UDDEHOLM DIEVER
Important material properties for heat-checking resistance are hot-yield strength, temper resistance, creep strength, ductility and toughness. Uddeholm Dievar outperforms premium H13 grades in all these properties. Ductility and toughness are especially of interest because the biggest difference lies in these areas. High toughness is needed to protect the die from a catastrophic failure and now Uddeholm Dievar has the answer here rated at 25 Joules Min/Avg giving the die user peace of mind in production. High ductility is also important because it delays the initiation of cracks and recent testing of Uddeholm Dievar at 44-46HRC in unnotched testing showed over 400 Joules impact value. High ductility and toughness also facilitate the possible use of a higher hardness level in the die as it is a known fact that higher hardness contributes to improved heat-checking resistance (Figure 5). Customers recently asked Uddeholm to test the new Dievar above
44/46HRC to see just how tough Uddeholm Dievar is compared to high- quality ESR H13. These customers recognized that if you can go up in hardness you will extend heat checking resistance, but the concern is a drop in toughness. Testing showed that Dievar even at 51HRC (Figure 6) had superior toughness to an ESR H13 grade in comparable sizes. If you are intending to raise your hardness in a die we strongly recommend that you ask your local Uddeholm technician to view you die and processes first so the optimal performance level can be reached.
which results in increased cleanliness, homogeneity and equal properties in all directions of the block. The ESR process is when you take the conventional cast ingot and remelt this through a slag bath, which then forms a new purified ingot with these superior properties. ESR furnaces at Uddeholms AB are equipped with protective gas
atmosphere and pressurized gas atmosphere that improves the cleanliness of the process and increases the steel properties again. After remelting the new ingot is heavily forged, this efficiently breaks down the solidified structure into a finer-grained and more ductile structure. Specialized heat- treatment processes give further improvements to quality. The cleanliness of the steel highly influences the ductility. Non-metallic
inclusions, primary carbides and a network of coarse secondary carbides have a significantly negative impact on the ductility of the material. Poor toughness, on the other hand, is more decided by a microstructure containing coarse grain size, grain-boundary precipitations and the presence of bainite and pearlite. When Uddeholm Dievar was developed the aim was mainly improvement of the ductility, toughness, hardenability and heat-checking resistance of dies. Today we see an increasing demand for Uddeholm Dievar and in sizes, which no one could have imagined when Dievar was originally developed with some dies as big as 18 tons in weight as the below picture (Figure 8) shows. On blocks this big, we have produced quality as high as 28 Joules and fine grain sizes of ASTM 7 and above.
Figure 6 clearly shows Uddeholm Dievar is tougher at higher hardness to premium H13
The hot-yield strength, temper resistance (Figure 7), creep strength, thermal conductivity and the thermal expansion are properties, which depend upon the chemical composition of the material. Uddeholm Dievar shows superior results in all these areas, mainly linked to the higher amount of molybdenum in combination with the vanadium content.
Figure 8 shows just how big some special sizes of Uddeholm Dievar can be manufactured
However, using the best material available is not a guarantee against early heat-checking problems. The focus must also be taken to look at other critical parameters such as design, die making, heat- treatment, surface treatment and casting parameters etc. However, if you have heat-checking problems with your tooling when using H11 or H13 then using Uddeholm Dievar is a great start to a successful die life improvement, as the customer case study (Figure 9) shows.
Figure 7 shows just one of the multiple advantages of Dievar chemistry over H13 to fight heat checking, superior temper back resistance
Uddeholm Dievar’s ductility and toughness reflect the quality of the steel and how the steel is produced. This, in turn, means that the whole production path is of great importance for the quality, from the melting shop to the electro slag refining, and further on to the forging/rolling and heat- treatment. Especially important is the ESR (Electro slag refining) process,
20 IMT October 2019 Figure 9 shows a customer case of Dievar and ESR H13 in production with
heat checking as the concern The article was written and contributions by: Richard Oliver – Uddeholms AB Product Manager Hot Work; Krister Axelsson – Uddeholms AB Application Engineer Hot Work; Sebastian Sivertsen – Uddeholms AB Hot Work Customer Service Technician
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