RU2526107C1 - Thermal treatment of casts from rustproof martensite steel - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: normalising is carried out at 900-920°C as well as pendulum annealing of three to five cycles. Threes include accelerated heating to 600-620°C, curing for 2-3 min and subsequent cooling in to 150-200°C, normalising at 1040-1060°C, curing at 600-620°C with air cooling, tempering from 950-1050°C in oil, drawback at 290-310°C with air cooling.

EFFECT: ruled out chemical and structural homogeneity, stable properties.

1 tbl, 3 dwg

Description

The invention relates to the heat treatment of castings of corrosion-resistant steel of the martensitic class, used for high-precision parts of mechanical engineering and instrumentation.

A known method of heat treatment of castings from corrosion-resistant steel of martensitic class 09X16H4BL according to GOST 977-88 "Steel castings. General specifications ", which consists in sequentially carrying out the following thermal operations:

- normalization at 1040-1060 ° C, cooling in air,

- leave at 600-620 ° C, air cooling,

- quenching from 950-1050 ° C, oil cooling,

- tempering at 290-310 ° C, air cooling.

However, in the manufacture of castings according to GOST 977-88, there is no stability in obtaining hardness, mechanical properties and machinability on metal-cutting machines.

The reason for this is the chemical and structural heterogeneity due to the crystallization features of 09X16H4BL steel during casting manufacturing.

The chemical heterogeneity of the steel is characterized by the presence of non-etched "white" zones, which are areas enriched in chromium, formed as a result of dendritic segregation during solidification of the casting (figure 1).

The structural heterogeneity of the steel is characterized by the presence of free δ-ferrite, which is formed at the crystallization stage with a certain ratio of alloying elements (figure 2).

The task of the invention is to eliminate chemical and structural heterogeneity to obtain stable properties of castings.

The problem is solved due to the fact that the known method of heat treatment of castings from corrosion-resistant steel of martensitic class, including sequentially normalization at a temperature of 1040-1060 ° C with cooling in air, tempering at a temperature of 600-620 ° C with cooling in air, hardening from a temperature of 950-1050 ° C into oil, tempering at a temperature of 290-310 ° C with cooling in air is supplemented by preliminary heat treatment, in which low-temperature normalization is carried out at a temperature of 900-920 ° C, pendulum annealing, consisting s of three to five cycles comprising rapid heating to temperature 600-620 ° C, 2-3 min exposure, followed by cooling in air to a temperature of 150-200 ° C.

The effectiveness of the use of pendulum annealing is based on the fact of a significant acceleration of the diffusion mobility of elements near the temperatures of phase transformations.

The use of pendulum annealing provides a more uniform distribution of alloying elements in the steel structure, which eliminates the chemical heterogeneity caused by dendritic segregation.

The problem of structural heterogeneity is solved by limiting the amount of chromium in the brand composition to 16.4% and accelerated cooling during the crystallization of castings.

A homogeneous martensitic microstructure obtained according to the results of the invention, is graphically presented in figure 3.

Comparative mechanical characteristics corresponding to defective structures (Fig. 1, Fig. 2) and the structure obtained according to the results of the invention (Fig. 3) are presented in the table.

Table Mechanical properties of castings Microstructure Temporary resistance
σ _b , kgf / mm ² Yield strength σ _0.2 , kgf / mm ² Elongation δ,% Impact strength kgf m / cm ² Hardness HRC 132 46 32 fourteen 15-17 Figure 1 135 119 10 1,6 41-42 Figure 2 137 113 10 5.5 41-42 Figure 3 ND mechanical properties 115 90 8 2,5 38-45 -

The implementation of the invention is as follows.

Castings are made with samples in defense of the heat, taking into account the chromium content in the heat at the level of 16.4%.

Then heating is carried out under normalization in the chamber electric furnace СНО-6.12.4 / 10-И2 at a temperature of 900-920 ° C in a box with an airtight lid for one hour after heating the charge and is cooled in air to the temperature of the workshop.

Next, the castings with the samples are subjected to pendulum annealing: they heat the cage by placing the castings and samples in a grate basket in a mine electric furnace СШЗ 6.12 / 7-I2 to a temperature of 600-620 ° C, hold for 2-3 minutes, cool in air to a temperature of ~ 150 -200 ° C. The heating and cooling operations are carried out sequentially five times.

All further heat treatment is carried out in accordance with GOST 977-88.

The mechanical characteristics are determined on the samples in defense of the heat, past the same heat treatment as the castings. The results of the mechanical properties test fully satisfy the requirements of GOST 977-88.

Claims (1)

The method of heat treatment of castings of corrosion-resistant steel of martensitic class 09X16H4BL, including sequentially normalizing at 1040-1060 ° C, tempering at 600-620 ° C with air cooling, quenching from 950-1050 ° C with oil cooling, tempering at 290-310 ° C with air cooling, characterized in that before normalization, low-temperature normalization is preliminarily performed at 900-920 ° C and pendulum annealing, consisting of three to five cycles, including accelerated heating to a temperature of 600-620 ° C, holding 2 -3 min and subsequent cooling in air to a temperature of 150-200 ° C.

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