Grindability of recycled steel: automotive crankshafts (CRANK-STEEL)

Purpose and goal

The growth of the market for recycled steel has allowed the increased use of this material for crankshafts, which brought many advantages to the automotive OEMs in terms of supply-chain diversification, price competitiveness, more localized use of resources and improved sustainability. CRANK-STEEL gained deeper understanding of (detrimental) material-effects on grindability and ultimately helped developing guidelines for steel grade and process improvements for better grindability and more extensive use of recycled steel.

Expected results and effects

The results revealed that the size and amounts of hard particles (e.g. oxide inclusions) in the steel have an effect on wear of grinding wheels. In addition, carbonitrides in the steel can affect the grain growth behavior during the material conversion processes. The data analysis showed that ground material associated with less favorable Barkhausen noise results is not confined to recycled steel, but also occur for ore-based steel batches. Instead, grindability appears to be batch dependent, regardless of steel type (ore/recycled).

Planned approach and implementation

Steel-manufacturing, forging, and heat treatment are controllable processes if fully understood which can translate to adjusting material properties affecting the grindability. A twofold strategy was pursued in the project consisting of (1) grinding tests combined with dedicated material characterization and modelling and (2) data analysis utilizing production data obtained along the value chain of crankshaft production. The project was carried out by Chalmers, RISE, Ovako, Volvo Lastvagnar, Scania, Volvo Cars och Bharat Forge Kilsta.