A heat treatment method for improving the torsional properties of cold-worked precipitation-hardened steel

Abstract

The present invention discloses a heat treatment method for improving the torsional performance of cold-processed precipitation hardened steel, the purpose of which is to obtain high strength and high torsional performance of cold-processed precipitation hardened steel after heat treatment. The specific heat treatment scheme is as follows: the furnace insulation temperature is 300℃~420℃, and water cooling is performed after insulation for 5min~60min; the furnace insulation temperature is 250℃~350℃ again, and water cooling is performed after insulation for 3min~10min. Compared with the prior art, it has the following advantages: the present invention can make inclusions / matrix nested with each other to form a complex interface, and its torsional performance is significantly improved under the premise of slightly improving strength; the heat treatment equipment required for this process is simple, and large-scale production can be achieved using existing heat treatment equipment.

Description

Technical Field

[0001] The invention belongs to the field of heat treatment of alloy materials, and in particular relates to a heat treatment method for improving the torsional performance of cold-worked precipitation hardened steel. Background Art

[0002] Cold-drawn precipitation-hardened steel wire has a strength of more than 1600MPa, and can also obtain a strength of more than 2000MPa through aging treatment after winding the spring. Therefore, it is widely used in the aerospace and military fields. However, endogenous or exogenous inclusions are inevitably present in the precipitation-hardened steel matrix. Under torsional deformation, stress concentration will occur near the precipitation-hardened steel inclusions, causing material failure below the tensile strength. Especially after cold working, the notch sensitivity of precipitation-hardened steel increases, and the stress concentration effect of inclusions becomes more significant, which is manifested in the torsional performance test as fewer torsion circles, step-shaped fractures, and longitudinal cracks. Summary of the invention

[0003] The invention discloses a heat treatment method for improving the torsional performance of cold-worked precipitation hardening steel, the purpose of which is to obtain high strength and high torsional performance of cold-worked precipitation hardening steel after heat treatment, and to obtain higher strength through aging.

[0004] The technical solutions are as follows:

[0005] The basic composition by mass percentage of cold-worked precipitation hardening steel is: chromium: 15% to 19%, aluminum: 0.5% to 1.5%, nickel: 5% to 10%, silicon not more than 1.0%, manganese not more than 1.0%, carbon not more than 0.1%, and the remainder is iron and unavoidable impurities.

[0006] The heat treatment method for torsional properties is to charge the cold-worked precipitation hardened steel into a furnace for heat preservation and then water-cooling, and then charge it into a furnace for heat preservation and then water-cooling:

[0007] The furnace is heated to 350℃~420℃, and then cooled by water after 5min~60min of heat preservation;

[0008] The furnace is reloaded and the insulation temperature is 250℃~300℃. It is kept warm for 3min~10min and then water-cooled.

[0009] The mechanism of the present invention is as follows: through the high temperature-low temperature double aging process, compared with the cold-worked precipitation hardened steel inclusion / matrix interface, the inclusion surface after heat treatment is coated with precipitated phases of various sizes, which is referred to as multi-scale coating. That is, after cold working, the alloy is first aged at a higher temperature to coat the surface of the inclusion with a larger Ni3Al phase, and then aged at a lower temperature to coat the larger Ni3Al phase with a smaller Ni3Al phase, thereby realizing multi-scale coating treatment of inclusions.

[0010] Compared with the existing technology, it has the following advantages:

[0011] The present invention can make inclusions / matrix nest with each other to form a complex interface, and the torsional performance is significantly improved under the premise of slightly improving the strength; the heat treatment equipment required by this process is simple, and large-scale production can be achieved using existing heat treatment equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is the sample morphology of the cold drawn precipitation hardened 1.0 mm steel wire after torsion test;

[0013] Figure 2 This is the sample morphology after the torsion test of the heat-treated cold-drawn precipitation-hardened 1.0 mm steel wire. DETAILED DESCRIPTION

[0014] The present invention is further described below in conjunction with embodiments and drawings.

[0015] In Example 1 and Example 2, the detection method of each parameter is as follows:

[0016] Tensile strength: GB / T 228.1-2010 Tensile test of metallic materials Part 1 Room temperature test method,

[0017] Torsion performance: GB / T 239.1-2012 Metallic materials and wires Part 1: Unidirectional torsion test method.

[0018] If the torsion fracture is step-shaped or longitudinal cracks appear, the number of torsion turns is recorded as 0.

[0019] The cold-worked precipitation-hardened steel used was a 1.0 mm steel wire with a strength of 1820 MPa and a longitudinal crack torsion of 0 turns. The morphology after torsion was as follows: Figure 1 Its composition is shown in Table 1.

[0020] Table 1

[0021]

[0022] Example 1

[0023] After 20 minutes of heat treatment at 350℃, the wire was cooled by water. After 3 minutes of heat treatment at 250℃, the wire was cooled by water. The wire strength was 1880MPa and the wire was twisted for 6 turns. The morphology of the wire after twisting was Figure 2 After aging at 450℃ for 1h, the strength increases to 2210MPa.

[0024] Example 2

[0025] After 5 min of heat preservation at 420℃, water cooling, heat treatment at 300℃ for 3 min, water cooling, the steel wire strength was measured to be 1960MPa, twisted 5 times, and the sample morphology after twisting was the same as that in Example 1. After aging at 450℃ for 1h, the strength increased to 2150MPa.

[0026] The above results show that the cold drawn precipitation hardened 1.0 mm steel wire treated in the embodiment has good mechanical properties, high strength and high torsional properties, and because the heat treatment temperature is low, it can effectively prevent the generation of internal stress and is suitable for large alloy parts.

Claims

1. A heat treatment method for improving the torsional properties of cold-worked precipitation-hardened steel, characterized in that: The basic composition of the cold-worked precipitation hardening steel is as follows by mass percentage: chromium: 15% to 19%, aluminum: 0.5% to 1.5%, nickel: 5% to 10%, silicon not more than 1.0%, manganese not more than 1.0%, carbon not more than 0.1%, and the balance is iron and unavoidable impurities; The heat treatment method: The furnace is heated to 350℃~420℃, and then cooled by water after 5min~60min of heat preservation; The furnace is reloaded and the insulation temperature is 250℃~300℃. It is kept warm for 3min~10min and then water-cooled.

2. A heat treatment method for improving the torsional properties of cold-worked precipitation hardened steel according to claim 1, characterized in that: The heat treatment method is as follows: keeping the temperature at 350° C. for 20 minutes and then cooling with water; keeping the temperature at 250° C. for 3 minutes and then cooling with water.

3. A heat treatment method for improving the torsional properties of cold-worked precipitation hardened steel according to claim 1, characterized in that: The heat treatment method is as follows: keeping the temperature at 420°C for 5 minutes and then cooling with water; keeping the temperature at 300°C for 3 minutes and then cooling with water.

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