The fl exibility of steel casting design applica- tions allowed for the high-volume production of this stainless steel 8.1-liter engine manifold for heavy duty trucks.
Temperature-Resistant Applications
High temperature resistance, or Resistance to fatigue depends on the
strength, ductility, service conditions, cor- rosion, residual stresses in the component, design (particularly in high-stress areas), surface fi nish and required service life of the component. Fatigue analysis is diffi - cult, but component testing is not unusual to verify the design and part durability. Strain-controlled cyclical properties, crack growth rates, integration of inspection standards and life prediction improve de- signs by reducing the traditional require- ments for factor of safety and allow for a more aggressive use of material. Analytical tools like computer modeling of service loads, along with the development of use- ful material properties, reduce the number of necessary design iterations. Castings allow the geometry to be tai-
lored to the service requirements. Steels for structural applications can be found in ASTM A27, A148, A747, A915 and A958.
Pressure-Containing Applications
These applications have similar char-
acteristics to structural applications. Specifi cations for pressure-containing applications have been developed to meet ASME Boiler and Pressure Vessel code. These steels can be ordered in ASTM A217, A487, A352, A389 and A757.
Impact-Resistant Applications Impact resistance, or toughness, is
required when a part is subject to low temperatures, performs a safety-critical function or is impact loaded in service. It can be improved through careful control of composition and heat treatment. Add- ing nickel is the common way to improve toughness. The toughness of all grades can be improved by lowering carbon, sulfur and phosphorus and using a quench and temper heat treatment. Further, tough- ness tests can be required when necessary. These steels can be ordered in ASTM A352 and A743 for stainless.
creep strength, is required to carry loads at elevated temperatures. As the temperature increases, the alloy content required also increases. Com- monly, chromium and molybdenum are added to the steel to improve elevated temperature properties. Higher carbon content also helps. The preferred heat treatment of carbon and low alloy steels is normalizing and tempering. These steels are found in ASTM A216 and A217. When the service temperatures exceed 1,200F (649C), the alloyed steels are no longer adequate, and the cast heat-resistant grades containing high levels of chromium and nickel are used. Such alloys are ASTM A297 and A351.
Wear-Resistant Applications Wear applies to mechanical wear and
chemical corrosion. Severe wear or cor- rosion environments require high alloy steels. Wear resistance is usually improved through using high hardness materials. Strength and hardness are related, so the high-strength materials are commonly used when wear is a problem. Increasing carbon content also increases wear resistance. Special materials like austenitic manganese alloys or high-chromium irons are used to give better wear resistance. Toughness must be adequate to avoid premature catastroph- ic failure. High-chromium irons offer good wear resistance in abrasive or corrosive environments. When impact loading is a part of the wear environment, austenitic manganese alloys work-harden, allowing them to resist wear while maintaining high toughness. Severe environments,
The REX 77 dive helmet is a stainless steel cast- ing combining a shell and locking mechanism that were cast separately on its bronze predecessor.
2010 Casting sourCe DireCtory Metal Casting Design & PurChasing 25
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