نیتروژن دهی یون-پلاسمایی فولاد ابزار ماشین آلات و قطعات

Ion-plasma nitriding of machines and tools parts instrumental steels

نیتروژن دهی یون - پلاسمایی فولاد ابزار ماشین آلات و قطعات 

ABSTRACT

Here introduced features of formation diffusion bond during ion nitriding in glow discharge plasma in gaseous mediums (mixture of nitrogen and argon). It is shown, that argon existing in saturated medium changes the nitriding process kinetics and the phase composition of the outer zone. Here presented investigation results on ion-plasma nitriding of instrumental steels, focused on microstructure and tool areas phase composition change, operating in most difficult conditions.

 

نیتروژن دهی پلاسمایی و عملیات رسوب سختی فولاد مارجینگ

Effect of Simultaneous Plasma Nitriding and Aging Treatment

on the Microstructure and Hardness of Maraging 300 Steel

تاثیر همزمان نیتروژن دهی پلاسمایی و عملیات رسوب سختی بر میکروساختار و سختی فولاد مارجینگ 300

ABSTRACT

Simultaneous nitriding and aging heat treatment of maraging 300 steel was carried out inside a DC-pulsed plasma nitriding reactor. A single heat treatment cycle was done, as the plasma nitriding and age hardening processes occur at the same ranges of temperatures and times. Samples of maraging 300 steel, in the solution annealed and solution annealed and aged conditions, were tested. Plasma nitriding and aging, carried out at 480 °C for 3 h, increased the surface hardness up to 1140 HV, producing case depths of 50 μm since ε-Fe3N and γ′-Fe4N nitrides were formed in the hardened surface layer. It is observed that the microstructure of the core material remains unaltered as the typical martensite plate-like microstructure of maraging steels. The core hardness of solution annealed samples increased from 331 to 597 HV after the plasma nitriding treatment proving the possibility of nitriding and aging at the same treatment cycle. The pre-aged samples did not show any overaging or martensite reversion to austenite after the simultaneous plasma nitriding and aging treatments, that could be showed by the core hardness of 620 HV and can be related to the time of total aging exposure of 6 h, including pre-aging and plasma nitriding.

 

نیتروژن دهی پلاسمایی فولاد زنگ نزن نوع AISI 420

Effect of plasma nitriding on the strength of

fine protrusions formed by sputter etching of

AISI type 420 stainless steel

تاثیر نیتروژن دهی پلاسمایی بر استحکام برآمدگی های ریز تشکیل شده

از اچ کند و پاشی (sputter etching)  فولاد زنگ نزن نوع AISI 420

ABSTRACT

Argon ion sputter-etching of AISI type 420 martensitic stainless steel was carried out to form conical protrusions with bottom diameter of 10–30 μm on the specimen surface by using a radio-frequency magnetron sputter-apparatus. Plasma-nitriding was applied to the protrusions with various mixing rate of nitrogen and argon gas. The shape of the protrusions was examined by using a scanning electron microscope, and the nitrides formed on the protrusions were identified by means of an X-ray diffraction analysis. Micro-Vickers hardness tests and nano-scratch tests were used to evaluate the deformation resistance of the protrusions. By plasma-nitriding at a nitrogen pressure of 130 Pa and a nitriding power of 50 W, about 1.3 times larger indentation resistance than that of the as-sputter-etched protrusions was obtained after a long nitriding time of 14 ks. When plasma-nitriding was carried out at a lower nitrogen pressure of 1.2 Pa and a higher nitriding power of 200 W for 7.2 ks, indentation and scratch resistances of the protrusions largely increased to the values almost three times as large as those of the as-sputter-etched protrusions. However, the protrusions were brittle due to the formation of thick nitride layers and the sharpness of the protrusions was lost. Reduction of the nitriding power to 50 W recovered the sharpness with small amount of surface nitride layer, but the indentation resistances were only 1.4 times larger values than those of the as-sputter-etched protrusions. On the other hand, plasma-nitriding using a mixture of nitrogen gas of 0.53 Pa and argon gas of 0.67 Pa at the power of 50 W produced almost twice larger indentation and scratch resistances than those of the as-sputter-etched protrusions within a short nitriding time of 1.8 ks, retaining the sharpness of protrusions without forming brittle nitrided layers.

 

نیتروژن دهی پلاسمایی فولاد ضدزنگ سوپرمارتنزیت

Plasma nitriding of HP13Cr supermartensitic stainless steel

نیتروژن دهی پلاسمایی فولاد ضدزنگ سوپرمارتنزیت HP13Cr

ABSTRACT

Supermartensitic stainless steels (SMSS) are commonly employed in the oil exploitation industry and present a good balance between the necessary physical and chemical properties and financial costs. Certain applications, such as in extreme corrosive and abrasive environments, demand improvements in the surface properties of these steels. In the present work, HP13Cr SMSS with a fully martensitic microstructure were plasma nitrided in the 350–450 °C range. The high diffusivity and low solubility of nitrogen in the martensitic structure allowed the production of thick layers (16–61 μm) containing ɛ-Fe2–3N, γ′-Fe4N and expanded phase (αN) in all the temperatures. In addition, anisotropic sputtering rate and N-diffusion were observed for different grain orientations. Mechanical properties were measured by instrumented indentation, appropriately corrected from roughness effects on the results. Hardness profiles increased from 3.8 GPa (bulk) to ∼14 GPa (near surface region) in all the working temperatures, whereas the elastic modulus was 230 GPa, presenting no statistically significant differences with respect to the bulk value. Nanoscratch tests revealed a hardened-ductile like behavior of these nitride layers. The surface tribo-mechanical behavior was correlated with elastic–plastic responses of the precipitate-containing texturized layers. Results are interpreted in light of the effectiveness of plasma nitriding to modify the surface properties of SMSS.