Heat treatment is critical to make good molds in metal forming!（1）

The relationship between heat treatment process and metal forming sheet metal processing, deep drawing, metal stamping, stamping die and progressive stamping die is reflected in the fact that heat treatment is a key step to enhance the performance of metal materials, which, by adjusting the hardness, plasticity and toughness of the material, provides a suitable material state for the molding processes such as sheet metal processing, deep drawing and stamping, and at the same time ensures that the stamping die and progressive stamping die in a continuous high load operation Maintain stable performance and life, thus ensuring the quality and efficiency of molded products.

 

Carry out 1050 ~ 1100 ℃ heating quenching, oil quenching, can meet the requirements, but the general hot work mold is not required so high hardness, so high hardness performance will be very poor, not good, generally in the HRC46 ~ 50 performance is good, durable.

 

Question added: General molds are hit with oil stone before taking nitriding, nitriding back to the oil stone to wipe the layer of black white, and then polished is very troublesome, do not wipe the white to hit the mirror, the material has H13, there are many kinds of imports, if there is a potion can be washed white, then you can directly polish it.

(1) can use stainless steel pickling solution, or hydrochloric acid cleaning.

Sandblasting can also be treated. If you grind it on a grinder, it's expensive, and it's a lot of work, so it's possible to make the size not up to standard. If you can't get it off with hydrochloric acid, I'm guessing you're using a high chrome mold steel? Is it D2 or H13, the oxidized layer of high chrome mold steel is harder to wash off. Stainless steel pickling solution should work, available at abrasive stores or stainless steel stores.

(2) Don't you have a stainless steel pickling paste?

The oxidized layer is difficult to wash off with hydrochloric acid on H13, which is a relatively high chromium mold steel. There is another way, since the mold has been oil stone ground, the surface is just smoother. In fact, you can start by sanding with just a coarse oilstone, or with an abrasive belt, and then go to heat treat afterward. Come back and then sand with a fine oilstone. Sanding with a fiber wheel first will effectively remove the black skin, then grind and polish. Or sandblasting, with 800 mesh boron carbide to do a sandblasting try, should be able to remove the black skin, but also do not need to make too much effort to regrind.

 

Heat treatment plant equipment is very much, the furnace is probably a box furnace, pit-type furnace, box furnace with the most, a lot of heat treatment can be dealt with in this, such as annealing, normalizing and quenching of the heating process, tempering these common heat treatment. In fact, it is an electrically heated furnace, the furnace will first be heated to a predetermined temperature, and then the workpiece is thrown in, waiting for a period of time to a predetermined temperature, and then held for a period of time, and then take out, or in the furnace together with the cooling, the well furnace is generally used as carburizing treatment equipment, is a buried to the ground of the furnace, the workpiece is placed in the furnace, sealing, and then to the furnace inside the drops of some carbon-rich liquids, such as kerosene or methanol, and then at high temperatures these liquids decompose into carbon atoms to penetrate the surface of the workpiece.

    Quenching pool is the place of quenching, is a pool, there is a water solution or oil, is the box furnace out of the workpiece quenching cooling place, generally is thrown directly into, and then wait for a period of time to fish out. There are other devices, such as high-frequency machine, is a 50 Hz industrial frequency electricity into a 200K Hz current of ultra-high-power equipment, such as common 200 kilowatts of maximum power, and then use an internal cooling water through the copper pipe made of coils placed on the outside of the workpiece, the general dozens of millimeters of the workpiece, a few seconds of the kind of dozens of seconds when you see the surface of the workpiece becomes red, the surface temperature of the workpiece to a predetermined value, and then have the workpiece quenched. To a predetermined value of time, and then there is a water jacket rises up to spray quenching liquid to the surface of the workpiece, to complete the quenching process. These are the common ones.

 

Hardware mold on the best parts size, shape and heat treatment requirements, and you take the heat treatment process curve to tell, otherwise it is difficult to say. These two types of steel is a class, is a high-carbon, high-chromium Leistungen steel, itself has a tendency to cold cracking. Heat treatment process is also more complex.

   The following is some experience in the absence of the above information: Hardened at 950-1000C, oil-cooled, HRC>58. To obtain hot hardness and high wear resistance, the quenching temperature is increased to 1115-1130C, oil-cooled. Thin and thin can be air-cooled, and to minimize distortion, also salt-cooled at 400-450C. Do not temper at 300-375C, as this will reduce the toughness of the tool and cause temper brittleness, and temper immediately after hardening. For hardening above 1100C, temper 2-3 times at 520C. Please note that high quenching temperatures may tend to decarburize the tool. For this reason, a pre-heat treatment - spheroidal annealing - can be carried out before quenching.

 

Question added: workers accidentally put a raw piece without heat treatment and a batch of debugging after heat treatment of the workpiece mixed together, now how to distinguish them from each other, do not cut the workpiece to see the metallurgical, that will damage the product, the heat treatment process 30Cr by normalizing, and then quenching, and then tempering, the raw piece is Castings without heat treatment. Both have gone through the shot peening process color change can not be distinguished, and hardness are between 35-45, relying on hardness can not be distinguished. If you can not distinguish by hardness and heat treatment oxidation color. I suggest that you identify by knocking sound. Castings and quenched + tempered state workpiece metallurgical organization is different, there are differences in internal consumption, by gently knocking, may be able to distinguish.

 

More than the specified heating temperature, resulting in grain growth, the mechanical properties of the bad such as brittleness, toughness decline, easy deformation and cracking, etc., control the heating temperature can be avoided overcooking. Refers to the steel in the solid-liquid phase line of the temperature range of a temperature above the heating, austenite grain boundaries occurred in the chemical composition changes, local or whole grain boundaries appear melting phenomenon. At this time, the grain boundaries will be enriched with S, P and other compounds, resulting in a decrease in the bonding strength of the grain boundaries and a serious deterioration of mechanical properties. After overcooking steel can not be remedied by heat treatment or processing methods.

 

Produce causes:

1) The presence of severe reticulated carbide segregation in the mold material.

2) There are machining or cold plastic deformation stress in the mold.

3) Mold heat treatment operation is improper (heating or cooling too fast, quenching and cooling medium selection, cooling temperature is too low, cooling time is too long, etc.).

4) mold shape is complex, uneven thickness, with sharp corners and threaded holes, etc., so that the thermal stress and tissue stress is too large.

5) Mold quenching heating temperature is too high to produce overheating or overcooking.

6) Mold quenching tempering is not timely or tempering insulation time is not enough.

7) mold repair quenching and heating, without intermediate annealing and re-heating quenching.

8) mold heat treatment, improper grinding process.

9) mold heat treatment after electric discharge machining, there are high tensile stress and micro cracks in the hardened layer.

1)Strictly control the inherent quality of mold raw materials

2) Improve the forging and spheroidal annealing process, to eliminate the network, band, chain carbide, improve the uniformity of the spheroidal organization.

3) After machining or cold-plastic deformation of the mold should be de-stress annealed (>600 ℃) before heating and quenching.

4) For molds with complex shapes, asbestos should be used to plug the threaded holes, wrap the dangerous sections and thin walls, and use graded quenching or isothermal quenching.

5) Annealing or high-temperature tempering is required when the mold is returned for repair or refurbishment.

6) Moulds in the quenching and heating should be taken to preheat, cooling measures to take pre-cooling, and select the appropriate quenching medium.

7) Quenching heating temperature and time should be strictly controlled to prevent overheating and overburning of the mold.

8) The mold should be tempered in time after quenching, the holding time should be sufficient, high alloy complex mold should be tempered 2-3 times.

9) Select the correct grinding process and suitable grinding wheel.