Views: 100 Author: EHI Technical Team Publish Time: 2026-06-22 Origin: Site
Cr12MoV (SKD11/D2) steel is a high-chromium low-distortion ledeburitic cold work die steel widely used worldwide. It is suitable for molds and wear-resistant parts that operate at room temperature under medium loads, high-volume production, and require high wear resistance and precision.
During production, two major challenges exist:
A large quantity of eutectic carbides form inside ledeburitic cold work die steel Cr12MoV (SKD11/D2). Conventional manufacturing processes fail to eliminate bulky blocky eutectic carbides or severe network carbides, resulting in low toughness, brittle cracking, and short service life of finished dies.
Due to its alloy composition, this ledeburitic cold work die steel exhibits low plasticity, high deformation resistance, poor thermal conductivity, and significant structural stress during cooling. Consequently, defects such as cracks readily emerge during forging.
Forged and hot-rolled Cr12MoV (SKD11/D2) cold work die steel is generally supplied in the annealed state. It may also be delivered after additional post-annealing processing including peeling, light drawing, grinding, and other finishing operations.
No visually observable cracks, laps, scabs, or inclusions shall be present on the surface of forged and hot-rolled Cr12MoV (SKD11/D2) cold work die steel.
The tonnage of the forging hammer shall be selected according to the dimensions and mass of the die blank. Each hammer tonnage corresponds to a specific blank weight, diameter, or side length.
The critical forging temperature range for Cr12MoV steel is an initial forging temperature of 1100–1150 °C and a finish forging temperature of 850–900 °C.
Insufficient heating penetration or excessive tensile deformation caused by low temperatures or short heating durations will induce internal cracks in forgings.
Excessively high heating temperatures lead to overheating or overburning of blanks, resulting in fragmentation and scrapping during forging.
Excessively long holding time triggers grain coarsening and severe surface decarburization.
The six-side forging method is adopted, a combined process of three-direction upsetting and drawing with a fixed forging ratio in each pass. This process breaks down eutectic carbides to achieve uniform or near-uniform distribution.
Single-direction drawing is an effective measure to fragment network carbides in practical production and is applicable to shaft-type workpieces. However, it introduces prominent anisotropy in finished parts.
After six-side forging (three upsetting passes paired with three drawing passes), carbides are distributed randomly and uniformly, forming an ideal microstructure that extends die service life.
Drawbacks of conventional spheroidizing annealing are as follows:
Carbide networks cannot be eliminated, and sharp-edged carbides remain intact.
Spheroidized carbides lack smooth spherical morphology with large variations in particle size.
Severe carbide segregation persists; eutectic carbides and dot-shaped carbides show almost no improvement.Molybdenum-bearing carbides only dissolve significantly into austenite above 950 °C, while vanadium carbides require heating above 1050 °C for substantial austenite dissolution.
The above microstructural defects directly impair the performance of subsequent final heat treatment (quenching + tempering), shortening die service life.
Conventional quenching and tempering procedures for Cr12MoV steel adopt low quenching temperatures, which retain microstructural defects originating from incomplete spheroidizing annealing. These processes cannot thoroughly eliminate network carbides, carbide segregation, eutectic carbides, and dot-shaped carbides, leading to short die service life and high production costs.
Immediately after finish forging, heat the workpiece to the initial forging temperature to fully dissolve all carbides and form uniform single-phase austenite. Rapidly cool the material to below the phase transformation temperature to suppress abnormal austenite grain growth. More importantly, this inhibits network precipitation and angular morphology of carbides, preventing fragmented carbides from reconnection. Follow this treatment with high-temperature tempering at 720–750 °C.
This composite process improves the internal quality of dies, shortens production cycles, and reduces energy consumption simultaneously.
Targeted adjustments and optimizations are applied to each manufacturing procedure based on the inherent microstructural characteristics of Cr12MoV steel. Three alternative optimized processes are introduced below:
Austenitize at 950–1000 °C, perform oil bath or salt bath quenching, then temper at 200–250 °C, achieving hardness of 58–62 HRC. Dies treated by this process deliver high hardness and excellent toughness but low compressive strength, making them unsuitable for cold extrusion dies.
Austenitize at 1100–1150 °C, conduct oil or salt bath quenching, followed by two tempering cycles at 500–520 °C, yielding hardness close to 60 HRC. Dies processed this way possess high hardness and compressive strength, suited for aluminum drawing dies and brass hot extrusion dies. However, poor toughness restricts their application to cold work dies.
Austenitize at 1020 °C, quench in oil or salt bath, then apply two tempering cycles at 400–420 °C to obtain hardness of 56–58 HRC. Workpieces treated by this process achieve optimal strength-toughness balance and high fracture resistance, making the process ideal for thread rolling dies and complex-edge cold stamping dies.
Austenitizing Cr12MoV steel at 1100–1150 °C dissolves nearly all carbides into austenite. Subsequent rapid cooling followed by immediate isothermal rapid spheroidization completely eliminates network carbides, bulky sharp-edged carbides, and coarse microstructure heredity. After final heat treatment, the grain size reaches Grade 10–12; carbide particles are refined and rounded, multiplying the impact toughness of the steel and drastically extending die service life.
Optimizing the non-uniformity of eutectic carbides is a critical technical breakthrough to fully exploit the performance potential of Cr12MoV steel. Integrating forging and heat treatment processes delivers dramatic improvements in workpiece internal quality while achieving remarkable energy savings and shorter production lead times. This combined technology merits extensive promotion and industrial application.
The core cause lies in the large volume of eutectic carbides inherent to the steel. Conventional forging, spheroidizing annealing, quenching and tempering processes cannot completely eliminate network-like, massive sharp-edged carbides and carbide segregation, resulting in insufficient toughness of the steel. In addition, this steel features poor plasticity, high deformation resistance and low thermal conductivity. Organizational stress easily develops during machining, which ultimately leads to brittle cracking of the mold and a drastic reduction in its service life.
The optimum forging method is six-side forging (three upsetting and three drawing), which enables uniform and disordered distribution of carbides and eliminates anisotropy. The critical forging temperatures are an initial forging temperature of 1100–1150 °C and a finishing forging temperature of 850–900 °C. Strict temperature control can effectively prevent defects such as forging cracking, coarse grains and surface decarburization of forgings.
