Napoved sil vročega valjanja debelih plošč jekla S960QL

Bernik, Matic (author), Fajfar, Peter (mentor), Klančnik, Grega (comentor)

Namen diplomske naloge je iz rezultatov enostopenjskih tlačnih preizkusov izrisati krivulje tečenja in primerjati napetosti, ki smo jih izračunali iz tlačnih preizkusov, z napetostmi, izračunanimi iz sil in dolžin preoblikovalne cone iz realnega procesa plastične predelave na valjalnem stroju za valjanje debele pločevine. Cilj je tudi primerjati napovedane, sile po Simsu, z izmerjenimi silami na samem ogrodju z uporabo temperaturnega modela valjanca. V teoretičnem delu je opisano preiskovano jeklo S960QL poleg splošnega opisa visokotrdnostnih malo-legiranih jekel in njihovih značilnih lastnosti s poudarkom na plastični predelavi (vroče valjanje) z vsemi potrebnimi pripadajočimi enačbami. V okviru eksperimentalnega dela smo na simulatorju termomehanskih metalurških stanj Gleeble 1500D izvedli enostopenjske tlačne preizkuse v vročem ter dobljene surove podatke obdelali in izrisali krivulje tečenja. Iz krivulj tečenja smo določili koeficiente za modelsko napoved sil po Hansel-Spittelovi enačbi, za kar pa smo morali narediti tudi enostaven temperaturni model valjanca za napoved povprečne temperature preoblikovanca ob danem času valjanja in dodatno oceniti ohlajevalno krivuljo z uporabo krivulj tečenja ob znani povprečni napetosti doseženi na ogrodju. Naredili smo tudi primerjavo izračunanih ter ocenjenih temperatur s pomočjo krivulj tečenja z izmerjenimi (s pirometrom) iz realnega procesa vročega valjanja. Za primerjavo povprečnih napetosti smo izvedli modelsko napoved po Simsu za specifičen realen proces z uporabo temperaturnega modela valjanca in potrdili izjemen pomen pravilno ovrednotenih temperatur za dobro ujemanje med napovedjo in industrijskim testom. Zaradi relativno blagih redukcij v delu grobega valjanja se izkaže, da je najboljše ujemanje med napovedanimi in izmerjenimi sila v primeru odčitavanja temperatur iz krivulj tečenja, preko znanih vrednosti logaritemske deformacije in povprečne napetosti (dobljeno iz valjalnega stroja). V primeru večjih redukcij na posamezen prevlek pa pričakujemo boljše ujemanje izmerjenih in napovedanih sil z uporabo modelske napovedi temperatur na račun povečanja globine penetracije deformacije in zajem področja z višjimi temperaturami, kot je podhlajena površina.

• Language: Slovenian
• Keywords: jeklo, HSLA, S960QL, vroče valjanje, sila valjanja
• Work type: Bachelor thesis/paper
• Organization: NTF - Faculty of Natural Sciences and Engineering
• Year: 2020
• PID: 20.500.12556/RUL-120356
• COBISS.SI-ID: 33502979
• Publication date in RUL: 18.09.2020

Secondary language

• Language: English
• Title: Prediction of roll force during heavy plates hot rolling of S960QL steel grade

Abstract

The aim of this diploma thesis is to plot the stress-strain curves (flow curves) from the results of single-stage pressure tests and compare the values of calculated stress from flow curves with resulting values of the stress obtained from the calculation of forces and other rolling data from the real process of plastic deformation on the heavy plate rolling mill. The aim is also to compare the predicted forces according to Sims with the measured forces on the framework, using pre-made temperature model. In the theoretical part we described the examinated steel S960QL, beside that we also described typical characteristics of HSLA steels in general and the process of plastic deformation (hot rolling) with all the required equations. As a part of experimental work, we performed single-stage pressure tests on thermo-mechanical simulator Gleeble 1500D and then used raw final results to plot the stress-strain curves. From the curves we determined coefficients for the Hansel-Spittel model force forecast, for which we had to make a simple rolling temperature model to forecast the average temperature of the rolled plate at given rolling time and estimate the cooling curve using the flow curves. We also compared calculated and estimated temperatures from flow curves, with measured temperatures (with pyrometer) from the real hot rolling process. For comparison of stress we performed a Sims model forecast for a specific real process, using the rolling temperature model and we confirmed the exceptional importance of correctly evaluated temperatures for a good match between the forecast and the industrial test. Due to the relatively mild reductions in the part of the rough rolling (»roughing«), the best match between the predicted and measured forces is in the case of reading the temperatures from the flow curves, using known values of logaritmic stress and average strain (obtained from the rolling mill). On the other hand in the case of major reductions per coating, we expect a better matching of measured and predicted forces using temperature model, due to increase in depth of penetration of deformation and capture of areas with higher temperatures than the undercooled surface.

• Keywords: steel, HSLA, S960QL, hot-rolling, rolling force