氮对马氏体不锈钢00Cr13Ni4Mo组织和性能的影响

采用热膨胀仪、光学显微镜以及CM12型透射电子显微镜研究了添加0.04%N(质量分数)对00Cr13Ni4Mo马氏体不锈钢相变以及正火和回火后不锈钢组织变化的影响;通过拉伸、冲击实验和阳极极化曲线测定研究了N对正火和回火后马氏体不锈钢力学性能以及点蚀点位的影响。结果表明:1050℃正火后,N全部固溶于马氏体基体中,有效提高了实验钢的强度,同时降低了韧性;550℃以上回火后,在马氏体板条内部以及板条之间形成逆变奥氏体,有效提高了马氏体不锈钢的塑性和韧性;N抑制逆变奥氏体的形成,从而抑制了不锈钢在回火过程中的软化;同时,回火过程中,Cr2N在马氏体板条界面及内部大量析出,造成不锈钢韧性和点蚀点位下降。采用传统的正火+Ac1温度以上回火热处理工艺不利于含N马氏体不锈钢获得良好综合性能。     

Influence of tempering treatment on microstructure and pitting corrosion resistance of a new super ferritic–martensitic–austenitic stainless steels with 17%Cr

Supermartensitic stainless steels (SMSSs) allow high mechanical strength with better corrosion resistance and toughness than conventional martensitic stainless steels. The SMSS steels with 12–13%Cr have been studied and applied in the oil and gas offshore production. The increase of Cr content, and the addition of Mo and W is now being investigated to increase mechanical and pitting corrosion resistance. In this work, a new 17%Cr steel, with Mo and W additions was studied. Depending on the final tempering treatment, the steel has a complex microstructure of austenite, ferrite, martensite and precipitates. The pitting corrosion resistance also depends on the microstructure produced by tempering. It was found that the pitting potential slightly decreases with the increase of tempering temperature and is further decreased by the double-tempering treatment. The pits initiate and grow preferentially in the martensite or tempered martensite islands, due to the lower Cr, Mo and W contents of these areas.     

深冷处理后回火温度对15Cr超级马氏体不锈钢组织及耐点蚀性能的影响

利用场发射扫描电镜、透射电镜以及电化学综合测试系统对15Cr超级马氏体不锈钢(SMSS)经不同热处理工艺处理后的显微组织变化和第二相碳化物及其对该钢腐蚀行为的影响进行了研究。结果表明,试验钢经不同热处理工艺处理后组织均由板条马氏体、奥氏体以及M₂₃C₆型碳化物颗粒组成,随着回火温度的增加,试验钢中逆变奥氏体含量增加,且在650 ℃回火时达到体积分数最大值41.41%。当回火温度高于600 ℃时第二相碳化物开始析出,且650 ℃回火后碳化物数量及尺寸较600 ℃增多。点蚀电位随着回火温度的增加而降低,第二相碳化物的析出降低了试验钢的点蚀电位,促进了亚稳点蚀位置的形成,从而降低了试验钢的耐腐蚀性能。     

回火温度对00Cr13Ni5Mo超级马氏体不锈钢组织及性能的影响

研究了1050 ℃正火+550～700 ℃回火处理对00Cr13Ni5Mo超级马氏体不锈钢中厚板显微组织和力学性能的影响。结果表明,在1050 ℃正火后,随着回火温度的升高,板条状马氏体逐步分解,产生了逆变奥氏体组织,600 ℃回火时其含量最高,之后随着温度的升高逆变奥氏体的含量逐步降低;试验钢的强度、硬度及屈强比均随回火温度的升高先降低后升高。650 ℃回火时,可得到细密的回火索氏体+逆变奥氏体的复相组织,试验钢具有较低的屈强比及良好的冲击性能。     

Correlations between microstructure and surface properties in a high nitrogen martensitic stainless steel

Nitrided and tempered AISI 410S stainless steel was tested under corrosion–erosion conditions and compared to conventional AISI 420 martensitic stainless steel. The corrosion–erosion resistance of the nitrided specimens was higher than that of the AISI 420 steel when tempered at 200 °C, but it decreased with tempering temperature in the range between 200 and 600 °C. The higher corrosion–erosion resistance of the high-nitrogen steel was credited to a more homogeneous distribution of chromium in martensite and a lower number of coarse second-phase particles, especially for tempering temperatures below 550 °C. The hexagonal ϵ-nitride was identified in specimens tempered at 200 °C, while finely distributed cubic CrN nitrides were observed in specimens tempered between 400 and 600 °C. Hexagonal Cr₂N nitrides were observed at 550 and 600 °C. These coarse, high-chromium precipitates were responsible for the drop in corrosion resistance of the nitrided specimens.     

热处理对超级马氏体不锈钢腐蚀性能的影响

对两种(含W、Cu,不含W、Cu)超级马氏体不锈钢(SMSS)进行1050℃保温0.5 h后淬火及不同温度(550℃、650℃、750℃)保温2 h的回火处理,在饱和CO2浓度下,Cl-浓度为2.12%的NaCl溶液中采用电化学方法研究其耐蚀性能。循环极化曲线分析结果证实,回火温度对耐腐蚀性能有重要影响,并且550℃时耐腐蚀性能最好;含W、Cu的SMSS具有较高的点蚀电位。交流阻抗分析表明,回火温度为550℃的样品具有最高的阻抗值,形成的钝化膜最稳定。     

Rapid Tempering of Martensitic Stainless Steel AISI420: Microstructure,Mechanical and Corrosion Properties

In this research, the effect of rapid tempering on the microstructure, mechanical properties and corrosion resistance of AISI 420 martensitic stainless steel has been investigated. At first, all test specimens were austenitized at 1050 °C for 1 h and tempered at 200 °C for 1 h. Then, the samples were rapidly reheated by a salt bath furnace in a temperature range from 300 to 1050 °C for 2 min and cooled in air. The tensile tests, impact, hardness and electrochemical corrosion were carried out on the reheated samples. Scanning electron microscopy was used to study the microstructure and fracture surface. To investigate carbides, transmission electron microscopy and also scanning electron microscopy were used. X-ray diffraction was used for determination of the retained austenite. The results showed that the minimum properties such as the tensile strength, impact energy, hardness and corrosion resistance were obtained at reheating temperature of 700 °C. Semi-continuous carbides in the grain boundaries were seen in this temperature. Secondary hardening phenomenon was occurred at reheating temperature of 500 °C.     

Influence of nitrogen uptake and heat treatment on the microstructural characteristics and corrosion performance of X190CrVMo20-4-1 steel produced by supersolidus liquid-phase sintering

Martensitic stainless steel powder exhibits a high nitrogen uptake when densified by supersolidus liquid-phase sintering in a nitrogen atmosphere, but the optimum uptake, which is beneficial to its resistance to corrosion, is unknown. In this study, the resistance of high-carbon martensitic stainless steel X190CrVMo20-4-1 densified in a nitrogen atmosphere against pitting corrosion was explored. This was to clarify the impact of nitrogen uptake in the steel matrix in the quenched and tempered condition on its corrosion resistance in an aqueous solution. Samples were subjected to potentiodynamic polarisation tests in a de-aerated, 1 wt% NaCl solution. Results revealed that the X190 steel densified in a nitrogen atmosphere at 40-kPa pressure, subjected to deep cryogenic treatment in liquid nitrogen at an austenitising temperature of 1150°C and tempered at 200°C, had the best pitting corrosion resistance with a breakdown potential of 142 ± 11 mV/SCE and a hardness of 738 ± 4 HV10. The matrix around the M₇C₃ carbides and MX carbonitrides suffered high pitting susceptibility. The implications of this study serve as a basis for the improvement of the functional properties of steels.     

Der Einfluß von Martensit auf das Korrosionsverhalten von 18 Cr-10 Ni-Stahl

The effect of martensite on the corrosion properties of 18 Cr-10 Ni steel The corrosion properties of the martensitic phases formed in an austenitic matrix by (i) cooling to low temperature (-196 and ?269°C resp. ?320 and ?452°F) and (ii) cold working at room temperature was investigated for two chromium-nickel stainless steels of the 18 Cr10 Ni type. Austenite and martensite have the same chemical composition but different lattice structures. In sulfuric acid, both martensitic phases formed at low temperature and by cold working arc preferentially attacked in the active range of corrosion. The effect of potential on the corrosion attack was elucidated by potentiostatically controlled experiments with subsequent light-optical and SEM-investigation of the specimens. Selective corrosion attack of the martensitic phase was found down to a potential being 0.8 V more negative than the cathodic limiting potential of the active corrosion range of a fully austenitic steel, irrespective of the way of the martensite transformation. The preferential attack of martensite may be explained by the supposition that the deposition of cathodically protecting layers possibly consisting of nickel is rendered more difficult at the martensitic surface areas. In sulfuric acid, no differences in the corrosion properties between austenite and martensite were found in the passive and transpassive range. In chloride containing aqueous solutions, the resistance to pitting is not effected by martensite formed at low temperature. From this it is concluded that also martensite formed by cold working does not effect the pitting resistance.     

The influence of microstructure on the tensile and fatigue behavior of SAE 6150 steel

The tensile and reverse-bending fatigue behaviors of the SAE 6150 steel in the dual-phase (DP), fully martensitic, and tempered states, respectively, have been investigated using mechanical tests, scanning electron microscopy (SEM), energy-dispersive x-ray (EDX) microscopy, and optical microscopy. Residual stresses, inherent microcracks, and retained austenite films in the martensitic steel, quenched from 900 °C, lead to the development of inferior tensile and fatigue strength. Tempering at 700°C relieves the residual stresses associated with martensite, causes the precipitation of microalloy carbides (MACs), and thus results in superior strength, increased fatigue resistance, and moderate ductility. The DP microstructure, consisting of martensite islets in a ferrite matrix, gives rise to a combination of good strength, excellent ductility, and commendable fatigue characteristics. MAC in the tempered steel and martensite islands in the DP variant enhance fatigue performance by causing crack tip deflection and concomitant crack path tortuosity. Strain incompatibility between martensite and ferrite in the DP steel, and cementite films and ferrite in the tempered variant are identified as fatigue crack initiation sites.     

Relationship Between Microstructure and Corrosion Behavior of Cr12Ni3Co12Mo4W Ultra-High-Strength Martensitic Stainless Steel

The effect of tempering temperature on the microstructure and corrosion behavior of Cr12Ni3Co12Mo4W ultra-high-strength martensitic stainless steel was investigated using transmission electron microscopy, atomic force microscopy, X-ray diffraction, and electrochemical tests. The microstructures of the ultra-high-strength martensitic stainless steel consisted of some retained austenite and lath/plant martensite with the carbides distributed within the matrix and at the grain boundaries. Tempering of the steel for 4 h at various temperatures resulted in various carbide grain sizes and different amounts of the retained austenite. The results showed that larger carbide grains led to diminished corrosion resistance, whereas larger amounts of the retained austenite resulted in improved corrosion resistance. The steels exhibited good corrosion resistance in 0.017 mol/L NaCl solution and exhibited pitting corrosion in 0.17 mol/L Na Cl solution. The martensite and prior austenite crystal boundaries dissolved in solution with pH 1.     

The characteristics of high temperature Gas Nitriding heat treatment and tempering in 0.8Mo added 17Cr-1Ni-0.5C

The effect of the High Temperature Gas Nitriding (HTGN) and tempering treatment of 17Cr-1Ni-0.5C-0.8Mo (CNMo) steel was experimentally investigated. The HTGN was carried out at 1050 °C for 1 h in a gaseous atmosphere containing 98.07 kPa of nitrogen. Chromium nitrides in the austenite and martensite phase appeared at the nitrogen-permeated surface layer after the HTGN treatment. The hardness of the outmost surface of the HTGN treated specimen measured 708 Hv. When it was tempered at 500 °C for 1 h, the hardness of the outmost surface was 763 Hv as a result of the precipitation of mostly micro Cr₂N, which was densely packed with a small amount of Cr₂₃C₆ and the secondary hardening effect. In addition, an improvement in the corrosion resistance was observed in the tempered specimen.     

Effect of heat treatment on the structural transformations and properties of high-nitrogen chromium steels

Conclusions  

GCr15钢表面激光淬火的组织与性能

利用HL-1500无氦横流CO2激光加工机对GCr15钢表面进行激光淬火处理。采用SSX-550型扫描电子显微镜(SEM)、XJL-02A立式金相显微镜(OM)、DMH-2LS努氏显微硬度计、ML-10滑动摩擦磨损试验机和ZF-3恒电位仪等设备对不同功率下相变硬化层的显微组织及性能进行研究。结果表明:相变硬化区的组织为细小针状马氏体和少量球状碳化物,过渡区的组织为马氏体、残留奥氏体、铁素体和碳化物;试样的硬化层硬度比基体提高了2.2～3.5倍,当激光功率为1050W时,硬化层深度最大,可达0.7mm,耐磨性比基体提高3倍,耐蚀性也显著提高。     

Influence of different heat treatments on corrosion resistance of martensitic stainless steels

The changes in microstructure, caused by different heat treatments, have considerable influence on the corrosion resistance of stainless steels. The heat treatment causes an alteration of carbide contained in steels. Changes in the constant B for these steels, (B = Rp · i_COR) have been observed in quenched, tempered and annealed conditions. Pitting corrosion resistance of martensitic stainless steels in quenched and tempered conditions in 0.1M H₂SO₄ by adding Cl^? ions has been investigated.     

Influence of Step Annealing Temperature on the Microstructure and Pitting Corrosion Resistance of SDSS UNS S32760 Welds

In the present work, the influence of step annealing heat treatment on the microstructure and pitting corrosion resistance of super duplex stainless steel UNS S32760 welds have been investigated. The pitting corrosion resistance in chloride solution was evaluated by potentiostatic measurements. The results showed that step annealing treatments in the temperature ranging from 550 to 1000 °C resulted in a precipitation of sigma phase and Cr₂N along the ferrite/austenite and ferrite/ferrite boundaries. At this temperature range, the metastable pits mainly nucleated around the precipitates formed in the grain boundary and ferrite phase. Above 1050 °C, the microstructure contains only austenite and ferrite phases. At this condition, the critical pitting temperature of samples successfully arrived to the highest value obtained in this study.     

降碳增氮对马氏体不锈钢淬火组织和性能的影响

采用激光扫描共聚焦显微镜、扫描电镜、硬度计、X射线衍射仪和盐雾试验机,研究了不同温度(950、1000、1050、1100℃)下30Cr13和30Cr14N钢在马弗炉中空淬后,氮含量对30Cr13钢显微组织、碳化物、硬度和耐蚀性能的影响。结果表明,淬火温度相同,30Cr14N钢比30Cr13钢硬度高、碳化物少和耐蚀性能好。氮不仅影响马氏体不锈钢的显微组织及硬度,还能通过降碳增氮,避免因碳化物过多的析出而引起的晶间腐蚀,而FeNiN的析出不会像Cr₂₃C₆析出造成显著的晶间腐蚀。因此,降碳增氮是改善马氏体不锈钢组织和性能的一种有效途径。     

低温去应力退火对板式换热器用316L不锈钢冷冲压波纹板耐蚀性能的影响

通过马氏体含量测试、XRD物相分析和电化学测试等手段研究了去应力退火对板式换热器用316L不锈钢冷冲压波纹板片耐腐蚀性能的影响。结果表明,随着去应力退火温度的升高,由于奥氏体和应变诱导马氏体相的协作变形导致了316L不锈钢冷冲压波纹板片中残留奥氏体向马氏体的继续转变,使马氏体含量增加并发生马氏体向回火马氏体的转变,造成其自腐蚀电位变得更负,耐腐蚀性能变差。     

Corrosion behavior of low-alloy steel containing 1% chromium in CO2 environments

Corrosion behavior of low-alloy steel containing 1% Cr (1Cr) with normalized (ferritic–pearlitic) and quenched-and-tempered (tempered martensitic) microstructures was investigated in CO₂ environments at 60 °C. The severe localized corrosion which was observed in N80 carbon steel, did not exist for 1Cr steel due to the formation of a compact and self-repairable Cr-rich scale. For 1Cr steel, the corrosion resistance with ferritic–pearlitic microstructure was better than that with tempered martensitic microstructure. An apparent corrosion scale spallation was observed on the surface of quenched-and-tempered 1Cr steel, while only slight scale spallation was seen for normalized 1Cr steel.     

Optimal heat treatment conditions and properties of bimetal (high Cr cast iron/alloyed steel) hammers

Abstract

This study intended to establish the optimal heat treatment conditions for the desired hardness and wear resistance property for the bimetal hammers developed by the authors. The objective of this study is to attain bimetal hammers that have a tough Cr–Ni alloyed steel shank and a high wear resistant high Cr cast iron head to replace conventional single alloy (high Mn steel) hammers. The results show that the optimal heat treatment condition obtained for the bimetal hammers is: destabilisation: 1000–1050°C for 2 h, quench: FAC and tempering: 480–500°C for 6 h. By employing this optimal heat treatment condition, the highest hardness value can be attained along with the best wear resistance property for the head portion and acceptable toughness for the shank portion. The microstructure of the head portion that corresponds to the optimal properties consists of eutectic M₇C₃ carbides, secondary M₇C₃ carbides, tempered martensite and almost nil retained austenite.