热处理工艺对12Cr1MoV钢显微组织和力学性能的影响

通过热模拟试验对12Cr1MoV钢进行了不同工艺的正火+回火热处理,研究了热处理工艺对该钢显微组织及力学性能的影响。结果表明:12Cr1MoV钢正火+回火后的正常显微组织为回火贝氏体+铁素体或回火贝氏体+铁素体+珠光体或铁素体+珠光体;如果回火温度过高或正火冷却速率不足,则分别会导致钢中出现两相区组织黄块马氏体和钒的碳化物沿晶界及晶内聚集长大的情况,显著降低钢的力学性能。     

正火控冷12MnCrNiMoV钢板性能和微观组织研究

研究了正火控冷 +高温回火热处理工艺对 12MnCrNiMoV钢板力学性能、冲击韧性的影响 ,用透射电镜分析了 12MnCrNiMoV钢的微观组织。结果表明 ,与正火钢板相比 ,正火控冷的钢板具有较好的强韧性 ,Akv ,-4 0℃ 提高约 45 % ,特征转变温度TFAT50 降低了 2 0℃。组织观察表明 ,正火控冷的 12MnCrNiMoV钢板组织中的粒状贝氏体中的M A岛主要以板条马氏体为主。高温回火后 ,正火控冷工艺的微观组织为板条铁素体 ,碳化物呈弥散均匀分布     

正火控冷12MnCrNiMoV钢板性能

研究了正火控冷+高温回火热处理工艺对12MnCrNiMoV钢板力学性能、冲击韧性的影响,用透射电镜分析了12MnCrNiMoV钢的微观组织.结果表明,与正火钢板相比,正火控冷的钢板具有较好的强韧性,Akv,-40℃提高约45%,特征转变温度TFAT50降低了20℃.组织观察表明,正火控冷的12MnCrNiMoV钢板组织中的粒状贝氏体中的M-A岛主要以板条马氏体为主.高温回火后,正火控冷工艺的微观组织为板条铁素体,碳化物呈弥散均匀分布.     

新型贝氏体钢的组织和冲击疲劳性能研究

通过显微组织观察和冲击疲劳实验,研究了不同热处理新型贝氏体钢的组织和冲击疲劳性能.结果表明:新型贝氏体钢正火低温回火的组织由贝氏体铁素体和奥氏体组成,淬火低温回火组织为回火马氏体和残余奥氏体,正火低温回火热处理的冲击疲劳寿命高于淬火低温回火热处理的冲击疲劳寿命.分析了多冲疲劳裂纹扩展的行为,讨论了正火低温回火提高冲击疲劳的原因.     

再热蒸汽热段管道弯头软化原因分析

某电厂再热蒸汽热段管道弯头在热推制后出现硬度偏低、组织异常的现象,为了分析该弯头组织性能劣化的原因,进行了模拟折弯试验及弯后热处理试验。结果表明:在热变形过程中弯头组织发生动态再结晶,马氏体向铁素体+碳化物转变,导致硬度下降,再结晶后继续变形使铁素体沿变形方向被拉长;在成型结束后没有通过正火+高温回火处理来消除这种不正常的形变组织,是该弯头软化的主要原因。     

纳米贝氏体/马氏体钢的热稳定性

将低温贝氏体相变前淬火得到由马氏体、贝氏体铁素体和残余奥氏体组成的纳米贝氏体钢,使用扫描电镜(SEM)、X射线衍射(XRD)和透射电镜(TEM)等手段观察在不同温度回火的纳米贝氏体钢的显微组织和硬度变化,研究了预相变马氏体对纳米贝氏体钢热稳定性的影响。结果表明:含有马氏体的纳米贝氏体钢在中低温(473~773 K)回火后其硬度比回火前的高,回火温度高于823 K其硬度迅速下降到266.2HV(923 K)。预形成的马氏体在473~573 K回火后向附近的残余奥氏体排碳,后者的碳含量提高到峰值1.52%,提高了残余奥氏体的热稳定性,延迟后者在高温时的分解,从而提高了纳米贝氏体钢的高温热稳定性;回火温度高于723 K则残余奥氏体分解成碳化物,贝氏体铁素体粗化、回复形成新的铁素体晶粒。     

一种热锻模具修复用堆焊焊条堆焊层的组织与硬度分析

对一种热锻模具修复用堆焊焊条的堆焊层成分、组织、硬度、热处理后的组织及硬度作了细致分析。焊芯采用H08A的5.0mm焊丝,并在焊条药皮中加入合金元素Ni、Cr和Mo,以向堆焊层中过渡合金元素Ni、Cr和Mo。试验中采用OLYMPUS GX71金相显微镜、Quanta600扫描电子显微镜及Genesis XM2 X射线能谱仪、Philips CM200透射电镜及Hanemann显微硬度计对堆焊层金属进行测试,结果表明,焊态下堆焊层显微组织为粒状贝氏体+少量铁素体,同时有白色马氏体组织存在,热处理后堆焊层显微组织为粒状贝氏体的回火组织+少量铁素体+碳化物。     

G18CrMo2-6钢在高温回火过程中第二相的演变

应用扫描电子显微镜、透射电子显微镜和能谱技术等手段研究了G18CrMo2-6钢正火组织中第二相在680℃下保温一系列时间段的转变。结果表明,在正火后贝氏体中析出相主要为马氏体/奥氏体(M/A)组元和合金渗碳体(M_3C);在回火保温初期M/A分解为铁素体(α)与M3C组织,随着保温时间延长M3C逐渐球化并溶解,M_(23)C_6在晶界析出并长大,同时基体上有细小弥散的MC相析出。即回火保温过程中组织随时间的延长发生M/A→α+M_3C,M_3C→M_(23)C_6+MC的变化。     

热处理对12Cr2Mo1R耐热钢断裂韧度的影响

本文对12Cr2Mo1R耐热钢板进行了正火+回火处理(NT),然后再进行模拟焊后热处理(SPWHT),研究了这两种状态钢板在不同温度下的J-Δa阻力曲线,并对断裂韧度J0.2BL值进行了分析。研究结果表明,这两种热处理态组织均以贝氏体为主,所含碳化物都由M3C、M2C、M7C3和M23C6组成,其中M代表合金元素Cr、Mo、Mn和Fe或者它们的组合;在相同热处理的状态下,温度越高,断裂韧度值越高;相同温度情况下,正火+回火态12Cr2Mo1R耐热钢表现出较高的断裂韧度,因为其碳化物含量较小,碳化物之间的间距相对较大。     

Mo和Ni对高强无碳化物贝氏体钢组织转变与力学性能的影响

测定了不含Mo和Ni、含Ni和含Mo三种成分实验钢的CCT曲线,利用扫描电镜、透射电镜观察了连续冷却及轧后空冷条件下三种钢的显微组织变化,并对其力学性能进行了检测分析。结果表明:添加少量Mo和Ni能有效延迟高强无碳化物贝氏体钢CCT曲线中高温铁素体相变,降低Ms点,促进贝氏体相变。Mo和Ni的添加可使实验钢轧后空冷组织由铁素体+粒状贝氏体+M/A混合组织转变为无碳化物贝氏体组织(BF+AR),Ni对贝氏体板条的细化作用比Mo显著,但组织中会出现少量粗大贝氏体;Mo对轧后相变过程中粗大贝氏体的形成有一定抑制作用,可使获得的无碳化物贝氏体组织均匀性更好。Mo和Ni均可有效提高高强无碳化物贝氏体钢的力学性能,其中Ni对抗拉强度的提升作用强于Mo,而Mo则更有利于冲击韧性的提高。含Ni的2#实验钢抗拉强度比不加Ni和Mo的1#实验钢提高252MPa,含Mo的3#实验钢-20℃下冲击吸收功比1#提高11J。     

Tempering of hard mixture of bainitic ferrite and austenite

Abstract

Recent work has shown that bainitic ferrite plates produced by transformation at low temperatures can be as thin as 20 nm with a hardness in excess of 650 HV30, tensile strength ~2.3 GPa and toughness ~30 MPa m^1/2. Because these properties rely on the fine scale of the microstructure, a study has been carried out in relation to the tempering resistance of steel over the temperature range 350 – 750°C. It is found that significant softening occurs only after the plates of ferrite begin to coarsen. The coarsening process is hindered by the intense precipitation of carbides resulting from decomposition of the carbon enriched retained austenite. The carbides themselves lead to some precipitation strengthening during the early stages of tempering. The ferrite is found to contain excess carbon, beyond its solubility limit, and X-ray analysis indicates that the carbon is associated with heterogeneous strains in the microstructure. It does not readily precipitate until the onset of substantial recovery during annealing.     

Effects of Carbon on the CG HAZ Toughness and Transformation of X80 Pipeline Steel

X80 pipeline steel produced by TMCP has high strength and high toughness with ultrafine grain microstructure. The microstructure coarsens and the toughness worsens at the coarse grained (CG) HAZ apparently after weld simulation. The experimental results indicated that the bainitic ferrite and the second phases formed at cooling are differently as the variation of carbon in base metal. In low carbon steels, the bainitic ferrite laths are long and narrow, the second phases are complex including residual austenite, martensite, the M-A constituent and the Fe3C carbide. The formation of Fe3C carbide is the main reason of the poor toughness in CG HAZ. The ultralow carbon in base metal, however, can improve the CG HAZ toughness through restraining the formation of carbides, decreasing the M-A constituent, increasing the residual austenite content, which are beneficial to the CG HAZ toughness.     

热处理对C12A耐热钢的组织与性能影响

通过对铸造C12A耐热钢进行热处理,观察其微观组织,测定其力学性能。试验结果表明：正（淬）火组织为板条马氏体＋部分针状马氏体＋少量残余奥氏体,其硬度比较高,塑性和韧性不是很好;正（淬）火＋回火组织为回火马氏体,其硬度不是很高,塑性和韧性比较好,具有良好的综合性能;退火组织为铁素体,其硬度低,塑性和韧性高;通过正火＋回火,研究回火温度对其微观组织和力学性能的影响。试验结果表明：回火温度对C12A钢的组织和性能有较大影响,其硬度随回火温度的升高呈先降后升趋势。     

Metallography of bainitic transformation in austempered ductile iron

Abstract

An unalloyed nodular cast iron has been used to investigate the development of microstructure on heat treating in the bainite temperature region. Specimens were austenitised at 900°C for 1·5 h, then austempered for 1, 2, or 3 h at 250,300, and 350°C, respectively, and examined by light, transmission electron, and scanning electron microscopy. Experimental results indicate a microstructure consisting of a stable, highly enriched, retained austenite with one of two lower bainitic ferrite morphologies. One of these morphologies is carbide free acicular ferrite for specimens austempered at 350°C for 1 h and the other is bainitic ferrite in which carbide is distributed within the ferrite produced by different heat treatment conditions. Austempering at 350°C for 2 h and at 300°C for 1 and 2 h resulted in the formation of transition carbides in bainitic ferrite platelets. The η carbide was formed at 350°C for 2 h by precipitation from a bainitic ferrite supersaturated with carbon. By contrast, ? carbide was associated with austempering at 300°C for 1 and 2 h and precipitates either on the austenite twin/bainitic ferrite boundaries or within the bainitic ferrite. The fracture mode of tensile and impact specimens in the austempered condition was fully ductile compared with as cast specimens, which had mixed fracture characteristics.

MST/1646     

贝氏体钢精细结构的TEM观察

使用ＴＥＭ研究了钢中贝氏体的精细结构及碳化物的形貌与分布，加入微量元素使贝氏体铁素体组织明显细化。贝氏体铁素体由亚单元或亚块组成，碳化物形貌不一，分布在条间，片内和亚块边界。贝氏体铁素体内有极为丰富的精细组织。文中讨论了贝氏体的相变机制。     

Microstructural characterization of controlled forged HSLA-80 steel by transmission electron microscopy

In this study, transmission electron microscopy (TEM) was used to evaluate the effect of controlled forging followed by cooling at various rates on microstructure of an HSLA-80 steel. The observations demonstrate that water-quenched steel has finer multiphase constituents of lath martensite, bainite and twined martensite, whereas air-cooling has resulted in a mixture of bainitic ferrite, retained austenite or MA constituents along with some Widmanstatten ferrite. When the steel is cooled in sand, the maximum volume fraction of polygonal ferrite (PF) was produced which, in turn, increased volume fraction of MA constituents. Precipitation of fine -Cu, Nb and Ti carbides and carbonitrides was observed and identified using energy dispersive spectrometric analysis (EDS) and electron diffraction.     

The approach to equilibrium during tempering of a bulk nanocrystalline steel: an atom probe investigation

A local electrode atom probe has been used to analyze the solute partitioning during bainite transformation in a novel, nanocrystalline bainitic steel. Atom probe results show the absence of any partitioning of substitutional elements between the phases involved. The results are fully consistent with the diffusionless transformation of austenite to bainite. However, substitutional elements are expected to redistribute approaching an equilibrium phase boundary as the mixture of bainitic ferrite and retained austenite is tempered. The compositional analysis of the austenite/ferrite interface by atom probe tomography indicates that retained austenite decomposes during tempering before equilibrium is reached at the interface.     

Transformation kinetics of unalloyed and high Mn austempered ductile iron

Abstract

The kinetics of bainitic transformation was studied in unalloyed and 1%Mn alloyed ductile irons. The samples were subjected to different austempering heat treatment cycles in dilatometry equipment. The results showed the effect of Mn on delaying the start and end of bainitic transformation, supposedly because of Mn segregation to the primary austenite grain boundaries. Decreasing austempering temperature led to precipitation of carbides inside the lower bainitic ferrite plates and therefore, more dilatation during the bainitic reaction. The dilatometric results were also used to calculate n and k in the Johnson-Mehl-Avrami equation and to derive the time-temperature-transformation diagrams. X-ray results were used to calculate the quantitative amount of precipitated carbides within lower bainitic ferrite and the dilatation during austempering.