Integrated modelling approach for evaluating the peritectic phase transition during continuous casting

Transcription

1 Presentation title, change View >> Header & Footer B. Santillana, D. Ruvalcaba, D. van der Plas Integrated modelling approach for evaluating the peritectic phase transition during continuous casting Thermo-Calc Annual Meeting Aachen 2014

2 Surface depressions Thermocouple Dips Couresy HJ Shin of CCC

3 Breakout modelling Temperature Contours of Simulated Longitudinal Depression Tangential Stress Contours of Simulated Longitudinal Depression

4 Medium Carbon critical chemistry Medium 0.1wt% C Aware: some chemistries are sensitive and we need to be especially careful with process

5 Steel grade + depression formation Medium carbon peritectic steels are most sensitive to depression formation and related surface defects 1. Shrinkage Phase transformation (d-ferrite to g austenite) Thermal: Localised high heat transfer 2. Shell strength Phases ferrite/austenite Solid fraction Mushy zone 3. Position in mould Ferro-static pressure. Force pushing shell into contact with mould mould shell

6 Average Mould Stability Index [-] Steel Chemistry Benchmarking solidification behaviour Carbon Equivalent vs. Mould Stability Index Caster 21 Strand Medium 0.1wt% C Low carbon d ferrite / g transformation high in mould high solid fraction dferrite g phase / g transformation resist ferrostatic lower pressure in mould low Poor creep mould strength shell of contact d ferrite steel/mould contact High carbon Medium Carbon Increased variability d ferrite / g transformation higher in mould 0.8 Mushy zone steel/mould contact Carbon Equivalent

7 Carbon Equivalent (of peritectic) Lower Cp Cp is shifted by chemical composition Cp Higher Cp Si, Ti, Cr, Mo C, N, Ni, Mn [1] Cp = C Mn +0.1Ni +0.7N 0.14Si 0.04Cr 0.1 Mo 0.24Ti

8 180G 1N31 1N92 1N91 1N81 1N82 114K 181C 1SK3 1P84 1P85 3VAA 2N75 1NBD 1N98 1N99 1NBI 1N96 1N86 1NBC 1N97 1NBG 1N87 110F 1HK3 184K 3HL1 3HL3 2N74 1N83 1N93 125N 1LN7 129N 2F66 1SH3 1N63 1NBE 3F61 123L 125C 129L 2F61 1LF5 3N73 115E 1CK3 3FAC 2NAU 114E 3F63 1S38 3F62 1T80 2F62 2F63 2F64 3FAB 114C 121L 1LH7 111C 184E 2FAF 182E 2NBA 2NBB 3F85 3F65 3N53 2FAD 1P66 1S39 1S42 1T82 3CK3 3LL1 1T94 1T84 1LH1 1H80 1H40 3FAD 2FAA 2F65 3CK1 3C44 3C56 1T96 1T86 1NBF 1NBJ 180G 1N31 1N92 1N91 1N81 1N82 114K 181C 1SK3 1P84 1P85 3VAA 2N75 1NBD 1N98 1N99 1NBI 1N96 1N86 1NBC 1N97 1NBG 1N87 110F 1HK3 184K 3HL1 3HL3 2N74 1N83 1N93 125N 1LN7 129N 2F66 1SH3 1N63 1NBE 3F61 123L 125C 129L 2F61 1LF5 3N73 115E 1CK3 3FAC 2NAU 114E 3F63 1S38 3F62 1T80 2F62 2F63 2F64 3FAB 114C 121L 1LH7 111C 184E 2FAF 182E 2NBA 2NBB 3F85 3F65 3N53 2FAD 1P66 1S39 1S42 1T82 3CK3 3LL1 1T94 1T84 1LH1 1H80 1H40 3FAD 2FAA 2F65 3CK1 3C44 3C56 1T96 1T86 1NBF 1NBJ Total Average of c_equiv_wolf Average of c_equiv_wolf Total Total 0.1 Total KA_C_RICHT KWAL_BAKG Steel B KA_C_RICHT KWAL_BAKG Steel A

9 Presentation title, change View >> Header & Footer 9 Header title Chemical Composition (wt%) C Mn A B Subtitle Steel A a typical peritectic grade Steel B an alloyed grade with high levels of Cr and Si that not considered in the Cp flae, thus underpredicted. Si P S Cr

10 cooling rate (ºC/s) Cooling rate (ºC/s) Heat transfer & shell thickness Meniscus Heat flux peak ~8 MW/m mm 14mm 7mm 11mm Trendline (7mm) Trendline (9mm) Trendline (11mm) Trendline 14mm) mould Isoline Time (s) Mould exit mm 9mm 11mm 14mm Trendline (9mm) Trendline (7mm) Trendline (11mm) Trendline(14mm) Solid shell T S T L Mush Frac solid

11 A B δ δ γ γ Both phases (δ and γ) will still coexists at 100% solid, means there will be a further solid-solid transformation δ γ This steel will continue shrinking after solidification, giving uneven contact with the mould => hot spots So cracking will be dominated by the unevenness of the heat transfer Way to solve it? Mould powder for peritectic grades to control heat transfer The peritectic phase transition happens at the dangerous region of between 0.9 to 0.99 fraction solid obviously this is highly influenced by the casting speed (kinetics!) On the other hand, this steel is a typical case of hot tearing sensitive, so it will not only shrink during solidification but the transition is happening at the danger zone So cracking will be dominated by the interdendritic cracks. Way to solve it? Adjust casting speed to a desired controlled process, mould powder will not have very much influence here.

12 Presentation title, change View >> Header & Footer Begoña Santillana Persistence is to the character of man what carbon is to steel (Napoleon Hill), unless other elements are added to the composition. Together we make the difference