显微组织对X80管线钢力学性能的影响

利用光学显微镜研究了20 mm厚度X80管线钢显微组织类型对强韧性的影响。结果表明:显微组织为针状铁素体和少量的粒状贝氏体时,钢的屈服强度达到512MPa;针状铁素体的晶粒细化、粒状贝氏体和板条贝氏体可以使X80管线钢具有更高的屈服强度,达到600MPa。细小而均匀的粒状贝氏体可以获得良好的冲击韧性。掺杂在一起的细小的针状铁素体、准多边形铁素体、粒状贝氏体促使裂纹扩展路径曲折,改善冲击韧性。     

含Nb-Ti低碳钢的析出与细晶强化效应研究

采用控轧控冷(TMCP)工艺制备的0.013%Nb-0.013%Ti钢和C-Mn钢性能对比显示,添加微量Nb-Ti明显提高了钢的强度和冲击韧性,原因是微量Nb-Ti细化了铁素体晶粒并得到更高体积分数的弥散分布(Nb,Ti)(C,N)析出颗粒。用Hall-Petch晶粒尺寸强化和Ashby-Orowan弥散强化模型计算铁素体晶粒尺寸、析出颗粒尺寸和体积分数等微观组织变量对强度的量化贡献,结果表明,Nb-Ti钢的主要强化机理为细晶强化和弥散强化,而降低韧脆转变温度的主要机理是晶粒细化和微合金碳氮化物析出降低了钢中的自由氮含量。     

终锻温度和变形量对贝氏体型非调质钢强韧性的影响

 用JB 30冲击试验机、MTS材料试验机和OM等试验方法分析了两种终锻温度（820 ℃和950 ℃）和三种变形量(3、4、6,锻造变形前后工件截面积的比值)条件下,贝氏体型非调质钢强韧性的变化及其微观组织的区别。研究结果表明：终锻温度和变形量对贝氏体型非调质钢强韧性的主要影响可以从铁素体含量、原始奥氏体晶粒和贝氏体束尺寸等因素来考虑。终锻温度降低、变形量增大、原始奥氏体晶粒尺寸减小导致贝氏体束尺寸减小,硬度、强度和冲击韧性增加;而当终锻温度为820 ℃和变形量为6时,由于变形诱导铁素体相变,铁素体体积分数达到10%,强度和硬度明显降低。     

基于应变设计用X80大应变UOE钢管的研发

在地质灾害多发地区,基于应变的管道设计对管线管提出了大应变的性能要求。通过实验室研究了不同组织类型对管线钢大应变性能的影响,发现多边形铁素体+贝氏体的组织具有很好的大应变性能和其他性能的匹配。更进一步研究了双相比例、组织形态等对大应变性能的具体影响,以及轧钢工艺参数对双相组织的影响。基于该组织设计及实验室研究,宝钢进行了Ф 1 219×26.4 mm厚壁X80大应变UOE管线管的试生产。试制钢管性能良好,能够满足西三线X80大应变管线管的技术要求。     

钒对高氮钢形变诱导相变的影响

通过实验室模拟试验,研究了高氮钒钢的金相组织和形变诱导铁素体体积分数,分析了钒对高氮钒钢变形诱导相变的影响.试验结果表明,钒的加入促进了形变诱导铁素体相变,细化了铁素体晶粒,提高了形变诱导铁素体体积分数.     

表层细晶化Q235中厚板轧制工艺的研究

采用Q235成分的连铸板坯，在首钢中厚板厂3300mm轧机上进行了中板表层组织细晶化的工业轧制实验，研究了轧制温度、轧制变形量分配、待温期间冷却方式对板材组织和性能的影响。结果表明，在奥氏体低温区增加精轧总变形量可以实现20mm成品板材的表层组织细化，屈服强度达到300MPa左右，铁素体晶粒达到8．5级，增加待温期间中间坯的水幕冷却有利于整个板材厚度截面的组织细化，屈服强度达到330MPa左右，铁素体晶粒达到9级，材料的强度接近Q345同规格板材的水平，具有优良的塑性和冲击韧性。     

含磷中碳钢力学性能的研究

研究了不同磷含量及晶粒度对中碳钢力学性能的影响,着重对屈服强度、冲击韧性及韧脆性转变温度的影响进行研究。研究结果表明,磷固溶于铁素体后显著地提高钢的强度;磷易偏聚在铁素体晶界,提高钢的韧脆性转变温度,且晶粒越粗大偏聚度越大。细化晶粒能减轻磷在晶界的偏聚程度,从而提高钢材强度、冲击韧性,且降低韧脆性转变温度。因此细化晶粒可有效地弥补含磷钢的韧性损失。     

Cr-Nb-Cu系X80HD2大应变管线钢冷却转变规律研究

研究26.4 mm厚度X80HD2大应变管线钢在未变形和变形条件下的连续冷却转变行为。通过Gleeble-2000热模拟试验机与光学显微镜(OM)、扫描电镜(SEM)、透射电子显微镜(TEM)等相结合的方法,测定未变形和变形奥氏体的连续冷却转变曲线,并对不同冷速和变形条件下的组织进行观察分析。结果表明:冷速较低时,均得到以粒状贝氏体为主的多相组织,高冷速下得到以板条贝氏体为主的多相组织;Cr、Cu等元素能够增强过冷奥氏体稳定性,抑制先共析铁素体的形成,扩大贝氏体的形成区间;第二相粒子析出强化,晶粒细化、组织类型及比例的变化是显微硬度随冷却速度增大的主要原因。     

抗大变形X70管线钢显微组织分析

利用金相显微镜、扫描电镜对试生产的抗大变形X70管线钢显微组织和夹杂物分布进行了观察和分析,并用能谱议对夹杂物进行了定性分析。结果表明,试生产的X70抗大变形管线钢组织为铁素体+贝氏体双相组织。板厚1/4处的铁素体体积分数为35%。钢中夹杂物较细小,在钢中弥散分布。夹杂物较软,主要含元素硫、钙和氧。     

超快冷工艺对X70管线钢组织的影响

通过热模拟机研究超快冷工艺中冷却速率和终轧温度对X70管线钢组织细化及马氏体/奥氏体小岛的影响.随着冷却速率的增大,铁素体晶粒尺寸减小,M/A岛的体积分数先增大后降低,M/A岛的尺寸变化则相反.提高终轧温度,铁素体晶粒尺寸略微增大,M/A岛的体积分数增加;但在900~940℃范围内,随着终轧温度的升高,试样中M/A岛的体积分数略减小,尺寸增大.      

Effects of Cooling Conditions on Tensile and Charpy Impact Properties of API X80 Linepipe Steels

In this study, four API X80 linepipe steel specimens were fabricated by varying the cooling rate and finish cooling temperature, and their microstructures and crystallographic orientations were analyzed to investigate the effects of the cooling conditions on the tensile and Charpy impact properties. All the specimens consisted of acicular ferrite (AF), granular bainite (GB), and martensite-austenite (MA) constituents. The volume fraction of MA increased with an increasing cooling rate, and the volume fraction and size of MA tended to decrease with an increasing finish cooling temperature. According to the crystallographic orientation analysis data, the effective grain size and unit crack path decreased as fine ACs having a large amount of high-angle grain boundaries were homogeneously formed, thereby leading to the improvement in the Charpy impact properties. The specimen fabricated with the higher cooling rate and lower finish cooling temperature had the highest upper-shelf energy (USE) and the lowest energy transition temperature (ETT), because it contained a large amount of MA homogeneously distributed inside fine AFs, while its tensile properties remained excellent.     

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。     

Effects of Cooling Conditions on Microstructure, Tensile Properties, and Charpy Impact Toughness of Low-Carbon High-Strength Bainitic Steels

In this study, four low-carbon high-strength bainitic steel specimens were fabricated by varying finish cooling temperatures and cooling rates, and their tensile and Charpy impact properties were investigated. All the bainitic steel specimens consisted of acicular ferrite, granular bainite, bainitic ferrite, and martensite-austenite constituents. The specimens fabricated with higher finish cooling temperature had a lower volume fraction of martensite-austenite constituent than the specimens fabricated with lower finish cooling temperature. The fast-cooled specimens had twice the volume fraction of bainitic ferrite and consequently higher yield and tensile strengths than the slow-cooled specimens. The energy transition temperature tended to increase with increasing effective grain size or with increasing volume fraction of granular bainite. The fast-cooled specimen fabricated with high finish cooling temperature and fast cooling rate showed the lowest energy transition temperature among the four specimens because of the lowest content of coarse granular bainite. These findings indicated that Charpy impact properties as well as strength could be improved by suppressing the formation of granular bainite, despite the presence of some hard microstructural constituents such as bainitic ferrite and martensite-austenite.     

Effects of Start and Finish Cooling Temperatures on Microstructure and Mechanical Properties of Low-Carbon High-Strength and Low-Yield Ratio Bainitic Steels

The effects of start and finish cooling temperatures on microstructure and mechanical properties of low-carbon high-strength and low-yield ratio bainitic steels were investigated in this study. Four kinds of low-carbon high-strength and low-yield ratio bainitic steels were fabricated by varying the start and finish cooling temperatures and cooling rates, and their microstructure and mechanical properties such as tensile and Charpy impact properties were measured. In the steels cooled down from the high start cooling temperature above Ar₁ [978 K (705 °C)], the volume fraction of acicular ferrite is lower than in the steels cooled down from the low start cooling temperature below Ar₁ [978 K (705 °C)]. The finish cooling temperatures and cooling rates affect the formation of bainitic ferrite, granular bainite, and martensite–austenite (MA) constituents. According to the correlation between microstructure and mechanical properties, the tensile strength increases with increasing the volume fractions of bainitic ferrite and MA constituents, whereas the elongation decreases. The yield ratio decreases as the volume fraction of MA constituents increases. Charpy impact absorbed energy is proportional to the volume fraction of acicular ferrite, and is inversely proportional to the volume fraction of granular bainite.     

φ1219×12．7mm X52MS耐蚀焊管的开发

主要介绍抗HIC及抗SSC耐蚀用X52MS管线管在宝钢UOE生产线的开发。通过化学成分合理设计与冶炼工艺要点控制,并采用TMCP（控制轧制＋ACC）厚板轧制工艺,设置合理的UOE焊管成型、焊接、扩径等工艺参数,成功开发出了X52MS φ1219×12．7mm耐蚀焊管,其力学性能及抗HIC、SSC性能优良,较好地满足了用户的使用条件。     

MULPIC冷却装置在品种钢研发中的生产实践

 舞钢新宽厚板生产线MULIPIC在线快冷装备具有高冷却速度等技术特点,结合控制轧制和在线快冷装备对船板、管线钢进行了开发研究,采用直接淬火工艺研究开发了高强工程机械用钢。结果表明： 60 mm厚度E36级TMCP船板钢,组织全部为铁素体＋珠光体,晶粒度10级以上,－40 ℃夏比横向冲击功在183 J以上;X70管线钢的组织为针状铁素体,力学性能合格率达98％;利用直接淬火（DQ）和离线回火工艺,生产出30 mm厚的WQ960D调质钢,屈服强度达到960 MPa,抗拉强度1030 MPa,－20 ℃纵向冲击功在43 J以上。     

Effects of Oxides on Tensile and Charpy Impact Properties and Fracture Toughness in Heat Affected Zones of Oxide-Containing API X80 Linepipe Steels

This study is concerned with effects of complex oxides on acicular ferrite (AF) formation, tensile and Charpy impact properties, and fracture toughness in heat affected zones (HAZs) of oxide-containing API X80 linepipe steels. Three steels were fabricated by adding Mg and O₂ to form oxides, and various HAZ microstructures were obtained by conducting HAZ simulation tests under different heat inputs. The no. of oxides increased with increasing amount of Mg and O₂, while the volume fraction of AF present in the steel HAZs increased with increasing the no. of oxides. The strengths of the HAZ specimens were generally higher than those of the base metals because of the formation of hard microstructures of bainitic ferrite and granular bainite. When the total Charpy absorbed energy was divided into the fracture initiation and propagation energies, the fracture initiation energy was maintained constant at about 75 J at room temperature, irrespective of volume fraction of AF. The fracture propagation energy rapidly increased from 75 to 150 J and saturated when the volume fraction of AF exceeded 30 pct. At 253 K (?20 °C), the total absorbed energy increased with increasing volume fraction of AF, as the cleavage fracture was changed to the ductile fracture when the volume fraction of AF exceeded 45 pct. Thus, 45 vol pct of AF at least was needed to improve the Charpy impact energy, which could be achieved by forming a no. of oxides. The fracture toughness increased with increasing the no. of oxides because of the increased volume fraction of AF formed around oxides. The fracture toughness did not show a visible correlation with the Charpy absorbed energy at room temperature, because toughness properties obtained from these two toughness testing methods had different significations in view of fracture mechanics.     

Effective grain size and charpy impact properties of high-toughness X70 pipeline steels

The correlation of microstructure and Charpy V-notch (CVN) impact properties of a high-toughness API X70 pipeline steel was investigated in this study. Six kinds of steel were fabricated by varying the hot-rolling conditions, and their microstructures, effective grain sizes, and CVN impact properties were analyzed. The CVN impact test results indicated that the steels rolled in the single-phase region had higher upper-shelf energies (USEs) and lower energy-transition temperatures (ETTs) than the steels rolled in the two-phase region because their microstructures were composed of acicular ferrite (AF) and fine polygonal ferrite (PF). The decreased ETT in the steels rolled in the single-phase region could be explained by the decrease in the overall effective grain size due to the presence of AF having a smaller effective grain size. On the other hand, the absorbed energy of the steels rolled in the two-phase region was considerably lower because a large amount of dislocations were generated inside PFs during rolling. It was further decreased when coarse martensite or cementite was formed during the cooling process.     

Effects of Strain Rate and Test Temperature on Torsional Deformation Behavior of API X70 and X80 Linepipe Steels

This study aimed at investigating effects of strain rate and test temperature on deformation and fracture behavior of three API X70 and X80 linepipe steels fabricated by varying alloying elements and hot-rolling conditions. Quasi-static and dynamic torsional tests were conducted on these steels having different grain sizes and volume fractions of acicular ferrite and polygonal ferrite, using a torsional Kolsky bar, and then the test data were compared via microstructures, tensile properties, and adiabatic shear band formation. The dynamic torsional test results indicated that the steels rolled in the single-phase region had the higher maximum shear stress than the steel rolled in the two-phase region, because their microstructures were composed mainly of acicular ferrites. Particularly in the API X80 steel rolled in the single-phase region, increased dynamic torsional properties could be explained by the decrease in the overall effective grain size due to the presence of acicular ferrite having smaller effective grain size. The possibility of the adiabatic shear band formation at low temperatures was also analyzed by the energy required for void initiation and difference in effective grain size.