JPH0116902B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a cold-work mold steel that has excellent wear resistance, toughness, machinability, and weldability as well as excellent frame hardening properties. (Prior Art) Recently, as the demand for sheet metal press molds for automobiles, molds for home appliance parts, etc. has increased, frame hardening, which is a relatively easily available mold heat treatment method, has become widely used. In particular, it is a very effective method in terms of reducing heat treatment costs because it is possible to easily obtain a hardened layer only in the necessary parts for punching dies, bending dies, drawing dies, etc. Furthermore, in order to reduce the total cost, the molds are increasingly used in a cast state. (Problems to be Solved by the Invention) However, conventional cold-work mold steels that can be subjected to frame hardening have had various problems.
For example, steel grades such as SK2 to 5, SKS2, and 3 have poor hardenability, so they require water cooling or oil cooling after heating, and the temperature range in which sufficient quenching hardness can be obtained is narrow, resulting in variations in hardness. big. Also, 1C-3Cr series,
Steel types such as the 1C-8Cr series have sufficient hardenability, but they tend to crack when repairing molds by welding and have poor machinability. (Means and effects for solving the problems) The present invention improves the drawbacks of the conventional cold-forming steel, and has the advantage of being easily hardened by air cooling after heating, having a deep hardening depth, and requiring manual labor. It is a steel for cold working molds that exhibits improved frame hardening properties, such as being insensitive to variations in frame heating temperature, as well as excellent performance in wear resistance, toughness, machinability, weldability, etc. That is, the steel of the present invention has (1) C: more than 0.60 and up to 0.85% by weight;
Si: 0.80-1.50%, Mn: 0.80-1.50%, Cr: 2.0
exceeding 3.50%, V: 0.05~0.50%, Nb: 0.02~
A cold-forming steel with excellent frame hardening properties, containing 0.30% Fe with the remainder essentially consisting of Fe. (2) C: more than 0.60 and up to 0.85% by weight,
Si: 0.80-1.50%, Mn: 0.80-1.50%, Cr2.0 and above 3.50%, V: 0.05-0.50%, Nb: 0.02-
0.30%, Ti: 0.30% or less, Ta: 0.30% or less,
Cold work die steel with excellent frame hardening properties, containing one or more Zr at 0.30% or less, with the remainder essentially consisting of Fe. The steel of the present invention has good frame hardening properties (surface hardness,
and hardenability), reduce the amount of C, and suppress the deterioration of toughness as much as possible due to the component composition that does not show the appearance of giant primary carbides, and has sufficient crack resistance and chipping resistance even when used as a casting mold. It has
Furthermore, the addition of Nb prevents crystal grains from becoming coarse due to overheating during frame hardening, and the steel has a stable hardened structure, hardness, and toughness. Next, the reason for limiting the components of the material of the present invention will be explained in detail. C: More than 0.60 and up to 0.85% After heating the flame and air cooling, it is necessary to exceed at least 0.60 in order to obtain sufficient hardness. However, if it exceeds 0.85%, the toughness of the hardened part will deteriorate significantly and the formation of net-like primary carbides will become noticeable during casting, so the upper limit was set at 0.85%. A particularly desirable range is 0.65 to 0.75% at which no primary carbide is generated. Si: 0.80~1.50% At least 0.80% to increase hardenability and wear resistance of the matrix by combined addition with Mn
Although more than 1.5% is necessary, machinability deteriorates when it exceeds 1.50%, so the upper limit was set at 1.5%. Mn: 0.80-1.50% Although 0.8% or more is required to improve hardenability
If it exceeds 1.50%, the crystal grains will easily become coarse due to overheating, which will not only impair toughness but also deteriorate machinability, so the upper limit was set at 1.50%. A particularly desirable range is 0.80~
It is 1.20%. Cr: more than 2.0 and 3.50% At least 2.0% is required in the above ranges of C, Si, and Mn in order to improve hardenability, form carbides, and contribute to improving wear resistance. However, if it exceeds 3.50%, the formation of net-like primary carbides becomes noticeable and the toughness deteriorates, so the upper limit was set at 3.50%. A particularly desirable range is more than 2.0% and up to 3.0%. V: 0.05 to 0.5% At least 0.05% is necessary for grain refinement, but even if 0.5% or more is added, the effect will not improve much, so the upper limit was set at 0.5% in consideration of economic aspects. Nb: 0.02-0.30% Along with V, it is a major element in the steel of the present invention, and is required at least 0.02% in order to refine crystal grains, prevent coarsening of crystal grains at high temperatures, and improve toughness. However, if 0.30% or more of NbC is added, coarse NbC will be generated and the high toughness, which is a characteristic of the steel of the present invention, will be impaired, so the upper limit was set at 0.30%.
A particularly desirable range is 0.02-0.2%. Ti: 0.30% or less, Ta: 0.30% or less, Zr: 0.30% or less These elements form carbides and contribute to preventing grain coarsening, but adding any of them in amounts of 0.3% or more will actually reduce toughness. Therefore, the upper limit for each
It was set at 0.3%. (Example) Next, the present invention will be described in detail based on an example. Example 1 An alloy having the composition shown in Table 1 was melted in an electric furnace and then cast into a 2-ton steel ingot, and a forged material (300W x 55H x L) was obtained through the blooming, forging, and annealing steps. .

【table】

[Table] (1) Frame hardening property The above 300W x 55H x L forged material is 70W x 50H.
A sample of 180L was processed and flame hardened in the longitudinal direction, and the surface hardness and hardening depth of the hardened part were measured and are shown in Table 2. According to Table 2, the steel of the present invention has small variations in quenching hardness, and it can be seen that not only can stable hardness of HRC60 or higher be obtained, but also that the hardening depth obtained at Hv600 is deep.

[Table] (2) Wear resistance, toughness Wear test pieces (20W
x 10T x 5L), Charpy specimen (10 x 10 x
55L) were cut out, and after frame hardening the worn and notched surfaces, the wear resistance and toughness were tested, and the results are shown in Table 3. According to Table 3, the steel of the present invention has wear resistance equivalent to that of the comparative steel, and the impact value is about twice as high.

【table】

[Table] Example 2 An alloy having the composition shown in Table 4 was melted in an electric furnace and a block of 75W x 55H x 200L was cast in a sand mold, and the frame hardening properties, wear resistance, toughness, machinability, and Weldability was investigated. (1) Frame hardening properties The above 75W x 55H x 200L casting block
After processing into a test piece of 70W x 50H x 180L, the corners were aligned in the longitudinal direction and frame hardening was performed to measure the hardness and hardening depth, and the results are shown in Table 5. According to Table 5, the steel of the present invention has small variations in quenching hardness, not only can stable hardness of HRC60 or higher be obtained, but also the hardening depth obtained at Hv600 is deep, and although it has a low alloy, it ranks No. 1 in comparative materials.
It is possible to obtain a hardening depth equivalent to or greater than that of (8Cr type). Furthermore, in order to investigate the resistance to overheating during quenching, Figure 1 shows the relationship between the flame heating temperature (quenching temperature) and the sieved fracture surface frequency number. It can be seen that the crystal grains hardly become coarse even when overheated.

【table】

[Table] (2) Wear resistance, toughness 75W x 50H with frame hardening
Abrasion test pieces (20W x 10T x 5L) and Charpey test pieces (10 x 10 x 55L) were cut from near the surface of a 180L cast block, and the results of wear resistance and toughness tests are shown in Table 6. show. According to Table 6, the wear resistance of the steel of the present invention is almost the same as that of the comparative steel, but the impact value is two to three times higher. Furthermore, even when compared with the impact value of Example 1, it exhibits a remarkable property in that the degree of deterioration in toughness is extremely small despite being a cast metal.

【table】

[Table] (3) Machinability Table 7 shows the above cast block 70W×50H×
The machinability of the 180L frame before hardening was investigated using a drill hole test.
As is clear from Table 7, the machinability of the steel of the present invention shows a tool life that is 2 to 3 times longer than that of the comparative steel.

[Table] (4) Weldability A welding test piece (50W x 30T x 150L) was taken from the cast block (75W x 55H x 200L) and 1-layer and 3-layer overlay welding was performed as shown in Note 6 of Table 8. The presence or absence of weld cracking was investigated under various conditions, and the results are shown in Table 8. In addition, work was discontinued in cases where cracks occurred during welding.

【table】

[Table] As is clear from the presence or absence of weld cracking in Table 8, the steel of the present invention exhibits very good weldability. This clearly shows that when the mold is manufactured by casting, casting defects can be easily repaired by overlaying, making it suitable as a casting mold material. (Effects of the Invention) As explained above, the steel of the present invention is easily hardened by air cooling during frame hardening of forged products, cast products, etc., has little variation in hardness, and has a deep hardening depth. Furthermore, since it exhibits excellent wear resistance, toughness, machinability, and overlay weldability, it is a suitable material that exhibits a long life when used for cold forming molds, particularly punching dies, bending dies, drawing dies, etc. It goes without saying that the steel of the present invention can be used in a range of applications for conventional cold tool materials, such as shear blades and roll materials. As described above, the industrial contribution of the steel of the present invention is extremely large.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between quenching temperature and fracture surface grain size in a casting mold.

Claims (1)

[Claims] 1. C: more than 0.60 and up to 0.85% by weight,
Si: 0.80-1.50%, Mn: 0.80-1.50%, Cr: over 2.0 up to 3.50%, V: 0.05-0.50%, Nb: 0.02-
A cold-forming steel with excellent frame hardening properties, containing 0.30% Fe with the remainder essentially consisting of Fe. 2. C: more than 0.60 and up to 0.85% by weight,
Si: 0.80-1.50%, Mn: 0.80-1.50%, Cr: over 2.0 up to 3.50%, V: 0.05-0.50%, Nb: 0.02-
0.30%, Ti: 0.30% or less, Ta: 0.30% or less,
Zr: Contains one or more of 0.30% or less,
A cold-forming steel with excellent frame hardening properties, characterized in that the remainder essentially consists of Fe.