Development of EPR test technique for alloy 800

The degree of sensitization (DOS) of austenitic stainless steels and some nickel-based alloys (e.g., alloy 600) is evaluated by the electrochemical potentiokinetic reactivation (EPR) test. In this study a number of test solutions based on H₂SO₄ + KSCN composition have been evaluated to establish a reliable EPR test method for alloy 800. Different passivation (vertex) potentials are also tested. It has been shown that dilute test solutions with lower vertex potentials resulted in single loop (SL) and double loop (DL) EPR test methods that distinguished between different sensitized samples and also between sensitized and desensitized samples. It has been shown that an SL-EPR test in 1 M H₂SO₄ + 0.002 M KSCN (de-aerated) at 26 °C at a scan rate of 3 mV/s from a vertex potential of 700 mV_SCE (180 s hold time) gave results that matched with the DOS indicated by microstructures and the Huey test results. Similarly, the DL-EPR test in 1 M H₂SO₄ + 0.002 M KSCN (de-aerated) at 26 °C, forward scanning from the OCP to + 700 mV_SCE and then backward scanning from there to the OCP at a scan rate of 2 mV/s produced a good measure of DOS as indicated by the Huey test results. The effectiveness of the EPR test was ascertained by testing on alloy 800 containing Ti and Al (alloy 800 HT) and Nb (alloy 800 Nb).     

EPR法评价晶间腐蚀敏感性的各种判据的比较

用电化学动电位再活化法与草酸浸法研究了１Ｃｒ１８Ｎｉ９Ｔｉ不锈钢的晶间腐蚀敏感性,并对动电位再活化法用于评价不锈钢晶间腐蚀敏感性的各种判据进行了综合分析,实验结果表明：各种判据与材料的敏化程度有良好的对应关系,且能灵敏定量地反映低敏化材料的晶间腐蚀敏感的变化,各种判据中电流比ｉｒ／ｉａ,电量比Ｑｒ／Ｑａ的数据波动性小,重现性好;而再活化电流ｉｒ志再活化电量Ｑｒ有数据波动较大,重现性较差,电量判据（     

Effects of cooling rate and annealing treatment on sensitization of austenitic-ferritic duplex stainless steel

Duplex stainless steel has higher corrosion resistance and better mechanical properties than conventional type 300 series stainless steel. The corrosion behavior of duplex stainless steel is strongly dependent on the ratio, shape, size and distribution of austenite and ferrite phase in the microstructure. The relationship between the microstructure and the corrosion behavior of the duplex stainless steel was studied. For this purpose, the duplex stainless steel samples were solution heal treated at 1150°C followed by either cooling at various rates (water quenching, air coooling, furnace colling with door opened and door closed) to 820°C and then water quenching to room temperature, or quenching to room temperature and annealing heat treatment at 840°C for various lengths of time. A double loop electrochemical polentiodynamic reactivation (EPR) test was carried out to examine the effect of various cooling procedures or annealing treatment on the sensitization of duplex stainless steel. The grain size, shape, and distribution of the two phases were examined under microscope. From the test results, the relationships were discussed among heat treatment, electrochemical properties and microstructure.     

铁素体不锈钢的晶间腐蚀性能研究

    分别采用Cu-CuSO₄-16% H₂SO₄沸腾试验和电化学再活化方法研究了八种400系列铁素体不锈钢的晶间腐蚀性能.结果表明：C含量及稳定化元素是影响铁素体不锈钢晶间腐蚀性能的关键因素;电化学测量方法评价铁素体不锈钢的晶间腐蚀性能时易受晶粒再活化的影响,可结合电镜观察表面提高测量的准确性.     

电化学动电位再活化法评定不锈钢晶间腐蚀敏感性的研究

本文用电化学动电位再活化法(EPR法)研究了奥氏体不锈钢在H_2SO_4+Na_2S_4O_6溶液中钝化区回扫电位、扫描速度、溶液温度、溶液浓度等因素对测试灵敏度的影响,确定了AISI304、316系列奥氏体不锈钢在此溶液中的最佳实验条件。并进行了不同敏化状态的奥氏体不锈钢在此溶液中的EPR测试。研究结果表明:采用Na_2S_4O_6作为活化剂的EPR法同样是一种快速、定量、非破坏性的评价奥氏体不锈钢晶间腐蚀敏感性的方法。但在实际应用时,对于304系列不锈钢选用H_2SO_4+KSCN溶液比较灵敏,而对于316系列不锈钢则选用H_2SO_4+Na_2S_4O_6溶液更为灵敏。     

Influence of grinding parameters on the corrosion behavior of austenitic stainless steel

Samples of the austenitic stainless steel grade X5CrNi18‐10 (1.4301, AISI 304) were ground industrially with various grinding parameters to study their influence on corrosion resistance. The ability of the mechanically ground surfaces to form a stable passive layer was evaluated by KorroPad test and a modified electrochemical potentiodynamic reactivation test based on a single loop (EPR‐SL). Furthermore, the surfaces were characterized by surface analytical methods. The main influence was determined regarding abrasive belt type. Surfaces mechanically ground with granulate abrasive belts constantly had a lower corrosion resistance than surfaces ground with single‐coated grain. The granulate abrasive belts generated more sensitized surface areas and left formations of welded sample material on the mechanically ground surfaces. A post‐treatment with a nonwoven abrasive proved to be an effective finishing process by which the surface defects and sensitized material got removed and the surfaces regained the expected corrosion resistance.     

A new approach for DL-EPR testing of thermo-mechanically processed austenitic stainless steel

Standard test methods such as the electrochemical potentiokinetic reactivation test (EPR) and double-loop EPR test (DL-EPR) are commonly used to characterise sensitisation behaviour in austenitic stainless steels and nickel-based alloys. In this study, the DL-EPR test is augmented by large-area image analysis (IA) to characterise and quantify the networks of attacked grain boundaries. A new analysis approach that is based on a grain boundary cluster parameter is proposed to describe the network of corrosion susceptible grain boundaries, which may be estimated from electron backscatter diffraction (EBSD) data. This method may provide a better assessment of the relative DOS of different heats of austenitic stainless steels.     

电子束焊工艺对304不锈钢焊缝的抗晶间腐蚀性能影响

采用3种不同的电子束焊接工艺焊接304不锈钢,通过显微组织观察、XRD分析、极化曲线测试、动电位再活化(EPR)试验研究了不锈钢焊缝的抗晶间腐蚀性能.结果表明:减少焊接热输入量和添加熔入性焊丝这两种方法都能减少电子束焊缝中铬的碳化物的析出,降低焊缝的敏化度,提高焊缝的抗晶间腐蚀性能;与减少焊接热输入量相比,添加熔入性焊丝对晶间腐蚀的影响更大,焊缝抗晶间腐蚀性能提高更显著.     

应用恒电位浸蚀技术检测奥氏体不锈钢晶间腐蚀敏感性

用恒电位浸蚀方法研究了304L奥氏体不锈钢晶间腐蚀敏感性,并用EPR法对恒电位浸蚀法的实验结果进行验证.研究结果表明,恒电位浸蚀法有可能发展成一种快速检测奥氏体不锈钢晶间腐蚀敏感性的方法     

恒电位脉冲法检测奥氏体不锈钢敏化

不锈钢在一定温度范围内经热处理敏化，在晶界附近形成贫铬区，引起晶间腐蚀，本文采用恒电位脉冲技术对奥氏体不锈钢的敏化进行检测，并讨论了该法检测敏化的最佳实验条件。与常用的双环ERP法相比较，恒电位脉冲法具有测定速度快、对试样损伤小、测定结果更准确等特点。根据扫描电子显微镜（SEM）的观察，敏化度较高的不锈钢电极，经过双环EPR实验后在电极表面发生较严重的孔蚀，这可能就是EPR法测定常会出现偏差的原因；而经恒电位脉冲法实验后的同类电极，则未发现明显的孔蚀现象，从而保证了检测方法的准确性。     

Comparative study between large-scale and small-scale electrochemical potentiokinetic reactivation performed on AISI 316L austenitic stainless steel

This work optimizes the application of electrochemical potentiokinetic reactivation (EPR) to assess the degree of sensitization (DOS) of AISI 316L and compares the large-scale and small-scale EPR with the aim of improving the study of the different zones of AISI 316L welded joints by using an electrochemical minicell. The optimized EPR allows to discriminate better than the standardized EPR among different DOS. Small-scale EPR shows greater sensitivity to assess the DOS than large-scale EPR: (i) at lower deformation levels; (ii) for shorter sensitization times; (iii) when localized microstructural regeneration is caused by the combined effect of deformation and subsequent sensitization.     

Use of EPR test to study the degree of sensitization in resistance spot welding joints of AISI 304 austenitic stainless steel

The degree of sensitization (DOS) in resistance spot welding (RSW) joints is considered as the combined effect of intergranular corrosion (IGC) and transgranular corrosion (TGC) in the heat affected zone (HAZ) and of interdendritic corrosion (IDC) in the weld nugget (WN). The DOS is evaluated from electrochemical potentiokinetic reactivation (EPR) tests. The application of EPR test to RSW joints is optimized and an electrochemical minicell is used to study the effect of heat input on IDC in the WN.     

带极电渣堆焊奥氏体不锈钢耐晶间腐蚀性能

用带极电渣堆焊和带极埋弧堆焊2种方法堆焊了Cr-Ni不锈钢,研究了这两种方法和焊接速度对堆焊层金属显微组织及耐晶间腐蚀性能的影响。显微组织观察表明,带极电渣堆焊和带极埋弧堆焊层的显微组织都为奥氏体+δ铁素体。带极电渣堆焊层金属中δ铁素体随着焊速的提高而增多,含量由6。8%增加到20.4%,带极埋弧堆焊金属中的δ铁素体含量比带极电渣堆焊的高,达到了23.6%;电化学动电位再活化试验结果表明,焊接速度8m/h的带极电渣堆焊层金属的再活化率仅为3.22%,耐晶间腐蚀的性能最佳,焊速快慢或焊接方法改变都将使带极电渣堆焊层金属的再活化率升高,耐晶间腐蚀性能下降。10%草酸溶液电解浸蚀试验的结果与EPR曲线结果一致。     

EPR法评价奥氏体不锈钢晶间腐蚀敏感性的研究

利用电化学动电位再活化（即EPR）法检测了奥氏体不锈钢晶间腐蚀敏感性的程度.研究了不同条件对敏化度的影响,特别是不同敏化时间、敏化温度、扫描速度、溶液温度对奥氏体不锈钢晶间腐蚀性能的影响,并与草酸电解浸蚀实验结果进行对比.结果表明：双环EPR法能定量、定性的检测不锈钢的晶间腐蚀敏感性.对304LNSS而言,敏化时间越长,温度越高,其晶间腐蚀敏感性越强.扫描速度越快,溶液温度越低,同一材料的Ra值越小.EPR法与草酸电解浸蚀试验结果相吻合.     

Role of grain boundary nature and residual strain in controlling sensitisation of type 304 stainless steel

The effects of residual strain and grain boundary character distribution on sensitisation of type 304 stainless steel at 525 °C were evaluated using electrochemical potentiokinetic reactivation (EPR) technique. The results indicated that a very low level of residual strain and a high fraction of annealing twins significantly improved the resistance to sensitisation. Image analysis indicated that the fraction of area attacked during the EPR test correlated well with the EPR data. The volume loss, calculated using atomic force microscopic examinations, during the EPR tests also correlated well with the EPR results.     

Electrochemical methods for testing the intergranular corrosion susceptibility of stainless steels

In addition to the standardized intergranular corrosion testing methods to detect sensitization in austenitic stainless steels, electrochemical test methods, i.e. the potentiokinetic reactivation test (EPR) and the anodic polarization and constant potential etching methods in perchloric acid solution containing sodium chloride, have been developed. The results of these electrochemical measurements are compared with those obtained from copper sulfate-sulfuric acid tests.     

Nachweis der IK-Beständigkeit von verschleißfesten Auftragschweißungen mit dem EPR-Verfahren und mit Salpetersäure-Flußsäurelösung

Investigation of the resistance against IGA of wearfacing weld claddings by using the EPR test and nitric-hydrofluoric acid solution The corrosion resistance against intergranular attack (IGA) of weld claddings from the electrode Tube S 17 8 Si (alloy type FeCrl8Ni8Si4Mn with ≤ 18% δ-ferrite) has been investigated using electrochemical potentiodynamic reactivation (EPR) technique, the nitric-hydrofluoric acid (SF) test according to ASTM A 262 practice D, metallographic and microstructure analytical methods (SEM, EDX). Samples produced by different welding techniques (shielded arc and open arc) and partly additional thermal treated have been investigated. In standardized SF-solution and in 2 M HNO₃ + 0.05 to 0.5 M HF at 30°C there is no correspondence between corrosion rate and IGA-susceptibility, possibly caused by inhibitive action of Fe-III-ions. SF etchants evaluate Cr-depleted zones and decomposed δ-ferrite. In the optimized EPR double loop test in 0.5 M H₂SO₄ + 0.01 M KSCN at 30°C the extend of sensitization is indicated by the ratio of reactivation to passivation charge with additional assessment of the microstructure. It is shown that the EPR-test in the evaluated manner is able to find out IGA at claddings up to 30% δ-ferrite. In the as-welded state all claddings are resistant. Treatments at 400°C resp. 450°C were tolerated up to at least 1000 resp. 100 h. Sensitization may be caused by precipitation of Cr-rich carbides and by decomposition of δ-ferrite, for IGA the amount and distribution of ferrite plays a decisive role.     

Interkristalline Korrosion von Auftragschweißungen einer FeCrNiSiMn-Legierung EB9/300rc

Intercrystalline corrosion of weld claddings of FeCrNiSiMn alloy type EB9/300rc The corrosion resistance against intercrystalline corrosion (IK) of weld claddings from the electrode EB9/300rc (alloy type FeCr18Ni8Si4Mn with ca. 18% δ-ferrite) has been investigated using electrochemical potentiodynamic reactivation (EPR) technique, the Straußtest, metallographic and microstructure analytical methods (REM, ESMA). In spite of the brittleness of the claddings investigated, the Straußtest failed in assessing sensitization of the (unbent) specimen. In the EPR double loop test in 0,5 M H₂SO₄ + 0,01 M KSCN at 30°C with a scan rate of 5 mV/s the extend of sensitization is indicated by the ratio of reactivation to passivation charge. Additional assessment of the microstructure of heat treated specimen enabled us to set up a grain disintegration diagram. Sensitization has been caused by precipitation of Cr-rich carbides and s?-phase at the grain boundaries and by decomposition of δ-ferrite followed by selective dissolution (?Ferritpfad”? corrosion). In the as welded state the claddings are not susceptible to IK.     

Use of eddy current testing method in detection and evaluation of sensitisation and intergranular corrosion in austenitic stainless steels

This paper deals with the applicability of eddy current testing (ECT) technique to assess and quantify sensitisation and intergranular corrosion (IGC) in thermally aged AISI type 316 stainless steel. Chemical and electrochemical tests specified by ASTM A262 Practices A and E (Strauss test) and G108, and ECT, were used to quantify degree of sensitisation (DOS). The DOS was categorised based on severity of the crack after bend test in increasing order as unaffected, fissured, cracked, and broken. The eddy current (EC) amplitude increased with increasing DOS in both the as-aged and Strauss tested conditions. The EC amplitude in as-aged condition was smaller than in Strauss tested condition. Empirical relationships were established between ECT amplitude and other DOS parameters.     

焊接接头微型剪切试验与机械性能试验之间的关系

在对工程应用中强度级别在450-750MPa之间的数十种焊接接头进行大量微型剪切试验、硬度试验和冲击试验的基础上，运用概率论与数理统计相关知识，通过最小二乘曲线拟合，回归得出了焊缝、熔合线和热影响区各狭窄区域内剪切强度氏与硬度试验HV10之间，剪切韧性形。与冲击韧性‰之间关系的经验公式。这些经验公式的相关系数都能满足显著性水平达到0．01的回归精度。