High-temperature corrosion and creep of Ni-Cr-Fe alloys in carburizing and oxidizing environments

The carburization of NiCr 32 20 and NiCrSi 60 16 has been studied in CH₄-H₂ mixtures in the temperature range 900–1100°C. The methods included thermogravimetric measurements and studies on reacted specimens by X-ray diffraction, metallographic, and chemical analysis. Upon carburization internal carbides M₇C₃ and M₂₃C₆ are formed (M=mainly Cr); the rate of carburization is determined by carbon diffusion in the Fe-Ni matrix with carbide precipitations. The effect of the alloying elements Ni and Si on the carburization resistance of austenitic alloys is explained. By the same methods the oxidation and carburization in CO-H₂O-H₂ mixtures have been studied. The important role of a stable chromium oxide layer for the carburization resistance was confirmed. Creep tests at 1000°C in a CO-H₂O-H₂ atmosphere where Cr₂O₃ is stable showed carburization occurring through cracks in the oxide layer. At high strain rates premature failure occurs by carburization, which is followed by internal oxidation and formation of cracks, voids, and holes.     

Environmental effects on the stress corrosion cracking susceptibility of 3.5NiCrMoV steels in high temperature water

Constant elongation rate tests (CERTs) were carried out to investigate the effects of environmental factors of dissolved oxygen and temperature on the stress corrosion cracking (SCC) susceptibility of 3.5NiCrMoV turbine steels. Tests were conducted in pure water of various dissolved oxygen concentrations at temperatures of 50 °C-200 °C in the range of strain rates from 5 × 10⁻⁸/s to 1 ×  10⁻⁶/s. Dissolved oxygen significantly affected the SCC susceptibility of turbine steels in water. The SCC susceptibility of the turbine steels increases as the dissolved oxygen concentration in water increases. The elongation of the turbine steels tested in aerated water at 150 °C at a strain rate of 1 × 10⁻⁷/s decreased to half of that of the steels tested in deaerated water in the same test condition. And the SCC susceptibility of the steels increased with decreasing strain rate, and with increasing temperature. The increase of the SCC susceptibility of the turbine steels in the higher dissolved oxygen environment is considered to be due to the higher content of dissolved oxygen enhancing the reduction reactions of oxygen on the metal surfaces (cathode) and accelerating the dissolution rate at the crack tips (anode) by galvanic attack of an aeration cell.     

Spheroidization of medium-carbon steels

Spheroidization experiments were made on a medium- carbon AISI 4037 steel, using both intercritical and subcritical annealing cycles. The results indicate that in the subcritical cycle the spheroidization occurred much more quickly than expected, so that shorter times were sufficient to achieve high formability. On the other hand, the hardness dropped faster in the intercritical cycle. Although more work needs to be done, these results suggest that using a subcritical spheroidization process instead of an intercritical process could achieve considerable savings in time, energy, and cost.     

304不锈钢精铸件点缺陷的形成与控制

针对典型304不锈钢精密铸件内出现的黑色点缺陷,对其表面形貌、成分进行了分析,并在此基础上总结了缺陷的形成机制,确定了相应的防止措施。研究结果表明,铸件内的点缺陷可以划分为两类:一类具有不规则截面,为脱蜡过程中剩余腊料的燃烧残留物;另一类为熔炼过程中,由于脱氧剂和除渣剂的去除不彻底而引入的夹杂。通过优化脱蜡和熔炼工艺,使得铸件内的点缺陷得到了很好的控制。     

奥氏体不锈钢车削时刀具磨损对切削因素和表面质量的影响研究

研究了奥氏体不锈钢车削加工过程中刀具后刀面磨损对切削力、切削温度、粗糙度及残余应力影响规律。试验结果表明:当刀具后刀面磨损在一定范围内,F_x与F_z随磨损量的增加而显著增大,而F_y基本保持不变;温度随刀具后刀面磨损量增加而显著增大;工件的表面粗糙度随刀具后刀面磨损量增大而增大;当车刀后刀面磨损为0.167 mm时,工件加工表面的残余应力最大。     

Effect of temperature on anodic behavior of 13Cr martensitic steel in CO2 environment

The corrosion behavior of 13Cr martensitic stainless steel in a CO₂ environment in a stimulated oilfield was studied with potentiodynamic polarization and the impedance spectra technique. The results showed that the microstructure of the surface scale clearly changed with temperature. This decreased the sensitivity of pitting corrosion and increased the tendency toward general (or uniform) corrosion. The capacitance, the charge transfer resistance, and the polarization resistance of the corrosion product scale decrease with increasing temperature from 90 to 120 °C, and thus the corrosion is a thermal activation controlled process. Charge transfer through the scale is difficult and the corrosion is controlled by a diffusion process at a temperature of 150 °C. Resistance charge transfer through the corrosion product layer is higher than that in the passive film.     

渗铝304不锈钢不同实验方法的SCC敏感性评价

采用恒载荷试验方法及慢应变速率试验(SSRT)方法研究了渗铝304奥氏体不锈钢在沸腾42％MgCl2溶液中的应力腐蚀破裂(SCC)性能，分析了渗铝不锈钢SCC机理，讨论了不同试验方法对渗铝不锈钢SCC敏感性评价的影响．试验表明：渗铝处理可明显提高304钢抗SCC性能，其机理为渗铝层的环境遮断作用及对基体的电化学保护作用．两种方法在评价各种渗铝钢材料SCC性能方面有统一性：恒载荷试验中SCC敏感性指标σth高的材料，SSRT中SCC敏感性指标δi也相对较高．但两种方法中渗铝试样的断口形态表现出差异：恒载荷试验为穿晶型SCC断口，而SSRT无SCC断口特征，为韧性断口。     

High-temperature oxidation of aluminum electroplated Fe-Mn alloys

Austenitic Mn-Al alloys (20–32 W/O Mn, 7–10 Al, 2–3 Si, 1C) were found to have satisfactory oxidation resistance up to 950°C under isothermal conditions in air. Surface enrichment of aluminum is a necessary condition for obtaining an almost pure alumina scale for uses at higher temperatures. Four different Mn-steels were Al-coated by the Capuano electroplating process. In all the steels there was an increase in the hot-oxidation resistance. The best results were obtained with steels containing both Al and Si, and this for temperatures up to 1100°C. No spalling was noticed during rapid cooling of the test pieces. Silicon was found to act as a diffusion barrier to outward iron diffusion. It appears that there is formation of a pure, thin film of alumina from the matrix which interacts with the aluminum diffusing from the superimposed, coating for the formation of good bonds.     

韩国不锈无缝钢管工业考察

详细介绍了韩国三美（ＳＡＭＭＩ）钢公司的不锈无缝钢管生产设备及工艺。