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7 methods to improve the quenching&tempering process

1. Control of tempering treatment
After the mold parts are taken out from the coolant, they should not stay in the air for a long time, but should be put into the tempering furnace in time for tempering treatment. When tempering, low temperature temper brittleness and high temperature temper brittleness should be avoided. In order to eliminate the internal stress, reduce the deformation and avoid the tendency of cracking, several tempering treatments are adopted after quenching for some die parts with precision requirements.

2. Protection of quenched parts
Quenching and tempering treatment is an important link that affects the deformation or cracking of stamping die parts during heat treatment. Effective protective measures should be taken for the parts that are easy to deform or crack, such as punch and die, so as to make the shape and section of the parts symmetrical and the internal stress balanced. The common protection methods are as follows: A. packing method; B. filling method; C. blocking method.

3. Determination of heating temperature
If the quenching temperature is too high, the austenite grains will be coarse, oxidation and decarburization will occur, and the tendency of deformation and cracking will increase. Within the specified heating temperature range, if the quenching heating temperature is too low, the inner hole of the part will shrink and the diameter of the hole will become smaller. Therefore, the upper limit of heating temperature should be selected; for alloy steel, if the heating temperature is too high, the inner hole will expand and the pore size will become larger, so the lower limit of heating temperature should be selected.

4. Improvement of heating mode
For some small punch dies or slender cylindrical parts (such as small punches), they can be preheated to 520-580 ℃ in advance, and then put into a medium temperature salt bath furnace to heat up to the quenching temperature. Compared with the direct use of electric furnace or reverberatory furnace to heat and quench, the deformation of the parts is obviously reduced, and the cracking tendency can be controlled. Especially for high alloy steel die parts, the correct heating method is: preheat first (530-560 ℃), and then rise to quenching temperature. During the heating process, the time of high temperature should be shortened as far as possible to reduce the quenching deformation and avoid the production of small cracks.

5. Selection of coolant
For alloy steel, isothermal quenching or step quenching in hot bath of potassium nitrate and sodium nitrite can be used to reduce quenching deformation. This method is especially suitable for stamping dies with complex shape and precise size. The austempering time of some porous die parts (such as porous die) should not be too long, otherwise the hole diameter or hole distance will become larger. Vacuum gas quenching can also be used. When the cooling effect of gas quenching is poor, professional vacuum quenching oil is recommended.

6. Quenching treatment before WEDM
For some stamping die parts processed by WEDM, the hierarchical quenching and multiple tempering (or high temperature tempering) heat treatment process should be adopted before WEDM to improve the hardenability of parts and make the internal stress distribution tend to be uniform and in a small internal stress state. The smaller the internal stress is, the smaller the tendency of deformation and cracking is.

7. Optimization of cooling mode
When the parts are taken out from the heating furnace and put into the coolant, they should be put into the air for proper precooling, and then put into the coolant for quenching, which is one of the effective methods to reduce the quenching deformation and prevent the cracking tendency of parts. After putting the coolant into the die parts, they should be rotated properly, and the rotation direction should be changed, which is conducive to maintaining a uniform cooling rate of the parts, and can significantly reduce the deformation and prevent the tendency of cracking.

The consequences of buying inferior Cr12MoV

Cr12MoV tool steel has high hardenability. The cross section is 300 ~ 400mm. It can harden completely. It can keep good hardness and wear resistance at 300 ~ 400 ℃.

Cr12MoV can be used to make various moulds and tools with large cross section, complex shape and bearing large impact load. It has the characteristics of wear resistance, hardenability, micro deformation, high thermal stability and high bending strength. It is second only to high speed steel. Cr12MoV is an important material for die cold heading. The consumption of cold working die steel(https://otaialloysteel.com/products/tool-steel/)ranks first.

In fact, some unreliable suppliers may, regardless of the interest of the customers, cheat customers with inferior products. These dishonest actions not only disrupt the market. At the same time, it also has a serious impact on customers.

The consequences for end users who purchase these crude Cr12MoV cold work tool steels are as follows:
1) The microstructure of inferior Cr12MoV die steel is seriously segregated. Because of the poor processing performance, drilling and tapping difficulties are often encountered.
2) The deformation of heat treatment is large and the risk of cracking and bending is high. It can’t guarantee the stability of the mold size, affect the appearance of the mold and even scrap.
3) There are many impurities in Cr12MoV die steel after scrap renovation. It makes the mold produce poor red hardness at high temperature. The hardness of the die decreases quickly and the knife edge is easy to wear.
4) The purity of die steel is poor and there are many non-metallic inclusions. The impact toughness of the die is poor, and the knife edge is easy to collapse and fall.

1.7147 carburized steel

1.7147 material is carburized steel (case hardening steel) with high strength and toughness and good hardenability. The quenching deformation is small, the low temperature toughness and the machinability are good, but the welding performance is low. It’s generally used after carburizing quenching or quenching and tempering.

1.7147 material equivalent steel grades:

1.7147 mechanical properties:

Yield R_p0.2 (MPa):764 (≥)

Tensile R_m (MPa):464 (≥)

Impact KV/Ku (J):43

Elongation A (%):43

Reduction Z (%):22

3 KINDS TOOL STEEL

Die steel can be roughly divided into cold work tool (die) steel, hot work tool (die) steel and plastic mould (die) steel, which are used for forging, stamping, cutting and die casting. Due to the different uses and complex working conditions of various dies, the die/tool steel should have high hardness, strength, wear resistance, sufficient toughness, high hardenability, hardenability and other technological properties according to the working conditions of the die. Due to different uses and complex working conditions, the performance requirements of die steel are also different.

1.1 Cold working tool (die) steel includes cold stamping die, drawing die, drawing die, embossing die, rolling die, rolling plate, cold heading die and cold extrusion die. According to the working conditions of the tools, the cold working dies should have high hardness, strength, wear resistance, enough toughness, high hardenability, hardenability and other technological properties. The alloy tool steel used for this kind of purpose generally belongs to high carbon alloy steel, and the carbon content is more than 0.80%. Chromium is an important alloy element of this kind of steel, and its mass fraction is usually not more than 5%. However, for some die steels with high wear resistance and small deformation after quenching, the highest chromium content can reach 13%, and in order to form a large number of carbides, the carbon content in the steel is also very high, up to 2.0% ~ 2.3%. The carbon content of cold working die steel is high, and most of its microstructure belongs to hypereutectoid steel or ledeburite steel. The commonly used steels are high carbon low alloy steel, high carbon high chromium steel, chromium molybdenum steel, medium carbon chromium tungsten plutonium steel, etc.

1.2 Hot work tool (die) steel is divided into hammer forging, die forging, extrusion and die casting, including hot forging die, press forging die, stamping die, hot extrusion die and metal die casting die. In addition to the huge mechanical stress, the hot deformation die has to bear repeated heating and cooling, which causes great thermal stress. In addition to high hardness, strength, red hardness, wear resistance and toughness, hot work die steel should also have good high temperature strength, thermal fatigue stability, thermal conductivity and corrosion resistance. In addition, high hardenability is required to ensure consistent mechanical properties of the whole section. For die casting die steel, the surface layer should not produce cracks after repeated heating and cooling, as well as withstand the impact and erosion of liquid metal flow. This kind of steel generally belongs to medium carbon alloy steel, with carbon content of 0.30% ~ 0.60%, which belongs to hypoeutectoid steel. Some steels become eutectoid or hypereutectoid steel due to adding more alloy elements (such as tungsten, molybdenum, vanadium, etc.). The commonly used steels are chromium manganese steel, chromium nickel steel, chromium tungsten steel, etc.

1.3 Plastic molud steel includes thermoplastic mold and thermosetting plastic mold. The steel for plastic mould is required to have certain strength, hardness, wear resistance, thermal stability and corrosion resistance. In addition, good processability is also required, such as smaller heat treatment, better processability, corrosion resistance, good grinding and polishing performance, good repair welding performance, high roughness, good thermal conductivity and stable size and shape under working conditions. In general, hot work die steel can be used for injection molding or extrusion molding, and cold work die steel can be used for thermoset forming and high wear resistance and high strength die.

The steel grades of tool steel

2.1 Cold work tool steel
High carbon low alloy cold working die steel
9SiCr, 9CrWMn, CrWMn, Cr2, 9Cr2Mo
Wear resistant cold working die steel
Cr4W2MoV, Cr5Mo1V, Cr6WV, Cr12, Cr12MoV, Cr12W
Impact resistant cold working die steel
4CrW2Si, 5CrW2Si, 6CrW2Si
Carbon tool steel for cold working die
T7, T8, T9, T10, T11, T12
High speed steel for cold working die
W18Cr4V
Non magnetic die steel
2.2 Hot work tool steel
Low heat resistance hot working die steel
5CrMnMo,5CrNiMo
Medium heat resistant hot working die steel
8Cr3
Hot working die steel with high heat resistance
3Cr2W8V
2.3 Plastic mould steel
Carbon plastic die steel
SM45,SM50,SM55
Pre hardening plastic die steel
3Cr2Mo,40Cr,42CrMo、
Carburized plastic die steel
20Cr,12CrNi3A
Age hardening plastic die steel

Corrosion resistant plastic die steel
2Cr13, 4Cr13, 9Cr18, 9Cr18Mo, cr14mo4v, 1Cr17Ni2 in the steel plate (plate), there are many materials are included in the die steel series: 45 (45), P20, S45C, S50C and so on.

100CrMo7 tool steels

The 100CrMo7 is chromium high-purity steels with high hardness, equivalent to tool steels, and with significant resistance to fatigue stress.100CrMo7 material is a much better alternative and the equivalent of the 100Cr6 material. Molybdenum-containing products have better hardening capacity and can be used with much larger cross-sections compared to the 100Cr6 grade.

100CrMo7 Steel equivalent standards:

100CrMo7 steel mechanical properties:
Hardness in spheroidized annealing condition +AC: < 217 HB

Hardness in spheroidized annealing condition after drawing +AC+C: < 251 HB

Hardness of tubes and sleeves <321 HB

Density ρ 7,79 g/cm3

1.3537 bearing steel

1.3537 steel is bearing steel. Small amount of Chromium and trace amounts of Molybdenum provides for some carbide formation, and it can hold decent polished edge.It has characteristics similar to 100Cr6 steel(1.3537 vs 100Cr6). The addition of molybdenum guarantees toughness for diameters up to 200mm.it has good wear resistance, with good non-deformability.

1.3537 Steel equivalent standards:

1.3537 steel  mechanical properties:
Hardness in spheroidized annealing condition +AC: < 217 HB
Hardness in spheroidized annealing condition after drawing +AC+C: < 251 HB
Hardness of tubes and sleeves <321 HB
Density ρ 7,79 g/cm3

1.3537 steel Application

1.3537 works better  for small to medium knives, after appropriate heat treatment might do well in a larger blade. It’s suitable for the construction of bearings,cylinders, small rolling mills, knives, etc.

1.7765 alloy carbon steel

DIN  1.7765 (2008) 1.7765 belongs to tool steel, alloy carbon steel, Pipe steel for machine weapons.

1.7765 Steel equivalent standards:

1.7765 steel Mechanical Properties:

Yield R_p0.2 (MPa):342 (≥)

Tensile R_m (MPa):159 (≥)

Impact KV/Ku (J):24

Elongation A (%):32

Reduction Z (%):11

23MnNiMoCr54 steel

23MnNiMoCr54 steel is based on low carbon steel, by adding Mn, Ni, Mo, Cr, Al and other alloy elements, through the solid solution strengthening, grain boundary strengthening and second phase particle strengthening of these elements, to improve the strength, plasticity and toughness of the steel, at the same time by controlling the harmful elements s, P in the steel to improve the fatigue life of the chain.

23MnNiMoCr54 steel Mechanical Properties:

Tensile strength (n / mm2): ≥ 1180
Yield strength (n / mm2): ≥ 980
Elongation after fracture (%): ≥ 10
Reduction of area (%): ≥ 50
Impact absorption energy (J) ≥ 40

1.6523 case hardening steel

1.6523 steel  is a low alloy nickel, chromium, molybdenum case hardening steel,1.6523 alloy steel  has good external and internal strength, so there with high wear-resistant. As a carburized steel, it is usually used to make many medium-strength tools.

1.6523 Steel equivalent standards:

1.6523 steel Mechanical Properties:

1.7131 carburized steel

EN 1.7131 steel (16MnCr5 material) is an European standard carburized steel (case hardening steel) with good hardenability and machinability. For larger cross-section parts, high surface hardness and wear resistance can be obtained after heat treatment, and low-temperature impact toughness is also high.

1.7131 steel – Equivalent Materials:

1.7131 steel Mechanical Properties:

Yield Strength Rp0.2 (MPa):≥461
Tensile Strength Rm (MPa):882
Impact KV/Ku (J):21
Elongation A (%):24
Reduction Z (%):41
Brinell hardness (HBW):413

655M13 case hardening steel

655M13 steel is a nickel-chromium alloy case-hardening steel that is specified for heavy duty highly-stressed applications. And it is  is suitable for deep hardening to develop a tough core.When carburised and hardened core strengths of 850 – 1230 N/mm² are attainable.Chromium increases hardenability whilst the nickel content increases toughness and resistance.

BS 655M13 – Equivalent Materials:

655M13 Mechanical Properties:

Yield Strength:540 Mpa

Tensile Strength:700/770 Mpa

Elongation:25%

Hardness:255 HB Max

655M13 case-hardening steel Application 

General applications include all industry sectors for applications requiring high surface wear resistance, high core
strength & impact properties. Typical uses include Gears, King Pins, Sprockets, Shafts etc

46Mn7 alloy structural steel

46Mn7 is a kind of moderate strength alloy structural steel, as a carbon quenched and tempered steel, its strength, abrasion resistance and hardenability are high. After quenching and has good mechanical properties, machinability is still good.

46Mn7 equivalent steel grades:

46Mn7 Mechanical Properties:

Tensile strength σb (MPa): ≥885

Yield strength σs (MPa): ≥735

Elongation δ5 (%): ≥10

Impact energy Akv (J): ≥47