Production Machining

MAY 2018

Production Machining - Your access to the precision machining industrial buyer.

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Page 22 of 63 :: 21 Helping Precision Machine Shops Be More ProducƟ ve and Profi table Technical Regulatory Management Quality Technical Regulatory Management Quality Craftsman's Cribsheet Miles Free – Director of Industry Research and Technology NUMBER 65 5 Ways Coarse Austenitic Grain Size Affects Your Machine Shop Austenitic grain size is a material characteristic that is usually reported on test reports and certifi cation documents for the steel materials we machine in our shops. Coarse austenitic grain size is a result of not adding grain refi ning elements to a heat of steel. Because these grain re- fi ning elements have not been add- ed, the steel has a coarse austenitic grain size. Typically, this practice is applied to free machining grades such as 11XX and 12XX steels. These steels are sold primarily for their ability to be machined at high production rates. What does Coarse Austenitic Grain Size imply for the parts that you make? 1. Better machinability. Coarse Grained Steels are more machinable and pro- vide longer tool life than fi ne grained steels. The elements added to make the austenitic grain size fi ne create small, fi nely dispersed hard abrasive particles in the steel 2. Better plastic forming than fi ne grained steels 3. More distortion in heat treat than fi ne grained steels 4. Lower ductility at the same hardness than fi ne grained steels 5. Deeper hardenability than fi ne grained steels Coarse austenitic grain size will show up on the test report as an ASTM value of 1 to 5. Values of 5 and higher are called fi ne grained steels and are the re- sult of additions of aluminum, vanadium or niobium. The methods for determining austenitic grain size are detailed in ASTM Standard E112, "Standard Test Methods for Determining Average Grain Size." While we think that chemistry may be the controlling factor for machining performance of the steel in our machines, the contribution of austenitic grain size is also important. As long as you are ordering your free machining steels (11XX and 12XX series) to coarse grain practice, austenitic grain size should not be an issue in your shop. All Craftsman's Cribsheets are available for viewing and download at

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