KINETICS OF TEMPER EMBRITTLEMENT IN 2.25Cr-lMo STEEL USED FOR HOT-WALL HYDROFINING REACTORS

Based on the theory of grain boundary segregation,a kinetics model of temper embrittlement caused by long-term service for hot-wall hydrofining reactors was studied.The kinetics model was applied to phosphorus (P) segregation in 2.25Cr-1Mo steel used for a hot-wall hydrofining reactor,and the kinetics of grain boundary segregation of impurity P in the steel exposed to the process environment of the hydrofining reactor was calculated on the basis of the model.The Auger electron spectroscopy test was performed in order to determine the grain boundary concentration of P.The experimental result is agreement with the theoretical calculated data. The results show that the kinetics equation is reasonable for predicting the levels of grain boundary segregation of impurity P in 2.25Cr-1Mo steel used for hot-wall hydrofining reactors.     

Electrical-thermal interaction simulation for resistance spot welding nugget process of mild steel and stainless steel

A three-dimensional finite difference electrical-thermal model for resistance spot welding nugget process of mild steel and stainless steel is introduced. A simulation method of the interaction of electrical and thermal factors is presented. Meanwhile, calculation method of contact resistance and treatment method of heater structure is provided. The influence of the temperature dependent material properties and various cooling boundary conditions on welding process was also taken intoaccount in the model. A method for improving the mild steel and stainless steel joint was analyzed in numerical simulation process. Experimental verification shows that the model prediction agrees well with the practice. The model provides a usefultheoretic tool for the analysis of the process of resistance spot welding of mild steel and stainless steel.     

Analysis of Bonding Features between the Particles and the Substrate during Cold Spraying

Cold spraying is a new coating process and manufacturing technology. The coating quality is upgraded with dense layers, higher bonding force and lower oxidation comparing with thermal spraying. Bonding of particles onto substrate is a result of extensive plastic deformation and related phenomena at the interface. The cold-sprayed copper and aluminum deposits on aluminum and steel substrates were prepared, and the features of interface were observed by using scanning electron microscope (SEM). Then the particle/substrate impact process was modeling through finite-element methods (ANSYS/LS-DYNA software). Numerical results show that the high plastic strain at the interface can result in an adiabatic shear instability at the interface. Due to these extremely high pressure and strain rate, it may be more appropriate to treat the material adjacent to the particle/substrate interface as a viscous ‘fluid-like’ material, various fluid-based phenomena, such as interfacial instabilities and roll-ups and vortices, can lead to interface material mixing. In numerical simulation, adiabatic shear instability both in the particle and the substrate at contact interface is regarded as a criterion for predicting the optimal process parameters and the bonding feature.     

On The Enhancement of Wear Resistance of Hardened Carbon Tool Steel （AISI 1095） With Cryogenic Quenching

Many experimental investigations reveal that it is very difficult to have a completely martensitic structure by any hardening process. Some amount of austenite is generally present in the hardened steel. This austenite existing along with martensite is normally referred as the retained austenite. The presence of retained austenite greatly reduces the mechanical properties and such steels do not develop maximum hardness even after cooling at rates higher than the critical cooling rates.Strength can be improved in hardened steels containing retained austenite by a process known as cryogenic quenching.Untransformed austenite is converted into martensite by this treatment. This conversion of retained austenite into martensite results in increased hardness, wear resistance and dimensional stability of steel. Wear can be defined as the progressive loss of materials from the operating surface of a body occurring as a result of relative motion at the surface. Hardness, load,speed, surface roughness, temperature are the major factors which influences wear. Many studies on wear indicate that increasing hardness decreases the wear of a material. With this in mind, to study the surface wear on a surface modified (Cryogenic treated) steel material an attempt has been made in this paper. In this study as a Part -I Hardening was carried out on carbon tool steel (AISI 1095) of different L/D ratio with conventional quenchants like purified water, aqueous solution and Hot mineral oil. As a Part -II hardening was followed by quenching was carried out as said in Part- I and the hardened specimen were quenched in liquid Nitrogen which is at sub zero condition. The specimens were tested for its microstructure, hardness and wear loss. The results were compared and analyzed. The alloying elements increases the content of retained austenite hence the material used was AISI 1095 (Carbon 0.9%, Si 0.2%, Mn0.4% and the rest Iron)     

Optimization of Grain Boundary Character Distribution in Fe-18Cr-18Mn-0.63N High-Nitrogen Austenitic Stainless Steel

Grain boundary engineering（GBE） is a practice of improving resistance to grain boundary failure of the material through increasing the proportion of low Σ coincidence site lattice（CSL） grain boundaries（special grain boundaries） in the grain boundary character distribution（GBCD）. The GBCD in a cold rolled and annealed Fe-18Cr-18Mn-0.63N high-nitrogen austenitic stainless steel was analyzed by electron back scatter difraction（EBSD）. The results show that the optimization process of GBE in the conventional austenitic stainless steel cannot be well applied to this high-nitrogen austenitic stainless steel. The percentage of low ΣCSL grain boundaries could increase from 47.3% for the solid solution treated high-nitrogen austenitic stainless steel specimen to 82.0% for the specimen after 5% cold rolling reduction and then annealing at 1423 K for 10 min.These special boundaries of high proportion efectively interrupt the connectivity of conventional high angle grain boundary network and thus achieve the GBCD optimization for the high-nitrogen austenitic stainless steel.     

The Effect of NiAI Coatings on Oxidation Behavior of AISI 403 Stainless Steel

This paper reports the oxidation behavior of stainless steel type 403 as a substrate material with and without NiAl coating. Evaluation of oxidation resistance was performed on uncoated and coated specimens at 850 and 1050℃. Acommercial diffusion process was used for the formation of NiA1 intermetallic coatings on the specimens. Before aluminizing, a layer of nickel, about 40μm, was deposited on specimens by electroplating. Various techniques including SEM, EDAX, optical microscopy and micro-hardness testing were employed to investigate the coatings before and after oxidation tests. Nickel-aluminides produced by two stage; plating-aluminizing, treatment with NiA1 on the surface increased the performance of stainless steel samples significantly.     

KINETICS OF TEMPER EMBRITTLEMENT IN 2.25Cr-1Mo STEEL USED FOR HOT-WALL HYDROFINING REACTORS

Based on the theory of grain boundary segregation, a kinetics model of temper em-brittlement caused by long-term service for hot-wall hydrofining reactors was studied.The kinetics model was applied to phosphorus (P) segregation in 2.25Cr-1Mo steelused for a hot-wall hydrofining reactor, and the kinetics of grain boundary segrea-tion of impurity P in the steel exposed to the process environment of the hydrofiningreactor was calculated on the basis of the model. The Auger electron spectroscopytest was performed in order to determine the grain boundary concentration of P. Theexperimental result is agreement with the theoretical calculated data. The results showthat the kinetics equation is reasonable for predicting the levels of grain boundarysegregation of impurity P in 2.25Cr-1Mo steel used for hot-wall hydrofining reactors.     

Thermo-mechanical coupled analysis of hot ring rolling process

A 3D rigid-plastic and coupled thermo-mechanical FE model for hot ring rolling（HRR） was developed based on DEFORM 3D software, then coupled heat transferring, material flow and temperature distribution of the ring in HRR were simulated and the effects of process parameters on them were analyzed. The results show that the deformation nonuniformity of ring blank increases with the increase of the rotational speed of driver roll and friction factor or the decrease of the feed rate of idle roll and initial temperature of ring blank. The temperature nonuniformity of ring blank decreases with the increase of the feed rate of idle roll or the decrease of initial temperature of ring blank and friction factor. There is an optimum rotational speed of driver roll under which the temperature distribution of ring blank is the most uniform. The results obtained can provide a guide for forming parameters optimization and quality control.     

New Steel Making Process through Reduction and Sintering of Cementite Powder

A new steel making process through reduction and sintering treatment of cementite powder was proposed, and microstructure of the material obtained by this process was examined by scanning electron microscopy and EBSP analysis.The cementite powder obtained by mechanical alloying was compacted under high pressure up to 1000MPa, and then reduced during sintering in a hydrogen (H2) gas atmosphere at elevated temperatures. The cementite compacts were completely reduced by the sintering at 1073K to 1273K for 18ks. The relative density of sintered material became 95% or more when the temperature was elevated above 1173K. The SEM observation and EBSP analysis indicated that the obtained steel has equiaxed ferrite-pearlite structure with grain size of around 5μm and the crystallographic orientations of ferrite grains are randomly distributed.     

THE INVESTIGATION ON PLASMA ARC TREATMENT OF CHROMIUM PLATED ALLOY STRUCTURE STEEL

The technology of plasma arc was used to modify the interface adhesion between chromium coating and steel substrate. The interface microstructure was studied as a function of plasma arc processing parameters. Microstructure analysis was performed by optical microscopy, scanning electron microscopy and electron probe. The microhardness distribution along the depth of a cross-section of the chromium coating and the substrate was measured. The results show the energy density of transferred plasma arc is obviously higher than plasma non-transferred arc. The molten interface wasbetween chromium coating and steel substrate obtained by plasma transferred arc. Interfaces between chromium coating and steel substrate can be divided by plasma non-transferred arc into three classes: non-molten, a little molten and molten. Good interface bonding was obtained by proper process parameters. The microhardness of chromium coating decreases with increasing energy density of plasma arc.     

600MW 1Mn18Cr18N护环的制造

主要阐述了600 MW 1Mn18Cr18N护环的热锻、固溶处理、外补液液压胀形冷变形强化等制造过程中质量控制要点及采取的工艺措施,保证了600 MW护环质量达到用户的要求,填补了600 MW 1Mn18Cr18N护环国内制造空白。     

Cr18Mn18N护环用钢电渣重熔技术的开发研究

阐述Cr18Mn18N发电机护环用钢电渣重熔技术的开发研究工作。选用合适渣系和重熔工艺生产了化学成分优良的低氧、低硫、高氮电渣锭用于发电机护环。     

SIMULATION OF HOT FORMING PROCESSION IN Mn18Cr18N STEEL

1.~onMn18Crl8N,analloysteelwithhigh--strengthandhigh--nitrogenhasbeenregaITledasthepri~choiceinmakingtheretainingringsOftUrbogeneratorsduetoitsgoodresistancetostresscormsion.However,becauseofthelargeqUantityofitsalloycontent,highresistanceandPOOrPlasticityinhotdefondng,itiseasytocrack.Therefore,howtOarsethelevelofscientilicalizationandconbollabilityofthehotfoeingp~essandimprovethequalityofptDducts,hasbecomeaproblemthathasbeenpaidagooddealOfattentionsbyresearchersintheplasticcircles.Inthi…     

Mn18Cr18N钢热成形晶粒变化的模拟研究

运用热耦合刚粘塑性有限元微观模拟技术,对Ｍｎ１８Ｃｒ１８Ｎ钢护环扩挤复合热成形和冷却过程进行了计算机模拟。得到了热力参数的分布状况和内部晶粒度变化的规律。当空冷约２１０ｓ时护环内晶粒可达细匀化。这为实现环的控制锻造与控制冷却,进而控制产品质量提供了理论依据。     

双18护环控制成形锻造的计算机数值模拟

采用计算机数值模拟技术对双18护环几种新的控制成形锻造方案进行模拟,通过对应变场、应力场、温度场和设备载荷模拟结果分析,确定了解决双18护环锻造开裂难题的控制成形锻造方案。     

28.4t 1Mn18Cr18N护环电渣锭生产

根据1Mn18Cr18N钢特点,通过精心制备电极及控制电渣重熔过程,成功生产了重达28.4 t的护环电渣锭。电渣锭表面质量优良,底部成型良好,顶部补缩密实平整。     

提高18Mn—18Cr—N扩环钢中氮含量及收得率的研究

护环作为发电机一个最关键的零件，由于其所起的作用及受力状态决定了要求超高的强度、良好的塑韧性、无磁性及优秀的抗应力腐蚀的能力，为了提高制造18Mn-18Cr-n护环的强度等级，经分析认为提高护环钢中的氮含量是一个关键的因素，在对影响18Mn-18Cr-N钢中氮含量的因素进行分析研究及实验室小感应炉的模拟实验的基础上，编制出冶炼工艺，并在电炉上进行了6炉次的实践，钢中的氮含量达到了0.69%，氮的收得率最高达到71%，大大高于常规工艺方法的水平，达到了日本制钢所室兰工厂该钢种的氮含量水平。     

提高18Mn-18Cr-N护环钢中氮含量及收得率的研究

护环作为发电机一个最关键的零件,由于其所起的作用及受力状态决定了要求超高的强度、良好的塑韧性、无磁性及优秀的抗应力腐蚀的能力。为了提高制造18Mn-18Cr-N护环的强度等级,经分析认为提高护环钢中的氮含量是一个关键的因素。在对影响18Mn-18Cr-N钢中氮含量的因素进行分析研究及实验室小感应炉的模拟实验的基础上,编制出冶炼工艺,并在电炉上进行了6炉次的实践,钢中的氮含量达到了0.69％,氮的收得率最高达到71％,大大高于常规工艺方法的水平,达到了日本制钢所室兰工厂该钢种的氮含量水平。     

采用VOD法冶炼1Mn18Cr18N护环钢

阐述了采用电炉与 VOD双联、真空精炼、大气下注的工艺生产 3 0 0 MW发电机护环用1 Mn1 8Cr1 8N钢的生产过程 ,着重讨论了 VOD原理及高 Mn、高 Cr时 N的溶解度和真空下 Mn的行为 ,以及生产方案的可行性及相应的措施     

Mn18Cr18N钢护环的包套冲挤成形数值模拟与试验研究

针对Mn18Cr18N护环钢热成形时易发生开裂、变形不均等缺陷，研究开发了一种新工艺，并对其中的包套冲挤成形进行了数值模拟和试验研究。通过试验验证了有限元模拟计算和实际变形的一致性，同时表明该方法不仅改善了坯料受力变形状态，合理调控了热力参数。有效防止了变形开裂缺陷，有利于提高产品质量和经济效益。