Increasing phase transformation rate in advanced high strength steel applications

Published: 10 March 2020

This work has focused on study of the Quenching and Partitioning (Q&P) process by assessing involved mechanisms, microstructure and mechanical properties, aiming at an acceleration of phase transformation rate to shorten the process time in addition to improving properties in service to the industry.

Figure1. Schematic of the Q&P treatment applied directly after laser welding on Domex 960 from SSAB, and resulting effect on martensite packet size (Via EBSD), precipitation (using SEM and EDX) and carbon diffusion (modeling by Thermocalc)

In the first part, this technique has been tested directly after laser welding. Results showed that Q&P not only can reduce the risk of brittle martensite formation after welding but also shortens the post welding treatment time compared to regular methods.

In the second part, application of Q&P for bearing steels to evaluate the feasibility, limitations and advantages of this method has been investigated. The promising results have shown that this method can be applied successfully and save a lot of time, cost and energy.

Figure 2. Application of Q&P for a (0.6C% -1.5% Si) steel, (a) example of microstructure taken by EBSD showing the amount, morphology and location of retained austenite in the martensitic matrix, (b) color contour map of diffusivity of carbon during partitioning and (c) Promising mechanical properties (2.5 Gpa Ts and 5% El) of a sample quenched to room temperature and partitioned at 400 ° C for 30 sec.

References: Forouzan, Farnoosh. Increasing phase transformation rate in advanced high strength steel applications. Diss. Luleå University of Technology, 2019.

Participating parties

LTU, UDS (Germany)

Funding

Erasmus mundus Doctrol Program Docmase

Timeframe

Jan 2015 to May 2019