Carbide precipitation and dissolution behavior at various temperatures during heat treatment has been studied in STD11 cold working die steel through confocal scanning laser microscopy; dilatometry; and X-ray diffraction analysis. The equilibrium phase diagram and phase fractions with temperature were calculated using a FactSage program. Confocal laser microscopic observation revealed that ${alpha}$ to ${gamma}$ transformation temperature is near $800^{circ}C$; M7C3 carbides melt at $1245^{circ}C$; and the melting temperature of STD11 is near $1370^{circ}C$. XRD results indicated that the M23C6 carbides dissolve in the matrix if austenitized at over $1030^{circ}C$; while the M7C3 carbides remain up to $1200^{circ}C$ although their amount decreases. The calculated equilibrium phase diagram showed good agreement with experimental results on carbide dissolution and phase transformation temperatures.