NM450 weldability
Weldability is a critical factor when selecting materials for a range of applications, particularly when selecting structural steel. This is especially true for high strength structural steels such as the NM 450 (X450) steel. It is very important to understand the weldability of NM 450 or X450 before choosing it for an application that requires welding.
NM 450, or X450, is a high wear and abrasion resistant steel with superior yield strength that can be specified for any application where wear and tear needs to be minimized. It is an austenitic low-alloy steel which is stronger than standard carbon steels, thus resulting in fewer maintenance needs. NM 450 has higher mechanical properties than its counterparts like Abrasion Resistant 400 (AR400) and Abrasion Resistant 500 (AR500).
When welding NM 450 (X450) steel, heat input and preheating are important considerations. When welding in an atmosphere, it is recommended to preheat to 475°F (± 25°F) to minimize microstructural changes and to reduce risk of cracking due to thermal shock. When welding X450, a low-heat input method should be utilized. Cold or short circuiting welding should be used when possible. A low-heat welding method minimizes the microstructural changes that can occur during welding and leads to less cracking. Higher heat input in welding of NM 450 steel can result in greater heat-affected zone cracking and toughness loss at the weld.
NM 450 steel can also be subjected to post-weld heat treatments. In order to maximize weld strength of NM 450, post-weld heat treatment is highly recommended. When welding NM 450, post-weld heat treatment should be carried out at the temperature of 950°F (± 25°F), for two hours, followed by rapid cooling with water. The heat treatment enables the NM 450 (X450) steel to regain its strength.
Welders need to be aware that NM 450 steel is an austenitic low-alloy steel which means it is not suitable for gas welding. The recommended welding techniques for this steel are gas and plasma arc. Shielding gases like argon and mixtures of argon and CO2 should be used in the welding process. Filler metals like solid wire or coated electrode is used during the welding process.
Overall, NM 450 (X450) steel is an excellent choice for applications where long service life and good weldability are paramount. Its superior abrasion and wear resistance makes it suitable for highly arduous applications, while its weldability enables it to be joined or welded together, making it a very appealing material in many applications. With the proper preheating, welding, and post-weld heat treatment, the welds and structure of the NM 450 (X450) steel will perform as expected for the intended application.
