电渣重熔过程冷却强度对含镁H13钢中碳化物的影响

研究电渣重熔过程冷却强度对含镁H13钢凝固组织和碳化物偏析的影响.采用光学显微镜、扫描电镜、透射电镜、X射线衍射仪等分析凝固组织及碳化物的特征.研究发现,钢锭的凝固组织均为马氏体组织、残余奥氏体及一次碳化物.H13钢电渣锭中主要析出的一次碳化物为V8C7、MC、M23 C6及M6C.随着冷却强度增加,电渣锭边部碳化物的尺寸减小且分布更加均匀,但是碳化物的类型不发生变化.电渣重熔过程中冷却强度增加促进钢中镁对夹杂物的变性能力,经过镁变性后生成的MgO· Al2O3为TiN的析出提供形核质点,MgO· Al2 O3和TiN的复合夹杂物能够促进一次碳化物异质形核,从而细化一次碳化物.     

奥氏体化温度对复合轧辊表面工作层组织的影响

通过离心铸造方法制备了外加铬铁颗粒增强双金属复合材料环形铸件,采用光学显微镜和扫描电镜对双金属复合材料铸件在不同热处理工艺条件下的组织进行了研究。研究结果表明:在本试验条件下,双金属复合材料环形铸件外部高铬铸铁层的铸态组织为:Cr7C3、少量Cr23C6型碳化物、少量Cr3C型碳化物、珠光体基体、残余奥氏体;经热处理后其组织为:Cr7C3、少量Cr23C6型碳化物、少量Cr3C型碳化物、回火马氏体、二次碳化物、残余奥氏体,并且碳化物形态及分布有所改善。     

耐冲击工具钢5Cr8MoVSi热处理过程中组织结构的变化

对5Cr8MoVSi钢热处理工艺研究表明，经840℃退火，碳化物类型以M23C6为主，并有少量的MC和M7C3.淬火组织中剩余碳化物以MC和M7C3为主，M23C6型碳化物在淬火加热时大部分溶解．该钢随淬火加热温度升高，淬火马氏体由板条状和针状马氏体混合组织过渡到以板条状马氏体为主．在沉淀硬化的回火温度(485℃)下，淬火针状马氏体仍显示出原马氏体针；而淬火板条状马氏体的板条状方向性几乎被完全切断，显微组织呈均匀化．该钢在1000～1050℃淬火时，残余奥氏体量为10．7％～12．3％，经485℃一次回火时，残余奥氏体量减少不大，因此，应进行二次或三次回火．淬回火HRC硬度最高为58～60．     

20CrNi2MoV钢连续冷却过程中的相变行为

利用热力模拟试验机研究了20CrNi2MoV钢在变形和未变形条件下的连续冷却相变行为及微观组织演变规律,绘制了该实验钢静态和动态连续冷却转变(CCT)曲线,分析了合金元素、冷却速度和变形条件等对其连续冷却相变行为的影响。结果表明:20CrNi2MoV钢中Cr、Ni、Mo等合金元素使得过冷奥氏体稳定性增强,贝氏体相变可以在较宽的中温转变温度区间发生;随着冷却速度的增加,20CrNi2MoV钢的铁素体相变温度下降,铁素体扩散型相变受到抑制,贝氏体中温区相变得到加强;变形使得20CrNi2MoV钢CCT曲线的铁素体和珠光体转变线明显左移,并且由于变形作用,贝氏体相变温度提高。     

长期高温时效12Cr1MoV钢中碳化物组织结构

12Cr1MdV低合金耐热钢在540℃运行20万h后，材料中碳化物的组织结构发生显著变化．研究结果表明：材料中大量的碳化物沿晶界析出并聚集粗化，析出的碳化物主要为M23C6，同时存在少量的M6C，碳化物的沿晶界析出及其粗化是材料结构和性能发生恶化的主要原因；弥散的细小的富Ⅴ碳化物MC（V4C3）在铁素体晶体内沉淀析出，有助于12cr1MoV低合金耐热钢的性能和组织结构的稳定；珠光体组织中Fe3C发生球化和分解，但无明显聚集长大，并由原先的M3C型分解转变为MC型．     

HK40耐热钢碳化物的沉淀研究

HK40(4Cr25Ni20)离心铸造耐热钢管是目前国内外石油化工中大量选用的炉用材料。这种以碳化物作为强化相的耐热钢,含碳量为:0.35—0.45%,铸态组织为:奥氏体加上块状具有伪六角洁构的 Cr7C3型晶界碳化物。在使用过程中由于加热使得基体中过饱和碳以细小、弥散分布的Cr23C6型碳化物在晶内沉淀析出,同时晶界Cr7C3型碳化物也转变为Cr3C6,起到了碳化物弥散强化作用,改善了钢的高温使用性能,提高了钢的蠕变断裂强度。 利用透射电镜研究了HK40钢铸态以及850℃高温时效500小时和在870℃下实际使用了4万小时合金组织的高倍形貌。用选区电子衍射…     

提高M12螺帽冷镦模具耐磨性的研究

Cr12MoV钢制造的M12螺帽冷镦模经超低温改性处理后，其显微组织发生了转变：钢组织中的残留奥氏体向马氏体转变，析出大量高弥散的碳化物微粒，强化了模具性能，尤其是耐磨性能显著增加，从而提高了冷镦模具的使用寿命。     

过共晶超高铬铸铁合金的组织与性能

研究了过共晶超高铬铸铁的组织和热处理工艺对其性能的影响,过共晶超高铬铸铁的铸态组织由初生碳化物M7C3 共晶(M7C3 M23C6) 马氏体 残余奥氏体组成,其中初生碳化物(M7C3)为六方形长秆状.在1050℃淬火的条件下,低温回火时,材料的硬度、冲击韧性的变化不大,回火温度提高到450℃后,材料的硬度显著升高,相应的冲击韧性下降;回火温度继续上升,材料的硬度下降,冲击韧性升高.     

喷射成形及时效处理对Cr12MoV钢组织及性能的影响

采用喷射成形技术制备了Cr12MoV钢,应用金相、X射线衍射分析、差热分析等实验手段对该钢的微观组织及性能进行了分析和研究.结果表明,喷射成形Cr12MoV钢的显微组织得到了显著的细化,与Cr12MoV钢铸态组织不同处在于其主要由奥氏体组成,由于喷射成形过程中的冷却速度快,奥氏体中高度固溶了碳及合金元素,其晶格常数达0.3620nm,且喷射成形钢的马氏体起始转变温度(Ms)亦低于常规工艺制备的钢的Ms.随着时效温度的升高,亚稳奥氏体逐渐发生了转变,Cr12MoV钢的硬度在570℃时效温度处出现峰值,由时效处理前的HRC38增大至HRC60,时效合金主要由马氏体构成.当时效温度高于570℃时,Cr12MoV钢的硬度剧烈下降,因此,570℃是喷射成形Cr12MoV钢进行时效处理的临界温度.     

一种新型冷轧辊用钢的组织演变

本文以一种新型冷轧辊用钢为研究对象,借助金相显微镜和扫描电子显微镜分析了试验钢在正火、球化退火、淬火、回火过程中的组织演变,研究了碳化物的成分变化和溶解析出行为。结果显示,试验钢正火后得到马氏体+部分颗粒状和少量块状碳化物的显微组织;球化退火后的显微组织为铁素体基体上分布有大量颗粒状碳化物+少量块状碳化物,球化退火组织评定为为2~3级;淬火后的组织为马氏体+部分颗粒状和少量块状碳化物;三次回火后的组织为回火马氏体+部分颗粒状和少量块状碳化物。试验钢中的块状碳化物在整个热处理过程中始终存在,1100℃以下奥氏体化时只发生边缘部分的少量溶解。颗粒状碳化物主要为M23C6型,在热处理过程中存在明显的溶解和析出行为,1100℃以下奥氏体化时部分溶解。     

Solidification microstructure formation in HK40 and HH40 alloys

The microstructure formation processes in HK40 and HH40 alloys were investigated through JmatPro calculations and quenching performed during directional solidification. The phase transition routes of HK40 and HH40 alloys were determined as L → L + γ → L + γ + M₇C₃ → γ + M₇C₃ → γ + M₇C₃ + M₂₃C₆→ γ + M₂₃C₆ and L → L + δ → L + δ + γ→ L + δ + γ + M₂₃C₆ δ + γ + M₂₃C₆, respectively. The solidification mode was determined to be the austenitic mode (A mode) in HK40 alloy and the ferritic–austenitic solidification mode (FA mode) in HH40 alloy. In HK40 alloy, eutectic carbides directly precipitate in a liquid and coarsen during cooling. The primary γ dendrites grow at the 60° angle to each other. On the other hand, in HH40 alloy, residual δ forms because of the incomplete transformation from δ to γ. Cr₂₃C₆ carbide is produced in solid delta ferrite δ but not directly in liquid HH40 alloy. Because of carbide formation in the solid phase and no rapid growth of the dendrite in a non-preferential direction, HH40 alloy is more resistant to cast defect formation than HK40 alloy.     

Microstructural evolution of a heat-treated H23 tool steel

The microstructure and the stability of carbides after heat treatments in an H23 tool steel were investigated. The heat treatments consisted of austenization at two different austenizing temperatures (1100℃ and 1250℃), followed by water quenching and double-aging at 650℃, 750℃, and 800℃ with air cooling between the first and second aging treatments. Martensite did not form in the as-quenched microstructures, which consisted of a ferrite matrix, M₆C, M₇C₃, and MC carbides. The double-aged microstructures consisted of a ferrite matrix and MC, M₆C, M₇C₃, and M₂₃C₆ carbides. Secondary hardening as a consequence of secondary precipitation of fine M₂C carbides did not occur. There was disagreement between the experimental microstructure and the results of thermodynamic calculations. The highest double-aged hardness of the H23 tool steel was 448 HV after austenization at 1250℃ and double-aging at 650℃, which suggested that this tool steel should be used at temperatures below 650℃.     

12Cr1MoV/TP347H异种钢焊接接头时效过程中界面组织演变

The interfacial microstructure evolution of 12Cr1MoV/TP347H dissimilar steel welded joints with a nickel-based filler metal during aging was studied in detail to elucidate the mechanism of premature failures of this kind of joints. The results showed that not only a band of granular Cr₂₃C₆ carbides were formed along the fusion boundary in the ferritic steel during aging, but also a large number of granular or plate-like Cr₂₃C₆ carbides, which have a cube–cube orientation relationship with the matrix, were also precipitated on the weld metal side of the fusion boundary, making this zone be etched more easily than the other zone and become a dark etched band. Stacking faults were found in some Cr₂₃C₆ carbides. In the as-welded state, deformation twins were observed in the weld metal with a fully austenitic structure. The peak microhardness was shifted from the ferritic steel side to the weld metal side of the fusion boundary after aging and the peak value increased significantly. Based on the experimental results, a mechanism of premature failures of the joints was proposed.     

奥氏体合金中溶质原子的晶界偏聚与晶界沉淀

用扫描电镜和透射电镜研究了晶界沉淀的形貌和化学组成,发现高温加热时生成富Ti 的厚片状晶界沉淀(MC);以后的低温加热时生成 Mo含量较高的薄片状晶界沉淀。不同冷却速度条件下的晶界沉淀(M_7C_3)的Cr 含量不同,加热后的冷却过程中,较低温度下析出的晶界沉淀(M_(23)C_6)中的Cr,Mn 含量较高。结果表明:溶质原子的错配度、点阵溶解度及沉淀温度对晶界沉淀产生影响。     

冷却速率对奥氏体不锈钢凝固过程影响的原位观察

通过采用激光共聚焦扫描显微镜对AISI304奥氏体不锈钢的凝固过程进行了原位动态观察研究.发现当冷却速率为0.05℃.s-1时,奥氏体不锈钢以胞状晶方式凝固,其凝固模式为FA模式,即δ铁素体相先从液相中形核并长大,γ相在1 448.9℃时通过与液相发生包晶反应（L＋δ→γ）在δ铁素体相界形成,当温度降到1 431.3℃时液相消失,δ铁素体相通过固态相变转变为γ相,富Cr贫Ni的残留铁素体位于胞状晶之间.当冷却速率为3.0℃.s-1时,奥氏体不锈钢以枝晶方式生长,冷却到1346.4℃时包晶反应在液相与δ铁素体相界之间进行,其残留铁素体位于枝晶干,与冷却速率为0.05℃.s-1时相比,其残留铁素体的数量增多,残留铁素体富Cr贫Ni的程度减轻.     

Effect of Nb and V on the continuous cooling transformation of undercooled austenite in Cr–Mo–V steel for brake discs

The increasing speed of trains necessitates the development of brake-disc materials that meet more stringent requirements. Therefore, Nb and V have been added to Cr–Mo–V steel to improve its thermal fatigue performance when used in brake discs. In this paper, the influences of Nb and V on the static continuous cooling transformation (CCT) behaviors of undercooled austenite were studied. The microstructures, hardness, and dislocation densities at different cooling rates and with the addition of different alloying elements were also investigated. The results show that the transformation products of ferrite, granular bainite, lower bainite, and martensite form under different cooling conditions. With increasing Nb and V contents, the CCT curves are shifted to the left, ferrite and bainite transformations are promoted, and the critical cooling rate of total martensite formation is increased. The added V mainly forms V-rich M₈C₇ precipitates and reduces the dissolved C content; therefore, the A_c1, A_c3, and M_s-point temperatures increase. Moreover, the stability of retained austenite is also reduced; its content therefore decreases. Compared with V, the effect of added Nb is weaker because of its smaller content. However, the addition of Nb improves the hardness at lower cooling rates because of the precipitation of fine NbC particles and refining of the microstructure.     

Precipitation analysis of as-cast HK40 steel after isothermal aging

As-cast HK40 steel was aged at 700, 800, or 900℃ for times as long as 2000 h. Microstructural characterization showed that the primary M₇C₃ carbide network contained a substantial content of manganese, in agreement with the microsegregation of manganese calculated by Thermo-Calc using the Scheil-Gulliver module. The dissolution of primary carbides caused the solute supersaturation of austenite and subsequent precipitation of fine M₂₃C₆ carbides in the austenite matrix for aged specimens. During prolonged aging, the carbide size increased with increasing time because of the coarsening process. A time-temperature-precipitation diagram for M₂₃C₆ carbides was calculated using the Thermo-Calc PRISMA software; this diagram showed good agreement with the experimental growth kinetics of precipitation. The fine carbide precipitation caused an increase in hardness; however, the coarsening process of carbides promoted a decrease in hardness. Nanoindentation tests of the austenite matrix indicated an increase in ductility with increasing aging time.     

激光熔覆Mo2C-Co基合金的工艺参数对其组织的影响

利用10kW的CO2激光器在409L铁素体不锈钢表面激光熔覆w(Mo2C)=20%的Mo2C/Co基涂层,运用SEM、EDS、XRD及显微硬度仪观察和分析激光功率和扫描速度对熔覆层成型性、尺寸、组织及性能的影响.结果表明:激光熔覆合理的工艺参数为:P=3.6kW,v=8mm/s;钴基熔覆层组织由平面晶、柱状晶、树枝晶构成,熔覆层中物相主要为Mo2C颗粒、亚共晶γ-Co和共晶碳化物Cr23C6、Cr7C3;由于Mo2C颗粒加入,凝固组织的晶粒尺寸减小、晶粒细化,涂层的显微硬度从870HV提高至1 400HV.