KVA STAINLESS™ patented weld processing technology has overcome the conventional limitations of high speed welding air-hardenable martensitic stainless steels. Previous production difficulties, such as cold-cracking of the heat affected zone under mechanical straining and forming, have been eliminated. The result is that high strength martensitic stainless steels can now be used in a wide variety of structural applications, with significant performance and cost benefits.
Realizing the potential of utilizing martensitic stainless steels in structural components and assemblies, KVA STAINLESS™ has developed novel welding and in-line cooling control methods to use these existing materials in exciting new applications. These technologies are the result of decades of metallurgical and thermal processing R&D and know-how by KVA STAINLESS™' founder, Mr. Ed McCrink, and development staff. KVA STAINLESS™' proprietary, simple to implement methods have overcome conventional difficulties, without resorting to lower-carbon, lower strength alloys and enables the production of ductile, tough and reliable weldments in low-cost MSS.
Key advantages of KVA STAINLESS™ weld processing technology:
As Figure 1 shows, KVA STAINLESS™ processed MSS exhibits a more uniform weld metal microstructure with less chromium carbide dispersion and segregation. Additionally, after a quench and temper heat treatment, a uniform, homogenous microstructure is obtained in the weld, HAZ and base metal, functionally equivalent to a seamless joint.
It is important to note that KVA STAINLESS™ seam-weld technology effectively reduces the hardness of the weld, in both the fusion zone and the HAZ. This reduction in hardness, and associated improvements in ductility, toughness and formability, allows air-hardenable MSS to be used in welded applications historically considered impractical. In addition, KVA STAINLESS™ seam-weld technology does not limit the part from fully transforming into a homogenous, uniform microstructure after a solution heat-treatment. The base metal, HAZ and fusion zone all reach uniform properties after hardening, yielding new possibilities for market participants to now utilize this material.
KVA STAINLESS™ weld processing can replace lengthly pre-and-post weld heat treatments, expensive weld filler metals, and be used to make welded MSS perform as well or better than exotic titanium alloys.
Ideal applications for KVA STAINLESS™ weld processing technology include:
Due martensitic stainless steel's (MSS) composition being specially formulated to render it heat treatable by a quench and temper process, it presents some unique problems during welding. The thermal cycle of heating and cooling, which occurs within the confined heat-affected-zone (HAZ) during welding, is equivalent to a rapid air-cooling quench cycle. The resulting high carbon martensitic structure produced is extremely brittle in the untempered condition. Cracking of the weld zone can occur immediately upon weld cooling or in service for several reasons, including:
These problems occur when welding MSS regardless of the prior condition, whether annealed, hardened, or quenched and tempered. They can occur with all types of welding, including gas tungsten arc welding/tungsten inert gas (GTAW/TIG), gas metal arc welding/metal inert gas (GMAW/MIG), plasma, laser-beam, friction, resistance and electron-beam. In all cases, the high temperature HAZ will be fully hardened in the "as-quenched" condition after welding. (Figure 2) Because of their response to welding thermal cycles, MSS have been considered the most difficult of the five stainless families to weld.
Any mechanical straining after welding (i.e. continuous tube mill forming /straightening) will cause the martensitic HAZ to crack. Conventional processing methods for martensitic weldments, such as pre-heating and lengthy post weld heat treatments (PWHT), do not lend themselves to cost-efficient, high-quality, high volume production.top