Ultrahigh-strength steels are designed to be used in structural applications where very high loads are applied and often high strength-to-weight ratios are required. This article discusses the composition, mechanical properties, processing, product forms, and applications of commercial structural steels capable of a minimum yield strength of 1380 MPa (200 ksi). These include medium-carbon low-alloy steels, such as 4340, 300M, D-6a and D-6ac steels; medium-alloy air-hardening steels, such as HI1 modified steel and H13 steel; high fracture toughness steels, such as HP-9-4-30, AF1410, and AerMet 100 steels; and maraging steels.

Structural steels with very high strength levels are often referred to as ultrahigh-strength steels. This article describes the commercial structural steels capable of a minimum yield strength of 1380 MPa (200 ksi). The ultrahigh-strength class of constructional steels includes several distinctly different families of steels. The article focuses on medium-carbon low-alloy steels, medium-alloy air-hardening steels, and high fracture toughness steels. The medium-carbon low-alloy family of ultrahigh-strength steels includes AISI/SAE 4130, the higher-strength 4140, and the deeper hardening, higher-strength 4340. Also from this family are descriptions for the 300M, D-6a and D-6ac, 6150, and 8640 steels. The medium-alloy air-hardening family of ultrahigh-strength steels includes H11 modified and H13 steels. The high fracture toughness family of ultrahigh-strength steels includes HP-9-4-30 steel and AF1410 steel. The article explains the mechanical properties and the heat treatments of the medium-carbon low-alloy steels, medium-alloy air-hardening steels, and high fracture toughness steels.

Air hardening steel is a type of steel that has deep hardenability and can be hardened in large sections by air cooling. This article discusses the principles of heat treatment of air-hardening steel, and describes the recommended heat treating practices for air-hardening high-strength structural steels, namely, H11 Mod, H13 steel, 300M steel, D-6A and D-6AC, and AF1410 steel. It also provides information on recommended heat treating practices for air-hardening martensitic stainless steels.

Electrical discharge grinding (EDG) is much like electrical discharge machining except that the electrode (tool) is a rotating graphite wheel. This article commences with a schematic illustration of a setup for EDG wheels and discusses the control operation of the EDG setup. It tabulates typical applications and conditions for the EDG of stainless steels using 300 mm diameter wheels. The article describes the process characteristics of the EDG in terms of applications, surface finish, corner radius, and wheel wear. It concludes with a graphical illustration of the effect of heat in electrical discharge grinding on the surface hardness of various work metals.

Stress-corrosion cracking (SCC) occurs under service conditions, which can result, often without any prior warning, in catastrophic failure. Hydrogen embrittlement is distinguished from stress-corrosion cracking generally by the interactions of the specimens with applied currents. To determine the susceptibility of alloys to SCC and hydrogen embrittlement, several types of testing are available. This article describes the constant extension testing, constant load testing, constant strain-rate testing for smooth specimens and precracked or notched specimens of SCC. It provides information on the cantilever beam test, wedge-opening load test, contoured double-cantilever beam test, three-point and four-point bend tests, rising step-load test, disk-pressure test, slow strain-rate tensile test, and potentiostatic slow strain-rate tensile test for hydrogen embrittlement.

Machining serves as a more specialized supplement to the forging process, particularly in the formation of cavities and holes. This article provides information on the enclosures, cavities, and holes in hammer and press forgings. It provides a checklist that serves as a guide to the procedure for reviewing the design of cavities and holes to be incorporated in forgings. The article also describes forging designs in which cavities and holes are related to rib and web designs, punchout, piercing, extruding, and combinations of these processes.

This article describes the joint preparation, fit-up and design of various types of laser beam weld joints: butt joint, lap joint, flange joint, kissing weld, and wire joint. It explains the use of consumables for laser welding and highlights the special laser welding practices of steel, aluminum, and titanium engineering alloys. Laser weld quality and quality assessment are described with summaries of imperfections and how its operations contribute to providing repeatable and reliable laser welds. Relevant laser weld quality specifications are listed.

Laser-beam welding (LBW) uses a moving high-density coherent optical energy source, called laser, as the source of heat. This article discusses the advantages and limitations of LBW and tabulates energy consumption and efficiency of LBW relative to other selected welding processes. It provides information on the applications of microwelding with pulsed solid-state lasers. The article describes the modes of laser welding such as conduction-mode welding and deep-penetration-mode welding, as well as major independent process variables for laser welding, such as laser-beam power, laser-beam diameter, absorptivity, and traverse speed. It concludes with information on various hazards associated with LBW, including electrical hazards, eye hazards, and chemical hazards.

As cast iron parts are extensively applied, fracture events will eventually take place. Consequently, it becomes essential to carry out failure analyses to identify the cause of fracture and to provide corrective actions that allow safe operation. This article presents a description of the main fracture modes and their characteristic fractographic features. It discusses the four principal fracture modes: dimple rupture (or fracture), cleavage, fatigue, and intergranular fracture. The article provides information on special cases of environmentally assisted fracture. It concludes with a description of fractographic analyses for identifying the direction of propagation of a crack.

In terms of the design of a forging, flash is an excess or surplus of metal that is trimmed or otherwise removed after forging operations are completed. This article discusses flash components and the functions of flash. It describes a series of conventional and unconventional flash designs and design adjustments, covering several forging processes and configurations. The article concludes with information on the checklists for the convenience of both designers of forgings and designers of forging dies and contiguous flash.

Electron-beam welding (EBW) can produce deep, narrow, and almost parallel-sided welds with low total heat input and relatively narrow heat-affected zones in a wide variety of common and exotic metals. This article discusses the joint configurations and shrinkage stresses encountered in various joint designs for electron-beam welding, as well as special joints and welds including multiple-pass welds, tangent-tube welds, three-piece welds, and multiple-tier welds. It provides a comparison of medium vacuum EBW with high-vacuum EBW. Scanning is a method of checking the run-out between the beam spot and the joint to be welded. The article describes various scanning techniques for welding dissimilar metals and provides information on the application of electron-beam wire-feed process for repairs. It concludes with a discussion on EBW of heat-resistant alloys, refractory metals, aluminum alloys, titanium alloys, copper and copper alloys, magnesium alloys, and beryllium.

This article provides an overview of the different classification and designation systems of wrought carbon steel and alloy steel product forms with total alloying element contents not exceeding 5″. It lists the quality descriptors, chemical compositions, cast or heat composition ranges, and product analysis tolerances of carbon and alloy steels. The major designation systems discussed include the Society of Automotive Engineers (SAE)-American Iron and Steel Institute (AISI) designations, Unified Numbering System (UNS) designations, American Society for Testing and Materials (ASTM) designations, Aerospace Material Specification (AMS), and other international designations and specifications.

Liquid metal induced embrittlement (LMIE) is the reduction of the fracture resistance of a solid material during exposure to a liquid metal. This article discusses the mechanisms and occurrence condition of LMIE and describes the effects of metallurgical factors, such as grain size, temperature and strain rate, stress, inert carriers, and fatigue, on LMIE. It provides a detailed discussion on LMIE in ferrous and nonferrous metals and their alloys. In addition, the article highlights the ways of preventing embrittlement in metals and alloys.