In Situ Observation of Solidification Process of AISI 304 Austenitic Stainless Steel

The solidification process of AISI 304 stainless steel during cooling at a rate of 0.05 K/s has been observed in situ using a confocal scanning laser microscope （CSLM）. The results show that the 8 phase appeared first in liquid steel, as the temperature decreased, the γ phase precipitated prior at δ-grain boundary at 1452. 2 ℃, the liquid steel disappeared at 1 431.3 ℃, and then the γ phase precipitated on the δ ferrite. Based on the Scheil-Gulliver solidification model, the solidification processes of AISI 304 stainless steel are simulated using the Scheil model in Thermo Calc, and the simulation results agree well with the results observed in the experiment.     

Tribological Investigation of Effect of Grain Size in 304 Austenitic Stainless Steel

Stainless steels are widely used in a variety of engineering applications such as food appliances, surgical instruments, nuclear reactors and cryogenic applications. The properties of stainless steel are greatly affected by the grain size. The present study investigates the effect of grain size on sliding wear behavior of AISI 304 stainless steel. The sliding wear properties are measured using a Pin-on-Disc machine. Annealing heat treatment process varies the grain size of steel at 1100 °C. The wear test is performed on different grain sizes of AISI 304 steel at various sliding speeds under dry condition. The wear rate of the steels at different sliding distances is plotted as a function of grain size. The maximum wear rate is obtained at an intermediate grain size. It is noted that frictional force and temperature initially increases and then reaches the saturation plateau. The results are used to establish a correlation between the grain size and sliding wear properties of stainless steel. The present study is useful in enhancing the life of various components made of the stainless steel.     

Microstructural Evolution During Friction Surfacing of Austenitic Stainless Steel AISI 304 on Low Carbon Steel

Austenitic stainless steel AISI 304 coating was deposited over low carbon steel substrate by means of friction surfacing and the microstructural evolution was studied. The microstructural characterization of the coating was carried out by optical microscopy (OM), electron back scattered diffraction (EBSD), and transmission electron microscopy (TEM). The coating exhibited refined grains (average size of 5 ??m) as compared to the coarse grains (average size of 40 ??m) in as-received consumable rod. The results from the microstructural characterization studies show that discontinuous dynamic recrystallization (DDRX) is the responsible mechanism for grain evolution as a consequence of severe plastic deformation.     

The Investigation of Strain-Induced Martensite Reverse Transformation in AISI 304 Austenitic Stainless Steel

This paper presents a comprehensive study on the strain-induced martensitic transformation and reversion transformation of the strain-induced martensite in AISI 304 stainless steel using a number of complementary techniques such as dilatometry, calorimetry, magnetometry, and in-situ X-ray diffraction, coupled with high-resolution microstructural transmission Kikuchi diffraction analysis. Tensile deformation was applied at temperatures between room temperature and 213 K (−60 °C) in order to obtain a different volume fraction of strain-induced martensite (up to ~70 pct). The volume fraction of the strain-induced martensite, measured by the magnetometric method, was correlated with the total elongation, hardness, and linear thermal expansion coefficient. The thermal expansion coefficient, as well as the hardness of the strain-induced martensitic phase was evaluated. The in-situ thermal treatment experiments showed unusual changes in the kinetics of the reverse transformation (α′ → γ). The X-ray diffraction analysis revealed that the reverse transformation may be stress assisted—strains inherited from the martensitic transformation may increase its kinetics at the lower annealing temperature range. More importantly, the transmission Kikuchi diffraction measurements showed that the reverse transformation of the strain-induced martensite proceeds through a displacive, diffusionless mechanism, maintaining the Kurdjumov–Sachs crystallographic relationship between the martensite and the reverted austenite. This finding is in contradiction to the results reported by other researchers for a similar alloy composition.

     

Surface Modification by Nitrogen Plasma Immersion Ion Implantation on Austenitic AISI 304 Stainless Steel

Surfaces of AISI 304 austenitic stainless steel plates nitrided by plasma immersion ion implantation (PIII) technology were studied by means of Auger electron spectroscopy (AES)and X-ray photoelectron spectroscopy (XPS)to determine the effect of the nitriding process on the surface and subjacent layers.Elemental compositions obtained by AES and XPS at varying depths indicate that the saturation of N is relatively constant as a function of depth,indicating the reliability of PIII technology for subsurface saturation.It is concluded that the concentrations of both Cr and O increase with depth,the subjacent oxide is driven by the Ar+ sputtering process used to access the lower layers,and then N is bound to Cr.     

Microstructure Evolution of Laser Welded 301LN and AISI 304 Austenitic Stainless Steel

Metallurgical and Materials Transactions A - Cold-rolled plates of metastable austenitic stainless steel (SS) 301LN are the main materials for manufacturing lightweight railway passenger cars,...     

Effect of Long-Term Thermal Exposures on Microstructure and Impression Creep in 304HCu Grade Austenitic Stainless Steel

Metallurgical and Materials Transactions A - This paper presents the results of microstructural evolution and mechanical properties in 304H Cu grade austenite stainless (SS 304HCu) during long-term...     

Ultrasonic Characterization of Strain Hardening Behavior in AISI 316L Austenitic Stainless Steel

The present work is aimed at characterizing the strain hardening behavior of AISI 316L austenitic stainless steel using ultrasonic velocity measurements. For this purpose, microstructural studies and ultrasonic velocity measurements were carried out on the samples deformed to different levels of strain at room temperature. Strikingly, the ultrasonic velocity?Cstrain plot of the alloy exhibited a three-stage behavior that was similar to the strain hardening rate?Cstrain response of the alloy. At strains lower than about 0.06 (stage A), a falling regime of velocity was observed that was related to the increase of dislocations density. This stage was followed by a stage of a nearly constant velocity (stage B). The initiation of this stage was concurrent with the onset of deformation twinning in the microstructure. Beyond a strain of about 0.2, the second falling regime of velocity (stage C) was developed. The occurrence of this stage was attributed to the difficulty of new twins formation with an increasing strain.     

铸态304L奥氏体不锈钢等径角挤压变形研究

 研究了铸态304L奥氏体不锈钢在等径角挤压(ECAP)变形过程中显微组织的演变过程。结果表明,经4道次剪切变形后树枝晶破碎、原始粗大晶粒碎化。显微组织的变化过程可归纳为：原始粗晶粒→晶粒被滑移带分割→位错发展形成高密度位错墙,与滑移带共同作用形成胞块结构→应变增加形成层片状界面→形成大角度晶界的细小晶粒。表明铸态304L奥氏体不锈钢经ECAP变形后塑性变形机制主要由滑移完成。     

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.     

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…     

氮对304奥氏体不锈钢组织和力学性能的影响

在０Ｃｒ１８Ｎｉ９奥氏体不锈钢成分基础上，加入一定的氮，并使钢中的镍含量控制在标准下限含量的条件下，研究了氮对组织和力学性能的影响。结果表明：加氮后钢的强度提高，奥氏体稳定不变，固溶态组织不变，而敏化后晶界析出物类型有所不同。     

Development and Application of On-Line Solution Annealing Process for 304 Austenitic Stainless Steel

After hot rolling, 304 austenitic stainless steel requires a solution annealing treatment to prevent intergranular corrosion and eliminate work hardening effects. Compared to traditional offline processes, on-line solution annealing offers advantages in terms of cost and time savings. However, both recrystallization behavior and M₂₃C₆ carbide precipitation behavior are significantly influenced by the cooling process after rolling, which poses conflicting requirements. This study investigates the precipitation behavior of M₂₃C₆ carbides and the recrystallization softening behavior during the continuous cooling process of hot-rolled samples. The kinetics equations are derived using the Scheil's additivity rule. The temperature profiles in different regions of the plate are studied using finite element analysis. A practical approach for online solution annealing is proposed and applied in industrial testing.