Microstructure and Precipitation Behavior in HAZ of V and Ti Microalloyed Steel

Three steels containing 0. 05%C-0. 1%V-0. 01%N (steel V-LN), 0. 05%C-0. 1%V-0. 02%N (steel V-HN), and 0. 05%C-0. 1%V-0. 02%N-0. 01%Ti (steel V-HN-Ti), which were all essentially vanadium microalloyed steels, were subjected to simulating the microstructure of a coarse grained heat affected zone (CGHAZ). The process involved reheating to 1 350 °C, rapid cooling to room temperature, and varying the welding heat input from 15 kj/cm to 54 kj/cm, including four cooling rates of t_8/5 equal to 7. 5 s, 20 s, 40 s, 100 s, and the relationship of heat input to tg/_s was calculated by Quiksim software. The microstructure and precipitation of vanadium and titanium carbon nitrides are studied. The results indicate that the microstructure consists of granular bainite and some side plate ferrite in the grain boundary when the steels are produced with the highest heat input. As the heat input decreased, numerous polygonal ferrites and grain boundary ferrites appeared, and the size apparently increased. When the steel contained high nitrogen, it was considerably easier to form martensite-austenite island, which was even worse for the toughness and other properties of the steel. For the limitation of cooling time, vanadium carbon nitrides could not precipitate sufficiently, but as titanium was added, the unmelted or precipitated TiN on cooling absorbed some fraction of nitrogen in the matrix and made more precipitate positions for the round V(C, N), and thus several useful round particles could be seen in titanium-contained steel, and most of them were around TiN. By this experiment, we can conclude that with the help of titanium, nitrogen-enhanced steel had a better prior austenite grain size, was considerably easier to precipitate, reduced free nitrogen in the matrix effectively, and provided a very effective mechanism for restriction grain growth in the HAZ.     

超低碳微合金X100管线钢CO2焊焊接接头的组织和性能

 采用CO2焊接方法焊接X100管线钢,分析了不同焊接工艺下焊接接头组织和性能的变化特征。随着焊接热输入的增加,焊接接头的屈服强度和抗拉强度降低,焊缝和热影响区处的冲击吸收功呈现先增大后减小的变化趋势,而焊缝组织均以针状铁素体（AF）为主。焊接热输入为1.17 kJ/mm时,粗晶区的显微组织主要是贝氏体铁素体（BF）,强韧匹配性最为优异;当热输入增加至1.91 kJ/mm时,粗晶区的组织除了BF外,还出现了粒状贝氏体（GB）,强韧水平明显降低。综合考虑,可将1.17 kJ/mm作为X100管线钢CO2焊接时的最佳热输入。     

Effects of Nb and V on Microstructural Evolution,Precipitation Behavior and Tensile Properties in Hot-rolled Mo-bearing Steel

Microstructural evolution,precipitation behavior,and tensile properties of four experimental Mo-bearing steels were studied to elucidate the effects of Nb and V on microstructural properties.The results indicated that the microstructure of hot-rolled steels consisted of polygonal ferrite and degenerate pearlite,and the morphology remained same after holding at 600 ℃for 1h.The smallest grain size was obtained in Nb-V-Mo containing steel,followed by Nb-Mo and V-Mo steels.Precipitation was less in the hot-rolled Mo-bearing steel.The maximum volume fraction of precipitates was obtained in Nb-V-Mo bearing steel,and the Nb-V-Mo complex carbonitrides were highly stable at 600℃.In the Mo-bearing steel,the yield ratio was lowest at room temperature but highest at 600℃,which was attributed to the precipitation of Mo carbides and drag effect of Mo solute on dislocation movement.     

Characteristics of Precipitation in an As-cast Nb-and V-containing High Nitrogen CrMn Austenitic Steel

The phase diagram of an Nb- and V-containing 18Mnl8Cr0.5N steel was investigated using thermodynam ic calculation. The compositions and characteristics of precipitates were investigated by scanning electron microsco- py, energy dispersive spectrometry, X-ray diffraction, and differential scanning calorimetry. Under equilibrium con- ditions, MX precipitates at 1 350 ℃. MX is a substitutional solid solution of Nb4 N3.38, and its composition （at. %） is approximately.. Nb 40, N 40, V 8, and Fe, Cr, and Mn balance. The precipitates, with shapes including irregular bulk, rod, and ellipsoid, are primarily distributed at grain boundaries and triple junctions, and their size is approxi- mately 5 10 μm. Finally, the microalloying of high nitrogen CrMn austenite steels, control of precipitate size, and the effect of precipitate on hot formin~ were discussed.     

超低碳贝氏体钢HAZ组织、性能及硼分布

用Gleeble-1500热模拟机对Cu-Nb-B系超低碳贝氏体钢进行不同焊接工艺下热模拟试验,选定峰值温度为1340℃,高温停留0.5s,t₈₅,分别取30,45,60s.研究了焊接热影响区(HAZ)组织、性能和硼的分布.结果表明:此类钢在不同焊接条件下,焊接热影响区均具有较好的低温韧性和较低的韧脆转变温度.进一步探讨了不同t₈₅;对钢中贝氏体组织组成及形态的影响,以及组织和低温韧性的关系.用径这显微照相技术(PTA)显示了硼在热影响区的行为.     

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.     

铌与钛对铁素体不锈钢析出和成形性的影响

研究了铌、钛对铁素体不锈钢析出相、织构和成形性的影响。结果显示:添加铌、钛后的析出相主要是TiN和(Nb,Ti)C,其析出尺寸分别为4μm和200 nm;同时,铌、钛的添加抑制了冷轧薄板α纤维织构的生长,促进了γ纤维织构强度的增加。添加稳定化元素铌、钛后,冷轧薄板的平均r值由1.05增加到1.46,起皱高度也由29.1μm下降到18.9μm,薄板成形性能的改善同再结晶织构的变化密切相关。     

Al、Ti处理对低合金钢焊接粗晶区组织的影响

研究了Al、Ti处理对低合金钢焊接粗晶区组织的影响.研究发现:用Al处理时,钢中形成的夹杂物为Al的氧化物和细小的TiN.Al的氧化物和TiN不能促进晶内铁素体的形成,焊接粗晶区主要由粗大的晶界铁素体和平行排列的侧板条铁素体组成.用Ti处理时,钢中形成大量的Al、Ti、Mg、Ca复合氧化物夹杂,其颗粒大小为0.5～3.0 μm,同时还有一定量细小的Ti的氮化物.复合Ti的氧化物具有促进晶内针状铁素体形核的能力,焊接粗晶区主要由晶界铁素体、少量的侧板条铁素体和大量的晶内针状铁素体组成.随焊接热循环高温保温时间增长,晶界铁素体粗大,侧板条铁素体数量减少.相变区的冷却速度减慢,晶界铁素体数量增多,针状铁素体的尺寸显著增大.     

Effect of Thermal Cycle on Microstructure and Fracture Morphology in HAZ of HQ130 Steel

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Microstructure Evolution and Precipitation Behavior of 0Cr16Ni5Mo Martensitic Stainless Steel during Tempering Process

The microstructure,morphology of precipitates and retained austenite and the volume fraction of retained austenite in 0Cr16Ni5 Mo stainless steel during the tempering process were analyzed using optical microscope(OM),transmission electron microscope(TEM),X-ray diffraction(XRD)and scanning transmission electron microscope(STEM).The results show that the microstructure of the tempered steel is mainly composed of tempered martensite,retained austenite,and delta ferrite.In the case of samples tempered from 500 to 700 ℃,the precipitates are mainly M_(23)C_6,which precipitate along the lath martensite boundaries.The precipitate content increases with the tempering temperature.During the tempering process,the content of retained austenite initially increases and then decreases,the maximum content of retained austenite being 29 vol.% upon tempering at 600 ℃.TEM analysis of the tested steel reveals two morphology types of retained austenite.One is thin film-like retained austenite that exists along the martensite lath boundary.The other is blocky austenite located on packet at the boundary and the original austenite grain boundary.To further understand the stability of reversed austenite,the Ni content in reversed austenite was measured using STEM.Results show a significant difference in nickel concentrations between reversed austenite and martensite.     

(Ti,V)C钢结硬质合金的烧结行为、物相及组织结构

以钛粉、钒铁粉、碳粉、铬铁粉、钼铁粉和铁粉为原料,用原位烧结法制备了(Ti,V)C钢结硬质合金.利用XRD、SEM和EDS对相组成、组织结构和微区成分进行了分析.结果表明:最佳烧结时间是1 h;烧结温度影响致密化程度,(Ti,V)C钢结硬质合金的最佳烧结温度是1 400 ℃;TiC钢结硬质合金的最佳烧结温度是1 420 ℃.(Ti,V)C钢结硬质合金的主要相组成为α-Fe、Fe3C、(Cr,Fe)7C3、(Ti,V)C.与TiC硬质相颗粒相比,(Ti,V)C颗粒形态更加圆整.     

V和Nb对12％Cr铁索体钢微观组织和蠕变特性的影响

利用光学显微镜和透射电子显微镜以及光电子能谱分析方法,研究了元素V和Nb对12％Cr铁素体耐热钢的微观组织和析出相的形态和分布的影响.结果表明:添加V和Nb的铁素体钢具有更窄的马氏体板条组织;附于MX型碳氮化物生长的M23C6碳化物呈细小的针状或短棒状析出,而单独析出的M23 C6尺寸较大,呈椭圆形.这些组织上的优化和MX型碳氮化物的弥散析出有效抑制了回火马氏体组织的回复和再结晶,提高了铁素体钢的蠕变抗力.     

Effect of Inclusions Containing Ti,Mg on Microstructure and Performance of HAZ in Low Carbon Steel

In order to study the effects of inclusions containing titanium,zirconium and magnesium on the impact toughness of heat affected zone (HAZ) of steel,two low carbon steels deoxidized by titanium,zirconium and magnesium were obtained.After some treatments,the inclusion characteristics (size,morphology and chemistry) analysis,Charpy-type test,microstructure and the fracture observation were carried out on the prepared specimens.The following results were found.The inclusions containing Mg can keep more stable in HAZ.The inclusion containing Mg can enhance the impact toughness of HAZ,and the impacting energy reaches 249J at 253K when simulated input energy is 150kJ/mm.The inclusions with diameter smaller than 1.5 μm play a key role of pinning effect.     

STE355钢模拟焊接热影响区的组织与性能

采用模拟焊接热循环的方法，研究了单次热循环和多次热循环时，Ｔｍａｘ和ｔ８／５对ＳＴＥ３５５钢热影响区组织和性能的影响，为制定最佳焊接工艺参数提供依据。     

12%Cr铁素体不锈钢焊接接头组织及韧性研究

对四种不同成分的12%Cr铁素体不锈钢做了焊接性试验。分析焊接接头的组织,测量了焊接接头的低温冲击功。试验结果表明,随着碳含量的增加,焊接粗晶区组织由单相铁素体逐渐转变成以马氏体为主,粗晶区宽度变窄,晶粒尺寸变小。细晶区组织以马氏体为主,组织细小均匀。熔合线处和热影响区的低温冲击功相比母材均显著降低。断裂路径分析结果表明,窄的粗晶区宽度和小的晶粒尺寸使断裂路径经过更多的奥氏体焊缝区,提高了整体的冲击韧性。     

Rapid Solidification Microstructure and Carbide Precipitation Behavior in Electron Beam Melted High-Speed Steel

Metallurgical and Materials Transactions A - The solidified microstructure and carbide precipitation behavior in an S390 high-speed steel processed by electron beam melting (EBM) have been fully...     

超低碳贝氏体钢焊接热影响区冲击韧性的研究

用Ｇｌｅｅｂｌｅ－１５００热模拟机对含铜超低碳贝氏体钢进行不同焊接工艺下热模拟试验。研究了焊接热影响区的组织、性能。探讨了不同ｔｓ／５对钢中贝氏体组织组成及形态的影响以及组织与低温韧性的关系。用径迹显微照相技术（ＰＴＡ）显示了硼在热影响区的行为。结果表明：在不同焊接条件下，此类钢焊接热影响区均具有较好的低温韧性和较低的韧脆转变温度。当以中等速率冷却时，高温时生成的一定量的粒状贝氏体可有效地分割奥氏     

铝、钛复合脱氧钢凝固过程中氧化物的析出行为

促进细小弥散氧化物粒子的析出是提高焊接热影响区韧性的有效手段。通过Al-Ti-O热力学计算,从理论上分析了铝、钛复合脱氧凝固过程中氧化物的析出规律,提出了Ti2O3在凝固前沿形成的热力学条件。试验结果表明,重点对铝、钛加入量和过程氧活度进行控制,可以得到细小的Ti2O3及其复合析出物粒子。对析出物的形貌、尺寸和分布进行...     

Ti在热轧钢板中沉淀强化行为的试验研究

研究了低C-低Mn—Ti钢中Ti的沉淀相在加热过程中的变化规律。在传统的加热温度区间内,Ti在奥氏体中的最大固溶度约为0．14％,而TiN、Ti2S回溶量很小。在580℃卷取时,Ti的析出相尺度在5nm以下,有很好的强化作用,Ti的析出相尺度及形态变化,对强化作用有较大影响。