JOMINY HARDENABILITY TEST. Objective. To study hardness as a function of quench rate and investigate the hardenability of steels. Introduction. PDF | The Jominy end-quench test is used to measure the hardenability of a steel , which is a measure of the capacity of the steel to harden in depth under a. The Jominy end-quench test is used to measure the hardenability of a steel, which is a measure of the capacity of the steel to harden in depth.
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The Jominy End Quench Test
Increasing the austenite grain size increases the hardenability of steels. The Rockwell hardness test measures a number which depends on the difference in the depth of an indentation made by two loads, a minor load followed by a major load. Measurement of hardenability Uses of Jominy data: A high hardenability hardeability required for through hardening of large components. Jominy end quench test can also be used to demonstrate the effects of microstructure and alloying variables on the hardenability of steels.
There are conversion charts between the hardness scales. Again, you have three steels.
The Jominy End Quench Test
The results are plotted in the graph below. Clicking on the circled data points will take you to images of the microstructure at that location in the sample. Slow quenching speeds are often hareenability to teat distortion and residual stress in components. Here a specimen is in place. Manufacturing Engineering and Technology. The geometry of the part also affects the cooling rate: Hardenability therefore describes the capacity of the steel to harden in depth under a given set of conditions.
The Jominy test provides a measure of the ability of a steel to harden by transforming into martensite under set conditions, i. Example Jominy end quench test data A plain carbon steel and an alloy steel were assessed using the Jominy end quench test.
It should not be confused with hardnesswhich is a measure of a sample’s resistance to indentation or scratching. Retrieved from ” https: This method of increasing the hardenability is rarely used since substantial increases in hardenability require large austenite grain size, obtained through high austenitisation temperatures.
It is typically used with lower carbon steels. Take a sample from the furnace and place it on the Jominy test fixtures and observe the cooling pattern. The cooling rate will be highest at the end being quenched, and will decrease as distance from the end increases.
Carbon controls the hardness of the martensite. As the water jet sprays onto the end of the hot, glowing specimen, a cold dark region spreads up the specimen.
For example, the cooling rate at a distance of 9. These include alloying elements and grain size.
Hardenability – Wikipedia
The Rockwell test is commonly used in the USA. This alternative longer video clip contributed by Oxford Brookes University shows both the transfer of the sample from furnace to Jominy machine, and the jet spraying one end of the sample.
Two specimens of a low alloy steel with 0. The proportions of the phases at any position depends on the cooling rate, with more martensite formed where the cooling rate is fastest.
Substances like brine and water cool the steel much more quickly than oil or air. The solubility of the elements varies between the different phases, and the interface between the growing phase cannot move without diffusion of the slowly moving elements.
Jominy end quench unit for testing the hardenability of steels. At higher carbon levels, the formation of martensite is depressed to lower temperatures and the transformation from austenite to martensite may be incomplete, leading to retained austenite.
James Marrow and Dave Hudson. The Jominy end quench test is the standard method for measuring the hardenability of steels.
The steel sample is normalised to eliminate differences in microstructure due to previous forging, and then austenitised. The variation of hardness was measured with distance from the quenched end. The water jet ojminy started and sprayed onto the bottom of the specimen until the specimen is cool. The indentor is either a conical diamond pyramid, or a hardened steel ball.
The graph below gives the Jominy end quench data in terms of the Rockwell hardness number. The inner depths of the material however, do not cool so rapidly, and in work-pieces that are large, the hardenabiltiy rate may be slow enough to allow the austenite to transform fully into a structure other than martensite or bainite.
In this heat flow simulation you can adjust various parameters and observe the effect on the heat flow and cooling of the specimen. Three medium carbon steels 0. A heat treatment that causes steel to harden is so much more than the meer plunging of hot metal into a fluid that is often a liquid. A jet of water emerges from the cone at the bottom, to touch the lower end of the sample. When a hot steel work-piece is quenchedthe area in contact with the water immediately cools and its temperature equilibrates with the quenching medium.
This data can be presented using CCT C ontinuous C ooling T ransformation diagrams which are used to select steels to suit the component size and quenching media. This composite microstructure of martensite and austenite gives a lower hardness to the steel, although the microhardness of the martensite phase itself is still high.
There are quite complex interactions between the different elements, which also affect the temperatures of the phase transformation and the resultant microstructure. The furnace used to heat the steel into the austenite phase field.
Similar tests have been developed in other countries, such as the SAC test, which uses a sample quenched from all sides by immersion in water. Retrieved 9 December The alloy steel clearly has the highest hardenability, forming martensite to a greater depth than the plain carbon steel.
This cools the specimen from one end, simulating the effect of quenching a larger steel component in water. Modern materials and manufacturing processes.