铌、钛对汽车排气系统热端用铁素体不锈钢高温力学性能的影响

对含铌及Nb-Ti铁素体不锈钢进行固溶和高温时效处理,采用高温拉伸试验对其进行高温力学测试.结果表明:随着时效时间的延长,铌钢高温屈服强度降低较快,而Nb-Ti钢高温屈服强度变化不大.采用相分析、扫描电镜、透射电镜对固溶铌及微观结构进行分析,发现时效过程中固溶铌含量均降低,含铌及Nb-Ti钢500h时效后固溶铌相差不大,铌钢中析出相主要是NbN相和M6C相(Fe3Nb3C),Ti-Nb钢主要析出相是NbTi(C,N)相和Laves相(Fe2Nb).长时间时效后,M6C相和Laves相严重粗化且分布变化明显.M6C相粗化后观察不到沿晶界连续分布,而Laves相粗化后主要在晶界连续分布,起到强化晶界的作用.     

3W-3Co系新型铁素体叶片钢高温组织演变及其对性能的影响

对3W-3Co系新型铁素体叶片钢620℃持久试样微观组织进行了观察,研究了试验材料在高温蠕变过程中组织演变及其对性能的影响。结果表明,试验钢经1 100℃×1 h油淬+720℃×2 h空冷后主要析出相为(Cr,W,Co) 23C6、Nb(CN)和(W,Mo) 3B2;在10 000 h内随着高温蠕变时间的延长,(Cr,W,Co) 23C6相在晶界和晶内聚集长大明显,导致材料塑性和硬度值下降,Nb(CN)、(W,Mo) 3B2和Laves相对材料塑性和硬度值影响不明显。     

0Cr19Ni15Mn5Mo2NbN铸钢晶界高温相析出及对力学性能的影响

利用光学显微镜、扫描电镜及透射电镜,结合Thermo-Calc热力学分析,研究了铌稳定化0Cr19Ni15Mn5Mo2NbN奥氏体不锈钢铸钢晶界处高温相析出行为及其对力学性能的影响。结果表明,0Cr19Ni15Mn5Mo2NbN钢晶界处存在Nb Cr(CN)、Nb(CN)2种大尺寸高温析出相,均为凝固末期液析形成。在铌含量确定条件下,这2种大尺寸晶界析出相在凝固末期的竞争析出行为受碳含量的影响。碳含量存在临界成分,碳含量低于临界成分时,Nb Cr(CN)首先液析形成;碳含量高于临界成分时,Nb(CN)首先液析形成。液析形成的NbCr(CN)热稳定性较高,1 050℃固溶处理无法使之完全溶入奥氏体。沿晶界分布的大尺寸析出相,对0Cr19Ni15Mn5Mo2NbN铸钢固溶热处理后的塑性及冲击韧性损害较大。     

P92耐热钢物理化学相分析

采用物理化学相分析方法研究了P92耐热钢的回火及时效后碳化物和金属间化合物的析出行为,并通过实验确定了P92钢中析出相的萃取和分离方法、钢中析出相的类型、含量及组成结构式等。研究结果表明,回火态试样中含有M₂₃C₆与M(CN)两种析出相,时效100 h后,X-ray分析结果出现Laves相。随着时效时间的增加,Laves相也明显增加,且W、Mo含量高的试样在时效后Laves相析出量增加较多, M₂₃C₆的析出量增加较少, M(CN)析出相含量变化不大。P92钢在短时间内析出的 Laves相有显著的强化效果,在1 000 h内增加Laves相析出量能有效提高P92钢室温及600 ℃下强度。     

控制轧制过程中Nb(C,N)析出状态的研究

本文从研究控制轧制基础的角度出发,研究了控制轧制各个阶段中Nb(C, N)粒子的析出行为、状态、分布、结晶构造以及对钢的晶粒细化、沉淀析出强化的影响关系.主要结论如下:1) 控制轧制过程中,析出的Nb(C, N)的结晶构造因钢中(C+N)/Nb分子比值不同而不同,当此比值>1时,析出物为F.C.C.构造的δ相析出物,呈球形.2) 控制轧制过程中,Nb(C, N)首先从γ晶界、变形带界面上开始析出,然后普及到整个晶内析出.3) 在1050℃以上变形过程中,轧后γ晶粒再结晶的发生先于Nb(C, N) 粒子的析出,因此在这样高温下停轧待温将会得到粗大的部分再结晶γ晶粒,对钢材冲击韧性不利.4) 经60％变形后在1000～900℃之间待温时,只要能保证得到0.015％体积分量的Nb(C, N)析出就可以保证在200s之内防止γ晶粒粗大化.5) 轧后冷却速度过慢,将会引起在α相区域析出的Nb(C, N) 粒子长大,从而失去沉淀强化效果.     

铌对00Cr12Ni不锈钢组织和性能的影响

 分别冶炼了3种不同铌含量的00Cr12Ni不锈钢,用光学显微镜和透射电镜观察了热轧退火态的显微组织,测量了试验钢的拉伸性能和不同温度的冲击功。试验结果表明：铌的添加显著抑制了退火时铁素体再结晶的发生。未添加稳定化元素铌的钢中析出相为Cr23C6,w(Nb)为0.28%的试验钢中析出相为Nb(C,N)和Fe3Nb3C,w(Nb)为0.49%的试验钢中析出相为Nb(C,N)和Fe2Nb,而且其析出相总体积分数明显高于其他2种试验钢。铌的添加提高了试验钢的强度,降低了试验钢的塑性和韧性,w(Nb)为0.49%的试验钢冲击功最低,但其韧脆转变温度也最低。     

GH150合金中μ相的差减定量法

μ相是高温合金中常见的TCP相之一,室温下的显微硬度很高,是一种脆性相。为了弄清μ相析出量与时效温度,时效时间及与室温拉伸塑性的关系,要求对μ相进行定量相分析。我们实验出一种较理想的定量μ相的方法,现介绍如下: 一、实验方法 1.μ相和MC相合量的测定 GH150合金的化学成分(％)为:Ni(50)、Fe(30)、Cr(15)、Mo(5)、W(3)、Ti(2)、Al(1)、Nb(1)、C     

时效温度对高钛GH2132合金性能影响的研究

在本研究范围内工业生产炉号的统计数据表明,当Ti＞2.21%时,GH2132合金经980℃×1 h,油冷+720℃×16h,空冷热处理后,往往出现650℃高温拉伸性能不合格的情况.高温塑性ψ不合格的原因是由于这种高Ti合金在720℃时效时析出的γ'-相[Ni3(Ti,Al)]过多过密,阻碍高温拉伸时晶体滑移和晶粒转动变形所致;720℃时效时高温塑性δ不合格的原因,是在720℃时效时,由于析出了η-相、G-相,消耗了较多的Ti,使γ'-相相对减少,晶界G-相周围γ'-相贫化区的出现,使晶粒易于转动,采取更利于晶内滑移的姿态,同时,在一定应力下试样工作区长度方向上参与变形(拉长)的晶粒数减少,使伸长率减小所致;720℃时效时,个别炉号持久寿命不合格的原因,是由于Ti、Si等元素偏析,导致晶界G-相析出较多,引起其周围γ'-相严重贫化,削弱了晶界,致使合金过早发生断裂所致.当把时效温度降低到700℃后,性能全部合格,是由于在该时效温度下析出的γ'-相和η-、G-等有害相数量减少的缘故.     

微合金元素Nb对热塑性的影响

<正>在Nb、V、Ti等微合金元素中,Nb对钢的热塑性影响最大,随着钢中Nb含量的增加,面收缩率和温度曲线中的塑性凹槽加深变宽。含Nb钢在高温变形过程中,Nb主要以奥氏体晶粒内部的位错为核心形核、长大,也可以在晶界上析出。Nb(CN)沿奥氏体晶界的析出是造成钢热塑性降低的主要原因。钢中N含量减少,即抑制碳氮化     

Ni-24Fe-14Cr-8Mo镍基合金锻造开裂原因探究

以 Ni - 24Fe - 14Cr - 8Mo 合金为研究对象,采用电子探针、扫描电镜、能谱分析、X 射线衍射等检测手段,研究了第二相的析出规律,以及对锻造开裂的影响作用。结果表明,Ni - 24Fe - 14Cr - 8Mo 合金锻态组织中除了纳米级 Mo₂C、Nb₂C 与 TiC 碳化物之外,晶界与晶内还存在大量 1 ～ 5 μm 的富 Nb、M o 球形 Laves 相; 在合金锻造裂纹附近存在的析出相为球形 Laves 相与短棒状 σ 相,后者直接造成塞积位错应力集中导致开裂; 短棒状 σ 相析出温度范围为 850 ～ 950 ℃ ,且密度增长迅速,高于 950 ℃ 则逐步回溶到基体中,1 000 ℃ 基本观察不到 σ 相的析出; Laves 相在 800 ～ 1 000 ℃ 时效过程基本没有发生形貌变化,析出相的数量也没有显著改变。通过将终锻温度提高至 950 ℃ 以上,避免棒状 σ 相大量析出,可以有效改善 Ni - 24Fe - 14Cr - 8Mo 合金锻造开裂问题。     

Simulation of effect of Nb and V on precipitated phases in 1Cr16Co5Ni2Mo1WVNbN steel

Thermo- Calc software was used to simulate the equilibrium precipitates in the 1Cr16Co5Ni2Mo1WVNbN steel at 650??, and the effect of Nb and V contents on precipitated phases in the steel was investigated. The calculation results show that the main equilibrium precipitates in steel are Laves phase, M23C6, MX and Z phase. With the increase of Nb content, the precipitation of MX phase increases significantly, while the amount of M23C6 carbids decreases, Laves phase increases slightly, the precipitation of Z phase decreases slightly. With the increase of V content, the precipitation of MX phase increases slowly, the amount of M23C6 carbides reduces slightly. There is no V element contained in Laves phase, and the increase of V content has little effect on the precipitation of Laves phase, precipitation of Z phase decreases slightly. The Nb and V contents have little effect on the precipitation temperature of M23C6, MX and Laves phase, and the starting precipitation temperature of Z phase decreases with the increase of Nb content, but increases with the increase of V content.     

2Cr12Ni4Mo3VNbN钢中析出相的热力学计算与试验分析

 利用Thermo-Calc热力学软件计算了2Cr12Ni4Mo3VNbN钢中各个元素在成分范围内均为中值时的平衡相图,同时计算了2Cr12Ni4Mo3VNbN钢中碳、铬、钼、铌、氮元素含量变化时的平衡相图,以此分析钢中主要平衡析出相和合金元素含量对析出相析出行为的影响。为验证热力学计算的可靠性,采用XRD、SEM及TEM等分析方法对热处理后的2Cr12Ni4Mo3VNbN钢中析出相类型进行了试验验证。结果表明,钢中的平衡析出相为MX相、M₂₃C₆、M₆C、Z相和Laves相。在热力学平衡条件下,MX相在850 ℃转化为Z相,M₆C在787 ℃转化为Laves相。但是在实际热处理过程,由于保温时间较短且冷却速度较快,上述转化过程不会发生,所以钢中主要析出相为MX相、M₂₃C₆和M₆C。平衡析出相种类与相分析的试验结果基本一致。MX相存在大尺寸的一次MX相和细小弥散的MX相,MX相主要受铌、氮元素影响,其析出量随氮含量升高而升高,析出温度随铌含量升高而升高;M₂₃C₆相的析出温度随碳含量增加而升高,析出量也随之升高;M₆C的析出温度随铬含量增加而降低,随钼含量增加而升高;在成分范围内,元素控制原则为增加碳含量以增加M₂₃C₆的析出强化作用,减少铬含量以避免热加工时进入δ-Fe相区,减少钼含量以降低Laves相析出倾向,减少铌含量以降低一次MX相的析出温度,氮含量需要采取中间量以减少一次MX相析出,增加低温阶段细小弥散的MX相析出。     

Influence of Laves Phase Precipitation and Coarsening on High‐Temperature Strength of Ferritic Stainless Steels

Downsizing trends in the design of internal combustion engines require ferritic steels with greater strength at elevated temperatures. One method of improving the high‐temperature strength is precipitation hardening with intermetallic phases such as the Laves phase. Thermodynamic calculations show, that the elements Nb and Si contribute to the Laves phase formation strongly. In this work, the influence of intermetallic precipitates on the mechanical properties of three different ferritic Fe? Cr stainless steels was investigated and compared to a reference material. The three main hardening mechanisms – precipitation–hardening, grain refinement, and solid‐solution strengthening – were studied with appropriate alloy compositions and thermo mechanical treatment. Investigations were performed with uniaxial compression tests of samples aged isothermally at 900°C for up to 1440 h. It is shown that, the solid solution effect of Mo and W increases the high‐temperature strength about 40%, also after long‐term annealing. The contribution of the Laves phase precipitates on the high‐temperature strength is rather small due to their rapid coarsening.     

退火温度对441铁素体不锈钢组织性能的影响

为探索超纯铁素体不锈钢热轧板材在退火过程中组织和力学性能的演变,对441进行了900～1 050 ℃的退火试验,利用OM、SEM和TEM表征了441在退火过程中显微组织的变化规律,并通过拉伸试验和冲击试验研究了退火温度对力学性能的影响.结果表明,随着退火温度升高,轧制组织发生再结晶,且晶粒逐渐长大.退火后441热轧板材...     

Characterisation of precipitates formed in 26% Cr super ferritic stainless steel

In this study, a newly designed super ferritic stainless steel, 26Cr–4Mo–2Ni, was developed and heated to 800°C for different durations to study the precipitation behaviour of various intermetallic phases, which determined its final mechanical and corrosion resistance properties. The types, numbers and distribution of typical precipitates were investigated. Besides TiN and Nb(C,N), which are common phases formed in Ti- and Nb-stabilised ferritic stainless steel, the Laves, chi (χ) and sigma (σ) phases were also detected in the grain boundary and grain interiors, depending on the aging times . The study focused on the morphology and regularity of these intermetallic precipitates. And the effect of precipitation on the mechanical properties and the corrosion resistance were discussed.     

固溶热处理对新型核用FeCrAl合金包壳管组织和力学性能的影响

通过新型核用锻态FeCrAl合金包壳管在不同温度及时间下的固溶处理实验,利用光学显微镜(OM)、扫描电子显微镜(SEM)、X射线衍射(XRD)、维氏硬度仪(HV)和电子万能试验机(EUTM)分析了固溶处理对FeCrAl合金包壳管显微组织以及力学性能的影响规律.结果 表明,当固溶热处理温度低于1200℃时,保温60 mi...     

S31254超级奥氏体不锈钢析出相演变及微观表征

利用热力学计算了S31254超级奥氏体不锈钢在500~1 200 ℃温度范围内的平衡态析出相,并结合热模拟试验、扫描电镜、透射电镜等方法,对不同析出物的析出行为进行了表征和分析。结果表明,S31254不锈钢奥氏体基体中可存在的第二相包括σ、χ、Laves等金属间相,Cr₂N、π型氮化物相以及M₂₃C₆型碳化物相,高Mo、高N、高Cr含量是该钢析出相种类复杂的主要原因;试验钢具有高的第二相析出倾向,σ相开始析出温度约为1 150 ℃,而在900~800 ℃区间可发现χ相和σ相的转变,χ相更易作为一种稳定相存在;析出相的析出位置和形貌呈现不同特点,晶界析出主要为σ相、χ相和Laves相,而晶内主要有呈针状和块状分布的χ相和呈棒状析出的Cr₂N相。     

Elimination of precipitate free zones in an Fe−Nb creep-resistant alloy

Precipitation of the Fe₂Nb intermetallic compound has previously been found to cause substantial hardening during aging of Fe rich Fe-Nb alloys. However, the formation of a wide precipitate free zone adjacent to the grain boundaries caused a degradation of creep resistance. In an effort to decrease the precipitate free zone width, thereby improving the creep resistance, an extensive study was made of the precipitation behavior of an Fe-1.7 at. pct Nb(Cb) alloy quenched from the δ-phase field. The quenched alloy was found to decompose via a two step reaction during aging at temperatures below 550°C. The first step in the decomposition reaction is thought to occur by clustering of Nb atoms in the ferrite matrix, similar to the clustering of Mo atoms which is known to occur during aging of Fe-Mo alloys. The second step in the reaction is not well understood. The precipitate free zones were formed by solute depletion in the vicinity of the grain boundary and the subsequent difficulty of nucleation of the Fe₂Nb precipitates in the regions of lowered solute concentration. Using two step aging treatments, an initial low temperature step to develop the Nb atom clusters followed by a higher temperature step to cause Fe₂Nb precipitation, the precipitate free zones were eliminated from the aged alloys. The origin of this effect is thought to be the heterogeneous nucleation of Fe₂Nb precipitates on the clusters developed during the initial aging step.     

H13热作模具钢大尺寸析出相特征及生成机制

针对H13钢中大尺寸析出相的存在形式及形成机制进行研究。研究发现,H13钢中大尺寸析出相包含3类——富钒的(V,Mo,Cr,Fe)C类、富Mo- Cr的(V,Mo,Cr,Fe)C类及硫化锰。富钒的(V,Mo,Cr,Fe)C类大尺寸析出相形状多呈现长条形,尺寸达数十微米,部分依附于硫化锰形核的析出相成类椭圆形;富Mo- Cr的(V,Mo,Cr,Fe)C析出相无规则形貌,钼、铬原子分数比相差不大,钒原子分数稍低。根据复合大尺寸析出相的结合形式,可以推测出大尺寸析出相的析出顺序。硫化物首先析出,富钒类(V,Mo,Cr,Fe)C相随后,富Mo- Cr类(V,Mo,Cr,Fe)C相则最后析出。结合大尺寸析出相的成分特征,Thermo- calc计算结果与试验结果一致。