Effect of Aging Temperature on Erosion-Corrosion Behavior of 17-4PH Stainless Steels in Dilute Sulphuric Acid Slurry

The effect of aging temperature on erosion corrosion （E-C） behavior of 17-4PH stainless steels in dilute sulphuric acid slurry containing solid particles was studied by using self-made rotating E-C apparatus. The effect of impact velocity on EC behavior of 17 4PH steels at different aging temperatures was analyzed. Surface micrographs of the specimens after E C test were observed by using scanning electron microscope （SEM）. The results showed that under the condition of the same solution heat treatment, when aging temperature ranged from 400 ℃ to 610℃, the hardness reached the highest value near the temperature 460℃. The characteristics of E-C for 17-4PH stainless steels at different aging temperatures were as follows： pure erosion （wear） was dominant, corrosion was subordinate and at the same time corrosion promoted erosion. The effect of aging temperature on E-C rate of 17-4PH steels was not significant at low impact velocity, but it was found that E-C resistance of 17-4PH steels aged near 460℃ was the most excellent due to the best precipitation strengthening effect of fine and dispersed e-Cu phase. With a prerequisite of appropriate corrosion resistance, the precipitation hardening could significantly improve the E-C resistance of the materials.

Rheological, mechanical and corrosive properties of injection molded 17-4PH stainless steel

The feedstock based on the binder 65%PW-30%EVA-5%SA has the best general rheological properties for the 17-4PH stainless steel powder. The 17-4PH stainless steel compacts sintered at 1 380 ℃ for 90 min have the best mechanical properties and the good microstructure with homogeneously distributed pore structure and the moderate-sized grains. Whereas the compacts sintered for 60 min and 120 min show an inadequate and an over-sintered microstructure respectively. The compacts sintered at 1380 ℃ for 90 min have the density of 7.70 g/cm^3, the strength of 1 275 MPa, the elongation of 5%, and hardness of HRC36. With the increase of sintering temperature, the density, strength and hardness increase, while the elongation decreases. The 17-4PH stainless steel has good corrosion resistance, showing an activation-passivation polarization curve. But the passivation potential range is narrow and the spot corrosion potential is low, indicating a low anti-spot corrosive properties.

Homogenization on solution treatment and its effects on the precipitation-hardening of selective laser melted 17-4PH stainless steel

17-4 precipitation-hardened(PH)stainless steel(SS)exhibits high strength and good corrosion resistance via Cu-precipitation hardening.Unlike conventional wrought 17-4PH SS,Cu segregation andε-Cu pre-cipitates are observed in additively manufactured(AM)17-4PH SS owing to the repeated rapid cooling after heating,which characterizes the AM process.In this study,solution treatment was conducted under various temperatures(1,000,1,050,1,100,and 1,200℃)and durations(1,2,4,and 8 h)to minimize the negative effects of Cu segregation andε-Cu precipitates on precipitation hardening.The mechanical prop-erties and microstructures of each condition for the Cu precipitation behavior were examined.Although theε-Cu precipitates did not disappear after solution treatment,the average diameter of theε-Cu precipi-tates tended to decrease with increasing solution treatment temperature and duration.Therefore,solution treatment at a temperature of 1,200℃ for 8 h was the best,resulting in improved strength compared to the conventional solution treatment at 1,050℃.Solution treatment on at least 1,100℃ is effective in AM.

核级17-4PH不锈钢小型部件去污与热老化评估

压水堆核电厂的稳压器喷淋阀是调节稳压器压力的重要部件,其阀杆材质为17-4PH,在此服役环境下,面临表面沾污、热老化的问题。本文研究了通过表面处理去除阀杆表面沾污层的可行性,通过电子束焊接技术对阀杆部件进行加长,讨论小尺寸部件的热老化问题。结果表明,表面处理降低放射性的效果良好,满足放射性废物管理要求;电子束焊接保证了焊接件的机械强度;力学性能实验结果表明,阀杆在此服役环境下,存在较大热老化风险。通过去污、焊接、力学性能分析,证明了该评估流程可用于被沾污的核电小型部件的热老化评估。

17-4PH不锈钢激光气体渗氮层显微组织与摩擦学性能

目的提高17-4PH马氏体沉淀硬化不锈钢的表面硬度及耐磨性。方法采用光纤激光器对17-4PH不锈钢进行激光气体氮化,采用不同激光功率在其表面制备渗氮层。利用光学显微镜(OM)、电子扫描显微镜(SEM)和X射线衍射仪(XRD)等设备分析渗氮层的显微组织和相组成;借助显微硬度仪测试渗氮层截面深度方向的硬度;采用多功能摩擦磨损试验机测试基体、渗氮层的摩擦学性能,并通过SEM分析磨痕形貌,揭示基体与渗氮层的磨损机制。结果在渗氮前样品组织为回火马氏体,经激光渗氮后样品表面形成了由板条马氏体组成的熔化区和回火马氏体组成的热影响区构成的渗氮层。经渗氮后,样品的硬度均得到提高。在激光功率3000 W下,渗氮层的表面硬度最高,达到了415HV0.2,约是基体硬度的1.2倍,渗氮层的硬度随着深度的增加呈下降趋势,在深度为2.6mm处其硬度与基体一致。在回火马氏体向板条马氏体转变的相变强化,以及氮原子(以固溶方式进入基体)的固溶强化作用下,提高了渗氮层的硬度。经渗氮后,样品的摩擦因数均高于基体,但渗氮后其磨损量相较于基体有所减少,在激光功率3000W下,其磨损体积最小,相较于基体减少了62%。在激光功率2500W下马氏体转变不完全,在激光功率3500W下渗氮层出现了裂纹,都降低了渗氮层的硬度,其耐磨性也随之减小,且都略低于在3000W下。磨损机制由渗氮前的以黏着磨损为主,转变为渗氮后的以磨粒磨损为主。结论在17-4PH马氏体沉淀硬化不锈钢表面进行激光渗氮后,其表面硬度和耐磨性均得到提高,在激光功率3000W下制备的渗氮层具有较高的表面硬度和优异的耐磨性。

切削17-4PH不锈钢时刀具磨损对切削过程的影响分析

为了探究刀具磨损对切削力和已加工表面温度的影响,考虑实际切削过程中的刀具磨损类型,建立了不同磨损类型的刀具几何模型,采用DEFORM软件建立17-4PH不锈钢正交切削有限元模型。基于有限元模型研究了刀具磨损对切削温度、分流点和接触表面应力等的影响规律,并通过切削实验验证磨损模型的可靠性,研究了后刀面磨损与切削力之间的演化规律。结果表明:前刀面磨损在一定程度上可以降低切削力和切削温度,其余磨损形式会增大切削力;随着后刀面磨损VB的增大,犁耕效应显著,切削力增大较为明显,而接触面的应力变化不明显。

时效温度对17-4PH钢微观组织及力学性能的影响

采用光学显微镜(OM)、扫描电镜(SEM)、电子万能试验机等方法研究了不同热处理工艺对17-4PH马氏体不锈钢组织和力学性能的影响规律。实验结果表明:热处理后基体中的析出相对时效温度变化比较敏感,尺寸随时效温度升高而增大。固溶+时效处理的试样与原始样相比其硬度和抗拉强度显著提升,而塑性无明显变化。此外,1040℃固溶+470℃时效后的试样综合力学性能最好。

Microstructure characteristics of segregation zone in 17-4PH stainless steel piston rod

The segregation of Cu and Ni in a 17-4PH stainless steel piston rod has been confirmed to be responsible for the cracking after heat treatment.Further investigation showed that the segregation zone was composed of three layers,namely the fine grain martensitic layer,the coarse grain martensitic layer and the coarse grain austenitic layer from the matrix to the crack surface.Three button ingots with the same chemical compositions as those three layers have been prepared to evaluate the grain size distribution,microstructure and mechanical properties.The effects of Cu and Ni segregation on the microstructures of those three layers have been explored by thermodynamic calculation.Based on the microstructure and mechanical properties results,an intensive understanding of the cracking in the segregation zone was therefore reached.

Relationship of microstructure transformation and hardening behavior of type 17-4 PH stainless steel

The relationship between the microstructure transformation of type 17-4 PH stainless steel and the aging hardening behavior was investigated. The results showed that, when 17-4 PH stainless steel aging at 595℃, the bulk hardness of samples attains its peak value （42.5 HRC） for about 20 min, and then decreases at all time. TEM revealed the microstructure corresponding with peak hardness is that the fine spheroid-shape copper with the fcc crystal structure and the fiber-shape secondary carbide M23C6 precipitated from the lath martensite matrix. Both precipitations of copper and M23C6 are the reasons for strengthening of the alloy at this temperature. With the extension of holding time at this temperature, the copper and secondary carbide grow and lose the coherent relationship with the matrix, so the bulk hardness of samples decreases.

磁痕显示对激光强化17-4PH叶片力学性能的影响

为增强17-4PH钢低压末级叶片的防水蚀性能,对17-4PH叶片进汽边进行激光固溶处理。经过激光固溶处理的末级叶片在后续磁粉探伤过程中,往往会出现明显的磁痕现象。为此,利用光学显微镜、扫描电镜、X射线衍射仪、电子探针等分析手段证明了在激光固溶区域边界处出现磁痕的原因为在边界出现的大量的奥氏体组织,降低了激光固溶边界处的磁导率,从而产生磁痕。利用XRD测定激光固溶叶片的残余应力为压应力,三点弯曲疲劳试验证明通过激光固溶可将17-4PH叶片的R=0.1疲劳极限由原750 MPa提高至860 MPa。

选择性激光熔化17-4 PH不锈钢零件的参数化研究和表征

本文对选择性激光熔化的17-4 PH不锈钢进行了参数化研究和表征。通过改变工艺参数包括激光功率和扫描速度以及扫描方式(设计参数)来研究试样的相对密度和显微硬度的变化。当使用中等能量密度和内外六角扫描方式时,试样的相对密和显微硬度最大;当使用低能量密度和交替带状扫描方式时,试样的相对密和显微硬度最小。在光学和扫描电子显微组织中,试样侧面有奥氏体、铁素体和小熔池。能量色散光谱分析表明,试样的化学成分变化导致相对密度和显微硬度发生变化。X射线衍射结果表明,中等能量密度试样的奥氏体相和铁素体峰强度最高。背散射电子衍射结果表明,随着能量密度的增加,奥氏体相增加,导致试样的显微硬度变化。相比于中等能密度试样,低能量密度试样易诱发更多的残余应力。采用不同能量密度得到的样品都具有较强的耐蚀性(0.05 mm/a),未出现明显的腐蚀裂纹。

温度对扭矩传感器弹性体17-4PH特性的试验

弹性体是扭矩传感器的核心部件,其性能直接影响扭矩传感器的准确性。文章分析了扭矩传感器数学模型,构建了温度作用下材料弹性模量理论模型,并针对弹性体材料17-4PH进行温度性能试验和变温环境下的扭矩校准试验。试验结果表明,弹性体材料17-4PH的弹性体与温度的变化成非线性关系,温度越高弹性模量下降的速度越快,构建的考虑温度影响的弹性模量模型的变化规律与传感器输出值变化一致,这为扭矩传感器的精密设计提供了可靠的依据。

不同状态2A12铝合金与17-4PH不锈钢间的摩擦磨损性能

为给某锁筒机构导向基座和导向杆摩擦副配对选材,研究了轧制态、固溶态、固溶+时效态2A12铝合金与时效态17-4PH不锈钢组成的摩擦副在干摩擦和抹润滑脂润滑条件下的摩擦磨损性能。结果表明:轧制态2A12铝合金的抗拉强度和显微硬度高于固溶态和固溶+时效态,远低于时效态17-4PH不锈钢;在抹润滑脂润滑条件下,轧制态2A12铝合金与17-4PH不锈钢配副的平均摩擦因数以及轧制态铝合金的平均体积磨损率明显低于干摩擦条件下,并且低于相同润滑条件下固溶态和固溶+时效态2A12铝合金;2种润滑条件下3种状态铝合金的磨损机制均以磨粒磨损为主、黏着磨损为辅,不锈钢的磨损机制为轻微磨粒磨损。锁筒机构可以选择轧制态2A12铝合金与时效态17-4PH不锈钢进行配对,通过涂抹润滑脂来减少摩擦磨损卡滞现象。

时效工艺对17-4PH不锈钢组织与力学性能的影响

对17-4PH不锈钢进行460~580℃,保温4 h的时效处理,采用显微组织观察、XRD分析、拉伸试验、硬度测试、冲击试验等研究了不同温度时效对17-4PH不锈钢组织与力学性能的影响。结果表明:不同温度时效处理17-4PH不锈钢的组织中主要为马氏体、碳化物和少量逆转变奥氏体。随着时效温度的升高,17-4PH不锈钢中马氏体组织逐渐粗化,逆转奥氏体含量逐渐增多,抗拉强度、屈服强度和硬度逐渐下降,伸长率和冲击吸收能量逐渐升高。当时效温度从460℃升高到580℃,17-4PH钢的硬度下降26.2%,冲击吸收能量提高299.5%,时效温度对17-4PH不锈钢的韧性影响显著。17-4PH不锈钢的拉伸断口主要由韧窝和撕裂棱构成。随着时效温度的升高,拉伸断口上韧窝数量明显增多,且韧窝尺寸有所增大,韧窝变深,分布也更为均匀,不锈钢的塑性增加。

17-4PH不锈钢高锁螺母裂纹产生的原因

在17-4PH不锈钢高锁螺母的加工过程中,发现其螺纹部位有裂纹产生。采用微观观察、加工工艺分析、挤压过程分析等方法研究了该螺母裂纹产生的原因。结果表明:裂纹是在挤压过程中产生的,挤压前坯料硬度偏高、挤压变形量偏大,使材料的塑性及心部流动性变差,最终导致螺母心部产生裂纹。对挤压前的坯料进行双重退火处理,可以避免螺母在加工过程中产生裂纹。

17-4PH不锈钢激光熔覆镍基碳化钨涂层数值模拟研究

采用双椭球热源,综合考虑了热传导、热对流、粉光相互影响、金属相变、凝固的相互作用,基于随温度变化的热物性参数,建立了17-4PH基体激光熔覆镍基碳化钨粉末的三维温度场流场数值模型,模拟不同激光功率和熔覆速度对温度场流场的影响,计算得出了熔覆过程温度场、速度场的瞬时变化规律。结果表明,随着激光功率的增加,熔池温度的峰值从1 850 K增加到2 210 K,熔池流速峰值从0.12 m/s增加到0.13 m/s。随着熔覆速度增加,熔覆层温度分布变化不大,但熔覆层厚度由649.117μm减小到313.759μm。研究结果为不锈钢激光熔覆镍基碳化钨成型提供相关理论依据。

离子渗氮工艺对17-4PH不锈钢性能的影响

对17-4PH不锈钢分别进行了真空固溶和时效处理及离子渗氮。结果表明:17-4PH不锈钢经1040℃真空固溶处理随后480℃时效处理后的硬度为41.0~41.5 HRC;离子渗氮温度对17-4PH不锈钢表面硬度影响不大,对基体硬度的影响较大,对渗氮层深度有一定的影响;渗氮剂的氮氢比对17-4PH钢表面和基体的硬度影响不大,对渗氮层深度有一定影响;在500℃采用N_(2)∶H_(2)=1∶3的渗剂对17-4PH钢进行离子渗氮时,随着渗氮时间的延长,渗层深度增加,表面硬度变化不大,基体硬度降低。

17-4PH不锈钢激光修复E级钢组织及力学性能研究

文章通过激光增材制造技术在E级铸钢表面成型了单层和多层17-4PH不锈钢试样,对其微观组织结构和力学性能进行研究,重点测试其表面残余应力和拉伸性能。结果表明:单层与多层激光增材制造试样成型效果良好,内部组织结构细小致密,无裂纹、气孔等缺陷,单层表层晶粒小于多层增材试样;多层增材制造试样抗拉强度最大,单层增材制造试样屈服强度最高,而E级铸钢断后伸长率与断面收缩率最高;此外,多层增材制造试样表层残余应力最大,单层增材制造试样表面显微硬度最高。

Effect of rare earths on mechanical properties of plasma nitrocarburized surface layer of 17-4PH steel

The aim of this investigation is to reveal the influence of rare earths(RE) addition on mechanical properties of plasma nitrocarburized 17-4PH steel.The nitrocarburized layers were characterized by optical microscope,scanning electron microscope equipped with energy dispersive X-ray analyzer,X-ray diffractometer,microhardness tester and pin-on-disc tribometer.The results showed that RE atoms could diffuse into the surface layer of 17-4PH steel plasma nitrocarburized at 500 °C for 4 h and did not change the ...

17-4PH不锈钢盐浴复合氮化处理研究

对比研究了不同温度下盐浴复合渗氮处理对马氏体不锈钢微观组织的影响及不同处理温度下材料硬度和耐磨性的变化。研究结果表明:盐浴渗氮处理后,17-4PH不锈钢渗氮层中主要物相为含扩展(含氮)马氏体、CrN、Fe4N以及Fe3O4,处理温度越高,不锈钢渗氮层中形成的Fe3O4以及CrN含量越多。含氮马氏体的晶格常数随氮化处理温度的提高而上升,该钢在盐浴渗氮中的激活能为190.9kJ/mol。17-4PH不锈钢进行盐浴渗氮处理后,能得到较厚的渗氮层。处理温度越高,渗氮层越厚。渗氮处理后,材料的滑动磨损量大大下降,由未处理状态时的21.1mg降低到580℃盐浴渗氮处理后的1.0mg。