New Technology for Bearing Steel Bars Production

摘要

The increased demand of rolling element bearings by modern society has in turn required an increase in the production of bearing steels. Quality is the primary target of all bearing steel producers and the most of the focus is on the steelmaking plant in order to fully control the whole production cycle from the raw materials (minerals or scrap) through to the finished products. Remarkable cost savings can be realised by minimising any losses due to product quality. A further step to reduce the total production cost is the possibility to produce and supply to the end user a material that doesn't requires any heat treatment before entering the bearing component production route. Normally, the heat treatment required is a soft/sphero annealing that allows the material to be cold-sawn into lengths without high tool wear whilst using standard machine tools and cutting media. Since 1980, there have been numerous different studies on the production of thermo-mechanically rolled low alloyed steel for direct drawing or cold forging applications. Other studies on high carbon steel and bearing steel have taken into consideration the possibility to roll at temperatures close to the critical temperature range in which austenite already starts to transform in pearlite. Unfortunately, thermo-mechanical rolling results in high deformation loads, and as such requires equipment designed to accommodate the high rolling loads and torques. As a result, many mills are unable to produce this type of material without significant additional investment, and this is a significant barrier to entry into this market. This paper reviews and discusses the study for a thermo-mechanical process for bar using in line heat treatment to obtain the required annealed structure that is necessary to allow further operation as sawing or cold cutting without any intermediate treatment. All the experimental work was performed in the ABS facility and in the Danieli laboratory, and an industrial application for such a process is in operation in the same plant where in line annealing and Q&T is part of the normal production schedule.