Development and Analysis of Nitriding Technology for Die Steel

Many Die steel manufacturers in order to improve the mold surface hardness, corrosion resistance and other properties, will maintain the original strength and toughness of the die steel, the surface of the die steel nitriding treatment, which can also extend the service life of the mold, so nitriding technology is the most valuable application of die steel production technology. So the following we give you a detailed explanation of the development of nitriding technology and analysis of die steel.

Analysis of die steel nitriding technology

Die steel work, its cavity surface and hot metal contact for a long time, easy to palletize, bonding phenomenon. At the same time, the cavity repeatedly heated and cooled, equivalent to a kind of alternating heat stress, easy to crack, that is, thermal fatigue phenomenon. The use of general strengthening treatment (such as quenching + tempering) requires additional surface protection measures and easy to produce large deformation.

Nitriding treatment is undoubtedly a good strategy. Nitriding temperature is generally around 500 degrees, not more than the tempering and tempering temperature of the heart, not only can maintain the toughness of the heart, and nitriding after slow cooling or air cooling, can achieve low deformation under the surface hardening treatment.

Research shows that hot work die steel nitriding treatment can improve its thermal hardness, wear resistance and reduce the die. bonding phenomenon with parts, cracking phenomenon, improve thermal fatigue resistance, and extend the working life of the mold.

At present, the practical nitriding surface heat treatment, in addition to the early carried out gas nitriding, salt bath nitriding, gas nitrocarburizing, ion nitriding, etc. In recent years, a new nitriding process - vacuum nitriding treatment, is becoming a potential development trend of surface heat treatment technology.

The development of nitriding treatment technology for die steel

Nitriding treatment of die steel has been reported in many researches, but there are still some technical problems in actual production. Usually, in order to get a good match between the core and surface performance of the mold after nitriding, the die steel should be properly heat treated before nitriding, the general heat treatment process is quenching + twice tempering, but some people also proposed quenching + a tempering process, for some large molds even use quenching + three tempering treatment; and the nitriding process itself is equivalent to a tempering treatment, the nitriding layer The nitriding process itself is also equivalent to a tempering treatment, which will have an obvious effect on the nitriding layer; even the quenching treatment before nitriding can also make the surface layer of the mold obtain a high enough hardness.

There has been a lack of systematic and in-depth research on the influence of the heat treatment state of the mold before nitriding on the organization and properties of the nitrided layer and the mechanism, and these factors will directly affect the actual production cost and production efficiency.

Gas nitriding, also known as hard nitriding, was used to replace quenching on metal die casting dies in the early days.

The process route is generally as follows: blank forming, tempering, machining, stress relief, nitriding and grinding. Gas nitriding crack sensitivity is large, need to grind off this layer after use.

In addition, due to the poor stability of iron nitride (Fe2N, FeN, FeN), easy to agglomerate coarsening, lower hardness, often choose low-carbon and medium-carbon alloy steel containing strong nitride forming elements, the formation of nitride elements can improve the hardness of the nitride layer, but reduces the rate of diffusion of nitrogen atoms in the steel, nitriding rate of only 0.01 to 0.015mm / h. Typical steel grades for hot work tool steel 3Cr2W8V for example, the nitriding time of two stages of nitriding is more than 50 hours.

Because of the above problems, from the seventies onwards, with the continuous development of nitriding technology, the application of gas nitriding on the mold gradually reduced.

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