{"id":47512,"date":"2025-05-13T10:00:47","date_gmt":"2025-05-13T08:00:47","guid":{"rendered":"https:\/\/www.bonomiacciai.it\/la-prova-jominy-come-gli-elementi-di-lega-aumentano-la-temprabilita-degli-acciai\/"},"modified":"2025-05-23T08:49:37","modified_gmt":"2025-05-23T06:49:37","slug":"the-jominy-test-how-alloying-elements-increase-steel-hardenability","status":"publish","type":"post","link":"https:\/\/www.bonomiacciai.it\/en\/the-jominy-test-how-alloying-elements-increase-steel-hardenability\/","title":{"rendered":"The Jominy Test: How Alloying Elements Increase Steel Hardenability"},"content":{"rendered":"
[vc_row][vc_column][vc_column_text css=””]After individually analyzing the alloying elements (Carbon, Chromium, Molybdenum, Nickel, Vanadium, etc.), it’s time to see their concrete effect on the hardenability of special steels<\/strong>, meaning their ability to generate a martensitic structure in depth during quenching. To evaluate this aptitude, one of the most widely used and universally recognized tests is the Jominy test<\/strong>.[\/vc_column_text][\/vc_column][\/vc_row][vc_row][vc_column]
<\/div>[\/vc_column][\/vc_row][vc_row][vc_column][vc_custom_heading text=”What is the Jominy Test?” use_theme_fonts=”yes” css=””][vc_empty_space][vc_column_text css=””]\n

The Jominy test<\/strong> is the standardized method (UNI EN ISO 642<\/strong>) that evaluates how steel behaves in response to heat treatment by checking the penetration of hardness in depth. The test involves a cylindrical specimen of \u00d8 25 \u00d7 100 mm<\/strong>, which is austenitized and then cooled at one end with a water jet (at specified pressure and temperature).<\/p>\n

The cylindrical surface of the specimen is then ground to allow for the measurement of hardness progression using the HRC scale<\/strong>, every 1.5 mm.<\/p>\n

The graph of “hardness (HRC) vs. distance from the quenched end (mm)”<\/strong> describes the hardenability<\/strong> of the steel under examination.[\/vc_column_text][vc_empty_space height=”16px”][vc_row_inner][vc_column_inner width=”1\/6″][\/vc_column_inner][vc_column_inner width=”2\/3″][vc_single_image image=”45509″ img_size=”” add_caption=”yes” alignment=”center” onclick=”img_link_large” css=””][\/vc_column_inner][vc_column_inner width=”1\/6″][\/vc_column_inner][\/vc_row_inner][vc_empty_space height=”16px”][\/vc_column][\/vc_row][vc_row][vc_column][vc_custom_heading text=”Why Alloying Elements Matter” use_theme_fonts=”yes” css=””][vc_empty_space height=”16px”][vc_column_text css=”” line_height=”relaxed”]Elements like Chromium (Cr), Molybdenum (Mo), and Nickel (Ni)<\/strong> slow down the transformation to pearlite\/bainite, allowing for the formation of martensite<\/strong> at greater depths. In general, all elements, with the exception of cobalt, each with their own characteristics, increase hardenability<\/strong>.[\/vc_column_text][vc_empty_space height=”16px”][\/vc_column][\/vc_row][vc_row][vc_column][vc_custom_heading text=”Graphical analysis: from C35 to 34CrNiMo6″ use_theme_fonts=”yes” css=””][vc_empty_space][vc_row_inner][vc_column_inner width=”1\/2″]

\"Jominy<\/div><\/figure>[\/vc_column_inner][vc_column_inner width=”1\/2″]
\"Comparison<\/div><\/figure>[\/vc_column_inner][\/vc_row_inner][vc_empty_space height=”8px”][vc_row_inner][vc_column_inner width=”1\/2″]
\"Jominy<\/div><\/figure>[\/vc_column_inner][vc_column_inner width=”1\/2″]
\"Jominy<\/div><\/figure>[\/vc_column_inner][\/vc_row_inner][vc_empty_space height=”8px”][\/vc_column][\/vc_row][vc_row][vc_column]
<\/div>[\/vc_column][\/vc_row][vc_row][vc_column][vc_custom_heading text=”Application case of the Jominy Test” use_theme_fonts=”yes” css=””][vc_empty_space height=”16px”][vc_column_text css=””]\n

As clearly shown by the graphs above, as the amount of alloying elements<\/strong> increases, the hardenability<\/strong> of special steels also increases, meaning the depth of hardening penetration<\/strong>.<\/p>\n

An application example is represented by pre-hardened steels<\/strong> used in molds for plastics processing. Beyond a certain thickness (approximately 300 mm), steel 1.2311 (40CrMnMo7)<\/strong> gives way to 1.2738 (40CrMnNiMo8-6-4)<\/strong>, which, thanks to its 1% Ni content, guarantees hardening penetration even in the center of the bar.<\/p>\n

[\/vc_column_text][vc_empty_space height=”16px”][\/vc_column][\/vc_row][vc_row][vc_column][vc_custom_heading text=”The Jominy Test: conclusion” use_theme_fonts=”yes” css=””][vc_empty_space height=”16px”][vc_column_text css=””]\n

The Jominy test<\/strong> concretely demonstrates how alloying elements can improve the hardenability of special steels<\/strong>, making it possible to design large-section components without sacrificing core hardness.<\/p>\n

Bonomi Acciai, a partner of Swiss Steel Group, supports designers in choosing the steel with the appropriate hardenability for each specific application. Contact us for a dedicated consultation.[\/vc_column_text][vc_empty_space height=”16px”][\/vc_column][\/vc_row][vc_row full_width=”stretch_row_content” css=”.vc_custom_1717678542423{background-color: #ebebeb !important;}” visibility=”hidden-phone”][vc_column]

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