Improving the Thermal Fatigue Strength of Hot-Working Tools by Laser Treatment

A method for increasing the thermal fatigue strength of a tool used in hot forming of bearing rings by applying circular laser tracks to the working surfaces is considered. Laser treatment is carried out with a power of 2.0...2.5 kW by applying on the end face working surface of the tool in the direction from the center to the periphery of the circular tracks with a common center coinciding with the center of the circumference of the end face; the tool is rotated at a constant angular rate, the spot diameter ds for each track is selected according to the dependence ds,i+1/ds,i = 0.85...0.90, and the laser radiation spots of adjacent tracks have a common point of contact. The results of pilot testing are presented, which confirmed the high technical and economic efficiency of the use of laser quenching for ejectors and punches. A tool made by machining, for example, an ejector of an AMP-70 automatic press, is subjected to volume quenching and tempering. The ejector material was steel 3Kh3M3F, quenching temperature in oil – 1030...1050 °С, tempering temperature – 580...610 °С. After volume quenching, additional machining is carried out, usually grinding, in order to remove the decarbonized layer of material formed during heat treatment and to give the working surface the required roughness class. The final stage in the tool manufacturing is the quenching of its working surface by laser treatment. Pilot testing showed that the use of laser treatment made it possible to increase the durability of ejectors of various types by 2 ... 3 times, of deforming punches – by 2.2 times.

The durability of parts of internal combustion engines under thermal stress loading

The paper analyzes the structural material-cast iron for diesel engines, from which the cylinder head covers are made. The main defect of these complex metal-intensive parts are heat-resistant cracks. The analysis of chemical composition of cast irons of various manufacturers is made. As a result of the conducted researches chemical compositions of the pig-irons having the greatest heat-fatigue durability are defined. It is established that to increase their strength and durability in operation, it is necessary to change the percentage of basic chemical elements (C, Si, Mn) in cast iron to use rare earth metals (Y, Ce, La). Specific recommendations are given on the choice of the chemical composition of cast iron for cylinder heads and covers, providing an increase in their fatigue strength and durability during operation. The best combination of mechanical and thermal fatigue strength was shown by samples containing carbon C-4.0%, silicon Si-2.0%, manganese Mn-0.18%, yttrium Y-0.1%, and copper Cu-0.8% with sulfur s – 0.008% and phosphorus P – 0.1%.