SU924124A1 - Method for heat treating steels - Google Patents

Description

The invention relates to mechanical engineering and can be used in the heat treatment of large semi-finished products from austenitic dispersion hardening steels. Large products of austenitic steels in most cases have a certain amount of g-ferrite in the structure, the inclusions of which are elongated along the fiber, as a result of which the impact strength across the fiber, especially in the dispersion-strengthened state, is sharply lowered.

A known method of heat treatment of products from dispersion hardening steels, which consists in heating at 1050 ° C, followed by air cooling and aging. [one].

However, heat treatment by this method does not allow to significantly increase the toughness across the fiber, as it does not eliminate the cause of EL ferrite in the structure.

Also known is a method of heat treatment of austenitic dispersion hardened steel, which consists in hardening from 1050 ° С and aging to maximum strength at 550 °, 15 hours (2].

However, the known method does not provide sufficient hit.

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viscosity across the fiber, as in this case (0-ferrite in the structure is preserved.

The purpose of the invention is to increase the impact strength across the fiber while maintaining high strength.

The goal is achieved by the fact that in the known method of heat treatment, including quenching and aging for maximum strength, the quenching temperature is set equal to A sn (70-20 ° C). This heating temperature provides an accelerated flow of diffusion processes, and the metastable <0 ferrite turns into austenite. At lower temperatures (as, for example, in a known method) diffusion is sluggish, and (0-ferrite remains in the structure, with a temperature rise above the specified limit, in some segregation areas, the reverse process can begin: ultimately lead to a reduction in toughness.

Heat treatment is carried out according to the modes given in the examples. In

all cases use templates,

cut from the same bar square 105 mm steel 9G28Yu9MBB.

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Using the Reghoabodgar device, it was established on samples from this 105 mm square that the instrumentally recorded temperature A _bn is equal to 1190 ° C.

Example 1. The blanks are heated to 1130 ° C (i.e. A'o "- 60 ° C) are held and hardened, and then subjected to aging, at 550 °, 15 hours.

A small amount of preserved in the microstructure (f-ferrite in the form of small rounded inclusions. The mechanical properties across the fiber are as follows:

105.0 xg / mm ^, Lt 93.3 kg / mm ⁵ ·, s * ¹ 30.0%, 31.0% an 6.3 kgm / sM *, ·

Example 2. The blanks are heated to 1170 ^σ Ο (i.e., to A ^ -20 ° C), they are held and hardened, and then subjected to aging at 550 ° C,

15 hours in the microstructure there is no-ferrite. The mechanical properties across the fiber are as follows:

100.5 kg / mm \ 6g, 89.0 kg / mm \ sL34.0%, 39.0% and _c 8.0 kgm / cm ".

Example 3. The blanks are heated to 1090 ° C (i.e., AED-100 ° C), held and quenched, then aged at 550 °, 15 hours. In the microstructure, a noticeable amount of about ^{1 —} Ferrite remains as elongated inclusions. rounded tops,

mechanical properties across the fiber 'to the following:

Be 10 7.5 kg / mm ^ ·, όγ 101.0 kg / mm%

. * ¹ 27.0%, Ψ34.0% a ·, 4.5 kgm / cm \;

Example 4. Preparations are heated to 1200 ° C (i.e. Ac _m + 10 ° C),

stand and harden, and then subjected to aging at 550 ^,

15 h. In the microstructure there are many elongated inclusions of ^ -ferrite angular

10 forms., Angular shape acquired due to the growth of e ^ -ferrite from austenite. The impact strength is equal to ac 2 kgm / cm ' ¹ .

Example 5. The blanks are treated by a known method, heated to 1050 ° C (i.e., A _cn 140 ° C), kept and hardened, and then subjected to aging at 550 °, 15 h. A significant amount of elongated SL ferrite inclusions, the mechanical properties across the fiber are as follows: 6¾ 112.0 kg / mm ",

6t 104.0 kg / mm ¹ , ¢ - 24.0%, 34.0%,

And _n 25 3.7 kgm / cm ^.

The results obtained after heat treatment. According to the proposed and well-known methods are summarized in tab _{30 to the} person ..

Heat Treatment Mode Mechanical properties kg / mm ¹ ^ kg / mm ^ a _m , kgm / cm ^g Known (quenching from 1050 °, aging at 550 °, 15 hours) 112.0 104.0 ²⁴ s / ° 34.0 3.7 Offered (quenching from IZO (A _CT1 - 60 ° С), aging at 550 °, 15 h) 105.0 98.3 30.3 37.0 '6.3

• As you can see, when processing by the proposed method while maintaining high strength (reduction is 7%), a significant (70%) increase in toughness is achieved ^

A distinctive feature of the proposed method, namely - the quenching temperature, equal to A _cn - (70-20 ° C) allows to significantly increase the structural strength and reliability of 55 products. Due to the increase in toughness by 70% while maintaining the same strength due to the achievement of the optimal combination of mechanical properties, the scope of application of austenitic dispersion-hardening steel expands.

VNIIPI Order 2732/38

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Claims (1)

Claim The method of heat treatment of steel, predominantly austenitic dispersion hardening, including hardening and aging to a maximum strength of 50, characterized in that, in order to increase the toughness across the fiber while maintaining strength, hardening is conducted from the temperature А ^ c - (70-20 ° C),