Characteristics of Welding Heat Affected Zone of Refractory Steel

Weld Heat Affected Zone of Steel That Is Not Easy to Harden

Introduction

In the welding process, the temperature of the heat affected zone (HAZ) will be higher than that of the other parts of the material, so it will lead to a change of the mechanical properties in the zone of influence. For some materials, such as high-strength steels, the microstructure of the welds in the HAZ can become especially hard and brittle. For welding processes that require high mechanical properties, it is important to choose the right welding parameters and materials in order to ensure that the HAZ does not become too hard. In this article, we will discuss the characteristics of welds in steel that is not easy to harden, and the methods employed to ensure the minimum hardening of the HAZ.

Characteristics of Welding on Steel That Is Not Easy to Harden

Steel that is not easy to harden can be generally divided into two groups: low-alloy and non-alloy steels. Low-alloy steels have a certain amount of alloying elements added to them in order to improve the strength and other properties of the material. Non-alloy steels, on the other hand, do not contain any alloying elements and are usually of a low strength.

One of the most important characteristics of welding on steel that is not easy to harden is the heat input rate. Low heat input rates help to reduce the hardening effect on the HAZ, as the welding processes are slower and the temperatures in the HAZ are lower. Low hydrogen welding processes, such as shielded metal arc welding (SMAW) and gas metal arc welding (GMAW), are often used in order to achieve the desired weldment.

Another characteristic of welding on non-alloy steels is the preheating of the material prior to welding. This is done in order to reduce the cooling rate and thus soften the HAZ. Low carbon steels should be preheated to around 100-160 ℃, while high carbon steels should be preheated to around 300-370 ℃.

Other Considerations

One of the other important considerations when welding on steel that is not easy to harden is the use of post weld heat treatment (PWHT). PWHT is a method of heating the material after welding in order to reduce the hardness and improve the toughness of the HAZ. PWHT should be considered when welding on steel that is not easy to harden, as it helps to reduce the hardness and improve the mechanical properties of the weldment.

Conclusion

Welding on steel that is not easy to harden requires careful consideration in order to minimize the hardening effect on the heat affected zone. Low heat input rates, low hydrogen processes, and preheating are all important considerations when welding these materials. PWHT is also important for ensuring that the weldment has the necessary mechanical properties and is free from cracking or other weld defects. By following these guidelines, it is possible to weld on steel that is not easy to harden while still achieving the desired mechanical properties.

Heat affected zone (HAZ) is a region of welded structure that has been heated and cooled during welding, particularly those that result from welding of steels that are not heat treated. Heat affected zone refers to the zone around a weld that has been heated to temperatures above room temperature but below the melting point of the base or bond material. This zone generally exhibits metallurgical changes such as grain coarsening, stress relief, and hardness changes.

High hardness and elevated residual stresses are two of the most profound alterations in low alloy HAZs,making this type of material difficult to weld. The depth of HAZ depends much on the welding process and filler metal composition, which are related to the magnitude of heat inputs and cooling rate. This is especially true with HSLA (high-strength-low-alloy) steels and other steels not caramelized heat-treated after welding.

The higher the weld heat input and cooling rate are, the wider the HAZ would be.The presence of HAZ also decreases the fatigue strength of the weld. Liquid penetration welding, like GTAW or GMAW, is more susceptible to generate a HAZ than the welds done by fusion welding processes like SMAW. Welds of various HSLA and non-heat-treated steels would definitely be prone to the HAZ.

Various factors could modify the influence of HAZ such as mechanical working or chemical treatment. Also, higher preheating temperature can be used to reduce the severity of HAZ. This effect is caused by several changes in the HAZ microstructure, such as grain refinement, development of a Widmanstätten ferrite structure, and occlusion of G phases and carbide.

In conclusion, heat affected zone is an important aspect of the welding process and should be taken into account when welding steels that are not heat treated. The proper selection of preheating temperature and welding process is important in order to reduce the negative effect of HAZ.