One critical steel parameter is hardenability. The most efficient reliable hardenability test is the Jominy Test, wherein a standard size and shape ingot of steel is heated until transformed to 100% austenite and then rapidly cooled, starting from one end. This treatment creates a hardness profile along the bar representative of the hardenability of the steel which is inversely proportional to its weldability. The hardness profile along the length of the bar is then determined by hardness testing to either the Vickers or, more usually, the Rockwell scale..
One of the results of the wide range of steels being produced under a strict quality regimen is the requirement to perform Rockwell hardness tests on a significant number of treated Jominy samples which require up to 15 test points each. The Rockwell hardness test is a simple and reliable test and Acciaierie Venete had been successfully using an automatic Rockwell tester for a number of years but the increasing quantity of samples seemed to require the implementation of an additional efficient measurement system.
It was then that Indentec was asked to prepare a quotation for a fixture of their Rockwell range of hardness testers, to take advantage of the market leading nose mounted indenter.
The system which was developed is based upon Indentec’s 4150SK Rockwell hardness tester which carries out tests in compliance with ISO 6508 and ASTM E18. To the standard testing machine a motorised lead screw was added, together with a dual axis stepper motor assembly and a single specimen support table. The firmware of the hardness tester was then re-designed to automatically carry out both user defined and ISO 642, ASTM A255 Jominy Standard test cycles. The machine therefore could operate, if required, as a stand-alone unit without the requirement for external PC control. The operator simply loads the Jominy samples and walks away, returning once the test cycle is complete to turn the specimens for testing on the underside.
However, in order to assist the management with the large quantities of data delivered by the testing system, a complimentary Windows-based software was also developed. The package was designed specifically for Jominy testing data. The user creates a master file with which to define test parameters, positions and tolerances. The operator then stores details specific to the specimens being tested. The package then starts the test process and records the test data which is shown live on screen, and a hardness graph is plotted in real time. At the end of the test automatic averages are calculated and all data can be downloaded to Excel, when additional data analysis is required or data need to be shared with other users.
The use of two automatic systems has increased productivity within the metallographic laboratory, positioning of the Jominy specimens is quick and reliable in a designed-for-purpose support table, and technicians perform other tasks while the Indentec tester runs the test cycle. The reliability of the system means that no human supervision is required and the operator returns only after the first half of a 10 minute cycle to turn the samples over. The increased accuracy of test point positioning and spacing provided by the use of a machine controlled dual axis stepper motor assembly has increased repeatability and decreased uncertainty in measurements.
Data storage, retrieval and management have been improved greatly by a file based Microsoft compatible software package.