Both the tungsten and silicon types of shock-resisting tool steel resist softening during tempering to a greater degree than carbon tool steels. Secondary hardening does not occur in these steels, except to a minimal degree in some high-W or high-Mo compositions (e.g., S5 and S7). The effect of tempering temperature on the hardness of various types and compositions of S steels is shown in Fig. 6.

Tools made of shock-resisting steel should be tempered immediately after quenching, or cracking is likely, especially if they are quenched in water or brine. Ideally, quenched tools should reach 50 to 70 °C (120 to 160 °F) before tempering begins. Some tool records indicate that double tempering is beneficial for S steels. It is especially important where higher toughness is required, for large parts (>50 mm, or 2 in.), and for the higher-alloyed grades (e.g., S5 or S7).

Surface treatments such as carburizing and carbonitriding are often applied to S1 steel. Types S4 and S5 do not take an effective carburized case.

For more information, click on the link below (subscription required). Then scroll to Figure 6.

Rafael Agnelli Mesquita; Reinhold Schneider; Cristiane Sales Gonçalves, Heat Treating of Cold-Work Tool Steels — Low- and Un-Alloyed Water and Oil Hardening Steels, ASM International, 2014. https://doi.org/10.31399/asm.hb.v04d.a0005972