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.

Comparison of Microstructures and Properties Obtained After Different Heat Treatment Strategies of High Strength Low Alloyed Steel

The influence of different heat treatment strategies on the microstructure and properties of 42SiCr steel was investigated.To compare the benefit of innovative treatment methods with more conventional ones,several strategies based on a new quenching and partitioning (Q-P) process were designed together with several strategies using more traditional quenching and tempering process.Different combinations of mechanical properties were obtained with ultimate strengths in the range of 1818-2120 MPa and ductility between 10% and 24%.Resulting microstructures were martensitic with 0-12% of retained austenite and they were analyzed by laser scanning confocal microscopy,transmission electron microscopy and X-ray diffraction phase analysis.