International Journal of Metallurgical Engineering 2013, 2(1): 27-34 DOI: 10.5923/j.ijmee.20130201.04 Development of a New Direct Quenched Abrasion Resistant Steel Es ko Kinnune n 1 , Ilkka Miettunen 1 , Mahesh C. Somani 1 , David A. Porter 1,* , L. Pentti Karjalainen 1 , Ilari Alamattila 2 , Anu Ke mppaine n 2 , Tommi Liimatainen 2 , Vilma Ratia 3 1 University of Oulu, Department of Mechanical Engineering, Centre for Advanced Steels Research, POB 4200, 90014 Oulu, Finland 2 Rautaruukki Oyj, Ruukki M etals, POB 93, FI-90101 Raahe, Finland 3 Department of Materials Science, Tampere University of Technology, POB 589, FI-33101 Tampere, Finland Abstract A new way of producing abrasion resistant steel with a hardness substantially greater than 500 HV via direct quenching has been investigated. To avoid the ductility problems associated with fully martensitic microstructures, we investigated the possibility of achieving the desired hardness by incorporating a small amount of soft ferrite in a martensite matrix. The approach used was to study the potential suitability of several candidate compositions with varying levels of aluminium and manganese using physical simulation and laboratory rolling combined with metallography and abrasive wear testing. Physical simulation included the determination of CCT diagrams for strained and unstrained austenite on a Gleeble thermo-mechanical simulator. The CCT diagrams quantified 1) the increase in ferrite formation temperatures as a function of aluminium content, 2) the level of alloying required to obtain fully martensitic microstructures at appropriate cooling rates, and 3) the influence of prior austenite straining on the ferrite and bainite transformation kinetics. On the basis of the simulation results, laboratory rolling trials were made. They showed that a hardness even above 600 HV could be obtained with the desired martensitic-ferritic microstructure by designing a suitable composition and selecting appropriate finish rolling and quench start temperatures. Abrasive wear testing was used to compare the wear resistance of the laboratory rolled material with that of commercial direct quenched abrasion resistant grades. Keywords Steel, Abrasive Wear, Multiphase Microstructure, Physical Simulation 1. Introduction Abrasive wear is a severe problem in the mining, earth moving and transportation industry, and huge savings could be made if suitably priced and easily fabricated materials with improved resistance to abrasive wear were available[1]. Steel is the most commonly used abrasion resistant material, and since the life of abrasion resistant steel is largely dependent on hardness, there is a desire to find ways of making and using steels with as high hardness as possible. Commercially available abrasion resistant steel grades are often fully martensitic with a hardness of 400, 450 or 500 HB (420 to 527 HV). During recent years, there has been an increasing interest in the use of abrasion resistant steel produced via direct quenching where austenite is quenched to martensite immediately following hot rolling without the need for intermediate cooling and reaustenitization. With hardnesses in the range 400 – 500 HB, relatively good combinations of abrasion resistance, toughness, * Corresponding author: david.porter@oulu.fi (David A. Porter) Published online at http://journal.sapub.org/ijmee Copyright © 2013 Scientific & Academic Publishing. All Rights Reserved cutability, bendability, weldability and resistance to hydrogen induced cracking can be obtained. However, as the hardness increases, these technological properties deteriorate and the production and use of the steel become ever more demanding. Consequently, it is difficult to profitably produce and utilize martensitic steels with a hardness higher than 500 HB (527 HV, 51 HRC). It has been postulated that the low ductility and toughness associated with overall hardness levels above 500 HB might be improved by changing the microstructure from 100% martensite to a mixture of ferrite and martensite thereby enabling more novel abrasion resistant solutions to be achieved[2,3]. The objective of the work described in this paper was to explore the practicality of such an approach when using direct quenching. This has been done by studying the potential suitability of candidate compositions with varying levels of aluminium and manganese using physical simulation, laboratory hot rolling and direct quenching together with metallography and abrasive wear testing. Physical simulation included the determination of CCT diagrams for strained and unstrained austenite on a Gleeb le thermo-mechanical simulator fo r designing composition and laboratory hot rolling schedules.