KVA Stainless Technology

KVA Stainless has developed proprietary and patented methods to produce welded and brazed tubular forms, stamped and shelled structures, using martensitic corrosion resistant steels. High strength structural shapes can now be integrated into high performance structural assemblies to reduce weight, increase strength and stiffness, without significant cost increases.

Excellent mechanical properties, including specific strength and stiffness, toughness and fatigue performance, in addition to corrosion resistance, can be achieved using martensitic stainless steels in place of other materials. Tensile strengths in excess of 200 ksi (1400 MPa) are capable from simple low cost, low distortion air hardening quench processes.

Stainless Steel

Stainless, or corrosion resistant, steels are defined as an iron-base alloys with a minimum 10.5% chromium content, which promotes the development of an invisible, adherent and self healing chromium-rich oxide surface film. Stainless steels are commonly divided into five groups, classified by their microstructure at room temperature: martensitic, ferritic, austenitic, duplex and precipitation hardenable....view Stainless Steel

Welding

KVA Stainless' processing technology has overcome the conventional limitations of high-speed welding of air hardenable alloys, historically considered difficult, if not impossible, to weld. Previous production difficulties, such as cold-cracking of the heat affected zone (HAZ) under mechanical straining and forming, have been eliminated....view Welding

Brazing

Assemblies designed to take full advantage of KVA Stainless processing technology can benefit from utilizing high-temperature furnace brazing in their design. Brazing, a joining process whereby a non-ferrous filler metal or alloy is melted and distributed between a close-fitting joint interface by capillary action, can be accomplished reliably, repeatable with low operator skill, low cost and no loss of base metal strength in a simultaneous furnace hardening/brazing cycle....view Brazing

Heat Treatment

One of the key benefits of KVA Stainless technology for structural applications has proven to be the ease of forming complex stamping geometries. The material can be readily formed in its softer, annealed state, with low force, low cost tooling. Once the desired geometry is created, parts and entire assemblies can be heat treated to uniform microstructures and hardness/strength levels tailored to the individual application....view Heat Treatment

Patents

KVA Stainless processing technology enables the use of proven high-strength, high-performance materials in new, exciting applications. Worldwide patent protection ensures a competitive edge against infringement....view Patents

KVA Stainless Technology - Martensitic Stainless Steel

KVA Stainless' research and development program is dedicated to promoting the use of martensitic stainless steels in novel applications. These and other air-hardening alloys, when processed with KVA Stainless' joining and thermal treatment technologies, enable cost-effective, superior mechanical and structural solutions.

KVA Stainless' martensitic stainless steel processing can benefit any market segment where component weight, strength and corrosion resistance are critical issues, providing a superior alternative to existing steels or alloys, while increasing the actual and perceived value of finished products.

Stainless Steel Overview

Stainless, or corrosion resistant, steels are defined as iron-base alloys with a minimum 10.5% chromium content, which promotes the development of an invisible, adherent and self healing chromium-rich oxide surface film. Stainless steels are commonly divided into five groups, classified by their microstructure at room temperature:

• martensitic
• ferritic
• austenitic
• duplex
• precipitation hardenable

Various alloying elements are added to the basic iron-chromium- carbon and iron-chromium-nickel systems to control microstructure and properties. These elements include manganese, silicon, molybdenum, niobium, titanium and nitrogen, among others. As shown in Figure 1, all stainless steels can be plotted in terms of their chromium and nickel equivalents to provide a graphic representation between composition and microstructure.

There are over 150 grades of stainless steel, of which austenitic stainless steels (type 304, type 316, 18/8, etc.) are the most widely used. Figure 2 depicts the family relationships for common martensitic, ferritic and austenitic grades.

Martensitic Stainless Steel

Invented by Harry Brearley in 1913 as the first ever-produced "rustless steel", and commercialized and standardized in the 1930s and 1940s, historical applications of martensitic stainless steels (MSS) include cutlery, surgical instruments, scissors, springs, valves, shafts, ball bearings, turbine equipment and petrochemical equipment.

MSS, alloys primarily of chromium and carbon, possess a distorted body-centered cubic (bcc) or body-centered tetragonal (bct) martensitic crystal structure in the hardened condition. These alloys are ferromagnetic, hardenable by heat treatments and mildly corrosion resistant.

The compositions of MSS, typically between 10.5 to 18 wt% chromium, are specifically formulated to render them amenable to a quench-and-temper (Q+T) heat treatment in order to produce high levels of strength and hardness. Although the chromium level is the same as in ferritic stainless steels (e.g. type 409), the higher carbon content of the martensitic grades results in a complete transformation to austenite at high temperature, followed by a subsequent change to the hard martensite phase upon rapid cooling. MSS are considered "air-hardenable," as all but the thickest sections fully harden during an air-quench heat treatment cycle to room temperature.

Similar to low-alloy steels, maximum strength and hardness of MSS primarily depend on carbon content. Figure 3 shows the hardness range, or ultimate tensile strengths, obtainable with common martensitic alloys. Low carbon martensitic stainless grades, such as AISI type 410, have tensile strengths in excess of 200 ksi (1400 MPa) in the fully hardened condition. Tensile strengths in excess of 300 ksi (2100 MPa) are possible in the higher alloyed MSS grades.

It is this air-hardening characteristic which has limited the historical use of MSS to traditionally non-welded components. However, this same potential material flaw has been exploited by KVA technology - to arrive at high strength, tough, corrosion-resistant parts through simple air-quenched thermal processing methods. This development was the direct result of the vision of KVA Stainless' founder, Mr. Ed McCrink, and firsthand experience in working with MSS alloys for more than five decades.

MSS processed with KVA Stainless' technology exhibits excellent mechanical properties: specific strength, stiffness, toughness, and fatigue performance, combined with increased corrosion resistance. These alloys are ideal, cost-effective materials for numerous demanding applications - ranging from miniaturized medical devices to massive oilfield pipelines - and everything in between. KVA Stainless processed MSS can replace difficult to form ultra high strength steels, expensive austenitic stainless steels, and exotic titanium alloys.

Ideal applications for KVA Stainless processed martensitic stainless steel include:

• Agriculture
• Automotive components & structures
• Aviation components & structures
• Bridge structures
• Gas & Oil Production/Pipelines
• Heat exchangers
• Medical devices
• Petrochemical & Process Piping
• Sports equipment
• Train/rail cars & equipment

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KVA Stainless Technology - Welding

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.

Historical Difficulties - Welding Martensitic Alloys:

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:

• Hydrogen induced cold-cracking
• Tensile stress
• Thermal induced stresses

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 1) 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.

KVA Stainless' Weld Processing Solutions

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:

• Improved ductility
• Enhanced toughness
• Eliminates cracking
• In-line process
• Enables high-speed welding of high-carbon alloys
• Compatible with all welding methods (GTAW, GMAW, plasma, laser, HF, resistance...)

As Figure 2 shows, KVA Stainless processed MSS exhibits a more uniform weld metal macrostructure 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:

• Welded MSS components
• Agriculture Automotive components & structures
• Aviation components & structures
• Bridge structures
• Gas & Oil Production/Pipelines
• Heat exchangers
• Medical devices
• Petrochemical & Process Piping
• Sports equipment
• Train/rail cars & equipment

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KVA Stainless Technology - Brazing

Assemblies designed to take full advantage of KVA Stainless processing technology can benefit from utilizing high-temperature furnace brazing in their design. Brazing, a joining process whereby a non-ferrous filler metal or alloy is melted and distributed between a close-fitting joint interface by capillary action, can be accomplished reliably, repeatably with low operator skill, low cost and no loss of base metal strength in a simultaneous furnace hardening/brazing cycle.

Joining High Strength Alloys

In the shift to higher strength alloys in order to improve product strength and/or reduce product weight, many industries are experiencing fabrication and manufacturing problems, particularly related to welding and joining. Higher strength steels typically suffer from limited weld process windows with restricted heat input and weld speed rates. Even with optimum weld parameters, microstructural changes occur in the weld and heat affected zone (HAZ) resulting in a loss of part strength. These changes in material properties are exacerbated by the fact that the weld toe serves as a stress concentrator, magnifying loads on the compromised HAZ microstructure. High strength alloy part failures in the weld-HAZ-base metal interface are not uncommon, resulting in reduced productivity and product performance.

KVA Stainless' Brazing Technology

Realizing the potential of utilizing martensitic stainless steels (MSS) in structural components and assemblies, KVA Stainless has developed novel joining 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 enabling low-cost martensitic stainless steel (MSS) products.

During the hardening heat-treat cycle for MSS, components can be joining using properly selected filler alloys and joint designs. The resulting interfacial bond, properly designed and implemented, can be made stronger than the hardened MSS base metal. Assemblies can be hardened and joined to form uniform, high-strength structures, with no loss of strength in areas adjacent to the braze joint - as is seen with conventional welding methods.

Key advantages of KVA Stainless brazing technology:

• Uniform properties throughout part
• Improved fatigue performance
• Minimal part-to-part variation
• Continuous or batch processing
• Improved appearance
• Low operator skill needed - easily automated

KVA Stainless' simple to implement methods eliminate conventional joining difficulties, such as welding operator skill requirements and part-to-part variation. The braze material can be easily and precisely applied to the part in pre-form or paste form prior to heat treatment. Dissimilar metals can be brazed together with proper process and atmosphere controls. Additionally, brazed MSS exits the furnace with a bright, clean appearance, free from unsightly oxidation and scaling that often accompanies welded stainless joints. Fatigue performance can be improved, due to the smooth transition from part-to-part made by the flow of the braze filler alloy Ð unlike conventional weld beads. Most importantly, secondary joining processes can be eliminated, saving assembly time and cost, while improving product quality and performance.

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.

Controlled atmosphere processing

Permanently joining parts (of the same, similar, or dissimilar materials) by brazing them in a furnace, under either controlled-atmosphere or vacuum, is a very cost-effective method for manufacturing simple or complex assemblies in production quantities, limited only by the physical and chemical properties of the materials themselves and the size of the assembly relative to the furnace.

Brazing does not deform or weaken the assembly, and the use of chemical fluxes and post-joining cleaning operations is eliminated or minimized. A high degree of flexibility in atmosphere selection and blending allows precise control of the factors which most influence braze quality, primarily removal of surface oxides, dewpoint control, carbon control, and wettability. Results are reproducible and compatible to accepted quality control techniques, and special operator skills are not required. Considerable attention must be paid to the selection of base metals, filler metals, joint design, fixturing, and atmosphere composition - KVA Stainless has extensive knowledge base for product success.

The characteristics of furnace brazing filler metals to consider include:

• Base metal compatibility (metallurgical)
• Base metal compatibility (temperature coefficient)
• Strength/stress requirements of joint
• Service temperature requirements
• Other environmental factors (e.g., resistance to corrosion, water, vibration, loads)
• Suitability for furnace brazing(adverse effect of volatile constituents, temperature break down, flow properties in atmospheres)
• Cost-to-performance tradeoffs

The most common atmospheres used in controlled-atmosphere furnace brazing operations are classified as exothermic, endothermic, dissociated ammonia, and industrial gas-based (generated or delivered). What all of these atmosphere types have in common is that they are used for moderate- to high volume production applications, mostly in a continuous or semi-continuous (retort or bell) furnace. They can also be used in vacuum furnaces, as a source for inert, purge, or backfill gas.

All of the brazing atmosphere types reduce oxide formation after precleaning and control the formation of oxides during brazing. They help to control wettability and braze flow, and assist in optimal microstructure formation.

Perhaps most importantly, controlled-atmosphere brazing eliminates the need for fluxing in most applications, which means lower labor costs since parts can be finish-machined or used immediately without post-braze cleaning. Also, the absence of flux residue is a benefit for parts with complex geometries where flux can become entrapped, or threaded holes where complete removal of flux is difficult or impossible.

The unique air-hardening property of MSS allows for simultaneous hardening and joining to be performed, with minimum distortion due to the slow cooling rates involved - versus conventional water or oil quench methods which induce significant thermal shock, distortion and residual stresses on parts. The result is that heat-treated MSS can now be used in a wide variety of structural applications, without significant cost increases.

Ideal applications for KVA Stainless brazing technology include:

• Complex MSS assemblies
• Agriculture
• Automotive components & structures
• Aviation components & structures
• Bridge structures
• Gas & Oil Production/Pipelines
• Heat exchangers
• Medical devices
• Petrochemical & Process Piping
• Sports equipment
• Train/rail cars & equipment

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KVA Stainless Technology - Heat Treatment

A key benefit of KVA Stainless technology is the ease of forming complex part geometries. The material can be readily formed in its softer, annealed state, with low force, low cost tooling. Once the desired geometry is created, the parts can be heat-treated to a high-strength condition with low-cost thermal processing methods.

High Strength Alloys

Many industries are transitioning to higher strength alloys in order to improve product strength and/or reduce product weight. Unfortunately, these high strength alloys are not always compatible with existing fabrication methods, particularly forming and welding. Higher strength steels typically suffer from limited formability and require heavier and larger presses and tooling. Part springback, blank tearing, splitting, wrinkling and die breakage are not uncommon, resulting in reduced productivity and product performance.

An alternate route to high strength products involves forming with the material blanks in a low strength, annealed condition, then heat treating the formed geometry to a high strength, hardened state. Many heat-treatable alloys require substantial thermal processing times in batch-type furnaces. Additionally, severe quench (cooling) rates are needed for common alloys - the thermal shock of rapid quenching in water or oil is messy, expensive and distortion inducing - and not ideal for thin-walled weight sensitive applications. These methods have traditionally been cost prohibitive for widespread use, and hence, have been limited in application.

General Types of Distortion:

• During fast heating
• During fast cooling
• Due to stresses while at heat (creep)
• Due to residual stresses
• During phase transformation
• Due to dissimilar metals

KVA Stainless Heat Treatment Technology

KVA Stainless' founder, Mr. Ed McCrink, has been pioneering the development of low-cost, high-quality thermal processing methods since the 1950s as the founder and CEO of Hi-Temp, Inc., which specializes in continuous thermal processing of hardenable stainless alloys. Mr. McCrink's experience, combined with the innovative spirit of KVA Stainless' development staff, has resulted in numerous patented thermal processing technologies enabling low-cost martensitic stainless steel (MSS) products.

KVA Stainless' proprietary, simple to implement methods eliminate conventional heat treating difficulties, such as long cycle times and excessive, unpredictable part distortion. The material can be readily formed in its softer, annealed state, with low force, low cost tooling. Once the desired geometry is created, parts and entire assemblies can be heat treated to uniform microstructures and hardness/strength levels tailored to the individual application. Components can be hardened to uniform, high-strength conditions throughout, with no loss of strength in areas welded prior to hardening.

Key advantages of KVA Stainless heat treating technology:

• Simple air-quench processes
• Minimal distortion
• Uniform properties throughout part
• Minimal part-to-part variation
• Continuous or batch processing
• Improved ductility
• Enhanced toughness

KVA Stainless processed MSS are ideal substitutes for boron-treated steels in hot stamping operations, or alternatively can be thermally processed with efficient, high throughput continuous furnaces or induction methods. Compared to forming pre-hardened thermomechanically processed alloys, such as dual phase (DP) advanced high strength steels, forming ductile, annealed MSS is very straightforward.

The unique air-hardening property of MSS allows for hardening to be performed, with minimum distortion due to the slow cooling rates involved - versus conventional water or oil quench methods which induce significant thermal shock, distortion and residual stresses on parts. The result is that heat-treated MSS can now be used in a wide variety of structural applications, without significant cost increases.

Similar to low-alloy steels, maximum strength and hardness of thermally processed MSS primarily depends on carbon content. Low carbon MSS grades, such as AISI type 410, have tensile strengths in excess of 200 ksi (1400 MPa) in the fully hardened condition. Tensile strengths in excess of 300 ksi (2100 MPa) are possible in the higher alloyed MSS grades.

Ideal applications for KVA Stainless thermal processing technology include:

• Formed MSS components
• Agriculture
• Automotive components & structures
• Aviation components & structures
• Bridge structures
• Gas & Oil Production/Pipelines
• Heat exchangers
• Medical devices
• Petrochemical & Process Piping
• Sports equipment
• Train/rail cars & equipment

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KVA Stainless Technology - Patents

KVA Stainless has spent over 40 years thinking outside the box to create and develop new and innovative ideas and products that encompass stainless steel alloys. Primarily an engineering company specializing in research and development, KVA Stainless has nine (9) United States Patents, International Patents, as well as a portfolio of patents pending. We continue to be innovators of Stainless Steel alloys for markets that include: Agriculture, Automotive components & structures, Aviation components & structures, Bridge & Building structures, Gas & Oil Production/Pipelines, Heat exchangers, Medical devices, Nuclear, Petrochemical & Process Piping, Sports equipment, Train/rail cars & equipment and many more!