Rietveld Quantitative Analysis of Carbides Precipitation in Normalized-tempered 2.25Cr-1Mo-0.25V Steel

The quantitative determination of the mass fractions of precipitates in steels is very difficult using traditional materials characterization techniques. The Rietveld full-pattern fitting algorithm was introduced to solve this problem. The precipitated multicomponents’ mass fraction of M3C, MC, M7C3 and M23C6 were evaluated precisely and relatively quickly. It is found evolution of carbides apparently occurs during tempering at high temperatures, and a two-step transformation mechanism is proposed for M7C3 during early tempering treatment. The method is an effective way on the investigation of precipitation kinetics, which may play a promising role in propertities’ enhancement and design of the heat-resistant steels.

Study of High Temperature Deformation and Recrystallization in W9Mo3Cr4V Steel

The behavior of high temperature deformation and recrystallization of W9Mo3Cr4V steel have been studied in this paper. Dynamic precipitation during deformation has also been investigated. In W9Mo3Cr4V steel, stress strain curves exhibit many features. The deformation structures and the effects of deformation parameters on dynamic recrystallization are more complicated than those in low alloy steels. For W9Mo3Cr4V steel, there is a large number of residual carbides on the matrix at high temperature. Also, many second carbides precipitate from the matrix during high temperature deformation. These two kinds of carbides (especially the latter) make the behavior of deformation and dynamic recrystallization in W9Mo3Cr4V steel different from those in low alloy steels. ABSTRACT:The behavior of high temperature deformation and recrystallization of W9Mo3Cr4V steel have been studied in this paper. Dynamic precipitation during deformation has also been investigated. In W9Mo3Cr4V steel, stress strain curves exhibit many features. The deformation structures and the effects of deformation parameters on dynamic recrystallization are more complicated than those in low alloy steels. For W9Mo3Cr4V steel, there is a large number of residual carbides on the matrix at high temperature. Also, many second carbides precipitate from the matrix during high temperature deformation. These two kinds of carbides (especially the latter) make the behavior of deformation and dynamic recrystallization in W9Mo3Cr4V steel different from those in low alloy steels.

Tribological behavior of CrN-coated Cr–Mo–V steels used as die materials

DIN 1.2343 and 1.2367 steels are commonly used as die materials in aluminum extrusion, and single/duplex/multi-coatings enhance their surface properties. The design of an appropriate substrate/coating system is important for improving the tribological performance of these steels under service conditions because the load-carrying capacity of the system can be increased by decreasing the plastic deformation of the substrate. In this study, the tribological behavior of CrN-coated Cr–Mo–V steels(DIN 1.2343, 1.2367, and 1.2999 grades) was investigated using different setups and tribological pairs at room and elevated temperatures. The aim of this study was to reveal the wear resistance of a suggested system(1.2999/CrN) not yet studied and to understand both the wear and the failure characteristics of coated systems. The results showed that(i) among the steels studied, the DIN 1.2999 grade steel exhibited the lowest friction coefficient because it had the highest load-carrying capacity as a result of secondary hardening at elevated temperatures;(ii) at room temperature, both abrasive tracks and adhesive layers were observed on the worn surfaces; and(iii) a combination of chemical reactions and progressive oxidation caused aluminum adhesion on the worn surface, and the detachment of droplets and microcracking were the characteristic damage mechanisms at high temperatures.

Tempering Behavior of 4.5Cr-2W-0.25V Steel

The tempering behavior of a Cr-W-V steel was investigated in this research. This new alloy with the com- position of Fe-4.5Cr-2W-0. 25V-0. 1C was austenitized at 1 000 ℃ for 30 rain and tempered at 600 and 700 ℃ for dif- ferent time up to 100 h. An OM analysis of the microstructure of air cooled and water quenched specimens before tempering showed that although under both conditions fully martensitic matrix formed, finer structure had formed in the water quenched specimens. The XRD and TEM results showed that the most stable carbides formed during tempering of the steel were M23C6 and M7C3, respectively. Other carbides such as M3C and M2C, formed in the first stages of tempering, and stable MC were also observed. The results showed that when the tempering time, tempera- ture and cooling rate were increased, mass percent of extracted precipitates was increased. In addition, the formation rate of the stable carbides such as M23 Cs and dissolution rate of the metastable carbides such as M3C and M2C were increased.

Effect of Morphology for Novel Bainite/Martensite Dual-Phase High Strength Steel on Its Hydrogen Embrittlement Susceptibility

With TEM、SEM, various high temperature deformed structures in W9Mo3Cr4V steel were investigated. The sub structures,recrystallized nuclei, as well as the dynamic precipitation were also studied and analyzed. The relationship between recrystallized structures and dynamic precipitation was discussed. The results showed that the deformed structures in W9Mo3Cr4V steel are more complicated than those in low alloy steels. Because W9Mo3Cr4V steel is a high speed steel, there are a large number of residual carbides on the matrix. Also, much dynamic precipitating carbides will precipitate during deformation at high temperature.

150 MW级新兴生物质发电机组用Cr-Ni-Mo-V钢转轴锻件制造工艺研究

对于150 MW级Cr-Ni-Mo-V钢发电机转轴锻件的制造工艺要点进行阐述,通过采用下注单真空钢锭制造技术路线,对其主要热加工工序制造工艺进行研究以及产品试制,经过各项理化检验,转轴锻件的化学成分、力学性能等指标满足技术要求。

Effect of V and V-N Microalloying on Deformation-Induced Ferrite Transformation in Low Carbon Steels

Deformation-induced ferrite transformation （DIFT） has been proved to be an effective approach to refine ferrite grains. This paper shows that the ferrite grains can further be refined through combination of DIFT and V or V-N microalloying. Vanadium dissolved in γ matrix restrains DIFT. During deformation, vanadium carbonitrides rapidly precipitate due to strain-induced precipitation, which causes decrease in vanadium dissolved in matrix and indirectly accelerates DIFT. Under heavy deformation, deformation induced ferrite （DIF） grains in V microalloyed steel were finer than those in V free steel. The more V added to steel, the finer DIF grains obtained. Moreover, the addition of N to V microalloyed steels can remarkably accelerate precipitation of V, and then promote DIFT. However, DIF grains in V-N microalloyed steel easily coarsen.

Study on the surface cracking in hot-rolled plates of Fe-23Mn-2Al-V austenitic steel

The study introduces the chemical composition, mechanical properties, physical properties and production processes of the Fe-23Mn-2Al-V austenitic steel. Investigations were made into the formation of cracks in the hot-rolled Fe-23Mn-2Al-V steel plates,with optical microscopy （OM）,scanning electron microscopy （SEM） and energy dispersive spectrum （EDS）. The results have shown that intergranular oxidation in the reheating furnace is the main cause of the cracks on the surface of the hot-rolled steel plates. The surface cracking can be largely avoided by controlling the remaining oxygen content in the reheating furnace and improving continuous casting （ CC ） processes to increase the thickness of fine equiaxed grain layer of the steel slabs.

The effect of V-Nb on the growth of austenite grains in 17CrNiMo6 gear steel

This study researches the effect of V-Nb on the growth of austenite grains in 17CrNiMo6 carburized gear steel. Results show that the carbonitride in V and Nb acts as second-phase particles in the steel, which can be used to block the migration of grain boundaries and the thinning of the austenite grains. This causes the crystals in the V-Nb microalloy 17CrNiMo6 steel to coarsen and the temperature to rise, thus reducing the cost of the carbonization that follows processing on the gears.

新型Cr-Mo-V热作模具钢的高温断裂机制

通过高温拉伸试验研究了新型Cr-Mo-V钢的高温断裂行为,探究不同拉伸温度(25~700℃)下试验钢的热力耦合区(断裂区)和热应力区(夹持区)的组织演变和碳化物分布特征,揭示钢中碳化物的种类、分布及尺寸与高温断裂行为之间的关系,阐明新型Cr-Mo-V热作模具钢在高温变形过程中裂纹附近显微组织的演化机制。结果表明:随着拉伸温度的升高,试验钢的抗拉强度和屈服强度降低,伸长率和断面收缩率升高,断裂方式由脆性断裂向韧性断裂转变,脆性断裂向韧性断裂的转变温度约为400℃;在高温变形过程中,试验钢的位错密度降低,回火马氏体发生分解、回复、再结晶及晶粒长大,M_(7)C_(3)和M23C6碳化物沿晶界析出长大,少量的细小颗粒状MC碳化物在晶内弥散分布;由于外力作用对变形区做功将导致变形区温度高于拉伸温度,这为断口附近细小碳化物回溶、大尺寸碳化物的长大提供热力学条件,导致热力耦合区小尺寸碳化物减少,大尺寸碳化物增多。

Hot Ductility of Vanadium Micro-alloying Steel Continuous Casting Slabs

The hot ductility of the V-containing micro-alloying steel CC (continuouscasting) slabs and precipitation of vanadium carbide in the tensile specimens were investigated. Theresults indicate that the precipitation ratio and precipitation rate of vanadium in the specimensreach maximum respectively at 900, -825 and 825 deg C. There is still l0 percent-l7 percent ofvanadium precipitated when the deformation temperature decreases to 800-700 deg C. Vanadium largelyaffects the ductility of the steel in the low ductility temperature Region III. Embrittlement ofsteel with higher V content is severer in the region and the embrittlement extends to lowertemperature.

平行磁场对含V型缺陷的管线钢的腐蚀行为影响

目的 研究平行磁场对含V型腐蚀缺陷的X70管线钢在库尔勒土壤模拟溶液中的腐蚀行为影响。方法 利用失重法来计算含V型腐蚀缺陷的X70管线钢在不同平行磁场强度下的腐蚀速率。采用扫描电子显微镜和X射线光电子能谱(XPS)对V型槽槽内外腐蚀样貌及腐蚀产物进行分析,并分析出各腐蚀产物相对含量。结果 发现平行磁场的加入,加速了V型槽槽外的腐蚀,减缓了V型槽槽内的腐蚀。随着磁场强度的增加,平行磁场对V型槽槽外和槽内的促进及抑制作用加强,无磁场时V型槽槽外腐蚀产物为Fe_(2)O_(3),然而随着磁场强度的增加,V型槽槽外腐蚀产物Fe_(2)O_(3)的相对含量增多,单质Fe的相对含量减少。而V型槽槽内的腐蚀产物Fe_(2)O_(3)随着磁场强度的增加逐渐减少,并且在40 mT时腐蚀产物变化为Fe_(3)O_(4),70 mT时腐蚀产物变化为FeO。结论 平行磁场的存在加速了V型槽槽外腐蚀,抑制了V型槽槽内腐蚀,并随着磁场强度的增加,磁场对管线钢腐蚀的促进及抑制作用均增强。本文的研究结果对理解管线钢在磁场作用下的腐蚀失效行为有一定的参考价值。

CARBIDES IN STEEL 4335 V

Three types of alloy carbides have been observed in tempered steel 4335V:M_3C,M_7C_3 and M_4C_3.The precipitation temperatures are 200—700,400 and 500 ℃ respectively.The com- position,morphologies and distribution patterns of the carbides as well as the relationship be- tween them and as-quenched substructures have been investigated.The influence of the car- bides on the low temperature impact toughness of the steel has also been discussed.

MICROSTRUCTURE IN LASER FUSED HIGH SPEED STEEL W6Mo5Cr4V2(M2)

Microstructure of the deepest zone of high speed steel W6Mo5Cr4V2(M2)melt after laser fu-sion was found to be so fine as the ehill zone of a solidified ingot.When narrower chill zoneformed,the long columnar dendrites grow into the melt and then the fine equiaxed cellularstructure appears in upper melt region nearly surface.The substructure of cellular grains anddendrites was observed to consist of martensite and retained austenile,while the carbides asM_6C_■ Cr_7C_3 and MC distributed at their boundaries.It is believed that the highermicrohardness up to HV_(0.1)=865-960 of the laser fused structure of the alloy is due to the oc-currence of martensite.

纵向V型肋卷边C形不锈钢梁抗弯承载力试验研究

为研究在冷弯薄壁C形不锈钢梁腹板增设纵向加劲肋后对其极限抗弯承载力的影响,本文考虑腹板高度、高宽比以及加劲肋尺寸的不同,进行4组试件的对照试验研究。结果表明:对卷边C形不锈钢梁腹板进行加肋能良好地抑制腹板鼓曲,有效提高其极限抗弯承载力;加大加劲肋的尺寸会略微提高其极限抗弯承载力,但刚度略有降低;增加卷边C形不锈钢梁的腹板高度可有效提升其极限抗弯承载力和抵抗变形的能力。

Preventing Occurrence of Transverse Corner Cracks on Nb, V and Ti Microalloying Steel CC Slabs

Based on their hot ductilities, Nb, V and Ti microalloying steels can be classified into two groups. The first group includes steels with lower carbon content (≤0.10%). Ductilities of steels of this group recover and rise with decreasing temperature when temperature lowers to below 825℃. Another group includes steels which contain more carbon (>0.12%) or contain more Nb and V. The low ductility temperature Region Ⅲ for steels of mis group extends to temperature as low as 725℃. The occurrence of the transverse corner cracks of the Nb, V and Ti microalloying steel CC slabs has be considerably decreased by stabilizing casting speed, increasing mold steel level automatic control ratio,enhancing caster segment radial alignment and adopting proper secondary cooling patterns to make slab corner temperature at straightening out off the low ductility temperature region.

Hot deformation behavior of medium carbon V-N microalloyed steel

Processing maps for a medium carbon V-N microalloyed steel(designated as VN steel) and a medium carbon V-N bared steel(designated as Non-VN steel) were developed to study the hot deformation behavior and the influence of vanadium and nitrogen, in the temperature range of 750-1 100 ℃ and strain rate range of 0.005-30 s-1. Experimental results show that the processing map for the VN steel exhibits two dynamic recrystallization and three instability domains, while that for the Non-VN steel has one dynamic recrystallization and three instability domains. The instability domains of VN steel are larger than those of the Non-VN steel, and the VN steel is easier to be unstable when being hot deformed at high temperature and high stain rate. The addition and precipitation of vanadium and nitrogen can hinder the dynamic recrystallization. Compared with the Non-VN steel, the VN steel has higher dynamic recrystallization critical strain and the corresponding stress.

Characterization and Modelling of High Temperature Flow Behaviour of V Modified 2.25Cr-1Mo Heat Resistant Steel Plate

In order to study the high temperature flow behaviour of the V modified 2.25Cr-1Mo steel plate to guide the industrial rolling practice, the hot compression tests were carried out at the temperatures from 900 ℃ to 1150 ℃ and the strain rates from 0.01s^-1 to 1 s^-1 on Thermecmastor-Z equipment. Based on the experimental data of the hot compression tests, a kind of Arrhenius-type constitutive equation was developed.The equation can accurately show the relationship between the flow stress and the deformation temperature, the strain and the strain rate. The measured true stress-true strain curves exhibit two kinds of flow stress curves. Moreover, the forming mechanisms of these two types curves were explained by softening, wok hardening theory as well as metallographic and hardness experimental results. The accuracy of the developed Arrheniustype constitutive equation was identified by three kinds of statistic parameters and also by comparison of the measured and predicted data. The reasonable value of the three types of statistic parameters and the good agreement between the experimental and predicted data can confirm the validity of the developed Arrheniustype constitutive equation for V modified 2.25 Cr-1 Mo heat resistant steel plate.

热丝激光熔覆Cr-W-Mo-V钢涂层组织与腐蚀磨损性能

随着海洋油气资源的开发,钻采装备面临腐蚀与磨损的耦合损伤。开发耐磨耐蚀涂层材料及制备技术是海洋装备安全、可靠运行的保障。利用热丝激光熔覆技术在20钢基材表面制备Cr-W-Mo-V钢涂层,通过光学显微镜(OM)、X射线衍射仪(XRD)、扫描电子显微镜(SEM)等分析涂层的显微组织和相组成,采用往复电化学腐蚀摩擦磨损试验仪分析涂层的干摩擦、电化学腐蚀及在3.5 wt.%NaCl溶液中的腐蚀磨损行为。制备的涂层组织均匀、致密,无裂纹、气孔等缺陷,主要由碳化物、马氏体和残余奥氏体组成,显微组织主要为柱状晶和胞状晶。涂层的平均硬度约为780 HV_(0.1),约是基材硬度的6.5倍,自腐蚀电位为-0.386 V,自腐蚀电流密度为3.45×10^(-6)A/cm^(2),具有优异的耐蚀性。在3.5 wt.%NaCl溶液中,随摩擦载荷的增大,涂层的开路电位下降,摩擦因数下降,腐蚀电流密度增大,摩擦对腐蚀有明显促进作用。随外加电位增加,涂层腐蚀电流密度增大,摩擦因数降低。热丝激光熔覆技术制备的Cr-W-Mo-V钢涂层结构致密、组织均匀,具有优异的腐蚀磨损性能,可用于海洋油气钻采装备在腐蚀磨损苛刻环境下零部件的表面改性。