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Microstructure characterization of welds in X5CrNiCuNb16-4 steel in overaged condition

Ziewiec A., Zielińska-Lipiec A., Kowalska J., Ziewiec K.

Advances in Materials Science

2019

Vol. 19, nr 1(59)

57--69

The paper presents the results of the investigation of microstructure of the welded X5CrNiCuNb16-4 (17-4PH) steel after solution treatment and aging at 620°C for different periods. The microstructure and the phase composition of the steel was investigated using light microscopy (LM), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), transmission electron microscopy (TEM) and the X-ray diffraction (XRD). Hardness was measured for samples aged at different times. Density distributions of Cu precipitates were established. The investigation has shown that the microstructure of the X5CrNiCuNb16-4 steel welds after aging at 620 ° C consists of tempered martensite, fine Cu precipitates and austenite. It was observed that the size of the Cu precipitates increases with increasing the aging time, what affects the decrease of hardness. Simultaneously, the quantity of reversed austenite increases with increase of aging time. It was revealed that enrichment of the austenite in Ni, Cu and C affects the increase of Ms, but this factor does not determine the stability of austenite.

Microstructure of Welded Joints of X5CrNiCuNb16-4 (17-4 PH) Martensitic Stainlees Steel After Heat Treatment

Ziewiec A., Zielińska-Lipiec A., Tasak E.

Archives of Metallurgy and Materials

2014

Vol. 59, iss. 3

965--970

The paper presents rezults of microstructure (LM, TEM) investigation and hardness measurments of welded joints in martensitic precipitation hardened stainless steel containing copper, subjected to heat treatment. For the aging temperature up to 540°C even for the very long times, the microstructure of the welded joints is similar to this one at lower temerature aging. After aging at 620°C a distinct change of the microstructure was observed. Non-equilibrium solidification conditions of the weld metal, segregation and the diffusion of copper and the elements stablilizing the austenite cause the occurrence of the reverse transformation of the martensite into austenite as fast as just 1 hour at 620°C. TEM investigations revealed the differences in dispersion of hardening copper precipitates after aging at temperature 620°C for 1 and 4 hours.

W artykule przedstawiono wyniki badań mikrostruktury (LM, TEM) oraz twardości złącz spawanych stali nierdzewnej martenzytycznej utwardzanej wydzieleniowo miedzią po obróbce cieplnej. Aż do temperatury starzenia 540° C mikrostruktura spoin nie wykazuje istotnych różnic niezależnie od czasu wytrzymania w porównaniu do tej obserwowanej w niższych temperaturach. Po starzeniu w temperaturze 620°C zaobserwowano wyraźne różnice w mikrostrukturze spoin. Nierównowagowe warunki krzepnięcia metalu spoiny, występowanie segregacji oraz procesy dyfuzji miedzi i pierwiastków stabilizujących austenit powodują wystąpienie przemiany odwrotnej martenzytu w austenit już po 1 godzinie starzenia w 620°C. Badania TEM wykazały, różnice w dyspersji cząstek umacniających w temperaturze starzenia 620°C przez 1 i 4 godziny.