Nb、Ti微合金钢中碳氮化物固溶与再析出的研究

利用光学显微镜(OM)、透射电子显微镜(TEM)研究了再加热温度、奥氏体区变形温度和组织转变温度的变化对Nb、Ti微合金钢组织性能及其碳氮化物固溶与再析出行为的影响.结果表明:钢中加入铌,主要利用铌的碳氮化物在奥氏体形变过程中的再析出,抑制形变奥氏体的再结晶,在随后的组织演变过程中细化了组织;而钢中加入较高含量的钛,主要利用钛的碳化物在铁素体中的析出,产生明显的沉淀强化作用.这主要是铌、钛的碳氮化物固溶后,在奥氏体和铁素体中再析出的不同所造成的.钢中复合加入Nb-Ti后既起到细化晶粒的作用,又起到析出强化的作用.细晶强化既提高钢的强度又提高钢的韧性,但沉淀强化在大幅提高钢的强度的同时恶化了钢的韧性.     

Nb、Ti微合金钢中碳氮化物固溶与再析出的研究

利用光学显微镜(OM)、透射电子显微镜(TEM)研究了再加热温度、奥氏体区变形温度和组织转变温度的变化对Nb、Ti微合金钢组织性能及其碳氮化物固溶与再析出行为的影响。结果表明:钢中加入铌,主要利用铌的碳氮化物在奥氏体形变过程中的再析出,抑制形变奥氏体的再结晶,在随后的组织演变过程中细化了组织;而钢中加入较高含量的钛,主要利用钛的碳化物在铁素体中的析出,产生明显的沉淀强化作用。这主要是铌、钛的碳氮化物固溶后,在奥氏体和铁素体中再析出的不同所造成的。钢中复合加入Nb-Ti后既起到细化晶粒的作用,又起到析出强化的作用。细晶强化既提高钢的强度又提高钢的韧性,但沉淀强化在大幅提高钢的强度的同时恶化了钢的韧性。     

固溶温度对8Cr4Mo4V轴承钢的中温相转变和力学性能的影响

在不同温度对8Cr4Mo4V钢固溶处理后在260℃盐浴中发生相转变而生成贝氏体组织,测定了钢的硬度和冲击韧性。使用扫描电镜、电子探针和光学显微镜等手段观察钢的微观组织,分析了合金元素扩散、贝氏体形核及贝氏体尺寸与固溶温度的关系,研究了固溶处理温度对力学性能的影响。结果表明,在1050℃和1065℃固溶处理后钢中的点状碳化物仍有剩余,阻碍了晶粒的长大;在1095℃和1110℃固溶处理后点状碳化物溶解,晶粒平均尺寸增大。固溶处理促使含Cr和V的碳化物溶解,但对含Mo碳化物的影响较小;高温固溶处理后Mo元素仍然存在于碳化物中,在基体中则较少。高温固溶处理使更多的Cr和V元素溶入基体中,降低了碳元素在基体中的扩散系数和贝氏体形核数目以及贝氏体的最终生成量,使贝氏体的组织粗化;随着固溶温度的提高,钢的硬度提高,而冲击韧性降低。     

初生α相含量对TC18时效组织及力学性能的影响

目的 探究TC18合金中初生α相含量对时效后次生α片层形貌及力学性能的影响.方法 通过改变两相区固溶温度控制初生 α 相含量,观察固溶后合金元素分布及相同时效后合金的组织形貌,研究固溶温度对合金拉伸性能的影响.结果 固溶过程中发生元素再分配,固溶温度低,初生α相含量高,β基体中β稳定元素含量高,β基体稳定性强,抑制时效过程中次生α片层析出,时效强化效果弱.固溶温度高,β基体稳定性弱,促进时效过程中次生α片层析出,时效强化效果显著.结论 固溶温度升高,初生α相比例降低,即β基体稳定性降低,促使时效过程中大量次生α相析出,显著提高合金强度.     

新型高钴镍合金钢的微观组织和性能

研究了新型高CoNi超高强度合金钢的组织和性能.在最佳热处理条件下,达到最佳强韧性,σb ≥1960MPa,σ0.2≥1740MPa,断裂韧性K1c≥112 MPa·m1/2,其组织为典型的淬火回火板条马氏体,等温回火处理产生二次硬化反应,析出与基体共格的细小弥散合金碳化物M2C沉淀使其得到强化.析出相与基体间的共格关系随回火温度的升高而失去,并转化为M23C6或 M7C3.分布在晶界的膜状奥氏体有韧化作用.在较高温度下回火,M2C粗化、失主与基体间的共格关系,并向其它碳化物转化,以及在晶内形成大量奥氏体,使性能下降.     

热轧态Inconel690合金中碳化物的溶解和析出

研究了热轧态690合金中碳化物的溶解和析出行为及其结构,结果表明:在热轧态合金中存在的碳化物多数沿晶界长条状分布,少量呈颗粒状分布于晶内,类型为M_(23)C_6.热轧态合金的晶界和晶内碳化物的完全固溶温度分别为1050℃、1080℃,在低固溶温度下未完全溶解的残余晶界碳化物直接导致后续TT处理晶界不再析出碳化物;将合金完全固溶处理后,在后续TT处理的晶界上会重新析出细小、半连续的碳化物.     

ZG35Cr25Ni12NNbRE钢中黑斑组织的成因探讨

ZG35Cr2 5Ni12奥氏体耐热铸钢经固溶时效后的显微组织由初晶奥氏体、共晶碳化物 ,以及在奥氏体基体上时效析出的二次碳化物组成 ;使用 3.5a(年 )后二次碳化物增多 ,共晶碳化物附近的“无析出区”消失 ,并在许多共晶碳化物内部形成黑斑组织。研究表明 ,黑斑组织是富含稀土元素的氮碳化物ε (Cr ,Fe) 2 (N ,C)相 ,是在长期高温过程中通过消耗共晶碳化物形成的     

新型耐热钢Super304H高温时效后的组织与性能

采用光学显微镜、扫描电子显微镜及X射线衍射等手段并通过显微硬度和冲击实验,研究了Supre304H钢经750～1350℃时效后的微观组织和性能.结果表明:高温时效后Super304H钢的微观组织为γ相+析出相;随时效温度的不同,基体晶粒尺寸及析出相的种类、分布发生不同的变化.在750℃左右因微细沉淀强化及细晶组织使得显微硬度达到最大值,而后随温度升高以及析出相、晶粒尺寸与固溶元素的变化,显微硬度呈现先快速下降后缓慢下降的趋势;时效试样的冲击功值随温度升高在850℃左右,由于M23C6沿晶界大量析出导致晶界脆化而达到最低值,后又因析出相的再溶解致使晶界脆化效果趋弱而逐渐升高.     

ZG35Cr25Ni12NINbRE钢中黑斑组织的成因探讨

ZG35Gr25Ni12奥氏体耐热铸钢经固溶时效后的显微组织由初晶奥氏体、共晶碳化物，以及在奥氏体基体上时效析出的二次碳化物组成；使用3.5a（年）后二次碳化物增多，共晶碳化物附近的“无析出区“消失，并在许多共晶碳化物内部形成黑斑组织。研究表明，黑斑组织是富含稀土元素的氮碳化物ε-（Cr，Fe）2（N，C）相，是在长期高温过程中通过消耗共晶碳化物形成的。     

4Cr14Ni14W2Mo钢的奥氏体晶粒度和孪晶及碳化物

对锻造的4Cr14Ni14W2Mo钢经相应热处理后的奥氏体晶粒度、孪晶及碳化物类型进行了研究。认为固溶处理后的奥氏体晶粒度主要取决于固溶加热温度,与锻造温度关系不大。固溶加热过程实质是再结晶过程的继续,即二次再结晶。奥氏体晶粒的大小只能通过控制再结晶温度的高低和时间长短来实现。该钢热处理后,碳化物类型为M_(23)C_6和M_7C_3两种,而以M_(23)C_6居多。其中M_(23)C_6为(Cr、Fe、W、Mo)_(23)C_6和(Fe、Ni)_(23)C_6两种结构,而M_7C_3为(Cr、Fe)_7C_3。     

On the microstructure and mechanical properties of high-speed steels

The microstructure of high-speed steels consists of a martensitic matrix with a dispersion of two sets of carbides. These carbides are usually known as primary and secondary carbides. The role of the primary carbides has been reported to be of no importance in strengthening the steels, due to their large size and large interparticle spacing. The present authors have studied the role of the primary carbides on the wear of high-speed steels and found them to be of no importance, and under certain conditions contributing to higher wear rates. It has been shown analytically and experimentally that in quenched and tempered high-speed steels, the precipitation of the secondary hardening carbide (cubic M₂C type) is the main reason for the improved strength and wear resistance. This shows that the secondary hardening phenomenon of high-speed steels is a direct result of the hardening caused by the precipitation of the cubic M_2C-type carbide. The present study has estimated that at peak hardness the volume fraction of secondary hardening carbides is approximately 20%. The measured strength of high-speed steels was found to be lower than the theoretically calculated strength due to non-homogeneous precipitation of the secondary hardening carbides. Areas which were observed to be free from secondary hardening carbides are real and are not artefacts. It has been shown that the strength of high-speed steel in the region of peak hardness depends primarily on the precipitation of the secondary hardening carbide and secondarily on martensitic strengthening.     

正火回火14Ni3CrMoV锻钢微观组织的TEM研究

利用透射电镜 (TEM)研究了 1 4Ni3CrMoV锻钢正火 +回火后的微观组织。结果表明 ,该钢在正火过程中形成的以贝氏体为主的组织在高温回火过程中发生了明显变化。碳化物大量析出 ,分布均匀 ,大部分仍保持一定的方向性 ,显示原贝氏体铁素体板条的位向。局部存在铁素体 +球化碳化物类组织。回火后没有发现块状残余奥氏体     

HRTEM Study on Precipitates in High Co-Ni Steel

The secondary hardening reaction is accompanied with precipitation of fine carbides in high CoNi ultrahigh strength steel. The crystal structure of the precipitating carbides is unambiguously determined by microbeam diffraction in transmission electron microscopy. It is identified that the needle-shaped carbides are M2C with a hexagonal structure. The concentration of substitutional alloying elements in the carbides quantified by energy dispersive X-ray spectroscopy (EDS) also supports the result above. The spatial structure of M2C is identical with L'3 type. Metal atoms are in a close packed hexagonal structure, the carbon atoms partly distribute with random in the octahedral interstices and the filling probability is less than 1/2. Particular attention was paid to the relationship of needle-shaped carbides/ferrite matrix at secondary hardening peak tempered at 482癈 for 5 h. Observation by high resolution transmission electron microscopy (HRTEM) confirms that carbides with black-white contrast are ful     

热处理对网状结构TiB_W/Ti60复合材料组织与性能的影响

使用大尺寸球形Ti60钛合金粉与细小TiB2粉,通过低能球磨与反应热压烧结,成功制备了增强相呈网状分布的TiB晶须增强Ti60合金基(TiB_W/Ti60)复合材料。对TiB_W/Ti60复合材料进行热处理,以改善其组织结构与力学性能。结果表明:随着固溶温度的升高,TiB_W/Ti60复合材料基体中初生α相(密排六方相)含量减少,相应地转变β组织(α′(马氏体)+残留β相(体心立方相))含量增加,TiB_W/Ti60复合材料的抗拉强度升高,塑性降低;经过1 100℃/1h固溶处理之后,TiB_W/Ti60复合材料的室温抗拉强度为1 470 MPa,延伸率为1.9%。经过时效处理后,转变β组织中的α′相分解成细小α+β相。经过1 100℃/1h固溶+600℃/8h时效处理后TiB_W/Ti60复合材料的硬度达到HV538,抗拉强度达到1 552 MPa,延伸率为1.5%,经过1 000℃/1h固溶+600℃/8h时效处理,其抗拉强度达到1 460 MPa,延伸率为2.2%。     

冷堆焊高碳Nb-Ti-V系钢质堆焊金属中的碳化物

研究了不同成分的冷堆焊高碳Nb-Ti-V系堆焊金属中碳化物的分布、形态,分析了碳化物在冷焊条件下的形成过程.Nb、Ti可以形成颗粒碳化物,但单独加入且含量较高时,碳化物尺寸过大,对基体固溶强化较弱,堆焊金属硬度过低;单独加入V时则形成了网状碳化物;适量Nb、Ti、V同时加入,获得了均匀分布的颗粒碳化物及强韧的基体,堆焊金属耐磨性优于D317的堆焊金属.     

Microstructures and high temperature properties of spray formed niobium‐containing M3 high speed steel

The billets of M3 high speed steel (HSS) with or without niobium addition were prepared via spray forming and forging, and the corresponding microstructures, properties were characterized and analysed. Finer and uniformly‐distributed grains without macrosegregation appear in the as‐deposited high speed steel that are different to the as‐cast high speed steel, and the primary austenite grain size can be decreased with 2% niobium addition. Niobium appears in primary MC‐type carbides to form Nb₆C₅ in MN2 high speed steel, whereas it contributes less to the creation of eutectic M₆C‐type carbides. With same treatments to forged MN2 high speed steel and M3 high speed steel, it is found that the peak hardness of these two steels are almost the same, but the temper‐softening resistance of the former is better. With higher high‐temperature hardness of the forged MN2 high speed steel, its temper softening above 600 °C tends to slow down, which is related to the precipitation of the secondary carbides after tempering. A satisfactory solid solubility of Vanadium and Molybdenum can be obtained by Nb substitution, precipitation strengthening induced by larger numbers of nano‐scaled MC and M₂C secondary carbides accounts for the primary role of determining higher hardness of MN2 high speed steel. The results of the wear tests show that the abrasive and adhesive wear resistance of MN2 high speed steel can be improved by the grain refinement, existence of harder niobium‐containing MC carbides, as well as solute strengthening by more solute atoms. The oxidational wear behavior of MN2 high speed steel can be markedly influenced by the presence of the high hardness and stabilization of primary niobium‐containing MC‐type carbides embedded in the matrix tested at 500 °C or increased loads. The primary MC carbides with much finer sizes and uniform distribution induced by the combined effects of niobium addition and atomization/deposition would be greatly responsible for the good friction performance of the forged MN2 high speed steel.     

Influence of secondary carbides precipitation and transformation on the secondary hardening of laser melted high chromium steel

The influence of secondary carbides precipitation and transformation on the secondary hardening of laser melted high chromium steels was analyzed by means of scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. The microstructure of laser melted high chromium steel is composed of austenite with supersaturated carbon and alloy elements and granular interdendritic carbides of type M₂₃C₆. Secondary hardening of the laser melted layer begins at 450 °C after tempering, and the hardness reaches a peak of 672HV at 560 °C and then decreases gradually. After tempering at 560 °C, a large amount of lamellar martensite was formed in the laser melted layer with a small quantity of thin lamellar M₃C cementite due to the martensitic decomposition. The stripy carbides precipitating at the grain boundaries were determined to be complex hexagonal M₇C₃ carbides and face centered cubic M₂₃C₆ carbides. In addition, the granular M₂₃C₆ carbides and fine rod-like shaped M₇C₃ carbides coexisted within the dendrites. As a result, the combined effects of martensitic transformation, ultrafine carbide precipitations, and dislocation strengthening result in the secondary hardening of the laser melted layer when the samples were tempered at 560 °C.     

Influence of nickel on secondary hardening of a modified AISI H13 hot work die steel

This paper focuses on the effects of nickel on secondary hardening of a modified H13 hot work die steel. Both the non‐nickel steel and the nickel‐added steel get a secondary hardening peak at 520 °C, and the secondary hardening peak trends to increase in the nickel‐added steel. On the basis of scanning electron microscope and transmission electron microscope observation, the rise of the secondary hardening peak is in connection with the precipitation of M₃C type carbides. More strip‐shaped and needle‐shaped M₃C type carbides precipitated from matrix. By means of internal friction, the result suggests that nickel does not affect the position of the Snoek‐Kê‐Köster peak, but the height of Snoek‐Kê‐Köster peak of the nickel‐added steel is higher, which indicates nickel enhances the interaction between dislocations and interstitial atoms, promoting the precipitation of carbides.     

纳米钛-锆合金制备技术的研究进展

纳米钛-锆二元合金为固溶体合金,平均晶粒度为6～7nm,晶格类型为面心立方晶格(fcc),相对于钛和锆元素的密排六方晶格(hcp)结构稳定性更高.综合评述了采用机械合金化技术制备纳米钛-锆合金在国内外所取得的主要研究成果,并展望了其发展方向.     

Effect of Long-term Thermal Exposure on Microstructure and Stress Rupture Properties of GH3535 Superalloy

The evolution of microstructure and the stress rupture properties of long term thermally exposed GH3535 alloy have been investigated. It was found that M6 C carbides presented in the solid solution heat treated samples. During long term thermal exposure at 700 C, fine M12 C carbides precipitated preferentially at grain boundaries. These carbides coexisted with the pre-exiting M6 C. The stress rupture life of700 C/1000 h exposed sample under creep testing at 650 C/324 MPa is 93 h. It is much longer than that of the solid solution samples. No noticeable changes could be detected in both the microstructure and stress rupture lives when the samples were exposed for time longer than 1000 h M12 C carbides were found to be beneficial to the creep properties. The cracks initiated at the interface of M6 C carbides and matrix, which led to a lower creep rupture life.