A new integration of hot pressing and carbon partition process to produce high strength steel components with better toughness

Shi-Hong Zhang,Wei-Jie Liu,Fei-Bao Zhang,Hong-Wu Song,Y Qin,F Vollertsen,S J Yuan,J Lin,T A Dean

doi:10.1051/matecconf/20152107005

Shi-Hong Zhang, Wei-Jie Liu + Show 7 more

Open Access

https://doi.org/10.1051/matecconf/20152107005

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Abstract

A novel one step method for hot pressing and quench & partition (Q&P) integration – hot Pressing-dynamic partitioning (HP-DP) process is presented, which can be processed by regular hot pressing equipment and process. The HP-DP formed steel is an upgrade of the existing hot pressed steel especially suitable for making high strength components with superior crashworthiness due to better toughness. Corresponding steel sheet based on conventional 22MnB5 is designed and prepared. After that, the physical simulation experiments for HP-DP are carried out on thermal-mechanical simulator. Microstructure of the steel subjected to HP-DP treatment, with a typical Q&P treated feature, is mainly composed of initial quenched martensite phase, final quenched martensite phase and retained austenite phase, which indicate the occurrence of carbon diffusion concomitantly with martensite transformation. Compared with conventional hot pressed samples, the HP-DP samples show both better tensile property especially elongation and impact energy absorption ability. The effect of HP-DP parameters on the stability of retained austenite and mechanical property is also discussed. The paper illustrates the promising application potential of the HP-DP process.

Highlights

The rapidly increased vehicle population brings many problems such as atmospheric pollution, energy crisis and safety requirement in case of accidents in recent years
Based on the above analysis, Liu [14] proposed the concept of quenching & dynamic carbon partition concept (Q&DCP), and developed Q&DCP steels which compositions are shown in Table 1 as an example [8]
It can be obviously seen that the carbon contents of retained austenite (RA) are around 1.0% before tensile tests, much higher than the initial steel content level of 0.19, which further verified carbon partition and enrichment of RA accrued during hot Pressing-dynamic partitioning (HP-DP) process

Summary

Introduction

The rapidly increased vehicle population brings many problems such as atmospheric pollution, energy crisis and safety requirement in case of accidents in recent years This indicates that the automotive industry has to find a solution to improve both the fuel efficiency and the safety of vehicles at the same time. The elongation of hot-pressed steel, e.g. 22MnB5, is around 6% [4], which means a relatively low level of product of strength and elongation (PSE)-only around 9 GPa%. Such ultrahigh strength allows a reduction in sheet thickness, but does not have a direct contribution to an increase of crash safety or absorbed crash energy which is determined by the PSE level of the formed part [5]. The developed steel, process design concept and the corresponding microstructure and tensile property are briefly introduced and discussed for the new developed process to show its promising application potential to make high strength automobile components with superior crashworthiness

Design concept of HF-DP process

Experimental methods

Results and discussion

Summary