Analysis of High Temperature Deformed Structure and Dynamic Precipitation in W9Mo3Cr4V Steel

In recent years,high temperature deformationand recrystallization have been commonly studied incarbon and low alloy steels[1— 6] .Ref. [3]and Ref.[6 ]have investigated the behavior of hightemperature deformation and recrystallization inhigh speed steels. Using TEM and SEM,variousdeformed structures and sub- structures,dynamicrecrystallized nuclei and dynamic precipitation inW9Mo3Cr4 V steel were studied.1　 Experimental Procedure1.1　 Sample preparation　　 The material used is a commer…     

W9Mo3Cr4V钢高温形变再结晶规律

本文在改造高频损耗电力变压器方面提出了利用原变压器的部分或大部分器件，通过理论计算，重新确定变压器的容量及匝数。改造后的样机试验表明，理论推导及采取的方法是可，有一定应用价值。     

Carbides in high-speed steels containing silicon

The effects of silicon additions up to 3.5 wt pct on the as-cast carbides, as-quenched carbides, and as-tempered carbides of high-speed steels W3Mo2Cr4V, W6Mo5Cr4V2, and W9Mo3Cr4V were investigated. In order to further understand these effects, a Fe-16Mo-0.9C alloy was also studied. The results show that a critical content of silicon exists for the effects of silicon on the types and amount of eutectic carbides in the high-speed steels, which is about 3, 2, and 1 wt pct for W3Mo2Cr4V, W6Mo5Cr4V2, and W9Mo3Cr4V, respectively. When the silicon content exceeds the critical value, the M₂C eutectic carbide almost disappears in the tested high-speed steels. Silicon additions were found to raise the precipitate temperature of primary MC carbide in the melt of high-speed steels that contained d-ferrite, and hence increased the size of primary MC carbide. The precipitate temperature of primary MC carbide in the high-speed steels without d-ferrite, however, was almost not affected by the addition of silicon. It is found that silicon additions increase the amount of undis-solved M₆C carbide very obviously. The higher the tungsten content in the high-speed steels, the more apparent is the effect of silicon additions on the undissolved M₆C carbides. The amount of MC and M₂C temper precipitates is decreased in the W6Mo5Cr4V and W9Mo3Cr4V steels by the addition of silicon, but in the W3Mo2Cr4V steel, it rises to about 2.3 wt pct.     

高 速 钢 中 的 碳 化 物 缺 陷

 大量碳化物的存在是高速钢组织的重要特征,也是影响高速钢质量和性能的关键因素。碳化物颗粒细小、形状规则和分布均匀的钢其质量和性能都好。但是,钢中的碳化物并不都这样理想,往往存在缺陷。根据对W18Cr4V、W6Mo5Cr4V2、W9Mo3Cr4V和W2Mo9Cr4VCo8等钢中碳化物的研究结果,分析了高速钢中常见的几种缺陷：①碳化物分布不均匀;②颗粒尺寸粗大,形状不规则,多为角状等;③碳化物微裂纹;④碳化物粘连等;⑤二次碳化物稀少。另外,还分析了以上碳化物缺陷产生的原因和危害性,并指出了减少缺陷应采取的措施。     

W4Mo2Cr4VNb钢的组织和力学性能

 由于钨、钼、钒合金元素价格昂贵,因而导致含较多这类合金元素的钢的成本较高。合理运用高速钢的合金化理论,研究出了一种低合金高速钢——W4Mo2Cr4VNb。此钢的(W+Mo+V)含量比通用高速钢W9低很多,而且通过调整碳含量及加入价格较便宜的微合金元素铌,使该钢具有较好的综合力学性能和较低的成本。文章研究了W4Mo2Cr4VNb钢的组织和力学性能。     

W9Mo3Cr4V钢的超细化处理

采用不同的工艺参数,对Ｗ９Ｍｏ３Ｃｒ４Ｖ钢进行高温变形,获得了一种超细的再结晶组织。进一步分析了产生这种超细组织的原因和条件,为高合金钢的超细化处理提出了一种有效的方法。     

HGH3126镍基合金热变形行为及组织演变

通过热压缩实验研究了HGH3126镍基合金（/%:≤0.005C,17.20Cr,4.21W,16.25Mo,5.49Fe,0.46Mn,0.20V）在变形温度为950～1200℃、应变速率为0.01～10 s^-1的热变形行为。基于Arrhenius方程和Zener-Hollomon参数模型,建立了HGH3126合金高温热变形的流变应力本构方程。通过对高温热变形后的HGH3126合金显微组织进行观察,分析了变形温度和应变速率对HGH3126合金动态再结晶行为的影响。结果表明,变形温度越高,合金动态再结晶越容易形核;应变速率越小,合金动态再结晶过程进行得越充分。当应变速率0.1 s^-1,变形温度1100℃时,该合金基本发生完全动态再结晶。     

钼钨钒合金化热作模具钢高温回火组织演变

为适应热冲压技术的发展需求,开发了一种新型高热导率高耐磨性能热冲压用模具钢材料。采用扫描电镜（SEM）、透射电镜（TEM）等检测手段对钼钨钒合金化新型模具钢的高温回火性能与组织特征进行了研究。阐明了新型热冲压模具钢回火过程碳化物析出与演变规律。实验结果表明:实验用钼钨钒合金化模具钢材料具有良好的回火二次硬化性能,在500～600 ℃温度区间回火时,回火组织硬度上升;在600 ℃回火出现二次硬化峰值;当回火温度超过600 ℃后,组织软化程度明显,回火硬度开始下降。实验模具钢在高温回火过程中的硬度变化与其合金碳化物的偏聚、析出和聚集长大密切相关。当在560 ℃以下回火时,实验钢组织中未有合金碳化物析出;当回火温度大于560 ℃时,回火组织中开始析出M₂C型碳化物;当回火温度高于600 ℃后开始析出MC型碳化物;当在620 ℃长时间回火后M₂C型碳化物转化为M₆C型碳化物,此时实验钢硬度开始明显下降;而当回火温度高于660 ℃时,新型实验钢组织中主要为M₆C和MC型合金碳化物。      

2Cr11Mo1VNbN钢再结晶动力学方程及本构方程的建立

采用Gleeble-3800热模拟试验机,在温度为1 000~1 200℃、应变速率为0.01~1 s-1和变形量为70%的条件下研究了2Cr11Mo1VNbN钢的热变形行为,建立了动态再结晶型本构模型以及动态再结晶体积分数模型。结果表明:2Cr11Mo1VNbN钢在高温小应变速率的变形条件下易发生动态再结晶,计算得出2Cr11Mo1VNbN钢发生动态再结晶时的临界应变以及变形激活能并得到了动态再结晶体积分数模型,最终构建出的动态再结晶型本构方程能良好地描述2Cr11Mo1VNbN钢的高温流变行为。     

(C+N)复合强化的Fe-Cr-Mn(W,V)钢高温性能的研究

研究了用于核反应推低放射性结构材料Ｆｅ－Ｃｒ－Ｍｎ（Ｗ,Ｖ）奥氏体钢。通过（Ｃ＋Ｎ）复合强化有效地提高Ｆｅ－１２％Ｃｒ０１５％Ｍｎ（Ｗ,Ｖ）钢高温强度和蠕变断裂寿命,并改善高温塑性。在温度６７３Ｋ以下,合金比ＳＵＳ３１６钢和ＪＰＣＡＳ钢强度和塑性优良。合金强度和塑性与形变的相互关系是和合金形变组织变化;密切相关。对６７３Ｋ以上塑性降低的原因进行断口和显微组织分析,控制晶界碳化物粗化是进一步提高高温     

The role of grain boundary migration in reheat cracking

Prior austenite grain boundary (PAGB) reheat cavitation has previously been shown to be controlled by a fine dispersion of incoherent PAGB particles and by the concentration of the overall deformation into deformation zones adjacent to the PAGB. A series of low-alloy baintic CrMoV steels have been investigated to establish the microstructural basis for PAGB deformation zones. It is shown that the fundamental cause of reheat cavitation in low alloy bainites is stress induced Grain Boundary Migration, which initiates at temperature immediately upon application of a load. The migrating boundary sweeps out a volume of material that is both particle and dislocation-free, relative to the secondary hardened grain interiors. This creates a mechanically weak zone at the PAGB. The overall strain during deformation is subsequently concentrated into these regions, producing extensive plastic deformation leading to failure by cavity growth and crack propagation within the PAGB deformation zone. The presence of large, stable carbides in high chromium CrMoV steels prevents PAGB migration and thus eliminates the PAGB deformation zones. Also matrix carbide coarsening in the high chromium steels leads to an increase in matrix recovery rates, which further permits more uniform deformation of the material.     

Effect of Nitrogen and Niobium on the Structure and Secondary Hardening of Super Hard High Speed Tool Steel

High‐speed steels have been used mostly for multi‐point cutting tools and for plastic working tools. High speed steels are ferrous based alloys of the Fe‐C‐X multi‐component system where X represents a group of alloying elements comprising mainly Cr, W or Mo, V, and Co. The properties of these steels can be improved by modifying their chemical composition or the technology of their production. One of the new trends in modifying the tool steels chemical composition consists in the addition of niobium and nitrogen. In this work, the effects of niobium and nitrogen on morphology of carbides and secondary hardening temperature of investigated high speed tool steels were studied. This experimental work shows that, the conventional ingots have many types of carbides of different shapes and sizes precipitate on the boundary together with thick needle like carbides. On the contrary, for nitrogen steel, the nitrogen alloying leads to form dense, fine and well distributed microstructure. While, on the case of niobium alloying, single carbide (MC), and different types of eutectic carbides were precipitated which have a major effect on the secondary hardening temperature.     

2.25Cr1Mo钢动态再结晶物理冶金模型的研究

??The hot compression tests of 2. 25Cr1Mo steel at 950-1200??, 0. 01-10s-1, and deformation of 60% were carried out on a Gleeble- 1500D simulator. The effects of deformation temperature and strain rate on the dynamic recrystallization of 2. 25Cr1Mo steel were investigated. The models for dynamic recrystallization critical strains and dynamic recrystallization fraction were established. The results show that 2. 25Cr1Mo steel is more likely to undergo dynamic recrystallization at high temperature and high strain rate. The deformation activation energy and critical strains in dynamic recrystallization as well as dynamic recrystallization fraction model of 2. 25Cr1Mo steel were obtained. The constitutive equation of 2. 25Cr1Mo steel was constructed and the dynamic recrystallization physical metallurgical model of finite element software data interface was established. The model provides the basic conditions for the forging microscopic simulation of large forgings.     

Secondary hardening and fracture behavior in alloy steels containing Mo, W, and Cr

In 4Mo, 6W, 2Mo3W, 2Mo2Cr, and 3W2Cr alloy steels, which cointain alloying elements, such as Mo, W and Cr, contributing to the secondary hardening by forming M₂C type carbide, the secondary hardening and fracture behavior were studied. Molybdenum had a strong effect on secondary hardening, while W had a very weak effect on it but delayed the overaging. The MoW steel exhibited both moderately strong hardening and considerable resistance to overaging. On the other hand, the secondary hardening effect was diminished by the Cr addition, because the cementite of M₃C type was stabilized at higher temperatures and the formation of M₂C carbides was thus inhibited. Although the Cr addition had no merit in the secondary hardening itself, it eliminated the secondary hardening embrittlement (SHE). This was observed as a severe intergranular embrittlement due to the impurity segregation for the Mo and MoW steels and as a decrease in upper shelf energy for W steel, even in the overaged condition.     

Secondary hardening and fracture behavior in alloy steels containing Mo, W, and Cr

In 4Mo, 6W, 2Mo3W, 2Mo2Cr, and 3W2Cr alloy steels, which contain alloying elements, such as Mo, W and Cr, contributing to the secondary hardening by forming M₂C-type carbide, the secondary hardening and fracture behavior were studied. Molybdenum had a strong effect on secondary hardening, while W had a very weak effect on it but delayed the overaging. The MoW steel exhibited both moderately strong hardening and considerable resistance to overaging. On the other hand, the secondary hardening effect was diminished by the Cr addition, because the cementite of M₃C type was stabilized at higher temperatures and the formation of M₂C carbides was thus inhibited. Although the Cr addition had no merit in the secondary hardening itself, it eliminated the secondary hardening embrittlement (SHE). This was observed as a severe intergranular embrittlement due to the impurity segregation for the Mo and MoW steels and as a decrease in upper shelf energy for W steel, even in the overaged condition.     

Effects of alloying additions and austenitizing treatments on secondary hardening and fracture behavior for martensitic steels containing both Mo and W

The effects of alloying additions and austenitizing treatments on secondary hardening and fracture behavior of martensitic steels containing both Mo and W were investigated. The secondary hardening response and properties of these steels are dependent on the composition and distribution of the carbides formed during aging (tempering) of the martensite, as modified by alloying additions and austenitizing treatments. The precipitates responsible for secondary hardening are M₂C carbides formed during the dissolution of the cementite (M₃C). The Mo-W steel showed moderately strong secondary hardening and delayed overaging due to the combined effects of Mo and W. The addition of Cr removed secondary hardening by the stabilization of cementite, which inhibited the formation of M₂C carbides. The elements Co and Ni, particularly in combination, strongly increased secondary hardening. Additions of Ni promoted the dissolution of cementite and provided carbon for the formation of M₂C carbide, while Co increased the nucleation rate of M₂C carbide. Fracture behavior is interpreted in terms of the presence of impurities and coarse cementite at the grain boundaries and the variation in matrix strength associated with the formation of M₂C carbides. For the Mo-W-Cr-Co-Ni steel, the double-austenitizing at the relatively low temperatures of 899 to 816 °C accelerated the aging kinetics because the ratio of Cr/(Mo + W) increased in the matrix due to the presence of undissolved carbides containing considerably larger concentrations of (Mo + W). The undissolved carbides reduced the impact toughness for aging temperatures up to 510 °C, prior to the large decrease in hardness that occurred on aging at higher temperatures.     

合金碳化物对剪板机刃具钢HM的组织和性能的影响

试验研究了HM钢(%:0.48C、5.1Cr、2.0Mo、1.0V、2.0W)和H13钢(%:0.38C、5.1Cr、1.4Mo、1.0V)的组织、冲击韧性和耐磨性。结果表明,HM钢中W、Mo元素含量较H13钢高,存在更多未溶碳化物阻碍奥氏体晶粒长大,细化晶粒,使平均冲击值比H13钢提高35.5%;HM钢高温回火时,马氏体基体弥散析出更多的碳化物,二次硬化效果显著,平均耐磨性比H13钢提高34.8%。     

Effect of Compositional Changes of Laves Phase Precipitate on Grain Boundary Embrittlement in Long-Term Annealed 9 Pct Cr Ferritic Steel

In 9 to 12 pct chromium steels, the high-temperature mechanical properties are known to be strongly dependent on the formation and coarsening of Laves phase precipitates at boundaries. During high-temperature deformation, the Laves phase precipitate coarsening to over a critical size has been considered to trigger cavity formation at the precipitate-matrix interfaces. This coarsening, accompanied by the diffusion of W, Mo, and Cr, should change the mechanical properties and chemical composition of both Laves phase precipitates and the matrix. In this study, we aimed to clarify the effects of compositional changes of Laves phase precipitates on cavity formation during coarsening. The values of the Fe/Cr and W/Mo ratios in Laves phase precipitates were shown to induce different levels of strain energy in the vicinity of the Laves phase precipitate, consequently promoting the formation of cavities. Therefore, the compositional change of Laves phase precipitates was found to play a critical role in the grain boundary embrittlement of high Cr steel at elevated temperature.

     

The microstructure of chromium-tungsten steels

Chromium-tungsten steels are being developed to replace the Cr-Mo steels for fusion-reactor applications. Eight experimental steels were produced and examined by optical and electron microscopy. Chromium concentrations of 2.25, 5, 9 and 12 pct were used. Steels with these chromium compositions and with 2 pct W and 0.25 pct V were produced. To determine the effect of tungsten and vanadium, three other 2.25Cr steels were produced as follows: an alloy with 2 pct W and 0 pct V and alloys with 0 and 1 pct W and 0.25 pct V. A 9Cr steel containing 2 pct W, 0.25 pct V, and 0.07 pct Ta also was studied. For all alloys, carbon was maintained at 0.1 pct. Two pct tungsten was required in the 2.25Cr steels to produce 100 pct bainite (no polygonal ferrite). The 5Cr and 9Cr steels were 100 pct martensite, but the 12Cr steel contained about 25 pct delta-ferrite. Precipitate morphology and precipitate types varied, depending on the chromium content. For the 2.25Cr steels, M₃C and M₇C₃ were the primary precipitates; for the 9Cr and 12Cr steels, M₂₃C₆ was the primary precipitate. The 5Cr steel contained M₇C₃ and M₂₃C₆. All of the steels with vanadium also contained MC.