Advantages of Alloys for Automotive Exhaust Systems

Two high-temperature alloys from Carpenter Technology Corporation (NYSE CRS) may offer either cost or performance advantages to the manufacturers of exhaust system components for cars, trucks, buses and other highway vehicles.

Both advances come at a time when exhaust system parts such as manifold bolts and studs must be made at lowest possible cost, yet provide resistance to higher temperatures and ever-longer service life.
Modified A-286 alloy, a lower-nickel version of Pyromet® Alloy A-286 (UNS S66286), provides high strength and good corrosion resistance at temperatures up to 1200°F (649°C). This alternative grade offers properties comparable to the original A-286 alloy, but at lower cost.

The yield strength, tensile strength and reduction in area of the new alloy are comparable to that of the conventional alloy at operating temperatures of 1000°F (538°C) to 1200°F (649°C). The ultimate tensile strength of both grades are 145 KSI (1000 MPa) at room temperature and 103 KSI (710 MPA) at 1200°F.

Like the conventional Pyromet® A-286 alloy, the modified alloy can be precipitation hardened and strengthened by heat treatment. This makes possible a high degree of uniformity in developing maximum strength - a process, with this alloy, that can be easily duplicated.

NCF 3015 alloy (UNS S66315) is a precipitation hardenable, iron-nickel base alloy with mechanical properties superior to iron-base alloys like A-286 alloy, and comparable to more costly nickel-base alloys like Pyromet® Alloy 80A (UNS NO7080).

This alloy may be considered for engine valve applications, catalytic converter components operate at higher temperatures, and manifold bolts which require higher strength at elevated temperatures.

NCF 3015 alloy may provide cost effective solutions where operating temperatures are in the 1200°F (649°C) to 1400°F (760°C) range. Fabricating characteristics are similar to those of Pyromet® A-286 alloy, including response to direct aging of cold reduced parts to achieve enhanced mechanical properties.

The ultimate tensile properties of NCF 3015 alloy, higher at all temperatures than Pyromet® 80A alloy, are 163 KSI (1124 MPa) at room temperature, 138 KSI (952 MPa) at 1200°F (649°C), and 92 KSI (634 MPa) at 1400°F (760°C).

Under some conditions, Carpenter reports, the new NCF 3015 alloy has demonstrated performance comparable to that of the highly alloyed, and more expensive Pyromet® 751 alloy. Both grades have been used for engine valves that operate at high temperatures.

Nominal analysis of Modified A-286 alloy is: carbon 0.08% max., manganese 2.00% max., silicon 1.00% max., chromium 13.50/16.00%, nickel 18.00/20.00%, molybdenum 1.00/1.50%, titanium 1.90/2.30%, vanadium 0.10/0.50%, aluminum 0.35% max., boron 0.003/0.010%, balance iron.

Nominal composition of NCF 3015 alloy is: carbon 0.08% max., manganese 0.50% max., phosphorus 0.015% max., sulfur 0.010% max., silicon 0.50% max., chromium 13.50/15.50%, nickel 30.0/33.5%, molybdenum 0.40/1.00%, titanium 2.30/2.90%, aluminum 1.60/2.20%, niobium 0.40/0.90%, balance iron.