Q-P Process Optimization With the Use of Quenching Dilatometer

The current efforts in production of low-alloyed steels are aimed at achieving high ultimate and yield strengths,while maintaining sufficient elongation and good weldability in these materials.Among advanced heat treatment processes capable of reaching this goal,there is also the Q-P process (Quenching and Partitioning).The process consists in rapid quenching of the material between the M s and M f temperatures in order to prevent full martensitic transformation.The immediately following heating leads to tempering of the martensite and to diffusion of excess carbon from martensite to retained austenite.This increases the stability of the latter.The aim of the Q-P process is to produce very fine martensite microstructure with retained austenite between martensite plates.The experimental programme was carried out on a high-strength low-alloyed steel containing 0.2% carbon and a higher amount of silicon about 1.5%.Higher silicon content in the microstructure contributes to stabilization of retained austenite by suppressing formation of carbides.This grade of steel is an advantageous material thanks to its low amount of alloying elements.This group of low-alloyed steels,if heat treated or thermomechanically treated in a suitable manner,offers a favourable combination of strength,elongation and toughness.The paper is aimed at possibility of the Q-P process optimization with the use of quenching dilatometer.The experimental material is CMnSiMo steel.Conventional process optimization consists of standard samples treatment in laboratory furnaces and baths.This procedure can be time consuming with higher requirements on the experimental material.Therefore,it was proposed that the Q-P process optimization can be done with the use of quenching dilatometer and in this way the development of new procedures can be accelerated.Q-P processes were conducted in the standard way and with the aid of a dilatometer.Comparison of the obtained results provided by the standard procedure and by the procedure using the quenching dilatometer showed very similar results.On the basis of the obtained results,it can be concluded that the quenching dilatometer can be a powerful tool in Q-P processes optimization.

Mechanical Properties Optimization Metal Bars and Sheets Made of 34CrNiMo6 Steel

Currently available and well known materials treated by a special procedures can provide superior properties in the comparison to presently obtained ones.Special treatment procedures are efficiently developed with the use of physical simulators nowadays.Physical simulators allow treatment optimization on small scale laboratory samples which can be subsequently transferred to real production processes later on.Nevertheless,there is always need of successful transfer from small scale laboratory experiments to real production of for example metal sheets.In the current paper thermo-mechanical procedure developed for 34CrNiMo6 steel under laboratory conditions is applied to metal sheets production.There were obtained very promising properties on the bulk material samples processed in the physical simulator,the challenge was to obtain similar properties on a real metal sheets by a transfer of laboratory procedure to metal sheet production process.In the considered case the combination of tensile strength and elongation were especially required for considered application in a train body.In order to achieve excellent elongation for high strength hardened steel,very fine microstructure has to be attained through the thermo-mechanical process optimization.Very good results were achieved on produced metal sheets.6% elongation was attained allowing the possibility of further material processing,e.g.bending of sheets,with tensile strength exceeding 1500 MPa.The study presented here confirms usefulness of thermo-mechanical simulators for new procedures development.With the use of the simulator of thermaldeformation cycles a materials with optimized properties for certain application can be efficiently developed.