夹杂对氢鼓泡形成的影响

通过粘接低熔点合金后拉伸,可使纯铁表面氢鼓泡被剖开,露出内部断口形貌.扫描电镜观察和能谱分析表明,氢鼓泡是含H2的空腔,大多数(88%)鼓泡核附近存在夹杂.这表明含H2空腔择优在夹杂界面处形成.当鼓泡中氢压产生的应力超过原子键合力(有可能被氢降低)时,裂纹从鼓泡核壁形成,产生断裂花样,氢进入已开裂的鼓泡就使它通过裂纹扩展而不断长大,直至鼓泡破裂,内部氢压释放.     

应力和夹杂对车轮钢中氢鼓泡的影响

车轮钢在恒应力下充氢表面出现氢鼓泡的临界电流和无应力试样相同,恒应力下临界可扩散氢浓度C_σ~*落在无应力试样的分散带内,t检验表明应力对C_0~*没有影响．恒应力下发生氢致滞后断裂的门槛电流密度和门槛可扩散氢浓度分别为i_(th)=3 mA/cm~2和C_(th)=0．52×10~(-6),远小于出现氢鼓泡的相应值i_c=5 mA/cm~2和C_0~*=1．18×10~(-6)．无应力时,氢鼓泡并不择优沿夹杂产生;但在恒应力下,氢鼓泡择优沿长条状夹杂形核,其临界可扩散氢浓度从1．18×10~(-6)降为0．56×10~(-6)．     

焊接热影响区针状铁素体的形核长大及其对组织的细化作用

通过观察焊接热循环冷却过程中不同温度取样直接淬火后的微观组织,研究了焊接热影响区(HAZ)晶内针状铁素体(IAF)的形核长大过程,论证了针状铁素体分割原奥氏体晶粒及细化晶内组织的机理.Auger电子能谱(AES)证实,在TiOx-MnS型复合夹杂物边界附近存在贫Mn区,IAF易于在这类复合夹杂物上形核,单个复合夹杂物能...     

X42QS管线钢表面氢鼓泡原因分析及热处理工艺改进

通过显微组织分析和工艺对比试验等对调质型X42QS管线钢在HIC检验过程中出现严重氢鼓泡问题进行研究。结果表明,X42QS淬火后仅在钢板表层获得板条贝氏体组织,在 650℃高温回火处理后,X42QS表层板条贝氏体转变成粗大的再结晶多边形铁素体,在HIC试验中沿粗大的铁素体晶界形成裂纹并扩展,最终导致严重的氢鼓泡问题。通过适当调整回火工艺,X42QS管线钢的氢鼓泡问题可以得到有效抑制。     

热循环对高铌管线钢焊接热影响区冲击韧性的影响

采用Gleeble-3500型热模拟试验机,研究了焊接热循环对Mn-Mo-Nb和高铌 HTP X80管线钢焊接热影响区(HAZ)冲击韧性的影响.结果表明,随焊接热输入量的增加,两种X80管线钢粗晶HAZ的冲击韧性均降低,但在相同的焊接热输入条件下,高Nb钢粗晶HAZ的冲击韧性均高于Mn-Mo-Nb管线钢.其原因是高Nb钢中由于未溶Nb(CN)状的存在,抑制奥氏体晶粒长大,在高的线能量条件下,能够保证奥氏体晶粒的细小均匀.     

X80管线钢焊接热影响区的韧性分析

X80管线钢在焊接过程中,热影响区由于受到焊接过程热的作用,其组织和性能会发生较大的变化.韧性是天然气长输管线的重要性能,采用热模拟技术、现代工程测试手段和显微分析方法,分析了不同热输入参数下X80管线钢焊接热影响区粗晶区(CGHAZ)韧性(夏比冲击功和CTOD)的差异及其原因.在一定范围内,较高焊接热输入下CGHAZ的韧性比较低热输入下CGHAZ的韧性明显高,超过一定范围,随着热输入的增加韧性激剧下降.造成不同热输入下韧性差异的根本原因是由CGHAZ显微组织的差异引起的.较低的热输入下CGHAZ中产生了一定量的低碳马氏体,从而导致韧性较差.     

氢对321不锈钢焊接热影响区力学性能的影响

利用Gleeble3800热模拟试验机和动态充氢慢应变拉伸试验研究了氢对321不锈钢焊接热影响区力学性能的影响,采用扫描电镜和光学显微镜分析了拉伸试样的断裂特征.结果 表明:氢导致321不锈钢慢应变拉伸试样断裂模式发生变化,裂纹启裂于试样表面,断口由脆性断口和韧性断口构成.氢会导致321不锈钢焊接热影响区产生严重的塑性...     

铁素体不锈钢焊接热影响区晶粒长大过程模拟

提出一种用Monte Carlo模拟单相合金的热影响区（HAZ）晶粒长大方法,可以将焊接实际时间与模拟过程对应起来,应用有限元方法计算出焊接热循环,并结合晶粒长大的Arrhenius公式,模拟了铁素体不锈钢EB26-1在一定规范下HAZ晶粒的演变情况,模拟结果表明,此方法可以预测HAZ中晶粒的分布以及存在于HAZ中很陡的温度梯度对晶粒长大的阻碍作用。     

X80管线钢焊接热影响区组织的模拟研究

采用物理模拟和数值模拟相结合的手段,利用SYSWELD有限元计算软件和Gleeble-3500热模拟试验机模拟焊接热过程,对X80管线钢焊接热影响区单道粗晶区、临界区以及经历2次热循环的亚临界粗晶区、临界粗晶区和过临界粗晶区的组织进行对比分析,归纳了不同冷却速度下组织形态、M-A组元、晶粒尺寸及第二相粒子的转变规律.     

Mechanisms of inclusion evolution and intra-granular acicular ferrite formation in steels containing rare earth elements

Inclusion characteristic and microstructure of rare earth (RE) elements containing steel were evaluated with scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS), element-mapping, optical microscopy (OM), and automated feature analysis (AFA) option equipped with ASPEX PSEM. Factsage was used to calculate the equilibrium inclusion composition. Based on the calculation, an inclusion evolution mechanism was proposed. Furthermore, line scanning analysis was used to elucidate the intra-granular acicular ferrite (IAF) nucleation mechanism. The result showed that two different inclusions exist in sample steel: (Mn-Al-Si-Ti-La-Ce-O) +MnS complex inclusion and isolated MnS inclusion. Almost all nucleation sites for IAF are complex inclusions, while single MnS inclusion cannot induce IAF. A possible formation mechanism of complex inclusion is proposed based on calculated results using Factsage, which agrees well with experimental results. A Mn-depletion zone (MDZ) which exists adjacent to the (Mn-Al-Si-Ti-La-Ce-O) +MnS complex inclusion can account for the IAF formation. However, the low volume fraction (1.49×10-7) of effective inclusion may result in only 10% (volume fraction) IAF.     

Effects of cooling time and alloying elements on the microstructure of the gleeble-simulated heat-affected zone of 22% Cr duplex stainless steels

The effects of austenite stabilizers, such as nitrogen, nickel, and manganese, and cooling time on the microstructure of the Gleeble simulated heat-affected zone (HAZ) of 22% Cr duplex stainless steels were investigated. The submerged are welding was performed for comparison purposes. Optical microscopy (OM) and transmission electron microscopy (TEM) were used for microscopic studies. The amount of Cr₂N precipitates in the simulated HAZ was determined using the potentiostatic electrolysis method. The experimental results indicate that an increase in the nitrogen and nickel contents raised the δ to transformation temperature and also markedly increased the amount of austenite in the HAZ. The lengthened cooling time promotes the reformation of austenite. An increase in the austenite content reduces the supersaturation of nitrogen in ferrite matrix as well as the precipitation tendency of Cr₂N. The optimum cooling time from 800 to 500 °C (Δt _8/5) obtained from the Gleeble simulation is between 30 and 60 s, which ensures the austenite content in HAZ not falling below 25% and superior pitting and stress corrosion cracking resistance for the steels. The effect of manganese on the formation of austenite can be negligible.     

Influence of Ti on non-metallic inclusion formation and acicular ferrite nucleation in high-strength low-alloy steel weld metals

The phase transition behaviors of non-metallic inclusions as a function of Ti content were investigated by monitoring changes in the microstructure and mechanical properties of high-strength low-alloy steel multipass weld metals. Weld metals with Ti contents ranging from 0.007 to 0.17 wt% were prepared using a gas metal arc welding process. The inclusion analysis was performed based on thermodynamic calculations and transmission electron microscopy, accompanied by energy-dispersive spectrometry and selected area electron diffraction. With increase in the Ti content of weld metals, the chaotic arrangement of ferrite laths in the columnar zone was transited to a well aligned arrangement and the impact toughness of the weld metals drastically deteriorated in response to the decrease in the Mn content of the inclusion. The effective inclusion phase for intragranular nucleation contained considerable amounts of Mn and a Mn depleted zone was observed around the effective nucleant.     

Role of alloying elements in steels on metal dusting

Metal dusting of Fe-Ni-Cr alloys has been observed in industrial processes in strongly carburizing atmospheres at temperatures from 450°C to 800°C. At temperatures below 650°C the alloys are generally not able to form dense, well adherent oxide layers in spite of relatively high Cr-contents, therefore, metal dusting can take place. Already a lot of experimental work has been done to elucidate the mechanism and to compare the resistance against metal dusting for high alloy steels [1]. The intention of this study was to obtain additional information concerning the role of alloying elements and the effects of carbide precipitates in austenitic high alloy steels such as Alloy 800. The susceptibility to metal dusting was determined by measuring the metal loss under metal dusting conditions of Fe-20%Cr-32%Ni alloys modified with additions of different carbide formers (W, Mo, Nb) or oxide formers (Si, Al). The samples were exposed at 600°C in a CO-H₂-H₂O-gas mixture for repeated periods up to 500 – 1500 h. The attack by the oxidizing and carburizing atmosphere leads to the precipitation of internal carbides and metal dusting and more or less to formation of an oxide layer. In comparison to the undoped material, the addition of carbide formers retards the initiation of metal dusting attack. The additions of Si and Al seem to prevent metal dusting under the given laboratory conditions. When carbides are present at the metal surface, they affect the initial oxide growth and have a negative effect on the protectivity of scales. Very striking is the effect of Ce, this rare earth element is generally known to favour Cr-oxide formation and to improve the adherence of the oxide layer [2], but in the case of metal dusting it clearly enhances metal dusting and metal wastage.     

Effect of alloying elements and structure on the resistance of structural steels to hydrogen embrittlement

Conclusions The data presented indicate that steels intended for operation in media containing hydrogen sulfide should be alloyed with chromium, molybdenum, vanadium, niobium, aluminum, and copper.The resistance to HE and HSC is highest for low-alloy steels with a fine-grained ferritic-pearlitic structure and alloy steels with a structure of temper sorbite.I. P. Bardin Central Scientific-Research Institute of Ferrous Metallurgy. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 1, pp. 2–14, January, 1978.     

Ti、N含量对焊接粗晶区晶粒尺寸及韧性的影响

利用焊接热模拟方法及析出相形貌观察,研究了不同Ti、N含量的高Nb管线钢焊接粗晶区的奥氏体晶粒尺寸及其分布规律、析出相对奥氏体晶粒尺寸及冲击韧性的影响.结果表明:焊接热影响区(HAZ)析出相粒子为富Ti的TixNb1-x(CyN1-y)复合粒子,其尺寸大多数在100 nm以下.分析认为高铌钢中Ti含量应控制在0.010%～0.015%间(Ti/N值在2～3间),该范围内奥氏体晶粒尺寸能被有效钉扎,冲击韧性值显著提高.     

TMCP钢焊接热影响区局部脆化区断裂韧度测试

针对强度(屈服点应力)级别为420-460MPa的三种TMCP钢,探讨通常的焊接热影响区局部脆化区断裂韧度测试方法的可行性及存在问题。由于多层焊热影响区组织复杂,需进一步研究确认试验中得到的断裂韧度能否代表局部脆化区的韧度。试验结果发现,对多层焊热影响区试样,试验后必须进行刨面(Sectioning)分析,首先检查疲劳裂纹前沿是否位于所测试的目标区域;其次当有延性裂纹扩展时,检查延性裂纹扩展是否偏离目标区域。当满足这些条件时,所测试的断裂韧度才能代表目标区域的韧度值。同时也试验研究了焊缝强度匹配对热影响区断裂韧度的影响。     

Influence of cooling rate on microstructure evolution and pitting corrosion resistance in the simulated heat-affected zone of 2304 duplex stainless steels

Pitting corrosion resistance of 2304 duplex stainless steel heat-affected zone with different cooling rates has been studied by potentiostatic critical pitting temperature (CPT) in 1.0 M NaCl. The results showed that, as cooling rate decreased from 100 to 10 °C/s in the temperature range of 1350–800 °C, the austenite fraction increased from 27.8% to 35.7%, and the CPT value increased from 14 to 19 °C. The morphologies after the CPT tests showed pitting occurred preferentially in the ferrite phase for all specimens. Moreover, relationship between pitting corrosion resistance and microstructure evolution was further discussed.