CN111004963A

CN111004963A - Die steel for die casting and processing method thereof

Info

Publication number: CN111004963A
Application number: CN201911409061.2A
Authority: CN
Inventors: 雷佳乐; 朱裕华
Original assignee: Chongqing Youte Mould Co ltd
Current assignee: Chongqing Youte Mould Co ltd
Priority date: 2019-12-31
Filing date: 2019-12-31
Publication date: 2020-04-14

Abstract

The invention provides die steel for die casting, which comprises the following components in percentage by mass: c: 0.36 to 0.43%, Si: 0.80 to 1.20%, Mn: 0.20 to 0.50%, Cr: 4.75 to 5.50%, Mo: 1.30% to 1.75%, V: 0.85% to 1.20%, Ni: less than or equal to 0.25 percent, S: less than or equal to 0.005 percent, P: less than or equal to 0.025 percent, Cu: less than or equal to 0.15 percent, and the balance of iron and inevitable impurities, wherein the metal structure of the alloy is subjected to a microstructure banded structure grade of SA 1-SA 3 (graded according to an SEP1614 standard evaluation picture) under a 50-time test, and the microstructure spheroidized structure grade of the alloy is subjected to a microstructure spheroidized structure grade of AS 1-AS 9 (sampled according to an NADCA #207-2008 hot work die steel limit detection evaluation standard). It has the following advantages: 1) after homogenization treatment and multidirectional forging treatment are used, the alloy has excellent cutting processability and polishing performance; 2) the material has high toughness and high plasticity through multidirectional forging and superfine treatment; the die-casting die steel material provided by the invention is particularly suitable for small and medium-sized die-casting dies, and can greatly reduce the cost for enterprises.

Description

Die steel for die casting and processing method thereof

Technical Field

The invention relates to the technical field of hot work die material processing and preparation, in particular to die steel for die casting and a processing method thereof.

Background

The die-casting die steel is a new hot-working die steel improved along with the rise of the die-casting industry. The die-casting die has severe working conditions, so that the problem that early failure is solved urgently by die-casting and heat treatment enterprises is solved. Taking the most common aluminum-magnesium alloy as an example, the temperature of molten metal is between 650-700 ℃, the surface temperature of the die reaches about 600 ℃ when the molten metal is brought into the temperature, and the surface of the die cavity of the die is equivalently tempered for multiple times in the production process; in the die casting process, the speed of molten metal entering an inner sprue is 40-180m/s, the surface of the die is repeatedly washed, and when initial thermal cracks appear on the surface, the cracks can be rapidly expanded; in the mold filling process, the pressure born by the mold is between 20 and 120MP, and the contact part of the mold and the molten metal is in a state of combined action of thermal stress and mechanical stress.

Therefore, the die casting die steel has the following properties: 1) the thermal stability refers to that the material can still maintain the structure and the performance under the high-temperature working condition, and has the capability of resisting softening, which is important for the die material with the metal liquid temperature higher than the tempering temperature of the die. 2) Hardness, because the surface of the die bears the high-speed scouring of molten metal in the die-casting process, the die material is required to have better wear resistance, and the hardness of the material needs to be ensured. 3) Toughness, in addition to the severe conditions of high temperature and high speed, the die-casting die also needs to cope with the die-clamping pressure, the die-filling pressure, the thermal stress of the cold and hot cycles, etc. applied by the die-casting machine.

When manufacturing die casting die steel meeting the performance requirements, the price necessarily brought by high performance is relatively high, so that the die casting die steel is not suitable for production of small and medium-sized enterprises in terms of cost performance.

Disclosure of Invention

The invention provides die steel for die casting and a processing method thereof aiming at the defects in the prior art, aiming at solving the problems that the current die steel for die casting is too high in cost and low in cost performance and is not suitable for small and medium-sized die casting dies, extrusion dies and hot forging dies.

In order to achieve the purpose, the invention adopts the following technical scheme:

a die steel for die casting, comprising by mass%:

c: 0.36 to 0.43 percent,

si: 0.80% to 1.20%,

mn: 0.20 to 0.50 percent of the total weight of the composition,

cr: 4.75 to 5.50 percent of the total weight of the composition,

mo: 1.30 to 1.75 percent of the total weight of the composition,

v: 0.85% to 1.20%,

Ni：≤0.25％，

S：≤0.005％，

P：≤0.025％，

Cu：≤0.15％，

the balance of iron and inevitable impurities,

the metal structure of the alloy is in a microstructure banded structure grade of SA 1-SA 3 (graded according to SEP1614 standard evaluation picture) under 50 times of test, and in a microstructure spheroidized structure grade of AS 1-AS 9 (sampled according to NADCA #207-2008 hot work die steel limit detection evaluation standard) under 500 times of test.

Further, the die steel for die casting has a grain size of 7 or more (according to ASTM112 Metal average grain size measurement method).

Further, the microstructures had band tissue grades of SB1 to SB4 under a 50-fold test.

The invention comprises a mould obtained using the above-mentioned ingredients.

A die steel processing method for die casting comprises the following steps: smelting the raw materials, homogenizing, forging the raw materials in multiple directions, and finally performing superfine treatment.

Further, the die steel processing method for die casting further comprises the following heat treatment processes:

annealing treatment is carried out at 820-850 ℃,

then quenching treatment is carried out at 1010-1050 ℃,

finally tempering treatment is carried out at 530 ℃ to 700 ℃.

The present invention includes a die obtained by using the die steel processing method for die casting.

The effects of the composition of the die casting die steel of the present invention are described below.

C: 0.36 to 0.43 percent

C is an essential additive element required to maintain a quenched structure in lower bainite having good machinability and to cause hardening due to precipitation of carbides of Cr, Mo (W), and V in a tempering treatment. If the carbon content is too large, the matrix (matrix) changes to martensite, resulting in a decrease in machinability, and excessive carbides are formed, resulting in a decrease in machinability. Therefore, the carbon content is limited to 0.43% or less. On the other hand, if the carbon content is too small, ferrite precipitation is caused, and therefore, the carbon content is defined to be equal to or higher than 0.36%.

Si: 0.80 to 1.20 percent

Si is an element that can be used as a deoxidizing element in steel manufacture, and this element promotes an increase in hardness and ensures machinability of the steel. In addition, Si can be used to prevent temper softening of martensite in the matrix and to suppress the HAZ softening width. In order to effectively exhibit these effects, the lower limit of the amount of Si is 0.8%. However, when it is added too much, segregation may increase, and dimensional change after heat treatment may also increase, and in addition, toughness may decrease. Therefore, the upper limit is 1.20%.

Mn: 0.20 to 0.50 percent

Mn is an element suitable for improving the hardenability of the lower bainite of the steel of the present invention, suppressing the generation of ferrite, and providing moderate quenching and tempering hardness. However, if the Mn content is too large, it is difficult to control the heat treatment for maintaining the lower bainite; promoting the transformation to become martensite; the toughness of the base material is increased to reduce the machinability. Therefore, the Mn content is limited to 0.50% or less. In order to provide hardenability, it is preferable that the addition amount of Mn is 0.20% or more.

Cr: 4.75 to 5.50 percent

Cr is an element that can be used to secure a predetermined hardness, and when the amount of Cr is less than 5.50%, quenching properties may be poor, and bainite may be partially formed to reduce hardness, and wear resistance may not be secured, and the amount of Cr is 4.75% or more, but when the amount of Cr is too large, a large amount of coarse Cr carbide may be formed, and the steel may shrink after heat treatment, and film durability may be reduced. Therefore, the upper limit of the amount of the component is 9.00%. The amount of Cr is preferably 5.50% or less.

Mo: 1.30 to 1.75 percent

Mo is formation of M₆C carbide and formation of Ni₃Two elements of the Mo intermetallic compound, and contribute to precipitation strengthening and therefore the minimum content thereof is 1.30%. However, when Mo is added excessively, the above carbide may be excessively formed to lower toughness, so that the upper limit of the content is 1.75%.

V: 0.85 to 1.20 percent

V contributes to increased hardness due to the formation of carbides such as VC. In addition, when a diffusion hardened layer is formed on the surface of the base body by nitriding treatment such as vapor nitriding, salt bath nitriding, or plasma nitriding, V is effective for increasing the surface hardness and for increasing the hardened layer, and therefore the content of V is 0.85% at a minimum; however, when the amount of V is increased too much, the amount of C dissolved may decrease, and the hardness of the martensite structure of the body may decrease, and therefore, it is preferably 1.2% or less.

Ni：≤0.25％

Ni is obtained by Al-Ni intermetallic compound such as Ni₃Al precipitation strengthening is an essential element to improve hardness, and, in addition, when combined with Cu, Ni is effective to retard hot-working brittleness caused by excessive addition of Cu and to prevent cracking during forging. But its content is preferably less than 0.25%.

S：≤0.005％

S is an element ensuring machinability and appears as a metallic inclusion MnS, but when it is added excessively, it may cause weld cracking and may cause the occurrence of pin holes upon welding, pin holes upon polishing, roughening of the surface subjected to electric discharge treatment, and the like as a result of mold machining, and provides a starting point of rusting, thereby causing deterioration in the properties of the mold itself, for example, promoting anisotropy in mechanical properties. Therefore, it is 0.005% in the upper limit.

P：≤0.025％

P can improve the machinability of the steel, but when the content of P is too large, the ductility and toughness of the steel are reduced, and cracks are caused at the time of forging and rolling. Causing hot shortness of the steel, the P content is therefore less than 0.025%

Cu：≤0.15％

Cu is suitable for precipitating and aggregating a Fe-Cu solid solution in the tempering treatment of the steel material of the present invention. The mutual synergy of solid solution precipitation and aggregation and the control of the structure to lower bainite provides excellent anisotropy to the steel of the present invention. Cu also has an effect of providing excellent corrosion resistance, but if the content of Cu is too large, it causes a reduction in hot workability of the steel, and the effect of Cu transforming the structure into martensite causes a greater reduction in machinability, so the upper limit of Cu is 0.15%.

Compared with the prior art, the invention has the following beneficial effects:

the invention provides novel die-casting die steel, which is basically similar to H13, SKD61 and 4Cr5MoSiV1 in theory in chemical components, but the structure is purer and the performance is more excellent after the raw materials are smelted and refined by vacuum degassing;

compared with the domestic H13, the method has the following advantages: 1) after homogenization treatment and multidirectional forging treatment are adopted, the material is more uniform, and the cutting processability and the polishing performance are excellent; 2) the material has high toughness and high plasticity through multidirectional forging and superfine treatment; 3) high wear resistance at high temperatures; 4) excellent overall hardenability; 5) good high-temperature strength and thermal fatigue resistance; 6) extremely low deformability during heat treatment; 7) compared with the traditional steel, the steel has better isotropy, has excellent toughness and plasticity in all directions, and is pressure-resistant hot-work die steel. The steel is subjected to electroslag remelting, so that the material quality is more uniform, and the hardenability is good;

the die-casting die steel material provided by the invention simplifies the processing technology, has the characteristics of low cost, high cost performance and the like, is particularly suitable for small and medium-sized die-casting dies, extrusion dies and hot forging dies, and can greatly reduce the cost for enterprises.

Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention.

Drawings

FIG. 1 is a drawing of an ingot tail end annealing microstructure according to the present invention;

FIG. 2 is a diagram of a dead-end annealing microstructure of the present invention;

FIG. 3 is a schematic view of a ribbon-like structure of the end of the spindle according to the present invention;

FIG. 4 is a schematic representation of a strap-like structure of the feeder tip of the present invention;

FIG. 5 is a metallographic diagram illustrating grain size detection of the ingot end according to the present invention;

FIG. 6 is a metallographic image of grain size measurements taken at the riser end of the present invention;

FIG. 7 is a drawing of the annealed structure of foreign die steel;

FIG. 8 is another foreign die steel annealing structure diagram;

FIG. 9 is a graph of the annealed structure of the die steel of the present invention;

FIG. 10 is a graph of another die steel annealed structure according to the present invention.

Detailed Description

The present invention is described in detail below, and in this specification, percentages are by mass unless otherwise specifically indicated. All the expressions of percentage by mass are the same as all the expressions by weight.

Referring to fig. 1-10, the steel with various compositions shown in table 1 is prepared by the following specific steps of weighing low carbon steel, ferrosilicon, ferrochrome, pure nickel and pure copper which are subjected to surface rust removal and oil stain removal, smelting the steel material in an electric arc furnace in a vacuum environment, performing vacuum degassing refining treatment, performing electroslag remelting, performing equalization treatment, performing homogeneous diffusion annealing at 820 and 850 ℃, performing quenching treatment at 1010 to 1050 ℃, and finally performing tempering treatment at 530 to 700 ℃. And then using a 3000t hydraulic press and an 1800t precision forging machine for forging, carrying out multidirectional forging on the processed cast ingots, carrying out superfine processing, and using a three-way forging method to weaken various differences generated by metal flow lines, further improving the compactness of the forged piece and the isotropy of the impact energy after heat treatment, wherein the isotropy is more than 0.87, and is shown in table 2.

TABLE 1

TABLE 2

Macroscopic detection

The macroscopic structure of the module inspection is inspected according to GB/T1299-2014, the cross section of the acid-dipped macroscopic sample cannot be visually provided with shrinkage cavities, inclusions, layering, cracks, bubbles and white spots, the center porosity and ingot type segregation are detected according to GB/T1299-2014, and the macroscopic detection result is shown in Table 3.

TABLE 3

Metallographic examination

The method comprises the detection of nonmetallic inclusions, an annealing microstructure, a banded structure and grain size, wherein the detection of nonmetallic inclusions is 1/2 at the radius, and the detection of other items is 1/2 at the radius and the center.

1.1 non-metallic inclusion detection results

The single item grade of the non-metallic inclusion does not exceed 1.0 grade, and the sum of various types of inclusions in A, B, C, D does not exceed 2.0 grade. The results are shown in Table 4.

TABLE 4

1.2 the results of the examination of the annealed microstructure are shown in Table 5, the annealed microstructure of example 3 is shown in FIGS. 1 and 2, and the metallographic microstructure is shown after magnification of 500.

TABLE 5

1.3 banding structure test results, the grades of the banding structure of the microstructure are SB1 to SB4 under the test of 50 times, as shown in Table 6, the banding microstructure of example 3 is shown in FIG. 3 and FIG. 4, and the microstructure is a metallographic microstructure after fine pearlite plus dispersed ferrite is 50 times.

TABLE 6

1.4 grain size detection results, the grain size of the die-casting die steel is not less than 7, according to the ASTM112 metal average grain size determination method, as shown in Table 7, the strip-shaped microstructure of example 3 is shown in FIGS. 5 and 6, and a metallographic micrograph magnified 50 times shows no obvious segregation zone.

TABLE 7

Under a scanning electron microscope, comparing the structure of the die steel of the invention shown in figures 9 and 10 with that of a certain foreign brand name H13 die steel, as shown in figure 7, figure 7 is a gold phase diagram magnified by 200 times, and figure 8 is a gold phase diagram magnified by 500 times, and compared with the prior art, the die-casting die steel of the invention has the advantages that the carbide particles are consistent in size, uniform in distribution and free of obvious orientation arrangement.

Impact performance

The impact properties of the small samples after tempering were examined according to NADCA # 207-.

TABLE 8

TABLE 9

Compared with the traditional H13 die steel, the smelting process of the invention is strictly controlled, and the purity of the obtained material is higher and the structure is compact, therefore, the isotropy of the die steel of the invention is better than that of the common H13, the optimal isotropy has higher value for the die steel to resist mechanical fatigue and thermal stress fatigue, and the service life of the die is also prolonged.

In addition, the invention adds trace Cu and Ni alloy elements in the components, thereby achieving the purposes of refining crystal grains, improving the comprehensive mechanical property of materials and the thermal fatigue resistance of die steel, improving the machinability and the anti-cracking capability of the die steel and further prolonging the service life of the die.

Through detection and analysis of various indexes, various performance indexes of the novel hot-work die steel reach the mechanical performance indexes of products such as W302 of BOHLER company and 8407 of ASSAB company.

Industrial applicability

In the mold industry, the hardness of each component in the following table is a standard commonly used in the industry, and the hardness of the material in the invention meets the hardness requirement in the table. That is, the present invention provides a die steel material for producing Sn-Pb-Zn alloy as a die casting mold, the hardening temperature of which is required to be 1020 ℃ and the hardness of which is 46 to 50HRC, and a die steel material for producing Mg-Al alloy as an insert material, the hardening temperature of which is required to be 1020 ℃ and the hardness of which is required to be 46 to 48 HRC. The die steel material provided by the invention is used as different parts, and is required to be quenched at different temperatures according to the requirements of products so as to meet different hardness requirements.

TABLE 10 die hardness values for die casting

TABLE 11 hardness values of extrusion dies

TABLE 12 hardness values of dies for hot forging

Material to be processed	Hardening temperature	Hardness HRC
			Magnesium-aluminum alloy	1020℃	44-52
Steel and iron	1050℃	40-50

The die steel material provided by the invention is suitable for manufacturing die casting dies, hot forging dies, warm forging dies, hot extrusion dies and the like, so the die steel for die casting manufactured by the material provided by the invention is claimed to be protected.

Finally, the above embodiments are only for illustrating the technical solutions of the present invention and not for limiting, although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions may be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all of them should be covered in the claims of the present invention.

Claims

1. The die steel for die casting is characterized by comprising the following components in percentage by mass:

c: 0.36 to 0.43 percent,

si: 0.80% to 1.20%,

mn: 0.20 to 0.50 percent of the total weight of the composition,

cr: 4.75 to 5.50 percent of the total weight of the composition,

mo: 1.30 to 1.75 percent of the total weight of the composition,

v: 0.85% to 1.20%,

Ni：≤0.25％，

S：≤0.005％，

P：≤0.025％，

Cu：≤0.15％，

the balance of iron and inevitable impurities,

the microstructure of the composite material has a banded structure grade of SA 1-SA 3 (graded according to SEP1614 standard evaluation picture) under a 50-time magnification test, and a spheroidized structure grade of AS 1-AS 9 (sampled according to NADCA #207-2008 hot work die steel limit detection evaluation standard) under a 500-time magnification test.

2. A die-casting die steel according to claim 1, wherein the die-casting die steel has a grain size of 7 or more (according to ASTM112 Metal average grain size measurement).

3. The die steel for die casting according to claim 1 or 2, wherein the microstructure band-like structure is classified as SB1 to SB4 under a 50-fold magnification examination.

4. A die obtained by using the die steel for die casting according to any one of claims 1 to 3.

5. A method of processing die steel for die casting according to claim 1 or 2, comprising: smelting the raw materials, homogenizing, forging the raw materials in multiple directions, and finally performing superfine treatment.

6. The method of processing die steel for die casting according to claim 5, further comprising the following heat treatment process:

annealing treatment is carried out at 820-850 ℃,

then quenching treatment is carried out at 1010-1050 ℃,

finally tempering treatment is carried out at 530 ℃ to 700 ℃.

7. A die obtained by the method of processing a die steel for die casting according to claim 5 or 6.