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.

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.

This article presents a detailed account on the process flow, composition, alternative sources, and the advancement of ironmaking, steelmaking and secondary steelmaking practices. Some steels, such as bearing steels, heat-resistant steels, ultrahigh strength missile and aircraft steels, and rotor steels have higher quality requirements and tighter composition control than plain carbon or ordinary low-alloy steels. The production of special-quality steels requires vacuum-based induction or electric remelting and refining capabilities. The article explores the types and characteristics of various steel manufacturing processes, such as ingot casting, continuous casting, and hot rolling. It provides an outline of specialized processing routes of producing ultralow plain carbon steels, interstitial-free steels, high strength low-alloy steels, ultrahigh strength steels, stainless steels, and cold-rolled products, and briefly explains the analytical techniques for liquid steels.

This article describes the heat treating (stress relieving, normalizing, annealing, quenching, tempering, martempering, austempering, and age hardening) of different types of steels, including ultrahigh-strength steels, maraging steels, and powder metallurgy steels. Tabulating the recommended temperatures for normalizing and austenitizing, it provides information on mechanism, cooling media, principal variables, process procedures, and applications of heat treating. In addition, the article gives a short note on the cold and cryogenic treatment of steel.

This article discusses factors involved in selecting welding processes and consumables and establishing procedures and practices for the arc welding of low-alloy steels. It provides information on welding consumables in terms of filler metals and fluxes and shielding gases. The article describes the various categories of low-alloy steels, such as high-strength low-alloy (HSLA) structural steels, high-strength low-alloy quenched and tempered(HSLA Q&T) structural steels, low-alloy steels for pressure vessels and piping, medium-carbon heat-treatable (quenched and tempered) low-alloy (HTLA) steels, ultrahigh-strength low-alloy steels, and low-alloy tool and die steels. It concludes with a discussion on repair practices for tools and dies.

Hardenable steels with high-alloy content includes a family of nickel-cobalt steels with high strength and high toughness. This article describes various heat treatments, namely, normalizing, annealing, hardening, tempering, stress relieving, overaging, quenching, refrigeration, and straightening treatment, applied to HP9-4-20, HP9-4-25, HP9-4-30, and HP9-4-45 steels. These steels have high fracture toughness when heat treated to very high strength levels. The article also describes heat treatments applied to other alloys such as AF 1410, AerMet 100, AerMet 310, and AerMet 340, which provide a good combination of high strength and toughness that make them attractive for aerospace application. It also presents tables that provide information on the effect of aging temperatures and heat treatment on mechanical properties and impact energy of these 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.

This article is a comprehensive collection of tables that list the values for hardness of plastics, rubber, elastomers, and metals. The tables also list the tensile yield strength and tensile modulus of metals and plastics at room temperature. A comparison of various engineering materials, on the basis of tensile strength, is also provided.