管线钢中针状铁素体的形成及其强韧性的分析

通过对一种商业用管线钢连续冷却相变曲线（CCT）的测定,研究了过冷奥氏体的相变规律。在分析显微组织形成规律的基础上,确定了能够在实验用钢中获得针状铁素体组织的控制热加工工艺（TMCP）制度,即制定两阶段多道次控制轧制和冷却速度为30℃/s控制冷却的工艺制度,并利用力学试验及微观分析手段,进一步分析了针状铁素体组织的微观结构特征和力学性能。结果表明,针状铁素体组织中彼此咬合的细小针状片条束、高密度位错和弥散析出相等微观结构特征对提高材料的强韧性具有重要作用。     

针状铁素体钢的力学性能与显微结构

本文介绍了一种采用TMCP工艺轧制的低合金高强度钢板的力学性能及微观组织。分析表明,微观组织是以针状铁素体组织为主的混合组织,材料有较高的强度和良好的韧性。     

Nb、Ti微合金化新型440MPa级船用钢板韧性研究

研究了某钢厂热连轧TMCP工艺14mm厚440MPa级钢板的强韧性,对微观组织进行了观察分析.试验结果表明,新型热连轧440MPa钢板具有良好的低温韧性,-40℃冲击功超过310J,韧脆转变温度低于-100℃.新型440MPa钢板良好的性能来源于低碳、Nb-Ti微合金化成分设计及TMCP工艺下获得细化的针状铁素体组织.     

两种冷却方式下双相钢2205堆焊层性能分析

采用药芯焊丝CO_2气保焊(FCAW)在低碳钢表面堆焊一层双相不锈钢表层,分析了水冷和空冷冷却方式对双相钢堆焊层的力学性能、耐腐蚀性能以及铁素体-奥氏体(α-γ)两相组织的影响。结果表明,水冷和空冷冷却方式对堆焊层的力学性能无显著影响;水冷时堆焊层铁素体含量为45.17%,比空冷更接近两相平衡,其显微组织为块状铁素体和沿晶界或亚晶界分布的针状奥氏体;水冷时堆焊层具有更优异的耐腐蚀性能,平均腐蚀速率为0.488 mm/a。     

低碳超低碳微合金化管线钢显微组织的研究进展

综述了纸碳及超低碳微合金钢显微组织研究的现状，介绍了奥氏体连续冷却转变时形成的各种铁素体的术语，讨论了多边及准多边铁素体、针状铁素体及晶内成核针状铁素体、粒状贝氏体铁素体等的形成机理和组织形貌。另外，还指出了文献中使用“针状铁素体”术语的一些混淆及不同理解，提出了在工程上分析复杂管线钢组织时，可将多种形态铁素体简化为铁素体及贝氏体两类。对当前西气东输管线工程中材料显微组织的判断可提供参考。     

热加工对管线用低碳钢性能的影响

通过热模拟实验,研究了一种管线钢相变组织的形成规律,在此基础上,进行两阶段多道次控轧和在适度冷却速度下控冷的控制热加工实验,分析了工艺参数对钢的组织结构和力学性能的影响。结果表明,开轧温度、终轧温度、终冷温度和冷却速度对管线钢的力学性能有强烈的影响。通过优化工艺,获得了以针状铁素体为主的混合组织,针状铁素体的含量越多,材料的力学性能越好。     

基于组织的DH36钢焊缝微观应力应变模拟研究

通过试验观察和数值模拟手段,揭示了海洋平台结构用钢DH36多层多道焊缝中典型区域的微观组织分布形态等对焊缝力学性能的影响,采用仪器化压痕法研究不同焊缝组织的断裂性能,对比微区组织对启裂、变形性能的影响。研究发现,在针状铁素体和晶界铁素体混合组织中,弹塑性变形不协调,产生应力应变集中,其中应力集中发生于针状铁素体,应变集中出现在晶界铁素体并向针状铁素体延伸,晶界铁素体条状分布的强度高于晶界铁素体网状分布的强度。     

针状铁素体的物理冶金学（待续）

针状铁素体能明显改善高强度低合金钢焊缝的力学性能，提高其抗环境损伤的能力，具有重要的工程意义。作者利用扫描电镜和透射电镜研究了针状铁素体的组织形态，并观察到高角度晶界结构和相界周围的“唇”带村度，探讨了其抗解理断裂的机理。并根据国内外的研究报道，综述了形成针状铁素体所必需的工艺条件和合金化条件。     

一种针状铁素体钢热轧板材的结构与力学性能

在透射电镜(TEM)下观测了一种管线用针状铁素体钢热轧板材的显微组织并研究了力学性能.结果表明,这种管线用针状铁素体钢热轧板材具有较优良的强韧性能,其显微组织与焊接组织在形态上有很大的差异.管线用针状铁素体钢热轧板材中有明显界面的板条束或针状片条束;没有明显界面的板条束或针状片条束,可根据条状物或岛状物的有方向性的线状分布依稀辨别界面的存在;板条或针状片条与非等轴晶共存等多种不同形态,并不象焊接组织那样通常是单一的针状片条束或板条束形态.     

大线能量焊接条件下低合金高强度钢针状铁素体形核影响因素及形核机理研究

综述了大线能量焊接条件下低合金高强度钢中针状铁素体形成的研究进展,概述了针状铁素体显微组织结构特点及其在低合金高强度钢中的主要性能,具体讨论了针状铁素体具有良好强韧性和抗断裂性等力学性能的原因,重点分析了大线能量焊接条件下影响焊接热影响区中针状铁素体形核长大的因素,包括合金元素及夹杂物的种类和尺寸,得出针状铁素体的形核机理是多种机理联合作用的结果。     

Processing of Ultralow Carbon Pipeline Steels with Acicular Ferrite

Acicular ferrite microstructure was achieved for an ultralow carbon pipeline steel through the improved thermome chanical control process (TMCP), which was based on the transformation process of deformed austenite of steel. Compared with commercial pipeline steels, the experimental ultralow carbon pipeline steel possessed the satisfied strength and toughness behaviors under the current improved TMCP, although it contained only approximately 0.025% C, vvhich should mainly be attributed to the microstructural characteristics of acicular ferrite.     

高等级海上风力发电机用钢的研发及力学性能

基于超快冷热机械控制工艺(TMCP),成分设计上遵循低碳含量、低碳当量、微合金化,焊接时采用大热输入的原则,成功研发出了屈服强度为460 MPa的高等级海上风力发电机用钢.阐述了开发的两种钢的化学成分设计及试制工艺流程,并对其综合力学性能进行分析.结果表明:开发的两种钢具有生产周期短、强度高、韧性好、抗层状撕裂性能好、...     

Formation mechanism and control methods of acicular ferrite in HSLA steels: A review

High strength low alloy (HSLA) steels have been widely used in pipelines, power plant components, civil structures and so on, due to their outstanding mechanical properties as high strength and toughness, and excellent weldability. Multi-phase microstructures containing acicular ferrite or acicular ferrite dominated phase have been proved to possess good comprehensive properties in HSLA steels. This paper mainly focuses on the formation mechanisms and control methods of acicular ferrite in HSLA steels. Effect of austenitizing conditions, continuous cooling rate, and isothermal quenching time and temperature on acicular ferrite transformation was reviewed. Furthermore, the modified process to control the formation of multi-phase microstructures containing acicular ferrite, as intercritical heat treatments, step quenching treatments and thermo-mechanical controlled processing, was summarized. The favorable combination of mechanical properties can be achieved by these modified treatments.     

超细晶粒钢制备工艺及机制与传统控轧控冷(TMCP)钢的异同

总结对比了传统控轧控冷(或热机械控制处理,TMCP)钢与超细钢开发制备所用的新型TMCP工艺的特征及其冶金机制.轧前急冷、低温加工与大应变变形(强加工)是超细钢制备工艺的3个必要条件.TMCP的晶粒细化主要靠加工硬化奥氏体的静态铁素体转变.新工艺晶粒细化主要靠形变诱导动态铁素体相变.     

Microstructural control by secondary processing of strip cast low carbon steel

Abstract

The secondary processing of low carbon steel strip produced by twin roll casting was investigated to examine its effect on microstructural development and mechanical properties. The as cast microstructure is predominantly acicular ferrite with regions of bainitepearlite and polygonal ferrite. Deformation at temperatures below Ar1 produces a heterogeneous microstructure with regions of moderately deformed acicular ferrite adjacent to highly deformed regions containing shear bands. Cold rolled and warm rolled steels show similar behaviour to conventional hot band in that dynamic recovery during warm rolling results in sluggish recrystallisation and produces a coarse final grain size. However, the initial as cast microstructure recrystallises at a slower rate than conventional hot band and produces a weaker recrystallisation texture. This can be attributed to the heterogeneous microstructure of the as cast strip such that, after rolling, nucleation occurs within shear bands and more ill defined sites, which results in nucleation of randomly oriented grains thereby producing a weak final texture. It was found that austenitising the as cast strip followed by rolling in the vicinity of Ar3 produces a uniform distribution of equiaxed, ultrafine ferrite UFF grains throughout the thickness of the strip. The production of UFF by twin roll casting and subsequent rolling represents a simple processing route for the production of fine grained low carbon sheet steel products.     

Microstructure and mechanical properties of C–Si–Mn(–Nb) TRIP steels after simulated thermomechanical processing

Abstract

Continuous and discontinuous cooling tests were performed using a quench deformation dilatometer to develop a comprehensive understanding of the structural and kinetic aspects of the bainite transformation in low carbon TRIP (transformation induced plasticity) steels as a function of thermomechanical processing and composition. Deformation in the unrecrystallised austenite region refined the ferrite grain size and increased the ferrite and bainite transformation temperatures for cooling rates from 10 to 90 K s^-1. The influence of niobium on the transformation kinetics was also investigated. Niobium increases the ferrite start transformation temperature, refines the ferrite microstructure, and stimulates the formation of acicular ferrite. The effect of the bainite isothermal transformation temperature on the final microstructure of steels with and without a small addition of niobium was studied. Niobium promotes the formation of stable retained austenite, which influences the mechanical properties of TRIP steels. The optimum mechanical properties were obtained after isothermal holding at 400°C in the niobium steel containing the maximum volume fraction of retained austenite with acicular ferrite as the predominant second phase.     

Acicular ferrite formation during hot plate rolling for pipeline steels

Abstract

The transformation of supercooled austenite in a commercial pipeline steel was investigated by means of continuous cooling transformation (CCT) and hot simulation experiments. Based on the obtained results, an improved thermomechanical control process (TMCP) was proposed, which could produce a mixed microstructure dominated by acicular ferrite. Results indicated that an increase in the cooling rate could improve the percentage of acicular ferrite in the final microstructure under the present experimental conditions. Furthermore, the acicular ferrite dominated microstructure could be obtained by a two stage controlled rolling in the austenite recrystallisation region plus the non-recrystallisation region and controlled cooling at a cooling rate of 30 K s^-1.     

碳对超低碳船体钢熔敷金属冲击韧性的影响

考察了埋弧焊材中含少量碳(w(C)<0.05%)对10CrNiCuA钢熔敷金属冲击韧性的影响。试验发现,随碳含量的增加,熔敷金属的冲击韧性得到了很大地提高。其主要原因在于,碳元素使熔敷金属的一次组织得到了明显地细化,并强烈地抑制了熔敷金属中侧板条铁素体的生成,使得熔敷金属中针状铁素体的含量稍有增加。