Boro-Austempering Treatment of Ductile Cast Irons

Abstract

Samples of ductile cast irons alloyed with Cu, Cu-Ni and Cu-Ni-Mo were austempered, borided and boro-austempered and characterized for hardness and micro-adhesive wear behavior. The kinetics of layer formation was also studied. The boriding method used was molten borax bath, in periods of 2 and 4 hours at temperatures of 850, 900 and 950 ºC. The direct austempering treatment was performed immediately following the boriding treatment (from 850, 900 and 950 ºC) using molten salt baths at temperatures of 240, 300 and 360 ºC for 4 hours (boro-austempering treatment). For comparative purposes, the conventional austempering treatment was also conducted. Optical microscopy, scanning electron microscopy, Brinell hardness measurements (on the substrate) and Vickers (on the layers) were performed, along with micro-adhesive wear tests. The boriding treatment resulted in the formation of high hardness layers, in the range of 1450 to 1750 HV, with high wear resistance. The wear resistance of borided and boro-austempered samples were increased by 40 times when compared to as cast or austempered samples, indicating the high efficiency of this type of treatment in increasing the wear resistance of this material.

Boro-Austempering Treatment of High Strength Bainitic Steels

“…Figures 4-A and 4-B show the layers obtained for reference steels after boro-austempering treatments. In both cases the obtained layers had thicknesses in the range of 85~90 microns, values similar to those obtained in ductile cast irons submitted to the same treatment[14]. The layers are composed of two regions, indicating a polyphase coating formation.…”

“…Hu et al stated that the presence of molybdenum may decrease the amount of granular bainite transformed from the supercooled austenite, contributing to the formation of bainite laths [20]. In both cases the obtained layers had thicknesses in the range of 85~90 microns, values similar to those obtained in ductile cast irons submitted to the same treatment [14]. The layers are composed of two regions, indicating a polyphase coating formation.…”

“…There is the possibility of direct cooling from this temperature to the austempering temperature, for carbidefree bainite formation. The combination of these two treatments is called boro-austempering and has already been applied successfully in ductile cast iron [14] and gray cast iron [15], allowing layer formation without the need to reheat the workpiece to proceed with austempering, resulting in a marked decline in manufacturing cost.…”

Microstructure and Properties of a Medium‐Carbon High‐Strength Bainitic Steel Treated by Boro‐Austempering Treatment

“…[24] The combination of austempering and boriding treatment is defined to be boro-austempering and has been applied successfully in cast irons. [25,26] From the viewpoint of reducing production cost, the integrated treatment of austempering and boriding is a potential alternative method to produce bainitic steels with higher hardness and better corrosion resistance. However, few studies on boro-austempering treatment of high-strength bainitic steels have been reported.…”

The Corrosion and Wear Behaviors of a Medium-Carbon Bainitic Steel Treated by Boro-Austempering Process

“…Since the boro-austempering treatment is successfully applied in cast irons [20,21], it has attracted much attention. However, very limited studies have been performed to fabricate high-strength bainitic steels by boro-austempering [18,19].…”