低合金钢在海水中局部腐蚀锈层结构的研究

使用光学显微镜、电子探针、电子显微镜、微电化学测试等方法对两种低合金钢在海洋条件下的局部腐蚀锈层结构进行了研究。研究工作表明,低合金钢虽然具有较碳钢严重的局部腐蚀,但当该种合金钢的局部腐蚀锈层具有合金元素富集、致密等特征时,局部腐蚀将受到抑制,其原因是蚀坑内含富集合金元素的腐蚀产物成了难溶性盐,复盖了蚀坑底部基体,阻滞了腐蚀过程,降低了局部腐蚀速度。而在蚀坑外的平坦区域则没有发现合金元素的明显富集——局部腐蚀由向深度方向转而朝着扩大蚀孔直径的方向发展。这种变化的规律可由微电化学的蚀坑内外ΔmV-d曲线明显地看到所研究的钢种中,AlCuP钢具有较为典型的上述特征。NlCuAs钢的局部腐蚀行为与碳钢相近。     

Nano-scale chemical analysis of rust on a 2% Si-bearing low alloy steel exposed in a coastal environment

Corrosion products of the rust layer formed on a 2% Si-bearing low alloy steel during atmospheric exposure at a coastal area in Japan for three years were characterized. The inner layer of the rust, i.e., near oxide/metal interface, has a layer structure and the average grain size of corrosion products is finer than that in the upper region that is few micro meter above the interface. A series of nano probe energy disperse X-ray spectroscopy (EDS) and selected area electron diffraction (SAED) analyses performed using a field emission gun (FEG) transmission electron microscope (TEM) revealed that the inner layer consists of an iron rich, coarse grained β-FeOOH matrix and the silicon enriched narrow band composed a mixture of α-FeOOH and nano-meter size silicon oxide. On the other hand, the α-FeOOH single phase area exists where the layer structure did not develop. The result of detailed microstructural analyses indicated that the silicon plays an important role in modifying the rust layer structure.     

低合金超高强度钢的微观组织与强化机理

使用光学显微镜、SEM、TEM、XRD观察G50钢淬火和低温回火后的微观组织形貌,结合低温回火前后G50钢的屈服强度和冲击韧性等力学性能的变化,分析其强韧化机理。结果表明,淬火态G50钢微观组织主要为细小的板条状马氏体,使用TEM可以观测到有残留奥氏体薄膜在马氏体板条之间,残留奥氏体量很低。G50钢的超高强度来自马氏体相变和晶粒的细化,低温回火处理后G50钢的微观组织是细小的板条状回火马氏体,在保持强度的同时提高了冲击韧性。     

某耐候钢桥锈层稳定化处理技术的探索

文中对闪光焊接在铁塔用耐候钢上的应用展开研究,闪光焊接是通过焊接面的短路进行加热,加载顶锻变形过程界面上动态再结晶形成焊缝。焊接件经退火后,焊缝与热影响区均得到与基体相近的珠光体+铁素体组织,焊接试样与基体力学性能趋于一致。耐候钢闪光焊接无需引入其他焊料从而保证了焊缝与基体化学成分相同,并可通过热处理消除焊缝与基体之间组织差异,获得焊缝与基体力学性能的一致性。这对于无涂装输变电铁塔应用,闪光焊接一方面保证了焊接构件机械性能稳定性,另一方面避免了焊缝与基体之间因组织成分差异所带来的较大电位差,在自然环境下导致电化学腐蚀,从而满足耐候钢焊接构件免涂装服役性能要求。

     

薄规格A588 Gr.A低合金耐候结构钢的试制开发

介绍了鞍山钢铁股份有限公司2 150 mm ASP生产线薄规格A588 Gr.A低合金耐候结构钢的试制情况。通过合理的化学成分设计,结合2 150 mm ASP生产线的工艺路线,成功试制出薄规格A588 Gr.A钢板,钢板组织为准多边形铁素体和珠光体,晶粒度达到10.5级,综合力学性能优异。     

Electrochemical behaviour and structure of rust formed on Si- and Al-bearing steel after atmospheric exposure

The corrosion resistance of Si- and Al-bearing steel was estimated by atmospheric exposure test, and the structure of the rust was examined by EPMA (electroprobe X-ray microanalysis) and TEM (transmission electron microscopy) analysis. Moreover, the electrochemical behaviour of rust was investigated by EIS (electrochemical impedance spectroscopy).The Si- and Al-bearing steel exhibited excellent corrosion resistance in the exposure test as compared with carbon steel (SM). EPMA and TEM analysis showed that Si and Al mainly existed in nanoscale iron complex oxides in the inner rust formed on this steel. The Al K spectrum of the rust exhibited a peak that was the same as that of Al₂O₃ in the EPMA and TEM-EELS (electron energy loss spectroscopy) analysis. This result suggests that Al was present in the complex oxides as Al³⁺. In the same way, Si was identified as being in an intermediate state in the complex oxides of the inner rust.EIS measurement of the exposure test samples revealed much higher rust resistance (R_rust) and corrosion reaction resistance (R_t) of Si- and Al-bearing steel compared to that of SM. Finally, it was found that nanoscale complex iron oxides formed in the inner rust of Si- and Al-bearing steel, resulting in increased R_rust and R_t, and corrosion suppression.     

铸造低合金钢的生产

通过对低合金钢中合金元素作用的介绍,针对低合金钢铸造性能特点,提出低合金钢铸造过程应注意的事项,尤其是要加强熔炼过程及铸件在后道工序热割处理过程的控制,是有效提高铸件质量,降低生产成本,提高市场竞争力的有力措施.     

Composition and protective ability of rust layer formed on weathering steel exposed to various environments

The compositional change of rust (corrosion products) layer formed on weathering steel exposed to atmosphere with different amount of air-borne sea salt particles in Japan have been investigated by the X-ray diffraction method. The mass ratio (α/γ) of crystalline α-FeOOH to γ-FeOOH, in the rust layer formed on the weathering steel exposed in an industrial environment, increases with an increase in exposure duration. The α/γ is closely related to the corrosion rate in environments when the amount of air-borne salt is less than 0.2 mg NaCl/dm²/day (2.31 × 10⁻⁷ g NaCl/m²/s). However this is not the case in seaside environments with a higher amount of air-borne salts. The mass ratio (α/γ^∗) of crystalline α-FeOOH to the total mass of γ-FeOOH, β-FeOOH and Fe₃O₄, in the rust layer formed on the weathering steel is related to the corrosion rate even in seaside environments certainly more than 0.2 mg/dm²/day (2.31 × 10⁻⁷ g/m²/s) of air-borne salt particles. When the α/γ^∗ is more than 1, a higher corrosion rate more than 0.01 mm/year (3.17 × 10⁻¹³ m/s) is not observed. The α/γ^∗ is a protective ability index of rust formed on weathering steel.     

合金钢高温防护涂料的研制及性能

针对合金钢在高温下出现的氧化、脱碳,以及由其造成的钢材制造过程中材料利用率降低、钢材主要性能下降的现象,提出在热处理、锻造、轧制等热加工前,在合金钢表面施加保护涂层.同时,讨论了合金钢高温防护涂料的研制过程、作用机理及性能.合金钢高温防护涂料在高温下会迅速烧结致密,并与钢材紧密结合,隔绝氧气,同时防止合金钢内部的碳元素...     

Electroslag cladding of low alloy steel with stainless steel

Abstract

Cladding of a low alloy steel slab with stainless steel was carried out using a modified electroslag remelting technique. It is shown that the thickness of the cladding that can be achieved via electroslag remelting is dependent on the fill ratio used. The effect of power input on the joint profile obtained is reported. A combination of low fill ratio and relatively low power input is essential to minimise penetration of the base slab by the liquid metal. A satisfactory joint profile and defect free joint can be obtained via the optimisation of these process parameters. The clad product was successfully forged and rolled, which indicates satisfactory strength of the clad joint.     

低碳低合金钢焊缝韧性的影响因素

综合论述了合金成分、氧含量、微量元素、冷却速度以及强度对低碳低合金钢焊缝韧性的影响.适当的合金成分、氧含量和微量元素是获得良好的焊缝冲击韧性的基本条件.对于一种焊接材料,根据WM - CCT图选择合适的冷却速度可获得理想的微观组织.不同强度级别对焊缝的韧性影响不同.     

PVD hard coatings on prenitrided low alloy steel

The combination of traditional surface treatments such as nitriding with modern plasma-enhanced surface technologies reveals the possibility, particularly in the application to low alloy steels, of obtaining mechanical properties comparable with those of high alloy steels. Gas-nitrided samples of the hardened and tempered low alloy steels 30CrMoV9 and 17CrMoV10 were TiN coated by r.f. magnetron sputtering and ion plating. The requirements to obtain a nitrided substrate that can be coated were given special consideration. For this, various surface modifications of the nitrided substrates were realized by bright nitriding, nitriding with a compound layer and additional steps before coating, such as polishing, grinding and sputter cleaning.

The properties of prenitrided coated steels essentially depend on the structure and properties of the outer part of the nitrided case. TiN on bright nitrided and nitrided substrates with the compound layer removed has a better adherence than on compound layers. The decomposition of the iron nitride during the plasma sputter cleaning of compound layers results in a lower surface hardness and lower adherence of TiN. The highest wear resistances in the Timken test were registered on samples where the compound layer had been removed before TiN coating.     

微量Nb对低碳低合金管线钢相变的影响

采用Gleeble-1500D型热模拟机,测定了不同Nb含量的低碳微合金管线钢在不同冷却速度下,过冷奥氏体连续冷却相变点,分析观察了显微组织,测定了其显微硬度.结果表明,在同一冷速下,随着Nb含量的增加,过冷奥氏体连续冷却相变点降低,组织中容易出现板条状贝氏体铁素体,显微硬度提高;在相同成分下,随着冷速的增加,含铌钢中铁素体越来越细小,由等轴大块铁素体组织向板条状贝氏体铁素体转变,显微硬度提高.     

低合金钢中合金元素高温氧化行为研究

对低合金钢进行了900~1 200 ℃高温氧化实验,对钢中Si、Mn、Cu、Cr和Ni等合金元素的高温氧化行为进行了研究。结果表明：高温下Si元素与Cu元素存在明显的富集,Si元素会氧化生成Fe2SiO4,阻碍铁离子在氧化铁皮中的扩散,使钢具有一定的抗氧化性;Cu元素可以改善钢的强度、韧性与耐腐蚀性,但是高温氧化后极易形成“富铜液相”,导致出现“铜脆”现象;在1 200 ℃下,Cr元素和Ni元素也会发生富集,Cr在高温下会在氧化铁皮和基体钢之间形成FeCr2O4,同样具有一定的抗氧化性;Mn的氧化物与Fe的氧化物很相似,两者相应氧化物有很高的互溶度;Ni元素对氧化过程没有较大的影响。     

合金元素对低合金耐磨钢组织及性能的影响

对不同合金元素含量的低合金耐磨钢进行淬火加回火热处理后,测试力学性能及－40 ℃冲击吸收能量,借助SEM、TEM等分析组织及析出相,研究合金元素对低合金耐磨钢的组织和性能的影响。结果表明：含有Ni、Cu、Cr、Mo等合金元素的试验钢淬火及190 ℃低温回火后均得到板条状马氏体组织,马氏体板条间有细小碳化物析出相。而没有添加Ni、Cu及少量添加Cr、Mo元素的试验钢淬透性降低,淬火及低温回火组织为马氏体及少量铁素体。添加Ni、Cu、Cr、Mo等合金元素的试验钢淬火及低温回火后得到较好的综合力学性能,最佳性能为屈服强度1218 MPa,抗拉强度1507 MPa,硬度429.5 HV,－40 ℃冲击吸收能量27.7 J。     

Influence of the alloy element on corrosion morphology of the low alloy steels exposed to the atmospheric environments

Morphology of the corroded surface of low alloy steels beneath rust after long-term exposure test in the atmospheric environment was analyzed. The form of the corroded surface was measured with the laser displacement sensor scanning the surface. The resultant height map was divided by the mesh and the maximum corrosion depth was calculated in each cell. The maximum depth was arranged by the extreme value analysis. From this analysis two kinds of corrosion patterns were distinguished; i.e., uniform corrosion and local corrosion. Electrolytic iron shows the only uniform corrosion pattern. The addition of Cu, Ni and Cr changed the form of the corroded surface from the uniform corrosion to the combined pattern (uniform corrosion + local corrosion). The addition of Cr has a marked effect in changing the corrosion pattern.     

Taxonomy for protective ability of rust layer using its composition formed on weathering steel bridge

For a quantitative evaluation of the protectiveness of a rust layer formed on a weathering steel bridge, the relationship between the corrosion rate of the bridge and the composition of the rust layers formed on the girders was first investigated. These corrosion rates were clearly classified by the protective ability index (PAI) of α/γ^∗ and (β + s)/γ^∗, where α, γ^∗, β and s are the mass ratio of crystalline α-FeOOH, the total of γ-FeOOH, β-FeOOH and the spinel-type iron oxide (mainly Fe₃O₄), β-FeOOH and spinel-type iron oxide, analyzed by XRD, respectively. The inequality of the former index α/γ^∗ > 1 expressed the protectiveness criterion of the rust layer, while that of the latter index, (β + s)/γ^∗< 0.5 or > 0.5, classified the corrosion rate of the non-protective rust layer. The PAI is useful for a quantitative evaluation of the protectiveness of a rust layer formed on a weathering steel bridge and is an important item for the corrosion assessment of the bridge.     

Investigation on the mechanism of steel/steel solid-state bonding at low temperatures

The solid-state bonding of ultralow-carbon steels was conducted by hot pressing and subsequent isothermal holding at low temperatures ranging from 873 to 923?K. The evolution of the interfacial strength was found to consist of two stages; the first stage, where the increase in interfacial strength is rapid and significant, and the second stage, where the increase is gradual. The evolution of strength in the first stage primarily takes place in contact regions produced by hot pressing. In the second stage, on the contrary, the evolution seems to result from the increase in the contact regions due to the shrinkage of voids. A molecular dynamics simulation was performed to clarify the atomic behaviour at the interface during the first stage. The results revealed that the disordered atomic arrangement caused by compression was rearranged with increasing isothermal holding time, leading to improved coherency between the contact regions and increased interfacial strength.     

一种低碳低合金钢的纳米压痕表征

对具有两种不同组织状态的一种低碳低合金钢进行了纳米压痕表征．结果表明,在双相组织试样中,马氏体的硬度高于铁索体的70％以上．在纳米压痕实验过程中,由于马氏体相的尺寸较小并被软的铁素体基体所包围,当压痕深度超过40nm时,纳米压痕硬度呈现出明显的基底效应．由于在铁索体一奥氏体两相区加工过程中发生C元素向奥氏体的分配,双相组织试样中的马氏体中富集了数倍于钢的名义含量的C元素．结果导致双相组织试样中马氏体的平均纳米压痕硬度比同一钢的全马氏体组织试样高出30％以上．此外,还讨论了C的富集分配对马氏体Poisson比和Young’s模量的可能影响．