Complex Weldment Properties: Trends in Predictive Power www.msm.cam.ac.uk/phase-trans

Colleagues H. S. Lalam, M. Murugananth, T. Sourmail, D. J. C. MacKay, T. Cool E. A. Metzbower, D. Moon L. Karlsson L.-E. Svensson E. Keehan, H.-O. Andren

Goldak’s (1990) grand challenges for the year 2000 residual stress microstructure use of fracture mechanics use of continuum damage mechanics weld pool arc models multipass welds distortion during repairs hydrogen cracking hot cracking

critical stress intensity Charpy fatigue tensile critical stress intensity corrosion

Axioms All properties can be measured. Measurements can be used in safe design. Measurements can be used in control. Self evident truth, statement which commands general belief, an unverifiable although widely accepted fact

Dogma Given a comprehensive description of material, process and structure, it is not yet possible to predict most properties. Dogma - statement of belief

hardness

Variables C, Mn, Si, Ni, Cr, Mo, V, Co, B, N, O….. Thermomechanical processing of steel Welding consumable Welding parameters Subsequent heat treatment

MULTIPASS ARC WELD Weld macro L.-E. SVENSSON

Loureiro & Fernandes, 1994

Ion, Easterling and Ashby, 1984

Ion, Easterling and Ashby, 1984

Ion, Easterling and Ashby, 1984

Ion, Easterling and Ashby, 1984

100 µm

Fe-1Mn-C wt % manual metal arc welds 0.2 0.4 0.6 0.8 1.0 Allotriomorphic Volume fraction Widmanstatten Acicular 0.11 0.09 0.07 0.05 0.03 Carbon / wt %

Young & Bhadeshia, 1994

Tempering Bhadeshia & Downs, 2002

Bhadeshia & Downs, 2002

Bhadeshia & Downs, 2002

Conclusions There are useful ways of expressing hardness Limited models relating hardness to microstructure No method for predicting hardness in general Dogma - statement of belief

large numbers of variables uncertainties exploit large knowledge base Solution non-linear functions large numbers of variables uncertainties exploit large knowledge base Dogma - statement of belief

non-linear functions

(Bayesian inference) Dogma - statement of belief

Bayesian inference Dogma - statement of belief

prior beliefs

the data

Baye’s rule likelihood prior

Baye’s rule

y x

Benefits Quantitative prediction of mechanical properties, minimal dangers of extrapolation New science New products New industries Dogma - statement of belief

Murugananth & Bhadeshia, 2002

Moon, Murugananth & Bhadeshia, 2002

Progress on material properties yield strength UTS reduction of area elongation Charpy fatigue creep rupture creep ductility ductile tear microstructure complex deformation ……………………...

Components of Creep Strength, 2.25Cr1Mo iron + microstructure 550 °C solid solution 600 °C precipitates Murugananth & Bhadeshia, 2001

elements in solution Murugananth & Bhadeshia, 2001

integrated model Summerfield et al., 1995

Siemens Mitsui Babcock Nippon Steel ABB

Remove gaussian assumption. Use method to define experiments. Reverse predictions Dogma - statement of belief

Recommendation Model mechanical properties with non-linear methods, large numbers of variables, within a Bayesian framework, exploiting all available data www.msm.cam.ac.uk/phase-trans