AWS WHC-4.02:2010

Carbon and Low Alloy Steels
Scope : This grouping of alloy steels, because of the combination of high strength and high toughness, is important to many engineering applications and thus is included in this volume of the Welding Handbook as a separate chapter. This chapter covers the weldability of certain selected steel alloys with compositions that include total alloy additions of more than about 10%. This chapter does not include stainless steels, chromium- molybdenum steels, 9%-nickel steels, such as ASTM A 353 and A 553, or tool steels.1, 2,3 Alloy additions are intended to improve the properties of steels. As a basic example, the tensile strength of plain carbon steel may be increased simply by raising the carbon content. However, this approach has several limitations. Principal limitations to alloy additions are that plain high-carbon steels have poor weldability and relatively shallow hardening during rapid cooling. Also, toughness and ductility are inadequate for many applications, and the range of mechanical properties usually is severely limited. Nevertheless, many high-strength carbon steels are used for structural applications in the quenched-and-tempered condition. Among the most important criteria for high-strength steels designed for critical applications is good fracture toughness at the service temperature. Another is that the steels have nearly uniform isotropic mechanical prop- erties. Relatively few commercial alloy steels meet such criteria and are often proprietary. The steels discussed in subsequent sections of this chapter are representative. Also included in this chapter are sections on the metallurgy of high-alloy precipitation-hardened steels (low carbon maraging steels and higher-carbon nickel-cobalt alloy steels), and austenitic manganese steels. A section on applications provides detailed descriptions of welding and fabrication procedures for several projects with high-integrity service requirements. A brief section on safe practices is presented, deferring to a comprehensive chapter on health and safety published in Volume 1 of the Welding Handbook and with references to national health and safety standards.