AWS C1.1M-C1.1:2012 pdf download.Recommended Practices for Resistance Welding
4.1.1.1 Low-Carbon Steels. Low-carbon steels contain less than 0.20% carbon and less than 0.50% manganese,with the remaining alloying elements totaling less than 1%. The maximum hardness attainable in carbon and lowalloy steels is dependent almost exclusively on the carbon content. In addition to this effect on maximum hardness, carbon has a relatively strong infuence on the depth or ease of hardening, otherwise known as hardenability. Manganese also combines with sulfur and reduces the tendency toward hot-cracking. Hot-cracking results from the low strength of the steel at high temperatures. The steel cannot accommodate the stresses which develop during cooling, and cracks form in the weld metal or in the heat-affected zone (HAZ).
Low-carbon steels have typical bulk electrical resistivities (i.e., the specific electrical resistivity of a given volume of metal) of 10- -20 μ9-cm [4 -8 u9-in], and have large plastic ranges. Both of these characteristics make low- carbon steel quite weldable using resistance welding processes. However, weld- and heat-affected zones in low-carbon steel welds with carbon levels greater than 0.13% may be susceptible to hardening due to rapid cooling during welding; therefore,the rapid cooling rates of resistance spot and seam welding are of concern for steels containing these levels of carbon. In this carbon range, precautions as described for medium and high-carbon steels may be required.
Several new designations of low -carbon steels have been incorporated into the nomenclature of the industry. These include bake-hardenable, dent-resistant, and interstitial-free (I-F) steels. Dent-resistant materials are defined as low-carbon steels that have higher resistance to plastic deformation than do the typical low-carbon steels. Dent-resistant steels have higher yield strength than typical steels. The yield strength increases during the paint bake cycle. The magnitude of this increase depends on the degree of deformation in the forming process. Deformation triggers the hardening effect;however, the increases in strength due to cold forming and the increases in strength due to heat treatment are not cumu-lative. This increase in strength due to heat treatment during the paint bake cycle is known as bake hardening.
Many of the new AHS steels exhibit this property, for example, the dual phase steels. IF steels are low-carbon steels that have less than 0.005% carbon with niobium (columbium) and titanium additions to improve formability. Welding of these materials is similar to most low-carbon steels, and similar welding schedules can be used.AWS C1.1M-C1.1 pdf download.