Speaker
Description
Hardening through water quenching is an important step in heat-treatment of steel for a wide range of products that require superior mechanical properties in as-quenched condition, therefore the demand for optimization of steel hardening process and for quality improvement of hardened parts is constantly growing. One way to meet this demand is to perform quenching through optimized cooling rates at corresponding parts of the product providing necessary microstructure and mechanical properties.
Critical cooling rate, martensite start temperature as well as hardenability of steel are significant properties for obtaining an optimal quenching effect. Through adjusting the cooling rates above and below the critical value, at specific regions of the specimen, a gradient in microstructure and mechanical properties within one workpiece may be produced. This can be done with a newly developed Impinging Jet Cooling Technology (IJCT), the working principle of which is related to an impingement of water flow on a hot austenitized metal surface. Local cooling rates produced by IJCT may be tuned, for instance by adjusting the position of nozzles and their diameters, jet-to-surface distances.
This work reports the effect of IJCT on thick boron containing steel sheets. The samples were water quenched using IJCT by different simultaneous cooling rates with the aim of producing microstructure and hardness gradient along the workpiece, specifically a hard fully martensitic region turning into a mixed bainite-martensite softer region within a single sample. The reliability of these experiments was assessed by recording the temperatures throughout the samples during cooling and related to CCT diagrams. Microstructure and property gradient were observed, studied and discussed using scanning electron microscope, light optical microscope and hardness measurements.
| Speaker Country | Sweden |
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