Materials characterization and mechanical properties of graded tool steels processed by a new co‐spray forming technique

Abstract

In order to meet the requirements of micro cold forming tools, a new co-spray forming process has been applied to produce graded materials from two different tool steels in this study. The two steel melts were atomized and co-sprayed simultaneously onto a flat substrate, resulting in a flat graded deposit when the two sprays were overlapped. To eliminate porosity and break up carbide network, the graded deposits were further hot rolled. The resultant graded tool steels were investigated with respect to porosity, element distribution, microstructure, hardness, strength, and toughness. The degree of overlapping of the two sprays determined the concentration gradient of the chemical elements in the deposits. The overlapping of the spray cones also contributed to low porosity in the gradient zone of the deposits. The porosity in the graded deposits could be essentially eliminated by means of hot rolling. The carbides and grain structures of the hot rolled tool steels were fine and homogeneous. By means of combining different tool steels in a single deposit, different microstructures and properties were combined.

Solidification Sequence of Spray-Formed Steels

“…[2] Several types of alloys such as steels, cast irons, Ni-alloys, Al-alloys, and Cu-alloys, as well as different geometries (billets, tubes, and rings) have been successfully produced by spray-forming. [3][4][5][6][7][8][9][10][11][12][13][14] In all cases, the spray-formed microstructures present noticeable features: (1) equiaxed grains with diameters from 10 to 50 lm; (2) a high level of microstructural homogeneity and macrosegregation free; (3) uniform and homogeneous distribution of eutectic and second phases. The advantageous microstructure produced by the spray-forming process is well-known from research; however, solidification at the deposition zone and the creation of such a characteristic microstructure are still an open discussion.…”

Materials for Micro Forming

“…It was also found that the carbide networks in the spray-formed deposits remained unchanged after HIPping, which would impair the fracture toughness of the materials. (2) Samples from the 30 mm thick flat deposits were hot rolled on a lab rolling mill to eliminate porosity and break up the carbide network [Cui14]. The samples (thickness 24-28 mm after milling) were preheated in a furnace to 1100°C, held at that temperature for 10-30 min, and rolled in three passes to a final thickness of approximately 10 mm.…”

Thermal Expansion Behavior of Co-Spray Formed Al-20Si/7075 Bimetallic Gradient Alloy

“…Carroll et al [ 3 ] completed the preparation and evaluation of SS304/IN625 functionally graded materials manufactured by DED additive manufacturing, which are useful in applications that require both strength and corrosion resistance at elevated temperatures. Cui et al [ 9 ] studied graded tool steel for the micro cold forming tools manufactured by co-spray forming, and this new graded tool steel adapted the required strength of a material while retaining the desired abrasive wear resistance.…”