300M超高强度钢电化学性能及应力腐蚀开裂

采用动电位扫描技术和慢应变速率拉伸试验研究了超高强度钢300M在3.5%NaCl溶液中的应力腐蚀行为,并利用扫描电镜观察了不同外加电位下的断口形貌.300M钢在3.5%NaCl溶液中开路电位下的应力腐蚀开裂机制为阳极溶解型,Cl^-的存在明显地增加了材料的应力腐蚀开裂敏感性.阳极电位-600 mV下300M钢溶解速率加快,表现出较高的应力腐蚀开裂敏感性,断面收缩率损失由开路电路下的52.6%升高至99.5%,裂纹起源于表面点蚀坑处,应力腐蚀开裂为阳极溶解型机制.阴极电位-800 mV下材料处于阴极保护电位范围,表现出较低的应力腐蚀开裂敏感性,强度和韧度与空气中拉伸的数值相近,开裂机制为阳极溶解和氢致开裂协同作用.在更低电位(低于-950 mV)下,300M钢的应力腐蚀开裂机制为氢致开裂,在氢和拉应力的共同作用下表现出很大的应力腐蚀开裂敏感性.     

硫化氢环境下两种不锈钢的应力腐蚀开裂行为

用U形弯试样浸泡和慢应变速率拉伸实验研究了3Cr17Ni7Mo2SiN和00Cr22Ni5Mo3N(2205)不锈钢在硫化氢介质中的应力腐蚀开裂(SCC)行为.2205不锈钢的SCC萌生孕育期较长,在pH较低的饱和H₂S溶液中具有明显的SCC敏感性,其SCC敏感性随溶液pH值的升高或H₂S含量的降低而迅速降低.3Cr17Ni7Mo2SiN的SCC孕育期均低于2205不锈钢,在pH ≤ 4.5、H₂S的质量浓度 ≥ 10³mg·L^-1的H₂S介质中均具有明显的SCC敏感性,其SCC敏感性受pH值和H₂S含量变化影响较小.3Cr17Ni7Mo2SiN的SCC以沿晶裂纹萌生,扩展后转变为穿晶应力腐蚀开裂;2205不锈钢近表面处首先发生奥氏体-铁素体相间氢致开裂,并促进SCC萌生,其SCC为穿晶应力腐蚀开裂.     

两种超高强度合金的应力腐蚀开裂行为研究

超高强合金因其优越的力学性能广泛应用于承力构件如起落架等,40CrNi2Si2MoVA超高强度合金是继30CrMnSiNi2A之后研究出的新超高强度合金,其强度高于30CrMnSiNi2A,但是其在实际服役环境中的服役性能特别是应力腐蚀性能是否优于30CrMnSiNi2A,是决定其成功取代30CrMnSiNi2A应用的关键。采用双悬臂应力腐蚀实验研究了30CrMnSiNi2A及40CrNi2Si2MoVA两种超高强度合金在质量分数为3.5%的NaCl溶液中的应力腐蚀开裂行为(SCC)。通过光学显微镜和扫描电镜(SEM)对两种超高强度合金的形貌以及断口显微组织进行了分析。实验结果表明,30CrMnSiNi2A比40CrNi2Si2MoVA更早失效,其耐应力腐蚀性能较差。两种材料在NaCl溶液中容易出现裂纹并迅速扩展,裂纹横向扩展,并出现明显的分叉行为,不同取向试样对材料应力腐蚀开裂行为的影响较小。断口分析结果表明两种超高强度合金在应力和腐蚀介质的共同作用下发生失效,裂纹扩展前期主要为解理穿晶断口,裂纹扩展中后期为沿晶形貌。     

1420合金的应力腐蚀断裂行为

采用电化学方法和慢应变速率拉伸(SSRT)技术，研究了时效制度对1420Al-Li合金的时效动力学及抗应力腐蚀性能的影响。通过透射电镜、扫描电镜观察与分析，探讨了不同时效处理工艺下1420合金的显微组织、慢应变速率拉伸断口形貌及其影响机制。结果表明，与120℃／12h相比，采用120℃，6h 190℃，6h处理不仅可以缩短合金到达时效峰值的时间，提高合金的强度，使其断裂强度、断裂时间、延伸率以及总断裂能等都得到显著提高，同时也改善了合金的抗应力腐蚀性能。     

夹杂物对超高强度钢应力应变场的影响

非金属夹杂物对钢性能的影响与夹杂物的特征参数密切相关.首先分析拉伸和疲劳载荷下超高强度钢中TiN夹杂物导致裂纹萌生的扫描电镜原位观察结果,采用MSC Marc有限元分析软件对夹杂物及周围基体的应力场进行计算,然后对拉伸载荷下不同特征参数的TiN夹杂物及周围基体的应力应变场进行模拟.结果表明,有限元法能够解释并预测夹杂物及周围基体的力学行为.三角形夹杂物尖角附近的应力集中最严重.矩形夹杂物内部高应力区的位置受夹杂物与外载荷方向夹角的影响.随邻近夹杂物间距的增大,基体内的最大应力由夹杂物外侧移至夹杂物之间.近表面夹杂物使得基体自由表面附近出现高应力区,基体内最大应力的位置受夹杂物与自由表面距离和尺寸的影响.     

几种新型不锈钢在超临界水中的应力腐蚀开裂行为

研究14Cr-ODS、16Cr-ODS与310奥氏体钢在600℃/25 MPa的超临界水中的应力腐蚀开裂行为。通过慢应变速率拉伸实验得到应力-应变曲线,以及不锈钢的抗拉强度和伸长率。应力-应变曲线显示14Cr-ODS与16Cr-ODS都出现颈缩,而310奥氏体钢没有颈缩,达到极限强度后直接断裂,表现为脆性断裂特征。用扫描电镜对断口形貌进行观察,结果表明:16Cr-ODS的伸长率达到20%,断口成杯锥状,存在明显颈缩,但没有应力腐蚀开裂敏感性;14Cr-ODS断面上有韧窝出现,没有明显的应力腐蚀开裂敏感性;310奥氏体钢断裂方式几乎全为沿晶脆断,具有应力腐蚀开裂敏感性。     

Threshold Stress Intensity of Hydrogen-Induced Cracking and Stress Corrosion Cracking of High Strength Steel

Stress corrosion cracking (SCC) of highstrength steels in an aqueous solution has been wide-ly investigated[1— 8] .It has long been accepted thatSCC of high strength steel in water is one kind ofhydrogen- induced cracking (HIC) [1— 5] .Because ofhydrolysis of the metal ions,the value p H of the lo-cal environment within a pit,crevice or crack on asteel surface can be decreased to about 3.5 [1] .Be-cause of crack- tip acidification,local conditions arealways favorable for release of hydro…     

超高强度马氏体时效钢的发展

马氏体时效钢是以无碳(或超低碳)铁镍马氏体为基体的经时效生产金属间化合物沉淀硬化的超高强度钢。该钢在高强度时效处理前具有良好的成形性，时效处理几乎不变形，时效处理后有高强韧性。文中论述了典型Ni-Co-Mo-Ti-Al马氏体时效钢和Ni-Mo-Ti(-Cr-Al)无钴马氏体时效钢的化学成分和力学性能，阐述了马氏体时效钢在400～500℃时效时马氏体基体内产生大量强化效果极高、韧性损失极小的金属间化合物沉淀相的时效结构和强化机制，以及Ni、Co、Mo、Cr、Mn、Ti等元素在马氏体时效钢中的合金化作用。概述了马氏体时效钢的生产工艺，应用和发展趋向。     

CrNiMo-CrNi3Mo-CrNiMo三层复合超高强度钢板开发

为了开发同时具有超高强度和良好韧性的低合金超高强度钢板,采用30MnCrNiMo连铸坯和33MnCrNi3Mo钢锭,经过真空复合焊接,高温轧制,淬火+低温回火热处理工艺研制出15 mm CrNiMo-CrNi3MoCrNiMo三层复合超高强度钢板;利用探伤、拉伸、冷弯、冲击、硬度等试验检验其结合度和力学性能;利用光学显微镜、扫描电镜等分析三层复合超高强度钢的组织和冲击断口形貌。结果表明,采用该工艺生产的三层复合超高强度钢板结合性良好,能够满足GB/T 7734-2015Ⅰ级探伤要求;复合钢板的综合力学性能良好,结合面处硬度值存在明显的过渡区域;结合面组织和基体组织均为回火马氏体组织。     

Caustic Stress Corrosion Cracking of Mild Steel

The stress corrosion cracking (SCC) behavior of cold worked mild steel in hot, aqueous, 33 pct NaOH solutions was studied with prefatigue cracked double cantilever beam specimens. SCC kinetics were studied under freely corroding potentials (E _corr ≈ −1.00 V_SHE) and potentiostatic potentials of −0.76 V_SHE near the active-passive transition. The pH of the liquid within the crack was determined and fractography was studied by scanning electron microscopy. Cracking was transgranular atE _corr, intergranular at −0.76 V_SHE, and produced no detectable change in crack liquid pH from that of the bulk solution. Crack rates were dependent upon temperature, potential, and stress intensity (K ₁). The apparent activation energy in Region II, where crack growth rate was independent ofK, was ∼ 24kJ/mol for both cracking modes. This was considered to be due to mixed rate control involving activation polarization and mass transport processes. The mechanism of cracking was entirely consistent with metal dissolution at –0.76 V_SHE and may involve hydrogen embrittlement and/or dissolution effects atE _corr. DOUGLAS SINGBEIL, formerly Research Student, University of British Columbia, is Research Scientist, Pulp and Paper Research Institute of Canada, 570-Blvd. St. Jean, Pointe Claire, Quebec, Canada H9R 3J9.     

抚顺特钢高强钢及超高强度钢发展现状

基于国内特殊钢冶炼高强钢技术的发展及现状、对抚顺特钢生产的高强钢、超高强度钢及超高强度不锈钢特殊冶炼技术工艺进行简要分析研究.简要介绍了目前抚顺特钢超高强度钢领域典型新材料特殊熔炼技术和制备工艺流程,分析讨论了高品质特殊钢目前工业化生产技术瓶颈及发展现状.     

82B高碳钢临界应变的数学模型

在Ettore Anelli提出的热轧控冷线棒材临界应变模型的基础上，用Therraeemaster-Z热模拟试验机得出成分为(％)：0．82C-0．6Mn-0．1Cr的82B钢在原始晶粒直径47-124pan，变形温度900-1050℃和变形速率(0．1-25)／s时的应力．应变曲线，并按照所确定的临界应变模型系数，建立了82B高碳钢的临界应变模型ε=0.01 d0^0.177 283[εexp(165 282.1RT)]0.142 722。结果表明，随热变形温度的增高，应变速率的减小和原始晶粒细小，钢更易进行动态再结晶，温度和应变速率的影响较钢中原始晶粒尺寸对钢的动态再结晶的影响更大。模型计算值和实验测量值相一致。     

超高强度钢25CrNiWVA和CrNiWVA的连续冷却转变

利用热膨胀法和金相检验法研究了新型低合金超高强度钢25CrNiWVA和30CrNiWVA连续转变曲线。试验钢的实测相变点温度和硬度与经验公式理论计算基本相似。     

Ti-IF钢动态再结晶模型

通过Thermecmastor-Z热模拟实验机对Ti-IF(无间隙原子)钢(%:0.009C、0.017Si、0.13Mn、0.012P、0.013S、0.05Ti、0.025Als)在750℃、850℃和变形速率0.1,1,20s^-1下进行单道次压缩变形实验。得出Ti-IF钢加工硬化率-应变曲线、动态再结晶状态图和动态再结晶体积分数方程。实验结果表明,对于无明显峰值应变的应力-应变曲线,采用加工硬化率方法确定峰值应变和稳态应变是一种有效的方法。     

Flow Stress Behaviors and Microstructure Evolution of 300M High Strength Steel under Isothermal Compression

The compressive deformation behaviors of 300M high strength steel were investigated over a wide range of temperatures （850- 1200 C） and strain rates （0. 001- 10 s^- 1 ） on a Gleeble-3800 thermo-mechanical simulator. The measured flow stress was modified by the corrections of the friction and the temperature compensations, which nicely reflect negative effects of the friction and temperature on the flow stress. The corrected stress-strain curves were the dynamic recrystallization type on the conditions of higher deformation temperature and lower strain rate. Flow stress increases with the increase of strain rate at the same deformation temperature and strain. By contrast, flow stress decreases with the increase of temperature at the same strain rate and strain. Dependence of the peak stress on temperature and strain rate for 300M steel is described by means of the conventional hyperbolic sine equation. By re gression analysis, the activation energy （Q） in the whole range of deformation temperature is determined to be 367. 562 kJ/mol. The effects of the temperature and the strain rate on mierostructural evolution are obvious. With the increase of the deformation temperature and the decrease of the strain rate, the original austenite grain sizes of 300M steel increase. At the same time, the corrected flow stress curves more accurately determine the evolution of the microstrueture.