N对微Ti高强焊丝熔敷金属韧性的影响

采用电化学分析的方法对熔敷金属中的N化物相分析发现,熔敷金属中与Ti结合的N量很低,70%左右的N仍以固溶形式存在,约为100ppm左右。通过透射电镜及X射线衍射分析发现,熔敷金属中的针状铁素体晶界分布着一定量的残留奥氏体。分析认为,N一方面对残留奥氏体的形成起到了促进的作用;另一方面,又被这部分残留奥氏体固定,使相对铁素体为过饱和的N量对熔敷金属的冲击韧性不产生有害的影响。     

元素V对奥氏体焊缝金属晶间腐蚀敏感性的影响

采用透射电镜(TEM)分析技术研究了1Cr19Ni23N焊条熔敷金属中钒含量对组织及对熔敷金属抗晶间腐蚀性能的影响.结果表明,低钒含量焊条熔敷金属组织中沿奥氏体晶界析出M23C6型富铬碳化物,在晶界附近形成贫铬层,导致晶间腐蚀的发生;高钒含量焊条熔敷金属组织中,V优先于Cr与C形成细小弥散的碳化钒分布在晶粒内部,使得该焊条在保持原较高碳含量的基础上,通过改变碳化物形态和分布达到了保持高强度和改善晶间腐蚀敏感性的目的.     

外场处理细化管线钢埋弧焊缝的显微组织

研究了电磁搅拌和氩弧表层快速加热等外场对管线钢埋弧焊缝显微组织的影响。结果表明,电磁搅拌改变了焊缝中非金属杂夹物的大小和尺寸分布,使尺寸位于0.2～0.6μm之间的夹杂物数量增加,促进了奥氏体晶粒内针状铁素体的生成和细化,针状铁素体的含量由85.1%提高到了91.7%,提高了熔敷金属的韧性。而氩弧加热处理使焊缝表层的柱状晶消失,针状铁素体晶粒明显细化,并消除了对性能有害的组织-晶界铁素体和侧板条铁素体。     

氧对00Cr13Ni5Mo熔敷金属组织和韧性的影响

文中研究了MAG焊保护气体氧含量变化对00Cr13Ni5Mo熔敷金属中氧化物夹杂类型、尺寸、数量、分布和残余奥氏体、逆变奥氏体含量以及冲击韧性的影响.结果表明,Si-Mn-O,Si-Mn-Al-O复合氧化物夹杂是导致00Cr13Ni5Mo熔敷金属冲击韧性下降的主要原因.氧化物夹杂对00Cr13Ni5Mo熔敷金属回火过程中产生的逆变奥氏体具有抑制作用,随着氧化物夹杂的增加,逆变奥氏体含量呈减少趋势.     

碳和氮元素对高强度奥氏体焊缝组织和性能的影响

采用扫描电镜(SEM)和透射电镜(TEM)等分析研究了碳、氮元素对奥氏体焊条熔敷金属组织和性能的影响.结果表明,随着碳含量的增加,熔敷金属晶界上M23C6碳化物析出物逐渐增多,析出颗粒增大,虽然熔敷金属的抗拉强度有所提高,但韧性明显降低,碳含量增加到一定程度后,对强度的影响趋于平缓,但对晶界碳化物的数量和尺寸仍然有强烈的促进作用,韧性持续降低,耐晶间腐蚀性能大大降低.随着氮含量的增加,抗拉强度呈持续上升趋势,同时韧性仍能保持在较高水平,晶界上析出碳化物少,抗晶间腐蚀性能良好.     

超级双相不锈钢多层多道焊接接头组织及腐蚀性能

选用2507超级双相不锈钢作为研究对象,研究钨极氩弧焊多层多道焊接接头的组织和腐蚀性能.采用两种不同保护气进行钨极氩弧焊,主要讨论焊接道次和氮气添加对组织和腐蚀性能的影响.结果表明,焊缝中心均有较高的奥氏体含量,其腐蚀速率是焊根部位的0.68倍;盖面和焊根奥氏体含量相近,但盖面由于其弥散且尺寸相对较大的晶内奥氏体表现出更好的耐腐蚀性,焊根是焊缝金属的薄弱区域.混合区由于热影响区的存在腐蚀速率最快.保护气中氮气的添加促进了奥氏体的生成,降低了腐蚀电流密度一个数量级,提高了整体的腐蚀性能.     

Comparison of two types of low-transformation-temperature weld metals based on solidification mode

Two types of low-transformation-temperature weld metals were devised, one associated with primary austenite solidification, the other primary ferrite solidification. The martensite start temperature of both low-transformation-temperature weld metals was about 125°C. Experimental results showed that low-transformation-temperature weld microstructure associated with primary austenite solidification was martensite with 8.0% retained austenite, whereas that one related to primary ferrite solidification primarily consisted of martensite and δ-ferrite. Accordingly, both welded joints had little distinction between distortion and residual stress, indicating that weld metal associated with primary ferrite solidification played the same function as primary austenite solidification on residual stress reduction. Moreover, the low-transformation-temperature weld metal associated with primary ferrite solidification had higher tensile strength and hardness than that based on primary austenite solidification.     

Effect of nitrogen on corrosion behavior of 28Cr-7Ni duplex and microduplex stainless steels in air-saturated 3.5 wt% NaCl solution

The corrosion behavior of 28Cr-7Ni-O-0.34N duplex stainless steels in air-saturated 3.5-wt% NaCl solution at pH 2, 7, 10 and 27 °C was studied by the potentiodynamic method. Two types of microstructures were investigated: the as-forged duplex and microduplex (average austenite grain size 5-16 μm) structures. The austenite volume fractions of the tested steels were between 0.35 and 0.64. The nitrogen effect on corrosion behaviors of both duplex and microduplex stainless steels were the same. At pH 2, the corrosion potential increased when the nitrogen content increased, however, corrosion current density as well as corrosion rate decreased. At pH 7 and 10, the effect of nitrogen on corrosion potential and corrosion rate could not be observed. Corrosion potential at pH 10 was lower than at pH 7. Pitting potential increased when the nitrogen content in the tested steels increased at all tested pH. For the nitrogen effect on the passive current density, it seemed that only at pH 2, the average passive current densities reduced when the nitrogen content increased. Nitrogen may have participated in the passive film or has been involved in the reaction to build up passive film. The ammonium formation and nitrogen enrichment at the interface metal/passive film with adsorption mechanism were discussed. The dissolute nitrogen might have combined with the hydrogen ions in solution to form ammonium ions, resulting in increasing solution pH. The steel could then easily repassivate, hence the corrosion potential and pitting potential would increase. However, the ammonium formation mechanism could not explain the decrease of corrosion potential in basic solution. Nitrogen enrichment at the metal/passive film interface with adsorption mechanism seemed to be an applicable consideration in increasing pitting potential. However, this mechanism did not involve the ammonium ion formation. In general, for the duplex and microduplex stainless steels tested, nitrogen increased the general corrosion resistances in acid solution and pitting corrosion resistance at all solution pH. Metallographic observation in both tested duplex and microduplex steels after pitting corrosion at all tested pH revealed that, the corroded structure in the tested steels without nitrogen alloying was austenite, but those with nitrogen alloying was ferrite. Even though ferrite had a higher chromium content than austenite but higher dissolved nitrogen in austenite than in ferrite may have increased the pitting resistance equivalent number (PRE) of austenite to be higher than that of ferrite.     

THE EFFECT OF BORON AS A FUNCTION OF AUSTENITISING TEMPERATURE

奥氏体化温度对硼钢淬透性的影响,从实验结果得到,在各种热处理条件下均随温度的提高逐渐降低。氧化及氮化的因素对硼钢淬透性的下降是有一定的影响,但硼原子本身在奥氏体中的分布情况对淬透性的影响是更重要的一个因素。 在渗硼试样中观察硼化合物的形成,指出,从高奥氏体化温度直接淬火后,硼的沉淀物是在奥氏体晶界上及晶粒内均匀分布的,但在等温处理、正火处理或慢冷试样中,硼化合物大部份沉淀在奥氏体晶界上。因此,硼钢在高温奥氏体化后失去良好淬透性的原因,可能是由于硼原子从奥氏体晶界上的回扩散作用,使晶界上得不到足够的硼原子降低晶界能,引起硼的效能暂时的消失。     

Effect of silicon on the spheroidization of cementite in hypereutectoid high carbon chromium bearing steels

The effect of silicon on the spheroidization of cementite in hypereutectoid high carbon chromium bearing steels has been investigated on the basis of microstructural analysis and thermodynamic calculations. The results showed that an increase of silicon content in high carbon chromium bearing steels retards the spheoridization of cementite. The thermodynamic calculations revealed that the shrinkage of the austenite phase field in bearing steels with increasing silicon content gave rise to an increase of volume fraction of cementite at an annealing temperature, possibly resulting in incomplete spheroidization. Furthermore, due to the low solubility of silicon in cementite, an increase of silicon content can raise the activity or chemical potential of carbon atoms in austenite at the austenite/cementite interfaces. Consequently, the difference in chemical potential of carbon atoms at the interfaces would be reduced with increasing silicon content, causing a decrease of the driving force for their diffusion from cementite to austenite.