Effect of Rolling and Post-Rolling Cooling Strategies on Microstructure and Properties of S355 Structural Steel| Chapter 4 | Engineering Research: Perspectives on Recent Advances Vol. 11

 

Structural rolled steels are the primary products of modern ferrous metallurgy. The S355 grade, according to EN 10025, specifies that steel sheets with 16–40 mm thickness should have a yield tensile strength of not less than 345 MPa and an ultimate tensile strength within the 470–630 MPa interval. These sheets are typically produced using low-carbon Mn-Si steel with micro-additions of carbide/nitride-forming elements (Nb, Ti, V, and Al). Enhancing the mechanical properties of rolled steel using energy-saving processing routes without furnace heating for additional heat treatment is advisable. This study compared the effect on the mechanical properties of structural steel for different processing routes, like conventional hot rolling, normalising, thermo-mechanically controlled processing (TMCP), and TMCP with accelerating cooling (AC) to 550oC or 460oC. The material studied was a 20 mm-thick sheet of S355N grade (EN 10025) made of low-carbon (V+Nb+Al)-micro-alloyed steel. It was found that using different processing routes could increase the mechanical properties of the steel sheets from S355N to S550QL1 grade without additional heat treatment costs. The optimal temperature for finish rolling during normalising rolling is 840oC, enabling the enhancement of steel’s mechanical properties to the E420N grade through grain refinement (ASTM grain size numbers 10–11). Further increase in steel strength was achieved by the application of TMCP. The best combination of strength and low-temperature toughness, equivalent to the S550Q grade, is achieved through TMCP followed by AC to 550oC. This process forms a quasi-polygonal/acicular ferrite structure with minor fractions of dispersed pearlite and martensite-austenite islands, resulting in ductile-brittle transition temperatures of –48.5oC and –36.5oC in the longitudinal and transverse directions, respectively. The contributions of various structural factors to the yield strength and ductile-brittle transition temperature were calculated and correlate well with experimental data. The proposed technologies eliminate the need for normalisation with furnace heating. The practical significance of the results has been demonstrated through reducing production costs connected with natural gas consumption.

 

Author(s) Details

 

Efremenko B.V.
Pryazovskyi State Technical University, 49044 Dnipro, Ukraine.

 

Stavrovskaia V.E.
Pryazovskyi State Technical University, 49044 Dnipro, Ukraine.

 

Sili I.I.
Pryazovskyi State Technical University, 49044 Dnipro, Ukraine.

 

Chabak, Y.G.
Pryazovskyi State Technical University, 49044 Dnipro, Ukraine and Institute of Materials Research, Slovak Academy of Sciences, 04001 Kosice, Slovak Republic.

 

Efremenko V.G.
Pryazovskyi State Technical University, 49044 Dnipro, Ukraine and Institute of Materials Research, Slovak Academy of Sciences, 04001 Kosice, Slovak Republic.

 

Please see the book here :- https://doi.org/10.9734/bpi/erpra/v11/6364