淬火温度对高硼铸钢显微组织和硬度的影响

研究淬火温度对含碳量小于0．4％和含硼量小于2．0％的高硼铸钢显微组织和硬度的影响。高硼铸钢铸态基体组织由珠光体和铁素体组成。淬火处理后，硼化物数量变化不明显，随着淬火温度升高，基体显微硬度和试样宏观硬度提高，淬火温度超过1000℃后，硬度略有降低。在900~1100℃内淬火，都可获得强韧性好的板条马氏体基体组织。高硼铸钢中的硼化物显微硬度超过1500HV，由F32B和少量FeB组成。     

合金元素对耐候熔敷金属力学及耐蚀性能的影响

采用周浸加速腐蚀试验,模拟工业大气腐蚀环境,通过组织分析、锈层微观成分及形貌分析、电化学分析等手段,研究了Ni,Cr,Cu元素对耐候熔敷金属耐蚀性能及力学性能的影响规律. 结果表明,Ni元素有利于增加组织中针状铁素体含量,提高熔敷金属−40 ℃冲击韧性,Cr元素增加,熔敷金属−40 ℃冲击韧性降低. 合金元素有利于提高腐蚀锈层中的α-FeOOH的含量,增加锈层致密度,提高锈层阻抗,降低自腐蚀电流密度. Cu元素有利于提高熔敷金属腐蚀初期和后期的耐蚀性能;腐蚀初期,Cr元素提高耐蚀性能的作用不如Cu和Ni,但是腐蚀后期Cr提高锈层耐蚀性能的作用明显.     

热处理工艺对5Cr钢力学性能和耐蚀性能的影响

利用光学显微镜、拉伸及冲击试验机等仪器研究了不同热处理工艺对5Cr钢组织和力学性能的影响,利用高温高压反应釜模拟腐蚀过程,并结合电化学测试对比分析了热轧态和调质态钢的耐腐蚀性能。结果表明:5Cr钢经淬火+回火处理后,组织中碳化物弥散析出,具有较高的强度和良好的塑、韧性。热轧态钢的腐蚀速率为0.188 mm/a,调质态钢为0.158 mm/a。调质态钢中作为阴极的碳化物(Fe₃C)少且均匀弥散分布,组织自腐蚀电位较高,腐蚀电流密度较低,电偶腐蚀程度较浅,耐腐蚀性能较好。     

热镀锌层上磷酸锌转化膜的生长与耐蚀性

热镀锌钢板在pH3.0、45℃的磷酸锌溶液中磷化2～600s,用扫描电镜、能谱仪和X射线衍射仪分析磷化膜的组织形貌和成分,并探讨膜层的生长行为。结果表明:磷酸锌晶体在锌晶粒内及晶界处均可成核,开始是以接近平行的片状生长,并逐渐向多方向生长成扇骨状的晶片。随着磷酸锌晶体的成核和生长,磷化膜的覆盖率增加,但晶体之间的孔隙难以完全消除;长大的磷酸锌晶片容易折断脱落,导致磷化后期膜层的质量增量减小;磷化膜主要由Zn3(PO4)2.4H2O组成。热镀锌钢板经磷化处理后,耐蚀性显著提高,磷化膜的耐蚀性随磷化时间和膜层覆盖率的增加而提高。     

Effects of boron concentration on the corrosion resistance of Fe-B alloys immersed in 460 °C molten zinc bath

In order to investigate the effects of boron concentration on the corrosion resistance of Fe-B alloys in molten zinc, Fe-B alloys, with the boron concentrations of 1.5 wt.%, 3.5 wt.% and 6.0 wt.% respectively, were dipped into a pure molten zinc bath at 460 °C and kept in different time intervals. The results show that, in comparison with 1Cr18Ni9Ti stainless steel, Fe-B alloy with 3.5 wt.%B exhibits excellent corrosion resistance, due to the dense continuous network or parallel Fe₂B phase which hinders the Fe/Zn interface reaction in Fe-B alloys. The energy dispersive spectrum (EDS) results indicate that the coarse and compact δ phase with the length about 40 μm generates near the matrix of Fe-B alloy and massive ζ phase occurs close to the liquid zinc. The corrosion process includes Fe/Zn reaction and the isolation and fracture of Fe₂B. The failure of boride is mainly caused by the microcrack.     

固溶温度对2507双相不锈钢力学性能及耐蚀性的影响

利用光学显微镜、扫描电镜、XRD、拉伸试验机和电化学综合测试仪等研究了不同固溶温度对2507超级双相不锈钢组织、力学性能和耐蚀性的影响。采用Thermo-Calc热力学软件计算了2507双相不锈钢的热力学平衡相图,并与测试结果进行了对比。研究结果表明,经1050 ℃及以上温度固溶后,σ相溶解;随着固溶温度的升高,铁素体相含量增加,奥氏体相含量降低,α/γ相体积分数比增加;1050~1100 ℃固溶30 min并水冷时,双相不锈钢具有较好的综合力学性能,屈服强度、抗拉强度和伸长率分别大于600 MPa、840 MPa和35%。1050 ℃固溶30 min时,双相钢可获得较好的耐蚀性能。     

铬、钼对耐候钢熔敷金属耐蚀性能和力学性能的影响

通过周浸加速腐蚀试验、锈层微观分析、电化学等方法,研究了铬和钼对耐候钢熔敷金属耐蚀性能和力学性能的影响.结果表明,熔敷金属中铬、钼含量增加,其耐蚀性能提高.钼对耐蚀性的提升优于铬.铬、钼分别以Cr₂O₃,Fe_xCr_3-xO₄,MnFe_xCr_2-xO₄,Mn_1-xFe_xCr₂O₄,NiFe_xCr_2-xO₄和MoO₃形式富集于锈层中,提高锈层致密性,抑制阳极溶解,增强锈层对基体的保护作用,从而提高熔敷金属的耐蚀性能.铬、钼含量增加,熔敷金属强度上升,冲击韧性明显下降.同时,熔敷金属中M-A组元和粒状贝氏体含量增加,针状铁素体含量降低.组织差异是造成熔敷金属强度升高、韧性降低的主要原因.     

热处理对K55钢耐蚀性的影响

研究了热处理对K55钢硬度、显微组织的影响,通过测定极化曲线分析其耐腐蚀性的变化规律。结果表明,热处理改善了K55钢的组织结构,腐蚀倾向降低,试样耐蚀性提高。淬火+高温回火试样硬度最高,正火+退火试样硬度最低。通过电化学测试得到的阳极极化曲线上不存在钝化区,热处理后K55钢均没有产生钝化倾向。正火后试样获得了均匀的细晶粒珠光体组织,腐蚀电流最小,自腐蚀电位最低,耐蚀性最好。     

Growth and corrosion resistance of molybdate modified zinc phosphate conversion coatings on hot-dip galvanized steel

The modified zinc phosphate conversion coatings（ZPC） were formed on hot-dip galvanized（HDG） steel when 1.0 g/L sodium molybdate were added in a traditional zinc phosphate solution. The growth performance and corrosion resistance of the modified ZPC were investigated by SEM, open circuit potential（OCP）, mass gain, potentiodynamic polarization and electrochemical impedance spectroscopy（EIS） measurements and compared with those of the traditional ZPC. The results show that if sodium molybdate is added in a traditional zinc phosphate solution, the nucleation of zinc phosphate crystals is increased obviously; zinc phosphate crystals are changed from bulky acicular to fine flake and a more compact ZPC is obtained. Moreover, the mass gain and coverage of the modified ZPC are also boosted. The corrosion resistance of ZPC is increased with an increase in coverage, and thus the corrosion protection ability of the modified ZPC for HDG steel is more outstanding than that of the traditional ZPC.     

Effects of Sn and Ca additions on microstructure,mechanical properties,and corrosion resistance of the as‐cast Mg‐Zn‐Al‐based alloy

Effects of Sn and Ca additions on microstructure, mechanical properties, and corrosion resistance of the as‐cast Mg‐6Zn‐2Al‐based alloy were investigated by SEM, XRD, tensile tests, electrochemical measurements, etc. The higher the Sn content, the higher the yield strength of the Mg‐6Zn‐2Al‐based alloy. Trace Ca addition refined both grains and divorced eutectics in the Mg‐Zn‐Sn‐Al alloys, leading to the best combination of strength and plasticity. Moreover, its influence was more significant for the alloy with a higher Sn content. Furthermore, the combined addition had a beneficial effect on the corrosion resistance improvement of the Mg‐6Zn‐2Al alloy. The Mg‐6Zn‐2Al‐3Sn‐0.2Ca alloy was the most corrosion‐resistant alloy among the nine alloys studied, better than AZ91 and ZA85. It could be ascribed to the decrease and the refinement of divorced eutectics, the higher hydrogen overvoltage of Sn and the Ca grain refinement.     

Corrosion resistance of a cast steel overpack for high-level radioactive waste disposal in Japan

The corrosion rate and stress corrosion cracking (SCC) susceptibility of a cast steel are studied for its application to metal containers (namely overpacks) for geological disposal of high-level radioactive waste. Specimens for corrosion tests are cut from a prototype overpack manufactured by full-scale casting. Casting defects are widely distributed in the prototype overpack; however, the flat-bottom hole equivalent diameters for all defects detected by an ultrasonic test are 3.6 mm or less, which is relatively small. Forged steels and rolled steels are also tested for comparison of their corrosion properties with the cast steel. The corrosion rates are obtained by immersion tests in bentonite saturated with synthetic seawater under anaerobic conditions at 80°C for up to 1 year. The corrosion rate for the cast steel calculated by the weight loss during the experiments is close to that for the forged steels and rolled steels. The SCC susceptibility is examined using slow strain rate tests in a 1.5-mol L⁻¹ carbonate–bicarbonate solution, in which the occurrence of high-pH SCC is often reported for carbon steels. The SCC susceptibility increased with the increase in the carbon content of the products; however, there are no clear differences between casting and forging.     

Influence of corrosion on the interface between zinc phosphate steel fiber and cement

The interface bond between steel fibers and concrete matrix is a key factor influencing bearing capacity of steel fiber reinforced concrete (SFRC). In order to improve the interface bond strength and corrosion resistance, a kind of method was put forward by depositing zinc phosphate (ZnPh) coating on steel fiber surface in this paper. The corrosion behavior was investigated in 5% NaCl solution by using linear polarization measurement. Microstructure analysis (SEM and EDX) and fiber pull‐out test in combination with linear polarization measurement were carried out. The results prove that ZnPh coatings fabricated on the carbon steel surface can not only protect steel fiber against corrosion, but also enhance the mechanical interlocking bonds between fibers and matrix.     

Long‐term atmospheric corrosion rates of hot dip galvanised steel and zinc‐aluminium‐magnesium coated steel

Zn coated steel (Z) and ZnAlMg coated steel (ZM3.7/3 = Zn–Al (3.7 wt.%)‐Mg (3.0 wt.%)) have been exposed for 6 years at twelve different weathering sites world wide. The mass loss of the coatings have been measured after 1, 2, 4, and 6 years exposure. From the results, it is shown that ZM3.7/3 had always a better corrosion performance compared to Z. The ratio of performance after 6 years of exposure varied from about 1.4 to 4.4 with a mean value of 2.8. At temperate marine sites (e.g., temperature between 9–20°C) with low to moderate SO ₂ pollution a good relationship was observed between the relative performance of ZM3.7/3 and the corrosion rate of Z. It was thus concluded that ZM3.7/3 has a better relative performance in harsh environments. The corrosion performance of ZM3.7/3 was shown to be connected to the formation of protective corrosion products.     

Nb微合金化对准贝氏体耐磨铸钢组织和性能的影响

研究了铌(Nb)微合金化对准贝氏体耐磨铸钢的组织和性能的影响。使用热膨胀测试仪、扫描电镜、拉伸及冲击试验和磨损试验等分析了含铌量不同的低碳(约0.26%)铸钢的组织和力学性能。结果表明,Nb的添加促进了准贝氏体的生长,当Nb含量从0%增加至0.062%时,原始奥氏体晶粒从120.81 μm减小至87.65 μm,平均晶粒尺寸减小27.4%。同时,Nb的添加降低了钢的磨损率,硬度也有所降低,但冲击吸收能量、侧膨胀值、屈服强度、抗拉强度和断面收缩率均有所提高。当Nb含量为0.024%时,磨损率最低为0.104%,耐磨性能最好,且综合力学性能最好,其硬度为420.4 HV0.1,冲击吸收能量为42.6 J,侧膨胀值为67%,屈服强度为826 MPa,抗拉强度为1326 MPa,断面收缩率为7.7%,残留奥氏体含量较高为8.4%。     

焊接方法对双相不锈钢焊接接头耐蚀性的影响

采用气体保护钨极氩弧焊（GTAW）、焊条电弧焊（SMAW）和埋弧焊（SAW）对2205双相不锈钢进行焊接,采用光学显微镜对接头组织进行观察,采用数点法计算铁素体相的含量,测定接头的耐点蚀和耐CO2应力腐蚀性能,研究焊接方法对接头耐蚀性的影响。结果表明,焊接方法影响焊缝组织形态及铁素体含量。GTAW焊缝由不规则的条状组织和两相交织分布的块状组织组成,而SMAW和SAW焊缝为方位不一的条状组织和少量的块状组织。GTAW和SMAW焊缝的铁素体含量为35％～55％,而SAW的不足20％。接头的耐蚀性与铁素体相比例密切相关,GTAW、SMAW和SAW的耐蚀性依次降低。从铁素体相比例和耐蚀性角度考虑,GTAW和SMAW能够获得满意的焊接接头。     

不同锰含量的Fe-Cr-Mn三元合金耐锌蚀能力

研制了4种Mn含量不同的Fe-Cr-Mn三元合金,并系统研究和分析了其在450℃熔融锌液中的腐蚀行为及组织变化规律。结果表明,4种不同锰含量的Fe-Cr-Mn三元合金腐蚀层的形貌基本相似,但与纯铁在液锌中的腐蚀形貌差别很大,其主要是由致密的δ相层和分布于η相中稀疏的ζ相颗粒组成,且δ相层厚度随锰含量的提高先增加后减少,其中属含Mn量为9.55%的Fe-Cr-Mn三元合金腐蚀层中致密的δ相层厚度最厚,表现出较好的耐锌蚀能力,同时,此三元合金基体与腐蚀层界面处存在Cr的富集区,此区约含27.48%的Cr,厚度在1μm左右。连续完整的富Cr抑制层的形成,能够减缓铁锌反应的速度,减慢对基体的腐蚀速度,提高了耐锌蚀能力。     

The study on corrosion resistance of high-strength spring steel

The corrosion resistance in medium carbon high-strength spring steel was investigated in neutral salt spray of 5% NaCl solution and potentiodynamic polarisation measurements. The results showed that the corrosion process in the salt spray environment could be divided into two stages. In the initial corrosion stage, the corrosion rates of tested steels were high and rapidly decreased with increasing corrosion time. At later stages where rust layers formed and the corrosion rates of the tested steels all tended to be stable, corrosion resistance was reinforced with the increase of alloying elements, which is just new finding about formation and evolution of corrosion products of spring steel to improve corrosion resistance further in this research. The observation of corrosion products of the tested steels by energy dispersive spectroscopy and electron probe micro-analysis indicated that both Cr and V which had an obvious synergy concentrated mainly in the inner region of the rust layers, and the corrosion medium Cl^– was mainly distributed in the outer region of the rust layers.     

回火工艺对ZG30Mn铸钢组织与力学性能的影响

基于光学显微镜(OM)对不同回火工艺参数下的ZG30Mn铸钢显微组织进行观察分析,同时进行拉伸性能、布氏硬度与冲击性能等力学性能检测。结果表明,经不同回火温度与回火时间处理后,ZG30Mn铸钢显微组织均以不同形态的回火索氏体为主。在相同的保温时间(90 min)下,随着回火温度(580、600、620、640 ℃)的升高,ZG30Mn铸钢的强度与硬度均不断减小,断后伸长率和冲击吸收能量均呈不断增大的趋势。在相同的回火温度(620 ℃)下,随着回火时间(30、60、90、120 min)的增加,ZG30Mn铸钢的强度与硬度均不断减小,但断后伸长率和冲击吸收能量呈现先增后减的变化趋势。回火温度对马氏体向索氏体转变过程起关键作用,温度的升高将影响α-Fe相回复和再结晶的效率,弥散的细小渗碳体逐渐长大并球化,导致强度与硬度降低,断后伸长率和冲击吸收能量增加。而回火保温时间将决定渗碳体的长大程度,随回火时间的增加,渗碳体的聚集长大导致断后伸长率和冲击吸收能量降低。     

N含量对13Cr超级马氏体不锈钢耐蚀性的影响

对13Cr超级马氏体不锈钢进行氮合金化,采用淬火-配分热处理工艺,研究了不同N含量对13Cr钢的微观组织及电化学腐蚀行为的影响。结果表明:随N含量增加,板条马氏体组织表现出明显的细化行为,奥氏体含量增加,且有VN生成,从而防止N与Cr结合生成Cr₂N,促使Cr在材料表面形成以Cr₂O₃为主的致密腐蚀产物膜,提高材料耐蚀性;试验钢表面以局部腐蚀为主,试样表面有点蚀发生。随着N含量的增加,形成腐蚀产物膜的孔隙度减小;表面钝化膜为双电层结构,增加了钝化膜的稳定性,点蚀坑数量明显减少且变小;提高N含量有利于试样耐点蚀性能的改善,0.35%N试验钢表面腐蚀产物附着牢固,平整且致密,晶粒大小均匀,可起到良好的保护作用。