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Niobium addition in crmo 1/4 v steel castings for steam turbine casing appliations

A steel casting, weight technology, applied in the field of niobium-containing steel castings, can solve problems such as reducing the secondary creep rate

Inactive Publication Date: 2014-06-25
BHARAT HEAVY ELECTRICALS LIMITED
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

Ti and Nb are added as carbide formers, which strengthen the alloy steel by forming fine matrix carbides that interact with dislocations and precipitate at subgrain boundaries, thereby reducing the secondary creep rate

Method used

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  • Niobium addition in crmo 1/4 v steel castings for steam turbine casing appliations
  • Niobium addition in crmo 1/4 v steel castings for steam turbine casing appliations
  • Niobium addition in crmo 1/4 v steel castings for steam turbine casing appliations

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Embodiment Construction

[0019] According to the present invention there is provided a chromium-molybdenum-vanadium (Cr-Mo-V) cast steel containing 0.04-0.08% by weight of niobium.

[0020] The cast steel contains 0.08-0.12 wt% carbon, 0.015 wt% or less sulfur, 0.02 wt% or less phosphorus, 0.30-0.60 wt% silicon, 0.50-0.80 wt% manganese, 1.20-1.50 wt% % of chromium, 0.90-1.00% by weight of molybdenum, 0.20-0.30% by weight of vanadium, iron except for occasional impurities, and added 0.04-0.08% by weight of niobium. The basic chromium-molybdenum-vanadium cast steel is subjected to a cast steel homogenization heat treatment followed by the addition of 0.04-0.08% by weight of niobium. The addition of Nb was performed in an induction melting furnace.

[0021] Various tests were performed on the niobium-containing castings thus prepared to evaluate their creep / stress rupture properties and tensile strength.

[0022] By adding 0.4-0.8% Nb to CrMoV steel, 3 castings are obtained. The steel melts were desig...

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Abstract

A chromium-molybdenum-vanadium (Cr—Mo—V) cast steel including 0.04 to 0.08% by weight of niobium is disclosed. The cast steel may include 0.08 to 0.12% by weight carbon. The cast steel may also have a sulphur content of 0.015% by weight or less, and a phosphorus content of 0.02% by weight or less. The silicon content may be 0.30 to 0.60% by weight, the manganese content may be 0.50 to 0.80% by weight, the chromium content may be 1.20 to 1.50% by weight, the molybdenum content may be 0.90 to 1.10% by weight, and the vanadium content may be 0.20 to 0.30% by weight.

Description

field of invention [0001] This invention relates to steel castings containing niobium. [0002] The invention further relates to niobium containing chromium-molybdenum-vanadium steel castings suitable for steam turbine casing or valve casing applications. Background of the invention [0003] In order to improve the mechanical properties and weldability of steel, various alloying elements such as Ti, Nb, Mo, W, B, etc. are added to low alloy steel and high alloy steel. Ti and Nb are added as carbide formers, which strengthen the alloy steel by forming fine matrix carbides that interact with dislocations and precipitate at subgrain boundaries, thereby reducing the secondary creep rate. [0004] Currently, CrMoV-based steel castings are used for steam turbine casing and valve casing applications up to about 540°C. Due to increasing power requirements and restrictions on CO2 emissions, there is a growing demand for higher steam turbine efficiency and output. By increasing the...

Claims

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Application Information

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Patent Type & Authority Patents(China)
IPC IPC(8): C22C37/06C22C37/10C22C38/02C22C38/04C22C38/12C22C38/18C22C38/24C22C38/26
CPCC22C38/54C22C38/46C22C38/02C22C38/48C22C38/06C22C38/04C22C38/44C22C38/18
Inventor K·辛格J·R·古拉姆S·R·卡塔姆P·那瑟M·普德萨V·K·阿格拉沃
Owner BHARAT HEAVY ELECTRICALS LIMITED