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

Type Analysis

Description

PH 13-8 Mo* stainless is a martensitic precipitation/age-hardening stainless steel capable of high strength and hardness along with good levels of resistance to both general corrosion and stress-corrosion cracking. In addition, the alloy exhibits good ductility and toughness in large sections in both the longitudinal and transverse directions. The excellent properties of PH 13-8 Mo stainless are obtained through close control of chemical composition and microstructure plus specialized melting which reduces impurities and minimizes segregation. Compared to other ferrous-based materials, this alloy offers a high level of useful mechanical properties under severe environmental conditions.
13-8 Mo stainless has good fabrication characteristics and can be age-hardened by a single low temperature treatment. Cold work prior to aging increases the aging, especially for lower aging tempratures.
13-8 Mo stainless has been used for valve parts, fittings, cold-headed and machined fasteners, shafts, landing gear parts, pins, lockwashers, aircraft components, nuclear reactor components and petrochemical applications requiring resistance to stress-corrosion cracking. Generally, this alloy should be considered where high strength, toughness, corrosion resistance, and resistance to stress-corrosion cracking are required in a steel showing minimal directionality in properties.
*PH 13-8 Mo stainless is a registered trademark of Armco Inc.

Corrosion Resistance

In condition H 950, PH 13-8 Mo stainless has rusting resistance similar to that of Type 304 Stainless in 5 weight percent salt fog. In strongly oxidizing and reducing acids and in atmospheric exposures, the general-corrosion resistance of PH 13-8 Mo stainless approaches that of Type 304. As with other precipitation hardening stainless steels, the alloy's level of general-corrosion reistance is greatest in the fully hardened condition and decreased slightly as the aging temperature is increased. Numerous tests representing a marine environment have shown the alloy, in both the wrought and welded conditions, to have a high level of resistance to stress-corrosion cracking. For best resistance to stress-corrosion cracking, a minimum aging temperature of 1000°F (538°C) is suggested.
For optimum corrosion resistance, surfaces must be free of scale and foreign particles and finished parts should be passivated.
Typical Stress-Corrosion-Cracking Resistance in an Atmospheric Marine Environment
0.062" (1.57 mm) thick strip

*Applied stress were 100, 90 and 75 percent fo the 0.2 percent yield strength, using smooth bent beam specimens tested in the longitudinal directiong.
**NF indicates No Failure in 1405 day's exposure.
***Heat treatment includes solution treatment at 1700°F, 15 minutes.

Elevated Temperature Use

PH 13-8 Mo stainless has displayed excellent resistance to oxidation up to approximately 1100°F. Long-term exposure to temperatures between about 600-900°F (288-482°C) 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 (28°C) less than the aging temperature.

Physical Properties

Specific Gravity:
   (Condition H 1000)............................... 7.76
Density:
   (Condition H 1000)
   ...................... 0.280 lb/cu in (7760 kg/cu m)

Electrical Resistivity
Condition A

Magnetic Permeability
Conditon H 950

Mean Coefficient of Thermal Expansion

Thermal Conductivity
Condition A

Heat Treatment

PH 13-8 Mo stainless is hardened by heating solution-treated material, Condition A, to a temperature of 950°F to 1150°F for 4 hours, then air cooling. The various heat treatments are as follows (note all times are "at temperature"):
Condition A(Solution treated or Annealed)
Heat at 1700°F +/-15°F (time dependent on section size), cool to below 60°F so that the material is completely transformed to martensite. Normally, 1 hour hold at temperature is suggested. Section under 36 sq. inches can be quenched in a suitable liquid quenchant; larger sections should be air cooled.
Condition RH 950 (Precipitation or Age Hardened)
Cold treat solution treated material to -100°F for 2 hours minimum. Air warm to room temperature. This must be done within 24 hours after solution treatment. Heat cold-treated material to 950°F +/-10°F for 4 hrs. Air cool.
Condition H 950, H 1000, H 1050, H 1100, H 1150 (Precipitation or Age Hardened)
Heat solution-treated material at specified temperature +/-10°F for 4 hrs. Air cool.
Condition H 1159M(Precipitation or Age Hardened)
Heat solution-treated material at 1400°F +/-10°F for 2 hrs. Air cool; then treat at 1150°F +/-10°F for 4 hrs. Air cool.
Heat Treating After Overaging
PH 13-8 Mo stainless in the H 1150 and H 1150M overaged conditions will not respond to further aging treatments. Therefore, if the alloy is obtained in either condition (for forging, optimum cold heading and machining) it must be solution treated at 1700°F, after these operations and before subsequent aging.
It should be kept in mind that the hardness for the H 1150 condition falls within the hardness range for the solution-treated condition; therefore, hardness cannot be used to distinguish between the H 1150 and solution-treated conditions.
Size Change Upon Aging
Upon aging a predictable size change will occur for PH 13-8 Mo stainless. Increasing amounts of contraction occur as aging temperature is increased.

Cleaning
Descaling following forging and annealing can be accomplished by acid cleaning or grit blasting. The acid treatment consists of 2 minutes in 50% be volume muriatic 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 temperature. Repeat cleaning procedure as necessary but decrease the time 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 remove hydrogen.

Workability

Hot Working
PH 13-8 Mo stainless 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 hr at temperature before forging. Do not forge below 1750°F. To obtain optimum grain size and mechanical properties, forging should be cooled in air to 60°F before further processing. Forging must be solution treated prior to hardening.

Cold Working
PH 13-8 Mo stainless can be fabricated by cold working to an extent which is limited by the high initial yield strength.

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.

Machining
PH 13-8 Mo stainless can be machined in both the solution treated and various age-hardened conditions. In Condition A the alloy gives good tool life and surface finish when machined at speeds 20 to 30% lower then those used for Custom 630 (17Cr-4Ni) or 20 to 30% lower than used for Stainless Type 302 and 304. The machinability as age-hardened will improve as the hardening temperature is increased.
Conditon H 1150M provides optimum machinability. Having procures Conditon H 1150M for best machinability, higher mechanical properties can be developed only by solution treating and heat treating at standard hardening temperatures.

Following are typical feeds and speeds for solution-treated Carpenter PH 13-8 Mo:

When using carbide tools, surface speed feet/minute (sfpm) can be increased between 2 and 3 times over the high-speed suggestions. Feeds can be increased between 50 and 100%.
Figures used for all metal removal operations covered are average. On certain work, the nature of the part may require adjustment of speeds and feeds. Each job has to be developed for best production results with optinum tool life. Speeds or feeds should be increased or decreased in small steps.

Welding
PH 13-8 Mo stainless can be welded using the inert-gas shielded or resistance welding processes. When a filler metal is required, PH 13-8 welding consumables should provide welds with properties similar to those of the base metal. When designing the weld joint, care should be exercised to avoid stress concentrators, such as shrap 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 annealed condition has been satisfactory; however, where high welding stresses are anticipated, it may be advantageous to weld in the overaged (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 overage condition, the part must be solution treated before aging.

Typical Mechanical Properties

Typical Longitudinal Room Temperature Mechanical Properties
Center or Intermediate test location

Typical Transverse Room Temperature Mechanical Properties
Center or Intermediate test location

Typical Room Temperature Torsional Properties

13-8 Mo - Inventory Stock