C-HRA-5奥氏体耐热钢晶粒尺寸分布对晶间腐蚀性能的影响

通过DL-EPR试验研究了混晶和晶粒均匀对C-HRA-5奥氏体耐热钢晶间腐蚀性能的影响,采用金相显微镜、SEM、EBSD等分析了晶粒尺寸、特殊晶界、碳化物析出相和晶间腐蚀特征等。结果表明:晶粒均匀组织试样的耐晶间腐蚀性能高于混晶组织试样;两种试样都含有Σ3占主导的低ΣCSL特殊晶界,前者的特殊晶界含量为54.2%,远高于后者29.5%;可认为晶粒均匀组织试样高耐蚀性的原因是高含量的特殊晶界打断了大角度晶界网络的连通性,对富Cr的M23C6的析出具有一定的抑制作用,改善部分晶界的贫Cr现象。

C-HRA-5钢焊接接头高温短时拉伸及持久强度预测

持久强度对于评价C-HRA-5钢焊接接头在复杂工况条件下的使用寿命具有极其重要的意义。通过不同温度下的高温短时拉伸试验,基于Larson-Miller参数,利用状态函数和全微分的特征,建立了C-HRA-5钢焊接接头持久强度预测的数学模型,外推10万小时的持久强度。结果表明:C-HRA-5钢焊接接头在650℃时强度和塑性最好,在700℃时呈现典型的微孔聚集性断裂,随着温度的升高,第二相颗粒和夹杂物增多,位错的塞积群增多,焊接接头的力学性能降低。700℃时外推拟合公式为lgσ=2.76018-0.13151 lgτ,外推10万小时的持久强度为σ^(973)_(10^5)=116.0203 MPa,高于ASME SA-213标准的要求。

Microstructure of Steel 5Cr21Mn9Ni4N Alloyed by Rare Earth

The microstructure, composition and shape of precipitated phase under as-cast and finished product state of 5Cr21Mn9Ni4N steel with different rare earth （RE） amount were studied. Mechanical properties of 5Cr21Mn9Ni4N steels withont RE addition and with RE added by 0. 2% in mass percent were tested respectively. The results indicate that the solid solution amount of RE is about 10^-6 -10^-5 order of magnitude in 5Cr21Mn9Ni4N steel. Dendrite of as-cast condition is refined obviously and dimension of interstitial phase is shortened when RE is added by 0.10%-0.20%. But the microstructure will be coarser if surplus RE is added. Precipitated phase under finished product state distributes evenly in nearly same size with RE added by 0. 2% which leads to a largely improved high temperature mechanical property.

Experimental Investigation of the Effect of the Material Damage Induced in Sheet Metal Forming Process on the Service Performance of 22MnB5 Steel

The use of ultra-high strength steels through sheet metal forming process offers a practical solution to the lightweight design of vehicles.However,sheet metal forming process not only produces desirable changes in material properties but also causes material damage that may adversely influence the service performance of the material formed.Thus,an investigation is conducted to experimentally quantify such influence for a commonly used steel（the 22MnB5 steel） based on the hot and cold forming processes.For each process,a number of samples are used to conduct a uniaxial tensile test to simulate the forming process.After that,some of the samples are trimmed into a standard shape and then uniaxially extended until fracture to simulate the service stage.Finally,a microstructure test is conducted to analyze the microdefects of the remaining samples.Based on the results of the first two tests,the effect of material damage on the service performance of 22MnB5 steel is analyzed.It is found that the material damages of both the hot and cold forming processes cause reductions in the service performance,such as the failure strain,the ultimate stress,the capacity of energy absorption and the ratio of residual strain.The reductions are generally lower and non-linear in the former process but higher and linear in the latter process.Additionally,it is found from the microstructure analysis that the difference in the reductions of the service performance of 22MnB5 by the two forming processes is driven by the difference in the micro damage mechanisms of the two processes.The findings of this research provide a useful reference in terms of the selection of sheet metal forming processes and the determination of forming parameters for 22MnB5.

Effects of Strain Ratio on Fatigue Behavior of G20Mn5QT Cast Steel

Due to traffic and wave actions, cast steel joints are subjected to variable-amplitude fatigue loading, which may cause fatigue problems. The ratio of the minimum strain to the maximum strain(strain ratio)can be employed to analyze the influence of variable-amplitude fatigue both in the elastic and plastic ranges. To evaluate the effect of the strain ratio on G20Mn5 QT cast steel, the fatigue tests of smooth specimens were carried out at the strain ratio of 0.1. The cyclic deformation and the relationships between the strain amplitude, the stress amplitude, the Smith, Watson and Topper(SWT)parameter and fatigue life were studied and compared with those at the strain ratio of-1. Compared with other methods, Basquin formula and Solonberg formula provide reliable and appropriate ranges of S-N curve and fatigue limit at different strain ratios respectively. The SWT parameter can be used to predict the fatigue life at other strain ratios accurately.

Effects of laser heat treatment on salt spray corrosion of 1Cr5Mo heat resistant steel welding joints

The surface of 1Cr5 Mo heat-resistant steel welding joint was processed with CO2 laser, and the corrosion behaviors before and after laser heat treatment(LHT) were investigated in the salt spray corrosion environments. The microstructures, phases, residual stresses and retained austenite content of 1Cr5 Mo steel welding joint before and after LHT were analyzed with optical microscope and X-ray diffraction, respectively. The cracking morphologies and chemical compositions of corrosion products after salt spray corrosion were analyzed with field emission scanning electron microscopy(FESEM) and energy disperse spectroscopy(EDS), respectively, the polarization curves were measured on a PS-268 A type electrochemical workstation, and the mechanism of corrosion resistance by LHT was investigated as well. The results show that the passive film of original sample is destroyed owing to the corrosive media penetrating into the subsurface, resulting in the redox reaction. The content of residual austenite in the surface and the self-corrosion potential are increased by LHT, which is contributed to improving the capability of salt spray corrosion resistance.

A study of local brittle zone (LBZ) of 10Ni5CrMoV steel after double thermal cycles

The 10Ni5CrMoV steel examined was a 16 mm thick plate. Specimens measuring 12 mm×12 mm×120 mm were thermally cycled using DM-100A weld simulator with various parameters. The main results are summarized as follaws. In the coarse-grained austenitized region（ Tm = 1 300℃ ＋ 1300℃ ） ,the microstructure is in good toughness. At the condition of Tm = 1 300℃ ＋ 850℃ and t8/5=43 s, the toughness decreases heavily because M-A constituent and twin martensite appear at the prior aastenite grain boundaries. When Tm= 1300℃ ＋ 850℃ or 1300℃ ＋ 730℃ and t8/5 = 85 s, local brittle zone is formed because of relatively coarse granular bainite.

MICROSTRUCTURE IN LASER FUSED HIGH SPEED STEEL W6Mo5Cr4V2(M2)

Microstructure of the deepest zone of high speed steel W6Mo5Cr4V2(M2)melt after laser fu-sion was found to be so fine as the ehill zone of a solidified ingot.When narrower chill zoneformed,the long columnar dendrites grow into the melt and then the fine equiaxed cellularstructure appears in upper melt region nearly surface.The substructure of cellular grains anddendrites was observed to consist of martensite and retained austenile,while the carbides asM_6C_■ Cr_7C_3 and MC distributed at their boundaries.It is believed that the highermicrohardness up to HV_(0.1)=865-960 of the laser fused structure of the alloy is due to the oc-currence of martensite.

SMA-5钢渣沥青混合料的组成设计与性能评价

为更好地促进小粒径钢渣在薄层沥青混合料中的应用,采用V-S(volumetric mix)法设计SMA-5沥青混合料的集料掺配比例;等体积替换掺加1.18~2.36 mm、2.36~4.75 mm两种粒径钢渣于SMA-5沥青混合料中,分析其对沥青混合料试件的粗集料间隙率VCAmix、最佳沥青用量的影响;借助车辙试验、小梁弯曲试验、冻融劈裂试验与浸水马歇尔试验对钢渣沥青混合料的高温稳定性、低温抗裂性与水稳定性进行评价。结果表明:掺入钢渣降低了集料间的骨架结构效应,提高了混合料沥青用量;复掺钢渣降低了沥青混合料的高温稳定性,但随着钢渣掺量增加,各掺配方案下沥青混合料的低温性能均降低,水稳定性、高温稳定性均提升;推荐SMA-5钢渣沥青混合料中2.36~4.75 mm粒径钢渣掺量75%为最优配比。

High-Temperature Oxidation Behavior of 5Cr21Mn9Ni4N Steel Micro-Alloyed by Rare Earth

The oxidation resistance of 5Cr21Mn9Ni4N steel micro-alloying by RE at 700 - 900 ℃ was investigated. The results indicate that oxidation exponent n and oxidation activation energy are increased, and oxidation velocity constant kp is decreased when 0.2% RE is added in 5Cr21Mn9Ni4N steel. The addition of RE elements does not alter phase constitution of oxidation scale, however it improves the configuration of oxidation scale, and increases thermal stability and adhesivity of oxidation scale, which results in the raise of oxidation resistance of 5Cr21Mn9Ni4N steel at high temperature. The oxidation scale constitutes of refractory steel transfer from manganic oxide mostly to ferric oxide mostly with the increase of temperature, which leads to descend of compactness and desquamation resistance of oxidation scale. The mass increase of ferric oxide in the oxidation scale and the looseness of oxidation scale are the main reason to descend the oxidation resistance of refractory steel.

Relationship between the Brittlement Susceptibility and H Permeation Current for UNS G11180 Steel in 5% NaCl Solution with H_2S

Sulfide stress corrosion cracking (SSCC) behaviour of UNS G11180 steel in 5% NaCl solution with H2S was studied by slow strain rate tensile test (SSRT), SEM and electrochemical hydro gen permeation technique. The results reveal different cracking mechanism and H permeation current (IH) through UNS G11180 steel plate in different concentration of H2S solution. The susceptibility to SSCC of UNS G11180 Steel in 5% NaCl solution with H2S was evaluated by the permeation current(IH, μA), which depends on the concentration (c×10-6) of H2S by the equation:IH = 8.525 ×c0.7249. lt is proved that the electrochemical H permeation method is a practical way to assess the susceptibility to SSCC.

Rolling-contact-fatigue behavior in backup roll of 5% Cr forged steel

With a focus on the backup roll, a rolling-contact-fatigue experiment was performed on samples of 5% Cr forged steel. The P-S-N fatigue curves were determined and the fatigue strength was calculated. The emergence of cracks on the test-sample surfaces was observed at different fatigue cycles. A micro-hardness tester was used to measure the hardness of the subsurface fatigue layer. The microstructures were analyzed at various magnifications with an optical microscope, scanning electron microscope, and transmission electron microscope. Based on these tests, the rolling-contact-fatigue mechanism of the large forged steel backup roll was also considered. The results showed that the contact-fatigue strength of the tested backup roll steel was 1 249 MPa;the surface fatigue crack lengthened continuously as the number of cycles increased and followed an S-shaped curve; the subsurface fatigue hardness reached its highest value at about 90 （HV） increment from the matrix hardness of 540 （HV） in the backup roll; the subsurface martensite/bainite microstructure was crushed and the dislocation density was greatly increased. Under alternating contact stresses,the surface/subsurface material was damaged and exhibited many microdefects. At the least, the surface fatigue layer on backup rolls should be fully removed before the microcracks enter a period of rapid propagation.

Effects of Lanthanum on Mechanical Properties of 5CrNiMo Forging Die Steel

The alteration of the strength, hardness and impact ductility of 5CrNiMo steel using three different additions of RE La element is studied in this paper. The mechanical properties of 5CrNiMo steel with RE La additions are be compared with that of the 5CrNiMo steel on the same heat-treatment condition without RE La element addition. The results show that the strength, hardness and impact ductility of 5CrNiMo steel will be improved obviously when the content of RE La element is proper, and as the content of RE La element is 0.033%(mass fraction), the 5CrNiMo steel has the best mechanical properties.

Effect of the Compound Layer of Plasma Nitriding on Thermal Fatigue Behavior of 4Cr5MoSiV1 Die Steel

With the Uddeholm self restricted method, the effect of compound layer of plasma nitriding on thermal fatigue behavior of 4Cr5MoSiV1 steel was studied by the way of adding Ar during plasma nitriding to remove the compound layer. The results show that the compound layer of plasma nitriding can delay the nucleation of heat cracks and hold back the propagation of heat cracks from surface to substrate because of its high hardness and strength. On the other land, the heat checking expands faster with the compound layer on the surface than that without it. After 3000 cycles of thermal fatigue test, both heat cracks with the compound layer are wider than the another without compound layer and the number of heat cracks of the former is more from the view of cross section.

Relationship between hydrogen concentration and mechanical properties of 5Ni-16Cr-Mo steel

The qualitative relationship between hydrogen concentration and notch tensile strength has been investigated for 5Ni-16Cr-Mo steel with different strength.The notch tensile strength was determined by means of slow strain rate test(SSRT)on circumferentially notched round bar specimens with the notch root radius of 0.15 mm after hydrogen charging.Meanwhile,the hydrogen diffusion behaviors of various strength steel were studied by thermal desorption spectroscopy(TDS)analysis.The SSRT results show that the T460 steel has higher susceptibility of hydrogen embrittlement in contrast with T520 steel.The activation energies and microstructure indicate that the dislocations and interfaces of martensitic laths are hydrogen traps in 5Ni-16Cr-Mo steel.By SSRT,the elastic limit of charged specimen loaded in air is higher than the flow stress without hydrogen charging before unloading,while the difference is defined as hydrogen-induced stress.The value of hydrogen-induced stress σ*increases linearly with hydrogen concentration:σ*=−0.622+2.015C0.The finite element analysis results of stress distributions near the notch tip have shown that the maximum principal stress increases with the notch root radius decreasing.

Microstructure Evolution and Simulation in 22MnB5 Steel during Hot Stamping

Hot stamping components with 1500 MPa ultra-high strength are obtained by press hardening during hot stamping, and the properties depend on the microstructures. It is very important that the microstructure evolution rule is found out during hot stamping process. To characterize the microstructure evolution during hot stamping, a method combining finite element and experiment is carried out. Samples were heated to 950°C and held for 300 second at a induction heating furnace, then taken out from the furnace and stayed in the air at different time (7 s, 11 s, 13 s, 22 s), respectively, finally the specimens were formed and quenched at a die. Microstructural observation as well as surface hardness profiling of formed specimens was performed. And the numerical simulation to predict the austenite transformation into ferrite, pearlite, bainite, and martensite and the volume fraction of each phase during the hot stamping process was made with ABAQUS software. The results show that the ferrite is observed when the specimen stays in the air for 22 s, and the temperature drops to 325°C when the dwell time increases from 7 s to 22 s. The results of numerical simulation and experimental results are in good agreement. So the method finite element can be used to guide the optimization of hot stamping process parameters.

5′-硝基水杨基荧光酮分光光度法测定钼

研究了5′-硝基水杨基荧光酮分光光度测定钼的方法。在磷酸介质中,表面活性剂OP存在下,钼(Ⅵ)与5′-硝基水杨基荧光酮形成稳定的桔红色络合物,其最大吸收波长为528 nm,表观摩尔吸光率ε528=1.22×10~5L·mol^(-1)·cm^(-1),钼的质量浓度在0.30 mg·L^(-1)以内符合比耳定律。方法应用于不含钨、钛或其含量极低的碳钢及低合金钢中微量钼的测定,所得结果与标准值相符。

高品质GCr15轴承钢二次精炼过程中夹杂物的演变规律

采用FE-SEM／EDS研究了转炉流程生产的GCr15轴承钢LF、RH 精炼过程中夹杂物的演变规律，分析了其演变机理。结果表明：钢中复合夹杂物的演变规律可归纳为：Al2 O3→MgO·Al2 O3→（CaO-MgO-Al2 O3-（CaS））复合氧化物夹杂和 Al2 O3→（Al2 O3-MnS）→（Al2 O3-MnS-Ti（C，N））复合氧硫碳氮物夹杂2种方式。LF精炼过程脱硫作用明显，钢中的硫化物夹杂数量大幅减少。LF精炼初期钢中主要是MnS、Al2 O3、TiN的单相夹杂物。LF 精炼结束后钢中的夹杂物演变为Al2 O3为核心外包氧化物及 MnS、TiN、Ti（C，N）、CaS 的复合夹杂物。精炼渣中的CaO 和耐火材料中的MgO 经还原后与钢中溶解氧反应导致LF精炼结束时D类夹杂物增加。RH及软吹处理进一步强化了去除钢中的硫化物，但D 类及其与A、T 类复合的夹杂物含量增加。在LF阶段，夹杂物尺寸主要集中在1～3μm范围内，到R H 阶段，夹杂物尺寸则主要集中分布在小于1μm的粒度范围。最大夹杂物尺寸由10．79μm降到5．68μm，单位面积夹杂个数由372个／mm2降到258个／mm2。RH 及软吹处理有效地降低了钢中大于3μm的夹杂物。

卷取温度对510L钢氧化皮结构的影响

利用模拟法研究了热轧卷曲温度对汽车大梁钢510L氧化皮结构的影响。结果表明,精轧后的510L钢表面氧化皮主要由FeO层和少量Fe3O4层组成;在不同的卷取温度下,FeO层发生不同程度的共析反应,最终形成不同结构的表面氧化皮;在450～550℃时,FeO层共析反应发生的速度最快,形成的最终氧化皮中Fe3O4含量也最多。

45钢焊接接头组织与性能分析

通过金相观察和硬度测试实验,研究了45钢在不同焊接电流下焊接接头的组织、性能变化规律,并分析了t8/5对焊接接头组织和性能的影响。结果表明:焊接接头中焊缝处金属的硬度最大;随着t8/5的减小,45钢在淬火区产生更多的脆硬马氏体,导致焊接接头硬度增大;增大t8/5,可以减少或避免淬火组织的产生,改善钢的焊接性能。