Universal Corrosion Resistant Steel

AISI-321-Stainless-Steel-Bright-Round-BarEquipment manufacturers in the aircraft/aerospace, automotive, and oil/gas industries require high strength, moderate impact toughness, and corrosive resistant martensitic and maraging steels to produce equipment components that operate in highly stressful and corrosive environments. Stainless steels such as 440(A,B,C,F) have high strength, wear and corrosion resistance. However, their low toughness both in terms of Charpy V-notch and fracture toughness considerably limits their application.

Ferrium S53 is an example of corrosion resistant tempered martensitic secondary-hardening steel with high strength and moderate impact toughness. However, the high cost of the material that goes into the steel, namely 14 wt.% concentration of Cobalt (Co), 2 wt.% of Molybdenum (Mo), and 5.5 wt.% of Nickel (Ni) makes this steel cost prohibitive for many applications.rust_by_struckdumb

Carpenter Custom 455, and Custom 465 are also examples of costly high strength, moderate impact toughness, maraging stainless steels with 8-11 % wt. of Ni and 1- 2.3 % wt. of Mo. Yet Carpenter’s custom steels with high strength and moderate impact toughness have provided solutions in many cases for aircraft/aerospace applications. In addition to the high cost of raw materials, both Ferrium S53 and Carpenter Custom stainless also consume large quantities of energy to perform double vacuum arc remelting (VAR) and the electroslag remelting (ESR) processes to produce these steels.

Neff Family 001

Recently the United States Patent & Trademark Office awarded ISAI a patent (8,071,017 B2) for a martensitic stainless steel that exhibits high strength and moderate impact toughness at a substantially lowers cost to produce than Ferrium S53 as well as other steels with similar mechanical and corrosion resistant properties. The US Navy, through the Small Business Innovative Research (SBIR), program initiated the first phase of the research for this stainless steel which is corrosion resistant in a 5% NaCI solution and other low aggressive corrosion media.

It took only three prototypes over a period of seven months to produce two articles of this steel resulting in a savings of millions of dollars in development costs. The reductions in cost and energy with the invention of this steel were surprising and unexpected. It also minimizes the use of scare and expensive metal, such as cobalt (Co).

UCR125 is a low cost replacement for 15-5 PH and Custom 450. It is a cobalt free stainless steel where the total alloying elements are 17.3% of the weight of the steel. In contrast, the alloying elements in 15-5 PH are 24.3% by weight, and in Custom 450 are 22.8% by weight. UCR125 is recommended for aerospace/aircraft and military purposes.

UCR135 is a low cost replacement for Custom 455, Custom 465, and Ferrium S53. It is a cobalt free stainless steel where the total alloying elements are 17.4% by weight. In contrast, the alloying elements in Custom 455 are 21.8%, in Custom 465 are 25.7% by weight, and in Ferrium S53 are 31.7% by weight. UCR135 exhibits a lower fracture toughness and Charpy Vnotch impact toughness energy performance than UCR125 and is recommended for automotive and oil/gas applications.

Mechanical Properties

The mechanical properties of the two articles of our stainless steels are contained in Table 1. UCR provides excellent resistance to general corrosion, corrosion fatigue, and stress corrosion cracking (SCC). UCR also has excellent resistance to fatigue and has high harden-ability.

Mechanical Properties

Steel Grade

Hardness

HR C

Tensile Strength

UTS,ksi

Yield Strength

YS,ksi

Elong %  R.A %  Charpy
v-notch,
ft-lb
SCV45Cr16 55 282 263 5 8 11
UCR125 54 297 12 12  35  18
UCR135 57 304 9 9 31  14

Table 1: Mechanical Properties of UCR Stainless Steel

Table 1 also includes the previously developed SCV45 stainless steel. Dr Vladimir Fedchun imagined, developed and patented the SCV stainless steel and SCV45 stainless steel was the basis for development of the UCR stainless steel.

Amphib TankThe mechanical properties of an article of UCR stainless steel depend on the concentration of the alloying elements and the heat treatments applied; and can be varied across a wide range of concentrations to produce different combinations of mechanical properties to satisfy the most demanding customers. In addition to being compatible to several industry grade corrosion resistant stainless steels, UCR was designed to provide mechanical properties comparable to, conventional high strength steels such as 300M and SAE 4340 with the added benefit of general corrosion resistance, eliminating the need for expensive toxic coatings such as cadmium. These coating processes also require subsequent hydrogen bake-out operations in order to avoid hydrogen embrittlement.

Table 2 presents the mechanical properties of several industry grade high strength corrosion resistance martensitic stainless steels and martensite-aged moderate corrosion resistant stainless steels.

Mechanical Properties

 Steel Grade  Hardness
HRC
 Tensile
Strength,
UTS, ksi
 Yield Strength,
YS, ksi
 Elong %  RA %  Charpy
v-notch,
ft-lb
 Ferrium S53  54  288  226  15  56  17
 Custom 450  53  254  239  14  63  20
 Custom 455  49  235  225  14  60  14
 Custom 465  51  254  239  15  65  16
 15-5 PH  46  190  175  14  54  15

Table 2: Mechanical Properties of Various Popular Stainless Steels

Chemical Composition

The low cost, high strength, and moderate toughness of our steel was achieved through an innovative alloying methodology where very expensive elements such as Co, Mo and Ni are either eliminated or significantly reduced to the lowest levels. The chemical composition of the UCR stainless steel is contained in Table 3.

Alloying Elements, wt. %

 Steel Grade  C  Cr  Ni  Mo  Ti  V

 UCR Stainless Steel

(US Patent 8,071,017 82)

 0.30-0.45% 8-13%  less than 3%  less than 1%  less than 0.2%  less than 0.5%

Table 3: Chemical Composition

Processing: Melting, Purification and Heat Treatment

The pilot-production of previously invented corrosion resistant martensitic Silicon, Copper Vanadium (SCV45) stainless steel was produced in power arc furnaces with a 40 Mt liquid metal capacity. After the homogenizing annealing process 5 Mt ingots were forged into bars 7-8” Dia.steel_reuters

The more recent UCR steel articles were melted in an open lab 100 lbs induction furnace. During the heating process, argon was supplied to the furnace. Ingots with a weight of 30lbs were annealed and rolled into 1” D bars and plates with dimensions of 1.5”x4”x5” which were annealed for recrystallization.

 

Small concentrations of phosphorus (P), sulfur (S), incidental elements, and the other inevitable impurities that make their way into the furnace will not critically affect UCR steel’s mechanical properties. High energy consumption processes such as vacuum arc remelting (VAR) and electroslag remelting (ESR) are not needed. Producing this stainless steel requires only a ladle refining furnace (LRF), and a vacuum decontamination process to remove hydrogen (H) and nitrogen (N).

Microstructure

Metallographic examination of the new stainless steel, displayed in Figure 1, that was subjected to quenching and low-temperature tempering exhibited a microstructure of tempered lath martensite, carbides TiC and retained austenite.

Figure 1 Microscopic View of UCR Stainless Steel

Corrosion Resistance

how-to-remove-rustCorrosion is recognized as one of the most serious problems facing modern society today and will only grow larger in the future. Corrosion has been the subject of scientific study for more than 150 years. It is a naturally occurring phenomenon commonly defined as the deterioration of a material (usually a metal) or its properties because of a reaction with the environment. Like other natural hazards such as earthquakes or severe weather disturbances, corrosion can cause dangerous and expensive damage to everything exposed to the elements. Employing our corrosive resistant steels can significantly reduce the total quantity of repair works of aircraft landing gears, automotive and oil/gas applications.

SCV Stainless Steel, US Patent 6,426,040

Table 4: Corrosive Resistant Properties of SCV and ISAI Stainless Steels Corrosion Resistance Characteristics

Heat Treatment Agent and Testing Conditions

Time of Testing,

hr

Durability Index According
 Oil Quenched at 1900F

Low Tempered at 380F

Sulfuric acid(93%) + 68F  288

600

2-3 durable enough

3-4 durable enough

Nitric acid (56%) + 68F 288

600

4 durable

1 absolutely durable

 Sea water + 400 ml of Sulfuric acid + 68F 790 1-2 durable enough

The design for corrosion resistance utilized the results of prior efforts with the SCV steels. The SCV stainless steels were found to be reluctant to the inter-crystalline corrosion and have sufficiently high corrosion resistance in different aggressive media.

Table 4 presents the results of corrosion resistance tests for SCV and UCR stainless steels.

100128-N-3327M-254 INDIAN OCEAN (Jan 28, 2010) Sailors assigned to the Warhawks of Strike Fighter Squadron (VFA) 97 change the tires on the nose landing gear of an F/A-18C Hornet aboard the aircraft carrier USS Nimitz (CVN 68). The Nimitz Carrier Strike Group is conducting operations in the U.S. 7th Fleet area of responsibility supporting maritime strategy. (U.S. Navy photo by Mass Communication Specialist 3rd Class James Mitchell/Released)

Both UCR stainless steels were subjected to salt spray test ASTM 117 (5% NaCl aqua solution) and after 400 hours of testing, no significant red rust on polished surfaces was revealed. Testing to date indicates that both UCR stainless steels should allow for the elimination of cadmium coating prior to paint protection. However, additional testing is needed to further address this key implementation consideration. Both UCR stainless steels also provide good protection against stress corrosion cracking. The corrosion resistant materials in both UCR stainless steels maintain resistance to crack propagation in the presence of a corrosive environment.

Both UCR stainless steels are the first inexpensive corrosion resistant steels to achieve good fracture toughness at this strength level, enabling a weight-neutral replacement for 300M class alloys. The alloy exhibits substantial uniform plasticity similar to 300M prior to the onset of instability. Deep hardening capability is another similarity.

Production Cost

True production costs for any alloy is difficult to assess as it depends on the cost structure of each individual producer. The relative cost of stainless steels, excluding any extras, are primarily determined by their alloy content, the relative cost of those alloying elements, and processing required to produce the steel. While the equipment and labor costs should be less for the UCR Steel, for the moment let’s consider that equal as well. That leaves the alloying material.

Based on the published prices of alloying materials, the estimated production cost of the alloying material for this new steel as well as several chosen industry grade corrosive resistant stainless steels may be found in Figure 2. The cost of alloying material for Ferrium S53 is six to eight times more than ISAI’s UCR steel articles yet these two steels have similar mechanical properties.

 

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Figure 2: Cost Comparison of Corrosive Resistant Steel

Benefits

Both of ISAI’s UCR stainless steels exhibit high strength, moderate impact and fracture toughness with corrosion resistance in salt spray test ASTM 117. It’s mechanical properties are similar to that of Ferrium S53, Custom 455, and Custom 465, including their corrosion resistant properties. It’s mechanical properties are superior to AISI 440A and equal to 300M.

The benefits of using UCR125 and UCR135 .vs. Ferrium S53, Custom 455, Custom 465, and other incumbent materials includes:

  • Significantly reduced cost of alloying material by eliminating Co and reducing to the lowest levels Mo and Ni from the alloying material
  • Further reduction in production costs by eliminating double vacuum arc remelting (VAR) and electroslag remelting (ESR) processes
  • Eliminating or reducing the need for toxic cadmium plating, in order to reduce EHS impact and expenses for both initial installation and on-going re-application
  • Reducing general corrosion and related expenses for part condemnation and equipment/system failure
  • Reducing the occurrence of difficult-to-predict SCC failures, and related expenses
  • Improving resistance to fatigue and corrosion fatigue