控轧控冷工艺对X60管线钢组织及力学性能的影响

探讨了控轧控冷工艺参数对X60管线钢组织和力学性能的影响,分析得出了控轧控冷工艺参数与力学性能关系的回归方程：σn=0.5075ts-0.2387tf-0.3242tc 1.9163vc 324.8287,δ5=-0.0071ts-0.0976tc 0.3162vc 123.97,给出了一种较佳的工艺制度,微观结构分析表明,针状铁素体为主的混合组织,有较高的屈服强度和良好的韧性。     

控轧控冷工艺参数对X80管线钢组织和性能的影响

利用光学显微镜、扫描电镜等分析方法,研究了控轧控冷工艺参数对X80管线钢组织和力学性能的影响。结果表明:终轧温度750℃时,试验钢的显微组织为多边形铁素体和粒状贝氏体,终轧温度为810℃时,显微组织为针状铁素体;在高冷速条件下,试验钢中M/A岛的尺寸、数量和体积分数均较大;具有双相组织试验钢的屈强比低,塑韧性好;M/A岛含量高、尺寸大的试验钢,其强度和屈强比高,塑韧性差。     

Nb-Ni系X70 管线钢基础参数研究

介绍了首钢首秦金属材料有限公司开发研制X70管线钢的成分设计、控轧控冷工艺和钢板实际性 能,钢板成品组织为细小均匀的铁素体＋少量针状铁素体,具有优良的综合力学性能。并分析了返红温度对钢板组织和屈强比的影响、终轧温度对钢板组织和断裂韧性的影响。     

控轧控冷工艺对X70级抗大变形管线钢组织与性能的影响

采用光学显微镜、扫描电镜及力学性能实验等研究了控轧控冷工艺对X70级管线钢的组织与力学性能的影响。结果表明:不同终轧温度下X70管线钢的显微组织主要由多边形铁素体、贝氏体和少量的珠光体组成,且随着终轧温度的升高,抗拉强度与屈服强度降低,硬度下降,冲击韧性提高,但屈强比变化不大,并且落锤性能较差;随着终轧温度的升高,晶粒尺寸逐渐增大,铁素体体积含量增多。在不同的终冷温度下,X70管线钢的显微组织主要由多边形铁素体和贝氏体组成,并且随着终冷温度的升高,抗拉强度大幅度降低,屈服强度则呈M形波动,硬度呈线性降低,冲击吸收能量大幅度升高且落锤性能较好,屈强比缓慢升高;随着终冷温度的升高,晶粒度等级基本保持稳定,铁素体含量呈线性增加。该大变形管线钢最优的轧制工艺为控制终轧温度为840℃,终冷温度为450℃。     

控制轧制对管线钢X65组织细化的影响

在实验室Ф450热轧实验机上进行了微合金管线钢X65控制轧制工艺的研究,以便为进一步工业化生产提供可靠的实验和理论依据。通过TEM分析可知,针状铁素体组织的典型形貌为非常微细的亚结构、高位错密度以及部分细板条铁素体,基体上弥散分布着M/A岛和渗碳体。实验表明,随开、终轧温度的降低,显微组织明显细化,针状铁素体体积分数增加且力学性能得到提高。     

控制热加工下管线钢中针状铁素体的形成

通过对一种商业用管线钢连续冷却相变曲线（CCT）的测定和热模拟实验,研究了过冷奥氏体的相变规律。在此基础上,提出了一种能够得以针状铁素体为主的混合组织的控制热加工工艺制度,并分析了针状体素体的微观特征。结果表明：在实验条件下,增加冷却速度,可明显提高管线钢最终组织中针状铁素体的含量。     

热处理对针状铁素体管线钢强度级别升级的影响

通过光学显微镜、透射电镜、扫描电镜、拉伸与冲击试验,研究了热处理对针状铁素体管线钢强度级别升级的影响规律.结果表明,在对反映沉淀析出强化效果的热处理参数的分析和研究的基础上,引入一种非淬火时效工艺,即在低于奥氏体化温度的某一温度进行等温时效,可以大幅度提高针状铁素体管线钢的强度级别.这种非淬火时效促进了微合金碳氮化物在铁素体区进一步沉淀析出.非淬火时效对针状铁素体管线钢强化是行之有效的,为针状铁素体管线钢的强度级别升级提供了新的途径.     

控轧控冷对高铌钢连续冷却相变的影响

通过Gleeble模拟一种高铌微合金管线钢控轧控冷过程,研究了其组织及相变特征和变形对相变过程的影响。由膨胀量变化分析及组织观察,建立了该钢的连续冷却相变CCT曲线。结果表明,铌元素及变形促进了针状铁素体的形成,采用两阶段控轧,当冷速由0.5℃/s增加到50℃/s时,组织由多边形铁素体、准多边形铁素体向针状铁素体转变,但冷速低于5℃/s时,组织转变对冷速变化较敏感,当冷速继续增加时,组织结构变化不明显,而基体中的M/A组元变得更细小、弥散。     

未再结晶区变形对X80级管线钢相变及组织的影响

通过Gleeble模拟双道次压缩变形后的连续冷却转变过程,研究了未再结晶区变形对X80级管线钢相变及组织的影响。试样在未再结晶区以不同变形量变形并以一定冷速冷却,记录冷却过程中膨胀量变化曲线,对试样进行微观组织观察和显微硬度测试。结果表明:在试验条件下,X80管线钢双道次变形后显微组织主要由针状铁素体和低碳贝氏体等构成;变形提高了试验钢相变温度,当变形量从0%增加到40%时,相变开始温度提高35℃;变形促进了针状铁素体转变,抑制了粗大粒状贝氏体组织形成,明显细化了组织;采用双道次控轧,在一定冷速及压下量配合下可获得以针状铁素体为主的组织。     

非调质CT80连续油管用钢的控轧控冷工艺

利用Gleeble-1500热模拟试验机进行了控轧控冷热模拟试验,分析了非调质CT80连续油管用钢的精轧变形温度、冷却速度和卷取温度对试验钢组织与性能的影响规律。基于控轧控冷热模拟试验结果,设定了试验钢实验室轧制工艺,在终轧温度830℃、冷却速度46℃/s和卷取温度450℃轧制工艺条件下,获得了具有针状铁素体+贝氏体+少量M/A岛组织构成的成品钢板,其屈服强度620 MPa,抗拉强度754 MPa,伸长率29.2%,屈强比0.82,各项性能均满足CT80连续油管用钢力学性能要求。     

变形温度对含Nb双相钢显微组织的影响

通过单道次压缩及连续冷却实验,研究了变形温度(810-720℃)对具有超细原始奥氏体晶粒的含Nb双相钢显微组织的影响.实验结果表明:实验钢最终组织为铁索体加马氏体的双相组织.压缩过程中,实验钢应力-应变曲线上出现峰值,且峰值应力随变形温度的降低先增大后减小;随着变形温度的降低,铁索体的含量先增大再减小,但增减幅度不大,在最低变形温度(720℃)时,铁素体品粒尺寸降低到2.8 μm,弥散分布于铁素体晶界上的马氏体含量达到22.7%;随着变形温度的增加,铁索体晶粒硬度减小,最低可降至230 GPa;EBSD取向分析显示,随着变形温度的降低,组织中小角度晶界增多.     

Optimization of flow stress in cool deformed Nb-microalloyed steel by combining strain induced transformation of retained austenite, cooling rate and heat treatment

In this study cool deformation was incorporated in the overall thermo-mechanical processing of a Nb-microalloyed steel. Included in this was the effect of cooling rate subsequent to hot rolling on precipitate formation in the ferrite phase. The results show that increasing the cooling rate prevents precipitate formation in the ferrite phase at the cool deformation temperature. As well, the amount of retained austenite under the low cooling condition in the temperature range of cool deformation, 700-300 °C, was measured by neutron diffraction. It is then shown that strain-induced transformation of retained austenite to martensite is the main factor in increasing the strength of cool deformed Nb microalloyed steel. Combining accelerated cooling, strain-induced transformation of austenite to martensite during cool deformation and a subsequent heat treatment stage to increase precipitation maximizes the flow stress of the steel. Finally, it is shown that this process also lowers the yield strength/ultimate strength ratio.     

Effects of Heat Treatment on Microstructure and Tensile Properties of a Fe-27Mn-12Al-0.8C Low-Density Steel

A low-density duplex steel of Fe-27Mn-12Al-0.8C (density 6.53 g/cm³) was directly quenched to room temperature and ordering treated at 500°C and 700°C after solution treatment. The heat-treated microstructures and corresponding room-temperature tensile properties were investigated. The κ phase precipitated in austenite in all the cases such that its size became coarser with increasing ordering temperature. Ferrite of the as-quenched steel consisted of the B2 domains and disordered ferrite with uniformly distributed nanosized D0₃ particles. Ferrite of the 700°C ordering steel exhibited basically identical features to the as-quenched steel, but with the coarser B2 domains, finer D0₃ particles, and less disordered ferrite. By contrast, the D0₃ domains were mainly observed in ferrite of the 500°C ordering steel. The yield strength of the 500°C ordering steel was higher than other two steels, which showed the similar yield strengths. The elongation of the as-quenched steel was higher than two ordering-treated steels. Deformation of austenite was manifested by the κ phase shearing by planar gliding dislocations. Intensive interactions of superdislocations were mainly observed in ferrite, depending on the type of the ordered phase. Factors influencing the strength and deformation behavior of the low-density duplex steel were discussed based on observation of deformed microstructure. Overall, the high-Mn/Al duplex steels with the ordered phases exhibit the high specific strength, the low density, and the moderate strain hardening that are suitable for the structural use requiring high strength and light weight.     

热输入对800 MPa级钢接头组织及性能的影响

系统研究了焊接热输入对新一代800MPa级高强度结构钢(RPC钢)焊接接头组织及力学性能的影响。研究结果表明，采用最新研制的超低碳贝氏体焊丝焊接800MPa级RPC钢获得了强韧性匹配良好的焊接接头；焊缝一次柱状品的宽度随热输入的增加而增大，焊缝金属二次组织中基本上消除了先共析铁素体和侧板条铁素体，组成焊缝的基本类型为板条贝氏体、针状铁素体和粒状贝氏体；随着热输入的增大，焊接接头的抗拉强度逐渐降低，而低温冲击韧度则先升高，然后又下降；在热输入为20kJ／cm时焊缝金属低温韧性出现峰值与焊缝获得细小密集的针状铁素体组织有关。     

工艺参数对Ti微合金化高强钢组织性能的影响

为实现高品质Ti微合金化高强钢的工业化生产,通过热模拟试验研究了加热温度、终轧温度、精轧阶段变形量、冷却速率和卷取温度对Ti微合金化高强钢组织性能的影响规律。结果表明,随着加热温度的升高,铁素体晶粒尺寸显著增大,试验钢硬度增大。随着终轧温度的降低和冷却速率的增大,铁素体晶粒尺寸逐渐减小,贝氏体含量增加,试验钢硬度增大。随着精轧阶段变形量的增大,铁素体含量增加,组织得到细化,细晶强化和相变强化共同作用的结果使得试验钢硬度逐渐降低。随着卷取温度的降低,试验钢的硬度先升高后降低,当卷取温度为610 ℃时,试验钢硬度最高。     

双相钢空蚀破坏的力学机制

对由铁素体和渗碳体组成的低、中、高碳钢进行振动空蚀实验,发现它们空蚀破坏的共同特点是铁素体的严重变形和破损.但由于铁素体的含量及分布形态不同,材料空蚀破坏的表现形式大不相同:铁素体含量高的低碳钢以大面积均匀塑性变形为主;铁素体含量与珠光体含量大致相等并呈网状分布的中碳(亚共析)钢是由于铁素体隆起脱落而破坏;以珠光体为主的高碳钢是由于铁素体从渗碳体的夹缝中向外挤出、两相分离而破坏.微射流冲击形成的应力波使低强度相屈服是造成上述破坏的原因.     

轧制工艺对460 MPa级低屈强比耐火耐候钢组织性能的影响

利用热模拟方法测定低屈强比耐火耐候钢不同速率冷却后的组织。对比轧后弛豫工艺与未弛豫工艺以及终冷温度对试验钢性能的影响,利用光学显微镜、扫描电镜、透射电镜分析不同工艺对钢轧后显微组织的影响。结果表明,随冷却速度的增加,钢板组织由多边形铁素体变为针状铁素体+粒状贝氏体复相组织;由于弛豫处理过程中过冷奥氏体部分转变为多边形铁素体,钢板屈服强度和屈强比均下降;随着终冷温度的降低,钢板的屈服强度和屈强比上升,与钢中针状铁素体的细化与M/A组元的弥散强化有关;轧后直接水冷,并控制终冷温度至500~560 ℃,可获得高强度与低屈强比的良好匹配。     

Effect of Ti on the microstructure and mechanical properties of MAG multipass weld metal

Metal active gas (MAG)welding has been carried out on microalloy controlled rolling steel (S355J2W)by two kinds of welding wires with different Ti content.The mechanical tests have been carried out on the welded joint.The optical microscope and scanning electron microscope (SEM)observations have been performed to investigate the effect of microalloy element Ti on the microstructure of weld metal and impact fracture,respectively.The microstructure of the MAG multipass weld metal includes the columnar grain zone (CGZ)consisting of primary ferrite (PF),ferrite with second phase (FS)and acicular ferrite (AF),and the fine grain zone (FGZ)consisting of polygonal ferrite due to the heat effect of subsequent welding pass.It has been found that the small amount of Ti can significantly increase the impact energy of the weld metal at low temperature and weakly affect tensile strength of welded joint.By adding small amount of Ti,the inclusions have changed from Mn-Si-O inclusions to Ti-bearing inclusions,which causes the Mn-depleted zones (MDZs)much larger and is beneficial to the impact energy by promoting the AF formation,refining the PF and pinning the austenite grain boundary during the subsequent transformation process.     

Cr-Mo-Nb-Ti-B系1180 MPa级复相钢的性能稳定性

设计开发了Cr-Mo-Nb-Ti-B系1180 MPa级高强复相钢产品。从组织控制的角度引入了贝氏体,以弥补铁素体与马氏体之间的软硬相高强度差,采用Gleeble-3500热模拟试验机、拉伸试验机和光学显微镜研究连续退火工艺中均热温度和过时效温度对复相钢力学性能及组织的影响规律。结果表明,均热温度在720~840 ℃时,随着温度的升高,贝氏体和马氏体含量逐渐增加,抗拉强度和屈服强度整体上不断提升,但超过840 ℃后抗拉和屈服强度降低。而随过时效温度的升高,抗拉强度呈单调递减趋势,屈服强度先波动后逐渐降低。当均热温度为790 ℃、过时效温度为280 ℃时,连退板的组织为铁素体、贝氏体和马氏体的复相组织,复相钢具备良好的加工成形性,折弯性、扩孔性能也均较同级别双相钢产品有大幅提升。     

Effect of alloying elements and coiling temperature on the recrystallization behavior and the bainitic transformation in TRIP steels

The effects of alloying elements and coiling temperature on recrystallization behavior and bainitic transformation were investigated based on 0.07C-Mn-Cr-Nb steel with a low carbon equivalent. Based on the ferrite recrystallization behavior, the proper intercritical annealing temperature of all studied steels was suggested to produce TRIP steel with good strength and elongation balance. All steels coiled at 550 °C showed much faster ferrite recrystallization behavior than steels coiled at 700 °C. In addition to the coiling temperature, the effect of increasing carbon content on the ferrite recrystallization was minor at a coiling temperature of 550 °C, but much more prominent at a coiling temperature of 700 °C. The highest Mo added steel showed the best strength and elongation balance, and the highest carbon and Mo added steel showed the highest tensile strength at a coiling temperature of 550 °C. The steel containing a higher amount of elemental Al (0.7 wt.% Al) exhibited much better elongation than the lower Al added steel (0.04 wt.% Al) in TS 780 MPa grade, about 24 % and 19 %, respectively.