Boronizing treatment and heat treatment process of martensitic stainless steel for steam turbine nozzle set

Abstract

The present invention is boronizing treatment and heat treatment process of martensitic stainless steel for steam turbine nozzle set. The boronizing treatment process includes the following steps: 1. heating nozzle set workpiece with solid granular boronizing agent in blade steam passages to 700 deg.c inside the furnace; 2. raising the temperature in the rate of 100 deg.c an hour to 950-1050 deg.c and maintaining for 5-12 hr; 3. lowering the temperature slowly in the rate of 50-100 deg.c an hour to 300-400 deg.c and discharging; and 4. cooling in the air to room temperature. After boronizing treatment, the workpiece is then tempering heat treated. The present invention has simplified treating process, the boronized layer has hardness up to HV1000-2000, good treating effect and low cost.

Description

(1) Technical field [0001] The invention relates to a martensitic stainless steel boriding treatment and performance heat treatment process for a nozzle group of a steam turbine. (2) Background technology [0002] With the development of large-scale supercritical power generation technology, the pressure and temperature of the steam entering the steam turbine nozzle group are greatly increased, and the oxide particles in the steam are greatly increased, which accelerates the erosion and wear of the steam channel of the nozzle group and reduces the thermal efficiency of the steam turbine. The life of the unit is shortened, and the maintenance cost of the unit increases. In order to effectively prevent the erosion of solid particles on the surface of the steam channel of the nozzle group, the surface of the blades of the nozzle group of high-power and high-parameter steam turbines should be subjected to boronizing heat treatment to improve the resistance of the surface of the ...

AI Technical Summary

Problems solved by technology

Boronizing of low-alloy steel is a mature technology widely used in industrial production, but the material used in the high-temperature nozzle group of steam turbine is martensitic stainless steel with high alloy composition and high thermal strength at high temperature. Contains a variety of alloying elements that hinder boronizing, so under normal boronizing conditions, it is difficult for boron atoms to penetrate into the material to achieve boronizing; in addition, the performance of this type of martensitic stainless steel is also much higher than that of general alloys. The boronizing temperature of steel, performance heat treatment and boronizing treatment will have adverse effects on each other; these all make it difficult to achieve boronizing strengthening on the surface of supercritical or ultra-supercritical steam turbine nozzle group steam channel materials

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