一种高铝多元合金钢的奥氏体晶界显示技术

基于化学侵蚀基本原理,采用控温控时水浴锅,结合光学显微镜观察,研究了1.79Al-1.5Mn-1.09Cr基高铝多元合金钢淬火原奥氏体晶界显示技术。结果表明:最佳侵蚀剂配方为30mL饱和苦味酸水溶液+1~2滴氢氟酸+适量海鸥牌洗发膏,不同淬火加热温度下试验钢的原奥氏体晶界可通过调整海鸥牌洗发膏用量而清晰显示;试验钢最佳侵蚀温度为室温;高温淬火试样较低温淬火试样的原奥氏体晶界更易被侵蚀而清晰显示。     

一种显示P91钢和P92钢原奥氏体晶界的浸蚀剂

对P91钢和P92钢的原奥氏体晶界显示技术进行了研究,配制出了一种浸蚀剂,其配方为1.5mL硝酸+1mL氢氟酸+2mL双氧水+10mL白猫洗洁精+50mL蒸馏水。结果表明:使用该浸蚀剂可清晰显示P91和P92钢的原奥氏体晶界;该浸蚀剂配置简单,使用方便,浸蚀效果良好,可大大提高工作效率。     

含高浓度缓蚀剂苦味酸溶液在奥氏体晶粒度直接腐蚀法中的应用

苦味酸是利用直接腐蚀法检测奥氏体晶粒度最常用的金相浸蚀剂之一,为了抑制晶内组织的腐蚀速率,通常会在配方中添加缓蚀剂。选用十二烷基苯磺酸纳作为缓蚀剂,通过调整缓蚀剂的配比,试验了不完全淬火+高温回火组织、完全淬火+高温回火组织以及粒状贝氏体组织奥氏体晶粒度的检测方法。结果表明:增加缓蚀剂的含量,可以有效抑制晶内组织的腐蚀速率。对于完全淬火后高温回火的试样,利用带状偏析,纵向检测奥氏体晶粒度,可以快速腐蚀显示出偏析带的奥氏体晶粒度。试验证实含有高浓度缓蚀剂的苦味酸溶液是一种通用的奥氏体晶粒度腐蚀剂。     

一种适用于GH4169镍基合金奥氏体晶粒度评级的浸蚀方法

采用传统浸蚀液对GH4169镍基合金进行浸蚀,可显示包括孪晶在内的奥氏体组织,但孪晶的存在加大了奥氏体晶粒度的评级难度。通过调整浸蚀液成分,提出了一种只显示奥氏体晶界的浸蚀方法。试验结果表明:采用高锰酸钾水溶液(1.5～2g KMnO4+7～10mL H2SO4+90～110mL H2O+0.1～0.3mL HCl),水浴加热至95℃对GH4169镍基合金进行浸蚀,可清晰地显示出奥氏体晶界,而不显示晶粒内孪晶,获得的显微组织可用来准确评定合金的晶粒度级别。     

A-100高强钢晶粒显示优选方法

采用不同的化学浸蚀液,研究了A-100高强钢晶界的显示效果;使用恒温水浴锅,测定了在不同温度的浸蚀液下晶界的显示时间;利用金相显微镜观察该钢晶界显示是否清晰。结果表明:A-100高强钢晶粒显示的推荐化学浸蚀液为过饱和苦味酸+雕牌洗涤剂溶液(结晶状)以及过饱和苦味酸+白猫洗涤剂溶液(结晶状);浸蚀液温度为40℃或45℃时,清晰显示晶界所用的时间最短。     

一种显示EH690海洋平台用钢原始奥氏体晶界的方法

利用控温水浴锅,探索了不同温度热处理EH690海洋平台用钢的原始奥氏体晶界的显示方法。结果表明:采用150mL过饱和苦味酸水溶液+3~5g洗发膏+1~5滴盐酸配制的侵蚀液,水浴加热至46℃进行化学侵蚀,能够清晰地显示出EH690海洋平台用钢的原始奥氏体晶界。     

45钢原始奥氏体晶界的显示方法

利用控温水浴锅,对经不同工艺热处理的45钢原始奥氏体晶界的显示方法进行了系统的研究。结果表明:对860℃保温1h水淬的45钢试样进行250℃回火15min后,再在70℃水浴锅中用30mL过饱和苦味酸+5mL缓蚀剂侵蚀10min,可清晰地显示出其原始奥氏体晶界。     

20MnSi钢奥氏体晶界侵蚀方法

钢的奥氏体实际晶粒度对钢材的性能影响很大,在一般加热速度下,加热温度愈高、加热时间愈长,则奥氏体晶粒愈粗大.粗大奥氏体晶粒冷却后获得粗大的转变产物,其强度、韧性、疲劳抗力等力学性能较差,且奥氏体晶粒粗大的钢材在淬火时易变形、开裂,因此检测奥氏体晶粒大小有重要的意义.对于使用广泛的20MnSi螺纹钢,未见有较好的奥氏体晶界侵蚀剂介绍.作者试用过盐酸苦味酸酒精溶液、氯化铜苦味酸水溶液等侵蚀剂,效果均不理想.考虑到苦味酸[C_6H_2(NO_2)_3OH]是弱酸,电离度比硝酸小,而且硝基(NO_2~-)没有硝酸根(NO_3~-)氧化性强,所以没有硝酸腐蚀能力强.用苦味酸酒精溶液侵蚀,试样中珠光体、贝氏体、回火马氏体同样可清晰显示,故显示奥氏体晶界的试剂中含苦味酸的试剂用得最为广泛.苦味酸水溶液比苦味酸酒精溶     

4330V调质钢奥氏体晶粒显示方法

对4330V调质钢晶粒的显示方法进行了研究,采用直接浸蚀方法,通过不同浸蚀剂的对比分析,找到了有效的浸蚀剂为苦味酸+H2O+海鸥洗涤剂,可以清晰显示出奥氏体晶粒大小。     

一种显示铬钼钒钢奥氏体晶界的方法

介绍了一种侵蚀奥氏体晶界的方法。在40℃恒温水浴下，用过饱和的苦味酸水溶液100mL 雕牌高效洗洁精2mL，可以清晰地显示2．25Cr-1Mo-0．25V钢的奥氏体晶界。     

A new etching route for revealing the austenite grain boundaries in an 11.4% Cr precipitation hardening semi-austenitic stainless steel

A detailed metallographic characterization of a precipitation hardening semi-austenitic stainless steel is described. A new etching procedure based on the Lichtenegger and Blöch color etching solution, which is frequently used in duplex stainless steels to differentiate delta ferrite from austenite, has been used to differentiate martensite, austenite and the Chi-phase in this stainless steel. By changing the etching conditions, this etchant now reveals the austenite grain boundaries when the steel is in the austenitic state. Moreover, this solution is able to reveal also the prior austenite grain boundaries when the steel is in its martensitic state. This etching procedure represents a great advantage because it reveals, at the same time, different features of the microstructure.     

A SEM (scanning electron microscopy)-based method to evaluate impurity segregation to prior austenite grain boundaries in high strength steels

The depth of grain boundary grooves on the etched surface of high strength Cr-Ni steels has been determined as a measure of P-segregation to prior austenite grain boundaries by a SEM (Scanning Electron Microscopy)-based grain boundary etching method (GEM). The mean depth and distribution of the depth can be decided by stereoscopy on the SEM micrographs of the replica of the etched surface. The results showed that the cast steel has less, but nonuniform P-segregation and the high temperature austenitization reduced the P-segregation on prior austenite grain boundaries in both steels.     

Relation between microstructures of martensite and prior austenite in 12 wt% Cr ferritic steel

Tempered martensitic 9–12 wt% Cr ferritic steels are used as heat resistant materials in power plant, where service under conditions of high temperature and pressure for several decades is required, and an adequate resistance to creep is one of the key requirements. In this type of steels, failure has been found to occur preferentially at prior austenite grain boundaries if the prior austenite grains are coarse. It appears that the prior austenite grain boundaries can act as a site of especial weakness in the tempered martensitic microstructure. It would therefore be useful to investigate whether the properties of prior austenite grain boundaries could be modified by some appropriate thermomechanical processing method. One approach to this is to attempt to increase the fraction of annealing twins in the austenite phase and to investigate whether this has an effect on the properties of the martensite after transformation and tempering. In this study, thermomechanical treatments involving hot-rolling have been applied and the fraction of austenite twins produced determined using electron backscatter diffraction analysis. The treatment giving the highest fraction of austenite twins was identified and the effect of the increase in twin fraction on the characteristics of the martensite was investigated. It was found that the fraction of coincidence site lattice boundaries in martensite along prior austenite grain boundaries increased with increasing fraction of prior austenite twin boundaries.     

Effects of sensitisation-induced martensitic transformation on the tensile behaviour of 304 austenitic stainless steel

The effects of sensitisation-induced martensitic transformation on the tensile behaviour of 304 austenitic stainless steel have been investigated. Yield strength is reduced by sensitisation, but ultimate tensile strength is nearly unaffected. Strain-hardening behaviour is changed by sensitisation, too. Although sensitisation may induce martensite formation near grain boundary, twin boundary, and austenite/martensite interface, the sensitisation-induced martensite does not exert a great influence on tensile behaviour in the 304 steel. In the unsensitised condition, martensitic transformation in the steel bulk induced by prior deformation and liquid-nitrogen immersion also does not change strain-hardening behaviour in the present steel.     

The effect of microstructure in the hydrogen embrittlement of a gas pipeline steel

Hydrogen embrittlement (HE) tests were carried out on a carbon-manganese pipeline steel having a low sulphur content (<0.01%). It was shown that the susceptibility to HE increased as the microstructures changed from ferrite-pearlite to martensite. In the hydrogenated state the fracture surface of the ferrite-pearlite and ferrite-bainite specimens consisted of small cleavage regions surrounding non-metallic (oxide) inclusions; these were called rosettes and were a characteristic feature of the embrittled state. In hydrogenated martensitic specimens, failure was almost entirely intergranular along prior austenite grain boundaries and cracking of martensitic laths. In the martensitic specimens a relationship between inverse time to failure and prior austenite grain size was established.     

Austenite and ferrite grain sizes in interstitial free steel

Abstract

An oxidation method has been employed to reveal prior austenite grain boundaries in C–Mn and interstitial free (IF) steels. The ability of this technique to reveal prior austenite grain boundaries is assessed by comparing its results with those of an etching method applied on the C–Mn steel. Optimum conditions were established by trial and error. The conditions varied with different steels and with heat treatment temperature. In the IF steel rapid grain growth at high temperatures in the ferrite range made a significant contribution to the prevention of grain refinement through transformation. Attempts to obtain the smallest prior austenite grain size in the IF steel to assess the ability of the oxidation technique to reveal fine austenite grains led to an average austenite grain size of 80 μm in warm rolled samples after the shortest holding time at 950°C.

MST/3203     

Improvement of Intergranular Stress Corrosion Crack Susceptibility of Austenite Stainless Steel through Grain Boundary Engineering

Intergranular stress corrosion crack susceptibility of austenite stainless steel was evaluated through threepoint bending test conducted in high temperature water. The experimental results showed that the frequent and efficient introduction of low energy coincidence site lattice boundaries through grain boundary engineering resulted in an apparent improvement of the intergranular stress corrosion crack resistance of austenite stainless steel.     

原奥氏体晶粒尺寸对珠光体钢组织及韧性的影响

探索了奥氏体晶粒尺寸对珠光体等温转变组织特征以及对韧性性能的影响规律.研究表明,在相同等温转变温度下,珠光体片层间距无明显变化,随奥氏体晶粒尺寸的增加,先共析铁素体量减少而珠光体团尺寸增加.珠光体断裂韧性受控于裂纹前沿塑性影响区尺寸(1～2)δc,其中δc为临界裂纹张开位移,当原奥氏体晶粒大于(1～2)δc时,裂纹扩展阻力主要来自穿越珠光体片层α、θ相的颈缩、破断.当原奥氏体晶粒尺寸接近或小于(1～2)δc时,裂纹主要沿晶界、珠光体团界、α+θ片层界面扩展,通过扩展路径发生多次弯折消耗能量,随原奥氏体晶粒尺寸增加,准静态断裂韧度J变化幅度较小.而冲击韧性缺口前沿塑性影响区远大于原奥氏体晶粒,大角度晶界将促使裂纹的转折而提高扩展阻力,提高裂纹前沿塑性区大角度晶界密度有利于提高冲击功,冲击韧性A随晶粒尺寸的增加显著下降.     

25CrMo车轴钢塑性的协调单元及其优化研究

采用OM、SEM、EBSD及TEM对25CrMo钢的微观组织进行定量表征,分析微观组织对试验钢塑性的控制作用。结果表明：随着晶粒的粗化,低碳板条马氏体钢的塑性逐渐增加,其与传统的理解不同,即具有大角度取向的原奥氏体晶粒(也包括束和块)不再是塑性的协调单元.只有属于小角度取向的马氏体板条对塑性的影响满足细晶增塑的原理,即在低碳板条马氏体钢中板条是塑性的有效控制单元.因此,在板条马氏体钢中,细化马氏体板条或增加小角度界面比例,是提高塑性的重要途径,其弥补了细化晶粒在大型构件中难以实现的不足.此外,也为高强度、高塑性材料的设计和开发提供了新思路.     

Effect of aging-deformation-treatment on the formation of intragranular ferrite in V-microalloyed steel

The influence of the aging-deformation-treatment on the formation of intragranular ferrite (IGF) in a vanadium microalloyed medium carbon steel (Fe–0.34C–1.53Mn) was studied. Effects of aging time on the volume fraction of IGF and austenite grain size were also investigated. The effect of the aging-deformation recrystallisation process on the amount of ferrite and the mechanism of IGF formation was discussed. The results show that aging-deformation-treatment makes the precipitation position of the carbonitride transfer from austenite grain boundary to intragranular, and the precipitated intragranular carbonitrides become the nucleation cores of the IGF during the recrystallisation. The content of precipitated carbonitrides, and the volume fraction of ferrites and the grain size of austenites, increase with the increasing aging time.