低碳钢中形变诱导铁素体相变过程中的应力—应变曲线研究

利用热模拟机Gleeble-3500在温度Ae3～Ar3之间对低碳钢进行了形变诱导铁素体相变的试验研究,发现常见的形变诱导铁素体相变过程中的应力—应变曲线可归纳为三种情况:"双峰"、"单峰"以及"过渡类型"。曲线上所表现出来的峰值是由形变诱导相变在晶界或者晶内发生而导致的软化效应所引起的,是加工硬化和相变软化的平衡点。对应变—时间曲线和应力—时间曲线的分析表明,形变对诱导相变过程中在晶内开始大量发生相变的时刻具有明显的推迟作用,形变诱导相变在形变接近结束之时才开始大量发生,导致大部分的相变过程发生在应变结束之后。研究发现,形变诱导铁素体相变具有亚动态相变的特征,是一个动态形核的亚动态相变过程。     

冷却速率对T91钢相变过程及组织的影响

利用DIL805A/D高精度差分膨胀仪,通过线膨胀行为测量获得相关动力学信息,结合冷却后的组织特征,研究了T91钢不同冷却速度(2～6000℃/min)下过冷奥氏体的相变过程和产物,确定了该钢组织转变的临界冷却速度以及淬火速率对马氏体转变点及组织的影响,绘制了连续冷却转变曲线。研究表明:T91钢的连续冷却过程中只存在铁素体和马氏体转变区,10℃/min为马氏体转变的临界冷却速度。不同淬火速率对T91钢马氏体开始转变温度有较大的影响,它不同于随冷速增加而相变点升高的经典理论。淬火速率通过碳原子气团、内应力的形成来影响过冷奥氏体状态,从而影响相变点;随淬火速度的增加,过冷奥氏体转变后的组织呈细化趋势。     

δ铁素体形成机制以及对马氏体耐热钢冲击功的影响

 通过Thermo-Calc热力学软件计算、定量金相分析、冲击试验和SEM试验分析,研究了化学成分和正火温度对材料中δ铁素体含量的影响,并分析了δ铁素体的形成机制,以及含量和位置分布对材料冲击韧性的影响。结果表明：化学成分和正火温度对δ铁素体含量影响显著,C+N含量增加能够显著降低材料中的δ铁素体含量;δ铁素体主要集中在原奥氏体晶界位置生成,显著降低材料的冲击功,并且在δ铁素体与马氏体基体界面位置会聚集大量富Nb碳化物,降低韧性的同时减少了MX相生成量。     

添加B对9Cr铁素体耐热钢应力松驰行为解析

以提高火力发电设备效果为目的，正在积极开发高强度铁素体耐热钢。为开发高强度耐热钢重要的是提高高温稳定性。应力松弛是其中之一。日本物质和材料机构研究了添加B对耐热钢的应力松弛。     

铜含量对T122耐热钢中δ铁素体含量及力学性能的影响

研究了T122铁素体型耐热钢中铜含量0~1.77%变化对组织与性能影响,结果表明铜含量增加,使钢中δ铁素体含量下降,钢的室温和高温强度明显提高。持久强度和长时时效后高温强度也随铜含量增加,明显提高。含铜0.90%时,钢的强度和塑性匹配最佳。     

化学成分和热处理温度对T122耐热钢中δ-铁素体含量的影响

采用Thermocalc热力学计算研究了化学成分和温度对T122钢中δ-铁素体含量的影响,计算和相应试验结果表明,化学成分和热处理温度变化对δ-铁素体含量影响显著,铬含量降低,氮含量和碳含量增加,能明显降低δ-铁素体含量。在1 030~1 070℃的温区热处理,δ-铁素体含量最低;超过1 200℃热处理会产生γ-Fe→γ-Fe+δ-Fe转变,即在低于1 200℃处理不含δ-铁素体的钢中会生成δ-铁素体。     

钒对T122铁素体耐热钢组织和性能的影响

研究了(%):0.11C- 11.89～12. 19Cr- 1.86～1.90W-0.37～0.38Mo-0.9Cu铁素体耐热钢T122 中 0.14%～0.31%V-0.05%Nb复合强化添加剂中V 含量对钢的组织和性能的影响。结果发现,随V 含量增加, 钢中δ铁素体量增加,室温拉伸强度、650℃拉伸强度和650℃持久强度逐渐降低;当V 含量为0.19%时T122 钢的室温拉伸强度、650℃拉伸强度和持久性能较高。 V 含量变化影响钢中M₂C、MX 和Laves相的析出, 0.19%V-0.05%Nb析出强化效果最好     

P91铁素体耐热钢细晶热影响区蠕变过程中组织演化

高铬铁素体耐热钢存在的一个问题是其焊接试样的蠕变强度远低于母材,为了从组织演化角度分析其产生机制,对P91铁素体耐热钢焊接试样在600℃、100 MPa应力条件下进行了中断蠕变试验,利用扫描电镜与EBSD对蠕变过程中不同区域的微观组织进行观察,分别计算不同区域的核心平均取向差(KAM),结果表明:细晶热影响区的KAM值随着蠕变时间的增加发生显著降低,蠕变断裂后与试验前相比下降约25%,而母材的KAM值虽然有所降低,但幅度远小于细晶热影响区。经过2 000 h蠕变试验后,在细晶热影响区已经形成大量的蠕变孔洞,而相同试验条件下母材中则没有观察到蠕变孔洞。上述结果表明细晶热影响区的高温组织稳定性明显劣于母材,而引起其组织劣化的原因可能与碳化物的析出行为有关。     

超临界与超超临界汽轮机耐热钢的研究进展

 ：从超临界和超超临界汽轮机耐热钢的发展、组织结构、强化机理、性能、热处理和应用等方面阐述了该耐热钢的研究、发展和应用等方面的概况和发展趋势。指出了超超临界汽轮机耐热钢研究过程中存在的问题,结合未来超超临界汽轮机技术的发展,对超超临界汽轮机耐热钢的研究进行了展望。     

应变诱发铁素体相变对低碳钢晶粒细化的影响

研究了在奥氏体低温区变形时显微组织的变化,并测试了其变形抗力。结果表明：在Ar3以上温度变形会产生应变诱发铁素体相变,使变形抗力下降。通过降低变形温度,铁素体晶粒得到细化。     

Effect of Niobium on Isothermal Transformation of Austenite to Ferrite in HSLA Low-Carbon Steel

Using thermomechanical simulation experiment,the kinetics of the isothermal transformation of austenite to ferrite in two HSLA low-carbon steels containing different amounts of niobium was investigated under the conditions of both deformation and undeformation.The results of optical microstructure observation and quantitative metallography analysis showed that the kinetics of the isothermal transformation of austenite to ferrite in lower niobium steel with and without deformation suggests a stage mechanism,wherein there exists a linear relationship between the logarithms of holding time and ferrite volume fraction according to Avrami equation,whereas the isothermal transformation of austenite to ferrite in high niobium steel proceeds via a two stage mechanism according to micrographs,wherein,the nucleation rate of ferrite in the initial stage of transformation is low,and in the second stage,the rate of transformation is high and the transformation of residual austenite to ferrite is rapidly complete.Using carbon extraction replica TEM,niobium carbide precipitation for different holding time was investigated and the results suggested that NbC precipitation and the presence of solute niobium would influence the transformation of austenite to ferrite.The mechanism of the effect of niobium on the isothermal transformation was discussed.     

热穿孔温度对T91钢管持久强度的影响

研究了φ75mm管坯穿孔温度对T91锅炉钢管高温力学性能的影响。结果表明，1200℃穿孔温度能获得持久强度和持久断裂塑性较好配合的综合性能。     

70kg级低碳贝氏体钢相变规律研究

利用MMS-200热模拟试验机和光学显微镜研究了70kg级低碳贝氏体钢板在不同终轧温度和冷却速度下的相变规律。结果表明,随冷却速度的增大,钢中依次出现多边形铁素体、珠光体、针状铁素体、粒状贝氏体、下贝氏体和马氏体组织,奥氏体向铁素体相变温度Ar3降低,晶粒细化。随着终轧温度的降低,铁素体诱导相变明显增加,铁素体晶粒细化。     

以铁水为主原料生产管坯T91钢的试制

介绍了以铁水为主原料采用"转炉+VOD+LF+方坯+热轧"生产管坯T91钢的生产工艺。通过工艺控制,转炉冶炼生产的T91钢纯净度高,残余元素含量低,完全满足管坯用钢要求。管坯轧后质量与模铸产品相当,可以替代长流程工艺生产的同质量水平的管坯。     

Characteristics of Strain-Induced Ferrite in Low Carbon Steel

Itiswellknownthatthestrain inducedtrans formationfromaustenitetoferritecanleadtograinrefinement .Thushighermechanicalpropertiessuchasstrengthandductilitycanbeobtained[1,2 ] .Someresearcheshavebeencarriedoutonthenucleationofstrain inducedferriteinthepastyears .PDHodgsonetalsuggestedthattheaustenitegrainsshouldbeascoarseaspossibletodecreasenucleationatgrainbo undaries[3 ] .PJHurleyetalconsideredthatthecel lularboundaryofdislocationsuppliesthesitesfornu cleationofstrain inducedferrite[4] .Yang…     

Effect of M3C on the Precipitation Behavior of M23C6 Phase during Early Stage of Tempering in T91 Ferritic Steel

Tempered martensitic structure is the service condition of T91 ferritic steel after adopting the austenitizing followed by tempering. Needle‐like M₃C particles are precipitated during air cooling after austenization, while the precipitation of M₃C is suppressed during the water cooling. The effect of existence of M₃C on the precipitation behaviors of M₂₃C₆ during the early stage of tempering, as nucleation site, number density and size distribution, was investigated by means of TEM observation. The TEM results indicate that, upon the same tempering time, the size of M₂₃C₆ is smaller and its number density is higher in the sample pre‐existing M₃C than in the sample without M₃C. This can be explained that existence of M₃C results in more M₂₃C₆ precipitates forming inside of grain, where a relatively low self‐diffusion coefficient of alloy element leads to M₂₃C₆ hardly coarsening. However, with the prolongation of tempering time, this effect becomes weaken. Microhardness results indicate that the existence of M₃C phase results in the increase of hardness after tempering due to the precipitation of finer and denser M₂₃C₆ particles.     

Modelling the Stress Relaxation Kinetics of Intercritically Deformed Austenite and Ferrite in C‐Mn Steel

In this study the softening kinetics of intercritically deformed C‐Mn steel have been characterised using the stress relaxation technique. In addition, the progress of softening has been monitored via optical microscopy of quenched samples. Physically based models for the softening kinetics of the separate phases were combined using the simple rule of mixtures, to predict the stress relaxation kinetics following intercritical deformation. Moreover, the strain and stress distribution developed during deformation has been taken into account using an analytical approach from the literature. Comparison of the model with experiments showed significant deviations. These were thought to be due to two effects concerning the role of phase interactions. Firstly, there was a region in the austenite phase having a low strain, leading to a fraction of non‐recrystallizing austenite. Secondly, the number of recrystallization nucleation sites was reduced. These two effects were tested by modifying the original model. The best agreement with experimental data was obtained when assuming the presence of a significant fraction of austenite that did not recrystallize.