Welding process for austenitic stainless steel and low carbon or low alloy steel
1. Introduction
Welding process for austenitic stainless steel and low carbon or low alloy steel is always of great interest to engineers in production and design. Austenitic stainless steel has excellent corrosion resistance and good mechanical properties, while low carbon or low alloy steels are widely used in structural engineering with certain strength and formability. With the excitement of light weight in construction and engineering applications, the use of austenitic stainless steel and low carbon or low alloy steel combination is more and more common, and the welding process between them has become an increasingly important issue.
2. Literature review
Over the past decades, more and more research has been done on welding process of austenitic stainless steel and low carbon or low alloy steel. Tzou and Yang [1] proposed a new method to control warpage by introducing a second pass along the ridge line of the joint. To reduce the cracking tendency, joung and You [2] used Ti-5Al-2Zr alloy to deposit a layer of fillet weld on the steel surface. The interlayer could be activated through a Mg addition to couple the different coefficients of thermal expansion of steel and stainless steel. Andreas et al [3] used interpass temperature control and surface grinding to significantly reduce the PGEA thermal stress during welding of dissimilar metals. More and more studies have been done to tackle the cracking problem and optimize welding process.
However, there is still a lack of literature review from the technical point of view. As the welding process and surrounding environment are always changing, it is necessary to study the impact of various process parameters such as welding current, joint geometry, welding speed and so on on the performance and structure of joint.
3. Welding process
The welding process between austenitic stainless steel and low carbon or low alloy steel is usually based on metal inert gas (MIG) welding process, as it provides greater control over heat input, lower dilution and better arc stability. According to the requirement of welding procedure, the qualified stainless steel MIG wires are usually selected and the welding current, voltage and welding speed are determined. To ensure the optimality of interration, it is necessary to have some specific pre-treatment before welding, such as preheating, grinding, and using of a backing strip.
In the joint welding process, preheating is necessary to reduce the thermal stress and prevent from cracking or other forms of damage. In order to ensure a good joining, the joint is preheated to 350°C to 400°C and maintained for at least 1 minutes before welding. The use of a backing strip can reduce the thermal stress and provide additional support for the weld, especially for the joints of heavy section thickness. Surface grinding can also effectively eliminate any welding residue and present a bevel angle for welding to obtain better structural integrity.
During welding, it is important to pay attention to the voltage, current, welding speed and other parameters to obtain the desired joint geometry. Usually with a wire reel size of 1.2 ~ 1.6mm and welding current of 90 ~ 130A, the welding speed should be kept in the range of 0.8 ~ 1.2 m/min. And it is necessary to correspond the welding speed with the welding current, too large or too small welding speed can cause welding burn, making the joint not close enough or too brittle.
Finally, after the welding, it is necessary to do the post-treatment, such as stress relief annealing, in order to obtain a homogeneous and higher mechanical strength of the joint.
4. Conclusion
In summary, welding process between austenitic stainless steel and low carbon or low alloy steel is an important welding procedure, the welding current, voltage, speed and other welding parameters should be strictly controlled in order to obtain desired joint geometry. Preheating and post-treatment, such as stress relief annealing are necessary to obtain an homogenous and higher strength joint. With more and more studies on welding of dissimilar metals, new and improved welding methods have emerged.
