The kinetics of small-impurity grain-boundary-segregation formation in cold-rolled deep-drawing 08C-Al and IF steels during post-deformation annealing

Abstract

An investigation of small-impurity grain-boundary-segregation (GBS) kinetics in deep-drawing steels (DDSs) allows us to improve the mechanical properties of these steels by optimizing the post-deformation heat-treatment parameters. The kinetics of the GBS formation for C, N, P and S was determined with a series of isothermal expositions of specimens in the spectrometer work chamber at temperatures of 250-650°C. The surface chemical composition of the samples was measured with Auger electron spectroscopy (AES). Isodose C-curves of the GBS for each detected impurity were plotted. The time -temperature intervals of the preferential GB enrichment with C, N, P, S were determined for the 08C-Al steel with various reduction ratios and for the IF-steels with various concentrations of the micro-alloying elements Nb and Ti. It was found that cold rolling of the 08C-Al steel with a reduction ratio from 48 % to 80 % dramatically increases the preferential carbon GBS temperature from 350°C to 450°C due to the necessity of the carbon detachment from Cottrell atmospheres with the annealing of dislocations. The influence of the IF-steel micro-alloying with Nb and Ti on the concurrent multicomponent GBS of interstitial and substitution impurities is also demonstrated in the article. Keywords: deep-drawing steels, IF-steels, grain-boundary segregation, Auger electron spectroscopy, annealing, dislocation structure, microalloying Preiskava kinetike segregacije ne~isto~po mejah zrn (GBS) v jeklih za globoki vlek (DDS) omogo~a izbolj{anje mehanskih lastnosti teh jekel z optimizacijo parametrov toplotne obdelave po hladni deformaciji. Kinetika nastanka GBS za C, N, P in S je bila dolo~ena s serijo izotermne izpostavitve vzorcev v delovni komori spektrometra pri temperaturah 250-650°C. Kemijska sestava povr{ine je bila izmerjena z Augerjevo elektronsko spektroskopijo (AES). Narisane so bile krivulje enakih odmerkov C za GBS za vsako odkrito ne~isto~o. Intervali~as -temperatura preferen~nih GB-obogatitev C, N, P, S so bili dolo~eni za 08C-Al jeklo pri razli~nih stopnjah redukcije in za IF-jekla z razli~nimi koncentracijami mikrolegirnih elementov Nb in Ti. Ugotovljeno je, da pri hladnem valjanju 08C-Al-jekla s stopnjo redukcije med 48 % in 80 % naraste preferen~na temperatura GBC ogljika iz 350°C na 450°C zaradi potrebe razdvojitve ogljika iz Cottrellovega oblaka z`arjenjem dislokacij. V~lanku je prikazan tudi vpliv mikrolegiranja z Nb in Ti v IF-jeklu na so~asno ve~komponentno GBS intersticijskih in substitucijskih ne~isto~.