放电等离子烧结制备超细晶奥氏体不锈钢的研究

将球磨后的304奥氏体不锈钢粉末,用放电等离子烧结技术烧结成型.烧结温度选取900℃,烧结压力分别选取30 MPa和50 MPa.烧结后的试样通过XRD、SEM、TEM等分析其相组成及晶粒度.结果表明:烧结后试样的基体为奥氏体,晶粒度大约为100～200nm;试样的密度接近于钢的密度,说明烧结达到了较高的致密度;试样硬度远远高于普通不锈钢的硬度.电化学腐蚀结果及金相照片可以看出,试样烧结越致密,其耐腐蚀性能越好.     

影响奥氏体热作模具钢性能的因素

 在700 ℃下,马氏体型热作模具钢难以工作,奥氏体型热作模具钢具有良好的高温强度。基于均匀设计方法,设计了6种不同成分的试验钢及相应的热处理工艺。试验测定了6种钢的硬度、室温冲击韧性、热稳定性,利用二次型逐步回归分析方法对试验结果进行了建模,得出了三者与成分、工艺之间的回归方程,并与H13钢和DIEVAR钢对比。结果表明：增加Si、Mn、V含量,降低Cr、Mo含量可以提高钢的韧性;同时在所设计的热处理工艺范围内可以使钢的室温冲击功达到300 J;在700 ℃保温20 h,硬度HRC减少1~3。     

铁素体不锈钢凝固组织的影响因素

 铁素体不锈钢凝固过程中形成的柱状晶会影响钢的成形性,减少甚至避免铸坯柱状晶的形成,促进等轴晶的形成,对铁素体不锈钢来说尤为重要。采用连铸和模铸的试验方法浇铸了铁素体不锈钢430,以分析影响其凝固结构的因素。结果表明,电磁搅拌对430不锈钢连铸坯等轴晶的形成作用显著。无论模铸试验还是连铸试验,冷却强度对430铸坯柱状晶的形成都有明显的影响。在模铸试验条件下,碳、氮含量越高,越有利于其凝固时等轴晶的形成;在连铸试验条件下,由于温度梯度大,碳、氮含量对凝固组织的影响被削弱,但如果对钢液进行搅拌,碳、氮含量的变化对凝固组织仍然有明显的影响。     

奥氏体不锈钢的组织超细化技术

在试验的基础上研究了获得奥氏体不锈钢超细组织的方法,研究结果表明,原始晶粒尺寸为100 μm的304N不锈钢经1道次等径角挤压变形 退火工艺处理后,晶粒尺寸可显著细化到2～7 μm,强度可提高50%以上,而塑性并不降低;增加等径角挤压变形的道次,经退火后可获得更细小、均匀的再结晶晶粒.     

Mechanical Behaviour of Aged High Nitrogen Austenitic Stainless Steels

The present investigation is aimed at studying the effect of ageing on mechanical behaviour of two high nitrogen austenitic stainless steels as these steels are exposed to high temperatures in their applications. Two steels with nitrogen contents greater than 0.6% were given solution treatment and were aged at 500–900°C for 1–100 h. It was found that the steels exhibit superior mechanical properties in solution treated condition while ageing has a deleterious effect on properties due to weak interfaces of depleted austenite matrix and Cr₂N lamellae. The plastic flow behaviour can be modeled using modified Ludwik equation in these steels.     

奥 氏 体 不 锈 钢 的 再 结 晶 动 力 学

 采用双道次压缩和应力松弛2种实验方法,研究了含铌奥氏体不锈钢347热变形后的再结晶动力学特征,确定了AVRAMI方程表达式,同时通过定量金相技术分析了对应2种实验方法的淬火试样中再结晶组织所占份数。比较不同实验方法所得结果可知：定量金相分析结果与应力松弛法结果较吻合,而与双道次压缩实验结果差异较大。仅进行1次应力松弛实验就可以得到一条再结晶率与时间的关系曲线,可大大减少实验量。     

A New Pb-free Machinable Austenitic Stainless Steel

 In the present paper, the machinability tests were conducted by using various processing parameters on a CA6164 lathe with a dynamometer. The metallurgical properties, machinability and mechanical properties of the developed alloy were compared with those of an austenite stainless steel 1Cr-18Ni-9Ti. The results have shown that the machinability of the austenitic stainless steels with free-cutting additives is much better than that of 1Cr-18Ni-9Ti. This is attributed to the present of machinable additives. The inclusions might be composed of MnS. Sulfur and copper addition contributes to the improvement of the machinability of austenitic stainless steel. Bismuth is an important factor to improve the machinability of austenitic stainless steel, and it has a distinct advantage over lead. The mechanical properties of the free cutting austenitic stainless steel are similar to that of 1Cr-18Ni-9Ti. A new Pb-free austenitic stainless steel with high machinability as well as satisfactory mechanical properties has been developed.     

Behaviour Model of Austenitic Stainless Steels for Automotive Structural Parts

One of the most important preoccupation of car manufacturers is to reduce emissions and hence to reduce weight of cars. One of the outstanding materials able to reduce weight while at the same time keeping the same crash absorption and hence safety, is austenitic steel. Austenitic stainless steels are used in crash relevant parts of cars. Moreover, designers can use their very good corrosion resistance and their well known surface aspect for structural visible parts like wheels, cross members, roof panels or tailgates. In this paper, stainless steels for automotive use are presented in detail. First, their chemical composition and tensile properties are explained. Then, a model for forming and crash behaviour is described. Using this model, stainless steels can be engineered into automotive parts and thus stainless steel can be considered as a workable and predictable material for the automotive industry.     

Sensitization Behaviour of Manganese‐Alloyed Austenitic Stainless Steels

Manganese is an essential alloying element in advanced austenitic stainless steels with specific properties such as high resistance to harsh corrosive environments, high strength or low material costs. These materials are often used for welded constructions which have to be highly corrosion resistant. Hence it has to be ensured that the heat input during welding does not initiate the precipitation of chromium carbide resulting in a susceptibility to intergranular corrosion. This leads to the question whether the sensitization behaviour of manganese‐alloyed austenitic stainless steels is comparable to that of the well‐known conventional chromium nickel austenites. In the present work the effect of heat‐input on the susceptibility of the CrNi‐steel 1.4301 and the CrNiMn‐steel 1.4376 to intergranular corrosion (IGC) was considered. Investigations were carried out by corrosion testing in the so‐called Strauss‐Test to elucidate the effect of the annealing temperatures on the microstructure. Furthermore, the influence of heat treatment on the mechanical properties was evaluated by tensile testing. As a result, it could be demonstrated that manganese‐alloyed austenitic stainless steels like grade 1.4376 exhibit a sensitization behaviour very similar to the conventional austenitic steel grades. The same kinds of tests on intergranular corrosion resistance can be applied for both types of materials.     

Some Strengthening Methods for Austenitic Stainless Steels

Austenitic stainless steels possessing good corrosion resistance have recently found growing applications as a constructional material. In this instance, increasing strength properties, which are typically quite low, is of great interest. Due to the low stacking fault energy, strain hardening of alloyed austenite is efficient for increasing tensile strength without impairing ductility seriously. In addition, certain grades are unstable, so that cold working creates strain‐induced martensite that enhances strengthening. Grain size refinement to micrometer scale or even finer can also increase the yield strength, still providing good ductility. In the present paper dislocation and phase transformation strengthening and thereby properties achievable in temper rolled austenitic stainless steels are discussed. Strengthening by the reversion annealing is also described and excellent results achievable are shown. Finally, the effect of bake hardening through the static strain ageing is presented. Long‐term research work in various projects indicates that the current knowledge of strengthening of austenitic stainless steels is close to the industrial utilisation.     

含氮奥氏体不锈钢的敏化行为

通过65％硝酸浸泡法和电化学动电位再活化法定量评价18—8奥氏体不锈钢的晶间腐蚀倾向，并利用分析电子显微镜确定晶界的贫铬区，利用透射电子显微镜及电子衍射技术确定晶界析出物的结构。试验结果表明：适量增加氮含量可提高18—8奥氏体不锈钢的耐晶间腐蚀性能。敏化状态下再活化率Rn在氮的质量分数为0．16％时最低；当氮的质量分数大于0．16％时，贫铬区最低铬含量随氮含量的增加而降低；贫铬区宽度在氮的质量分数为0．16％时最窄，氮含量继续提高则贫铬区宽度扩大。     

奥氏体不锈钢302和304的轧制

由于奥氏体不锈钢加Ｔｉ后污染钢液,在钢中形成ＴｉＮ和Ｔｉ(ＣＮ)夹杂,国外含Ｔｉ奥氏体不锈钢的生产量很小(只占0.5%),所以不含Ｔｉ的302和304奥氏体不锈钢得到了广泛应用。302钢号相当于1Ｃｒ18Ｎｉ9,304钢号相当于0Ｃｒ18Ｎｉ9。1　302和304不锈钢的轧制特点(1)钢的导热性差,导热系数相当于低碳钢的27%,加热速度较慢,一般为130℃ｈ。(2)在900～1250℃时有良好的塑性,但热变形抗力很大,随着加工过程中温度的下降,变形抗力急剧增高,因而要控制终轧温度和变形程度,通常轧制时为使终轧温度不低于950℃,轧辊表面不浇冷却水,并控制最大相对压…     

316L奥氏体不锈钢的氮合金化

采用金相显微镜、XRD、拉伸试验机及高低温冲击试验机等,并结合Thermo-calc软件计算研究了氮对316L奥氏体不锈钢微观组织、析出相、力学性能和耐点蚀性能的影响.结果表明:氮合金化能够抑制316L不锈钢中σ相和Chi相的析出,增加Cr2N的析出倾向,对奥氏体晶粒细化不明显;氮的添加能够提高316L不锈钢的室温强度和-100℃以上温度的夏比冲击功,降低-100℃以下的夏比冲击功,但对室温拉伸塑性影响不明显.此外,氮能够改善316L不锈钢的耐点蚀能力.     

影响430热轧成品宽度因素的分析

基于现场试验数据,系统地分析了影响430铁素体不锈钢热轧成品宽度的因素,结果表明,原料坯宽度和轧制温度的波动对430成品宽度影响较大,中间坯厚度波动的影响基本可以忽略;为消除立辊磨损造成的成品宽度增加,应定期对立辊进行标定。     

Hot Working of High Nitrogen Austenitic Stainless Steel

With hot rolling in laboratory and Gleeble thermal simulator,the hot working of a high nitrogen austenitic stainless steel(HNASS)was researched.The results showed that dynamic recovery(DRV)and dynamic recrystallization(DRX)in HNASS occurred during hot working,and both of them had well-defined stress peaks in flow curves under different conditions.During hot rolling experiment at temperature from 950 to 1050 ℃,recrystallization phenomenon does not take place in test material until the deformation ratio is up to 40%.Recrystallization influences remarkably the strength and ductility of material,and the test HNASS possesses better combination of strength with ductility.According to the curve of θ-σ(strain hardening rate-steady state stress),the DRX critical strain of test material was determined.Also,the activation energy of hot working was calculated to be 746.5 kJ/mol and the equation of hot working was obtained.     

High‐Interstitial Stainless Austenitic Steel Castings

Interstitial atoms are most effective in strengthening austenitic steels. In stainless grades, chromium strongly reduces the solubility limit of carbon. High‐nitrogen contents require costly pressure or powder metallurgy to dissolve N in the melt. The combination of both elements comes with a high‐interstitial solubility at normal pressure of air. Sand casting with 18 mass% Cr and Mn each and 0.85 mass% (C + N) were industrially produced. The investigation revealed: proof strength R_p0.2 = 457 [MPa], true fracture strength R = 1714 [MPa], fracture elongation A = 44%, notch impact toughness KV = 290 J combined with a DBTT of ?94°C, an impact wear resistance comparable to Hadfield steel X120Mn12 but combined with a good corrosion resistance. Deep freezing and cold working does not effect the low relative magnetic permeability. This unique combination of properties offers advantages in application.     

Energetics of Plastic Deformation of Metastable Austenitic Stainless Steel

The change in the internal energy during uniaxial tensile deformation of austenitic stainless steels EN 1.4301 (AISI 304) and EN 1.4318 (AISI 301LN) was determined by measuring the extent of γ→α'‐martensite transformation and the temperature increase of the samples. From the results the fraction of the stored energy of cold work and the free energy change related to the strain‐induced γ→α'‐martensite transformation were determined. The fraction of stored energy varied around 0.4. With the metastable steel grades the free energy change related to the γ→α'‐martensite transformation was found to vary between ‐98 MJ/m³ and ‐206 MJ/m³ depending on the austenite stability of the steel. Furthermore, the magnitude of the mechanical driving force was estimated by comparing the results with the free energy change of thermally induced transformation.     

含Ti奥氏体不锈钢连铸小方坯的质量

介绍了我国第一台特殊钢方坯连铸机,连铸含Ti奥氏体不锈钢的铸坯质量情况,内容包括:铸坯的低倍组织结构、非金属夹杂物、化学成分偏析、铸坯表面及钢材性能。连铸的工艺条件保证了产品的性能要求。     

等径角挤压变形奥氏体不锈钢的组织演变

 用实验方法研究了奥氏体不锈钢在等径角挤压冷变形(路径RC)过程中组织变化。实验结果表明：当剪切方向与孪晶带方向成一定角度时，在剪切力的作用下，孪晶逐渐由大块孪晶→由剪切带分割的孪晶(楼梯状)→小块状→奥氏体亚晶或马氏体晶粒；部分孪晶在剪切力作用下，剪切带可直接碎化成具有大角度位向差的细小晶粒(奥氏体亚晶+马氏体晶粒)，可发生马氏体相变；当剪切方向与孪晶带方向相同时，孪晶带区域也可发生马氏体转变；3道次变形后，具有明显特征的孪晶已很少，此后继续进行剪切变形，孪晶碎化组织(含马氏体)和奥氏体剪切滑移带(含碎化晶粒)的变形以剪切滑移方式进行，当奥氏体的滑移遇到阻力时，可局部形成局部形变孪晶来协调变形；随变形道次的增加，马氏体转变也越多，在多次剪切以及道次中的交叉滑移作用下，马氏体板条逐渐被高密度位错墙分割而碎化成细小的晶粒；8道次变形后，可获得60~230 nm的等轴晶粒。     

Effect of Carbon on Stainless Austenitic CrMnCN Steel Castings

The effect of up to 0.5 mass% C on a steel with 18 to 19 mass% Cr and Mn each and about 0.6 mass% N was investigated by tensile tests, notch impact tests and corrosion tests. The experimental results show that the solution anneal temperature and the sensitisation to intercrystalline corrosion depend on the carbon content which raise the strength and cold work hardening. Up to 1 mass% C+N the ductile to brittle transition temperature remains at about ?90 °C. Corrosion in diluted aqueous solutions of H₂SO₄, HCl and NaCl is described.