Cold Work Die Steel Grades and Applications

Today, the commonly used cold work tool steel in China is still CrWMn low alloy tool steel and Cr12MoV, Cr12 high alloy tool steel and other steel materials. However, due to the serious segregation of carbides, especially when the size of the die is large, it is easy to reduce the directionality and toughness of the distortion. Now introduce some newly developed cold work die steels at home and abroad for the reference of cold heading fasteners .

• Low-alloy cold work die steel The main features of this steel are good processability, low quenching temperature, small heat treatment distortion, good toughness, and appropriate wear resistance. Adding chromium or manganese to the steel can improve the hardenability and allow the steel to retain a certain amount of retained austenite after quenching and tempering at low temperatures, reducing distortion; adding silicon or nickel can make the matrix toughening and tempering Resistance, at the same hardness, has higher strength and toughness than other similar steels. Adding molybdenum or vanadium can refine grains. Table 1 shows the chemical composition of the low alloy cold work mold. Table 1 shows the chemical composition of low-alloy cold work tools (W%)

Grade C
Cr
Mo
V
Si
Mn
Ni
W
GD
0.69
1.15
0.45
0.18
0.70
0.85
0.85
-
DS
0.59
1.15
0.25
0.20
0.65
0.88
0.88
0.50
D1
0.95
0.50
-
0.20
-
1.20
-
0.50
CrWMn
0.98
1.05
-
-
-
0.95
-
1.40


After quenching at 900 °C and tempering at 200 °C, GD steel (6CrMnNiMoVSi steel) still maintains an appropriate amount of retained austenite (about 15%), uniform and fine undissolved carbides, which helps to reduce distortion and improve the toughness of the steel. Moreover, the distortion of GD steel after heat treatment is less than that of CrWMn steel. It is used to make cold stamping molds (such as cutting scissors, etc.) that are easily chipped and fractured. It has a high service life, hardness of 60 to 61HRC, and impact value of 145J/cm 2 .
After tempering at 900 °C and tempering at 200 °C, DS steel has high toughness, hardness 59 ~ 60HRC, impact value 210J/cm 2 , and impact toughness is higher than 6CrW2Si tool steel.
• Base steel Base steel generally refers to steel whose composition is the same as that of the base body in the quenched structure of HSS. Some base steels developed in China, such as 65Cr4W3Mo2VNb (abbreviated 65Nb) steel, 65W8Cr4VTi (abbreviated LM1) steel, 65Cr5Mo3W2VTi (abbreviated LM2) steel.

Table 2 shows the chemical composition of the base steel.
The chemical composition of the base steel is shown in Table 2 (W%)
Grade C
Si
Cr
W
Mo
V
Nb
Other 65Nb
0.65
-
4.1
2.75
2.25
0.95
0.25
-
LM1
0.65
-
4.5
8
-
1
-
0.2Ti
LM2
0.65
1.0
4.9
2
3.1
1.2
-
0.2Ti


The main components of several matrix steels developed in China are equivalent to the matrix in the quenched structure of HSS, but the carbon content is slightly higher than that of the matrix to increase the amount of primary carbides and improve the wear resistance. In addition, a small amount of strong carbides are also added. The form element is tantalum or titanium to form relatively stable carbides that prevent grain growth during quenching and improve the steel's process performance.
The strength and toughness of the LM1 and Cr12MoV steels are compared with the former hardness of 62.5HRC and the latter of 61.5HRC, the former is 30J/cm2 for the unnotched specimen and the latter is only 5J/cm2. Base steel has a high toughness and is widely used in the production of cold extrusion, thick plate cold punching and cold heading molds. 65Nb steel can also be used for ferrous metal extrusion dies.
• High-toughness cold die steel To improve the toughness of the cold die steel and further increase the wear resistance of steel, China developed LD, ER5 and GM steel, etc., Japan's TCD, AOF11, DC53 steel, the United States' DIE steel , Sweden's ASSAB88 steel, Austria's K340, K360.
The chemical composition of these steels has the following characteristics: appropriately reduce the chromium content to improve the segregation of carbides, increase the content of tungsten, molybdenum, and vanadium to increase the ability of secondary hardening and improve the wear resistance. Most of these steels use higher quenching temperatures. (1140 to 1160 °C) and 1 to 3 times of high temperature tempering (520 to 560 °C) Compared with Cr12 cold working die steel, it has higher toughness and better wear resistance, and thus the produced mold has a higher life It is more suitable for the use of punch presses and multi-station cold heading machines.
The suitable quenching temperature of LD steel is 1100 to 1150 °C, the tempering temperature is 530 °C to 550 °C, and the hardness is 59 to 62HRC. The cold die, blanking die, and cold die are used instead of Cr12MoV steel. The service life of the die is significantly improved.
After quenching at 1120 °C and tempering at 580 °C for three times, ER steel has the best secondary hardening effect. The strength, toughness and resistance to impact wear are all superior to those of Cr12 steel and are suitable for the production of precision, heavy-duty and high-speed cold punching dies with a high service life.
GM steel has high secondary hardening capacity due to the proper proportion of alloying elements and carbon. After quenching at 540 °C for 1120 to 1140 °C for two times, the hardness can reach 64 to 66HRC, which ensures excellent wear resistance. GM steel production and making use of a mold with a multi-station progressive die punch, the service life ratio increased several times Cr12MoV steel, high-strength bolts for the production of rollers, rolled 12.9 40 ~ 42HRC bolt, increasing life expectancy than 10 Cr12MoV steel More than times. The GM steel can also be quenched at 1070 °C, tempered at 150 °C twice, low temperature quenching, low temperature tempering process, hardness 62 ~ 63HRC, especially suitable for the production of cold heading molds.