Type Analysis | Description | Corrosion Resistance | Elevated Temperature Use | Physical Properties
Heat Treatment | Workability | Typical Mechanical Properties

Type Analysis

Description

15Cr-5Ni is a martensitic precipitation hardening stainless steel offering high strength and hardness along with excellent corrosion resistance. Generally similar to Custom 630 (17Cr-4Ni) in composition and properties, 15Cr-5Ni is chemically balanced to eliminate all but trace amounts of delta ferrite, thus providing superior transverse toughness and ductility plus a higher degree of forgeability.
15Cr-5Ni has fabrication characteristics similar to those of other precipitation hardening stainlesses, and can be age-hardened by a single-step, low temperature treatment.
It has been used for applications requiring high transverse strength and toughness, such as valve parts, fittings, and fasteners, shafts, gears, engine parts, chemical process equipment, paper mill equipment, aircraft components and nuclear reactor components.

Corrosion Resistance

The general-corrosion resistance of 15Cr-5Ni alloy is comparable to that of Type 304 and similar to that of 17Cr-4Ni in most media. Good resistance to stress-corrosion cracking is gained by hardening at temperatures of 1025°F and higher. Compared to 17Cr-4Ni, 15Cr-5Ni alloy shows substantially better stress-corrosion-cracking resistance in boiling 42% MgCl2solution and slightly superior resistance in H2S NaCl-Acetic Acid solutions. Erosion-corrosion resistance of 15Cr-5Ni is also good due to its good combination of corrosion resistance and high hardness.
For optimum corrosion resistance, surfaces must be free of scale and foreign particles and finished parts should be passivated.
Typical General-Corrosion Resistance

Elevated Temperature Use

15Cr-5Ni alloy has displayed excellent resistance to oxidation up to approximately 1100°F. Long term exposure to temperatures between about 600-900°F can result in reduced toughness in precipitation hardenable stainless steels. The reduction in toughness can be minimized in some cases by using higher aging temperatures. Short exposures to elevated temperatures can be considered, provided the maximum temperature is at least 50°F less than the aging temperature.

Physical Properties

Heat Treatment

15Cr-5Ni is normally supplied in the solution-treated condition (Condition A). It can be hardened by heating solution-treated material to a temperature of 900-1150°F for 1 to 4 hrs, depending on the temperature, then air cooling. The various heat treatment are as follows:

• Condition A (Solution Treated or Annealed): Heat at 1900°F +/-25°F, for 1/2 hour, cool to below 90°F so that the material is completely transformed to martensite. Sections under 3" can be oil quenched and sections over 3" should be rapidly air cooled. Do not use in this condition without age hardening due to low toughness, poor impact strength, and susceptibility to stress-corrosion cracking.

• Condition H 900 (Precipitation or Age Hardened):
  Heat solution-treated material at 900°F for 1 hour and air cool.

• Condition H 925, H 1025, H 1075, H 1100, H 1150 (Precipitation of Age Hardened):
  Heat solution-treated material at specified temperature +/-15°F for 4 hous and air cool.

• Condition H 1150M(Precipitation or Age Hardened):
  Heat solution treated material at 1400°F +/-15°F for 2 hrs, air cool; then heat at 1150°F +/-15°F for 4 hours and air cool.

Size Change Upon Aging
Upon aging, a predictable size change will occur for 15Cr-5Ni. For the H 900 treatment, a contraction of 0.0004 to 0.0006 in./in. is obtained. Aging at 1150°F causes a contraction of 0.0008 to 0.0010 in./in.

Cleaning
Descaling following forging and annealing can be accomplished by acid cleaning or grit blasting. The acid treatment consists of 2 minutes in 50% by volume nuriatic acid at 180°F, followed by 4 minutes in a mixture of 15% by volume nitric acid, plus 3% by volume hydrofluoric acid at room temperature. Water rinse and desmut in 20% by volume nitric acid at room temperatures. Repeat cleaning procedure as necessary by decreasing the times by 50% (i.e., 1 and 2 minutes, respectively).
The heat tint from aging can be removed by polishing, vapor blasting, or pickling 4 to 6 minutes in a mixture of 15% by volume nitric acid, plus 3% by volume hydrofluoric acid, followed by a water rinse. Repeat the acid cleaning procedure if necessary, but decrease the time by 2 to 3 minutes. Desmut in 20% by volume nitric acid at room temperature.
After acid cleaning, bake 1 to 3 hours at 300/350°F to remover hydrogen.

Heat Treating After Overaging
15Cr-5Ni alloy in the H 1150 and H 1150M conditions will not respond to further aging treatments. Therefore, if the alloy is obtained in these conditions (for forging, optimum cold heading and machinability), it must be solution treated at 1900°F after these operations before subsequent aging. Forging billets are supplied in condition H 1150, and the H 1150M condition is used for optimum machinability and cold headability.

Workability

Hot Working
15Cr-5Ni alloy can be readily forged, hot headed and upset. Material which is hot worked must be solution treated prior to hardening if the material is to respond properly to hardening.

Forging
Heat uniformly to 2150/2200°F and hold 1 hour at temperature below forging. Do not forge below 1850°F. To obtain optimum grain size and mechanical properties, forgings should be cooled in air to below 90°F before further processing. Forgings must be solution treated prior to hardening.

Cutting
Bars and forging billets should be cold cut by sawing. Abrasive wheel cutting can cause small surface cracks, particularly when cutting annealed stock, and should be avoided.

Cold Working
15Cr-5Ni alloy can be fabricated by cold working (i.e., heading, rolling, etc.) to an extent which is limited by the high initial yield strength. This alloy is generally used in the form of bars and forgings not requiring much forming.

Machining
15Cr-5Ni alloy is readily machined in both the solution treated and various age-hardened conditions. In the solution-treated condition, it machines similarly to stainless Types 302 and 304. The machinability will improve as the hardening temperature is increased. Condition H 1150M provides optimum machinability. Having procured condition H 1150M for best machinability, higher mechanical properties can only be developed by solution treating and heat treating at standard hardening temperatures.

Welding
15Cr-5Ni can be satisfactorily welded by the shielded fusion and resistance welding processes. Oxyacetylene welding is not recommended, since carbon pickup in the weld may occur. When a filler metal is required, AWS E/ER630 welding consumables should be considered to provide welds with properties matching those of the base metal. When designing the weld joint, care should be exercised to avoid stress concentrators, such as sharp corners, threads, and partial-penetration welds. When high weld strength is not needed, a standard austenitic stainless filler, such as E/ER308L, should be considered. Normally, welding in the solution-treated condition has been satisfactorily; however, where high welding stresses are anticipated, it may be advantageous to weld in the oaveraged (H 1150) condition. Usually, preheating is not required to prevent cracking.
If welded in the solution-treated condition, the alloy can be directly aged to the desired strength level after welding. However, the optimum combination of strength, ductility and corrosion resistance is obtained by solution treating the welded part before aging. If welded in the overaged condition, the part must be solution treated and then aged.

Type Mechanical Properties

Typical Mechanical Properties
Longitudinal direction, intermediate location.

**compressive yield strength for Condition H 900 is 178 ksi (1228 MPa)
*The modulus values for 15Cr-5Ni alloy at elevated temperature can be conveniently expresses as a percent of the room temperature values as follows:

Typical Room Temperature Mechanical Properties
Transverse direction, intermediate location

Typical Room Temperature Torsional Properties

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