Distortion in quenching an AISI 4140 C-ring – Predictions and experiments

A combined experimental and numerical examination of welding residual stresses

Residual stresses formation in multi-pass weldment: A numerical and experimental study

Les traitements de surface sont des moyens de plus en plus utilises pour augmenter la resistance en fatigue des pieces metalliques en ameliorant les proprietes du materiau. Chez PSA Peugeot Citroen, certaines pieces sont traitees thermochimiquement (par cementation ou carbonitruration) avant d'etre grenaillees de maniere a tirer profit des avantages respectifs de chaque procede. Cette etude a pour but de comprendre l'effet du couplage entre ces deux traitements de surface sur la generation des champs mecaniques. Des investigations experimentales ont permis de mettre en evidence les effets suivant du grenaillage sur un materiau cemente (ou carbonitrure) dans la couche superficielle: (a) le grenaillage augmente la durete, (b) il augmente considerablement le niveau des contraintes residuelles, (b) il permet de transformer de l'austenite residuelle en martensite. Un modele element fini du grenaillage des pieces ayant ete traitees thermochimiquement a ete etudie. L'etat mecanique apres traitements thermochimiques a ete determine experimentalement par diffraction des rayons X. Le modele du grenaillage prend en compte cet etat initial en termes de contraintes residuelles, deformations plastiques et de variable d'ecrouissage. Le materiau est donc a gradient de propriete et se comporte tel un veritable composite. La loi de comportement en profondeur est obtenue en liant le profil de durete aux proprietes du materiau. Le modele permet d'estimer, entre autres, les profils des contraintes et des deformations plastiques des pieces prealablement traitees thermochimiques.

Modélisation numérique du grenaillage des pièces initialement cémentées ou carbonitrurées

Distortion while quenching steel is a commonly found problem in industrial practice. This issue arises from the combined effect of thermal contraction and martensite transformation stresses. This problem may be exacerbated in components with long geometries. This work presents the results of a numerical and experimental investigation that assessed the effect of both the austenite grain size (AGS) of three sizes 8, 9 and 10 ASTM, and the immersion route on the distortion of a long component of SAE 5160 steel during oil quenching. The transformation kinetics were calculated using JMatPro and were validated by quench dilatometry. A three-dimensional finite element model was developed in Deform 3D. This model was then validated using thermocouple data. Results showed that the distortion was minimized when the long component was dipped sideways in the quenching medium instead of immersing the component from the distal ends when the AGS was 8 ASTM.

Effect of Immersion Routes on the Quenching Distortion of a Long Steel Component Using a Finite Element Model

This paper describes the recent development of models in JMatPro for the calculation of phase transformations and material properties that are critical to the prediction of distortion during the heat treatment of steels. The success of these models is based on the accurate description of all the major phase transformations taking place, including the formation of ferrite, pearlite, bainite and martensite, as well as the calculation of the properties of the different phases formed during the heat treatment process. One advantage of the current models is that they can be applied to many types of steels, including medium- to high-alloy types. A wide range of properties such as density, thermal expansion coefficient, thermal conductivity, strength and hardness can be calculated, all as a function of time, temperature and cooling rate, even for an arbitrary cooling profile. The material data calculated from JMatPro have been exported directly to Finite Element (FE)/Finite Difference(FD)-based packages for forging/deformation simulation.

Modelling phase transformations and material properties critical to the prediction of distortion during the heat treatment of steels

Processing parameters have direct impacts on the quality of the steels produced. This is particularly true for microalloyed steels, the production of which involves a thermomechanical controlled rolling process, which combines multi-pass hot rolling with accelerated cooling. On one hand, hot rolling may finish below A3 temperature when austenite starts to transform to ferrite. On the other hand, controlled cooling is applied to obtain the desired microstructure from austenite decomposition. To optimise the TMCP parameters of such alloys, not only a clear understanding of each metallurgical phenomenon involved is required, but also the interactions among them. This paper reports our recent work on modelling of microstructural evolution and deformation resistance during multi-pass hot rolling of steels. The model considers the following metallurgical phenomena as well as their interactions: - Precipitation of MX type carbides, nitrides or carbonitrides. - Interactions between precipitation and recrystallisation and their effects on grain refinement. - Effect of grain size and cooling path on transformations from austenite to ferrite, pearlite, bainite and martensite. - Effect of rolling parameters, recrystallisation and microstructure on the deformation resistance of the alloy. The model predicts the evolution of microstructural features such as precipitate size and amount, recrystallisation fraction and effective strain, grain size, and austenite decomposition, as well as the alloy’s deformation resistance during hot rolling. It has been applied to a wide range of steels and demonstrated good agreement with experimental observations. Therefore, it has the great potential to be implemented in a production line to help optimise the rolling schedule for both C-Mn and microalloyed steels.

Jean Philippe Schille

Papers

Modelling phase transformations and material properties critical to the prediction of distortion during the heat treatment of steels

An Integrated Model for Rolling Schedule Design of Microalloyed Steels