Inclusion and its deformation behavior in 304 stainless steel

Non-metallic inclusion is the main reason for the presence of surface defects in cold-rolled steel strip. In this study,the composition,morphology,and size of the non-metallic inclusion in hot-rolled 304 stainless steel strips are analyzed. Cold-rolled 304 stainless steel strips with different cold-rolling reduction have been prepared,and the morphology and size of inclusion in these cold-rolled strips are also analyzed. Furthermore,the deformation behavior of a non-metallic inclusion during the cold-rolling process is studied. The results showthat Ca O-SiO2-MgO-Al2O3,a kind of brittle compound oxide,is the main type of inclusion in hot-rolled 304 stainless steel strips.During the cold-rolling process,ductile deformation of this type of inclusion is not obvious,where large inclusions are crushed,and the average size of inclusions in cold-rolled strips decreased while the cold-rolling reduction increased.     

The erosion behavior of 304 stainless steel at elevated temperatures

The objective of this paper is to characterize the solid particle erosion behavior of an annealed 304 stainless steel (SS) over the temperature range of 300 to 763 K. Silicon carbide was used as the erodent. Impact velocity and angle were kept constant at 115 m/s and 90 deg (normal), respectively. The results indicated that the erosion rate of 304 SS as a function of test temperature went through a minimum at around 548 K. None of the empirical models or parameters proposed in the literature for correlating room-temperature erosion resistance with a variety of mechanical or thermophysical properties of the eroding or erodent material explained the observed erosion ratevs temperature behavior. However, the results were qualitatively explained on the basis of a localization model for erosion. An analysis of the erosion data also indicated that oxidation of the eroding material and related effects on erosion were unimportant even at the highest test temperature of 763 K.     

Fatigue-crack propagation behavior of type 304 stainless steel at elevated temperatures

The fatigue-crack propagation behavior of Type 304 stainless steel was investigated within the framework of linear elastic fracture mechanics at temperatures of 75‡, 600‡ 1000‡ and 1200‡F. The cyclic frequency for the elevated temperature tests was 4 cpm. It was found that, in general, fracture mechanics concepts may be used to describe the crack propagation behavior at these temperatures, and that increasing the temperature had a significant effect in increasing the fatigue-crack growth rate.     

Dissolution behavior of 304 stainless steel in HNO3/HF mixtures

The dissolution behavior of type 304 stainless steel was studied in typical pickling environments in an effort to reduce the unnecessary loss of the critical metals nickel and chromium during the pickling process. Dissolution rates were determined for a 90-minute exposure to HNO₃/HF solutions ranging from 0.8 M to 3.5 M HNO₃ and 0.5 M to 2.6 M HF at 30°, 50°, 70°, and 90 °C and containing 0 to 0.21 M dissolved Fe, Cr, or Ni. Dissolution rates increased as a function of increasing HNO₃ concentration from 0.4 M to 1.5 M HNO₃, decreased at higher HNO₃ concentrations, and increased with increasing HF concentration. Experiments to determine the effect of temperature on the dissolution reaction gave a lower activation energy for solutions with higher HNO₃ concentrations. The dissolved Fe and Cr decreased the dissolution rate of 304 stainless steel, while dissolved Ni had essentially no effect. The Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) studies of films resulting from exposure to several HNO₃/HF solutions indicated that the fluoride did not penetrate the thin nonprotective films but remained on the outer surface of the film. The scanning Auger microscopy (SAM) studies indicated that the fluoride was uniformly distributed over the surface. Both the dissolution and surface studies are consistent with a dissolution process which is controlled by reactions occurring either in solution or at the film-solution interface.     

Fatigue-crack propagation behavior of type 304 stainless steel in a liquid sodium environment

The fatigue crack growth of Type 304 stainless steel in a liquid sodium environment at 800 and 1000°F was characterized using a linear-elastic fracture mechanics approach. Tests were conducted in low (< 2.0 ppm) and high (20-40 ppm) oxygen sodium and the results were compared to those of tests conductedin vacua and in air. Similar crack propagation characteristics in air at room temperature and at elevated temperatures in sodium and vacuum is evidence that the thermally activated component of crack propagation observed in air is an environmental effect. Related work on environmental effects on fatigue or crack propagation properties are reviewed and discussed.     

Elevated-temperature low-cycle fatigue behavior of different heats of type 304 stainless steel

The low-cycle fatigue results of three heats of Type 304 stainless steel have been ob-tained at 593°C under selected cyclic-loading conditions. The results are compared with those generated for a reference heat of steel for which extensive low-cycle fatigue data are available. Observation of the microstructures of specimens in the pretest condition after a given heat treatment and examination of fatigue fracture surfaces were con-ducted by means of optical and scanning electron microscopy and X-ray analysis. The three heats of stainless steel, which exhibit different microstructural features, show approximately the same continuous-cycling low-cycle fatigue behavior as that of the re-ference heat. However, the three materials show improved fatigue strength during tensile hold-time conditions where significant creep occurs. The fatigue properties determined in the present study for the different heats of steel are consistent with the observed mi-crostructural features. Finally, the creep-fatigue properties of the heats as well as the microstructural observations are discussed in terms of a damage-rate approach re-cently developed by the authors.     

The martensite phases in 304 stainless steel

A detailed analysis of martensite transformations in 18/8 (304) stainless steel, utilizing transmission electron microscopy and diffraction in conjunction with X-ray and magnetization techniques, has established that the sequence of transformation is γ → ∈ → α. ε is a thermodynamically stable hcp phase whose formation is greatly enhanced as a result of plastic deformation. Comparison with the ε → α transformation in pure Fe-Mn alloys lends further support to the above sequence and suggests that a transformation line between ε and α in Fe-Cr-Ni alloys can be expected. In the 304 stainless steel used in this investigation, formation of α was induced only by plastic deformation and subsequent to formation of ε. Nucleation of α occurs heterogeneously at intersections of ε bands or where ε bands abut twin or grain boundaries (which represent unilaterally compressed regions). From electron diffraction, the Nishiyama relationship between γ and α phases appears to predominate at the start of the transformation, but then changes to that of Kurdjumov-Sachs. Based on these observations, a sequence of atom movements from the hcp structure to the bcc structure is proposed which has the basic geometric features of the martensitic transformation. Formerly with Department of Materials Science and Engineering, University of California, Berkeley, Calif.     

Effect of surface roughness on low-cycle fatigue behavior of type 304 stainless steel

The effects of surface roughness on the low-cycle fatigue life of Type 304 stainless steel at 593°C in air have been investigated. It is observed that, at a strain rate of 4 × 10⁻³ s⁻¹ and a total strain range of 1 pct, the fatigue life (N _f cycles) decreases with an increase in surface roughness. Information on crack growthvs strain cycles has been generated, as a function of surface roughness, by the measurement of striation spacing on fractured surfaces of specimens tested to failure. Crack propagation follows the Ina ∞N (wherea is the crack length afterN strain cycles) relation for longer specimen fatigue lives (N_f > 2700 cycles) and departs from Ina ∞N for shorter fatigue lives. A quantitative estimate is made of the number of cycles N_o(r) to generate a crack length equal to 0.1 mm (≈ 1 grain diam). The initial surface roughness significantly affects only the initiation component of specimen life time. The effect of roughness on crack initiation is described byN ₀ (R) = 1012R^−0.21, whereR is the surface roughness (root-mean-square value) in microns.     

Effect of surface roughness on low-cycle fatigue behavior of type 304 stainless steel

The effects of surface roughness on the low-cycle fatigue life of Type 304 stainless steel at 593°C in air have been investigated. It is observed that, at a strain rate of 4 × 10^?3 s^?1 and a total strain range of 1 pct, the fatigue life (N _f cycles) decreases with an increase in surface roughness. Information on crack growthvs strain cycles has been generated, as a function of surface roughness, by the measurement of striation spacing on fractured surfaces of specimens tested to failure. Crack propagation follows the Ina ∞N (wherea is the crack length afterN strain cycles) relation for longer specimen fatigue lives (N_f > 2700 cycles) and departs from Ina ∞N for shorter fatigue lives. A quantitative estimate is made of the number of cycles N_o(r) to generate a crack length equal to 0.1 mm (≈ 1 grain diam). The initial surface roughness significantly affects only the initiation component of specimen life time. The effect of roughness on crack initiation is described byN ₀ (R) = 1012R^?0.21, whereR is the surface roughness (root-mean-square value) in microns.     

Intercrystalline structure distribution in alloy 304 stainless steel

The intercrystalline structure distribution function (ISDF) describes the probability density for the occurrence of grain boundaries in the polycrystalline medium with five specified geometrical parameters: three describing intercrystalline lattice misorientation and two describing the orientation of the grain boundary plane. This paper extends the ISDF analysis to Bunge’s formalism which represents the distribution in terms of a series expansion of symmetric generalized spherical harmonics. An exemplary calculation of the ISDF is illustrated for alloy 304 stainless steel tubing. The results confirm the observation that gS3 and gS9 boundaries, arising from twinning, are prevalent in the structure. The distribution of twinning boundaries and other special boundaries is represented by Euler plots in the five geometrical parameters defining boundary structure. One remarkable feature of this material is a nearly isotropic distribution of boundary misorientation in the two parameters defining the boundary plane orientation. These results are compared with other published experimental data and theoretical calculations for the distribution of special boundaries.     

Prediction of fatigue crack formation in 304 stainless steel

Strain-controlled fatigue tests have been conducted on center-holed 304 stainless steel specimens. The fraction of total fatigue life spent until formation of an “engineering” crack ranged from about 15 to 85 pct, indicating the potential importance of being able to predict the fatigue crack formation life. A “just formed engineering crack,” as defined here, is a through crack long in the thickness direction, which has just emerged from the center hole. An energy based parameter, ΔσrΔε,, has been shown to correlate with the appearance of fatigue cracks in the center-holed 304 stainless steel specimens. This parameter is suggested to be more useful in predicting fatigue crack formation life than Δσ or Δε, alone. A good correlation was found over the limited range of data for two types of 304 stainless steel, a powder metallurgy (PM) stainless steel with higher than normal strength prop-erties and an ingot metallurgy (IM) stainless steel with normal strength properties. A better correlation was found for strain-controlled fatigue tests which did not go into compressive strain than for com-pletely reversed fatigue. Formerly a graduate student with the Materials Science and Engineering Department, Northwestern University, is     

304不锈钢熔体氮溶解度的测定

介绍并比较了纯铁液中氮溶解度测定方法--直接法和间接法,并在经典的间接法的基础上,重新设计了气体氮的配气、控制和计量系统,以及渗氮的方式.用该方法测定了304不锈钢熔体在不同温度和氮分压下的氮的溶解度值.     

Research on martensitic transformation of 304 stainless steel

采用光学显微镜、扫描电镜、磁性测量和力学分析等手段,研究了304奥氏体不锈钢形变过程中发生开裂的原因,研究发现开裂是由于形变过程中发生了马氏体相变,导致塑性变差引起的,开裂处的磁性率达到了22.9%。发生马氏体转变的原因是由于w（Ni）低于标准下限,其组织稳定性下降,在形变过程中诱发了马氏体转变。     

The sintering of 304L stainless steel powder

An examination of the shrinkage kinetics for a 304L stainless steel powder showed that initial densification is controlled by a strain assisted volume diffusion mechanism. At temperatures above 1330 K, grain growth reduces the shrinkage rate; however, at lower sintering temperatures, the shrinkage rate is temporarily increased by the proximity of the moving grain boundaries to the interparticle necks. The activation energies of volume diffusion (240±20 kJ/mol) and grain growth (285±35 kJ/mol) were in good agreement with prior results.     

The sintering of 304L stainless steel powder

An examination of the shrinkage kinetics for a 304L stainless steel powder showed that initial densification is controlled by a strain assisted volume diffusion mechanism. At temperatures above 1330 K, grain growth reduces the shrinkage rate; however, at lower sintering temperatures, the shrinkage rate is temporarily increased by the proximity of the moving grain boundaries to the interparticle necks. The activation energies of volume diffusion (240 ± 20 kJ/mol) and grain growth (285 ± 35 kJ/mol) were in good agreement with prior results.     

Hydrogen assisted cracking of type 304 stainless steel

This paper reports a study of hydrogen assisted cracking in type 304 stainless steel. It shows that the most detrimental effect in increasing the susceptibility of the material to hydrogen cracking is the formation of martensite upon deformation. This is particularly damaging if the martensite is localized at the grain boundaries. With martensite present intergranular impurities such as phosphorus play a secondary role. As martensite becomes more difficult to form, the importance of impurities increases.     

304不锈钢马氏体组织转变探讨

采用光学显微镜、扫描电镜、磁性测量和力学分析等手段,研究了304奥氏体不锈钢形变过程中发生开裂的原因,研究发现开裂是由于形变过程中发生了马氏体相变,导致塑性变差引起的,开裂处的磁性率达到了22.9%。发生马氏体转变的原因是由于w（Ni）低于标准下限,其组织稳定性下降,在形变过程中诱发了马氏体转变。