Transformation In Stainless Steel Research Articles

Solidification sequences in stainless steel dissimilar alloy welds

A series of laser and gas tungsten arc welds traversing stainless steels of different chemical compositions has been studied, to elucidate the role of austenite or ferrite nucleation and cooling rate on solidification behaviour. It has been found that a steel with a high CrEQ/NiEQ ratio can be induced to solidify as metastable austenite by initiating the weld in a steel with a lower CrEQ/NiEQ ratio in which the thermodynamically stable solidification mode is austenitic. The austenite dendrites are then found to continue growth across the weld junction into the undiluted regions of the high CrEQ/NiEQ ratio material. By providing austenite particles in this way, nucleation is rendered unnecessary and it is found that solidification to metastable austenite can be induced at cooling rates significantly lower than previously encountered. The results of these and other experiments in which the welding speed was changed during the experiment are interpreted to yield new information about the mechanisms of solidification and transformation in stainless steels during welding under conditions consistent with high cooling rates.MST/1240

Ne implantation induced transformation in stainless steel

This paper reports a microstructural investigation of the changes induced by Ne-implantation in stainless steel of the austenitic type. At a critical dose of 2.3·10 17/cm 2 a martensitic phase transformation was observed. In particular, attention has been paid to the effect of the stress field of neon bubbles on the nucleation of martensite. It is found that the critical size of the nucleus as well as the activation energy is drastically lowered. No definite orientation relationship between martensite and austenite has been detected. This is probably caused by the small size of martensite particles and the deformation in the vicinity of the bubbles.

Local Control of Magnetic Property in Stainless Steel Surface by Ion and Laser Beams

MeV ion and Ar-ion laser beams were impinged onto 304 stainless steel foils to investigate the localized modification of the magnetic property associated with the phase transformation. The intensity of the magnetization was found to increase by MeV Au+ implantation because of the localized martensitic transformation, whereas that of the Ar-ion laser-irradiated areas was found to locally decrease at a laser power of 350 mW and almost extinguish at 550 mW with a beam spot size of 13.2 µm (at 1/e intensity) because of the localized retransformation into austenite. These results indicate that the beam-induced localized phase transformation in stainless steel can be applied to permanent magnetic recording.

The influence of phase transformation in stainless steel during static and fatigue loading

A comparative study of the mechanisms of plastic deformation under static tensile and dynamic zero-to-peak axial loadings (R = 0) has been carried out for an annealed austenitic stainless steel Type 321S12. For the tensile test the high value of the strain-hardening exponent and the high nominal tensile strength/yield strength ratio are associated with the strengthening effects involved in an austenite-martensite transformation. To induce this transformation a minimum value of strain displacement is necessary and such strains are first attained at the surface layers and only occur in the core grains for the regime of plastic instability beyond the level of the nominal tensile strength. The S/N curve reveals three distinct regimes of fatigue and the fatigue limit is ∼ 55% higher than the macro-yield strength of the alloy. Explanations given of the fatigue-crack process in the various regimes of the S/N curve are based on a comparison of the tensile and fatigue loading conditions.

Effect of alloying on the martensitic transformation in stainless steels

1. The addition of cobalt to Fe−Cr alloys lowers Ms and Mf without noticeably reducing the amount of martensite at the end of the transformation. 2. Nickel lowers the temperature range of the martensitic transformation, its effect increasing in the presence of cobalt, which is characterized by a change in the linear variation of Ms=f(% Ni) to quadratic. 3. Molyblenum lowers Ms and Mf greatly, substantially increasing the amount of retained austenite. 4. In the steels investigated, nickel and cobalt lower and molybdenum slightly increases the initial temperature of the reverse α→γ transformation. 5. Reducing the amount of chromium from 13 to 9% stimulates the martensitic transformation, as the result of which the concentrations of nickel, cobalt, and molybdenum can be increased in alloys with 9% Cr, with retention of a martensitic structure. Only limited amounts of these elements can be added to the steel with 13% Cr due to suppression of the martensitic transformation.

Magnetic Study of Martensitic Transformation of Stainless Steel

Magnetic Study of Martensitic Transformation of Stainless Steel

Magnetic Study of Martensitic Transformation of Stainless Steel

Saturation magnetization and roll magnetic anisotropy were measured for several single- and poly-crystals of 18 Cr-12 Ni-70 Fe alloy as functions of roll reduction in various crystallographic directions. It was found that the saturation magnetization increases as the roll reduction does for a polycrystal, (001) [100], (001)[110] and (110)[1\bar10] rollings, whereas it never increases for the (110) [001] rolling. This means that martensitic transformation does not take place for this rolling. The direction of easy magnetization was parallel to the roll direction for a poly-crystal, (001) [100] and (110) [1\bar10] rollings, while it was normal to the roll direction in the case of (001) [110] rolling until it was changed to parallel at about 60% reduction. Powder patterns on the surface of the rolled specimen showed that most of the martensitic transformation took place at the intersections of crossed slip bands which are parallel to {111} planes. A variation of saturation magnetization with martensitic tran...

Influence of dislocation substructure on the martensitic transformation in stainless steel

The dislocation arrangements in austenite, deformed above the athermal M s , temperature, are dependent upon alloy composition, strain and deformation temperature and influence the subsequent transformation to martensite on quenching. In varying degrees, small amounts of deformation were found to stimulate the transformation of two alloys, 18 12 Cr-Ni and 15 13 Cr-Ni which form laths of martensite along {111} A. This behavior is correlated with the formation of long range stress fields by deformation, while mechanical stabilization at large strains is attributed to the destruction of nucleation sites and the hindrance by high densities of dislocations of the growth of martensite laths.

The martensite transformation in stainless steel

Thin films of Fe-18Cr-12Ni have been examined both in the fully austenitic condition and after partial transformation in the bulk to faulted h.c.p. (ε) and to b.c.c. martensite (α′). The ε appeared to be a consequence of α′ formation rather than a necessary intermediate stage in the transformation. Fe-10Cr-15Ni and Fe-5Cr-20Ni thin films were examined in the fully martensitic condition. In these two alloys adjacent regions of α′ were delineated by subgrain boundaries and were not twin-related, though twin relationship was established for adjacent α′ crystals in Fe-18Cr-12Ni. For all alloys the α′ has a dense dislocation substructure.

The martensite transformation in stainless steel

Abstract The nucleation of the low temperature h.c.p. ε and b.c.c. α phases produced by deformation in a 304 stainless steel has been studied by transmission electron microscopy. The ε phase has been found to be an intermediate phase in the nucleation of α martensite from the austenitic matrix.

The martensitic transformation in stainless steels of the austenitic-martensitic class

1. Heating to 525–950°C after austenitizing at 1050°C reduces substantially the stability of austenite. Destabilization of austenite is explained by a depletion of the solid solution in chromium and carbon by chromium carbide precipitation. 2. Prolonged holding at room temperature after austenitizing or heating at up to 500°C stabilizes the austenite. The martensitic transformation after thermal stabilization has the following peculiarities: Undercooling of the austenite down to −196°C is possible at relatively slow cooling rates; the transformation of austenite to martensite proceeds isothermally after a certain in induction period. The effect of isothermal temperature and holding time on the transformation rate is represented by a curve showing a maximum. 3. These rules do not apply to an ordinary martensitic transformation of unstabilized austenite. 4. Thus, in thermally stabilized steel Kh15N9Yu the martensitic transformation proceeds so as to indicate that its kinetics is determined by the thermal vibrations of the atoms.