CN107916321A - A kind of heat treatment process of hot die steel - Google Patents

Abstract

The purpose of the present invention is to provide a heat treatment method for hot work die steel 4Cr5Mo3Co2SiV, wherein the quenching heat treatment process is: heat preservation at 1050°C-1080°C for 0.5-1h, oil cooling; tempering heat treatment process is: heat preservation at 520-570°C 1.5～2.5h, oil cooling; secondary tempering heat treatment: 200±10℃, heat preservation 1.5～2h, oil cooling. Compared with the prior art, the hot work die steel treated by the method has better mechanical properties.

Description

A heat treatment process for hot work die steel

technical field

The invention belongs to the field of alloys, and in particular provides a heat treatment process for hot work die steel.

Background technique

Hot work die steel requires materials with high hardenability, high temperature strength, high wear resistance, high toughness, high thermal cracking resistance and high melting loss resistance. According to its main chemical composition, it can be divided into W series, Cr-Mo series, Cr-W-Mo series and other types. The hot work die steel of the American brand is divided into three types: chromium hot work die steel, tungsten hot work die steel and molybdenum hot work die steel, all of which are crowned with the letter H, which are represented as H10~H19, H21~H26 and H42, respectively. H43 et al. Among them, the carbon content of the first two steels is in the range of 0.30% to 0.50%, the carbon content of the latter steel is in the range of 0.50% to 0.70%, and the total content of Cr, W, Mo and V alloy elements in the three steels is 6%. ~25%.

At present, the most widely used and most representative hot work die steel is 4Cr5MoSiV1 (H13) steel, which is an improved type of 4Cr5MoSiV steel. Hot work die steel is an ideal steel to replace 3Cr2W8V steel, and its service life can be increased by 2-3 times. Its main features are: high hardenability and high toughness; excellent thermal cracking resistance, it can be water-cooled in the workplace; moderate wear resistance, and carburizing or nitriding process can also be used to improve its surface Hardness, but the thermal cracking resistance should be slightly reduced; because of its low carbon content, the secondary hardening ability in tempering is poor; it has softening resistance at higher temperatures, but the service temperature is higher than 540 ° C (1000 ° F) When the hardness drops rapidly (that is, the maximum working temperature is 540 ° C); the deformation of heat treatment is small; medium and high machinability; medium resistance to decarburization. At the same time, it can also be used to manufacture important components in the aviation industry. The delivery state is annealed, and the hardness is less than HB235. Common sample heat treatment process - quenching: preheating at 790±15°C, heating at 1000°C (salt bath) or 1010°C (furnace control atmosphere) ±6°C, holding time for 5-15 minutes and air cooling, tempering at 550±6°C. The hardness in the quenched state is about HRC55, and the hardness in the tempered state is about HRC52.

4Cr3Mo3SiV (H10) hot work die steel has good hardenability, toughness and high temperature hardness, and can replace 3Cr2W8V and other steels to make hot stamping dies, hot forging dies, hot rolling dies and plastic pressing dies. The mass fractions of Cr and Mo are both about 3%, good resistance to cold and heat fatigue, small heat treatment deformation, and good corrosion resistance. Good forging and cutting process, no special heat treatment required. At 500-600°C, it has higher hardness, thermal strength, wear resistance, good hardenability and high toughness, tempering resistance and thermal stability are higher than H13 steel, impact toughness and fracture toughness Higher than 3Cr2W8V steel. It can manufacture hot extrusion dies, hot stamping dies, hot forging dies, etc. It is also used as structural parts for aircraft, rockets and other heat-resistant 400-500°C operating temperatures. The delivery state is annealed, and the hardness is less than HB235. Common sample heat treatment process—quenching: preheating at 790±15°C, heating at 1010±6°C (salt bath) or 1020±6°C (furnace-controlled atmosphere), holding for 5-15 minutes, air cooling, and tempering at 550°C. The hardness in the quenched state is about HRC60, and the hardness in the tempered state is about HRC55.

Contents of the invention

The object of the present invention is to provide a heat treatment method for hot work die steel 4Cr5Mo3Co2SiV, and the hot work die steel treated by the method has better mechanical properties.

Technical scheme of the present invention is:

Selection of quenching process for hot work die steel 4Cr5Mo3Co2SiV:

Carbide Cr ₂₃ C ₆ has poor stability, high degree of aggregation, and is easy to grow. It reaches the maximum solubility at 1050-1070°C, and the temperature cannot be too low; the more carbides dissolve, the more dissolved alloy elements, the higher the quenching hardness, but the higher the hardness , the grain grows, so there is a balance between temperature selection and grain size. The quenching heat treatment process formulated for the 4Cr5Mo3Co2SiV steel of the present invention is: heat preservation at 1050° C. to 1080° C. for 0.5 to 1 hour, and oil cooling.

Selection of tempering temperature for hot work die steel 4Cr5Mo3Co2SiV:

Quenching of 4Cr5Mo3Co2SiV steel is to prepare the structure for tempering. After tempering, fine and dispersed carbides are obtained to optimize the strength, hardness and impact toughness of the steel. The tempering heat treatment process of the present invention is: heat preservation at 520-570°C for 1.5-2.5 hours, oil cooling; secondary tempering heat treatment: 200±10°C, heat preservation for 1.5-2 hours, oil cooling.

The composition and mass percentage of the hot work die steel 4Cr5Mo3Co2SiV in the present invention are: C: 0.35-0.45%, Si: 0.40-0.75%, Mn: 0.20-0.50%, Mo: 2.50-3.50%, V: 0.25-0.75% , Cr: 4.00-5.00%, Co: 1.50-2.50%, S: ≤0.010%, P: ≤0.030%, Fe balance. After the sample of this composition is tempered, the tempered structure is relatively fine, and the carbides are dispersed and evenly distributed in the matrix in the form of fine particles and elongated needles.

Its preferred composition and mass percentage are: C: 0.38-0.42%, Si: 0.50-0.70%, Mn: 0.30-0.45%, Mo: 3.10-3.50%, V: 0.35-0.55%, Cr: 4.00-4.60% , Co: 1.50-2.30%, S: ≤0.010%, P: ≤0.030%, Fe balance.

Through analysis and research, it can be determined that the most suitable heat treatment process for 4Cr5Mo3Co2SiV steel is: quenching: 1050±10°C for 0.5h, oil cooling, tempering: 530±10°C, holding for 2h, oil cooling, secondary tempering: 200±10°C, Keep warm for 2h, oil cold. Properties of 4Cr5Mo3Co2SiV steel after tempering heat treatment: tensile strength 2200-2250MPa, yield strength 1700-1800MPa, elongation 8-8.5%, area reduction 31-33%, hardness HRC55-56, impact toughness AKu 26-27J .

Description of drawings

Figure 1 Effect of quenching temperature on the tensile strength of sample 1.

Fig. 2 Effect of quenching temperature on the hardness of sample 1.

Fig. 3 Metallographic structure of quenched (1020°C) sample.

Figure 4 The metallographic structure of the quenched (1050°C) sample.

Fig. 5 Metallographic structure of sample in quenched state (1080°C).

Fig. 6 Effect of tempering temperature on the tensile strength of sample 1.

Fig. 7 Effect of tempering temperature on the hardness of sample 1.

Fig. 8 Metallographic structure of tempered (530°C) sample.

Fig. 9 Metallographic structure of tempered (550°C) sample.

Fig. 10 Metallographic structure of tempered (570°C) sample.

Figure 11 Effect of quenching temperature on the tensile strength of sample 2.

Figure 12 The effect of quenching temperature on the hardness of sample 2.

Figure 13 Effect of tempering temperature on the tensile strength of sample 2.

Figure 14 Effect of tempering temperature on the hardness of sample 2.

Figure 15 Effect of quenching temperature on the tensile strength of sample 3.

Figure 16 The effect of quenching temperature on the hardness of sample 3.

Figure 17 Effect of tempering temperature on the tensile strength of sample 3.

Figure 18 Effect of tempering temperature on the hardness of sample 3.

Detailed ways

The alloy composition of the sample is shown in Table 1:

Table 1 Sample Alloy Composition

sample C Si mn Cr Mo V co S P Fe 1 0.40 0.77 0.38 4.10 2.99 0.59 1.69 0.006 0.017 Remain 2 0.36 0.42 0.21 4.03 2.51 0.27 1.52 0.005 0.012 Remain 3 0.44 0.98 0.47 4.99 3.48 0.73 2.46 0.003 0.015 Remain 4 0.38 0.51 0.30 4.20 3.05 0.42 1.81 0.005 0.016 Remain 5 0.42 0.70 0.41 4.56 3.10 0.35 1.95 0.006 0.018 Remain 6 0.37 0.65 0.45 4.25 3.32 0.51 1.55 0.008 0.013 Remain 7 0.40 0.58 0.35 4.60 3.50 0.55 2.03 0.004 0.015 Remain 8 0.41 0.62 0.43 4.39 3.46 0.49 2.38 0.009 0.014 Remain

Example 1

(1), Quenched performance:

Take sample 1 for quenching heat treatment, 1020±10°C, 1050±10°C, 1080±10°C, holding time 30min, oil cooling, its mechanical properties are shown in Table 2, hardness is shown in Table 3, and the metallographic structure of the sample is shown in Figure 3 ~5.

Table 2 Mechanical properties of sample 1 after quenching

It can be seen from Table 2 and Figure 1 that compared with 4Cr5MoSiV1 (H13), the alloy of the present invention has a yield strength of 300-400MPa and a tensile strength of 500-800MPa, especially when quenched at 1050°C, its strength is the highest.

Table 3 Hardness of sample 1 after quenching

It can be seen from Table 3 and Fig. 2 that compared with 4Cr5MoSiV1 (H13), the average hardness of the alloy of the present invention is HRC2-8 higher, especially when it is quenched at 1050°C, its hardness is the highest, reaching HRC62.

(2), tempered performance:

Take sample 1 after oil-cooling at 1050±10°C for 30 minutes and conduct tempering heat treatment. The mechanical properties are shown in Table 4, and the metallographic structure of the sample is shown in Figures 8-10.

Table 4 Mechanical properties of sample 1 after quenching + tempering

Sample No R _m , MPa R _p0.2 , MPa A,% Z,% HRC QUR 530℃-1# 2257 1775 8.5 33 55.4,55.5,55.4 27 530℃-2# 2271 1790 8.0 31 56.1,55.5,55.7 26 550℃-1# 2133 1749 8.5 38 57.1,57.1,56.8 26 550℃-2# 2120 1745 8.5 35 56.5, 56.7, 57.2 27 570℃-1# 1819 1574 10.0 39 51.8, 52.1, 51.3 27 570℃-2# 1812 1560 10.5 38 52.1, 51.8, 52.7 27

It can be seen from Table 4, Figures 6 and 7 that as the tempering temperature increases from 530°C to 570°C, the strength of the sample decreases gradually, the hardness increases first and then decreases, and the plasticity increases gradually, but the impact toughness The change is not obvious.

Example 2

(1), Quenched performance:

Take sample 2 for quenching heat treatment, holding time 30min, oil cooling, its mechanical properties are shown in Table 5, and its hardness is shown in Table 6.

Table 5 Mechanical properties of sample 2 after quenching

It can be seen from Table 5 and Figure 11 that compared with 4Cr5MoSiV1 (H13), the alloy of the present invention has a yield strength 100-400MPa higher and a tensile strength 300-600MPa higher, especially when it is quenched at 1050°C, its strength is the highest.

Table 6 Hardness of sample 2 after quenching

It can be seen from Table 6 and Figure 12 that compared with 4Cr5MoSiV1 (H13), the average hardness of the alloy of the present invention is HRC2-4 higher, especially when quenched at 1050°C, its hardness is the highest, reaching HRC60.

(2), tempered performance:

Take sample 2 after oil-cooling at 1050±10°C for 30 minutes for tempering heat treatment, and its properties are shown in Table 7.

Table 7 Mechanical properties of sample 2 after quenching + tempering

Sample No R _m , MPa R _p0.2 ,MPa A,% Z,% HRC QUR 530℃-1# 2143 1681 9.0 35 53.7, 53.9, 54.1 28 530℃-2# 2169 1675 8.5 32 53.8, 54.6, 54.1 27 550℃-1# 2057 1641 9.0 38 55.2, 54.7, 54.8 27 550℃-2# 2074 1683 9.0 39 54.8, 54.1, 55.1 27 570℃-1# 1703 1452 10.5 39 49.4, 50.3, 49.1 28 570℃-2# 1679 1487 11.5 40 50.1, 49.7, 50.3 29

It can be seen from Table 7 and Figures 13 and 14 that as the tempering temperature increases from 530°C to 570°C, the strength of the sample decreases gradually, the hardness increases first and then decreases, and the plasticity increases gradually, but the impact toughness The change is not obvious.

Example 3

(1), Quenched performance:

Take sample 3 for quenching heat treatment, holding time 30min, oil cooling, its mechanical properties are shown in Table 8, and its hardness is shown in Table 9.

Table 8 Mechanical properties of sample 3 after quenching

It can be seen from Table 8 and Figure 15 that, compared with 4Cr5MoSiV1 (H13), the alloy of the present invention has a yield strength of 300-400MPa and a tensile strength of 500-800MPa, especially when quenched at 1050°C, its strength is the highest.

Table 9 Hardness of sample 3 after quenching

It can be seen from Table 9 and Figure 16 that compared with 4Cr5MoSiV1 (H13), the average hardness of the alloy of the present invention is 3-9 higher than HRC, especially when it is quenched at 1050°C, its hardness is the highest, reaching HRC61.

(2), tempered performance:

Take sample 3 after oil-cooling at 1050±10°C for 30 minutes for tempering heat treatment, and its properties are shown in Table 10.

Table 10 Mechanical properties of sample 3 after quenching + tempering

Sample No R _m ,MPa R _p0.2 , MPa A,% Z,% HRC QUR 530℃-1# 2143 1681 9.0 35 53.7, 53.9, 54.1 28 530℃-2# 2169 1675 8.5 32 53.8, 54.6, 54.1 27 550℃-1# 2057 1641 9.0 38 55.2, 54.7, 54.8 27 550℃-2# 2074 1683 9.0 39 54.8, 54.1, 55.1 27 570℃-1# 1703 1452 10.5 39 49.4, 50.3, 49.1 28 570℃-2# 1679 1487 11.5 40 50.1, 49.7, 50.3 29

It can be seen from Table 10 and Figures 17 and 18 that as the tempering temperature increases from 530°C to 570°C, the strength of the sample decreases gradually, the hardness increases first and then decreases, and the plasticity increases gradually, but the impact toughness The change is not obvious.

The above-mentioned embodiments are only to illustrate the technical concept and characteristics of the present invention, and the purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly, and not to limit the protection scope of the present invention. All equivalent changes or modifications made according to the spirit of the present invention shall fall within the protection scope of the present invention.

Claims (4)

1. A kind of 1. heat treatment process of hot die steel, it is characterised in that：

   Quenching heat treatment technique is：0.5~1h, oil cooling are kept the temperature at 1050 DEG C~1080 DEG C；

   Tempering heat treatment process is：1.5~2.5h, oil cooling are kept the temperature at 520~570 DEG C；Double tempering：200 ± 10 DEG C, insulation 1.5~2h, oil cooling.
2. 2. according to the heat treatment process of hot die steel described in claim 1, it is characterised in that：

   Quenching heat treatment technique is：0.5h, oil cooling are kept the temperature at 1050 ± 10 DEG C；

   Tempering heat treatment process is：2h, oil cooling are kept the temperature at 530 ± 10 DEG C；Double tempering：200 ± 10 DEG C, keep the temperature 2h, oil cooling.
3. 3. according to the heat treatment process of hot die steel described in claim 1, it is characterised in that the composition of the hot die steel And mass percent is：C：0.35~0.45%, Si：0.40~0.75%, Mn：0.20~0.50%, Mo：2.50~ 3.50%th, V：0.25~0.75%, Cr：4.00~5.00%, Co：1.50~2.50%, S：≤ 0.010%, P：≤ 0.030%th, Fe surpluses.
4. 4. according to the heat treatment process of hot die steel described in claim 3, it is characterised in that the composition of the hot die steel And mass percent is：C：0.38~0.42%, Si：0.50~0.70%, Mn：0.30~0.45%, Mo：3.10~ 3.50%th, V：0.35~0.55%, Cr：4.00~4.60%, Co：1.50~2.30%, S：≤ 0.010%, P：≤ 0.030%th, Fe surpluses.