Effect of Rare Earth (Niobium) on Costed and Hot-Rolled Microstructure and Properties of Heavy Rail Steels

A compared investigation was made on the microstructure and mechanical properties of continuous casting square blanks of BNbRE and U71Mn heavy rail steels having eutectoid composition. The variation of solidified structure of the square blanks was demonstrated by measuring hardness. The observation to the structure and inclusions in the head, waist and base of the hot-rolled rails of the test steels were carried out with optical microscope and SEM. It is found that the casting blanks of both tested steels compose of three areas with constant hardness and three hardness varying areas, and there is considerable P-eutectic structure in the blank of the U71Mn steel. The distribution of the inclusions in the UT1Mn steel rail is mainly oxides in both rail head and rail base, and is mainly MnS in the waist of the rail. There has strong effect of the addition of rare earth elements on them. The discussion on these results was made.

Effect of vanadium micro-alloying on the microstructure evolution and mechanical properties of 718H pre-hardened mold steel

The effects of different contents of vanadium(V)(0.1,0.2,and 0.3 wt%)on the microstructure evolution and mechanical properties of 718H steel were investigated.The precipitate was characterized by means of atom probe tomography(APT)and bright-field transmission electron microscopy(TEM).The increase in V content has great benefits for strength,but has an adverse effect on impact toughness.The strength increase can be attributed to the influence of V addition on dislocation density,misorientation gradient,and fine scale MC precipitates.Precipitation strengthening mainly contributes to the V-added steel by analyzing various strengthening mechanisms.However,fine scale MC precipitates can pin dislocation leading to a decrease in its mobility.A large number of immovable dislocations will increase the dislocation accumulation,internal stress and brittle cracking,resulting in a gradual decrease in impact toughness with the V addition.In addition,compared with V-free steel,the dissolved V content in austenite decreases the grain boundary energy and inhibits the diffusion of the C atoms,ultimately reducing the transformation range of pearlite(P).

Improvement of Mechanical Properties of Cr-Ni-Mo-Cu-Ti Stainless Steel With Addition of Vanadium

The effect of vanadium （V） addition on the mechanical properties of a Cr-Ni-Mo-Cu-Ti stainless steel was studied and its influence on microstructural changes was also investigated. Results indicate that the structure of the solution-treated specimens mainly comprises of austenite-martensite, and adding V leads to the formation of a consid erable amount of ferrite. Under this condition, austenite phase is not mechanically stable, and transforms to martensite by plastic deformation. The addition of 0.5% - 1.0% （in mass percent） of V increases the hardness and the strength of the 80% cold rolled and aged steel, without any effect on ductility. Improvement in mechanical properties is presumably attributed to the formation of a small amount of ferrite in the primary structure, and the formation of certain precipitates is accelerated by the addition of V during aging. By contrast, excessive V decreases the strength and ductility simultaneously. This is due to the strong effect of ferrite formation compared to the beneficial effect of precipitation. The loss of ductility caused by adding higher amount of V is due to the formation of ferrite phases which in turn are suitable nucleation sites for crack propagation.

Microstructures and Properties of 550 MPa Grade High Strength Thin-walled H-beam Steel

The microstructures and mechanical properties of 550 MPa grade lightweight high strength thin-walled H-beam steel were experimentally studied. The experimental results show that the microstructure of the air-cooled H-beam steel sample is consisted of ferrite, pearlite and a small amount of granular bainites as well as fine and dispersive V（C,N） precipitates. The microstructure of the water-cooled steel sample is consisted of ferrite and bainite as well as a small amount of fine pearlites. The microstructure of the water-cooled sample is finer than that of the air-cooled sample with the average intercept size of the surface grains reaching to 3.5 gna. The finish rolling temperature of the thin-walled high strength H-beam steel is in the range of 750 ~C-850 ~C. The lower the finish rolling temperature and the faster the cooling rate, the finer the ferrite grains, the volume fraction of bainite is increased through water cooling process. Grain refinement strengthening and precipitation strengthening are used as major strengthening means to develop 550 MPa grade lightweight high strength thin- walled H-beam steel. Vanadium partially soluted in the matrix and contributes to the solution strengthening. The 550 MPa grade high-strength thin-walled H-beam steel could be developed by direct air cooling after hot rolling to fully meet the requirements of the target properties.

Effects of Rare Earth on Structure and Mechanical Properties of Clean BNbRE Steel

The mechanisms of RE in clean BNbRE steel were studied by means of experimental measurement, microstructural observation and theoretical analysis. For BNbRE steel, the state and the content of RE were measured, and the effects and the mechanisms of RE on sulfide inclusions, microstructure and properties of steel were determined. On the condition of increasing the cleanliness of steel, the mechanisms of RE in steel were changed to certain degree. Small amount of RE has the effect of cleaning, modifying inclusions and alloying in clean steel, too. With increasing the cleanliness of BNbRE steel, addition of RE should be decreased properly. Under experimental conditions, the optimum addition of RE is -0.01 % （mass fraction） for clean BNbRE steel, while RE can evidently improve plasticity and impact toughness of BNbRE steel.

Influence of Vanadium Element on Microstructure of Electron Beam Welded Titanium Alloy to Stainless Steel Joint

Electron beam welding experiments of titanium alloys with different vanadium content to stainless steel,as well as alpha titanium to stainless steel using vanadium sheets as filler metal and transition portion were carried out.Microstructures of the joints were examined by scanning electron microscope.The properties were evaluated by microhardness and tensile strength.It was shown that electron beam welding is not feasible due to the brittle Ti-Fe intermetallics with high hardness.Increase of vanadium content in base metal can restrain but can't avoid the formation of cracks.When vanadium content was too large,the joint was embrittled by FeTi compound with supersaturated V and also cracked after welding.Crack free joint was achieved by using vanadium transition portion which can prevent the contact of Ti and Fe elements.However,the formation of brittle σ intermetallics reduced the tensile strength of the joint,only up to 134MPa.

Effect of Annealing on Microstructure and Mechanical Properties of Ultrafine-Grained Low-Carbon Medium-Manganese Steel Produced by Heavy Warm Rolling

An ultrafine-grained(UFG) low-carbon medium-manganese steel was fabricated by the heavily warm rolling(HWR) and subsequent quenching, and the effects of annealing temperatures on microstructure and mechanical properties of the UFG HWRed steel were investigated. The results show that the HWRed steel exhibits simultaneous improvements in strength,uniform elongation and work hardening, which is mainly attributed to the refinement of martensitic microstructures. The HWRed steels comprise only a-phase when annealing at lower temperatures below to 550 °C and at higher temperatures above to 700 °C. Whereas, UFG c-austenite is formed by reverse transformation when the HWRed steel was annealed at intermediate temperatures from 550 to 700 °C and the volume fraction increases with increasing annealing temperatures,consequently resulting in a dramatic increase in ductility of the annealed HWRed steels. It was found that the transformed UFG austenite and ferrite remained ～500 nm and ～800 nm in size when the HWRed steel was annealed at 650 and700 °C for 1 h, respectively, showing an excellent thermal stability. Moreover, the HWRed steel annealed at 650 °C exhibits high strength-ductility combinations with a yield strength of 906 MPa, ultimate tensile strength(UTS) of1011 MPa, total elongation(TEL) of 51% and product of strength and elongation(PSE: UTS 9 TEL) of 52 GPa%. It is believed that these excellent comprehensive mechanical properties are closely associated with the UFG austenite formation by reverse transformation and principally attributed to the transformation-induced plasticity(TRIP) effect.

Microstructures and mechanical properties of ferrite-based lightweight steel with different compositions

The microstructures and mechanical properties of ferrite-based lightweight steel with different compositions were investigated by tensile test,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,X-ray diffraction（XRD）and thermodynamic calculation（TC）.It was shown that the ferrite-based lightweight steels with 5wt.%or 8wt.%Al were basically composed of ferrite,austenite andκ-carbide.As the annealing temperature increased,the content of the austenite in the steel gradually increased,while theκ-carbide gradually decomposed and finally disappeared.The mechanical properties of the steel with 5wt.%Al and 2wt.%Cr,composed of ferrite and Cr7C3carbide at different annealing temperatures,were significantly inferior to those of others.The steel containing 5wt.%Al,annealed at 820°C for 50sthen rapidly cooled to 400°C and held for 180s,can obtain the best product of strength and elongation（PSE）of 31242MPa·%.The austenite stability of the steel is better,and its PSE is higher.In addition,the steel with higher PSE has a more stable instantaneous strain hardening exponent（n value）,which is mainly caused by the effect of transformation induced plasticity（TRIP）.When theκ-carbide or Cr7C3carbide existed in the microstructure of the steel,there was an obvious yield plateau in the tensile curve,while its PSE decreased significantly.

Microstructure and mechanical properties of hot-rolled V-microalloyed Al-containing medium-Mn steel

The microstructure and mechanical properties of a V-microalloyed Al-containing medium-Mn steel after hot rolling and intercritical annealing(IA)are explored.The tested steel exhibits a fne multiphase microstructure consisting of bimodal sizes of ferrite and retained austenite plus considerable amount of fne VC and/or M3C precipitates.Physical-chemical phase analysis shows that about 71.0%of the total V is in VC phase and more than 93%of VC particles is less than 5 nm.The calculated precipitation strengthening values of VC are^347 and^234 MPa for the specimens intercritically annealed at 625 and 750℃,respectively.An excellent combination of strength and ductility as high as^50 GPa%and yield strength(YS)of 890 MPa was obtained at intercritical temperature(TIA)of 725℃,although it does not correspond to the maximum precipitation strengthening of VC phase.Therefore,it is suggested that an optimization of TIA corresponding to both excellent combination of strength and ductility and high YS should be further explored through chemical composition and IA process optimization.

钒在钢轨钢中的作用研究

介绍了钒在钢轨钢中溶解、析出、分布情况 ,分析了钒对钢轨钢组织结构及对钢轨钢性能的影响。

稀土、铌对重轨钢铸、轧态组织与性能的影响

对比研究了BNbRE与U71Mn重轨钢连铸方坯的组织和常规力学性能;通过测量硬度,揭示了接近共析成分的重轨钢连铸坯结晶组织的变化特征。采用金相和SEM等手段,对BNbRE钢和BNb钢热轧轨的轨头、轨腰和轨底角3种部位的组织和夹杂进行了观测,发现实验钢的铸坯有3个硬度恒值区和3个硬度变化区,U71Mn钢的铸坯里有可观的P共晶组织;未加稀土的BNb钢轨夹杂物,有轨头和轨底为氧化物和轨腰MnS居多的分布特征等。文章得出,加稀土不仅改善和细化了钢的铸、轧态组织,改变了夹杂物,还明显地减少了硬度变化结晶区尺寸及其硬度值的变化幅度,有效地抑制和甚至消除了磷共晶组织。

CrNb低合金热轧轨组织和性能研究

在 U74普通碳素轨的基础上 ,增加 Si含量 ,调整 C、Mn含量 ,加入合金元素 Cr、Nb,设计出 Cr Nb低合金钢轨钢。研究了该钢的组织和性能及 Cr、Nb合金元素的作用。结果表明 :Cr Nb钢的屈服强度、抗拉强度比 U74提高 2 1.36 %、13.6 5 %。奥氏体晶粒度和珠光体片间距得到了细化。Cr元素使 CCT曲线明显右移 ,Nb元素在奥氏体再结晶过程中细化了奥氏体晶粒。

Ti对高强耐候钢力学性能的影响

通过光学显微镜、透射电镜（TEM）以及力学性能测试等手段分析了薄板坯连铸连轧（TSCR）工艺生产Ti微合金化高强耐候钢的成分及工艺对显微组织和力学性能的影响．研究结果表明：钢中加入Ti，屈服强度有明显的提高；钛质量分数为0．05％～0．08％时，高强耐候钢的晶粒尺寸随着钛含量的增加基本不变；高强耐候钢强度的提高主要取决于钢中有效钛的含量，有效钛不仅与钛的含量有关。而且还与S，N的含量有关；在有效钛含量一定的条件下，析出强化的大小主要取决于轧后的卷取温度．

钒、铬微合金化对高碳钢微观组织与力学性能的影响

为了开发性能更优的高碳盘条钢,在原有70钢的基础上,以铬、钒微合金化设计开发新钢种,并分析了铬、钒对试验钢的微观组织和力学性能的影响。铬、钒单独微合金化,使索氏体化率增大、片层间距减小、原始奥氏体晶粒细化;与70钢相比,随铬、钒含量的增加,钢的抗拉强度逐渐升高,断口伸长量下降。铬钒复合微合金化对钢中微观组织的改善明显好于单独微合金化;与70钢相比,铬钒复合微合金化钢的强度显著升高,塑性略有降低;与80钢相比,铬钒复合微合金化钢的强度和塑性均较高。

热输入对双相不锈钢管接头力学和腐蚀性能的影响

采用两种焊接工艺对双相不锈钢管道进行全位置焊接 ,对比研究了不同热输入条件下焊接接头的组织、力学性能和抗腐蚀性能 ,并用扫描电镜分析了缝隙腐蚀后蚀坑的组织特征。结果表明 ,焊接热输入是影响焊接接头相比例的一个重要参数 ,焊接采用高热输入时 ,尽管会使凝固组织铁素体晶粒易长大 ,但却会促使较多的奥氏体转变。同时相比例又影响着焊接接头的拉伸、冲击韧度等力学性能。蚀坑扫描电镜结果显示铁素体相优先被腐蚀 ,露出管状的奥氏体组织 ,这是由于合金元素在两相中的分配比例不同造成的电化学势差 。

重载铁路用高强耐磨合金护轨研究

针对现有淬火护轨在热处理过程中易发生扭曲变形、质量稳定性较差和硬度偏低不耐磨等问题,在设计并试制出11#试验钢的基础上,采用11#试验钢开展免热处理的高强耐磨合金护轨的全尺寸试制和性能研究。将试制出的高强耐磨合金护轨在大秦重载铁路上试铺,跟踪其服役情况,并与现有淬火护轨进行对比。结果表明:11#试验钢的抗拉强度达到1 280MPa,布氏硬度高于360HB,且具有良好的强韧性配合;全尺寸试制的合金护轨的抗拉强度达1 298MPa,工作面布氏硬度达385HB,断后伸长率为9.5%,且与2个道岔厂生产的淬火护轨相比,不但硬度较高,而且力学性能稳定,可以有效解决由于热处理设备和生产工艺的差异而造成护轨性能波动的问题,合金护轨的使用寿命是淬火护轨的3倍以上,大大减轻了工务部门换轨和维修的工作量,降低了成本。

含磷和钒热轧TRIP钢组织控制及力学性能研究

为探讨含磷和钒热轧TRIP钢的组织控制和力学性能,采用不同变形温度(900和800℃),研究其相变行为,并在此基础上进行热轧试验.研究表明:随着冷速增加,变形温度对铁素体相变开始温度(Ar3)的影响逐渐增大;相同冷速条件下,变形使贝氏体相变开始温度(Bs)升高;变形对贝氏体相变的促进作用,随着变形温度的降低而减弱.终轧温度800℃,试验钢组织由多边形铁素体、粒状贝氏体和一定量的残余奥氏体组成,综合力学性能优异:R P0.2=455 MPa;R m=930 MPa;δ=21.7%;n=0.23;r=0.84.

热处理工艺对高钒高速钢组织与滚动磨损性能的影响

研究了20种热处理工艺对高钒高速钢的硬度、冲击韧性、残余奥氏体量与滚动磨损性能的影响,并利用SEM对其显微组织进行了分析,筛选出了适合滚动磨损的热处理工艺。研究结果表明:淬火温度升高,其残余奥氏体量升高;回火温度升高,其残余奥氏体量减少。淬火温度为900～1 000℃时,回火温度对耐磨性的影响不大;1 050～1 100℃淬火,450～550℃回火时,滚动磨损性能大幅度提高。以滚动耐磨性为评价指标,综合考虑热处理工艺对力学性能、滚动耐磨性、设备损耗及生产成本的影响,最适宜的热处理工艺为:淬火加热温度1 050℃,回火温度450～550℃。

高锰TRIP/TWIP钢变形行为的研究进展

高强度高塑性是汽车用钢发展的主要趋势.Fe-Mn-Al-Si系TRIP/TWIP钢、Fe-Mn-C系TWIP钢和Fe-Mn-Al-C钢具有高的强度、优良的塑性和成形性,为新一代汽车材料.近年来,这些奥氏体汽车用钢的研究与开发受到了高度重视.本文对高锰TRIP/TWIP钢的组织性能、晶体学行为、强韧化机制、应变硬化行为和高速变形方面的研究工作进行了综述.

显微组织对X70管线钢力学性能的影响

采用扫描电镜、电子背散射衍射技术和常规力学性能测试等手段研究了两种X70管线钢的显微组织和力学性能。结果表明:管线钢的低温韧性不仅与其有效晶粒尺寸有关,而且还与其组织中的马奥岛和析出相有关;但是,与管线钢中大角度晶界所占的百分比没有直接的关系。有效晶粒尺寸越小,马奥岛和富钛氮化物数量越少、尺寸越小,管线钢的低温韧性就越好。富铌碳化物与高密度的位错和亚结构不仅能提高管线钢的屈服强度,而且还能增大其加工硬化速率,从而使其抗拉强度明显升高,屈强比减小。由此可见,通过显微组织的优化,可以得到高强度高韧性的管线钢。