V对C-Mn钢针状铁素体组织的改善

1　前言在焊接用低 C钢中 ,相互交错的细针状铁素体是所希望的显微组织 ,因为通过诸如普通的粗大贝氏体转变成细针状铁素体 ,可提高钢的韧性。通过金相观察 ,已较早认识到焊接金属中氧化物含量的重要性 ,焊接钢的夹杂物在铁素体片晶内形核 ,而不是在晶粒边界 ,这为针状铁素体组织的发展提供了有说服力的证据 ,否则 ,在晶粒边界成核将形成粗大组织。然而 ,关于针状铁素体形核的精确机理目前仍不清楚 ,很多理论还在辩论。通过对钢和夹杂物的密度的测量和比较 ,已认识到 ,并不是每一个铁素体单元都可以被夹杂物核化 ,而只有约 1 / 1 0是通过夹…     

Microstructure and Transformation Characteristics of Acicular Ferrite in High Niobium-Bearing Microalloyed Steel

 The transformation behavior and microstructural characteristics of a low carbon high Nb-bearing microalloyed pipeline steel have been investigated by deformation dilatometry and microstructure observation. The continuous cooling transformation curves (CCT) of the tested steel was constructed. High Nb content and deformation enhancing the formation of acicular ferrite; the microstructures are range from PF, QF to AF with increasing cooling rates from 0.5 to 50℃/s and dominated by acicular ferrite in a broadened cooling rate higher than 5℃/s. The chaotic microstructure consists of non-equiaxed ferrite and interwoven ferrite laths distributed high density dislocations and sununits. The results of isothermal holding show that acicular ferrite microstructure is formed in region of 550-600℃. With the holding time or temperature increased, some low misorientations boundaries change to high misotrentationn as dislocations moving and grain boundaries coarsening.     

回火工艺对针状铁素体钢组织和性能的影响

对针状铁素体钢进行540～630℃回火后的组织、性能进行了研究.与轧态相比,630℃回火后钢的屈服强度提高75 MPa,伸长率的平均值降低1.9%,冲击功的平均值提高1.75 J.对回火前、后钢板的组织和析出物进行了对比分析,结果表明:回火后晶粒内部的位错密度减小,亚晶板条部分消失;回火后析出物粒子的平均尺寸减小;回火温度越高,析出物粒子的平均尺寸越大.630℃回火以后,在1～10 nm尺度范围内的粒子分布频度增加2～3倍,铌的析出量增加了166.9%,钒的析出量增加了584.6%.细小析出物的增加和亚晶板条的部分消失是强度提高、塑性改善的主要原因.     

Microstructure Refinement and Mechanical Properties of 304 Stainless Steel by Repetitive Thermomechanical Processing

Repetitive thermomechanical processing (TMP) was applied for evaluating the effect of strain-induced α′-martensite transformation and reversion annealing on microstructure refinement and mechanical properties of 304 austenitic stainless steel. The first TMP scheme consisted of four cycles of tensile deformation to strain of 0.4, while the second TMP scheme applied two cycles of tensile straining to 0.6. For both schemes, tensile tests were conducted at 173 K (? 100 °C) followed by 5-minute annealing at 1073 K (800 °C). The volume fraction of α′-martensite in deformed samples increased with increasing cycles, reaching a maximum of 98 vol pct. Examination of annealed microstructure by electron backscattered diffraction indicated that increasing strain and/or number of cycles resulted in stronger reversion to austenite with finer grain size of 1 μm. Yet, increasing strain reduced the formation of Σ3 boundaries. The annealing textures generally show reversion of α′-martensite texture components to the austenite texture of brass and copper orientations. The increase in strain and/or number of cycles resulted in stronger intensity of copper orientation, accompanied by the formation of recrystallization texture components of Goss, cube, and rotated cube. The reduction in grain size with increasing cycles caused an increase in yield strength. It also resulted in an increase in strain hardening rate during deformation due to the increase in the formation of α′-martensite. The increase in strain hardening rate occurred in two consecutive stages, marked as stages II and III. The strain hardening in stage II is due to the formation of α′-martensite from either austenite or ε-martensite, while the stage-III strain hardening is attributed to the necessity to break the α′-martensite-banded structure for forming block-type martensite at high strains.     

Inclusion Characteristics and Acicular Ferrite Nucleation in Ti-Containing Weld Metals of X80 Pipeline Steel

X80 steel weld metals with Ti contents of 0.003 to 0.13 pct were prepared by the single-pass submerged-arc welding process. The effects of Ti content in weld metals on the constituent phases of inclusions and chemical compositions of the constituent phases, as well as the potency of acicular ferrite (AF) nucleation on the inclusions were investigated. Moreover, the crystallographic orientation relationship between the AF and inclusion was examined. The results show that with an increase in Ti content, the primary constituent phases of the inclusions change from the (Mn-Al-Si-O) compound to a mixture of spinel and pseudobrookite solid solutions, and eventually to pseudobrookite. The spinel solid solution is characterized by the MnTi₂O₄ constituent. Compared to pseudobrookite, spinel has a lower Ti concentration, but a significantly higher Mn content. In the case of the presence of a considerable amount of spinel, the Mn element is enriched strongly in the inclusions, resulting in the development of a Mn-depleted zone (MDZ) in the matrix around the inclusions, which enhances the driving force for AF formation. AF shows the Baker–Nutting orientation relationship with MnTi₂O₄. The formation of MDZ and the presence of the Baker–Nutting orientation relationship promote the ability of inclusions to nucleate the intragranular AF.     

钛脱氧钢中针状铁素体的形成

通过实验研究了钢中加钛脱氧后针状铁素体的形成及夹杂物的变化。对实验钢的化学成分、组织变化、析出相成分、钢中氧含量及夹杂物尺寸进行了分析。实验证明,在钢中加钛处理后,钢中产生了大量的以钛氧化物或钛铝等复合氧化物为核心的针状铁素体,钢的组织明显细化,随着钛加入后孕育时间的延长,钢中夹杂物的尺寸变小,孕育时间存在最佳值。     

Microstructure and Property of Coarse Grain HAZ X80 Pipeline Steel

The coarse grain HAZ microstructure and property of X80 pipeline steel with different carbon content was investigated. The weld thermal simulation test was carried out on Gleeble 1500 thermal mechanical test machine. The Charpy tests were completed at --20 ℃ for evaluating the toughness of coarse grain heat affected zone （CGHAZ）. The microstructure was examined by optical microscope （OM） and transmission electron microscopy （TEM）, and the austenite constituent was quantified by X-ray diffraction. The results showed that the ultra-low carbon can improve the toughness of CGHAZ by suppressing the formation of carbide, decreasing the martensite austenite （M-A） constituent and increasing the residual austenite in the M A.     

HTP X80管线钢的晶粒细化与组织控制

 通过热模拟实验研究了HTP X80管线钢的晶粒细化与组织控制的工艺要点,确定了奥氏体再结晶温度区和非再结晶温度区,揭示了高Nb含量的HTP钢在连续冷却过程中的相变特点。所得到的技术要点对细化奥氏体晶粒,避免混晶的出现,以及通过控制冷却得到理想的相变产物具有指导性。     

Microstructural aspects of sulfide stress cracking in an API X-80 pipeline steel

Crack growth in an API X-80 exposed to sour gas environments was investigated using modified wedge-opening-loaded (MWOL) specimens. The MWOL specimens were tested in the as-received condition and after annealing followed by water spraying to simulate improperly welded regions. It was found that water-sprayed MWOL specimens were susceptible to stress sulfide cracking in a NaCl-free NACE solution. Crack growth was relatively slow when subjected to an initially appliedK _I of 30 MPa . Under these conditions, crack growth rates continually decreased until crack arrest was exhibited at a thresholdK _I (K _ISSC) of 26 MPa . The exhibited crack growth rates were related to the facility with which nucleated microcracks joined the main crack front. Apparently, preferential nucleation and growth of microcracks within the main crack tip plastic zone accounted for the exhibited embrittlement. In particular, favorable microcrack growth followed a path consisting of fractured (cut) carbide regions, as well as various interfaces, including globular inclusions and grain boundary precipitates.     

控轧控冷工艺对汽车大梁板组织及冷弯性能的影响

在攀钢热轧板厂对汽车大梁板进行了控轧控冷试验,分析了终轧温度、轧后冷却方式以及卷取温度对汽车大梁板显微组织及冷弯性能的影响。结果表明：采用较低的终轧温度830 ℃、卷取温度600 ℃以及前段冷却的轧后冷却方式,汽车大梁板的铁素体晶粒细小均匀,珠光体分布弥散,并获得了良好的冷弯性能。     

Effect of Thermomechanical Controlled Processing Parameters on Microstructure and Properties of Q460q Steel

With tensile test, impact test, and optical microscopy, the effect of thermomechanical controlled process-ing (TMCP) parameters on the microstructure and properties of Q460 steel was studied and analyzed. The TMCP parameters for Q460q steel were optimized by laboratory experiments, and then, industrial trial was carried out. The result indicated that the microstructure and properties of the Q460q steel in industrial trial were in agreement with the results obtained in laboratory experiments and could meet the national standard of Q460q steel.     

大型球罐用低碳针状铁素体钢成分组织性能的研究

从化学成分、显微组织、断口形貌、力学性能方面对JFE—HITEN610U2L钢进行了研究。结果表明：该钢以低碳高锰，加入微量镍、铬、钼、钒、铌等元素的合金化方式，通过适当的控制热加工工艺，获得了以针状铁素体为主的混合组织，表现出良好的力学性能。当针状铁素体条束比较粗大时，-50℃冲击试样的断裂方式从韧窝断裂转变为解理断裂，韧性明显下降。     

X80石油管线钢的组织性能控制

分析了生产厚度为18.4mm X80管线钢组织性能控制的几个技术要点,简要阐述了加热制度、组织均匀性、轧制压下量和冷却速度控制不当对钢组织性能产生的不利影响。     

Effect of Thermomechanical Controlled Processing Parameters on the Microstructure and Properties of Q460q Steel

 Thermal mechanical control processing (TMCP), the combination of controlled rolling and controlled cooling, provides a powerful means of developing high-strength low alloy (HSLA) steels by intensive microstructural control. In the present investigation, the effects of TMCP parameters, consisting of the finish cooling temperature and the start rolling temperature in non-recrystallization region, on the final microstructure and mechanical properties of Q460q steel have been studied by tensile, Charpy impact tests, optical microscopy. The TMCP parameters for Q460q steel have been optimized by laboratory experiments. And the microstructure and properties of industrial product were coincident with the results of laboratory experiments.     

热连轧工艺生产厚规格X80管线钢的工艺及组织性能

研究了马钢热连轧生产厚规格X80管线钢的显微组织、析出物的种类、大小、分布和力学性能,研究表明:通过合理的成分设计和轧制工艺,传统热连轧生产的厚规格X80管线钢的组织均匀,合理;析出物细小弥散,其析出物为Nb、V、Ti的复合析出物,根据形态可以分为两类,第一类析出物是以含Ti为主的(Ti、Nb)(C、N)析出物,主要作用是阻止奥氏体晶粒长大;第二类析出物以含Nb为主的(Nb、Ti)C析出物,主要作用是析出强化.在充分发挥细晶强化、位错和亚晶强化和析出强化等强化机制的条件下,厚规格X80管线钢力学性能优良,屈服强度达到580 MPa,屈强比合适;-20 ℃的夏比冲击功和剪切面积分别为290 J和100%,-15 ℃的DWTT剪切面积为100%.各项性能均满足西气东输二线标准要求.     

Thermomechanical Control of Microstructure and Precipitation in Vanadium Microalloyed Steel: Influence of Finish Rolling and Coiling Temperatures

Six hot compression tests are conducted using the Gleeble3500 thermomechanical simulator to investigate the microstructural evolution and precipitation behavior in low-C–Mn V-microalloyed steel. The specimens are subjected to hot isothermal compression deformation of 87%. The optical microscopy and transmission electron microscopy using carbon extraction replica method are used to characterize the microstructures and precipitation after the simulated thermomechanical controlled process and coiling. The results indicate that increasing the finish rolling temperature benefits the refinement of ferrite grains but has little influence on the refinement of the precipitates. It is also observed that lower coiling temperatures (CTs) promote the formation of fine precipitates. When the CT is 500 °C, the average precipitate size is found to be 86 nm. Furthermore, it is found that the CT significantly influences the nucleation sites of the precipitates inter alia, the matrix, interphase, grain boundaries, and dislocations. As expected, at higher CTs, nucleation is predominantly on the defects rather than the matrix.     

高强度船板钢中针状铁素体的原位观察

采用高温共聚焦显微镜对高强度船板钢中针状铁素体进行原位观察,并利用金相显微镜分析原位观察后其组织形态。结果表明,随着保温时间的增加,平均奥氏体晶粒尺寸增大。保温时间为900 s时获得的奥氏体尺寸更有利于针状铁素体的形核。随着保温时间的延长,铁素体开始相变的温度先减小后增加,而铁素体的相变结束温度逐渐减小。     

X80抗大变形管线钢的生产工艺与组织性能研究

设计了X80级抗大变形管线钢的合金成分,采用TMCP热轧及轧后两阶段控制冷却技术,完成了试验室制备并实现了工业试制。利用SEM、TEM和拉伸、冲击实验等分析方法研究了不同冷却条件对组织与性能的影响。研究结果表明,采用空冷+水冷两阶段冷却工艺后可得到铁素体+贝氏体双相组织的X80抗大变形管线钢,当加速冷却中终冷温度为450℃、冷却速度为20℃/s时,组织中铁素体与贝氏体相得到最佳配比,M/A相尺寸约为1μm,组织均匀性良好,试样得到最优的强度塑性匹配。