Relationship between microstructure and hydrogen induced cracking behavior in a low alloy pipeline steel

Hydrogen induced cracking(HIC) behaviors of a high strength pipeline steel with three different microstructures, granular bainite lath bainite(GB + LB), granular bainite acicular ferrite(GB + AF), and quasi-polygonal ferrite(QF), were studied by using corrosion experiment based on standard NACE TM0284. The HIC experiment was conducted in hydrogen sulfide(H_2S)-saturated solution. The experimental results show that the steel with GB + AF and QF microstructure present excellent corrosion resistance to HIC, whereas the phases of bainite lath and martensite/austenite in LB + GB microstructure are responsible for poor corrosion resistance. Compared with ferrite phase, the bainite microstructure exhibits higher strength and crack susceptibility of HIC. The AF + GB microstructure is believed to have the best combination of mechanical properties and resistance to HIC among the designed steels.     

不同热处理制度下激光增材制造12CrNi2钢组织研究

采用激光增材制造技术制备12CrNi2合金钢核电应急柴油机凸轮轴可以明显降低产品研发周期,优化产品结构.本研究采用光学显微镜(OM)、扫描电子显微镜(SEM)、X射线衍射仪(XRD)和电子万能试验机对激光增材制造12CrNi2合金钢热处理前后的组织和力学性能进行了研究.微观组织观察发现,试样存在带状特征和柱状晶形貌,圆弧带间为致密的冶金结合,顶部由于无后一道的重熔热作用,柱状晶形貌十分显著.沉积态组织主要由铁素体组成,试样不同部位的铁素体形貌存在一定的差异.经退火处理后,铁素体边界出现大量白色粒状析出物,延伸率显著提高,达到22.9%.经淬火及不同温度回火处理后,带状特征和柱状晶形貌消除,得到马氏体及其回火组织,抗拉强度达到1 000 MPa.与沉积态抗拉强度831 MPa相比,热处理态试样的抗拉强度显著提高.经固溶时效处理后,晶粒明显粗化.     

Microstructures and Toughness of Weld Metai of Ultrafine Grained Ferritic Steel by Laser Welding

3 mm thick 400 MPa grade ultrafine grained ferritic steel plates were bead-on-plate welded by CO2 laser with heat input of 120-480 J/mm. The microstructures of the weld metal mainly consist of bainite, which form is lower bainite plates or polygonal ferrite containing quantities of dispersed cementite particles, mixed with a few of low carbon martensite laths or ferrite, depending on the heat input. The hardness and the tensile strength of the weld metal are higher than those of the base metal, and monotonously increase as the heat input decreases. No softened zone exists in heat affected zone (HAZ). Compared with the base metal, although the grains of laser weld are much larger, the toughness of the weld metal is higher within a large range of heat input. Furthermore, as the heat input increases, the toughness of the weld metal rises to a maximum value, at which point the percentage of lower bainite is the highest, and then drops.     

Microstructures and Toughness of Weld Metal of Ultrafine Grained Ferritic Steel by Laser Welding

3 mm thick 400 MPa grade ultrafine grained ferritic steel plates were bead-on-plate welded by CO2 laser with heat input of 120～480 J/mm. The microstructures of the weld metal mainly consist of bainite, which form is lower bainite plates or polygonal ferrite containing quantities of dispersed cementite particles, mixed with a few of low carbon martensite laths or ferrite, depending on the heat input. The hardness and the tensile strength of the weld metal are higher than those of the base metal, and monotonously increase as the heat input decreases. No softened zone exists inheat affected zone (HAZ). Compared with the base metal, although the grains of laser weld are much larger, the toughness of the weld metal is higher within a large range of heat input. Furthermore, as the heat input increases, the toughness of the weld metal rises to a maximum value, at which point the percentage of lower bainite is the highest, and then drops.     

Effect of intercritical temperature on the strain hardening of dual-phase bainite/ferrite steel

Medium-carbon dual-phase bainite/ferrite steels with different bainite and carbide volume fractions were prepared via intercritical annealing and austempering. Bainite dominated the microstructure at high intercritical temperatures, and carbides and ferrite phase dominated at low temperatures. Carbides existed in two types, undissolved alloy–cementite and vanadium carbide. The ferrite grain size was reduced to 1.22?±?0.7 µm at 790°C. Modified Crussard–Jaoul (MC–J) model was used to analyse the strain hardening process, and the highest strain hardening rate was obtained at 755°C. The high carbide fraction at 755°C increased the ferrite dislocation density and enhanced the ferrite phase strength. The high dislocation density in ferrite and the small strength difference in bainite and ferrite enhanced the strain hardening rate at 755°C.     

Strengthening behavior analysis of weld metal of laser hybrid welding for microalloyed steel

The weld metal with high strength and good toughness was obtained for medium thickness microalloyed steel by using high power laser hybrid welding technology. Mechanical properties of weld metal were evaluated by using room temperature tensile test and low temperature three-side Charpy V-notch (CVN) impact test. The results show that the yield strength and ultimate tensile strength of weld metal are up to 713 MPa and 918 MPa, respectively. Both of them are almost 1.5 times higher than those of base metal. Under the strict three sides CVN condition, the −40 °C low temperature impact absorbed energy is up to 32 J and also higher than that of base metal. Weld metal predominately consists of granular bainite and carbon-free bainite. Both of them mainly contain lath morphology bainitic ferrite. The lath morphology bainitic ferrite with fine grain size plays an important role in higher strength. Dispersive carbide and high density dislocation are found in strengthening weld metal.     

淬火冷却速率对海洋平台用Ni-Cr-Mo-B钢性能的影响

使用热膨胀仪、SEM电镜、EBSD、硬度、拉伸和冲击等观察和检测手段,研究了淬火冷却速率对海洋平台用Ni-Cr-Mo-B钢的显微组织、有效晶粒尺寸(EGS)和力学性能的影响。结果表明,不同冷却速率的合金钢,其显微组织包括板条马氏体(LM)、板条贝氏体(LB)、粒状贝氏体(GB)和F(铁素体)。随着淬火冷却速率的降低合金钢的显微组织分别为LM(>20℃/s)、LM/LB(20~2℃/s)、LB(2~1℃/s)、LB/GB(1~0.2℃/s)、GB/F(0.2~0.02℃/s),其硬度由100℃/s时的393HV逐渐降低至0.02℃/s时的291HV。回火后合金钢的屈服强度由水冷的836 MPa降低至炉冷的726 MPa,而延伸率几乎不变,约为20%。油冷合金钢的-60℃冲击功最高(199 J),水冷次之(54 J),空冷和炉冷合金钢的最低(<30 J)。其原因是,油冷合金钢具有LM_T/LB_T混合组织,较小的EGS (1.6 μm)对解理裂纹的阻碍作用较强;而空冷、炉冷合金钢的组织分别为GB_T/LB_T、GB_T/F,其EGS较大(分别为2.4和2.8 μm),对解理裂纹的阻碍作用较弱。     

Cooling process and mechanical properties design of hot-rolled low carbon high strength microalloyed steel for automotive wheel usage

For the purpose of developing Nb–V–Ti microalloyed, hot rolled, high strength automotive steel for usage in heavy-duty truck wheel-discs and wheel-rims, appropriate cooling processes were designed, and microstructures and comprehensive mechanical properties (tension, bending, hole-expansion, and Charpy impact) of the tested steels at two cooling schedules were studied. The results indicate that the steel consists of 90% 5 μm polygonal ferrite and 10% pearlite when subjected to a cooling rate of 13 °C/s and a coiling temperature of 650 °C. The yield strength, tensile strength, and hole-expansion ratio are 570 MPa, 615 MPa, and 95%, respectively, which meet the requirements of the wheel-disc application. The steel consists of 20% 3 μm polygonal ferrite and 80% bainite (granular bainite and a small amount of acicular ferrite) when subjected to a cooling rate of 30 °C/s and a coiling temperature of 430 °C. The yield strength, tensile strength, and hole-expansion ratio are 600 MPa, 655 MPa, and 66%, respectively, which meet the requirements of the wheel-rim application. Both the ferrite–pearlite steel and ferrite–bainite steel possess excellent bendability and Charpy impact property. The precipitation behavior and dislocation pattern are characterized and discussed.     

选区激光熔化用高强合金钢粉末制备及其成形性研究

目的 研究真空感应熔炼气雾化法(VIGA)制备球形24CrNiMoY高强钢粉末并验证其激光3D打印性能。方法 阐明不同雾化气压对粉末形貌、流动性等粉体特征的影响,分析选区激光熔化技术快速成形合金钢样品的微观组织和力学性能。结果 在9.0 MPa雾化气压下制备的粉末球形度最佳,粉末松装密度达到4.89 g/cm³,流动性能为21.4 s/(50 g),粉末含氧量0.023%,空心球率＜3%,粉末的微观组织主要是马氏体。经过激光工艺参数调控,SLM成形合金钢试样的激光熔池内存在两个明显不同的微区:激光熔化区(LMZ)和热影响区(HAZ)。LMZ主要是马氏体组织,HAZ主要为下贝氏体组织。合金钢试样的平均显微硬度为(402±5.7)HV0.2,其抗拉强度达到(1 246±12) MPa,断后伸长率为(11.6±0.5)%。结论 VIGA方法制备的 24CrNiMoY高强钢粉末满足SLM技术使用要求,具有良好的激光3D打印成形性。     

Microstructural engineering and strength-impact toughness prediction in ultra-low carbon bainitic steel

The strength–toughness combination of an ultra-low carbon, low alloyed ‘air-cooled’ steel has been enhanced by developing and refining the granular bainite (GB) structure. Suitable alloy design and thermo-mechanical treatment involving forging, austenitisation (950–1150°C) and air-cooling resulted in the formation of GB matrix along with small islands of martensite–austenite constituents and allotriomorphic ferrite grains. Microstructural characterisation and phase transformation behaviour were studied by scanning electron microscopy and electron backscattered diffraction analysis. The effect of microstructural parameters on the strength-impact toughness combination was investigated. The steel showed an exceptionally low yield ratio, which is beneficial for seismic resistance application.     

道间温度对10CrNi5MoV钢气体保护焊接头力学性能的影响

通过屈服强度和冲击韧性测试、组织分析,研究了两种焊接热输入条件下道间温度对10CrNi5MoV钢气体保护焊接头力学性能的影响。结果表明,随着道间温度从40℃提高到300℃,焊接热输入为8 kJ/cm和18 kJ/cm的焊缝金属屈服强度分别从868 MPa和855 MPa单调下降至728 MPa和693 MPa,-50℃冲击韧性分别从70 J和69 J升高至117 J和72 J(道间温度分别为200℃和100℃),然后降低至67 J和43 J;焊缝金属的组织差异是不同道间温度下焊接接头力学性能不同的原因。随着道间温度从40℃提高到300℃,焊缝金属中马氏体组织逐渐消失,粒状贝氏体组织逐渐增多,针状铁素体组织比例先增加再减少,含量最高时的道间温度与冲击韧性峰值水平相一致。     

高强贝氏体基体钒微合金化TRIP钢的性能

对一种钒微合金化TRIP钢进行冷轧连续退火,研究了钢的组织特征和力学性能。结果表明,贝氏体基TRIP钢的组织由贝氏体/马氏体和少量的残余奥氏体组成。随着贝氏体区等温时间的延长,钢的抗拉强度下降,屈服强度和延伸率提高。残余奥氏体由块状向薄膜状转变,体积分数增加,薄膜状残余奥氏体主要分布在贝氏体板条间,厚度为50-90 nm。在400℃等温180 s连续退火钢板呈现出相对低抗拉强度(960 MPa)、高屈服强度(765 MPa)和高延伸率(22.0%)的特性,而且加工硬化指数(0.20)、各向异性指数(0.94)和强塑积(21120 MPa.%)也较为优良。     

Effect of controlled rolling/controlled cooling parameters on microstructure and mechanical properties of the novel pipeline steel

The study of controlled rolling/controlled cooling process parameters which affect the microstructure and mechanical properties of a novel pipeline steel has been optimized by the orthogonal experiment with four factors and three levels in this paper.However,the parameters of thermo-mechanical control process(TMCP)optimized by the Gleeble-3500 hot simulator could not satisfy performance requirements of the X100 pipeline steel.In order to improve the performance of this steel,the influence of finish cooling temperature(FCT) on the microstructure and property is studied in detail.It is found that,as this steel is thermo-mechanically treated by this set of parameters(the start heating temperature,finish rolling temperature(FRT),FCT and cooling rate of 1,180℃,810℃,350℃ and 35℃/s,respectively),the microstructures are mainly composed of granular bainite(GB)and acicular ferrite(AF).The effective grain sizes are below 20μm;the steel reaches the optimal balance between the strength and the toughness;the yield strength is 695 MPa;the tensile strength is 768 MPa;the elongation is 16.6%;the impact energy is 262 J at room temperature.All indexes could meet the requirements of X100 pipeline steel.     

厚规格多相组织X80管线钢组织控制与断裂行为研究

目的 研究厚规格X80管线钢的力学性能及断裂行为与微观组织之间的关系。方法 通过硬度实验、拉伸实验、夏比冲击实验及落锤撕裂实验（DWTT）,研究X80管线钢力学性能,利用OM和SEM观察微观组织和断口形貌。结果 多边形铁素体（PF）、粒状贝氏体（GB）、准多边形铁素体（QPF）、针状铁素体（AF）和贝氏体铁素体（BF）多相组织的结合保证了钢板优异的强韧性。在落锤撕裂实验裂纹扩展过程中,裂纹扩展至QPF时呈平直扩展,裂纹扩展至GB时,较为曲折迂回,说明GB能有效阻碍裂纹扩展。细小的马氏体-奥氏体（M-A）组元和AF同样能够有效阻碍裂纹的扩展。结论 研究结果可为厚规格多相组织X80级管线钢的服役使用提供理论依据。     

热轧D级船用钢板焊接接头的力学性能与显微组织

采用CO2气体保护焊法对16mm厚的热轧态D级船用钢板进行焊接,通过拉伸、冲击和金相检验等试验方法对焊接接头的力学性能与显微组织进行了研究。结果表明：采用YCJ501-1焊材对D级船用钢板进行焊接时,接头具有较高的抗拉强度和较好的低温冲击韧性;焊缝组织主要为针状铁素体、先共析铁素体和少量粒状贝氏体;热影响区组织主要为铁素体、珠光体和少量针状铁素体,针状铁素体的存在是接头具有良好力学性能的主要原因。     

L360QCS微合金钢焊接接头抗SSCC性能分析

经过反复焊接工艺试验,确定了合理的L360QCS微合金钢焊接工艺参数,针对L360QCS微合金钢焊接接头进行了抗SSCC试验研究。结果表明,焊接接头屈服强度为410 MPa,抗拉强度为528 MPa,平均冲击功值为145J,弯曲试验、刻槽锤断试验均未见缺陷,各类力学性能指标合格;根焊层、填充层、盖面层平均硬度值分别为136.6HV、146.3HV、157.1HV;根焊层、填充层微观组织晶粒细小,为等轴铁素体+珠光体盖,盖面焊层组织晶粒较粗大,为粒状贝氏体+珠光体+针状铁素体;焊接接头SSCC试验未出现裂纹,经XRD、SEM分析,腐蚀产物膜为呈堆砌状态的四方晶系晶体FeS。L360QCS微合金钢焊接接头能够满足NACE TM0177-2005标准规定的抗SSCC性能要求。     

选区激光熔化24CrNiMoY合金钢组织演化与力学性能

目的 为了获取具有高抗拉强度与高伸长率的24CrNiMoY合金钢,用选区激光沉积(SLM)方法进行打印。方法 以24CrNiMoY合金钢粉末为材料,当搭接宽度为0.09 mm、扫描角度为67°、扫描线长度为10 mm、扫描速度为1 000 mm/s时,在能量密度分别为102、116、129、142 J/mm³条件下打印合金钢样品,采用金相、X射线衍射、扫描电镜、透射电镜及拉伸试验等分析手段,对制备样品的微观组织和力学性能进行研究。结果 在所采用的能量密度范围内,SLM制备24CrNiMoY合金钢的显微组织主要是板条马氏体组织,随着能量密度的增加,样品内部的气孔缺陷先减少后增加,硬度和拉伸性能以及冲击韧性呈现先升高后降低的趋势。在能量密度为116 J/mm³时,打印合金钢样品具有最优的综合力学性能,致密度为99.53%,硬度为(388±5.9)HV0.2,抗拉强度为(1 210±11) MPa,屈服强度为(1 124±10) MPa,断后伸长率为(6.2±0.4)%,冲击韧性为80 J/cm²。结论 在SLM打印24CrNIMoY合金钢样品中,较高的致密度及精细的板条马氏体是合金钢样品具有良好力学性能的关键要素,该研究可为SLM打印高抗拉强度与高伸长率的24CrNiMoY合金钢制动盘零件提供重要参考。     

Fracture toughness of nanostructured railway wheels

This paper describes nanostructured railway wheels made of Si–Mn–Mo–V low-carbon steel through an advanced metallurgy process and fabrication technology. The microstructure of the wheels, particularly in the rim portion, is composed of carbide-free bainite that consists of bainitic ferrite laths and retained austenite films along the lath boundaries. The thickness of the laths and films is in nanometer scale. For comparison, traditional pearlite–ferrite wheel steels are also investigated. Test results show that carbide-free bainite steel is superior to pearlite–ferrite steel not only in yield strength but also in fracture toughness. Theoretical explanation of these phenomena is also elucidated.     

ULCB钢相变产物粒状与板条状贝氏体组织性能研究

对ULCB钢的主要相变组织粒状贝氏体与板条贝氏体进行了力学性能比较,结果显示粒状贝氏体与板条贝氏体是完全不同的两种组织,较高温度相变产物粒状贝氏体组织较为粗大,对强度和韧性有不利影响,而较低温度相变产物板条贝氏体组织对强度和韧性是有益的.     

10CrNi5MoV钢厚板窄间隙熔化极气保焊研究

以10CrNi5MoV钢为研究对象,进行了窄间隙熔化极气保焊对接试验,并对焊接接头的力学性能、金相组织和显微硬度进行了分析。结果表明,焊接接头具有良好的综合力学性能,焊缝组织以贝氏体为主,并有少量的针状铁素体和粒状贝氏体,过热区组织主要是贝氏体,最高硬度出现在焊接热影响区。