样在受1900 MPa应力,室温连续恒载2万小时及120℃连续恒载1万小时后,原有析出相束发生转变,但析出相及逆转变奥氏体数量略有增加,尺寸略微变大,且发现在120℃温度环境下析出相变化速率比室温时变化速率大。从微观组织角度说明了经室温2万小时恒载及120℃恒载1万小时后,材料性能不会发生明显变化。 另外,本文在时效工艺改进方面做了初步研究。发现在现行的510℃×3h时效工艺基础上延长时效时间到8h,此时强度基本不下降,而韧性得到了较大改善。若从提高时效温度方面着手改进时效工艺,那么当温度不超过540℃时效3h,组织结构保证不发生明显变化。     

18Ni马氏体时效钢时效过程的X-射线分析

18Ni马氏体时效钢具有较高的强度和韧性,本文用X-射线衍射法测定了时效过程中亚结构,逆转变奥氏体和点阵参数变化规律,指出,合金经低于520℃不同温度三小时时效处理后,合金基体马氏体具有精细亚结构的稳定性;逆转变奥氏体在～480℃弥散析出,它的产生和消失伴随着亚结构的长大与细化。用这些结构参数解释了力学性能变化的规律性,并为合金正规热处理和软化冷加工处理制度的选择提供了参考依据。     

节镍无磁不锈钢Cr18Ni6Mn3N的组织及性能

研究了节镍无磁不锈钢Cr18Ni6Mn3N的热轧及固溶后的力学性能和耐蚀性能,分析了其固溶和时效析出后的组织演变规律、冷变形过程中形变诱发马氏体相变及其磁性能.结果表明:该不锈钢的固溶组织为单相奥氏体,其力学性能和耐蚀性能均高于SUS304不锈钢;800℃保温4 h后,在晶界析出粒状氮化物,随着保温时间延长,逐渐沿晶界凸起片层状析出物并向晶内生长,保温20 h后,凸出的片层状析出物直径达20μm.冷轧压下率18.3%时尚未发现形变诱发马氏体组织,随着变形量增大,马氏体含量增多,磁导率上升,但与相同条件下的SUS304不锈钢相比,冷轧板固溶后相对磁导率可降至1.002,因此可用于低成本无磁不锈钢领域.      

00Cr13Ni7M04C04W2Ti马氏体时效钢的时效动力学研究

研究用马氏体时效不锈钢(%:0.007C、13.44Cr、7.47Ni、4.15Mo、4.21Co、1.84W、0.12Ti)由15 kg真空感应炉熔炼和真空白耗炉重熔精炼而成.试验得出经1100 ℃ 1 h同溶处理的中12 mm轧制试样450～550℃时效硬化曲线,分析了该钢的时效硬化指数和激活能.结果表明,00cr13Ni7M04C04W2Ti钢的时效析出相为六方结构的条状R-相(Co-Cr-Mo金属间化合物),其尺寸为10-30 nm,R.相的析出动力学可用Arrhenius方程描述,低于525 ℃时效存在预沉淀现象,并且时效硬化指数随时效温度升高而增加,时效过程表观激活能为156.8 kJ/mol.     

15Ni马氏体时效工具钢的研究初探

马氏体时效钢是依靠马氏体强化和经时效在马氏体内析出金属间化合物的第二相强化而获得超高强度的钢。本文研究了15Ni马氏体时效工具钢的化学成分、经816℃×2h油冷的固溶处理以及480℃×2h时效处理后的显微组织和热处理硬度。对15Ni马氏体时效工具钢的合金化特点进行了初步的分析讨论。     

Microstructure and mechanical properties of a 2000 MPa grade co-free maraging steel

The precipitation kinetics in the aging temperature range of 713 to 813 K in a 2000 MPa grade Co-free maraging steel (Fe-18.9 pct Ni-4.1 pct Mo-1.9 pct Ti, mass pct) has been studied. Study on microstructure and mechanical properties showed that a great deal of Ni₃Ti and a type of unknown spheroidal precipitates both with average diameter of 2 to 3 nm are formed in the early aging stage at 713 K, which results in a high strength and a relatively low fracture toughness. Ni₃Ti precipitates grow into needle or rod shape and become the main precipitation as the aging time is prolonged. Strength increases and fracture toughness (K _IC ) decreases with growth of the precipitates. The ultra-high strength of the maraging steel subjected to long-time aging at 713 K is attributed to the high resistance to coarsening of the precipitates. The strengthening in the underaged condition at 713 K is a combination of dislocations cutting through precipitates and the Orowan mechanisms. Aged at 813 K, the size of Ni₃Ti precipitates is seriously nonuniform at the early stage and a small amount of interlath reverted austenite is formed. Thereafter, Ni₃Ti precipitates coarsen sharply accompanied with the embrittlement. Intralath reverted austenite appears subsequently. In the later stage of aging, the coarsened Ni₃Ti precipitates dissolve into the striplike intralath reverted austenite that is disorderly embedded in the matrix. All of these result in a low strength and low fracture toughness under overaging condition. Analysis shows that the formation of reverted austenite contains the diffusion and Kudjumov-Sachs (K-S) and Nishiyama-Wassermann (N-W) shear mechanisms.     

钛含量对0Cr13Co8Ni5Mo马氏体时效不锈钢冲击韧性的影响

 通过具有不同Ti含量的三炉试验钢,研究了Ti含量对0Cr13Co9Ni5Mo 马氏体时效不锈钢的力学性能、金相组织和奥氏体含量的影响。研究结果表明：添加较多的Ti可显著降低基体组织中的有效C、N含量,大幅降低固溶、时效处理后残余/逆转变奥氏体含量,最终使冷脆转化温度显著上升,在提高强度的同时降低了钢的韧性。     

Investigation on Metallurgical Factors Controlling Charpy Impact Toughness in 1Cr21Ni5Ti Duplex Stainless Steel

 Based on the fact that toughness degradation occurred in 1Cr21Ni5Ti duplex stainless steel during slow cooling in a temperature interval of 400-600 ℃ following brazed welding, a simulated embrittlement treatment was utilized to evaluate its embrittlement tendency. Accumulated experiences have shown that high Ti and Al contents led frequently to severe toughness deterioration. To elucidate this phenomenon, four heats with various Ti and Al contents were prepared in laboratory scale melts, which were used to investigate the inherent embrittlement nature. The results have shown that 550 ℃ aging led only to a modest toughness reduction, whereas, aging around 475 ℃ resulted in ferrite embrittlement, regardless of Ti, Al levels. However, high Ti, Al levels reduced the austenite phase, which, in the case of its inferior shape and distribution due to insufficient hot deformation, failed to resist cleavage type cracks initiated in the ferrite phase. Increasing hot forged areas reduction could modify the shape and distribution of austenite, resulting in the enhanced resistance of the austenite to the cleavage type cracks, which have been confirmed to be beneficial for brittlement suppression of 1Cr21Ni5Ti duplex stainless steel.     

The precipitation sequence of Ni3Ti in Co-free maraging steel

TEM, microdiffraction, and X-ray microanalysis were used to study the precipitation processes in Co-free maraging steel. Austenite crystals were found to nucleate in the martensite matrix as the first step in the precipitation sequence of Ni₃Ti. The austenite reversion is a result of Ni segregation. Ni₃Ti nucleates in the austenite. The shape and orientation of Ni₃Ti is determined by the austenite precursor. The same sequence occurs for heterogeneous nucleation on dislocations and grain boundaries. At the later stages of growth Mo is incorporated in the Ni₃Ti lattice.     

低温贝氏体转变对中碳钢韧性的影响

摘要：沉淀硬化钢中纳米富Cu相的析出，使微应变（α）发生改变，这不仅影响力学性能，也对腐蚀性能产生作用。为了探索α对腐蚀性能和力学性能的影响规律，通过XRD谱型分析，对商用钢LJ338ESR 在300～600℃不同时间时效析出富铜纳米相后的α、硬度和电荷转移电阻（Rf）进行了研究。结果表明，300～450℃时效，8h前α值随时效时间延长而升高，8h后由于析出相与基体失去共格，α随着时效时间延长而降低；硬度与α变化相似。600℃时效，α在时效2h达到峰值，这归因于共格微应变和逆变奥氏体两种相反因素的共同影响；600℃逆变奥氏体生成，使硬度变化较小。析出相与基体保持共格时，Rf和α随时效时间的变化呈良好的反比关系，即Rf随α的增大而减小。     

The strength and fracture toughness of 18 Ni (350) maraging steel

The influence of microstructure on the strength and fracture toughness of 18 Ni (350) maraging steel was examined. Changes in microstructure were followed by X-ray and neutron diffraction and by optical and electron microscopy. These observations have been correlated with the fracture morphology established by scanning electron microscopy. Air cooling this alloy from the austenitizing temperature results in a dislocated martensite. During the initial stage of age hardening, molybdenum atoms tend to cluster (forming preprecipitates) and the cobalt assumes short range ordered positions. Subsequent aging results in Ni₃Mo and σ-FeTi with overaging being associated with the formation of equilibrium reverted austenite and Fe₂Mo. The fracture behavior is examined in terms of elementary dislocation precipitate interactions. It is suggested that the development of coplanar slip in the underaged conditions leads to its increased stress corrosion susceptibility and decreased fracture toughness. The optimum aged condition is then associated with cross-slip deformation. The fracture behavior of the overaged condition is a dynamic balance between a brittle matrix and the ductile (crack blunting) reverted austenite.     

LJ338ESR钢富铜纳米相引起的微应变、硬度和耐蚀性变化

摘要：沉淀硬化钢中纳米富Cu相的析出，使微应变（α）发生改变，这不仅影响力学性能，也对腐蚀性能产生作用。为了探索α对腐蚀性能和力学性能的影响规律，通过XRD谱型分析，对商用钢LJ338ESR 在300～600℃不同时间时效析出富铜纳米相后的α、硬度和电荷转移电阻（Rf）进行了研究。结果表明，300～450℃时效，8h前α值随时效时间延长而升高，8h后由于析出相与基体失去共格，α随着时效时间延长而降低；硬度与α变化相似。600℃时效，α在时效2h达到峰值，这归因于共格微应变和逆变奥氏体两种相反因素的共同影响；600℃逆变奥氏体生成，使硬度变化较小。析出相与基体保持共格时，Rf和α随时效时间的变化呈良好的反比关系，即Rf随α的增大而减小。     

Precipitation reactions and strengthening behavior in 18 Wt Pct nickel maraging steels

The crystallography, structure, and composition of the strengthening precipitates in maraging steels C-250 and T-250 have been studied utilizing analytical electron microscopy and computersimulated electron diffraction patterns. The kinetics of precipitation were studied by electrical resistivity and microhardness measurements and could be described adequately by the Johnson-Mehl-Avarami equation, with precipitate nucleation occurring on dislocations and growth proceeding by a mechanism in which the dislocations serve as collector lines for solute from the matrix along which pipe diffusion occurs. The strengthening of the Co-free, higher Ti T-250 steel is caused by a refined distribution of Ni₃Ti precipitates. High strength is maintained at longer times from the combined effect of a high resistance of these precipitates to coarsening and a small volume fraction of reverted austenite. In the case of the Co-containing, lower Ti C-250 steel, strengthening results from the combined presence of Ni₃Ti (initially) and Fe₂Mo precipitates (at longer times). Loss of strength at longer times is associated, in part, with overaging and mainly from the larger volume fraction of reverted austenite. The resistance to austenite reversion is dependent on the manner in which the relative nickel content of the martensite matrix is affected by the precipitating phases, and the difference in the reversion tendency between the two steels can be explained on this basis. Formerly with the University of Illinois, Formerly with the University of Illinois     

Effect of Tube Spinning With Performance and Microstructure Subsequent Heat-Treatment on Evolution of T250 Maraging Steel

 The effects of spinning deformation and subsequent heat treatments on the mechanical properties and microstructure of 18Ni Co-free Maraging steel (T250) tube were evaluated comparatively with the perform. An obvious radial shrinkage is detected in spun tubes after heat treatment and the magnitude of the shrinkage induced by solution treatment is almost the same as that by aging. Plastic deformation during spinning elongated the grains severely in the direction of metal flow. The solution treatment resulted in a drastically refined grain and recrystallised microstructure, removing the effect of plastic deformation, relieving the tangential residual stress and strain and improving hardness. Subsequent aging obtained a tempered microstructure, enhancing hardness values strikingly for precipitation strengthening. XRD (X-ray diffraction) analysis indicated that the reversed austenite formed in a plate-like along the grain boundaries and the volume fraction of austenite in spun tube was more than double that in the preform. These results imply that the residual stress and stain induced by spinning process and reversed austenite forming during aging might have the similar contribution to the radical shrinkage.     

Martensite Formation from Reverted Austenite at Sub-zero Celsius Temperature

Inter-critical annealing of soft martensitic stainless steel leads to formation of fine-grained reverted austenite, which is stabilized by partitioning of Ni. Generally it is reported that reverted austenite is not affected by immersion in cryogenic liquids, such as boiling N₂ and He. The present data show that reverted austenite that is apparently stable at boiling nitrogen temperature does transform isothermally to martensite during holding at 195 K. The results are explained in terms of thermally activated martensite formation.