18Ni马氏体时效钢时效机理的研究

采用小角Ｘ射线散射、Ｍｏｓｓｂａｕｅｒ谱、透射电镜等方法研究了１８Ｎｉ马氏体时效钢的时效过程。结果表明，１８Ｎｉ合金在固溶处理后５００℃等温时效过程中，首先发生调幅分解，然后在调幅组织的Ｎｉ－Ｍｏ－Ｔｉ富集区以原位形核方式析出含Ｆｅ的Ｎｉ３（Ｍｏ、Ｔｉ）型金属间化合物，随时效时间延长，Ｎｉ３Ｍｏ和Ｎｉ３Ｔｉ粒子聚集长大并部分溶解，同时析出球形Ｆｅ２Ｍｏ金属间化合物，并形成逆转变奥氏体。     

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。     

18Ni马氏体时效钢铸件组织和力学性能

利用金相显微镜、扫描电镜和万能电子材料试验机对马氏体时效钢铸件的组织和力学性能进行了考察。结果表明,马氏体时效钢铸件热处理后强度较高,受制于其内部铸造缺陷。     

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.     

T-250马氏体时效钢管径缩现象机理研究

研究马氏体时效钢管工艺过程的组织变化和径缩现象的原因,结果表明,材料经过旋压后,形貌发生明显的扭曲且边缘地区硬度增大。经固溶处理后,颗粒细化并且形貌恢复正常,残余应力消除。时效处理后,部分马氏体转变为奥氏体,并产生沉淀强化相。分析认为,马氏体时效钢的径缩现象主要因旋压后的热处理使形变残余应力消除,晶粒有序化和马氏体奥氏体相的转变所造成,沉淀析出相也有部分贡献。     

18Ni马氏体时效钢的相变超塑性

本文研究了18Ni(2450MPa级)马氏体时效钢的相变超塑性。通过冷变形量、应力以及冷却速度对相变应变影响规律的研究,开发了该合金的相变超塑性成形工艺。当冷变形量为60％时,在最佳工艺条件下,经14cyc γ?α’循环相变,可获得320％的极限延伸率。经TEM观察发现,该合金应力诱发马氏体形态为块状马氏体。     

时效时间对SLM 18Ni300马氏体时效钢组织性能的影响

对激光选区熔化(Selective laser melting,SLM)成形马氏体时效钢进行固溶及500℃时效不同时间的热处理,分析时效时间对其组织性能的影响.结果表明:SLM 18Ni300钢经固溶+时效处理后,其组织为马氏体、逆转变奥氏体和Ni3(Mo,Ti)析出相,随时效时间增加,析出相数量逐渐增加并聚集长大,同...     

18Ni系马氏体时效钢焊条的研制

研制了一种18Ni系马氏体时效钢焊条,主要用于现场补焊,通过反复调整焊芯和药皮成分,确定了合适的焊芯合金成分和焊条药皮组成.采用该配方试制的焊条进行了一系列焊接试验及力学性能试验,并使用光学显微镜（OM）、扫描电镜（SEM）、透射电镜（TEM）分析了微观组织及断口形貌.结果表明,该焊条具有良好的操作工艺性,飞溅小,脱渣性良好,在经时效热处理后,熔敷金属力学性能优良,磷硫杂质元素及扩散氢含量低,与母材有着良好的强韧性匹配.     

Different Behavior in Electron Beam Welding of 18 Ni Co-free Maraging Steels

Microstructures of two different 18 Ni Co-free maraging specimens A and B and their electron beam (EB) weld joints were investigated comparatively by optical microscopy and scanning electron microscopy (SEM). It is shown that both of the steels are typical lath martensite; however, grain size of specimen A is about three times as large as that of specimen B. X-ray diffraction (XRD) reveals that the amount of the reverted austenitic phase in A is obviously less than that in B. Most of the austenite distributes in plate form along grain and lath boundaries while some of it distributes as fine particles within the matrix. The microstructural differences between the two specimens led to diverse behaviors in EB welding. The specimen A is weldable but B shows obvious welding defects of pits and burn-through holes in weld face. The welding microstructure exhibits a typical dendritic morphology, and the grains in the heat-affected zone recrystallized and grew because of high temperatures of welding EB. The weldablity of the examined materials is related to the microstructure characteristics that markedly affected thermal conduction performance.     

时效温度对18Ni(250)马氏体时效钢低周疲劳性能的影响

采用光学金相(OM)、扫描电镜(SEM)和疲劳寿命测试等方法研究了1700 MPa级18Ni(250)马氏体时效钢在不同时效温度下的疲劳性能。结果表明,18Ni(250)马氏体时效钢在480 ℃时效处理具有最佳力学性能和低周疲劳性能;循环应力响应行为呈现出软化特性,滞后回线几乎为直线,塑性应变量很小;不同时效温度下,疲劳条带与裂纹扩展方向相垂直,疲劳条带和瞬断区形貌均不同。     

T250无钴马氏体时效钢薄壁件焊接工艺试验

为了确保T250无钴马氏体时效钢薄壁筒形压力容器的焊接质量和可靠性,制备薄壁片状、筒形焊接试件及角焊缝焊接试件进行了钨极氩弧焊焊接工艺试验。试验结果表明,T250钢具有良好的焊接性,薄壁件钨极氩弧焊不易出现冷裂纹,焊前不需预热,焊后不需进行消除应力的热处理;焊接时,应严格控制焊接电流,防止出现焊接缺陷;焊接后,焊接接头的强度不高,需要通过时效或固溶+时效处理才能达到超高强度钢的强度,其时效工序不可忽视。     

The rolling texture of 18% Ni-350 maraging steel

Texture development in hot rolled sheet and hot forged tube of 18%Ni- 350 maraging steel has been studied after various degrees of cold deformation and flow turning, respectively. Hot rolled sheet exhibited considerable mechanical anisotropy. Weak texture development was observed following flow turning compared to cold deformation. Above 80% deformation, an increase in work hardening was accompanied by an increase in the orientation density of the texture component (001 )[110]. Deformation of 97% leads to the development of the texture component (111)[110], with the highest orientation density 10.3 times random and a constant orientation density of 9 times random along (φ1 at ϕ = 55° and φ2 = 45°. This texture was correlated with the appearance of shear bands in the microstructure.     

Reclamation and additional alloying of 18Ni(350) maraging steel

The possibility of gainfully utilizing grade 18Ni(350) maraging steel scrap has been investigated, along with the effect of additional alloying with niobium. A vacuum induction melting and casting furnace was used for melting and additional alloying. The cast ingots were hot forged and their properties compared with those of the stock material. The composition of the reprocessed material was found to be within the prescribed range for 18Ni(350) steel, except for some loss in titanium content. The hardness and tensile strength of the recycled steel were similar to those of the stock material. A slight decrease in hardness in the aged condition could be attributed to loss of titanium during remelting. Charpy V- notch impact test-ing indicated significantly higher toughness in the remelted material; this has been attributed to a homo-geneous, refined microstructure and a lower level of inclusions. Additional alloying with 2% Nb not only improved the mechanical properties but also affected the amount of reverted austenite obtained after ag-ing.     

00Cr12Ni9Mo4Cu2Ti马氏体时效不锈钢离子渗氮组织和性能

对00Cr12Ni9Mo4Cu2Ti马氏体时效不锈钢进行了离子渗氮处理,研究了不同渗氮条件下所形成的渗氮层的相结构与性能。结果表明:经离子渗氮后的00Cr12Ni9Mo4Cu2Ti马氏体时效不锈钢的表面硬度、耐磨性都有明显的提高,表面硬度最高达到了1350HV0.05。当样品在400℃渗氮时,表层新相主要由α相组成;当渗氮温度上升至500℃时,表层新相主要由αN相、γ′-Fe4N相、ε相组成,并有大量的CrN相形成;当渗氮温度高于600℃时,ε相、CrN的含量继续增加,γ′-Fe4N相逐渐减少,αN相几乎完全分解。伴随着CrN相的生成,样品的耐磨性得到了提高,表面耐腐蚀性能有一定下降。实验还观察到该马氏体时效不锈钢渗氮层中有微裂纹产生,裂纹的形成与样品的残余内应力和氮化物相生成有关。     

T250马氏体时效钢旋压时效后的组织和力学性能

通过金相、透射电镜及力学性能测试,研究了时效温度和保温时间对T250马氏体时效钢旋压后组织和性能的影响。对不同加热温度和保温时间下时效处理的组织、性能研究表明,T250马氏体时效钢旋压后固溶并在510℃×3 h时效可以获得强度和塑性较高的力学性能,其抗拉强度及伸长率均可满足技术要求。     

Effect of aging treatment on the mechanical properties of C-250 maraging steel by flow forming

The technique of forward flow forming has been used to produce a long, thin walled tube made of C-250 maraging steel. The forward flow forming can save raw material, increase strength, and reduce the production process time. Because the work hardening effect on solution-treated C-250 using flow forming is minimal, the flow-formed tube requires an additional heat treatment to obtain higher hardness and strength. With the direct aging treatment, low elongation values are obtained, making this treatment unsuitable for the engineering design. It was found that the 540 °C/6 h/AC over-aging treatment results in better strength and elongation values. The strengthening phase of the flow-formed C-250 maraging steel was found to be the intermetallic compound of Fe₃Mo.     

超高强度马氏体时效不锈钢超声疲劳过程中的热效应

以新型1900 MPa级超高强度马氏体时效不锈钢为研究对象,通过激光扫描共聚焦显微镜对其超声疲劳试样断口进行观察与分析。结果表明,在超声疲劳实验过程中,所有的试样在表面均产生了烧蚀的痕迹。对于表面起裂的超声疲劳试样,即使在不同的应力幅值下（640~560 MPa）,试样的疲劳寿命均在10⁵周次左右,且烧蚀现象更为严重。而对于基体内起裂的试样,烧蚀现象较为轻微,且烧蚀处均在断口两侧几乎对称的位置。经对比分析可知,超声疲劳过程中产生的热效应对表面起裂试样的疲劳寿命有很大的影响,而内部起裂试样的疲劳寿命对超声疲劳热效应不敏感。