Round Bar / Forgings Exhaust Valve Alloys For Heavy Duty Internal Combustion Engine Exhaust Valve

Alloy 31V (31V alloy) for heavy-duty internal combustion engine exhaust valves

PRODUCT

Alloy 31V (31V alloy) for heavy-duty internal combustion engine exhaust valves.

EQUIVALENT DESIGNATION

UNS N07032, CarTech^® 31V Alloy, Pyromet® 31V

PRODUCT FORM

Round bar, forgings, forging stock etc.

APPLICATION

Because of its excellent balance of properties, alloy 31V has been considered a candidate for many demanding applications, including rapid fire military gun barrels, hardware in coal gasification units and exhaust valves in heavy-duty internal combustion engines.

SKETCH OF EXHAUST VALVE

PRODUCTION PROCEDURE OF EXHAUST VALVE

Blanking → Electric heating upsetting forging of head blank → Heat treatment of head blank and rod → Friction welding → Rough turning or grinding → Finish turning → Cut fixed length → Semi-fine grinding the stem → The valve stem chrome plating → Fine grinding the stem → NDT of the finished valve → Delivery

SURFACE CONDITION OF EXHAUST VALVE

PRODUCTION SITE OF EXHAUST VALVE

OVERVIEW

Alloy 31V is a sulfidation and corrosion resistant precipitation hardenable alloy possessing an unusual combination of corrosion resistance and strength to temperatures as high as 1500°F (816°C).
This alloy displays good resistance to hot sulfidizing and oxidizing environments such as those encountered in diesel engine service, as well as sour environments such as those encountered in deep sour gas and oil wells.

CHEMICAL COMPOSITION (wt%):

Table 1

PHYSICAL PROPERTIES

Density: 8.01 g/cm³ (0.289 lb/in³)

Melting range: 2250 - 2420°F (1232 - 1327°C)

MECHANICAL PROPERTIES

Typical room and elevated temperature mechanical properties

Specimen: 0.75 in (19mm) round bar

Heat treatment:

1 Heat treated at 2050°F(1121°C) 1 hour, AC, 1550°F(843°C) 4 hours, AC, 1350°F(732°C) 4 hours, AC

2 Heat treated at 2050°F(1121°C) 1 hour, AC, 1300°F(704°C) 24 hours

3 Heat treated at 1875°F(1024°C) 1 hour, oil quenched, 1300°F(704°C) 24 hours

CORROSION RESISTANCE

Laboratory crucible tests aimed at assessing the capability of alloy 31V to withstand high temperature sulfidation attack were carried out in a mixture of 10 CaSO4 - 6 BaSO4 - 2 Na2SO4 - 1 C at 1600°F (871°C) for up to 80 hours. The results shown in the hyperlink titled "Comparative Sulfidation Test Results-Various Alloys" indicate that alloy 31V has superior resistance compared to commercial diesel valve alloys like alloys 751 and 80A, which suffered catastrophic attack. All three alloys have excellent resistance to hot corrosion by lead oxide at 1675°F (913°C).
In a molten mixture of 90% Na2SO4 / 10% NaCl at 1700°F (927°C) / 100 hours, alloy 31V showed only slight attack while alloy 751 suffered catastrophic attack.
Evaluations in both laboratory and field environments have been conducted to establish alloy 31V as a candidate for consideration as a sulfide stress cracking resistant material for oil field applications in sour environments.
Comparative tests have shown that alloy 31V is superior to alloy X-750 (an established alloy for sour service) in the NACE TM-01-77 solution, which consists of an acidified, deoxygenated sour brine solution saturated with hydrogen sulfide.

Comparative sulfication test results- various alloys at 1600°F(871°C)

HEAT TREATMENT

Solution treatment

A lower solution temperature, 1875°F (1025°C), will result in somewhat finer grain size and is sometimes employed to optimize properties below 1200°F (649°C).
Age

Solution treated stock may be given a single or double age for optimum compatibility with manufacturing processes. The single-age cycle is 1300°F (704°C) for 24 hours, followed by an air cool. The double-age cycle includes a stabilizing age in the range from 1550/1600°F (843/871°C) for 4 hours, air cool, plus a final age at 1350°F (732°C) for 4 hours, air cool.

WORKING INSTRUCTION

Hot working

Alloy 31V can be hot worked within the temperature range of 1800/2100°F (980°/1150°C). Careful control of the forging temperature and frictional heat build-up should be maintained.
Large amounts of deformation below 1800°F (980°C) should be avoided.
Forgings may be air or fan cooled. Water quenching should be avoided, especially for large sections.

Machinability

The machinability of this alloy is similar to other iron-nickel base precipitation hardened alloys, such as Alloy X-750.
The alloy can be machined in either the solution annealed or age hardened condition. Machine tools should have ample power, and cutting speeds should be slow.
For better chip action on chip breakers and an improved finish, use material in the age hardened condition.

COMPETITIVE ADVANTAGE:

(1) More than 50 years experience of research and develop in high temperature alloy, corrosion resistance alloy, precision alloy, refractory alloy, rare metal and precious metal material and products.
(2) 6 state key laboratories and calibration center.
(3) Patent technologies.

(4) Average grain size 9 or finer.

(5) High performance

BUSINESS TERM